Proactive Lubrication Management is Key to Achieving Machine Reliability
Weyerhaeuser containerboard packaging plant, located in Valiant, Oklahoma, provides paperboard, including linerboard and corrugated medium for the manufacture of container boxes. Like all industry these days, the economics of running a plant requires a keen eye on operating costs. In an effort to increase uptime and reduce maintenance costs, the mechanical maintenance team at the Valiant plant undertook a program to reduce dryer bearing failures with lubrication management, which included aggressive contamination control and oil analysis.
Operating conditions in a paper plant are hostile. Risk of ingress of free water, steam and particulate contamination is ever present. Additionally the lubricant is often subjected to extreme temperatures when over-pressurized steam leaks past a gland seal, possibly reducing the lubricants viscosity below acceptable levels. In the 1980s the increasing failure rate of dryer bearings was producing unacceptable levels of unscheduled shutdowns. Correcting this problem became a primary focus for the plant’s technical staff. No single event triggered the investigation, but a generally high rate of failures prompted a review of the lubricating system of the #1 paper machine (#1 PM).
There are 92 dryers on the machine and bearing failures peaked at 25 per year on the drive side during this period. Sometimes, as many as 7-8 bad bearings on both the drive and tending side required replacement during a shutdown. Likewise, frequent unplanned shutdowns adversely affected production output and profitability. The high frequency of bearing failures was deemed abnormal and triggered a thorough investigation. The team set out to determine why the bearings were failing and to implement a maintenance program designed to target and control the root causes.
is Too Short
Research into the SKF Bearing Company’s L10 life calculations suggested that the dryer machine bearings should yield a life of 14.3 years, not the 3.7 years the plant was seeing. Operating at 26% of expected bearing life led the team to look further.
SKF states that bearings typically fail due to fatigue, poor lubrication, contamination, faulty mounting and careless handling. The plant opened in 1971 and the #1 PM had relatively new bearings that were well within their expected fatigue life. Likewise, faulty mounting and careless handling were ruled out, leaving poor lubrication management and contamination as the likely root causes.
During the initial investigation of industry literature, it was apparent that both particle and water contamination substantially decrease bearing life. Particles, especially those of clearance-sized particles in the 1 to 10 micron size, seriously diminish lubrication effectiveness and slash bearing life (Figure 1).
Likewise, moisture contamination similarly cuts bearing life (Figure 2). It is interesting to note that the most dramatic life extension is achieved when moisture is controlled to below 500 ppm (0.05%), which is difficult to achieve in the wet environment of a paper mill.
The research about rolling-element bearing life was conclusive. Contamination kills bearings. In addition to other improvements in lubricant specification and practice, the team decided to undertake an aggressive program of contamination control.
A History Lesson From Weyerhaeuser
Monitoring and Oil Analysis Lights the Path
Decreasing oil contamination has produced real financial benefits. The average number of failed drive-side bearings has dropped from 25 per year in 1980-1989, to 4.6 per year since 1990. (Figure 4).
Through effective management of the root causes of failure, including a major focus on precision lubrication management, Weyerhaeuser has substantially reduced the frequency of bearing failures.
Failures have been reduced by as much as 80% on the drive-end of the paper machine. This case teaches a great lesson. When a focused team of experienced individuals systematically dissect a problem, a solution is usually found. In this case, precision lubrication management and contamination control team up with oil analysis and vibration analysis to provide Weyerhaeuser with the competitive edge of improved reliability through the deployment of technology.
1) ASLE 76-AM-7B-1
2) SKF: New Life Handbook June 1989
3) SKF: Technology Evolution, Contamination and Bearing Life