I am having trouble getting a clean slit edge. How can I solve this problem?

I am having trouble getting a clean slit edge. How can I solve this problem?

The first thing to do is to make sure the top slitter blades and bottom rings are in good condition. If the blades have nicks or are dull to the touch using the face of your thumbnail, replace the slitters. Next, make sure the relationship between the bottom slitter ring and the incoming web path is set properly. The bottom ring should protrude into the web path by approximately 1/16” – 1/8” (1.5 – 3.0 mm) so the top slitter blade contacts the web and the bottom ring at the tangent point.

Third, be sure the top slitter’s cant angle is properly set. The cant angle describes the top slitter blade’s tilt from the vertical position. A proper cant setting angles the top blade away from the web after the slit point. Some slitters have “keys” that set the cant angle for particular substrates. Make sure the keys are on the proper side of the slitter. Older designs can be adjusted by the Operator.

Finally, make sure that adequate side load pressure is applied by the top slitter blade to the lower slitter ring. A slight drag when turning the top slitter against the bottom ring is a fair measure of adequate side loading. Inadequate side load pressure will result in poor slit quality. Excessive side pressure will result in worn slitter blades.

I am getting variation in sheet length. What should I do?

I am getting variation in sheet length. What should I do?

The most often asked troubleshooting question concerns sheet length variation. Troubleshooting these problems can be frustrating but the following are some of the basic things to check:

If the sheets are always short: 

  1. Check for slippage at the nip roll. This can be due to a hard or glazed rubber roll, too little nip pressure, or too much roll stand brake pressure.
  2. Check to see if the knife drive belt is riding up on the flange of the lower pulley.
  3. Check to see if the draw drive belt is tracking properly on the paper pulley.

If the sheets are always long: 

  1. Check for improper pinch at the mouth rolls of the tape system.
  2. Check to see if the draw drive belt is riding up to the flange of the lower pulley.
  3. Check to see if the knife drive belt is tracking properly on the upper pulley. If the machine is equipped with a Change Pulley arrangement using a Poly-V belt, be sure it is not slipping. This can be due to belt wear or insufficient tension.
  4. Check the take-ups to be sure they are functioning properly.

If the sheets are both long and short: 

  1. Check couplings for the signs of misalignment, damage to flex packs, and loose keys.
  2. In most cases, timing belts are used. If these are damaged (for example broken cords), they will not transmit the necessary power to maintain sheet length. As mentioned above, improper tracking can also be a problem. All belts should be checked since belts which ride against the pulley flanges can ride up on the flange and have the affect of changing the ratio slightly. This, in turn, affects sheet length.
  3. Backlash can be found in a number of places depending on what components make up the drive. Any gearbox in the system can have backlash. As mentioned above, keys and keyway throughout the drive system must be checked for looseness. On many machines, backlash can be located by locking the draw roll pulley in place and trying to rotate the knife pulley. If there is movement, have someone look at the drive train while this pulley is rocked back and forth. Different types of variable speed transmission are used. Some use belts and others use chain. Check the condition of the belt or chain. Frequently, this is the problem. Be sure the belt or chain tension is properly set. The adjusting screw/nut mechanism that expands and contracts the cones must not have any play. For specific information, refer to the manufacturer’s instructions.
  4. Check the material flow as it passes through the knife section. Unstable flow causing the web position to fluctuate can cause sheet length variation. Adjustment of the air doctor boards can help stabilize the flow.
  5. Check the condition of the paper rolls. If they are out of round, it may be necessary to run slower to obtain better sheet length accuracy.

When I slit and run two piles, one sheet is square and the other is out of square What adjustments can I make to address this?

When I slit and run two piles, one sheet is square and the other is out of square What adjustments can I make to address this?

Be certain there is enough tension to keep the web taut and the slitters are set properly.

Watch the flow between the pull roll section and tape take away section. Make sure the material is staying flat through the cutter. (This is done on MAXSON sheeters using air washed doctor boards.)

In the tape take away section, make sure the conveyor belt pinch is equal from side to side. To be sure the sheets are pulled out straight, evenly spread the tapes out over the material.

I’m having trouble running 0.024” (400 gsm) thick board on my stationary bed knife cutter. The leading edge has a lip or “bead” on it and the trailing edge is fuzzy. What can I do to fix this problem?

I’m having trouble running 0.024” (400 gsm) thick board on my stationary bed knife cutter. The leading edge has a lip or “bead” on it and the trailing edge is fuzzy. What can I do to fix this problem?

Both problems are caused by material flow through the knife area and knife cut angles. There are a few areas you can look at to solve this problem.

The first thing to try is repositioning the doctor boards before the bed knife to give it more of a “water fall” effect or steeper approach angle into the cut point.

The second thing to reexamine the knife angles. The upper and lower cross cutting blades’ angles should match the flow of the web so as not to contact the board until at the point of cut.

The third thing to determine if “blocking” is occurring. “Blocking” is the phenomena that occurs when the sheet length is longer than the circumference of the the knife revolver. Under such circumstances, the speed of the fly knife on a stationary bed cutter is traveling slower than the speed of the web at the time of cut. Under such conditions, the trailing edge of the sheet is being pulled away from the cutting action, which is tantamount to tearing the sheet away. Running at reduced speed minimizes the poor cut quality on the trailing edge. Changing the shear in the cutter or installing a larger knife cylinder are other, more extensive solutions.

The last area to look at is the tape take away pinch rolls, make sure the pinch is enough to pull the web taught while it is being cut but not so tight as to tear the web as it is being cut.

I have trouble maintaining edge trim at the slitters. How do I insure a steady ribbon of edge trim?

I have trouble maintaining edge trim at the slitters. How do I insure a steady ribbon of edge trim?

  1. Slitter Condition: To determine cut quality, both male and female knives should be either new or resharpened. Sharp knives maintain a consistent cut necessary for slitting a narrow continuous stream of light weight material.
  2. Slitter Set-up: It is important to determine proper cant angle. The slitter manufacturer is generally the most qualified to suggest cant angles. Look to them also for the amount of over speed and penetration required.
  3. Trim Take Away: Adjustment rings to support the trim and help prevent tearing may be added. The diameter of the rings should be approximately the same as the female knife.
  4. Take Away Suction: It is good idea to have the ability to adjust the volume of suction of the removal system. Adjustment the suction allows for proper pull on the trim stream against the knives. This process shears the material and prevents tearing.
  5. Edge Alignment: Web steering or edge guidance is suggested particularly if a narrow trim is required. If these units are not available, the roll stand’s guidance components must be in good repair to allow incremental side lay adjustments.
  6. Line Speed: The width of edge trim may determine maximum achievable line speed. Web fluctuation relative to speed may cause wandering. This produces a varying width of edge trim. A slower operating speed may overcome this condition.

What causes a crescent or bow-shaped cut?

What causes a crescent or bow-shaped cut?

There are several possible sources for this problem.

First, check the bed knife to make sure it is straight across the entire surface. This is done by measuring from the edge of the knife to the back of the knife in a half dozen evenly spaced intervals along the length of the blade. MAXSON recommends no more than 0.010″ (0.25 mm) variation along the blade.

The position of the bed knife may also be causing a bow-shaped cut. Examine the knife to determine if it is seated properly into the bed knife base, free of foreign debris underneath.

Finally, check the condition of the doctor board before the knife. If it appears to sag in the middle, then it is not supporting the sheet properly. Correct as required.

When taking a side trim, I sometimes find one side of the pile builds up higher than the other side. Why does this happen?

When taking a side trim, I sometimes find one side of the pile builds up higher than the other side. Why does this happen?

Assuming the caliper of the material doesn’t vary across the machine, this condition usually indicates a slit quality problem. Check for improper penetration of the upper slitter blade, inadequate side pressure when engaging the top slitter to the bottom ring, or simply a dull slitter blade.

During start-up, I get as many as 10 to 15 short sheets until the line speed steadies. Once I reach this point, my sheet length control is maintained. What is causing this variation?

During start-up, I get as many as 10 to 15 short sheets until the line speed steadies. Once I reach this point, my sheet length control is maintained. What is causing this variation?

If your sheet length monitor reads out the proper sheet length, then the variation is caused by web slippage at the point of nip (between the squeeze roll and the draw drum).

Check your roll stand for proper brake pressure. As a rule of thumb, the initial brake setting should be set so that a full roll can be turned by one man.

Another area of adjustment would be the squeeze roll pressure. By increasing the nip pressure, you should realize better sheet length control on start-up.

We don’t have a squareness problem when sheeting a 50” wide roll. However, when we slit the same roll into 2 piles, 25” across, one sheet is square, while the other is not. What is causing the sheets to be out of square?

We don’t have a squareness problem when sheeting a 50” wide roll. However, when we slit the same roll into 2 piles, 25” across, one sheet is square, while the other is not. What is causing the sheets to be out of square?

Check your draw roll section to make sure the cutter’s draw drum and squeeze roll are properly aligned. Remove the before knife doctor board to ease the ability to measure alignment. Using a plumb bob, measure the distance from the plumb bob’s line to the nearest point on the squeeze roll and the nearest point on the draw drum. The difference between these two measurements should be the same on the operator side and the drive side.

A more radical approach on stationary bed knife design is changing the ‘shear’ in the cutter. Shear describes the angle of the cutting helix across the width of the cutter. Reducing the amount of shear will help minimize the problem, since less angle across the cut requires less adjustment for squareness. On the other hand, less shear in the cutter also increase the noise level of the cutting action. It’s best to consult with your sheeter manufacturer if considering this approach.

Like sheet length accuracy, there is always some variation in squareness. Most operations typically adjust squareness to split the difference.

I notice length variation when I sheet material. What can I do to prevent short sheets?

I notice length variation when I sheet material. What can I do to prevent short sheets?

Short sheet lengths are usually associated with excessive brake pressure at the roll stand or inadequate nip roll pressure. See if less brake and heavier nip at the cutter’s squeeze roll remedies the problem.

The surface of draw drum and squeeze roll should also be checked. If either roll is glazed or slippery, the web may not be pulled in uniformly, which can lead to short sheets.

To remove the glaze on the rubber covered squeeze roll, wash it clean or rub its surface with a fine grit sandpaper.


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