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Basic Principles of Vacuum Technology, Brief Overview Introduction 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. Subject to change Internet: www.festo.com/catalogue/... 1 Basic principles of vacuum technology, brief overview Introduction 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. 2 Internet: www.festo.com/catalogue/... Subject to change Basic principles of vacuum technology, brief overview Introduction 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. Subject to change Internet: www.festo.com/catalogue/... 3 Basic principles of vacuum technology, brief overview Introduction 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. 4 Internet: www.festo.com/catalogue/... Subject to change Basic principles of vacuum technology, brief overview Introduction Typical applications Subject to change Internet: www.festo.com/catalogue/... 5 Basic principles of vacuum technology Introduction 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.
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