The number of sprocket teeth is to improve the smoothness of the chain transmission and reduce the dynamic load. But the number of small sprocket teeth should not be too much, otherwise = i will be very […]
In order to improve the smoothness of the chain transmission and reduce the dynamic load, it is better to have a small number of teeth on the small sprocket. However, the number of teeth of the small sprocket should not be too much, otherwise i will be very large, which will cause the chain drive to skip teeth earlier. 工作一段时间后，磨损使销轴变细、使套筒和滚子变薄，在拉伸载荷F的作用下，链条的节距伸长。 After the chain works for a period of time, wear causes the pin to become thinner, and the sleeve and rollers become thinner. Under the action of tensile load F, the chain's pitch is extended. After the chain pitch becomes longer, the pitch circle d moves toward the tooth top 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 uniform and improve the service life, the number of sprocket teeth and the number of chain links are the best. If the quality is not guaranteed, the common factor should be as small as possible.
The larger the chain pitch, the higher the theoretical carrying capacity. However, as described in the previous section: the larger the pitch, the greater the dynamic load caused by the change in chain speed and the impact of the chain linking into the sprocket, but the chain load capacity and life will decrease. Therefore, a small-pitch chain should be used as much as possible in the design. The actual effect of selecting a small-pitch multi-row chain under heavy loads is often better than that of a large-pitch single-row chain.
Center distance and chain length
If the center distance of the chain transmission is too small, the wrap angle on the small sprocket will be small and the number of teeth of the sprocket meshing at the same time will be small. Generally, the center distance a = (30 ～ 50) p, and the maximum center distance ≤80p. The chain length is expressed by the number of links in the chain. The formula for calculating the belt length according to the belt drive can be used to derive that the number of links calculated from this must be rounded to an integer, preferably even. The formula above can be solved by the formula for finding the center distance a: In order to facilitate the installation of the chain and adjust the tension of the chain, the center distance should generally be designed to be adjustable; or a tensioning device should be provided.
Form of failure
There are several types of chain drive failures:
(1) Fatigue failure of the chain plate Under the repeated action of loose side tension and tight side tension, the chain plate will undergo fatigue failure after a certain number of cycles. Under normal lubrication conditions, the fatigue strength of the chain plate is the main factor limiting the load capacity of the chain transmission.
(2) The impact fatigue of rollers and sleeves is the first to bear the impact of the chain drive. After repeated impacts, after a certain number of cycles, the rollers and sleeves may suffer impact fatigue failure. This type of failure mostly occurs in medium and high speed closed chain transmission.
(3) If the glue between the pin and the sleeve is improperly lubricated or the speed is too high, the working surface of the pin and the sleeve may be glued. Gluing limits the limit speed of the chain drive.
(4) Chain hinge wear After the hinge wears, the chain link becomes longer, which is likely to cause tooth skipping or disconnection. Open drive, poor environmental conditions, or poor lubrication seals can easily cause hinge wear, which dramatically reduces the life of the chain.
(5) Overload breaking This breaking often occurs in low speed and heavy load transmission. Under a certain service life, starting from a failure form, an expression of limit power can be obtained. For the sake of clarity, a line graph is often used. It is the limit power curve corresponding to various failure forms under normal lubrication conditions. The shaded area in the figure is the area actually used. If the lubrication seal is bad and the working conditions are bad, the wear will be very serious, and its ultimate power will be greatly reduced.
The power that can be transmitted by each type A series roller chain when the recommended lubrication method is used. If the lubrication is not good or the recommended lubrication method is not used, the value in the figure should be reduced; when the chain speed v≤1.5m / s, it is reduced to 50%; when 1.5m / ss, it is reduced to 25%; when v> 7m / s and improper lubrication, the transmission is unreliable. When tensioning the device, the calculated center distance should be reduced by 2 ~ 5mm to make the chain have a small initial sag.