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Static Electricity Causes and Cures

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Static Electricity Causes and Cures Static Electricity Causes and Cures Static Electricity Causes and Cures Contents What Is Static Electricity? 4 How Is Static Created? 5 What Factors Affect Static Electricity? 6 Methods Of Elimination 7 Modes Of Operation of Static Eliminators 8 Addressing Common Electrostatic Problems 14 Overview Of Solutions 15 Glossary, Tribolelectric Series 18 About Meech 19 Static Electricity - Causes and Cures About Meech: Static electricity causes productivity, Our mission is to develop effective and quality and safety problems throughout durable products that are relevant to industry. In the form of electrostatic our customers’ needs; to maintain the attraction or repulsion it generates highest levels of response and service dust contamination and product and to develop the best possible misbehaviour. As an electrostatic support system for our clients in our discharge it gives shocks to operators, field of electrostatics. starts fires and destroys electronic components by the million. As the first specialist manufacturer of static elimination equipment worldwide Meech has specialised in industrial to be approved as an ISO 9002 electrostatics for over 40 years. This registered company, we take our experience enables us to develop commitment to quality seriously. products which match the changing needs of our customers. The Meech The international quality approvals range encompasses four technologies covering some, or all of our products and includes over 40 products. include: Static Electricity - Causes and Cures Introduction Quality products must be supported The purpose of this booklet is to look by good service. Meech Distributors at what static is, how it occurs, the throughout the world share our methods available to counteract it and commitment to quality and participate how Meech uses these methods in a in our continuous training programme. variety of industrial applications. It is This keeps them informed about not intended to be an exacting, developments in applications and scientific reference manual; instead its technology so they can offer the aim is to answer the most commonly highest level of customer service and asked questions about static electricity support. posed by Distributors and Customers alike. To understand this booklet it is helpful to familiarise yourself with the various terms which can be found in the glossary at the end of this booklet. Static Electricity - Causes and Cures What Is Static Electricity ? When a material or object holds a material, the lower the capacitance net electrical charge, either positive the higher the voltage and vice versa. or negative, it is said to have a static Plastics generally have very low charge. The term static is a relative capacitive values and hence a small one as in many cases static charges charge can produce very high will slowly decrease over a period of voltages. Conversely metals tend time. The length of time that this takes to have high capacitive values and is dependent on the resistance of the therefore a relatively high charge will material. For practical purposes the produce low voltages. This is why, in two extremes can be taken as practice, problems with static electricity plastics and metal. Plastics generally are most noticeable when working with have very high resistivities. This plastic, as it is the voltage level which allows them to maintain static charges causes the attraction of dust, operator for long periods of time; on the other shock and misbehaviour of materials. hand metals have very low resistances and an earthed metal object will hold There are two main types of static its charge for an imperceptibly small electricity, volumetric and surface. period of time. Volumetric static charges are charge Static electricity is usually measured imbalances within the body of a in volts. Whilst mains voltages of 220 material whereas surface static volts AC are considered dangerous, electricity is only present on the very levels of static electricity of 100 kV are outer surface of a material. common. The voltage present on a mate- In practice nearly all the static rial is dependent on two factors; the electricity problems found in industry amount of charge on the material and relate to surface charges. Whilst there the capacitance of the material. The is no way of neutralising volumetric simple relationship is Q=CV where static charges they rarely cause a Q is the charge, V the voltage and C problem and their effects are normally the capacitance of the material. It can minimal when compared to surface be seen that for a given charge on a static charges. Static Electricity - Causes and Cures How Is Static Created ? There are three main causes of static the two materials are pressed together electricity; friction, separation and the greater the exchange of electrons induction. and hence a higher charge is generated. Friction As two materials are rubbed together A practical example is if a piece of the electrons associated with the polythene is rubbed on a nylon carpet surface atoms on each material come with gentle force a moderate into very close proximity with each negative charge will be generated on other. These surface electrons can be the polythene, whereas if the force is moved from one material to another. increased a larger negative charge will The direction in which the electrons be achieved. The speed of the rubbing travel either from Material A to action also has that effect on the level Material B or vice versa depends on of charge, the faster the rubbing the the Triboelectric Series (See page 18). higher the level of charge. This is due Materials on the positive side of the to the surface electrons gaining heat Triboelectric Series will tend to give energy generated by the friction. This up their surface electrons and become extra energy allows them to break their positively charged whilst conversely atomic bonds and transfer to other materials on the negative side of the atoms. series tend to gain electrons and hence a negative charge. The harder Contact + Friction + Separation Static Electricity - Causes and Cures Separation Induction The method of charging by separation Whilst of interest technically, induction is similar to that of friction. When two does not play a significant role in our materials are in contact the surface field. Static charges can be generated electrons are in close proximity to when materials are in the presence of each other and upon separation have a strong electric field. The surface of a tendency to adhere to one material a material in close proximity to a high or the other dependent upon their positive voltage will tend to become relative positions on the Triboelectric positively charged. The method of Series. charging is caused by ionisation of the air between the surface of the material The faster the separation of the and the voltage source which carries materials, the higher charge generated surface electrons away from the and conversely, the slower the material to the source, (ionisation is separation the lower the charge. A explained in methods of elimination). common example is of a PVC web An example of induction is operators moving over a Teflon coated roller, as working near charged materials. The the materials separate the electrons operator will himself become charged will tend to adhere to the Teflon, and on touching an earthed object will generating a net negative charge on discharge to it, giving the operator an the Teflon and a net positive charge on electric shock - often mistaken for a the PVC. shock from the mains supply. Contact + Pressure + Separation Static Electricity - Causes and Cures What Factors Affect Static Electricity Among the many factors that affect electricity than most plastics. the generation and maintenance of Atmospheric humidity deposits small a static charge are humidity, the type quantities of water on all surfaces in of material, repetition and change in their environment and hence surface temperature. static charges on materials have a tendency to dissipate to earth by Type Of Material current flow through the surface Some materials are more readily moisture. charged than others. For example materials such as acetate will gain a Repetition charge very readily whilst glass will Repeated actions such as friction gain a charge less readily. Also the or separation will increase the level relative position of materials on the of charge found on a material. For Triboelectric Series will determine example a plastic web moving over a whether a material charges positively series of Teflon rollers will increase its or negatively dependent on the other surface charge after every roller. material with which it has come into contact. For example hard rubber, Battery Effect when rubbed against nylon, will The combination of many charged become negatively charged whilst items can lead to extremely high when it is rubbed against polythene charges. For instance individual sheets will become positively charged. of plastic with relatively low surface charges when stacked together can Humidity generate extremely high voltages. Generally speaking the dryer the environment, the higher the level Change In Temperature of static charge and conversely the As a material cools down it has a higher the humidity, the lower the static tendency to generate charge. The charge. In relative terms water is a action of the cooling is to leave a net significantly better conductor of charge on the material throughout its Static Electricity - Causes and Cures entire volume. If the material is a very 1. Movement of electrons through the good insulator the internal (volumetric) material itself. static charge can be maintained for extremely long periods of time. 2. Movement of electrons through However over time this charge another material in contact with normally migrates to the surface at the surface. which point it becomes a surface static charge. An example of this is an 3. Movement of electrons through injection moulding which is seemingly ionisation of the surrounding air.
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