Title of the Invention

Metallurgical treatment vessel etc Field of the Invention

This invention relates to a metallurgical treatment vessel. Background of the Invention

It is known to install a gas diffuser plug into the base of a metallurgical vessel such as a ladle or furnace, to provide for the introduction into a melt of a gas such as argon for advantageous effects such as melt homogenisation, degassing and removal of non-metallic inclusions. Such location of a diffuser plug results in a weakening of the floor of the vessel from the introduction of joints vulnerable to metal penetration, the integrity of the floor of the vessel being thus disrupted and the possibility of resultant melt leakage.

Furthermore, such plugs have resulted in the localised introduction of purging etc gas with a melt treatment time penalty for the introduction of the volumes of gas required.

Object of the Invention

A basic object of the invention is the provision of an improved metallurgical treatment vessel. Summary of the Invention According to the invention, there is provided a metallurgical treatment vessel comprising a multi-use, isostatically pressed, one-piece refractory vessel, comprising refractory sidewalls and an integral refractory base, the vessel being adapted, in use, to contain an induction heated melt, with a gas introduction device connected to an external surface of the refractory base, and with the granulometry of the refractory

material of both the base and sidewalls being such that both are gas permeable whereby gas introduced into the base by the introduction device percolates via interstitial routes into the base and also from the base into the sidewalls, whereby a gas emitting area is provided not only over the melt contacting surface of the base, but over the melt contacting inside surface of the sidewalls of the vessel. Advantages of the Invention

The location of the gas introduction device and at an external surface and distal from the upper, melt-contacting surface of the refractory base advantageously maintains the integrity of the refractory base, and because of the gas permeability characteristics of the base and sidewalls there is no longer localised gas introduction over a relatively small zone of the refractory base, but on the contrary it has been found that gas is introduced into the melt not only from substantially the entire base area of the vessel, but also from the sidewalls, thereby providing a gas introduction area, and hence a melt processing area, many times exceeding that resulting from the use of a diffuser plug and consequently there can be expected a reduction in melt treatment times compared with prior art techniques. Of course, unless further steps are taken, gas is simultaneously emitted from the outside of the side walls but such gas loss is immaterial compared with processing and production improvements. Of course, the granulometry and pressing need to ensure that gas flow paths exist around particles of refractory material.

Preferred or Optional Features of the Invention

The metallurgical treatment vessel is a melting crucible, a holding or transporting crucible, or a ladle.

The gas introduction device is a manifold in contact with the outer surface of the refractory base of the vessel distal from the melt contacting surface of the base.

The manifold is of metal.

The metal is steel. The steel is stainless steel of grade selected to present economic optimum resistance to the external inductive heating field being applied to the working volume of the vessel.

A gas emitting surface or outlet of the manifold abuts against a lower surface of the gas permeable refractory base. The external surface of the refractory base is recessed or grooved, for at least partial engagement of the manifold within the base, and thus a mechanical connection.

A gas sealant is introduced between the manifold and the contact area of the refractory base. An inorganic coating such as sodium silicate (water glass) is applied to all external surfaces of the vessel, with the exception of the area presented to the manifold, to limit losses of purging gases through the outsides of the side walls and the base.

The metallurgical vessel is of alumina, magnesia, alumino chrome, or zirconia. A gas supply tube is attached to a base of the manifold.

The gas supply tube is of stainless steel.

The gas supply tube is externally threaded at its end remote from the manifold.

The vessel has a granulometry that results in optimal particle distribution which maintains a sufficiently high porosity with narrow interconnecting channels that resist

metal ingress yet permit gas flow through the refractory and into the melt. Said granulometry gives rise to a large swarm of finely dispersed bubbles into the melt for maximum effectiveness rather than a smaller number of large bubbles.

One example of suitable granulometry as applied to the vibrocast product is as follows:-

3 - 1mm 17%

1.5 - 0.5mm 33%

0.5 - 0.2mm 17%

-0.08mm 33% The invention also includes a method of operating the aforesaid metallurgical treatment vessel in which the pressure of the purging gas introduced into the refractory vessel via the gas introduction device is within 50-125 p.s.i. A certain minimum pressure is necessary to achieve a suitable flow rate. The minimum pressure is to overcome back pressure resistance from ferro-static head of metal in the vessel, the refractory material of the vessel and the associated gas feed pipe system. The minimum pressure required will vary from vessel to vessel.

The purging gas is introduced into the e.g. crucible from the time that the charge has become fully molten to the time when discharge is to commence.

Flow commencement, duration, and cessation of purging gas is controlled manually.

Flow commencement, duration, and cessation of purging gas is controlled automatically.

Brief Description of the Drawing

The drawing shows a metallurgical vessel in the form of a crucible, provided with a gas introduction device in the form of a manifold. Detailed Description of the Drawing In the drawing is shown a multi-use (typically 30-100 melts), one-piece metallurgical vessel 1 e.g. in the form of a crucible, is isostatically pressed and has a granulometry so as to be gas permeable, having sidewalls 2 and an integral base 3, with a gas introduction device in the form of a manifold 4 in gas-tight engagement with external surface 5 of the base 3 distal from the metal contacting surface 6 of the base 3 and 6A of the sidewalls 2. The device 4 is sealed in position with a gas sealant, and comprises a spigot 7 to enter a circular recess 8 in the base 3, for mechanical engagement of the manifold 4 with the vessel 1 , a collar 9 and an externally threaded tube 10 to receive an internally threaded gas supply pipe (not shown) connected to a gas supply source, e.g. a bottle of argon (not shown), with suitably interposed adjustable valving (not shown) to control the flow rate and/or pressure. With such an arrangement it has been established that a proportion of the gas introduced by the manifold 4 travels from the base 3 into the sidewalls 2, thereby providing a substantially increased surface area for emission of purging etc gas from the area of the metal contacting surfaces 6, 6A of the base 3 and sidewalls 2. To inhibit losses of purging gas through the external surfaces 5 of the base 3 or 5A of the sidewalls 2, these surfaces are coated with an inorganic wash e.g. of sodium silicate (water glass) which when heated by thermal transfer from the inner surfaces has been found to seal those pores in the external surfaces 5, 5A of the vessel 1.