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.

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. 

What can I do to minimize roll change time?

Well run sheeter operations require about 1 – 2 minutes to change a roll for shaftless roll stands and 5 – 8 minutes to change a shafted roll when using air shafts.  To minimize roll change time:

  • While the current roll is being sheeted, prepare the next roll to be loaded
    • Strip the wrapper and headers from the roll
    • Inspect the roll for edge damage, addressing as required
    • For shaftless roll stands, positon the rolls off line, ready for loading
    • For shafted roll stands , using a second set of shafts, pre shaft the rolls
  • Stop the sheeter before the tail end of the roll is pulled off the core.
    • This allows easily splicing the start of a new roll to the tail of the last roll, avoiding rethreading the sheeter at the decurler, slitters, delivery and stacker
    • A flapping tail at the end of the run can cause a jam up in the sheeter or misalign up stream settings
  • Remove the expired core
    • For shafted roll stands:
      • First, use material handling equipment (hoists, fork lifts) safely
      • Cut end of web from core, leaving webs threaded into sheeter
      • If using chucks, remove non-brake side chuck and slide off core
      • Better, consider using air shafts instead of chucks
    • For shaftless roll stands:
      • Cut end of web from core, leaving webs threaded into sheeter
      • Open arms of roll stand and remove core
      • Load the new roll
  • Load the new roll
    • For shafted roll stands:
      • Chuck roll tightly against the chuck left on the brake side of the shaft,
        • Insures that the far side of the roll is always in the same place
        • Keeping the drive side common, reduces set up time in half
      • Carefully load shafted rolls
      • Splice the leading edge of the new roll to the tail of the web in the sheeter
    • For shaftless roll stands, regardless of the width:
      • Position roll between arms and chuck up roll on floor
      • Slightly raise the roll and position behind sheeter
        • Add scales or markings on the floor at the unwind location
        • Use this aid to position the rolls quickly for alignment
      • Splice the leading edge of the new roll to the tail of the web in the sheeter
  • Thread the web through the sheeter
    • Slowly jog the web into the sheeter, taking care not to break the splice
    • Insure that the splice is removed in the delivery system, so as not to be stacked in the pile
    • Once the new web is fed through the sheeter, run at minimum speed
    • Make final adjustments to align the webs to the previous width set up

What maintenance issues should I be prepared to address after replacing my existing rotary cutter’s mechanical drive with an electronic dual drive system?

In older stationary bed knife (or ‘dead knife’)  cutter designs a single motor drives the pull roll section and powers a second drive train to change the speed of the revolver relative to the speed of the draw drum.  Typically mechanical designs such as expansion pulleys, change gears or gear boxes were used within the second drive train to vary the sheet length.  Although simple to operate and straightforward to adjust such mechanisms suffered from:

  • Lengthy set up time in changing sheet size
  • Excessive waste due to multiple cuts required to fine tune the cut off
  • Routine maintenance to address lubrication and wear components.

As electrical drive motor controls improved in performance, opportunities to replace the mechanical drive systems increased.  In this design one servomotor couples to the draw drum that with the squeeze roll pulls the web(s) into the sheeter.  A second servomotor is joined to the knife revolver using high torque drive pulleys and belts.  A microprocessor governed by Operator controls and a keypad entry input,  maintain the rotational speed of the two motors.

Dual-Motor-Retrofit-01.jpg
The advantage of the design:

  • Changing the sheet length at the touch of a keypad
  • No waste to confirm cut off length
  • Accuracy to within +/- 1/64″ (+/- 0.38 mm) of setting
  • Minimal maintenance

The routine recommended maintenance of a dual drive system includes:

  • Check the drive belts for tautness on a daily basis
  • Grease drive train bearings every 1000 operating hours
  • Check (and replace as required) the drive enclosure air filters every three months

How can I reduce slitter set up time on a sheeter?

A good first step – where possible – is to have your scheduling department arrange sheeter orders so you don’t have to reposition or introduce additional slitters each time for each production run.

Most set up time associated with slitting is positioning the bottom rings.  Here are some time saving tips:

  1. If there are popular widths that are run on the sheeter, scribe those positions onto the bottom slitter shaft to permit quick location of the bottom slitter rings.
  2. If sheet widths are fairly few, you may choose to have multiple bottom rings already positioned on the slitter shaft to avoid moving them about.
  3. If production runs are short and size changes frequent, consider outfitting the bottom slitter assembly with an air bladder shaft and digital read out system to allow fast, accurate placement of slitters.
  4.  In some installations the ability to preset the slitters off line in a cartridge assembly to allow rapid change over might be be considered.
  5. Ultimately, a slitting assembly can be fully programmed to automatically set up slitter positions – both upper and lower.

As for the top shear slitters; use slitter blades with pneumatically loaded blade holders.  Air loaded slitters are quicker, easier and more forgiving in set up than their older mechanical type cousins.

Is it possible to increase the speed of an older sheeter?

The short answer is yes – by changing the pulley ratio between the cutter motor and the main drive shaft.

But there are several implications to making this change. Make sure that the rotating cylinders, particularly the draw drum and knife revolver, are dynamically balanced. Operating unbalanced components at higher speed will prematurely wear out their bearings and the pulleys or gears in the cutter drive train.

Be certain that the delivery and stacking systems can operate at higher speeds. The design of the layboy section may not be conducive to overlapping sheets at higher speeds and delivering them without damage into the piler.

Perhaps the cutter’s motor was not sized to run at new, higher speeds under full load. If excessive load is encountered because of higher speeds, the cutter drive will fault.

Because of these reasons, no changes should be made without consultation of the sheeter manufacturer.

I have retrofitted an electronic drive onto my cutter to improve sheet length accuracy. Now I have problems with the drives faulting or tripping out. What can I do?

Modern AC frequency drives actually generate “noise” – electrical harmonics and transients that can affect other electrical components. Maxson uses proven grounding methods to minimize noise associated with drives. Among the standard designs employed by Maxson in their dual motor drive retrofits:

    1. Inclusion of an isolation transformer between the main line and the electrical cabinet to prevent faults caused by power spikes.
    2. Mounting line reactors between the drive and its associated breaker. The line reactor prevents noise generated by the AC drive from flowing back to other drives.
    3. Use of VFD (variable frequency drive) shielded cable from the drive to the associated motor. Since dual motor drives use encoders for positioning of the motors, shielded cable should be used between the encoder and the drive also to avoid noise transmission.

Unlike my older equipment, my new sheeter has a dual motor drive system governing sheet length and a programmable logic controller that manages machine functions. When the sheeter shuts down, how can I troubleshoot the cause?

Actually it is a lot easier to troubleshoot a machine that is controlled with electronics. Most new sheeters have a programmable logic controller (PLC) governing the operations of the sheeter instead of relay logic. Typically a dual motor drive with two motors, two AC drive and a motion controller takes the place of the mechanical drive train. The PLC is interfaced to operator controls and the drive system.

The electronic modules of these systems have light emitting diodes (LEDs) that are crucial in trouble shooting the sheeter. By looking at the LEDs on the input and output modules of the PLC you can verify if the signal is being transmitted to a device or not. Green lights on the modules confirm that the signal is being inputted from the PLC or outputted to the device. Red lights indicate a problem.

In the case of a PLC controlled device, if it is determined that the signal is being sent to the component ( for example, the load table motor), a trained electrician should verify that the proper voltage is being supplied to the device at the time it is being run. This is done at the device’s power infeed to insure that the fuses or motor starter is not damaged. By moving the voltmeter to the component, the electrician verify that it is grounded properly or if there is noise being generated on the line causing the problem. Our experience is a loose wire or connection is the root of the grounding problem, but you could find out that the component has failed.

The drives and the motion controller also have LEDs that illuminate for a particular fault and in most cases have a liquid crystal display (LCD) that describes the status of the drives.

On MAXSON equipment, the operator’s main console includes screen that display the cause and location of a fault, jam, or open safety interlock that prevents the sheeter from running. By using the LED, LCD, or annunciated fault information and the electrical schematics for the sheeter you can isolate the component causing the problem and initiate corrective action or provide sufficient information for the sheeter manufacturer to assist you.

How can I increase the productivity of my sheeter? There seems to be a lot of time when the sheeter is not running because the operators are getting and loading rolls, removing skids, and doing paperwork.

It starts with scheduling. Orders should be set up ahead of time so the rolls and skids are available for the job.

Next, stage the rolls behind the sheeter so the operators are not waiting for them. An adequate number of skids should also be placed near the stacker so they are readily available to the operator.

While the machine is running, the operator, or the helper, should prepare the next set of rolls by removing the wrappers and core plugs and complete any production paperwork that is required. The operator should also get the skid tags prepared so when the load is removed from the stacker, the label can be affixed and the sheeter can be started right back up . After the sheeter is up and running, the load can then be taken to the wrapping area and prepared for shipping or warehousing.

What skill level should a sheeter operator possess?

An operator must be thoroughly familiar with how the machine works. Mechanical aptitude is helpful in learning this. The operator must also know the safety requirements for the machine. Training in the setup procedures is necessary. Experience in web handling is helpful.


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