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What is Gear Hardening? - Gear Hardening machine | Gear Single Shot Hardening Machine
The necessity of gear hardening
Some parts (including gears) in the workpiece in the twisting and bending and other alternating load, the impact of the load, its surface layer to bear a higher stress than the heart. In the case of friction, the surface layer is also constantly being worn, so some parts of the surface layer of high strength, high hardness, high wear resistance and high fatigue limit requirements, only the surface strengthening to meet the above requirements. As the surface hardening has the advantages of small deformation and high productivity, it is widely used in production.

Gear hardening purpose
The purpose of gear hardening is to subject the undercooled austenite to martensite or bainite transformation to obtain martensite or bainite structure, and then with the different temperature of the tempering to significantly improve the strength of steel, hardness, wearness, fatigue strength and toughness, so as to meet the various mechanical parts and tools of different requirements. Gear hardening principle: the workpiece into the inductor (coil), when the inductor into a certain frequency of alternating current, the surrounding that produces alternating magnetic field. The electromagnetic induction of the alternating magnetic field causes the enclosed inductor to produce a closed current - eddy current. Induction current distribution in the workpiece section is very uneven, the workpiece surface current density is high, gradually reduced inward, this phenomenon is called skin effect. The workpiece surface high-density current energy into heat, so that the surface temperature, that is, to achieve surface heating. The higher the current frequency, the greater the difference between the surface layer and the internal current density, the thinner the heating layer. The surface hardening can be achieved by rapidly cooling the temperature of the heating layer beyond the critical point temperature of the steel.

single tooth hardening machine
4-meter single tooth hardening machine

The heat treatment deformation of the carburizing gear directly affects the accuracy, strength, noise and life of the gear. Even after the carburizing heat treatment, the grinding process is reduced, and the deformation level of the gear is still reduced. There are many factors that affect the deformation of carburizing heat treatment, and only the various factors can control the deformation to a lesser extent. Control gear deformation must also be in the manufacturing process of the gear to try to solve.
(1) the impact of metallurgical factors on the deformation of the gear material, the test shows that the higher the hardenability of steel. The greater the deformation. When the hardness of the heart is higher than 40HRC, the deformation will increase obviously. Therefore, the hardenability of steel with a certain requirement, harden the band with the narrower. The more stable deformation, steel mills to provide "low, stable deformation" of steel. A1 / N content ratio is controlled in the range of 1 to 2.5, the hardening band can be narrowed and the deformation is reduced. In addition, the material segregation and banding of the material affect the uneven deformation and carburization of the spline holes.
(2) The effect of the preliminary heat treatment on the deformation of the gear, the normalizing hardness is too high, the mixed crystal, a large number of sorbite or Wei's structure will make the hole deformation increases, so use temperature control normalizing or isothermal annealing to deal with forgings.
(3) The impact of carburizing on the deformation, the temperature uniformity. Carbon layer uniformity, uniformity of the cooling medium temperature affect the gear deformation, while the higher the carburizing temperature, the thicker the carburized layer. Low oil temperature, large gear deformation. So to improve the equipment, optimize the process, improve the quality of gear heat treatment.

(4) The effect of hardening on the deformation, quenching and cooling behavior is the most important factor affecting the deformation of the gear, hot oil quenching than cold oil quenching deformation, as well as control at 100 ℃ ± 120 ℃. The cooling capacity of oil is also critical to deformation. Stirring methods and intensity are affected deformation, hardening on the quenching of the plate disc gear, according to a variety of gear deformation. Adjust the punching press parameters to reduce the deformation, adjust the pressure inside and outside the die and bulging heart block and the size of each section of the fuel injection and the table to control the deformation.

The purpose is to make the workpiece heated and cooled evenly, the parts of the workpiece carburizing layer uniform to reduce the thermal stress uneven, uneven tissue stress, to reduce the deformation, can change the clamping method, disk parts and oil surface vertical, Equipment, the use of compensation washers, support washers, superimposed gaskets, spline hole parts available carburizing mandrel and so on.

Gear single shot induction hardening machine
Gear single shot induction hardening machine

First, master the deformation of the heat treatment, moving tolerance with the location, improve product qualification rate;
Second, according to the deformation law, the application of anti - deformation, contraction end of the pre - expansion hole, improve the qualified rate of deformation after quenching;
Third, the use of non-symmetrical or uneven thickness of the workpiece using the amount of processing methods. Heat treatment and then processing;

Fourth, after heat treatment with the knife to adjust the spline hole, or electrolytic processing fine grinding spline hole, or carburizing and then heating the mandrel bar quenching, after pressing the mandrel, to ensure that the size of the spline hole and other means to reduce the deformation.

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