- Detail

Design and calculation of roller chain transmission

1 the main failure forms of roller chain transmission

the main failure forms of chain transmission are as follows:

(1) fatigue failure of chain plate under the repeated action of loose side tension and tight side tension, the chain plate will be fatigue damaged after a certain number of cycles. Under normal lubrication conditions, fatigue strength is the main factor limiting the bearing capacity of chain drive

(2) vulnerable parts of roller sleeve 5: impact fatigue failure of sheet metal. The meshing impact of chain drive is first borne by the roller and sleeve. Under repeated impact, after a certain number of cycles, the roller and sleeve will undergo impact fatigue damage. This kind of failure often occurs in medium and high speed closed chain drives

(3) when the gluing lubrication of the pin shaft and the sleeve is improper or the speed is too high, the working surface of the pin shaft and the sleeve will be glued. Gluing limits the limit speed of the chain drive

(4) the chain hinge is worn. After the hinge is worn, the chain link becomes longer, which is easy to cause tooth skipping or chain disconnection. When open transmission, bad environmental conditions or poor lubrication and sealing, it is very easy to cause hinge wear, which sharply reduces the service life of the chain Zhao Yu said

(5) overload breaking this kind of breaking often occurs in the transmission of low-speed heavy load or serious overload

2 rated power curve of roller chain transmission

(1) limit transmission power curve under certain service life and good lubrication conditions, the limit transmission power curve of various failure forms of chain transmission is shown in Figure 1. Curve 1 is the limit power of hinge wear under normal lubrication conditions; Curve 2 is the limiting power limited by the fatigue strength of the chain plate; Curve 3 is the limit power limited by the impact fatigue strength of the sleeve and roller; Curve 4 is the limit power of hinge gluing. The shaded part in the figure is the area actually used. If the lubrication is poor and the working condition is bad, the wear will be very serious, and the limit power will be greatly reduced, as shown by the dotted line in the figure

(2) allowable transmission power curve in order to avoid the above failure forms, figure 2 shows the allowable power curve of roller chain under specific test conditions

the test conditions are: Z1 ＝ 19, the number of chain links LP ＝ 100, the single row chain is horizontally arranged, the load is stable, the working environment is normal, the lubrication method is recommended, and the service life is 15000h; Relative elongation of chain due to wear Δ P/p is not more than 3%. When the actual use conditions are inconsistent with the test conditions, appropriate corrections should be made, so that the calculated power of the chain drive should meet the following requirements

in the formula P0 -- allowable transmission power (kw), which can be found in Figure 2

p-- nominal transmission power (kw)

ka -- working condition coefficient, see Table 1

kz -- coefficient of small sprocket number, see Table 2. When the working point falls on the left side of a curve vertex in Figure 1 (belonging to chain plate fatigue), check the table. When the working point falls on the right side of a curve vertex (belonging to roller and sleeve impact fatigue), check the table

kl-- chain length coefficient, according to the number of chain links, check table 3

kp-- multi row chain coefficient, refer to table 4

Table 1

Table 2

Table 3 correction coefficient KL

Table 4 working principle and advantages of multi row chain mechanical performance testing machine the advantages of mechanical performance testing machine the application of this kind of experimental property can make the strength and stiffness of the tested data get a positive coefficient Kp

3 design steps and transmission parameter selection of roller chain transmission

(1) transmission ratio I the transmission ratio of chain is generally ≤ 8, It is allowed to reach 10 at low speed and where the overall size is not limited. If the transmission ratio is too large, the wrap angle of the chain on the small sprocket is too small, and the number of teeth engaged is too small, which will accelerate the wear of the teeth, prone to tooth skipping, and damage the normal engagement. Generally, the wrap angle should not be less than 120., The recommended transmission ratio is i=2~3.5

(2) the number of sprocket teeth Z1 and Z2 should first reasonably select the number of small sprocket teeth Z1. The number of small sprocket teeth should not be too small. If it is too small, the transmission will be unstable, the dynamic load and chain wear will increase, the friction consumption power will increase, the specific pressure of the hinge will increase, and the working tension of the chain will increase. However, Z1 cannot be too large, because Z1 is larger and Z2 is larger, which not only increases the transmission size, but also easily causes chain disconnection after the hinge is worn, which will shorten the service life of the chain. Because if the hinge of the chain is worn, the chain pitch will become longer and the sprocket pitch d'will move to the tooth top. Pitch growth Δ P and pitch circle outward displacement Δ It can be seen from the relationship of D

Δ When p is constant, the more the number of teeth, the outward displacement of pitch circle Δ The larger the d 'is, the more likely it is to have tooth skipping and chain breaking

the number of small sprocket teeth of roller chain is selected according to the recommended range in the following table

the number of large sprocket teeth Z2 is determined by z2=iz1, and generally Z2 ≤ 120

when selecting the number of sprocket teeth, the problem of uniform wear should be considered at the same time. As the number of chain links is better to choose an even number, the number of sprocket teeth is better to choose a prime number or a number that cannot divide the number of chain links

(3) the increase of chain speed and the limit speed of sprocket is limited by dynamic load, so it is generally best not to exceed 12m/s. Refer to figure 2 for the optimal speed and limit speed of the sprocket. The speed close to the maximum allowable transmission power in the figure is the best speed, and the vertical line on the right side of the power curve is the limit speed

(4) chain pitch the larger the chain pitch is, the larger the size of each part of the chain and sprocket teeth is, and the greater the drag capacity of the chain is, but the speed unevenness, dynamic load, noise, etc. of the transmission will increase. Therefore, in the design, under the condition of sufficient bearing capacity, the single row chain with small spacing should be selected. When high-speed and heavy load, the multi row chain with small spacing can be selected

(5) the length of the chain and the center distance of any instrument. If the center distance of the chain drive is too small, the wrap angle on the small sprocket is also small, and the number of sprocket teeth engaged is also reduced; If the center distance is too large, it is easy to make the chain shake. Generally, the center distance a= (30~50) P and the maximum center moment Amax ≤ 80p can be taken

the length of the chain is usually expressed by the number of links LP. According to the formula of calculating belt length by belt transmission, the central moment of A-chain transmission in

formula can be derived

the number of nodes of the chain calculated from this must be rounded to an integer, and preferably even. Then calculate the actual center moment according to the number of rounded chain links with the following formula:

in order to facilitate the installation of the chain and adjust the tension of the chain, the general center distance is designed to be adjustable. If the center distance cannot be adjusted and there is no tensioning device, the calculated center distance should be reduced by 2~5mm. This allows the chain to have a small initial sag to maintain the tension of the chain drive

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