Solving the problem of roller chain corrosion

Robert Young of Tsubaki UK provides an overview of the causes and the cures for chain corrosion.

Surface corrosion of roller chain is a problem faced frequently by both maintenance engineers and machine designers.

Caused by contact with process chemicals, salt, routine washdowns or simply exposure to the dismal UK weather, corrosion can have a significant impact on production efficiency.

Surprisingly, the problem is also becoming more common as maintenance schedules are being stretched and fewer production environments can tolerate contamination from traditional external lubricants.

The good news is that there is a range of solutions available to suit most applications, including many new and innovative products that are designed to solve specific problems.

Roller chain that is suffering from corrosion can be identified in a number of ways; there is often an audible indication such as unusual or loud noises, excessive chain vibration, poor chain articulation or very slack chain, or in some instances physical component failure.

A visual inspection will usually be enough to confirm that there is a problem - things to watch out for include any damaged or deformed components, especially the sides and edges of link plates, the edges of pins, and the surfaces of rollers.

Pin rotation caused by increased friction inside the roller and wear marks on sprocket teeth surfaces are also telltale signs.

Without careful lubrication simple water ingress can reduce standard carbon steel roller chain to a stiff, inefficient and wear prone drive element in a very short space of time.

Salt water exposure has a more detrimental effect, as do a wide range of acids, alkalis and other reactive compounds commonly used in industrial processes.

These substances even in weak dilution can cause roller chain surfaces to corrode, in turn causing stiff links and excessive wear, while pins and link plates can be weakened as the steel structure is attacked.

Weakened chain will typically become elongated due to wear, reducing precision and resulting in time consuming maintenance.

Extreme wear can also lead to catastrophic failures if the problem is not addressed; failures such as this inevitable cause downtime and can have serious safety implications.

Any corrosive problem is exacerbated by raised temperatures, increasing the speed of the reactive process particularly in liquids and vapours.

This is a typical scenario in the food industry where food processing often releases large amounts of steam and hot caustic washdowns are common.

Severe corrosion can reduce the life of standard roller chain from years to weeks, operating without lubricant or with inadequate lubrication will compound the problem and reduce wear life still further.

The result is an expensive drive system that will require excessive maintenance, frequent replacement and provide a troubled operating life.

This is neither desirable from a maintenance point of view or from an OEM designers perspective where a manufacturer will be judged on the performance of its product.

Milder environments such as outdoor applications inland where some form of basic weather protection is afforded such as an open canopy or guard, or, a factory environment where infrequent spillage exposes the chain to weak liquid splashes can be overcome by using good quality standard carbon steel chain cared for with regular lubrication.

Remote or hard to access areas will need to be fitted with an auto-lubrication system and regularly inspected to ensure lubrication is effective.

Water does enter grease and oil gradually and will reach the chain surface, but fresh applications of lubricant will ensure that the old lubricant is replaced and corrosion is minimised as much as possible under the circumstances.

In environments where lubrication cannot be used but moisture is occasionally present, paper processing for example, a lube-free sintered roller chain will provide basic corrosion resistance but also allow for "dry" operation, free from external lubricant but still maintaining low wear and high strength characteristics.

Tsubaki's Lambda lube-free chain is a good example; the first such chain on the market and now in its third generation the internal lubricating properties of the sintered steel make it ideal for indoor applications where wear life is a problem.

Slow moving, coastal and outdoor applications where roller chain is fully exposed to the elements require a nonstandard solution.

There are two possible routes depending on the load carrying capacity required of the chain; firstly there is carbon steel chain that has been manufactured with a hard wearing water resistant coating similar to hard anodising.

An example of this is Tsubaki WP coated chain; this product offers the advantage of water resistant properties equal to that of stainless steel chain while retaining the high strength characteristics of carbon steel chain.

Tsubaki's WP chain is unique in that it is a carbon steel chain designed to last in wet conditions, including those where salt is present.

This means that users in industries where moisture is a problem (ie water treatment and food processing) no longer have to specify costly oversized stainless steel chains to overcome problems where chains are failing frequently due to excessive corrosion.

Stainless steel chain is another option, but is not as strong as carbon steel chain and so has to be specified at least 20% larger, this has a corresponding weight and cost penalty.

Where, higher corrosion resistance is required along with some element of increased strength then AS stainless steel chain might be an option, having a 50% higher maximum allowable load than normal stainless steel.

In applications where the chain is actually submerged in water or weak solutions of detergent (common on theme park rides and commercial washing machinery) stainless steel chain is the ideal solution.

In this situation, the down side is usually that the chain can not be lubricated conventionally and excessive wear becomes a problem.

There is a another solution though; Tsubaki has developed LS chain, a stainless steel roller chain that employs engineered plastic sleeves between the pin and roller, the plastic isolates the wearing parts and is impervious to water corrosion, providing a long lasting, noncorroding solution.

Tsubaki has many years experience in developing suitable products for special environments and in instances where normal stainless steel does not have the necessary corrosion resistance then alternative variants such as NS (using SS316) and even titanium chain may be possible, particularly where high or low temperatures are required.

In drive chain applications where very high tensile strength is not required and mild but wet conditions prevail, typically in the food processing industry, there is another, lighter plastic and stainless steel combination chain available.

Plastic Engineered Chain uses stainless steel side plates and pins for corrosion protection and strength where it is needed but is much lighter thanks to a higher proportion of plastic in the links and rollers.

Resistant to detergents and steam as well as food ingredients such oils and lactic acid, this product can provide an ideal solution for avoiding corrosion in food processing machinery such as a bakery.

Harsher conditions such as frequent exposure to steam at high temperatures and more highly corrosive chemicals requires one of two solutions; the first and most obvious one is physical protection, sealed, enclosed guards that contain an oil bath are very effective and can often operate with standard carbon steel chain, providing the shaft seals are adequate.

There are a number of downsides to this solution though; the assembly is heavy and takes up a large amount of space, there is a high cost involved and maintenance access becomes both difficult and time consuming.

The second and more innovative solution is to employ a chain type that can operate in these conditions unguarded, thereby avoiding most of the cost and inconvenience of sealed guard enclosures.

DP chain from Tsubaki does exactly this, offering significantly improved anticorrosion performance compared with old style zinc plated and nickel plated chains.

In tests, DP treated chain endured salt-water (brine) spray for more than 500 hours, providing five times the anticorrosion performance of zinc-plated chain and 20 times the performance of nickel-plated types.

Tsubaki has developed groundbreaking materials and coating technology to enable it to manufacture new DP chain without the use of environmentally undesirable chromium and yet still produce a superior result.

The new process involves "double plating" firstly by galvanising the metal and then surface treating it with a special coating to protect against corrosive environments.

The coating does not reduce chain strength, but adds a tough protective shell that guards against surface scratches.

The process also produces a smooth and consistent surface finish, maximising resistance to wear.

Problem solving chains from Tsubaki are available direct from the company and locally from UK national distribution partners.

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