For friction materials (automotive brake pads, clutch linings, industrial friction composites), angular, sub-angular quartz particles are the optimal shape, rather than fully spherical or highly flaky grains. The particle morphology directly affects friction coefficient, wear rate, noise, rotor abrasion and mechanical strength of the final friction composite.
1. Why angular / sub‑angular quartz works best
Angular quartz has sharp edges and irregular facets. When embedded inside the friction composite matrix, these angular features deliver three core benefits:
- Stable friction coefficient: The angular profile creates consistent micro‑interlocking between friction material and mating counterface (cast iron rotor). It maintains steady friction across different temperature and pressure conditions, avoiding sudden friction drop (fade).
- High abrasion resistance of the friction pad: Irregular grains mechanically anchor into the resin matrix. Compared with spherical quartz, angular particles resist pull‑out during sliding friction, reducing pad wear rate.
- Controlled cutting action: Moderate sharpness provides friction without excessive aggressive scratching.
Sub‑angular quartz (partially rounded edges from comminution) is preferred over sharply jagged, freshly crushed quartz.
- Extreme sharp, highly angular quartz: too aggressive, causes heavy rotor wear, increases brake noise and vibration.
- Sub‑angular: edges are slightly blunted, balancing friction performance and counterface protection.
2. Why spherical quartz is not suitable for friction materials
Spherical quartz particles have smooth, rounded surfaces. They tend to slide and roll within the friction matrix instead of forming stable micro-contact.
- Friction coefficient becomes lower and less stable;
- Particles are easily pulled out from the binder under shear force;
- Poor friction stability at high temperature.
Spherical quartz is mainly used for LED encapsulation, semiconductor fillers, and resin casting, not friction composites.
3. Flaky quartz: not recommended
Thin, plate-like flaky quartz has low compressive strength. Flakes easily fracture under contact pressure. It cannot sustain stable friction and will accelerate composite wear.
4. Supporting particle parameters paired with shape
Shape must be combined with other specifications for friction grade quartz:
- Particle size: Typically medium coarse to fine powder (D50 from 5–45 μm). Too fine quartz reduces friction; oversized grains create harsh braking and rotor scoring.
- PSD: Controlled narrow distribution to avoid oversized sharp coarse grains.
- Hardness & purity: Quartz Mohs 7; iron and heavy metal impurities must be controlled to avoid thermal degradation of phenolic resin binder during high-temperature braking.
- Surface texture: Clean particle surface to improve bonding with phenolic resin matrix; silane modification can enhance matrix adhesion and reduce particle pullout.
5. Process tip for producing friction-grade quartz
To obtain sub‑angular quartz: use controlled crushing + closed circuit air classification. Avoid ultra-fine grinding that fully rounds particle edges. Adjust mill and classifier parameters to retain the irregular grain profile while trimming the sharpest, needle-like fragments.
The best particle shape of quartz for friction materials is sub‑angular quartz. Fully angular sharp quartz causes excessive rotor abrasion and noise; spherical quartz fails to maintain stable friction coefficient. Sub‑angular grains provide reliable friction, good retention in the resin binder, and mild, controlled wear on the mating rotor. Combine this morphology with optimized PSD and low impurity levels to meet brake and clutch friction composite requirements.
