Thermal Expansion Technology To Improve Mold Life
Different materials are generally treated by different heat treatment methods. The plastic molds of the low-carbon steel and low-carbon alloy steels are generally subjected to a carburizing treatment method, which has a fast percolation speed, a deep layer, and a layer. The composition gradient and hardness gradient can be easily controlled and low cost. After being carburized, the plastic molds of this type have a carbon content of 0.8% to 1.05% on the surface (0.5 to 2.0 mm). After the layer is quenched and tempered at low temperature, the hardness becomes high, and the wear resistance and fatigue strength are also increased, thereby prolonging the use time of the mold.
However, if the crystal grains are coarse at the time of carburization, embrittlement of the bleeding layer may occur, and the surface of the mold may be peeled off. At the same time, since the carburizing temperature is high and heat treatment is required after the infiltration, the deformation of the mold is large. Therefore, such plastic molds with high precision requirements are not suitable for carburizing. Carburizing methods for plastic molds are commonly found in solid carburizing, gas carburizing, vacuum carburizing and ion carburizing. Because of its high carburizing efficiency, mild carbon concentration gradient, small deformation of the workpiece, environmental protection, and the advantages of slits and small holes, ion carburizing is currently used in plastic molds and dies.
Nitriding is a heat treatment method in which nitrogen atoms are infiltrated into the surface of a workpiece at a specific temperature and in a specific medium. After the nitriding, the surface hardness, wear resistance, fatigue strength and corrosion resistance of the mold are greatly improved, and the mold is after the carburizing treatment. Nitriding is different from carburizing. It is carried out at a lower temperature and has a small deformation of the mold and is suitable for molds with high precision.
Common nitriding processes for molds include liquid nitriding, gas nitriding and ion nitriding. Compared with the traditional nitriding method, ion nitriding has a fast osmotic speed, can control the nitriding structure through different gas components, reduce the surface brittleness of the nitriding layer, and the hardness distribution of the permeable layer is gentle, and it is not easy to cause spalling and thermal fatigue. Energy-saving and pollution-free. Therefore, almost all molds are suitable. However, ion nitriding does not have a good effect on the area of the mold having small holes or grooves. For some plastic molds with complicated shapes, it is not easy to uniformly heat, and the obtained layer is not very uniform.
Carbonitriding is a method of simultaneously infiltrating the surface of the workpiece into carbon and nitrogen to form a carbonitrided layer. Using this method, the mold has small deformation, high permeation speed, low cost, and the surface of the plastic mold treated by this method. It has extremely high hardness, high anti-adhesion, abrasion resistance, seizure resistance and scratch resistance, and the service life of the mold can be increased by 2-4 times. However, after gas nitrocarburizing, the mold often deforms due to the expansion of the surface compound, so it is not suitable for precision plastic molds.