What is Hot Processing?

Larry Ray Palmer

The metalworking term "hot processing" refers to a powder metallurgy process that combines the alternating action of heat and mechanical or vacuum pressure to create hard and brittle metals from high-purity metal powders. It is widely used in the metalworking industry to enhance the physical properties of metals such as steel, titanium and aluminum. Hot processing is also called hot pressing or hot isostatic processing. The process uses three types of heating: inductive, indirect resistance and direct hot pressing.

Hot processing may be used to refine and condition the precious metals that are involved in making jewelry.
Hot processing may be used to refine and condition the precious metals that are involved in making jewelry.

As a result of hot processing, the processed metal takes on the physical characteristics of wrought metals, developing both hardness and brittleness. This added hardness makes hot processed metal useful for a variety of applications where extreme durability is required. The metals and alloys created in this manner are commonly used for heavy-duty cutting equipment, such as carbide-tipped drill bits and saw blades.

Hot processing is accomplished through sintering, which is the heating of a powdered material to a state just below the melting point where it becomes flexible like a plastic. This causes the powdered metal to fuse together, forming strong molecular bonds. The technique of hot processing also produces higher purity levels because the metal powder used for hot processing is generally a high-purity material at the start of the operation.

During the hot processing procedure, the structure of the metal is condensed and stabilized. Using vacuum hot pressing, an inert gas, usually argon, is used to place consistent pressure on all sides of the forming metal. This pressure, combined with the heat and sintering, creates a highly compacted and dense end product that is many times harder than the untreated metal would be. In addition, the process removes voids and imperfections in the metal as the pressure pushes inward on the forming metal to further enhance the metal's natural properties and further refine the impurities of the metal.

The sintering process used in the hot processing of metals is essential for the manufacture of a variety of metal products. Liquid sintering is used in the creation of tungsten carbide or cemented carbide for cutting tools. Bronze is sintered for use in wheel bearings because of its physical characteristics and porosity. Stainless steel is sintered and used for filters in the food and drug industries. Hot processing and sintering might even be used to refine and condition the precious metals that go into making jewelry, aeronautic parts and surgical equipment.

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