Ball mill cylinder

Detailed Introduction, Manufacturing Process, and Inspection Process of Ball Mill Cylinders

I. Functions and Structural Features of Ball Mill Cylinders

• High strength and rigidity: Resist radial deformation (deflection of cylinders with diameter ≥5m must be ≤1mm/m);

• Wear resistance: Inner walls must withstand long-term erosion by media and materials (service life ≥5 years);

• Sealing performance: Ensure tightness at connections with hollow shafts at both ends to prevent material leakage;

• Stability: Center-of-gravity deviation during rotation ≤0.1mm/m to avoid severe vibration.

• Shape: Cylindrical (diameter 1-5m, length 3-10m), with flanges at both ends connected to hollow shafts via welding or bolts;

• Inner wall: Welded with wear-resistant liners (high manganese steel ZGMn13 or high chromium cast iron), fixed by bolts (spacing 300-500mm);

• Material: Cylinder body commonly uses Q235B carbon structural steel (small to medium-sized) or Q355B low-alloy high-strength steel (large-sized, yield strength ≥355MPa), with wall thickness 15-50mm (increasing with diameter).

II. Manufacturing Process of Ball Mill Cylinders (Taking Large Q355B Cylinders as an Example)

1. Raw Material Pretreatment and Cutting

• Raw material: Q355B steel plates with thickness 15-50mm are selected, accompanied by material certificates (chemical composition: C≤0.20%, Mn 1.2-1.6%, yield strength ≥355MPa);

• Cutting:

• Cut steel plates according to the expanded cylinder size (circumference = π×diameter), leaving 50-100mm welding allowance in the length direction;

• CNC cutting (flame or plasma), with cutting surface perpendicularity ≤1mm/m and no edge cracks (checked with a 10x magnifier).

2. Rolling and Welding (Key Process)

• Rolling:

• Preheat steel plates to 150-200℃ (to prevent cold working hardening), roll into cylinders using a three-roll plate rolling machine (diameter deviation ±5mm);

• Reserve a 2-3mm gap at the joint, with misalignment ≤1mm (to ensure welding quality);

• Welding:

• Longitudinal seam welding: Use submerged arc automatic welding (wire H08MnA, flux HJ431), with two-layer welding (backing weld + capping weld), welding current 600-800A, voltage 30-36V;

• Post-welding treatment: Immediately perform post-heating at 250-300℃ for 2h to eliminate welding stress, and clean roots with carbon arc gouging (to ensure penetration).

3. Assembly and Circumferential Seam Welding (Splicing of Multi-Segment Cylinders)

• When the cylinder length exceeds the length of a single steel plate, it needs to be rolled in segments and then assembled:

• Butt two cylindrical segments with coaxiality ≤2mm/m and circumferential seam misalignment ≤1.5mm;

• Circumferential seam welding: Same as longitudinal seam process; after welding, grind the weld reinforcement to ≤2mm (to avoid stress concentration).

4. Flange Assembly and Welding

• Flange processing: CNC lathes machine flanges (same material as the cylinder) with flatness ≤0.1mm/m and bolt hole position tolerance ±0.5mm;

• Assembly welding: Assemble the flange with the cylinder port (perpendicularity ≤0.5mm/100mm), use symmetric welding (to reduce deformation), and perform 100% ultrasonic testing (UT) after welding (compliant with JB/T 4730.2 Grade II).

5. Annealing and Roundness Correction

• Overall annealing: Anneal large cylinders (diameter ≥3m) at 600-650℃ for 4h, cool slowly to below 300℃ and then air-cool to eliminate residual welding stress (residual stress ≤150MPa);

• Roundness correction: Correct roundness with a press, ensuring cylinder roundness ≤3mm/m (checked with templates or laser roundness meters).

6. Liner Mounting Surface Processing and Surface Treatment

• Turn the inner wall of the cylinder (liner mounting area) to a roughness of Ra≤12.5μm and flatness ≤2mm/m;

• Sandblast the outer wall to Sa2.5 grade, then apply primer (epoxy zinc-rich paint, thickness ≥60μm) and topcoat (polyurethane paint, thickness ≥40μm).

III. Inspection Process of Ball Mill Cylinders

1. Raw Material Inspection

• Steel plate chemical composition: Spectral analysis verifies C and Mn contents (compliant with Q355B standards);

• Mechanical properties: Tensile tests measure yield strength (≥355MPa) and elongation (≥20%); impact tests (-20℃ impact energy ≥34J).

2. In-Process Inspection (Key Nodes)

• After rolling: Measure circumference with a tape measure (deviation ±5mm); check arc fit with templates (gap ≤2mm);

• After welding:

• Weld appearance: No pores or slag inclusions; undercut depth ≤0.5mm, length ≤10% of total weld length;

• Non-destructive testing: 100% UT for longitudinal and circumferential seams (Grade II qualified); 100% penetrant testing (PT) for T-joints (flange-cylinder connections) to ensure no cracks.

3. Dimensional Accuracy Inspection

• Diameter and roundness: Measure one cross-section every 1m along the cylinder length, with diameter deviation ±5mm and roundness ≤3mm/m;

• Straightness: Check with a laser collimator, with full-length straightness ≤5mm (for diameter ≤5m).

4. Hydrostatic Test (Sealing Performance Inspection)

• For cylinders requiring sealing (e.g., wet ball mills), perform a 0.3MPa hydrostatic test, maintaining pressure for 30min with no leakage (minor sweating at flange connections is allowed, but must stop after tightening).

5. Final Inspection of Finished Products

• Appearance quality: No significant protrusions on the inner wall (≤1mm); coating adhesion on the outer wall (grid test ≥5B);

• Liner test mounting: Install 3-5 random liners, check fit (gap ≤1mm) and bolt hole alignment.