US3675911A

US3675911A - Arrangement for discharging predetermined amounts of molten metal from a vessel

Info

Publication number: US3675911A
Application number: US874817A
Authority: US
Inventors: Walter Kapun
Original assignee: Wiener Schwachstromwerke GmbH
Current assignee: Wiener Schwachstromwerke GmbH
Priority date: 1968-11-11
Filing date: 1969-11-07
Publication date: 1972-07-11
Anticipated expiration: 1989-07-11
Also published as: DE1956482B1

Abstract

For discharging predetermined quantities of molten metal a gas tight vessel having a discharge conduit is arranged to hold the molten metal. The vessel is connected to a source of a pressurized gaseous medium so that the gaseous medium assists in the discharge of the molten metal. Sensing means are used to generate an output signal, which is representative of the velocity of flow of the molten metal from the vessel, and the signal is passed to an integrating mechanism attains a predetermined value corresponding to the predetermined quantity of molten metal to be discharged, the discharge flow from the vessel is discontinued.

Description

United States Patent Kapun [451 July 11,1972

[54] ARRANGEMENT FOR DISCHARGING PREDETERMINED AMOUNTS OF MOLTEN METAL FROM A VESSEL [21] Appl. No.: 874,817

Holz ..266/38 3,363,461 1/1968 Minkoff ...73/ l 98 3,396,870 8/1968 Diamond et a1. 164/ 1 55 3,425,483 2/1969 Dearth 164/ 155 3,504,899 4/1970 Breuer et al. ..266/38 FORElGN PATENTS OR APPLICATIONS 1,216,560 5/1966 Germany ...73/194 EM 1,217,638 5/1966 Gennany ..73/I94EM Primary ExaminerGerald A. Dost Attorney-McGlew and Toren [5 7] ABSTRACT For discharging predetermined quantities of molten metal a gas tight vessel having a discharge conduit is arranged to hold the molten metal. The vessel is connected to a source of a pressurized gaseous medium so that the gaseous medium assists in the discharge of the molten metal. Sensing means are used to generate an output signal, which is representative of the velocity of flow of the molten metal from the vessel, and the signal is passed to an integrating mechanism attains a predetermined value corresponding to the predetermined quantity of molten metal to be discharged, the discharge flow from the vessel is discontinued.

1 Claim, 5 Drawing Figures P'ATENTEDJUL 11 I972 3, 675.911

sum 2 or 2 'FIG.4

INVENTOR BY WHLTEQ KIWW lg-UXM ATTORNEY ARRANGEMENT FOR DISCHARGING PREDETERMINED AMOUNTS OF MOLTEN METAL FROM A VESSEL SUMMARY OF THE INVENTION This invention is directed to the discharge of predetermined amounts of molten metal from a vessel, such as a melting furnace, and, more particularly, it is directed to an arrangement for use with closed vessels in which the discharge of molten metal is assisted by a pressurized gaseous means, such as compressed air.

In die casting machines or ingot-casting installations, an exact amount of molten metal must be supplied for each casting operation. In the past the desired amount of metal has been measured by a ladle which receives the metal from a holding furnace. Such an operation is not only very time-consuming, but the metallurgical conditions requiredto produce uniform castings are affected very adversely because the molten metal cools rapidly as it is ladled from the holding furnace into the mold, for example, an ingot mold, and also because slag and other impurities must be skimmed from the surface of the molten metal bath.

To eliminate these disadvantages it has been attempted to provide an automatic discharge of the metal from the melting furnace.- However, the apparatus which has been proposed for such automatic discharge has not met with the desired success.

Means, such as pumps and the like, for handling non-aggressive metals cannot be used for handling the molten metals because of the aggressive character of such metals, particularly aluminum and aluminum alloys and also because of their high melting temperatures since the melting temperatures of the materials used in such means are low.

An apparatus has been disclosed which is especially useful where a pressurized gaseous medium is used in assisting in the discharge of the molten metal. In such apparatus the molten metal is contained in an enclosed gas tight furnace vessel in which the surface of the molten metal is subjected to a gas pressure and the metal is discharged through a gas tight pipe located near the bottom of the vessel. In this apparatus the metered amount of molten metal will depend on the gas pressure and the duration of the withdrawal of the metal, provided that the level of the molten metal in the furnace vessel remains constant. However, each time the molten metal is discharged from the vessel its level drops and the discharge pressure and/or the duration of the discharge must be varied if equal amounts are to be drawn off from the vessel.

Accordingly, it is necessary to utilize means which sense the level of the molten metal in the furnace. Since the furnace atmosphere is hot and the metal is aggressive, the sensing means used are often damaged and result in inaccurate readings. Other devices are known for this purpose, which comprise an overflow or valves and similar means for eliminating the influence of a varying level in the molten metal.

From the metallurgical viewpoint, it is particularly desirable to use as a furnace vessel a trough-shaped two-chamber induction furnace. In such furnaces the amount of discharge will depend on whether the furnace is energized or deenergized since the electrodynamic pressure influences the metered amount discharged. A satisfactory solution to this problem has not as yet been provided.

In die casting machines, special care is to be taken to avoid any loss of time when the molten metal is being discharged from the melting furnace. Since with the means presently available a loss of time cannot be prevented, the pouring operation will be adversely effected if the molten metal cools too quickly as it is discharged. Further, the molten metal may oxidize in contact with the air. The molten metal may be contaminated when it is transferred to a die casting machine through an open tundish during the pouring operation. To obtain a satisfactory casting, it is essential that contamination of the molten metal be prevented and that the metal be held at the required pouring temperature.

The electrodynamic pressure in the melting channel of the furnace may cause the refractory furnace lining to spall off and mix with the molten metal. Such a contamination may occur especially in installations in which the molten metal is discharged from the furnace by means of induction pumps. In other known apparatus relatively delicate or insubstantial components, such as valves, nozzles and floats, are permanently in contact with the molten metal or the furnace atmosphere. Still other apparatus are known in which the stroke of a plunger of the die casting machine is measured as the extent of the discharge material. Such an arrangement has the disadvantage that the flow of the molten material into the charging chamber results in irregular undulatory movements on the surface of the molten material so that any measurements of the level surface are highly inaccurate. It has also been attempted to use the principle of Heros fountain for metering purposes wherein a change in the pressure of the atmosphere in the furnace chamber causes the molten metal to be discharge through a duct into a charging chamber or a pouring cylinder of the die casting machine. This apparatus is not capable of exactly metering the required charge.

Therefore, it is an object of the present invention to measure a predetermined amount of molten metal independently of the level of the metal in the furnace vessel and of any other influences which tend to affect the measured amount. In accordance with the present invention, this object is attained by means of a device which determines the velocity of flow of the molten metal and supplies an output signal to an integrating device which discontinues the discharge flow when the accumulated signal has reached a predetermined amount corresponding to the amount of molten metal to be discharged. The velocity of flow of the metal can be measured directly by electromagnetic action in which a voltage, induced by a magnetic field in the molten metal being discharged, is measured; or alternatively, in furnaces using a pressurized gaseous medium for assisting in the discharge of the molten metal, the velocity of flow can be indirectly measured by measuring the velocity of flow of the pressurized gas.

Where the velocity of the pressurized gas is measured, that portion of the velocity of the gas required to increase the pressure in the furnace to the point at which discharge commences must not be included in the measurement. Therefore, in accordance with the invention, a switch is provided which actuates the measuring means when the discharge flow of metal begins.

The integrating mechanism consists suitably of a motor having a rotational speed that depends on one of current or voltage and a revolution counter which is connected to the motor and initiates the stoppage of the discharge flow of metal after a preset number of revolutions has been attained.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a somewhat schematic sectional view of a troughshaped two-chamber induction furnace disclosing a particularly suitable embodiment of the present invention in which means are provided for supplying a pressurized gaseous medium into the fumace for assisting in the discharge of the molten metal;

FIG. 2 is a diagram representing different curves in which the velocity of the metal being discharged is plotted against time;

FIG. 3 is a somewhat schematic illustration of an electromagnetic sensing device for measuring the velocity of flow of molten metal through a discharge conduit from a vessel;

FIG. 4 is a view of an integrating mechanism for use in the arrangement disclosed in FIG. 1; and

FIG. 5 is a view similar to FIG. 1, disclosing another embodiment of apparatus for measuring the discharge flow of molten metal from a vessel.

DETAILED DESCRIPTION OF THE INVENTION In FIG. 1 a trough-shaped two-chamber induction furnace is shown and is formed of a furnace vessel 1, consisting of sheet steel with a refractory lining 2. The furnace vessel 1 is divided into a charging chamber 3 and a discharge chamber 4 interconnected by heating ducts 5. The power for the induction furnace is supplied by a furnace transformer 6 which heats the metal inductively within the heating ducts because the heating ducts and the adjacent parts of the furnace chamber form a secondary winding cooperating with the coil of the furnace transformer.

For discharging a molten metal 7 from the furnace vessel 1, assisted by a pressurized gaseous medium, the discharge chamber 4 and the charging chamber 3 are sealed by means of gas

tight covers

8 and 9 respectively. Branch conduits 10, 10 extend from a air conduit 10 and pass through the gas

tight covers

8 and 9, respectively, and communicate with the discharge chamber 4 and the charging chamber 3. A compressor 11 is positioned at one end of the conduit 10 and an inlet solenoid valve 12 is located between the compressor 11 and the branch conduit 10" while an outlet solenoid valve is located at the opposite end of the conduit 10 downstream from the branch conduit 10'. To discharge molten metal from the furnace vessel 1, the inlet valve 12 is opened and the outlet valve 13 is closed so that the gaseous medium pressurized by the compressor 11 is delivered into the charging chamber 3 and discharge chamber 4 for pressurizing the surface of the molten metal 7 and causing it to flow from the discharge chamber 4 through a discharge pipe 14 mounted in the upper end of the chamber. As soon as the desired amount of metal has been evacuated through the discharge pipe 14, the inlet valve 12 is closed and the outlet valve 13 is opened and the pressurization of the surface of the molten metal is relieved.

T is the time during which the furnace is pressurized (metering time),

F is the outlet cross-section (constant), and

k is the pinch effect factor, the outflowing volume to be metered is where v (t) is the discharge velocity as a function of time (FIG. 2).

FIG. 3 shows an arrangement for measuring the velocity of the molten metal flowing through the discharge conduit 14. As shown in FIG. 1, the discharge conduit has a discharge duct 19 which is defined by a pair of oppositely disposed segments 16 formed of insulating refractory material, such as asbestos cement, and a pair of oppositely disclosed electrodes 17 formed, for example, of graphite. In other words, as shown in FIG. 3, the discharge duct 19 is rectangular in cross-section and is formed on two opposite sides by the segments 16 and on the other two opposite sides by the electrodes 17. A permanent magnet or electromagnet 18 surrounds the segments 16 and the electrodes 17 and produces a strong magnetic field about the discharge cross-section of the duct. When molten metal flows through the discharge duct 19, a voltage is generated between the two electrodes 17 and the voltage is proportional to the velocity of flow of the molten metal.

The voltage generated is applied through an amplifier 20 to an integrating mechanism 21. The integrating mechanism may consist of an ampere-hour meter,which in response to a predetermined preset value, which is the analog of the amount to be metered, operates the control valves in the conduit 10 for discontinuing the discharge flow of the metal.

In FIG. 4 a specific embodiment of the integrating mechanism is illustrated and comprises a motor 22, the rotational speed of which is determined by one of the current or voltage supplied to the motor. Coupled to the motor shaft is a screw-threaded spindle 23 and a slider 24 which is longitudinally movable along the spindle and bears in turn on a slideway 25. When the spindle 23 has performed a number of revolutions, the slider is displaced longitudinally and operates one of a pair of longitudinally spaced limit switches 26 depending on the direction in which the revolutions of the motor moves the slider 24. The limit switch contacted then operates the

solenoid valves

12 and 13 for regulating the discharge of the molten metal from the furnace vessel.

Preferably, one of the limit switches is displaceable relative to the other. If the direction of rotation of the motor is reversed after each discharge cycle, the distance between the limit switches corresponds to the predetermined amount of metal to be discharged. Accordingly, a scale 27 associated with the displaceable limit switch can be calibrated directly to represent the amount of molten metal to be discharged and the selected amount can be set so that the limit switch defines the extent of the longitudinal movement of the slider for measuring the selected amount of molten metal to be discharged.

In FIG. 5 the arrangement of the furnace vessel 1, with its discharge conduit 14 and the conduit system 10 for supplying pressurized gaseous medium into the furnace vessel, is the same as illustrated in FIG. 1 with the difference residing in the indirect measurement provided for the discharge velocity of the molten metal from the furnace vessel.

In the conduit 10 for supplying a gaseous medium into the furnace vessel a velocity-sensing device 29 is positioned between the compressor 11 and the inlet valve 12. The value of the velocity obtained in the device 29 is converted in a transducer 30 into an electrical value which passes into the amplifier 20 and is delivered therefrom into the integrating mechanism 21.

The volume of metal discharged from the furnace vessel depends on the pressure which is generated by the compressor and the volume of air or gaseous medium which is supplied into the vessel.

However, in measuring the velocity of the air or gaseous medium, the amount required to build up the pressure in the furnace until the metal begins to flow from the outlet opening of the discharge conduit 14 is not included in the output signal to the integrating mechanism.

To compensate for the pressure build-up required to initiate discharge flow, a switch 31 is positioned at the outlet from the discharge conduit to initiate the measurement of the velocity of the air or gaseous medium once discharge flow has been commenced. This switch consists of a known non-contacting proximity switch which is operated as the molten metal starts to flow from the discharge conduit.

In accordance with the present invention an exact metering of the molten metal discharged from a holding or melting furnace is possible without involving any measurement of the changing level within the vessel or of any of the other factors which tend to influence the amount of flow discharged from the vessel. There are no delicate or insubstantial parts which are permanently in contact with the aggressive molten material or with the hot furnace atmosphere. Besides, there is no need for means which prevent a formation of additional oxides or which prevent an ingress of oxides or other impurities into the pouring device.

Therefore, the arrangement, in accordance with the present invention, may be used in combination with all melting and holding furnaces, particularly for trough-shaped two-chamber induction furnaces using a gaseous medium to assist in the discharge of the molten material. In the past it has not been possible to use automatically metered-pressure-assisted discharge with such furnaces.

What is claimed is:

1. A device for discharging a predetermined quantity of molten metal comprises a vessel for holding the molten metal to be discharged, a discharge conduit connected to said vessel for discharging molten metal from said vessel, sensing means arranged to generate an output signal representing the velocity of flow of the molten metal from said discharge conduit, an integrating mechanism arranged to receive and integrate the output signal from said sensing means, control means in operative communication with said integrating mechanism for interrupting the discharge of molten metal through said conduit in response to a signal from said integrating mechanism when the cumulative output signal directed to said integrating mechanism has attained a predetermined value, said integrating mechanism comprises a motor having a motor shaft arranged to rotate at a speed in relationship to the output signal representative of the velocity flow of the molten metal from said vessel, a variable revolution counter in communication with the motor shaft of said motor for counting the revolutions thereof, said counter in operative communication with said control means for discontinuing the discharge of molten metal when said counter has counted a predetermined number of revolutions, a threaded spindle secured to and extending axially from the motor shaft of said motor, a slide member mounted on said spindle and movable longitudinally therealong as said spindle rotates, a pair of limit switches disposed in spaced relationship in the axial direction of said spindle and one of said limit switches being arranged to be contacted by said slide member at the end of a predetermined number of revolutions by said spindle whereby said control means are operable for interrupting the discharge of molten metal through said discharge conduit.

* l i t 1 I UNITED: sqUwriazs 'PATENT OFFICE CERTIFICATE OF CORRECTION Pa'teht 3 75,9 v w t July 11, 197

Inventor WALTER;

QIt i s certified Lthait errora-p pe'ai's the above-identified patent and that said Letters; Patent. are hereby corrected as shown below:

In the heading of the patent, the inventdr's address should read;

- Wurzb'achga sse, Wien, Austria Signed and sealed this 2nd day of January 1973.

Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC 6O375-Pfl a [1.5. GOVERNMENY PRINTING OFFICE: 1969 O-366-31