My bearing went blue - what happened?

Ball bearing failing can wreak havoc, causing unplanned downtime which costs money and affects efficiency.  More worryingly it can also be dangerous for those operating equipment.  If your bearing fails before its predicted lifespan then it’s really important to find out why.  Luckily bearings reveal the cause of failure through obvious markers and of these markers is discolouration.  If your failed bearing is anywhere between a blue and gold colour then there are two possible causes: overheating or lubrication problems.  We’ll go through both problems in this article in more depth

Overheating

If the rings, balls or cages of your bearing are in any shades ranging from blue to gold then your bearing has failed due to overheating.  It normally appears in a kind of “rainbow” effect of a few different shades; balls will usually be black or blue. This normally happens when bearings are exposed to very high temperatures of over 400°F, although bearings are available which are designed to withstand very high heat.   When the heat rises to this extreme the bearing can anneal changing the material make-up of the bearing.  This means it’ll be less hard which reduces the bearing capacity and causes failure.  The high temperature can also degrade or destroy lubricant which makes failure even more likely. In exceptional circumstances the bearing can actually deform (almost “melt”) under the excessive conditions.  

Overheating is caused when potential temperature rise isn’t predicted correctly or proper provision are not put in place to deal with high temperatures.  Lubricant failure (discussed below) can also contribute.  Heavy electrical loads, inadequate heat paths and insufficient cooling or lubrication when loads and speeds are excessive can all contribute to temperatures rising.  Schaeffler recommend common sense cures like thermal or overload control, adequate heat paths or introducing supplemental cooling to avoid repeating the mistake. 

Lubrication

A blue or brown ball track and ball indicates that lubricant is not doing its job properly and lubricant failure is actually a precursor to overheating which will cause the eventual failure of the bearing.  Lubricant degrades, the balls, rings and cages are exposed to excessive wear and the bearing eventually overheats. That being said excessive heat can contribute to the initial degradation of lubricant, which, in turn heats it up even more.  The other cause of lubricant failure is a restricted lubricant flow.  Using the wrong kind or wrong amount of lubricant and reapplying too frequently or too little will also contribute to a failed bearing. 

The difficulty with lubrication is that each kind of bearing requires a different lubrication course.  Your bearings should come with guidelines from the supplier and if you need further advice manufacturers will be able to help.  Since lubrication can be a bit tricky it’s really important to know the signs of a bearing failure which is caused by this problem. 

So if you find that your bearing has gone blue you can now take steps to make sure it doesn’t happen again!