1. Raw materials
Mold silicone rubber generally consists of a base rubber, a cross-linking agent, a catalyst, and a filler.
(1) The base rubber is 107 silicone rubber, which is called hydroxyl-terminated polydimethylsiloxane. This mold silicone rubber can be cured at room temperature, has good fluidity, no deformation, and only slight linear shrinkage.
(2) Crosslinking agent is ethyl orthosilicate. The amount of crosslinking agent has a significant effect on the curing time, tear strength and elongation of silicone rubber. Practice has proved that the amount of crosslinker added is 5% (mass fraction) of the base rubber.
(3) The catalyst is dibutyltin dilaurate. The amount of catalyst added has a direct relationship with the curing time. It should not be too much, generally 1% -2% (mass fraction).
(4) Fillers include talc, quartz, and white carbon black. Talc powder is generally used as a filler. When white carbon black is used as a filler, the mechanical strength, tear strength and uniformity are significantly improved.

2. Molding process
Take the manufacture and copy of Maitreya mold as an example to explain the manufacturing process of silicone rubber mold.
(1) Select the bottom opening as the positioning part, and inject gypsum into the cavity with a height of about 30mm higher than the bottom, and dig out a pit for later positioning.
(2) Stick plasticine. Paste a layer of rice paper on the surface of the utensil, and then evenly paste 5mm thick plasticine on the surface.
(3) Gypsum master. In order to support and fix the RTV mold and prevent its elastic deformation, a plaster mold is first made outside the mud layer. Make plaster images one by one according to its approximate parting surface. Pay attention to the positioning between the plaster molds. The plaster slurry is plaster: water = 1: 1.
(4) Manufacture of RTV mould. The gypsum is lifted out of the mold in the reverse order, the plasticine is removed, cleaned up, the mold release agent is coated on the utensil and the gypsum mold, and the mold is closed.
(5) At the same time, weigh each component of RTV in proportion, and stir thoroughly after mixing. During the stirring process, the reaction between RTV and ethyl orthosilicate under the action of the organotin promoter will produce low-molecular-weight alcohols. When the silicone rubber is poured, pores will be generated in the mold body, so it must be removed under reduced pressure. Foaming is generally carried out in a closed container with a vacuum of 100 mmHg for about 5 minutes.
(6) Inject the depleted silicone rubber into the cavity of the closed mold, and cure at room temperature for about 24 hours.
(7) Take off the plaster mold and cut it with a razor according to the expected parting line;
(8) Carefully peel off the silicone rubber from the utensil, remove the utensil, and then fit the silicone rubber mold with the plaster mold as it is. The silicone rubber mold is completed.