The analysis of brake drum work surface cracking
In the automobile brake system, brake drum and the brake disc isthe main parts, wheel brake large cars generally is a drum brake,disc brake applied in cars and light-duty vehicles. In the use of the process of automobile brake drum casting, happened to work and generate crack, brake drum rupture phenomenon, a serious threat to the safety of people. In order to improve the reliability of the brake drum and the brake disc used, put forward morerequirements on casting materials, iron materials to meet or exceed the HT250 standard, wood hardness (brake shoe work) over 180HBS. Some of the heavy truck brake drum, using vermiculariron material.
A method and the results of test force
Macroscopic examination
Through observation, found that the brake drum work cracking.Brake brake brake shoe (or brake caliper) and brake drum work and generate friction, generate heat in the friction at the same time,so that the brake drum brake and brake in cycles of Bu producedcracking, the formation of thermal fatigue. Also in the brake drumwork and crosscutting and found on the shrinkage of larger, near the work but not have osteoporosis in stereo microscope Bu now,this is the tissue defect of the brake drum casting. In the process of using these defects will become the source of fatigue. In addition,the brake drum cylindrical without processing, easy to cause the casting wall thickness unevenness, leading to the jitter.Macroscopic observation showed that, should belong to thethermal fatigue crack damage failure.
Chemical composition analysis
On the brake drum of the chemical constituents of comparative analysis.
Analysis shows that, the brake drum material composition belongs to grey cast iron, in which Si and P element and Mn elementcontent is high, slightly lower. In general, the mass fraction of ironnot as the acceptance criterion of casting iron, but the qualitativedecision score is effect of microstructure and mechanical properties of factors of cast iron. The chemical composition and the standard of the brake drum rounding.
Fracture analysis
Open a maximum crack, preparation of TEM sample, observed byultrasonic cleaning in SEM Bu, found on the fracture originated in the work of Bu microporous, in the crack propagation phaseobserved toughness fatigue striation, instantaneous fracture to quasi cleavage plus dimple (Shao Liang), micro fracture analysis confirmed that the brake drum is fatigue fracture.
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