Repost: Two-stage (baking) vulcanization of silicone rubber
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Release time:
Mar 02,2026
After a first-stage vulcanization, since the temperature (150℃) is relatively low, some low-molecular-weight substances still remain in the vulcanized rubber, thereby affecting the product’s performance. For example, in silicone rubbers vulcanized with BP or DCBP, the acidic substances—such as benzoic acid—generated by the decomposition of the vulcanizing agent persist in the vulcanized rubber after the first-stage vulcanization. When the product is used under high-temperature, sealed conditions above 200℃, these substances cause cracking, leading to a significant drop in hardness and a sharp deterioration in physical and mechanical properties, ultimately rendering the product unusable. To address this issue, a second-stage vulcanization is required to remove various low-molecular-weight substances from the rubber. Moreover, the second-stage vulcanization can also eliminate moisture or crystal water from fillers, thereby preventing hydrolytic aging of silicone rubber products during use or storage.
Generally, the two-stage vulcanization temperature is slightly higher than the service temperature of the product. The initial temperature is 150 ℃ (or lower), and then the temperature is gradually increased to between 200 ℃ and 250 ℃, maintaining a constant temperature for anywhere from several hours to as many as 10 hours. For original products, a longer intermediate stage with gradual temperature increase is typically employed to prevent bubbling. For general products made from BP-vulcanized vinyl silicone rubber, the following two-stage vulcanization conditions can be used:
A) Heat from room temperature to 150℃ in 1 hour, then further heat to 200℃ in another 1 hour, and finally hold at 200℃ for 4 hours, for a total of 6 hours; or heat from room temperature to 150℃ in 1 hour, then further heat to 200℃ in another 1 hour, then further heat to 250℃ in another 1 hour, and finally hold at 250℃ for 4 hours, for a total of 7 hours.
B). For thick products, adopt a gradual temperature-raising procedure: first, heat from room temperature to 150 ℃ over 1 hour, hold at 150 ℃ for 1 hour, then raise the temperature to 180 ℃ over 1 hour, and subsequently to 200 ℃ over 1 hour. After reaching 200 ℃, maintain this temperature for 4 hours, for a total of 8 hours. Alternatively, heat from room temperature to 150 ℃ over 3 hours, then raise the temperature to 200 ℃ over another 3 hours, followed by a further increase to 250 ℃ over 3 hours. Finally, hold at 250 ℃ for 4 hours, for a total duration of 13 hours. The curing conditions for DBPMH-vulcanized vinyl silicone rubber strips are listed in the table.
Table: Two-stage vulcanization conditions for vinyl silicone rubber strips
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