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We have told a little about static electricity in the two previous volumes of “Nordisk Emballagemarknad”. Many people have commented the articles saying that they have been interesting and that static electricity is present everywhere once you come to think about it - but - it is nothing that would make you rich, is it? No that’s just it! It is not very likely that one would make a lot of money by having electrostatically charged surfaces moving around in production totally out of control.
This article is intended to, after briefly recapitulating the main issues from the two previous articles, cast some light on the economical consequences that may be the result from handling electrostatic problems or in not doing so.
In order to make our discussion easier to survey we choose to regard three main types of problems where static electricity to a large extent may influence the economic outcome;
In addition to these points it is of course worth mentioning work environment problems where static electricity may cause discomfort or inflict personal danger and eventually knock out a whole factory due to explosion or fire. This is something most of us are probably aware of. In the same way there is an ever growing awareness of the problems static electricity may cause in handling of sensitive electronics devices. What we would like to show here are some practical examples on rather ordinary problems which nevertheless may have a substantial economical significance if handled correctly. or wrongly.
Static electricity may cause reliability problems which cost a lot of money
In sheet fed printing, whether offset, flexo or screen printing, static electricity may give serious problems at the infeed due to incorrect feeding
or doubled sheets, slurring in print units and poor stacking at the delivery. The result is almost always that printing presses are run with a
reduced speed. It is not unusual that only half speed is used and one simply notices that it is impossible to run any faster. With antistatic equipment it is often possible to run with full speed and also with such a high quality that one does not have to print as many extra copies as one would usually do in e.g. screen printing.
The manufacturing of plastic carrier bags and plastic bags for packaging of e.g. bread, toilet paper and similar products is an interesting problem area. Except for problems in the extrusion and printing of the film, which one would usually have to expect, the converting into a plastic bag or plastic carrier bag is a bit difficult. There are two common methods being used, in one the plastic bag is sealed and cut off by welding and then falls down onto a stack or straight into a designated box. In the other method the finished bag is collected by a rotating arm which picks the plastic bag by vacuum and after half a turn drops the bag onto two spears (a wicketer). When there are difficulties in positioning the bags it is impossible to pack the correct number of bags in the correct box. If plastic bags are not correctly positioned in the packaging machine at the bakery the bread is going to end up laying on the floor.
A few quality problems which cost money;
Display windows e.g. for mobile phones are made by injection molding. The display windows are gathered and transported to a quality control area where they are inspected and covered with a protective tape. Dust particles under the protective tape leads to an immediate reject.
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By discharging the items with blowing of ionized air already as they leave the mould and in addition to that items are collected in a suitable dust free and sealable container and reaches the quality control station dust free.
When inspecting and applying protective tape, equipment for discharging and blow cleaning is being used again and the display windows are put in a dust free sealable container for further transport to the assembly. A reclaimed mobile in a shop due to dust underneath the display window is very expensive.
Coffee is now commonly packaged in different types of plastic laminates after demands to rid the aluminum layer due to environmental reasons. The aluminum layer has had the excellent property of eliminating most of the otherwise unwanted static electricity, why the transition has been difficult in many places.
Static charging of the plastic has caused coffee to stick to the plastic leading to coffee in the welding seam which consequently has been leaky, with quality problems and reclaims as a result - customers do not want a soft package if it is supposed to be hard. By discharging the foil, prior to sealing, the coffee can be removed from the welding seam and the package remains airtight.
Some examples where active charging with static electricity can save money;
A machine is personalizing and shrink-wrapping magazines. The shrink-wrapped magazines are gathered in a stacker in bundles of 25 where after they are removed by a pusher. As the bundle reaches the conveyor on its way to the automatic strapping machine the bundle changes direction and speed causing the top of the bundle to slide, i.e. it telescopes and flows out and you need to have an operator guiding the bundle right. By charging the magazines in a controlled manner in the stacker the bundles can be transported automatically and the extra operator can be avoided.
In the manufacturing of plastic bags on rolls one often wants to package them in an attractive box made of board with a saleable print. To separate the rolls automatically is not a problem, but how can you automatically make the tail of the roll end up inside the box and let the machine close the flap without getting a bag stuck in the middle? By charging the last few turns of bags with static electricity in a controlled manner one gets a solid roll without a loose tail and one avoids extra operators which would otherwise be called for to straighten out the bags in the packaging machine.
How can I calculate if it pays off to install equipment for charging or discharging?
The question may appear simple, but it is far too often that decisions are made without a proper decision basis. One could perhaps point out that also the lack of a decision does also mean a decision - namely - not to do anything.
The easiest way to make a calculation is to draw a pay-off calculation. The pay-off method is an investment estimate technique which in its basic form disregards from the influence of the interest rate on the calculation and estimates the time needed to pay back the investment (pay-off time) as the cost of the investment divided by the annual yield. Pay-off times as short as two weeks is nothing very unique to equipment for controlling static electricity, and will of course lead to immediate actions. Where you set the limit for what is economically motivated varies between companies and branches of industry, but a pay-off time of 2-3 years is usually regarded as motive enough to make an investment decision.
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How do I produce an input to estimation?
It does not matter what method is being used, the calculation can of course never be better than the data upon which the calculation is based. The first step to take must be to make an inventory of the different problems or possibilities associated with static electricity and work out costs for the different applications the could come into question. A first inventory can probably be made by yourself, but in many companies there are problems which one has not been able to identify as static problems maybe also conduct measurements of static electricity. Many problems are of standard types which are easily specified because there are many similar installations already made. Other problems must be studied more closely to give accurate data, but it is often enough to settle with an approximate estimate at an early stage.
The apparently simple and straight forward task of making internal cost estimates for machines, production lines, personnel etc. can often prove to be quite hard. Variations can be found according to methods for braking down costs and accounting for them, company policy, or accessibility of data. In many cases one can find detailed data for every machine, operation, or per hour labour cost, component costs etc. which makes it easy to make very accurate estimates. When data are missing or are too unreliable one can often find other ways to put a price on the problems.
Costs for problems with static electricity can often be related to rejects or reclaims, in doing which one can start with these costs and then make an estimate of how many reclaims and how much rejects that can be avoided.
A simple calculation
Let us assume that in a larger sheetfed offset printing press the production cost is 100£ per hour with operating time of 60 hours per week at full operation with the present crew. For simplicity we further assume that there are 50 production weeks in a year and that costs for paper and ink will be additional for each specific print job e.g. could be overlooked in our calculation. The production cost per year would then amount to 300’000£. An installation of antistatic equipment gives a capacity increase of % or 30’000£. With an installation cost of 5’000£ the pay-off time is only 2 months.
Is static electricity a maintenance matter or a question for the board?
Static electricity is a matter which in most cases would be regarded as being insignificant in relation to the survival and financial result of a company, in most cases this is probably true. BUT, if you consider that the problems with static electricity which bother the company leads to higher costs in production, reclaims, aftersales etc. It gets much more interesting. Every reduced cost can be added directly to the company profit.
Besides that every static problem that is eliminated means a direct profit it also means that production can be run more reliably at relatively higher capacity utilization. This, of course, leads to yet a higher profit and improved customer relations where delivery reliability and higher quality may give room for a higher price.
Perhaps it is correct that one gets rich not on big incomes but on small expenditures - so maybe one can get rich on static electricity
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