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10/08/12

Chain Lubrication

Optimum chain lubrication provides safety and cost advantages. As machine elements, chains enable the transmission of movements and tractive forces. An optimum chain lubrication has a considerable effect on the wearing behaviour and with it on the service life of the chain.

Design and function of a chain

Today roller chains are used most often in technology applications. Their chain joints consist of inner and outer links connected with pins. The pins of the inner links are located in sleeves, which are in turn seated in a roller. This roller causes a reduction in the drive forces and the wear when operating the chain.

Chain drives consist of a drive pinion, a chain, a chain tensioner and a chain sprocket. The tractive force is transmitted to the chain via the drive pinion. This force is absorbed in the chain by both the links and the pins, which lie in linear contact to the bush­ings, and then have contact with the rollers via the bushings. The actual movement of the chain takes place during deflection over the chain sprocket.

Lubricating chains

An optimum chain lubrication has a considerable effect on the wearing behaviour and with it on the service life of the chain. Statistical tests have shown that approx. 60 % of all chain defects can be traced back to incorrect or insufficient lubrication.

To achieve effective lubrication, a sufficient quantity of lubricant must be brought into the chain joints during each lubricating process. Here the lubricant must pass through a narrow gap between the links to penetrate into the chain joint. The amount of lubricant required for this purpose is relatively small.

The lubricant must always be applied to the link edges. Lubrication can be effected by manual or drip lubrication for chain drives with a speed of up to approximately 3 m/s. In this case oil is applied by brush, oil can, spray or drip oiler. The lubricant should only be applied to the link top. Higher chain speeds require automatic lubrication systems.

With manual and drip lubrication, the quantity of lubricant should be sufficient to prevent rapid ageing of the lubricant within the relubricating intervals. With manual lubrication of a continuously running chain, relubrication should be carried out at least once a day or every eight operating hours if possible. 

Selection criteria for chain lubricants

The design of chains and their operation exclusively in the mixed friction range result in many problems in use. These include material abrasion due to line contact, oscillating movements and jolts, high surface pressures on the links and pins and the effects of en­vironmental influences, such as high or low tempera­tures, dust, and moisture on the function of the chain. This results in demanding requirements for the chain lubricants used.

Adhesive strengtht
The lubricant is not to be thrown off at the deflection points of the chain, where high centrifugal forces can occur.

Regenerability
Abrasive old lubricant residues and remains can result in heavy wearing. These must be dissolved by the lubricant and transported out of the joints.

High-temperature stability
As the decision in favour of a chain drive is often made due to high operating temperatures, the lubricant must retain its full functionality within these temperature ranges.

Corrosion protection
Is important for all chains used under corrosive conditions to prevent rust from forming on the chain elements.

Protection against media
This means the lubricant must be resistant to acids and alkaline solutions or aggressive gases.

Carbonisation tendency
Mineral oils tend to form residues at high tempera­tures which can considerably increase wearing or can block the chain joint up to the point of immobility.

Wetting and creep properties
As the friction points are located inside the chain and, especially on small chains, the joint access points are extremely narrow, the chain lubrication must have outstanding creep properties (high pene-tration capacity).

Wear protection
Due to operation in the mixed friction range, chains are subjected to heavy wearing. Therefore, wear protection is especially important. This takes place by adding solid lubricants, such as MoS2, graphite or PTFE, which act purely physically by separating the friction partners from each other. However, this can also be carried out with additive packages which cause surface refinement.

Noise damping
As the labour protection laws no longer allow any unnecessary sources of noise, it is important here to prevent this by choosing the right lubricant. Generally, it can be said that a higher basic viscosity also results in more effective noise avoidance.

Compatibility with plastics
Chains frequently come into contact with plastics or partially consist of plastic materials, e.g. O-ring chains. In this case, compatibility with the lubricant must be ensured.

Hydrocapillary effect
If a chain is exposed to water, the water will penetrate into the chain links. The task of the chain lubricant is to prevent corrosion, to creep under the water and to force it out of the chain.

Use in food processing technology
Lubricants for which the corresponding approvals of the NSF (National Sanitation Foundation) are available are suitable for chains used in the food processing industry.

Our technical service will answer any further question you may have on the subject of chain lubrication.

OKS speciality lubricants for chain lubrication
OKS offers you a broad range of speciality lubricants for chain lubrication under various conditions of use.

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