US3279001A

US3279001A - Pouring apparatus with radioactive means for determining molten metal level in riser conduit

Info

Publication number: US3279001A
Application number: US301393A
Authority: US
Inventors: Lenz Rudolf
Original assignee: BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Germany; BBC Brown Boveri France SA
Priority date: 1962-08-29
Filing date: 1963-08-12
Publication date: 1966-10-18
Anticipated expiration: 1983-10-18
Also published as: AT239458B; DE1458134A1; CH415976A; GB969887A

Description

Oct. 18, 1966 R LENZ 3,279,001

POURING APPARATUS WITH RAEIOACTIVE MEANS FOR DETERMINING MOLTEN METAL LEVEL IN RISER GONDUIT Filed Aug. 12, 1963 COMPRESSED AIR $0URCE INVENTOR fiudoh Lenz EPA/Jaw United States Patent 3 Claims. 'ct. 21-79 Metal mouldings, more particularly of light metal, are often poured by taking the molten metal from a container. for example, the crucible of a melting or heatretaining furnace, with the aid of a suitable pumping device, and feeding it in suitable quantity to the pouring moulds. lf identical mouldings are being poured, the quantity of metal required for pouring each piece is always the same.

If identical pieces are to be poured in large numbers, special precautions are expediently taken to ensure in the simplest possible fashion that identical quantities of metal are taken oil. In this connection, certain difficulties arise from the fact that the surface level of the molten bath varies continuously while the contents of a crucible are being poured, with the result that the height through which the metal has to be lifted while being taken off varics in like manner.

The chief pumping devices for the purpose mentioned are: The introduction of gas under pressure into the crucible, which is closed in gas-tight fashion, or part thereof, with the result that the metal is forced upwards through a riser pipe. Furthermore, pumps acting on the basis of dynamic forces, for example, centrifugal pumps, may be used, and finally, consideration may be given to electromagnetic pumps, for example, those in which the molten metal is moved under the action of a moving magnetic field. In all these pumping devices, the quantity of material delivered per unit of time first of all depends to a considerable extent on the pressure to be overcome, i.c. in the present case on the height of the surface level of the bath in the crucible.

in an arrangement in which this introduction of gas under pressure into the closed crucible acts as the pumping device, it is already known to equalize the quantities taken off by making an equal increase in the time for which the gas acts each time the surface level of the bath drops. This method does indeed enable the quantity of metal taken off each time the pressure acts to be kept constant, but the periods of time required for individual take-offs increase with the height through which delivery has to be effected. This has a particularly disadvantagcous effect if pouring is to be carried outautomatieally, for example, by passing the pouring moulds at a predelermincd rate beneath the outlet aperture of the delivery In a process for taking molten metal from a container which serves to receive it, for example, from the crucible of a metal-melting or heat-retaining furnace from which the metal is delivered via a riser conduit by means of a pumping device, this disadvantage is avoided according to the invention by measuring the degree to which the container is filled or the height of the surface level of the metal bath therein and automatically varying the output of the pumping device in dependence on this measured value so that equal quantities of metal are delivered in equal periods of time throughout the whole take off operation.

The surface level of the bath may be ascertained in various ways. For example, a float in the bath may be used, controlling the output of the pumping device via a Patented Oct. 18, 1 966 ice 2 driving device. Another possibility resides in arranging the crucible on a weighing device, and ascertaining the variation in height of the surface level of the bath from the variation in the weight of the crucible.

Of the arrangements mentioned as pumping devices, mechanical devices such as centrifugal pumps are above all suited to the intended purpose. Electromagnetic pumps are also suitable provided that they can be satisfactorlly incorporated into the overall arrangement, according to the conditions of the individual case. Delivering the molten metal by gas under pressure let into the closed container is scarcely suitable, since the pressure in the closed container can only be varied with considerable delay, which increases as the volume of the container not filled with metal increases.

Various devices with which the process according to the invention can be carried out are illustrated in the accompanying drawings.

In these drawings, FIG. 1 is a somewhat schematic view of an apparatus for taking molten metal from a container wherein the pump for discharging the metal is controlled by a variable speed compressed air motor, and the motor speed is regulated by a float which measures the level of the metal in the container;

FIG. 2 is a view similar to FIG. 1 illustrating a mcdi lied construction wherein the pump for discharging the metal is controlled by an electric motor and the motor speed is regulated as a function of the weight of the metal in container; and.

FIG. 3 is also a view similar to FIG. 2 illustrating still another embodiment containing an additional feature wherein the electric motor driving the metal discharging pump is, during the periods of time between individual take-offs of metal, further controlled as a function of the change in level of the molten metal in the riser scction of the discharge pipe to maintain a constant holding output level.

With reference to FIG. I, I represents the crucible of a melting or heat-retaining furnace. The molten metal contained therein is taken off via a riser conduit 3 by a centrifugal pump 2. In the example in FIGURE 1, a compressed-air motor 4, fed from a compressed-air container 7, serves to drive the pump.

A float 5, via a driving device 6 which may, for example, consist of a toothed rack and a toothed wheel, controls the degree of opening in throttle valve 8 in the conduit between container 7 and motor 4 and thus the output of the motor 4 in dependence on the surface level of the molten metal. Suitable design of the transmission device 6, for example, by lnterposing cam-discs or the like, can readily make the degree to which the valve 8 opens functionally dependent on the position of the float in such a way that the quantity of metal delivered by the pump 2 per unit of time remains constant independently of the head of pressure It. In certain circumstances, it may be expedient to arrange a shunt path with a pre-set throttle valve '10 in parallel with the valve 8, as shown in dashed line in the drawing. Opening of the shut-elf valve 9 for equal periods of time, which can be kept constant, for example, by means of a timing relay, will then result in equal quantities of metal always being taken from the container 1.

A somewhat different device according to the invention is illustrated in FIGURE 2. In this case, an clec' trie motor 4' is provided in order to drive the pump 2, and is fed from a current source 12. A weighing device 11 serves to ascertain the quantity of metal, or the surface level thereof in the container 1, and adjusts a resistance 13 or other setting member in dependence on the weight resting on the said weighing device.

Suitable subdivision of the resistance enables the speed of the pump 2 in this case also to be adapted to the particular height through which delivery has to be effected in such a way that the quantity delivered per unit of time remains constant.

A further configuration will be explained with reference to FIGURE 3.

In order to keep the quantity delivered as nearly as possible exactly constant, it is expedient to force the molten metal up to a definite level S in the riser pipe before each take-off operation begins, so that when takeoff begins, only a short and constant path up to the out-let end of the pipe remains to be traversed. In addition, such a measure confers a further special advantage, especially when magnesium and magnesium alloys are being poured. As is known, magnesium has a very great affinity for oxygen, and tends to burn when air is admitted at relatively high temperature. The molten magnesium is therefore covered with a salt-or kept under protective gas in order to prevent the access of oxygen.

However, neither measure can be made sufficiently effective in a riser pipe through which the magnesium is pumped, so that deposits of magnesium oxide occur in the riser pipe and reduce its free cross-section, i.e. can lead to the pipe becoming blocked. This phenomenon is confined to a short and easily exchangeable piece of-pipe if the metal is always at a constant level S in the pipe.

In order to achieve this state of affairs, the pump 2 must be driven at a relatively low .output which, however, is closely dependent on the height of the surface level of the bath in the crucible, and which will hereinafter be called the holding output. In practice, the holding output must for this purpose be regulated in dependence on the height of the surface level in the pipe.

There are various known processes for measuring the height of the surface level of a liquid in a pipe, the measured values being capable of serving to a more or less satisfactory extent as nominal values for regulation purposes.

It has proved particularly expedient to ascertain the metal level in the riser pipe 2 with the aid of hard X-rays, more particularly 'y rays emitted by radioactive isotopes.

If it were desired to transmit these rays through the pipe perpendicularly to its longitudinal axis, the quantity of rays penetrating the pipe would in many cases change only very slightly as compared to the empty condition with the pipe filled with molten metal. It is accordingly scarcely possible to control a regulator device. This is more particularly the case, for example, with normal steel pipes through which magnesium is being delivered. This difficulty can be eliminated by considerably broadening the pipe at those points at which measurement with 'y rays is to be carried out. 'However, it is better to u a pipe with two bends and a vertical piece between, and to pass the rays through the vertical piece in the axial direction.

Outside the container 1, the riser pipe 3 comprises a broad vertical piece between two substantially right-angle bends, as shown at 3'.

Rays are transmitted through the piece of pipe 3' from a radiation source 14, for example, a radiating isotope in a lead capsule open at the bottom, and are absorbed to a greater or lesser degree according to the height of the metal in this piece of pipe. Since the column of liquid traversed by the rays may be made very much greater than the thickness of the walls of the pipe, a variation in the liquid level S results in considerable variations in absorption. The rays passing through the piece of pipe 3' are converted in intrinsically known manner in a suitable receiving appliance 15 into an electrical quantity which varies sufficiently, when the liquid level S varies, to enable the holding output of the motor 4 and the pump 2 to be regulated via known auxiliary means 16, in such a way as to keep the surface level S constant during the periods of time between individual take-ofis of metal.

Regulation of the holding output is made inoperative while molten metal is being taken off, and the output of the pump is controlled in dependence on the weight or height of the surface level of the bath in the container 1, as herein-before described with respect to FIG. 2.

The invention is not bound to the example of embodiment described, but may be modified in various ways. In particular, the measuring and pumping devices described may be replaced by devices acting identically or similarly.

I claim:

1. Apparatus for pouring molten metal comprising a container for molten metal, a riser conduit connected to said container, a pump for pumping molten metal from said container through said riser conduit, means for periodically actuating said pump, means for measuring the level of molten metal in said container, means controlling the output of said pump in dependence upon said molten metal level measurement, radio active means for determining the level of molten-metal in said riser conduit, and means responsive to said last measurement con trolling the output of said pump in the intervals between said periodic operations to maintain a constant level of said molten metal in said riser conduit.

2. Apparatus as defined in claim 1 in which said radioactive means comprises a source of radioactive radiation and a radioactive receiver positioned on opposite sides of the space in said riser conduit adjacent to its outlet.

3. Apparatus as defined in claim 2 in which said riser conduit comprises a readily replaceable vertically disposed section adjacent to its outlet and said radioactive source and said radioactive receiver are positioned one above and one below said vertically disposed section.

References Cited by the Examiner UNITED STATES PATENTS 3,015,129 1/1962 Hays et al. l82 3,056,178 10/1962 tIagielski 22 .70

J. SPENCER OVERHO'LSER, Primary Examiner. R. D. BALDWIN, Assistant Examiner.

Claims

1. APPARATUS FOR POURING MOLTEN METAL COMPRISING A CONTAINER FOR MOLTEN METAL, A RISER CONDUIT CONNECTED TO SAID CONTAINER, A PUMP FOR PUMPING MOLTEN METAL FROM SAID CONTAINER THROUGH SAID RISER CONDUIT, MEANS FOR PERIODICALLY ACTUATING SAID PUMP, MEANS FOR MEASURING THE LEVEL OF MOLTEN METAL IN SAID CONTAINER, MEANS CONTROLLING THE OUTPUT OF SAID PUMP IN INDEPENDENCE UPON SAID MOLTEN METAL LEVEL MEASUREMENT, RADIO ACTIVE MEANS FOR DETERMINING THE LEVEL OF MOLTEN METAL IN SAID RISER CONDUIT, AND MEANS RESPONSIVE TO SAID LAST MEASUREMENT CON-