Iron Type Design
In the design of iron mold sand coating process tooling, the design of iron mold is a more critical and difficult link. Each set of tooling is generally equipped with 10-15 pairs of iron molds, which account for a relatively high proportion of investment in the whole set of tooling. Once a design error occurs, it is generally difficult to repair, not only causing a large amount of waste or even nothing
The law produces normal production, and at the same time causes huge investment losses. The iron type design is to thicken on the basis of the pattern to form an iron type foundation body, and then use the pattern to thicken the thickness of the sand coating on the foundation body.
Boolean minus forms an iron-shaped cavity. For example, the thickness of the sand-covered layer is designed to be 5 mm, and the thickness of the iron behind the sand layer is 30 mm. In this way, first uniformly thicken the pattern by 35 mm to form a base body, and then use a 5 mm thickened entity to Boolean subtract the base body, so that the desired sand-coated cavity (Figure 5) can be obtained, and then the gating system, Stiffeners, handles and other aspects are designed. The choice of the thickness of the sand coating is a key content. When it is too thin, the iron mold cools the molten iron in the cavity too quickly, which is close to the degree of iron mold casting, so that the casting will form a white structure; if it is too thick, the cooling effect of the iron mold will be close to the degree of resin sand or green sand process.
At the same time, if the sand coating is too thick, it is difficult for the iron mold to use the heat of the casting to heat it, and the required sand coating temperature will not be able to carry out normal cycle production. Studies have shown that when the thickness of the sand-coated layer reaches 30 mm, the iron mold loses its rapid cooling effect on the casting.
In actual production, the thickness of the sand coating on different castings is generally 4-8 mm. At present, the design of the sand-coated part of the castings generally adopts the equal-thickness design. In fact, in order to better control the solidification sequence of castings to obtain better quality castings, solidification simulation should be performed on the castings during the design process, and different sand coating thicknesses should be designed for the rapid cooling and hot joints, that is, the sand coating Carry out thickening design. There is also the problem of the ratio between the weight of the molten iron and the weight of the iron during the design of the iron mold. If the iron mold is too light, the molten iron will make the temperature of the iron mold too high.
In order to produce, it must be strongly cooled to reach the required sand coating temperature, which not only affects normal production, but also increases the thermal fatigue of the iron mold and causes it to break prematurely, which seriously affects its service life. If the design of the iron type is too heavy, the heat of the molten iron cannot make the iron type reach the required level
It is difficult to achieve continuous production at the temperature of sand coating. According to experience, the weight ratio of molten iron and iron mold is generally 1: (7-8).