Purchased component
Carbon Brushes & Brush Gear
✓ Expert reviewed All content on this page has been reviewed by a senior motor engineer.
Process flow
Upstream manufacturing of this bought-in item is not covered yet; see the incoming inspection and approval tests.
Incoming inspection & approval tests
- Brush resistivity, hardness and densityPer material data sheet
- Brush spring forcePer drawing; spring force gauge on samples
- Brush wear and commutation in endurance testRun on the motor at rated load; wear rate and sparking within limits
- End-cap material and flammabilityUL 94 rating per specification (e.g. V-0)
Buyer FAQ
- How do I choose a brush grade?
- Match it to voltage, current density and commutator speed: metal-graphite (copper-graphite) brushes for low-voltage, high-current motors; electrographite or resin-bonded grades for higher voltage and speed. The brush supplier should test the grade on your motor.
- What limits brush life?
- Sparking from poor commutation, spring force, commutator surface condition and run-out, current density, and dust or humidity. Track wear per 100 hours in endurance tests.
- What should be specified for brush holders?
- Holder clearance around the brush, spring force and its variation, and the material's heat resistance. Too much clearance causes brush chatter; too little causes sticking.