Molded silicone rubber foaming products are simply prepared from special silicone rubber raw materials and foaming agent.

It is made by one-time molding, which produces a large amount of air in the vulcanization process, resulting in a large number of small holes in the silicone rubber.

But we must pay attention to the following problems.

First: the foaming agent whose decomposition products do not affect the heat resistance of silicone rubber shall be selected. Generally, organic blowing agents such as BN and urea are used, and their decomposition products are removed in the secondary vulcanization.

Second: properly control the amount of vulcanizing agent and foaming agent to match the foaming speed with the vulcanization speed. Increasing the amount of foaming agent will increase the porosity of the sponge and reduce the density; Increasing the amount of vulcanizing agent will reduce the porosity of sponge pore, increase the density and produce thicker pore wall. In addition, the vulcanization temperature also has a great influence on the porosity of the sponge.

Third: proper use of vulcanizing agent can better control the porosity and density of sponge (of course, it depends on experience here). Generally, the vulcanizing agent dbpmh and BP or TbpB and dCBP have better effect.

Fourth: No. 2 fumed silica or No. 2 fumed silica and precipitated silica can be used as reinforcing agent. The plastic value of the compound shall be strictly controlled. If the plastic value is too large, it is easy to cause excessive expansion during hole generation, forming a rough opening structure, and even many holes are broken; If the plasticity value is too small, the hole is insufficient and the product is hard. It is easy to control the plasticity value of the compound with weak reinforcing filler, and it is best to use the returned compound on the same day.

Fifth: foaming agent should be evenly dispersed in the compound. Generally, the foaming agent particles are easy to agglomerate and difficult to disperse. The raw rubber / foaming agent master batch ratio (1:1) can be made first, and then mixed to improve the dispersion effect.

Sixth: for the rubber material with molded silicone rubber foaming process, pay attention to remove the bubbles in the rubber material to prevent damage to the sponge structure. The rubber used for molded sponge products shall be cut according to the mold specification after mixing and slicing, and the surface shall be coated with isolating agent for mold vulcanization. Talc powder is generally used as the isolating agent, and white carbon black can also be used. There are two methods for shaping vulcanization of silicone rubber sponge model products: one is the one-step method, that is, the rubber compound will form a sponge with a certain shape and size in the mold at one time, and the two-stage vulcanization will no longer produce holes; The other is a two-step process, that is, the rubber compound is vulcanized in the mold for a short time to form a preliminary hole and just form a layer of surface, and then placed in the oven to form a certain shape and size.