Reasons for easy loosening of brake shoes and linings[汽车修理知识]

CarThe braking performance is directly related to traffic safety. Many major traffic accidents are often related to too long braking distance and sideslip during emergency braking. About 40% of major accidents are the cause of braking. In view of this, this article makes a few simple analyses on the reasons why the automobile brake shoes and brake shoe linings are easy to loose after riveting.
The connection and fixation between the truck brake shoe and the brake shoe lining generally adopts the method of riveting (the brake shoe and the brake shoe lining of the car are mostly bonded), and the semi-hollow countersunk aluminum rivet is mainly used. The size of riveting is shown in the figure below.
There are many reasons for the loosening of brake shoes and brake shoe linings, and specific problems should be analyzed in specific handling. The common causes and treatment measures are as follows:
1. When the brake shoe lining is riveted, due to careless operation, the inner arc fitting surface of the brake shoe lining exceeds the allowable gap. When riveting the brake shoe lining, you must pay attention to the brake shoe lining and There should be no debris between the brake shoes, and the arc surface of the brake shoes must be derusted to make the riveting meet the requirements.
2. Due to the repeated drilling and riveting of the brake shoe lining, the wear of the rivet hole of the brake shoe increases. When riveting the brake shoe lining, the size of the rivet has been determined. When the brake shoe lining is riveted on the brake shoe, the clearance between the rivet and the rivet hole on the brake shoe is too large; It looks like it has been riveted on the surface, but when the car is braked, the relative movement of the two will produce shearing force on the rivet. After repeated braking, the rivet can be cut to make the brake shoe lining Fall off. Therefore, whenever the wear of the rivet hole on the brake shoe increases, the brake shoe should be replaced in time. If the brake shoe rivet hole is slightly worn, you can tap the rivet lightly when riveting the brake shoe lining to slightly expand the diameter of the rivet and reduce the matching gap between the brake shoe rivet hole and the rivet. Carry out riveting so that the brake shoe lining will not fall off.
3. The curvature of the brake shoe lining and the brake shoe is not correct. There are three reasons for this situation. One is that the loneliness of the brake shoe lining does not meet the requirements; the other is that the curvature of the brake shoe does not meet the requirements or the brake shoe is deformed; and the other is the brake shoe lining and the brake. The arc of the hoof does not meet the requirements. Therefore, when riveting the brake shoe lining, check first to see if the brake shoe lining and the brake shoe are within the allowable gap, otherwise, the brake shoe or brake shoe lining that does not meet the requirements should be dealt with. Replace the film.
4. After the brake shoe lining is drilled, a 2/3 depth reaming must be carried out, and the angle of the reaming drill bit must be adapted to the r angle at the rivet mouth. Generally, the r angle of semi-hollow countersunk head rivets is 120°±2°, so when performing 2-3 depth reaming, the drill bit angle must also be ground to 60°±2° to ream the rivet and brake shoe lining. It is consistent with each other so as not to produce gaps during riveting. In actual work, if you do not pay attention to this problem, but only pay attention to the selection of a drill bit of the same size, regardless of the drill bit angle, carry out deep hole reaming, which will cause poor contact of the riveting working surface and cause the brake shoe lining to fall off .
After the brake shoe lining is drilled, during deep drilling, its reaming center must be concentric with the original hole center, otherwise it will be difficult to match the brake shoe arc when the brake pad is riveted, resulting in a large gap . At the same time, since the deep reaming hole is not concentric with the original hole, the riveting angles of the rivets are different when the brake shoe lining is riveted, so the force direction is different during braking, and the rivet on the same brake shoe lining is not stressed during braking. Both. Over time, the rivet is cut by shearing force, causing the brake shoe lining to fall off. After the brake shoe lining is drilled, the reaming depth is inappropriate, which will also cause the brake shoe lining to fall off. The reaming is too deep (the reaming depth is more than 2/3), it is easy to make the brake shoe lining break at the bottom of the reaming inside the arc when the brake shoe lining is working, and the brake shoe lining will fall off; the reaming is too shallow (reaming depth) Less than 2/3), the extension length of the rivet is not enough, the riveting tightness of the brake shoe lining is affected, and the brake shoe lining is also easy to fall off.
5. The hole size of the brake shoe lining is inappropriate. Drilling is too large, causing a large gap between the rivet and the hole. The riveted brake shoe lining will slide relative to the brake shoe during braking, causing the brake shoe lining to loosen and fall off; If the rivet is too small, it will be difficult to insert the rivet into the brake shoe lining, and it is easy to burst at the bottom of the inner arc of the brake shoe lining.