In the process of gear transmission design, especially closed transmission, if the hardness of the gear is not fully considered in the design, it will have a great impact on the performance of the transmission system.Such as common gear failure: tooth surface depression, tooth root fatigue crack, etc.It is related to gear hardness and gear quality.According to the meshing condition of the tooth surface, the gears of the gear reducer are divided into soft tooth surface and hard tooth surface, which are reflected in the following applications:
1: Soft tooth surface gear transmission (tooth surface hardness ≤ 350HBs), at least one of a pair of gears has a soft tooth surface, which is usually used for general medium and low speed gear transmission, and the accuracy requirement is not high.
2: Hard tooth surface gear transmission (tooth surface hardness > 350 HBS), both gears are hard tooth surface.It is usually used for gear transmissions with strong load capacity and small size.
In some equipment, such as winches, soft tooth surfaces are usually used, while hoists now mainly use hard tooth surfaces.
The following three points are usually considered in the design:
1. Close the soft tooth surface gear transmission under normal working conditions.Soft tooth surface steel gear transmission (≤350HBs): mainly based on the contact strength of the tooth surface, designed according to the contact fatigue strength of the tooth surface; and then checked according to the bending fatigue strength of the tooth root.
2: It is suitable for gear transmissions with closed hard tooth surfaces.Hard tooth surface (> 350 HBS) steel gear and cast iron gear transmission: the dedendum is mainly based on the bending strength of the dedendum, and is designed according to the bending fatigue strength; then it is checked according to the contact fatigue strength of the tooth surface.
3: For open gear transmission.The main failure modes are tooth surface wear and tooth fracture.The design standard is: only calculate the modulus according to the design calculation of the bending fatigue strength of the tooth root, and add 10%-20% to the design modulus to consider the influence of wear.
