Roller chain or bush roller chain is the type of chain most commonly used for transmission of mechanical power on bicycles, motorcycles, and in industrial and agricultural machinery. It is simple, reliable, and efficient, but requires more attention to maintain than may be desired by potential owners. There has, therefore, been of late a tendency towards the use of other modes of power transmission such as the cog, or timing belt.
Though Hans Renold is credited with inventing roller chain in 1880, sketches by Leonardo da Vinci in the 16th century show a chain with a roller bearing.
Construction of the chain
There are actually two types of links
alternating in the bush roller chain. The first type is inner links, having two inner plates held together by two sleeves or bushings upon which rotate two rollers. Inner links alternate with the second type, the outer links, consisting of two outer plates held together by pins passing through the bushings of the inner links. The "bushingless" roller chain is similar in operation though not in construction; instead of separate bushings or sleeves holding the inner plates together, the plate has a tube stamped into it protruding from the hole which serves the same purpose. This has the advantage of removing one step in assembly of the chain.
The roller chain design reduces friction compared to simpler designs, resulting in higher efficiency and less wear. The original power transmission chain varieties lacked rollers and bushings, with both the inner and outer plates held by pins which directly contacted the sprocket teeth; however this configuration exhibited extremely rapid wear of both the sprocket teeth, and the plates where they pivoted on the pins. This problem was partially solved by the development of bushed chains, with the pins holding the outer plates passing through bushings or sleeves connecting the inner plates. This distributed the wear over a greater area; however the teeth of the sprockets still wore more rapidly than is desirable, from the sliding friction against the bushings. The addition of rollers surrounding the bushing sleeves of the chain and provided rolling contact with the teeth of the sprockets resulting in excellent resistance to wear of both sprockets and chain as well. There is even very low friction, as long as the chain is sufficiently lubricated. Continuous, clean, lubrication of roller chains is of primary importance for efficient operation.
The need for lubrication, not just to the outside of the chain but especially to the inner surfaces between the pins and bushings and to the bushings and rollers, is a source of irritation for almost all users of roller chains. From bicycle owners, who must clean and lubricate the chain
by hand or with specialized gadgets, to the owners of complex machinery utilizing high speed chain drives, who utilize expensive sophisticated lubrication systems to keep the chain lubricated, all the way up to the owners of gigantic surface mining
draglines and bucket-wheel excavators, struggle with the goal of giving their roller chains clean, continuous lubrication.
It is no surprise, then, that some owners, from one end of the scale to the other, simply use the "do-nothing" alternative. They accept more friction, less efficiency, more noise and more frequent replacement as they only minimally maintain the lubrication of their roller chains. This is a classic "trade-off." Many major roller chain manufacturers such as Tsubaki, Diamond, Morse, Renold, and Rexnord have developed low-maintenance roller chains such as o-ring (grease sealed into the joints) and Duralube or Lambda (with an oil-impregnated sintered metal bushing).
Variants in design
If the chain is not being used for a high wear application (for instance if it is just transmitting motion from a hand operated lever to a control shaft on a machine, or a sliding door on an oven), then one of the simpler types of chain may still be used. Conversely, where extra strength and/or durability are required, the chain may be "siamesed"; instead of just two rows of plates on the outer sides of the chain, there may be three, four, or more rows of plates running parallel, with bushings and rollers between each adjacent pair, and the same number of rows of teeth running in parallel on the sprockets to match. Timing chains on automotive engines, for example, typically have multiple rows (called strands) of plates.
Roller chain is made in several sizes, the most common ANSI standards being 40, 50, 60, and 80. The first digit(s) indicate the pitch of the chain in eighths of an inch, with the last digit being 0 for standard chain, 1 for lightweight chain, and 5 for bushed chain with no rollers. Thus, a bicycle chain with half inch pitch would be a #40 while a #160 sprocket would have teeth spaced 2 inches apart, etc. Metric pitches are expressed in sixteenths of an inch; thus a metric #8 chain (08B-1) would be equivalent to an ANSI #40. Most roller chain is made from plain carbon or alloy steel, but stainless steel is used in food processing machinery or other places where lubrication is a problem, and nylon or brass are occasionally seen for the same reason.
Roller chain is ordinarily hooked up using a master link (also known as a connecting link), which typically has one pin held by a C clip rather than friction fit, allowing it to be inserted or removed with simple tools. Half links (also known as offsets) are available and are used to increase the length of the chain by a single roller.
- Roller chains are used in low- to mid-speed drives at around 600 to 800 feet per minute; however, at higher speeds, around 2,000 to 3,000 feet per minute, V-belts are normally used due to wear and noise issues.
- A bicycle chain is a form of roller chain. Bicycle chains may have a master link, or may require a chain tool for removal and installation. A similar but larger and thus stronger chain is used on most motorcycles although it is sometimes replaced by either a cog belt or a shaft drive, which offer lower noise level and less maintenance requirements.
- In older automobile engines from the United States and other countries, roller chains would traditionally drive the camshaft(s) off the crankshaft, generating less noise than a gear drive as used in very high performance engines, and offering more durability than the timing belt frequently used on more modern engines. Many modern automobile engines still use roller chains.
- Chains are also used in forklifts using hydraulic rams as a pulley to raise and lower the carriage; however, these chains are not considered roller chains, but are classified as lift or leaf chains.
The effect of wear on a roller chain is to increase the spacing of the links, causing the chain to grow longer. Note that this is not from any actual stretching of any metal, as too many engineers and mechanics intuitively believe, but is due to the effect of wear at the pivoting parts. It could be said that the roller chain loosens with wear. Now, it is true that cable, or wire, will indeed stretch. An excellent example of stretching is what happens to the actuating cable for the parking brake/emergency brake in motor vehicles. Here the metal "necks down." it shows its ductility, and so it gets thinner as it elongates over time.
Although it is unusual for a chain to wear until it becomes so worn out that it breaks, a worn chain leads to the rapid onset of a great increase in the rate of wear of the drive sprocket and driven sprockets with which it mates. The sprockets cannot change the spacing of their teeth to match the ever-widening chain links' spacing or "pitch." The wear a worn chain causes on the sprockets is asymmetrical. It grinds a characteristic hooked shape into the rearward face of the sprocket teeth. As this pattern progresses, the sprocket teeth naturally begin to hook the rollers of the chain links, preventing them from rolling off the sprocket teeth until later in the rotation than they should. This causes a jittery transmission of power rather than smooth; in bicycles, for instance, this translates into the common problem of the chain "jumping" off its sprockets. In automotive engine timing chains this translates into a jittery timing of both the valves and the distributor, which becomes especially evident when trying to time the ignition with a timing light. The only cure in such cases of roller chain wear becoming extreme is to replace not only the chain, but also both the drive sprocket and driven sprocket.
It is advisable either to monitor the exact length of a drive chain (the generally accepted rule of thumb is to replace a roller chain which has elongated 3% on an adjustable drive or 1.5% on a fixed-center drive), or just replace it at established intervals of use to minimize wear on the sprockets. Thus, any savings in maintenance costs from skimping on lubrication result in increased costs for monitoring wear and for replacement. This need for frequent maintenance, comprising lubrication, assessing wear, and replacement of the chain and/or the sprockets, represents the major drawback of the utilization of roller chain.
The most common measure of roller chain’s strength is tensile strength
. Tensile strength represents how much load a chain can withstand under a one-time load before breaking. Just as important as tensile strength is a chain’s fatigue strength. The critical factors in a chain’s fatigue strength is the quality of steel used to manufacture the chain, the heat treatment of the chain components, the quality of the pitch hole fabrication of the linkplates, and the type of shot plus the intensity of shot peen coverage on the linkplates. Other factors can include the thickness of the linkplates and the design (contour) of the linkplates. The rule of thumb for roller chain operating on a continuous drive is not for the chain load to exceed a mere 1/6 tor 1/9 of the chain’s tensile strength, depending on the type of master links used (press-fit vs. slip-fit). Roller chains operating on a continuous drive beyond these thresholds can and typically do fail prematurely via linkplate fatigue failure.