May 1, 2009
Are greased applications causing unexpected downtime in your operation?
by John Geyer
Improper greasing practices can translate into significant financial loss due to downtime coupled with unplanned and expensive maintenance and repair costs. Because of this, it is critical to understand the importance of proper grease-related lubrication and maintenance practices in aggregate operations.
To practice proper grease application and lubrication procedures for equipment reliability, companies should consider three key causes of grease-related problems: improper grease selection (wrong product choice for the application), under-greasing (lack of lubrication), and over-greasing (too much lubrication).
Choosing the right grease and oil viscosity combination is the most important factor in practicing proper grease maintenance. OEM specifications for lubricating oils normally include viscosity at ambient operating temperature, additive requirements, base oil type, and even considerations for different environmental conditions. Grease specifications, however, often lack the necessary details to make a proper selection, leaving it up to the lubrication engineer to make assumptions for the application involved.
Due to the lack of specificity in many of these applications, it is important to learn how to properly select the right grease or combination of greases for individual application in the plant. Consider the following factors when selecting the most effective grease product for your specific needs:
§ Is the application located in an indoor or outdoor environment?
§ Are there high levels of contaminants? If so, what are they?
§ Is water a factor? If so, is the water directly sprayed at the bearing surfaces or is the bearing submerged or subjected to cascading water? Does the water contain other fluids such as solvents or coolants?
§ Are there external temperature extremes the grease must operate within, i.e. extreme heat or cold?
§ What are the operating temperatures of the bearing under load?
§ Are the equipment revolutions per minute (rpm) running at a low or high speed?
§ Does the grease have to pump through a centralized system? If so, how far and under what conditions?
§ Can the application be greased easily or are there safety concerns to get to the application when the equipment is running?
§ Have there been previous failures believed to be related to the incumbent lubricant used?
Extreme heavy-duty, high-load applications usually require grease with a higher oil viscosity. Often, these applications have much lower rpms and the grease needs to be able to maintain proper film thickness between the metal-to-metal surface contact points to prevent premature wear. High loads often squeeze lighter-viscosity oils out of the bearing and leave contact points vulnerably exposed.
Equipment running at higher rpms, such as small electric motors, usually requires lower oil viscosity. If a grease is too thick or too high in oil viscosity for the bearing to properly function, fluid friction develops within the bearing. The resulting buildup of friction and pressure makes the bearings overheat, which causes rapid oxidation of the grease and can lead to premature bearing failure.
Understanding the need and the methods for appropriate grease selection will go a long way toward improving lubrication programs and the reliability of lubricated machinery. When in doubt, consult your lubricant supplier who will have a wealth of knowledge to help you choose the correct greases for your specific equipment.
Not enough lubrication
A second and much more common cause of grease-related equipment failures is a lack of lubrication from improper or poor maintenance practices. Under-greasing creates extreme heat caused by friction buildup and will eventually lead to high levels of metal-to-metal contact between bearing components – causing equipment failure or breakdown. Equipment failure, downtime, and lost productivity can be costly byproducts of under-greasing or failing to properly lubricate components. It also shortens the grease life considerably.
Following a company’s reorganization, a customer approached our lubrication engineer about bearing failures on a specific portion of his plant, asking how the failures could be related to improper greasing. The customer suspected that the wrong grease was being used.
Research revealed that, during the reorganization, an employee had been laid off – an employee who conducted and maintained regular grease re-lubrication intervals at this plant on a monthly basis. After the layoff, the bearings had gone well over six months without any grease maintenance.
The lack of adequate lubrication, coupled with the extreme conditions experienced at this plant, began to cause bearing failures. Without proper lubrication of the bearings, equipment can be shut down and production ceased. Lubrication and maintenance is cheap compared to the alternative – a plant that is not running.
This situation exemplifies the critical role grease plays in equipment reliability and reinforces the value of a regular program to monitor lubricant applications. Maintaining the proper amount of grease is crucial. Be sure bearings are properly greased during installation and re-grease the bearings at the appropriate intervals based on your particular equipment needs and operating parameters.
Too much lubrication
Over-greasing can be as bad as under-greasing. Over-pressurizing bearing seals by applying too much grease can lead to higher grease usage, overheating, and mechanical failures. If the bearing seal is damaged or blown out, equipment or bearing life can be shortened by more than 50 percent due to the introduction of external contaminants.
Remember, today’s typical hand grease gun produces pressures as high as 10,000 pounds per square inch when greasing bearings. This can easily produce pressure extremes that rupture or damage the bearings’ internal and external seals. The seals were designed to keep foreign matter out. If damaged, they can not effectively do their job.
There are instances, due to over-lubrication, when bearing pressure builds to high enough levels that the bearing itself actually ruptures. While the seals will usually go first, a ruptured bearing can potentially shut down a piece of equipment or, possibly, an entire plant.
In addition, over-greasing limits the life of grease in an application. Over-lubrication causes excessive heat buildup in the bearings, especially if the grease has nowhere to go as pressures rise. If the bearing is unable to function properly, the seal will typically expand outwards and eventually fail. This causes the grease and bearing components to become exposed to dirt and external contaminants. With the introduction of foreign contaminants, bearing life and grease life is compromised.
Measuring and maintaining appropriate grease levels is key to avoiding the negative effects of under- and over-lubrication. One application to consider is a pressure-relief fitting designed to prevent over-pressurization at the zerk fitting by relieving and discharging grease when too much grease or pressure is applied. Automatic lubricators can also help reduce operating costs by providing a precise and controlled supply of lubricant in applications such as bearings in fans, electric motors, and hard-to-reach areas.
These types of lubricators also help maintain proper grease levels in difficult applications that need to be greased regularly, ensuring that maintenance workers are not subjected to hazards and possible injury due to the precarious locations of these grease fittings.
Ultrasonic technology is another option. This allows you to grease a bearing based on decibel (Db) ratings. Rising decibel levels within the bearing are indicators that the bearing may need re-lubrication. The key is to apply only as much grease as is needed to reduce the decibels to a pre-determined base level. These devices are exceptional for learning and keeping record of how much grease can be applied to a sealed bearing.
Industrial greases are widely used to lubricate bearings in today’s high-performance industrial equipment. Grease excels at sealing out contaminants, minimizing re-lubrication intervals, and reducing leaks. Simply put, it is used where oils cannot be due to various equipment requirements.
Successful grease lubrication in industrial applications requires using the right grease in the right quantity at the right intervals for the application to ensure optimum life and equipment reliability.
To further understand how to avoid grease failure, consider working with a lubrication consultant or your lubricant provider. This way, you can achieve a high level of grease-related reliability and maximize the efficiency and uptime of your equipment.
John Geyer is the C&I account manager for Off-Highway at Chevron Lubricants. If you have lubricant-related questions, contact Chevron via telephone at 925-842-1000 or via e-mail at firstname.lastname@example.org.
Editor’s note: This story first appeared in MRO Today and is reprinted with permission.