1. The shrinkage rate of rubber compound is a very complicated and varied problem. It is also a problem that mold designers need to consider carefully. At present, there is no real, complete, and practical calculation formula. It can only rely on Empirical estimation or accumulation of actual measurement data can be used as a reference. Because even if it is a kind of rubber material, the same mold, and under the same process conditions, the three-dimensional network technology forum，If the vulcanization temperature is the same, the vulcanization pressure is the same, and the amount of raw material added is the same) vulcanization, the shrinkage rate obtained is not the same
Therefore, the shrinkage rate of the product measured by the test is also an approximate value, plus it is affected by the shape, hardness, molding process and other factors of the product. Therefore, it is necessary to introduce a correction value on the average value of the measured shrinkage rate, as follows:
1. The shrinkage rate of rubber O-ring products changes as a saddle-shaped curve with the increase of the hardness of the vulcanized product.
2. The shrinkage rate of rubber O-ring products increases with the increase in the amount of raw material injected into the vulcanized product. When the quality of the raw material>product quality is 5%-10%, the shrinkage rate is relatively stable.
3. 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)
4. For the mold with porous cavity, the shrinkage rate of the vulcanized product in the middle cavity is greater than that of the vulcanized product in the edge cavity.
5. The shrinkage rate of thin products (section thickness less than 3mm) is 0.2%---0.6% larger than that of thick products (section thickness above 10mm)
6. The more sandwich fabrics, the smaller the shrinkage rate;
7. The expansion and contraction rate of rubber O-ring sea products has a wide range of fluctuations. Rubber O-ring sea products generally use primary or secondary vulcanization. The first foam vulcanization (re-holes) mold cavity is based on the size of the product. Reduce it by about 60%, and enlarge it by 7%-10% according to the size of the product for the second time as setting vulcanization.
8. The shrinkage rate of rubber O-ring products increases with the increase of the rubber content of vulcanized products
9. The shrinkage rate of rubber O-ring products increases with the increase of vulcanization temperature, and the shrinkage rate increases by 0.1%—0.2% for every 10 degrees of temperature increase.
10. The shrinkage rate in the calendering direction and the direction of flow in the mold is greater than the shrinkage rate in the vertical direction
11. The more the filler, the smaller the shrinkage rate; the higher the amount of glue, the greater the shrinkage rate
12. The shrinkage rate of injection-molded vulcanized products is slightly smaller than that of molded-press vulcanized products.
13. The shrinkage rate of the round section and square section of the same specification is similar
14. Rubber O-rings lined with metal inlays have a small shrinkage rate and shrink in the direction of metal inlays.