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News

ISC: Systematic improvements to sintering processes

Fraunhofer-Gesellschaft Zur Forderung Der Angewandten Forschung E.V. : 12 January, 2003  (New Product)
Every schoolchild knows that carbon burns easily. So what about brake disks? Those used in Formula-1 race cars and certain top-of-the-range Porsche and Mercedes cars are made of silicon carbide reinforced with carbon fibers. Their braking performance is so exceptional that similar materials will soon find their way into mid-range family automobiles.
But like their all-metal cousins, they tend to overheat if pushed to their limits over winding mountain roads. The same in trucks, where the kinetic energy of several tons of freight is converted to heat. To prevent the hot disks from eroding through contact with oxygen in the air, extensive tests must be performed to assess the properties of the materials: How do they behave at different temperatures, and what are the associated oxidation effects? Will it shrink or deform?

All such questions can be investigated using laboratory apparatus developed to maturity by scientists at the Fraunhofer Institute for Silicate Research ISC. 'Our first device, little TOMMI, was already able to observe sintering and melting processes without direct contact,' reports business unit manager Dr. Friedrich Raether. 'That was a major step, because it is important not to interfere with the raw ceramic or glass part in the oven. The series of measurements to identify changes in the shape of the test object require great precision, down to an accuracy of two micrometers.' Other parameters recorded include the creep behavior of the material and the mass of the object. TOMMI's younger brother, the bigger TOM II, enables the researchers to obtain a full set of thermo-optical measurements on objects up to four centimeters in size. They can also measure heat transfer between the test object and the firing chamber, and vary the composition of the gas. This allows the exhaust gas from the burner to be set to imitate that in a real industrial furnace.

The resulting data on the physical and technical properties of the material are input to simulation programs that the researchers use to optimize the process. 'We have already examined many different ceramic products using our new apparatus, from insulators for high-voltage power lines and light-bulb sockets to dental bridges and crowns or microelectronic components,' relates Raether. 'There is a specific economic target for such mass-produced articles: Is it possible to discharge the furnace and reload it after just 80 percent of the usual firing time, without any loss of product quality?' This also represents a considerable energy saving, given that a furnace may be heated to a temperature of up to 2000 C.
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