Bearing Life: Extend the life of remote bearings with single point automatic lubricators
Centralized lubrication systems deliver an engineered amount of lubricant on a frequent or even continual basis. Their end point bearing surfaces can last up to three times longer than similar applications that use manually applied lubrication. Ideally, mating bearing surface areas requires only enough fluid film to stop the bearing surface high points from colliding into one another. This state is termed "full film lubrication," and centralized systems are designed to achieve a constant "full film lubrication" state.
Manually lubricated bearing points are often not as lucky, and tend to suffer in two ways: from neglect, in which the bearing is merely forgotten and lubricated infrequently, if at all; and from over-lubrication, in which the bearing receives excess lubricant in the mistaken belief that "more is better". In both instances bearings are subjected to friction. Too little lubricant, and bearing surfaces collide. This metal to metal contact in turn causes friction, which causes the bearing to overheat and accelerate wear. Conversely, too much lubricant causes "churning" or fluid friction, which once again overheats the bearing and promotes wear acceleration.
A centralized lubrication system is usually comprised of a pump, controller, sensing device(s), lubricant metering devices, and distribution tubing/mounting hardware. In most cases, the return on investment for a centralized system is quickly realized through equipment uptime, extended bearing life, energy reduction and reduction in lubricant use. The only exception to this is in remote or forgotten locations where only one or two points require lubrication and installing remote electrical or compressed air power, or running lengthy exposed distribution lines is often not feasible. Typical examples of this include roof fans, remote pumping stations, cranes, elevator drives, conveyor drives, etc. These kinds of locations are the perfect application for the single point automatic lubricator.
Although not new in the marketplace, the single point automatic lubricator solution is often overlooked. Designed initially as a mechanical, spring-loaded device, it has evolved into a much more complex electronically-controlled device. There are presently three major styles of single point lubricators available: the spring-loaded lubricator, the chemical discharge lubricator and the electro-chemical discharge lubricator. All of these perform a similar function, but the degree of control is vastly different for each device type.
THE SPRING LOADED LUBRICATOR
Often called an "automatic grease cup," this simple device consists of a "jam pot" style reservoir housing a compressible spring and is attached to a follower plate. The reservoir is filled by a grease nipple in the cup base; with the reservoir full of grease, spring tension pushes against the follower and discharges the grease into the bearing cavity. Invented in the first part of the 20th century, this device virtually pioneered the science of automatic lubrication. The unit’s rate of control however, is highly variable and often difficult to monitor consistently due to spring tension (often adjustable at the device), bearing back-pressure, grease thickness and ambient temperature (warmer temperatures allow the grease to flow faster).
THE CHEMICAL DISCHARGE LUBRICATOR
A one-time use device, the chemical discharge lubricator comes pre-filled with grease and is mounted directly at the bearing point. The metal reservoir is divided into two sections separated by a follower plate type piston. Grease is contained on the lower bearing side of the reservoir. In the upper chamber, an inflatable bladder contains an electrolyte solution into which an operator, via a mechanical screw device on top of the reservoir, releases a metallic pellet into the solution. A chemical reaction ensues which produces a gas that pressurizes the bladder; as the bladder inflates, the piston pushes the grease into the bearing cavity at a controlled rate.
Chemical discharge units are sold with different pellet sizes, which control the rate of gas production and rate of flow; units are generally calibrated for one, two, three, six, 12, or 24 month dispensing periods. Once the chemical process is activated, the unit cannot be turned off. Certain units produce a hydrogen flammable gas and workers must exercise extreme care when handling spent units.
THE ELECTRO-CHEMICAL DISCHARGE LUBRICATOR
Another one-time use device, the electro-chemical discharge lubricator performs in a similar fashion. Lubricant is displaced as a result of a hermetically sealed bellow displacing against a follower piston pushing against the lubricant. Expansion gas is created via an electro-chemical reaction; electronically controlled battery power is pulsed into an electrolyte to create a gas, which is then released into the bellows.
Unlike the chemical reaction lubricator, this electronic device is fully adjustable and can be turned on and off. These types of lubricators produce a much safer inert Nitrogen gas.
These types of lubricators are comparatively inexpensive (under $50.00) and primarily work best with grease lubricant. The manufacturers of the chemical and electro-chemical lubricators provide engineering charts that allow the operator to compensate for grease weight, temperature and atmospheric pressure. Like all automatic lubricating devices they must be checked, filled or replaced, on a regular basis and their use is best monitored through an active preventive maintenance program.
Ken Bannister is a principal management consultant with Engtech Industries Inc. in Cambridge, Ont. You can reach Ken at(519)622-4211 or by e-mail at firstname.lastname@example.org.