Brötje tackles electrostatic discharge (ESD)
10/03/2008
Specialist footwear components manufacturer Brötje has launched new shell moulds and insole bedding from specially developed Contourex-foam for use in safety footwear for workers across all sectors.
The new products have a channelled resistance that footwear testing institutions PFI and Satra have confirmed at 103 Ohms. Brötje has incorporated this statistic into the name of the new range, calling the products the Contourex-103 shell moulds.
They are elastic-joint sealed, inherently stable and open-pored, meaning they absorb moisture from the foot. The manufacturer has also used conducting materials in the insole bedding. With a special adhesive technology, which does not impair the channelled resistance, the 103 cover material is adhered to the Contourex-103 foam parts. The conducting effect is achieved by both the Contourex-103 foam as well as by the cover material through physical means. According to the manufacturer, the foam is therefore “absolutely, continuously, effective”.
Lightning strikes, discharges from door handles, and hair standing on end, are easily seen and clearly discernable types of static charge. But many everyday activities can cause electrostatic charges in the body, including running over a carpeted floor (1,500 to 35,000 volts), running over an untreated vinyl floor covering (250 to 12,000 volts), working at a workbench (700 to 6,000 volts), putting papers into a transparent film cover (600 to 7,000 volts) and lifting a normal plastic bag from a workbench (1,200 to 20,000 volts).
People can normal feel a static discharge from 3,000 volts upwards. However, lower charges that lie under the threshold of human perception can also cause problems. Unfortunately, semiconductors could be damaged by minimal voltage. Many electrical components are damaged y discharges of less than 1,000 volts. For some of the more highly developed components, a charge of 10 volts can cause damage.
Brötje argues that it is important for workers to have information about the relative sensitivity to ESD damage for devices with which they are working.
The ongoing development in electronics means moves towards increasingly smaller components. The microscopically small distances between the insulator and the circuits inside of the components are also becoming smaller all the time, while the components’ sensitivity to static rises. Appropriate protective measures become, therefore, increasingly important. Miniscule static discharges are only damaging for the components, but they also add the fact that the effective damage that they cause is not perceptible to the naked eye.
How can we control ESD? The foundations of static protection are relatively simple:
prevention and earthing.
The problematic factors in any anti-static system are the people, who work with the electronic components. The awareness of the threat that ESD represents, as well as the knowledge and observation of the guidelines established for ESD protection, are likewise as important as all anti-static equipment.
Earthing, Brötje continues, is a very important measure for the elimination of the static charges that are generated in conductors. People themselves are conductors and generate a considerable amount of static electricity. For this reason, static charges in people, who come into contact with static-sensitive components or assemblies, must be prevented.
A particular importance is placed upon workers wearing proper, conductible ESD shoes. Through the shoes, constant contact with an earthed floor is guaranteed.
Manufacturers of conductible ESD shoes must observe the various safety guidelines (e.g. DIN-EN or ASTM standards), which exist in different markets.
For the diverse requirements against static, there are also shoes which discharge more or less well. With an ESD or conductible shoe, the requirements related to the conductibility are fulfilled for nearly all areas. The supreme commandment for a conductible shoe is the complete consistency, meaning running sole, mid sole, fire sole and insole. The materials must continuously discharge any static charges. The weakest member in this chain determines the overall channelled resistance. The more the channelled resistance is, the better the discharge.
For the selection of the materials, it should be observed that they are resistant to hydrolysis and the conducting substances could not be leached out. Likewise, the wearer of conducting shoes must be able to pass safely through control points at any time.
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