Effect of mold condition on shrinkage tendency of castings

The effect of mold conditions on the shrinkage tendency of castings is mainly due to mold wall expansion. On the other hand, it depends on the pressure of molten iron itself.

For the mold wall rigidity, it can be mainly summarized as two points: the tensile strength of molding sand and the compactness of sand mold. On the one hand, the pressure of molten iron on the mold wall is the expansion pressure of molten iron on the surface of the mold wall in the graphite expansion stage, on the other hand, the static pressure of molten iron on the mold wall. The control of mold condition can be summarized as the control of tensile strength and compactness of sand mold, while the influence of other factors is only the lower limit of the control factor. Due to the limited conditions, this study is all furan resin sand mold. Because in the actual production, in addition to the requirements for the strength of resin sand, there are also restrictions on the curing time. Therefore, this paper also studies the curing time of resin sand.

In order to study the influencing factors of tensile strength and curing time of resin sand, the curing reaction of resin sand must be studied first. For the curing reaction of furan resin sand, some scholars at home and abroad think that there are condensation reaction and polymerization reaction at the same time in the curing process, during which acid only plays a catalytic role. Because of the catalysis of acid, each component in the resin first shrinks, and emits heat, which promotes the system humidity to rise, as follows.

On the one hand, the temperature increases the double bond opening, on the other hand, it increases the catalysis of strong acid. Under the joint influence of these two aspects, the double bond opens rapidly and reconnects rapidly. During this period, a lot of heat is released, and this cycle makes the shrinkage reaction accelerate rapidly. Because of polycondensation and polymerization, the resin molecules are cross-linked from linear to shape, so the mold has necessary strength.

Li zongmeng and Wang Wenqing thought that the dehydration polycondensation seldom happened in practice, but mainly through hydroxyfuran a-h. However, the strength of the mold is mainly formed by the condensation reaction between hydroxyl groups and the addition reaction of C = C double bond, which makes the resin sand have strength.

Although the two parties have different opinions on whether the double bond on the furan ring is opened in the polycondensation reaction, it can be seen from the consensus of the two parties:

1) The necessary strength of furan resin sand is due to the cross-linking reaction among the resin members to form a three-dimensional structure;

2) In the curing reaction, acid mainly plays a catalytic role, but does not participate in the hardening reaction;

3) In the curing reaction process, a large amount of heat is generated and the hardening reaction is accelerated.

It can be seen from the above that the strength of resin sand is mainly determined by the resin content, while the reaction speed is mainly determined by the content of curing agent (acid content) and environmental temperature.