FACTORY FOCUS HEALTH & SAFETY
AVOIDING SHOCKS FROM static electricity in finishing
Problems with static charge build-up caused by airborne contaminants in the finishing of metal and plastic products can be safely addressed by selecting the appropriate control solution
A
nyone who works in the finishing industry will be aware of the huge
problems caused by airborne contaminants. If left unchecked the costs in time and materials alone can run into thousands of pounds. Typically this problem stems from an electric field and static charge build-up which causes contaminants to be attracted to the product. If this ends up in the coating it often results in a blemish which can mean the rejection of the product.
STATIC AND DUST ON METAL PARTS Static and dust attraction is normally associated with plastics and non- conductive materials but there are exceptions. The best-known is probably in the automotive sector. The bare chassis of a car is grounded metal and so incapable of holding much charge but there is still an electrostatic dust attraction because the static charge is in the airborne particles. These in turn are attracted to the chassis because it is conductive and grounded. Some years ago an engineer at the Ford
plant in Dagenham calculated that it probably cost over £1000 whenever a Fiesta was found to have a painting blemish due to statically attracted dust. This included taking the chassis off-line, tacking off the blemish by hand, putting it back on-line and repainting it. The answer for most automotive plants is to install an ionised air gate immediately before the spray booths. This blows ionised air at high speed around the profile of the vehicle. The ionised air kills the static charge on the dust, allowing the speed of the air to remove it. This type of system can be operated with blown or compressed air. For large applications the greater purchase cost of a blown air system will be paid back typically within six months due to its much lower running costs.
UNPLEASANT SHOCKS A further example is where metal parts are stored or transported on stillages or trolleys which are insulated from earth, typically by nylon wheels or feet. The static charge can build up until it is above the dust attraction level and will
18 MAY 2014 | FACTORY EQUIPMENT
coatings can result in metal products becoming non-conductive and closer to plastics from an electrostatic viewpoint.
STATIC AND DUST IN PLASTICS This is the main area where static electricity causes problems in industry. In addition to contamination of plastic products static can generate production problems and cause fires or explosions. Electrostatic dust contamination is present throughout the plastics industry. While nobody worries if a plastic drain
positively attract airborne dust. This can cause operators to receive unpleasant shocks. The simple solution is to make sure that the stillage or trolley is connected to ground. With a normal concrete floor this may be as simple as hanging a small metal chain from the body so that it touches the floor. The solution is more complicated if the floor is a non-conductive composite. Gravity-fallen dust is inevitable in
many factories and removing this from metal products isn’t always straightforward. An ordinary compressed air blow-off gun could make the problem worse; the fast-moving air can create a static charge when it impacts with the product. This may blow off the dust but the now statically charged dust is floating around waiting to be re- attracted to the product. The solution is an ionised airgun which will remove dust without causing a static charge. In auto-refinishing an ionised airgun is
typically employed to clean and neutralise metal panels prior to repainting and increasingly plastic body panels which will contain a much higher static charge. However, metal parts are not always conductive. Anodised aluminium and additional treatments or
An ionised airgun will remove dust without causing a static charge
pipe is covered in dust when it’s on sale at a builder`s merchant it’s a different matter with higher value products for example where dust shows through the paintwork. Quality standards are increasing in all sectors. Injection mouldings come out of the tool in a high statically charged state and start attracting dust immediately. The decision of when to clean and neutralise them depends on the time between moulding and painting and whether there is intermediate activity such as trimming or incorporation into an assembly. Many injection moulders accept that
cleaning and static control may have to be a multistage operation. Initially dust may be attracted to the product by electrostatic forces but if stored for days before further processing the attraction can be replaced by a molecular bonding. This can be a stubborn adhesion which does not respond to electrostatic or ultrasonic cleaning; it often needs labour-intensive wiping by hand. The automotive plastics industry is a
major customer for dust and static control equipment. Bumpers have to be cleaned and neutralised before painting to avoid expensive reworking. Fraser makes smaller ionised air gates for bumper lines - mini versions of the automobile lines mentioned previously. To discuss solutions for industrial static
control, Fraser Anti-Static has been a preferred industry partner for over 20 years and always happy to help.
Fraser Anti-Static T: 01398 331411
www.fraser-antistatic.co.uk Enter 318
/ FACTORYEQUIPMENT
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