ROLLER CHAIN
Roller chain or bush roller chain is the type of chain drive most commonly used for transmission of mechanical power on many kinds of domestic, industrial and agricultural machinery, including conveyors, wire- and tube-drawing machines, printing presses, cars, motorcycles, and bicycles. It consists of a series of short cylindrical rollers held together by side links. It is driven by a toothed wheel called a sprocket. It is a simple, reliable, and efficient means of power transmission.
CONSTRUCTION OF THE CHAIN
Two different sizes of roller chain, showing construction.
There are 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 as well as correct tensioning.
VARIANTS DESIGN
Layout of a roller chain: 1. Outer plate, 2. Inner plate, 3. Pin, 4. Bushing, 5. Roller
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 but the smooth drive of a smaller pitch is required, the chain may be "siamesed"; instead of just two rows of plates on the outer sides of the chain, there may be three ("duplex"), four ("triplex"), 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 of plates called strands.
Roller chain is made in several sizes, the most common American National Standards Institute (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 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 horseshoe clip rather than friction fit, allowing it to be inserted or removed with simple tools. Chain with a removable link or pin is also known as cottered chain, which allows the length of the chain to be adjusted. Half links (also known as offsets) are available and are used to increase the length of the chain by a single roller. Riveted roller chain has the master link (also known as a connecting link) "riveted" or mashed on the ends. These pins are made to be durable and are not removable.
USE
An example of two 'ghost' sprockets tensioning a triplex roller chain system
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 toothed belt or a shaft drive, which offer lower noise level and fewer maintenance requirements.
The great majority of automobile engines use roller chains to drive the camshaft(s). Very high performance engines often use gear drive, and starting in the early 1960s toothed belts were used by some manufacturers.
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.
Chainsaw cutting chains superficially resemble roller chains but are more closely related to leaf chains. They are driven by projecting drive links which also serve to locate the chain onto the bar.
Sea Harrier FA.2 ZA195 front (cold) vector thrust nozzle - the nozzle is rotated by a chain drive from an air motor
A perhaps unusual use of a pair of motorcycle chains is in the Harrier Jump Jet, where a chain drive from an air motor is used to rotate the movable engine nozzles, allowing them to be pointed downwards for hovering flight, or to the rear for normal forward flight, a system known as Thrust vectoring.
CHAIN STRENGTH
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 for the chain load to not exceed a mere 1/6 or 1/9 of the chain's tensile strength, depending on the type of master links used (press-fit vs. slip-fit)[citation needed]. Roller chains operating on a continuous drive beyond these thresholds can and typically do fail prematurely via linkplate fatigue failure.
The standard minimum ultimate strength of the ANSI 29.1 steel chain is 12,500 x (pitch, in inches)2. X-ring and O-Ring chains greatly decrease wear by means of internal lubricants, increasing chain life. The internal lubrication is inserted by means of a vacuum when riveting the chain together.
CHAIN STANDARDS
Standards organizations (such as ANSI and ISO) maintain standards for design, dimensions, and interchangeability of transmission chains. For example, the following Table shows data from ANSI standard B29.1-2011 (Precision Power Transmission Roller Chains, Attachments, and Sprockets) developed by the American Society of Mechanical Engineers (ASME). See the references[8][9][10] for additional information.
ASME/ANSI B29.1-2011 Roller Chain Standard SizesSizePitchMaximum Roller DiameterMinimum Ultimate Tensile StrengthMeasuring Load25
ASME/ANSI B29.1-2011 Roller Chain Standard Sizes |
Size |
Pitch |
Maximum Roller Diameter |
Minimum Ultimate Tensile Strength |
Measuring Load |
25 |
0.250 in (6.35 mm) |
0.130 in (3.30 mm) |
780 lb (350 kg) |
18 lb (8.2 kg) |
35 |
0.375 in (9.53 mm) |
0.200 in (5.08 mm) |
1,760 lb (800 kg) |
18 lb (8.2 kg) |
41 |
0.500 in (12.70 mm) |
0.306 in (7.77 mm) |
1,500 lb (680 kg) |
18 lb (8.2 kg) |
40 |
0.500 in (12.70 mm) |
0.312 in (7.92 mm) |
3,125 lb (1,417 kg) |
31 lb (14 kg) |
50 |
0.625 in (15.88 mm) |
0.400 in (10.16 mm) |
4,880 lb (2,210 kg) |
49 lb (22 kg) |
60 |
0.750 in (19.05 mm) |
0.469 in (11.91 mm) |
7,030 lb (3,190 kg) |
70 lb (32 kg) |
80 |
1.000 in (25.40 mm) |
0.625 in (15.88 mm) |
12,500 lb (5,700 kg) |
125 lb (57 kg) |
100 |
1.250 in (31.75 mm) |
0.750 in (19.05 mm) |
19,531 lb (8,859 kg) |
195 lb (88 kg) |
120 |
1.500 in (38.10 mm) |
0.875 in (22.23 mm) |
28,125 lb (12,757 kg) |
281 lb (127 kg) |
140 |
1.750 in (44.45 mm) |
1.000 in (25.40 mm) |
38,280 lb (17,360 kg) |
383 lb (174 kg) |
160 |
2.000 in (50.80 mm) |
1.125 in (28.58 mm) |
50,000 lb (23,000 kg) |
500 lb (230 kg) |
180 |
2.250 in (57.15 mm) |
1.460 in (37.08 mm) |
63,280 lb (28,700 kg) |
633 lb (287 kg) |
200 |
2.500 in (63.50 mm) |
1.562 in (39.67 mm) |
78,175 lb (35,460 kg) |
781 lb (354 kg) |
240 |
3.000 in (76.20 mm) |
1.875 in (47.63 mm) |
112,500 lb (51,000 kg) |
1,000 lb (450 kg |
For mnemonic purposes, below is another presentation of key dimensions from the same standard, expressed in fractions of an inch (which was part of the thinking behind the choice of preferred numbers in the ANSI standard):
Pitch (inches) |
Pitch expressed
in eighths |
ANSI standard
chain number |
Width (inches) |
1⁄4 |
2⁄8 |
25 |
1⁄8 |
3⁄8 |
3⁄8 |
35 |
3⁄16 |
1⁄2 |
4⁄8 |
41 |
1⁄4 |
1⁄2 |
4⁄8 |
40 |
5⁄16 |
5⁄8 |
5⁄8 |
50 |
3⁄8 |
3⁄4 |
6⁄8 |
60 |
1⁄2 |
1 |
8⁄8 |
80 |
5⁄8 |
Notes:
1. The pitch is the distance between roller centers. The width is the distance between the link plates (i.e. slightly more than the roller width to allow for clearance).
2. The right-hand digit of the standard denotes 0 = normal chain, 1 = lightweight chain, 5 = rollerless bushing chain.
3. The left-hand digit denotes the number of eighths of an inch that make up the pitch.
4. An "H" following the standard number denotes heavyweight chain. A hyphenated number following the standard number denotes double-strand (2), triple-strand (3), and so on. Thus 60H-3 denotes number 60 heavyweight triple-strand chain.
A typical bicycle chain (for derailleur gears) uses narrow 1⁄2-inch-pitch chain. The width of the chain is variable, and does not affect the load capacity. The more sprockets at the rear wheel (historically 3-6, nowadays 7-12 sprockets), the narrower the chain. Chains are sold according to the number of speeds they are designed to work with, for example, "10 speed chain". Hub gear or single speed bicycles use 1/2" x 1/8" chains, where 1/8" refers to the maximum thickness of a sprocket that can be used with the chain.
Typically chains with parallel shaped links have an even number of links, with each narrow link followed by a broad one. Chains built up with a uniform type of link, narrow at one and broad at the other end, can be made with an odd number of links, which can be an advantage to adapt to a special chainwheel-distance; on the other side such a chain tends to be not so strong.
Roller chains made using ISO standard are sometimes called as isochains.