A mill was having issues with the top roll applicator beam on their SymSizer not opening on sheet breaks. It became a safety issue, as long handled crowbars were needed to assist the beam to open. This was also a risky situation for the health of the applicator beam if the roll were to wrap during a sheet break.
A thorough investigation into the DCS control system and hydraulic control components was conducted but the problem remained. There were two unexplored potential causes of this problem – binding of the applicator beam pivot bearings and defective beam turning hydraulic cylinders.
Pivot bearing binding was put on the back burner, as the bearings were a simple design (plain spherical type) and had a very small pivoted radius. They had also not been an issue with other size presses of this design. Plus, they would require significant downtime to change them out.
Efforts to isolate issues with the turning cylinders uncovered an unusual observation. When commanded to unload, there was no tension on the tending side cylinder rod. The rod end could be wiggled back and forth on its rod pin. Hydraulic pressure to the cylinder rod end was confirmed - but there was no pulling force being generated by the cylinder.
It was decided to change the beam turning hydraulic cylinders. The cylinder change only took an hour or so. The rod and cap end of the new cylinders were bled of air. NOTE: Always bleed air from new cylinders or better yet, fill the cylinder with oil prior to making any moves).
Upon startup, the applicator beam unloaded with no problems and has not been a problem since.
The root cause of the cylinder failure was actually binding in the tending side cylinder rod end packing assembly. Years of starch and debris getting into the rod end packing eventually caused the packing to prevent the cylinder from stroking without assistance from the crowbar. There were no bellows on these cylinders.
It is good practice to keep the protective bellows intact on all hydraulic cylinders around a size press to prevent starch, coating, chemicals, and other debris getting into the rod sealing compartment.
For more information on maintaining your sizer in top working condition, contact your Valmet representative.