In order to select the shrinkage rate of large cast polyurethane elastomer products more accurately, the influences of process conditions, environmental factors and product structure on the shrinkage rate were systematically investigated, and the change curves of shrinkage rate with time were measured. The reasons were analyzed. The results show that the product structure has the greatest influence on the shrinkage rate, the process conditions also have a greater influence on the change of shrinkage rate, while the fluctuation of environmental conditions is the reason for the late fluctuation of shrinkage rate.　　The selection of shrinkage rate is one of the key factors to determine the success of mold design. Especially for large (part size in 1 o00 m / n or more) polyurethane elastomer products, because of its shrinkage rate is large (generally in the 1.5% or so), if the shrinkage rate is not selected properly, light is to increase the amount of mold repair, extend the manufacturing time of the mold, increase the cost of the mold; heavy is due to the size of the mold is too large and scrapped. Therefore, it is important to analyze the reasons for the shrinkage of polyurethane elastomers and study the qualitative relationship between shrinkage and process conditions for the design of cast polyurethane elastomer molds. In this paper, through a large number of process experiments, a more comprehensive study of process conditions, structural factors and environmental conditions on the impact of shrinkage.

The changing law of shrinkage of polyurethane elastomer is:

1) increase with the increase of mold temperature;.

2)with the prolongation of the aging time is jagged change; and

3) with the increase of the ambient temperature and reduce.

4)Fluctuation with the increase of ambient humidity; and

5)Different mold structures have different degrees of hindrance to shrinkage, with the longitudinal direction being the smallest and the transverse direction being the largest; and

6)Shrinkage increases with the increase of flow path length before a certain length, and decreases with the increase of flow length after exceeding a certain length.

It can be seen that the process conditions have a certain impact on the shrinkage rate, and the most significant effect of temperature; the structure of the product itself has a greater impact on the shrinkage rate, polyurethane elasticity of the system is mainly caused by the different flow paths; environmental factors are the later impact factors, their changes are the main factors of the fluctuations in shrinkage rate.