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Large diameter ring gear vacuum carburizing and quenching

Recently, the heat treatment branch carried out carburizing and quenching for two ring gears. The material is 20CrNi2Mo. The technical requirements are that the hardness of the tooth surface is 56~60HRC, and the depth of the carburized layer is 1.8~2.0mm. The modulus is 14, and the distance between the tooth groove and the inner hole is 50mm left stone. According to the conventional heat treatment allowance and heat treatment process, it is very easy to cause the workpiece to be scrapped due to the deformation of the workpiece after quenching.

1.Preliminary analysis

( 1 ) Allowance of conventional heat treatment process

Before carburizing, the common normal line allowance is 0.8mm + 0.1mm, and the remaining surface allowance is 5mm on one side. For this ring gear with low structural strength, the process allowance and process method cannot guarantee the final workpiece size.

(2) Take measures now

The vacuum carburizing and quenching of the piece is carried out by increasing the heat treatment process allowance and making special tooling.

2.Process preparation

(1) Process reserve

The process allowance before vacuum carburizing: 10mm for the end face, 0.8mm+0.1mm for the common normal, 1mm for the diameter of the tip circle, 62mm for the inner hole according to the minimum hole diameter, and within a wide range of 62mm ( φ1281mm position) drilling and tapping 8x M12 threaded holes to make the tooling when carburizing and quenching.

(2) Vacuum carburizing and quenching tooling

Flange type tooling is adopted, and the dimensions are as shown in the figure.

(3) Preparation for vacuum carburizing into the furnace

①Before vacuum carburizing, the non-carburizing surface of the workpiece is brushed with anti-seepage coating for anti-seepage protection.

②The flange-type tooling is closed on the lower end face of the workpiece before vacuum carburizing, and six places of φ40mm x 155mm round steel are welded along the φ800mm circle on the bottom surface of the tooling to prevent the upper end face tooling from sinking and deforming during the heating process of vacuum carburizing and quenching. The vacuum quenching does not play a supporting role, and the round steel is staggered from the four uniformly distributed through holes of φ400mm. The purpose of the through holes is to use this hole to leak oil after quenching.

③The upper end face tooling is closed, and the upper end face closing tooling does not have 4 through holes of φ400mm evenly distributed, and the other dimensions are the same.

④Vacuum carburizing furnace hanger is directly worn down from φ400mm for vacuum carburizing.

(4) After vacuum carburizing

Due to the difficulty in loading and unloading of the tool, the workpiece is not returned to the processing workshop after vacuum carburizing, and is directly quenched.

3.Increase the heat treatment aging process

After quenching, the inner hole is too large before vacuum carburizing. In order to prevent the workpiece from being too large due to the processing stress and deformation after the aging process is carried out, an aging process is added to prevent the aging process. Only the inner hole is processed before, and the diameter of the inner hole is 18mm, and the other parts do not move the knife. After aging, other parts are processed for subsequent workpiece aging.

4.Conclusion

Through the production and use of special tooling, the thin-walled ring gear is finally qualified and meets the requirements of design size and hardness. The implementation of this method has accumulated experience for the subsequent vacuum carburizing and quenching of similar workpieces, which directly brings better economy. Benefit, making a vacuum heat treatment ring gear carburizing and quenching process mature.

Selection of carburizing equipment: The RVC series vacuum carburizing furnace produced by SIMUWU is a high-quality product for the vacuum carburizing process of tools and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum carburizing process.