Chain Maintenance
The frequency of conducting checks and chain maintenance is relative and depends on:
- the working environment – temperature, dustiness, humidity, draught and chemical gases
- the chain load – the maintenance must be more frequent at higher specific pressure on the chain joint
- the working conditions – continuous, single-shift or scheduled operation.
When servicing, it is necessary to concentrate particularly on:
- Fluent entering of the chain onto the chain wheel and fluent exit off of the chain wheel.
If a jerky movement occurs, it is probable that the chain is excessively extended or the chain wheel is damaged. Usual permitted operational chain extension is maximally 2% of the nominal length. - Planeness of Chain Gear
When checking the planeness of the whole gear, it is also necessary to check if there is whipping of the particular wheels and clearance in the placing. The biggest axial misalignment of the chain wheels or the deviation of the wheels is max. 3‰, i.e. 3mm/1m. - Chain Tension
In case of the use of a tension pulley, it is necessary to check its functionality and if it is not installed, it is necessary to check the sagging of the unloaded (lower) strand. The usual value is approximately 2% of the axial distance. - Appearance of the Chain and Chain Wheels
When checking the chain appearance it should be observed whether the chain is intact, if the chain plates loosen or not and if the rollers can rotate freely. We should also check if it experiences visible abrasion at any place. Great attention must be paid to connecting links, attachments and chain wheels. - State of Lubrication
When checking the lubrication it is necessary to ascertain if the chain is lubricated adequately, the lubrication does not contain abrasive or other impurities and if the lubrication does not degrade or if it is not dry. Should there be a light scouring when the roller turns, there are impurities or dry lubrication between the roller and the bush. When there are impurities or if dried lubricant, it is necessary to clean the chain of all the lubrication residues and re-lubricate the chain. Both the chain and the chain wheels should be thoroughly cleaned. Improperly lubricated chain also causes excessive extension of the chain.
Cleansing of the Chain
Cleansing of the chain must be conducted cold. To get rid of the old lubricant we need to use the appropriate solvent, for example petrol or trichloroethylene. The chain must be rinsed in a bath and rubbed off with a brush. Dry impurities must be disposed of by a hard scrub. In practice the use of petroleum or diesel turned out to be effective. After thoroughly cleaning the outer surface of the chain, the the chain must be left submerged in a solvent ( petroleum has a high capillarity) at least for 24 hours so that the impurities in the less accessible cavities also get removed. During this process the chain should be moved in the bath several times. After a thorough wash we take the chain out and check the cleanliness in the cavities - the polluted solvent mustn’t pour out. After drying no creaking must be heard from the friction surface which would indicate dry lubricant or impurities on the friction surfaces. If everything appears satisfactory, a visual check should be carried out of the cleanliness and intactness of the chain parts.
Grease Removal
Cleaning the chain with the help of petroleum or diesel leaves an oily film on the chain which must be disposed of by rinsing the chain in a chlorine or fluorine - based solvent.
Lubrication
An efficient way of chain lubrication which prolongs the time between individual lubrication of the chain is by submerging the chain into the bath with a dissolved lubricant. A plastic lubricant for sprocket chains can be used as a lubricant. The bath should have a temperature of at least 80°C and the whole chain must be heated so that the lubricant gets into all the cavities. As soon as the air bubbles cease to emerge, the chain is taken out of the bath and the excessive lubricant is left to drain away. After cooling the chain is packed to prevent pollution by impurities or dust. When choosing a method of lubrication it is necessary to take into consideration the speed of the chain. For the speed of up to 4 m/s it is optimal to lubricate the chain by putting 4-12 oil drops per minute onto the inner part of the chain ( i.e. between inner and outer plates and between inner plates and a roller ). Applying the oil onto the outer side of the chain is not suitable because centrifugal force can greatly hamper proper lubrication. Manual grease lubrication is also permissible. We can also use spray lubrication with high capillarity. With the speed of up to 7 m/sec, an oil bath with slinger disk is recommended. Lubrication with the help of oil box (approx. 20 drops / minute) is also acceptable. With the speed of over 7m / sec it is necessary to pay particular attention to lubrication. Pressure circulating lubrication is recommended, with the speed of over 12m/ sec lubrication by oil mist. The mentioned speeds are only for orientation. When transmitting high outputs the role of lubrication is even more significant. It is necessary to choose the lubricating grease or oil with regards to working conditions so that it does not come to lowering lubricating and conserving power.
Insufficient lubrication significantly reduces the operating life of the chain. The purpose of lubrication is:
- reduction in friction
- protection against corrosion
- off take of heat
- off take of impurities from friction surfaces
- reduction in noise
- reduction in heating up of the chain
- reduction in mechanical wear of particular parts of chain and chain wheels
- reduction in excessive extension of the chain.
