US3693698A

US3693698A - Method of casting volatile metals

Info

Publication number: US3693698A
Application number: US811450A
Authority: US
Inventors: Angel Tontchev Balevski; Ivan Dimov Nikolov
Original assignee: Institute po Metaloznanie i Technologia na Metalite
Current assignee: Institute po Metaloznanie i Technologia na Metalite
Priority date: 1968-04-05
Filing date: 1969-03-28
Publication date: 1972-09-26
Anticipated expiration: 1989-09-26
Also published as: NL156947B; NO132527C; NO132527B; DK128441B; FR2005617A1; AT292933B; SU438161A3; NL6905344A; LU58324A1; CH507760A; BE731038A; GB1261753A; SE365437B; DE1917356A1

Abstract

A method of casting of metals wherein the metal is heated under a pressure sufficient to prevent evaporation or disassociation, is transferred to a mold while the pressure is maintained and is finally cooled under the aforementioned pressure. Thereafter, the pressure is reduced to allow removal of the cast article.

Description

Balevski et al.

3,693,698 1*Sept. 26, 1972 METHOD OF CASTING VOLATILE METALS Inventors:

Assignee:

Notice:

Filed:

Appl. No.:

Angel Tontchev Balevski; Ivan Dimov Nikolov, both of Sofia, Bulgaria lnstitut p0 metaloznanie i technologia na metalite, Sofia, Bulgaria The portion of the term of this patent subsequent to Oct. 6, 1987, has been disclaimed.

March 28, 1969 Foreign Application Priority Data [5 6] References Cited UNITED STATES PATENTS 3,196,501 7/1965 Balevsky et al ..164/1 19 3,420,291 1/ 1969 Chandley et al ..164/1 19 X 3,380,509 4/1968 I-Ientrich et al. ..164/306 X 3,532,154 10/1970 Balevski et a1 ..164/119 2,434,775 l/l948 Sosnick ..75/20 FOREIGN PATENTS OR APPLICATIONS 989,353 4/1965 Great Britain ..164/312 Primary Examiner-J. Spencer Overholser Assistant Examiner-V. Rising Attorney-Karl F. Ross [57] ABSTRACT A method of casting of metals wherein the metal is heated under a pressure sufficient to prevent evaporation or disassociation, is transferred to a mold while the pressure is maintained and is finally cooled under the aforementioned pressure. Thereafter, the pressure is reduced to allow removal of the cast article.

2 Claims, 4 Drawing Figures April 5, 1968 Bulgaria ..9749

164/133, 164/258 Int. Cl. ..B22d 27/14 Field of Search ..164/1 19, 306

PATENTED P I 3.693.698

sum 1 or 2 1 Angel 71 Balevski Ivan D. Niko/0v F 4 INVENTORS'.

BY Russ I Attorney PATENTEDSEP26 I972 SHEEI 2 [IF 2 Angel I Ba/evski Ivan D. Niko/0v INVENTORS.

METHOD OF CASTING VOLATILE METALS The application relates to application, Ser. No. 667,409 filed Sept. 13 1967, now US. Pat. No. 3,532,154.

The invention relates to a method and an installation for obtaining castings from materials which evaporate or disassociate intensively at the temperature at which it is poured in the mold or from materials which may contain components which evaporate or dissociate intensively at that temperature, or even before this temperature is reached.

It is known that it is possible to obtain alloys as easily melting components are melted and their hardly melted components are added to molten material in which they disolve themselves. However, this possibility is strongly limited because ordinarily, with the increase of the concentration of the high melting components, the melting temperature of the alloy as a whole also increases. Thus, before obtaining the desired composition it is necessary to raise the temperature to such a degree at which large and noncontrollable losses of some of the components may take place as they start to evaporate intensively, or, in certain cases, even begin to sublimate. Because of this it has been considered impossible to obtain castings out of alloys of easily evaporating components with a considerable content of high melting components.

With other materials, processed by foundry techniques, difficulties arise due to their tendency to dissociate slightly before the temperatures at which they become sufficiently pourable, is reached. Sometimes difficulties arise even in the production of such materials; these difficulties resemble the abovedescribed dificulties with the metal alloys i.e. some of the initial components are disposed to dissociation even before reaching the temperature needed for the obtaining of the material for foundry practices by bonding of these components.

In practice the evaporation or the dissociation is limited to a certain extent by covering the surface of the molten material by a layer of flux or surface-active protective means. The layer of flux hinders the outflow of vapors or the disintegrated products of the molten material, but only until the vapor, or the dissociational pressure, reaches the atmospheric pressure. At higher pressure the flux layer breaks through and in this way loses its protective effect.

The melting of the components inside an autoclave, of course, with the use of flux, creates the possibility of obtaining the alloy under an increased pressure, at least equal to or higher than the vapor pressure of the easily evaporating component at the temperature necessary for obtaining of the alloy or, respectively, the dissociation pressure of the easily-diassociating material. The autoclave melting however still does not solve the problem for obtaining castings of such material, because when the pressure is lowered the molds are poured at atmospheric pressure, the above-described undesirable effect of evaporation or dissociation of the easily evaporating or easily dissociating components will inevitably take place. To enclose in an autoclave the entire system of melting, the foundry mold and the connection pipes represent only a theoretical possibility for solving this problem, as the realization would be an extremely expensive arrangement which in principle would be in a position to make only single castings.

, to the pouring of themolten material into the mold and the removal of the pressure after the solidification of the finished casting, in order to take it out of the mold, also will have as a consequence an evaporation or a dissociation, as well as an eventual boiling of the molten material.

The object of the invention is a method for obtaining castings by which the above-described disadvantages are eliminated, i.e., a method for obtaining of castings from materials in an arbitrary interrelation between the temperatures of melting, or evaporation or of dissociation of these materials or of their components.

According to the invention, this is achieved by carrying out the entire process from the point of heating of the initial solid material or components thereof for melting, or at their combining together, in order to obtain the cast material, up to the point of the removal of the solidified castings from the foundry mold under a regulated gas pressure. At that the gas which exerts thepressure, is selected according to its chemical attitude towards the melted components, as the magnitude of the pressure is regulated according to the requirements of the individual phases of the process itself, but always remains sufficiently large in order to prevent an evaporation, or a dissociation. At that, the pressure continues to act above the molten material even then, when it ceases to act above the solidified casting.

In applying the method according to the invention it is possible to utilize the gas pressure which is already created in the installation for the introduction of the molten material into the mold. It is sufficient to increase this pressure from the side of the reservoir holding the molten material, or to lower it from the side of the foundry mold, in order to generate a difference of the pressures giving rise to a flow of the molten material towards the foundry mold with velocity depending on this difference.

Without changing the substance of the method according to the invention, other known methods for introducing of the molten material into the foundry mold may be used, such as gravitational, by turning the installation in such a way so that the molten material pours from the reservoir into the mold, or by means of a piston pressure.

The invention is further clarified by means of the accompanying drawing, in which:

FIG. 1 is a vertical section through an installation for the realization of the method according to the invention, in which the molten material is introduced into the mold under the action of a gas pressure;

FIGS. 2 and 3 are vertical sections of an installation acting gravitationally; and

FIG. 4 is a vertical section of an installation with a piston pressure.

The material to be poured, or its components, is placed in the crucible 1 which, together with the heating device 2, is closed hermetically in the chamber 3. The pipe 4 intended for pouring of the molten material closed by the device 5 in such manner that with the gradual increase of the temperature inside the chamber 3 the pressure in it may be raised by feeding a cornpressed gas from the reservoir 6 through the

valves

7 and 8. At the same time the valve 9 is closed, while the valve 12 is opened, so that the chamber 10 is under the atmospheric pressure, which permits necessary auxiliary operations using the foundry mold 11.

When the molten material is ready, the chamber 10 and the mould 11 are isolated from the atmosphere by closing the valve 12 and gas is fed to them from the reservoir 6 through the valve 9. In this way a constant gas pressure is created in the entire system which is sufficiently high in order to prevent evaporation or dissociation of the molten material. The partition 5 may be removed.

Furthermore, by inducing the desired difference of the pressure between chamber 3 of the reservoir for the molten material and the chamber 10 for the foundry mold, which may expediently be accomplished by means of an additional increase of the pressure inside the chamber 3, the molten material rises inside the feeding pipe 4' and fills the mould l1. Immediately after that the pressure inside the chamber 3 and chamber 10 equalize anew, for instance by an increase of the pressure inside the chamber 10 up to the pressure inside the chamber 3, at which the molten material inside the feeding pipe returns into the reservoirl for the molten material. Now the partition 5 may be closed and inside the chamber 10 for the foundry mold, steps may be taken for an accelerated cooling of the filled mold 11; after the solidification of the casting the pressure is dropped by closing the valve 9 and opening the valve 12. After this is done the completed casting may be taken out of the mold 11. The process is repeated as after replacing ofv the empty mold, the pressure inside the chamber 10 being raised again by opening of the partition 5 and a new portion of the molten material being forced into disassociation mold 11.

The process may be carried out in practice without losses due to evaporation or diassociation if the free surface of the molten material in the reservoir 1 is protected by a layer of expediently selected flux. Inasmuch as the gas pressure inside the chamber 3 is maintained higher than the vapor pressure, or the dissociational pressure, of any of the components of the founding material, the protective flux layer remains unbroken and no elimination of vapor or of products of dissociation will take place. An equivalent embodiment of the installation for the realization of the method may be obtained by a hermetical enclosure of the crucible containing the melted founding material. In such a case by analogous control of the pressure inside the crucible the same process may be realized, as the heating device and the chamber in which it is placed, may be left free under atmospheric pressure.

It is evident from FIGS. 2 and 3 that the gravita tionally acting installation for the fulfilment of the method according to the invention, possesses the basic elements of the installation of FIG. 1 and retains the technological sequence of the operations, while for the pouring of the molten material into the mold it is necessary that the entire arrangement be revolved from the position shown at FIG. 2 to the position shown at FIG. 3. The reservoir for the molten material is closed hermetically so that it is unnecessary for the reservoir, together with the heating device 2, to be enclosed to the chamber as in the case with the installation shown in FIG. 1. The components of the founding material placed in the crucible 1 of the installation shown in FIG 2, are heated by means of the heating device 2 and thy are subjected under the action of the gas pressure given rise to by the gas reservoir 6 on opening of the

valves

7, 8 and 9, this pressure being sufficiently large so that it does not allow the evaporation or the disassociation of the founding material, or any of its components at the temperature which must be reached in order to fulfill the pouring of the material. Upon the attainment of this temperature, the arrangement is revolved to the position shown at FIG. 3, with the partition 5 kept opened, in order to fill in gravitationally the foundry mould 11 with the molten material.

In completing the casting of the material the partition 5 is closed. By an expedient forming of the feeding pipe 4 this closing may be done after revolving of the arrangement back to the original position (FIG. 2) and by closing of the valve 9 and opening of the valve 12, the already solidified casting may be taken out of the mold 11, which is not under pressure.

If in the path of the molten material in the feeding pipe 4 is placed a dosage cylinder 13 (FIG. 4) with a moving piston 14, then part of the molten material, which has found its way into this cylindrical by the action of the difference of the gas pressures, may be forced into the mold by displacing the piston 14. A dosage cylinder has a predetermined displacement per stroke to control material feed. The valve 15 makes it possible for the pressure behind the piston 14 to equalize with the pressure inside the melting chamber 3 inorder to enable the return of the remaining molten material in the feeding pipe back to the reservoir. Upon the completion of the stroke of the piston, atmospheric pressure is established inside the chamber 10 by the closing of the valve 9 and by opening of the valve 12. Then the casting may be taken out of the mold 11.

Every one of the described installations may be applied for casting of reaction-active materials, by chosing a neutral, respectively a reduction protective gaseous medium.

We claim:

1. A method of casting a volatile or disassociable meltable material at a temperature above its boiling or decomposition point, comprising the steps of:

a. melting said material in a first chamber and generating a pressure therein at a superatmospheric level sufficient to prevent volatilization of the molten material;

b. providing a mold in a second chamber communicating with the first-mentioned chamber;

0. mechanically blocking communication between said chambers while venting said second chamber to the atmosphere during melting of said material in said first chamber and the buildup of the pressure therein to said superatmospheric level;

d. disconnecting said second chamber from the atmosphere and raising the pressure therein from a source other than said first chamber to a superatpreventing superatmospheric pressure above the mospheric level less than the first-mentioned level molten material in both said chambers at all times to create a pressure differential between said and throughout steps and and chambers; g. supplying pressure from an external source to said e. thereafter mechanically opening communicatio 5 first chamber during step t malmflin the p between said chambers to drive the molten materi- Sure 531d first chamber cqnstam f f i fi t chamber i said Second 2. The method defined m claim 1 wherein said molchamber and said mold at least in part under the P mammal Permmed to flow y gravity to Said mold force of said pressure differential; p f. maintaining dissociation and evaporation 10

Claims

1. A method of casting a volatile or disassociable meltable material at a temperature above its boiling or decomposition point, comprising the steps of: a. melting said material in a first chamber and generating a pressure therein at a superatmospheric level sufficient to prevent volatilization of the molten material; b. providing a mold in a second chamber communicating with the first-mentioned chamber; c. mechanically blocking communication between said chambers while venting said second chamber to the atmosphere during melting of said material in said first chamber and the buildup of the pressure therein to said superatmospheric level; d. disconnecting said second chamber from the atmosphere and raising the pressure therein from a source other than said first chamber to a superatmospheric level less than the firstmentioned level to create a pressure differential between said chambers; e. thereafter mechanically opening communication between said chambers to drive the molten material from said first chamber into said second chamber and said mold at least in part under the force of said pressure differential; f. maintaining dissociation - and evaporation - preventing superatmospheric pressure above the molten material in both said chambers at all times and throughout steps (a) and (e); and g. supplying pressure from an external source to said first chamber during step (e) to maintain the pressure in said first chamber constant during step (e).

2. The method defined in claim 1 wherein said molten material is permitted to flow by gravity to said mold in step (e).