Fuelling innovation

Article published in ERJ's July/August 2018 issue 

Much rubber development work is happening under the hood – and it’s not all-electric. Patrick Raleigh reports

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mid all the talk about a shift to electric vehicles in the automotive industry, there seems no let-up in the pace of rubber development work in and around the combustion engine.

Much of the focus is on speciality rubbers, as seen for instance with Chemours development of a new Viton fluororubber targeted particularly at turbo-charger hose applications.

For the last 24 months demand for FKM has been growing very aggressively, Jean-Marc Imbert, global product manager, Viton Fluoroelastomers, said in an interview at DKT2018 in Nuremberg, Germany.

Imbert picked out a new peroxide-cured HFP (hexafluoropropylene) grade as indicative of a continuing R&D drive at Viton.

“We have improved on the mechanical performance of the grade to [make it] one of the best candidates for turbo-charge engine hoses, according to Imbert.

Another focus, he said, was on increasing the compatibility with silicone – most standard constructions in this application have an inside made of fluoroelastomers and silicone on the outside.

“So, the interlayer between must maintain its properties over time,” explained the Viton global product manager.

He also pointed to exhaust gas recirculation applications, which require resistance to acids at very high temperatures. Here, he said demand for fluoroelastomers, such as bisphenol-cured Viton 9307, has remained “very, very strong.”

As well as requirements for resistance to harsher chemicals and substances at higher temperatures, Imbert said requirements around low-temperature performance are also increasing.

“When you look at the latest generation of [petrol] fuel injection engines, there is a need for glass transition temperatures (Tg) of below minus 30 degrees,” said Imbert.

This, he said, is not only [to do with] cold-start behaviour, it is also because in a direct injection system the pump is applying high levels of pulsations to the rubber. To keep the [flexibility] at high pulsation levels you need to reduce Tg.”

New HNBR

Automotive timing belts are a target for Arlanxeo with its development of new fully hydrogenated nitrile rubber (HNBR) – that incorporates a termonomer never used before with these rubbers.

Terpolymer Therban ST 3107 VP is claimed to offer a “unique solution” for complex applications requiring both good low-temperature flexibility and excellent oil resistance, said Susanna Lieber, global head of technical marketing for Therban.

Arlanxeo has filed a patent application for the polymer, which was developed at the company’s sites in Dormagen, Germany and La Wantzenau, France.

“Our new Therban product can reduce the glass transition temperature by up to 10°C in rubber compounds, while maintaining excellent media resistance,” added Lieber.

The elastomer is further claimed to offer “good resistance to high temperatures and in contact with fuels, oil and gas, as well as excellent mechanical properties.”

Much of Zeon Corp.’s focus is also on the automotive industry, which, among other materials, uses of its hydrogenated nitrile rubbers HNBRs for resistance to fuels, lubricating oils, coolants and other media components.

However, recent trends in engine cooling have resulted in the use of more aggressive coolant technologies and higher temperature performance requirements. This, for example, has pushed heat-resistance specifications up by about 20% to 150°C – in some cases in combination with low temperature requirements down to minus 40°C.

In tackling these challenges, Zeon is developing grades of its Zetpol HNBRs that match the performance of certain fluoroelastomers. These include HP-Zetpol, which is based on a “unique architecture and a specific cure site monomer.”

According to the company, its application technologists have developed HP-Zetpol compounds with better heat resistance and significantly improved compression set resistance compared to conventional peroxide-cured HNBR.

The improvement of compression set resistance is magnified over longer ageing time and especially in cross-sectioned articles, such as O-rings, according to technical service manager Dr. Björn Nelson.

“This makes HP-Zetpol a material of choice for the recent coolant technologies,” Nelson stated in a Zeon press release for the DKT 2018 expo.

Also on show by Zeon at DKT were HT-ACM acrylic rubbers for automotive sealings and gaskets as well as for hoses in engine-air management systems. These included HyTemp H570, said to maintain high temperature resistance, while also improving low-temperature and oil resistance.