Infrared inspection is one of the most common condition-based monitoring techniques maintenance and reliability engineers use nowadays. Oftentimes, infrared inspection is used in conjunction with other CBM techniques to monitor the conditions of machines and catch issues before they become catastrophic.

Thermal imaging is excellent for detecting a lack of homogeneity in equipment by indicating hot and cold patches in surface temperature. Heat is a common early indication of equipment damage or malfunction, especially in motors and mechanical gearboxes, so it's crucial to keep an eye on it as part of your preventive maintenance program. A thermal imager uses color to match every pixel of an electronic image to a specific surface temperature. A thermal image shows exactly which section of the motor is overheating and to what degree.

 

Infrared Inspection Guidelines

Motor 

When checking a motor, make sure it's operating at 40% of its normal load. Data can be compared to typical operating circumstances for a thorough evaluation. You may check the operating temperatures of bearings, as well as the temperature and temperature changes of the unit's complete surface, by capturing an image of the entire motor.

Motors have a normal thermal pattern. An experienced and well-trained thermographer is familiar with motor heat patterns. Thermal imaging can detect gearbox issues such as restricted airflow, unbalanced voltage, approaching bearing failure, and insulation degradation. A skilled thermographer can also identify misalignments in a shaft coupling associated with a motor. Misalignment in a shaft coupling linked with a motor can also be detected by a qualified thermographer.

Gearboxes

A gearbox will fail if the oil level in the gearbox drops too low or loses its ability to lubricate. This is because lubricants are needed by gearboxes to make their mechanical movements smooth and at the proper operating temperature. Neglecting the monitoring of gear oil will result in overheating. Maintenance for gearboxes is consisted of checking and replacing oil levels regularly. 

Oil sampling and analysis are used by some maintenance teams to add a predictive aspect to gearbox maintenance. Oil analysis, which is normally done by a third-party laboratory, determines whether the oil in a gearbox has lost its ability to lubricate and detects any metal particles in the oil, which is a telltale sign of gear wear and a potential failure.

These gearbox maintenance procedures take a lot of time and money. Gearboxes are also located in inaccessible or dangerous locations. This makes oil level check and sampling tedious. Thermal imaging makes oil level checking and sampling easier. An IR camera can detect whether a gearbox is running hotter than normal since gearboxes usually overheat before they fail.

Thermal scanners can scan inaccessible and hazardous places while the machine is running. All essential gears that are running hotter than normal should have thermal and visible-light photographic photos were taken.  Hot oil can be seen pouring down gearbox casings using thermal imaging. Lastly, you can check for leaking seals using Thermal imaging.

While all excessive heat generated in mechanical gearboxes is the consequence of friction, it could also be the result of something other than insufficient lubrication. The friction produced by damaged bearings, misalignment, imbalance, overuse, or even normal wear could be the source. Thermography is an excellent initial step in determining the occurrence of incipient failure gearbox.

 

Methods in Thermal Inspection 

In infrared inspections using a thermal camera, there is no standardized method. You must fit your technique to the equipment being inspected and the level of detail required. The three most common techniques that can be used in most situations are baseline, thermal trending, and comparative.

Baseline Thermography - After purchasing a piece of equipment, you scan it and use the results as a baseline for future inspections. Current thermal scanners have capabilities to display thermal images on your camera in the field or on your PC using software tools. Once you have established your baseline, it is easier to pinpoint failures and abnormalities down the road.

Thermal Trending Thermography - With the information you acquired after using baseline thermography, you can now compare how temperature is distributed in the same components over time with thermal trending inspections. Thermal Trending Thermography helps you notice diminishing performance over time, allowing you to schedule downtime maintenance before the equipment fails.     

Comparative Thermography - Comparative thermography requires comparing the results of scanning similar components with your thermal camera under similar settings. This technique is based on the assumption that similar or identical components will have similar temperature profiles under similar loads. It is normal to spot misfits once you have tested three or more components. There's one more factor to consider, which is the exact temperature difference that might be declared an anomaly and this varies depending on the equipment being compared.

 

Troubleshooting After Infrared Inspection 

Thermal imaging helps in identifying what causes your machinery to overheat. If an oil pump fails, for example, the input and exit temperatures will be the same. Maintenance professionals should do a follow-up inspection by examining the oil level, oil quality,metal-particle content of the oil, acoustical testing, or vibration analysis. The test that will be used will depend on the cause of the abnormality.

Scheduling a regular inspection that includes critical motors or drives will ensure the success of your maintenance program. Use the software that came with the thermal imager and save the image as a reference for other tests. Use the data as a baseline to compare and determine if the repairs were successful.

Source. www.machinerylubrication.com