The bottom rings on the slitter rig have a slight wobble, which causes a wavy edge on the side of the sheet. What can I do to fix this problem?

A wavy edge on the slit side of sheets, suggest the bottom slitter rings may have a slight wobble.  It could be the slitter rings or it could be the condition of the bottom slitter shaft.

First, make sure the inside diameter of the bottom slitter ring is sized properly for the shaft so that there is a slide fit.  Typically a clearance of 0.002” (0.05 mm) is sufficient; anymore could induce a wobble.  Either the shaft is undersized or (more likely) the inside diameter of the slitter ring is oversized.

Next, check the face of the slitter ring edge for parallelism to the ground bottom slitter shaft. Using a dial indicator, the cutting face should vary no more than 0.003” (0.07 mm); otherwise the slit edge will weave accordingly within the stacked pile. Variations greater than 0.010” (0.25 mm) can be easily remedied by regrinding to a better tolerance.

Over time, steel slitter shafts can become ‘dimpled’ by slitter ring set screws that secure the rings’ positions.  When positioning a slitter ring over a deformed area, be mindful that the deformation may ‘tilt’ the ring. 

For deviations of less than 0.010” (0.25 mm) run out on slitter rings that are locked into position to the shaft by a set screw, drill and tap a second set screw location 120 degrees from the first. Through a combination of loosening and tightening the two set screws, you should be able to minimize the wobble and bring the slit edge into conformance.

By the way, wide 2” (76 mm) or wider slitter rings are less disposed to wobble than narrow rings.

I had been running my sheeter without any sheet squareness problems, but lately when I sheet 3 or 4 piles across the width of the sheeter, the sheets on the drive side are out of square. What can I do?

There maybe several causes contributing to “out of square” sheets. It is best to work your way through the cutter, correcting any maladjustment you encounter.

First, make sure the top slitters are set properly against the bottom rings. If the top slitters penetrate into the web flow too much, the web will deflect and wrinkle.

Second, inspect the rubber covered squeeze roll. Be sure the roll has not worn unevenly across the sheeter. Also confirm that the nip pressure is set equally on both sides of the squeeze roll.

Third, be sure that the doctor board before the knife is level across the cutter and set properly to the lower cross cutting blade.

Next, look at the delivery mouth section after the cutter. The pinch should be even across the machine, with slight resistance when pulling the leading edge of the cut packet by hand through the tape section. Also, be sure that the top and bottom tapes are evenly distributed across the delivery system.

I am running four rolls of paper, splitting it in half at the slitter section prior to cutting it. At the pile, the width of each pile varies noticeably. Why?

Are you taking an edge trim on each side of the rolls? Widths vary to within 0.015” (0.38 mm) from roll to roll. When put on a roll stand, incoming webs can wander as much as 0.125” (0.17 mm), particularly from the furthest roll stand. To ensure width accuracy on multiple pile work is maintained, you need to take edge trim or have individual web guidance.

When I run two rolls of board on my machine, the sheets are not the same length. Why?

This effect is called “stair cut” and is common on all sheeters when multiple webs are pulled in through the draw roll.

Basically, what happens is the bottom web wraps the draw roll at a given angle and diameter. The second web wraps the draw roll at the same angle and diameter plus the thickness of the bottom web. Therefore, the distance the top web travels is greater and this causes the difference in length.

Two factors affecting stair cut are draw roll diameter and web thickness. The larger the draw roll diameter, the less stair cut – the thicker the material, the more stair cut.

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.

When I slit and run two piles, I have trouble with wrinkles on one side. How can I resolve this problem?

There are several things that might be causing wrinkles:

    • Check the roll stand brake pressure to be sure the web is taut across the width of the sheeter. Be careful because if too much tension is applied, you will get short sheets.

 

    • Measure the slitter penetration. You need to have the top blade overlap the lower blade just enough to get a clean cut. This is usually about 0.015”- 0.030” (0.38 mm – 0.76mm).

 

    • Make sure the lower slitter ring is set so the top blade contacts the material after it is wrapping the lower ring. This is usually done by adjusting the lead in roll.

Review the cant angle on the top slitter. If there is too much cant, (too much of an angle off the vertical) the middle slitter will be trying to push the material out of the way. Since it has no place to go it wrinkles. Lastly, check the squeeze roll and make sure the nip pressure is even and the web is being pulled straight.

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?

Here are several issues and conditions that have an impact on edge trim performance:

    • 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.
    • 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.
    • 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.
    • 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.
    • 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.
    • 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.

I have a problem with sheet length accuracy on my existing sheeter. On cutoffs less than 30” (762 mm) the sheet length is within tolerance, but it deteriorates on longer cutoffs. I also see more variation during start up and slow down of the line. Is ther

The condition you describe is typical of a mechanical system which has begun to show signs of wear. There are two courses of action which you can take:

  • Check all pulleys and shafts for mechanical lash or wear. Check for wear in gear boxes or transmissions and repair or replace as necessary. This should bring your machine tolerance to an acceptable level, although you must periodically check for wear as part of your maintenance program.
  • A more cost effective long term solution would be upgrading the cutter drive system with a dual motor drive retrofit package. This proven technology will bring your machine in-line with today’s precision accurate sheets regardless of sheet size or line speed. By replacing mechanical components with an electrical system, sheeter downtime for maintenance purposes is reduced.

When running two rolls of board superimposed on my dual knife rotary sheeter, the cut edge is clean, but the slit edge is dusty. What can be done to improve the quality of the slit edge?

There seems to be no clear cut answer to this problem. There are a few adjustments you might try. Bear in mind, that it may require a combination of things to bring the slit quality up to acceptable standards.

    • Reposition the slitter’s mounting dovetail bar to insure that the slit edge is supported as it is being cut.
    • Set the surface speed of the lower slitter rings to as much as 5% over speed relative to the line speed.
    • Use a larger ring diameter on the bottom slitters relative to the upper slitter knife’s ring diameter, as much as 6 to 8 inches (150 – 200 mm)
    • Try less penetration when setting the top slitter blade. One slitter manufacturer recommends approximately a 0.015″ (2 mm) total overlap between upper and lower slitter points.
    • Minimize wrap over the bottom slitter rings which will reduce penetration of the lower ring into the web path. Position the lead in roll prior to the slitter to permit no more than 0.015″ (2 mm) penetration.
    • Add a support ring on the outboard bottom slitter. This supports the edge trim and prevents tearing as the trim removal system pulls the trim edge away. The support ring diameter should match the bottom slitter ring diameter.

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