Ball mill bull gear

Detailed Introduction, Manufacturing Process, and Inspection Process of Ball Mill Bull Gears

I. Functions and Structural Features of Ball Mill Bull Gears

• High strength and wear resistance: The tooth surface must have sufficient hardness (≥240HBW after quenching and tempering) to resist wear, while the tooth body requires good toughness (impact toughness ≥40J/cm²) to withstand meshing impacts;

• High-precision meshing: Tooth profile errors must be controlled within Grade 7 of GB/T 10095, ensuring contact area with the pinion (≥50% along tooth height, ≥60% along tooth length);

• Structural stability: Large gears (diameter ≥3m) often adopt split structures (2-4 segments) for ease of transportation and installation. The joint surfaces must ensure positioning accuracy (radial misalignment ≤0.1mm).

II. Manufacturing Process of Ball Mill Bull Gears (Taking 42CrMo Split Gears as an Example)

1. Blank Preparation (Forged Steel)

• Raw material: 42CrMo steel plates or forgings with thickness ≥100mm are selected, with spectral analysis verifying composition (C 0.38-0.45%, Cr 0.9-1.2%, Mo 0.15-0.25%);

• Forging/cutting:

• Integral forging: Heat to 1100-1150℃, forge into ring blanks using a hydraulic press (for diameters ≤5m). After forging, normalize (860℃×3h, air-cooled) to relieve stress, reducing hardness to 200-230HBW;

• Split cutting: Large gears are cut into segments (e.g., 2 segments) with a machining allowance of 10-15mm. Joint surfaces are milled flat (flatness ≤0.05mm/m).

2. Rough Machining and Assembly (Split Gears)

• Rough turning: CNC vertical lathes machine the outer circle, inner bore, and end faces, leaving a 5-8mm grinding allowance for the inner bore;

• Assembly positioning: Fix segmented blanks with locating pins and bolts (bolt preload ≥800N·m) to ensure circumference deviation at joints ≤1mm;

• Rough gear hobbing: Roughly cut tooth profiles with a gear hobbing machine, leaving a 3-5mm finishing allowance (including deformation compensation after quenching and tempering).

3. Quenching and Tempering (Key Process)

• Heat to 840-860℃, oil-cool after insulation (quenching), then temper at 580-620℃ for 4h (high-temperature tempering). Final hardness is 250-280HBW, ensuring tensile strength ≥800MPa;

• 100% ultrasonic testing (UT) after quenching and tempering (compliant with JB/T 4730.3 Grade II), with no cracks or flakes allowed.

4. Finish Machining

• Semi-finish turning: Machine joint surfaces, inner bore, and reference end faces, leaving a 2-3mm grinding allowance;

• Precision gear hobbing: CNC gear hobbing machines process tooth profiles, controlling pitch deviation to ±0.05mm and tooth direction error to ≤0.03mm/100mm;

• Drilling: Machine assembly bolt holes (diameter φ30-φ60mm) with positional tolerance ±0.1mm and cumulative hole distance error ≤0.2mm;

• Grinding: Grind inner bore (tolerance IT7) and reference end faces (perpendicularity ≤0.02mm/100mm) to ensure fitting accuracy with the cylinder flange.

5. Surface Treatment and Assembly

• Tooth surfaces are sandblasted (roughness Ra12.5μm) and coated with anti-rust primer; non-machined surfaces are painted with topcoat (total thickness ≥100μm);

• During on-site assembly of split gears, check joint gaps with feeler gauges (gap ≤0.05mm). After bolt tightening, re-measure gear ring radial runout (≤0.1mm).

III. Inspection Process of Ball Mill Bull Gears

1. Raw Material and Blank Inspection

• Chemical composition: Spectral analysis confirms qualified Cr and Mo contents in 42CrMo;

• Forging quality: Macrostructure inspection of forgings (etching method) shows no shrinkage or porosity (grade ≤2). Tensile tests verify yield strength ≥600MPa.

2. Heat Treatment Inspection

• Hardness testing: Brinell hardness tester measures tooth surfaces and cores (250-280HBW) with uniformity deviation ≤30HBW;

• Metallographic structure: Samples show tempered sorbite (grade ≤3) with no network carbides.

3. Tooth Profile Accuracy Inspection

• Gear measuring center testing:

• Cumulative pitch error ≤0.15mm (for 5m-diameter gears), individual pitch deviation ±0.03mm;

• Total profile deviation ≤0.08mm, tooth direction error ≤0.05mm/100mm;

• Radial runout: Gear runout tester measures gear ring radial runout (≤0.1mm).

4. Final Inspection of Finished Products

• Assembly accuracy: After assembling split gears, laser trackers detect overall roundness (≤0.15mm);

• Meshing test: Meshing tests with pinion samples (2-hour no-load operation) show qualified contact spots and no abnormal noise;

• Appearance quality: Penetrant testing (PT) of tooth root fillets (R≥3mm) reveals no cracks or burrs (depth ≤0.5mm).