ESD Systems - Questions And Answers

I have a production line that unwinds, advances, and rewinds a polyester flexible circuit sheet (750ft long x 12in. wide x 5mils thick). The sheet is wound and interleaved with paper into rolls approximately 15' in diameter. As the polyester material unwinds off the roll, the paper is separated and wound back up onto a discard roll. Here we have a Simco Aerostat XC ionizer pointed at the polyester material approximately 16' from point of contact at a 40-60 degree angle. From here, the material is ran through a printer across aluminum plates and then backed out. It then loops into the next machine that consists of a stainless steel table (6ft long x 14in wide) and is advance at a rate of 14in./s every 30seconds. Our second ionizer is placed here pointing up at the material and the point of contact with the table. The middle 1/3rd of the table is a vacuum plenum (0.06' holes spaced 1' apart) that is used to keep the material from moving during the 30 second lapse between advances. The table is grounded. Initially we were seeing negative charges on the sheeting in the neighborhood of 2000 volts. With the ionizers in place, we are still seeing a negative charge in the neighborhood of -200 volts or less. What else can we do to neutralize the effect? Can we port ionized air up through the vacuum table? I have also tried to take a couple of sheets of polyester and place one at the beginning of the table between the polyester in question and the table itself and another at the oppositte end. This seems to help but is not a permanent fix. -Brett Campbell, Automated Assembly Corporation, Lakeville, MN

You can try increasing the coverage of balanced ionization by adding a few additional eliminator bench top ionizers just before and after the aluminum plates and the stainless steel vacuum plenum. Use of the same material at the vacuum plenum will also help reduce tribocharging as noted below.

The Simco Ionizer recommends a separation distance of about 12 inches or 1 foot as opposed to 16 feet. The rate of material advancement is only 28 inches every 2 seconds, where the coverage is almost 18 square feet or about 6 linear feet at about 36 inches wide. As long as the material isn't subjected to low relative humidity (RH) or sped up, the ionizers should continue to work. You will want to ensure that the current ionizers are both in balance and meet the manufacture's specs for charge decay time. Increasing the area of coverage may help reduce the decay time, depending on the distance from the ionization source (the father away, the more balanced ion flux you'll need).

We have a similar bench top ionizer, the Eliminator Bench Top Ionizer that has a charge decay of less than 1.5 seconds from 1 foot away. The Decay Time will increase as the distance between the charged material and the ionizer increases.
Your solution of putting the same material (polyester flexible circuit sheet) at the initial and final contact point of the table will help to reduce the tribo charging as similar materials do not charge as high as materials further apart in the triboelectric series chart.

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