US 2937789 A
Description (OCR text may contain errors)
May 24, 1960 M. TAMA CONTROLLED METAL DISPENSING 6 Sheets-Sheet 1' Filed Oct. 16, 1953 w ml hvi 1! l; I;
INVENTOR: MARIO TAMA,
HIS AGE 75.
May 24, 1960 M. TAMA CONTROLLED METAL DISPENSING 6 Sheets-Sheet 2 Filed Oct. 16. 1953 k w o m E n R M mm L M 5 "mm mm 0 T 9 N m w m K A f :IIM
INVENTOR. MARIO TAMA, BY
May 24, 1960 M. TAMA 2,937,789
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1 RIO TAM H AGENTS.
May 24, 1960 M. TAMA 2,937,789
CONTROLLED METAL DISPENSING Filed Oct. 16, 1953 6 Sheets-Sheet 4 QOUNTER INVENTOR: MARlO TAMA,
May 24, 1960 M. TAMA 2,937,789
CONTROLLED METAL DISPENSING Filed Oct. 16, 1953 6 Sheets-Sheet 5 INVENTOR: MAPJO TAMA, BY
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May 24, 1960 M. TAMA 2,937,789
CONTROLLED METAL DISPENSING Filed Oct. 16. 1953 6 Sheets-Sheet 6 INVENTOR: MARIO TAMA, BY euw M HIS AGE/V75- United States Patent CONTROLLED METAL DISPENSING Mario Tama, Morrisville, Pa., assignor, by mesne assignments, to Ajax Magnethermic Corporation, a corpora- The invention relates to mold casting, and relates more particularly to methods and machines for supplying molten metal from a furnace to a mold; still more par- I ticularly, the invention relates to a method and apparatus for repeatedly intermittently dispensing substantially equal amounts of metal into molds, from a container holding a mass of molten metal.
This is a continuation-in-part of my application Serial No. 277,786, filed March 21, 1952, now Patent No. 2,674,640, dated April 6, 1954.
I In the mass production of castings made either in permanent molds or in die casting machines, it is required to supply repeatedly accurate amounts of metal, free from slag or oxide, delivered to the molds at the proper temperature and in short periods of time. As all the castings are of identical shape and weight, it is important that the quantity of metal delivered each time to the mold be uniform. With each discharge, the level of the metal mass inside the container, such as a melting or a holding furnace, decreases for a volume substantially corresponding to the mass dispensed during the preceding discharge. In order to dispense uniform quantities at each succeeding discharge, it will either be necessary to tilt the furnace, or to compensate in another manner for the increase in height that the metal level must be raised to between its momentary position and the point of discharge.
It is accordingly among the objects of the invention to provide for methods and means to compensate accuratelyfor the change of position of the metal level within the container to the end that substantially equal amounts are-dispensed at each discharge.
Broadly speaking, this is accomplished in accordance withthe instant invention by a change of the discharge period'with each succeeding discharge.
, The quantity dispensed during each discharge is quite Small in comparison to the quantity held at the beginning of the operation in the furnace, and consequently the necessary adjustment is small. Accordingly, the adjustment to be made must be accurate. I
.j The foregoing and other objects of the invention will be best understood from the following description of eXemplific'ations thereof, reference being had to the accompanying drawings, wherein:
Fig. 1 is a vertical sectional view of a furnace in accordance with ,the invention;
I fig. 2 is a sectional view taken on line 2-2 of Fig. 1;
Fig. 3 is a vertical sectional view of a furnace similar to-the preceding views, but operating in accordance with amodified principle; I
-'Fi-g. 4 is a schematic vertical sectional view schematic'ally illustrating the furnace shown in Figs. 1 and 2', showing a first embodiment of the instant invention;
Fig. 5 is a sectional view similar to Fig. 4, but embodying amodification; I
Fig. 6 is a sectional view similar to Fig. 4, embodying a further' modification;
Fig. 7 is a sectional view similar to Fig. 5, but embodying a further modification;
Fig. 8 is a vertical sectional view of a modified furnace illustrating a further modification;
Fig. 9 is a horizontal front view of a furnace in accordance with the invention embodying a still further modification; and
Fig. 10 is an elevational side view of the modification shown in Fig. 9.
In carrying the invention into effect in the embodiments which have been selected for illustration in the accompanying drawings and for description in this specification, and referring now particularly to Figs. 1 and 2 there is provided a casting device generally indicated at 11. It includes a holding furnace 12 that is capable of maintaining a bath of molten metal 13 at the proper temperature. The normal level of the molten metal is indicated at 14.
The furnace is provided with means for heating the molten metal 13, for instance with an induction coil 16, that induces heat in the melting channels 17, 18 and 19 of the furnace 12. The furnace 12 is preferably provided with automatic temperature control equipment (not shown in the drawing).
The induction furnace 12 is of the single-chamber type and is open on top at 21 and has a cover 22 to close the top 21 reasonably air-tightly by means of a gasket 23. The cover 22 is removably positioned and may be fastened by rapid fastening means, such as screws 24, or quickaction clamps, along the periphery of the cover. A charging bowl 26 is provided at one side of the furnace 12 and may be closed by a tiltable cover 27 that is sealable by rapid fastening means similar to the cover 22.
The holding furnace 12 should have enough capacity to allow operation for a reasonable time before recharging. The important factor is the surface size. For instance, a furnace with a surface area of 1,000 square inches contains about pounds of aluminum per inch of metal depth. If a level difference of 3 inches is permitted, the furnace does not have to be refilled until 300 lbs. have been processed. Furnaces with a surface area ranging from 500 to 1000 sq. in. are probably best for the instant purpose. In a furnace having a surface of 500 sq. in., the metal surface would be lowered by only about inch for every pound of metal discharged.
As shown in Figs. 1 and 2, a centrifugal airblower 10 is attached to the furnace and has a conduit 15 connected to the hearth of the furnace at a point above the level 14 of the molten metal. Two solenoid operated valves 20 and 25, respectively, are used to regulate the pressure of the air delivered by the blower 10. The valves 20 and 25 are switched in such a way that one of them is open when the other is closed. The second valve 20 is connected to the open air by a tube 30. It is operated by a timing device or timer, schematically indicated in Fig. 2.
Although in the foregoing it has been mentioned that air is used, there may instead be used any suitable gas.
The holding furnace 12 is provided with a discharge device, generally indicated at 28. The furnace 12 has a lateral recess or pocket 29 in one of its side walls, and the recess 29 is open towards the exterior at an opening 31. A cover 32 is removably mounted to said side to cover the opening 31 of the pocket 29. Said cover 32 comprises a flange 33 that is fastened to the furnace side walls by means of fastening devices, such as bolts 34. The cover 32 has an outer metallic shell or enclosure 36 of sheet metal or the like and is provided with a pro jcction 37 inclined against the horizontal direction. On the interior the cover has a refractory lining 38. The cover 32 is apertured at 41 axially of the projection 37 and has sealed in said aperture a tube or nozzle 42. When mounted, the lower end 43 of the tube 42 is disposed below the metal level 14 and the tube intersects the said metal level and extends with its upper end 44 through the aperture 41 to the exterior of the cover 32. The tube 42 surrounds a passage 46 for the discharge of molten metal, and the axis xx of the tube intersects the horizontal direction at an acute angle for instance at an, angle of from 15? to 60, and the angle shown in the drawing is 26 3. The passage 46 forms with the terminal of the upper end portion 44 anoutlet 47 for the discharge of the molten metal off the furnace, and forms with the terminal of the lower end portion an inlet 48.
There is provided a means for throttling the metal flowing through the passage 46, and that means is disposed below the level of the molten metal. That throttle means is constituted by the constriction formed by the inlet 48. This constriction 48 is always located below the molten metal level and is disposed near the entrance for the molten metal of the passage 46 of the tube or nozzle 42. The throttle means serves to regulate the speed of flow in the passage 46 of the molten metal. It maintains the flow constant, regardless of any build-up in the wider upper part of the passage 46 of the tube 42. Such a build-up may form in the parts of the tube which are alternatingly exposed to molten metal and air. However, in the handling of molten metals, no appreciable amounts of build-up occur below the molten metal level line. Practical experience with the instant throttle means has shown that the lower part of the tube which is submerged in the molten metal stays clean, probably due to the high velocities induced by the throttle means, causing the rapidly impelled molten metal to drive away any impurities that may have been accumulating in the lower part of the passage 46 during idling.
It is important that the throttle means be located near the part of the tube that is immersed in the molten metal. If that means were, instead, above the metal line, its crosssection would undergo constant change, and might finally be practically clogged due to a build-up of solidified skins or oxides, as it would be alternatively exposed to air and molten metal.
The throttle means creates a pressure drop near the entrance of the passage 46 of the tube 42. Owing to this pressure drop, the pressure created inside the furnace chamber by the blower will have to be sufficiently large to overcome the throttle resistance, so that the metal level can be raised from its normal level position 14 to and above the pouring lip 52. The cross-section of the throttle, for instance of the inlet 48, controls the rate of flow through the tube 42, maintaining it constant irrespective of any build-up in the wider part of the passage 46.
The tube 42 is preferably made of good refractory material which is not subject to attack by the molten metal, either below or above the metal level line. I have found silicon carbide to be a suitable material for such a tube, particularly for use in connection with aluminum and its alloys. I have also found that graphite can be used, but preferably only in the section below the metal level.
The upper end 44 of the tube 42 is heated near the outlet 47, for instance by means of an electric resistor heater coil 51. The coil 51 may be fed from an electric source, which has not been shown in the drawing.
The metal level 14, for all practical purposes should be as near as possible to the pouring lip 52 which is formed by the lower arcuate portion of the outlet 47. The vertical distance of the metal level 14 from the lip 52 should be less than 3 to 4 inches.
When the exchangeable cover 32, including the tube and the coil for the tube, is mounted on the side of the pocket 29, the holding furnace 12 is thereby completed and ready to receive a charge of molten metal. The induction furnace 12 is provided on the interior with a refractory lining 53 and to the exterior of said refractory lining 53 with a castable insulation 54. On the exterior of the furnace there is mounted a metallic shell or enclosure 56 made of sheet metal or the like, which corresponds to the metallic enclosure 36 of the cover 32.
When the cover 32 is mounted, the metallic enclosures 36 and 56 will surround the furnace 12. This metallic sheet metal shell is arranged to provide for air or gas tightness, as the refractory material 53 and 54 and 38 and 3-9, respectively, is too porous to be relied upon for air or gas impermeability.
In Fig. 1 there is schematically shown a die casting machine 62 having a cold chamber 63 into which the metal is discharged from the pouring lip of the nozzle.
The operation is as follows.
The furnace -12 of Figs. 1 and 2 is filled with molten metal through the charging bowl 26 after opening of the tiltable cover 27. The metal is filled up to the level 14 which is near the pouring lip of the nozzle. The cover 22 as well as the cover 27 is closed by the quick acting fastening means, and thereafter the blower 10 is started.
The airblower 10is kept running throughout the entire casting period, irrespective of how long a single discharge takes, or how often intermittent discharges are made, through the nozzle 42. A conventional throttle (not shown) may be applied to the intake side of the blower to adjust the air pressure.
The valves 20 and 25 are switched simultaneously in such a way that one is closed while the other is open. When the valve .25 is open, the. air flows from the blower 10 to the sealed interior of the furnace 12 into the space above the metal level 14. Experience has shown that it takes only a fraction of one second to build-up pressure and to start the flow of molten metal over the pouring lip 52 of the nozzle 42.
When sufficient air pressure is applied on the interior of the furnace 12, metal will be discharged upwardly, outwardly through the nozzle 42, leaving the pouring lip 52 in a flow towards the mold 62.
When the valve 20 is opened, the valve 25 will be closed and the air contained in the space above the molten metal within the furnace will be ejected into the open air through the tube 30, to release the pressure from the molten metal.
The timer, which is preferably of the electronic type of any well-known suitable construction, and is shown schematically in Fig. 2, is used to limit the time between valve operations.
As the pattern of flow is closely proportional to the time of pressure application, the time control is a practical way to achieve uniformity of weight in consecutive castmgs.
Instead of using a furnace ,of the type shown in Figs. 1 and 2, there may also be used a furnace illustrated in Fig. 3 (which is of the type described in my co-pending application Serial No. 281,333, filed April 9, 1952, now Patent No. 2,707,720, dated May 3, 1955).
It comprises a furnace generally indicated at 71 which includes an induction heating mechanism 72 (similar to the aforedescribed mechanism 16, 17, 18 and 19) to heat the molten metal inside a chamber 74 and which has electric means including induction coils 73 operable to restrain, by an arching effect induced by the induction effected by the coils 73, an outflow from the nozzle 42 as long as current is applied to the coils 73, and to release for molten metal discharge when the current is shut off. The furnace 71 is tiltable by a tilting apparatus 75 that may be operated hydraulically, about a pivot 76. The device of Fig. 3, in a sense, works opposite to the device shown in Figs. 1 and 2, in that the latter discharges when the blower 10 operates, for instance as driven electrically, while the former operates when electric current is shut off and thus prevents discharge when electric current is applied.
( However, pressure may not only be applied above the level 14 of the molten metal as shown in Figs. 1 and 2, but may also be applied to the molten mass by electric induction pumping action as shown in Fig. 8 in accordance with the principles explained in my co-pending application Serial No; 29,263, filed May 26, 1948, now Patent No; 2,707,718, dated May- 3; 1955.
Having described in an illustrative, though not in any way intended as a restricted, sense, the types of furnaces to" which the instant invention is'applicable, there will now be described the invention as applied to the foregoing types of furnaces. For the purpose of illustration, it will be described as applied to any metal container generally known as a teapot container. I
Turning to Fig. 4, there is provided such a teapot container 81 having a refractory lining 82 and which forms on the interior, a chamber 83'for a mass of molten metal 84: A nozzle .85 is provided that has at its lower end a constriction 8 6' and reaches with the lower end into the metal bath 84', and extends with the upper end through the wall of thecontainer 81 to' the exterior in the vicinity of a mold 87. The teapot container, or holding furnace 81, will hold the chamber 83 a certain amount of molten metal 84, so; that the upper level will be determined by the lower lip 88 of the nozzle 85.
As the casting operations progress, the quantity of molten metal 84 gradually decreases, and the level 89 of the metal 84 will sink correspondingly.
Means are provided generally indicated at 90 to apply pressure, for instance by a compressed gaseous substance from a compressor (not shown) to the part of the chamber 83 that is above the level 89. When pressure is thus applied to the level 89, a certain predetermined amount of molten metal will be discharged through the nozzle 85 depending on the force or value of the pressure applied and the period of time throughout which the said pressure value is applied. 7 a
When the pressure is applied, the metal 84 will be forced out through the nozzle 85 and be discharged therefrom. The discharge, owing to the restriction 86, will be in a gentle'free parabolic flow 84f, into the mold 87.
.In Figs. 4 7 the pressure has been assumed to be gaseous pressure delivered by a compressor in accordance with the furnace of Figs; 1 and 2 or Figs. 9 and 10, but it will be understood th'at'the' pressure may instead be supplied by induction pumping in accordance with the furnace of Fig. 8, or the furnace of Fig. 3 wherein it is supplied by gravity.
In describing the invention in connection with the gas pressure as shown in Figs. 4-7, the container 81 is provided with a-cover 91-, and with means 90 that comprises an inlet 92 which is interconnected to a compressor (not shown in Fig. 4).
A control mechanism 93 is provided to control the time value throughout which the pressure value is applied during each discharge.
When the pressure is constant the pouring time increase is substantially linearly proportional to the decrease in metal level, at least within a certain range. It will thus only be necessary, within that range, to count the shots, and accordingly to reset the timer for a predetermined equal setting corresponding to a definite additional time quantum or increment following each shot.
Thus, the control mechanism 93 may be a timer and be connected to a counter 106 (Fig. 8) of conventional design, or other cumulating mechanism to reset the timer 93. A switch 107 may trigger the counter and timer in such a manner that the timer 93 is first reset by the counter 106 and then the timer starts the operation of the power induced by the induction coil 108 that threads submerged channels 109 to pump through the nozzle 85 for the period set by the timer 93, the molten metal for discharge.
The control mechanism 93 may be a timer of the type described in my aforementioned co-pending application Serial No. 277,786, which may preferably be an electronic timer, and which is used to apply during accurately measured, selectively variable periods of time a predetermined value of pressure. As the duration of each discharge is short, the increase or increment of time required for each succeeding discharge is correspondingly short; according"- ly, the time control mechanism 93 must-be sensitive.
As the chamber 83 is substantially uniform, at least within the range volume between two re-fills, and the quantity dispensed is the same for each discharge, the level 84 will decrease, at least throughout said range, substantially uniformly. Consequently, by maintaining constant pressure,- the timer 93 will need to be reset for each subsequent discharge.
Instead of the foregoing, the time cycle may be lengthened, as the pressure be increased, proportionately as the level drops. This may be accomplished in various ways by measuring the momentary position of the level 89, and feeding the intelligence from the measuring device to an adjustor which, in turn, resets the timer to lengthen the time cycle of the pressure action delivered to the furnace from the compressor.
An embodiment of this feature is shown in Fig. 5.
The furnace 81 is provided with an adjustor 98 that is connected to the control mechanism 93 for the compressor and may again be a timer, preferably an electric timer. In accordance with the illustration of Fig. 5, a terminal 99 may be floating on the level 89 and a second terminal 100 be interconnected to a source 94. The measured change in resistance of the mass of molten metal 84 in the furnace may be translated in the adjustor 98, which may comprise a potentiometer, into voltage changes or resistance variations that can be fed to the timer 93, resetting the latter after each discharge in accordance with the momentary quantity of metal 84 as established by the momentary position of the level 89. The adjustor 98 may comprise the switch unit to start the discharge operation at the same time triggering the adjustor for a new resetting immediately before the actual timing and the operation start.
A similar result may be accomplished by an arrangement in accordance with the illustration of Fig. 6. In this arrangement, the level is indicated by capacity. One of the terminals of the electric circuit 101 is a metal plate 102 that is mounted in the chamber 83' above the metal level 89 and which has a capacity to the metal surface varying as the level changes its position. A second terminal 100 is again in contact with the metal bath 84. This changing capacity may be translated, in the adjustor 98, into a frequency change of a tuned oscillating circuit; and be translated into a voltage change by means of a frequency modulation detector or amplifier, and fed fromthe adjustor 98 to the control mechanism 93, which may again be an electric timer. If the plate 102 is replaced by a coil (not shown), the change in metal level may be utilized in a similar manner.
A similar result may be obtained by providing the furnace 81 with a float (Figs. 9 and 10) on the level 89 of the molten metal 84. The float 110 is provided with an upright rod 111 that forms a part of a differential transformer 112 which may, in a similar manner (as shown in Figs. 5-7 though not shown in Figs. 9 and 10) be connected in circuit to an adjustor to reset a control mechanism for the pressure source, which in Figs. 9 and 10 may again be a compressor operating through a valve 25.
Example In a teapot shaped holding furnace provided with an inductor of 20 kw. power and having a metal surface of 21" x 21" with rounded corners a full test of accuracy was carried out. The furnace was charged with pounds of an alloy of aluminum with 13% silicon. A pressure of 2 p.s.i. above atmospheric pressure was applied to the metal surface by reducing the pressure from the plant 100 p.s.i. compression over reducing valves. A total of 150 consecutive shots were made, starting with a pouring time of 0.571 second and finishing with a pouring time of 1.282 seconds; The total addition of correcting time was 0.711 second and the time increment per shot was 0.0059 second. The maximum and minimum weights of casting ob- "7 tained in this way wereone pound plus two ounces and one pound minus three-quarter ounces respectively. While the shots, were made, the metal level decreased by about 4". The weight of each casting was determined with a laboratory scale.
The example shows how small is the duration of each operation, and how accurate the timing needs to be adjusted to in order to obtain uniformity of castings within permissible limits of error. The time increment after each shot is measured in thousandths of a second and yet it is possible to control these small quantities automatically.
The sequence of operation in the die casting industry is such that the interval of time allowed between shots is in the order of 15 to 30 seconds. 1
It will be apparent to those skilled in the artthat the novel principles of the invention disclosed herein in connection with specific exemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claims they shall not be limited to the specific exemplifications of the invention'described herein.
Having thus described the invention, what I claim as new and desire to be secured by Letters Patent, is as follows: I g
1. In a method of repeatedly discharging substantially equal amounts of molten metal from a container with a metal level decreasing with each discharge, the steps comprising, applying equal pressure to said molten metal for a time for each discharge, and increasing said time by the same increment for each succeeding discharge to compensate for the level decrease in the container during the preceding discharge.
2. In a method for repeatedly dispensing substantially equal amounts of molten metal from a teapot container with decreasing metal level, the steps comprising, applying equal pressure to the molten metal during periods of time increasing from one dispensing operation to the next in equal increments to compensate for the level decrease in the container during the preceding discharges.
3. A metal melting furnace having means for automatically ladling a predetermined amount of molten metal comprising a chamber to hold molten metal, a discharge channel disposed in said chamber, pump means for causing the molten metal to be discharged through said discharge channel, a float positioned in said chamber such that its position is varied in accordance with the level of the molten metal therein and actuating means operatively connected to said float and responsive to the level of the molten metal as indicated by the position of said float for causing said pump means to be operated a period of time suflicient to discharge a predetermined amount of molten metal from the chamber regardless of the level of the molten metal.
4. A metal melting furnace comprising a chamber to hold molten metal, a discharge channel disposed in said chamber, pump means for causing the molten metal to be discharged through said discharge channel, switch means for initiating operation of said pump means, and a circuit including a timer responsive to the level of the molten metal in the chamber for automatically terminating the operation of said pump means after a period of time determined by the setting of the timer and the level of the molten metal.
5. A metal melting furnace having means for automatically ladling a predetermined amount of molten metal comprising a chamber to hold molten metal, a discharge channel disposed in said chamber, pump means including a solenoid valve adapted to render said pump means operative upon operation of said solenoid valve for causing the molten metal to be discharged through said discharge channel, actuating means controlled by the level of the molten metal for operating said solenoid valve for a period of time sufiicient to discharge a predetermined amount of molten metal from the chamber regardless of the level of the molten metal therein.
References Cited in the file of this patent UNITED STATES PATENTS 1,813,381
OTHER REFERENCES Iron Age, July 28, 1959, page 118 relied on. Instruments, 1st Quarter 1950, vol. 4, No. 4, pages 14 and 15 relied on.