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Technology Focus

Eliminating Static with Diecutting

by Mark Baril, Cut Smart Manufacturing, Inc.

May-June, 2008
Static can become a problem for diecutting and other finishing processes so in order to control it, operators and production managers should understand the problem completely – from causes to solutions.

Static electricity is an accumulation of an electrical charge on an insulated area of a material. It is an imbalance of positive and negative charges. In order to understand what causes the electrical build-up, we really need to go back to high school science class. In basic terms, everything in our world is made of atoms. Atoms contain protons, neutrons, and electrons. Each of these three parts carries an electrical charge – positive, neutral, and negative. Some materials (made of atoms) have loosely held electrons while others have more closely held electrons. It is the movement of electrons from one atom to another that creates more or less electrical charge within each. Materials with loosely held electrons are called conductors and these materials are great at giving away their electrons. Many metals are great conductors. Materials with tightly held electrons are called insulators and these materials are great at keeping and attracting more electrons. Many plastics fall into this category. There also is that vast array of materials that falls somewhere in between. Two different insulating materials passing by one another will cause a static build-up because they are slightly different in the way they hold onto their electrons.

So simply stated, it is the contact between two different materials that causes electrons to move from one to the other. Friction, passing, and rubbing of materials together during the typical converting operation naturally cause the materials to be charged, one positively and one negatively. Materials with opposite electrical charges tend to be attracted to one another while materials with the same electrical charge tend to push away or repel one another. This becomes very important in waste removal after diecutting.

Effects from Static Electricity
The result of this static build-up typically causes the following problems:

  • Safety Problems for Operators. The most obvious problem can be seen in the operator having to handle the finished sheets or the material during the diecutting process. Humans make great conductors and when an operator touches a charged stack or roll of material, or just gets close, the static charge wants to jump to him. In many cases this discharge can be an annoyance that the operator doesn’t look forward to on a regular basis but realizes, “it’s just part of the job.” In other cases, it can be a safety concern and, in some unusual diecutting operations where laminating or perhaps the introduction of flammable chemicals is added to the mix, this electrical charge can be a tremendous safety hazard.
  • Manufacturing and Feed Problems. Because the material being processed becomes charged with static electricity, it naturally will be attracted to and repelled from just about everything in the manufacturing line. In cases where the sheets themselves or the waste from the diecut sheets are expected to be cut and then just fall away, this natural attraction can cause some problems. A charged insulating material may be negative on one side and positive or neutral on the other. When part of it is removed and allowed to flip around and do as it will, the forces of the electrical charge will overcome gravity and, in many cases, waste will be stuck to the finished diecut part. In some cases this will cause jam-ups, while in others it will simply result in contaminated product. In extreme cases, static electrical build-up also can be the cause of problems with electrical control equipment within and around the press or other cutting equipment.
  • Contaminated Product. Not only does the rectangle or hole being removed from the final part become a problem because of the tendency to ‘stick’ but slivers of material (caused by cutting or dust that is kicked up when the operator walks around the machine) can cause challenges. All of this oppositely charged material floating around will cause problems with both the production run and quality of the finished product. Delivering a statically charged finished part to the customer also can lead to some problems. Medical product manufacturers seem to be most aware of this problem because of their need to produce contamination-free product.

Solutions to Static
In any of these effects, the problem needs to be dealt with in some defined, reproducible, and controlled manner. As related to diecutting, three common solutions to this challenge exist. All three attempt to do the same thing – neutralize the charge. The common themes within all three systems are cleanliness and correct positioning.

  • Static Elimination Bars. These bars are made up of an insulated row of electrodes. When electricity is supplied to them they generate positive and negative ions (an ion is a positively or negatively charged atom). These ions are naturally attracted to the charged material passing closely by the bar and when they meet, the static charge on the material is neutralized. This process has been in use in converting lines around the world for many years.
  • Ion Blower Systems. These systems create positively and negatively charged ions just as the static elimination bars do; but instead of delivering the ions at very close range, they blow the ions at a semi-controlled area of the production line. These machines are quite common in areas just before and after cutting where the part or waste is out of the sheet and still needs to have the static electricity neutralized. Static elimination bars, in many cases, are preferred over the blower system because the area of neutralizing is very specific and controlled in the bars. However, given the unusual situation in which many specialty cutters find themselves, a blower system may be the only choice. Some of these systems also combine with higher movement air systems to neutralize and remove contaminants at the same time.
  • Tinsel Systems and Brushes. Yes, this looks pretty much like the tinsel found on a Christmas tree. Working with the concept that the static charge on the material will find a conductor to jump to, simple static neutralizing tinsel remains one of the least expensive and most popular ways to get rid of static electricity. Most production lines and diecutters possess limited places where the material can be hung, but the same is true of the static elimination bars. Depending on the product, the tinsel itself can cause material damage due to scratching if the sheets move directly into the tinsel. This would be the certain downfall of using this process as the only means of static elimination.
  • Jogger/Aerators. Typical jogger/aerator/load turner systems can be coupled with the ion blower systems mentioned earlier to do their base job and help to eliminate static at the same time. If static exists within the sheets to be diecut, the aerator helps separate the sheets that may tend to stick together before entering the machine.

Conclusion
What the future may hold is quite clear. As technology improves, systems are being built that tell us what is happening with static within diecutting machinery. These systems will deliver the information, control it, allow operators to manipulate it, and then automatically deal with the problem at various points in the line. While this will be great for large converters that can afford the new systems, for many manufacturers, the more conventional static control systems mentioned earlier in this article still will be the best solution to control static during the diecutting process.

InsideFinishing would like to thank the International Association of Diecutting and Diemaking (IADD) for permission to publish this article, which was published in the May 2007 issue of The Cutting Edge. Mark Baril of Cut Smart Manufacturing, Inc., a member of the IADD TechTeam™, can be reached by visiting www.cutsmart.com.