Why does overheating of brake pads cause weak braking ability?
Because overheating will cause the thermal attenuation of the brake pad friction material, resulting in the decrease of the brake disc friction.
Thermal attenuation is a phenomenon that the friction coefficient decreases when the initial speed of braking is high, the pressure increases, and the temperature of the friction pair increases due to frequent braking. Thermal attenuation will directly affect the safety of vehicles and machinery. Serious thermal attenuation may even cause brake failure and cause accidents. The causes of heat attenuation are complex. Let's briefly introduce them.
The heat attenuation is particularly obvious in polymer based friction materials, because such friction materials will use resins as binders. However, phenolic resin will undergo thermal decomposition at high temperature to decompose phenol and other liquids. These liquids will adhere to the friction plate surface to form a lubricating film. On the other hand, at high temperature, the resin will decompose carbon dioxide and other gases. The oxide film on the metal surface of the coupling is easy to adsorb gas, and finally a layer of air cushion film will be formed between the friction plates. The oxide film here is also one aspect of the decline in friction performance. Under high temperature, the metal surface is easy to oxidize and form an oxide film. This oxide film has low strength, is hard and brittle, and is easy to crack under the action of friction. It peels off from the surface and becomes abrasive particles, which not only reduces the effective area of the friction plate, but also further damages the surface. In some metal friction materials, low melting point metals may melt and precipitate, forming a lubricating film on the surface of the friction plate, reducing the friction performance. For example, the melting point of tin is only 231 ° C. when the brake pad is overheated, tin in it may melt and precipitate.
The reasons for the thermal deterioration of friction materials are still relatively complex. The above is only a general introduction. Please remember to replace the brake pads in time.