Testing Support Mats for Catalytic Converters/Diesel Particle Filters

Support mats are functional components of exhaust systems, their purpose being to provide a reliable mounting for the catalyst or diesel particle filter under high thermal loads and expansion, while providing a secure seal to prevent exhaust gases bypassing the catalyst.

To determine the compressive behavior of these support mats under simulated exhaust system conditions, Zwick has developed a high-precision testing machine for use in temperatures up to 1050°C with possible simultaneous gap change.

The testing machine can also be used to determine friction coefficients under all relevant conditions. It is used mainly for development work (fundamental research) at the Faurecia factory in Augsburg, Germany, and also for quality control.

Inside catalytic converters and diesel particle filters there is a sensitive ceramic material. It must be shielded from mechanical loads throughout its life and must always be adequately supported, which means that the differing expansion rates of the metal exhaust system casing and the ceramic insert must be effectively evened out in all operating conditions. This is achieved with support mats made of high-temperature insulation wool.

The support mats must therefore be highly durable at exhaust temperatures up to 1050°C and at the same time possess certain defined mechanical properties. To characterize the mechanical and thermal properties of catalytic converter support mats, the pressure curve over time (‘ageing experiment’) and the friction coefficient of the material are determined under temperature and pressure influence. Zwick has built a materials testing machine with an additional, horizontal test axis, with which the mechanical and thermal material properties of catalytic converter support mats at service temperatures of up to 1050°C can be determined very accurately. Augsburg company Faurecia, which produces around 2.5 million catalytic converters annually, uses these testing machines for research and also for series production checks in order to meet automobile manufacturers’ demanding quality requirements.

The testing machine is equipped with two 10kN compression platens which can be heated up to 1050°C and are used to apply the vertical force for determining stiffness. At these high temperatures, it is necessary to use a non-contact extensometer to measure the separation between the hot compression platens. For simultaneous determination of the friction coefficient, two layers of the material to be tested are placed between the two compression platens. The layers of material are separated in the middle by a metal sheet onto which a horizontal force can act to generate frictional forces.

When the compression platens have reached the test temperature, controlled compression of the support mat begins. During this, controlled reduction of the compression platen separation is achieved by means of a laser extensometer with an accuracy of ± 5 μm and the resulting compressive force is measured with a load cell located in the load train. The second, horizontal test axis consists of an electro-mechanical 5kN actuator which moves the metal sheet horizontally between the two layers of material. The force required for this is recorded by a separate load cell and is then converted to the temperature-specific friction coefficient. This actuator can be operated independently of the vertical axis or synchronized with it.

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