Powder Production Methods-Mechanical crushing and grinding--Mechanical Alloying-

ERASMO BALANDRÁN RODRÍGUEZ

JORGE NORIEGA

SALVADOR TINOCO VARGAS

Crushing

It is the most widely used method of powder production for hard metal and oxide powders, where raw materials are converted into intermediate or final products.

Depending on the degree on which the material is sintered.

Crushers are widely used as a primary stage to produce the particulate product finer than about 50– 100 mm in size.

Crushers

Jaw crusher: two crushing plates, inclined to each other forming a horizontal opening by their lower borders

Gyratory cone crusher includes a solid cone set on a revolving shaft and placed within a hollow body

Hammer crushers are used either as a one-step primary crusher or as a secondary crusher for products from a primary crusher

Grinding The grinding energy is transferred to materials through such

media as balls, rods and pebbles by moving the mill body. Based on the mode of motion of the mill body, ball-medium mills are classified as tumbling ball mills, vibration mills and planetary mills

==== Tumbling Ball Mills

Cylindrical Ball Mills

Conical Ball Mills

A conical mill body consists of two cones and short cylindrical part located between them. Such a ball mill body is expedient, since efficiency is appreciably increased.

Rod Mills

For fine grinding, rod mills are also used, in which the rods are 40–80 mm in diameter and play a part in the grinding media.

Planetary Mills

A planetary mill consists of a revolving base disk and rotating mill pots. Materials are ground by the large centrifugal force generated during revolution and rotation.

Vibratory Ball Mills

In the vibratory tube mill, oscillatory motion of the balls is used. The balls gyrate around the chamber wall, sometimes traveling horizontally in a spiral trajectory.

Vibrating Grinders

Vibrating grinders are also called cone inertia crushers. The grinder consists of a body with a conical inner surface in which is arranged an internal moving milling cone.

Jet Mills

The jet mill, also called the fluid-energy mill, is based on a cold stream impact process in which the materials are disintegrated by collision of a particle with a particle, a stationary target or a wall of the containing chamber.

Mechanicals Alloying

This process permits the synthesis of novel alloys that are not possible by any other technique.

Combine the advantages of precipitation strengthening and oxide-dispersion hardening in some nickel and iron-base super alloys.

The process consists of repeated welding–fracturing– welding of a mixture of powder particles in a high-energy ball mill.

Process

1.- The MA process starts with mixing of powders in the given proportion and charging the powder into the mill along with the grinding medium.

2- For MA process control, a process control agent (PCA) is introduced into the powder mixture, especially when the latter involves a substantial fraction of a ductile component. The PCAs are ordinary organic compounds which act as surfactant agents. Most of these compounds decompose during milling.

Advantages over conventionalmetal processing techniques

● Mechanically driven displacement reaction allows the direct formation of powder product without first having to manufacture the bulk alloy and then convert it to powder

● It enables the reduction of a number of oxides and halides to pure metals at room temperature, which ensures energy savings

● If a number of components are reduced simultaneously, it is possible to produce an alloy without first having to convert the oxides to pure metals and then to the desired alloy.

Examples

One example of MA is in the crystals, they are coming until nano- meter, get the nanocrystal materials, where the resistance of the material is incremented, in weak ceramics the material could be deformed plastically when it was in nanocrystal state.

Bibliographic Handbook of non-ferrous metal powders