FEATURE DRIVES, CONTROLS & TRANSMISSIONS
CORRECT LUBRICATION avoids premature bearing failure
Tristin Hurst, ABB UK’s product manager for mechanical power transmission components reveals the common causes of bearing failure and shares useful tips to extend their life
appropriate seals. The manufacturer of the bearings will be able to give advice on the correct sealing options. Step 3: Install the bearings correctly.
Research shows that improper lubrication accounts for 80% of failures
ince the first anti-friction bearing was patented in 1794 by Philip Vaughan the design has changed little on the outside. Modern variants however, are packed with engineering innovations that reduce friction, prevent contaminant ingress and retain lubrication thereby increasing a bearing’s lifespan and improving its performance. Together with improvements in condition
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monitoring, engineers now have easier and more accurate ways of measuring everything from a bearing’s vibration to lubricant viscosity. However, bearings still fail. Research shows that improper lubrication accounts for 80% of such failures with four main causes identified: ● Lubricant contamination occurs when debris enters the bearing raceways and mixes with the lubricant giving it a grainy texture which causes vibration and wear of the raceways and eventual failure. ● Unsuitable lubrication including incorrect viscosity or additives for the operating conditions. Grease that is too thick gets trapped between the rolling elements and causes the raceways to run dry. ● Aged lubricant that has not been replenished and reaches the end of its useful life can fail to distribute properly throughout the bearing. The raceways and rolling elements do not get an even film of lubricant and wear more quickly. ● Insufficient lubrication quantity is a result of engineers’ fear of blowing bearing seals by over-greasing and over- pressurising the bearing.
INADEQUATE SELECTION Inadequate bearing selection causes 10% of premature failure. When selecting a
8 MARCH 2015 | FACTORY EQUIPMENT
bearing it is important to verify the level of radial internal clearance between the raceways and rolling elements. There needs to be sufficient expansion available when the bearing is operating. Reduced internal clearance will impede
lubrication flow around the bearing and prevent lubricant reaching the raceways and rolling elements. Improper mounting accounts for 5% of bearing failures with load imbalance and misalignment increasing bearing vibration leading to failure. A shaft fit that is too tight can increase start-up load and causes wear. Failure linked to operating conditions, transport, storage and handling represent 4% of premature failures. Overloading is one such cause, creating shallow depressions in the raceways that cause the bearing to vibrate when running. This increases temperature and wear.
SIX OF THE BEST TIPS Step 1: Specify the correct bearing type for the application. Bearings should be replaced with the same type specified by the original manufacturer or better as they are designed for that machine’s operating duty and loads. If the load and operating requirements for the machine have changed consult with the equipment manufacturer or a bearings manufacturer to determine if they need to be swapped- out for a different type. Step 2: Assess the operating
environment and specify the protection options. The ingress of dust, dirt and moisture all contribute to corrosion, wear, lubricant wash-out or contamination and rapid bearing failure. Bearings mounted in harsh conditions should be fitted with
Keep the bearing in its original packaging until needed as this keeps contaminants out and factory lubrication in. When fitting unsealed bearings use a heater to fit the bearings at a temperature of 110°C for a secure fit and ensure the heater does not exceed 125°C. If pre-sealed bearings are required, adapter mounted bearings are an alternative method of installation, requiring no specialist tools, avoiding damage to the bearing and dispensing with the need to use heaters to fit them. Step 4: Define and specify the correct
lubricant. Industrial applications use greases between NGLI Class 1 and 3 for re-lubrication of bearings. Automatic lubricators set up properly for your bearing sets will ensure re-lubrication at appropriate intervals. During maintenance ensure grease matched to that bearing set is provided to the workshop. This avoids the use of incompatible grease when re-assembling. Step 5: Carry out regular and appropriate
maintenance for each bearing set. Manufacturer maintenance intervals should be followed based on the operating time, speed and load for the bearings. A visual inspection and a temperature check should be done every 2,000 hours with a probe or thermal imaging equipment to highlight if the bearings are running hot. Vibration analysis will help identify problems and allow them to be remedied before failure. Step 6: Use a bearings management
policy. To keep the specification, installation, re-lubrication, maintenance and replacement of bearings in-check this policy should be used to keep a precise record of the installed base. Doing this will help keep the bearings in the best possible condition, ensures maintenance tasks are carried out and end-of-life bearings replaced.
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Enter 301 / FACTORYEQUIPMENT
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