There are many types of friction materials. The friction materials for automotive brakes and clutches are almost all organic friction materials using resin or rubber as a binder. Up to now, nearly 100 kinds of natural and synthetic materials that can be used to manufacture organic friction materials have been found. Several or a dozen materials are selected and mixed in a certain ratio to produce friction materials having different characteristics. The selection and blending ratio of raw materials is called formula. Formulation is the most important technical element in the production of friction materials.
The formula is varied and varied, but it never changes. To sum up, any practical formula is composed of the following four basic types of basic materials:
Adhesive: About 5%~25% Reinforcer: About 20%~50% Friction modifier: about 30%~60% Process conditioner: about 0.5%~1%
(1) Adhesives: such as thermosetting resins and rubber. The role of the binder is to bond the components of the formulation together to form a solid of sufficient strength, proper hardness, and as high a temperature and abrasion resistance as possible. The temperature resistance of the adhesive is a major factor affecting the performance of the friction material. Therefore, its type and amount are the key considerations in formula design.
(2) Reinforcing fibers: such as asbestos fibers, natural mineral fibers, man-made mineral fibers, organic fibers, plant fibers, plain fibers, carbon fibers. The reinforcing fibers must be able to provide sufficient strength, have good heat resistance and wear resistance, and must not scratch the dual.
(3) Friction performance modifiers: There are many types of friction performance modifiers, and their use is different. It is necessary to make different combinations for the selected resin and fiber types, and to form a formulation system that meets different uses.
a\ can increase the coefficient of friction: Non-metallic minerals and their products are often used. For example: barite (barium sulfate), wollastonite, alumina, alumina (corundum), iron oxide red (black), coke powder, and the like. The main function of these raw materials is to make the brake pads have a sufficient friction coefficient, which can generate sufficient braking force not only in the normal temperature section of about 100 ° C, but also in the high temperature section of 400 to 500 ° C.
b\ Stable friction coefficient: The main raw materials are graphite, molybdenum disulfide, mica, talc, soft metal and so on. These materials have very low hardness and provide lubrication on the friction surface, which stabilizes the friction coefficient and is used to protect the friction pair.
c\ Organic friction performance modifier: Commonly used rubber parts, tire powder, etc. The addition of these materials helps to reduce the hardness and density of the material, stabilize the coefficient of friction, and reduce wear, but excessive use can cause thermal decay.
d\ Metal powder (chip): In some heavy-duty brake pad formulations, there is also a certain amount of metal powder or chips added. Commonly used are iron powder, copper powder (chip), aluminum powder and so on. The metal component is added primarily to improve the high temperature friction and wear properties of the material.
(4) Process modifiers: such as mold release agents (stearic acid and other salts, oleic acid, etc.) and special additives (coupling agents, flame retardants, etc.). The role of these materials is to improve the processability of the product and increase the yield of the product.
The above four types of raw materials do not play a single role in the formulation. The subtlety of the excellent formula is that the potential of various material interactions is just right, so that it meets the general requirements of strength, hardness, thermal expansion, processing technology, cost, etc., while ensuring that the friction material is suitable within the operating temperature range. Relatively stable friction performance and long wear life.