Sintering furnaces are large heat chambers, often of conveyor belt assembly, that heat powdered materials below their melting points to make dense, less porous, compact and solid metal, glass, ceramic, composite, alloyed and plastic products.
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Sintering furnaces usually consist of multiple chambers that heat loose powder material to temperatures as high as 1350° C to become large, bulky items that are formed with specific material properties not be accomplished by standard metal casting. The finished product is less porous than the raw powder and has well defined dimensions. These ovens are generally quite large and electrically heated. Their components are usually made of a nickel chromium alloy, which allows temperatures up to 1150° C, but the highest heat sintering furnaces, which are able to generate over 1300° C, are made of silicon carbide. Sintering furnaces produce many different parts and products, usually for industrial applications. These include structural parts, fasteners, bearings, tools, magnets and dental zirconium used in dental labs, among many others. The heating process takes up to 3 hours to complete, and the parts are in a cooling chamber for no longer than a half hour. Most sintering is referred to as solid state, meaning the powder is heated but never melted. Some sintering processes do melt the material, which is easier and less expensive. However, it causes degradation and oxidization of the raw material, and is therefore seldom practiced.
Larger industrial sintering furnaces are multi-chamber and use a woven wire mesh conveyor belt to transport the parts through the different steps of the sintering process. Multiple items are sintered at a time. Molds and forms are filled with the powder and separated by ceramic sheets. The chambers include a loading/unloading area, and the hot zone chamber, which heats the powder up to 60-90% the material's melting point. After the powder has adhered together in the hot zone, the products are taken to a rapid cooling chamber, where the products are subjected to low temperatures for less than an hour. Some newer sintering furnaces also have a controlled oxygen chamber, to decrease oxidation. All furnaces use protective forming, endo or exo gases that protect against oxidation and corrosion of the material. The gas is usually created in a chamber next to the furnace. Some furnaces create a vacuum to rid the process of any oxygen. Modern sintering furnaces are completely automated and controlled by CAD operating systems.
