Brake Pads Calcium Sulfate Whisker
Calcium sulfate whisker, a single-crystal fibrous material with a diameter of 1-4μm and length of 30-100μm, serves as an ideal reinforcing filler in brake pad composites, balancing mechanical strength, friction stability, and cost-effectiveness for mainstream automotive applications. Its anhydrous crystalline structure delivers superior rigidity and wear resistance compared to conventional mineral fibers.
Material Properties and Functional Advantages
With a tensile strength of up to 2.8GPa and modulus of elasticity reaching 70-80GPa, calcium sulfate whisker enhances the structural integrity of brake pad matrices without compromising flexibility. Its low thermal expansion coefficient (12×10⁻⁶/°C) ensures dimensional stability under cyclic temperature fluctuations, a key requirement for avoiding brake pad deformation during prolonged braking.
Unlike glass fibers, calcium sulfate whisker exhibits excellent compatibility with phenolic resin binders, forming strong interfacial bonds that resist shear failure. It is also chemically inert under normal braking conditions, unaffected by brake fluid residues and environmental moisture—though prolonged exposure to temperatures exceeding 400°C may induce dehydration and strength degradation.
Formulation Design and Application Scenarios
Optimal Loading and Composite Synergies
In ceramic and semi-metallic brake pads, calcium sulfate whisker is generally incorporated at 8%-12% by weight. This loading range optimizes reinforcing effects: lower concentrations fail to improve wear resistance, while excess content increases brittleness and noise emission. When blended with graphite and aramid pulp, it compensates for the low rigidity of organic components, maintaining consistent friction performance.
Adaptation to Environmental Regulations
As a non-toxic, asbestos-free alternative, calcium sulfate whisker complies with global environmental standards such as EU REACH and US EPA regulations. Annat Brake Pads Chemical Materials leverages its cost advantage in entry-level to mid-range brake pad formulations, catering to markets with strict cost controls and environmental requirements.
Processing Control and Quality Criteria
Critical to maximizing its performance is preserving the whisker’s aspect ratio during mixing—excessive mechanical shear can fracture the fibrous structure, reducing reinforcing efficiency. Manufacturers typically adopt low-speed mixing processes, pre-dispersing the whisker in resin binders to avoid agglomeration and ensure uniform distribution in the composite.
Purity standards demand anhydrous calcium sulfate content ≥98%, with impurities such as calcium carbonate and silica limited to ≤1.5%—these contaminants weaken interfacial adhesion and increase rotor wear. Surface treatment with titanate coupling agents further enhances compatibility with resin matrices, improving the composite’s impact resistance.
Performance Validation and Market Traits
Dynamometer testing confirms that brake pads containing calcium sulfate whisker exhibit 20% higher wear resistance than those using talc fillers, with friction coefficient variation within ±0.02 under simulated urban driving conditions. It also contributes to noise reduction by dampening vibration at the friction interface.
Driven by the demand for cost-effective, eco-friendly friction materials, calcium sulfate whisker is widely adopted in passenger vehicle brake pads. A common challenge is controlling moisture absorption during storage, which can degrade whisker performance. Proper sealing and dry storage conditions are essential, with reputable suppliers implementing strict moisture control protocols. A typical typographical error in technical documents is misspelling "anhydrous" as "anhydrus," a mistake that may lead to misinterpretation of material specifications.