The Application of Wollastonite in Brake Pads Production
In the complex and highly – regulated realm of brake pads manufacturing, the choice of materials is a cornerstone for achieving outstanding braking performance, ensuring vehicle safety, and promoting long – term durability. Wollastonite, a calcium – inosilicate mineral, has found its niche in brake pads production, bringing with it a distinct set of characteristics that offer both remarkable benefits and certain drawbacks. This article will comprehensively explore its application in the brake pads production process, spotlighting its properties, functions, and the influence on the overall performance of brake pads.
1. Wollastonite: Fundamental Properties and Structure
Wollastonite is a naturally – occurring mineral with the chemical formula \(CaSiO_3\). It typically forms in metamorphic rocks and has a needle – like or fibrous crystal structure. The aspect ratio (length – to – diameter ratio) of wollastonite fibers can range from 5:1 to 20:1, which is crucial for its reinforcement capabilities in brake pads. Its Mohs hardness is around 4.5 – 5.0, making it a moderately hard material.
The density of wollastonite is approximately 2.8 – 2.9 g/cm³. It has good thermal stability and can withstand temperatures up to around 1100 – 1200°C without significant decomposition. This thermal stability is highly relevant for brake pads, as they are frequently exposed to high temperatures during the braking process.
2. Incorporation into brake pads mixture
When formulating a brake pads mixture, wollastonite is blended with various other components. Binders, such as phenolic resins, are essential for holding the mixture together. These resins create a matrix that embeds the wollastonite fibers and other ingredients like fillers (such as mica, graphite, or kaolin) and reinforcement fibers (such as aramid or glass fibers). In a typical brake pads mix, wollastonite usually accounts for 10 – 30% by weight.
The proportion of wollastonite in the mixture is determined through extensive research and testing. If the content is too low, its reinforcing and friction – modulating effects may not be fully realized. For instance, a lower percentage of wollastonite may result in reduced mechanical strength and less – stable friction performance. Conversely, an excessive amount can lead to brittleness in the brake pads. If the wollastonite content exceeds 30%, the brake pads may become more prone to cracking under mechanical stress during braking.
3. Role in brake pads friction materials
As a component in brake pads friction materials, wollastonite serves multiple crucial functions. Firstly, its fibrous structure provides reinforcement. It can enhance the mechanical strength of the friction material, reducing the likelihood of wear and tear during braking. In wear – resistance tests, brake pads with wollastonite showed a 20 – 30% reduction in wear rate compared to those without it under the same braking conditions.
Secondly, wollastonite can contribute to the friction characteristics of the brake pads. It helps in maintaining a relatively stable friction coefficient. Under normal braking conditions, brake pads with an appropriate amount of wollastonite can maintain a friction coefficient in the range of 0.3 – 0.5. This consistent friction coefficient is vital for ensuring smooth and reliable braking performance.
Advantages of Using Wollastonite in Brake Pads Production
- Enhanced Mechanical Strength: Wollastonite’s fibrous structure significantly improves the mechanical strength of brake pads. In tensile – strength tests, brake pads with 20% wollastonite showed a 30 – 40% increase in tensile strength compared to those without it. This increased strength allows the brake pads to withstand the mechanical stresses generated during braking more effectively, reducing the risk of premature failure.
- Good Friction – Modulating Ability: Wollastonite can effectively modulate the friction coefficient of brake pads. In braking tests with different braking forces, brake pads with wollastonite showed a 15 – 25% reduction in friction coefficient variation compared to those without it. This more stable friction coefficient makes the braking process more predictable and safer, especially in emergency braking situations.
- Thermal Stability: Its ability to withstand high temperatures up to 1100 – 1200°C is a significant advantage. In high – speed braking scenarios, where brake pad temperatures can rise rapidly, wollastonite – containing brake pads can maintain their structural integrity. This thermal stability helps in preventing brake fade, ensuring consistent braking performance even under extreme conditions.
Disadvantages of Using Wollastonite in Brake Pads Production
- Limited Heat – Dissipation: Although wollastonite has good thermal stability, its thermal conductivity is relatively low. In heat – dissipation tests, brake pads with wollastonite showed a 10 – 20% slower heat – dissipation rate compared to some other high – performance materials. This slower heat – dissipation can potentially lead to overheating of the brake pads during continuous or heavy – duty braking, reducing their effectiveness.
- Surface Reactivity: Wollastonite may react with certain components in the brake pads mixture under high – temperature or high – humidity conditions. In some cases, this reactivity can cause the formation of unwanted chemical compounds, which may affect the long – term performance of the brake pads. For example, in humidity – accelerated aging tests, brake pads with wollastonite showed a 10 – 15% decrease in friction coefficient stability over time compared to those without it.
- Cost – Volume Ratio: Wollastonite is not as abundant as some other common minerals used in brake pads production. As a result, its cost – volume ratio can be relatively high. Using wollastonite can increase the overall production cost of brake pads by 5 – 15% compared to using more inexpensive materials. This cost factor may limit its widespread use, especially in cost – sensitive markets.