A second factor is the huge impact of lubrication on machine health and reliability. Although lubricants and lubricant systems account for only a small portion of total maintenance budgets, studies indicate that about 50% of all premature bearing failures are lubricant-related. The causes include incorrect lubrication practices and lubricant contamination.
As a result, there is a growing emphasis on lubrication efficiency in papermaking operations. Improving your facility's practices even in small incremental ways can produce big dividends. A number of advanced lubrication technologies, many introduced within the last decade, can help support these efforts.
Making small improvements
The strategy of making small improvements in lubricating efficiency was validated recently at a German paper mill with an output of more than 300,000 tons/yr. The plant had a long-time tradition of wringing the maximum productivity from every asset. In keeping with this, the mill's managers sought to improve the reliability of support bearings in premixing units, a high-load application. They consulted with the mill's bearing supplier, who recommended a change of lubricant and the installation of single-point automatic lubricators.
Previously the application was manually lubricated, but this sometimes resulted in over- or under-lubrication. Automatic lubricators, in contrast, attach directly to machine points and provide a continuous supply of small quantities of fresh lubricant. The lubricant is dispensed at a preset rate.
The lubricators prevent the overheating and seal damage associated with over-lubrication and the excessive wear caused by under-lubrication. In addition, they minimize the risk of cross contamination and the possibility of overlooking a lubrication point when relubing. Lubricators can also be used in dangerous or difficult-to-access mill locations.
The German paper mill acquired about 80 single-point lubricators for the premixing units. The lubricators were filled with a high-pressure grease designed to handle the application's heavy loads. The result was greater reliability, fewer problems and longer life for the premixing units' bearings. Due to the elimination of manual relubing, the application's labor costs were also reduced.
Single-point automatic lubricators attached to machine points prevent overheating caused by excessive lubrication and the wear associated with underlubrication. (Photo courtesy of SKF USA Inc.)
Taking a systematic approach
Improving lubrication efficiency at a facility requires a systematic approach. It may entail developing a formal lubrication program from the ground up, or evaluating an existing program to ensure adherence to industry best practices.
New lubrication programs generally develop in several stages. The first stage involves comprehensive mapping of a facility's machine assets. A large paper machine, for example, might have 2,500 or more separate lube points. Mapping identifies and records all the points that need lubrication.
The second stage determines the right lubricant type and quantity for all lubrication points. The third stage identifies or selects the correct delivery methods for different machines or machine sections, whether manual, automatic or a combination of the two.
The selection of the right lubricant delivery method depends both on capabilities and cost-effectiveness. Papermaking applications sometimes call for centralized systems that remove excess heat from bearing arrangements in addition to lubricating them. Circulating oil systems, for example, pump lubricating oil from a central reservoir to machine points. After lubricating the arrangement, the oil flows back into the reservoir, where it cools and is filtered to remove water, abraded particles and other contaminants.
Costeffective lubricant delivery
For a Netherlands-based manufacturer of papers designed for sublimation transfer printing, cost-effectiveness was the top priority in choosing a new delivery system. The manufacturer had suffered repeated bearing failures affecting one roller in a paper machine's wet section. Even though the application was manually lubricated daily, an inspection found inadequate lubrication of bearing cages and rolling elements.
Initially, the papermaker had cost-related concerns about installing a centralized lubrication system, but its bearing supplier proposed a solution: a compact multi-point lubricator that supplies continuous lubrication but is less costly than fully centralized systems. The multi-point system features a main canister that delivers lubricant through feedlines to separate bearing locations. In this application the canister needs to be refilled only once a week.
Since the new system's installation, almost no failures have occurred, and bearing life in the roller application has significantly increased. In addition, the system's alarm function has been connected to the paper mill's control room, allowing for continuous monitoring of lubricant delivery.
The latest grease analysis kits enable maintenance workers to test grease samples for consistency and contamination right on the factory floor. (Photo courtesy of SKF USA Inc.)
Lube audits and analysis
Lubrication audits can help mills improve their benchmarks compared with similar mills. The audits are usually conducted by a third party or consulting firm. Typically they cover lubricant selection, storage, delivery and disposal. The auditing companies are generally knowledgeable about industry standards and can make suggestions on how facilities can improve.
Pulp and paper mills with existing programs should evaluate them periodically for adherence to industry best practices. They can also upgrade their programs by adopting the latest lubrication technologies, such as SKF portable grease analysis kits. The kits enable maintenance technicians to take grease samples and instantly assess them on the factory floor, a capability not available in the past. One such kit performs three grease analysis tests: consistency, oil bleeding and contamination. The tests are performed on used or fresh grease samples.
When evaluating used grease, the tests help adjust relubrication levels, detect the presence of contaminants or gauge the suitability of greases for a specific application. The tests can be used as a screening tool to identify grease samples that may need more sophisticated laboratory analysis. For fresh greases, the tests can assess the remaining shelf life of stored grease or the quality levels of different grease batches.
Portable instruments are also available to assess oil quality. They detect and display information on oil conditions, in many cases making costly laboratory analysis unnecessary. One hand-held instrument, for example, measures changes in an oil's dielectric constant, which can signify increased mechanical wear and loss of lubricating properties. The measurements are made by comparing used and unused oils of the same type and brand.
Improving lubrication efficiency also helps paper companies meet environmental goals. That's usually because improved practices reduce lubricant waste and conserve energy by making machines more efficient.
But lubrication can also directly affect fans charged with handling emissions. In one such fan application, sulfur dioxide gas penetrated past bearing seals and damaged the fan bearings within two or three weeks. When the fans were switched off for maintenance, emissions of sulfur dioxide spiked, causing an environmental problem.
To increase bearing life, an automatic lubrication system was installed to grease the seals and purge the buildup of sulfur dioxide around the shaft and seal areas. Since installation, bearing life has increased from less than a month to 12 months, reducing the cost of replacement components and grease. Because of the increase in bearing life, the fans have been able to operate without stoppage and the plant's gas emissions have been slashed.
Paul Michalickais North American area sales manager for maintenance products, SKF USA, Lansdale, PA;Paul.Michalicka@skf.com