"Iron out" previous damages by the help of lubricants. High-performance gear oils score when it comes to reducing wear in gears

If conventional industrial gear oils of type CLP are not up to the loads in the gears, this will cause problems for the whole plant. Unsuited lubricants can promote micro-pitting, pitting, marks and breakouts at the tooth flanks. Usually, the breakdown of a gear has serious impacts on the whole operation. The use of modern high-performance gear oils can control and minimise the risks.
 
Gears transmit and transfer energy, movements and forces under various and often extreme conditions. In operation, the lubricant takes a decisive part. It is an element of construction and determines both performance and lifetime of the gears as well as efficiency and safety of the whole plant. For these reasons, the lubricant should be chosen with care. Industrial gears are lubricated with gear oils according to DIN 51517 part 3 (CLP oils) usually. However, these oils are not up to the high requirements in any application.

This was also experienced by the maintenance engineers of a rolling mill. The pinion stand gear box of a Duo roll stand was lubricated with industrial CLP gear oil and maintenance was carried out according to the rules. Still, an inspection revealed alarming damages. Due to the oil’s insufficient load-carrying capacity there was a formation of pittings which caused large breakouts at the tooth flanks, their progress could not be stopped any more. Razor-sharp edges and burrs were clearly visible and perceptible. The breakdown of the whole gear because of roller bearing damages seemed to be inevitable.

And in January 2003 the shaft bearings really failed because of metal abrasion in the system. When the gears were opened, it became obvious that metal abrasion amounted to several kilograms already. The required spare parts were not on stock at the plant and not available immediately either and therefore downtimes as well as high repair and follow-up costs were looming.

In this situation the engineers responsible for maintenance contacted ADDINOL. The engineers of ADDINOL inspected the damaged gear thoroughly, they did not rule out further operation. However, there was one precondition: the immediate change to ADDINOL Eco Gear 220 M. Normally, it is not necessary to flush the gears before applying the high-performance gear oil, but because of the heavy load with metal abrasion flushing was carried out in this case.

The first inspection of the gear seven months after the oil change showed that the condition of the tooth flanks did not worsen. The load-carrying parts were smoothened and their run was stable. Their condition was documented by the help of photos. After this first check-up inspections, were carried out once a year. In addition, the application of the gear oil was monitored regularly by oil analyses of an independent laboratory. In 2005 the gear was filled with fresh oil for a second time.

Here the oil was changed without talking to maintenance and they used a conventional industrial gear oil type CLP. Before long the tooth flanks showed surface roughness again and the gears were filled with the high-performance gear oil of ADDINOL promptly. 

The latest inspection was carried out at the end of 2010. It showed, that the damage had improved significantly since the oil change in January 2003, previous damages (scuffing, pitting and a displaced edge in the rolling circle) are smoothened perceptibly and this process has been finished years ago. Furthermore, records state that damage could be transformed from a progressive to a regressive one by using the high-performance gear oil. The condition of the gear’s toothing checked at the yearly inspections is stable.

Results of the accompanying oil analyses confirm these findings. According to the independent laboratory wear parameters are decreased clearly, viscosity and additivation are within the normal range.

These results could be achieved by Eco Gear and its smoothening effect on pre-damages. The product is available on a mineral and a synthetic basis and possesses a special substance combination according to the manufacturer. Due to this additive package the oils adapt to changing load conditions in the toothing ensuring a wear-free and friction-reduced run in turn, according to ADDINOL. If the high-performance gear oils are used in new gears, they prevent wear from the very beginning. The lubricants meet and outperform the requirements of specification DIN 51517-3 and ISO 12925-1.

German article published in Betriebstechnik & Instandhaltung (view German article here)