SILICONE RUBBERS

General Characteristics of silicone rubbers

(VMQ Vinyl MethylSiloxane)

Renowned chemist Frederick Kipping was a pioneer in the study of organic compounds with carbon and silicon molecules and was responsible for the name 'silicone'. Silicone is a combination of quartz rock and carbon at high temperatures, obtaining a silicon-based rubber. From this basic substance other physical states such as gels, oils and solids are formed.

Silicone has a high transparency, is versatile and has an excellent behaviour in different physical and chemical working conditions. It can be transformed by injection, compression moulding, extrusion, autoclave, casting, etc.

Thermal Resistance: Silicone rubberus have an excellent behaviour and stability at temperatures from -55 ºC up to +255 ºC and our THT silicones can work up to ºC in dry heat. There are silicones which can reach working temperatures of -90 ºC, such as the Phenyl-Vinyl-Methyl-Siloxanes (PVMQ). We have special vapour resistant (wet heat) silicones which are stable up to +150 ºC constant temperature.

Non toxicity standards:Inert material which can comply the following international standards for medical, pharmaceutical and foodstuff contact:: FDA CFR 177.2600 (US Food and DrugAdministration), BgVVBfR cap.15 (Bundesinstitut für Gesundheitlichen Verbraucherschutz Und Veterinärmedizin), USP Clase VI (US Pharmacopoeia), EC 1935/2004 Regulation, Journal officiel de la Republique Française brochure 1227.

Non porous Surface: Non adherent to most products and adhesives, silicone is water repellent and water-proof.

Dielectric properties: Silicone rubbers are one of the best electric insulators with the possibility of working from -40 ºC to +180 ºC. We can supply special conductive silicone formulations.

Mechanical properties: Compared to other organic elastomers, silicone does not stand out for its mechanical properties, but combined with its high temperature resistance it is unbeaten by other rubbers. We have specific formulations for high mechanical strength, abrasion resistance, high elasticity, high tear strength, etc.

Weather resistance: Offers excellent resistance to all weather conditions, ozone, pyralene and UV radiation.

Chemical resistance: Silicone rubbers have a good response when in contact with most chemical compounds, but are affected by fats, solvents and petrols.
With fluorosilicones we obtain superb anticorrosion results in most conditions.

Colours: Standard silicone is translucent, but can be pigmented with foodstuff contact approved colours to achieve any RAL upon request. We can also supply luminescent, fluorescent and metallic colours. We transform platinum-cured silicones for those items exposed to sun rays, that need a high transparency or to avoid yellowing due to ageing.

Vulcanisation: Silicone rubbers are vulcanised with different catalysts depending on the process used to vulcanise them. The most common catalysts are:
DBPH (2,5-Dimethyl-2,5-di (tert-butylperoxy) hexane), mostly used for moulding.
DCBP (2,4-dichlorobenzoyl peroxide)
and addition catalysts commonly known as platinum curing, being especially suited for medical, pharmaceutical applications and foodstuff contact used in extrusion.

Post-curing: Peroxide- or platinum-cured silicones must be post-cured at ºC for a minimum of ten hours in air recirculating ovens to remove all volatile residues and make them suitable for foodstuff contact, as well as certifiable as medical grade.

Hardness and density: We offer from 25 Shore A to 90 Shore A hardness in compact silicone(our standard being 65 Shore) and 0.25 gr/cm3 to 0.8 gr/cm3 density in sponge silicones (our standard is 0.25 gr/cm3). 20 shore A compact silicones and 0.15 gr/cm3 are in development and approval stages.

Main products and shapes: Tubes, reinforced tubes, hoses, cords, profile, flat die-cut gaskets, moulded seals, inflatable seals, heat-vulcanised seals, encapsulated o-rings, rectangular profiles, square profiles, moulded parts, sheets, rolls, with textile or metal inserts, multicomponent parts, etc.

Main applications: Pharmaceutical, chemical, medical, aeronautics, space industries, laboratories, foodstuff, cosmetics, packaging, fluids, metal carpentry, construction, lighting, electronics, car industry, machinery manufacturing, etc.

Technical Data Sheet

Resistance Table

Tolerance Margin

In the extrusion processes of silicone rubbers, greater tolerances are needed, than those molding processes since when the silicone is extruded and it exits through the tool / row it expands and during the curing and post-curing processes it undergoes contractions and deformations.

The deformation at the extrusion outlet can be controlled by different supports, which will depend on the degree of control, size and section that is required. The characteristics of the profile to be manufactured determine the applicable tolerance in each dimension. In certain synthetic rubbers, the E1 standard cannot be achieved.

In the process of longitudinal cutting, precision and tolerance will be given by the technology we use in cutting.

In the molding process, every piece has to be manufactured with a surplus of rubber to complete the figure of the mold and so the excess flows through the short burr, an excess of material will cause the vertical axis (Thickness) to vary. We must take into account that for the correct application of the standard, there are fixed dimensions, which are those of the horizontal part of the mold (H) and those of thickness (V), which are those of vertical axis. For the calculation of vertical tolerances, the maximum height of the piece must be used.

There are 3 types of internationally accepted tolerances, "E" for Extrusion, "L" for Longitudinal cutting and "M" for Molding:

• Class E1, L1 y M1 = Maximum quality
• Class E2, L2 y M2 = Good quality
• Class E3, L3 y M3 = No criticism