Freudenberg Sealing Technologies commissions molten-salt extrusion line for large seal profiles

Weinheim, Germany – Freudenberg Sealing Technologies (FST) is commissioning an advanced extrusion line for the production of vulcanised seal profiles using molten salt.

The line expands the company’s range of vulcanised materials and geometries for applications requiring high resistance to abrasion, chemicals and extreme operating conditions, said FST 3 Nov.

The line uses the liquid curing method (LCM), in which the vulcanisation medium is molten salt heated to around 200°C.

FST said the system operates in a closed loop, with the salt continuously recovered and returned to the process.

At the core of the new machinery is a 19-metre salt bath within a 36-metre extrusion line. Two mobile extruders run on rails, allowing quick changeover between "very fine profiles and large sealing cross-sections."

The extruded profile is first sprayed with hot salt to stabilise its shape and then fully immersed for complete vulcanisation, before washing and cooling to remove remaining salt.

According to FST, the molten-salt method ensures uniform heat transfer and prevents oxygen exposure, improving surface quality and consistency. It also enables more flexibility in material selection.

“The LCM process allows the use of peroxide cross-linking and other systems in continuous production, and therefore supports a wide range of elastomer compounds,” FST said.

The company is currently processing a “wide range of elastomers” on the line including NBR, EPDM and FKM for applications where sealing components must remain elastic and durable over long lifetimes. Additional compounds are in development.

The new capacity targets growth areas such as wind power and hydrogen.

Large wind turbines, according to FST, require very large seal profiles that must compensate for long-term movement in tower foundations under severe weather loads.

The seals, FST said, are expected to have a service life of up to 35 years in wind turbines, and the new LCM system expands options available for large seal profiles or ‘established dimensions.’

In hydrogen production, alkaline electrolysers require special materials and seal sizes that are resistant to the potassium hydroxide solution used in the process.

The new technology can support the production of large seal diameters, which “sometimes have to work with extremely delicate profiles with high tolerance requirements.”

Further uses include seals for process equipment operating at high temperatures or in aggressive media, such as industrial ovens and systems in the food sector.

The line is supported by integrated measurement systems for continuous monitoring of product characteristics.

FST said tolerances as low as 0.1 mm on profiles with 1 mm wall thickness are now achievable, compared with 0.3 mm previously. The process also supports materials meeting FDA requirements.

“We are expanding our ability to supply both very large and very fine seal profiles with high precision,” the company said.

“The molten-salt process gives us a broader materials portfolio and greater flexibility in responding to customer-specific demands.”