The production process of solid silicone rubber is a precise process relay, which involves three core steps from raw rubber to finished product: mixing, molding, and vulcanization. Each step directly determines the performance and quality of the final product. Unlike the automated injection of liquid silicone rubber, the processing of solid silicone rubber relies more on experience accumulation and process control, which is why it is called a "craft activity".

Everything starts with mixing. Raw rubber is usually supplied in block or strip form, and first needs to be thoroughly mixed with reinforcing fillers, structural control agents, vulcanizing agents, and other additives on the open or internal mixer. White carbon black is the most commonly used reinforcing filler, with a dosage usually between thirty to sixty parts. It can significantly improve the tensile strength and tear strength of the rubber material, but excessive use can lead to processing difficulties and high hardness. The addition of structural control agents such as hydroxyl silicone oil can regulate the flowability and vulcanization characteristics of the rubber material, preventing the phenomenon of "structuring" - that is, the rubber material gradually becomes hard and loses processability during storage. The choice of vulcanizing agent determines the final vulcanization method: the peroxide vulcanization system is suitable for high-temperature molding vulcanization, and the vulcanization temperature is usually between 150 and 180 degrees Celsius; The platinum vulcanization system is suitable for addition vulcanization, which can be completed at lower temperatures with no by-products and lower shrinkage rate. The mixing temperature is generally controlled at 40 to 60 degrees Celsius. If it is too high, it will cause the vulcanizing agent to decompose prematurely, while if it is too low, it will be unevenly dispersed.

After mixing is completed, it enters the molding stage, which is the greatest flexibility of solid silicone rubber compared to liquid silicone rubber. Compression molding is the most classic method, which involves placing the weighed rubber material into a mold, applying pressure and heating on a flat vulcanizing machine, and after a certain period of time, opening the mold to remove the product. The molding process is suitable for products with complex shapes and large sizes, such as sealing rings, gaskets, miscellaneous parts, etc. Extrusion molding is used to produce continuous products with fixed cross-sectional shapes, such as silicone tubes, silicone strips, silicone foam strips, etc. The rubber material is pushed into a specific extrusion mold through an extruder screw, and after continuous extrusion, it is cured by hot air vulcanization or steam vulcanization. Rolling forming can be used to prepare thin films and adhesive tapes, by rolling the mixed rubber into sheets of the desired thickness through the rollers of a rolling machine. Although injection molding can also be used for solid silicone rubber, its flowability is not as good as liquid silicone rubber, usually requiring higher temperatures and pressures, and its application is relatively limited.

Sulfurization is the last and most critical link in the entire process chain. The control of vulcanization temperature and time directly affects the crosslinking density, which in turn determines the mechanical properties, compression set, and aging resistance of the product. Insufficient vulcanization can lead to softening, low strength, and significant permanent deformation of the product; Excessive sulfurization can cause the product to become brittle, reduce elasticity, and result in surface frosting. For peroxide vulcanization systems, a two-stage vulcanization process is usually used: first, the main vulcanization is completed at the molding temperature, and then the post vulcanization is carried out in an oven at 150 to 200 degrees Celsius for several hours to eliminate residual volatiles and improve crosslinking uniformity. This post vulcanization treatment is particularly important for seals that require low compression permanent deformation.

Regarding liquid silicone rubber, please refer to our website for details: IOTA Liquid Silicone Rubber