Proper lubrication of rolling bearings in rotating equipment involves delivering the right lubricant, in the right quantity, to the right location. Advanced lubricant-dispensing technologies, some recently introduced to the market, make this task easier.
These technologies include automatic lubricators, lube selection and calculation software programs, and precision metering devices. They can assist lubrication professionals in effectively targeting lubrication and improving the health and performance of rotating equipment.
More than one-third of all bearing failures can be traced to lubrication-related errors. In bearings lubricated with grease, undergreasing leads to metal-to-metal contact between bearing components during operation, resulting in eventual bearing failure. Overgreasing causes lubricant churning, increasing bearing operating temperatures and leading to a loss of lubricant viscosity.
Using excessive lubricant, moreover, can have an impact beyond a particular machine or application. The practice can increase a plant's overall lubricant usage and expenditures. It also increases lubricant disposal costs and can harm efforts to achieve sustainability. Sound lubrication practices, in conjunction with advanced dispensing technologies, however, can reduce lubricant usage and associated costs.
Figure 1. Single-point Lubricator (Courtesy of SKF USA Inc.)
In the past, many industrial plants routinely employed a general-purpose grease in all rotating-equipment applications. But a single grease formulation cannot offer optimal performance in every application. A better practice is to select lubricants that best meet specific application requirements.
Lube selection software programs, available from many lubricant and bearing manufacturers, can make the selection process easier. These programs identify a prospective grease or oil based on application variables such as speed, load, ambient temperature and contamination.
Automatic lubricators ensure that the lubricant selected is delivered in the right amount to the right location, improving precision and reducing the guesswork associated with manual relubing. Depending on facility size and the number of machine points requiring lubrication, lubrication managers can employ single-point automatic lubricators, multipoint automatic lubricators or custom-designed lubrication systems.
Single-point Automatic Lubricators
Single-point automatic lubricators are self-contained units that attach to a bearing housing or machine point. They dispense lubricant at a preset rate for a period of up to one year, requiring only periodic visual inspection and eliminating the labor involved in manual relubrication. The units find application in fans and blowers, pumps, cranes and conveyors, and are especially useful in hard- to-access locations.
The most common types include gas- activated units and those activated by mechanical springs. Although spring- activated lubricators are still in use, the trend is toward gas-activated lubricators, such as SKF System 24, due to its reliability in high-vibration applications (Figure 1).
Updated versions of this lubricator feature a gas cell that generates a large-molecule inert gas with low sensitivity to high temperatures. This improves dispensing accuracy. When activated, the gas pushes grease from the container at a predetermined rate.
The lubricators, which come in 60- and 125-milliliter capacities, also feature tool-free adjustment of lubricant flow. Users input application variables such as grease type, operating conditions, speed and load into the DialSet software program and adjust the lubricator dial according to the program's recommendations.
Single-point lubricators with higher capacities than those currently available are now in the development stage. These robust lubricators are expected to have lubricant capacities of 200 ml or more, extending the range of single-point lubrication and finding use in heavy-duty applications such as mining.
Figure 2. Multipoint Automatic Lubricator (Courtesy of SKF USA Inc.)
Multipoint and Custom-designed Systems Automatic Lubricators
Multipoint automatic lubricators supply grease through multiple feed lines emanating from a centralized, refillable grease cartridge (Figure 2). The lubricators typically feature a high-pressure pump powered by an electric motor. Larger systems can supply up to 20 separate lubrication points.
A recent lubricator success story involved a major fruit juice and beverage producer. The company installed an LAGD 1000 multipoint lubricator, which supplies standard NLGI 2 grease to 16 different lubrication points on a wet-section conveyor line. The grease is supplied through tubes up to 5.5 meters long, at a rate of 0.2 gram per day.
The lubricator features a progressive divider that evenly distributes grease flow into different outlets independent of outlet pressure; consequently, all outlets dispense the same amount of grease. On the fruit juice and beverage producer's conveyor line, the lubricator prevents water from accumulating in conveyor bearing housings and has resulted in a fivefold increase in bearing life expectancy. Its 1,000-ml (1-liter) capacity has increased the intervals between refilling.
Industrial facilities with more demanding applications may require custom-engineered lubrication systems. In high-speed fans, for example, circulating oil systems can provide a continuous flow of cooled and filtered oil directly to bearing arrangements. In certain metal-fabricating applications, customer-engineered oil/air systems can supply small quantities of oil to bearings via compressed air, enabling bearings to run coolly at high speeds.
Levelers and Metering Devices Oil Levelers
In oil-lubricated applications, oil levelers can precisely adjust the oil level within a bearing, gearbox or other component. Levelers typically consist of two communicating oil reservoirs. The lower reservoir is connected to the application and has an oil level identical to the application's oil level.
The upper reservoir stores replacement oil in an airtight container. When the oil level in the lower reservoir drops below its preset level, air enters the upper reservoir and triggers a flow of replacement oil to the application. Oil levelers automatically compensate for oil leakage and allow oil levels to be adjusted during machine operation.
In addition, there are a variety of metering and dispensing tools available that increase the precision and efficiency of manual grease lubrication. These include battery-driven grease guns that minimize the manual effort involved in lubrication. A new SKF grease gun, for example, dispenses a 420-ml grease cartridge in approximately 10 minutes. This grease gun can be used in conjunction with a new grease meter, which measures dispensed grease by weight and volume. This reduces the risk of undergreasing or overgreasing bearings.
For more information about advanced dispensing, selection and metering technologies, contact your bearing or lubricant supplier.
About the Author
Paul Michalicka is the North American area sales manager of maintenance products for SKF USA Inc. For more information, visit www.SKFUSA.com or call 800-440-4SKF.