US 3017676 A
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1962 l. E. EWEN 3,017, 76
- APPARATUS FOR PROVIDING GAS-FREE LIQUID METAL TO A CASTING MOULD FOR THE CONTINUOUS CASTING 0F METAL Filed Sept. 3, 1958 Inventor:
1A N E. EWEN By W4 A ttorn e ys United States Patent APPARATUS FOR PROVIDING GAS-FREE LIQUID METAL T 0 A CASTING MOULD FOR THE tlflNTiNUOUS CASTING 0F METAL Ian E. Ewen, Edinburgh, Scotland, assignor to The United Wire Works Limited, Edinburgh, Scotland, 2 British company Filed Sept. 3, 1958, Ser. No. 758,776 Claims priority, application Great Britain Sept. 6, 1957 4 Claims. (Cl. 22-572) This invention relates to the casting of metal, and especially to the continuous casting of metal, such as copper, copper base alloys, aluminium, aluminium alloys and the like.
Many continuous casting processes have hitherto been proposed to produce castings of indefinite length by providing a mould, of which one end is mounted on the underside of a molten metal container and the other end, which projects below the underside of the container, is suitably cooled. The molten metal flows into the mould, and, when it reaches the cooled portion of the mould, the metal freezes, and the casting which is formed is withdrawn.
For the successful operation of the process, it is essential that the metal entering the casting mould should be gas free, as molten metals, particularly copper base alloys containing dissolved gas, can give rise to internal cavities and surface segregation of the lower melting point constituents on solidification of the metal and thus produce defective castings.
In prior processes, the molten metal has been maintained in a degassed condition by electric heating of the molten metal container and by removing dissolved gas by maintaining a nitrogen atmosphere over the molten metal. It has been demonstrated that nitrogen is quite inert and does not dissolve into copper base or aluminium base alloys, and its presence over the surface of the molten metal causes dissolved gases, such as hydrogen, to be removed in accordance with the law of partial pressures.
While process-es based on electric heating of the holding furnace and nitrogen degassing of the metal have been brought into commercial production, difficulties with the gassing of the metal have been experienced when the metal contain-er is heated by hydrocarbon fuels, such as oil or gas. The use of these fuel heating arrangements have certain advantages in the metallurgical industry, particularly where continuous casting techniques are replacing other methods of casting, as they are usually already existing, which enables the change-over to continuous casting techniques to proceed quickly without the delay and the capital expense involved in installing electrically heated holding furnaces. Also, the heat input of hydro-carbon fuels can be controlled by means of relatively simple devices.
An object of the present invention is to provide means for obtaining gas-free metal in a molten metal container which is heated by hydro-carbon fuels.
According to the present invention we provide apparatus for use in the continuous casting of metal comprising a liquid metal container, a fuel-fired burner therefor, and a guard tube made of refractory material, said tube surrounding the container in spaced relationship thereto, and the space between the container and tube being vented so that combustion gases permeating through the wall of the tube may escape through the vented space.
Further, according to the present invention we provide apparatus for use in the continuous casting of metal comprising a liquid metal container, a fuel-fired burner, a guard tube made of refractory material surrounding the container in spaced relationship thereto, the space between the container and tube being vented, and means for introducing an inert gas into the container and maintaining a positive pressure of said gas in the container.
Still further, according to the present invention we provide in or for apparatus for use in the continuous casting of metal, a liquid metal container to be heated by a fuel-fired burner, and a guard tube of refractory material surrounding same in spaced relationship thereto.
Still further, according to the present invention we provide, in a process for the continuous casting of metal, in which a molten metal container is heated by a fuelfired burner, the step of protecting the wall of the container from direct contact with the flame and products of combustion of the burner by a surrounding guard tube of refractory material and a vented space between the tube and container, so that combustion gases permeating the wall of said tube may escape through said vented space.
Still further, according to the present invention we provide, in a process for the continuous casting of metal in which a molten metal container is heated by a fuel-fired burner, the steps of protecting the wall of the container from direct contact with the flame and products of combustion of the burner by a surrounding guard tube of refractory material and a vented space between the tube and container, and maintaining a positive pressure of inert gas in said container so that combustion gases permeating the wall of said tube are prevented from entering said container and escape through said vented space.
An embodiment of the invention is shown, by way of example, in the accompanying drawing, in which the single FIGURE is a fragmentary diagrammatic illustration, mostly in vertical section, illustrating a preferred form of apparatus embodying the principle of the present invention.
Referring to the drawing, there is shown a continuous metal casting furnace assembly, comprising a fuel-fired furnace body 1 having a refractory furnace lining 2, a fuel burner 3, a combustion chamber 4, an exhaust port 5, a refractory lined cover 6, a sand seal 7, a tundish 8 for introducing molten metal, a tundish cover 9, an inert gas inlet pipe 10, a refractory inert gas pipe 11, a floating baffle '12, a fixed bafiie 13, inert gas outlet holes 14, a refractory guard tube 15, an annular space 16 between the latter and a molten metal container l7, a casting mould 18, -a cooling device 19, a casting 20, withdrawal means 21, a casting mould support generally indicated at 22, a furnace clean-out hole 23, and a hole 24 in fixed baflle 13.
In operation, molten metal from a melting furnace, not shown, is transferred to the molten metal container '17, through tundish 8. The molten metal flows through the open ended mould 18, and is solidified in the mould due to the action of the cooling device 19, and the solidified casting 20 is withdrawn under the action of the Withdrawal means 21. The molten metal is maintained at a suitable casting temperature by means of burner 3, the flame and the products of combustion passing around the refractory guard tube 15 and exhausting through port 5. Hydrogen or other deleterious gases permeating the guard tube 15 and entering space 16 can pass out to atmosphere through the vent 25 and are prevented from entering the molten metal container 17 by the action of the positive inert gas pressure maintained in the container 17 while casting. The inert gas is supplied through pipe 10, refractory tube 11 and outlet holes 14, the tube 11 also acts as a guide for the baflle 12. The inert gas passes up through the molten metal removing in its passage any soluble gases in the metal, assisting mixing of the metal in the container and maintaining a slight positive pressure inside the molten metal container 17, excess gas flowing out through leakage points in the top part of the furnace assembly. A gas pressure of about 0.1 water gauge suflices.
The floating baffle 12, prevents undue turbulence when charging molten metal, and the fixed bafile 13 with the restricted orifice 24, maintains a pool of undisturbed gasfree molten metal over the mould inlet, and prevents fresh charges of gassy metal passing to the mould, and also prevents sudden temperature rises in the mould.
Dense graphite is a suitable material for constructing the molten metal container as it is easily machined to the desired shape and is inert to most non-ferrous metals. Graphite, however, is prone to oxidation at normal molten metal temperatures and it is not practical to heat the container by direct contact with the flame or products of combustion of the hydro-carbon fuel. The graphite molten metal container is, therefore, protected, by means of a more refractory material, such as plumbago or other well-known crucible mate-rials. Dense graphite is also suitable for constructing the mould 18.
A suitable material for the guard tube is a refractory material, for example, a fired clay graphite mixture.
The upper end of the mould 18 forms a spigot which is a push fit in a socket provided in the bottom of the container 17 and the spigot and socket have bevelled metal sealing faces engaging at 25, and the said faces are urged into metal sealing engagement by adjustable pressure applying means acting externally and endwise on the bottom of the mould 18. In the embodiment shown, the mould 18 has a central casting hole, and said pressure applying means consists of a nut or internally screwthreaded tube 26 mounted on the externally screwthreaded end of a fixed tube 27, the tubes 26 and 27 being concentric with the casting hole and the cast rod passing therethrough. By this arrangement, metal from the container is prevented from entering between the spigot and socket walls and the mould can be much more easily withdrawn for replacement than hitherto. When the mould has a plurality of casting holes, the pressure applying means consists of a rod or tube abutting the mould and mounted on a set screw.
The mould 18 is provided at the outlet end of its casting hole with an externally screw-threaded sleeve 28 screwed into the mould 18 which is internally screwthreaded to receive same. The sleeve 28 is of the same internal diameter as the casting hole and is made of material which is more wear-resistant than the mould 18, suitable materials being steel, bronze, ceramic or sintered wear-resistant material. By the use of such a sleeve, the useful life of the mould is very considerably prolonged. The sleeve 28 may alternatively be a push fit and be held in position by the tube 26 or a plate.
Modifications may be made without departing from the scope of the invention as defined in the following claims.
1. In an apparatus for providing gas-free liquid metal to a casting mould for the continuous casting of metal, a closed inner container for the liquid metal, a fuel fired burner exterior of said container for heating the same and the metal contained therein, a guard tube of refractory material surrounding said container in spaced relation thereto and interposed between said container and said burner to protect said container from direct heating by said burner, the walls of said container and of said guard tube having a porosity which permits a limited passage of gases therethrough, the space between said container and said surrounding guard tube being vented to atmosphere and being sufficiently narrow to permit the container and the metal therein to be heated by heat from the burner passing through said guard tube and through said space to the wall of said container, and means for introducing an inert gas under pressure into said container and into the liquid metal therein for removing soluble gases from the said liquid metal and for maintaining within said container 2. positive pressure slightly greater than the pressure of the combustion gas which permeates the wall of said guard tube and enters said space, whereby combustion gas entering said space through the wall of said guard tube will be vented to atmosphere and whereby said inert gas will permeate the wall of said container to oppose passage of said combustion gas into said container through the wall thereof, said inert gas and the soluble gases removed from the liquid metal by said inert gas permeating the wall of said container and entering said space from which it is vented to atmosphere along with the combustion gas which permeates the wall of said guard tube and enters said space.
2. Apparatus as claimed in claim 1, in which the container has a battle member adapted to float on the surface of the molten metal therein to prevent turbulence in the latter when a fresh charge of metal is added.
3. Apparatus as claimed in claim 1, said means for introducing the inert gas into said container comprising an inert gas pipe extending downwardly into the interior of said liquid container and having outlet openings therein in proximity to the bottom of said container, said pipe being adapted for connection to a source of inert gas under pressure.
4. Apparatus as claimed in claim 3, a fixed bafile in said liquid metal container in proximity to a bottom discharge orifice therein and having a restricted opening therethrough, said fixed bafile being adapted to maintain a pool of undisturbed gas-free molten metal over a mold inlet associated with the discharge orifice of said liquid metal container.
References Cited in the file of this patent UNITED STATES PATENTS 1,808,370 Munson June 2, 1931 1,961,529 Rowe June 5, 1934 2,109,930 Sanford Mar. 1, 1938 2,145,416 Crampton Jan. 31, 1939 2,405,355 Harrison Aug. 6, 1946 2,583,438 Nieman et al. Jan. 22, 1952 2,821,472 Peterson et al Jan. 28, 1958 FOREIGN PATENTS 534,670 Canada Dec. 18, 1956