Get a Smo-o-o-th Start-up with a Re-knifed Cutting Cylinder
More than once someone has told us that until the shingle knives “wear-in”, they have trouble starting up with a re-knifed cutting cylinder. Here’s the most common reason:
Uneven Knife Seats
If you can feel a groove in a cutting cylinder where knives sit, it means that when new knives are installed, they will no longer be at the same cutting height. A fact of life is that knives wear, and they don’t always wear at the same rate.
Accepting this, grooves in the knife seats mean that new knives will be at different heights when the cutting cylinder is re-knifed. Until the knives “wear in” and become the same height, they will not cut the same. And don’t forget — the more it takes to “wear in” a new set of shingle knives, the less knife life and performance you are receiving.
How do you Fix the Problem?
If there are replaceable inserts or knife blocks — replace them! If the grooves are in the body of the cutting cylinder, they must be built up and the cutting cylinder machined so that the knives are again positioned at the correct height. And, of course, everything must be concentric after refurbishing.
The Benefits of Replacing Worn Parts and Repairing Worn Knife Seats?
Smo-o-o-ther start-ups, longer knife life and better performance.
Why do I need to install new bumpers on the cutting cylinder or having shingle length problems?
Here’s the answer from the experts at Reichel & Drews:…
The bumpers on cutting cylinders have two important functions in the shingle cutting process.
First, bumpers provide tension while shingles are being cut by “pulling” the sheet from the shingle cutter measuring rolls or measuring drum through the cutting cylinder. Bumpers are there to provide constant tension, resulting in the correct shingle length, and this is the reason it is so important that bumpers – strips and plugs – should be replaced regularly and are the correct height.
Reichel & Drews recommends the bumper height for strips at 1/16″ below the new knife tip diameter, and for plugs to be even with the new knife tip diameter.
Note: This dimension needs to be adjusted for specialty shingles such as the double thickness of laminated shingles.
The second function of the bumpers – particularly the strips – is to prevent the cut shingles and the web from “following” the cutting cylinder. The bumpers (usually strip type) are located on the trailing edge of the shingle knives – after the cut point – to make sure that the warm, tacky asphalt cut edges of shingles and sheet do not stick to the shingle knives and attempt to follow the revolution of the cutting cylinder. Even partial sticking of cut shingles to the shingle knives can result in damaged shingles. This is most often seen at the tab cutout for 3-tab shingles and the dragon teeth for laminated shingles. Make sure there are no missing bumper strips before a cutting cylinder is given the OK for operation.
Replace ALL the bumpers EVERY TIME the cutting cylinder is reknifed. Bumpers of different heights (worn vs. new) on the cutting cylinder will cause a sheet to “walk” or “weave.” If new and old bumpers are combined on the same cutting cylinder, the new, higher bumpers will have more positive contact with the sheet. Sometimes a tracking problem thought to be caused by a measuring belt or measuring rolls may really be because the bumpers are not correct.
Sometimes the corner of a shingle knife chips or breaks. Why?
Often this problem can be traced t the installation of shingle knives in the cutting cylinder and there are two specific things for which to check.
First, are the shingle knives seated properly in the cutting cylinder?
Occasionally, granules or grit may prevent a shingle knife from setting flush in the cutting cylinder, and because the knife is now higher than the other shingle knives in the cutting cylinder, a piece will break off when the shingle knife makes contact with the anvil roll during the cutting operation. Make sure the cutting cylinder is thoroughly disassembled and cleaned before installing a new set of shingle knives. Use a dial indicator to detect a “high” shingle knife before the cutting cylinder is installed in the shingle cutter.
Second, are the shingle knives installed with a gap between each knife?
Reichel & Drews recommends leaving a gap of .002″ – .005″ between shingle knives in the cutting cylinder. This is more critical where a shingle knife with a hook intersects another shingle knife, i.e. a cut-off knife meeting a slitter knife. The compression of the cutting action, though slight, creates a stress point for shingle knives butted together, and can result in chips to the cutting edge. Use a piece of shim stock when reknifing a cutting cylinder to get the correct gap between shingle knives.
Please Contact Us to learn more about our Cutting Cylinder & Shingle Knife Operating Tips.