The speed increasing gear is the key driving part in the screw compressor, with a working speed of 2000 ~ 4000r/min and a matching motor power of 90 ~ 250kW. This kind of gear is divided into two types: gear shaft (250 ~ 350mm long) and gear with inner hole.Tooth width is 50 ~ 70mm, tooth radial maximum size is 150 ~ 385mm, modulus m = 3, gear accuracy level 6, made of 20CrMnTi steel.
According to the design of the drawing, the surface hardness of increasing gear is 54 ~ 60HRC, and the hardness of the core is 35 ~ 40HRC. The original outsourcing increasing gear has broken teeth in use, and the reasons for inspection and analysis are the insufficient hardness of the tooth root and the network carbide in the permeation layer.For this reason, the gear is carburized, normalized and quenched in a well - type carburizing furnace.The technological process of increasing gear is forging → normalizing → rough machining (forming) → carburizing → normalizing → semi-finishing → quenching and tempering → finishing → flaw detection.
Heat treatment process:
The first normalizing is a preparatory heat treatment, which is mainly for the convenience of cutting of forging billets.
The second normalizing is to completely eliminate the mesh cementite in the cementite layer to avoid grinding cracks and improve the performance of the gear.Oil cooling is adopted during quenching. According to different shapes and sizes of gears, horizontal or vertical quenching is adopted along the axis of gears to reduce quenching deformation.
After quenching and tempering, check the hardness of the accelerating gear, the tooth surface is 54 ~ 60HRC, and the heart is 35 ~ 40HRC. The metallographic structure of the gear is fine tempered martensite + granular carbide, the secondary layer is acicular tempered martensite, and the heart is tempered soxite + ferrite.The depth of hardened layer is 1.0 ~ 1.3mm. The deformation of the common normal length direction of the gear is ≤0.03 ~ 0.07mm.
More than 100 sets of gear increasing speed are treated by the above heat treatment process. After processing and inspection, none of the gear has crack and deformation error, and the metallography and hardness meet the requirements.