High Flexibility Even in Tough Environmental Temperatures

Silicones respectively silicone rubbers belong to the class of elastomers, but differ in the fact that the main chain is not composed of carbon compounds, but of alternating silicium and oxygen atoms. The silicium atoms carry organic substituents, preferably methyl groups.

Silicones are chemically crosslinked and thus form a network structure. The inorganic polymer chain of silicon and oxygen has a greater bonding energy, which means that the properties are significantly stronger than those of purely organic elastomers.

As a result, application temperatures of permanently 180 °C or briefly 200 °C are possible.

Typical Aapplications of Silicone Are:

 

Thermal properties

Mechanical properties

Electrical properties

Fire properties

Abbreviation​

Chemical name

VDE Ref,

Continuous operating temperature 3000h [°C]

Continuous operating temperature 20.000h [°C]​

Melting area [°C]​

Tensile strength [Mpa]​

Stretch [%]​

Hardness

Volume resistivity at 20°C Dielectric strength Dielectric constant at 1MHz, 20°C

LOI​

Flame retardancy

Halogen-free​

SIR​

Silicone rubber​

2G​

200​

-50 to 180​

networked​

6-14​

>250​

50A - 85A​

>10^15​

30​

3,0 - 4,0​

25 - 30​

very good

Yes​

Manufacturing Competencies Silicone

Depending on their molar mass, silicone rubbers can be divided into liquid silicones (LSR) and solid silicones (HTV), resulting in different processing methods.

Solid silicones (HTV)

Solid silicones are copolymers of dimethylsiloxanes (main chain) and isolated vinylmethylsiloxanes (functional group). Due to their low intermolecular interaction, they have a soft, pasty consistency. With a viscosity of 10,000 to 50,000 Pa-s, solid silicones are easy to process at room temperature.

In the first step, the silicone is mixed with the crosslinker and other additives (such as stabilizers, color, fillers, etc.) on a roller or in a kneader. The silicone compound thus obtained is then cold extruded onto the conductor by using an extruder and then crosslinked by heat input.

The amount of crosslinker and the proportion of functional (vinyl) groups determines the crosslinking density and thus the final properties (such as tensile strength, tear resistance, elongation, hardness, etc.) of the silicone compound.

Peroxides (including halogen-free peroxides) or platinum-catalyzed systems are usually used as crosslinkers. By means of modern extruders or extrusion heads, several silicone layers can be applied to the conductor simultaneously in co-extrusion.

Fluid Silicon

Liquid silicones (LSR)

Liquid silicones are usually 2-component systems consisting of the platinum catalyst (component A) and the Si-H crosslinker (component B), which are crosslinked exclusively by addition. Due to short-chain linear polysiloxanes with a viscosity of approx. 5-500 Pa's and a relatively low filler content (max. 30 %), liquid silicones have a pourable to pasty consistency and are mainly processed via injection molding.

Thanks to its low viscosity, LSR can be applied to the cable at room temperature. For this purpose, the cables are passed horizontally or vertically through the LSR and then crosslinked via heat input. Unlike HTV, LSR does not have to be rolled or compounded beforehand. Both components arrive in different containers and are processed directly. Due to the additional crosslinking by using a platinum catalyst, the crosslinking is residue-free and halogen-free, which makes LSR very popular for applications in the medical sector.

HEW-Silindo Cable

HEW Silindo® - For a noticeably improved silicone feel

For highly sensitive applications, mainly in the medical field, the Silindo® surface developed by HEW-KABEL offers significant advantages.

HEW Silindo® noticeably and permanently improves the conventional silicone haptics. Completely free of foreign material in the silicone or on the surface, HEW Silindo® prevents "sticking" to other materials. This surface property is retained even after more than 400 autoclave cycles.

Properties of HEW Silindo®

  • Completely new surface:
    (no foreign material in the silicone or on the surface).
  • Permanent improvement of the surface haptics
    (anti-adhesive, no "sticking")
  • Minimized sliding friction even after more than 400 autoclave cycles
  • Suitable for the following sterilization options:
    • Steam sterilization (autoclave)
    • STERRAD® NX®
    • Disinfection washing machine
    • Gas sterilization (ethylene oxide)
    • Gamma sterilization
    • Wipe disinfection