Causes of sprocket wear

The reasons for the severe wear of the sprocket chain pocket are as follows:

(1) The greater the adhesive wear load, the higher the surface temperature, and the more serious the adhesion phenomenon. For a metal material with a certain hardness, the wear test is carried out under different pressures to obtain the relationship between the wear rate and the pressure. When the pressure reaches more than 1/3 of the material hardness, severe wear will occur. According to the stress distribution diagram, it can be known that the maximum stress contact point is the maximum pressure, and its value is 884.4 MPa. Because the quenching hardness at the chain nest is HRC48~52, the corresponding hardness value is 4800MPa. Therefore, the pressure is far less than 1/3 of the material hardness, so adhesive wear is not the main form of sprocket wear.

(2) Contact fatigue wear

The friction pair of sprocket and chain is under alternating contact stress, and fatigue pitting is easy to form on its friction surface. The index for judging the fatigue strength of metal contact is the contact fatigue limit, that is, the maximum stress at which pitting does not occur under a certain number of stress cycles. The contact fatigue limit of 40Cr after surface quenching treatment is σ0H=HRC17 +200, calculated as σ0H=1016MPa. According to the stress distribution diagram, the maximum stress value of the sprocket socket is 884.4 MPa. Its value is very close to the allowable contact fatigue limit of the surface of the sprocket, and it is relatively easy to cause pitting failure at the maximum stress. However, due to the poor lubrication conditions of the sprocket and the chain, pitting corrosion has not been formed in time, and wear has already been caused. At this time, the main damage form is wear rather than pitting corrosion. Contact fatigue wear is the main form of sprocket wear, which basically determines the service life of the sprocket.

(3) Abrasive wear

Because the chain is inevitably in contact with coal powder, a little coal powder sticks on it and is brought to the contact point of the sprocket chain socket. The coal powder contains a little sharp and hard sand, which will cause the surface material of the sprocket to fall off during the friction process. This is abrasive wear. Abrasive wear is related to the hardness of the friction material and the hardness of the abrasive. From the diagram of the influence of abrasive hardness on wear, it can be seen that when the hardness of the abrasive is close to that of the friction material, the friction material will wear at a high speed. Because the coal powder is mixed with a little sharp and hard sand, this is also one of the main reasons for accelerating the wear of the sprocket.