When sheeting light weight paper grades, the sheets have a tendency to jam at the stacker. Even though we direct air at the back of the pile, the problem still persists. Are there other ways to overcome this problem?

Generally, jam ups at the pile are caused by sheet packets lacking sufficient rigidity that they buckle as they drop or are pushed out into the pile.  There are a number of set up issues to consider depending on the type of jam up.

Insufficient momentum to drive the sheets forward

When there is not enough force to drive the sheet packets out into the jog box, ‘hang backs’ (tail end of the sheet does not fall into the stacker) ensues.  Here are a few thoughts:

  • Make sure that the drop wheels or the top tapes at the end of the delivery system are providing sufficient nip to assist in driving the sheet packet out over the stacker. Each pile should have at least two drop wheels or top tapes to deliver the sheet flow into the jog box.
  • Try reducing the overlap percentage in the slow speed tape section. This increases the speed of the sheet flow into the stacker
  • Make sure that the jog box (side jogger blades and front stop to back stop) is not set too tightly that the sheets cannot fit into the piling area.
  • If not already a part of the design, consider retrofitting a ‘tapes over the pile’ package to the delivery and stacking system. In this retrofit, driven top tapes that match the speed of the slow speed bottom tapes extend out over the pile.  With the proper nip, the top tapes help to pull the sheets to the stacker’s front stops.

Leading edge of the sheet packet buckles against the front stop of the stacker

Usually the sheets start to buckle when the packet hits the front stop, there is too much impact being absorbed.  Some ideas:

  • Increase your overlap percentage to slow the sheets down as they feed into the pile.
  • Place wedges at the corners of each pile that are being stacked. Use the wedges to prop the front end of the pile up about one inch (25.4 mm).  This will prevent the leading edge from rolling over and jamming.
  • Add foam to the front stops to absorb the impact of the sheets, so they don’t crumple so easily. Make sure that you allow for the added thickness in setting the jog box.
  • When not overlapping sheets, but delivering in ‘tandem’ fashion, hang lightweight metal bands, such as strapping material, over the pile. The bands should be positioned so they reach beyond the front of the stacker

Leading edge of sheet drops or crashes as it enters the stacking area:

Jam ups can also occur when the sheets nose dive into the stacker.  This is where providing sufficient air delivery can lend support, but there are other suggestions:

  • Check the pile height. The higher the pile, the less likely sheets will curl down as they drop into the stacker. For lightweight papers, the maximum drop should be no more than two inches (51 mm).
  • Use edge turners and crimpers at the end of the slow speed tape section to help corrugate the sheet. This provides rigidity in the length direction, strengthening the sheet packet.

On startup, when running two rolls of paper, I have difficulty with sheet hang backs in the first 6″ (150 mm) of the pile. I am not using a custom pallet. I am using standard skids. How can I overcome this situation?

If the hang backs are only in the first 6″ (150 mm) of the pile, my first conclusion might be that the material will not deliver with such a substantial drop off from the delivery section to the skid. Try to get whatever additional height can be gained by raising the side jog blades to the top of the slots. By making this adjustment, you may be able to gain an inch or so in height.

Another inch may also be gained by using wedge blocks or full length sticks down the outside edges of the pile. As the pile builds to normal delivery height, the sticks can then be easily pulled from the pile.

If the sheeter is equipped with a variable speed delivery, then a reduction in the amount of overlap during initial start-up of a skid may reduce hang backs.

While everyone’s objective is a neatly jogged pile, you should check the position of the side jogger blades to make sure they are not set too tightly. Open the jog box slightly so that the sheets being delivered do not get pinched to a stop before they reach the front stops.

When I slit a web into two streams across, the cut sheets tend to interweave in the overlap section, As a result, the front edge of the sheets are damaged by the center jogger blade. What can I do to prevent this?

Make sure there is adequate belt tension in the bottom slow speed tape section, so that the weight of the sheets does not cause any excess drooping.

Adding an edge turner between the two streams in the slow speed tape section prior to the stacker will also help to split the two piles.

A final way to separate the two streams is to steer them with the upper tapes. You can set the tapes to fan outward from the center slit at the point of overlap through the use of tape guides

I have an automatic pile lowering feature on my stacker. When the pile lowers, the sheets skew, causing an unevenly jogged stack. How can I improve pile quality?

Your problem could be caused by the following:

  1. One of the jogger blades is lower than the other. Set all jog blades to the same depth. The load table’s guides are loose or worn. If the table sways when rocked, inspect the guides and address accordingly.
  2. The front to back jog box may be misaligned. Make sure the front stops and the oscillating back jog fingers of the stacker are properly set.

When sheeting light weight board, the sheets have a tendency to turn under at the edges entering the stacker. What can I do?

Try to give the sheet some added rigidity by using edge turners and crimpers. Edge turners (or “shoes”) flare the edges of the sheet in the delivery system. Crimpers are placed in the center of the web path to corrugate the sheet, giving it added stiffness.

When using edge turners and crimpers be careful about the placement of top tapes near them. If the tapes are too close to the edge turners or crimpers they will crease or mark the sheet.

When sheeting paper at higher speeds, the sheets roll over in the pile. To compensate, my operator reduces speed. Is there another way to solve this problem?

Your pile height may be too low. Ideally, the gap between the top of the pile and deliver roll should only be ½ to ¾ of an inch. Raise the position of the feed down sensor so the sheets can fall freely into the stacker.

If this does not correct the problem, try adding air at the pile. By directing air out across the stacker, the sheets float out over the pile.

At the same time, air can also be directed down into the stacker, forcing the tail end of the sheet down into the pile.

In the stacker, we experience turned up edges on the sheets. What causes the sheets to fold this way?

Turned up edges are caused by too much up curl in the web. Adjust the amount of decurl accordingly until you get a flat sheet.

Turned down corners can be the result of not enough bottom delivery tapes supporting the sheet. This occurs most frequently along the slit edges of the sheet. Move the bottom tapes to within an inch (25 mm) of the side edge.

The sheet packet hits the stacker front stops too hard, damaging the leading edge of the sheet. Besides slowing down the sheeter, is there anything I can do?

Sheet damage can be prevented by increasing the amount of overlap. This is done by reducing the speed of the slow speed tapes (either adjusting it mechanically through the a gearbox or electrically through a motor).

When sheeting easily damaged or soft material, consider applying rubber to the front stop boards or fingers to absorb the impact of the sheet.

If the damage appears on one side of the sheet, check the sheet squareness and make sure the front stops are square to the back of the stacker across the width of the machine


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