US3776439A

US3776439A - Fail-safe liquid pumping and flow control system

Info

Publication number: US3776439A
Application number: US00240417A
Authority: US
Inventors: J Settle
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-04-03
Filing date: 1972-04-03
Publication date: 1973-12-04
Anticipated expiration: 1990-12-04
Also published as: DE2314861A1; JPS4915008A; GB1413002A

Abstract

A fail-safe liquid metal pumping and flow control system is described wherein metal is transferred from a holding furnace to a continuous casting mold, individual molds, ladles, etc., through a siphon having an electromagnetic pump with dual direction output situated along the length of the siphon to control the flow of liquid metal therethrough. The system initially is primed by applying vacuum to the siphon through a suitable valve and the siphon is vented to terminate liquid metal flow upon sensing of an anormal process condition, e.g., loss of electrical power to the electromagnetic pump, to inhibit further siphoning of liquid metal from the reservoir. Also disclosed is a pumping system wherein the holding furnace is initially disposed at an attitude to inherently raise the liquid metal level into operating engagement with an electromagnetic pump drawing liquid metal from the holding furnace. The furnace then is tilted upon the subsequent sensing of an anormal process condition to gravitationally return metal from the electromagnetic pump to the holding furnace. The electromagnetic pump thus provides the lifting force to drive the molten metal up to and over the pouring spout, thereby providing complete electrical control of the pouring rate, while failure of power or the pump will cause the flow to terminate to provide the fail-safe feature.

Description

United States Patent 1 Settle Dec. 4, 1973 FAIL-SAFE LIQUID PUMPING AND FLOW CONTROL SYSTEM [75] Inventor: Joseph F. Settle, Scotia, NY.

[73] Assignee: General Electric Company,

Schenectady, N.Y.

[22] Filed: Apr. 3, 1972 [21] Appl. No.: 240,417

[52] US. Cl. 266/38, 164/147, 164/155, 164/281, 266/34 V [51] Int. Cl. C21b 7/14 [58] Field of Search 164/147, 155, 281; 266/34 V, 38; 417/50 [56] References Cited UNITED STATES PATENT 3,380,511 4/ 1968 Campbell 164/55 3,367,396 2/1968 Sickbert et al.... 266/34 V 1,856,430 5/1932 Roesen 164/147 2,552,876 5/1951 Tama 417/50 2,707,720 5/1955 Tama 266/38 2,707,718 5/1955 Tama 266/38 2,397,512 4/1946 Schwartz et a1. 266/38 2,224,982 12/1940 Morin 164/147 FOREIGN PATENTS OR APPLICATIONS 1,283,271 12/1960 France 164/281 Primary ExaminerGerald A. Dost Attorney-Vale P. Myles et al.

[5 7] ABSTRACT A fail-safe liquid metal pumping and flow control system is described wherein metal is transferred from a holding furnace to a continuous casting mold, individual molds, ladies, etc., through a siphon having an electromagnetic pump with dual direction output situated along the length of the siphon to control the flow of liquid metal therethrough. The system initially is primed by applying vacuum to the siphon through a suitable valve and the siphon is vented to terminate liquid metal flow upon sensing of an anormal process condition, e.g., loss of electrical power to the electromagnetic pump, to inhibit further siphoning of liquid metal from the reservoir. Also disclosed is a pumping system wherein the holding furnace is initially disposed at an attitude to inherently raise the liquid metal level into operating engagement with an electromagnetic pump drawing liquid metal from the holding furnace. The furnace then is tilted upon the subsequent sensing of an anormal process condition to gravitationally return metal from the electromagnetic pump to the holding furnace. The electromagnetic pump thus provides the lifting force to drive the mo]- ten metal up to and over the pouring spout, thereby providing complete electrical control of the pouring rate, while failure of power or the pump will cause the flow to terminate to provide the fail-safe feature.

4 Claims, 3 Drawing Figures llllllllllllfllll PATENTEDBEB m 3,776,439

SHEET 10F 2 VACUUM SOURCE PATENTEU 4W5 3,776,439

SHEET 20F 2 7s 4 EMERGENCY POWER. SUPPLY REVERSIBLE CYCLO- \J CONVERTER A 92 \n City FAIL-SAFE LIQUID PUMPING AND FLOW CONTROL SYSTEM This invention relates to a fail-safe liquid pumping system and in particular, to a system wherein the pump is charged by the flow of a liquid from a reservoir seeking its own level and the liquid is gravitationally returned to the reservoir upon the subsequent observation of an anormal process condition.

In various casting operations, and particularly in continuous casting operations, it is necessary to transfer liquid metal from a holding furnace to the casting mold at a controlled rate. For example, in a continuous casting operation, the controlled rate of liquid metal transfer corresponds to the discharge rate of solidified metal from the mold. While this liquid metal transfer can be accomplished by manually tilting a ladle or controlled filling of a tundish to pour molten metal into the mold, more automated casting systems employ an electromagnetic pump to controllably transfer metal directly from the holding furnace, i.e., a continuously heated liquid metal reservoir, to the mold thereby eliminating any need for constantly refilling a limited volume ladle or tundish. When the electromagnetic pump is employed to regulate the gravitational flow of liquid metal from the holding furnace to the mold, however, loss of electrical power to the electromagnetic pump terminates control of molten metal flow tending to produce a potentially disastrous situation.

To inhibit the loss of flow control associated with gravitational flow systems, it has been proposed that electromagnetic pumps be utilized to lift the molten metal from the holding furnace to the continuous casting mold. While such a pumping. system will gravitationally return molten metal to the holding furnace upon loss of pump power, the pump must be primed prior to operation. Because electrical power is employed to maintain the pump prime, inadvertent power decreases below a specific level can result in loss of prime. Moreover, because'the electromagnetic pump functions only to overcome the gravitational forces tending to return the liquid metal to the holding furnace, the degree of flow control in such system is limited.

It is therefore an object of this invention to provide a fail-safe gravity flow system for pumping .liquids.

It is also an object of this invention to provide a liquid metal pumping system wherein the electromagnetic pump controlling liquid metal flow is reversible to provide a large range of flow control.

It is also an object of this invention to provide a selfpriming liquid metal pumping system wherein liquid metal within the system is gravitationally returned to the main reservoir upon termination of pumping.

A fail-safe liquid pumping system in accordance with this invention generally includes a reservoir containing an electrically conductiveliquid, a conduit having one end immersed within the reservoir below the minimum liquid level to withdraw liquid from the reservoir and flow control means disposed along the length of the conduit for regulating the flow of liquid therethrough. Liquid flow initiation means also are provided in the system for charging the flow control means with liquid flowing to seek its own level and means are provided to return liquid from the system to the reservoir upon sensing of an anormal pumping condition. In a preferredembodiment of the invention, the liquid flow initiation means includes means for evacuating the conduit to produce siphoning action therethrough and flow back of liquid to the reservoir is achieved by venting the siphon. Alternatively, the pump is inherently primed by the level of liquid in the reservoir and liquid within the system is returned to the reservoir upon the sensing of an anorrnal process parameter by tilting of the reservoir to lower the liquid level adjacent the flow control means.

Although this invention is described with particularity in the appended claims, a more complete understanding of the invention may be obtained from the following detailed description of various specific pumping systems when taken in conjunction with the appended drawings wherein:

FIG. 1 is a sectionalized pictorial illustration of a liquid pumping system in accordance with this invention,

FIG. 2 is a schematic showing of the fail-safe feature of the invention by which the continuous flow of liquid through the system'is terminated upon de-energization of the electromagnetic pump regulating liquid flow, and

FIG. 3 is a sectional view of an alternate flow control system wherein the holding furnace is tilted to return molten metal to the furnace by gravity upon detection of an anormal condition.

A liquid metal pumping system 10 in accordance with this invention is illustrated in FIG. 1 and generally includes a holding furnace 12 from which molten metal 14 is drawn by siphon 16 to supply continuous casting mold l8. Charging of the siphon is accomplished by temporarily inserting a centrally apertured ceramic plug 20 into the discharge end 22 of the siphon to apply vacuum source 24 to the system while a linear electromagnetic pump 26 is situated along the downstream portion of the siphon to control the flow of molten metal subsequent to the initiation of siphoning action. Venting is accomplished by means of valve 28 which communicates the apex of the siphon with the atmosphere or with an inert gas supply (not shown).

Holding furnace 12 is a large melting or holding vessel typically formed of a brick outer structure 30 and an interior fire brick lining 32. An aperture 34 is provided within the sidewall of the furnace above the liquid metal level therein to permit the direct application of a-flame to the liquid metal from burner nozzle 36 to maintain the metal within the melting or holding furnace in a molten state. Suitable means, such as an opening (not shown) normally also would be provided to admit charge to the holding furnace, or ingots to be melted as needed.

Siphon 16 typically is a metal sheathed ceramic tubular member having an intake end 38 situated within the molten metal below the minimum depth of molten metal within the holding furnace. The discharge end 22 of the siphon, in conventional fashion, is located in a lower vertical planethan the liquid level within the holding furnace to permit siphoning action to occur upon charging of the siphon with molten metal. While the physical configuration of the siphon will vary dependent upon the material to pass therethrough, e.g., whether the siphon is being utilized to transport ferrous or non-ferrous metals, thesiphon typically would be formed of a cast iron outer sheathing 42 having a ceramic lining 44 of, for example, alumina, for the trans port of most ferrous metals. Because of the extremely high temperatures produced by the direct application of flame to the molten metal within the holding furnace for the higher melting point metals, the cast iron sheathing of the siphon normally would terminate prior to insertion within the liquid metal reservoir. In conventional fashion, resistance or induction heaters 46 are provided along the length of the siphon to preheat the siphon prior to pumping and to permit complete drainage of the liquid metal from the siphon upon termination of pumping. In some applications it is possible to preheat the siphon while preheating the holding furnace prior to charging. This is accomplished by restricting somewhat the flow of hot gas out of the charging opening by means of temporarily placed ceramic brick or tile, thereby causing the hot gas to be forced through the siphon.

Priming of siphon 16 in accordance with this invention is accomplished by inserting plug 20 into the discharge end of the siphon and drawing a vacuum by means of vacuum source 24 through valve 48. Thus, with valve 48 opened and plug 20 inserted in discharge end 22 molten metal is lifted from the holding furnace 12 to the apex of the siphon and down the discharge leg whereafter the vacuum source can be sealed off, i.e., by closing valve 48 and removing the plug from the discharge end of the siphon, to permit the initial gravitational discharge of molten metal to continuously siphon molten metal from the holding furnace to continuous casting mold 18. Although siphon 16 is completely sealed, the arrival of molten metal at the apex of the siphon can be determined by positioning a thermal sensing device 50 adjacent the pump discharge or by the visual observation of the initial leakage of molten metal at the discharge end of the siphon.

Control of the volume of molten metal flow through the siphon is achieved by linear electromagnetic pump 26 disposed along the downstream side of the siphon. Electromagnetic pumps suitable for this invention may be one of four general types flat linear, annular, helical or centrifugal. These pumps are well known in the art with helical and linear pumps being illustrated in U.S. Pat. Nos. 3,260,209 and 2,985,106, respectively, issued to R.G. Rhudy and assigned to the assignee of the present invention. The electromagnetic pump illustrated in FIG. 1 is a Hat linear pump and generally comprises a plurality of stacked metallic laminations 54 having slots 56 along the interior face of the laminations to accept coil windings 58 extending therethrough with the end turns of the coils protruding outwardly from the stacked laminations. To obtain maximum flow control, the circular siphon preferably is flattened adjacent electromagnetic pump 26 to permit the close positioning of a linear electromagnetic pump stator on each side of the siphon. In conventional fashion, molten metal within the electromagnetic pump is moved by the sequential energization of coil windings 58 to drag the molten metal along, or to impede the gravitational flow of the metal, dependent upon the phase sequence of coil energization.

Because the termination of electrical energization for electromagnetic pump 26 would remove control over the flow rate of molten metal from holding furnace 12 to overflow receptical 60 utilized within the continuous casting mold to reduce metal turbulence, it is highly desirable that molten metal flow through the siphon be terminated upon de-energization of the pump. One valving system to accomplish this result is shown in FIG. 2 wherein venting of siphon 16 is controlled by valve 28 mounted at the end of conduit 61 remote from the siphon. Although valve 28 could be of any conventional configuration, the valve preferably includes a metal ring 62 which is seated against ceramic lining 44 of conduit 61 to function as the valve seat. The valve is sealed by an annular cast iron or ceramic plunger 64 having an asbestos gasket or similar lining 66 along the periphery thereof to mate with metal ring 62 while spring 68 provides the necessary mechanical bias to maintain the valve in a normally closed position. When electrical power to cycloconverter 70 controlling the frequency and phase of power to the electromagnetic pump is terminated, relay 72 is deactivated to trip contacts R and R" to their normally closed position thereby energizing coil 74 from emergency power supply 76. Energization of the electromagnetic coil then retracts plunger 64 to vent siphon 16. Upon venting of the siphon, molten metal downstream of the siphon apex flows to mold 18 while molten metal upstream of the siphon apex flows back to holding furnace 12 to terminate the flow of molten metal through the siphon. While the use of a power source with controlled frequency and voltage provides optimum pumping characteristics, flow can also be controlled by use of a variable voltage source and switching means to change the phase relation of the power provided to the pump.

An alternate embodiment of this invention utilized to return molten metal to the holding furnace upon the sensing of an anormal process condition is illustrated in FIG. 3 wherein reference numerals corresponding to those of FIG. 1 are utilized for like components. The holding fumace 12A utilized for casting, however, rather than being stationary as in FIG. 1 is rotatable about shaft 78 by means of a motor 80 driven screw 82 engaged with gear 84 fixedly secured to the shaft. Rather than utilizing a siphon to discharge molten metal from the holding furnace, the intake end 86 of discharge conduit 88 is communicated through the sidewall of the holding furnace at a level below the mo]- ten metal level and electromagnetic pump 26A controlling the rate of metal flow through conduit 88 is situated at a location below the normal level of molten metal within the holding furnace to inherently charge the electro-magnetic pump as the molten metal seeks its own level within the conduit. In order to assure charging of the electromagnetic pump, the molten metal should rise to at least midway within the electromagnetic pump to permit the moving electromagnetic field to drag the molten metal upwardly through conduit 88. When an anormal process condition is observed, such as loss of energization to electromagnetic pump 26A, motor 80 is energized to tilt holding furnace 12A in a direction terminating communication between discharge conduit 88 and molten metal 14A, i.e., to produce a molten metal level illustrated by dashed line 90 in FIG. 3. The molten metal within the electromagnetic pump then gravitationally discharges to return to the holding furnace inhibiting freeze-up of the pumping system. An additional advantage of the rotatable holding furnace illustrated in FIG. 3 resides in an ability to tilt the holding furnace in an opposite direction, i.e., to produce a molten metal liquid level as illustrated by line 92, in order to reprime the pump and maximize the quantity of molten metal potentially removable from the holding fumace.

Although the foregoing specific embodiments of this invention have been disclosed as utilizing loss of electrical energy to the electromagnetic pump to terminate pumping, it will be obvious that any anormal process condition can be observed to initiate the termination of molten metal flow from the holding furnace. For example, the molten metal level within casting mold 18 can be observed, i.e., utilizing thermocouples 94 (illustrated in FIG. 1) or an optical sensor (not shown) to terminate discharge of molten metal from the holding furnace upon observation of an inordinately high molten metal level within the mold. The appended claims therefore are intended to include such variations of this invention as fall within the scope of this invention.

I claim:

1. A fail-safe liquid pumping system comprising:

a. a reservoir containing an electrically conductive liquid,

b. conduit means having one end immersed within said liquid to a depth below the minimum liquid level within said reservoir, said conduit means being canted to extend upwardly from said reservoir before turning downwardly for discharge of said liquid from the other end of said conduit, the discharge end of said conduit means being at an elevation lower than the minimum molten metal level within said reservoir to siphon metal from said reservoir,

electromagnetic pump means disposed along the downwardly extending leg of said conduit means for controlling the flow of liquid through said conduit,

d. flow initiating means for lifting said liquid from said reservoir to said flow control means to initiate pumping of liquid from said reservoir, and

e. flow terminating valve activated upon detection of an anormal process parameter to inhibit further lifting of the liquid from said reservoir to said flow control means.

2. A fail-safe liquid pumping system according to claim 1 wherein said means responsive to the anormal process parameter include means for tilting said reservoir by an amount to reduce the reservoir liquid level adjacent said conduit means below the level of the flow control means disposed along the conduit.

3. A fail-safe liquid metal pumping system according to claim 1 wherein said electromagnetic pump means is reversible to impede the gravitydischarge of molten metal from said conduit means upon energization of said electromagnetic pump means in a first direction and to assist gravity discharge of molten metal from said conduit means upon energization of said electromagnetic pump means in a second direction.

4. A liquid metal pumping system for a casting'operation comprising:

a. a reservoir of molten metal,

b. conduit means having one end immersed within said molten metal reservoir to permit siphoning of molten metal from said reservoir upon charging of said siphon,

c. electromagnetic pump means disposed along the length of said siphon for controlling the gravitational flow of molten metal from said reservoir through said conduit means,

d. flow terminating means situated between said reservoir and said electromagnetic pump means to vent said siphon upon observation of an anormal operating condition in said casting operation, and

e. means for energizing said electromagnetic pump means in opposite directions to enhance or impede the gravitational flow of liquid metal through said conduit means.

Claims

1. A fail-safe liquid pumping system comprising: a. a reservoir containing an electrically conductive liquid, b. conduit means having one end immersed within said liquid to a depth below the minimum liquid level within said reservoir, said conduit means being canted to extend upwardly from said reservoir before turning downwardly for discharge of said liquid from the other end of said conduit, the discharge end of said conduit means being at an elevation lower than the minimum molten metal level within said reservoir to siphon metal from said reservoir, c. electromagnetic pump means disposed along the downwardly extending leg of said conduit means for controlling the flow of liquid through said conduit, d. flow initiating means for lifting said liquid from said reservoir to said flow control means to initiate pumping of liquid from said reservoir, and e. flow terminating valve activated upon detection of an anormal process parameter to inhibit further lifting of the liquid from said reservoir to said flow control means.

3. A fail-safe liquid metal pumping system according to claim 1 wherein said electromagnetic pump means is reversible to impede the gravity discharge of molten metal from said conduit means upon energization of said electromagnetic pump means in a first direction and to assist gravity discharge of molten metal from said conduit means upon energization of said electromagnetic pump means in a second direction.

4. A liquid metal pumping system for a casting operation comprising: a. a reservoir of molten metal, b. conduit means having one end immersed within said molten metal reservoir to permit siphoning of molten metal from said reservoir upon charging of said siphon, c. electromagnetic pump means disposed along the length of said siphon for controlling the gravitational flow of molten metal from said reservoir through said conduit means, d. flow terminating means situated between said reservoir and said electromagnetic pump means to vent said siphon upon observation of an anormal operating condition in said casting operation, and e. means for energizing said electromagnetic pump means in opposite directions to enhance or impede the gravitational flow of liquid metal through said conduit means.