What parameters should be paid attention to when selecting semi-autogenous mill liners?

Ⅰ. Size determination: "Mill cylinder parameters + material characteristics" as the core

1. Liner type: "Position-specific adaptation" to mill structure

• Cylinder liners (main body): Bear direct impact and wear from materials and steel balls, require high wear resistance and impact toughness;
  • Adaptation scenario: General material grinding (ore, limestone), matching mill cylinder length (usually divided into multiple sections for splicing);
• End liners (front/rear ends): Bear axial impact from materials, need thickened edge design;
  • Adaptation scenario: High filling rate (30-35%) mills, prevent material leakage from end gaps;
• Lifter bars (integrated with cylinder liners): Responsible for lifting materials and steel balls, require reasonable height and angle;
  • Adaptation scenario: Low-speed mills (14-18 r/min) need higher lifter bars, high-speed mills need moderate height to avoid excessive material throwing;
• Grid liners (discharge end): Control material discharge speed, require precise grid gap;
  • Adaptation scenario: Classification grinding processes, grid gap matching finished product particle size (usually 15-30mm).

2. Thickness (δ): Balance "wear life" and "mill load"

• Soft material (Mohs hardness ≤5, such as coal, gypsum): δ=80-100mm, avoid excessive thickness increasing mill load;
• Medium-hard material (Mohs hardness 5-7, such as limestone, iron ore): δ=100-120mm, balance wear resistance and load;
• Hard material (Mohs hardness ≥7, such as granite, basalt): δ=120-150mm, thickened design to resist high impact wear;
• Special note: For large-diameter mills (Φ≥5m), thickness can be increased by 10-20% on the basis of the above ranges, and the liner weight per unit area should not exceed 30kg/m² to avoid overloading the mill drive system.

3. Length & Width (L×W): "Modular splicing" matching mill cylinder

• Width (W): Consistent with the mill cylinder section division (usually 500-1200mm), the width of adjacent liners must be the same to ensure tight splicing;
• Length (L): For cylinder liners, L=(1/4-1/6)×mill circumference (modular design, easy to install and replace); for end liners, L matches the mill end cover radius (sector-shaped structure, usually 8-12 pieces spliced into a full circle);
• Splicing principle: The total length of liners in each circumferential layer is equal to the mill inner circumference (error ≤5mm), and the length of axial adjacent liners is staggered (staggered joint design) to avoid continuous gaps.

4. Bolt hole parameters: "Fixed reliability" as the core

• Hole diameter (d₀): Matching with fixing bolts (usually M24-M42 high-strength bolts), d₀=bolt diameter + 2-4mm (reserve installation adjustment space);
• Hole depth (h): h=bolt head height + 5-10mm (ensure bolt head is completely embedded in the liner, avoid collision with materials), and a counterbore design is required (counterbore diameter = d₀ + 8-12mm) to protect the bolt head;
• Hole pitch (P): P=300-500mm, determined by liner size (the larger the liner area, the smaller the hole pitch), ensure that the maximum distance between adjacent bolts does not exceed 500mm to prevent liner deformation under impact.

Ⅱ. Tolerance selection: Ensure "splicing tightness" and "fixed stability"

1. Liner splicing tolerance: Control "gap size" to prevent material leakage and impact

• Circumferential splicing (between adjacent liners in the same layer): Clearance ≤3mm, avoid material entering gaps and causing liner loosening or wear;
• Axial splicing (between liners in different axial layers): Clearance ≤5mm, allow slight thermal expansion space (mill operation will generate heat, liner thermal expansion coefficient ~11×10⁻⁶/°C), prevent jamming due to thermal expansion;
• Flatness tolerance: The splicing surface flatness ≤0.5mm/m (using a straightedge inspection), avoid uneven splicing leading to local stress concentration.

2. Liner-cylinder fitting tolerance: Ensure "close contact"

• Fitting gap: ≤0.5mm (measured with a feeler gauge), avoid gaps causing liner vibration under impact (leading to bolt loosening or liner cracking);
• Perpendicularity tolerance: The liner working surface (contact with materials) is perpendicular to the back surface, tolerance ≤1mm/m, ensure uniform force on the liner.

3. Bolt hole tolerance: Guarantee "bolt matching"

• Hole diameter tolerance: H12 (e.g., d₀=30mm, tolerance range 0~+0.18mm), ensure bolt can pass through smoothly while avoiding excessive clearance;
• Hole pitch tolerance: ±2mm, ensure bolt holes align with the cylinder bolt holes (cylinder bolt hole tolerance H10), avoid installation difficulties;
• Counterbore tolerance: Counterbore depth tolerance ±1mm, counterbore diameter tolerance H10, ensure bolt head is flush with the liner working surface.

Ⅲ. Key parameters: Beyond size and tolerance, determine "service life" and "grinding efficiency"

1. Material performance parameters: Adapt to "wear mechanism"

• Hardness: For abrasive wear (soft material, high filling rate), HRC≥55 (e.g., high-chromium cast iron); for impact wear (hard material, large particle size), HRC=45-50 (e.g., manganese steel Mn13) to balance hardness and toughness;
• Impact toughness (αₖᵥ): ≥15J/cm² (for high-chromium cast iron) or ≥100J/cm² (for manganese steel), avoid brittle fracture under large material impact (particle size ≥100mm);
• Wear resistance: Volume wear rate ≤0.15cm³/(kg·m) (tested by ASTM G65), ensure service life ≥8000 hours (medium-hard material working condition).

2. Structural design parameters: Optimize "grinding efficiency"

• Lifter bar height (h₁): h₁=1.2-1.5×maximum material particle size (e.g., maximum particle size 80mm, h₁=96-120mm), too low cannot lift materials, too high increases power consumption;
• Lifter bar angle (θ): θ=30°-45°, for low-speed mills (≤16r/min) use 30°-35° (increase lifting height), for high-speed mills (≥18r/min) use 40°-45° (avoid material excessive throwing);
• Wear-resistant groove design: The working surface of the liner is provided with transverse or longitudinal wear-resistant grooves (depth 5-8mm, spacing 50-80mm), which can store materials to form a "material wear-resistant layer" and reduce direct wear of the liner.

3. Working condition adaptation parameters: Match "mill operation parameters"

• Filling rate adaptation: When mill filling rate is 30-35% (high filling), select thicker liners (δ+10-20mm) and higher lifter bars (h₁+10-15mm); when filling rate is 25-30% (low filling), use standard thickness and lifter bar height;
• Rotational speed adaptation: Low speed (≤14r/min) → emphasize wear resistance (high-chromium cast iron); high speed (≥18r/min) → emphasize impact toughness (manganese steel or composite materials);
• Corrosion adaptation: For wet grinding (material contains water or corrosive media), select corrosion-resistant alloy liners (e.g., high-chromium nickel alloy) or add corrosion-resistant coating (thickness ≥0.3mm) on the liner surface.