There is an increased focus on bearing lubrication in most paper mill production environments. Bearings are the heart of the machine and each unscheduled shutdown due to bearing failure is a major expense. Mills are intensifying efforts to find cost-effective ways to reduce their costly downtime and improve maintenance practices.
World-class companies have introduced predictive maintenance programs and preventive maintenance is becoming standard practice during scheduled shutdowns.
It is well-known that too much grease causes a bearing to build up heat. Too little grease causes the bearing to run dry. Both lead to premature bearing failure. This case study presents the significant savings achieved at a Swedish mill when it decided to focus on applying the exact amount of grease to its bearings.
During the early 1990s, a sulfite factory in southern Sweden conducted a major study of the grease requirements for greasing points. The result was a significant reduction in total maintenance costs. Despite this, there were still concerns about the amount of grease dispensed into each greasing point. According to the technical manager in the maintenance department, a new grease meter, put into use in 1997, solved this problem.
A year earlier the factory had introduced vibration studies of the bearings.
“From the vibration analyses we could see which greasing points were not being lubricated enough. Other lubrication points were overgreased, and both mistakes led to runnability problems and machine breakdowns,” the manager said.
In the study of the manually lubricated lubrication points (6,300 points divided across 12 sections), maintenance staff followed the bearing manufacturer’s (SKF) recommendations. Besides these greasing points, there is also a dual-line automated grease system in one section and a smaller amount of multiline devices. Grease requirements were continually monitored to determine optimum grease lubrication practices.
“We followed the sample lubrication forms that are included in the SKF handbooks. In my experience, it is unusual to do such a thorough study as we did. With many hours of overtime, we mapped 90 to 95 percent of the greasing points, which included all the measurable lubrication points,” said the manager.
More exact greasing practices lead to a significant reduction in grease consumption. Statistics show the consumption between the years 1995 to 1999 dropped from 18,647 pounds in 1995 to 10,463 pounds in 1998. This is a reduction of 8,124 pounds, or 44 percent.
Improved lubrication practices have also led to longer bearing, component and machine life, which has resulted in a significant drop in unscheduled breakdowns Furthermore, the total number of spares removed from inventory has dropped to about half since these lubrication practices were introduced in the early 1990s.
The greasing recommendations turned out to be hard to follow in practice.
“There could be quite a significant difference between various lubrication personnel and different departments. The wide difference in results depended mostly on human factors, because it was difficult to count the exact amount of grease dispensed by counting pump strokes, which was the only method we used. That is why the lubrication points were still often overgreased,” the manager said.
Manual greasing was performed with manual grease guns, or with electric or pneumatic grease pumps. By counting the number of shots, one could gain a certain amount of control over the amount of grease applied. However, pumping up to 200 times to grease a particular lubrication point sometimes makes the method unreliable in practice.
In 1997, Assalub introduced a grease meter and the Swedish sulfite pulp plant purchased a few. Today it has a total of 12 Assalub grease meters, 10 of which are a combination of grease gun and grease meter, a product which the mill has assembled themselves. The factory also uses some electric grease pumps; however, the factory is old and many lubrication points can be reached only with the manual grease gun.
Use of the new grease guns with grease meters resulted in a drop in grease consumption, as shown in various departments in the factory. The grease consumption in manual greasing was reduced 20 to 50 percent; the average reduction was 33 percent. The departments included bleaching, machine dryer section and steam plant.
The technical manager was pleased with these results.
“Before, we greased based on experience. Now the process is more exact and not so dependent on who is doing the greasing. Despite this, the lubrication personnel are happy with the new grease meters. They feel more confident because they can be sure that they have applied the correct amount of grease at each lubrication point,” the manager said.
Financially, it was easy for the factory to support the purchase of the grease meters and grease guns. The total investment for the new grease guns with grease meters was approximately $10,800, a sum that is now quickly being absorbed by the reduction in grease consumption. The company continues to track its grease lubrication cost/consumption. The latest savings figures are even more promising.
For this mill, the grease meter has helped to reduce grease consumption and has provided a reliable lubrication procedure. It has also indirectly contributed to a reduction in total replacement spares inventory and increased bearing efficiency, machinery runnability and a significant drop in unscheduled bearing failure and production downtime.
Manual lubrication tends to be done according to a planned schedule rather than when the bearing needs it. You may also find that your study will help you pinpoint how often a bearing needs to be lubricated.
Assalub AB is a manufacturer of centralized lubrication systems and equipment for the handling of lubricants. The product line includes the above-mentioned grease meter with digital display for manual precise lubrication of bearings, pneumatic grease pump which completely empties the grease drums (99 percent empty) and centralized dual-line grease lubrication system.
The Assalub grease indicator unit can be fitted on your current manual grease gun or a grease gun connected to a mobile grease pump. These products are used in the pulp and paper, steel industries, power generation and mining industries.