Zhengzhou Gou's electromagnetic induction heating equipment manufacturer proposes measures to improve the nitriding deformation of sheet gears

We all know that the lamella gear is an important part of the LC280A lathe. It is made of 40Cr steel. The workpiece diagram is shown in Figure 2-12. The sheet gear module is 2mm and the number of teeth is 40. The heat treatment is nitriding treatment, the depth of the nitriding layer is 0.15mm, and the surface hardness is 500HVl. During production, it was discovered that the noise during gear operation was too high, reaching 90dB, causing noise pollution. The inner hole size tolerance is 0.07mm, and the public normal size tolerance is 0.05mm.      

Analysis believes that deformation during the nitriding treatment of gears is one of the reasons for the excessive size of the workpiece and excessive noise. The nitriding process of the sheet gear is 520°C x 10h. Due to the infiltration of nitrogen atoms, the volume expands and the gear deforms. The inspection found that the high amount of ferrite in the matrix structure was the main reason for the large deformation of the workpiece. The standard requires that the volume fraction of free ferrite in the workpiece must be less than 5%. During the inspection of the thin gear, it was found that the volume fraction of free ferrite in the pearlite after normalizing was greater than 5%, and the grain size was level 4, which was an unqualified structure. Analysis shows that the large amount of free ferrite in the matrix structure is the main factor causing large dimensional deformation of the workpiece.

In response to the above analysis, Zhengzhou Gou's electromagnetic induction heating equipment manufacturer proposed the following measures to improve the process:

(1) Increase the normalizing of the blank, and the rough turning margin is 1 - 1. 5mm, and then perform quenching and tempering treatment. After quenching and tempering, a fine sorbite structure is obtained. The volume fraction of flake ferrite in the structure is <5 platinum, each Item deformation is slight.

(2) After finishing turning, perform stress relief annealing in a protective atmosphere to eliminate the processing stress generated during machining. The stress relief annealing process is (300 -400) ℃ x 2h.

(3) The nitriding treatment adopts a stepped heating mode to reduce temperature difference thermal stress, and adopts a two-stage nitriding process, as shown in the figure below.    

(4) Clean the gear before nitriding, then use a screw to pass through the center hole, and add nuts asbestos pads to seal the two ends to prevent the inner hole from being nitrided. Hang the gear vertically or place it vertically when nitriding.

After adopting the improved technology in production, the depth of the nitriding layer of the gear is 0.15mm, the surface hardness is 500HVI, the inner hole deformation is <0.005mm, the change of the common normal is <0.006mm, the gear quality is excellent, the machine tool accuracy is level 7, and the noise is <87dB, reaching the technical level. Requirements indicators.