The many components in a paper machine – both big and small – when working together correctly, keep the paper making process running smoothly. Unfortunately, with all of the large moving parts of the process, it is easy to neglect some of the less visible components that are of equal importance. A prime example of “less visible components” are the rockers and rocker plates within many common dryer sections.
Rockers are wedge shaped components that sit on a rocker plate and support the tending side dryer can bearings. The rocker and plate assemblies are designed to hold the dryer cans in an aligned position, while allowing cross-machine thermal expansion of the dryer can.
Rocker Shown in Correct Position
Missing, damaged or worn rockers can wreak havoc in your dryer section
The main causes of wear and damage to rockers and rocker plates are time and neglect. Rockers are generally made of harder material than the plate. Over time, rockers wear into the softer plate and create divots. The rate of wear can vary, based on machine size (the larger the diameter of the dryer, the faster the rockers and plates can wear), dryer section speed, dryer can misalignment, extreme ambient conditions, etc. Additionally, if steam syphons are not working properly, condensation gets trapped inside the dryer. As volume builds, the trapped condensation adds considerable more weight to the dryer can itself, which in turn produces additional weight and/or downward forces on the bearings. This extra weight will contribute to increased wear on the tending side rocker assemblies.
Several factors can lead to missing rockers. Rockers may not be replaced after bearing repairs. Excessively high felt PLI (pressure per lineal inch) can actually lift the lower dryers causing rockers to fall over, or completely fall out of place if the cover/inspection plates are removed and not reinstalled.
Problems caused by missing, damaged or worn rockers and rocker plates include:
- Dryer can misalignment
- Dryer cans unable to operate to design specs due to bearings sitting on the sole plate instead of on the rockers
- Additional forces exerted on bearing housing resulting in damage to housing and wear between the housing and roll journal
- Dryer steam syphon failure
- Bearing failure
Rockers shown are improperly positioned
- Journal failure
Issues can easily be avoided
Regular visual inspections of the rockers and rocker plates can go a long way in avoiding larger issues in the dryer section. These costly issues can be avoided by simply removing the inspection plates (if they exist) and inspecting for the following:
- Missing rockers
- Rocker position
- Rocker wear
- Broken, worn or damaged plates
- Damaged bearing housings
Example of the importance of precision alignment
A large paper mill that had installed new steam joints began having steam joint failure immediately after installation of the new parts. They contacted the steam joint manufacturer believing the new parts to be defective. The manufacturer would not warranty the parts until the mill confirmed that the dryer cans, bearing housings and rocker plate assemblies were correctly aligned.
OASIS was brought in for the inspection and subsequent realignment. Once the components were precision aligned, the life of the steam joints increased exponentially.
If you would like to learn more about the importance of inspecting rockers and rocker plates, please contact us. Be sure to subscribe to the OASIS Industry Blog for technology updates and other educational information from the exciting world of precision measurement!
