Elastomers

From Quantity to Quality

Elastomers are long-chain polymers that have thermoplastic properties in the uncrosslinked state. They soften with increasing temperature and are thus extrudable. Only through vulcanization (crosslinking) a narrow- or wide-meshed structure is formed. Depending on the material, crosslinking is carried out by halogen-free peroxides or by radiation crosslinking. This gives elastomers many additional qualities, such as high temperature stability, flexibility and good mechanical resistance, even at very low temperatures. Due to their high elasticity, elastomers return to their original shape after tensile and compressive stress.

Thus, elastomers are used for:

Cables and lines for medical technology
Military cables (navy/air force)
Heating cables

	Chemical properties	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
EPDM	Ethylene propylene diene rubber	3G	100	-40 to 90	networked	5-25	200 - 450	40A - 90D	>10^15	30	3,0 - 4,0	25 - 35	Low to good	yes
EVA	Ethylene vinyl acetate rubber	4G	150	-40 to 120	networked	5-15	>200	70A - 90D	10^12 - 10^14	30	4,0 - 7,0	<22	low	yes
XVH	HEW jacket mixture	-	150	-60 to 125	networked	>10	>200	40D - 60D	>10^12	20	-	>26	very good	yes
FKM	Fluororubber	-	200	-20 to 180	networked	5-13	200	60A - 61D	-	-	6,0 - 9,0	40	very good	yes

At HEW-KABEL, we have excellent expertise in the processing of elastomers. In our in-house compounding department, we develop and produce application-optimized sheathing and insulation materials, which are processed using state-of-the-art production equipment. This results in numerous application possibilities and products that are precisely tailored to the needs of our customers.

Manufacturing Competencies Elastomers

Extrusion

To apply elastomer as insulation or sheathing to the conductor, the material is processed in an extruder. Hot extruders are used for this purpose, which usually consist of a motor, barrel, screw and extrusion head.

In the first step, the plastic granulate is fed into the barrel via a hopper and continuously melted with the help of frictional energy. The screw, as it is called, conveys and compresses the molten mass, which is then shaped with constant pressure via the extrusion head and a suitable die. Pressure and processing temperature vary depending on the material used.

Following extrusion, crosslinking must be carried out in the case of elastomers. This "upgrading" is what makes it possible to use the material in environmental conditions that it would otherwise not be able to withstand.

Crosslinking EPDM, EVA and FKM

In the case of EPDM, EVA and FKM, crosslinking or vulcanization takes place directly after extrusion using a special process in a pressurized salt bath. The so-called PLCV process (pressurized liquid continuous vulcanisation) has the advantage over conventional processes that pressure and temperature can be set independently of each other. This makes it possible to achieve high temperatures at low pressure.

Molten salts, which have very good thermal conductivity, serve as the heat transfer medium and thus contribute energy to the system very efficiently. This energy is needed to start the decomposition reaction (which is rate-determining for the crosslinking reaction) of the peroxide crosslinkers. Cables and wires that have been crosslinked in a pressurized salt bath have - compared to conventional processes - a smoother surface and improved mechanical properties.

Crosslinking XVH

Further processing of XVH does not have to take place directly after extrusion, since crosslinking is not achieved by a chemical reaction but by short-wave electromagnetic radiation (gamma rays). Crosslinking via gamma rays require complex radiation protection measures. Therefore, our lines are cross-linked at an external company. Depending on the material and wall thickness, the radiation dose must be calculated and adjusted.

The mechanism of radiation crosslinking is based on the excitation of a molecule. This forms a polymer radical by splitting off a hydrogen atom, which generates crosslinking with another polymer chain. The advantage of radiation crosslinking is that it takes place at room temperature and does not require any further crosslinking agents. Cables that have been radiation crosslinked can withstand significantly higher temperatures and exhibit significantly improved wear behavior as well as more stable fire behavior.