The concept of chain has been with us for many years. Early chains discovered in c. 2500 BC were for decorative purposes rather than for power transmission.  These chains were used to draw a bucket of water out of a well.

Sketches discovered as recently as 1965, produced by Leonardo da Vinci in the late 15th century, show examples of what looks incredibly like leaf chain, and even inverted tooth chain, although it is not known whether any of these were ever crafted.

 Leonardo da Vinci sketches (15th century)

By the middle of the 19th century, there were a number of chain designs available.  The hollow center, plate chain was used primarily for conveying applications and is the precursor to today’s hollow pin chain.  The hollow pins were used to attach rods to the chain.  Strap chain was comprised of metal links joined with leather straps.  This produced a chain which conformed well to the profile of the sprocket teeth but wore out quickly.  By the 1850s, with the introduction of steel Galle chain (invented by Frenchman André Galle in 1829), chain was beginning to find more practical applications.  This was given a tremendous boost in the 1860s with the advent of the bicycle and increasing demands from steam powered engines.  The need for a more efficient and durable design of chain, therefore, became of great importance. 

Hollow center, plate chain	Strap chain	Steel Galle chain

The problem with chain of the period was that it used only plates and pins, with the result that the thin articulating plate quickly wore and failed due to high bearing pressures.  Strength to weight ratios was low, and erratic pitch control and poor engagement caused early failure.  A more fundamental redesign was necessary.

In 1864, James Slater took out the first chain patent for a chain, which incorporated rollers on each pin.  This was known as bowl chain, and the incorporation of rollers tackled the problem with wear at engagement with the sprocket.

 James Slater bowl chain

In 1880, the bushing/roller concept was patented by Hans Renold.  This design introduced an additional member, the bushing, between the pin and the plate.  This design gave significant benefits.  First, the load transmitted between one link and the next was distributed over almost the full width of the chain, resulting in much lower bearing pressures.  Secondly, the improvement in gear engagement characteristics gave a much more reliable performance.  This innovation changed the prospects for transmission chain overnight, giving potential for higher transmission loads, lower wear, higher efficiency and lower noise, the result of which was the birth of the modern day chain design.

Little has changed in the appearance of the modern day chain when compared to the chain of the late 19th  century, although today a multitude of innovative features are designed into the chain to cope with the most demanding operating environments.  Development and refinement of manufacturing processes such as surface finishing and heat treatment along with the use of high-quality steels have brought further substantial improvements to chain life.

Types of Chain

Chain can be divided into categories depending on its construction and function.

Roller Chain
Suitable for thousands of applications.
Roller chain is also known as transmission or drive chain.

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Conveyor Chain
For applications where items need to be transported.
Conveyor chain is also known as engineered chain.

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Leaf Chain
For fork lift trucks and other lifting applications.

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Specialty and other chain types

Roller Chain Design and Components

Chain is a series of journal bearings joined together by side plates.  These bearings are where chain wear occurs and where lubrication is needed.

The chain roller can be either curled (made from sheet and curled round) or solid (made from solid round stock and extruded).  Solid rollers give improved resistance to shock loading and fatigue.  Curled rollers can have the tendency to open under heavy load.  Rollers are normally heat treated to improve wear performance.

Bushings, as with rollers, can be either curled or solid with the same benefits and drawbacks. They are normally heat treated to improve wear and sometimes tapered to ensure a straight inner diameter after assembly, which can reduce break in stretch and remove the need for initial adjustments.

Side plates are generally waisted; the wider the waist, the better the load-bearing characteristics.  Side plates tend to be heat treated to improve performance and shot peened to improve fatigue resistance.  Hole quality is also a significant factor for longer chain life.  Fatigue performance is improved by manufacturing processes such as multiple hole-punching operations and pre-stressing of the holes by ball drifting.

Pins tend to be ground to give a smooth surface for improved wear.  They are through-hardened for resistance to heavy loading or carburized for a hard surface finish but a softer more flexible core.  Once assembled in the outer plate, the pins are riveted for added security.

Chain Performance

The performance of a chain is governed by a number of key factors. The tensile strength is the most obvious, since this is the means by which a chain installation is roughly sized.  It should be noted that since steel has a yield strength of approximately 65% of the ultimate tensile strength, any load above this limit will cause permanent deformation, and this will result in rapid failure.

Reference to the S-N Curve Chart (Load vs. Cycles) below shows that at loads below this 65% line, finite life may be expected, and, at subsequent reductions in load, the expected life increases until the fatigue endurance limit is reached at around 10,000,000 loading cycles.

Loads below the endurance limit will result in infinite fatigue life.  The failure mode will then become wear related, which is the preferred mode of failure for chain as it can be monitored.  In practice, if a load ratio of tensile strength to maximum working load of 8:1 is chosen, then the endurance limit will not normally be exceed.  Careful consideration of the expected maximum or peak working loads should be given, since these are often much higher than the designer may think.

Factors Affecting Chain Life

If a chain is correctly selected, it should be capable of running for 10,000,000 loading cycles or 15,000 hours of continuous operation; however, there are many external factors which will affect the chain performance.

Lubrication is one of the most important factors affecting chain performance.  Insufficient or inadequate lubrication causes increased wear rate, chain seizures, and galling of pin surfaces.  Replacement of the chain is the only real answer to an incorrectly lubricated chain.  The four basic methods for lubricating chain drives are manual, drip, bath, and stream lubrication.  The recommended method is determined by the chain speed and power transmitted. 

The other main factors affecting chain performance are speed, power, and environment.  Many chains will fail due to overload. In these cases, failures will be seen by elongated plate holes prior to plate failure and pin bending prior to breakage.  These failures are solely due to an incorrectly selected chain and should never occur.  Fatigue failures can be seen on chains that are running above their maximum working load and again can be avoided if correctly selected.

Choosing the Correct Chain

The standard roller chain can be used in thousands of applications where fatigue and wear resistance is of prime importance; however, there are a number of occasions where standard roller chain is not suitable and must be replaced by “problem solving” chains.  In wet conditions, standard carbon steel chains will suffer from insufficient lubrication and corrosive attack from the environment.  There are various ways of reducing the effect of a wet environment and increasing chain performance: 

1. Use a lubricant with good hydro-capillary properties, which will help remove moisture from the bearing areas of the chain.
2. Take into account the corrosive environment in the selection calculations.  Increasing the chain size will reduce the bearing pressure and increase wear life.
3. Use corrosion-resistant plated chains, such as Renold Hydro Service™ Chain or Stainless Steel chain.

When heat-treated carbon steel chains are run in temperatures above their components tempering temperatures, a number of things should be considered:

1. Hardness of components will draw back (soften), and increased wear will be observed.
2. Chain lubricants can carbonize or scorch and break down.
3. Chain strength will reduce, and stiff joints will result.
4. Accept that strength will be reduced and up-size accordingly.

High-temperature lubricants can be used to eliminate the lubrication breakdown effect and improve the wear resistance; however, depending on actual temperatures the annealing (softening) of components will always be the main problem.  For temperature ranges above 480°F, it is preferable to use stainless steel chains.  The type and grade of stainless steel is dependent on the actual temperature that the chain is subjected to.

When using chains in low-temperature applications, problems will occur with brittleness of chain components leading to a reduction in shock resistance, stiffness of links caused by the freezing of condensation, and the reduction in performance of the chain lubricants.

The lower temperature limit for using a carbon steel chain is -40°F; however, the tensile strength should be reduced to allow for the reduction in transmission capabilities of the chain.  Stainless steel chain is recommended for temperatures below –40°F.  The type and grade of stainless steel, as with high-temperature applications, is, again, dependent on actual temperatures. 

In corrosive environments, there is the tendency for a reduction in fatigue performance due to corrosion pitting and oxidation.  There will also be a reduction in wear performance from abrasive corrosion debris in the bearing area and a reduction in strength.

In mildly corrosive environments, plated chains such as Renold Hydro Service™ chain can offer some protection without a reduction in tensile strength; however, in more severe environments, many different stainless and plastic materials could be used.

When using chains in abrasive conditions, the primary mode of failure is an increased wear rate due to abrasive particles collecting inside the journal bearings of the chain. Various methods can be adopted to improve chain performance in these applications:

1. Increasing the surface hardness of the pin and bushing such that the surface is harder than the abrasive particles.
2. Use a high wear resistance chain such as Renold Synergy® chain.
3. Use a chain with seals or ‘O’ rings to keep the particles out of the bearing area.
4. Use a chain with increased clearances so the particles can escape.

One of the most significant variations of the carbon steel chain is a maintenance-free or self-lubricating chain such as Renold Syno® chain.  Typically, these chains are used in food or hygiene-sensitive environments where it is impossible or impractical to lubricate the chain.  Generally, the main feature of these chains is a sintered steel bushing, which is oil impregnated.  Plates, pins and rollers can have additional surface treatments or plating processes added, which further prevent corrosion.  Note that some of these types of chain cannot accommodate the same power and speed as conventional carbon steel chains.  Some chain manufacturers will incorporate polymer sleeves between pin and bushing as the self-lubricating feature, but these tend to be typically on larger pitch chains.