The important role of adjusting sand mold temperature in large gray iron casting

In order to adjust the sand temperature, the air temperature must be considered. Although the curing reaction of resin sand is exothermic, the air temperature directly affects the sand temperature. If the temperature is below 10 ℃ or above 30 ℃, it may have a negative effect on the curing reaction rate of resin sand. Although the effect of low temperature (below 10 ℃) can be partially offset by the heating of solidification reaction (the reaction speed is too slow), it is difficult to offset the effect of high sand temperature (the reaction speed is too fast) through the water circulation system when the temperature is high (above 30 ℃).

It has been reported that the sand temperature can be reduced by adding ice to the water cooling system to counteract the effect of high gas temperature, but for some cases with large production, there are problems such as high cost and long cooling time. Therefore, the curing rate can only be adjusted by adjusting the content of curing agent.

At present, the use of a + B furan resin curing agent is a more and more widely used means to adjust the curing reaction speed in foundry production. Agent a is generally a high acidity curing agent, and agent B is a low acidity curing agent. The curing speed of resin sand can be adjusted by adjusting the chemical examples of agent a and agent B. For example, in the case of low temperature, increasing the proportion of agent a and lower the proportion of agent B can improve the curing speed of resin sand. In the case of temperature quotient, reducing the proportion of agent a and increasing the proportion of agent B can reduce the curing speed of resin sand, so this method is not only cost-effective but also easy to operate. Although the content of a and B curing agent is adjusted simultaneously in the actual production, the total amount of curing agent is generally about 30% to 70% according to the author’s experience.

The reason why the increase of sand compactness can improve the mold rigidity and reduce the tendency of mold wall expansion is that the sand compactness improves the mold density and surface hardness. Zhycasting senior engineer team is studying the production process of piston ring

It is found that when the hardness of sand mold surface exceeds 70HB, there is no shrinkage defects of piston rings, and when the hardness is lower than 60HB, the probability of shrinkage defects is up to 50%. It is also found in some data that with the increase of mold density from 1.23g/cm3 to L.56% g / cm3, the size of casting after pouring is reduced from 3.051 inch to 3.005 inch (model size is 3.000 inch), so it can be seen that increasing mold density and surface hardness can reduce the tendency of mold wall expansion. To a certain extent, improving the compactness of sand mold can reduce the adverse effects on castings caused by the low strength of sand mold. In fact, in the molding process of large-scale iron castings, generally for some parts that are easy to bulge, sand impact operation is required to improve the compactness of the sand mold in this part and avoid shrinkage defects in this part.