Process furnaces use heat to change materials, with direct or indirect fire and various fuel sources. Brazing, carburizing, and annealing are common applications. Other furnace types include electric arc, blast, and induction furnaces.
A process furnace is generally defined as an industrial furnace that uses heat to produce state and chemical changes in materials. The heating mechanism can be direct fire where the material is in contact with or near combustible fuel, or indirect fire where the heat is carried by an exchanger to the material to be heated. Process furnace designs often use coal, oil, or a blend of fuel gases as the fuel source. They are built for a variety of applications including annealing, brazing and case-hardening of materials.
Brazing is a method of joining two types of materials that have a high melting point by mixing them with a molten filler metal of a lower melting point in a process furnace. The two main types of process furnace designs used for brazing are retort and vacuum chamber furnaces. Retort furnaces incorporate hydrogen gas to clean the brazed components. Vacuum chamber brazing is used where a highly purified material is desired and furnace temperatures can reach 3,002° Fahrenheit (1,650° Celsius). High-strength, corrosion-resistant metal alloys for aerospace engine components and electronics are produced by brazing, and the filler metals used include silver and copper, or more often nickel and gold.
The carburizing process furnace is used to treat steel alloys by introducing more carbon into it, which increases its surface hardness and durability. It works by infusing the furnace chamber atmosphere with carbon compounds that diffuse into the surface layers of the steel at a temperature between 1,508-1,724° Fahrenheit (820-940° Celsius). The cementing cycle typically takes several hours per batch of material.
An annealing process furnace heat treats materials to remove mechanical stress and oxidation. They typically operate in temperature ranges from 932° Fahrenheit (500° Celsius) to remove metal deformation, to 1,220° Fahrenheit (660° Celsius) to remove oxides. The temperature range of an annealing furnace is fully programmable for unique jobs and materials, within an accuracy level of plus or minus 4.1° Fahrenheit (0.5° Celsius). Their full operating range is from 572 to 2,012° Fahrenheit (300-1,100° Celsius).
There are several other types of process furnace designs, including electric arc furnace, blast furnace, and induction furnace. The electric arc process furnace is often used to produce pig iron and refine steel. Blast furnaces are used to smelt and purify a wide variety of metals, from iron to copper and gold. Induction furnaces use the principle of electrical induction produced by changes from high voltage to low voltage current as a heat source. They are used extensively to melt and alloy a range of ferrous iron and steel and non-ferrous metals.
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