What parameters should be paid attention to when selecting copper bushings?

I. Size Determination: Focus on “Shaft Diameter + Fit Clearance”

1. Inner Diameter (d): “Dynamic Matching” with Shaft Diameter

• Low speed and heavy load (e.g., punch presses, crusher shafts): A smaller clearance (0.01-0.03mm) is required to avoid increased local wear caused by shaking between the shaft and bushing;
• High speed and light load (e.g., motor shafts, fan shafts): A larger clearance (0.03-0.08mm) is required to reserve space for thermal expansion of the copper bushing (thermal expansion coefficient of copper ≈16×10⁻⁶/°C, higher than that of steel) to prevent high-temperature jamming;
• Good lubrication (e.g., oil bath, forced lubrication): The clearance can be moderately increased (0.05-0.12mm) to improve the fluidity of lubricating medium;
• Harsh environment (e.g., dust, dry friction/boundary lubrication): The clearance must be strictly controlled (≤0.03mm) to reduce impurity intrusion and dry wear;
• Material adaptation adjustment: Pure copper (red copper) is relatively soft, so the clearance should be taken at the lower limit (≤0.02mm) to avoid deformation; brass and bronze can be selected according to conventional clearances;
• Calculation formula: Recommended inner diameter d = shaft diameter + fit clearance. The shaft diameter accuracy is usually h6/h7 (shaft tolerance zone), and the copper bushing inner diameter tolerance is correspondingly selected as H7/H8 (hole tolerance zone) to form a “clearance fit”.

2. Outer Diameter (D): “Static Fixing” with Housing

• Light load, disassembly-required scenarios (e.g., general machinery maintenance parts): Transition fit (bushing tolerance g6, housing tolerance H7), allowing slight clearance or interference (±0.01mm) to balance fixity and disassembly convenience;
• Heavy load, vibration scenarios (e.g., agricultural machinery, construction machinery): Interference fit (bushing tolerance r6, housing tolerance H7), interference amount 0.01-0.04mm (the larger the diameter, the greater the interference amount) to ensure the copper bushing is firmly fixed and avoid vibration loosening;
• Housing material adaptation: When the housing is made of soft materials such as aluminum alloy, the interference amount is halved (0.005-0.02mm) to prevent housing deformation and cracking.

3. Length (L): Balance “Support Stability” and “Operational Flexibility”

• Risk of being too short: Insufficient support area, excessive load per unit area, which is prone to local crushing and deformation of the copper bushing;
• Risk of being too long: Poor heat dissipation in the middle of the copper bushing (although copper has excellent thermal conductivity, an excessive length-diameter ratio is prone to heat accumulation), increased processing difficulty and higher costs;
• Recommended ratio: L=(1.2-3)×d (inner diameter) for conventional scenarios;
• Special adaptation: For slender shafts and vibration working conditions, it can be increased to L=(3-4)×d, but axial oil grooves (width 2-3mm, depth 0.5-1mm) must be designed to assist heat dissipation and lubrication;
• Material limitation: Pure copper has low strength, so the length should not exceed 3d to avoid bending deformation.

II. Tolerance Selection: Ensure “Fit Precision” and “Operating Stability”

1. Dimensional Tolerance: Control “Consistency of Fit Clearance”

• Inner diameter tolerance: H7 grade (e.g., d=50mm, tolerance range 0~+0.025mm) or H8 grade (0~+0.039mm) to ensure uniform clearance of copper bushings in the same batch;
• Outer diameter tolerance: g6 grade (e.g., D=60mm, tolerance range -0.012~-0.002mm) or r6 grade (+0.028~+0.038mm), matching the housing tolerance to form a stable fit;
• Key requirement: The coaxiality tolerance between the inner and outer diameters of the same copper bushing ≤0.01mm to avoid uneven clearance and local wear caused by eccentricity.

2. Geometric Tolerance: Improve “Operational Smoothness”

• Roundness tolerance: ≤0.005mm (inner diameter ≤50mm) or ≤0.01mm (inner diameter >50mm) to avoid “point contact” between the shaft and bushing caused by ovality, which intensifies wear;
• Cylindricity tolerance: ≤0.01mm/m to ensure uniform fit between the inner wall of the copper bushing and the entire length of the shaft, achieving balanced force;
• End face perpendicularity tolerance: ≤0.01mm/m to avoid axial movement caused by uneven force on the end face.

3. Surface Tolerance: Optimize “Friction Performance”

• Inner wall roughness: Ra≤0.8μm (polished treatment) to reduce the friction coefficient with the shaft (the friction coefficient between copper and steel ≈0.15, which can be reduced to 0.08-0.1 after polishing);
• Outer wall roughness: Ra≤1.6μm to improve the fit with the housing and enhance fixing stability;
• Edge chamfering: Both ends are chamfered at 1×45° or 2×30° to avoid scratching the shaft or housing during installation and guide the inflow of lubricating medium.

III. Key Parameters: Beyond Size and Tolerance, Determine “Service Life” and “Compatibility”

1. Material Performance Parameters: Select According to “Operating Requirements”

2. Operating Condition Adaptation Parameters: Match “Actual Operating Conditions”

• Load adaptation: For pressure ≤15MPa, brass is optional; for 15-30MPa, tin bronze is selected; for >30MPa, aluminum bronze (high strength, impact resistance) is preferred;
• Speed adaptation: For linear speed ≤3m/s, pure copper or brass can be selected; for 3-10m/s, tin bronze (wear resistance) is suitable; for >10m/s, forced lubrication + bronze material must be matched;
• Corrosion environment: For humid, acid-base media (e.g., chemical equipment), aluminum bronze or tin bronze (superior corrosion resistance to brass and pure copper) is preferred;
• Oil-free/low-oil scenarios: Lead-containing bronze (e.g., ZCuSn10Pb1) is selected, as lead forms a self-lubricating layer to reduce dry wear.

3. Structural Design Parameters: Optimize “Usage Effect”

• Oil groove/oil hole design: For heavy load and high-speed scenarios, axial oil grooves (width 2-3mm, depth 0.5-1mm) or annular oil grooves should be opened on the inner wall of the copper bushing, and oil holes (aperture 2-4mm) should be set at the ends to ensure continuous lubrication;
• Wall thickness design: Conventional wall thickness δ=(D-d)/2=3-8mm; for heavy load scenarios, it can be increased to 8-15mm; for pure copper materials, the wall thickness should be increased by 20% compared with brass/bronze to compensate for insufficient strength;
• Stop design: For severe vibration scenarios, a stop groove (width 3-5mm, depth 1-2mm) can be opened on the outer wall of the copper bushing, and fixed with a stop pin to prevent circumferential rotation.