What are your biggest concerns as gear boxes trend toward smaller sizes and heavier loads?

TLT Sounding Board September 2015

Technology moves in only one direction—forward. But new innovations always are accompanied by new challenges. According to respondents to this month’s question on shrinking gear boxes, key lubrication issues include reduced service life of the equipment, heat generation, foaming, contamination from mixing incompatible lubricants, inadequate sump size, shorter drain intervals and filtration. Many readers also commented on the need to re-educate end-users. “There is a lack of lubrication knowledge among our customers, which causes confusion while they’re too busy doing other things,” noted one respondent. Regarding the best test methods for lubricants to be used in smaller gear box applications, the most popular answers were the 4-ball test and FZG. But many readers question the adequacy of any test to produce accurate results. “There are few lab tests that can demonstrate real world applications,” said one.

Service life.

Pitting and wear trend metals.

Operating temperature.

Excessive heat buildup and less room to control foaming.

Lack of cooling. Tendency to reduce bearing surface areas.

The increasing role of material plasticity.

Educating end-users about the need to change from old practices to new practices because of the trend toward smaller gear boxes and heavier loads.

Temperature and load.

Are the sizes able to handle the torque applied? What change in tooth contact are we getting when we do not have a steady load? Is the selected lubricant adequate?

Quality and condition of oil to keep these smaller sizes operating in good condition.

Long-term life of the gears and bearings. High-quality lubricants versus low-price gear lubes.

Contamination affecting the life of the gearbox.

Thermal stability of the lubricant, loading of particles leading to fatigue wear.

Quicker oxidation of the gear oils.

Taking heat away from the gear box without a cooling device.

Potential for shorter drain intervals due to oxidation and increased wear of the gearbox.

Lubricant is worked and stressed more. Inadequate lubricant gets oxidized quickly. Life of lubricant is then shortened.

Short life is expected and run to failure with lower gearbox cost and higher labor cost precluding the value of rebuilds. Very hard to justify oil sampling. Some come filled with grease, and changing the lube not an option. Lubed for life like some cheap bearings supplied with no fittings.

My concern is that the heat balance is not right. The cooler cools down the oil, but the oil is already overheated in the meshing gears and bearings. Entrained air cannot escape due to too low oil level. Oil samples are no indication anymore on gearbox condition as all wear is captured in the filter. A filter analysis procedure is required.

Oil (lubricant) temperature.

Fatigue wear and micropitting wear.

Viscosity index and oxidation resistance.

Effectiveness.

Long OEM approvals limit the ability for oil suppliers to iterate formulations at the same rate as gearbox innovations.

There is a lack of lubrication knowledge among our customers, which causes confusion while they’re too busy doing other things.

Oil level and are the breathers working properly?

Wrong oil added. Contamination.

Heat buildup increase in oil breakdown.

Heat, unintended wear, premature failure.

The gearbox owner reading the maintenance manual. The manufacturer doing the due diligence on recommending the right lube.

A sump size that will have enough oil for proper lubrication.

Temperature and loading.

Sealing out contaminates and keeping the lubricant clean and dry.

Contamination ingress through breathers and seals.

Foam.

Thermal oxidative stability. Additive efficiency and depletion. Extended lubrication service intervals.

Lubricant residence time.

Heat distribution.

Temperature, temperature and temperature.

Problem is the fluids that might be used in them to leave a smaller carbon footprint can lead to higher temperatures, faster oxidation and more degradation by products being created leaving lower lubricating capabilities.

Durability and reliability.

Longevity—especially in applications like wind turbines, which are so difficult to service.

Excessive wear on gears from overloading. Shorter lubricant life due to smaller sumps and higher loads.

Micropitting (fatigue wear).

Higher operating temperature, shorter lubricant life.

Current antiwear technologies cannot cope with the increasing stress on surfaces.

Educating the customer network about the need for quality lubes and reasonable service intervals.

Extreme-pressure capabilities of lubricants.

Higher temperatures.

Wear and heat management.

Less margin for mistakes.

Smaller size gearbox coupled with heavier loads calls for improved metallurgy in the gear materials and some sort of cooling to handle the heat generated. Obviously, the gear lubricant also must be able to successfully protect the gear surfaces.

Large gears with impact loading.

Durability, life time, lubricant environmental issues, biodegradable lubes.

Load capacity of the gears and bearings materials.

As gearboxes get smaller, the demands get greater. Without adequate lubrication such as the use of PAGs, this is getting extremely hard to do.

Consistency in quality of current gear lubes and the continued need to innovate future formulations.

Implementing high-heat stability antioxidants.

Determination of proper ISO viscosity grades. Another current trend is utilization of VFDs to limit the number of different gear ratios; that is, the gear motors will operate at different rpms to satisfy production rate requirements. Gear motors are prefilled with a gear lubricant to satisfy pitch line velocities at 60 Hz motor speeds.

Filtration.

The overselling of synthetics in gearboxes—are they needed?

EP additives. Contamination.

The tendency for great foaming and increased heat are potential issues that need to be addressed.

Which is the most important property when selecting a gear oil?
Cost 8%
Durability/wear protection 81%
Oxidative/thermal stability 21%
Drain interval 10%
Based on responses sent to 13,000 TLT readers. Total exceeds 100% because some respondents chose more than one answer.

Which test methods best demonstrate a lubricant’s suitability for these new and more demanding gear box applications?
TAN monitoring.

4-ball test and FZG.

High-temp, high-load gear tests.

ASTM D5704.

Load wear index.

4-ball testers with two different dimensions of balls with contact temperature measurement.

Testing for metal wear particles. The key would be the timing when sampling would be taken.

ASTM D3233A, D2760, D4172.

Contol of heat and wear and fatigue.

Oxidation: D2893. Air/foam: D892, FVA-54, FZG - ISO 14635-1. Demulsibility: ASTM D1401 and/or D2711.

ISO particle counts.

Must be a combination of tests. The problem is the correlation with the real practice. Field trial is the best test method.

D5185 and particle count.

Heat stability and oxidation related tests (CMHT, TOST, RPVOT) and wear protection under higher temp (FZG modified).

FZG Test, Timken OK Load, 4-ball EP and wear tests, ASTM D892 Foaming.

EP characteristics and viscosity.

Operating temperature and speed. If you can get a sample, then add iron and copper PPM and viscosity, EP additive depletion. Water content depending on the gear type, speed, duty and operating environment.

Standard gear and bearing tests, maybe made tougher. Air separation, filterability.

SRV test.

Oxidation stability and wear protection.

FZG test.

Insoluables and oxidation products.

Viscosity.

Oil analysis.

Apply lube, monitor, match up lube to demands expected, heat, load and speed.

Particle count. PQ. Foaming tendency. Acid number. Analytical ferrography. Viscosity.

There are few lab tests that can demonstrate the real world applications.

Drooping lubrication pump system. Full bath.

Field tests are always the ultimate method.

Not sure about a method. We think PAG base stocks provide the highest benefit as they cannot degrade into sludges and varnishes like other base stocks. Higher lubricating and VI lead to better lubrication.

Simulation/modeling.

Two roller machines run the surfaces with rolling-sliding motion and high loads for millions of cycles to reproduce any type of wear and damage conditions.

OEM requirements will dictate guidelines.

Extreme-pressure tests.

Film strength.

I’m not aware of any gear tests that can predict performance in these applications. FZG may be of some help but doesn’t answer the questions of load protection and cooling.

That’s the problem—there is very little that simulates this condition.

Nothing is better than a test bed with the real thing.

Throw it in the pool and see if it can swim. 

Which area of gear oil performance has the largest potential for improvement?
Wear protection 38%
Protection against surface fatigue 34%
Oxidative/thermal stability 36%
Corrosion/rust protection 8%
Resistance to foam and entrained air 21%
Based on responses sent to 13,000 TLT readers. Total exceeds 100% because some respondents chose more than one answer.

Editor’s Note: Sounding Board is based on an email survey of 13,000 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.