Mineral drag reducing materials in friction materials

Friction materials play the role of transmission, braking, deceleration and parking in sports machinery and equipment. They are widely used in automobiles, trains, airplanes, mines, metallurgy, chemical industry, electric power, engineering machinery, etc., among which the consumption in automobile industry accounts for more than 80%.

Friction material is a typical composite material, which is usually composed of bonding component (rubber or resin material), reinforcement component (organic or inorganic fiber) and filler component (mainly mineral powder). Among them, mineral materials can not only play the role of reinforcement, but also play the role of filler, and account for the largest proportion, and have the most significant impact on the performance and use efficiency of friction materials, which is the most important in friction engineering field Objects of concern.

Mineral drag reducing materials in friction materials

Friction reducing mineral fillers used in friction materials are mainly minerals with layered structure and low hardness, such as graphite, molybdenite (MoS2), talc, serpentine and hydrotalcite like. Among them, graphite, molybdenite and talc have been widely used, while serpentine and hydrotalcite like are the most promising mineral friction reducing materials.

graphite

Graphite is one of the crystalline minerals of carbon. Layered structure, the structural layer is composed of carbon atoms in hexagonal ring, the covalent bond (strong bond) between carbon atoms in the layer, and the molecular bond (weak bond) between the layers, which determines that the minerals are in sheet shape and low hardness.

The friction coefficient of graphite is less than 0.1 in the lubricating medium, and the larger the scale is, the smaller the friction coefficient is and the better the lubricating performance is. When graphite and Sb2S3 are used as brake pad materials, the friction stability will be improved obviously.

talc

As the filler of friction material, talc can absorb resin well (it has good binding ability with resin), improve the strength of block friction material, and have obvious anti-wear effect. However, at about 970 ℃, talc decomposes to form a mixture of 3mg SiO4 and SiO2, which can improve the strength and hardness of the friction material and show a good effect of strengthening and increasing resistance.

Molybdenite

Molybdenite is a layered sulfide mineral. At room temperature, the shear strength of molybdenite is very low and the friction coefficient is low (0.03-0.15). When the temperature is higher than 350 ℃ (in the air), molybdenite will undergo the following oxidation reaction to form MoS3, and release SO2 gas. The mass loss rate is up to 20%, and the friction coefficient increases. Under the protection of inert gas or vacuum, the friction coefficient of Molybdenite begins to increase obviously. Therefore, molybdenite is often used as high temperature friction regulator, but its price is high, and it is mostly used in high-grade friction material products.

Chrysotile

Chrysotile is a layered silicate mineral with hydroxyl group. The nano layered structure of chrysotile and weak interlaminar binding force make it show good lubrication performance. Its phase transformation products (forsterite and enstatite) at high temperature have high hardness and high strength. SiO2 produced by high temperature phase transformation can also promote the strength of friction materials. Therefore, as a friction material, chrysotile has a good performance at low and high temperature, and it is an excellent friction regulator. At the same time, the hardness of chrysotile is obviously higher than that of graphite, talc, molybdenite, etc., which has better effect of enhancing and reducing friction.

Hydrotalcite like compounds

Hydrotalcite like compounds, also known as hydrotalcite like compounds or layered bimetallic hydroxides, are a kind of layered compounds composed of positively charged metal hydroxides and negatively charged anions filled between layers. They have strong adsorption capacity and structure memory performance, and have significant application value as catalytic materials, ion exchange materials, adsorption materials and environmental materials.

In recent years, the research of hydrotalcite like materials as friction reducing materials has been highly valued. Mg Al hydrotalcite, CO Al hydrotalcite, Cu mg Al hydrotalcite and Ni mg Al hydrotalcite like materials have been successively carried out. It is found that they can significantly reduce the friction coefficient, wear and surface temperature of Fe based friction pairs.