Atomization has been classified into categories, namely gas, water and centrifugal. Virtually, any material that can be melted can be made into powder by disintegration of the liquid. Aside from chemical reactivity, which may necessitate specific atmosphere or materials, the process is independent of the normal physical and mechanical properties associated with the solid material. The method is being widely adopted, especially because of the relative case of making high purity metals and prealloyed powders directly from the melt. The basic procedure employed is to force a liquid through an orifice, possibly at a bottom of a crucible and impinge a gas or liquid stream on the emerging melt. A great deal depends on the exact design of the orifice. It may induce turbulence in the melt which atomizes the material directly and allows the impinging gas or liquid to reduce the size of the particle still faster.
(Upadhyaya G. S., Powder metallurgy technology, p. 10)
Compressibility
Compressibility is a measure to which a powder will compress or densify upon application of external pressure. Compressibility is reported as the density in g/cm3, rounded to the nearest 0.01 g/cm3, at a specified compaction pressure, or as the pressure needed to reach a specified density. Typically, a cylinder or rectangular test piece is made by pressing powder in a die, with pressure applied simultaneously from top and bottom.
Compressibility of the powder is influenced by factors like: inherent hardness of the concerned metal or alloy, particle shape, internal porosity, particle size distribution, presence of nonmetallics, addition of alloying elements or solid lubricants.
(Upadhyaya G. S., Powder metallurgy technology, p. 26)
Crushing
The major equipments are mortar and pestle, heavy drop hammer, and jaw crushers. In jaw crushing the crushing chamber is formed by one fixed jaw and one movable jaw between stationary side support walls. The movable jaw is mounted eccentrically at the top and is driven by a motor via a flywheel. During the crushing process, the material is drawn down into the tapered crushing chamber as a result of the eccentric jaw motion and is reduced in size by compression and frictional forces. In addition, the angle between the jaws can be altered to give optimum adjustment to the crushing of the material. The final crushed product particle size can be adjusted to values between 15 and 1 mm by adjusting the gap at the base of the jaws. The standards jaws and side walls are manufactured from hardened steel. If the feed material is very abrasive or particular impurities are to be avoided, these components are also available in stainless steel or hard tungsten carbide. If the fixed jaw is removed, access is given to the crushing chamber and the equipment can be cleared easily. In addition, the connection of an exhaust device allows work to be carried out in dust free conditions.
(Upadhyaya G. S., Powder metallurgy technology, p. 33)
Perforating
Perforating involves the simultaneous punching of a pattern of holes in sheet metal. The hole pattern is usually for decorative purposes, or to allow passage of light, gas, or fluid.
(Groover M. P., Fundamentals of modern manufacturing: Materials, processes and systems, p. 446)
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