The key to study the heat transfer behavior of casting die interface is the temperature change near the interface. It is necessary to obtain the internal temperature of the casting and mold to solve the heat transfer coefficient of the interface, whether using the inverse algorithm or extrapolation method. How to accurately measure the temperature near the casting mold interface becomes the key to solve the heat transfer coefficient of the interface.
At present, temperature measurement methods can be divided into contact and non-contact two categories. The non-contact temperature measurement method is based on the principle of thermal radiation, and the temperature measuring element does not need to be in direct contact with the measured medium. This method has a wide range of applications, but because the measured medium is greatly affected by environmental factors, measurement range, emissivity and other factors, the temperature measurement error of this method is large. The contact temperature measurement method is based on the principle of heat balance, which makes the temperature measuring element and the measured medium reach the same temperature. Because this method has high temperature measurement accuracy and is not affected by the measured medium, thermocouple is generally used to measure temperature in industrial production.
In addition to the influence of temperature measurement method on the temperature measurement near the casting die interface, the accuracy of thermocouple installation position is also a very important factor. Most of the research work is to install the thermocouple by drilling holes in the mold, or to bury the thermocouple in the mold during the mold molding, so as to realize the temperature measurement of different positions in the mold. In the process of metal mold casting, Ho, pehlke and Liu Baicheng installed thermocouple in the mold by drilling holes in the mold, which realized the measurement of the internal temperature of the mold. Denis et al. And Shao Heng et al. Arranged the thermocouples in the mold shell in advance before the mold shell molding of investment casting, and then carried out the sintering molding, so as to realize the installation of the thermocouples in the mold shell.
The above thermocouple installation method will bring a lot of uncertainty and difficulties. First of all, in order to measure the temperature inside the mold, the holes drilled in the mold are generally blind holes, so it is difficult to ensure the accuracy of the distance between the blind hole end and the mold surface. The way of arranging thermocouples before molding can not guarantee the accuracy of the distance between thermocouples and mold surface because the thermoelectric dipole is easy to move during molding; secondly, when placing thermocouples in the hole, it is difficult to ensure that the end of thermocouples closely fits the mold wall, even if the thermocouples can be tightly supported on the mold wall, because the size of the thermocouples is fixed, they are closely connected with the mold wall In fact, the surface is only in partial contact, which makes the measurement error larger.
Chen Liping of Shanghai Jiaotong University solved the problem of easy movement of thermocouples in the process of sand mold manual molding by prefabricating the sand blocks of thermocouples in advance. The shape of the sand block is consistent with the contour of the casting, and the material is consistent with the mold material. It is prefabricated in advance before the mold molding, and the thermocouple is arranged in a specific position. During the mold molding, the sand block is bonded with the surface of the casting. At this time, the distance from the thermocouple to the surface of the sand block is the distance from the surface of the casting, and the thermocouple is completely embedded in the sand mold, realizing the closest contact with the sand mold .
Dour et al. Designed a non immersion probe to realize temperature measurement. The probe used a non-contact infrared thermocouple. The heat transfer behavior of the interface between Al-12% Si alloy casting and H13 mold during die casting was studied by using the probe. Guo Zhipeng et al. Used the prefabricated temperature measurement unit to measure the internal temperature of the mold, and then studied the heat transfer behavior of the casting mold interface in the die.
Therefore, by prefabricating the temperature measurement unit in advance and accurately installing the thermocouple on the temperature measurement unit, the problems of inaccurate installation position of thermocouple and loose fit between thermocouple and die wall can be solved.