US2257713A - Metal treating - Google Patents

Description

Sept. 30, 1941. J. H. L. DE BATS 2,257,713

METAL v'IREA'IING Filed Oct. 19, 1940 2 Sheets-Sheet 2 R w Oe H mD m v 40/1 O l H In A w w e. z J W4 -als (or alloys) can be state, as, for example, in furnaces, particularly,

Patented Sept. 30, 1941 UNITED STATES PATENT OFFICE METAL 'ral-:Arma Jean Hubert Louis ne nata, aast orange, N. J. Application October 19, 1940, Serial No. 361,851 1o claims. .(fcl. zia- 212) 'I'his invention relates to method and apparatus for treating metals to produce superior castings from molten metal and has for an object the provision of improvements in this art.

'I'here is an increasing demand for metal of high purity either alone-a pure metal, as suchor in definite predetermined ratios with other ingredients. It is recognized that the desired metproduced in the molten electric furnaces. 'I'he difliculty comes in getting the metals (or alloys) into castings (herein meaning any solid-from-molten condition) because the air reacts upon the molten metals with such extreme rapidity.

'I'here are various vacuum casting methods but they are very expensive, slow and uncertain. There are protective gas methods but these require rather elaborate equipment and considerable care inuse. There are processes involving protective solid substances and diluents but these obviously change the character of -the metal,

hence are mainly useful when the protective substance is also utilized as a desired alloying ingredient. One way of proceeding would be to permit the metal to solidify in the furnace in which it was brought to purity but obviously these vessels, such as electric furnaces, are neither suitable nor economical for handling solid metal castings. Other methods might be mentioned.

`The manner in which the metal solidies also greatly aifectsfits quality because the crystal growth may be so variable in any one casting as tually be larger at the upper end of a mold of I initially uniform size. Hence the casting may be diiiicult to remove.

The present invention'` utilizes a carefully chosen combination of steps which together provide accurate control, eliminate the former difliculties, and produce a metal (or alloy) of unusual purity or accurate predetermined character.

According to this method the metal (or alloy) is brought to the desired state of purity in a melting furnace or ladle, preferably an electric furnace which produces vertical currents of metal circulation extending to the surface of the metal to eliminate gas inclusions or "kill the metal. A high frequency induction furnace is one suitable lform. The metalmay either be melted and purified in the furnace or alternatively, for greater speed, may be'x poured molten into the furnace, treated until purified, and circulated while protected fully from the air until killed After purification the metal is transferred without space separation into al mold which increases in size as fast as the metal can enter it and in `which the metal enters through, an opening the full size of the mold. Consequently the metal fills the mold almost instantly. This results in the surface solidiiication of the castto cause serious difficulties in subsequent working operations, even after annealing, and in many cases uniformity can never'be re-established. In the case of alloys (or mixtures) there may be suchsegregation inthe casting that the metal is worthless-or, at best, less perfect than desired.

For example, in the usual chill casting method the metal is frozen 'in a thin layer on the outside, after which the casting shrinks and the mold expands to permit separation, and thereafter the cooling is slower because of loss of metal-to-metal contact and the hot air gap between, and consequently the crystal growthl interiorly becomes slower and more uncertain, the crystals getting larger and. larger toward the center of the casting. This action is aggravated by the incremental pouring procedure which continues to add molten metal to the upper parts of the mold while metal therebelow solidiiies, the mold-continuing to expand from the continued heating. Because of this the casting may acing all at once and the shrinkage from the walls of the mold simultaneously throughout the entire facing area of the casting. Moreover, the entire action of pouring and surface solidiiication is Aso rapid that the temperature of the mold is not appreciably raised. 'I'he mold is made to have a high heat dissipating value so as to aid in avoiding temperature rise during the very short pouring period. It may be formed of copper or other highly heat conductive metal and have very thick walls or be rapidly cooled by fluid.

As soon as the metal cools to form a shell on the outside of the casting-a cooling gas isforced through the space between the casting and mold to lcontinue the rapid cooling and prevent enlarged crystal growth interiorly of the casting.

exemplary embodiment thereof will be described herein, reference being made to the accompanying drawings, wherein:

Fig. 1 is a verticalsection through the appay ratus before pour `Fig. 2 is aesimilar partial view after pouring;

Fig. 3 is a similar view during the later cooling stage;

' Fig. 4i is a similar view showing the billet removal stage; and

Fig. 5 is a vertical section of a modified pouring arrangement.

Referring to the drawings, the apparatus suitable far practicing this invention comprises a furnace or teeming ladle i@ in which the metal may be puried and kept molten. Preferably it is an electric furnace which produces a vertical circulation of the metal to bring all parts ,rapidly to the` furnace to free it completely of air or gases. A high frequency induction furnace may serve this purpose. The effect of air or gas removal is to kill or quiet the metal so that porosity in the castings is avoided. For certain metals the gas inclusions or gas-forming inclusions may be removed in whole or in part by other methods. A removable cover il fits fairly closely to completely prevent air entry and to permit escape of released gases.

The furnace or ladle may hold a large quantity of metal or just enough to ll one mold.` lin it the metal may be melted or may be received in molten condition. ,Y

The bottom of the furnace or ladle is provided with a pouring opening I2 substantially as large as the cross section of the opening of the mold I3 to be lled and this pouring opening is closed by a plug I4 which may be opened by a handle I5, as shown in Fig. l, or by a push Y from below to float up, as shown in Fig. 5.

The furnace bottom is shaped, as by an annulartapered projection or nozzle I6, to flt tightly against the top of the mold. For further exclusion of air a liquid seal 20 of low melting point metal may be provided, the mold being hot enough (say 360 F.) to keep it molten. Either the furnace, or mold, or both, may have vertical movement to make the connection before pouring commences and to break the connection after pouring. 0r underl certain conditions the connection may be permanent. As shown, the moldv may be raised and lowered by a fluid ram I1. The furnace may be raised and loweredby a crane or hoist (not shown) or by hand if small.

The mold is lled substantially instantaneously and without free fall. This avoids splashing and insures that the casting will solidify simultaneously throughout its full length, also that the.

mold will not expand to any extent during pouring but will expand, if at all, uniformlyl from top to bottom after pouring and during the cooling period.

The means for effecting this mode of lling the mold comprises a close fitting piston or plunger I8 which also ts the bottom opening of the furnace and which is operated by a uid ram i9. The ram may be operated in one or both directions by compressed air and be evacuated by suction on the other side wherebythe plunger may be lowered approximatelyA with the speed at which the metal would fall by gravity. In a sense the metal will be sucked into the mold bythe piston of the plunger, the metal seal above and the close t of ,the plunger below serving to prevent the intake of airy during this action.

At the beginning of the mold lling operation `thepiston of the plunger is moved up against Vthe plug and may push the same up until the full opening of thenozzleis available for metal flow. This brings .metal immediately against the top of-the piston. Preferably the top of the piston is covered by insulation to prevent` adheg, .also stainless steel, high silicon steel, alumiepargne sion of metal thereto. The metal may be superheated by a hundred degrees or more to i it and then cooled to the desired temperature for pouring.

After the plug has been fully opened the plunger descends at high speed to allow the mold to nil in an instant. initially the piston stops at the position shown in Fig. 2 but as soon as a shell of metal forms in sumcient thickness w support the interior molten metal of the casting-which experience will soon indicatethe piston is lowered further, as shown in Fig. 3, to bring the lower end of the casting opposite an annular air (or gas) manifold 2i in order that the air may be forced up through the space now formed between casting and mold to hasten the cooling of the casting. An inert gas which burns at the outlet, like carbon monoxide, may be used for some metals. For other metals other known protective gases which are suited thereto may be used and after the castings are sufficiently cool to avoid-deleterious action the selection of. gases increases as does also the availability of air. At the same time the mold and furnace are separated or an outlet is opened at the topof the mold to allow the air to escape. ff there is metal left in the furnace the plug may be replaced after the mold is full. Preferably the mold is made to take all the metal in the furnace. The bottom of the piston may be closed against a seal 22 to prevent cooling uid from escaping.

After complete solidicatlon the casting is removed from the mold, either by further lowering of the plunger if of sufficient length, or by pushing the casting out the top of the mold, the furnace being raised or the mold being lowered to accomplish this. The casting may be readily taken oif the end of the piston because it does not adhere to the refractory surface of the upper end of the piston. This may be formed of graphite which ts tightlyin the mold and acts as a lubricant to promote easy movement. If the carbon would aiect the metal (such as steel) a refractory cover of a different material may be placed above it. Preferably the mold is lined with seamless copper. The whole mold may be of thick copper -to provide inertia against quick heating or the mold may be cored for rapid water circulation, in which case the outer parts may be of aluminum, steel or graphite. If it is desired to cast tubes a core is placed in the mold and an annular piston is used. This may be cooled on both sides of the wall by the mold and then by the cooling gas.

it is thus seen that the purified and killed metal is cast without possibility of contamination and is solidified under conditions which minimize segregation and improper crystalization. As applied to steels the method will produce super-high carbon metal never approached heretofore. It is easy to produce this steel with a higher carbon-content than heretofore and in greater quantities and at a low cost. Previously steel of a very high carbon content was difficult to produce because the air rapidly burned out the excess carbon. Hereby steels up to 2% carbon, or all the iron can hold in solution, may be readily made. Such steels are very advantageous for razor blades, knives, surgical instruments and the like. They are mucheasier -to roll and are much harder after tempering than other steels. 'liey can be rolled thinner and do not burr on the e ge.

-proved through increase in ductillty; and through freedom from porosity can be rolled much thinner than formerly without developing pin holes. This is of great advantage for sheet for tin cans because the sheets can be much thinner but still rigid and free from porosity.

While one embodiment of the invention has been described, it is to be understood that the invention may have various embodiments within the limits of the prior art and the scope of the subjoined claims.

I claim:

1. The method of treating metals to produce sound castings of uniform predetermined purity which comprises, providing in an enclosed vessel a body of molten metal of predetermined purity free from gas inclusions, pouring the metal from the bottom into a mold in a solid column the full size of the mold with substantially the speed at which the metal falls by gravity but without space separation of the metal, partially solidifying the metal to form a retaining shell the full length of the casting, and thereafter forcing a cooling gas through the shrinkage space froml one end to the other between the mold and casting to accelerate the. normal rate of solidiflcation.

2. The method 'of treating metals to produce sound castings of uniform predetermined purity which comprises, causing the molten metal to circulate to the surface by heating free from contamination until the metal is free from gas inclusions, pouring the metal from the bottom -into a mold in a solid column the full size of the mold without space separation to fill the mold substantially instantaneously, partially solidifying the metal to form a retaining shell the full length of the casting, and forcing air through the space from one end to the other between the casting and mold after partial solidiilcation' to accelerate the normal rate of solidication and thereby inhibit excess crystal growth.

3. The method of treating metals to produce sound castings of uniform predetermined purity which comprises, causing a body of molten metal in a vessel closed against inflow of air to circulate to the surface by heating free from contamination until the metal is free from gas inclusions, and pouring the metal from the bottom through an opening the full size of the mold to flll the mold substantially instantaneously but without space separation of the metal.

4. The method of treating metals to produce sound castings of uniform predetermined purity which comprises, heating a body of the molten metal in a high frequency induction furnace closed against the inflow of air until all of the gases are eliminated, pouring the killed metal without space separation upon a piston in a vertical mold while withdrawing the piston substantially with the speed of gravity to fill the mold almost instantaneously, and accelerating they cooling of the casting by forcing a cooling gas through the shrinkage space between mold and casing after a shell forms on the casting.

5. The method of treating' metals to produce sound castings of uniform predetermined purity which comprises, heating a body of the molten metal in an induction electric furnace closed against the inflow of air which circulates the metal to the surface until substantially all the gases are eliminated, pouring the killed metal without space separation upon a refractory surfaced piston in a vertical mold while withdrawing the piston with such rapidity that substantially none of the metal solidifies until after the mold is completely'filled, allowing the metal to solidify until a shell is formed on the surface, dropping the casing until lthe shell uncovers an air space to force air up through the shrinkage space betweenmold and casting, and thereafter removing the casting from the mold.

6. The method of treating metals to produce sound castings of uniform predetermined purity which comprises, lling a vertical mold substantially instantaneously with molten killed metal the full size of the mold without space separation from the body of supply metal, and solidifying the metal at a substantially uniform rate over the entire mold-.facing surface, first by rapid cooling through the mold walls until a shell is formed throughout the length of the casting, and then by a stream of harmless cool- `ing fluid directed through the shrinkage space from one end of the casting to the other.

'7. Apparatus for treating metals to produce sound castings, comprising in combination, a closed electric induction furnace for producing a forced circulation of metal to the surface to eliminate all gas inclusions, a vertical mold pro-1v vided with a cooling gas opening near its bottom, a pouring opening in the bottom of said furnace the size of said molda piston in said mold, means for lowering said piston suddenly to a point just above said -gas opening and for thereafter lowering the casting to said gas opening to permit gas to be forced through the shrinkage space between the mold and casting.

8. Appparatus for treating metals to produce sound castings, comprising in combination, a closed vessel for maintaining a body of killed molten metal, said vessel being provided with a bottom nozzle and removable plug therefor, a

mold below said nozzle, a liquid metal seal bey endof the pistonto prevent escape of gas when Athe piston moves down further to uncover said gas inlet to the sides of the casting.-

9. Apparatus for treating metals to produce sound castings, comprising in combination. a vertical mold, means to fill said mold very rapidly in a column the full size of the mold, said means including a close-fitting piston in the mold, and a cooling gas inlet in the side of the mold which admits cooling uid around the sides of the casting when the piston passes the inlet.

10. Apparatus as set forth in claim 9 which further includesmeans to force cooling fluid under pressure to said inlet to ow up along the casting and out at the top of the mold.

JEAN HUBERT LOUIS DE BATS.

CERTIFICATE OF CORRECTI Q N'.

Patent No. 2,257,715. eptember 5o, 19141.

JEAN HUBERT LOUIS DE BATS.

It is hereby certified that error appears in the printed .specification of' the above numbered patent requiring correction as follows: Page 2, first column, line4 8, for the word "far" read `I `or; line l5, for "furnace" read surface; page 5, second column, line l2, claim 5, for "casing" read -casting-; 'rection'therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this lith day of November, A. D. l9hl.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

and 'that the'said Letters Patent should be readwith this cor-V

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