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January 12, 2007
Spiraling Roller Surfaces
Contributed by Tim Walker
Several specialty rollers have spiraling patterns on their surface. Why are spiral roller surfaces so common and what is their advantage?
Some examples of spiraling roller surfaces are:
1. Spiral tape applied to a roller.
(Spirals are almost always begin at the roller's center and helix outward in opposite directions to either end of the roller.)
2. Spiral ridges cut into a roller surface, either as square or triangle waves cut into a hard metal surface.
3. Spiral grooves at angles from almost parallel to the machine direction to 45 degrees or more off MD parallel.
4. Spiral grooves cut into a rubber covering at an biased angle off perpendicular to the axis of rotation.
5. Diamond groove pattern with two spirals running the full length in both directions.
Why so many spirals?
1. The mesmerize engineers and operators into think they provide spreading, much like the optical illusion of a spinning barber's pole.
2. Grooves and ridges an effectively channel an entrained air layer, much like grooves of a car tire help channel water when driving through a puddle. In this case, the spiral shape doesn't add anything to the traction benefits.
3. Ridges can effectively break up a large wrinkle into several non-damaging micro-wrinkles, but will not have any spreading effect.
4. A spiral roller that is slipping relative to the web, such as dragging a fabric over a spiral roller with the V-shape pointing upstream is a spreader. A rotating spiral that matches the web speed does not spread, like a snow plow doesn't move snow if the truck isn't moving.
5. The angled cut in the rubber roller spreaders (such as Finzer's FlexSpreader or American Roller's ArcoStretcher) don't need to be spiraling to spread the web. The mechanics of spreading is related to the lateral flexing of the flutes between the spirals.
6. Spiral ridges and grooves will run quieter than axial ridges and grooves that may create a beat or harmonic noise (and be surprisingly loud).
7. Spiral ridges and grooves will break up wrinkles better than MD ridges or grooves that may catch and hold wrinkles, especially with thinner webs.
So spirals do have advantages, but don't let them mesmerize you into benefits that aren't there.
-tjw
Posted by Tim Walker at January 12, 2007 02:13 PM
