How To Adjust the Hardness of Mold Silicone Rubber

The hardness of mold making silicone is usually determined when the silicone manufacturer produces the raw material, and the hardness is fixed after the user uses the liquid silicone raw material molding. Then if you think the hardness of the silicone is too hard or too soft, what can be done to solve it? Let me share some methods for your reference.

shore hardness tester

1. How To Reduce Hardness

1. Mix high hardness and low hardness liquid silicone rubber, for example, mix 30shore A and 10shore A hardness silicone in 1:1 ratio to get about 20shore A hardness silicone. Using this mixing method, it must be noted that addition silicone and condensation silicone cannot be mixed, otherwise the silicone will never be cured.

2. In addition, we can use silicone oil to reduce the hardness, it should be noted that after adding silicone oil not only the silicone hardness will become softer, but also the viscosity will become thinner. Generally, adding 1% of silicone oil will reduce the hardness by about 0.9 to 1.1 shore A, and adding 10% of silicone oil will reduce the hardness by about 5 shore A. Adding too much silicone oil will destroy the molecular weight of silicone, resulting in weakening the tear strength and tensile aspect of silicone after curing and molding, thus affecting the service life of silicone molds.

2. How To Improve Hardness

Increasing the hardness of silicone can be done by increasing the vinyl content and hydrogen content of the hydrogenated silicone oil, or adding white carbon black to increase the hardness. For addition molding silicone, add hydrogenated silicone oil to part B of the silicone and mix well, wait for about 15 minutes and mix it with part A. The adding ratio of hydrogenated silicone oil is recommended to be within 5%. For condensed silicone, you can consider adding more curing agent or curing at elevated temperature, but this has very little effect on improving the hardness. After all, it is difficult to feel the error of silicone hardness in the range of ±2 shore A.

Experience reminder: The adjustment of the hardness of silicone is not a simple ratio, it needs to go through multiple tests to get a relatively consistent result. Regardless of whether it is to reduce the hardness or increase the hardness, it is only suitable for small-range adjustments.


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