Web Cleaning & Static Control
Working at high speeds: Static charges during printing and processing
BY GRAHAM DAWSON, ARROWQUINT
most direct path, like lightning, often causing marking or pin-holing of the web.
WHERE DOES THIS HAPPEN? The relationship between static charge effects and web tension are dependent to a large extent on speed and overall tension. The effects of static- induced forces of attraction or repulsion on higher tension webs moving between steel rollers are seldom seen, because the forces of tension in the web are far higher than the electrostatic forces trying to stick the web to the rollers. However, if web tension is allowed to reduce or is removed, the situation reverses and the electrostatic charges become the dominating factor. These static effects are also more noticeable
C
ontrolling tension and wander on any web process is difficult, especially where
the feed reel has variations in winding accuracy or tension. However, where the web material is non-conductive these difficulties are compounded by the forces induced by electrostatic charges in the web. Increase the speed and demand a more
accurate end product, and web control can become very expensive to achieve. Moving non- conductive surfaces such as plastics, dry paper and boards against each other produces electrostatic charges which can reach exceedingly high energy levels as speeds increase. These energy levels cause materials to behave as though magnetised, making them stick together or float apart. If the energy levels are allowed to rise too high they will discharge to ground through the
where the web passes over insulating rollers, including anodised aluminium, where like polarity charges can build up and cause the web to float over a roller without actually making contact. This effect increases any tendency of the web to wander as well as possibly affecting the tension in the problem area. Similarly, opposite charges, or charged webs passing over grounded, conductive rollers can make the web stick to the rollers, increasing tension or causing snatching. Prime candidates for tension problems related
to static charges are slitter-rewinders, where different materials run at different speeds and where speed is often increased and decreased progressively at the beginning and end of a wound reel. Printing presses also suffer from web wander, which can affect both print register and fold quality, whilst slit and merge systems also suffer to a lesser degree.
WHAT IS THE ANSWER? Static charges must be properly controlled at critical points in the web path; as well as
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discharging the web, this may mean using static charges to pin the web to a selected roller to prevent wander or float. Having successfully brought static levels under control, higher web speeds will be within reach without compromising quality. Arrowquint is the UK agent for Eltex Elektrostatik
in Germany, a supplier of static control systems either as a new installation or retrofit.
BUSINESS GROWTH Last year, Arrowquint reported that it had increased its business with the print and packaging sector by 60 per cent. Dawson identifies some of the reasons for this increase. “When we visit a company with a problem
caused by electrostatic build-up, we have a pretty good idea of how that problem is going to solved, the cost implications for the customer and the time needed. This allows us to provide a level of service that customers appreciate. Also we have been able to talk to customers about some new products from Eltex this year and this has definitely helped.” Arrowquint has worked with Eltex in the UK for
over 40 years. Its latest product range is being marketed under the BASIX banner; currently, the range consists of the ES47 power supply and the R47 discharge bar. Despite the competitive price points, Eltex has managed to manufacture a high quality, compact system that is highly energy efficient and easy to install and maintain.
www.arrowquint.co.uk
www.convertermag.co.uk
March 2017
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