Mold silicone rubber molding process

1. Raw materials

The mold silicone rubber is generally composed of a base glue, a crosslinking agent, a catalyst, a filler, and the like.

The base glue is 107 silicone rubber, called hydroxy-terminated polydimethylsiloxane.

The mold silicone rubber can be cured at room temperature, has good fluidity, no deformation, and only a slight line shrinkage.

The crosslinking agent is ethyl orthosilicate. The addition amount of the crosslinking agent has a significant influence on the curing time, tear strength and elongation of the silicone rubber. It has been proved that the addition amount of the crosslinking agent is preferably 5% (mass fraction) of the base rubber.

The catalyst was dibutyltin dilaurate. The amount of catalyst added has a direct relationship with the curing time, and it should not be too much, generally 1% to 2% (mass fraction).

The fillers are talc, quartz powder and white carbon black. Talc powder is generally used as a filler. When silica is used as the filler, there is a significant improvement in mechanical strength, tear strength and uniformity.

2. Molding process

Taking the manufacture and reproduction of the Maitreya Buddha mold as an example, the rubber mold manufacturing process will be described.

(1) Select the bottom opening as the positioning part, invert the gypsum into the cavity, the height is about 30mm above the bottom, and dig the pit for later positioning.

(2) Stick the plasticine. A layer of rice paper was placed on the surface of the object, and a 5 mm thick plasticine was evenly applied to the surface.

(3) Gypsum master. In order to support and fix the RTV mold, to prevent its elastic deformation, a plaster master is first made outside the mud layer. Gypsum images are made one by one according to their approximate parting surface. Pay attention to the positioning between the plaster molds. The gypsum slurry is gypsum: water = 1:1.

(4) RTV molding die making. The gypsum is demolished in the reverse order, the plasticine is removed, cleaned, the disintegrator is applied to the utensil and the plaster mold, and then the mold is closed.

At the same time, the components of the RTV are weighed proportionally, and mixed well after mixing. Since RTV reacts with tetraethyl orthosilicate under the action of the organotin of the promoter during the stirring process, low molecular weight alcohols are produced, and when the silicone rubber is poured, pores are generated in the body of the molding die, so that the pressure is required to be removed. The foam was carried out in a closed vessel having a vacuum of 100 mmHg for about 5 minutes.

The silicone rubber which has been depleted of air bubbles is injected into the cavity of the mold, and is cured at room temperature for about 24 hours.

Disengage the plaster master, cut it with a razor according to the expected parting line, carefully peel off the silicone rubber from the utensil, remove the utensil, and then mold the silicone rubber mold as it is, and make the silicone rubber mold and finished.