Gearbox Lubrication- Practices
Modern gears are performing heavier work and carrying greater loads than ever before. Gear manufacturers are redesigning, modernizing, and using finer steels to produce precision gears that will give better performance. Demands on global industry are often forcing users to raise production above rated machine capacity. This is done with the knowledge that gear life will be reduced, but that the increased cost will be offset by the increased production achieved. There is a demand from all industries for more power in smaller packages. Gears are used to transmit this power, and the same squeeze is on the gearbox—so how is it possible to increase the load capacity of gears?
Lubricant manufacturers have helped in addressing this need by developing better gear oils to help carry these increased loads safely. Lubrication Engineers continues with extensive research and testing programs to develop higher-performance gear lubricants to stay ahead of the demands of industry.
Gear Oil Selection
When selecting a gear oil for a particular application, there are ways that the risk of failure can be reduced. The first requirement is thorough attention to detail.
It is easy to accept the machine manufacturers’ recommendation word for word, but they can never anticipate all the conditions under which the gearbox may operate. The manufacturers’ recommendation, therefore, must be a guideline and not necessarily the final word on the product to be used. Operating conditions must also be determined in order to make the best possible recommendation. Check for the following items:
• Location of machine: Is it out of the way or difficult to get to? Then it may not be lubricated as often as it should.
• Atmospheric conditions: What surrounds the machine in the way of heat, dust, moisture, chemical vapors, etc., that may affect lubrication?
• Housekeeping: Accumulations of dirt and other indications of poor maintenance.
• Overloading: Visible indications of operation above rated speeds.
Failure/Wear Analysis
During the first inspection of a set of gears that are properly installed and lubricated, the combined action of rolling and sliding will smooth the working surfaces of the teeth and give them a highly polished look. Under continued operation trouble may occur that will show up as a breakdown of the tooth surface. The type of failure will often indicate the reason and recommended remedy. Some examples of severe gearbox operating conditions include:
• Rapid fluctuations in operating temperatures, high speeds, and heavy loads.
• Any operating environment that causes condensation inside the gear case or oil reservoir, resulting in formation of sludge and causing the gear oil to foam.
• Operation in moist or dusty environments, or where chemical fumes are present. In such instances, set change intervals accordingly.
Prepping the Gearbox
In order to obtain the optimum performance from new gear lubricants, it is necessary to properly prepare the enclosed gear reservoir. First, drain oil presently in the box as completely as possible while the unit is still warm. This helps remove contaminants and oxidized oil that can impair the performance of the new gear lubricants. If contaminated oil remains in the gearbox, foaming can occur.
Second, do not use a volatile, chlorinated solvent or solvent-type flushing compound to wash out the gearbox. Any solvent trapped in the voids of the reservoir will cause corrosion. Also, the presence of even a very small amount of solvent-type flushing compound will reduce the viscosity of a gear oil. Further, without a coating of oil for even a short time, “flash rusting” of internal parts of the gearbox can take place.
Third, to properly flush the gearbox, use one of the new gear lubricants, or a light viscosity of R&O compressor oil filling to one-third the recommended operating oil level. Circulate under no-load conditions for 15 minutes and drain.
Fourth, if the used gear oil has oxidized badly with a dark color, burned smell, and is thick and slow to drain, use a light viscosity of R&O compressor oil. Fill to one-third the recommended operating volume and circulate under a no-load condition for 10 minutes, then drain completely and refill to one-third volume. Operate 15 minutes under a no-load condition and drain.
Fifth, remove any rust-preventative materials before charging with operating gear oil. Use the flush procedure explained in step three to remove rust preventatives, manufacturing debris, metal chips, and core sand.
Sixth, remove and clean gear oil filters if present in the system.
Seventh, clean the vent plug and reinstall correctly. Ideally replace the vent plug with a dessicant breather. This will help to prevent airborne and water contamination of the gearbox when it “breathes.”
Eighth, when working with enclosed gearboxes or oiling systems that do not have a drain or circulating system, the used oil and flushing oil should be removed by suction. Use of pressure to force out or blow out this oil may damage seals. Some gearboxes have reinforcing ribs on the bottom. Be sure to allow for that when suctioning to remove the old lubricant.
Ninth, recharge the gearbox reservoir with the appropriate gear lubricant. Be careful not to overfill, because this can cause foaming.
Tenth, install an “oil sight glass” to the gearbox drain port at the bottom of the reservoir or with an elbow for drain ports located on the side of the gear equipment.
Regarding the service life of gear oils should include information regarding operating, environmental, and mechanical conditions of the equipment. Even in the best of situations, gear and circulating oils will not last indefinitely. Therefore, from the standpoint of both service and economy, gear oil should be removed and replaced with fresh lubricant when the oil has deteriorated or has become contaminated. When severe operating conditions are present, change intervals may need to be shortened depending on oil analysis results.
Improving Gearbox Reliability
The number-one cause of failure in any mechanical application is due to contamination. Since every industrial plant has a sizeable investment in the equipment that is owned and an investment in the lubricant that is purchased to protect that equipment, it only makes sense to protect both investments from contamination. Lubrication Engineers supplies industry with a range of high-performance mineral and synthetic gear oils to more closely meet the requirements for various applications found in plants.
To protect the investment in these quality gear lubricants, Lubrication Engineers recommends that all industrial customers use a best-practices approach in “Reliability Centered Maintenance: Controlling Contamination.” Reliability products currently in use by LE’s customers include:
• Oil Safe lubricant transfer containers are critical to best-practice lubrication programs. Color-coded and fully sealing, these containers ensure the accurate delivery of clean lubricant from bulk storage to gearbox point of use every time. Proper labeling of all gearboxes then ensures that the correct lubricant is delivered in the correct quantities to the correct application in the plant. Expensive downtime is then avoided due to the incorrect application of gear lubricants.
• Breathers: Since humidity and moisture are also a contaminant this is a major problem for gearboxes. Oil within a gearbox is subject to fluid volume changes, as well as temperature and pressure variations during operation. These differential pressures cause air exchange through the breather/filter cap, allowing dirt and water to be drawn into the system. Installation of breathers at these critical ingression points is a cost-effective means to prevent contaminants from entering the fluid reservoirs as differential pressures occur.
Conclusion
Our Lubrication Engineers provides consultative support for our valued customers. Industrial clients are enjoying increasing profits due to the reduced maintenance and operating costs relating to their gearboxes and many other applications. High performance lubricants alone cannot provide these savings; it is vital to prevent the contamination of gearboxes in plants in order to remove any possibility of expensive downtime. Reliable gearboxes result in increased profits.