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.

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.

How long should it take to make a full size change from single pile to two pile service on a sheeter?

Let’s look at setting sheet length first. Setting up for length changes on a modern sheeter can be done fairly quickly. There are four items to be set. One is the overlap carriage located in the delivery system. This is typically a hand wheel adjustment with a scale indicating the sheet length.

The next item is the front stop in the stacker. In some cases this moves in unison with the overlap carriage and in others, it must be individually adjusted. If individually adjusted, a scale may be provided or it may require using a tape measure to measure from the stationary fingers at the back of the pile to the front stop. Either way this is a simple movement.

The third item is to set the actual sheet length. On machines equipped with dual motor drives, this is as simple as entering a number on the control panel. On other machines, it requires setting a variable speed transmission, usually with a hand wheel. If the machine has a sheet length monitor, the transmission is adjusted until the desired sheet length is displayed. If not, material must be run through the machine and measured until the correct length is obtained.

The last item to be addressed on stationary bed sheeters is squareness. On many machines with dual motor drives, this is done automatically when sheet length is entered. On other machines, it requires the operator to reposition the knife section using a ratchet mechanism and the scale provided.

Setting up for width changes requires setting the bottom slitter rings to the desired position, typically by loosening a set screw and measuring with a tape measure. The top slitters are the adjusted to the bottom slitter rings.

Next, tapes and edge turners are moved into position based on the paper flow through the tape system.

Once the paper reaches the stacker, the jogger blades are moved into position to line up with the edges.

Depending on the machine and the skill of the operator, this could take from 10 – 20 minutes.

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