Heat treatment and surface finishing are critical for custom gear performance, as they directly affect hardness, wear resistance, fatigue life, and corrosion protection.
Heat treatment alters the gear’s microstructure. Common processes include: Case hardening (carburizing, carbonitriding, or nitriding) – adds a hard, wear-resistant surface layer (55–62 HRC) while keeping a tough, ductile core; essential for automotive and industrial gears.
- Through hardening (quench and temper) – uniform hardness (30–50 HRC) for moderate loads.
- Induction hardening – selectively hardens tooth flanks and roots with minimal distortion.
- Annealing or normalizing – relieves stress before machining.
Surface finishing includes:
- Shot peening – induces compressive stress to prevent fatigue cracks.
- Phosphate or black oxide coating – provides temporary rust protection and helps retain lubricant.
- Zinc or nickel plating – for corrosion resistance in wet or marine environments.
- PTFE or MoS₂ coating – reduces friction for high-speed, low-lube applications. Without proper heat treatment, gears will suffer premature wear, pitting, or tooth breakage. Custom manufacturers usually subcontract heat treatment to specialized furnaces and provide hardness test reports (e.g., microhardness traverse graphs).
Always specify your required surface hardness, case depth, and core hardness on your drawing.