Application

Silicone elastomers

Structurally between inorganic and organic compounds

Due to their typical inorganic structure and organic residues, silicone structures are between inorganic and organic compounds. They are hybrids and show a unique range of properties not achieved by any other plastic.

At the beginning of the 20th century, English chemist Frederic Stanley Kipping succeeded in synthesizing the first organic silicon compounds, the basis of polyorganosiloxanes. With the search for alternatives to natural rubber, Kipping's work and other earlier work on the chemistry of silicon became interesting for industrial research.

In 1940, US chemist Eugene G. Rochow and German chemist Richard Müller almost simultaneously discovered a way to produce chloromethylsilanes, the most important precursors for the manufacture of silicones, on an industrial scale. The process is now known as the Müller-Rochow synthesis.

Silicone polymers are produced either with linear oligomers in a polycondensation process or with cyclic siloxanes in a ring-opening polymerization process.

Reinforcing agents and fillers are components of silicone compounds. Their type and quantity influence the mechanical and chemical behavior of the silicone elastomers produced by cross-linking. They can also be easily colored with suitable pigments and dyes.

Typical areas of application

Due to their special and widely adaptable property profile, silicone elastomers can be used advantageously for several applications. Their good electrical insulation properties and the constant physical characteristics over a wide temperature range make them an excellent choice for use in the electrical and electronics industry.

Thanks to their water-repellence, resistance to aging and weather, and absorption of stretching and oscillating movements, complex challenges in structural and civil engineering can be resolved. They have diverse use in automotive and aircraft engineering, the chemical industry, the plastics industry and several further areas.

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Industries and solutions

Benefits

BUSS compounding systems offer the following specific benefits for processing silicone elastomers

Continuous process

The BUSS Kneader is part of a continuous process with all the advantages of a continuous, uninterrupted production. High-precision dosage systems guarantee adherence to exact formulation specifications, whether at low or high throughput. High product homogeneity and more efficient production are the advantages of continuous production processes such as with the BUSS Kneader.

Liquid injection at any pin position

Injection pins, which can be mounted in the BUSS Kneader at any position along the process section, allow liquid components to be injected directly into the molten polymer at the optimum location for the process. The mixing process begins immediately, without smearing on the barrel wall and enables mixing over the shortest possible process length.

Precise temperature control

The BUSS Kneader allows precise temperature control due to controlled energy input and uniform, moderate shear rates as well as their temperature monitoring by thermocouples, which are mounted in drilled kneading pins surrounded by polymer at relevant positions along the process section.

Uniform, moderate shear rates

Uniform shear rates allow controlled mixing at lower temperatures whilst imparting only the required shear energy for the task at hand. The narrow shear rate distribution compared to alternative systems ensures uniform shear histories for every individual particle. This results in high-quality processing with reduced energy input.

Large number of mixing cycles

A large number of mixing cycles is achieved with the latest BUSS multiple-flight kneaders in the compounding machinery. The unique new screw geometries enable maximized splitting and recombining of the compounds, with numerous striations and excellent mixing over a very short process length.

Compounding requirements

from silicone elastomers

The BUSS Kneader has been used very successfully for several decades by leading market participants from the silicone industry. This, on the one hand, for polymer manufacturing via polycondensation or polymerization processes, in which the kneader is used as a high-volume, continuous reactor. The handling of very broad viscosity ranges, the precise addition of reactants through hollow-drilled kneading pins, the excellent temperature management as well as operation at a very low pressure are key for its use.

The actual compounding of silicone elastomers (HTV) and silicone sealing masses (RTV) is a further area of use. Reinforcing materials such as highly dispersed silica or classical fillers and further formulation components are compounded and undesired accompanying materials degassed. The moderate shear rates combined with the extremely high convolution numbers enable excellent mixing results and the handling of very highly viscous masses without local overheating.

The modular and therefore adjustable structure of all the systems and the well-established BUSS process expertise make the BUSS Kneader the first choice for manufacturing silicone polymers and compounding silicone masses in all classes.

Typical plant layout

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