Axial Distance and Sagging of Chain
The recommended axial distance is forty times the pitch of the pins in the chain. One hundred and sixty times the pitch is usually considered the maximum.
For smooth operation the chain is required to be correctly pre-stretched, either by setting the sag rate of the free strand or by using a tension pulley. The chain sag should be so adjusted that the free strand shows minimum sag of 1% and maximum sag of 3% of the axial distance. When a tension pulley is used, this should be so placed after the driving chain wheel that the stretching force acts against the chain sag. The magnitude of the stretching force should reach 1% of the breaking load. The pulley should allow for a tension rate of 2.5 times the chain pitch. In this case the use of an offset link, which reduces the permissible load by up to 30%, should be avoided.
A good position for the shafts is next to each other with the axis in the horizontal position, or slanted with the height of one shaft offset, but the position of the shaft axes must always be in the horizontal position. Less suitable is the vertical arrangement of the chain wheel, i.e. the shafts positioned on top of each other. A horizontal arrangement with the upper chain strand unloaded is completely unsuitable. The axes of the chain wheel shafts must always be positioned horizontally.
When in operation, the chain should neither be pushed forward nor be exposed to any lateral force. The operating load causes a steady extension of the chain which should not exceed 2%. Otherwise the chain wheels will be subjected to excessive wear.
Requirements for Assembly and Maintenance of Transmission Gear
- When constructing a transmission gear, care should be taken to ensure that the upper chain strand exercises the pulling function while the lower strand is free.
- The chain must run smoothly on the chain wheel; when inserting the chain (roller) into the tooth gap of the chain wheel, it must be free of any jerky movement.
- If a tension pulley is used, it is placed behind the driving (small) wheel, it should have an odd number of teeth and engage at least 3 teeth of the chain.
- If no tension pulley is used, the chain should have its lower strand slightly sagged, the sag must, however, not exceed 3% (see "Axial Distance and Chain Sag").
- A chain too tightened exerts excessive load on the bearings, features greater resistance, causes faster wear of the chain wheels and its service life is compromised. On the contrary, a chain that is too slack causes, through its oscillations, an unstable run and in extreme cases the chain can even fall off the transmission gear.
- Where large axial distances are in question (of more than 60 times the pitch) the free chain strand should be supported by a pulley or a guide gib.
- Where vibrations occur on the tensioning assembly a vibration damper should be provided.
- The chain should not be pushed, twisted or exposed to lateral forces.
- In an application, the chain should not be extended by more than 2% or by more than 1% in case of high speed chains.
- The jointing and driving links are exposed to increased stress resulting in higher wear rate. During operation these chain elements should therefore be checked at regular time intervals.
- Chain wheels must not show any peripheral and, in particular, frontal run-out. The chain wheel design for roller and bush chains should be in line with the standard specifications (DIN 8192, DIN 8196, and ČSN 01 4811).
- The maximum permissible axial mismatch or error in parallelism of the chain wheels in the plate is 3 per mil, i.e.3 mm/m.
- By reason of the driving force distribution onto a larger number of chain wheel teeth, the girdle angle of the driving wheel should be 120° as a minimum and at least 90° in the case of larger driving wheels (having more than 25 teeth).
The new chain in the operation features settlement of the pressed joints for some time after installation. As this feature causes a slight increase in the clearance between the individual chain elements in the direction of the force action, the chain should be checked up on during the run- in period with regard to a possible excessive enlargement in the sag of the free chain strand. In view of their shorter run-in period, roller chains are pre-stretched after manufacture. In case of mounting a new chain on a chain wheel with a large number of teeth (over 60), there may be a situation where it is necessary to push the chain onto the wheel teeth or to tap it on with a wooden mallet.
The seeming reduction of the chain link pitch is caused by the lubricating grease filling the gaps between the roller, bush and pin. After some turns of the chain wheel the grease will be forced out and the chain will settle into the grooves.
The service life of the chain is significantly affected by dirt, dust, humidity and temperature, especially if it is lower than -10°C or higher than 160°C. Continuously lubricating the chain with oil keeps it free of dirt. When lubricating with grease, impurities may stick to it, making it an abrasive paste. In this case, it is very important to disassemble the chain as needed in order to degrease it, remove dirt and residuals and relubricate it with a suitable lubricant.
The recommended values of correction factors apply to easy loads. In case of more strenuous loads it is necessary to increase their value.
Table for selecting the correction factor depending on the operating temperature of the chain
|Operating temperature of the chain (°C)||Correction factor|
|-40 to -20||4,0|
|-20 to -10||3,0|
|160 to 200||1,3|
|200 to 300||2,0|
The chains should be well preserved and stored in a dry and well-ventilated place having a relative humidity of 54% to 75%. The store should be sealed off from admission of gases and dust. No chemicals are permitted to be stored together with the chains (see ČSN 02 3301, Art.44). The recommended storage temperature is between +5°C up to +40 °C.