Why The Back Up Roll You Bought Is Not Durable

Published 2024-10-15 by Ascon engineering team

What A Proper Back Up Roll Contains

Because of the environment it works in, the back up roll withstands a large radial force, which makes it the most critical mechanical part of the equipment after the work roll.

Many equipment builders do not understand the structure and assemble back up rolls themselves from ball bearings and bushing parts. Those are not durable and the accuracy is poor. A proper back up roll consists of a mandrel, bearing sleeve, needle rollers, seal, fastener and heat resistant extreme pressure grease, with heat treatment hardness, material selection, clearance fit, assembly and debugging all specified.

What Service Life Should Look Like

On a tension leveling line running below 450 m/min, back up roll service life should be between half a year and two years, depending on the initial plate shape and the working environment.

If a back up roll fails in two or three months, tell the supplier. That is either a quality problem or improper use, and it is worth establishing which before buying the next set.

Cause One: Roll Quality

Open the roll. If the internal structure is assembled from standard parts such as complete bearings, it is basically an inferior product. The inside should be needle rollers, or needle rollers with cages, because the back up roll itself is a non standard bearing.

Then measure circumferential runout with the roll installed on the cassette. If runout is greater than 0.01 mm the roll is defective and should be replaced.

Cause Two: Wrong Selection

When sheet thickness exceeds 0.3 mm, or line speed exceeds 300 m/min, light duty back up rolls with cages are not the right choice. Heavy duty rolls with a full complement of rollers should be used instead.

After dismantling a roll, if the internal cylindrical needle rollers are held by a ring cage made of nylon, brass or cast iron, it is a light duty type. For those duties, ask the supplier to replace it with the full complement version.

• Sheet thickness above 0.3 mm: use heavy duty full complement rolls
• Line speed above 300 m/min: use heavy duty full complement rolls
• Nylon, brass or cast iron cage inside means light duty construction
• Circumferential runout above 0.01 mm on the cassette means defective

Cause Three: Cassette Accuracy

The accuracy of the roll cassette directly affects whether the back up roll survives. A cassette that has lost alignment loads individual rolls unevenly, and the roll that takes the extra load fails first.

This is why replacing rolls repeatedly without checking the cassette produces the same failure every few months. If two sets of rolls have failed early in the same position, measure the cassette.