In the evaluation standard of gear accuracy, a total of 12 accuracy grades are stipulated. According to the order of accuracy from high to low, they are represented by the numbers 1, 2, 3… 12 in sequence. In practical applications, the commonly used accuracy grades are mostly between 5 and 9. At the same time, based on the differences in requirements for motion accuracy, transmission smoothness, and uniform load distribution, the tolerances corresponding to each accuracy grade are further subdivided into three groups, namely the first tolerance group, the second tolerance group, and the third tolerance group.
The determination of the gear accuracy grade requires comprehensive consideration of the purpose of transmission, usage conditions, transmission efficiency, circumferential speed, and a series of other economic and technical indicators.
The gears of grade 5 accuracy belong to the high accuracy grade. The processing method is: generating processing on a gear machine with minimal periodic errors. The final treatment of the tooth surface usually adopts the grinding process. For large gears, after hobbing and gear cutting, grinding or shaving is carried out. The tooth surface roughness can reach 0.4 – 0.8. Its application scope includes: gears used in high-precision indexing mechanisms; gears applied to high-speed operation and with high requirements for operation smoothness and noise; gears used in high-speed steam turbines, etc.
The gears of grade 7 accuracy are regarded as a relatively high accuracy grade. During processing, generating processing is carried out on a high-precision gear machine. For unquenched tooth surfaces, they are cut using high-precision tools; quenched gears need to be finely processed, such as gear grinding, shaving, and grinding. The tooth surface roughness can reach 1.6. Applicable scenarios include: gears used for high-speed, small-load or reversing; feed gears of machine tools and gears requiring motion coordination; medium-speed reduction gears; gears used on aircraft; medium-speed herringbone gears, etc.