Read Part 1 here.
Reliable equipment performance is essential for maintaining productivity and profitability in many operations. Even in the best-maintained equipment, bearings and other components will have a limited service life when operating in harsh environments. Many predictive methods are available to help develop performance trends and diagnostic capabilities. When properly used, these methods can help plan or avoid downtime.
Vibration analysis allows for the detection of any change in frequency signature. This assumes the bearing housing is accessible. In hostile environments, where maintenance crews cannot safely approach the equipment, a good solution is fixed transducers that are hard-wired to a remote area or office. Significant changes in vibration are detectable and can be correlated to key frequencies of rotating equipment. As a result, they can help identify mechanical looseness, shaft/coupling imbalance or bearing damage. Depending on the size of an operation and type of equipment, vibration analysis equipment can be purchased, leased or brought in by an outside source on a contract basis.
The best maintenance plan combines installation, lubrication and predictive data to record and trend bearing performance. Bearing suppliers can provide valuable assistance in predicting bearing performance. Based on a thorough understanding of the equipment and operating conditions, suppliers can offer both service and application engineering assistance. Some suppliers provide field engineering teams that offer onsite inspection and expert problem solving support.
Seals are added to the housing design to protect bearing and other rotating components and retain lubricant. Equipment performance, assembly requirements, lubricant system, shaft orientation and other factors are part of the selection criteria.
Safety should always be a top priority when performing equipment maintenance. This is especially true when handling or replacing heavy bearings and components. Consider the following best practices:
- Watch for pinch points and keep fingers outside the assemblies.
- Some bearings have separable components and are strapped together for shipment. Do not attempt to lift the entire bearing assembly using shipping straps. Use only nylon slings, hooks and fixtures that have the appropriate load rating, are clean and have been certified for the job.
- Exercise caution when handling bearings and housed unit assemblies. They are covered with fluid coatings for protection and can be slippery.
- Wear safety glasses and protective covering for skin that might be exposed to the bearing coatings.
- When heating bearings for installation do not expose them to direct flame. This action represents a fire hazard and can affect the bearing steel. Note that, under some conditions, heavily damaged bearings can generate extreme heat and present a fire hazard.
- Never strike a bearing with a large hammer or similar hard object. Such strikes can result in brittle fracture of the bearing, dislodging sharp metal particles that may cause personal injury. Strikes can also cause cracking or brinnelling, which reduces bearing service life.
The crusher operation at a cement plant in Romania removes huge rocks from its quarry operations and reduces them to pebbles.
“The problem was that about every three months the competitor’s bearings on the motor belt pulley that drives the hammers inside the rock crusher unit failed,” said a Timken senior service engineer in Romania. “The company wanted to know if Timken could help.”
Timken application engineers studied the entire system using Timken analytical tools. They searched for the most suitable bearing solution and conducted lubrication analysis to find the right type and amount of grease and the proper relubrication intervals. They also offered design modifications to the unit so that it could accommodate the new Timken spherical roller bearing, which replaced the previous cylindrical and ball bearings.
Spherical roller bearings are ideal for this application because of the dynamic distortions, misalignments and accidental axial load impacts that occur during the rock crushing process. The proposed solution, based on Timken spherical roller bearings, extended the equipment’s operational performance and allowed implementation with minimal reworking of the existing parts.
As a first installment, Timken provided eight bearings, as well as Timken premium all-purpose industrial grease and motorised single-point lubricators. Since Timken service engineers installed the new bearings, the crusher has run for more than 18 months without a bearing breakdown.
“Our old solution often led to high operating temperatures and bearings burned up every three months,” said the plant’s maintenance manager. “The new Timken solution not only made all these problems vanish, but also allowed us to move from costly unexpected breakdowns to annual scheduled maintenance. Particularly pleasant to us was the fact that the Timken solution fit into the existing housing with little changes, thus allowing a quick implementation.”
Cement plant machinery must operate reliably in brutal conditions. Rolling element bearings are fundamental components in most rotating equipment. They are under particular pressure in these harsh environments, facing threats ranging from contaminants to vibration. Operators in severe environments can lengthen bearing life, increase equipment productivity and reduce costs by properly selecting, mounting and maintaining bearings. Taking care to follow best practices for installing, lubricating and sealing bearings, while managing a predictive maintenance plan, will help keep equipment moving in the most challenging operations.
Written by Claudiu Popescu, Laurentiu Ionescu and Jerry Rhodes, The Timken Company, USA. This is an abridged version of the full article, which appeared in the March 2014 issue of World Cement. Subscribers can view the full article by logging in.
Read the article online at: https://www.worldcement.com/europe-cis/03032014/special_bearing_selection_and_care_for_harsh_environments_part_2/
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