US1912981A

US1912981A - Method of pressure casting and means therefor

Info

Publication number: US1912981A
Application number: US529201A
Authority: US
Inventors: John E Hoy
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1931-04-10
Filing date: 1931-04-10
Publication date: 1933-06-06
Anticipated expiration: 1950-06-06

Description

June 6, 1933. 1 E. HOY 1,912,981

METHOD OF PRESSURE CASTING AND MEANS THEREFOR Filed April lO, 1931 a //l//%/'// f H92 lNvl-:No Y BY ATTORNEY Patented .time 6, 1933 ,l

-fisizsi Ari-:Nr ori-ics .Tenn n. nov, or MIDLAND, MIoHIsA-N, AssrsNon 'ro run now cnnMIcAL coMrANY, or MIDLAND, MIcnIGAN, A conronArIoN or MICHIGAN Y METHOD F PRESSURE CASTING AND MEANS TBEREFOB 'Application :tiled April 10. 1931. Serial I0. 529,201.

.p 1While the present improvements relate more particularly to the castingof magnesium and so called light metal alloys in which magnesium is the predominant constituent,

5 it will be understood that the improved method and means involved are also adaptable for the castingl of other" metals. Diiiiculties encountered in melting and handling in molten state magnesium or an alloy largely comsed of this metal are welllmown and those diculties are still present when it is attempted to introduce such metal into a mold in any processof casting. For example, when castings are made in the ordinary way bysimply pouring the' molten magnesium or hght metal alloy into a mold, there is a pronounced tendency for the metal in contact with air or moisture to oXidize and burn, and at the same time where the casting is in the orm of a pig, billet., ingot, or heavy section casting, it solidifies adjacent to the mold surface first, and as the solidification continues it contracts which causes a depression or pipe, normally in the upper end ot the casting when it is in the form of an ingot, and sometimes a porous interior due to the contraction. Where such ingot is to be subsequently forged, extruded, or otherwise worked without remelting, it is necessary to cut oit the end containing the pipe if a good inished article is to be made. It has been well recognized that it would be highly desirable to find a method or procedure wherein the castings could be made with little or no oxidation and at the samel time the porosity and piping difficulty avoided. While many attempts have been made to overcome these diiiculties', the solutions evolved have in general been only partially satisfactory; I have now discovered a procedure and apparatus wherein castings, for instance ingots, can be made with almost no oxidation and at the same time with the elimination of piping -and porosity. I am aware that molds have been made for casting steel wherein the casting, after solidiication, has pressure applied to it 'for the Puri) also aware thatdie castings have been made from aluminum, zinc, lead, and the ose of consolidating thev metal. I am' However, the die castings are relatively small and chill almost instantly. The smallness of these castings, generally speaking, substantially overcomes the piping difficult1es encountered with large heavy section castings. My present improved procedure, however, differs markedly from such processes and consists in part in melting and maintaining the metal to he cast in molten condition in a suitable container, and where the metal is of a readily oxidizable nature I prefer to keep the molten metal under cover of a flux or the like to avoid Vor minimize oxidation or burning of the metal. The molten metal is then allowed to pass into a pressure pot in similar manner to die casting practice from whence it is forced through a heated oriiice into a mold, for instance an mgot mold, such mold being fed from the bottom and closed at the top except forl a small vent opening. As soon as the mold is filled, the metal is subjected to a chilling procedure wherein the metal freezes from the into the mold to compensate for shrinka e,

porosity, and piping of the metal. After t e whole ingot issolidified, the pressure in the pressure pot causing the molten metal to iiow into the mold, is released and the ingot removed, following which the mold can be put hack in place and the cycle repeated.

Accordingly, among the objects of the present invention is the provision of a procedure and apparatus for handling and casting metals, specifically readily oxidizable metals such as magnesium and its alloys, with a minimum of burning and the elimination of porosity and piping. Another object is to provide a method of casting fan ingot or heavy section casting and causing" it to freeze from the top downwardly while supplying A additional metal under pressure at the lower end of thefcasting' to overcome porosity and piping. .Other objects and advantages will appear as the description proceeds. To the Vaccomplishment of the foregoing and related ends, the invention, then, consists in the steps 42, jects downwardly into the molten metal, but

'30 leakage therethrough and apparatus hereinafterr fully described and particularly ointed out in the claims,

t-he annexed drawing and the following de,-

s'cription setting forth in detail certainmeans and modes for carrying o ut my invention/ In said annexed drawing:-

Fi'g. 1 is a diagrammatic plan view of one/ being separated from the other parts of container 4 by means of a curtain 6 which prohas a free passage thereunder for molten i' metal. A loose cover 7 is laid over the opening to reservoir 5 so as to keep out dirt or the like and at the same time reduce the heat loss from the surface of the molten metal. Within container 4 is placed a pressure pot 8 having a filler opening 9 controlledby a valve 10 of suitable construction, said valve 10 being adapted to seal oli' opening 9 and prevent when pressure is applied to the interior of the pressure pot. The upper end of the pressure pot is tted with Y a removable cover 11 having a connection 12 for the passage of air or an inert gas under pressure into the The gas passing through said connection 12 is preferably admitted thereto throu h an orifice 13 which in turn is connecte Ato a valve-controlled supply line 14. Where the gas used is not substantially inert to the metalxorv of an oxygen-consuming nature, I prefer to supply a small amount of oxygen-consuming material, such as powdered sulphur, to the gas passing through connection 12 into the top of the pressure pot. This, may be accomplished in any convenient manner, for instance, by dropping` a small amount of sulphur into funnel shaped opening 15 having a suitable valve connection forv dropping the sulphur into connection 12 priorto passing the gas therethrough into the top of the pressure pot. Upon admission of -the sulphur into the top of the` pressure pot, 'it will immediately combine with any oxygenu present and thus act to prevent'oxidation of the metal. A valvecontrolled vent 16 is.. provided in pressure pot cover 11 for releasing the pressure therein afterl the casting has been formed and solidified. The outlet end of the pressure pot is provided wtih a nozzle 17 having a suitableseat 18 for tightly contactingwith the entrance openin to mold 19. Mold 19 maybe heldin place y any suitable means'during top of the pressure pot.

490 per cent magnesium and 10 the filling step, for instance, by means of bolts or studs 20. The upper end of the mold is closed except for a small vent 21 whlch permits air or the like in the mold to pass out while the (mold is bein lilled, such opening 21 being small enough, owever, to cause the molten metal to freeze therein and thus prevent the molten 'metal from continuing to flow therethrough.` The sides of the mold are preferably provided with fins 22 or equivalent `and the whole enclosed in a jacket 23 having inlet 24 and outlet 25. As soon as the mold is completely filled, air steam, water spray, or the like is forced into jacketf23 through connection 24 and out through connection 25 which causes the casting to freeze from the top down towards the inlet 18,`thus permitting the molten metal to flow under pressure through nozzle 17 into the ingot to supply the extra metal necessary to overcome porosity and piping due to contraction of the metal during solidiication.

The container 4 may be initiall supplied with molten or solid metal either through the top of reservoir 5 or through filling compartment 26. The upper part of compartment 26 is separated from reservoir 5 by meansof curtain 6 and is similarly separated from the rest of the interior of container 4 by means of curtain 27,- said curtain 27 preferably extending downward to the same level as curtain 6 or slightly lower. It is to be noted that curtainsdG and 27 should project downward to a point below the lowest level attained by the molten metal in container 4 while it is in operation. Where the metal to be cast is of a readily oxidizable nature such as magnesium and its alloys, I prefer to place a small amountof a suitable flux over the surface of the metal in reservoir 5 to protect the metal from the effects of air. While I prefer to use a flux, I do not wish to be limited to that eX- act material since, obviously, an inert gas could be used in equivalent manner. Such liux should be lighter than the molten metal `so that it will oatthereon and offer the maximum protection from oxidation. Under normal operating conditions filling compartment 26 will be provided with a snug fitting cover to eliminate as vmuch air as possible therefrom, l such cover being removed each time that it is necessary to replenish the supply of metal in container 4, following which it is immediately replaced.

a specific example of the use of m improved procedure and apparatus, I will describe it in terms of castin a magnesiumaluminum alloy/.consisting o approximately per cent aluminum. The metal to be placed in receptacle 'or container 4 may be either molten or in solid form. `Where the metal-is used in solid formfcover 7 may be removed and reservoir 5 and adjacent available space within the containerpiledfull. Heat 1s then supplied'by kle a little flux over the surface of the metal.-

means of burner 2 or the equivalent to melt the metal, following which additional metal is added until the liquid level rises to a point near the top of the container, for instance as indicated b line 28. To revent oxidation of the meta in reservoir 5, prefer to sprin- Such iux may consist, for instance, of finely divided or powdered anhydrous magnesium chloride which remains in that form under 4normal casting conditions, or a mixture of potassium chloride andv lithium chloride which is normally fluid under the same conditions. While the proportions of this latter mixture may vary considerably, I have found that the mixtureconsisting of 80 per cent potassium chloride and 20 per cent lithium chloride issatisfactory for use with'the 90 per cent magnesium-10 r cent aluminum alloy described. This ux mixture has a meltingpoint below that of the alloy noted and has also a specific gravity slightly lower than the metal. Ordinarily only a very small amount of flux is used, in fact only enough to place face of the metal. Having the metal heated to a suitable casting temperature, for 1n- 'stance at a temperature in the neighborhood of 1200o to 1300 F., it is ready for casting. At the same time with the bottom filling ingot mold 19 anchored in place over filling i nozzle 17, the apparatus'is ready for casting the billet from the molten metal; Valve 10 is then4 lifted from its seat 9 to permit theb molten metal to flow into pressure pot 8 so as to fill it up to the level of the metal in reservoir 5, following which valve 10 is closed downon valve seat 9. A small amount of powdered sulphur is next placed in funnel 15 and dropped into passageway 12. Air is then supplied to the topof pressure pot 8 from supply connection 14, orifice 13 limiting 'the flow so that the pressure is applied in uninous supply of air or the like to the top of form steady manner to the top of the molten meta-l in the pressurepot. This causes the metal to flow out through orifice 17 into the bottom of mold 19, the fiow preferably being kept at a slow enough rate to avoid turbulence and agitation of the molten metal, i. e. How non-turbulently, as it enters and lls the mold since turbulence and agitation will tend i to entrain air into themetal and cause voids and oxide skins in the finished casting. The

airor other gas in mold 19 passes out through orifice 21 in the top thereof while the metal level is rising therein. As soon as the metal reaches the top and starts to fiow through said orifice it chills and seals off the opening.

`When the mold is full, thepressure on the metal begins to build up due to the continp the pressure pot through supply line 14. This pressure may be built up to from 50 to 400 pounds per sq. in.or more depending upon type and size of castingbeing made. As soon a very thin layer over the upper sur' as the mold is fined, or ifa-aired, after the final ressure on the metal has been reached, a coo4 ing fluid, for instance water spray, is dlrected upon the outer surface of the mold through opening 24. The hot water or steam generated in the jacket'passes out through orifice 25. The cooling fluid may be directed around the mold within the jacket in a spiral direction over coolingfins as shown in the d rawing, or in other equivalent manner if deslred. The cooling of the in ot in this manner causes it to freeze from t el top down towards the bottom which permits the bottom ofthe metal casting to remain molten and in condltion to continuously receive the molten metal y under pressure delivered thereto through nozzle 17 to compensate for shrinkage and eliminate internal porosity not infrequently developed due to internal strains set up during solidification. When the ingot is completely solidified, valve-controlled vent 16 is opened so as 'to release the pressure on the metal in the pressure pot. The mold can then be unfastened and the solidified ingot re moved therefrom. The apparatus is then ready for repeating the cycle as soon as the mold is mounted in place. After the initial charging of the receptacle or container 4 with metal, the subsequent supplying of metal thereto either in molten or ingot form is preferably taken care of through filling compartment y26 .as described above.

While I have described my invention in terms of applying sulphur to the space above the metal in the pressure pot, I do not wish to be limited to that exact procedure since, obviolisly, an inert gas could be utilized where the metal is of a readily oxidizable nature, and where the metal is not readily oxidizable, even air alone can in mostv instances be satisfactorily used. n

Other modes of applying the principle of my invention may be employed instead of those explained, change being `made as regardsl the means and the steps herein disclosed, provided those stated by any ofthe following claims or their equivalent be employed.

I therefore'particularly point out and distinctly claim as my invention 1. In a method of forming heavy section castings, the steps which consist in filling the casting mold from the bottom with molten metal, solidifying the casting progressively from top to bottom, and supplying additional mdlten metal to the bottom of said casting throughout the period of its solidification.

, 2; In a method of forming an ingot from a body of molten light metal mmh as magnedownward direction, and supplying anadditional amount of molten light metal under pressure to said ingot through the 4bottom auf of untillthe'ingt is completely 'Solidi' 3. The method of forming a uniform, pipe free ingot for working, from a molten bod of light metal such as magnesium or an a 4. In a method of the character described,

the steps which consist in cooling and solidiying a bottom poured heavy section casting progressively from top to bottom, and supplying additional molten metal under gradually increasing pressure to the bottom of said casting until the casting is completely solidified.

5. In a method of casting ingots, the steps which consist in supplying the molten metal to a pressure pot, applying pressure to the molten metal therein to cause it to' flow nonturbulently into and fill an ingot mold through the bottom thereof, solidifying the solidificatiom ingot progressively from top to bottom, and supplying additional molten metal to the bottom of said ingot during the period of such solidification.

6. In a method of casting ingots, the steps which consist in supplying the molten metal to a pressure pot,introducing an inert gas under pressure into said pressure pot to cause the molten metal therein to flow non-turbulently into and -lill an ingot mold through the bottom thereof, solidifying the ingot g progressively `from top to bottom, and supplying additional moltenmetal to the bottom of said ingot during the period of such 7. In a method of casting ingots of readily oxidizable metal such as magnesium or an alloy thereof, the steps which consist in heating a body of-said metal under cover of a suitable flux, transferring part of'saidl metal into a pressure pot immersed therein, applying pressure to the metal after transference to cause it to iiow non-turbulently into and fill an ingot mold through the bottom thereof, cooling and solidifying the ingot progressively in a downwarddireetion, and supplying additional molten metal under gradually increasing pressure to the bottom of the ingot during the period of such solidification to overcome porosity and pip- In a method of4 casting ingots of read# ily oxidizable metal such as magnesium or an alloy thereof, the stepsl which consist in heating a body of said metal undercover of a suitable iux, transferring part of said MQtal into a pressure pot immersed therein.

supplying an inert gas producing material to the pressure space above said transferred metal, appl lng air pressure to the metal after trans erence to cause it to flow into and fill an mgot mold through the bottom thereof,- cooling and solidifymg the ingot progressively in a downward direction, and supplying additional molten metal under pressure to the bottom of the ingot during the period ofsuch solidication to overcome porosity-and piping.

9. In an apparatus for casting, the combination of a receptacle for the molten metal to be cast, means for-heating said receptacle, a pressure pot Within said receptacle, a valve means for supplying molten metal from said receptacle to said pressure pot, a bottom lilling mold, a nozzle connecting said pressure pot with said mold, means including a jacket surrounding said mold for progressively cooling in a downward direction the metal cast therein, means for applying pressure to the interior of the pressure pot to force the molten metal into the mold, said means including a mechanism having a flow-reducing orifice for the pressure medium supplied to the interior of the pressure pot, and means to make said pressure medium non-reactive to the molten metal.

l0. In an apparatus for casting, the combination of a receptaclel for the molten metal to be cast, means for heating said receptacle, a pressure pot within said receptacle, a valve means for supplying molten metal from said receptac e to said pressure pot, a bottom-filling mol a nozzle connecting said pressure pot with said mold, means including a jacket surrounding said mold for progressively cooling in'a downward direction the metal cast therein, means including a' mechanism having a flow-reducing orifice for supplying a gas under pressure to the interior of the pressure pot to yforce the molten metal into the mold, and means for supplying to said gas a material making it inert to the metal lbeing' cast.

. Signed by me this 4th day of April, 1931. l JOHN E. HOY.