GB2057103A - Molten metal dispenser - Google Patents

Abstract

A furnace or hold vessel 10 has an exit (20, 22, 26) below the normal level of molten metal therein and is capable of sustaining an interior pressure reduction sufficient to retain the molten mets against out-flow via the exit. Valve means (44) is used to permit gas inlet to and depressurising of the furnace or hold vessel for control of dispensing. A system (52, 54) is employed to sense and normally maintain a minimum quantity of molten metal in the exit. The exit has a refractory inner tube (26), and a temporary stopper (50). Temperature (40) and pressure (36) sensing is normally provided, as may be weighing means for the furnace or hold vessel which is preferably heated by coreless electric induction (16) with secondary heating means (24) for the exit. <IMAGE>

Description

SPECIFICATION Molten metal dispenser The invention relates to the dispensing of molten metals and arises from our need repeatedly to dispense charges of molten steel.

This need is in relation to our proposals for the manufacture of articles, such as edged tool blades, from cast blanks by substantial dimension reduction of those blanks. Our copending applications nos. 20592/77 and 24727/77 show how this has been found to permit the highly advantageous use of blanks made by feederless casting as the inevitable voids, cavities or other imperfections in such blanks are reduced and removed during dimension reduction to give grain structures that are satisfactory even for loadbearing work-implements, such as forks and spades.

A good solution to the problems associated with dispensing molten steel in successive discrete quantities could, of course, be of much more general application. These problems arise mainly from the high temperatures required of molten steel for satisfactory pouring or flow purposes. At such temperatures, e.g. 1 3700C, refractory materials tend to have a short working life regardless of the simplicity or sophistication of, the dispensing system.

Conventionally, dispensing systems for all molten metals range from relatively simple tilting systems to pour from a ladle lip, through nozzle and stopper systems, to electro magnetic pumps.

However, application of such systems to dispensing molten steel is not widespread and, when done, has generally tended to be on a fairly large scale and to require continuous operation.

One example comprises a channel induction furnace sealed and pressurised with inert gas, and means for periodically and temporarily increasing the gas pressure to force molten metal out through a spout-like exit from the furnace. Another example also uses a channel furnace with dispensing by use of the molten metal as the moving part of a linear electric motor to cause outflow of metal over a ramped exit having associated stator windings.

It is an object of this invention to provide a molten metal dispensing system that is capable of much smaller scale application and batch operation, at the same time capable of offering other advantages in minimising the amount of refractory that is subjected to the poured metal and in facilitating servicing and maintenance.

Accordingly, the invention provides a molten metal dispensing system comprising, for the molten metal, a furnace or hold vessel that has a normally open exit within the normal depth of said molten metal and that is capable of sustaining an internal pressure sufficiently lower than external pressure at said exit to retain the molten metal against out-flow via said exit, and means selectively operable to control a difference between said internal and external pressures so as to permit and control out-flow of molten metal via said exit.

It will be appreciated that the furnace or vessel, or at least its exit, may be subjected externally to pressurised gas, i.e. superatmospheric, but it will usually be much more convenient to have the furnace or hold vessel depressurised relative to atmosphere, preferably to vacuum or near-vacuum conditions. Then, controlled inlet of gas to the furnace or hold vessel permits dispensing control, particularly utilising alternating gas inlet to and depressurising of the furnace or hold vessel via valve means connected to upper porting above the maximum level of molten metal.

The possibility of air entering via the exit and bubbling through the molten metal in the furnace or hold vessel is avoided if the exit has a length sufficient to be able always to hold a minimum quantity of molten metal. Vacuum pump and gas inlet valve control gear may include a metal sensor system at said exit, say of a nucleonic type, to ensure maintenance of the desired amount of metal in the exit.

Preferably, an elongate refractory lined exit passage for the molten metal incorporates or is otherwise associated with heating means to maintain a prescribed temperature of molten metal therein. Such heating means is conveniently of a small coreless induction type, especially where the furnace or hold vessel also has coreless induction heating.

The exit for molten metal may be at the lowest part of the furnace or hold vessel and be comprised of a tube of refractory material that is readily replaced should that be necessary.

Problems associated with nozzle and stopper type dispensing systems in giving rise to higher wear rates and obtaining clean shutting off of the flow are avoided, especially at steel pouring temperatures and with the less ready flow of steels compared with iron and other metals such as zinc, copper and aluminium. The invention can, however, be practised with such other metals if desired.

A safety feature is usually incorporated by way of a temporary mechanical stopper for the exit, possibly interlocked with operability of a vacuum pump and/or associated valving. Such a stopper will be used fairly infrequently, but may be employed when refilling the furnace or hold vessel unless a pressure-tight charging system is used. In general, adequate control for successive dispensing of desired quantities of molten metal can be achieved by monitoring the level of molten metal, by measuring the vacuum pressure required to support the molten metal, and/or by weight, say as measured by load cells associated with the furnace. Alternatively, of course, a metal level sensor or weighing system could be associated with moulds to be filled.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawing that is a partly sectional and partly schematic view of a coreless induction furnace 10.

The furnace 10 has a body 12 that is lined in any convenient way, e.g. ramming or casting, with refractory material 14 shown as embedding a main induction coil 1 6. At its base 1 8 the furnace body 12 has an aperture 20 shown occupied by a tubular extension 22 of the refractory lining material 14 within which is embedded a subsidiary induction coil 24. An inner exit tube 26 for molten metal is shown within the tubular refractory extension 22 and, ideally, is readily removable therefrom for replacement purposes.

This tube 26 will, of course also be of refractory material and may be of higher grade, different or otherwise more wear resistant material, and thus be more expensive but nonetheless economical due to its relatively small size.

The top of the furnace 10 is indicated as being closed by a lid 28 that should have any suitable gas-tight fit to the furnace body 12, for example in a manner used hitherto in vacuum degassing of electrically melted steels. Three apertures 30, 32 and 34 are shown in the furnace lid 28 for gas inlet/vacuum purposes, fitting of a pressure transducer 36, and a quartz window 38; respectively. The purpose of the quartz window is to allow molten metal temperature sensing by an infra red pyrometer 40. The aperture 30 carries a connection 42 to valve gear 44 for alternatively venting to atmosphere at one side 46 and connection to a vacuum pump at the other side 48.

Obviously, the indication of a changeover valve at 44 is but a simplified diagrammatic illustration and individual interlocked electrically or pneumatically operated valves may be used in practice, say with interlocks to prevent venting when the vacuum pump or its valve are inoperative and/or to close a temporary stopper 50 for the exit tube 26.

A nucleonic metal detector system utilising gamma rays is indicated by transmitting and receiving blocks 52, 54 to set a minimum occupancy by molten metal of the exit tube 26 by control of the valve gear 44 according to the output from the receiver block 54, in any convenient way that leads to venting/vacuum pumping to maintain that minimum occupancy except when discharging is required.

In operation, for repeated discharging of predetermined amount of molten metal, the furnace will contain molten metal maintained at a desired discharge temperature by the main heating coil 1 6 and the subsidiary heating coil 24, and the temporary stopper 50 will be clear of the exit tube 26. Prior to first discharge and between the repeated discharges, the metal detector system 52, 54 will serve in maintaining internal pressure conditions that effect retention of the molten metal with a minimum occupancy thereby of the exit tube 26 to prevent ingress of ambient air. Whenever a discharge is required, generally into one of a plurality of moulds indexed to a position below the exit tube 26 by any suitable feed system, the valve gear 44 will be operated to vent, then reevacuate if required, so as to meter out the prescribed amount of molten metal with high accuracy.

If the exit tube 26 becomes blocked within the furnace or hold vessel, say by foreign matter in the molten metal, it may be cleared by evacuating to pull metal in the exit tube back into the furnace or hold vessel proper.

It will be appreciated that the above described apparatus is eminently suitable for computer control to set discharge amounts and effect accurate operation.

Claims (17)

1. A molten metal dispensing system comprising a furnace or hold vessel for molten metal, the furnace or hold vessel having a normally open exit within the normal depth of said molten metal therein and being capable of sustaining an internal pressure sufficiently iower than external pressure at said exit to retain molten metal against out flow via said exit, and means selectively operable to control a difference between said internal and external pressures so as to permit and control out-flow of molten metal via said exit.

2. A system according to claim 1, wherein the furnace or hold vessel has, connected to upper porting above the maximum level of said molten metal therein, valve means operable for alternating gas inlet to and depressurising of the furnace or hold vessel in order to dispense desired charges of said molten metal via the exit.

3. A system according to claim 2, further comprising a vacuum pump connected to said valve means.

4. A system according to any preceding claim, wherein said exit is from the lowest interior position of said furnace or hold vessel.

5. A system according to any preceding claim, wherein said exit is at least partly downwardly directed.

6. A system according to claim 5, further comprising means for detecting a minimum quantity of metal in said exit in order normally to maintain that quantity therein.

7. A system according to any preceding claim, wherein said exit comprises an elongate refractory-line passage.

8. A system according to claim 7, wherein said passage is formed by a tube of refractory material replaceable separately from other refractory lining of the furnace or hold vessel.

9. A system according to any preceding claim, further comprising heating means at said exit to maintain a molten state of the metal within the exit.

10. A system according to claim 9, wherein said heating means is of coreless electrical induction type.

11. A system according to claim 10 with claim 8, wherein coil means of said heating means is disposed about said tube.

12. A system according to claim 9, 10 or 11, wherein, said heating means is ancillary to main heating means of the furnace or-hold vessel.

1 3. A system according to claim 12, wherein said main heating means is of coreless electrical induction type.

14. A system according to any preceding claim, further comprising means for monitoring the level of molten metal in said furnace or hold vessel.

1 5. A system according to any preceding claim, further comprising means for measuring pressure required to support said molten metal against being dispensed.

16. A system according to any preceding claim, further comprising means for measuring the weight of molten metal in said furnace or hold vessel.

17. A system according to any preceding claim, further comprising a selectively operable stopper for said exit.

1 8. A molten metal dispensing system arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawing.