Polyaryletherketone PEEK™ Polymer For The

The automotive industry constantly strives to increase the performance level and minimise the weight of in-engine components. Therefore, thermoplastic materials are often used to replace parts of the engine which are traditionally constructed from metals. The Polyaryletherketone PEEK™ polymer is the leading high performance thermoplastic for automotive applications. It combines outstanding tribological performance with excellent mechanical properties over a wide temperature range.

Tribological performance may be defined as the friction and wear of interacting surfaces in relative motion. Therefore, the tribology of dry and lubricated contacts is critical for the operation of internal combustion engines. PEEK™ polymer has excellent friction and wear properties which are optimised in the specially formulated tribological grades, namely. 450FC30 and 150FC30 PEEK™ polymer. These materials feature optimum levels of PolyTetraFluoroEthylene (PTFE) and a graphite solid lubricant to reduce the value of the coefficient of friction, with carbon-fibre reinforcement to enhance mechanical properties.

Most automotive applications are required to operate at temperatures in excess of 120°C. Therefore, a high continuous operating temperature (260OC, UL746B) and excellent mechanical properties at this temperature make PEEK™ polymer the natural choice. Figure 1 gives a general overview of the physical properties (low, medium or high) critical for material selection in the automotive industry.

Although at PEEK™ polymer materials are easily processed using conventional moulding equipment, an easy flow 150FC30 PEEK™ polymer grade is available.

A detailed tribological evaluation of PEEK™ polymer is available upon request.

The distributor rotor arms for some high performance cars such as the Ferrari Testarossa are commercially manufactured from PEEK™ polymer. During operation the component rotates at up to 3500 rpm with 12 charge and discharge cycles per revolution. Due to the nature and position of the application, additional fatigue stresses are imposed on the sample by uneven road surfaces and engine vibrations, whilst conducted heat from the engine means that during operation the component experiences an average temperature of 120°C.

The rotor arm comprises a thick-walled moulded section of PEEK™ polymer with four metal inserts. These inserts become an integral part of the component by positioning them in the tool and injection moulding PEEK™ polymer around them thus a complex finished component may be mass-produced without the need for additional machining. Dimensional accuracy over a wide temperature range is crucial to the efficient function of the rotor arm in maintaining a gap between the conducting insert and the electrical contacts of the distributor.

PEEK™ polymer excels in such high performance applications as it combines the required mechanical properties with ease of processing and extends component service-lifetimes.

Magneti 5P entered full time commercial production of these rotor arms after application based trials and is currently evaluating PEEK™ polymer for devices such as batteries, windscreen wipers, ignition and alternator systems.

Perhaps the most demanding in-engine automotive applications of PEEK™ polymer are those of thrust washers and seats for power transmissions. In a service-lifetime these components are immersed in lubricating oil and operate over the temperature range –7°C to 140°C whilst withstanding dry and lubricated tribological contacts, with pressures up to 10MPa and velocities of up to 5ms-1. Under these conditions materials must be dimensionally and thermally stable to allow the correct flow of lubrication to other parts of the system.

PEEK™ polymer is used in such demanding applications because it exhibits a unique combination of properties, which make it the natural and cost-effective choice.
Large automotive manufacturers find that PEEK™ polymer may often be used to replace metals as it enhances un-lubricated tribological contacts while reducing the weight of components and production costs.

Although the physical properties of PEEK™ polymer are unusually high for a thermoplastic material, it is readily processed using conventional techniques to form components with fine tolerances, removing the need for individual machining.

Due to the extraordinarily high tribological demands required from these materials, PEEK™ polymer FC30 grades are used as they combine a low value for the coefficient of friction with outstandingly low wear rates over a wide pressure and velocity range.

Glycodur produce shock absorber bearings for some of the large automotive manufacturers in Germany. These bearings are metallic with a polymer coating to enhance tribological properties and to prevent corrosion of the substrate.

In an attempt to improve service-lifetimes and the quality of their shock absorber coatings, Glycodur conducted polymer compounding research using PEEK™ polymer as a base material. After consultation with the technical team, studies were initiated using the high flow powder grade material 150P PEEK™ polymer.

Due to the excellent performance of the PEEK™ compound coatings in laboratory scale tests, larger and more demanding controlled road tests were performed. These experiments involved imposing the tribological contacts sustained on an estimated car journey of 187,500 miles at an average operating temperature of 90°C.

The success of the new bearing coatings is such that they were fitted in a Paris-Dakar ratty car for advanced testing in rough and unsurfaced terrain.

Formula One racing teams are constantly looking to decrease the weight of vehicle components while improving the overall performance. Therefore, when a new design of alternator was proposed by the Italian automotive electronics specialist Magneti Maretti, PEEK™ polymer was used as the construction material. A spokesman for the company said, “What was needed was a material that was tight yet could maintain its mechanical strength and electrical resistance at high temperatures whilst enduring heavy vibration”.

The material chosen for this application was 450GL30 PEEK™ polymer, a 30% short glass-fibre reinforced compound, as it offered outstanding mechanical and fatigue properties. Although the volume resistivity of 450GL30 PEEK™ polymer is typical of the generic class of thermoplastic materials (1017 W cm at 230C. IEC 93), the outstanding retention of this property (1015 W cm at 1500C. IEC 93) over a wide temperature range makes PEEK™ - polymer the natural choice for such applications.

The alternator cover is a complex component, which is formed by insert moulding with three metal components. This indicates the ease of processing of filled PEEK™ polymer compounds.




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