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Test basis of brake drum
The analysis was mainly based on GB/T 7216-2009 "metallography of gray cast iron", GB/ t13298-2015 "examination method of metal microscopic arrangement", GB/ t9439-2010 "gray cast iron", t7711-2007 "heat treatment of gray cast iron" and other standards.
The cause and proof of brake drum cracking and cracking
5 brake drums with cracks and cracking characteristics were selected as samples from 30 brake drums found in car maintenance factory, and the samples were sampled in the crack densely covered areas for test investigation. The sampling method is: cut a piece of steel ingot 2cm square in the dense crack area on the working surface touched by drum wall and brake lining (high temperature did not occur during cutting to prevent phase transition), mark the inner and outer wall of steel ingot and number corresponding samples. After the sample is prepared, it will be metallographically polished and corroded (5 nitric acid alcohol solution corroded for 15 seconds at room temperature). The following arrangement is obtained.
It is not difficult to find one or two dark patches in each sample after preliminary investigation on the appearance of corroded samples, and the patches are usually perpendicular to the crack extension direction and parallel to the direction of brake friction, and often in the middle direction of the crack. Therefore, it is not difficult to guess that the dark patch is the phase change arrangement formed by the local high temperature rapid formation caused by thermal imbalance during the work of brake drum, and the crack first starts from the phase change direction and extends to both ends perpendicular to the direction of brake friction, and ends at the arrangement without phase change.
How to solve the problem of brake drum cracking
Car brake drum is an important functional components of cars, is also the main components to measure the performance of cars, together with the daily maintenance is the first to be inspected parts, relevant materials appear, brake drum failure mainly has five ways: cracking, cracking, bottom, excessive wear, abnormal wear. The following mainly discusses one of the main causes of the first two cracking modes - thermal fatigue cracking caused by high temperature chill.
Brake drum sampling plan and inspection basis
1. Brake drum sampling plan
The brake drum in the sample of the product is origin of scrap product replacement for car repair shop, from shijiazhuang, the city of chaff, and positive definite three areas of six repair shop to buy 30 samples, the choice of the garage are relatively large, the vehicles involved more varieties, the product model is more, and the repair shop service goals are all over the country, so the acquisition has certain representativeness of sample as shown in figure 1.
The location and extent of damage to the sample are different, which then allows the profiler to better understand the quality hazard points of the sample.
Sample from appearance, most of the sample bearing damage is friction surface crack, and the causes of cracks in the onset of brake drum is, cars went down the mountain, high temperature, long brake drum will attack if wade, immediately after the downhill brake drum with water and a sharp contraction, so the friction brake drum surface crack along the axis direction of attack, the crack extension with continuous brake, brake drum rupture. Some brake drum in warranty found that its friction surface presents a piece of shiny spots, this is the brake drum in high temperature and water and constitute.