Die cut blank size variation

Stan asks:

We are having an issue with board shrinkage (C flute).
The sheet length off the die cutter is approximately 58” (direction of corrugation).
This overall length shrinks by approx 0.125” to .375” making the inside dimension too small for the product.
Have you encountered this phenomenon in your corrugated experiences? If so, is there a remedy and what is the cause?

I will assume that we are talking about a rotary diecutter operation.

This is not unusual. Check the sheet transfer system, bearings, ink drying, plates, die cylinders and ejection rubber compatibility. Has the liner changed? I also discussed this with my friend Dwayne Shrader who used to work for a diecutter OEM and he offered these additional thoughts.

  • Anvil covers/blankets. Are they excessively worn? Also, covers can come in different thicknesses, make sure you have the correct ones. Worn covers cause a change in the sheet speed as is moves through the diecutter section. As little as .125 difference in diameter can be problematic.
  • Verify the knife and rule height on your cutting die. The proper knife/rule height should be listed on the OEM nameplate of the machine. It should be either on the feed section and/or be on the die-cut section. Incorrect rule height can change the speed of the board as it moves through the machine too.
  • Check the impression setting on the diecutter. Operators like to crank the impression down to compensate for worn anvils. Over impression causes the surface speed at the sheet to change and this leads to size variations.
  • Is the cutting die properly secured to the cylinder? Is there a bolt in every hole as it should be, or has the operator skipped holes for the sake of a quick set-up?
  • As Ralph said, make sure your rubber is the correct height and in good condition too.
  • Is your machine servo driven or does it have a gear train? A worn and sloppy gear train can cause the speed of the diecutter to float(variable change). If it’s a servo machine, is the servo functioning properly? You’ll probably need to contact your OEM to have that checked out.
  • And here’s one that is often overlooked. If it’s an open/close (modular) machine is the machine lock adjusted properly? If the lock isn’t holding the sections tightly closed, it’s the same as having a worn gear train. Look at the frame splitlines of the sections (Where the frames come together). If you see them “breathing” (opening and closing with each feed, or just while the machine is running), check to make sure the lock is properly adjusted.
  • Has your board had sufficient time to cure off of the corrugator, or are you running hot board? If your diecutting before the board cures you’ll have a hard time predicting shrinkage and controlling finished blank size.
  • There are many other variables that can affect die-cut blank size stability, but we hope this helps you resolve your issue or at least gives you a place to start.

    Let us know what you find and please come back to us if you have more questions. Also, if anyone else out there has any ideas they’d like to share, please feel free to leave a comment.

    —Ralph

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    4 Responses to “Die cut blank size variation”

    1. TYLER HOWLAND Says:

      on a non servo driven DC… is also amount of pressure…?

    2. Stephen Macdonald Says:

      Also, some die cutters have anvil compensators built into the die cut section. With this you can change the speed of your anvil allowing you to make the correct adjustment to compensate for anvil covers that are worn or die boards the were knifed or built out of spec.

      Steve Mac

    3. Steve MacDonald Says:

      is your machine equipped with an anvil compensator? With this you can adjust the speed of the anvil allowing you to lengthen or shrink the size of the D/C blank. This helps when anvil covers are worn or die boards are made out of spec

    4. g.white@tfplabs.com Says:

      Excellent response!
      Sent on the Sprint® Now Network from my BlackBerry®

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