Annealing furnaces are industrial furnaces that heat treat metal materials to improve their ductility, softness and cold working properties, as well as to refine their shapes and relieve internal stress. They become more homogenous and have increased mechanical and electrical properties as well.
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Annealing furnaces are used mostly in metallurgy as a secondary post-fabrication process, but glass is also sometimes annealed. The products are placed in the furnace chamber and heated above their recrystallization temperature, then rapidly cooled. The result is a metal product with changed properties and an altered microstructure. Any metal product or shape can be annealed, regardless of size, including strips, sheets, tubes and rods. Steel, stainless steel, copper, silver and brass are all annealed metals and alloys, as well as glass. Nonferrous metals are mostly used because they are able to be quickly cooled in cold water or slowly in air, while ferrous metals are only slowly cooled off. Metal parts that are preparing for further fabrication and shaping like stamping, rolling and forming are often annealed in a furnace to improve their workability properties; finished and assembled products are rarely annealed. The aerospace, aircraft, automotive, building and bridge construction, architectural, manufacturing and metal forming industries all use annealing furnaces to heat treat metal parts.
In an annealing furnace, a clean, non-contaminated, oxygen, carbon and nitrogen free atmosphere is required, in order to prevent oxidation and degradation of the metal part being heated. To rid the chamber of these gases, a controlled atmosphere is created. It is filled with an endothermic gas like hydrogen, which exhibits a high heat transfer rate. In addition to protecting the metal, hydrogen lessens the production cycles because of its high thermal conductivity. Depending on the size of the metal parts and production runs, annealing furnaces can consist of a single chamber or several. For high part volumes, annealing furnaces have a loading/unloading chamber, a heating chamber and a cooling chamber, which lowers the metal's temperature by bathing the products in cold water or exposing them to cold air. The time and temperature cycles vary with every product, depending on the composition of the material, its condition and the desired results. There are two main types of anneal furnaces-batch fed, which are smaller and manually loaded and unloaded, and continuous furnaces, which are automated and use a conveying system to provide constant work loads through the unit.
