US3677332A - Vacuum casting process - Google Patents

Abstract

The disclosure relates to a process and apparatus for casting metals by controlling the relative pressure of the space above the molten metal body to be cast with respect to the pressure within the interior of the mold. Numerous features of the mechanism are shown and described.

Description

I United States Patent [151 3,677,332 Smiernow [451 July 18, 1972 s41 VACUUM CASTING PROCESS 3,435,878 4/l969 Howard et al. ...164/51 2 871 533 2/1959 Swainson 164/1 33 [72] Inventor: George A. Smlemow, 825 S. 48th Street,

Philadelphia, Pa. [9143 3,523,785 8/1970 Gero 164/ l 33 X [22] Wed: June 13 1969 FOREIGN PATENTS OR APPLICATIONS [2 1 App]. No: 32 89 902,495 l2/l944 France 164/133 Primary Examiner-J. Spencer Overholser [52] US. Cl. ..l64/l33, 266/42, 266/34 V, Assistant ExaminerV. K. Rising l64/62, 164/63, 164/65 Arrorney-Jacksom Jackson and Chovanes 5 1] Int. Cl. ..B22d 35/00, 822d 37/00 [58] FieldofSearch ..164/62,6l,65,155,133,63; [57] ABSTRACT The disclosure relates to a process and apparatus for casting metals by controlling the relative pressure of the space above [56] "Mamas and the molten metal body to be cast with respect to the pressure UNITED STATES NT within the interior of the mold. Numerous features of the mechanism are shown and described. 3,099,053 7/l963 Ehot ..164/64 3,125,440 3/1964 Homak et al ..75/49 2Clflna,4l)rawlngflgures 7 9 7a 7 7 a: "t 8a a! v ll "10"! "1.01:, a a, I 1 l1 //W7 /W A" 82 Q I m $1, 54 a! \a H J a 7/ g 1% m g '4 .2- a f Qg '2; 9; /02 /2# Patented July 18, 1972 4 Sheets-Sheet l INVENTOR. 650190: 6 M/ER -aw Patented July 18, 1972 4 Sheets$heet Patented July 18, 1972 4 Sheets-Sheet 4 VACUUM cssrnvc rnocsss DISCLOSURE OF INVENTION This invention relates to the manufacture of castings by a vacuum pouring process, and particularly to a vacuum pouring apparatus suitable for pouring all ferrous, non-ferrous and special alloy castings and ingots of different design, weight and size in all kinds of molds: sand, semi-permanent, permanent, etc.

It is the main purpose of the invention to provide a new process of vacuum pouring for the manufacture of very sound castings and ingots of improved quality, without blow-holes, flaws, or any other defects. When I refer to castings and ingots here I mean to include finished or semi-finished metal products which may be in different operations be referred to as ingots, blooms, billets, slabs, wirebars and castings. The invention aims to provide a single apparatus for vacuum pouring, which is simple in construction and design, and which assures a relatively economical method of manufacturing sound castings and ingots of improved quality.

Another object is to provide a process and apparatus for vacuum pouring which improves the filling of the molds and permits the molds to be filled quickly, with little cooling of the liquid metal; thereby making it possible to manufacture very thin section castings, particularly from high viscosity alloys.

Another object is to provide a vacuum pouring process and device that permits the manufacture of castings with improved surface and higher dimensional accuracy. This is achieved through the vacuum during pouring and crystallization, and also due to the possibility of using low permeability molds, hard rammed from very fine-grained sands, or of using permanent and semi-permanent molds, which cannot be used in common pouring methods.

Another object is to provide a vacuum pouring process and device that permits the manufacture of castings and ingots with improved mechanical properties, due to crystallization in vacuum and/or under pressure.

Another object is to provide a vacuum pouring process and device that permits the manufacture of castings and ingots with a decreased weight of heads and risers, or without them, thus increasing the yield of castings and ingots from the liquid metal, reducing the cutting off and cleaning costs.

A further object is to provide a vacuum pouring process and device that permits the manufacture of castings and ingots from highly oxidizable alloys, due to vacuum and/or neutral atmosphere in the mold which prevents the liquid metal from coming in contact with the air. A still further object is to provide a relatively economical vacuum pouring process and device for the manufacture of castings from very high temperature melting alloys, which can be done due to rapid filling of molds with little cooling of the liquid metal.

Other objects and advantages of the invention will become apparent from the following detailed description of the apparatus. This description is made in connection with the accompanying drawings in which the same parts throughout the views are indicated by the same numerals as given in the description.

The drawings show vacuum pouring mechanism for practicing the invention.

FIG. 1 is a diagrammatic partially broken plan view of the device of the invention.

FIG. 2 is a diagrammatic partially broken axial section of the mechanism of FIG. I, showing the insertion ofa mold into the lower chamber.

FIG. 3 is a view similar to FIG. 1 showing the lower chamber closed and metal being poured into the mold.

FIG. 4 is an enlarged fragmentary vertical section of the metal ladle and pouring nozzle, along with the upper chamber.

The lower reducedpressure chamber 16 represents a steel casting with two raising and lowering doors, in-door 22 and out-door 23. At the bottom of thechamber 16 is a verticalhydraulic cylinder 45 which is hermetically sealed withrubber gasket 46.Cylinder 45, whosepiston 49 enterschamber 16, is

fed through pipe line I30. Topiston 49, a roller table 53 is fixed by means of leveling springs 51. Chamber I6 is mounted on beams 9. At the top of the lower reducedpressure chamber 16,upper vacuum chamber 17 is fixed hermetically throughrubber seal 73 bybolts 72.

The inside wall of thechamber 17 is protected from radiating heat by a refractoryhelical pipe coil 91, through which passes cooling water.Lid 76 of upper chamber l7 has double walls withspace 75 between the walls for circulation of cooling water. Lid 76 has aquartz glass window 79 for the visual control of theliquid metal 98.Lid 76 swings onhinge 80 and can be hermetically closed throughrubber seal 82 bybolts 83.

The bottom ofupper chamber 17 is formed by refractory cushion lll on which a refractory pouring basin orladle 97 is placed. Thebasin 97 is surrounded byhelical inductor coil 102 of copper tubing, insulated between turns, through which water is passed for cooling the copper. If necessary, high frequency alternating current may be applied to the terminals of the helix, inducing current in theliquid metal 98 and maintaining the metal at the desired pouring temperature. The high frequency current is supplied by a special high frequency generator, not shown on the figures.

The bottom and walls ofbasin 97 are formed by rammed refractory materials. Apouring channel 118 on the bottom of the basin, incushion 111, is formed by heavy duty high refractory tubing I13 having embedded in it ahelical coil 114 of copper tubing, insulated between turns, through which water is passed for cooling. Under thepouring channel 118 in the ceiling ofchamber 16 is placed arefractory ring 119, through which the liquid metal frombasin 97, throughchannel 118, is poured into themold 70.

Assembled molds inflasks 65 onbottom boards 66 reach the vacuum pressure pouring station by a roller conveyor 1 to the roller turntable 4. When the mold is on table 4, the table is turned to the position shown in FIG. 1. The in-door 22, sliding onrails 27, is raised bycable 29 driven by means ofmotor 34,reducer 35, and drum 3], all of which are mounted onstructure 32. The mold is pushed on the roller table 53 intochamber 16 by means of the piston rod ll, supported bypiston rod guides 12, from thepneumatic cylinder 10. Then the mold, pushed simultaneously by piston rod ll and by thepiston 41 from an auxiliary horizontalhydraulic cylinder 40, fed frompipe line 43, is fixed inchamber 16 by four flask guidingpins 67 in such a manner that apouring gate 68 is placed just in front under thepouring ring 69. Then the indoor 22 is closed and by means ofpiston 49 and verticalhydraulic cylinder 45, the mold is raised and pressed to the ceiling ofchamber 16. The levelingsprings 5| assure tight contact between the top surface of the mold and the ceiling ofchamber 16. Then a reduced pressure is created inchamber 16 byvacuum pump 55, through tank 57 andpipe line 58. This reduced pressure is controlled by gage 60 andvalve 59.

A vacuum pump is connected to vacuum chamber l7 through the high vacuum gas pipe line 89a and three-way valve 90. When reduced pressure inchamber 16 and vacuum inchamber 17 are created, pouring can start.

It will be evident that in the preferred embodiment of the invention the vacuum in theupper chamber 17 either will be of a high or reasonable order of magnitude, for example in the range between 10" and I00 millimeters of mercury and preferably between 10' and l millimeter of mercury, often controlled by the desired degassing pressure for the particular metal. The reduced pressure in the lower chamber [6 and hence in the mold at the time of pouring, since the mold derives its pressure from the lower chamber, will be considerably higher than the pressure in the upper chamber, at least l.5 times, and thus will serve to oppose the force of gravity in causing metal to flow into the mold, causing a gradual filling of the mold, free from spatter, avoiding gas cavities, and allowing for a controlled flow rate. It will be understood that depending on the character of the metal or alloy being poured. higher or lower pressure will be used in thechamber 16 and in the mold, but in general for best results the reduced pressure in thechamber 16 should be in the order of 2 millimeters of mercury to approximately one atmosphere.

It also will be evident that in some cases it may be desirable to vary the pressure inchamber 16 and in the mold during pouring in order to control the flow rate.

It will be evident that the residual gas in thechambers 16 and I? need not necessarily be air, but residual gases which will be inert to the particular metal or alloy may be used, for example, depending on the composition of the metal, inert gases such as helium or argon, or relatively inert gases such as nitrogen. Reducing gases such as carbon monoxide or hydrogen may be used. Naturally, in certain cases as where the metal has abnormal solubility for a particular gas, such gas may be avoided.

Pouring is controlled electrically by a high frequency cur rent which flows throughhelical coil 114 and by the amount of cooling water which passes through the same pipe coil. Before the electric current is applied, cold water passes through the helical pipe coil 1 l4 and the metal inchannel 118 is solidified, thereby stopping pouring. By decreasing the amount of cool ing water and applying high frequency electric current to the terminals of the coil 4, current is induced in the solidified metal inchannel 118. These induced currents cause rapid heating and melting of metal inchannel 118 and filling of mold '70. The filling of themold 70 withliquid metal 98 is done in a precisely controlled way due to maintaining of programmed difference in vacuum inchamber 17 and reduced pressure in the mold fromchamber 16. When the electric high frequency current is cut off from coil "4, the amount of cooling water passing through pipe "4 is increased, which solidifies the metal in channel U8 and stops pouring. After the sprue and casting are solidified, the vacuum pumps are stopped, pressure inchamber 16 becomes atmospheric and the in and outdoors 22 and 23 are raised. By loweringpiston 49, roller table 53 is also lowered to the level ofroller conveyor 120. Pushed by pneumatic piston rod ll, the mold comes out fromchamber 16 on the lead-away roller conveyor to a shake-out station. Then the cycle may be repeated with the next mold.

Other constructions of pouring basins or ladies can be used, for example, a bottom pouring basin with stopper which is opened and closed by means of an electrical solenoid, as well known in the art.

It will be evident that where desired the mold may be preheated to any desired temperature.

It will further be evident that while the invention may find its widest application in the casting of relatively common metals and alloys. such as steel, stainless steel, heat resisting alloys, copper base alloys, aluminum base alloys, magnesium base alloys, nickel base alloys, chromium base alloys, and the like, it is also applicable to the casting of metals and alloys less commonly encountered and particularly those which are highly reactive, as for example titanium, zirconium and niobi- The principles of the present invention may be utilized in different ways, numerous modifications and alterations, substitution of parts and changes in construction being contemplated; it being understood that the process and apparatus shown in the drawings and described above and the particular methods set forth are given merely for purposes of explanation and illustration, without intending to limit the scope of the claims to the specific details disclosed.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A process of casting molten metals, using a ladle or the like having a pouring nozzle in the lower part thereof and a mold having an entrance opening or gate, which comprises applying the pouring nozzle of the ladle in line with the entrance opening of the mold, artificially cooling the molten metal within the pouring nozzle to initially block the pouring nozzle by solidified molten metal, maintaining a first pressure on the molten metal in the ladle, retaining a higher pressure in the mold, then melting the metal in the pouring nozzle so that the molten metal flow can begin Into the mold and controlling the flow of molten metal to the mold by the relative difference in pressures between the pressure in the ladle and the pressure in the mold.

2. A process of casting molten metal from a ladle or the like having a pouring nozzle at a lower position, into a mold having an inlet opening or gate, which comprises bringing the inlet opening of the mold into line with the pouring nozzle of the ladle, artificially cooling the molten metal in the pouring nozzle to cause it to solidify and initially block the pouring nozzle by solidified molten metal, maintaining a vacuum above the molten metal in the ladle in the range from 10' to lOO millimeters of mercury, maintaining a pressure within the mold in the range of between 2 millimeters of mercury and about one atmosphere and at least l.5 times the absolute vacuum pressure on the upper surface of the molten metal within the ladle, then melting the metal within the pouring nozzle so that molten metal can begin to flow into the mold, and controlling the flow of molten metal to the mold by the relative difi'erence in pressures between the pressure above the molten metal in the ladle and the pressure in the mold.

Claims (2)

1. A process of casting molten metals, using a ladle or the like having a pouring nozzle in the lower part thereof and a mold having an entrance opening or gate, which comprises applying the pouring nozzle of the ladle in line with the entrance opening of the mold, artificially cooling the molten metal within the pouring nozzle to initially block the pouring nozzle by solidified molten metal, maintaining a first pressure on the molten metal in the ladle, retaining a higher pressure in the mold, then melting the metal in the pouring nozzle so that the molten metal flow can begin into the mold and controlling the flow of molten metal to the mold by the relative difference in pressures between the pressure in the ladle and the pressure in the mold.

2. A process of casting molten metal from a ladle or the like having a pouring nozzle at a lower position, into a mold having an inlet opening or gate, which comprises bringing the inlet opening of the mold into line with the pouring nozzle of the ladle, artificially cooling the molten metal in the pouring nozzle to cause it to solidify and initially block the pouring nozzle by solidified molten metal, maintaining a vacuum above the molten metal in the ladle in the range from 10 6 to 100 millimeters of mercury, maintaining a pressure within the mold in the range of between 2 millimeters of mercury and about one atmosphere and at least 1.5 times the absolute vacuum pressure on the upper surface of the molten metal within the ladle, then melting the metal within the pouring nozzle so that molten metal can begin to flow into the mold, and controlling the flow of molten metal to the mold by the relative difference in pressures between the pressure above the molten metal in the ladle and the pressure in the mold.

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