Electricity: electrical systems and devices – Discharging or preventing accumulation of electric charge – Of paper or paper handling machine
Patent
1996-04-09
1998-06-02
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Discharging or preventing accumulation of electric charge
Of paper or paper handling machine
361220, H05F 300
Patent
active
057610223
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the controlled reduction of electrostatic potential difference between bodies.
The build up of static electricity is a problem in many different situations, particularly in the office, car, hotel, hospital, home and factory. The problem is often exacerbated by the use of synthetic materials--for example in carpets and furnishings, belting and textiles, in clothing and footwear and in machinery such as lifts and escalators. The problem is particularly evident in certain machines such as textile machines where synthetic fibres can generate static charges.
2. Description of the Related Art
The problem can be aggravated by air conditioning and conditions of low humidity in general.
People working in such environments acquire and build up a high voltage static charge on their persons. Objects in such environments can also acquire undesirable charge. When objects and/or persons having substantially unequal potential come into very close proximity, the local electric field can exceed the electrical breakdown strength of the air, leading to an undesirable discharge which is generally in the form of an air-gap spark.
One annoying and potentially dangerous manifestation of the problem is the personal shock experienced when such a charged person approaches and touches a door handle, say, or a filing cabinet or other piece of office equipment. The shock is due to a spark discharge across the narrowing air gap as the hand or other part of the body approaches the item in question. The discharge may be heard and may actually be seen in a darkened room. The shock is often quite painful and a reflex reaction from it can--especially with moving machinery--cause the hand or other part of the body to suffer some contingent injury.
Damaging discharges can also take place from charged personnel or objects at relatively low voltage. Such discharge, at voltages as low as 50 volts potential difference, or even less, can damage semiconductors and sensitive electronic devices and are so small that they are usually not detectable by humans in terms of pain or being an observable discharge of any kind. Electrostatic discharges produce associated magnetic and electromagnetic radiation which can be disruptive to nearby or remote electronic equipment in addition to damage which might be caused by direct current flow.
Static is a known problem in many industrial operations inasmuch as it interferes with the operations themselves. In the case of synthetic yarn processing, charges an the running yarn or on fibres can seriously interfere with such operations as warping, spinning, carding and texturising as a result of mutual repulsion between adjacent running threads or the filaments of a multi-filament yarn or by the build up of fibres on machinery parts by electrostatic attraction. When machinery containing charged fibres is temporarily stopped, the fibres can cling adversely to adjacent surfaces, thus preventing the successful restart of the machine. Furthermore, the large size of industrial equipment means that static discharges are potentially dangerous and can even be fatal.
Many ways of preventing static build up have been proposed. In general, they fall into three categories.
Firstly, they can involve non contact procedures, such as the production of an electrical field to ionize air molecules which facilitate the conducting away of the electrostatic charge. However, such methods themselves may give rise to hazard because of the high potentials which are sometimes used to ionise the air. Such equipment is expensive to purchase and some requires a continuous electricity supply to operate.
Secondly, they can involve the use of astatic materials (i.e. those which have a low separation of charge when rubbed), to prevent the creation and consequent build up of static charge.
Thirdly, they can involve the continual dissipation of static, for example, by large bench mats, floor mats, conductive comets or work coats, as static is generated. This includes both ea
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Gaffin Jeffrey A.
Sherry Michael
Statpad Limited
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