How to judge the quality of passenger car brake discs?

To determine the quality of passenger car brake discs, you can start from the following aspects:

Appearance check

Surface flatness: the surface of high-quality brake discs is flat and smooth, and there should be no obvious unevenness, cracks, sand holes, air holes and other defects when touched by hand or observed with the naked eye. These defects may lead to uneven braking force when braking, affecting the braking effect.

Edge Integrity: The edges of the brake disc should be neat, with no missing corners, burrs or deformation. Incomplete edges may cause abnormal wear during braking and even damage the brake pads.

Coating quality: Some brake discs have an anti-corrosion coating on the surface, and a good coating should be even and firm, with no flaking or blistering. The coating not only prevents the brake disc from rusting, but also improves its wear and corrosion resistance.

Dimensional accuracy

Thickness Tolerance: The thickness of the brake disk should be in accordance with the vehicle manufacturer's regulations, and the thickness tolerance should be small. Generally speaking, the thickness tolerance of passenger car brake discs is between ±0.05mm and ±0.1mm. Uneven thickness will result in uneven force on the disc during braking, causing shaking.

Flatness Error: The flatness error of brake discs should be controlled within a certain range, usually no more than 0.03mm to 0.05mm. Poor flatness will cause poor contact between brake pads and brake discs, affecting the transmission of braking force.

Material Composition

Types of materials: common brake disc materials include gray cast iron, ductile iron, etc. High-quality brake discs are mostly made of high-performance cast iron. High-quality brake discs are mostly made of high-performance cast iron materials, such as alloy cast iron with added chromium, molybdenum, nickel and other alloying elements, which can improve the strength, hardness and wear resistance of the brake disc.

Metallographic organization: through metallographic analysis can observe the microstructure of the brake disc material, high-quality brake disc metallographic organization should be uniform, good graphite morphology, moderate pearlite content. For example, the pearlite content is generally more than 80%, and the graphite should be fine, uniform spherical or worm-like distribution, such an organization can ensure that the brake disc has good mechanical properties and friction properties.

Hardness test

Overall hardness: the hardness of the brake disc should meet the requirements of the relevant standards, the general hardness of gray cast iron brake discs in the HB170 - HB240 between the hardness of ductile iron brake discs in the HB200 - HB250 between. Hardness is too high, the brake disk will be too brittle and hard, easy to crack; hardness is too low, will lead to wear too fast.

Hardness uniformity: brake discs in different parts of the hardness difference should be small, the general requirements of the hardness difference does not exceed HB20 - HB30. uneven hardness will make the brake disc in the use of the process of localized abrasion serious situation, affecting the service life and brake performance.

Dynamic balance performance

Balancing precision: The dynamic balancing precision of high-quality brake discs is high, generally requiring the amount of residual unevenness to be controlled within 10g.cm to 20g.cm. Poorly balanced discs will vibrate when rotating at high speeds, which not only affects braking comfort, but also increases the wear and tear of the disc and suspension system.