Materials and Performance Parameters

Carbon materials are preferred for brushes due to light weight, conductivity, thermal efficiency, and self-lubrication. Carbon brushes are categorized into:

• Metal-graphite: Silver-graphite or copper-graphite, ideal for high-power motors.
• Non-metal-graphite: Electrical graphite, carbon-graphite, or resin-graphite, suited for low-noise, wear-sensitive scenarios.

Key parameters (interrelated and balanced for performance):

• Resistivity: Higher values suppress sparking but reduce efficiency and may cause overheating.
• Flexural strength: Higher strength enhances wear resistance.
• Hardness: Increased hardness boosts durability but raises noise and commutator wear.
• Density: Higher density improves wear resistance, correlating with lower resistivity and higher strength.

Manufacturing Process

1. Compression molding: Mix carbon powder, additives, and binders, then press into shapes.
2. Cutting and sintering: Cut into sizes and sinter to stabilize properties.
3. Precision machining: Refine dimensions (e.g., curved surfaces) and drill holes.
4. Assembly: Embed copper wires, add springs/connectors, and install stop rods.
5. Inspection and packaging: Ensure quality before delivery.

Practical Usage Tips

• Spring pressure: Excessive pressure accelerates wear; insufficient pressure causes sparking. Recommended ranges:
• Electrical graphite: 1.5–3.0N/cm²
• Metal-graphite: 1.5–3.5N/cm²
• Resin/carbon-graphite: 3–5N/cm²
• Natural graphite: 1.2–2.5N/cm²
• Contact film: A balanced film thickness enhances conductivity and lubrication. Too thin: increased wear; too thick: overheating and sparking.
• Pigtail diameter: Must match current capacity to avoid arcing. Example specifications:

Impact on EMC

Commutating sparks from carbon brushes in series-wound motors disrupt electromagnetic compatibility (EMC). Mitigation steps include:

• Using softer brushes, smoother commutators, and optimal spring pressure.
• Balancing resistivity and segment span to reduce sparking (without compromising wear resistance).
• Adding circuit components (capacitors, inductors) or adjusting rotor alignment.

Current Status and Future

Cordless tools (AC-to-DC) have reduced carbon brush use, as brushless motors (1000+ hour lifespan) outlast brushed ones (300–500 hours). However, brushed motors with carbon brushes remain cost-effective for extreme/harsh conditions.

Carbon brushes remain critical to series-wound motor performance, with ongoing advancements targeting lower wear and smarter design.

This overview aims to aid in selecting and applying carbon brushes effectively.