Composition of brake pads (friction materials)
There are various types of friction materials. The friction materials used for automotive brakes and clutches are almost all organic friction materials that use resin or rubber as adhesives. Up to now, nearly a hundred natural and synthetic materials have been discovered that can be used to manufacture organic friction materials. People choose several or more raw materials and mix them in a certain proportion to produce friction materials with different characteristics. The selection and proportion of raw materials are called formulas. Formula is the most important technical element in the production of friction materials. The formulas are diverse and ever-changing, but they are inseparable from their roots. In summary, any practical formula consists of the following four basic categories of materials:
Adhesive: Approximately 5%~25%
Enhancers: Approximately 20%~50%
Friction regulator: approximately 30%~60%
Process regulator: approximately 0.5%~1%
(1)Adhesive:
Such as thermosetting resins and rubber. The function of the adhesive is to bond the various components in the formula together, forming a solid with sufficient strength, appropriate hardness, and the highest possible temperature resistance and wear resistance. The temperature resistance of adhesives is the main factor affecting the performance of friction materials. Therefore, its type and dosage are key considerations in formula design.
(2)Reinforced fiber:
Such as asbestos fiber, natural mineral fiber, artificial mineral fiber, organic fiber, plant fiber, plain fiber, and carbon fiber. Reinforced fibers must be able to provide sufficient strength, have good heat resistance and wear resistance, and cannot scratch the coupling.
(3)Friction performance regulator:
There are many types of friction performance regulators with different uses, and different combinations must be made based on the type of resin and fiber selected, combined with usage requirements, to form a formula system that meets different purposes.
a/can improve the friction coefficient:
Commonly used are non-metallic minerals and their products. For example, barite (barium sulfate), wollastonite, alumina, bauxite (corundum), iron oxide red (black), coke powder, and so on. The main function of these raw materials is to provide sufficient friction coefficient for the brake pads, which can generate sufficient braking force not only in the room temperature range of around 100 ° C, but also in the high temperature range of 400-500 ° C.
b/stable friction coefficient:
The main raw materials include graphite, molybdenum disulfide, mica, talc, soft metals, etc. The hardness of these raw materials is very low, which plays a lubricating role on the friction surface, stabilizes the friction coefficient, and is used to protect the friction couple.
c\ organic friction performance regulator:
Commonly used ingredients include rubber, tire powder, etc. Adding these materials can help reduce the hardness and density of the material, stabilize the friction coefficient, and reduce wear, but excessive use can lead to thermal decay.
d\ metal powder (chips):
In some heavy-duty brake pad formulations, a certain amount of metal powder or chips is also added, commonly used including iron powder, copper powder (chips), aluminum powder, etc. The main purpose of adding metal components is to improve the high-temperature friction and wear performance of the material.
(4)Process regulator:
Such as release agents (stearic acid and other salts, oleic acid, etc.) and special additives (coupling agents, flame retardants, etc.). The purpose of these materials is to improve the processability of the product and increase its yield.
The four types of raw materials mentioned above do not play a single role in the formula. The subtlety of an excellent formula lies in precisely unleashing the potential of various material interactions, ensuring that the friction material has appropriate and relatively stable friction performance and long wear life within the temperature range of use, while meeting general requirements such as strength, hardness, thermal expansion, processability, and cost.
