Patent Grant
7279128
The present invention relates generally to molten metal pressure pour furnaces, and in particular, to such furnaces wherein a repeatedly precise dose of molten metal is discharged from the furnace. The present invention further relates to a molten metal flow valve that can be used with molten metal pressure pour furnaces.
Pressure pour or dosing furnaces can be used to discharge repeated and measured doses of a molten metal from the furnace for filing a continuous line of molds. The opening to the sprue of a mold is brought in contact with the outlet of the furnace and a gas is used to exert pressure on the molten metal in the furnace, which forces a measured dose of the melt into the sprue, through the gating system and into the mold cavities. Molds can be sequentially filed in the process.
U.S. Pat. No. 4,220,319 to Rohmann discloses a single chamber pressure pour furnace. A metered discharge from the furnace is accomplished by differential pressure sensing of air in the pressurized chamber. The pressure at which molten metal in the chamber rises to the end of the outlet tube prior to each discharge is sensed. This pressure reading is used as the baseline pressure at the start of a pour. The pour is terminated by release of pressure in the chamber when the chamber pressure reaches a selected value.
U.S. Pat. No. 5,477,907 to Meyer et al. discloses a pressure chamber that is isolated from a heating chamber by a wall with an opening through it. A backloading air regulator is used to account for the pressure increase in the pressure chamber that is required for the molten metal to rise to the end of the outlet tube before the timed period of discharge is started. Further backflow of molten metal into the heating chamber is allowed through the opening in the wall when the pressure chamber is pressurized.
U.S. Pat. No. 5,913,358 to Chadwick discloses the use of a non-return valve in the wall between the pressure chamber and heating chamber to prevent the backflow of molten metal when the pressure chamber is pressurized. The non-return valve is disclosed typically as a ball and socket valve that acts automatically to prevent reverse flow. A potential disadvantage of this arrangement is that the molten metal, or particulate in the melt, could lodge the ball in a position that permanently blocks flow of the molten metal from the heating chamber to the pressure chamber as required to replenish the supply of melt in the chamber.
U.S. Pat. No. 5,590,681 to Schaefer et al. discloses a plug valve assembly integral with upstream and down stream launder sections. The upstream launder section is connected to a low pressure casting furnace, and the upstream launder section is connected to a supply of molten metal. Flow between the supply and the low pressure casting furnace is controlled by the plug valve assembly.
One object of the present invention is to provide a pressure pour furnace wherein the pressure differential between the molten metal at a selected level in the pressure chamber and the pressurized gas used to perform a pressure pour in the pressure chamber is used to provide a repeatedly precise measured discharge of melt from the furnace. Another object of the present invention is to control the flow of molten metal to the pressure chamber of a pressure pour furnace with a compact metering valve arrangement that will also provide an efficient method of blocking backflow of the molten metal from the pressure chamber into the heating chamber, or metal supply chamber, when the pressure chamber is pressurized.
In one aspect, the present invention is an apparatus for, and method of, discharging a dose of molten metal, or melt, from a furnace comprising a receiving chamber, heating chamber and pressure chamber. Molten metal is supplied to the receiving chamber; maintained at a desired temperature in the heating chamber; and discharged from the pressure chamber. A sealing plate having a sealing port in it is disposed between the heating chamber and the pressure chamber to control the flow of melt from the heating chamber to the pressure chamber by the insertion or removal of a sealing means in the sealing port. Insertion of the sealing means in the sealing port also prevents the back flow of melt from the pressure chamber to the heating chamber when the pressure chamber is pressurized. A gas injected into the pressure chamber is used to force the melt from an outlet dosing tube in the pressure chamber and into a suitable container. The dosing tube may be extend from the pressure chamber for connection with a mold for filing and retracted into the pressure chamber after the mold is filled. In one example of the invention, the means for blocking the back flow of melt from the pressure chamber to the heating chamber is a sealing means that substantially blocks the back flow of melt through the sealing port in a composite high thermal conductivity ceramic sealing plate and port.
In another aspect, the present invention is a system for delivering doses of molten metal from one or more molten metal pressure pour furnaces when the molten metal is supplied from one or more metal melting furnaces by a launder network. One or more heat treatment processes may be performed on the molten metal before being delivered to the metal pressure pour furnaces by the launder network.
In another aspect, the present invention is a metering valve that can be formed from a sealing plate that prevents the flow of molten metal between two adjoining molten metal containing components such as a launder and the pressure chamber of a pressure pour furnace. The sealing plate has a sealing port disposed in it to allow the flow of molten metal when a sealing means is not inserted in the sealing port and to prevent the flow of molten metal when the sealing means is inserted in the sealing port.
These aspects of the invention are further set forth in this specification, and other aspects of the invention are as set forth in this specification.
For the purpose of illustrating the invention, there is shown in the drawings a form that is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.
a) illustrates one example of a metering valve used to control flow of a molten metal between adjoining molten metal containing components.
b) and
a) through
a) illustrates a metering valve of the present invention that is used to regulate the flow of a molten metal into a low pressure pour furnace.
b) diagrammatically illustrates an integrated arrangement of molten metal supply sources, molten metal heat treatment vessels and a plurality of the metering valves of the present invention that are used to regulate the flow of a molten metal into a plurality of low pressure furnaces.
a) illustrates a double metering valve arrangement of the present invention that is used to regulate the flow of a molten metal into a low pressure pour furnace.
b) diagrammatically illustrates an integrated arrangement of molten metal supply sources, molten metal heat treatment vessels and a plurality of the double metering valve arrangements of the present invention that are used to regulate the flow of a molten metal into a plurality of low pressure furnaces.
Referring now to the drawings, wherein like numerals indicate like elements, there is shown in the drawings, one example of the molten metal pressure pour furnace 10 of the present invention. The furnace comprises a receiving chamber 12, heating chamber 14 and pressure chamber 16. The furnace's exterior support structure 18 is formed from a suitable material such as a mild steel, and may be lined with a suitable refractory 20 such as multicomponent refractory materials as known in the art. As explained in further detail below: receiving chamber 12 is supplied with molten metal, or melt, from a suitable source; heating chamber 14 maintains the melt at a suitable temperature; and pressure chamber 16 discharges a measured dose of melt from the furnace. When furnace 10 provides molten metal to a continuous line of molds, the pressure chamber usually holds a sufficient quantity of melt for filling multiple molds in succession. When required the molten metal in the pressure chamber is replenished with melt from the heating chamber. Molten metal load line 11 (shown as a dashed line) in
Receiving chamber 12 can be supplied with molten metal, such as, but not limited to, a liquid aluminum composition, by a suitable pumping system or launder. In one example of the invention, the supply of melt is provided by a launder delivery system connected to a melt and metal treatment system wherein the launder delivery system maintains a substantially constant level of molten metal in the receiving chamber. For example, aluminum ingots and scrap may be melted in a stack furnace to produce liquid aluminum that is collected in a holding furnace. The liquid aluminum may be further treated to remove hydrogen gas, oxides, impurities and other active metals in a filtering vessel that is fed from the holding furnace. Either a gravity feed or pumped launder delivery system may be connected between the holding furnace or filtering vessel and receiving chamber 12. A means for sensing the level of molten metal in the receiving chamber or launder delivery system, such as a laser sensing system or mechanical float switch, can be used to sense the level of melt for control of the flow of molten metal from the holding furnace or filtering vessel to the receiving chamber so that a substantially constant height of melt is continuously maintained in the receiving chamber. Receiving chamber 12 may also include means for degassing the melt in the chamber, such as a carbon diffusion lance, floor purge plugs or a rotary dispersion lance top, as used to inject chlorine gas, nitrogen or argon into liquid aluminum. Further the launder delivery system may be arranged so that a single supply of melt is distributed to a plurality of pressure pour furnaces.
Heating chamber 14 is partially separated from receiving chamber 12 by furnace arch 23 which is formed from a suitable refractory composition. Heating chamber 14 includes suitable means for heating melt in the chamber, such as electric heating elements 20, or fossil fuel fired burners. Fossil fuel fired burners are less advantageous in that combustion gas byproducts may contaminant melt in the heating chamber. Suitable resistive electric heating elements are preferably of a high watt density type such as those formed from a silicon carbide composition. Furnace arch 23 serves as a means for retaining heat and a protective atmosphere within the heating chamber, and prevents any melt perturbations in the receiving chamber from propagating into the heating chamber. Normally the heights of the melt in the receiving and heating chambers are the same. Heating elements 20 are a part of a furnace heating system that maintains a pre-selected temperature of the molten metal in the heating chamber. One or more means for sensing temperature of the melt in the furnace, such as immersed thermocouple 21 is used as an input to a processing means, such as a programmable logic controller (PLC). The processing means provides an output signal to the means for heating the molten metal in the heating chamber. For example, if electric resistive heating elements are used, the output signal may be used to control the switching of silicon controlled rectifiers (SCRs) in an SCR heater controller. Temperature sensing may include differential temperature sensing of the molten metal in the receiving and heating chambers. Preferably heating chamber 14 includes a non-reactive gas purging system wherein a gas, such as nitrogen, is used to purge the air above the surface of the molten metal in the heating chamber to minimize the formation of oxide on the surface, and minimize the diffusion of contaminants into the molten metal, such as hydrogen gas in liquid aluminum. Optionally porous floor plugs may also be provided in the heating chamber to purge contaminants in the molten metal, such as hydrogen gas in aluminum, by flowing a non-reactive gas, such as nitrogen or argon, through the melt.
Pressure chamber 16 is separated from heating chamber 14 by a composite sealing plate and port 22 as best illustrated in
The means for substantially blocking the back flow of molten metal from the pressure chamber to the heating chamber comprises a sealing means inserted into the sealing port. In this non-limiting example of the invention, the sealing means comprises sealing element 30a at one end of sealing tube 30, wherein sealing element 30a is generally hemispherical in shape and seats into a generally conically-shaped sealing port to substantially block the back flow of molten metal from the pressure chamber when the pressure chamber is pressurized as further described below. The sealing tube and element may be cast from a heat-resistant and wear-resistant material, such as a nitrite bonded silicon carbide or other ceramic composition.
As shown in the non-limiting example of the metering valve of the present invention in
Sealing port 22 and the sealing means for allowing or preventing flow of the melt through the port comprise a metering valve that generally controls the flow of melt to adjoining molten metal containing elements. In this particular application, the adjoining molten metal containing elements are the heating chamber and the pressure chamber of a molten metal pressure pour furnace.
Dosing tube 32 extends obliquely through wall or lid 26 into the molten metal in the pressure chamber and serves as a means for discharging a metered amount of melt from the pressure chamber. In other examples of the invention the orientation of the dosing tube relative to the top wall of the furnace may be different. As shown in
b) and
Immersion tube heater 36 can be optionally provided to heat melt in the pressure chamber if necessary to compensate for the loss of heat from the melt in the pressure chamber. The auxiliary heater may comprise a resistive silicon carbide heating element disposed within a silicon nitrite tube that penetrates through lid 26 into the molten metal. A thermocouple within the tube can be used to protect against overheating of the heating element. Immersion temperature sensing device 37, such as a high thermal conductivity silicon nitride thermocouple, is used as a sensor for regulating the output of heater 36.
As best seen in
In one non-limiting method of operation, the pressure chamber is substantially filled with melt from the heating chamber to a height equal to the height of the melt in the heating chamber by raising sealing tube 30 with a suitable actuator so that sealing element 30a unseats from the sealing port to allow the flow of melt from the heating chamber to the pressure chamber. Sealing tube bellows 29 provides a pressurized seal around the opening through which the sealing tube penetrates into the pressure chamber and allows maintaining the seal as the sealing tube is raised or lowered. After filling the pressure chamber, sealing tube 30 is lowered so that sealing element 30a seats in the sealing port to substantially block the back flow of melt into the heating chamber as illustrated in
In some examples of the invention, gas is initially injected into the pressure chamber to force melt in the chamber up the dosing tube to approximately the external end of the riser tube. This level of melt, which is referred to as the “ready level” is used as a reference point for the start of every pour from the pressure chamber. The ready level for a particular application may be any height of melt in the dosing tube that is suitable for the process. A means for sensing the presence of the melt at the external end of the riser tube is provided. In one example of the invention, the means comprise a pair of low voltage electrically conducting probes 48 that form a normally open circuit when they are not immersed in molten metal, and a closed circuit when the are immersed in molten metal to indicate that the melt is at the external end of the riser tube. A means is provided to move the probes out of the opening of the riser tube. In this example, the means comprise pivot arm 50, which is shown in the lowered and raised (dashed lines) positions in
Once the melt is raised to the external end of the dosing (riser) tube (or other melt ready level), the opening of a container, such as the opening in a mold sprue, is brought into the vicinity of the external end of the riser tube, with the center of the sprue opening approximately aligned with the center of the opening in the riser tube. Dosing tube 32 is extended out of the pressure chamber by means of a suitable actuator so that a substantially pressurized seal is achieved between the end of the riser tube and the opening in the mold sprue. Dosing tube sealing bellows 34 expands to maintain the pressure seal around the opening through which the dosing tube penetrates when the tube is in its extended position. In some examples of the invention, a double dosing tube bellows arrangement can be used as illustrated in
A requisite amount of gas is injected into the pressure chamber to discharge a measured dose of melt into the mold. The volume and time rate of gas injection can initially be established by an algorithm used by the processing means. After pressure pouring the desired amount of molten metal into the mold, the riser tube is retracted into the pressure chamber by means of a suitable actuator. The molds are indexed by moving the filled mold and placing an empty mold in its place. Between mold transitions, probes 48 can be repositioned into the end of the dosing tube to pressurize the pressure chamber to the level required to bring the melt back up to the end of the dosing tube. The empty mold is then filled by the process as described above for the previous mold.
Typically a filled pressure chamber can be used to fill a number of molds, after which the level of melt in the pressure furnace drops to a level that requires replenishment of the melt in the pressure chamber from the heating chamber. One non-limiting method of level sensing of the melt in the chamber can be accomplished as a function of the applied gas pressure in the chamber since increasing applied gas pressure is proportional to the level of melt in the chamber. When replenishment is required, sealing tube 30 is raised to allow a refill of the pressure chamber. Gas exhaust port 43 is normally open when melt flows from the heating chamber to the pressure chamber through the sealing port during a refill. In alternative examples of the example, vacuum pump 92 can be used to draw a vacuum on the pressure chamber to increase the refill flow rate through the sealing port. This is of particular advantage chamber when a slower refill rate will not support a fast indexing speed of molds. In other examples of the invention, a gas may be injected under pressure into the volume above the melt in heating chamber 14 to increase the refill flow rate through the sealing port. If the heating chamber includes the optional non-reactive gas purging system as described above, the purging system may include means for gas pressurizing the melt in the heating chamber. Pressurization of the melt in the heating chamber for increased refill flow rate may optionally be combined with vacuum draw on the pressure chamber. When the melt in heating chamber 14 is under pressure, furnace arch 23 seals the gas volume in the heating chamber from ambient air pressure. In alternate examples of the invention, means may be provided for sealing receiving chamber from ambient air pressure when melt in the heating and/or receiving chamber is pressurized with a gas.
Use of the differential pressure method in some examples of the invention enables accurate control of the measured dose from the riser tube as the quantity of melt in the pressure chamber reduces and the magnitude of applied pressure must increase. The algorithm for pressure control may be adaptively adjusted for future pours into the same type of mold by feedback of the sensed differential pressure during the previous pour.
a) through
Gas is injected into the pressure chamber until the melt is raised in dosing tube 32 to a level that is designated as the “ready level”. Alternative, and possibly a combination of, methods may be used to sense the melt reaching the ready level. As illustrated in
With melt held at the ready level in the pressure chamber, subroutine 133 is executed to sense whether a mold has been indexed for filing by the mold line machinery. When subroutine 133 receives a signal from the mold line machinery that a mold has been indexed for filing, subroutine 134 energizes the dosing tube extend actuator. The dosing tube extend actuator may be any suitable drive device for extending the dosing tube for mating with the sprue of a mold. In the example of the invention shown in
Subroutine 140 injects more gas into the pressure chamber in accordance with a predetermined mold fill profile. For example, one or more pressure levels over discrete time periods may be achieved during a mold fill profile according to mold configurations and the remaining amount of melt in the pressure chamber. Once the mold fill profile has executed subroutine 142 initiates subroutine 144 to release gas from the pressure chamber and return the melt in the chamber to the ready level. As illustrated in
Subroutine 152 determines whether a refill (recharge) of melt in the pressure chamber is required. Typically this is predetermined based upon the volume of the cavities in the molds being filled and the capacity of the pressure chamber. However, in other examples of the invention, a direct means of sensing the level of melt in the pressure chamber may be utilized. If a recharge is not required, subroutine 154 energizes the dosing tube retract actuator. The dosing tube continues to retract away from the surface of the indexed mold until subroutine 156 senses that the dosing tube has fully retracted, when subroutine 158 de-energizes the dosing tube retract actuator. Full retraction of the dosing tube may be accomplished by the use of a mechanical limit switch on the external dosing tube assembly. Execution of subroutine 160 blows a stream of air across the external opening of the dosing tube to remove any remnant of melt from the mold fill, and subroutine 162 sends a signal to the mold line machinery that the indexed mold has been filed. At this point the process returns to subroutine 133 on
If subroutine 152 determines that a recharge of melt in the pressure chamber is required, as illustrated in
Alternative examples are contemplated within the scope of the invention. For example, rather than pressure discharging the measured melt directly into a mold from furnace 10, the discharge may be to an intermediate reservoir from which a container is filled by gravity release of melt from the reservoir. Alternatively the discharge may be to a launder that gravity feeds the molten metal into a mold. In some examples of the invention it may not be necessary to extend and retract the dosing tube. In these examples, the dosing tube sealing bellows may or may not be used. Further contemplated within the scope of the invention is the disclosed features of the pressure chamber in combination with a heating chamber and/or a receiving chamber of various configurations.
The metering valve of the present invention may also be used to control the flow of a molten metal between any adjoining molten metal containing components other than the heating chamber and pressure chamber of a molten metal pressure pour furnace. For example,
a) illustrates an alternative method of controlling the flow of molten metal to a low pressure furnace. In this method a double metering valve chamber 68 of the present invention is used. Double metering valve chamber 68 is connected between launder 70 and pressure chamber 56 of low pressure molten metal furnace 54. As shown in
While each of above examples of the invention utilize a single sealing port in a sealing plate, the scope of invention includes providing more than one sealing port in each sealing plate, with each of the sealing ports having appropriate sealing means to selectively control the flow of molten metal between the adjoining molten metal containing components.
The foregoing examples do not limit the scope of the disclosed invention. The scope of the disclosed invention is further set forth in the appended claims.
This application claims the benefit of U.S. Provisional Application No. 60/410,408, filed Sep. 13, 2002, and U.S. Provisional Application No. 60/413,183 filed Sep. 24, 2002.
| Number | Name | Date | Kind |
|---|---|---|---|
| 1448529 | Fleming | Mar 1923 | A |
| 2185376 | McParlin | Jan 1940 | A |
| 3084925 | Stauffer et al. | Apr 1963 | A |
| 3708088 | Lesher | Jan 1973 | A |
| 6103182 | Campbell | Aug 2000 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20040050525 A1 | Mar 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60413183 | Sep 2002 | US | |
| 60410408 | Sep 2002 | US |
