Silicone rubber is a high-performance material used in a wide range of applications, and its excellent properties are largely due to the vulcanisation process. Vulcanisation is a key step in the transformation of raw rubber into an elastic and stable vulcanised rubber. This article will briefly describe the vulcanisation process of silicone rubber.

Principle of vulcanization

Vulcanisation is the formation of cross-links between the molecular chains of silicone rubber by means of cross-linking agents, thus improving its mechanical strength, heat and chemical resistance. The vulcanisation process is usually carried out under certain conditions of temperature, pressure and time to ensure that the silicone rubber performs to the desired standard.

Types of vulcanization

The three main types of silicone rubber vulcanisation are High Temperature Vulcanisation (HTV), Room Temperature Vulcanisation (RTV) and Additive Vulcanisation:

1.High Temperature Vulcanisation (HTV)

Process: HTV silicone rubber is vulcanised at temperatures between 150°C and 200°C, usually using organic peroxides as vulcanising agents. This type of vulcanisation is suitable for applications requiring high heat resistance and high mechanical strength.

Applications: automotive seals, cable jacketing and high temperature resistant gaskets.

2.Room temperature vulcanisation (RTV)

Process: RTV silicone rubber can be vulcanised at room temperature, and commonly used vulcanising agents include acetic acid, amines and oxides etc. RTV silicone rubber takes longer to vulcanise, but is easy to work with and does not require heating equipment.

Applications: Sealants, adhesives and electronic potting materials.

3.Additive Vulcanisation

Process: Platinum catalysts are used to vulcanise RTV silicone rubber at low to medium temperatures, resulting in fast vulcanisation with no by-products. This method is suitable for products with high requirements for transparency and low compression set.

Applications: medical silicone products, food contact materials and transparent seals.

Steps in the vulcanisation process

1.Mixing

Before vulcanisation, the silicone rubber base material is mixed with vulcanising agents, fillers and other additives. The mixing process is usually carried out using either a compactor or an open kneader to ensure that the components are evenly dispersed.

2.Moulding

After mixing, the silicone rubber compound is subjected to a moulding process, such as calendering, extruding or moulding. The moulding process creates the desired shape of the silicone rubber and prepares it for vulcanisation.

3.Vulcanisation

Depending on the type of vulcanisation, the silicone rubber is vulcanised at the appropriate temperature and pressure. The curing time depends on the thickness of the silicone rubber and the requirements of the application. During vulcanisation, crosslinking agents react with the silicone rubber molecules to form a three-dimensional mesh structure.

4.Post-treatment

After vulcanisation, the silicone rubber products need to undergo necessary post-treatments, such as heat treatment, surface treatment and cleaning, to remove residual vulcanising agents and by-products and to enhance product quality.

Summary

The vulcanisation process of silicone rubber is a critical step in transforming it into a high performance elastomer. Improvements in heat resistance, mechanical strength and chemical stability of silicone rubber can be achieved through different methods such as high temperature vulcanisation, room temperature vulcanisation and overmoulding vulcanisation. Understanding the vulcanisation process helps to select the right vulcanisation method for different applications.