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Application Notes:
Inspecting Bearings |
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When a motor bearing fails, the motor heats up and lubrication begins to break down. The windings overheat and then the temperature sensor cuts out and stops the motor. Worst case, the shaft binds up, the rotor locks up and the motor fails completely.
Many predictive maintenance (PdM) programs use thermography to monitor the apparent temperatures of operational equipment, using the heat values to detect and avoid equipment loss. By using thermal imagers to capture two-dimensional infrared maps of bearing and housing temperatures, technicianscan compare current operating temperatures to benchmarks and detect potential failures.
What to check?Generally speaking, vibration analysis is the PdM technology of choice for monitoring large, accessible, relatively high-speed bearings, but it can only be done safely when transducers can be placed on the bearings.
Mechanical equipment should be inspected when it has warmed up to steady state conditions and is running a normal load. That way, measurements can be interpreted at normal operating conditions.
What to look for?Problems with bearings are usually found by comparing the surface temperatures of similar bearings working under similar conditions. Overheating conditions appear as "hot spots" within an infrared image and are usually found by comparing similar equipment.
In general, it is a good idea to create a regular inspection route that includes all critical rotating equipment. If a route for regular vibration analysis already exists, thermography can be added easily to these existing bearing monitoring efforts.
What represents a "red alert?"Equipment conditions that pose a safety risk should take the highest repair priority. Beyond that, determining when action is required in your facility to keep a bearing from causing the loss of a crucial piece of equipment is an case-by-case undertaking that gets easier with experience. For example, on one difficult-to-monitor line, an auto manufacturer moved from vibration analysis to a combination of vibration and thermography to determine that normal operating temperatures for bearings on the line fell within a specific range.
When using thermography on bearings not normally monitored using vibration analysis or even when spot-checking bearings, try to follow the lead of the automotive company and establish some "alarm" criteria, as you would for other condition-monitoring technologies.
What's the potential cost of failure?For a failed bearing in a specific motor, pump, drive or some other critical component, you can do analysis of the cost of the repair, lost production opportunity and lost labor costs.
Follow-up actionsAll rotating equipment generates heat at the friction-bearing points in the system - the bearings. Lubrication reduces friction and thereby reduces and to varying degrees (depending upon the type of lubrication) dissipates the heat. Thermal imaging lets you literally "picture" this process while revealing the condition of bearings. When thermal images indicate an overheating bearing, you should...
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