1.2.1 Power Transmission Uses
Power transmission machines use either chains, gears, or belts. Table 1.1 provides a comparison of typical applications.
Usually, chain is an economical part of power transmission machines for low speeds and large loads. However, it is also possible to use chain in high-speed conditions like automobile engine camshaft drives. This is accomplished by devising a method of operation and lubrication.
Basically, there are lower limits of fatigue strength in the gear and the chain, but not in the belt. Furthermore, if a gear tooth breaks, the gear will stop at the next tooth. Therefore, the order is gear > chain > belt in the aspect of reliability.
In most cases:
- An increase in gear noise indicates that the end of the service life is near.
- You will know that the chain is almost at the end of its life by wear elongation or an increase in vibration caused by wear elongation.
- It is difficult to detect toothed-belt life without stopping the machine and inspecting the belt carefully.
It is possible to decrease gear noise by adjusting the gears precisely or by adapting the drive to a helical or double helical gear. Both of these are expensive, and thrust load may occur with the use of helical gears.
Chain is more suitable to long-term continuous running and power transmission with limited torque fluctuation. Gears are more fit to reversing or intermittent drives.
The greater the shaft center distance, the more practical the use of chain and belt, rather than gears.
|Type||Roller Chain||Tooth Belt||V Belt||Spur Gear|
|Surrounding Condition||Avoid Water, Dust||Avoid Heat, Oil, Water, Dust||Avoid Heat, Oil, Water, Dust||Avoid Water, Dust|
(High Speed/ Low Load)
(Low Speed/ High Load)
Less Durability Due to Less Engagement
|Excess Load onto Bearing|
Generally, under the same transmission conditions, the cost of toothed belts and pulleys is much higher than the cost of chains and sprockets.
See the following features and points of notice about roller chain transmission.
Features of Chain Drives:
- Speed reduction/increase of up to seven to one can be easily accommodated.
- Chain can accommodate long shaft-center distances (less than 4 m), and is more versatile.
- It is possible to use chain with multiple shafts or drives with both sides of the chain.
- Standardization of chains under the American National Standards Institute (ANSI), the International Standardization Organization (ISO), and the Japanese Industrial Standards (JIS) allow ease of selection.
- It is easy to cut and connect chains.
- The sprocket diameter for a chain system may be smaller than a belt pulley, while transmitting the same torque.
- Sprockets are subject to less wear than gears because sprockets distribute the loading over their many teeth.
Points of Notice:
- Chain has a speed variation, called chordal action, which is caused by the polygonal effect of the sprockets.
- Chain needs lubrication.
- Chain wears and elongates.
- Chain is weak when subjected to loads from the side. It needs proper alignment.