I. quality problems in quenching and cooling 1. Insufficient hardness and insufficient hardening depth, low quenching and cooling speed are the causes of insufficient hardening hardness, uneven hardness and insufficient hardening depth of gear. However, according to the different material, shape, size and heat treatment requirements of actual quenched gear, it can be divided into three stages: insufficient cooling speed in high temperature stage, insufficient cooling speed in medium and low temperature stage and low temperature stage. Different conditions such as insufficient cold speed. For example. For the small and medium-sized gears, the lack of quenching hardness is often caused by the lack of cooling speed in the middle and high temperature stage. When the gears with large module require deeper hardening layer, it is necessary to improve the cooling speed at low temperature. For quenching oil, generally speaking, the steam film stage of the oil is short, the medium temperature cooling rate is fast, and the low temperature cooling rate is fast, so high and uniform quenching hardness and sufficient hardening depth can be obtained. The way of loading and hanging the workpiece also has an obvious effect on the quenching and cooling effect. In order to get a better effect, the quenching oil should flow smoothly and be equipped with a good stirring device. The depth of the hardened layer can be increased by increasing the cooling rate of the quenching medium. In the case of the same carbon concentration distribution in the carburizing layer, the quenching oil with higher cooling rate at low temperature is often used to obtain a deeper hardening layer. Therefore, the carburizing time of the workpiece can be correspondingly shortened and the required hardening layer depth can be obtained by using the quenching oil with faster cooling rate. The greater the depth of carburizing hardening layer is, the more obvious the effect of this method is. 2. The high hardness of the core after quenching may be related to the high cooling rate of the selected medium or the high cooling rate of the medium at low temperature. One of the solutions is to change the quenching oil to meet the requirements. The second method is to contact the quenching medium manufacturer and add appropriate additives to reduce the cooling rate of quenching oil at medium and low temperature. The third method is to use steel with lower hardenability. 3. The problem of quenching deformation. Many factories are puzzled by the quenching deformation. According to custom, the solution to the problem of deformation usually involves many departments, and the solution is often comprehensive measures. Recently, an article on quenching deformation has been published. The causes of deformation are mainly attributed to insufficient cooling speed and uneven cooling. On this basis, a solution to improve cooling speed and try to achieve uniform cooling is proposed for reference [1]. Measures to improve the quenching cooling rate are also listed in the reference. In application, measures in the same direction of action should be reasonably selected and added. It can solve the problem of quenching deformation of most gears. For example, the deformation of the internal spline hole of the gear is often due to the insufficient cooling speed of the selected quenching oil at high temperature, or the long vapor film stage of the oil. To improve the cooling rate of oil at high temperature and the cooling rate of oil in the whole cooling process can generally solve the problem of internal spline hole deformation. For the small and medium gears, especially the more precise ones, it is necessary to select and use the isothermal graded quenching oil well to control the deformation. 4. The problem of quenching crack of gear mainly occurs in induction heating quenching. The problem is solved by choosing water-based quenching medium, such as PAG type quenching medium (such as modern Yu 8-20 produced by Beijing Huali Fine Chemical Co., Ltd.) to replace the original tap water. PAG medium is used for induction heating and quenching. High and uniform quenching hardness and deep and stable hardening layer can be obtained, and the risk of quenching crack is very small. 5. Where there is such a requirement for bright problem, bright quenching oil or fast bright quenching oil shall be selected. Generally, if the brightness of bright quenching oil is good, the cooling speed is not high enough, while if the cooling speed is high, the brightness of quenching oil is not good enough. In addition, the brightness of hot oil is generally poor, which can be replaced with new oil or supplemented with additives to improve the brightness.

 

2. The selection of quenching medium for gear at present, the main quenching medium for gear is various quenching oil, water-soluble quenching medium and common tap water. The following discusses the selection methods and precautions of these media in gear quenching. 1. Tap water is the most economical and clean quenching medium. Tap water is often used for quenching and induction hardening of gears with low carbon content, poor hardenability and simple shape. As quenching medium, the cooling characteristics of tap water are as follows: