Lube-Free Chains Reduce Maintenance
Lube-free chains are no longer considered specialized products for use only in food processing and other clean environments. Their strength and durability make them potential replacements for standard drive or conveyor chains wherever lubrication must be done frequently and is difficult or time-consuming.
Lube-free chains lower maintenance costs and reduce downtime because wear life is extended (Fig. 1). Maintenance personnel don’t have to spend time or commit to regular lubrication schedules. There is little chance this type of chain will run dry and seize up due to overheating, or break and fly off a sprocket because of excessive wear. Lube-free chain is ideal for clean applications where machines or conveyed materials must be free from contact with oil.
Whether a chain is used to connect a drive shaft to a driven component or to move a conveyor, articulation of the chain over sprockets causes friction and results in wear. The more times a chain engages a sprocket, the more it wears. Short, fast-moving chains tend to wear out sooner than longer, slow-moving strands.
The chain elongates as wear occurs on pin surfaces and on the inside diameters of bushings. When chain elongates by a certain percentage, defined by the manufacturer for each type of chain, it should be replaced. The usual, allowable elongation for standard roller chain, used with sprockets having 60 teeth or less, is 1.5%. That is the point at which the hardened surfaces of pins and bushings are just about worn through and considered at the end of their useful life.
There is no established longevity for roller chain. How long it lasts depends on the severity of service and speed at which the chain operates, which determines the number of times it articulates over the sprockets. With proper lubrication and correct tension, some chains may last 15,000 hr, while others have to be replaced sooner.
As chain wears and elongates, it no longer fits properly on the sprockets. Tension drops off and the chain tends to ride up on sprocket teeth, causing wear. If maintenance personnel fail to observe the signs of chain and sprocket wear, elongation, noise, chain riding high on sprockets, and loose, whippy chain, an unexpected failure could occur, causing unnecessary downtime.
A thin film of lubricant, covering all surfaces that rub together, minimizes steel-on-steel contact and acts to dissipate friction-generated heat. Methods of applying lubricant where it is needed most and the frequency of lubrication depend on operating conditions. Application of too much lubricant is wasteful and messy because the excess is thrown off.
If maintaining proper lubrication is difficult because of chain location or if excess lubricant is frequently thrown off, a lube-free chain should be considered when replacement becomes necessary.
Three types of lube-free chain
O-ring, rollerless sinterered bushing, and sintered bushing roller chain are available.
Lubricant contained within O-ring chains maintains the required film of oil on metal-to-metal surfaces, eliminating the need for periodic lubrication. However, this chain must be externally lubricated to keep the O-rings from drying out and failing.
O-ring chain is called sealed chain because lubricant is contained by tiny O-rings positioned between each pin link plate and roller link plate. This type of lube-free chain provides better wear life than standard types. The increase in wear life depends on O-ring life. However, friction between O-rings and link plates tends to make it difficult for this chain to bend and articulate. Users sacrifice energy because it takes more power to operate a conveyor or drive system using this type of chain.
Rollerless sintered bushing chain
Rollerless sintered bushing chain, sometimes referred to as SL chain, is made with bushings impregnated with lubricant. Movement between each pin and bushing causes lubricant to be expelled onto the pin surface, minimizing pin/ bushing wear, extending chain life, and eliminating the risk of chain seizure due to insufficient lubrication.
With sintered bushing rollerless chain, the same point on the bushing engages a sprocket tooth on every cycle, accelerating bushing wear. Even with that disadvantage, tests show the wear life of sintered bushing rollerless chain is better than sealed chain at speeds up to 500 fpm.
Sintered bushing roller chain
Sintered bushing roller chain combines the best features of sintered bushing rollerless chain and standard roller chain. Its oil-impregnated bushing is maintenance-free and provides a wear life up to 40 times that of unlubricated standard roller chain. Some key construction features are oil-impregnated sintered bushings, plated pins, and hardened, seamless rollers (Fig. 2).
The smooth, hard surface of the pin reduces the coefficient of friction between the pin and bushing. The oil-impregnated bushing provides effective, long-term, internal lubrication without the use of O-rings. Since the rollers are free to rotate, they contact the sprocket teeth at different points with a rolling engagement each time around, reducing chain and sprocket wear (Fig. 3). This construction results in smooth articulation of the chain over the sprocket, reduced chain pull, and extended life.
The chain selection process depends on the application — drive or conveying. Chain manufacturers provide selection charts, tables, and instructions.
A service factor, ranging from 1.0 to 1.7, is determined from tables and depends on the power source and shock loads of the application. The greater the shock load, the higher the service factor. Design horsepower is calculated from the horsepower to be transmitted and the service factor.
The manufacturer’s horsepower rating table should be used to select the proper chain and sprocket. For a smooth chain drive, select a small pitch. On the other hand, sprockets with fewer teeth are more economical. If a single strand chain does not satisfy load requirements, use a multiple strand chain, possibly with a smaller pitch. The number of large sprocket teeth can be reduced by using the fewest possible teeth on the small sprocket. More than 15 but less than 120 teeth are suggested for large sprockets.
— Edited by Joseph L. Foszcz, Senior Editor, 847-390-2699, email@example.com
Extended wear life lowers maintenance costs and reduces downtime.
Use lube-free chain when lubrication is difficult or thrown off.
There are three types of lube-free chain: O-ring, rollerless sintered bushing, and sintered bushing with roller.
– Power source (usually electric motor)
– Type of equipment driven
– Horsepower transmitted
– Full load rpm of the drive and driven shafts
– Shaft diameters
– Shaft center-to-center distance
The author is available to answer questions about lube-free chain. He may be reached at 413-536-1572.