Viscosity, Thermography, and Three Hot Gearboxes

If you are involved in a thermography program then you know that the key purpose is to identify potential maintenance issues based on the operating temperatures of a component. All components have a designated normal or safe operating range based on the specific application and context of loads, speeds, pressures, etc. Thermography, as a condition monitoring technology, monitors the operating temperatures of a component to aid in pinpointing specific locations of temperature flux.  

In components that require lubrication, there is an additional consideration that is necessary. Mixing lubricants or providing a lubricant with the incorrect viscosity for a specific application can cause temperature to increase, but might not necessarily be an indication of impending failure. While working with a tire manufacturer, we helped them see the difference proper viscosity has on a component’s operating temperature.

The Background

During a routine thermography route, an IR Technician discovered a row of conveyor gearboxes operating at temperatures in excess of 200°F (93°C). Normal operating temperatures would be considered in the 150°F range or less, and the cooler a component operates the more longevity it potentially has.

This row of conveyors is also a part of an ongoing lubrication program restructuring due to poor practices and limited understanding of lubricants at the facility. The facility is currently in the early stages of working with outside assistance to develop practices for optimizing the number of lubricants on-site as well as optimizing lubrication task intervals for re-grease, oil top up, and oil changes. This activity also ensures that the correct lubricant is being applied to each individual component.

This finding proved to be an eye opener to the importance of proper lubricant selection. When these conveyors were installed, no consideration was given to the gear type, operating loads, and speeds when filling them with the proper lubricant. More importantly, no attention was paid to the manufacturer nameplate information which included the recommended lubricant. Across the board many conveyor gearboxes are filled with an ISO 220 gear oil, but in actuality the requirements vary.

When components fail, a standardized approach to replacement components should be in place. When it's not, the most economical component (manufacturer and model) is often purchased as a replacement. However, this new component may or may not use the lubricant required by the previous component or the lubricant actually in use. Over time, new component types are installed and lubricant products change leaving an assortment of equipment requirements being addressed by an assortment of lubricant products.

The Investigation

During the routine assessment, three gearboxes of the same make and model consisting of a helical worm gear stood out because of the high amount of heat being generated. The following thermographic images show the highest temperature of those gearboxes.

Gearbox 1.png

Gearbox 2.png

Gearbox 3.png

Gearbox #1 had a maximum temperature of 210°F Gearbox #2 had a maximum temperature of 204°F Gearbox #3 had a maximum temperature of 203°F


Based on the make and model, as well as the required lubricant information available on the component, it was determined than an ISO 680 gear oil is required, but the Lubrication Technician reported using an ISO 220 in these gearboxes. He also stated that the larger the gearbox the higher the viscosity requirement, which does not hold true. However, the fact that an ISO 220 was used in all small conveyor gearboxes showed that this was the rule of thumb for the area.

The Recommendations

First and foremost, it was recommended that all essential personnel receive practical machinery lubrication training. This type of training will provide education on proper lubricant selection, focusing what is inside the gearbox to determine the required lubricant and not it's size. For this specific case, the gearboxes needed to be converted to higher viscosity gear oil, so a shift from the ISO 220 to an ISO 680 was recommended to increase the reliability of the gearboxes.      

The Results

Once the three gearboxes were converted to the ISO 680 and allowed to operate, a follow-up thermography assessment was performed. All three gearboxes had a drop in temperature between 26°F to 41°F. 

Des-Case Corporation

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