A chain drive is a method of transmitting movement and power from a drive sprocket with a specialized tooth shape to a driven sprocket with a matching tooth shape, using a chain as the intermediary component.
The main advantages of chain drive are:
Compared to belt drives, chain drives have several advantages. They do not experience inelastic sliding or slipping, resulting in accurate transmission ratios, reliable operation, and high efficiency.
Chain drives also have the ability to transmit large amounts of power, strong overload capability, and a small transmission size under the same working conditions. Additionally, they require less tension and place less pressure on the shaft.
Finally, chain drives can operate in harsh environments with high temperatures, humidity, dust, and pollution.
The main disadvantages of chain drive are:
- Can only be used for transmission between two parallel shafts;
- High cost;
- Easy to wear and easy to stretch;
- Poor transmission stability;
- Additional dynamic loads, vibrations, shocks and noise are generated during operation and should not be used in drives that are rapidly reversed.
Compared to belt drives, chain drives do not have elastic sliding or slipping, and can maintain an accurate average transmission ratio. They require less tension, exert less pressure on the shaft, and reduce friction loss in the bearing. Chain drives have a compact structure and can operate under harsh environmental conditions, such as high temperature and oil.
In comparison to gear transmission, chain drives have lower manufacturing and installation accuracy requirements. They have a simple transmission structure when the center distance is large. However, the instantaneous chain speed and transmission ratio are not constant, leading to less stable transmission and some impact and noise during operation.
Despite these drawbacks, the average transmission ratio of chain drives is accurate, and the transmission efficiency is high. They can adapt to a large range of distances between shafts and can be used in environments with high temperature and humidity. However, chain drives can only be used for parallel shaft transmission and have fluctuating instantaneous transmission ratios and high transmission noise.
Since the links in chain drives are rigid, they experience a polygon effect, resulting in non-uniform motion.
Kinematics can alter the instantaneous transmission ratio of chain drives, leading to increased dynamic loads and vibrations. As such, these factors must be taken into account when selecting appropriate chain drive parameters.
Chain drives have a broad range of applications, including in transportation, agriculture, light industry, mining, petrochemicals, and machine tools.
The main parameters
(1) Number of sprocket teeth
To improve the smoothness of the chain drive and reduce the dynamic load, it is better to have a smaller number of teeth on the small sprocket. However, the number of teeth on the small sprocket should not be too high.
Over time, wear and tear can cause the chain’s pins, sleeves, and rollers to become thinner, elongating the pitch of the chain. As a result, when the chain is wrapped around the sprocket, the pitch circle moves towards the top of the tooth.
To avoid using transition joints, it’s generally advisable to have an even number of chain links. For even wear and an improved lifespan, the number of sprocket teeth should ideally match the number of links.
If the quality of the chain drive is uncertain, the common factor between the number of teeth on the small sprocket and the number of chain links should be as small as possible.
(2) The pitch of the chain
The theoretical carrying capacity increases with an increase in the pitch of the chain. However, as mentioned in the preceding section, a larger pitch results in a greater dynamic load caused by the change in chain speed and the impact of the chain link into the sprocket. This, in turn, reduces the chain’s carrying capacity and lifespan. Therefore, it is advisable to use a small pitch chain whenever possible.
In fact, when handling heavy loads, choosing a small pitch multi-row chain often proves to be more effective than selecting a large pitch single-row chain.
(3) Center distance and chain length
If the center distance of the chain drive is too small, the wrap angle on the small sprocket will be small, and the number of meshed sprockets will also be small. Conversely, if the center distance is too large, the chain will be prone to shaking.
A general rule of thumb for determining the center distance is to use the formula a = (30 ~ 50) p, with a maximum center distance of ≤ 80p.
The length of the chain is typically expressed in terms of the number of chain segments. Using the formula for determining tape drive length, the number of links calculated should be rounded to an integer, preferably an even number.
With the above formula, it is possible to calculate the center distance a.
To facilitate chain tensioning and adjustment, the center distance should generally be designed to be adjustable or include a tensioning device.