PRODUCT CATEGORIES

Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Heat treatment process of gear vacuum carburizing and quenching

Gears are one of the most common and most widely used parts in modern mechanical combinations. There are gears in almost all machinery such as ships, airplanes, automobiles, and cranes, which shows its role and usage. In the process of mechanical use, gear failure occurs from time to time, mainly including gear tooth fatigue fracture and tooth surface fatigue damage. In the process of manufacturing and producing gears at this stage, vacuum carburizing and quenching heat treatment is still the mainstream process, but this method has a big drawback, that is, the deformation problem after the gear carburizing and quenching heat treatment, which greatly reduces the quality of the gear. .

Reasonable heat treatment of gears during processing is conducive to enhancing its bearing capacity and prolonging its service life. The most commonly used method of heat treatment is vacuum carburizing and quenching, which can effectively improve the performance of gears. However, this method is relatively complicated and often Due to some factors, the gears will be deformed and other phenomena. There are many reasons that affect heat treatment deformation, such as gear structure, material, forging quality, pre-heat treatment quality, etc., and these factors also affect each other and are difficult to control. A detailed and reasonable analysis of the heat treatment deformation phenomenon of gear vacuum carburizing and quenching is made. , and formulated effective improvement measures for its processing technology.

1 Gear parameters and vacuum heat treatment process

1.1 Gear parameters

The gear material selected in this paper: 20CrMnTiH, the specific parameters are: modulus=1.191mm, left-handed 25°, common normal=16.44(-0.05, 0) mm, φ=39.831(-0.1, 0) mm in the diameter of the tooth tip circle, Inner diameter φ=16(0, +0.018) mm. The gear is a symmetrical hollow structure, with large inner and outer diameters, no web support, and relatively thin wall thickness, which is prone to deformation after heat treatment.

1.2 Gear vacuum heat treatment process

The gear vacuum heat treatment process is respectively carried out through a vacuum carburizing and quenching furnace with a length of 15 meters and a vacuum tempering furnace with a length of 8 meters. 92045) ℃, then constant temperature carburizing for three hours, after the end of carburizing, the temperature is uniformly cooled to (860 ± 5) ℃ for 40 minutes, and then constant temperature vacuum quenching for 50 minutes, in which the quenching liquid needs to be 80 ℃, and then it is carried out for a period of time. Low temperature tempering at (160±5)℃ for 2 hours. In the original process, when the gears are carburized, the four gears are laid flat.

1.3 Analysis of heat treatment deformation of gear vacuum carburizing and quenching

Measured the four values of 0° and 180° up and down the four gears after carburizing treatment by the original process, and found that the outer diameter and common normal of the gears have swelled to a certain extent, and two gears also have elliptical distortion; After the subsequent quenching process, the outer diameter and the common normal of the gears are obviously reduced. After these two processes of expansion and contraction, the gears are inevitably deformed, and the end face of the four gears is the most serious. up to 1.9mm. Although the deformation of the common normal line of this batch of gears is not serious, the end face distortion still caused a lot of trouble to the machining steps. One of the gears still has a lot of oxide scale after grinding, so it can only be scrapped. In the original process, all the gears were laid flat, which greatly affected the uniformity of the gas circulation during the carburizing process, resulting in uneven thickness of the carburized layers of the four gears. From the above analysis, it can be seen that the gear

The deformation of carburizing and quenching heat treatment includes four conditions: the change of expansion and contraction, the change of taper, the change of ovality and the distortion of tooth surface.

2.Improvement of heat treatment process of gear vacuum carburizing and quenching

2.1 Improve the way the gears enter the furnace and how to place them

Change the loading method of the gear entering the vacuum carburizing furnace, and change it to leaning and stacking, and the inclination angle is 45°. This improved method can effectively avoid the high temperature creep of the gear due to its own weight; In this way, the gear can be kept warm when it comes out of the oven, and it can prevent it from directly contacting the cold air. After the gear is vacuum carburized, the upper and lower end faces of the gear are reversed during vacuum quenching. Although the high temperature creep of the gear during quenching is an inevitable phenomenon, the reversed gear can offset the taper caused by carburizing to a certain extent.

2.2 Analyze the deformation of the gear entering the furnace and the improved placement method

After improving the placement method, the outer diameter and common normal of the gear are measured and found that the change has decreased, and it can be clearly found that the roughening effect of the carburized pier has been alleviated. However, based on the temperature instability in the furnace and the high temperature creep phenomenon , The two gears have some conical changes. After the gears are reversed in the vacuum quenching process, the conical deformation phenomenon has been effectively eliminated. After quenching, the common normal of two gears is still out of tolerance, and no black oxide scale remains after the fine grinding allowance is controlled by the grinding process. And the carburizing thickness and hardness of the gears meet the requirements, it can be seen that changing the gear placement method can effectively improve the carburizing situation of the gears.

2.3 Preliminary heat treatment of gear blanks

Preliminary heat treatment of the tooth blank is a very necessary step. First, this step can effectively reduce the forging stress and avoid the deformation problem caused by the redistribution of stress in the cutting teeth; second, this step can significantly uniformly refine the bad structure. It should be noted that the effectiveness of the preparatory heat treatment must be ensured, otherwise the cutting performance and machining accuracy will be easily damaged. It can be seen that the preparatory heat treatment of the gear blank can effectively improve the gear deformation.

3 Conclusion

In summary, various factors in the gear processing process will have a certain impact on the gear deformation. Under different conditions, the primary and secondary relationships of these factors are not the same. Therefore, it must be considered and analyzed according to the specific situation. And it takes repeated practice and exploration to find certain rules. After the above improvement method, the scrapping problem caused by the deformation of the gear vacuum carburizing and quenching heat treatment is effectively improved, the cost is effectively reduced, the effect is relatively satisfactory, and it has certain economic benefits.