Gear is a mechanical component that transmits power and motion through tooth meshing, widely used in industries, automobiles, aerospace, and other fields. The following is an analysis of the structure, classification, parameters, materials, and selection points of gears:
Basic Structure And Classification Of Gears
1. Core structure and terminology Tooth profile: Common involute and circular arc tooth profiles affect meshing efficiency and noise.
Module: The core parameter that determines the size of the gear (module=pitch circle diameter/number of teeth).
Pressure Angle: Usually 20 °, which affects the contact stress of the tooth surface. High pressure angle (25 °+) has stronger bearing capacity.
Tooth Width: It needs to be matched with the load. Being too narrow can easily cause wear, while being too wide increases costs and weight.
2. Common Gear Types Classified By Axis Relationship: Parallel Axis Gears: Spur gears (low-cost, high noise), helical gears (smooth transmission, requiring axial fixation).
Intersecting Shaft Gears: Bevel gears (spur/helical gears, used for steering transmission, such as car differentials).
· Key Design Parameters Modulus (m): International standardization (ISO 54), with a value range of 0.5-50mm, determines the size and strength of the gear. Number of teeth (Z): affects the speed ratio (i=Z ₂/Z ₁). Generally, when the number of teeth on a small gear is ≥ 17, root cutting should be avoided. Spiral angle (β): The core parameter of helical gears and worm gears, where β ↑ → contact line length ↑ → load ↑, but axial force ↑. Accuracy level: ISO 1328 standard is divided into 12 levels, with level 1 being the highest (aviation grade) and level 8 being the industrial general grade.
· Key Points Of Strength Calculation Contact fatigue strength: According to Hertz formula, it is related to material hardness and surface roughness. Bending fatigue strength: Check the tooth root stress to avoid overload fracture.
Carbon steel (45/40Cr) with a hardness of HRC28-35 after quenching and tempering, used for medium load gears (machine tools, reducers). General industrial gears, cost priority.
Cast iron (HT250) is shock-absorbing and wear-resistant, suitable for low-speed heavy loads (<3m/s). Suitable for agricultural machinery and mining equipment.
Copper alloy (tin bronze) has excellent wear resistance and is used to match steel worm gears with worm gears. Suitable for cranes and elevator gearboxes.
After carburizing and quenching, the surface hardness of alloy steel (20CrMnTi) is HRC58-62, and the core toughness is good. Suitable for automotive transmission gears and wind power gearboxes.
Engineering plastic (nylon 66) is lightweight and corrosion-resistant, but has low bearing capacity, limited to<50 ℃. Suitable for transmission of food machinery and light industry equipment.
Material Type
Carbon steel (45/40Cr) with a hardness of HRC28-35 after quenching and tempering, used for medium load gears (machine tools, reducers). General industrial gears, cost priority.
Cast iron (HT250) is shock-absorbing and wear-resistant, suitable for low-speed heavy loads (<3m/s). Suitable for agricultural machinery and mining equipment.
Copper alloy (tin bronze) has excellent wear resistance and is used to match steel worm gears with worm gears. Suitable for cranes and elevator gearboxes.
After carburizing and quenching, the surface hardness of alloy steel (20CrMnTi) is HRC58-62, and the core toughness is good. Suitable for automotive transmission gears and wind power gearboxes.
Engineering plastic (nylon 66) is lightweight and corrosion-resistant, but has low bearing capacity, limited to<50 ℃. Suitable for transmission of food machinery and light industry equipment.
Key Processes
Carburizing and quenching: surface hardening depth of 0.8-1.2mm, improving wear resistance.
Grinding/shaving teeth: achieving high-precision tooth surface (Ra ≤ 0.4 μ m) and reducing transmission noise.
Nitriding treatment: Small deformation, used for precision gears (such as post grinding treatment).
Key Processes
Carburizing and quenching: surface hardening depth of 0.8-1.2mm, improving wear resistance.
Grinding/shaving teeth: achieving high-precision tooth surface (Ra ≤ 0.4 μ m) and reducing transmission noise.
Nitriding treatment: Small deformation, used for precision gears (such as post grinding treatment).
GEAR SELECTION PROCESS
Clarify The Transmission Requirements
Input/output speed, power/torque, expected
lifespan (e.g. 10000 hours). Install space constraints (diameter, width).
Parameter Calculation
Calculate the modulus (m ≥ ③√ (2000T)/(ψ d_Z [σ _f]), where T is the torque and the width coefficient of the teeth is ψ d_d). Determine the number of teeth, helix angle, and pressure angle (usually 20 °).
Structural Design
Select gear type (spur/helical) and accuracy level (such as ISO 7).
Strength Verification
Use AGMA or ISO 6336 standards to verify the contact and bending fatigue safety factor (≥ 1.3).
Process Adaptation
High load gears require gear grinding, and stainless steel or coatings are preferred for corrosive environments.
MATERIAL SELECTION AND PROCESSING TECHNOLOGY
Gears are the core components of power transmission, and their performance needs to be optimized from multiple dimensions such as materials, processes, and design. When selecting, it is necessary to balance load, efficiency, and cost, and verify the reliability of the solution through simulation and testing. In high-speed and precision scenarios, gears should be preferred, while sprockets are more suitable for situations that require flexible layout.
Common Faults
Glue bonding: Insufficient lubrication or rough tooth surface → Use synthetic high-temperature grease instead.
Abnormal noise: Incorrect installation → Check the parallelism of the axis (error ≤ 0.02mm/m).
Broken teeth: Overload or material defects → Check the load safety factor.
Daily Maintenance
Lubrication: Use extreme pressure gear oil (ISO VG 220-460) and replace it regularly (>2000h).
Wear inspection: Regularly check for pitting and peeling on the tooth surface (replacement is required if the tooth thickness exceeds 10%).
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