Monitoring bearing temperatures is a simple technique for indicating bearing issues. We always use our predictive technologies such as our SV3X vibration analyzer for vibration and envelop analysis as well as ultrasonic detection. In virtually every case, we use infrared thermography scans or temperature readings to verify they are in the acceptable range.
Our experienced has shown that when bearings begin to have trouble particularly with over and under lubrication issues, temperature is a great indicator. We recommend, after our clients install or conduct a preventive maintenance bearing repack, that they monitor the bearing temperatures at least once a shift for a few days.
In most cases, the temperatures will always rise fairly rapidly after start up and continue an ascent for few hours. After three or four hours the temperatures normally stabilize or even reduce some as the bearing dissipates the heat. It may remain at these levels for around 24 hours as the bearing and grease break in. After a day though you would expect to see the levels come down and fall to within the manufacturer’s acceptable temperature range.
Whenever a bearing lubrication issue occurs you can typically see the temperatures continue on an upward climb. If the bearing can not cool itself due to too much grease or increased friction from too little grease, the temperature gives it away. If the temperatures do not stabilize after 4-6 hours or if the temperatures exceed the manufacturers recommended range, it is always smart to bring the machine down and inspect the bearings. There are actually other bearing faults that can also create friction and reveal themselves through elevated temperatures so a simple inspection is always well advised.
If you find that the amount of grease looks to be correct and you can not see any mechanical faults always make sure you are using the correct grease. Selecting the correct lubricant for the bearing is critical and applying the wrong one can be catastrophic. Remember to do your homework when selecting a lubricant so you can be assured it can handle the duty requirements.
Besides making sure you have the correct lubricant, it can never hurt to ensure you have the correct bearing. Even if the bearing box and nameplates say it is the correct bearing, simply inspect the new bearings against each other as well as the old bearings to make sure they all look the same. If you find any aspect of a bearing that is different from the others you should consider checking with the supplier. Some suppliers modify their bearings for a customer’s special need or they can just make a mistake. In either case, the different bearing may not meet the original specifications you need, resulting in a premature failure.
We provide our SV3X and Protect Wireless systems for online monitoring of a newly repaired or installed bearing during its break in period and we always recommend including temperature monitoring. If you can not have an online system monitor your bearings during the break in period make sure you at least follow the temperatures so you are notified of a potential problem before it goes catastrophic.