Size press roll wear causes reel wrinkles and culls, a case study

A printing & writing paper machine experienced excessive wear on the bottom size press roll on the back edge. This caused excess starch to be applied to the sheet, sometimes causing the paper to wrinkle at the reel and be culled.

Analysis

A thorough inspection was performed on the SymSizer and found that the root cause of the problem lay in the top roll applicator beam synchronization shaft. The shaft had actually broken several months before and temporary adjustable jack screws were fabricated to limit the beam's travel.

The purpose of the top roll beam synchronizing shaft is twofold - to act as a hard stop for loading the beam, and also to balance any uneven loading forces between both ends. Without this balancing effect, the unbalanced loading forces were transmitted through the beam mounting brackets of the pivoting roll and into the roll nip. The uneven nip load caused the drive side roll to wear faster right at the sheet edge.

Results

Once the synchronizing shaft was replaced and the loading forces were balanced - the roll wear problem disappeared.

This example highlights the importance of the synchronizing shaft and should act as an incentive for mills with SymSizers to check for free movement of their synchronizing shafts. The shaft should be able to be moved by hand with the beam unloaded. If you suspect you have nip load profile issues, check this shaft for free movement. Over time, it can freeze up from being in the same location.

For assistance with your size press, contact your Valmet representative.