When most people think of the metal-making process, they picture a stream of molten metal pouring into a mold — it makes a nice visual for films and commercials. But when you consider making parts with powder metal, it may be a little harder to picture the process — or why one would bother with powder metal…
The first step in the overall powder metallurgy (PM) process is making metal powders. There are four main processes used in powder production: solid-state reduction, atomization, electrolysis, and chemical. Solid-State Reduction In solid-state reduction, selected ore is crushed, typically mixed with carbon, and passed through a continuous furnace. In the furnace, a reaction takes place,…
Metals occur in nature sometimes in free or native state, but most of these occur in nature in the form of chemical combination, i.e., in the form of their stable compounds which are associated with gangue or matrix. The earthy impurities such as sand, clay, rocks etc. associatedwith ore are collectively known as gangue or matrix. Thus a large number of metals in nature…
(a) Electrolytic refining This is one of the most convenient and important method of refining and gives a metal of high purity. This method is applicable to many metals such as Cu, Ag, Pb, Au, Ni, Sn, Zn etc. The blocks of impure metal form the anode and thin sheets of pure metal form the cathode. A…
The ore is generally associated with rock impurities like clay, sand etc. called ‘ gangue or matrix‘. The purification of ore means removal of gangue from the powdered ore. This process is otherwise called concentration of the ore or ore dressing. Thus, the percentage of the ore in the concentrated ore is higher than that in…
Sizing a hopper outlet or feed tube to achieve the required discharge rate is more difficult, but no less important, than overcoming arching, particularly for fine powders. All bulk materials have a maximum rate at which they discharge through a hopper opening of a given size (e.g., a Hall flowmeter test). For example, for free-flowing…
Flow of metal powders is determined by standard methods developed by ASTM and MPIF. Flow rate is the time required for a powder sample of a standard weight (50 g) to flow under atmospheric conditions through a funnel into the cavity of a container or mold. A determination of the flow rate of a powder…
Flow characteristics are dependent on several variables, including interparticle friction, particle shape and size, type of material, environmental factors, and weight of the bulk. Characteristics of powder surfaces, such as surface oxide films and lubricant films, also affect flow characteristics. The presence of oxide films on powder particle surfaces alters the friction between particles and…
Milling in an attrition mill (Fig. 24) is effected by the stirring action of an agitator that has a vertical rotating shaft with horizontal arms. This motion causes a differential movement between the balls and the material being milled, thus providing a substantially higher degree of surface contact than is achieved in tumbler or vibratory mills. Fig. 24…
There are many methods that have been used to produce aluminum and aluminum alloy powders including gas and centrifugal atomization, ultrasonic or pulsed atomization, melt spinning with attrition, and mechanically alloying. Gas atomization is used for several applications. In gas atomization, a high-velocity gas jet disintegrates molten aluminum into droplets that solidify to form the powder. In the Alcoa…