A Tech Bite from Greener Technical Service Manager Mark Green
Learning how to set up knives with adjustment screws can require time consuming trial and error. This Greener Tech Bite presents a fast, dependable, 8-step method for adjusting knives with adjustment screws on flow wrappers.
1. Bring the Jaws to Operating Temperature
To start, remove the old knives and anvils and bring the sealing jaws to operating temperature.
2. Check Sealing Adjustments
Then make sure your sealing adjustments are correct. Run some trial packages—with product if possible. Cut the packages apart with scissors, test the seals with your standard method, and make any necessary readjustments.
Clearance, the narrow gap between the upper and lower sealing jaw serrations, should be adjusted when the jaws are set up and generally left unchanged. Never use clearance to adjust the knife.
3. Clean the Knife and Anvil Slots
Once your seals are set, clean the slots to ensure a stable base for the knife and anvil.
4. Install the Anvil
Install a new anvil with the radiused, working surface facing up. The bottom edges of the anvil will be chamfered, unless your anvils have a radius on both sides.
The height of the anvil should range between the root and the mid-point of the serrations.
Jaws from some manufacturers have deeper slots that require shims to raise the anvil up to this level.
Always replace the anvil along with the knife. A new knife paired with a worn, scored anvil requires excess pressure to cut and will fail prematurely and cause sealing problems.
5. Install the Knife
Before you install the knife, back the adjustment screws out at least halfway. Then insert the knife with the bottom angle facing the screws.
Snug the knife retaining screws lightly. Do not overtighten.
6. Adjust the Knife
A. Using only the two outside screws, over-adjust the knife so that it protrudes slightly from the sealing jaw face.
B. Then back the two outside adjustment screws out from under the knife. The light tension from the set screws should hold the knife in place.
C. Roll the upper and lower jaws together. The anvil will push the knife back into the knife slot so that it is flush and level with the anvil.
D. Now turn the outer adjustment screws inward, using two fingers, until you feel them contact the bottom of the knife. Then turn each outside screw in an additional one-eight of a turn.
E. Insert a single sheet of copy paper between the jaws and roll the jaws together. You should have two short cuts on the outside edges. With small, incremental adjustments to the outside screws, increase the knife height until the small cuts are about one inch, or 25mm, long.
F. Now turn the center adjustment screw in, using two fingers, until you feel it contact the bottom of the knife. Then turn this screw slightly more—less than one-sixteenth of a turn—and run another sheet of copy paper through the jaws.
At this point the knife should either either cut all the way across, or you will lose the cut completely.
If you lose the cut, turn in the outside screws in extremely small increments until the one-inch cuts on the outer edges return.
Then repeat the previous adjustment process with the center screw until you get a clean, smooth cut.
7. Reset Over Adjusted Knives
If the knife is hitting hard, such that you can hear it banging and feel the heavy impact with your hands, it has been over adjusted.
In this case, back out all adjustment screws counterclockwise for one-half a turn and roll the jaws together, using the anvil to once again level the knife.
Then return to step 6D and repeat the knife adjustment process.
If at any time during this process you adjust one side of the knife to get it to cut and it causes the opposite side to stop cutting, do not adjust the opposite side. This indicates that you have over adjusted the knife.
In this case, back out the adjustment screw you last adjusted one-half a turn counterclockwise. Then roll the jaws together, using the anvil to push that side of the knife back in.
On the same side, adjust the knife out in small increments until you get a smooth, clean cut without banging.
8. Lock the Set Screws
And as a final step, once a good cut is achieved, go back and lock the set screws.
Troubleshooting
If your knife fails to cut after following these procedures, you may need to address other conditions on your flow wrapper such as spring pressure adjustments, worn springs, damaged bearings, and damaged sealing jaws or shafts.
To learn more about the full range of adjustments on your flow wrappers and vertical baggers, or to discuss training programs for your packaging team, contact Greener Corporation.
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