EP0271612A1

EP0271612A1 - Molten metal handling system

Info

Publication number: EP0271612A1
Application number: EP86202344A
Authority: EP
Inventors: Hugh C. Behrens
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1986-12-19
Filing date: 1986-12-19
Publication date: 1988-06-22

Abstract

A metal handling system for delivering molten metals, such as magnesium and its alloys, to a continuous casting machine (11) without exposure of the molten metal (13) to the ambient atmosphere and at reproducible pressures and quantities. The metal (13) is conveyed from a crucible, melting pot or an electrochemical cell (10) to a casting machine (11), e.g. a die caster, strip caster, sand mold, and the like. The elements for conveying the molten metal (13) include a magneto-hydrodynamic pump (12) and heated conduits (14) to carry the molten metal (13) to the casting machine (11). Preferred features of the handling system include a flowmeter (15) and a shot size delivery mechanism (16). Optionally, two or more sources of molten metal, e.g. two remote melting pots, can be tied together to provide a continuous source of metal, pretreated by flow control elements, to one or more casting machines.

Description

The present invention resides in a method for the delivery of molten metals, such as magnesium and alloys thereof, to a continuous casting machine, without exposure of the molten metal to the ambient atmosphere. The method of the invention is conducted at reproducible pressures and quantities to enable advanced casting technologies to be utilized to their fullest potential.
The art of metal casting has made significant advances in the past with the advent of rotary die casting machines and continuous strip casters. While advances have been made in die casting machines only a few changes have occurred in the techniques for delivery of the molten metal to the machine. The industry still delivers the molten metal to the machine in heated ladles or heated tiltable crucibles. Several advances which seemed logical, e.g. molten metal pumps based on the Einstein design, heated troughs and/or pipes, shot size delivery apparatus, and the like have not been universally employed. Some of the disadvantages of such prior art apparatus are that for metals, such as, for example magnesium or magnesiu m alloys, the use of pumps required external cooling systems or extended shafts to place the pump at a distance from the high temperature zone of the crucible or melting pot. Each of these aspects has apparent problems obvious to those skilled in the art. Likewise, heated troughs and/or conduits have been employed to deliver molten metal by means of a tiltable crucible, or the like. Such conduits or troughs are usually heated by gas fired burners or electrical resistance heating devices to maintain the metal in a molten condition. The disadvantage of each technique is obvious, gas fired heaters create an undesirably hot work place environment and resistance heaters are difficult to control when a molten metal is the resistance.
In addition, most of the systems expose the molten metal to the ambient atmosphere permitting oxidation of the metal thereby introducing metal oxide impurities into the castings resulting in generally poor quality castings. The extent of oxidative losses is particularly detrimental when casting magnesium.
Further, none of the prior systems is readily controlled to enable repetitive shot or draw conditions to be automatically uniform.
In accordance with the present invention there is described a molten metal handling system, particularly useful for delivering metals in their molten state from a melting pot or crucible to a casting station, e.g. die caster, strip caster, sand molds, and the like, remote from the melting pot or crucible without exposing the molten metal to the ambient atmosphere. The essential elements of the handling system of the invention are a pump and heated conduits to carry the molten metal to the casting station. In addition to the pump and heated conduit, the molten metal delivery system may optionally include two or more sources of molten metal and flow control elements, e.g. two remote crucibles or melting pots and associated flow control elements, i.e. orifices. The sources of molten metal can be connected to a common delivery conduit to provide a continuous supply of molten metal to the casting station. Optionally, the system also includes a flow meter for measuring the amount of molten metal flowing through the conduit and a shot size and deliver apparatus.
The foregoing objects, features and advantages of the invention will be apparent from the following description of preferred embodiments, as illustrated in the accompanying drawings, in which:

Figure 1 is a schematic diagram, in elevation, of a preferred molten metal delivery system;
Figure 2 is a substantially isometric, partial sectional view of the interior of a pump;
Figure 3 is a partial cross-sectional view of an annular, linear induction flowmeter;
Figure 4 is a partial cross-sectional view of a flat, linear induction flowmeter;
Figure 5 is a side view, in cross-section, of the flowmeter illustrated in Figure 4; and
Figure 6 is a cross-sectional view of a shot size and delivery apparatus;

In accordance with the present invention and with particular reference to Figure 1, a crucible or melting pot (10), remotely located with respect to a die casting machine (11), is connected to the die casting machine (11) by means of an electromagnetic pump (12) which is submerged in the molten metal (13) in the melting pot (10). The pump (12) is provided with a molten metal inlet (12a) and is connected at its outlet end to a conduit (14). A plurality of said conduits may optionally be provided to convey molten metal from one or more such melting pot(s) (10) to the die casting machine (11). Intermediate the conduit (14) there is located a flowmeter (15) which may be an annular linear induction or a flat linear induction flowmeter. A shot size and delivery apparatus (16) is connected to an outlet end of the conduit (14) of the flowmeter (15) and a nozzle (not shown) for the die casting machine (11). A flow control means such as, for example, an orifice (not shown) may be inserted into the conduits (14) upstream or downstream of the flowmeter (15) if a plurality of melting pots are used. Such flow control means is also preferably employed if one or more die casting machines are supplied with molten metal from the same melting pot or from a plurality of melting pots and when a single pressure is preferred for conducting the molten metal to the die casting machine(s).
The melting pot (10) is preferably insulated and provided with a cover (not shown) and is heated with either gas fired burners or electrical resistance heaters. The melting pot (10) is of conventional design and the shape and size is not critical. Of course, the selection of the number of melting pots or the size of a melting pot should be sufficient to enable continuous operation during each shift of casting.
The die casting machine (11) is any standard present day, high or low pressure, continuous or intermittent, casting machine, sand molding table(s), or the like. It is to be understood that the system described above can also supply molten metal to a strip caster.
The pump (12) is of an appropriate size to supply a requisite volume of molten metal, at the desired pressure, to the die casting machine. The molten metal is conveyed by an electromagnetic force generated by the pump.
The conduit (14) is made of a Schedule 40 carbon steel pipe, although other materials may be used depending on the composition and the tendency of the molten metal, such as, for example, magnesium or magnesium alloys, to extract minor alloy components from the surface of the conduit. Surrounding the conduit (14) are a series of electrical resistance heating coils or rods (17a; 17b) preferably capable of carrying a 220-240 volt AC power. The power to the heating rods is controlled through a power switching mechanism (not shown). Operation of the switching mechanism is controlled by a thermal switch (not shown) which, upon sensing that the conduit has achieved a designated temperature, several degrees above the melting point of the molten metal, will intermittently switch the electrical power on and off as needed to maintain the conduit at the requisite temperature. It is well known that operating at reduced voltages will extend the service life of the resistance heating coils. Accordingly, the system operates initially on 220-240 volts, but upon reaching a temperature of from one to several hundred degrees below the melting temperature of the metal, the system can be and preferrably is, switched to 110-120 volts AC to continue the heating to the desired temperature and is thereafter maintained on the 110-120 volt circuit to maintain the temperature. The thermal switch is controlled by a thermocouple (not shown) which is an adjunct to the thermal switch which, in turn, operates the power switching mechanism, which delivers the correct voltage (power) to the heating coils. It is, of course, to be understood that the thermal switch may be replaced with more sophisticated control means, such as two, three, or more automatic controllers. The entire assembly of the conduit, heating coil and thermocouple are encased in an insulating medium (18a; 18b), such as, an alumina/silicon oxide fiber blanket, one such being a material sold under the tradename Fiberfrax.
The connection of the conduits, one to the other, may conveniently be made with, for example, a split "V" clamp, such as the clamp described in U.S. Patent No. 4,313,625.
In modern day casting machines, it is essential that the molten metal be delivered in amounts and under pressures such that a mold wll be filled but not over-filled. In accordance with the present invention the molten metal is conveyed through the tubular conduit (14) to the shot size and delivery mechanism (16) and thence to the casting machine (11).
The pump of the present invention is particularly illustrated in Figure 2 and is an annular linear induction pump which is capable of operating at a temperature in excess of 700°C without external cooling. The pump is capable of developing a hydrostatic head of molten metal in excess of 10 meters. The preferred design of the pump emplys only six coils versus twelve or more coils that are presently used in pumps.
The pump is generally identified by reference number (12) and comprises a central or inner tube (22) for conveying molting metal therethrough. The central tube (22) is connected to the conduit (14) (Figure 1) for conveying molten metal from the melting pot or crucible (10) to the casting machine (11), or the like. The pump of the invention may also be employed for pumping molten metal directly out of an electrochemical cell. The central tube (22) is provided with a central core (23) having a plurality of guide vanes (25) mounted at circumferentially spaced positions on the central core. The inner tube (22) and core (23) form an annular flow channel (24) for the molten metal. Optionally, the central tube is provided with a sleeve (26) of a non-magnetizable insulating material, e.g. a ceramic material but preferably of a thermally pretreated mica. A plurality of laminated core elements (28) are provided each comprising a multiplicity of sheet metal laminae (29) and an insulating sheet (30) of a thermally pretreated mica, positioned between each pair of sheet metal laminae. The core elements (28) are positioned in a circumferentially spaced relationship around the inner tube (22) and, optionally, the sleeve (26). Each core element has a plurality of spaced leg portions (31) in whihch the spaces between each pair of leg portions is occupied by an electrically conductive coil (32) having a plurality of windings (33) which are insulated from each other by a sheet or strip of a thermally pretreated mica (34). In a preferred embodiment of the invention, each core element (28) has seven (7) leg portions thus providing six (6) spaces between the leg portions forming, in effect, six (6) receptacles for six (6) coils. An outer housing (36), enclosing the pump components, is sealed (not shown) to the ends of the inner tube (22).
In accordance with a particular aspect of the present invention, the core elements and coils of the pump employ a thermally pretreated mica which has been substantially freed of impurities. It was discovered that impurities, which are naturally present in mica, are released or driven off when the mica is heated to a temperature above 700°C, preferably above 850°C.
Conventional electrical grade mica, when subjected to the high temperatures encountered in pumping molten metals, release impurities of unknown identification. Accordingly, mica sheets produced for conventional insulation of electrical equipment which have not been thermally pretreated, as hereinafter described, were found to release such impurities in the form of a black soot beginning at a temperature above 400°C. The residue of such impurities were found to be the primary cause of a shorting-out of the coil windings and/or laminated cores.
It has now been found that if conventional commercially available mica, for example in sheet form, which is the usual form of mica employed to insulate transformer laminations as well as other electrical appliances, is heated to a temperature above 700°C and preferably above 850°C under an oxidizing atmosphere, e.g. air, for a period of time sufficient to eliminate impurities from the mica, the thermally pretreated mica will withstand high temperatures (above 700°C when subsequently placed into use without producing a black soot and a cooresponding shorting-out in the laminated cores and/or coil windings. Preferably, the pretreatment time varies from 1 to 24 hours depending on the temperature to which the mica is subjected. Generally, the higher the pretreatment temperature, the shorter the period of time needed to eliminate impurities from the mica. Mosre preferably, the pretreatment time is in excess of about 8 hours. Conventional mica used as a core laminate or coil insulation even when padded with argon and immersed into molten metal produced a black soot on the mica surfaces, whereas mica when pretreated in accordance with the present invention and similarly employed in an argon padded atmosphere showed no visible evidence of such soot formation. In every instance where untreated mica was employed as an insulating material in a pump used for the conveyance of molten magnesium, shorting-out of the coils or core elements occurred. In many instances shorting-out occurred on pre-use tests and/or shortly after immersion of the pump into the molten metal.
Accordingly, the present invention resides in the discovery that conventional commercially produced amber mica, as well as mica from other sources, can be treated by heating in an oxidizing atmosphere to remove impurities to yield an electrical insulating material which exhibits superior performance in high temperature applications. The amber mica when treated at a temperature above 700°C, preferably above 850°C, can be used for extended periods of time in, for example, electromagnetic pumps for pumping molten metal without cooling as is conventionally done in such pumps. The use of a thermally pretreated mica also permits the design of a more compact pump and longer in-service life in applications where the pump is submerged in the molten metal. The discovery has extensive utility for other electrical equipment which is subjected to high temperatures and where external cooling is not possible or desirable.
One embodiment of an annular flowmeter which may be employed in the metal handling system of the invention is illustrated in Figure 3. As in the case of the pump (12), the flowmeter of the invention is also designed to withstand the high temperatures of a molten metal without a breakdown of the electrical components of the flowmeter through which the molten metal flows and without any internal or external cooling of the flowmeter.
Flowmeters that are employed in the present invention generally comprise a central or inner tube. A central core is positioned within the central tube providing therewith an annulus through which molten metal can flow. Circumferentially positioned around the central tube are at least two laminated core elements each comprising a multiplicity of laminae of magnetizable metal sheets. Each core element has a plurality of spaced leg portions forming a space between each pair of leg portions. Circumferentially wound about said inner tube are at least three electrically conductive coils which are positioned within the space provided between the leg portion of the core elements and which the first and third are electrically connected in series so that the first coil will conduct current in a direction opposite to the direction of current flow in the third coil to hereby establish a magnetic field between the ends of the leg portions of the core element The intermediate or even numbered coil or coils are wired to transmit an induced current or voltage to a measuring device such as an ammeter or voltmeter. The core elements and coils are encased in a housing which is sealed to the central tube at each terminal end thereof. The windings of each coil are electrically insulated from each other with the thermally pretreated mica described hereinabove. Similarily the sheet metal laminae of each core element are electrically insulated from each other with said thermally pretreated mica. The inner-most windings of the coils and the inner ends of the leg portions of the core elements are likewise preferably electrically insulated from the central tube by an insulating sleeve.
In operation, a single phase alternating current is impressed across alternating, series connected, coil windings to generate a magnetic field internally of the central tube in the annulus. When metal flows through the annulus of the central tube and thus across the magnetic field there is generated in the metal an induced current which induces a voltage in an intermediate coil winding(s) which can be measured. A direct relationship is established between the volume of metal flowing through the tube, the magnetic field generated by the electrically energized coils, and the voltage that is induced across the windings of the non-energized coil, i.e. in the windings of the intermediate coil(s). The amount of metal flowing through the annulus of the central tube is directly correlated to the voltage generated in the windings of the non-energized coil.
One embodiment of an annular flowmeter of the invention is illustrated in Figure 3 and is generally identified by reference number (40). The meter comprises a central or inner tube (42), preferably having an outside diameter of about 4.5 cm and a length of about 25 cm. In a preferred embodiment, three coils (44) each of which has a plurality of windings (45) of an electrical conductor, are positioned on the central tube. Preferably, each coil is positioned on a sleeve (46) made of an insulating material which fits snugly over the central tube (42). It will be understood that a single sleeve may be employed extending over the length of the central tube. The coils (44) and sleeve(s) (46) are spaced along the length of the central tube (42) and held in place between four leg portions (47) of a core element (48). Each coil is wound with an electrical insulating strip (49) of the thermally pretreated mica between the layers of windings (45). Each core element (48) comprises a multiplicity of sheet metal laminae (51) and a thermally pretreated strip or sheet of mica (50) between each sheet metal laminae (51). The coils and core elements are assembled on the central tube and are encased in an outer casing or housing (52). The ends (53) of the housing are sealed to opposite, terminal ends (43) of the central tube (42). A central core (54), provided with a plurality of radially extending core guides or vanes (55), is centrally positioned in the central tube (42) thus providing an annular passageway (56) with the interior surface of the central tube (42) for flow of molten metal therethrough. The housing (52) is preferably padded with an inert gas such as, for example, argon.
The outermost or end most coils are electrically connected in series to an electric power source (not shown) to produce the appropriate polarities for the magnetic fields generated by the coils. The intermediate coil(s) is connected to a measuring device, e.g. an ammeter or voltmeter to measure the induced current that flows in the intermediate coil or to measure the voltage when power is supplied to the outer coils and molten metal flows through the annular space between the central core (54) and the inner wall of the central tube (42).
Calibration of the ammeter to the flow of molten metal is made by causing various amounts of metal to flow into a container for a predetermined time period. The container and molten metal is then weighed and readings are taken from the ammeter and correlated to such measured flows. The ammeter recorded flow rates that came within ±2 percent of the actual flowrate of molten metal through the central tube.
Another embodiment of a flowmeter that can be employed is a flat linear flowmeter illustrated in Figs. 4 and 5. The flowmeter is generally identified by reference member (60) and comprises a pair of laminated magnetic core members (62a; 62b) positioned on opposite sides of a flattened portion (68) of a tube (66) through which the molten metal flows. Each laminated core member is encased in a non-magnetizable housing member (70a, 70b). The housing members are sealed and preferably provided with hinges (72) on each side to position the housing members on opposite sides of the flattened portion (68) of the central tube (66) such that they can be removably, yet fixedly, mounted on the tube when in service, using a hinge pin as a securing element. Preferably, the sealed housing members containing the laminate core members are padded with an inert, non-oxidizing gas, such as argon. The core members are slidably mounted within the housing in guide clips (74) within their respective housing members and are held in an endwise adjustable position by means of a pair of screws (76), or the like, at each end of each core member.
Each core member is constructed of a multiplicity of sheet metal laminates which are separated from each other by an electrical insulating sheet in the same manner as described in the embodiment illustrated in Figure 3. In a preferred embodiment of the invention shown in Figure 3, the core member has three (3) leg portions (63) in which each of the outer leg portions is provided with outer-most coils which are electrically connected in series. One coil, e.g. the first coil (64a), is connected to a power source at its outer-most winding end, the inner-most end being connected to the inner-most end of the third coil (64c) and the outer-most end of this coil completing the circuit to the power source. The intermediate leg portion of the core member is provided with a second or intermediate coil (64b) connected to an ammeter or voltmeter to measure the induced current or voltage which is generated in the coil when power is supplied to the outer coils while a molten metal is flowing through the tube. Preferably, each coil comprises a substantially flat deoxygenated copper conductor which is insulated with the thermally pretreated mica strip or mica sheet, as hereinbefore described between each layer of the coil winding(s). Each laminate core member also has a thermally pretreated mica strip positioned between each pair of adjacent sheets.
It is preferable to provide a thermally pretreated mica insulator (78) at the housing interface, i.e. between the housing members (70a, 70b)
The flowmeter is operated in the following manner. The electrically energized coils, i.e. the first and third (or outer most) coils (64a) and (64c) and wound to generate a magnetic field of alternating opposite polarities. The coils are energized from a single phase, 8-16 volt source, for example. The second or intermediate coils (64b), of each laminate core member is connected to an ammeter (or a voltmeter). When more than three leg portions and thus more than three (3) coils are employed, the intermediate coils are connected in parallel. The ammeter is calibrated for flow of the molten metal in the tube at various flow rates.
The coil windings for the pump and flow meters can also be made of Invar® (a ferro-nickel alloy of 36% Ni, 64% steel and 0.2% carbon, having a melting point of 1500°C and a density of 8.0), or the like material, but are preferably made of deoxygenated copper. The central tube, which is in contact with the molten metal, is made of a non-magnetizable metal or a ceramic material. For example, when measuring the flow of molten metals such as magnesium or magnesium alloys the central tube is preferably made of stainless steel such as 347 SS (a columbium stabilized nickel alloy) or 430 SS ( a chromium/molybdinum steel alloy). The central core which is conventionally made of carbon steel is preferably made of a cobalt/iron alloy having a Curie point above the temperature of molten metal being conducted through the central tube. Further, in the case of pumping molten magnesium or magnesium alloys, the external housing components which are in contact with the molten metal are preferably made of 347 or 430 stainless steel.
With respect to the sheet metal laminae of the core elements, temperature is a major consideration and if external cooling is not employed, and preferably it is not, cobalt/iron alloys are the metal of choice because the Curie point is not exceeded at operating temperatures of to 815°C.
It is preferred to operate the coils at a frequency of 60 Hz., although a lower frequency of as low as 10 Hz may be used.
In modern day casting machines, it is essential that the molten metal be delivered in amounts and under pressures such that the cavity of a mold will be filled but not over-filled. However, most casting operations still use ladles as a means to transport molten metal from a melting or holding vessel to a ram chamber of a shot size and delivery mechanism. Accordingly, in present day die casting or strip casting machines production is in the nature of a batch or semi-batch operation to supply molten metal to the mold cavity of a die casting machine. In addition when the metal is magnesium or a magnesium alloy difficulties are encountered in excluding the ambient atmosphere from coming into contact with the molten metal which creates a safety hazard and which also causes contamination of the metal with the oxides of the molten metal.
It would therefore be advantageous to have a system wherein the molten metal is delievered from a remote location through conduits to a shot size and delivery mechanism and have the mechanism (through a pressure-time relationship) deliver a definite or predetermined quantity of the molten metal to the mold. To prevent or exclude the molten metal, particularly magnesium or magnesium alloys, from comming into contact with the ambient atmosphere, an inert gas or a mixture of air, to which CO₂ and sulfur hexafluoride may be added, is optionally employed to sweep the ram chamber of the shot size mechanism and the mold cavity of the die casting machine.
The ram chamber is provided in a hydraulic ram having only a nominal relationship to the volume of metal to be used to fill the mold cavity. The term "nominal relationship" is intended to convey the idea that the ram chamber is not intended to be of a size to hold an exact amount of molten metal sufficient to fully charge or fill the mold cavity. The ram chamber is but a convenient means to accumulate an amount of molten metal in excess of that necessary to fill the mold cavity. A sufficient amount of molten metal will be present in the ram chamber so that a positive pressure is applied to the molten metal in the ram chamber and in the mold (and sprue leading from the mold) to fill all the fine crevasses or recesses of the mold cavity.
With particular reference to Figure 6, and in accordance with the present invention, molten metal is conveyed to the casting machine (11) via the heated conduit (14) and the shot size and delivery system. The shot size delivery system in Figure 6 is generally identified by reference number (100) and comprises a hydraulic ram comprising a cylinder (102) and a ram or piston (104). Molten metal enters a chamber (106) in the cylinder through a conduit (108). The ram chamber (106) has only a nominal relationship to the volume of metal to be used to fill the mold, the true measurement of the volume being a factor of the pressure of the molten metal being delivered to the chamber (106) and the time the molten metal is allowed to flow into the chamber before the ram (104) is activated to force the metal under a predetermined pressure into a cavity (122) in a mold (120) of a die casting machine. It is of course to be understood that the molten metal being delivered to the chamber (106) under pressure flows into the mold cavity (122) during the "loading" or "charging" step since there is no resistance to the free flow of the metal until the ram (104) starts its movement and closes off an inlet port (110) in the cylinder (102). Associated with the chamber (106) is an inert gas sweep system, generally indentified by reference number (130), for introducing an inert gas into the chamber (106) and mold cavity (122). The sweep system includes a reservoir (132) for an inert gas connected by a conduit (134) to a gas supply (not shown). The reservoir (132) is connected by a conduit (136) to an inlet port (138) provided in the cyclinder (102) for supplying the inert gas to the chamber (106). The gas flowing into the chamber will also flow into the mold cavity (122) of the die casting machine during the period prior to the introduction of the molten metal into the chamber (106) and the mold cavity (122) and throughout the period prior to the ram (104) closing off the molten metal intlet port (110) and prior to pressurization of the chamber (106) and the mold cavity (122). Upon pressurization, the molten metal flows into the mold cavity under sufficient pressure to ensure that the smallest details or contours of the mold cavity are adequately filled with the molten metal.
In the operation of the device of the present invention the hydraulic ram (100) is programmed to be retracted to allow for the delivery of molten metal, under a positive head pressure, such as is developed by, for example, the pump (12), Figures 1 and 2, for a period of time sufficient to deliver a quantity of metal to the ram chamber (106) and mold cavity (122) sufficient to fill the mold cavity when the ram is in a fully extended position. The hydraulic ram (104) is actuated and moves forward forcing the molten metal from the ram chamber into the mold cavity and closing off the molten metal inlet port (110) thus causing the ram (104) to pressurize the molten metal in the mold cavity (122). When the ram (104) is in its forward-most position, and following a predetermined time period to allow for solidification of at least the surface of the metal at the mold interface, the mold is opened and the article ejected. The mold is then closed
and the ram (104) retracted to repeat the sequence. Since ambient air will fill the mold after ejection of the article, it is often necessary, if not essential from the safety standpoint particularly when casting magnesium, to flush the mold with an inert gas or mixture of gases, such as air, containing about 50 percent CO₂ and from .01 to 1.0 percent sulfur hexafluoride (commonly used to blanket the surface of molten magnesium to prevent oxidation of the surface or at least reduce the rate of oxidation at the surface) to remove any oxygen from the mold cavity before the next shot of molten metal is introduced into the chamber (106). The inert gas is also used to blanket the surface of the magnesium in the chamber and the mold cavity during the mold filling operation. Thus, in accordance with the present invention, the inert gas flows into the chamber (106) through the inlet port (138), which is located along the travel of the ram (104), at a point where the gas will be released into the chamber and thus into the mold cavity during the travel of the ram to its most retracted position. Since almost all molds have vents, the inert gas, if pressurized above ambient atmospheric pressure, will fill the mold cavity (122) and force the air which is entrapped in the mold cavity (on closing of the mold) to be vented from the cavity as it is filled with the inert gas. The gas inlet port (138) is positioned to begin the flushing operation prior to the piston being fully retracted and also prior to the introduction of molten metal into the chamber (106) to effectively protect the incoming metal from contacting any ambient atmosphere during the casting operation. Of course, since the inlet port (138) for the inert gas is not closed off until the molten metal inlet port (87) is closed off, the operation provides a positive flow of inert gas which will blanket the surface of the molten metal in the chamber and mold cavity during the filling and final conveyance of the molten metal into the mold cavity.

Claims

1. A system for delivering molten metal from a source of molten metal to a desired location, comprising a pump submerged in the molten metal for pumping the molten metal from the source to said desired location for processing the molten metal, said pump having no external cooling means and operating on the principle of magneto-hydrodynamics (MHD), and a conduit for transporting the molten metal from the pump to said desired location, said conduit being insulated and electrically heated and constructed of a material which is non-reactive with the molten metal.

2. The system of Claim 1, wherein intermediate said pump and said desired location there is provided a measuring device for measuring the flow of molten metal through said conduit.

3. The system of Claim 1, wherein intermediate said pump and said desired location there is provided a shot size measuring and delivery mechanism for delivering a measured amount of molten metal from the source to said desired location.

4. The system of Claim 1, wherein said desired location includes at least one die casting machine having a mold, wherein said die casting machine is supplied with molten metal from at least one source of molten metal.

5. The system of Claim 1, wherein said pump comprises a tubular member, a core member centrally positioned in said tubular member in a spaced relationship to an inner surface of said tubular member to form an annular passageway for the molten metal, a plurality of electromagnetic stator core elements arranged about an external surface of said tubular member in a circumferentially spaced relationship to each other, each core element comprising a multiplicity of sheet metal laminates separated one from the other by a thermally pretreated mica, each stator core element having a plurality of spaced leg portions, an electrically conductive coil having a plurality of windings positioned in the space between each pair of leg portions, and wherein said coil is made of a deoxygenated copper conductor which is insulated between the windings thereof with said thermally pretreated mica, a housing enclosing said stator core elements and coils and sealed to said tubular member, and a three phase electrical current carrying conductor sealably extending through said housing and electrically connected to said coils.

6. The system of Claim 5, wherein said stator core elements have seven (7) leg portions and a coil positioned in each of the six (6) spaces provided between each pair of leg portions, and wherein said coils are alternately connected to the three phases of said conductors.

7. The system of Claim 2, wherein said device for measuring the flow of molten metal comprises a housing, a central tubular member in said housing, a plurality of laminated core elements circumferentially positioned about said tubular member, each core element having a plurality of leg portions forming a space between each pair of leg portions, a coil positioned on said tubular member and within the space provided between each pair of leg portions, wherein at least three said coils are provided, each coil having a plurality of windings of a deoxygenated copper conductor wound about said conduit; wherein at least two of said coils are connected in series, but in a reverse direction current flow, to a single-phase alternating current source, wherein at least one said coil is positioned between a pair of said electrically energized coils and is connected to a measuring device; and said housing containing said coils and core elements being sealed to said central conduit.

8. The system of Claim 2, wherein said device is an electromagnetic flow meter comprising a central tubular member, a core positioned in said tubular member, said core defining an annular passageway between the core and an inner surface of said tubular member for flow of molten metal therethrough, said tubular member having arranged circumferentially about its external surface a plurality of electromagnetic core elements each having a plurality of leg portions, each core element comprising a multiplicity of sheet metal laminae separated one from the other by a thermally pretreated mica insulator, a current conducting coil positioned between each pair of leg portions of the core element, each coil comprising a plurality of windings of a flat conductor made of deoxygenated copper, a thermally pretreated mica insulator positioned between the windings of the coil, a housing sealed to said tubular member, a single phase electrical current carrying conductor sealably extending through said housing and electrically connected to said coils, and wherein at least three coils are positioned on said tubular member in a spaced apart relationship, wherein at least two of said coils are connected in series and electrically energized from a single phase alternating current source, and wherein at least one said coil(s) is connected to a device for measuring the flow of molten metal through said tubular member.

9. The system of Claim 2, wherein said device for measuring the flow of a molten metal comprises a tubular member having a flattened portion, a laminated magnetic core element positioned on each side of the flattened portion of the tubular conduit, said core element having a plurality of leg portions, a coil having a plurality of windings of a deoxygenated copper conductor wound around each leg portion, wherein the conductors of alternating coils are connected to each other and to a current generating device, and wherein the conductor of at least one intermediate coil is connected to a measuring device, and a housing sealingly enclosing said tubular conduit, magnetic core members and coils.

10. The system of Claim 2, wherein said measuring device is an electromagnetic flowmeter for use in measuring the flow of molten metal having induceible electromagnetic properties, said flowmeter comprising a tubular member which is flattened along a longitudinal portion thereof to form a pair of opposed, substantially flat, planar surfaces, an electromagnetic core element made of a multiplicity of sheet metal laminates positioned on each of the flattened surfaces of the tubular member, said laminates being separated one from the other by a thermally pretreated mica, each core element having a plurality of leg portions, an electric current carrying coil made of a plurality of windings of a substantially flat, deoxygenated copper conductor which is likewise insulated between the windings with said thermally pretreated mica, and a housing for sealingly enclosing each of said laminated core elements and coils from the environment, a single phase electrical current carrying conductor extending into each said housing and being electrically connected to the coils positioned on the leg portions of the core element, at least three said coils being mounted on the leg portions of each core member, wherein the outer coils are connected to the conductor to produce a magnetic field, and an intermediate coil(s) is connected to a current measuring device.

11. The system of any one of Claims 5 to 10, wherein said multiplicity of sheet metal laminae of said core elements are made of an alloy of cobalt and iron having a curie point above the temperature of the molten metal which is conveyed through said central tubular member.

12. The system of any one of claim 5 to 11, wherein said tubular member is made of a non-magnetizable material selected from a metal, metal alloy, and ceramic material, and said housing is made of stainless steel.

13. The system of any of Claims 5 to 12, wherein said core member is made of a cobalt/iron alloy having a curie point above the temperature of the molten metal passing through the tubular member.

14. The system of any one of Claims 5 to 13, wherein said tubular member is made of a stainless steel alloy, and each said coil is made of a flat winding of a deoxygenated copper conductor which is insulated between the windings thereof with said thermally pretreated mica.

15. The system of any one of Claims 5 to 13, wherein said mica is selected from naturally occurring amber mica or synthetic mica which has been heated to a temperature above 700°C in the presence of an oxidizing gas for a period of time sufficient to remove impurities from the mica and until the mica is substantially free of visible soot formation when heated to a temperature of about 500°C in an argon atmosphere.

16. The system of Claim 15, wherein the mica is heated to at a temperature above 850°C for a period of time sufficient so that no discernable soot is formed when the mica is used as an insulating material in said core elements and coils at a temperature above 700°C.

17. The system of any one of Claims 5 to 16, wherein said housing is padded with an inert gas for protecting said coils and core elements from the environment.

18. The system of Claim 3 wherein said delivery mechanism is adapted to deliver a predetermined quantity of said molten metal from said source into a mold having a mold cavity and for preventing oxidation of the metal by preventing the metal from comming into contact with the ambient atmosphere, said mechanism comprising a cylinder forming a chamber and a ram positioned in the chamber for reciprocating movement in the chamber, an inlet port in the cylinder for conveying molten metal from said source into said chamber, said inlet port being positioned along the length of the cylinder and along the length of travel of the ram to pressurize a quantity of the molten metal in the chamber and for forcing the molten metal in a pressurized condition into said mold cavity to fill the cavity with molten metal when the ram is moved to a fully extended position, a gas inlet port positioned in an upper portion of said cylinder for supplying an inert gas from a source into the chamber and mold cavity, said gas inlet port being positioned along the length of the cylinder and along the length of travel of the ram to allow for the flow of inert gas into the chamber during movement of the ram to a retracted position and during an interval in which the ram has moved from its fully retracted position to at least a position in which the ram has passed the molten metal inlet port.

19. A method for delivering a measured quantity of molten metal to a casting machine having a mold cavity comprising the steps of conveying the molten metal under a positive head pressure from a source of molten material to the shot size and measuring device of Claim 18 comprising the steps of supplying an inert gas to said chamber through a gas inlet port in said cylinder, moving the ram to an extended position to convey a predetermined amount of molten metal into the mold cavity, moving the ram to a retracted position and supplying said inert gas to the chamber under sufficient pressure to sweep the chamber and mold cavity of oxidizing ambient atmosphere, sequentially closing the molten metal inlet port and the gas inlet port to the chamber upon movement of the ram to the extended position and continuing movement of the ram until the mold cavity is under sufficient pressure to insure complete filling of the mold cavity with molten metal, and admitting said inert gas to the chamber and the mold cavity during retraction of the ram and throughout the step of filling molten metal into the chamber.

20. A method for preparing the thermally pretreated mica of any one of Claims 5 to 10, for use as an electrical insulating material in electrical components capable of operating at a temperature above 500°c and up to the Curie temperature of the materials of construction of the electrical components, comprising the step of heating the mica to a temperature above 700°C in an oxidizing atmosphere and for a period of time sufficient until no discernable soot is formed upon subsequent heating of the mica in the electrical components to a temperature above 500°C in an atmosphere of argon.

21. The method of Claim 20, wherein the mica is selected from naturally occurring amber mica or synthetic mica and is heated prior to installation in the pump or flowmeter to a temperature above 850°C in the presence of an oxidizing gas and for a period of time of from 1 to 24 hours.