The chain drive is a transmission method in which the movement and power of a drive sprocket having a special tooth shape is transmitted to a driven sprocket having a special tooth shape through a chain.
The main advantages of chain drive are:
- Compared with the belt drive, no the inelastic sliding and slipping phenomenon, the average transmission ratio is accurate, the work is reliable, and the efficiency is high;
- The transmission power is large, the overload capability is strong, and the transmission size under the same working condition is small;
- The required tension is small, and the pressure acting on the shaft is small;
- It can work in harsh environments such as high temperature, 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 with the belt drive, the chain drive has no elastic sliding and slipping, and can maintain an accurate average transmission ratio;
The required tension is small, the pressure acting on the shaft is also small, and the friction loss of the bearing can be reduced;
It can work under harsh environmental conditions such as high temperature and oil.
Compared with gear transmission, chain drive manufacturing and installation accuracy requirements are lower;
When the center distance is large, the transmission structure is simple.
The instantaneous chain speed and instantaneous transmission ratio are not constant, so the transmission is less stable and there is a certain impact and noise in the work.
The average transmission ratio of the chain drive is accurate, the transmission efficiency is high, and the distance between the shafts is adapted to a large range, which can be used in an environment with high temperature and high humidity;
However, the chain drive can only be used as a parallel shaft transmission, and its instantaneous transmission ratio fluctuates, and the transmission noise is large.
Since the links are rigid, there is a polygon effect (ie, motion non-uniformity).
This kinematics changes the instantaneous transmission ratio of the chain drive and causes additional dynamic loads and vibrations that must be considered when selecting the chain drive parameters.
Chain drives are widely used in transportation, agriculture, light industry, mining, petrochemical and machine tool industries.
The main parameters
(1) Number of sprocket teeth
In order to improve the smoothness of the chain drive and reduce the dynamic load, the number of teeth of the small sprocket is better.
However, the number of small sprocket teeth should not be too much.
After the chain has been in operation for a period of time, the wear causes the pin to become thinner, the sleeve and the roller to be thinner, and the pitch of the chain to be elongated.
After the chain pitch becomes longer, the pitch circle moves toward the top of the tooth when the chain is wound around the sprocket.
Generally, the number of chain links is even to avoid the use of transition joints.
In order to make the wear even and improve the life, the number of sprocket teeth is preferably the same as the number of links.
If the quality is not guaranteed, the common factor should be as small as possible.
(2) The pitch of the chain
The larger the pitch of the chain, the higher the theoretical carrying capacity.
However, as mentioned in the above section: the larger the pitch, the greater the dynamic load caused by the change of the chain speed and the impact of the chain link into the sprocket, which in turn reduces the chain carrying capacity and life.
Therefore, the design should use a small pitch chain as much as possible.
The actual effect of selecting a small pitch multi-row chain during heavy load is often better than selecting a large pitch single-row chain.
(3) Center distance and chain length
If the chain drive center distance is too small, the wrap angle on the small sprocket is small, and the number of meshed sprockets is small;
If the center distance is too large, the chain will be easily shaken.
Generally, the center distance a = (30 ~ 50) p, the maximum center distance ≤ 80p.
The chain length is expressed in terms of the number of segments of the chain.
According to the formula of the tape drive length, the number of links thus calculated must be rounded to an integer, preferably as an even number.
Using the above formula, we can solve the formula for finding the center distance a.
In order to facilitate the tension of the chain and the adjustment chain, the center distance should generally be designed to be adjustable;
Or there should be a tensioning device.