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Using the ‘invisible force’ electrostatic


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Electrostatic charges build conductive surfafaces such a


s plastics, filmor up on non-


paper. These charged surfaces behave like magnets, with polarities repelling each other whilst opposites attract. The favourite school demonstration of this principle uses a plastic comb which, when rubbed on a tie will pick up small pieces of paper with ease. These forces of attraction or repulsion are what createmost static problems, but they can be easily harnessed to give positive benefits.


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Generating controlled electrostatic charges is a relatively simple procedure involving seemingly simila r equipment to that used in electrostatic discharging. An electrode is connected to a high voltage generator and positioned near to the material to be charged. However, the voltages used aremany times greater than those in discharging and can bemade to penetrate thematerial being charged. However, because charging is a ‘dc,’ rather than‘ac’process, it generates a specific charge polarity on the surfaface of the subjectmaterial.


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These qualities of selective polarity and penetration can be used in two ways: Firstly, if a charge is directed through a single layer ofmaterial at a grounded surfa


face such as a


roller, thematerial will stick to the roller. Secondly, if charging bars of opposite polarity are positioned on either side of a compound web comprising several layers of


24 July/August 2016 Using static charging to stop film wander during rewinding www. w.arrowqu owquint o.uk .co. www.convertermag.co.u k gers inprocess


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ewlooseproductioncategategories:printing, paperproce


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material, the resulting charges will cause the layers to stick processes are


generally known as static firmly together. These


pinning, nailing or tacking.


Let’s lookmore closely at each of the categories to see how the principles of electrostatic charging can be used to improve efficiency and running speeds.


FILM CASTING PROCESSESNG PROCESSES FILM ASTI


Filmis generally hot cast or extruded froma die onto a chill roller. As the filmleaves the die andmeets the cool roller its width reduces or ‘necks’due to shrinkage, usually giving a‘thick edge.’ Both the initial shrinkage and trimming the thick edge considerably reduce the filmwidth and generate a substantial amount of waste. Although trimmed waste can normally be recycled, the energy used inmelting,


casting, cooling and trimming is a total loss. Shrinkage can be substantially reduced by pinning the hot filmto the chill roller using an electrostatic charging system. The resulting filmhas a wider useable section, whilst the reduction in trimmed waste results in overall savings in production costs. This can be applied as either a full width pinning or,more commonly, as an edge pinning process.


Edge pinning on filmcast unit tominimise necking REWINDINGREWINDING


nightmare to rewind n Light films and wide w


eatly without wander ebs can be a


or ‘telescoping’on the reel, both of which are generally not acceptable to the next process or the customer.


By statically charging the web


immediately befofore the rewind reel, the web is firmly pinned to the reel and cannot wander or telescope.


Far frombeing the universal problem perceived bymany, electrostatic charges can be deliberately induced and controlled to bring positive benefits in improved production enhanced product quality and reduced waste across a range of paper processing and service sectors.


As amanager in a competitive and cos t conscious industry, ask yourself if any of the scenarios in this article apply to your


operations. If so, you too could benefit from the use of electrostatic charging. Yo competitorsmay well be already reaping the benefits in lower costs, higher quality and quicker product turnaround. Arrowquint is a UK-based company


Your


specialising in static control solutions. The company will appraise and evaluate


customers’problems and suggest a flexible ffer solution s ffordable. The


and adaptive approach and offe which are both effe


ffective and affo


company is also able to provide a high level of technical support necessary to ensure that installed systems will work as intended fofor the whole of their lives.


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