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Static Electricity Control

A new static control product from Leatex can effectively reduce static electricity problems on the production floor.

A new static control product from Leatex can effectively reduce static electricity problems on the production floor.Lightning is one often observed result of static electricity (SE). SE develops within the clouds, and as this buildup of SE discharges into the atmosphere, lightning is seen. The potentially damaging effects of lightning are well-known. However, SE and its potential for damage and injury in the workplace, as well as its effect on production, are less understood.The most obvious consequence of SE is the hazard posed to employees from the shocks they regularly receive. These shocks are the result of electrostatic discharge (ESD), which is described as the sudden transfer of charge between bodies of different electrical potentials.Although ESD is not believed to cause any permanent physical injury, the idea of being shocked many times a day by tens of thousands of volts is one of the least enjoyable aspects of working in a textile mill. The typical injuries directly associated with ESD which can be severe result from the persons repulsion from the shock and subsequent collision into machines, walls or other objects. Additional consequences include reduced employee and machinery productivity resulting from machine jams or damaged electronic components; and the reduced product quality resulting from lint attraction, fabric tangles, and especially, employee reluctance to touch fabric unless absolutely necessary.What Is Static ElectricityOne of the most common definitions of SE is electricity at rest, which seems to make sense because electric current is the movement of electricity. However, a better description of SE is an electrical charge caused by an imbalance of electrons on the surface of a material the result of the surface of a material adding electrons (becoming negatively charged) or losing electrons (becoming positively charged). Causes of SE include heating, machine processing and material separation. The effect is magnified by the tendency of the material being processed to gain or lose electrons when the material comes into contact with other materials. Heating a material and causing it to dry out, as well as quickly heating and cooling the surface, make the material less conductive and more likely to develop a charge. The machine processing of a material agitates the materials surface, generating an atmosphere for the ready transfer of electrons between materials. The separation of two materials after they have been in contact causes some electrons to jump from one material to the one with the stronger attraction. It appears the separation of the materials after they have been in contact is the main cause of SE, not friction between the materials.The process of material contact, electron transfer and separation is affected by the size of the contact area, the humidity of the environment and the speed of the separation.Tribocharging And TheTriboelectric SeriesAll materials in their natural state have a neutral charge because, at the atomic level, the number of positively charged protons in the nucleus of an atom is equal to the number of negatively charged electrons.Tribocharging is the creation of a charge on a material by contacting and separating it from another material, causing electrons to transfer between the two materials.The triboelectric series is a ranking of common materials based on their tendency to gain or lose electrons because of tribocharging. Frequently, in a triboelectric series, steel is listed as neutral. The materials above steel are listed as having a positive charge, or having a tendency to lose electrons. The materials below steel are listed as having a negative charge, or having a tendency to gain electrons (See Table 1). The listing compares a materials tendency to gain or lose electrons when it comes into contact with other materials on the list. The electrons tend to transfer from the materials higher on the list to the materials lower on the list. The further apart on the list two materials are, the stronger the charge that is created as they are separated.ESD In TextilesThe textile industry has developed and tried many programs to address SE in the workplace without significant success.The industry processes many materials, notably man-made materials, that readily transfer electrons to other materials to create charges. It also has processes notably drying at high speeds and temperatures that create optimum conditions for tribocharging. On many processes the charge measured on numerous materials has ranged from 20,000 volts to more than 100,000 volts. These conditions make ESD and static control (SC) in the textile industry a very big challenge.Following is a review of some of the methods currently used by the industry and a brief review of the latest alternative.Traditional SC MethodsThe most basic SC method is the grounding of equipment and machines in the plant. This is primarily important for electrical safety, but it also allows high charges of SE to be reduced although not eliminated. A second SC method is to use climate control devices, which have been built into some newer textile plants or installed in older mills. Unfortunately, this is prohibitively expensive for most mills, and it frequently replaces a static problem with a maintenance problem. The use of a humidification system may reduce the SE, but it also will increase the maintenance of the equipment and machines because of the corrosive atmosphere it creates. Other mills inexpensively adjust their climate by opening up their steam pipes to increase the relative humidity, a maintenance and safety nightmare. Another SC method is the addition of antistatic chemicals during the wet processing of a substrate. Typically 1 to 2 percent on weight of goods of a cationic surfactant is used. While this method improves the static dissipative effect of the surface of the material, thereby reducing the buildup of SE, it does not eliminate it. Concerns with these products include recurring annual cost, tendency to cause substrate yellowing, and addition to the mill effluent.Frequently used SC devices include static bars and other active electrical eliminators. They generate positively and negatively charged ions that help dissipate the charge on the material. They require power supplies to step up plant voltages to higher voltages 5,000 volts to 20,000 volts at low amperages. While these products reduce static levels in other industries, the static levels experienced in textile processing are frequently unable to be sufficiently reduced by this method. Additionally, while these products can be purchased off the shelf, they often need to be custom-built for the specific machine size. Also, most static bars need to be positioned within 1 inch of the processed fabric in order to achieve maximum performance.The final type of SC typically used in the textile industry is tinsel, which utilizes copper to help transfer the electron imbalance from the material to a ground through induction. Tinsel is an inexpensive and readily available method for SC, but it has limited effectiveness. The primary reason for this limitation is that any contamination either in its manufacture or use will severely degrade its effectiveness.Alternative SC MethodA recent SC development is the introduction of CONTAX by Leatex Corp., Philadelphia. Contax is a highly engineered construction of extremely conductive materials that economically removes static from textiles on contact. The technology has been used in the aerospace, electronic and military industries for many years. The product works through conduction and induction, transferring the SE on the textile to the Contax.Contax has taken extremely high levels of SE to minimal levels on all types of textile machinery and textile fibers. It has been used in a number of mills and has produced immediate and significant improvements in employee comfort and safety, as well as improvement in productivity and quality. It is easy to install and is adaptable to all textile manufacturing processes.Case StudyA major vertical manufacturer of knitted apparel was experiencing recurring severe SE problems, which seemed to get worse every year. A worker had been injured as the result of a severe jolt of SE. The company used a chemical antistatic product that somewhat reduced the SE, but problems persisted.The company approached Leatex to find a solution to its SE woes. Leatex had begun working on its Contax technology, and was looking for the right situation in which to test its ideas. The textile manufacturers products included various fibers, blends and constructions; and its many processes included drying, napping, tube reversing and cutting, making it a perfect testing facility.In the first test, Contax was placed across the width of the exit to a loop dryer so that goods leaving the dryer would come into contact with it. High levels of SE were eliminated. The performance was evaluated and compared to that on a control dryer that did not use Contax. Regardless of fabric type or construction, Contax removed the static. Eventually, the success was repeated on all of the companys dryers and napping machines.The next test was conducted on the machine that had caused the employee injury a tube reverser, which turns a knitted tube inside-out for further processing. Analysis of the process determined it could generate more than 100,000 volts. Because Contax was placed at the exit of the reverser, where it could come into contact with the fabric, it eliminated the static problem.The final trial was conducted on an automated cutting machine, which takes four separate tubes of fabric and cuts them simultaneously. As the tubes were running through the machine, one or more of the strands would jam or tangle, causing the machine to either shut down or cause poor cutting, creating off-quality material. Contax was placed on the trays that the tubes ran across, removing and eliminating the static and improving yields.SC System BenefitsBetter SC in a mill will enhance the comfort, morale and safety of the workforce. Other benefits include increased productivity of the machinery and workforce, and improved quality of the finished product because the workers are no longer reluctant to touch the goods as they are processed. A good SC product must effectively and economically eliminate SE problems. Investing in a SC system that accomplishes these items will pay for itself many times over. Editors Note: Brian D. McChesney is vice president of Leatex Corp., Philadelphia, a supplier to the textile industry since 1922. McChesney has worked with the company since 1988.

November 2003