Copper Bushings

To correctly select the size, material and specification of copper bushings, it is necessary to combine matching conditions (such as load capacity, operating speed, lubrication requirements) and installation scenarios (such as shaft diameter, housing material, working environment), and focus on the compatibility of core parameters. The following is a detailed explanation from three dimensions: size determination, tolerance selection, and key parameters:

The size of copper bushings must be accurately matched with the shaft diameter and mounting housing. The core is to determine three key parameters: inner diameter (matching with the shaft), outer diameter (matching with the housing), and length:

Core principle: The inner diameter of the copper bushing needs to be slightly larger than the shaft diameter (forming a fit clearance). The clearance size is adjusted according to operating characteristics to balance operational flexibility and stability:

• 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".

The outer diameter of the copper bushing needs to form a stable fit with the mounting housing (usually cast iron, steel plate or aluminum alloy) to prevent the bushing from sliding in the housing during operation:

• 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.

Length selection should avoid insufficient support due to being too short and heat dissipation or processing problems caused by being too long:

• 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.

Copper bushings work in a dynamic friction environment, so tolerance control must avoid loose fit, jamming or excessive wear:

• 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.

• 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.

• 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.

Copper bushings are mainly divided into three categories: pure copper, brass and bronze. Performance differences determine the applicable scenarios:

• 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.

• 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.