Bowed Rolls - 101
As soon as possible after a shutdown run your hand across the face of the Bowed Roll. Any “Hot Spot” indicates a bearing issue. Exception: usually the end bearings will run hotter. They see more stresses and there are more seals in this area that generate heat. The real key how does it feel compared to the last shutdown.
Quick Answer to how many bearings in a Bowed Roll:
Take the diameter of the roll in inches and subtract one and the fraction and divide it into the face length (part with the sleeve) of the roll. Bowed Rolls for the Paper mill come in diameters of 5 1/8”, 6 ¼”, 7 1/8”, 10 1/2” and 13 ¼”.
Example: a 5 1/8” diameter roll with a 100” face will have about 25 bearings. (100/ 4)
Wire Reinforce sleeve or not
Above 1200 fpm reinforce the sleeve. Centrifugal forces will expand a rubber sleeve above this speed. The wire reinforcing prevents the roll from “growing” in diameter and thus losing its bow.
Air Groove or not
A spinning object will carry with it a surface layer of air. This layer of air will be difficult for a thin sheet of paper to penetrate. Air grooves will give the air a place to go when the sheet encounters the Bowed Roll.
Circumferential grooving to
0.060 wide x 0.090 deep
2 grooves per inch - Slow speeds, low porosity webs
4 grooves per inch - 2500 FPM and up
6 grooves per inch - High speed winders, OEM spec
The above are generally accepted industry standards. Each installation can have unique conditions that would warrant variations. Call for an detailed analysis of your Bowed Roll requirement