Whether it is carburizing, carbonitriding and quenching, induction heating quenching or whole heating quenching, heat treatment quality of quenching process of gear are possible:
1, lack of hardness after quenching, uneven quenching hardness, hardening depth is not enough.
2, quenching after the heart hardness is too high.
3. Quench deformation exceeding tolerance.
4. Quenching cracking.
5, the surface brightness is not enough after oil quenching.
Such quality problems in factories are often related to gear material, pretreatment, quenching heating and quenching cooling. After eliminating the problems of material, pretreatment and heating, the role of quenching medium and related technology is particularly prominent. In fact, in recent years the research on quenching abroad also proved that, in improving the quality of heat treatment work, the most noteworthy is the quenching. Quenching cooling is mostly carried out in liquid medium. Gear quenching usually consists of quenching oil, water soluble quenching medium and tap water. Therefore, the following will be the first analysis of the relationship between the above quality problems of gear quenching may occur with the characteristics and usage of quenching medium, and pointed out that the cooling rate required to solve different problems of quenching liquid distribution characteristics. Then the cooling rate distribution characteristics of common quenching medium and the matters needing attention in selection are introduced.
First, the quality problems in quenching cooling:
The lack of hardness and hardened depth of quenching cooling rate is low gear quenching hardness insufficient, uneven hardness and hardening depth is not enough reason, however, according to the actual quenching gear material, shape and size and heat treatment requirements are different, can be divided into high temperature phase in low temperature stage, insufficient cooling rate and low temperature cold stage insufficient cooling rate lack of speed in different situations. For example. For small and medium-sized gear, quenching hardness is often inadequate in the stage of high temperature cooling rate caused by insufficient, and a high modulus gear require a deep hardening layer, improve the cooling speed is very necessary.
1, in general, quenching oil, oil vapor film stage short and medium temperature cooling rate, low temperature and fast cooling speed, often can obtain high and uniform quenching hardness and enough hardening depth. The workpiece mounting mode also has obvious influence on quenching cooling effect. To make the quenching oil flow, and the equipment and the use of good mixing device, can get better effect. Increasing the low temperature cooling rate of quenching medium often increases the depth of hardened layer. The carbon concentration distribution under the same conditions, the low temperature quenching oil cooling rate higher, often get deeper hardening, therefore, the quenching oil cooling speed can be shortened, the workpiece carburizing time, can also obtain the hardening depth requirements. The greater the required depth of carburizing hardening layer, the more obvious the effect of shortening the carburizing time.
2, after quenching the heart hardness is too high, this kind of problem may be related to the cooling speed of the selected medium is too fast or medium low temperature cooling speed is too high. One solution is to change the quenching oil to meet the requirements. The two way is to contact with the manufacturer of quenching medium, adding proper additives to reduce the cooling rate of quenching oil at medium and low temperature. The three way is to use low hardenability steel.
3, quenching deformation problem quenching deformation, so many factories broke the brain. According to the habit, the settlement of the deformation problem usually involves many departments, and the solution is often the comprehensive measures. Recently published articles about the quenching deformation, the deformation caused by the cooling rate is mainly attributed to the insufficient and uneven cooling, and on this basis to improve the cooling rate and try to realize the principle of uniform cooling solutions, reference [1]. The measures to improve the cooling rate of quenching are also listed in the references. The quenching deformation of most gears can be solved. For example, the internal gear spline deformation, quenching oil is often selected high temperature cooling rate, or vapor film stage due to the long oil. High speed cold oil and improve oil cooling speed in the cooling process, the deformation problem can be solved in general spline hole. For small and medium gear, especially the more precise gear, choosing and using isothermal quenching oil is the necessary measure to control the deformation.
4, gear quenching cracking problem, mainly appeared in induction heating quenching. Choose a good water quenching medium, such as commonly used at home and abroad of PAG quenchants (such as quenching liquid WA, Changzhou dragon state company WR) instead of the original use of tap water, the problem will be resolved. PAG medium is used in induction heating quenching. High and uniform quenching hardness and deep and stable hardened layer can be obtained, and the quenching crack is extremely dangerous.
5, the problem of light applications, should choose bright quenching oil or quenching oil. Usually, the bright bright quenching oil cooling speed is not high enough, and the cooling quenching oil high speed of light is not good enough. In addition, the brightness of hot oil is generally poor, can be replaced by new oil or add additives to improve the brightness.
Two. Selection of quenching medium for gear oil
At present, the main medium used for gear quenching is quenching oil, water soluble quenching medium and ordinary tap water. The selection methods and precautions of these media in gear quenching are discussed below.
1. Tap water
Tap water is the most economical and clean medium for quenching. Some low carbon content, poor hardenability and simple shape of gear quenched and tempered and induction heating quenching, often tap water.
As a quenching medium, tap water is cold
