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If the Bearing is Hot: (It might be greased or not)

This paper will present the relationship between a normally greased and over greased bearing using infrared thermography. It will compare an IR image of a normally greased bearing with that of an over greased bearing, highlighting the importance of correct lubrication. Using a test stand setup as an example, it will show how infrared technology was able to detect and record the temperature rise of a bearing that has been over lubricated.

In addition, it will how Infrared Imaging, detected coupler damage & misalignment from a previous paper

Applying this technology could assist in reducing unscheduled downtime and may contribute to cost avoidance.

My recent work with infrared thermography has led me to conclude,"If the bearing is hot, it may be greased or not."

Keywords: Infrared thermography, over lubrication, lube lack, misalignment, cost avoidance, unscheduled downtime


Machine components such as bearings are affected in many ways by a multitude of forces. Some are inherent to the machines design such as; alignment, lubrication, speeds, torque etc...all of which must be maintained to a strict guideline or failure may occur. If one bearing is worn, it will eventually overtax another causing its demise. If a shaft is misaligned, it can cause stress on bearings and couplers. If lube lack or over lubrication is present, bearing wear can contribute to premature machine failure. All these conditions have one thing in common; they usually generate heat as an indication of a problem. Misalignment can cause an overtaxed bearing or coupler to fail. Lube lack & over lubrication can cause a bearing to lose integrity causing misalignment thereby causing more stress on another component and again, failure. Needless to say, maintaining good "Machine Karma" is the best solution in avoiding these pitfalls.


I have used Vibration Analysis for many years to detect potential machine failure. About 14 years ago, I incorporated IR technology into my predictive maintenance program. Vibration Analysis takes time and trending to eventually make an assessment of machine health. I've found, with IR technology, detection can be faster and apparent temperature can be related to "2" conditions...its good....its bad.

Fig. 1

Fig 1. IR scan of bearing assembly

Fig. 2

Fig. 2 Photo of bearing assembly

Figure 1 shows the bearing of interest. It has been running for over 30 minutes; well past the standard 20 minute NOP (Normal Operating Temperature).
The apparent temperature at the bearing is an acceptable 126.2°F.

Let us assume that, a PM was to be performed on this equipment during a scheduled downtime later in the day and, one of the procedures state; "Service all lubrication points"

This procedure would be performed as the PM required and, the maintenance crew would feel confident that their job was performed well. They would also assume the machine would continue to run properly.

I have learned from experience never to assume because, there are a few vital areas that have been overlooked in this simple process.

1.) Did the bearing really need grease?
2.) What type of grease did the bearing require?
3.) How much grease is necessary?

Now we can state with all confidence that Question #2 What type of grease to use, has been satisfied because, the Pm required EPA type grease and, that is what was used to service the bearing.

This leaves 2 other questions in question to determine if the procedure was followed correctly.

These 2 questions are usually the ones' that get most machines in trouble.

Questions #1 Did the bearing really need grease and Question#3 How much grease is necessary; will pretty much be realized in short order because; if the bearing had needed grease, it will continue to run unhindered; on the other hand, if it had not needed grease, another scenario will emerge, "Bearing Failure"; too much grease was introduced.

You can see the possibility of this condition in Fig#3

Fig. 3

Fig 3

Just "1" stroke of the grease gun was all it took to take this perfectly normal happy bearing into the realm of potential failure.

One stroke of the grease gun was introduced into the bearing after a 30 minute warm-up run.

Almost immediately, the apparent temperature increased from 126.2°F to 130.1°F.
Every minute until a 10 minute period elapsed, the apparent temperature increased until it stabilized at 182.8°F.

After viewing the thermogram, we can see a simple procedure such as greasing a bearing is not so simple, who knew?

It is common practice to grease components is a "static state". We then assume to have extended the serviceable life of the

I think it's safe to conclude from this example, that a temperature rise will ensue, each time this bearing is serviced eventually causing it to prematurely fail. Most of the time, just the opposite occurs when we assume.

Based on this example, I believe infrared imaging can be used as an important tool when performing machine lubrication.

Additional Example:

Fig 4a & 4b show how heat can be a good indicator of another machine condition.

Fig 4a depicts IR scan of a coupler between pump & motor. Although the apparent temperature does not appear extremely high, I expected to see little or no heat, if the coupler was properly aligned and intact.

This machine was inspected during a scheduled downtime. Upon close inspection, the coupler was found to be damaged. A new coupler was installed and the machine was realigned & rescanned with the IR (See fig 4b) In this case Infrared inspection was able to detect a damaged and misaligned coupler.

Fig 4

Fig 4a. IR Scan Before Repair Fig 4b IR Scan After Repair


• Infrared inspection of the bearings & couplers revealed conditions associated with over lubrication and misalignment


Infrared-imaging cameras allow the detection of heat generated by abnormal conditions which, makes possible the early detection of catastrophic failure.

Article submitted by Richard L. Harrison, Predictive Maintenance Specialist, Cummins Engine Company, RMEP Plant, Whitakers, NC 27891

Richard Harrison has been a Vibration Analyst at Cummins Engine Company for the past 23 years. He holds a Mechanical Machine Repairer Journeyman's card from the state of N.C. as well as a Federal Journeyman's card. In addition, he maintains an ITC Level-1 Infrared Thermography Certification.  His responsibilities include monitoring machine health and troubleshooting machine tool problems; using several diagnostic tools and technologies such as: Vibration analysis, infrared thermography, oil sample and ultrasonic analysis.

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