Basic principles of vacuum technology, brief overview Introduction

Basic principles of vacuum technology What is a vacuum? Vacuum ranges Units of measurement A vacuum is a space entirely devoid of P P There are a large number of national The vacuum level is often expressed matter (“absolute vacuum”). [pa] [mbar] and international units of as a % value. However, these are In practice we talk about a vacuum GV measurement. The most commonly always relative values. when the air pressure in a space lies used units are Pascal (Pa) and bar FV below atmospheric pressure. HV 100Pa =1hPa GV = Rough vacuum 1hPa =1mbar FV = Medium vacuum 1 mbar = 0.001 bar HV = High vacuum UHV UHV = Ultra-high vacuum

What is a vacuum used for? Measuring the pressure or vacuum Atmospheric pressure The vacuum plays a vital role in In the rough vacuum range, the h[km] 1 Mount Everest research in the fields of chemistry, pressure gauges used are mainly 2 Festo biology and physics. mechanical, but some digital pressure 3 Sea level It is also indispensable in many gauges are also used. industrial processes. In the high and ultra-high vacuum range, highly sensitive pressure gauges are used.

p[hPa]

Understanding vacuum Vacuum specification options Effects of changes on vacuum technology Airisagasmixturewithapprox. A vacuum can be specified as an As altitude increases, the air pressure 1025 particles per m3 of air at one bar absolute value, i.e. with a positive in the atmosphere falls. This same air pressure. signfrom1to0bar,with0as effect reduces the attainable vacuum Particles exert pressure or force on the absolute zero. Or it can be specified level of an ejector. Nevertheless, the walls of a defined space. The fewer as a relative value with a negative performance level of 80% remains particles there are in the space, the signfrom0to–1bar,with0asa unchanged in this case. lower the force exerted on the walls. reference point, or as a %.

Pressure = Force Area

100% vacuum would mean that there are no particles present. Pressure = 0.

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Components for vacuum generation Vacuum ejectors Displacement vacuum pumps Kinetic vacuum pumps These function according to the Air flowing into a space is Air is forced to flow in the delivery venturi principle, i.e. they are driven mechanically shut off, compressed direction through the application of purely pneumatically and have a and ejected. This allows a very high additional mechanical force. This much simpler design compared with vacuum to be achieved at a very low method achieves only a relatively low other vacuum generators. flow rate. vacuum level despite a high suction rate.

Principle • The most important components • Depending on the principle, air is 1 1 Pressure side are the jet nozzle (venturi nozzle) either carried away in a flow by a 4 2 Suction side and at least one receiver nozzle. rotating impeller on the suction 3 Inlet valve • Acceleratedcompressedair side or compressed using vaned 4 Exhaust valve generates a suction effect between chambers. 5 Piston both nozzles (vacuum). • The pump types available 3 • There are different design include vacuum blowers and 5 2 principles: single-stage and multi- vacuum compressors, for example. stage ejectors.

Features • High vacuum level with relatively • Low-weight, compact design • Minimal maintenance expenses • Large flow rates, low vacuum level small flow rate • Any mounting position • Generally large dimensions and • High maintenance costs • Maintenance-free and wear-free • High vacuum level up to –0.98 bar high weight • Low-cost operating pressure • Restricted mounting position

Application • Wide range of applications, • Broad application spectrum in • Used mainly for precision processes e.g. handling technology and industry and research. in industry. process engineering.

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Vacuum in handling technology Practical use of vacuum Important selection factors Benefits of a vacuum Theextensiverangeofvacuum Lifting Conveyance • Weight, temperature, shape and • Gentle handling component variants makes them ideal Loading Turning roughness of the workpiece surface • Compact, low-weight, space-saving for use in many industrial • Speed per unit of time design Gripping applications. • Stroke travel and conveying • Fast cycle times possible Machining distances • Low maintenance costs • Low-cost Holding

Insertion

Moving

Feeding Repositioning Transporting

Comparison of ejectors Variables/criteria Single-stage Multi-stage Suction flow rate Average High At low vacuum level up to approx. 50% Evacuation time Very short Very short In higher vacuum range from 30 … 50% In lower vacuum range up to 30 … 50% Initial costs Low Relatively high Noise generation Relatively high Low

Both principles have their advantages components, both principles can and disadvantages which are difficult coveralargenumberofdifferentareas to compare. With optimally adapted of application.

Important comparison variables Evacuation time Air consumption Efficiency Suction flow rate Evacuation time = Time (s) required to Air consumption = Air consumption The efficiency formula makes it easier The efficiency of an ejector is often – generate a specific vacuum. (l/min) of the ejector required to to compare the different principles: and incorrectly – measured using the generate a specific vacuum. Efficiency = Evacuation time, air suction flow rate at 0 bar. consumption and volume dependent on vacuum. Suction flow rate = Suction air volume (l/min) that an ejector can draw in.

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Vacuum in handling technology Energy cost comparison To generate compressed air from Vacuum ejectors: Electric vacuum pumps: For a comparison of features, a atmospheric air, you need to reckon • High air consumption, but • Very high vacuum (up to 99.99%) calculation example and an energy on approx. € 0.02 per m3 volume at compensated by its energy-saving attainable cost comparison  following 7 bar pressure when calculating the function • High suction rates (vacuum blower) sections. costs involved (e.g. investment, • Maintenance-free, no moving parts of up to 1,200 m3/hr. possible material, labour, etc.). • Low weight and component • High current consumption because dimensions and can be installed in of continuously operated pumps any mounting position • High initial costs and ongoing • No electrical connections required maintenance costs • Relatively high vacuum level (up to • Largeweightandunitvolumeas 85% vacuum) attainable well as fixed mounting position • Low initial costs

Leakage in vacuum systems When a vacuum suction gripper This might be caused, for example, by Remedial actions to achieve the cannot fully seal the system against rough and uneven workpiece surfaces required vacuum: atmospheric air, we talk about leaking or air-permeable workpiece materials. • Useofhigh-performanceejectors systems. • Reduction of the suction cup diameter

Selection aid for vacuum generators In all cases, it is recommended that Procedure: • Determining the correct ejector size you perform a test setup to determine • Determining the leak rate – Intersection of the leak rate (now the leak rate, thereby enabling you to – Perform the test setup known) with the curves of other ascertain which vacuum ejector you – Read the vacuum value achieved ejectors need. –Comparetheresultwiththe – Determine the attainable vacuum course of the curve in the by means of projecting ‘Suction capacity as a function of downwards from the vacuum’ chart ( 28) intersections with the leak rate – Difference with respect to suction • Select the ejector that reaches the capacity = leak rate required vacuum level.

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Typical applications

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What is a vacuum? In physics, a vacuum is defined as In practice, however, this state cannot Furthermore, every space contains “a state of emptiness that can be be achieved. We therefore talk instead particles of matter such as protons achieved by experiment” – in other about a vacuum when the air pressure andelectrons,aswellaszero-mass words, nothing. in a space is lower than the particles – photons – which transport This definition refers to the state of a atmospheric pressure or when the energy at the speed of light. space entirely devoid of matter density of air molecules is reduced. (sometimes also referred to as an “absolute vacuum”).

What is a vacuum used for? Since the 17th century (“Magdeburg In chemistry, reactions in substances Today, the vacuum plays a vital role in Vacuum technology has also played a hemispheres”) mankind has been are investigated in a vacuum, biology important industrial processes, many part in the development and studying vacuum. Today, we cannot is interested in the effects of a of which would not be possible implementation of new ideas in imagine modern research without it. vacuum on organisms, while some without it. Noteworthy examples handling technology, i.e. lifting, areas of physics (quantum physics, include semiconductor manufacture holding, rotating and transporting all field theory, etc.) are concerned with or mass spectroscopy. kinds of parts. particles that can be examined more accurately in a vacuum.

Understanding vacuum Airisagasmixturecontaining To attain a state of vacuum, a space Pressure gauge In reality, however, this is rarely approx. 1025 particles per m3 at must be empty, i.e. devoid of all achievable. In an ultra-high vacuum, one bar air pressure. gaseous material. the pressure may indeed be low The consequence of this is that the (approx. 10–8 to 10–11 mbar), but the pressure in this space is very low, as it particle number density is still 13 3 Nitrogen contains no or only a small number of approx. 2.5 x 10 particles per m . particles, which exert a force on an Small number of particles The following rule therefore applies: area as a result of their impact at constant temperature The fewer particles there are, the Oxygen against the walls.  low pressure lower the pressure.

Pressure is therefore defined as Pressure gauge Other gases follows: Pressure = Force In the atmosphere, this gas mixture is Area made up of the following gases and proportions: In theory, in an absolute vacuum, 78% Nitrogen i.e.wheretherearenomoreparticles 21% Oxygen of matter in the space, pressure = 0. Large number of particles 1% Other gases at constant temperature  (e.g. carbon dioxide and high pressure argon)

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Vacuum ranges

In practice, the large vacuum range P P that can technically be achieved – [pa] [mbar] which now consists of more than Handling range: 16 powers of ten – is generally GV This vacuum range is used in handling subdivided into smaller ranges. technology. The vacuum ranges below are FV classified according to physical attributes and technical HV GV = Rough vacuum requirements. FV = Medium vacuum HV = High vacuum UHV UHV = Ultra-high vacuum

Vacuum range Pressure range (absolute) Applications Rough vacuum Atmospheric pressure … 1 mbar Applications in industrial handling technology. In practice, the vacuum level is often specified as a percentage, i.e. the vacuum is defined in proportion to its ambient pressure. The material and the surface finish of workpieces play a major role in vacuum applications. Medium vacuum 10–3 …1mbar Steel degassing, light bulb production, drying of plastics, freeze drying of foodstuffs, etc. High vacuum 10–3 …10–8 mbar Smelting or annealing of metals, electron tube manufacture. Ultra-high vacuum 10–8 …10–11 mbar Spraying of metals, vacuum metallizing (coating of metals) as well as electron beam melting.

Measuring the pressure or vacuum Pressure is defined as the force per For this reason, all measuring The most common mechanical unitarea.Airisagasmixturemade instruments must be “calibrated”, function types are: up of many particles (atoms and i.e. individual measuring instruments molecules). These particles are in with the same function must be • Bourdon tube pressure gauge continuous motion. Wherever they adjusted so that they produce the • Aneroid pressure gauge meet, they exert a force. same result under the same • Diaphragm pressure gauge The pressure and vacuum are conditions. • Digital pressure gauge measured by taking a specific unit Inordertobeabletoevaluateor area and measuring the number and measure the vacuum medium, there In the high and ultra-high vacuum intensity of this impact on this area. are a number of items of technical range, pressure gauges with highly Measurements are necessary in order equipment that are indispensable for sensitive response mechanisms are to be able to check and monitor applications in the fields of industry used. A great many additional factors processes. and research. play a role in determining the 1 Bourdon tube Pressure gauges (vacuum gauges) are measurement results in this case. 2 Spring support used generally as well as in the rough 3 Spring end piece vacuum range. These gauges are It is important to remember that there 4 Segment scaled according to the level of are two different options for specifying 5 Tie rod accuracy required. Pressure gauges or representing the same 6 Gearing work according to many different measurement result. 7 Indicator shaft operating principles and can function 8 Coil spring mechanically or digitally. 9 Indicator aJ Dial face

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Vacuum designations and specification options It is important to mention at this point both colloquial and technical misunderstanding, these designations that there a number of different language. need to be explained here. designations for the term vacuum in In order to avoid any uncertainty or

Vacuum Correct designation – specified as % only in the range 0 … 1 bar absolute pressure.

Operating pressure Vacuum as an absolute value Vacuum as a relative value Correct designation, operating Applications: Applications: pressure of 0 bar relative pressure is In the field of science as well as in the In the rough or operating vacuum equivalent to 1 bar absolute pressure. medium-high and high vacuum range (e.g. for Festo applications). A vacuum is generally specified as ranges. Principle: relative operating pressure, i.e. with a Principle: Vacuum is specified as a relative negative sign. Vacuum is specified as an absolute value in proportion to ambient value in proportion to absolute zero, pressure, i.e. the specified vacuum Operating pressure can be specified i.e. 0 bar is the lowest value and value has a negative sign, because correctly in two different ways, i.e. as corresponds to 100% vacuum. In the the ambient pressure (atmospheric arelativeoranabsolutevalue.Both vacuum range, 1 bar is thus the pressure) has been assumed as the specification options are also applied highest value and corresponds to the reference point with a value of 0. The to vacuums and are explained in more average ambient pressure. lowest value, i.e. also 100% vacuum detail below. Feature: corresponds to –1 bar relative Vacuum values have positive signs. operating pressure. Vacuum range 1 … 0 bar Feature: Vacuum values have negative signs. Vacuum range 0…-1 bar

Specification options for the pressure or vacuum Operating pressure Vacuum Absolute pressure [bar] [%] [bar] 6 – 7 5 6 4 5 3 4 2 3 1 2 0 0 1 –0.1 10 0.9 –0.2 20 0.8 –0.3 30 0.7 –0.4 40 0.6 –0.5 50 0.5 –0.6 60 0.4 –0.7 70 0.3 –0.8 80 0.2 –0.85 85 0.15 –0.9 90 0.1 –0.95 95 0.05 –1 100 0

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Units of measurement As already described in the section It should be mentioned here that the Vacuum specifications that use bar as For the sake of simplicity, vacuum is “Designations and specification current official unit of measurement the unit of measurement are always generally expressed as a percentage options”, there are two ways of for the vacuum is the pascal (Pa). considered as relative values in the range 0 to 100%. representing a vacuum: However, this is rarely used in (described under “Vacuum as a This is always a relative value. practice. In reality, the preferred units relative value”). The conversion tables (international • As a pressure unit of measurement are bar, mbar or %, The most commonly used pressure vacuum/pressure conversion tables) (relative or absolute) particularly in the rough vacuum units bear the following ratios to one below are a useful aid for expressing • As a percentage range (e.g. handling technology). another: these values relative to the other units In the following pages also, only the of measurement. There are a large number of national units of measurement bar and % are 100Pa =1hPa and international units of used. 1hPa =1mbar measurement in common use that can 1 mbar = 0.001 bar be used to specify a vacuum as a pressure unit. These units of measurement are listed in the conversion table (international vacuum/pressure conversion table) below.

International vacuum/pressure conversion table 2 2 Unit bar N/cm kPa atm, kp/cm mH2O torr, mm Hg in Hg psi bar 1 10 100 1.0197 1.0197 750.06 29.54 14.5 N/cm2 0.1 1 10 0.1019 0.1019 75.006 2.954 1.45 kPa 0.01 0.1 1 0.0102 0.0102 7.5006 0.2954 0.145 atm, kp/cm2 0.9807 9.807 98.07 1 1 735.56 28.97 14.22 mH2O 0.9807 9.807 98.07 1 1 735.56 28.97 14.22 torr, mm Hg 0.00133 0.01333 0.1333 0.00136 0.00136 1 0.0394 0.0193 in Hg 0.0338 0.3385 3.885 0.03446 0.03446 25.35 1 0.49 psi 0.0689 0.6896 6.896 0.0703 0.0703 51.68 2.035 1

International vacuum/pressure conversion table with absolute and relative value comparison 2 2 Relative vacuum Residual Pressure, N/cm kPa atm, kp/cm mH2O torr, mm Hg in Hg pressure, relative absolute [%] [bar] [bar] 10 0.9 –0.101 –1.01 –10.1 –0.103 –0.103 –76 –3 20 0.8 –0.203 –2.03 –20.3 –0.207 –0.207 –152 –6 30 0.7 –0.304 –3.04 –30.4 –0.31 –0.31 –228 –9 40 0.6 –0.405 –4.05 –40.5 –0.413 –0.413 –304 –12 50 0.5 –0.507 –5.07 –50.7 –0.517 –0.517 –380 –15 60 0.4 –0.608 –6.08 –60.8 –0.62 –0.62 –456 –18 70 0.3 –0.709 –7.09 –70.9 –0.723 –0.723 –532 –21 80 0.2 –0.811 –8.11 –81.1 –0.827 –0.827 –608 –24 90 0.1 –0.912 –9.12 –91.2 –0.93 –0.93 –684 –27

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Atmospheric air pressure Definition Our planet – which includes us as On average, the air pressure at sea If, starting at sea level, we now begin To make things simpler, the air well as everything on the earth’s level is 1,013.25 mbar. If we imagine to climb higher, this imaginary air temperature and mass are considered surface – is surrounded by a layer of an air column with a cross-section column becomes shorter and the air as constants when deriving the air several kilometres thick. This layer area of 1 m2, which extends from the mass is reduced. Because the air formula. of air is known as the earth’s earth’s surface (sea level) to the pressure falls as the air mass In the derivation of the formula, the atmosphere or, more simply, the outermost edge of the atmosphere, decreases, we can conclude that densityofthelayerofair(ρ)aswellas atmosphere. Gravity causes the the air exerts pressure on this 1 m2 of atmospheric air pressure falls as the pressure at the earth’s surface weight of this mass of air to exert the earth’s surface with a mass altitude increases. This is why we say (p(h=0)) are based on assumptions pressure on the earth’s surface. of 10,000 kg approx. that “the air is getting thinner”. from empirical values. The pressure generated is known as These courses of action and atmospheric pressure or air pressure. Air pressure dependent on altitude simplification of the formula Our atmospheric conditions can also can be calculated using the derivation are an idealisation. -H- Note be compared with conditions under Boltzmann barometric equation. This − × NASA describes an altitude of Ꮇ ghᎼ water. We live at the bottom of a “sea calculation is affected by a wide p(h) = p(h=0) exp p(h=0) of air”. approx. 120 km above the earth’s variety of factors. The gravitational force of the air above surface as the outermost edge of the p(h) = Air pressure dependent us generates pressure which we call atmosphere. Air molecules can, In order to achieve accurate results, it on altitude air pressure. however, be found at much greater is important to consider not only the p(h=0) = Pressure at the earth’s At present, the official unit of altitudes. It is therefore impossible output altitude, but also factors such surface (1.013 bar) measurement for air pressure is hPa. to definitively identify the “edge” of as local gravitational force, ρ = Density of the layer of air This abbreviation stands for the atmosphere. atmospheric density and (1.29 kg/m3) hectopascal (1 hPa = 1 mbar). temperature. h = Altitude g = Acceleration due to gravity Generally applicable statements • At sea level, atmospheric pressure • At the summit of Mount Everest h[km] 1 Mount Everest is approx. 1,013 mbar. (8,848 m), atmospheric pressure is 2 Festo • By 2,000 m above sea level, the only 330 mbar. 3 Sea level pressure has fallen by approx. 1% • At an altitude of 16,000 m the per 100 m to 763 mbar. pressure is 90 mbar, while it is • At approx. 5,500 m, the pressure is 15 mbar at 30,000 m and approx. only 50% of the value at sea level. 8 mbar at 50,000 m.

p[hPa]

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Effect of changes in air pressure on vacuum technology

The pressure drop that occurs with As described earlier, air pressure at 0.4026 bar (402.6 mbar). PB increasing altitude does, of course, sea level (0 m) is approx. 1,013 mbar. Assuming that we take the same [bar] have an effect on vacuum technology At sea level, a vacuum generator with vacuum generator and go higher than 1,013 mbar PA or even on the vacuum generators a performance level of 80% vacuum the previous 2,000 m above sea level themselves. achieves absolute pressure of in order to generate or use a vacuum, 763 mbar Because the air pressure in the approx. 0.2 bar (200 mbar). the maximum attainable vacuum level atmosphere falls with increasing This air pressure falls with increasing would continue to fall while the altitude. Up to a height of 2,000 m, performance level would remain altitude, the maximum attainable there is a linear drop in pressure by unchanged at 80% because the differential pressure and, approx. 12.5 mbar per 100 m to ambient pressure in the atmosphere [p] consequently, the maximum 763 mbar. continues to drop. attainable holding force of a vacuum However, although the same vacuum At a height of approx. 5,500 m above suction gripper are also reduced. In generator still has the same sea level, the air pressure is only other words, the attainable vacuum performance level of 80% vacuum, approx. 50% of the pressure value at level of a vacuum ejector reduces with 0m 2,000 mm this figure of 80% refers to the sea level (506 mbar). (sea level) (height above increasing altitude. Nevertheless, the ambient pressure that has fallen to Thepossibleholdingforceofa sea level) performance level of 80% vacuum, for 763 mbar because of the increase in vacuum suction gripper falls p = Performance of vacuum example, remains unchanged altitude. This vacuum generator can proportionally with the attainable generator X = 80% ( Figure on right). therefore only achieve a maximum vacuum value. absolute pressure of approx.

Valid standards and guidelines In accordance with Festo standard FN Scaling factor: measurement results. Example: 942 011, the standards and When measuring characteristics (air The measurement results are therefore A current air pressure guidelines have been defined for the consumption, pressure, evacuation related to the reference pressure. They pamb = 975 mbar produces a scaling vacuum range. time and suction capacity), are converted using a scaling factor S = 1.039. The required fluctuations in the ambient pressure factor (S), which is calculated on the vacuum is therefore produced at a Vacuum: must be taken into account. Given that basis of the following equation. measured value of 750 bar All vacuum generators based on this all pressure values measured in the (0.75 mbar) absolute to P = 780 bar standard that are covered in this research laboratory are relative pref (0.78 mbar). S = system description operate exclusively pressure values referring to the pamb in the rough vacuum range. In current ambient pressure, the accordance with the Festo guideline, fluctuations in ambient pressure (pref = 1,013 mbar) the average air pressure at sea result in a degree of dispersion in the level (1,013.25 mbar) must always be taken as the reference value when specifying and calculating pressure values.

DIN standards, research reports and Festo guidelines DIN 1 314 DIN 28 401 FB 190 FR 970 003 Pressure, basic definitions and units Graphical symbols (summary) Vacuum Guideline – Basic Principles FluidUnitsandVariables (Research Report, Festo Research, DIN 28 400 DIN 28 402 Dr. Berger) FR 970 004 Vacuum technology Quantities, symbols and units Flow Rate Measurement Part 1 General terms (summary) Part 2 Vacuum pumps Part 3 Vacuum gauges Part 8 Vacuum systems, components

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Vacuum generator Introduction Generating a vacuum in a closed 1. The gas is evacuated from the The range of vacuum generators is A direct comparison of these vacuum space means dropping the air or gas closed space into an external very extensive. All work according to generators would not be objective pressure. To do this, the gas particles space or into the atmosphere. different technical principles and enough, as they differ fundamentally must either be removed or reduced in 2. The gas is combined within the methods and are often categorised from one another in terms of their quantity. vacuum system, i.e. condensed, under the umbrella term “vacuum technical construction, their mode of There are basically two ways of doing absorbed or chemically pumps”. operation, their ranges of application this: combined. We need to categorise the vacuum and their efficiency. generators into three types here and In this section we will describe the classify them according to their mode various types of vacuum generator of operation: referred to here based on their • Vacuum ejectors, functionality and focus on their • Gas-absorbing vacuum pumps, technical features and benefits. • Gas-feeding vacuum pumps.

Vacuum ejector – High vacuum, relatively low flow rate General Compared with the often highly Vacuum ejectors basically function or low pressure with a relatively low they have in common is the fact that complex and unwieldy mechanical according to the venturi nozzle flow rate. the venturi principle is applied designs used to generate a vacuum, principle, i.e. the vacuum is generated They operate according to two different wherever the vacuum is generated. the operating principle of ejectors is using pneumatically driven nozzles design principles using very different, extremely simple. Yet despite its without moving parts. often complex equipment such simplicity, this principle offers Vacuum ejectors are characterised by asvalves,filters,silencers,switches, enormous potential as an extremely their ability to generate a high vacuum etc. However, the crucial element that practical solution.

Function principle A classic ejector consists of a jet nozzle) accelerates the air to up to compressed air from the jet nozzle Single-stage ejector nozzle (venturi nozzle) and, 5 times the speed of sound as it flows creates a suction effect at the gap to depending on the design principle, at through the jet nozzle. the receiver nozzle, which in turn Venturi nozzle least one receiver nozzle. There is a short gap between the exit creates a vacuum at the output (jet nozzle) Compressed air enters the ejector. The fromthejetnozzleandtheentryinthe (vacuum port). narrowing of the jet nozzle (venturi receiver nozzle. The expanded Receiver nozzle

Vacuum port

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Vacuum ejector – High vacuum, relatively low flow rate Design principles Single-stage ejector: Multi-stage ejector: falling air pressure. The drawn-in air Again, the air is generally discharged The design principle for a single-stage This design principle also includes a from the first chamber, combined with via a silencer at the end of the last ejector includes a jet nozzle and only jet nozzle. Behind the first receiver the compressed air from the jet receiver nozzle. one receiver nozzle. After exiting the nozzle there are additional nozzle nozzle, is thus used as a propulsion receiver nozzle, the exhaust air is stages, each of which has a bigger jet for the other chambers. generally discharged via a silencer or nozzle diameter in proportion to the directly into the atmosphere.

Features • Completely maintenance-free and • No heat build-up • Small line lengths between vacuum • Multiple functions possible in a wear-resistant because there are no • Compact design, smallest possible generation and application single device moving parts dimensions • Easy to install, can assume any • Dry and filtered compressed air is • Low initial costs • Suitable for pulsed applications mounting position useful • Low energy costs, as the ejector is • Fast reacting • Low weight • Supply port 4 … 6 bar optimal only switched on when in use

Applications • Part feeding systems in the • Industrial robot applications in all • Process engineering • Transport of liquids and bulk automotive industry sectors material • Packaging industry

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Displacement/kinetic vacuum pumps General Another component for generating a In order to come up with a useful Vacuum pumps vacuum is the vacuum pump. classification of the pump designs and operating principles used in vacuum technology, it is best to Gas-absorbing Gas-feeding subdivide them according to their Vacuum pumps Vacuum pumps method of operation.

Displacement Kinetic Vacuum pumps Vacuum pumps

Gas-absorbing vacuum pumps Function principle As their name suggests, gas-absorbing them into a liquid, solid or sorptive closed space is reduced and a vacuum vacuum pumps do not discharge the state within the vacuum system. In is created. gas particles, but instead convert this way, the volume of gas (air) in the

Gas-feeding displacement vacuum pumps – High vacuum, low flow rate Function principle In displacement vacuum pumps, the Thefigureontherightisasimplified 1 1 Pressure side gas (air) freely enters an expanding illustration of how the principle of a 4 2 Suction side space, and is then mechanically shut displacement vacuum pump works. 3 Inlet valve off, compressed and ejected. The main Although there is a wide range of 4 Exhaust valve feature of vacuum pumps of this type solutions with varying designs, the 5 Piston is the fact that they can achieve a very operating principle of all pumps is the 3 high vacuum with very low flow rates. same. 5 2

Features • High vacuum level of up to 98% • Minimal maintenance expenses • Generally restricted mounting • Larger dimensions attainable positions

Applications • Packing machines • Manual vacuum handling • Clamping devices • Research

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Gas-feeding kinetic vacuum pumps – Low vacuum, high flow rate Function principle With kinetic vacuum pumps, the gas Vacuum blowers are categorised as Vacuum compressors are another type particles (air) are forced to flow in the kinetic vacuum pumps. of kinetic vacuum pump with similar delivery direction through the These vacuum generators operate features. application of additional force during according to the impulse principle, The drawn-in air is compressed in the 1 evacuation. i.e. during the transfer of kinetic 3 vaned chambers of an impeller in The main feature of these vacuum energy to the air by a rotating multiple stages with low pulsation by pumps is that only a relatively low impeller 1, the air is drawn in and means of centrifugal force. As with the vacuum can be generated. However, compressed 4 on the suction blower, high suction rates can be 2 3 they do achieve very high flow rates side by the blades on the 24 achieved here with limited vacuum (high suction capacity) at the same impeller. performance. time.

Features Vacuum blowers and compressors • Large volumes extracted in a very • High maintenance costs • Only low vacuum performance short time possible

Applications Vacuum blowers • Handling of extremely porous • Where large suction rates per unit materialssuchasclampingplates of time are important or cardboard boxes, etc.

Compressors • For precision industrial applications

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Practical use of vacuum Handling is a subfunction of material technology are feed technology assembly processes today. Vacuum technology has proven to be flow and is subdivided into the areas components and systems, pick-and- Vacuum technology is now an extremely effective in the handling of a of storing, changing quantities, place devices, manipulators and important part of this handling wide variety of materials and parts moving, securing and checking. robots. technology and has become and has thus opened up entirely new Handling requires the availability of The way in which parts are handled indispensable in many of the areas of application and solutions for specific geometric bodies (component has a major influence on productivity industries and fields of application in handling technology. parts or assemblies). Among the in automated production and which it is used. equipment used in handling

Handling tasks The following keywords and symbols Lifting Conveyance All of these tasks combined cover an Industrial fields of application of illustrate the significance of vacuum Loading Turning almost unlimited range of vacuum technology include, technology in handling technology as applications in industry. for example: Gripping well as the various tasks that it is • Special machine construction used to perform. Machining • Packaging industry • Food industry Holding • Woodworking industry Insertion • Metalworking industry • Automotive industry Moving • Electrical engineering industry Feeding Repositioning Transporting

General Vacuum technology generally tends to Nevertheless, there are also a great come under the umbrella term of many applications where this gripper technology. technology is being pushed to its limits. In handling technology, a large number of applications use This is where vacuum technology mechanical gripper technology to frequently comes into play and, great effect. indeed, is creating entirely new concepts and possibilities.

Advantages Vacuum in handling technology • Simple component and system • Low weight, i.e. suitable for • Low-cost means: design extremely dynamic movement • Low maintenance costs • Gentle handling of fragile parts • Compact, space-saving design • Fast cycle times possible • Can be adapted to suit many requirements

Important factors to consider The decision to use vacuum • Weight of the workpiece Having such a wide range of vacuum Festo provides a software tool which technology or another handling • Temperature of the workpiece or its component variants makes it easy to helps you select or find the right technology depends on a number of surface find the right components for just vacuum components for your specific different factors. Some of the most • Speed per unit of time for cycle about any application, taking into applications. important factors to consider are completion account the above factors, with described here. • Shapeoftheworkpiecesurface product features such as heat • Roughness of the workpiece surface resistance, speed, suction capacity • Stroke travel and conveying etc. distances for handling

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Single-stage and multi-stage ejectors General Nowadays, wherever vacuum There are, of course, still a great many arguments in favour of ejectors are As already explained in the section technology is used, you will also find special applications in which the their low initial costs, low “Components for vacuum generation” increased use of vacuum ejectors. vacuum pump is as indispensable as maintenance costs and greater  2, there are two different design ever. Nevertheless, many applications flexibility in terms of application principles for vacuum ejectors. How- in handling technology favour the use compared with other vacuum ever, the venturi operating principle of ejectors. The most convincing generators. applies to both types.

Function principle As described earlier, all ejectors work All ejectors based on this principle depending on the design principle, at according to the venturi operating have a jet nozzle (laval nozzle) and, least one receiver nozzle. principle.

Design principle Single-stage ejector: Single-stage ejector: Multi-stage ejector Multi-stage ejector This ejector principle includes a jet Like the single-stage ejector, this nozzle (laval nozzle) and one receiver design principle also includes a jet 1 nozzle. nozzle (laval nozzle), in which the 1 3 The extraction of ambient air and the compressed air flowing in is generation of a vacuum therefore take acceleratedtouptofivetimesthe place within a chamber and the gap speed of sound, followed by a receiver 2 2 between the jet nozzle and receiver nozzle. nozzle. 1 Supply port/jet nozzle Behind the first receiver nozzle there The compressed air or drawn-in 2 Vacuum/suction cup connection are additional nozzle stages, each of 3 ambient air is generally discharged 3 Exhaust air/receiver nozzle which has a bigger nozzle diameter in into the atmosphere (environment) via proportion to the falling air pressure. a silencer connected directly after the Thedrawn-inairfromthefirst receiver nozzle. chamber, combined with the compressed air from the jet nozzle, is thus used as a propulsion jet for the 1 Supply port/jet nozzle other chambers. 2 Vacuum/suction cup connection After exiting the last receiver nozzle, 3 Exhaust air/receiver nozzle the exhaust air is generally discharged into the atmosphere (environment) via a silencer.

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Single-stage and multi-stage ejectors Basic information A direct comparison of the design Manufacturers of vacuum ejectors Viewed objectively, handling vacuum generator can be measured or principles of single-stage and multi- tend to favour one of the two design technology using a vacuum comes evaluated. stage ejectors frequently gives rise to principles, thus making it difficult to down to a few important variables, discussions regarding the advantages get an objective opinion. with which the performance of a and disadvantages of both principles.

Efficiency η as a function of vacuum Δpu

Evacuation time = Time (s) required These variables – evacuation time, air η Δ = 1 ( pu) t(Δpu)×Q to generate a specific vacuum. consumption and the volume depend- + 1 V×60smin ent on the vacuum – produce a Air consumption = Air consumption formula, which can be used to η(Δpu) = Efficiency of the vacuum (l/min) of the ejector required to calculate the efficiency of a vacuum generatorinrelationto generate a specific vacuum. generator. This is the most objective low pressure η criterion that can be used to assess t(Δpu) = Evacuation time [s] the performance of different vacuum Q = Air consumption [l/min] generator types. V = Volume to be evacuated (standard volume) [l]

∆pu [bar]

In practice, the job of a vacuum generator is to generate a specific vacuum in the shortest time possible, using as little air (energy) as possible.

Misapprehension Suction flow rate = Suction air In practice, the performance of an sure and the result is then used as the Performance comparisons of vacuum volume (l/min) that an ejector can ejector is often – and incorrectly – ejector rating. In fact, the suction flow ejectors based on the suction flow rate draw in. measured on the basis of the suction rate falls progressively with an in- therefore have only a limited level of flow rate. The misapprehension lies in creasing vacuum, i.e. a high suction accuracy. Apart from this, the suction thefactthatthesuctionflowrateis flow rate does not necessarily result in flow rates of the specimens are often measured at atmospheric pres- a short evacuation time. compared at the same vacuum level.

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Single-stage and multi-stage ejectors Comparison The aim of this comparison of single- • Evacuation time Variables such as noise level, air A comparison of single-stage and stage and multi-stage ejectors is to • Air consumption supply time or attainable vacuum also multi-stage ejectors in practice evaluate variables or criteria that • Efficiency play an important role. produces the following general occur in practice and that can be used observations, which should be borne to measure the performance of the in mind before proceeding any further. ejectors.

General findings Variables/criteria Single-stage Multi-stage Suction flow rate Average High At low vacuum level up to approx. 50% Evacuation time Very short1) Very short1) In the higher vacuum range from 30 … 50% In lower vacuum range up to 30 … 50% Initial costs Low Relatively high Noise generation Relatively high Low

1) see diagram below

Evacuation time In general, the multi-stage ejector Looking at the chart illustrating this Operating pressure p as a function of the evacuation time t can, up to a pressure range of approx. comparison, it is obvious that single- 30 … 50% vacuum, generate this stage ejectors have a clear advantage pressure faster or evacuate the over multi-stage ejectors in this case. volume faster than the single-stage The higher the vacuum level, the more ejector. time the multi-stage ejector takes to However, a pressure of generate it. –0.4 … –0.8 bar or a vacuum of p[bar] between 40 and 80% is normally required in practice. 1 Multi-stage ejector 2 Single-stage ejector

t[s]

Air consumption Multi-stage ejectors have, on average, clear advantage over single-stage the advantage is not so clear-cut. considerably reduces the energy- a much lower level of air consumption ejectors . Although multi-stage ejectors have a saving benefits. and thus consume less energy than However, if we look at this information lower level of air consumption, their single-stage ejectors, giving them a in context with the evacuation time, evacuation time is higher. This

Suction flow rate Single-stage ejectors have a lower draw in higher volumes over the same this progressive curve falls off rapidly rate fall below the values achieved suctionflowratethanejectorsbased amount of time. for multi-stage ejectors (see chart). In with single-stage ejectors. on the multi-stage principle. Multi- However, as the vacuum level other words, as pressure increases, stage ejectors in the low vacuum increases (from approx. 30 … 50%), the initial gains of a higher suction range of approx. 30 … 50% can thus

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Single-stage and multi-stage ejectors Noise level, vacuum level and air supply time In comparison, single-stage ejectors atmosphere in “weakened” form in however, counteracted with suitable There are very few differences in air have a relatively high level of noise the case of multi-stage ejectors, the silencers. supply time, although a single-stage generation. Because the compressed noise level is, accordingly, lower than Both design principles reach the same ejector has a smaller volume to supply air is slowed down by the series of with single-stage ejectors. The noise vacuum level, although single-stage with air, which gives them a minimal nozzle stages before it reaches the levels in single-stage ejectors are, ejectors do so in a shorter time. time advantage.

Summary The cause of the somewhat poorer considerably less efficient than a another, are changed. This example illustrates how all of evacuation time of the multi-stage single-stage ejector. It is important, Although increasing the laval nozzle these variables are dependent on ejector lies in the fact that although however, to remember that these diameter while maintaining a constant each other. If one variable changes, the second and subsequent nozzle findings must be viewed as generali- operating pressure increases the this affects the other variables as well. stages generate a high suction sations and should therefore be used suction rate, it also extends the capacity, these are decoupled at a for reference purposes only. Irrespec- evacuation time and, in extreme Laval Evacuation relatively low vacuum level. This tive of the design principle, different cases, the desired vacuum cannot be nozzle ∅ time means that when the pressure is results are obtained when the initial reached without increasing the higher, only the first nozzle stage values, which interact with one operating pressure. Vacuum Operating draws in air. This first nozzle stage is level pressure

Conclusion The comparison shows just how exist on this basis. possess attributes that defy any more manageable than the multi- difficult it is to reach an objective It is also easy to see how minor generalisation. In conclusion, it can stage principle. conclusion about the pros and cons of technical adjustments affect the be said that the single-stage ejector The multi-stage ejector, on the other both operating principles. ejectors and how both operating achieves its best results in applica- hand, achieves its best results And that’s to say nothing of deciding principles can be optimised to suit the tions with average or higher pressure wherever a relatively low vacuum (up on a preferred operating principle or a relevant application (e.g. by varying (vacuum). The simple design makes to approx. –0.3 bar) needs to be “test winner”. Basically, the benefits the laval or receiver nozzle diameter). this operating principle more cost- generatedquicklyandwherever of both principles lie in very specific Both operating principles can thus effective and, in terms of dimensions, energy costs play an important role. areas and they justify their right to achieve degrees of efficiency or

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Energy cost comparison between vacuum ejectors and vacuum pumps (electric) Given that energy is a scarce, valuable cannot be overlooked. You should compressed air from atmospheric air, range(10…20bar),thecostsfor and, above all, expensive resource, therefore remember one golden rule at taking into account all costs such as compressed air increase by energy costs play an important role in all times: air is expensive. material, depreciation, labour costs, approx. 100%. choosing a suitable vacuum system. etc., with electricity tariffs (industry) of The air consumption of a vacuum With electrically driven vacuum €0.10/kWh,youmustreckononcosts Before proceeding any further, it is system might not initially seem to be a pumps, on the other hand, energy of approx. € 0.02 per 1 m3 volume at importantthatwementionsomeof particularly important consideration. costs can be measured and assessed 7 bar (normal supply pressure). These the criteria that should be considered However, the amount of energy that is much more easily on the basis of costs apply in the low pressure range when making a comparison of vacuum necessary to operate a pneumatic current consumption. up to 10 bar. In the high pressure ejectors and vacuum pumps. vacuum ejector with compressed air Thefactisthatinordertogenerate

Vacuum ejector For • Energy consumed only as required. Circuit diagram 1 • Energy-saving function: Circuit diagram 2 Compressed air or energy is only Many ejectors (compact ejectors) consumed during the suction have this function. Compressed air operation and during “workpiece is only consumed during generation handling” in an operation cycle. of the vacuum. Once the vacuum The vacuum generator remains level has been reached, the ejector switched off for the rest of the time is switched off. The vacuum is (discharge, return). Ejectors have maintained and monitored using fast response times (start and stop valves and switches times) and can therefore be ( circuit diagram 2). switched off when no vacuum is 1 = Compressed air connection Energy-saving function = 1 = Compressed air connection required ( circuit diagram 1). 2 = Suction cup connection 4 2/2-way valve + 2 = Suction cup connection • Vacuum ejectors require absolutely 3= Exhaustport 5 Switch + 3= Exhaustport no servicing apart from the prefilter 4 2/2-way valve 6Non-return valve 4 2/2-way valve and have no moving parts. 6 Non-return valve • Their low weight/mass ratio and 5 Switch their small unit volume, not to 6 Non-return valve mention the fact that they can be installed in any mounting position, are also worth noting. • A relatively high vacuum of up to 85% can be attained.

Against • With Festo ejectors, the suction rate • Higher compressed air consumption is relatively limited at per m3 vacuum increases energy approx. 16 m3/hour. costs dramatically. However, this is compensated by the air/energy- saving functions.

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Vacuum pump For • With some designs a very high • High suction rates of up vacuum level (up to 10–4 mbar to 1,200 m3/hr. possible. = 99.99999%) can be attained.

Against • Electro-mechanical vacuum pumps • High initial costs and ongoing • Large weight/mass ratio and large are almost always in continuous maintenance costs. unit volume as well as fixed operation, the vacuum require- mounting positions. ments are regulated by means of valves. This means that current consumption and, consequently, energy costs are very high.

Energy cost comparison/sample calculation In this example, we are comparing a • The electricity price is based on • The costs for compressed air refer • Additional assumed numerical vacuum ejector (pneumatic), both industry tariffs (€ 0.10/kWh). to, as mentioned earlier, a 1 m3 values such as time specifications, with and without an air-saving volume with 7 bar pressure. All for example, may apply depending function, with a vacuum pump costssuchasmaterial,depreci- on the application. (electrical) of similar performance. ation, labour costs, etc. are taken Using a calculation example, we want into account in the calculation to create a cost or energy cost (€ 0.02/m3). comparison over a period of one year.

Electricity price Compressed air costs System capacity Remarks [€/kWh] [€] [kW] 0.05 0.02 approx. 1,100 Large system 0.10 0.02 approx. 1,100 Large system 0.10 0.03 approx. 20 Small system

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Calculation base Ejector operation cycle

• Ejector with air-saving function: Thefigureontherightshowsan tE tE = Evacuation time 1 Air consumed (energy consumption) operation cycle for a vacuum system. t1 = Transport only while the workpiece is being The individual work steps of the t1 ta =Discharge received (picked up) (= 0.5 s). system are subdivided into time ta t2 =Return • Ejector without air-saving function: sectors. The amount of time allocated 1 =Pick-up 2

Air consumed (energy consumption) to the work steps depends on the [bar] =Timesaved u

for reception (pick-up) and vacuum generator. p t2 transport of the workpiece (= 2 s). • Vacuum pump: t[s] 2 Energy consumed for the entire operation cycle, as the pump is not normally switched off (= 5 s).

Variables/criteria Assumed numerical values Initial costs for vacuum pump [€] 715 Initial costs for ejector [€] 337 Maintenance costs/year for vacuum pump [€] 306 No. of operating days/year 250 No. of operating hours/day 16 Time per operation cycle [s] 5.0 Time for pump ON [s] 5.0 Time for ejector ON1) [s] 2.0 Time for ejector ON2) [s] 0.5 Price per kWh (industry tariff) [€] 0.10 Price per m3 for compressed air at 7 bar [€] 0.02 Supply pressure for ejector [bar] 6 Energy used to generate compressed air (1m3 at p = 7 bar) [kWh/m3] 0.095

1) Without air-saving function 2) With air-saving function

General calculations When comparing the energy costs for both vacuum generators, the following calculations must first be performed:

• Number of products per year • Proportion of pump operation to • Proportion of ejector operation • Proportion of ejector operation with (hours) operation cycle (%) without air-saving function to air-saving function to operation Formula: Formula: operation cycle (%) cycle (%) Total running time (s)/Time per Time for pump ON (s)/ Formula: Formula: operation cycle (s) Time per operation cycle (s) x 100 Time for ejector ON1) (s)/Time per Time for ejector ON2)(s)/Time per = 250 x 16 x 3,600/5 s = 5/5 x 100 operation cycle (s) x 100 operation cycle (s) x 100 = 2,880,000 hours = 100% =2/5x100 =0.5/5x100 =40% =4%

1) Without air-saving function 2) With air-saving function

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Vacuum ejector calculation The calculations for the vacuum (air consumption at P = 6 bar: ejector with and without the air- 505 l/min) saving function give us the following partial results:

• Running time per year • Air consumption per year • Energy costs per year Formula: Formula: Formula: No. of products (units) x Time for Running time per year (min)/ Air consumption (m3) ejector per unit (s) Air consumption (l/min) xPriceperm3 for compressed 2,880,000 unit x 2 s 96,000 min/505 l/min air (€) 1) = 5,760,000 s (96,000 min) 1) = 48,480 m3 48,480 (12,120) m3 x€0.02 2) = 1,440,000 s (24,000 min) 2) = 12,120 m3 1) = € 969.60 2) = € 242.40

Variables/criteria Assumed numerical values Air consumption at P = 6 bar [l/min] 505 Total air consumption per year at P = 6 bar1) [m3] 48,480 Total air consumption per year at P = 6 bar2) [m3] 12,120 Air saving per year2) [m3] 36,360 Air saving per year2) [%] 75 Energy costs per year1) [€] 969.60 Energy costs per year2) [€] 242.40 Energy saving per year2) [€] 727.20

1) Without air-saving function 2) With air-saving function

Electric vacuum pumps calculation The calculations for the vacuum pump give us the following partial results:

• Running time per year • Energy consumption per year • Energy costs per year Formula: Formula: Formula: Operating hours per day Running time per year x Energy Energy consumption per year x Operating days per year consumption per hour xCostsperkWh 16 hours x 250 4,000 hours x 0.55 kW 2,200 kWh x € 0.10 = 4,000 hours = 2,200 kWh = € 220

Variables/criteria Assumed numerical values Energy consumption/operating hour [kWh] 0.55 Energy consumption/year [kWh] 2,200 Energy costs/year [€] 220

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Cost comparison of the vacuum ejector and vacuum pump The costs of the vacuum system are • Investment costs Investment costs are one-off costs, made up of three cost types: • Maintenance costs while maintenance and energy costs • Energy costs are incurred annually.

Result Adirectcostcomparisonshowsthat The ejector without the air-saving and investment costs into account, the vacuum pump has the lowest function has considerably higher this reduces the advantage that the energy costs, closely followed by the energy costs than the other vacuum vacuum pump has over the other ejector with the air-saving function. systems. If we also take maintenance systems due to its low energy costs.

Cost type Vacuum pump Ejector Ejector without air-saving function with air-saving function Investment [€] 715 337 337 Maintenance1) [€] 306 – – Energy1) [€] 220 969.60 242.40

1) annual costs for a vacuum pump after approx. 4,000 to 6,000 hours

Conclusion The calculation example shows that maintenance costs associated with their simple design keeps initial costs dominated by the vacuum pump and ejectors more than justify their their continuous use and wearing and maintenance costs to a minimum. where ejectors are not used. This is existence. parts confirm this conclusion. There are, of course, a great many not the case, however, with handling The high investment costs for vacuum Whileejectorsmayusemoreenergy, areas of application that are technology. pumps as well as the annual

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Leakage in vacuum systems Ideally, when using vacuum When a vacuum is generated, the Unfortunately, these ideal surface In these applications, the vacuum applications in handling technology, sealing rim of the suction cup can conditions do not always exist on the suction grippers cannot completely the workpiece surfaces on which the fully seal the system against external workpieces to be moved. The seal the system against atmospheric suction cups have to rest should be atmospheric air. We therefore materials are often air-permeable air. If atmospheric air constantly smooth and impervious. A suction cup describe this as a leak-proof system. (e.g. sheets of paper) or very rough enters the system during vacuum fits tightly against this type of surface. The holding force of the suction and uneven. generation, we describe this as a gripper on the workpiece increases as leaking system. the vacuum level in the system increases compared with the external atmospheric pressure.

Leak-proof systems

In vacuum technology, the When a specific volume is being Evacuation time tE asa function of vacuum pu performance of the vacuum generator evacuated, the course of the time/ for the handling of leak-proof material pressure curve travels upward depends, among other things, on how proportionally, i.e. the higher the quickly the system can generate a vacuum level, the stronger the fall in specific vacuum. This rating is known the suction capacity of a vacuum [s] E as the evacuation time of the vacuum generator and the longer it takes to t generator. attain an even higher vacuum level.

pu [bar]

Leaking systems The requirements for handling porous continuously evacuating the air conditions (leak-proof system). performance level. To determine the materials (leaking systems) are (leakage air) entering the system. However, in this case the leakage air leakage air volume, it is recommended different. In order to attain or maintain The maximum attainable vacuum that entering the system prevents the that you carry out a test the desired vacuum level, the vacuum a vacuum generator can produce is vacuum generator from reaching or ( 27, “Selecting vacuum generators generator must be capable of normally measured under ideal being able to attain its maximum according to leakage flow”).

Remedy In general, there are two options for Option 1: Option 2: To select the correct vacuum optimising or increasing the vacuum Using a high-performance vacuum Reducing the suction cup diameter or generators for handling leakage flow, level in leaking systems. generator. orifices. you need to perform a test setup as Advantage: Advantage: outlined above. With the aid of charts, • Power transmitted as required • Leakage is reduced (energy costs) you can then select the right vacuum Target Actual Target • Simple solution Disadvantage: generator. Disadvantage: • Power transmission may be below This selection aid is described in • Leakage remains high the required vacuum level. detail on page 27. Actual • High energy costs 

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Selecting vacuum generators according to leakage flow A reliable method is needed to e.g. the selection of vacuum determine the exact leak rate in generators with larger dimensions, be vacuum systems or applications. Only taken and the functional reliability of then can optimal remedial action, the vacuum system guaranteed.

Graphical representation as a tool

• Graphical representation Suction capacity qn as a function of vacuum pu All curves in the chart have an almost of the suction capacity in relation to linear downward course. The vacuum/operating pressure in a maximum suction capacity of the chart (all ejectors in a single chart). individual vacuum ejectors is reached at atmospheric air pressure (0% vacuum). The higher the vacuum level, the lower the suction capacity of a vacuum [l/min]

n generator, up to a maximum limit. q This chart is very useful for finding out 1 VAD-y quickly and reliably whether a 2 VAD-¼ vacuum generator is needed to 3 VAD-x achieve the desired vacuum level with 4 VAD-M5 leaking materials.

pu [%]

Test setup • Perform a test setup The operating pressure (vacuum) of with an ejector as the vacuum the system is now measured at a generator, a vacuum gauge constant supply pressure. The (pressure gauge) as the measuring performance of an ejector under instrument as well as a suction 1 Supply port normal operating conditions, i.e. gripper and workpiece as the 2 Suction cup connection without leakage, can be determined leakage source. The test setup is 3 Exhaust port from its technical data as well as from illustrated in the following figure. the ‘Suction capacity as a function of vacuum/operating pressure’ chart. The measurement results from the test setup are then compared with the known data.

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Selecting vacuum generators according to leakage flow Procedure Where systems are clearly leaking The following procedure is with the relevant application and can (e.g. because of porous or rough recommended for finding a suitable generate the required vacuum level: workpieces), the leak rate must be vacuum generator that is compatible determined.

Determining the leak rate • Perform the test setup In a test setup like the one illustrated In a leak-proof system, the value The leak rate can then be determined • Read the vacuum or operating earlier, a workpiece is picked up using indicated on the vacuum gauge must on the basis of the measured vacuum pressure achieved a defined suction gripper size, a correspond to the value contained in value in conjunction with the chart • Compare the result with the course vacuum generator and pressure the technical data for the vacuum (Suction capacity as a function of of the curve in the chart supply(5.5…6bar). generator. vacuum/operating pressure). • Suction capacity difference = leak In a leaking system, the vacuum rate attained is read from the vacuum gauge.

Example In a test setup using the ejector 2 residual airflow can be read from the Result: VAD-¼, a vacuum level of 35% is suction capacity scale. The residual airflow or leak rate is achieved at full pressure supply. This residual airflow corresponds to =22l/min. Starting from this result, if we draw a theleakrateofthesystem,asinthe The only disadvantage of this method horizontal line and a vertical line case of a leak-proof system the liesinthefactthatitisimpossibleto intersecting the ejector curve 2,the residual airflow would be = 0. tell whether the leakage is caused by the workpiece itself or by a rough surface underneath the edge of the suction gripper.

Determining the correct ejector size • Compare the intersection of the Conversely, with a known leak rate of If we now extend the horizontal line generators (at the same leak rate) leak rate (now known) with the 22 l/min, we can now read the that we drew previously in the chart to from the intersection with the curves curves of other ejectors. vacuum level attainable with other determine the leak rate (Procedure 1), of other ejectors and the subsequent • Determine the attainable vacuum vacuum generators from the “Suction we can determine the vacuum level downwards projection to the vacuum by projecting the intersections with capacity as a function of vacuum” attained with other vacuum scale. theleakratedownwards. chart. • Select the ejector that reaches the required vacuum level.

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Selecting vacuum generators according to leakage flow Example

If we extend this horizontal line, it Suction capacity qn as a function of vacuum pu Result: must intersect another curve. In the In this application, the next largest case of the next largest vacuum vacuum generator 1 would attain a generator 1 VAD-y,theline vacuum level of 52%. intersects at 52% vacuum. If this vacuum level were sufficiently The curve for the next smallest high for the application, this would be vacuum generator 3 is overshot and the right choice of ejector. Otherwise, there is no intersection. In other a higher-performance ejector should [l/min] words, the low performance value n be chosen (curves not available in this q would mean that no vacuum is chart). generatedwiththisleakageflow,as 1 VAD-y the quantity of air drawn in is lower 2 VAD-¼ than the quantity of air that is 3 VAD-x discharged because of the leakage. 4 VAD-M5

pu [%]

Conclusion This method is useful for determining However, it should be noted that Leakage, for whatever reason, should • Energy costs the correct ejector size where the leak leakage can occur at other positions, be avoided if at all possible. Where there is a leakage flow, the rate is known. e.g.: • Safety risk air consumption (energy • seals, A leakage flow increases the risk of consumption) of an ejector is much • tubing connectors, the vacuum system no longer being higher than that of a leak-proof • couplings able to attain the required pressure system. in a vacuum system. and the workpiece being dropped • Time during handling. A leakage flow means it takes longer to reach the required vacuum level.

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Technical symbols Vacuum ejector Vacuum gauge Filter This system description uses technical The technical symbol used in the Measuring and checking device for the Filters the drawn-in air and prevents symbols to represent individual function charts for all Festo vacuum analogue vacuum display. contamination of the ejector. components in function charts as well generators. as in component descriptions. These symbols are illustrated and described in this section.

Vacuum suction cups Non-return valve Reservoir container Standard,extra-deep,round,oval. Prevents the drawn-in air from flowing Air reservoir to support the setting In technical circuit diagrams, this back against the intake direction, down of a workpiece that was symbol represents the complete i.e. the valve permits flow in one previously picked up. suction gripper (suction cup direction only. holder+suctioncup+accessories).

Bellows suction gripper Solenoid valve Throttle 1.5 convolutions, 3.5 convolutions. In Different valve types (mostly 2-way For controlling the flow rate or technical circuit diagrams, this valves) perform the ON/OFF or exhaust pressure. symbol represents the complete function in vacuum technology. suction gripper.

Silencers Dampens the compressed air, which flows from the venturi nozzle at ultrasonic speed, before it is discharged into the atmosphere.

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Circuit diagrams with vacuum components Circuit diagrams help provide a system. The technical drawings below general understanding of the mode of contain examples of pneumatic circuit operation of vacuum components as diagrams. These are intended as a well as a schematic representation of reference to help you understand the their function within the overall symbols used in vacuum technology.

Basic vacuum circuit

Regulated vacuum circuit

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Vacuum ejectors Vacuum generators are the central Festo only uses ejectors that operate Festo offers a wide selection of • Basic ejectors element of any vacuum system. according to the single-stage design ejectors of different types and with • Inline ejectors The mode of operation of vacuum principle. different equipment to suit a whole • Compact ejectors ejectors and the venturi principle host of application and performance were already explained in the Basic requirements. Each group is, in turn, subdivided into principles section ( 12). These vacuum generators are a wide range of performance classes subdivided into the following ejector and equipment types. groups:

Standard and inline ejectors The functions of standard and inline The ejector design basically consists Control, monitoring and other Because they are so compact, ejectors ejectors are essentially limited to the of just a single jet nozzle that functions depend on external and of this type can generally be used basic function of an ejector, operates according to the venturi additional components within the directly wherever a vacuum is i.e. generation of a vacuum. principle. vacuum system. required,eveninlargequantities. These ejectors are therefore much They are also used in vacuum 1 3 smallercomparedwithothervacuum processes that do not require complex ejectors. and sophisticated control technology.

VN-… VAD-… 2

Ejector/venturi nozzle 1

1 = Compressed air / nozzle 2 = Vacuum / suction port 2 3 = Exhaust air/receiver nozzle 3

1 Ejector 2 Suction cup holder 3 Suction cup

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Compact ejectors In practice, demands on vacuum Vacuum ejectors are therefore capable Depending on the ejector and design, • Solenoid valves systems in terms of function, speed of much more than just vacuum these function units contain the • Filter (performance) and, increasingly, generation. Compact ejectors have a following components in addition to • Non-return valves economy tend to be extensive. number of components integrated in the vacuum generator: • Silencers or on the housing, which makes them • Vacuum switch complete function units.

Vacuum ejector VADMI-… Taking a vacuum ejector VADMI--… as The individual components are an example, we can see the identified in the sectional drawing components and functions of a (34). The functions, benefits and complete function unit. special features are described in the notes.

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General information

1 aA

aJ 2 9

3

8 7 4 6

5 6

Components 1 Solenoid valve for ejector pulse 3 Special silencer 7 Non-return valve aJ Manual override (VADMI-…, VAD-M…-I-…) 4 Vacuum switch 8 Supply port aA Solenoid valve for vacuum 2 Venturi nozzle (jet and receiver 5 Filter for air to be evacuated 9 Manual ejector pulse control generation nozzle) 6 Two vacuum ports

Description Function Benefits 1 Solenoid valve for ejector pulse If the voltage is switched off at the valve for ejector pulse, the vacuum is • Rapid purging of vacuum –3/2-wayvalve solenoid valve for vacuum generation rapidly purged at port 6 as a result • Fast and precise setting down of – Controls ejector pulse aA andswitchedonatthesolenoid of the application of pressure. workpieces • Short vacuum ejector operation cycles

2 Venturi nozzle (jet and receiver When pressure is supplied to the receiver nozzle and directed into the • Ejector performance can be nozzle) supply port 8, compressed air flows silencer 3. A suction effect, which modifiedandcontrolledbyvarying – Most important ejector into the jet nozzle. The narrowing of evacuates the air from the filter 5,is thenozzlediameterorsupply component the nozzle accelerates the compressed created between the jet nozzle and the pressure – Used for vacuum generation airtoupto5timesthespeedof receiver nozzle. A vacuum is created sound. This air flow is collected by the at the vacuum port 6.

3 Special silencer (closed, surface Thesilencerismadefromair- silencer dampens this air flow, thus • Minimises the noise level from the or round type) permeable plastic or a metal alloy. reducing the noise level before the exhaust air during ejector operation – For noise reduction in exhaust The air flow exits the jet nozzle at up compressed air (exhaust air) enters air to 5 times the speed of sound. The the atmosphere.

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Components Description Function Benefits 4 Vacuum switch with PNP or NPN On the vacuum switch, the vacuum status. If the vacuum range falls below • Air-saving function: The vacuum output range for holding the workpiece is set the required level, the signal controls generator is switched off within the – For pressure monitoring using two potentiometers. Once the the switching on of the vacuum required vacuum range vacuum level is reached, a signal generator. If the required vacuum can • Safety function: Control of vacuum switches off the vacuum generator no longer be generated because of a generator if vacuum level goes (air-saving function). The non-return malfunction, the vacuum generator is above or below the required values valve 7 maintains the vacuum in this switched off.

5 Filter for air to be evacuated A large plastic filter is integrated operation, the air is filtered before it • No contamination of the system – With contamination indication between the vacuum port 6 and the enters the vacuum generator. • Protection of components – 40 μm grade of filtration vacuum generator 2 or non-return A removable display window shows • Display ensures maintenance is valve 7. During the suction the degree of filter contamination. carried out regularly

6 Two vacuum ports (V) or (2) Vacuum components can be Depending on the application, you – With female thread connected here (e.g. vacuum suction can use either one output or both gripper). outputs simultaneously.

7 Built-in non-return valve After the vacuum generator is air, thus preventing a drop in • The vacuum is maintained after the switched off, this non-return valve pressure. vacuum generator is switched off prevents a backflow of the drawn-in (air-saving function in connection with the vacuum switch 4 ).

8 Supply port (P) or (1) The compressed air supply port (P) or (1) for generating the vacuum is con- tained in the ejector housing.

9 Manual ejector pulse control The intensity of the air flow and, suction gripper, can be adjusted • The system can be optimised for the consequently, the time taken to manually. vacuum application remove the workpiece from the

aJ Manual override Stem on the solenoid valve that can that is already present cannot be • Manual switching of the solenoid be switched without an electrical disabled. valve signal. However, an electrical signal

aA Solenoid valve for vacuum When the signal is activated, vacuum. The air flow is interrupted • Air-saving function in connection generation compressed air flows through the when the signal is turned off. with the vacuum switch 4 and the –3/2-wayvalve vacuum generator and creates a non-return valve 7 – Controls vacuum generation

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Important variables Selecting a suction gripper The main criteria to consider when • Total volume of the vacuum system • Cycletimeofanoperation • Ejector economy selecting a suction gripper: • Additional functions

Total volume The sum of the volumes is needed to Thevolumetobeexhaustedfromthe • Suction cup volume calculate the cycle time of an system is made up of the following: • Suction cup holder volume operation. • Tube volume

Cycletimeofanoperation

When defining quantities, the time Individual criteria for determining the Evacuation time tE for 1 l volume at 6 bar operating pressure pu factor plays a decisive role. The duration of an operation cycle: evacuation time is used to determine • Evacuation time: Time taken for the how economical an ejector is. ejector to generate the required vacuum

• Air supply time: Time taken to set [s] E t 1 down the workpiece under suction VN-05-H-… 2 (purging of the vacuum) VN-07-H-… 5 • Handling/return time VN-05-M-… 6 VN-07-M-…

pu [bar]

Ejector economy

Factors for determining the energy • Air consumption per unit of time Air consumption qn as a function of operating pressure p1 consumption of an ejector: (specified in the ejector technical data) • Number of operation cycles per unit of time [l/min] n q 2 VN-07-H-… VN-07-M-… 8 VN-07-L-…

p1 [bar]

Comparison of vacuum generators

Efficiency is a criterion which The product section of this catalogue Efficiency η as a function of vacuum Δpuat Pnom 6bar facilitates an objective comparison of contains information to help you various vacuum generator types. determine the efficiency of an ejector ( 18). The chart allows you to compare the efficiency curves of other vacuum

generators. η

Δpu [bar]

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Suction grippers General data Vacuum suction grippers provide the They are a simple, low-cost and Festo offers a wide range of suction • Universal suction gripper “link“ between the vacuum generator reliable solution for handling gripper designs: • Flat suction gripper and the workpiece being transported. workpieces,parts,packaging,etc. • Bellows suction gripper • Special suction gripper

Mode of operation When the suction gripper comes into draws in the air on the underside of atmospheric pressure holds the contact with the workpiece surface, the suction cup. A vacuum is created. workpieceonthesuctioncup. thesameairpressure(atmospheric Given that air pressure within the The larger the vacuum, the greater the pressure) prevails on the top side and vacuum is lower than that on the holding force pressing the suction cup Vacuum underside of the suction cup. The outside of the suction cup, onto the workpiece. activated vacuum generator now

Materials Thesuctioncupsareavailablein Depending on the range of The criteria for selecting the right different materials. application, the following conditions suction cup material are summarised • Nitrile rubber play an important role when deciding in a table ( 44). • Polyurethane on the quality of the materials to be • Polyurethane, heat-resistant used: • Silicone • Resistance to wear • Fluoro rubber • Intensity of stress • Butadiene rubber, anti-static • Industry in which gripper is to be used (food industry, electronics) • Workpiece quality (surface, weight, sensitivity, etc.) • Environment (chemically aggressive media, temperatures)

Shapes Suction grippers can move a wide variety of products and materials Furthermore, it is possible to pick up variety of workpieces. (shapeless, compact or porous) with a workpieces with masses ranging from Therangeofworkpiecesurface wide variety of surfaces (even, uneven, a few grammes right up to several structures and contours available round, sloping or undulating) to be kilogrammes. demands versatile gripper technology. handled easily, cost-effectively and, Vacuum technology allows a wide above all, reliably.

Accessories For every suction cup there is a The suction cup holders are Suction cup holders are more than suction cup holder to fit. characterised based on the following just mounting devices for suction Depending on their design, these can criteria: cups. be used for a variety of applications. • Holder size • Suction cup connection • With or without height compensator • Position and type of vacuum port • Mounting thread

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Suction grippers Advantages of a bellows suction cup When the volume of a bellows suction In practice, this so-called flexible cup is evacuated, the suction cup vertical stroke can be used as a short shape contracts slightly. The work- vertical stroke to lift workpieces gently piece is lifted gently in the process. from their supports.

The evacuation of a bellows suction Phase 1 Phase 2 cup is divided into 2 phases: The suction cup is positioned on top A vacuum is created within the of the workpiece without the influence suction cup. The workpiece is drawn of any external forces. in and a state of equilibrium is achieved depending upon the size of the vacuum and the weight of the workpiece.

Workpiece Workpiece

Suction gripper selection guidelines When designing a suction gripper for a specific handling task, there are several criteria to be taken into consideration:

Parameter Effects on Required suction No. of suction cups Suction cup shape Suction cup material force Workpiece dimensions   –

Workpiece weight   

Workpiece rigidity –  

Surface texture of the workpiece Harsh    

Dry, wet   –

Round, diagonal, curved – – 

Environmental influences such as weather, cleaning agents, approval for – – –  use in the food industry, temperature Distribution of suction grippers on the   – workpiece Arrangement of suction gripper in    relation to direction of movement Max. acceleration   

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Physical variables The physical variables described that are needed to calculate the main below are components of the formulae criteria.

Coefficient of friction µ The coefficient of friction is the friction In practice, it is very difficult to obtain In order to be able to select a design, Surfaces factor between the suction gripper precise specifications for this value. the following theoretical guide values Oily μ = 0.1 and workpiece. It defines the Suitable experiments should therefore apply: Wet μ = 0.2 … 0.3 tangential forces. be carried out for the relevant Rough μ = 0.6 application. Wood, metal, glass, stone … μ = 0.5

Safety value S The regulations for the prevention of In the case of critical, non-uniform or Ahigherfactorshouldalsobeselected accidents (UVV) stipulate a safety porous materials or rough surfaces, in the case of a vertical suction factor of 1.5. This minimum value the factor should be increased to ≥ 2. gripper position or swivel motions. Fv must be incorporated in the The safety value is also important for calculations. the position of the suction gripper. Fh With a horizontal suction gripper position, where the applied load acts vertically on the suction cup, a value of between 1.5 and 2 may be used.

Fh Fv

Theoretical holding force TH This force is calculated with a dry • Mass of the workpiece m Only the result from the most surface for the various load conditions • Coefficient of friction μ unfavourable application load of the application. • Acceleration of the system (m/s²) condition is taken into consideration. The following factors are taken into • Acceleration due to gravity account in this formula: (9.81 m/s²) • Safety value S

Breakaway force FA The breakaway force depends on the application, the result of the This allows you to determine the When selecting a suction gripper, you suction cup diameter and suction cup theoretical holding force TH holding force of each suction gripper. can refer to the suction cup technical shape. calculation must be divided by the The breakaway force of the selected data to find out its breakaway force. If several suction grippers are used number of suction grippers. suction cup must always be greater simultaneously in a vacuum than the determined holding force TH.

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General procedure based on a calculation example Purpose & benefits For safety and financial reasons, it is you create an optimal system design involved in selecting a vacuum Thefigurebelowillustratesstep-by- importantthatyoudesignall for the application in advance, so that system. step the recommended in-house processes and methods in accordance the system can be sized and selected A calculation example is provided to procedure at Festo, which is used for with their intended application. This is in accordance with requirements. illustrate how the theory is applied in the design or selection of a vacuum the only way of ensuring optimal To simplify this task, this section practice. You can follow the step-by- system. deployment and utilisation of your provides a step-by-step description of step system design process with the system. (This also applies to vacuum thebasicprocedureandtheory aid of this example. technology.) It is therefore vital that

Problem definition Suction cup selection Assembly/mounting attachments Vacuum generator The problem definition produces To design a suitable suction cup you The following criteria should be When selecting a vacuum generator, specifications as well as system need to calculate the masses, holding considered when selecting mounting the following values must be requirements. forces and breakaway forces attachments: calculated: • Material/surface ( 43). • Workpiece surface • Total volume • Dimensions Workpiece surface finishes and • Position of the vacuum port • Cycle time • Directions of movement suction cup material requirements • Type of vacuum port • Energy costs • Cycle time/time allowed must also be taken into account • Type of mounting • Design specifications ( 43). A table listing the available holders is provided to help you select the right holder.

Problem definition Assembly/mounting attachments –Description –Retainer – Data – Height/angle compensator

Suction cups Vacuum generator – Workpiece (mass, surface) –Volume – Load conditions (forces) –Cycletime – General conditions –Energycosts – Vacuum – General conditions

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Software tool As a special service Festo offers you above all, quick way of designing your your system individually and select free software. The software tool in vacuum systems. It allows you to suggested products from the Festo question is a reliable, convenient and, specify the vacuum components of range. Vacuum selection software www.festo.com/en/engineering

Software tool: Vacuum selection

Selection program for calculating the mass of the workpiece

Program for selecting the suction gripper

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Problem definition Problem Assembly/ definition mounting components

Suction Vacuum cups generator

A workpiece of mass X is to be transported from point 1 to point 2 using a vacuum system. Specifications for the workpiece and general conditions for the vacuum system are listed in the section below (assumedvalues)andshouldbe referred to when performing the 2 necessary calculations.

Vacuum system, comprising: • Suction cups • Assembly/mounting attachments • Vacuum generator

1 We need to find out which vacuum system from the Festo product range is the right one for this application. To do this, we need certain values or forces (required values).

Assumed values Required values For the workpiece For the handling system Material Sheet steel Compressed air supply 6 bar The values specified below must be Surface Even, smooth, slightly oily Directions of movement Lift vertically calculated to determine the correct (e.g. from the press) Travel horizontally vacuum system. Dimensions Length: 200 mm 90° Rotate Other general conditions must be Width: 100 mm Travel vertically taken into account here. Height: 2 mm Max. acceleration 5 m/s2 The following sequence is Cycle time max. 3.5 s recommended: Time requirements For picking up: < 0.5 s • Mass (weight) of the workpiece For setting down: 0.1 s • Holding force and force of Safety factor 1.5 acceleration Design • Total volume conditions 2 suction grippers for • Cycle time vibration-free transport; spring-action picking up/ Other general conditions setting down of the workpiece; • Material and surface finish vacuum line ports at side; • Height and angle compensation suction grippers mounted • Costs using male threads.

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Selection of suction cups Problem Assembly/ definition mounting components

Suction Vacuum cups generator

Check list Load Workpiece surface Suction cup material Forces What does the workpiece weigh? What kind of surface finish does the What requirements must the vacuum What kind of loads do the suction workpiece have? generator fulfil? grippers have to carry? • Areas of application • Holding forces – load cases in the • Resistance requirements, various directions of movement temperature • Breakaway force – determining the breakaway force per suction cup (definition of suction cup diameter)

Step 1: Calculating the mass m of the workpiece

m=LxWxHxρ Example: m=Mass[kg] m= 20cmx10cmx0.2cm L=Length[cm] x7.85g/cm3 W=Width[cm] m = 314 g H=Height[cm] m = 0.314 kg ρ =Density[g/cm³]

Step 2: Selection of the suction gripper According to the surface finish of the workpiece Different suction cup shapes are Standard suction cup Oval suction cup Bellows recommended for the suction gripper, depending on the surface finish of the workpiece: • For flat and slightly undulating For narrow, oblong workpieces such surfaces, e.g. sheet metal or as profiles and pipes • For inclined surfaces, from 5 to 30° cartons. depending upon suction cup diameter Extra deep suction cup • Undulating, round surfaces, flexible workpieces with large surface areas • Fragile workpieces such as glass • For round or deeply undulating bottles workpieces • Useasacost-effectiveheight compensator

Result If, in the sample exercise, we were using sheet steel with an even, smooth surface, a standard suction cup would be the best solution.

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Step 2: Selection of the suction gripper According to the material quality of the workpiece Depending on the application, the • Life expectancy There are different material designs • For high temperatures following conditions need to be taken • Environment (e.g. chemically available, such as: • Antistatic design for electronics into consideration: aggressive media, temperatures) • For smooth or rough surfaces components • Continuous load in multiple shift operation

Material properties Nitrile rubber Polyurethane Polyurethane Silicone Fluoro rubber Butadiene rubber (heat-resistant) (anti-static) Material code N U T S F NA Colour Black Blue Red-brown White Grey Black with white transparent dot Resistance to wear/ ** *** *** * ** **  resistance to abrasion

Areas of application Very high stress – * * * – – Food processing – – – * – –  Oily workpieces * * *** – * * High ambient temperatures – – – * * – Low ambient temperatures – * * * – –  Smooth surface (glass) * * * – * – Rough surface (wood, stone) – * ** – – – Antistatic – – – – – * Minimal marking – * * * – –

Resistance Weather * ** ** *** *** **  Resistance to tearing ** *** *** * ** ** Permanent deformation ** * ** ** *** ** Mineral based hydraulic oil *** *** *** – *** – Synthetic ester based hydraulic oil * – – – * – Non-polar solvents (e.g. white spirit) *** ** ** – *** – Polar solvents (e.g. acetone) – – – – – – Ethanol *** – – *** * – Isopropanol ** – – *** *** – Water *** – – ** ** – Acid (10%) – – – * *** – Alkaline (10%) ** * * *** ** – Temperature range, long-term [°C] –10 … +70 –20 … +60 –10 … +80 –30 … +180 –10 … +200 –10 … +70 Shore hardness A [°] 50 ±5 60 ±5 72 ±5 50 ±5 60 ±5 50 ±5

Special features Low-cost Wear resistant Oil resistant Approved for Chemical and Antistatic use in the food temperature industry resistant

Area of application Conventional Rough surface Automobile Food industry Glass industry Electronics application industry industry

*** Very suitable * Suitable ** Fairly suitable – Not suitable

Result For the workpiece in the problem example we would choose a suction cup made from polyurethane (material code U).

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Step 3: Calculating the holding force and breakaway force Determining the holding force To determine the holding force you need to know the mass of the -H- Note workpiece, on the one hand, and the The forces of acceleration that operate designing a suction gripper system. acceleration, on the other. in a fully automatic system must be taken into consideration when

Case 1 Horizontal suction gripper position, Example: F = mx(g+ a) x S vertical direction of movement (best H F = 0.314 kg x (9.81 m + 5 m)x1.5 case) H s2 s2 FH ≈ 7N

Case 2

Horizontal suction gripper position, a Example: m F = mx(g+ )xS 5 horizontal direction of movement H s2 F = 0.314 kg x (9.81 m + )x1.5 H s2 0.1

FH ≈ 28 N

Case 3

Vertical suction gripper position, m Example: F = ()x(g+ a) x S vertical direction of movement (worst H 0.314 kg F = ( )x(9.81 m + 5 m)x2 case) H 0.1 s2 s2 FH ≈ 93 N

Result: In accordance with the problem This value must be used for designing definition, the result of 93 N from the system. Case 3 must be taken into account, as the system also transports the workpiece in a vertical suction gripper position with vertical force.

1) FH = Theoretical holding force of the a = Acceleration of the system S = Safety factor μ = Friction factor suction gripper [N] [m/s²] (minimum value is a safety 0.1 for oily surfaces m=Mass[kg] Note the emergency off acceler- factor of 1.5, for critical, non- 0.2 …0.3 for wet surfaces g = Acceleration due to gravity ation. uniform or porous materials or 0.5 for wood, metal, glass, [9.81 m/s2] rough surfaces the factor stone … should be 2.0 or higher) 0.6 for rough surfaces

1) The specified friction factors are average values and should be verified for the workpiece in question.

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Step 3: Calculating the holding force and breakaway force Determining the breakaway force

FA = Theoretical breakaway force F Example: = H FA 93 N [N] n F = A 2 FH = Theoretical holding force of the suction gripper [N] FA ≈ 47 N (Result  45) n = Number of suction grippers (2 suction grippers are planned in the problem example)

Breakaway force FA dependent on suction cup diameter and suction cup shape Round suction cup FA Oval suction cup FA at at –0.7 bar –0.7 bar Ordering Suction Standard Extra deep Bellows, Bellows, Ordering Suction Oval data cup ∅ 1.5 convol- 3.5 convol- data cup size utions utions

[mm] [mm]  ess 2 0.1 N  ess 4x10 2N 4 0.4 N 4x20 3.4 N 6 1.1 N 6x10 2.9 N 8 2.3 N 6x20 5.9 N 10 3.9 N 4.7 N 3.9 N 8x20 8N 15 8.5 N 9.8 N 8x30 10.9 N Breakaway force FA too low 20 16.3 N 17 N 12.9 N 8.2 N 10x30 15.2 N  30 40.8 N 37.2 N 26.2 N 20.8 N 15x45 32 N 40 69.6 N 67.6 N 52.3 N 42.4 N 20x60 62.8 N 50 105.8 N 103.6 N 72.6 N 63.4 N 25x75 92.5 N Reliable range 60 166.1 N 162.5 N 30x90 134.4 N for the problem example 80 309.7 N 275 N 213.9 N 100 503.6 N 440.8 N  150 900 N Suction cup diameter too big for 200 1,610 N workpiece

In this example we opt for 2 suction grippers: -H- Note • Round design The load capacity of the vacuum • Suction cup diameter 40 mm suction gripper must be greater • Breakaway force of 69.6 N than the calculated value.

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Selecting assembly/mounting attachments Problem Assembly/ definition mounting components

Suction Vacuum cups generator

Check list Workpiece Vacuum port Type of connection Type of mounting Consideration of the workpiece Positioning of the vacuum tubing Selecting the vacuum port for the Mounting the suction cup holder on surface • top suction cup holder the handling unit, e.g. robot arm • Angle compensator for very uneven • at side • Thread, push-in connector, barbed • Female/male thread surfaces fitting • Spring-mounted holders for sensitive workpieces as well as varying pick-up heights

Selecting the suction cup holder The suction cup holder as well as the The suction grippers should be • Choice of vacuum ports 1: Vacuum port 1 “angle compensator” and “vacuum mounted with external threads. –top filter” accessories are selected on the • Spring-loaded holders: –atside basis of the previously defined In the event of excess stroke and • 3connectiontypes1: Mounting suction cup diameter. height tolerances, it is recom- –Push-inconnectorQS threads for holder 2 According to the problem example, the mended that you use a holder with – Barbed fitting PK Suction cup workpieces must be picked up and set a height compensator – the same –ThreadG connection 3 down with the aid of a spring. applies for sensitive workpieces that • Different mounting threads for The vacuum lines should be attached need to be placed gently and with holder 2: at the side using push-in connectors. the aid of a spring. – Female thread –Malethread

Round suction cup From problem example  Suction cup ∅ 2 4 6 8 10 15 20 30 40 50 60 80 100 150 200 [mm] Holder size 1 2 3 4 5 6 Suction cup connection 3mm 4mm M4x0.7 M6x1 M10x1.5 M20x2 3 Ordering data  esh

Oval suction cup Suction cup size 4x10 4x20 6x10 6x20 8x20 8x30 10x30 15x45 20x60 25x75 30x90 [mm] Holder size 4 5 Suction cup connection M6x1 M10x1.5 3 Ordering data  esh

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Holder type From problem example 

HA HB HC HCL HD HDL HE HF  Height compensation – – –

Vacuum port 1 Top – – –  At side – – – – –  Threaded connection G Push-in connector QS – – Barbed fitting PK – –

Mounting threads for holder 2 Female thread – – – – – – –  Male thread –

Result Taking all requirements into account: Suction cup holder HD, size 4

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Selecting vacuum generators Problem Assembly/ definition mounting components

Suction Vacuum cup generator selection

The criteria referred to in the check • Total volume list therefore play an important role in • Cycle time -H- Note the selection of a suitable ejector. • Economy • Functions Almost all Festo vacuum ejectors • Design specifications achieve a vacuum level of approx. All ejectors can thus be used for 85%, with the exception of the new handling tasks involving light to VN ejectors, which are specially heavy workpieces or loads. designed for low pressure of approx. 50%.

Check list Total volume Cycle time Economy Functions How high is the total volume to be How long does an operation cycle How high are the energy costs? What additional functions should the drawn in? take? • Calculate the energy costs based on vacuum generator have? • Take into account the suction cup • Calculate the evacuation time the air consumption and number of • Filters, controls, non-return valves, volume • Determine the handling/return time operation cycles vacuum switches, exhaust function, • Take into account the suction cup • Calculate the air supply time etc. holder volume • Calculate the tube volume

Design specifications What specifications exist? • Dimensions, weight, mounting position, etc.

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Step 1: Determining the total volume of the system (volume to be drawn in) The suction cup, holder and tube volumes must be determined and added together to form the total volume.

Suction cup volume V1 Suction cup holder volume V2 Tube volume V3 Total volume VT

The suction cup volumes are specified Because of the huge range of different Once the suction cups, suction cup VT =V1 +V2 +V3 in the datasheet for the relevant holder types and connection options, holders and connection options have VT = 3,132 + 678 + 12,566 3 3 vacuum suction grippers ESG, VAS, tables listing all of the suction cups been defined, the tube volume can be VT = 16,376 mm (16.38 cm ) VASB. and their relevant volumes have been determined. The suction cup volume may be created in the datasheet for the ESG specified in a table or chart, product family. Tubing PUN: depending on the product family. Outside/inside ∅ [mm] In our sample application we opted In our sample application we chose 3.0/2.1 for 2 suction grippers: the following suction cup holders: 4.0/2.6 6.0/4.0 • Round design • Suction cup holder HD 8.0/5.7 • Suction cup diameter 40 mm Size 4 with QS connector 10.0/7.0 • Breakaway force of 69.6 N 3 V2 = 678 mm The following formula must be used For these suction cups, the datasheet when calculating the volume: specifies a suction cup volume 2 3 V = π x D xL of 1,566 mm per suction cup. 3 4

3 3 V1= 2 x 1,566 mm =3,132mm D= Tubeinside∅ [mm] L = Tube length [mm]

In the sample application a suction cup holder with QS-6 couplings is used. A tube with an outside diameter of 6 mm is therefore required. In order to connect the vacuum generator to both suction cups, a tube length(L)ofapprox.1m(1,000mm) is required.

42 V = π x x 1 000 3 4 = 3 V3 12 566 mm

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Step 2: Determining the cycle time

TC = Evacuation time tE + handling An operation cycle can be subdivided (tE) tE = Evacuation time 1 time t1 + air supply time tS +return t1 = Transport into individual time intervals, which (t1) time t2 tS =Discharge must be either measured or (tS) t2 =Return calculated. The individual times 1 =Pick-up added together produce the cycle 2 =Timesaved time. p[bar] (t2) t[s] 2

Evacuation time tE The evacuation time, i.e. the time time can be found in the Calculation: Example 1: VADMI-45 taken for a volume to reach a certain datasheet of the relevant vacuum In Step 1 of the sample application we tE =VT xtE1/1,000 3 3 vacuum level, is very useful for generator. This example depicts charts determined a total volume for the tE =17cm x 25 s/1,000 cm 3 assessing the performance of a for some of the vacuum generators of vacuum system of VT = 16.38 cm tE = 0.425 s (0.43 s) vacuum generator. The evacuation the VN-… product family. (17 cm3). Using a basic rule of three, we can now calculate the evacuation Example 2: VADMI-70 time tE for this system with any tE =VT xtE1/1,000 Evacuation time tE for1litrevolumeat6baroperatingpressurepu 3 3 vacuum generator. According to the tE =17cm x 11 s/1,000 cm problem definition, tE < 0.5 s, based tE = 0.187 s (0.19 s) on a vacuum level of 80%. Example 3: VN-07-H tE =VT xtE1/1,000

[s] 3 3 E

t t =17cm x8s/1,000cm 1 VN-05-H-… E t = 0.136 s (0.14 s) 2 VN-07-H-… E 5 VN-05-M-… 6 VN-07-M-… tE = Evacuation time (VT ) 3 tE1 = Evacuation time (V = 1,000 cm ) pu [bar] VT = Total volume (from example)

Handling time t1 Thetimerequiredtohandlethe process (e.g. determined using a workpieceaftertheendofthesuction stopwatch = 1.5 s).

Air supply time tS

Time needed by the vacuum system to The specifications apply to 1 litre Using a basic rule of three, we can tS = Evacuation time (VT) 3 tS1 = Evacuation time (V = 1,000 cm ) build up the pressure (vacuum) again volume at 6 bar operating pressure at now calculate the air supply time tS VT = Total volume (from example) and set down the workpiece. The air max. vacuum level. for this system. supply time can be found in the technical data for the relevant vacuum Example 1: VADMI-45 Example 2: VADMI-70 Example 3: VN-07-H generator. tS =VT xtS1/1,000 tS =VT xtS1/1,000 tS =VT xtS1/1,000 3 3 3 3 3 3 tS=17cm x 1.9 s/1,000 cm tS=17cm x 0.59 s/1,000 cm tS=17cm x 1.1 s/1,000 cm tS =0.03s tS=0.01s tS=0.02s

Return time t2 CycletimetC Thetimeneededbythevacuum Example 1: VADMI-45 Example 2: VADMI-70 Example 3: VN-07-H system to return to the initial position tC =tE +t1 +tS +t2 tC =tE +t1 +tS +t2 tC =tE +t1 +tS +t2 after the workpiece has been set down tC = 0.43 + 1.5 + 0.03 + 1.5 tC =0.19+1.5+0.01+1.5 tC =0.14+1.5+0.02+1.5 (e.g. determined using a stopwatch tC =3.46s tC =3.2s tC =3.16s =1.5s).

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Step 3: Checking economy of operation Energy costs are determined on the basis of air consumption.

Determining the air consumption per operation cycle QC These charts are also included in the When combined with the vacuum Air consumption Q as a function of operating pressure p datasheet for the relevant vacuum switch it provides an air-saving generator (e.g. VADM-…, VADMI-…). function, i.e. no air is consumed The VADMI-… vacuum generators have during transport of the workpiece. a built-in non-return valve which The VN-… vacuum generators do not maintains the vacuum after the have this function. This means, vacuum generator has been switched therefore, that the vacuum generator off (prerequisite: there must be no remains in operation so that it can Q[l/min] leakage in the system). hold the workpiece during transport.

p[bar]

Qz = Air consumption per operation cycle Example 1: VADMI-45 Example 2: VADMI-70 Example 3: VN-07-H tE = Evacuation time for application Q Q Q Q = Air consumption per vacuum generator = = = Ꮛ + Ꮠ QZ tE x QZ tE x QZ tE t1 x [l/min] 60 60 60 Q = 0.43 s x 11 l Q = 0.19 s x 31 l Q = (0.13 s + 1.5 s) x 28 l Z 60 s Z 60 s Z 60 s = = = QZ 0.08 l QZ 0.10 l QZ 0.76 l

DeterminingthenumberofoperationcyclesperhourZh

Zh = Operation cycles per hour Example 1: VADMI-45 Example 2: VADMI-70 Example 3: VN-07-H tZ = Time per operation cycle 3, 600 s 3, 600 s 3, 600 s t = Evacuation time for application = = = E Zh Zh Zh tZ tZ tZ 3, 600 s 3, 600 s 3, 600 s Z = Z = Z = h 3.46 s h 3.2 s h 3.16 s = = = Zh 1, 040 Zh 1, 125 Zh 1, 139

Determining the air consumption per hour Qh

Qh = Air consumption per hour Example 1: VADMI-45 Example 2: VADMI-70 Example 3: VN-07-H QC = Air consumption per operation cycle Qh =QC xCh Qh =QC xCh Qh =QC xCh Ch = Operation cycles per hour Qh = 0.08 l x 1,040 Qh =0.10lx1,125 Qh =0.76lx1,139 Qh = 83.20 l (0.08 m³) Qh = 112.5 l (0.12 m³) Qh = 865.64 l (0.87 m³)

Determining the energy costs per year KEA 1) KEA = Energy costs per year Costs for compressed air : Qh = Air consumption per hour t t 1 m³ at 7 bar: € 0.02/m³, = 3 operating operating KEA Qh x Compressed air costs m x x at an electricity price of Day Year €0.10/kWh

2) Vacuum generator Air consumption per cycle QZ CyclesperhourZh Air consumption per hour Qh Energy costs per year KEA [l] [m3] [€] VADMI-45 0.08 1,040 0.08 5.76 VADMI-70 0.10 1,125 0.12 8.64 VN-07-H 0.76 1,139 0.87 62.63

1) Material, depreciation and labour costs, etc. are reflected in the price 2) Energy costs for shift operation 16 hours/day and 220 days/year

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Step 4: Taking additional functions/components and design specifications into account Selecting additional functions/components: Selection of these components is and application of the system. All guided by specific requirements in details regarding performance or terms of performance and functional- components are provided in the ity, as well as by the place of operation datasheet on the relevant product.

Solenoid valves Vacuum switch A vacuum system needs solenoid Operation cycles can be accelerated • Reliability through pressure valves for controlling vacuum and optimised by adding an extra -H- Note monitoring generation. These switch the vacuum valve as an ejector pulse generator. The nominal flow rate of the • Adjustable switching point on and off. • Fast hysteresis adjustment solenoid valve must not be lower Vacuum generator Vacuum generator • Digital/analogue signal output than the suction capacity of the • VADM-…, VADMI-… • VADMI…- vacuum generator at atmospheric • Display • VAD-M-…, VAD-M…-I-… • VADM…-I-… • Ports pressure. (Both specifications can be found in the datasheet for the relevant product.)

Filter Pressure gauge Silencers • Reliability: no contamination of the • Extension of the product life cycle • Manual pressure monitoring of the • Noise pollution kept to a minimum system and reduction of maintenance system intervals • Safety function

Taking design specifications into account The following design specifications • Size must be taken into account when • Weight configuring a vacuum system: • Resistance

Calculation example summary Selection of suction cups Selecting assembly and mounting Selecting vacuum generators attachments The cycle time and economy of the Taking the mass and force The result takes all system We compared three vacuum ejectors were used as selection calculations plus all criteria into requirements into account: generators chosen at random from the criteria. account, we get the following result: Festo product range: Quantity 2 units Holder type HD Compact ejectors VADMI-45 Design round Size 4 VADMI-70 Suction cup ∅ 40 mm Inline ejectors VN-07-H Breakaway force 69.4 N Material Polyurethane

Result Cycle time Economy Compact ejector VADMI-45 All three vacuum generators lay within The vacuum generator VADMI-45 came TheVADMI-45,ontheotherhand,has a reasonable timeframe in the sample off best in terms of energy consump- a smaller nozzle diameter and thus application and were below the tion and, consequently, energy costs. significantly lower air consumption. maximum time of 3.5 seconds The two compact ejectors VADMI-45 However, it cannot generate the specified in the problem definition. and VADMI-70 produced almost vacuum as quickly as the VADMI-70. identical results in relation to energy The number of cycles per unit of time costs. Although the larger VADMI-70 and the quantities are almost has a somewhat higher air consump- identical for all three vacuum tion per unit of time, it can generate generators. the vacuum faster.

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Products for vacuum technology

Vacuum generator Vacuum suction gripper A vacuum ejector is the central Thesuctiongrippersaretheconnect- element of any vacuum system. ing element between the vacuum Festo offers an extensive range of system and the workpiece. vacuum ejectors for all kinds of Given the huge variety of surface applications and performance finishes, shapes and temperatures as requirements: well as different workpiece masses, a Basic and inline ejectors comprehensive range of suction cups Vacuum generators and possible combinations is needed. VN-…, VAD-…/VAK-… With its suction cup range and the Compact ejectors modular suction gripper ESG, Festo Vacuum generators has a solution for every application: VADM-…/VADMI-…, Modular suction gripper ESG-… VAD-M…/VAD-M…-I-… Suction cups VAS-…/VASB-…

Vacuum accessories Controlling, measuring, checking, filtering, etc. are important functions which, if not already included as standard in a vacuum system, can be added through an extensive range of accessories. Vacuum security valve ISV-… Vacuum gauges VAM-… Vacuum filters VAF-… Vacuum switches VPEV-…

Other accessories: Height compensators, adapters Tubing QS push-in fittings

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