How to deal with silicone mold shrinkage problems ?

Lately, some friends from FB talked to me about the silicone rubber, and they mentioned the problems of the shrinkage.

Generally, all silicone mold would have the problem of the shrinkage, the difference would be how much it would shrink. 

For example, the shrinkage of the addition cure silicone rubber would be lower than that of the condensation cure silicone rubber. 

And also, the larger the product is, the more the shrinkage would be. 

Then what do to with it? Here are some suggestions. 

A. Choose the right hardness to make the mold.
Normally, different silicone should be choose according to different product's features, for example:
- For products within 20cm: with intricate designs, soft silicone is suitable, such as 10-20 shore A.
- For products of 20cm-80cm: with intricate designs, 20-25 shore A is suitable; with simple designs, 25-30 shore A is suitable.
- For products of 80cm-150cm with intricate designs, 30 shore A is suitable; with simple designs, 30-35 shore A is suitable.
- For products more than 150cm, with intricate designs, 30-35 shore a A is suitable; with simple designs, 35-40 shore A is suitable.
When using a soft silicone to make a large mould, saying 100cm, then the shrinkage must be large than the moulds made by a harder one. 

B. control the addition of catalyst if you are using the condensation cure silicone rubber
Usually, more catalyst would be added if we want to cured fast, but more catalyst would make the silicone mould shrinkage more.
We, SEMOST silicone company has our own R&D Dpet. and have several different kinds of the catalyst, we can adjust the working time and the curing time as you require.
So, if you want to cure fast, let us know you detailed requirements and the temperature as well as the humidness, we can make it for you. 

C. add the fiberglass into the silicone to make the mold if possible.
In fact, we suggest all the large silicone mould should have the fiberglass in it for shaping up, and also, increase the tear&tensile strength of the silicone would. The ageing-resistant performance and the duplication times would increase at the same time. 

D. make the outer mold for the silicone mould
This may have the same function of the fiberglass in point C. And making the outer mold for the silicone mould that made by brushing way would be suggested strongly.
Outer mold can be made by the plaster, resin, ect. 

E. do not remould so fast.
Pls let the silicone mold cured completely, which would take about 24 hours, then remould.
And some other experienced craftsman would put the mould for another 24hours to start the production.
You know, the chemical needs enough time to act. Enough reaction would make the mould stronger. 

F. when you produce the products, pls put the mold flatly, then pour the plaster or other materials into it smoothly. When you do not usually the mold, you should store it flatly, not fold it,and you also can pour the plaster into it and not remould the finished plaster products, leaving it in the mold to keep the mold in original shape.

G. enlarge the mother mould
If possible, enlarge the mother mould by 3~5‰. After cured the silicone mould may shrink, then you can make the products.
This is a way that not so practical, but still it is way. 


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