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.