Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – By means introducing treating material
Patent
1988-11-16
1990-07-31
Kastler, S.
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
By means introducing treating material
266218, 266270, C21C 534
Patent
active
049444964
DESCRIPTION:
BRIEF SUMMARY
The invention relates to devices and apparatus for injecting gas into high temperature liquids, e.g. molten metals.
It may often be necessary to introduce gas into molten metal in a container or vessel. Gas is injected, for instance into the bottom area of a vessel for diverse purposes, including rinsing; clearing the relatively cool bottom area of solidification products, to help remove them from the vicinity of the vessel bottom outlet where the vessel has such an outlet; equalising the temperature throughout the melt; and stirring to help disperse alloying additions uniformly in the melt. Usually an inert gas is used, e.g. argon. Reactive gases are sometimes substituted if the melt needs some particular chemical treatment such as deoxidising.
Previous gas injection proposals have included the provision of a solid porous plug or brick in the refractory lining of the vessel wall or bottom. Installations featuring porous plugs may be simple, but they possess various drawbacks.
For example, dimensional variations in component parts of a gas-injecting system can lead to loss of gas whereby insufficient gas may reach the porous plug, or excessive quantities of gas may have to be supplied to compensate for the losses.
Also, for example, it is known that the vessel lining may lift-off from the vessel shell between filling and emptying the vessel. Such lift-off is apparently caused by different thermal expansions of the lining and the vessel shell. Lift-off creates a gap between the shell and the adjacent refractory, the gap for instance being of the order of 15 mm. Lift-off is an especial problem with dolomite linings, but is not confined to such linings. A consequence of lift-off can be loss of gas. Thus, insufficient gas may ultimately reach the vessel contents via the porous plug, or excessive amounts of gas must be used to compensate for that which is lost. Lift-off may also disturb the seating of the plug in the lining, resulting in a potential hazard of leakage of melt from the vessel.
Further, porous plugs are potentially hazardous, inter alia because they may crack due to thermal shock when molten metal is introduced into the vessel. Failure of the plug can obviously have extremely dangerous consequences.
The present invention aims to overcome drawbacks associated with prior gas injection systems, and to provide safe, cost effective equipment for use in gas injection and to minimise or prevent loss of gas through leakage.
The invention aims, inter alia, to provide a substantially gas tight gas-injection system having improved means to convey gas positively to the injection plug means; the gas-conveying means is desirably adjustable to compensate for dimensional variations.
In another aspect, the invention aims to provide a gas conveying means able to cope with the occurrence of lift-off, yet still able to convey gas positively to the injection plug means.
The invention also aims to provide gas injection equipment which is capable of containing melt leakage caused by failure of the plug itself or of its seating in the vessel wall.
In this invention, gas is conveyed to molten metal via a refractory nozzle block having a passage therein, the passage being closed, or including a plug closure, at the discharge end of the nozzle passage; the closure or plug is porous, foraminous or is traversed by capillary passages, for distributing the gas into the metal. To minimise or prevent loss of gass through leakage, a gas duct enters the nozzle passage and leads direct to the closure or plug; the duct in some embodiments is adjustable in length, e.g. to accommodate dimensional variations in components of the gas injection system. Since, moreover, the nozzle block may tend to be lifted in its seating in the vessel wall, certain embodiments of this invention are designed to include a gas duct that is expansible, and hence is capable of ensuring there is always a positive feed of gas, direct to the closure or plug, in the event of lift-off occurring.
To contain potential melt leakages past or through the plug or closur
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Radex-Rundschau, Heft 3, 1983, B. Grabner et al., pp. 179-209.
Gelsthorpe John R.
Thrower Anthony
Injectall Limited
Kastler S.
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