When I run multiple webs of light weight material, it sometimes wrinkles prior to cutting. How do I avoid that?

Wrinkling of webs can be caused by baggy edged rolls, misaligned rolls between the unwind position and the sheeter’s draw drum, severe wrap around rollers, or when running multiple rolls, friction between webs.  Here are some suggestions:

Baggy edged rolls
An unevenly coiled roll has imbalanced tension across the face of the web.  In such cases, as the roll unwinds, one side of the web is not pulled as tightly as the other.  This ‘baggy edge’ can result in wrinkles.

There should be a mechanical skew adjustment that can address this condition.  In some cases, a correction is allowed at the unwind.  A mechanism, usually mounted on the Operator side, moves the shaft (in the case of shafted roll stands) or the arbor’s arm (in the case of a shaftless roll stand) forward toward the cutter (slackening) or away from the cutter (tightening).  In other designs, there is a carrier roll located between the unwind and the cutter that can be pivoted in a similar fashion to provide a likewise result.

Sometimes, the slackness of the material is near the center of the roll, not the ends.  If this condition is a continuing issue, a bowed roll strategically placed after the unwind and prior to the cutter infeed might be required to evenly spread the web(s).

Misaligned rolls
Unevenly positioned rolls are usually associated with ill machine installation or when an existing roll is replaced.  In both cases, use of skew adjustment maybe inadequate to resolve the wrinkling problem.

Before attempting to identify the existence of a misaligned roll(s) begin with these ground rules:

Move all skew adjustments to their center position to insure maximum correction in either direction after rolls are levelled and trammed.

Clearly identify the web path from the unwind to the cutter’s bottom pull roll (also known as the draw drum).

Always begin the measurement process at the cutter and move sequentially back to each roll in the web flow, toward the associated unwind position.  This is because the position of the draw drum cannot easily be adjusted, whereas the rolls in the web conditioning system and associated carrier rolls can be more simply altered.

Also record all rolls’ level and tram prior to adjusting any of the cross members.  It might be determined that a series of rolls within a frame are out of square and that shimming the decurl assembly’s frame will achieve the desired solution, rather than realigning several rolls.

First, using a precision machinist level, measure and record the horizontal of each roll in the web path, beginning with the draw drum and then in sequence to the next roll moving back to the unwind.  Rolls, across the face, should be within +/- 1/64” (+/- 0.38 mm) of levelness. Be attentive to any trends or groupings of rolls that are uneven, as it may indicate a section of the machine frame that may need to shimmed.  Repeat the process for each web path.

Review the results and adjust roll levelness throughout as the data dictates.

Second, using a tape measure, check tram between adjoining rolls, beginning with the distance between the draw drum and the bottom slitter shaft, then the bottom slitter shaft and the lead in roll, then the lead in roll and so on.  Be attentive to any trends or groupings of rolls that are out of tram.

The most accurate method for determining parallelism between rollers is to wrap the tape measure around both rolls and record the length, on both the drive side and Operator side of the machine.  Any difference in the two recordings is twice the out of parallel distance, so 1/32” differential indicates 1/64” variance in tram from side to side.

Review the measurements for tram and make adjustments as required.

Severe wrap around rollers
Wrinkles can be drawn around rollers if the wrap is excessive (90° or greater), the roll diameter is small (3” diameter or less) or both.  If the web path can not be easily altered to minimize the degree of wrap, consider replacing the existing roll with a 6” diameter roller.

Friction between webs
When sheeting multiple webs, the best practice is to keep them separated until immediately before the cutter infeed.  This approach avoids the gathering of webs that can lead to wrinkling.  Locating carrier rolls for each web that supports the flow yet keeps them apart from one another avoids folds caused by friction between webs. 

Should I run material down the center of the machine or off an edge?

There are many variables to be considered; however, as far as most sheeters are concerned mechanically, it doesn’t really matter. Here are a few questions which must be asked.

1. What type of roll stands are being used. Shafted with chucks? Shafted with air shafts? Shaftless? 

If shafted with chucks is the answer, the roll changes may go faster if an operator only has to remove one chuck leaving one clamped in position at all times. This would be especially true when running from multiple roll stands where roll edge alignment must be achieved. Running from an edge in this example is the answer.

2. Does the sheeter have any form of edge guidance system or web steering? 

If equipped with one of these systems, it is often faster to locate the roll edge to be roughly in line with the sensing devise for the system than to relocate the sensor and have to reset the sheeter as well. This applies even more so when the sheeter is equipped to cut to a registration mark, water mark or notch, because this usually requires operator positioning of a scanning devise. Clearly you would set up from an edge in this instance.

3. Is multiple pile work being done? 

If the majority of the work is two pile service, this presents a strong case for running from center line. The center slitter can remain fixed as well as edge turners and center jogger blade. The two outboard slitters would have to move to the variety of sheet widths on wider machines. This would eliminate a reach problem for the operator as well.

Single pile work and odd number pile work (multiples of three, five and seven) may prove to allow faster setups from the edge of the sheeter, where at least one of the slitters and downstream edge turners and jogger blades can remain fixed.

4. Is the sheeter in line? 

It is fairly common for a sheeter to be in line with a paper machine, treater line extruder, or printing press. In this instance, equipment prior to the sheeter may determine how the sheeter is to be set up. Packaging equipment on the out feed of the sheeter could have the same impact.

Always consider the fewest moves when trying to determine whether to run from the center or edge of your sheeter.

From time to time, we have to sheet poorly wound rolls with baggy edges. How do you compensate for this roll defect?

Add a bowed roll prior to the decurl to help smooth out the web. With this in place, the decurling action should not create or induce wrinkles. If you are sheeting multiple webs, then each web should have its own bowed roll.

When decurling 0.028” thick (500 gsm) coated recycled board, the surface of the sheet gets cracked. What can I do?

You might consider ordering your board “coated side in”, so that the web feeds into the decurl section with coated side down. If this is not practical, investigate ordering your roll stock on larger diameter cores. (Most of the cracking occurs at the end of the roll where more decurl is needed.) Cores diameters of up to 16″ (400 mm) are used on heavy board to minimize the curl set.

How do I eliminate “checking” or “alligatoring” (the fracturing the board surface) at the decurl station?

This problem usually occurs on heavier board grades, when the Operator attempt to overcome the curl set created in the web near the core. There are four factors to consider in avoiding “checking”:

1. Core Size – If possible insure that the maximum core diameter is used. Typically board grades are wrapped on 12″ cores. The larger the core diameter the less curl set is introduced, and as a result, less mechanical decurling is required.

2. Brake Pressure – Maintain sufficient brake pressure to insure web tension to the end of the roll. For a decurl unit to work properly the web must remain taut between roll stand and cutter.

3. Penetration of the Breaker Bar or Roll – The greater the penetration into the web path of the decurl bar, the more wrap around the breaker bar and the increased likelihood of “checking”.

4. Diameter of the Breaker Roll – The smaller the diameter of the breaker roll, the sharper the angle of web wrap around the roll as it penetrates into the web path. Roll diameters of 2″ – 2¾” (50 – 70 mm) are effective on 0.024″ thick (400 gsm) board. Smaller diameters may result in “checking”.

5. In most cases, “checking” can be eliminated by reducing the penetration of the breaker and maintaining the web tension as the roll diameter decrease.

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