Importance of Measurement and Control of Molten Metal Temperature

Control of the temperature at which molten iron is poured into ladles and then into mould is an important shop floor control. The prevention of defective castings

Excessively hot metal can cause or contribute to:

  • Draw defects at hot spots formed by recesses and reentrant angles in castings.
  • Internal shrinkage cavities or porous areas revealed in the machine shop.
  • Dimensional inaccuracy caused by swelling of the castings.
  • Distortion lifting or breakage of the cores.
  • Poor surface finish
  • Poor surface finish

Cold metal gives

  • Misrun defects, lack of defination and poor fluidity.
  • Cold lap defects.
  • Blow holes, particularly on top surfaces of casting or adjacent to cores.
  • Sub surface blowholes revealed by the first machining cut.
  • Inadequate fusion of chaplets.
  • Defects caused by slag or ladle dross carried into the mould with the metal stream, or formed in the runner system.

The efficiency of molten metal treatment processes

In the carburizing of molten iron by the addition of graphite to the ladle, the carbon pick-up at 1300C can be only about one-fifth of the recovery obtained at 1500C.

In the de-sulphurizing of molten iron with sodium carbonate or calcium carbide, the efficiency of sulphur removal depends on molten temperature. For example, with sodium carbonate the amount of sulphur removed can be doubled if the treatment temperature is increased from 1300C to 1400C.

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