Safe solutions to static
October 1st 2005 Static can be a serious problem for many modern industrial processes, affecting both the health and safety of employees and product quality. However, harnessed correctly, it can provide positive manufacturing benefits. Alan Chadwick of Meech Static Eliminators explains
It was in 600BC that the philosopher and mathematician Thales of Miletus first described rubbing amber on the fur of a cat and consequently being able to pick up feathers. This is the first known account of the natural force of static electricity and the word electrostatic, meaning ‘electricity at rest‘, was introduced.
When a material holds a net electrical charge, either positive or negative, it is said to have a static charge.
In many cases this charge will decrease slowly with time, the actual length of time being dependent on the resistance of the material. For practical purposes, the two extreme examples can be taken as plastics and metal. Plastics generally have high resistivities, allowing them to maintain static charges for long periods. Metals, on the other hand, have low resistances and an earthed metal object will hold its charge for only a very short period of time.
Until about 50 years ago, static was not a significant problem in industrial processes. Many of the key factors affecting the generation and maintenance of a static charge were not present in the manufacturing environment. Such factors include type of material, ambient temperature, humidity and repeated actions such as friction or separation. In the early days of textiles manufacture, for example, the raw natural products such as wool and cotton absorbed water from the atmosphere and so had a very low static charge. Also, the factory environment, with its steam pipes providing both heat and humidity, meant that the likelihood of generating static charges was low.
However, raw materials and manufacturing processes have changed substantially over the last 50 years, as has the factory environment. Firstly, man-made materials such as nylon, polyester and various plastics now dominate and are more readily charged than natural materials. Furthermore, a consequence of the widespread introduction of air conditioning and dry air heating is that the atmosphere has become drier, humidity levels have been reduced and static issues have been brought to the fore. These issues are widespread, with industrial processes suffering to a greater or lesser extent from static-related problems of product contamination, slow machine speeds, shocks to operators and risk of fires/explosions.
Recognising the severe adverse impact of these trends on manufacturing productivity and profitability, Meech International set out to address the problems associated with static and to develop cost-effective solutions. Manufacturers have benefited in terms of improved quality, higher process yields, reduced machine downtime, faster machine speeds and improved health and safety standards.
One of the earliest approaches to the control of static charge was the use of “passive” ionisation in the form of conductive materials such as carbon fibre brushes. This was the first and most basic method that proved to be capable of reducing the level of static charge but not of removing it completely.
Static control took a major step forward with the introduction of effective "active" electrical ionisation systems in the 1960s.
These systems relied on normal AC mains voltage being boosted to around 5kV through a special transformer and being carried to sharp emitter pins, where the high energy generated a large number of negative and positive ions. A statically charged surface of either polarity passing close to this ion cloud would then be neutralised. Such systems worked well but were limited in terms of working distance (typically 20mm), had a relatively short working life and also caused electrical shocks if the pins were inadvertently touched.
Progressive enhancements to this AC technology have improved system performance. In particular, the recent development of resistively coupled systems has provided improved reliability, shockless operation and extended the working range up to 150mm.
The introduction of Meech Pulsed DC technology for static control has provided not only an effective alternative to AC systems but the ability to optimise solutions for specific materials and more demanding processes. In harness with a Meech 986 Feedback system, an "intelligent" Pulsed DC system can react automatically to process conditions and self-adjust to provide the most effective static charge neutralisation.
As manufacturing processes and materials technologies continue to develop, so the associated effects of static charge will present bigger challenges. Recent examples include the rapid growth in digital printing and increasing adoption of RFID technology. Meech International constantly monitors the requirements of these new processing environments and develops new solutions to truly keep static under control.
Bulletin
The effective understanding and control of static electricity has made Meech a market leader in its field since the 1960s.
This knowledge has enabled it to develop a range of solutions that tackle all aspects of static control, including its measurement, creation and elimination.
The company’s product range addresses four primary application areas - air, ESD, static and cleaning and includes 60 solutions, some of which have BASEEFA approval for use in hazardous environments.
The company says it was the first specialist manufacturer of static elimination equipment to be approved as an ISO9000 registered company.
For more information contact:
Alan Chadwick,
Meech Static Eliminators,
2 Network Point,
Range road,
Witney,
Oxfordshire OX29 0YD
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