US2248868A - Method and apparatus for preparing metal castings - Google Patents

Description

July 8, 1.941.

J. D. HANAWALT METHOD AND APPARATUS FOR PREPARING METAL CASTINGS Filed April 1:5. 1940 -/Her/ 6'05 16 I 14 kaa/um u w 10' f0 10 .5

1" 7 19 60 x3 20 jg s o 1?; 3: 16 18 Y 0 03 l A 35 1t 17 :5 E5 Pg 3 1 i 3 :L 5 j '17 jl \+:1t 1a 18 INVENTOR Jasqob a Manama/f 1 BY {757 VM ATTORNEYS Patented July s, 1941 METHOD AND APPARATUS FOR, PREPARING METAL CAS'IINGS Joseph D. Hanawalt, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich-., a corporation of Michigan Application April 13, 1940, Serial No. 329,508

13 Claims.

This invention relates to a method and apparatus for preparing metal castings. More particularly, it concerns the preparation of heavysection vacuum castings of readily oxidizable metals, such as magnesium.

Vacuum casting processes are well known in the art, but for the most part have been applied only to the production of small metal parts. In

a few instances, however, attempts have been made to extend the technique to the formation of heavy-section castings, such as ingots and billets. For example, it has been proposed to form ingots by immersing the sprue of an ingot mold in molten metal, evacuating the mold to allow the metal to enter, closing the sprue when the mold is filled, and then solidifying the metal in themold from the sprue upward. In a variation of this method, the mold, when filled, is cooled to solidify the metal from the top downwardly, shrinkage during solidification being filled by additional metal forced in through the sprue, Unfortunately, because of cooling difiiculties and other disadvantages, these and similar casting methods are of limited applicability, and have met with little success.

It is therefore an object of the invention to provide a method for making metal castings, especially ingots, which avoids the disadvantages of prior practice. Another object is to describe a method which is particularly adapted to making heavy-section castings of readily oxidizable light metals, such as magnesium, and which, when so used, prevents the occurrence of oxide inclusions and other impurities in the cast metal. A further object is to devise apparatus for use in such a method.

In brief, the process of'the invention includes primarily the steps of filling a casting mold from the. bottom with molten metal, inverting the filled mold while the metal therein is still substantially all molten, solidifying the metal in the inverted mold from the lower end upwardly, and removing the casting thus formed.

In practice, the filling of the mold is usually carried out by immersing the inletor spruethereof in a reservoir of the molten metal to be cast, and then evacuating the mold to allow the.

metal to enter. When the mold is filled, evacuation is discontinued, and the mold is withdrawn from the'reservoir and rotated to such position that the coolest portion of the full mold, usually the portion opposite the sprue, is lowest, e. g. so

that the sprue is higher than the mold. The

lower portion of the rotated mold is then cooled to solidify the molten metal progressively from the lower end upwardly. During the solidification it is desirable to heat thesprue of the mold to maintain the metal therein molten until the metal in the mold is solidified. In this way, the shrinkage during solidification is filled by gravity with metal from the sprue, so that piping is large- 1y prevented.

The process and apparatus of the invention may be explained in greater detail with reference to the accompanying drawing, in which-- Figure 1 is a vertical central section of a cylindrical ingot casting mold, showing-the mold being filled from a reservoir of molten metal; and

Figure 2 is an elevation of the same mold during the solidifying operation, after it has been filled and inverted.

The apparatus shown in Figures 1 and 2 consists essentially of an elongated hollow mold body 3 forming a slightly tapered cylindrical mold 4 which is open at the wider end 5 of its taper.

At, its other end, the mold terminates in a sprue or pipe 6 which is integral with the mold body.

As shown in Figure l, the walls of the mold body 3 become progressively thicker from the sprue 6 to the open end 5 of the mold to provide added cooling capacity at the open end. The mold body 3 may be supported, lifted, and inverted by means of trunnions I which are attached to the body approximately at its longitudinal center of gravity, and are adapted to fit into hearings in a supporting framework 8.

vAt its open end 5, the mold is closed by a cover fiange 9 which is demountably secured to mally closed valve means, which, as shown, consists'of a self-centering cover plate ll held tight ly against the end of the sprue by rods I8 which the mold body by capscrews I. At the center of ,the flange 9 is a narrow tapered orifice H,

which opens into a flanged nipple l2 welded to the cover flange 9. The flanged nipple I2 may be bolted to a corresponding terminal flange [3 which is connected by a gas line l4 to a 'valved vacuum-line l5 and a valved gassupplyline I 6. The sprue 6 of the mold is provided with nor-:-

are. under-tension from springs IQrestingon lugs 20 attached tothemold body 3-. The cover plate 11 may be moved out, of contact-with the end of the sprue by a "linkage 2| whichis at tached to one of the tension rods l 8, and is oper-v ated by a handleliZ. The sprue 6 is also pro vided with heating means in the form of a rshielded ring burner 23 whichmay be connected to a'valved fuel gas line'24. If the sprue 6 is so designed that molten metal does not tend to run out of the full mold, thevalve closing means for the sprue may be omitted.

In a preferred method of preparing metal castings according to the invention, the assembled mold, usually preheated to a casting temperature,

is lifted by suitable hoisting means applied to its trunnions I with the sprue 8 extending downwardly, and is moved into position over a reservoir 25 of molten metal 26. The mold is then lowered until the sprue is immersed in the metal, well below the surface layer of flux or dross, and the sprue'cover plate I! is moved out of position by pulling down on the handle 22. The valve in the vacuum line I5 is then opened so that the mold is gradually evacuated, causing molten metal to enter through the sprue 6 in nonturbulent flow. When the mold is completely filled the molten metal attempts to enter the gas outlet orifice H in the cover flange 9; however, because of the large cooling area presented by the flange 9, and the narrowness of the orifice, the molten metal entering the latter instantly freezes, forming a solid plug. When this occurs, the vacuum line I5 is closed, the terminal flange I3 is unbolted, the sprue cover plate I! is 'replaced, and the mold is at once withdrawn from sprue and the top of the mold are heated to maintain the metal in the sprue molten by means of a ring burner 23; in this way shrinkage of metal in the mold during solidification is filled by gravity from the sprue. (To this end, it is desirable that the volume of the sprue be approximately equal to that of the shrinkage of the casting during solidification.) When solidification mold is replaced prior to casting by a gas, such as sulfur dioxide, which is relatively inert to the metal being cast. In practice the sprue cover plate I! is withdrawn, and'in'e'rt gas is fed into the mold by opening the valve in the gas line l6, this operation being carried out just prior to dipping the sprue. in the reservoir of molten metal. As a result of this stage, the metal being cast does not come into contactwith air in the mold, and oxide inclusions in"'the casting are prevented.

It will be appreciated that the process of the invention possesses a number of, distinct advantages. Thus, the mold can be removed from the reservoir of molten metal immediately after it is filled. Shrinkage during solidification is fed by gravity from the sprue. The solidification operation is simple and effective since the first metal to enter the mold, which is chilled by contact with the relatively cool mold and is therefore the coolest metal, is the first to be solidified. That is, because the mold has been inverted, the most suitable thermal gradient for a mold occurs naturally in the process. Moreover, cooling is from the bottom up. In addition, because the mold isinverted immediately after filling, it

needs to. be evacuated only during the filling; that is, vacuum does not have to be maintained on the mold during the solidification period. This latter fact is especially advantageous, since the joint between the mold and its cover flange, which is the most likely source of vacuum leaks, is not under vacuum except when it is the coolest and hence is the most nearly vacuum tight. A further advantage of the process resides in the fact that because of the inverting operation, and consequent superior cooling of the mold, settling and segregation of the metal being cast are minimized.

It is to be understood that the foregoing description is illustrative rather than strictly limitative, and that the invention is co-extensive in scope with the following claims.

I claim:

1. A method of forming metal castings which comprises: filling a casting mold from the bottom with molten metal; inverting the filled mold while the metal therein is still substantially all molten; solidifying the metal in the inverted mold from the lower end upwardly; and removing the casting thus formed.

2. A method of forming metal castings which comprises: filling a casting mold having a sprue therein by passing a molten metal from a supply thereof upwardly into the casting mold through the sprue; rotating the filled mold while the metal therein is still substantially all molten to such position that the coolest portion of the mold is lowest; solidifying the metal in the rotated mold progressively from the lower portion upwardly; and removing the casting thus formed.

3. A method of forming metal castings which comprises: immersing the inlet of a casting mold in a reservoir of molten metal; evacuating the mold to allow the metal to enter; discontinuing the evacuation when the mold is filled; withdrawing the filled mold from the reservoir and inverting the mold while the metal therein is still substantially all molten; cooling the lower part of the inverted mold to solidify the metal progressively from the lower end upwardly; and releasing the casting thus formed.

4. A method of formingingots of a readily oxidizable light metal which comprises: immersing the sprue of an ingot mold in a molten body of the said metal; evacuating the mold to allow the metal to enter; discontinuing the evacuation when the mold is filled; withdrawing the mold from the body of molten metal and invetting the mold while the metal therein is still substantially all molten; cooling the lower part of' the inverted mold to solidify the metal therein progressively from the lower end upwardly while heating the sprue to maintain the metal therein molten until. the metal in the mold is solidified, Thereby shrinkage during solidification is filled by metal from the sprue; and releasing the ingot thus formed.

5. A pmoess according to claim 4, wherein a gas inert to the readily oxidizable metal is in- Jected into the mold prior to casting to displace the air therefrom.

8,. A process according to claim 4, wherein the readily oxidizable metal is magnesium or a mag-' nesium-base alloy.

7 In an apparatus for casting molten metal, the combination of: a mold having a sprue at one end thereof and a gas outlet at the opposite end; heating means adapted to maintain the sprue at a temperature above the freezing temperature of the ametal being cast; connections gas outlet; and handling means secured to the mold whereby it may be lifted and inverted.

8. In an apparatus for casting molten metal, the combination of: a mold open at one end and having at the other end thereof a sprue integral end.

10. An apparatus according to claim 8, wherein the mold handling means consist of trunnions mounted approximately at the longitudinal center of gravity of the mold body.

11. In an apparatus for casting molten metal, the combination of: a mold having a sprue at one end thereof and ga outlet at the opposite end; valve means normally closing the sprue; heating means adapted to maintain the sprue at a temperature above the freezing temperature of the metal being cast; connections whereby the mold may be evacuated through the gas outlet; and handling means secured to the mold whereby it may be lifted and inverted.

12. In an apparatus for making heavy-section castings, the combination of: an elongated mold body forming a slightly tapered ingot mold open at its wider end and having at the other end thereof a sprue integral with the .mold body;

handling means secured to the mold whereby it may be lifted and inverted; a demountable flange closing the mold at its open end and having a narrow orifice therein; connections for applying suction to the flange orifice; valve means normally closing the mold sprue; and heating means adapted to maintain the sprue at a temperature above the freezing temperature of the metal being cast.

13. In an apparatus for making heavy-section castings of readily oxidizable light metals, the combination of: an elongated mold body forming a slightly tapered ingot moldopen at its wider end and having at the other end thereof a sprue integral with the mold body, the walls of the mold body becoming progressively thicker from the sprue end to the open end; trunnions attached to the mold body at approximately its longitudinal center of gravity, whereby the mold may be lifted and inverted; a demountable flange closing the mold at its open end and having a narrow orifice therein; connections for applying suction to the flange orifice and for supplying thereto a gas inert to the metal being cast; valve means normally closing the mold sprue; and heating means adapted to maintain the sprue at a temperature above the freezing temperature of the metal being cast.

JOSEPH D. HANAWALT.

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