A Comprehensive Guide to Brake Pad Friction Materials: Types, Characteristics, and Future Trends
I. Types and Characteristics of Friction Materials
(1) Asbestos Friction Materials
Asbestos was once a commonly used friction material in brake pads. It has high strength and heat resistance, capable of withstanding temperatures up to 316°C, and is relatively inexpensive, so it was widely used in the early days. However, asbestos has been medically proven to be a carcinogen. Its needle-like fibers can easily enter the lungs and remain there, causing irritation and potentially leading to lung cancer, with a latency period of 15-30 years. Moreover, asbestos has poor thermal conductivity, and the heat accumulated from repeated braking can heat up the brake pads, thereby changing braking performance and even causing brake failure. Therefore, asbestos friction materials have now been basically phased out.
(2) Semi-Metallic Friction Materials
Semi-metallic friction materials are often used in disc brake pads for cars and heavy-duty vehicles. Their formulations typically contain 30%-50% ferrous metal substances, such as steel fibers, reduced iron powder, and foam iron powder. They have good heat resistance, high power absorption per unit area, and high thermal conductivity, which can meet the braking requirements of cars during high-speed and heavy-load operation. However, they also have drawbacks such as high braking noise and brittle cracking at the edges. In low-temperature environments, they can also cause significant wear on the surface of brake discs or drums.
(3) Non-Asbestos Organic (NAO) Friction Materials
In a broad sense, NAO friction materials are non-asbestos and non-steel fiber friction materials (now disc pads also contain a small amount of steel fibers). The base materials are usually a mixture of two or more fibers (mainly inorganic fibers, accompanied by a small amount of organic fibers). They have good friction coefficients and heat resistance, and can adapt to the braking needs of various vehicle models. Compared with asbestos brake pads, NAO brake pads perform better in terms of wear resistance and noise, have a significantly longer service life, and are beneficial to extending the service life of brake drums and discs. However, they do not have the good thermal conductivity and high-temperature controllability of semi-metallic brake pads.
(4) Ceramic Friction Materials
Ceramic brake pads are composed of ceramic fibers, iron-free fillers, adhesives, and a small amount of metal. They have the advantages of high temperature resistance, no noise, no dust, no corrosion to wheel hubs, long service life, and environmental protection. They are widely used in the Japanese and North American automotive markets, and new European models have also begun to be equipped with them. However, due to the high price of ceramic friction materials, they have not been well developed in the domestic market yet, and domestic consumers' attention to comfort and environmental protection needs to be improved.
(5) Carbon Fiber Friction Materials
Using carbon fiber as the reinforcing material, carbon fiber has the characteristics of high modulus, good thermal conductivity, and heat resistance, making carbon fiber friction materials the best-performing among various types of friction materials. They have high power absorption per unit area and low specific gravity, making them particularly suitable for the production of aircraft brake pads. Some high-end cars abroad also use them. However, due to their high price, their application range is limited, and their output is small.
II. Selection of Friction Materials for Different Vehicle Types
Different vehicle types have different focuses on the selection of brake pad friction materials due to their different uses, performance, and design requirements.
• Cars: They usually focus on comfort and braking stability, and generally choose semi-metallic friction materials or NAO friction materials. Semi-metallic friction materials are relatively affordable and have good braking performance; NAO friction materials are more environmentally friendly, have low noise, and can improve the driving experience.
• Trucks and heavy-duty vehicles: They need to bear greater weight and braking pressure, so they have extremely high requirements for the heat resistance and wear resistance of friction materials. Semi-metallic friction materials can meet the braking needs of such vehicles during heavy loads and high-speed driving due to their good heat resistance and high strength.
• High-performance cars and racing cars: Pursuing extreme braking performance, carbon fiber friction materials or ceramic friction materials are ideal choices. They can provide strong and stable braking force during high-speed driving and intense driving, ensuring safe braking of the vehicle, while reducing the vehicle weight and improving fuel economy.
III. Industry Development Trends
(1) Environmental Protection
With the enhancement of global environmental awareness, the environmental requirements for brake pad friction materials are becoming higher and higher. Asbestos-free, low-heavy-metal, or even heavy-metal-free friction materials have become the development direction. For example, ceramic friction materials and NAO friction materials are gradually expanding their market share due to their compliance with environmental protection concepts.
(2) High Performance
As cars develop towards high performance and high speed, brake pad friction materials are required to have more excellent performance, such as higher stability of friction coefficients, better anti-fade performance, and lower braking noise. Researchers are constantly exploring new material combinations and formulations to meet these increasingly strict performance requirements.
(3) Customization
Different vehicle types and driving conditions have different needs for brake pads. In the future, friction materials will tend to be customized. According to the specific use of the vehicle, the operating environment, and the special requirements of customers, tailor-made friction materials will be created to provide the best braking performance.
As Shandong Huaruifeng Machinery Co., Ltd., we keep up with the industry development trends, continuously invest in research and development, and are committed to providing customers with high-quality, high-performance, and environmentally friendly brake pad products. Whether in material selection or production processes, we strictly control to ensure that every brake pad can safeguard the driving safety of the vehicle.
