Recently a manufacturer made this statement and asked Cut Smart this question; "My diecutting operators have prompted me to write and ask about static control. Our company has neglected the problem for years, and my operators tell me that they are getting sick of being shocked when running certain jobs. Is there a quick fix to the static problem and if so where should I turn for help?"
This is a subject that will certainly make your hair stand on end, and although we make no claim to be experts in Static Control, perhaps we can shed some light on the basics of this problem as it relates to diecutting.
CAUSE - 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 our high school science. In the most simple terms possible (I like it that way) everything is made of atoms. Atoms contain protons, neutrons, and electrons. Each of these three parts carry 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 are great insulators. There is also that great array of materials that fall somewhere in between. Two different insulating materials being passed 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, rubbing, and passing of materials together during the typical converting operation naturally cause the materials to be charged, one positively and one negatively.
The one final bit of basic science needed here is the positive/negative thing. 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.
EFFECT - 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 that has to handle the finished rolls or the material during the process. We humans make great conductors and when we touch a charged roll of material, or just get close, the static charge wants to jump to us. In many cases this discharge can be an annoyance that you don't look forward to on a regular basis but, "hey 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 needed, this electrical charge can be a tremendous safety hazard.
Manufacturing and Feed Problems - Because the material you are processing becomes charged with static electricity it will naturally be attracted to and repelled from just about everything in your manufacturing line. In many cases, where the cut parts stay in the web and are delivered in rolls, the static pull really has no effect because it is overwhelmed by the tension caused by the unwind, feed, and rewind systems. In other cases where the parts themselves or the waste from the parts is 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 you will find your waste stuck to your finished parts. 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 can also 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 you are trying to remove from your final part become a problem because of the tendency to "stick", so do the slivers of material caused by your cutting or the dust kicked up when your operator walks around his/her machine. All of this oppositely charged material, just floating around, will cause both running problems and quality problems with your product. Delivering a statically charged finished part to your customer can also 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 - In any of the effects mentioned above, the problem needs to be dealt with in some defined, reproducible, and controlled manner. There are three common solutions to the problem as it relates to diecutting. 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 it is neutralized. This process has been in use in converting lines around the world for many, many years.
ION Blower Systems - These systems create positive 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 just after cutting where the part or waste is out of the web and still needs to have the static electricity neutralized. The static guys prefer the elimination bars to the blowers because the area of neutralizing is very specific and controlled in the bars, but given the unusual situations many specialty cutters find themselves in, a blower system may be your only choice. Some of these systems also combine with higher movement air systems in order to neutralize and remove contaminants at the same time.
Tinsel Systems and Brushes - Yes, this stuff looks pretty much like the stuff you put on a Christmas tree. Running with the idea that the static charge on your material would like to 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. There are limited places on most production lines 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 web moves into the tinsel.
CONCLUSION - And finally - what the future may hold is quite clear. As technology improves, systems are being built that tell us what is happening with static within our machinery. These systems will deliver this information, control it, allow us to manipulate it, and then automatically deal with the problem at various points in the line. While great for large converters that can afford the systems, for many manufacturers, a few tricks, a couple of pieces of static control equipment and a few more years of being Zapped are probably what the future holds. Again, we certainly are not experts in the static control field but if you have questions on where you can find any of the equipment talked about here and you need to talk with an expert, give us a call and we'll do our best to point you in the right direction.
Please contact Cut Smart if you would like more information on this subject.
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