The rotary diecutter cover is a terrific production tool, but its effectiveness depends in large part upon paying careful attention to the installation and maintenance of the cutting dies and anvil covers. The main function of the anvil cover—which we manufacture from urethane with a stainless steel backing—is to support the material being processed and provide a consistent surface (or anvil) against which the cutting die can form the product. We like to think of it as the female die.
The rotary diecutting process is simple in theory; however, many mistakes are made daily that lead to inferior diecutting and reduced life of both cutting dies and anvil covers.
So, let's look at some ways to increase the life of anvil covers.
Proper setup of the cutting die cylinder
It is important when mounting the cutting die to use all the bolt holes provided by the die manufacturer. Check the cutting die cylinder for broken bolts. Re-drill and use inserts if necessary to have access to all the bolt holes in the cylinder. Wipe the cylinder down before mounting the die to remove any buildup of paper dust or other material which could lodge under the die and cause variation in the rule height.
Remember: we are not just mounting the dieboard. We are mounting the cutting rule, scoring rule, scrap ejection rubber, etc. (the various components of tooling) to the cylinder. The cutting rule must be lying tight to the cylinder, which is impossible if even one bolt hole is plugged or unused. Tighten bolts starting in the center of the die and work out toward the end of the cylinder. Use a pre-set air torque wrench to avoid breaking mounting bolts.
Proper setup of the anvil cylinder
This point may seem obvious, but it never hurts to repeat it: always remove the cutting die before installing, removing or rotating anvil covers. The cutting rule in the die is very sharp and can cause serious injury. Dies should be handled with extreme care.
Before installing the anvil covers, make sure that the anvil cylinder and the cover mounting slot are free of any burrs, paper dust or other debris that may affect a snug, uniform fit of the mounted cover. Diligent anvil cylinder and slot cleaning will eliminate high or low spots that can cause irregularities in the diecutting process and make the covers difficult to install.
Another critical element in the anvil cover mounting process is to use the correct cover-mounting bolts. It is important that you use bolts either supplied or recommended by the manufacturer of the anvil covers. If bolts are too short, they may loosen during the diecutting process and cause unwanted movement of the covers. Short bolts can also cause a pounding effect that will result in premature cover wear and weaken the cover's lock. Bolts that are too long will cause a high spot, which will result in inconsistent diecutting. The natural operator response is to increase impression, which will decrease the cover's useful life.
The actual installation of an anvil cover requires six steps: Position the first cover in the center of the cylinder (off center if even number of covers). Hand start the correct mounting bolt (usually a socket head cap screw). Do not over tighten. The female lock is now in place in the slot. Pay attention to rotation arrows. Rotate the cylinder to bring the male lock into place aligned with the female. It is essential that the male and female locks line up. Using a dead-blow mallet (approximately 42 oz.) start at one end of the lock and tap across the cover until the male lock is seated in the female lock. Repeat the process for all covers working out toward the end of the cylinder.
If the cutting die and anvil covers are installed properly, the anvil covers will not suffer from too much impression. Improper installation and/or lack of rotation will require that more impression be used in the diecutting process, which will result in reduced cover life and a poor quality diecut product.
A rule of thumb: the cutting rule, assuming it's the proper height, will effectively diecut, penetrating the urethane anvil cover no further than the root of the cutting rule teeth.
Maintenance: Rotating covers
Of all the factors that affect anvil cover life, and there are many, perhaps the most important is a regular program of cover rotation.
When removing a cover, do not pry between the cover and the cylinder. This will damage the lock, stretch the blanket and possibly create burrs on the cylinder. Insert the proper removal tool, supplied by the manufacturer, between the male and female lock. Prying should be slow and careful.
Remove anvil covers starting at one end and working toward the other. Be sure
to number each cover as it is removed from left to right, e.g., 1 to 10. Check
the cylinder and slot, as mentioned before, to remove any paper dust, burrs
or other debris. Covers are reinstalled as shown in Figure A.
Figure A
Rotation
will vary from plant to plant depending on the size of the machine, number of
shifts being run, type of board being processed, etc. As a rule, the first rotation
should occur between 100,000 and 150,000 impressions. Thereafter, rotate every
150,000 impressions. In plants where accurate records of impressions are not
kept, a good rule of thumb is to rotate once a week. Any rotation is better
than none.
Machines equipped with trimmers will also benefit from rotating anvil covers. After installing new covers, run, rotate, run, then trim. Then repeat the sequence. This will eliminate cutting into brand-new urethane.
Finally, inspect all cutting dies after each run. Proper maintenance should include repairing or replacing any damaged cutting rule and re-rubbering as required before returning the die to storage.
Paying attention to the little details will extend the life of your tooling and reduce your overall diecutting operating costs.