AFLAS® 400E Lamination to Other Elastomers for Automotive Hose Applications
AFLAS® fluoroelastomers were launched in 1975 by AGC. They are composed of alternating units of tetrafluoroethylene (TFE) and propylene, and are fully saturated, which puts them under the classification of FEPM-type rubbers. They are similar in performance to, and therefore often confused with, FKM-type rubbers.
Due to its outstanding chemical and heat resistance – continuous service temperature of 200°C (392°F) – AFLAS® is used in various applications such as chemical plants, wire & cable, oil & gas, automotive, downhole applications and in the Japanese food processing industry.
As demands on internal combustion engines become stronger, conditions become harsher, and so engine materials need to be protected from more aggressive environments. Engine oils contain amine-based additives that act as anti-oxidants – in contact with hot metals, oils will break down into undesirable products that could potentially damage engine components – and given its excellent resistance to alkaline substances, AFLAS® is ideal for use in oil seals that need to resist high temperatures.
People who are familiar with AFLAS® rubbers will be aware these are not cheap materials. Their performance in harsh environments warrants the added price – slightly above FKMs though still an order of magnitude below FFKMs, but when lifetime is not an issue because maintenance is easy, then AFLAS® becomes a ‘nice to have’ rather than an essential.
Recently, AGC Inc. has added two new grades to its AFLAS® portfolio: 600X, which is similar to its 100S grade for compression moulding into seals and gaskets, and 400E, which is an equivalent to 150E, for extrusion applications such as cable and hose. The two new grades were designed to offer some improvements over their predecessors. Both grades cure far more rapidly; T90 is now around three minutes1 – very similar to EPDMs, AEMs, VMQs, etc. – and this gives a distinct benefit to AFLAS® 400E: the ability to co-cure.
For applications like air, oil, fluid and coolant hoses AFLAS® is very well suited, and the ability of 400E to co-cure with other materials means that a multilayer construction can be used instead of an expensive full-AFLAS® hose, particularly in price-sensitive applications such as automotive, without sacrificing the technical performance or the lifetime of the part. Adhesion has been improved over the previous AFLAS® grades as well – at an expected operating temperature of 150°C adhesion of AFLAS® 400E to ACM, AEM, VMQ and EPDM rubbers, without the use of adhesive primers, was measured at >9 N/in versus <2 N/inch for conventional AFLAS®.
Recent trends in the automotive industry, driven by legislation and environmental concerns, are centred around efficiency – getting the most out of as little as possible – and this is being effected by lightweighting and engine downsizing. Smaller engines are traditionally synonymous with low power; however, there has been a shift in the industry to introduce turbochargers to more petrol engines, and to increase the effectiveness of the turbos. While this is having the desired effect on power output, the flipside is that temperatures and pressures in the turbocharger systems are increasing, which worsens the conditions and hence accelerates the oxidation of oils and fluids, thus amplifying the chemical and physical stress on the components.
And these effects are seen around the whole engine system. For example, the evolution of acidic nitrous (NOx) and sulphurous oxides (SOx) in the oil is a challenge for many components, so alkaline additives are an essential part of the oil chemistry used to combat this acid evolution, and the combination of these with high pressures and high temperatures means hoses made from conventional elastomers are more susceptible to failure. Similarly, the degradation of coolant media such as ethylene or propylene glycol can generate acidic species that, apart from causing engine corrosion, in combination with steam would present a challenge for many rubber hoses.
AFLAS® FEPM can provide a host of benefits in challenging environments across a number of industrial and commercial applications. The introduction of AFLAS® 400E in particular allows for the use of multilayered systems where the FEPM provides the principal functional layer while other materials can be employed to provide the structural integrity and flexibility as necessary.
1 180° peel test at STP and at 150°C to ISO 36:1993
Chris Kent, Fluoropolymer Technical Service