Sintering

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Sintering involves heating the powdered metal compacts in vacuum or a reducing gaseous atmosphere to a temperature that is below the melting point of the primary constituent of the material. The metallic particles metallurgically bond and alloying takes place via diffusion processes.

Various Functions Of Sintering Furnace Atmospheres

  • Delubrication
  • Oxide reduction
  • Sintering (diffusion processes)
  • Carburization/decarburization
  • Prevention of air ingress

De-Lubrication
In pre-heat zone:

  • Lubricants melt, exude to surface of parts, or vaporize
  • Oxidizing atmosphere needed to pyrolize lubricant decomposition products
  • Gas flow adjusted to flush by-products of reaction towards charge end of furnace
  • Inadequate de-lubrication leads to sooting and blistering of parts in hot zone of furnace

Sintering ProcessHot Zone

  • Low dew point
  • Low oxygen content
  • Admixed graphite fully in solution by time parts reach hot zone temperature
  • Oxides are reduced
  • Diffusion of alloy additions takes place
  • Degree of alloying at end of hot zone determines microstructure after sintering

Cooling Zone

  • Unheated region at end of hot zone
  • Water jacketed cooling zone reduces part temperature prior to discharge
  • Atmosphere in cooling zone:
    • Prevents ingress of air
    • Prevents oxidation of parts

Sintering Atmospheres

  • Nitrogen - Hydrogen
  • Endothermic gas
  • Dissociated ammonia
  • Hydrogen
  • Vacuum

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