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Classification of Gears and Gear Transmission Mechanisms

Posted: 2014-03-25 03:59:11  Hits: 1796
Ⅰ Summary
Gear is the most important basic part of mechanical products. Gear transmission is a main form of transfer machine power and movement. Compared with mechanical transmission such as belt, friction, hydraulic, it has a larger range of power, higher transmission efficiency, more exact transmission ratio, longer service life, safer and more reliable. Therefore, it has become an indispensable driving part of many mechanical products. Gear design and manufacturing level can directly affect mechanical performance and quality. Gear has a prominent position in industrial development, thus it is regarded as a symbol of industrialization.
Ⅱ Classification of Gears
A. Classification by Tooth Profile
1. Involute gear (The most widely used).
2. Cycloidal gear. 
3. Arc gear.  
B. Classification by Gear Shape
1. Cylindrical gear: shaft gear, disk gear, spur gear, helical gear.
2. Bevel gear: straight bevel gear, spiral bevel gear, contrate gear.
3. Non-circular gear: special-shaped gear (elliptical gear is the most widely used).
4. Rack: Spur gear, helical gear.
5. Worm and worm gear: cylindrical worm, enveloping worm drive, and spiroid drive. 
C. Classification by Tooth Line Shape
1. Spur gear: inner tooth gear, outer tooth gear. 
2. Helical gear: inner tooth gear, outer tooth gear.
3. Herringbone gear: disk gear.
4. Arc gear: single-circular-arc gear, hyper gear.
5. Harmonic gear: circular spline, flexible gear.
6. Cycloid gear: cycloidal gear, pinwheel.
7. Chain wheel: Roller chain, silent chain.
8. Synchronous pulley: rectangular tooth, circle-arc tooth.
Remark: chain wheels and synchronous pulley do not belong to gear drive. Due to similar process, they are listed in this table as attachments.
D. Classification by Gear Surface
1. Inner tooth gear: gear ring.
2. Outer tooth gear: shaft gear, disk gear.
E. Classification by Gear Material
1. Ferrous metals material:
  1.1 Steel: high-quality carbon structural steel, structural alloy steel, stainless steel.
  1.2 Cast iron: ferrosteel and nodular cast iron.
2. Nonferrous material: copper alloy, aluminium alloy.
3. Non-metallic material: plastic, cloth rubber platen.
4. Powder metallurgy (sintering): iron-based, copper-based.
F. Classification by Tooth Surface Hardness and Heat Treatment Process
1. Soft tooth surface gear, tooth surface hardness ≤ 32HRC: normalization, thermal refining.
2. Hardened face gear, tooth surface hardness ≥ 45HRC: tooth high-frequency quenching, integral quenching, carburizing & quenching, hardness nitriding treatment, tufftride process, boriding. 
G. Classification by Gear Manufacturing Method 
1. Cast gear: investment casting
2. Machining gear: 
  2.1 Generating method: hobbing, gear milling, gear-shaping, gear shaving, gear lapping, gear grinding.
  2.2 Forming method: gear milling, gear broaching, gear grinding.
3. Pressure gear: precision forging, cold extruding, precision stamping, Precision rolling.
4. Sintered gear: Powder metallurgy (Produce powder→ pressing→ sintering→ made post-treatment processing gear).
5. Plastic gear: plastic gear.
Ⅲ Classification of Gear Transmission Mechanisms
A. Classification by Gear Drive Type
1. Gear drive with parallel axes: Straight spur gear (external gearing, inner gearing), helical gear (external gearing, inner gearing), herringbone gear transmission, gear and rack driving, non-circular gearing.
2. Intersecting shaft conical gear transmission: Straight tooth bevel gear transmission, Spiral bevel gear transmission.
3. Two axis staggered gear drive: Staggered shaft helical gear transmission, worm gear drive.
B. Classification by Gear Ratio
1. Stable drive ratio: Circular gear mechanism (cylindrical gear, bevel gear, worm gears, chain wheel, cog belt).
2. Change drive ratio: Non-circular gear mechanism (elliptical gear).
C. Classification by Gear Shaft Position 
1. Plane gear mechanism.
2. Space gear mechanism.

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