Mechanical components come in various types and designs that tie to their function. Being ‘mechanical’ often means there are surface contacts and movements relative to each other. This rubbing effect needs lubrication or oiling to allow for unimpeded operation.
Three components we will discuss here are bearings, gears and cylinders. These components form majority of machine parts of which lubrication is essential.
Bearings are the most common machine part that can be found everywhere from heavy industrial plants to household items. A bearing permits rotational motion of a shaft while providing the support for the shaft to remain in place. A good example is the wheel bearing on your car. It must have bearings so that the axle can rotate the wheels while still attaching itself to the vehicle.
Bearings can be divided into two types – journal (also known as plain or sleeve) and roller. Journal bearing facilitates sliding movement with a rotating shaft. Roller bearing, as its name suggests, has rolling elements consisting of metal balls or cylindrical-shaped pieces trapped in cage and races.
Bearings can be lubricated either by oil or grease. They can operate at low to high rotational speeds. For a low-speed application, a high viscosity oil is typically recommended. The opposite is true for a high-speed application. Both oils and greases are commonly used in bearings, the selection of which is determined by the machine design.
The next component that requires lubrication are gears. Gears are machine parts that transmit motion and power through teeth engaging and disengaging between themselves. Gears allow the rotational motion of the axle to change angles, directions, torque and speed to other axles.
Without gears, we will have difficulty driving because of torque (power) vs speed varying requirements at different stages of driving. The car needs high torque before it can move from a parked position. Once it moves, the need for torque is lesser as the car picks up speed. Change in gear ratios allows this shifting to happen. Since engines only rotate in one direction, we wouldn’t even be able to reverse our car in the absence of gears.
Gears are exposed to sliding contact coupled with high load on their teeth surfaces. This is why extreme pressure capability are needed in a gear lubricant. Oil is more commonly used in gears rather than grease, but there are applications that grease is preferred, such as open gears.
The third component in our discussion here is cylinders. The mechanism involves the reciprocating motion of a piston parallel to the wall of a cylinder. Specific components that make up the system are piston rings, piston rod, and cylinder bore. Machines with this type of set-up are internal combustion engines, reciprocating compressors and piston pumps.
A lubricant must provide sliding wear protection between the piston rings and cylinder wall. The environment in a cylinder is rather harsh. The oil is subjected to high compression and heat. In an internal combustion engine, fuel and soot will lead to a faster oil degradation. These conditions necessitate an oil with superior oxidation resistance and detergency ability. Of course, the oil must have the right viscosity thick enough to form sufficient oil film thickness and thin enough to spread to the components via splash lubrication. For this application, grease is not suitable because fluid circulation is required for the cooling effect.
Besides the above three components, can you think of any other mechanical component that is protected by a lubricant?
About the Author:
Aaron Said is ILD/Sinopec’s National Technical Manager. He is responsible for developing and delivering value-added lubricant technical services to client for reliability improvement, lubricant optimization, and cost-savings. Among his professional credentials are Certified Lubricant Specialist (CLS) and Oil Monitoring Analyst I (OMA) from Society of Tribology & Lubrication Engineers (STLE) and the International Council of Machine Lubrication (ICML)’s Machine Lubricant Analysist I.