To correctly select the size and tolerance of the bronze bushing, it is necessary to combine the matching conditions (such as load, speed, clearance requirements) and installation scenarios (such as shaft diameter, hole seat size), and pay attention to the matching of core parameters. The following is a detailed explanation from three dimensions: size determination, tolerance selection, and key parameters:
一. Size determination: "Shaft diameter + fit clearance" as the core
The size of the bronze bushing must match the shaft diameter and the mounting hole seat. The core is to determine the three parameters of inner diameter (matching with the shaft), outer diameter (matching with the hole seat), and length:
1. Inner diameter (d): "dynamic matching" with shaft diameter
Basic basis: The inner diameter of the bushing needs to be slightly larger than the shaft diameter (forming a matching clearance), and the size of the clearance depends on the working conditions:
Low speed and heavy load (such as stamping equipment): a smaller clearance (0.01-0.03mm) is required to avoid local wear caused by shaking of the shaft and bushing;
High speed and light load (such as fan shaft): a larger clearance (0.03-0.08mm) is required to reserve space for thermal expansion (the thermal expansion coefficient of bronze is higher than that of steel) to prevent high temperature jamming;
Good lubrication scenario (such as oil bath lubrication): the clearance can be slightly larger (0.05-0.1mm); poor lubrication scenario (such as dry friction): the clearance needs to be strictly controlled (≤0.03mm) to avoid impurities from entering.
Calculation formula: Recommended inner diameter d = shaft diameter + matching clearance, the shaft diameter accuracy is usually h6/h7 (tolerance zone of the shaft), and the bushing inner diameter tolerance is correspondingly selected H7/H8 (tolerance zone of the hole) to form a "clearance fit".
2. Outside diameter (D): "statically fixed" to the hole seat
The outer diameter of the bushing needs to form a "transition fit" or "interference fit" with the mounting hole seat (usually cast iron or steel) to prevent the bushing from sliding in the hole seat:
Light load, disassembly scenario: transition fit (such as bushing tolerance g6, hole seat tolerance H7), allow slight clearance or interference (±0.01mm);
Heavy load, vibration scenario: interference fit (such as bushing tolerance r6, hole seat tolerance H7), interference amount 0.01-0.05mm (adjusted according to the diameter size, the larger the diameter, the greater the interference amount), to ensure that the bushing is firmly fixed.
3. Length (L): Balance "support stability" and "heat dissipation"
Too short: insufficient support area, too large load per unit area, easy to cause bushing deformation;
Too long: difficult to dissipate heat (although bronze has good thermal conductivity, long bushings are prone to high temperatures due to poor heat dissipation in the middle), and increased processing difficulty;
Recommended ratio: usually
L=(1.5−3)×d (inner diameter), special scenarios (such as slender shafts) can be increased to
L=4−5d, but an oil groove design is required to assist heat dissipation.
To correctly select the size and tolerance of the bronze bushing, it is necessary to combine the matching conditions (such as load, speed, clearance requirements) and installation scenarios (such as shaft diameter, hole seat size), and pay attention to the matching of core parameters. The following is a detailed explanation from three dimensions: size determination, tolerance selection, and key parameters:
一. Size determination: "Shaft diameter + fit clearance" as the core
The size of the bronze bushing must match the shaft diameter and the mounting hole seat. The core is to determine the three parameters of inner diameter (matching with the shaft), outer diameter (matching with the hole seat), and length:
1. Inner diameter (d): "dynamic matching" with shaft diameter
Basic basis: The inner diameter of the bushing needs to be slightly larger than the shaft diameter (forming a matching clearance), and the size of the clearance depends on the working conditions:
Low speed and heavy load (such as stamping equipment): a smaller clearance (0.01-0.03mm) is required to avoid local wear caused by shaking of the shaft and bushing;
High speed and light load (such as fan shaft): a larger clearance (0.03-0.08mm) is required to reserve space for thermal expansion (the thermal expansion coefficient of bronze is higher than that of steel) to prevent high temperature jamming;
Good lubrication scenario (such as oil bath lubrication): the clearance can be slightly larger (0.05-0.1mm); poor lubrication scenario (such as dry friction): the clearance needs to be strictly controlled (≤0.03mm) to avoid impurities from entering.
Calculation formula: Recommended inner diameter d = shaft diameter + matching clearance, the shaft diameter accuracy is usually h6/h7 (tolerance zone of the shaft), and the bushing inner diameter tolerance is correspondingly selected H7/H8 (tolerance zone of the hole) to form a "clearance fit".
2. Outside diameter (D): "statically fixed" to the hole seat
The outer diameter of the bushing needs to form a "transition fit" or "interference fit" with the mounting hole seat (usually cast iron or steel) to prevent the bushing from sliding in the hole seat:
Light load, disassembly scenario: transition fit (such as bushing tolerance g6, hole seat tolerance H7), allow slight clearance or interference (±0.01mm);
Heavy load, vibration scenario: interference fit (such as bushing tolerance r6, hole seat tolerance H7), interference amount 0.01-0.05mm (adjusted according to the diameter size, the larger the diameter, the greater the interference amount), to ensure that the bushing is firmly fixed.
3. Length (L): Balance "support stability" and "heat dissipation"
Too short: insufficient support area, too large load per unit area, easy to cause bushing deformation;
Too long: difficult to dissipate heat (although bronze has good thermal conductivity, long bushings are prone to high temperatures due to poor heat dissipation in the middle), and increased processing difficulty;
Recommended ratio: usually
L=(1.5−3)×d (inner diameter), special scenarios (such as slender shafts) can be increased to
L=4−5d, but an oil groove design is required to assist heat dissipation.
