I am having trouble with delivering and stacking certain materials because of static. Is there anything I can do to my existing sheeter to overcome this problem?

Humidity

  • Humidity affects static build up. “Relative humidity” is the percentage of moisture held in the air compared to the maximum it could hold at that temperature.  The reason static is more problematic in cold weather is because of low humidity of the air.  If the relative humidity drops below 30%, the static conditions become noticeable.  So introducing moisture into the environment, either by steam or vaporizer in the sheeting area can reduce static.
  • Here’s an old timer’s trick when sheeting coated grades. Mount a full width, 12” (308 mm) long absorbent pad prior to the cutter infeed.  Position the felt such that it comes in contact with the incoming web flow.  The moist mat dampens the web, offsetting static buildup.

Locating Static Prone Areas

  • Static build up can be neutralized by ionization devices such as static eliminating bars or air ionizers. The key is properly locating the units on a sheeter for maximum effectiveness.  Static can be a problem when material slides over itself as when overlapping sheets in the delivery section or being jogged into place in the stacker.
  • A more comprehensive approach is to use a static detection field tester. Map the flow of material through the sheeter, recording results along the course from roll stand to stacker.  Use these results to identify where static systems should be located.

Ionization Devices

  • In the unwind and web conditioning areas, (prior to the webs being converted into sheets), consider hanging metallic tinsel across the web paths after an outfeed roll. Keep the garland within ¼” (0.06 mm) from the moving surface.  Insure that the tinsel is grounded to the metallic side frames of the machinery.
  • Rubber or polyurethane covered rolls act as an accumulator of static charge. To offset static build up in the draw drum section of the cutter, mount a static bar about 1” (25 mm) above a cutter’ squeeze roll.
  • Static eliminating bars mounted in the high speed tape section above and below the sheet path, reduce the sheet clip’s charge prior to the overlapping process.
  • Mounting a second pair of static bars above and below the sheet path in the slow speed tape section will treat some of the induced static build up. Note that if a full width apron is used as the conveying design, rather that narrow width belts, static bars on the underside of the sheet flow will be ineffective.
  • At the end of the delivery system as the sheets enter the stacker, use compressed air or blower motor air to break up the overlapped clips. Mount the nozzles or fingers facing the stacker at the end of the slow speed tape section.  Position them in a manner that air is introduced in the tail end of the sheet.  The volume of air will be dependent on the weight of the sheet(s) and the cut off length – typically more air is required on longer lengths.
  • On particularly static prone material, the air at the pile may need to be ionized at the nozzles or additional static blowers maybe required over the stacker directed down at the pile to prohibit sheets ‘climbing up’ jogger blades.

When sheeting carbonless paper, the sheeted stock sometimes wraps around the cutting section. Once we get past this point, we also have difficulty stacking. Do you have any suggestions?

It would appear that static is the cause of most problems. There are several things you can try to prevent material from wrapping around the knife cylinder:

  1. Wrap the cylinder with a felt or short nap non-conductive material.
  2. Introduce compressed air above the doctor board between the rubber covered nip roll and the knife cylinder.
  3. Ground the knife cylinder and other rolls in the machine by use of carbon brushes as used in small electric motors.
  4. Try adding a “knocker” on the knife cylinder, (a strip of chipboard taped to the back of the fly knife blade) in such a fashion that after the cut, the strip would tend to force the leading edge down into the tape section.

To help handle static prone sheets entering into the pile, try the following:

  1. Insulate the jogger blades with chip board so no metal comes in contact with the sheeted stock.
  2. If the sheeter is equipped with vibratory jog, try running with the vibrators turned off. Add “drag wires” at the pile to help knock the sheets down into the pile.
  3. Introduce a blast of compressed air under the sheets as they travel off the delivery belts.
  4. If you are running a single web of material, try running multiple webs.
  5. Move the top tapes to the outside of the machine so there is nothing for the sheets to cling to as they are delivered into the stacker.

We have a problem when running light weight label stock. The sheets have a tendency to skew in the tape system, and this damages the corner of the sheet as it hits the stacker’s front stop. What can I do to alleviate this problem?

Here are a few suggestions:

    • Check your tape tension to make sure it is the same across the width of the delivery section. You may want to set the lower tapes tighter to support the sheet.
    • Make sure the pinch of the overlap carriage or “stop” wheels are set properly. The nip should be snug to the touch when pulling on sheets in the overlap area.
    • Also check the alignment of the overlap carriage or “stop” wheels across the width of the sheeter. The settings can be misaligned after a jam up. Measure the distance from the last, bottom high speed roll to the overlap carriage on the drive and operator sides.
    • Experiment with edge turners and crimpers to add more corrugation to the sheet. These will steer the sheets into the stacker.

We recently sheeted an order of coated paper, and had lots of problems due to static. Do you have any suggestions for sheeting coated stock?

If the problem is in the cutting section, such as the web wrapping around the squeeze roll or the knife revolver, an old trick is to mount a cotton felt across the infeed of the sheeter and then wet it. The dampness of the felt will help to neutralize static, and prevents jam-ups in the cutting section.

If the problems are occurring at the stacker, try introducing compressed air prior to the sheets entering the pile. By introducing a layer of air between sheet packets, static can be overcome. On MAXSON sheeters, the use of air at the pile has increased speeds by more than 200 fpm (60 mpm).

We frequently have jam-ups in the overlap section. As a result, our operator compensate by running the sheeter at slower speeds. Is there anything else I can do?

There are several different conditions that could cause this:

    • Check the distance between the overlap carriage (or stop rollers) and the last, bottom high speed roll. If the distance is less than the sheet length, then the tail of the cut packet will hang on the end of the high speed tape section and the leading edge of the next sheet will run into it, causing a jam. Allowing up to ½” (10 mm) oversize in positioning the overlap carriage isn’t unacceptable.
    • Check the nip in the high speed tape section between the upper and lower tapes. Sometimes, the sheet packet slips as it is delivered from the cutter to the point of overlap, because of loose tapes. If you notice that the gap between cut sheet packets is shortening up, you may need to tension the tapes in the high speed section, better distribute the tapes across the sheets, or adjust the nip between upper and lower tapes at the delivery mouth.
    • If you are using edge turners (or “shoes”), that they are not set so tight into the flow of the sheets that they tend to slow down the cut packet in the high speed tape section. This would have the same effect as poor tape nip.
    • Check your overlap carriage to make sure the bake-o-lite rings are fastened tightly to the driven shaft. The outer diameter of the black ring rolls are sized to match the speed of the slow speed tapes. If the rings have loosened, then they may not be driving the sheet packet away from the point of overlap.
    • Consider adding an Airfoil System to suck down the tail end of the sheet to permit the leading edge of the next sheet to pass over it. Speed increases of up to 200 fpm (60 mpm) have been realized by utilizing this Maxson design.

What can I do about static buildup when sheeting coated material?

Static bars are the best defense against this problem. Maxson sheeters utilize as many as 5 static bars on a sheeter.

One bar is mounted above the rubber coated squeeze roll to neutralize static buildup in the cutter.

The remaining bars are mounted in the delivery section, in both the high and low speed tape sections. As many as two bars should be positioned prior to the overlap and as many as two bars prior to entering the stacker. In all cases, the bars should be within 1″ (25 mm) of the sheet path

When sheeting a soft coated material, the Operator notices tape marks. The marks do not extend along the entire surface of the sheet. Where is this occurring, and how can I solve it?

This type of tape mark is likely caused by setting the pinch at the overlap carriage too tightly. To be certain, take samples of sheet packets from the high speed tape section, prior to overlapping and samples in the slow speed tape section prior to stacking. If the cause of the tape marks is the overlap carriage, the tape marks should correspond to roughly the percentage of overlap.

Adjust the nip of the overlap carriage (or stop wheels) by raising it until the marks disappear. It’s important not to raise the overlap carriage too much, because the sheets will begin to skew when operating at higher speeds affecting pile quality.

I notice full length tape marks on the cut sheet. Where is this occurring, and how can I solve it?

Tape marks are more apt to happen when sheeting heavier caliper stock and highly coated materials. The markings originate in the high speed tape section at first pinch point of the top and bottom tapes.

This problem can be corrected by allowing for more space between the 2 sets of tapes. Reduce the tension on both the bottom high speed tapes and the top high speed tapes. This should eliminate the full length marking.

It may be necessary to adjust the pinch roll at the delivery mouth of the top high speed tapes to create more room for the sheets.


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