1. The shrinkage of rubber O-ring products increases with the increase of rubber content of vulcanized products.   
2. The shrinkage of rubber O-ring products changes into a saddle curve with the increase of hardness of vulcanized products.   
3. The shrinkage of rubber O-ring products increases with the increase of curing temperature. The shrinkage increases by 0.1% - 0.2% for every 10 ℃ rise in temperature.   
4. The shrinkage rate of rubber O-ring products increases with the increase of raw material injection of vulcanized products. When the raw material quality is more than 5% - 10% of the product quality, the shrinkage rate is relatively stable.   
5. The shrinkage of the rubber in the rolling direction and the flow direction in the mold is greater than that in the vertical direction.  
6. The better the plasticity of the rubber, the smaller the shrinkage; The higher the hardness of the rubber, the smaller the shrinkage (except for high hardness).   
7. The more the amount of filler, the smaller the shrinkage; The higher the glue content, the greater the shrinkage.   
8. The shrinkage rate of the vulcanized products in the middle mold cavity is larger than that of the vulcanized products in the edge mold cavity.   
9. The shrinkage of vulcanized products by injection molding method is slightly smaller than that of vulcanized products by molding method.   
10. The shrinkage of thin products (section thickness less than 3mm) is 0.2% - 0.6% greater than that of thick products (section thickness more than 10mm).  
11. The shrinkage of circular section and square section of the same specification is approximate.   
12. The more sandwich fabrics, the smaller the shrinkage;  
13. The shrinkage of rubber O-ring products lined with metal inlay is small and shrinks towards the direction of metal inlay.   
14. The expansion and shrinkage of rubber O-ring marine products fluctuate widely. The rubber O-ring marine products generally adopt primary or secondary vulcanization. The mold cavity of the first foaming vulcanization (forming pores) is reduced by about 60% according to the size of the product, and the second time is enlarged by 7% - 10% according to the size of the product. The shrinkage of the molding vulcanizate is a variable and extremely complex problem, which is also the most important issue for the mold designer to consider carefully. At present, There is no real, perfect and practical calculation formula yet, and it can only be estimated by experience or accumulated actual measurement data as a reference. Because even if the same rubber compound, the same mold and the same process conditions are used for curing, the shrinkage rate obtained is not the same
Therefore, the shrinkage of the product measured by the test is also an approximate value. In addition, due to the influence of the product shape, hardness, molding process and other factors, it is necessary to introduce a correction value on the average value of the shrinkage measured. The correction direction is in accordance with the above 1-14.   
2、 Flash
The flash thickness is directly related to the quality of semi-finished products (raw material addition), vulcanization pressure, rubber hardness, and mold structure. The more raw material addition, the thicker the product flash, the higher the vulcanization pressure, the thinner the product flash, the higher the rubber hardness, and the thicker the product flash. For sheet products, the thickness of flash should be taken into account when calculating the shrinkage in the opening direction.   
3、 The hot plate size of the curing press is smaller than the mold size
1. The size of the mold shall not be too much smaller than the size of the hot plate, which is easy to cause deformation of the hot plate.   
2. The edge of the mold cavity shall be within 70% of the size of the hot plate.