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

I have a 65″ wide sheeter and run 28″ wide rolls most of the time. How can I get the maximum use of my sheeter?

You have two choices. First, if you have the ability to slit in line on your sheeter consider purchasing wider rolls and run two piles across the sheeter. You should buy your rolls wide enough for double width and an additional ¾” to allow for a slight edge trim on both sides to insure accurate width.

Another approach, if you have two roll stands, is to stagger the rolls across the width of the sheeter. In this way, you can run the two webs side by side without the need of taking an edge trim.

I have six shaft type roll stands on my envelope sheeter and spend a lot of time setting up the rolls and aligning them. What can I do to increase my run time and get more production from the sheeter?

There are several alternatives to minimizing down time due to roll changes.

First, you may consider having a second set of shafts so that you can “preshaft” the next set of rolls while the current set is being run. Another option is to invest in air shafts. They have the advantage of eliminating chucks, which can be awkward and time consuming to position.

Depending on your order mix, perhaps you might consider investing in shaftless roll stands. Shaftless roll stands offer several advantages over shafted designs. A self loading shaftless roll stand doesn’t require a method of lifting the rolls into position thereby providing quicker and safer set up times. If your production has evolved to shorter runs and more size changes, two or three shaftless roll stands can be loaded within 10 minutes compared to the 30 – 45 minutes of loading six shafted roll stands.

I run two rolls of light weight material on my sheeter and I have trouble keeping the back web in line because it seems to bounce up and down and track from one side to the other. What can I do?

There are a couple of things that can be done.

See if the roll stand can be moved closer to the sheeter, so as to shorten the distance of an unsupported web.

If the roll stand cannot be moved, install a carrier roll between the roll stand and the sheeter infeed. The carrier roll design should include two low inertia rolls assembled so as to provide an “S” wrap to the web. This design has shown better web tracking while supporting the web thereby avoiding web fluctuations into the sheeter.

I have an older style roll stand behind my sheeter with a spring-loaded handle to control the friction on the brake drum. What can be done to upgrade this to a better system and possibly introduce automatic tension control?

There are a couple of ways to improve your brake and tension system. First, replace the mechanical brake drum arrangement with a pneumatic type brake disc. This will provide the Operator with the ability to adjust the brake pressure more accurately. Next, consider the tension control system itself. There are many types of automatic tension control systems. Three of the most popular designs that are used are the ultrasonic, proportional and load cell.

The ultrasonic type uses a sensor to measure the reducing diameter of the roll and through an electro-pneumatic converter converts the electrical signal to a pneumatic output, decreasing the brake pressure, as the roll gets smaller.

The proportional style uses two signals, one a series of pulses from the sheeter’s encoder associated with the length that is being drawn in to the cutter and the second from the roll stand after each complete rotation. The two inputs calculate the roll diameter and then send a signal to the converter governing the brake pressure.

The load cell mode of tension control monitors the pressure exerted by the web on an idler roll. This electrical signal is sent to the converter, reducing the brake if the pressure is to great and increasing brake if the pressure is less than the preset limit.

How long does it take to change a roll and what should you do to minimize roll change time?

There are two types of roll stands, shafted and shaftless.

Shaftless roll stands require the least time to change since all that is required is to position the roll in place, insert the chucks, and raise the roll.

Having the rolls stripped of their wrappers, staged and ready to load will expedite this process. This procedure can be done in less than 5 minutes.

Shafted roll stands take more time since the shaft must first be removed, then one chuck taken off. The shaft must be inserted through the new roll’s core, the chuck replaced, and the roll raised into position by means of a hoist or other lifting device. This process can easily take 15 minutes for each roll.

Several things can be done to minimize this time. Again, have the rolls prepared first. Having a second shaft and pair of chucks allows the next roll to be prepared in advance. The use of air shafts eliminates the need for handling chucks and speeds up the process.

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