The selection of shrinkage is one of the key factors that determine the success of the mold design. Especially for large (part size above 1 o00 m/n) polyurethane elastomer products, due to its large shrinkage rate (usually around 1.5%), if the shrinkage rate is not selected properly, the modulus of lighter will increase the modulus to extend the mold’s Manufacturing time increases the cost of the mold; more importantly, it is scrapped due to the excessive size of the mold. Therefore, analyzing the reasons for the shrinkage of the polyurethane elastomer and studying the qualitative relationship between the shrinkage rate and the process conditions are of great significance to the design of the casting polyurethane elastomer mold. In this paper, through a large number of process experiments, the effect of process conditions, structural factors and environmental conditions on the shrinkage rate has been comprehensively studied.
The change rule of the shrinkage rate of polyurethane elastomer is:
1) Increase with the increase of mold temperature;
2) It changes in a zigzag shape with the extension of the curing time;
3) Decrease with the increase of ambient temperature;
4) Fluctuates with the increase of environmental humidity;
5) Different mold structures have different resistance to shrinkage, with the smallest longitudinal direction and the largest transverse direction;
6) Before a certain length, the shrinkage rate increases with the increase of the flow path length, after a certain length, the shrinkage rate decreases with the increase of the flow length.
It can be seen that the process conditions have a certain influence on the shrinkage rate, and the influence of temperature is the most significant; the structure of the product itself has a greater influence on the shrinkage rate, and the polyurethane elastic system is mainly caused by the difference in the flow path; Environmental factors are later influencing factors, and their changes are the main factors that cause fluctuations in the shrinkage rate.
