Please describe a problem you encountered and solved involving gear lubrication.
TLT Sounding Board December 2009
TLT readers were nearly unanimous in agreeing that determining proper oil viscosity is the No. 1 issue relating to proper gear lubrication. No. 2 seems to be convincing the end-user. Said one reader: ‘Customers continually think that a gearbox running hot needs a higher viscosity fluid. The challenge is convincing them that they actually need a lower viscosity fluid.’ Contamination of oil also was cited by many readers—correcting poor handling and storage procedures in the remedy. Several readers said they had to seal the gearbox to prevent water ingress. Finally, many readers said that changing from a mineral-based lubricant to a synthetic solved their gear lubrication problems.
A gearbox in intermittent service that had an internal oil pump. This allowed the gearbox to be started without lubricant on the gear teeth above the static oil level. We added an external oil pump that was started prior to the startup of the gearbox to provide lubricant prior to startup.
Low-speed operation with very high loading on case-hardened teeth resulted in destructive pitting. Use of a gear oil with molybdenum disulfide has reduced the rate of pitting. Replacement of gears with ones capable of higher loads is the long-term fix.
Keeping water out of outdoor gearboxes. We added desiccant breathers and closed all other entry points for air.
Scoring of high-speed gear. Problem sorted out with a better gear pattern.
Wear of a gear wheel as a result of unlubricated application.
Intermittent gearboxes were failing too often. We changed the lubricant to a higher GL rating for extreme pressure and solved the problem.
When we change petroleum-based mineral oil for synthetic lubricants, we change all of the system’s seals to avoid leakage.
The most challenging problem that I have ever encountered is changing an entire food plant from H-2 to H-1 lubricants. The main problem (which is ongoing) is not the work involved with the changeover but, rather, convincing personnel that there are H-1 lubricants available today that can be used satisfactorily in all types of equipment. Education has been the main tool used in trying to solve this problem. But even after presenting numerous facts and documentations which prove that there are food-grade lubricants that provide superior lubricity, many people are not willing to accept the truth.
Metal fines would get clogged into the gear oil and cause wear. I added a metal anticloggeranitiator device. I call it WD-40!
No problems with gear/axle lubricants have been reported.
Wear of brass syncro rings. We used a metal deactivator as a tankside additive to solve the problem.
A customer was complaining about high gear temperatures and wear in a compactor gear. He changed the oil in the gear to a higher viscosity oil (he changed from ISO 220 to ISO 320) to no avail. I suggested moving to a lower viscosity—ISO 150. At first he dismissed my recommendation and was convinced the lower viscosity oil would only cause higher wear rates. He was also sure that the high-temperature was caused by wear. I explained that oil drag may be the cause of the problems. He finally agreed to try the lower viscosity oil in the gear. He was then quite surprised at the results: lower gear temperatures and less wear. This case study illustrates the importance of viscosity in choosing a gear oil.
Water. We switched to a high-film strength PAO-based EP gear oil that rapidly separates from water and were able to increase the service life two to five times.
One that comes to mind was a ski lift gearbox where the overnight oil temp was too cold for safe startup. A heater was put on the oil sump.
Energy savings in a coal pulverizer worm gear. Used a PAO.
I have frequently found an EP oil being used in a non-EP application. The difficulty does not lie in figuring out the right lubricant but in convincing the customer that the original lubricant is the cause of the premature failures. Too often I hear the statement, “We have always used this lubricant.” I so desperately want to say, “Yes, and you’ve always had these problems—maybe the two are related.”
Convincing a customer to repair leaking seals and getting him to stop increasing viscosity to slow the leak.
The big challenge is making sure you use an effective lubricant to solve mechanical variations during gear manufacturing such as surface roughness and coating.
In some cases, liquid-based lubricants cannot be used, so gears have to rely on solid lubrication technologies. There has been comparatively less work in this area (compared to bearings or sliding applications), so the first try often doesn’t work out. The solution is research to understand the lubricant coating wear and transfer process, which differs from other applications.
Loss of efficiency in small, high-speed planet gearing due to frictional heating. Solved with specially designed low viscosity synthetic grease containing molydisulfide and other solid lubricants.
Micropitting caused by EP-fortified lubes at high-temperatures. A new formulation was developed containing phosphate esters, biobased superlubricity additive and WS2 nanopowder.
More horsepower being put through a gearbox than the application engineer had designed into his/her drawings. The gearbox handled the horsepower but not the heat that was being generated.
Larger sump capacity and external cooler installed to fi x a heating problem.
Chattering in limited-slip applications. Resolved with additional limited-slip additive.
Additive enhancement for increased surface area protection under high stress.
An ongoing issue is manufacturers recommending oils that are too light for the application.
Excessive wear of girth gears mainly due to overlube/washing of loaded flanks. Utilized airless system and relocated application to loaded flanks rather than pinion.
Wrong viscosity used—users should carefully check all service manuals. They also should color code and label all gearboxes.
Coal pulverizers in power plants using the OEM specification of ISO 320 when it should be an ISO 460 and using the correct compounded gear oil in place of the EP oils on bronze worm gears.
A problem I encountered was an issue with seals in a gearbox. Seals would deteriorate in less than 30 days. Solved the problem with a naphthenic-based gear oil with no EP additives. This was possible after reviewing the application of the gearbox. This reduced the replacement of seals from every 30 days to once a year.
Moisture in cooling tower fan gearboxes. Routed the gearbox vent outside the cooling tower enclosure away from the water spray.
Heat. The gearbox was machine shop-manufactured and had a severe misalignment problem. We ended up tossing the gearbox and had one made properly.
A lot of plants in our area are pressing the equipment to run faster, harder and with less maintenance. The gearboxes began to run hot and make noise (chattering). In some instances gear oils with the Borate additive solved the problem; in others synthetic gear oils to handle the heat were required. As always the most important factor in selecting a gear oil is viscosity.
An overheating problem was solved by contacting the manufacturer to get information on the type of lubricant recommended for the application. In this case the wrong lubricant (too high viscosity) was used.
Unavoidable water contamination in a scarf chopper gearbox in a steel tube mill. Failures were reduced with frequent scheduled (monthly) oil changes and improved seal design.
Contamination was beyond limits. We controlled it by improving oil handling and storage.
How important do you think gears and gear lubricants are in contributing to improved fuel economy for your operating equipment?
Very important 61%
Somewhat important 30%
Not very important 5%
Do not know 5%
Based on responses from 101 TLT readers. Total exceeds 100% because some readers chose more than one answer.
Editor’s Note: Sounding Board is based on an e-mail survey of 7,200 TLT readers. Views expressed are those of the respondents and do not reflect the opinions of the Society of Tribologists and Lubrication Engineers. STLE does not vouch for the technical accuracy of opinions expressed in Sounding Board, nor does inclusion of a comment represent an endorsement of the technology by STLE.