Mumbai University > Mechanical Engineering > Sem 3 > Production Process 1

Marks: 10M

Year: May 2016

• Powder metallurgy is the manufacturing science of producing solid parts of desired geometry and material from powders.
• It is also referred to as powder processing considering that non-metal powders can be involved.
• Powders are compacted into a certain geometry then heated,(sintered), to solidify the part.
• Metal powders play an extremely important role in powder metallurgy.
• All metal powders, because of their individual physical and chemical characteristics, cannot be produced in the same way.
• There are several methods for producing metal powders each giving different size and structure of the particles
• ATOMIZATION:
  • It is as excellent and very widely used method of producing metal powders
  • In case of low melting point metals, the molten metal is kept in a tank. It is raised by the suction produced by hot air, through a pipe to the atomizing nozzle.
  • A fine stream of molten metal is broken into small droplets, which solidify into metal powder particles.
  • The size of particles can be controlled but the shape of particles remains irregular. However, the technique used for high melting point metals is slightly different.
  • A stream of molten metal coming from an orifice at the bottom of a reservoir is broken up by a jet of atomizing fluid (which may be inert gas, air , water or steam) into metal powder particles.
  • It is possible to control the powder characteristics (average particle size, particle shapes, particle size distribution, particle chemistry, and particle structure) by changing the process variables (such as temperature, stream velocity, etc.) In the atomizing process.
• ELECTROLYSIS:
  • Electrolytic deposition or electrolysis is a widely used method of producing powders of iron, coppers, silver, and several other metals.
  • For producing iron, for example, a tank containing a suitable electrolyte is taken. In it steel plates are placed as anode and stainless steel plates are placed as cathode.
  • The two electrodes are connected to a powerful de source. In about 50 hours, a 2 mm thick deposit of is obtained on the cathode plates. This deposit of electrolytic iron is stripped, washed, screened, and sized. The iron powder may be annealed if its brittleness is to be reduced.

• REDUCTION:

  • In this process, metal oxide is reduced to metal powder through contact with a reducing gas at temperature below the melting point.
  • For example, in case of iron the iron oxide is crushed and passed through a furnace. The hydrogen atmosphere in the furnace reacts with the oxygen of iron oxide at a temperature of nearly 10500c and pure iron with sponge – like structure is obtained.
  • In addition to iron, other commonly produced commercially by this method include nickel, cobalt, molybdenum, and tungsten.

• MACHINING AND GRINDING

  • Machining has been used to produce coarse magnesium powder.
  • Milling and grinding processes utilize various types of rotary mills, stamping mills, crushers, and grinders, break down brittle metals into powders of almost any fineness but of irregular shaped particles.
• There are several other methods involving precipitation, condensation and other chemical processes that are employed for producing metal powders.