Static Eliminators for Unwinding, Rewinding and Slitting
- Published: August 08, 2025
By Dr. Kelly Robinson, PE, PhD, Electrostatic Answers
For an unwinding or a rewinding roll, where can we put a static dissipater so that it works? In unwinding, rewinding and slitting, the roll diameter changes, which complicates static control.
For example, the diameter of the Unwinding Roll in Figure 1 decreases, which makes the distance to the static dissipater increase. The neutralizing ions that form at sharp points in the static dissipater move through the air to the Unwinding Roll. When ions must move farther, dissipation is slower.
For tinsel and other passive dissipaters, being closer is even more important. Passive dissipaters form more neutralizing ions when they are closer. Tinsel works best when it touches the Unwinding Roll. However, touching the moving roll also wears out the tinsel. So, mounting it just a half-inch away is fine.
Two common methods to control static on unwinding and rewinding rollers are:
- Use a long-range static bar.
- Move the static dissipater.
Using a long-range static bar is often a good answer. The static bar in Figure 1 may be mounted in a fixed location. These long-range static bars are designed to neutralize from distances in the range 6 to 30 inches. This is sufficient for most unwinding rolls.
Powered static bars can tell us when they need to be cleaned. Internal circuits monitor their ion output. When the output gets too low, the static bar tells us to clean it.
Long-range static bars have lower ion output than short-range bars. Short-range static bars are designed to neutralize static at speeds of 1,000 fpm (300 mpm) or even higher. You may need to use two long-range static bars mounted side-by-side if your line speed is faster than about 100 fpm (30 mpm).
Test if the powered static bar is working properly by using a hand-held electrostatic fieldmeter to measure ERoll-After after being treated by the static dissipater and before the web exits the Unwinding Roll. The reading should not exceed +5 KV/in. Also measure ERoll-Before before the static dissipater. When ERoll-Before is bigger than +10 KV/in, the powered static bar should neutralize at least 90 percent of the static charges.
Moving the static dissipater to follow the changing roll diameter can also be a good answer. The Static Bar in Figure 2 is mounted to the Lay-on Roller frame. The distance from the static bar to the Unwinding Roll stays the same. This is an important advantage because a regular, short-range static bar may be used. Short-range static bars have the highest ion output so that they can effectively dissipate static at speeds exceeding 1,000 fpm (300 mpm).
Use a mechanically strong static bar when mounting to the Lay-on Roller frame. Vibrations from the Lay-on Roller shorten the service life of the Static Bar in Figure 2.
Test if the powered static bar is working properly by using a handheld electrostatic fieldmeter to measure ERoll after being treated by the static dissipater and before the web exits the Unwinding Roll. The reading should not exceed +5 KV/ in. If possible, turn the static bar off for just a short time and measure ERoll-Of. When ERoll-Off bigger than +10 KV/in, the powered static bar should neutralize at least 90 percent of the static charges.
The lonizing Rod in Figure 3 swings towards the core as the Unwinding Roll expires. This Ionizing Rod must be grounded with a wire that runs up the Support Chain or Rope to the Support Bracket.
The lonizing Rod in Figure 3 hanging from Roll handling interferes with roll handling. The Ionizing Rod must be moved out of the way to load a new roll. Install a bracket to hold the Ionizing Rod when loading a new roll. Of course, the operator must be trained to put the lonizing Rod back in place once the new roll is loaded. This extra operation during roll handling is a disadvantage.
I cannot determine if the lonizing Rod in Figure 3 is working just by a visual inspection. It must be tested regularly, just like any passive ionizer, to verify that it is working properly. Test if the dissipater is working properly by using a hand-held electrostatic fieldmeter to measure ERoll-After after being treated by the static dissipater and before the web exits the Unwinding Roll. The reading should not exceed +5 KV/in. Also measure ERoll-Before before the static dissipater. When ERoll-Before is bigger than ‡10 KV/in, the passive static dissipater should neutralize at least 80% of the static charges.
The changing roll diameter complicates static control on unwinding and rewinding rolls. Two common methods for controlling static unwinding and rewinding rolls are (1) to use a long-range static bar or (2) move the static dissipater to follow the changing roll diameter. Both methods have advantages and disadvantages. Two key advantages for a using powered static bar are that it can tell us when it needs to be cleaned and it does not require extra operations during roll handling as are needed for passive dissipaters.
About the Author
Dr. Kelly Robinson writes on static issues occurring in converting processes. Robinson founded Electrostatic Answers, has 40-plus yeas experience in industrial problem solving and was named Top Manufacturing Consulting Services Provider 2023 by Managing MFG. He can be reached at This email address is being protected from spambots. You need JavaScript enabled to view it..
