one. raw materials

Mold silicone rubber is generally composed of base rubber, cross-linking agent, catalyst, filler, etc.

(1) The base glue 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) The crosslinking agent is ethyl orthosilicate. The amount of crosslinking agent added has a significant effect on the curing time, tear strength and elongation of silicone rubber. Practice has proved that the amount of crosslinking agent should be 5% (mass fraction) of the base rubber.
(3) The catalyst is dibutyltin dilaurate. The amount of catalyst added is directly related to the curing time, and it should not be too much, generally 1%-2% (mass fraction).
(4) Fillers include talcum powder, quartz powder, and silica. Generally, talcum powder is used as filler. If white carbon black is used as filler, the mechanical strength, tear strength and uniformity are significantly improved.

two. Molding process

Taking the manufacture and reproduction of Maitreya Buddha molds as an example, the manufacturing process of silicone rubber molds is explained.

(1) Select the opening at the bottom as the positioning part, turn over and pour gypsum into the cavity, the height of which is about 30mm higher than the bottom, and dig out a pit for later positioning.
(2) Paste plasticine. Paste a layer of rice paper on the surface of the utensils, and then evenly paste plasticine with a thickness of 5mm on the surface.
(3) plaster mold. In order to support and fix the RTV model and prevent its elastic deformation, a plaster model is first made outside the mud layer. Make gypsum statues piece by piece according to their approximate parting surface, pay attention to the positioning between the plaster molds, and the gypsum slurry is gypsum: water = 1:1.
(4) RTV molding die production. The plaster is moulded in the reverse order of production, remove the plasticine, clean it up, apply a parting agent on the utensils and the plaster mould respectively, and then close the mould.
(5) At the same time, the components of the RTV are weighed in proportion and fully stirred after mixing. During the stirring process, the reaction between RTV and ethyl orthosilicate under the action of the accelerator organotin will produce low-molecular-weight alcohols. When the silicone rubber is poured, pores will be formed on the molding die body, so it must be decompressed and removed. Bubble is generally carried out in a closed container with a vacuum degree of 100mmHg, and the time is about 5min.
(6) Inject the silicone rubber with all the bubbles into the cavity of the closed mold, and cure at room temperature for about 24 hours.
(7) Release the plaster mold and cut it with a razor according to the expected parting line;
(8) Carefully peel off the silicone rubber from the utensils, remove the utensils, and then fit the silicone rubber mold with the plaster mold as it is, and the silicone rubber mold is completed.