US3024507A - Method of vacuum casting - Google Patents

Description

March 13, 1962 J. B. GERO 3,024,507

METHOD OF VACUUM CASTING Filed July 30, 1959 2 Sheets-Sheet 1 I I l I r l I l l FIG. 2

ATTORNEY INVENTOR v 4+ I //BY J? gr (75 I March 13, 1962 J. B. GERO 3,024,507'

METHOD OF VACUUM CASTING Filed July-30, 1959 2 Sheets-Sheet 2 i INVENTOR a. 23/01 BY ATTORNEY United States Delaware Filed July 30, 1959, Ser. No. 830,983 5 Claims. (Cl. 22-209) This invention relates to methods and apparatus for vacuum casting of molten metals and, especially, to vacuum casting of heavy forging ingots and the mass production of rolling ingots wherein gaseous components of harmful nature are in part removed from the molten metal during the period that the molten metal is being poured into an ingot mold or ladle.

The invention, in one preferred form is directed especially to treatment of molten steel in that state which is commonly referred to as unskilled. This term is employed to distinguish a molten steel in which certain gases are present in a relatively uncombined state as contrasted with a molten steel in which gases have been caused to combine with a material such as aluminum to provide a so-called killed metal. It should be understood that the invention is not, however, limited to this or any other particular application.

Degassing of large forging ingots during the pouring operation is a more recent development of vacuum casting and is employed primarily for the removal of hydrogen from killed steels in order to diminish the susceptibility of a steel to form internal hair-line fissures commonly referred to as flakes during cooling cycles to room temperature from the hot working temperature.

Degassing is conventionally carried out at the present time by utilizing a special vacuum chamber in which is mounted an ingot mold or a ladle. This vacuum chamber necessarily comprises a heavy housing structure usually made up of a top section and one or more lower sections which can be secured together in sealed relationship in order to make these sections airtight. For sealing purposes, having regard for the high temperature conditions which exist in pouring molten metal, it is customary to employ heavy rubber sealing rings. These rings are located in suitable sealing flange portions which extend around outer peripheral surfaces of the sections in protectively spaced relationship to hot metal passing into the ingot mold during a pouring operation, Water cooling may be employed in some cases.

In a conventional structure of this class, the top section of the vacuum chamber is provided with a pouring aperture which is normally closed by a fusible diaphragm. After a vacuum has been created in the housing structure, hot metal is transported to a pony ladle located on the top of the chamber housing. As the hot metal is poured into the pony ladle, the heat of the metal will, after a short interval, melt the diaphragm and the molten metal falls into the chamber. The vacuum within the chamber operates to disperse the metal into molten droplets and to remove gases such as hydrogen and limited amounts of oxygen and nitrogen.

It.is found that establishing a satisfactory vacuum with such a form of vacuum casting apparatus is a costly and complex procedure requiring expensive equipment and careful manipulation to maintain a satisfactorily high vacuum. The vacuum must be capable of being held in the presence of very high temperatures, either for short or long periods, and the equipment should be of such construction that it may be simply and quickly spaced in an operative position for the production of large forging ingots or small rolling ingots and readily disengaged when not in use. Existing equipment does not meet these requirements. It is also pointed out that, if it becomes necessary to vacuum pour more than one ingot "atent O from each ladle or heat, a series of vacuum chambers are necessary further complicating the problem.

It is an object of the invention to improve methods and apparatus for vacuum casting and to devise means for more effectively and quickly establishing and maintaining a vacuum in order to produce quality steels with desirable magnaflux and micro-cleanliness ratings and better physical properties to permit production vacuum pouring of multiple large or small ingots from one heat or ladle; and to make possible the development of new and unique alloys as a result of the removal of inclusion forming materials.

Another object of the invention is to devise a new combination of sealing compound and casting apparatus for vacuum casting whereby unusual sealing effects may be accomplished and also whereby the evacuation of air to produce a vacuum may be carried out in a highly convenient manner.

Still another object of the invention is to provide a method of vacuum casting in which chemically reactive materials may be introduced into a body of molten metal as it is being poured under vacuum to the end that there may be induced reactions tending to further reduce th occurrence of harmful gases.

A further object of the invention is to devise a method of vacuum casting in which the percentages of reactive alloying elements used in forming desired alloys of steel may be modified or controlled while a vacuum is in effect to provide desirable results.

Another object is to control the degree of vacuum exerted as well as to modify vacuum conditions by furnishing an atmosphere of predetermined chemical nature which may be conducted through a region of pourin and then evacuated.

The method and apparatus of the invention hereinafter disclosed presents several unique techniques for dealing with the problems outlined and accomplishing the foregoing objectives with respect to various types of vacuum casting. These techniques are, in preferred embodiments of the invention, based on the concept of creating a vacuum by evacuating gases through a sidewall portion of a molten metal containing pouring box from which molten metal is to be poured, and supporting such a box in airtight relationship for a limited period directly on an ingot mold. Thus, it becomes possible to eliminate a separate vacuum chamber which has heretofore conventionally enclosed the ingot mold and several other novel techniques arerendered feasible.

In this connection, it will be appreciated that an immediate obstacle to holding a box and mold member in sealed relation is the high temperature effect of the molten metal on any conventional sealing means which is capable of producing an airtight joint including the thermal shock and expansion of the mold.

I have discovered that a high vacuum seal may be produced and maintained for a short interval by a new technique which may be conveniently referred to as Transient Thermal Sealing. This technique may, I find, be accomplished by the use of special sealing means including a novel sealing compound which has the ability to temporarily resist flowing or decomposing from relatively intense heat conducted through the metal body portions of the pouring box and mold during the time interval which corresponds to the short period in which molten metal is passing from the pouring box to the ingot mold.

As an example of one sealing means which is suitable for this purpose, I may employ a new composition of matter comprising a mixture of three essential components(I) a low molecular weight glycidyl polyether, (II) a condensation product of a low molecular weight glycidyl polyether and ethylene glycol and ('III) a curing agent composed of pyromellitic dianhydride mixed with the anhydride of a dicarboxylic acid. When these components are combined in the hereinafter described proportions a resinous mixture is obtained which upon exposure to heat at elevated temperatures resists melting and cures to a solidified adherent elastic body. In addition to the above ingredients it may be desirable to include various fillers and a cure accelerating agent.

The composition of matter noted above is intended to be representative of sealing compound means which is sufficiently fluid to wet and adhere to metal surfaces of casting members; which is characterized by the ability to cure when brought into contact with metal surfaces heated to temperatures of from 250-500 F. to form a tough elastic adhesive; and which in this cured state is capable of resisting flowing or melting in the presence of much greater temperatures, i.e. 500l000 F. for a limited period of time corresponding approximately to an ingot pouring interval.

In combining the sealing compound described with a molten metal containing box in airtight relationship with an ingot mold, in accordance with the invention, there is, in effect, produced an exceedingly high vacuum sealed conduit through which molten metal may be conducted from the basket to the ingot mold.

By the expression exceedingly high vacuum, I refer to micron guage readings of an outer magnitude of as low as four (4) microns at the point where the vacuum pumping means blanks off. This micron reading is in contrast to optimum micron readings possible with conventional equipment of from 300-500 microns.

I further find that I may exert this exceedingly high vacuum at the conduit region in close proximity to the stream of molten metal which is poured from the basket and also in close proximity to the metal collecting in the ingot mold to produce unexpected results of great significance. The high vacuum, when thus exerted, not only disrupts and disperses the molten stream of metal in the form of a spray of fine particles, but also causes this metal, as it collects in the mold, to be vigorously agitated and to ebullate in a particular manner wherein portions of collected material continuously rise up around the inner surfaces of the ingot mold and fall over into the central portions of the mass.

I have further discovered that, by exerting a vacuum in the manner described, I am enabled to greatly increase the removal of harmful gases and to modify the percentage of alloying additive which may be retained in the steel. It is believed that the combined effect of removing gases as the stream is dispersed in the conduit region and also removing gases which are thrown up by the continuous ebullience produced is the reason for this improved vacuumizing, although this is stated by way of opinion only.

I have further discovered that I may introduce reacting materials directly into the conduit region Where the molten metal leaves the box and where some degassing takes place. I find that by bringing reactive materials in a suitable dispersed state into the conduit region and simultaneously dispersing the molten metal into minute droplets in the presence of these dispersed reactive materials, there may be carried out desirable chemical reactions in both the dispersed and collected material which reactions beneficially use up small quantities of harmful gases. Resultant reaction products are rapidly carried off through the vacuum equipment. I may also introduce alloying additives into the stream of molten metal as it is poured under vacuum, either during or after the use of reactive materials.

A further novel feature of this step of adding a material at the particular period indicated consists in the fact that substantially all of an alloying additive may be thus introduced and caused to serve its intended alloying purposes without undesirable side reactions taking place.

These and other novel features and objects will be more apparent from the following description of preferred embodiments of the method and apparatus as shown in the accompanying drawings, in which:

FIG. 1 is a side elevational view illustrating diagrammatically casting apparatus as employed in the invention;

FIG. 2 is a detail plan view;

FIG. 3 is a vertical cross-sectional view of the vacuum casting apparatus of the invention as it appears when receiving molten metal; and

FIG. 4 is a detail cross sectional view of a modified sealing arrangement.

Referring more in detail to these figures, numeral 2 denotes an ingot mold 2 of the invention having an ingot cavity 4 which tapers downwardly, as shown in FIG. 1. This mold member is preferably seated on a heavy fiat bottom stool 6.

At its upper side, the ingot mold is formed with a flat seating surface 8 which extends around the ingot cavity 4 to provide a support for a removable pouring box member, generally indicated by the arrow 10.

In accordance with the invention, I have devised as component parts of this pouring box 10 an upper metal containing section 10a and a lower conduits section 10b. These box sections are separated by a transverse wall through the center of which is formed a pouring aperture 12 which is normally closed by a fusible closure cap 14 of aluminum or other suitable material. The cap 14 is secured by bolts as 16 and 18. In the presence of hot metal discharged from a transporting ladle 22, shown at the upper side of FIG. 1, the closure member 14 becomes fused and will then allow the hot metal to flow through the aperture 12 and then through the conduit section 10b to finally be received in the mold cavity 4.

The lower conduit section 1% also receives an annular refractory hot top 19 which is necessary on all killed steels. The refractory 19 must be thoroughly heated and dried before placing on the vacuum mold. Of importance to the success of the invention is the seal 20 between the hot top and mold. The best seal to prevent the flow of steel between the mold and hot top is tamped steel wool. Wet refractory cements give off water and gas which makes trouble. Back pouring is the practice for open atmosphere pouring.

I further construct the box 10 with means for evacuat' ing gases through the conduit section 10b, as indicated in FIG. 1. The evacuating means includes a passageway formed through the sidewall portion of the conduit sec tion, as shown, and into which is tightly fitted a tubular member 26. Attached at some convenient point to the outer end of the tubular member 26 is a vacuum pump unit 29 of some conventional nature.

When the box 10 is arranged in the seated position shown in FIG. 1 and the vacuum pump 29 is started, air will be evacuated from the conduit section and the ingot cavity and a vacuum will be created when the high vacuum type seal of the invention is exerted between the pouring box and the mold. The effectiveness of my seal is indicated by the degree of vacuum attained. Normally I find an absolute pressure of forty microns is reached in about two minutes, and twenty microns in about four minutes. Pressures below ten microns are consistently reached in ten minutes. The lowest pressure developed has been four microns. Speed of pump down is extremely critical in pouring a series of molds. Time delays cause temperature losses in the molten metal and solidification or skulls in the ladle or box.

Another important feature of the invention is the method of so-called transient thermal sealing in which the sealing compound earlier noted is applied at the junction of the relatively hot seating surface 8 of mold 2. As utilized in the invention the sealing compound is employed in a substantially fluid condition so that it may be applied to the metal surfaces of the box and mold and will wet and adhere to these surfaces and penetrate slightly into the pores of the metal surfaces. It will be understood that the sealing compound is applied with the pouring box resting on the mold surface 8 and, in ordinary working conditions, the mold and box under usual foundry conditions will be at temperatures of from 200 F. to 500 F.

In FIG. 1, I have indicated the sealing body applied in one desirable form on the mold and box and denoted by the numeral 30. As is further shown in FIG. 3, the sealing compound occurs as an irregular mass of material which fills in around the outer line of junction of the mold and box in such a position that, while it effectively seals this region, it is, nevertheless, protected by the thickness of the box wall section as well as the thickness of the mold itself.

I have also discovered that the use of a sealing compound such, for example, as that indicated by the compound 30, may be very desirably carried out by utilizing specially formed surfaces at the portion of the mold which supports the pouring box. For example, as illustrated in FIG. 4, I may form a mold body 2a with a recessed portion 21), constituting in effect an annular groove extending all the way around the mold body 2a. This groove is of a radial width substantially exceeding the thickness of a pouring box section 10g. In this groove I locate a body of sealing compound 30a, which completely fills the groove so that the pouring box section 10g is embedded in the sealing compound and substantial portions of the body of sealing compound are present at both the inner surface 10f and the outer surface 10k. A second heat resistant sealing body is employed at the base of the mold, as indicated by reference character 10m in FIG. 3, and between the mold body and the flat bottom stool 6.

The purpose of this arrangement is to deal with and compensate for, the abrupt thermal expansion and contraction of the mold and box which takes place during the pouring of the molten metal. The sudden change in temperature may, I find, produce a rapid stress amounting to a thermal shock which, in some cases, operates to break down and render useless sealing means which have been tried in earlier efforts in the art to hold a seal. In the arrangement of a seat of the invention, the compound being of a compressible somewhat elastic nature, is compressed at one side of the other of the box 10g with the compound being squeezed between this member and an adjacent groove surface of the mold. This operates to preserve a sealing effect on one side of the box even though the seal is broken on the other side when the expansion occurs. In thus combining both an inner and outer sealing means with the inner and outer surfaces of the pouring box, a desirable cooperative effect is present by utilizing the refractory material 19 and the steel wool backing 20 to shield the sealing compound to a limited but desirable extent.

The sealing compound is of the class of compounds containing in general polyepoxide materials. Epoxy resins are prepared by the reaction of a dihydric phenol and epichlorohydrin in the presence of sufficient alkali to maintain the reaction mixture substantially neutral.

The predominant constituent of the reaction product is represented by the formula:

O the value of n decreasing as the quantity of epichlorohydrin is increased.

Considering for purposes of illustration the most widely employed dihydric phenol, bis (4-hydroxy phenyl) dimethyl methane (hereinafter termed Bisphenol A) the di lycidyl ether has the formula:

where n of Formula 1 is zero. By employing a mole ratio of epichlorohydrin to Bisphenol A of 10:1 the diglycidyl ether is produced in a fairly pure state. As the mole ratio is decreased the proportion of higher molecular weight polyethers increases. In general, mole ratios of 2:1 to 10:1 give average molecular weights of about 350 to 450. In practice it is found that though the size of the major portion of the polyether molecules may be controlled, some small proportion of longer and shorter length molecules will be present. In addition side reactions may occur with some formation of intermediates, but the quantity of these side products does not noticeably infiuence the properties of the resin.

In preparing the sealing compound 30 I produce component I, the low molecular weight glycidyl ether by using as a dihydric phenol, bis (4-hydroxy phenyl) dimethyl methane, having an average molecular weight of from 350 to 450. With other dihydric phenols this range will vary slightly. Referring to Formula 1 the average molecule of the ether will contain between 1 and 1.5 R's (aromatic radicals) and n will vary from 0 to. l. The epoxide equivalent (weight of resin in grams containing 1 gram equivalent of epoxy) should be between about and 225. Assuming the resin chains to be substantially linear with an epoxy group terminating each end, then the epoxide equivalent is One-half the average molecular weight. The viscosity of the polyether will vary from 5,000 to 20,000 c.p.s. as measured with a Brookfield LVT-SX viscometer with No. 5 spindle at 6 rpm. at 25 C. Many commercially available epoxy resins with suitable properties may be used. Among these are Bakelite ERL-2774 and Bakelite ERL-3794, Epi-Rez 510, Epon 820 and Epon 828. Bakelite is the trademark of Union Carbide Corp; Epi-Rez is the trademark of the Jones-Dabney Co., Div. of Devoe & Reynolds Co.; Epon is the trademark of the Shell Chemical Corp.

Component II is the reaction product of component I with a glycol, for example, ethylene glycol. The ratio of epoxy to hydroxy can be varied from l/0.5 to /2 with little effect on the finished compound. The reaction may be carried out by mixing the desired quantities of epoxy and ethylene glycol and heating to 150 to C. for 1 hour or until the mixture becomes homogeneous.

The product has a molecular weight of 385 to 485 and is believed to consist primarily of the product resulting from the reaction of one epoxide ring with an hydroxyl group of the glycol. Since component I can be considered to contain an average of two epoxy groups per molecule, it is quite certain that the primary condensation wherein R represents a divalent aromatic hydrocarbon radical and n is an integer. By varying the ratio .of epichlorohydrin to the dihydric phenol, compositions of varying molecular weight (varying n) may be obtained,

product resulting from such controlled conditions may be represented by the formula:

For convenience I shall refer to the condensation product as the 50% condensate of component I with a glycol.

Component II lends flexibility to my resin composition, but must be used in controlled amounts. I have found empirically that the ratio of component I to component II may vary from E o as with good results. When the quantity of component II is more than 88 parts, the resin after curing is gel-like and weak. When the amount of component II is less than 80 parts, the composition cures to a brittle, easily cracked material.

The third component (III) of my composition is a curing agent which acts to cross-link the epoxy compounds. The curing agent which I prefer to use is a mixture of a primary curing agent, pyromellitic dianhydride, and a secondary curing agent selected from the group of organic acid anhydrides. The anhydride mixture is used in stoichiometric quantities based on the amount of epoxy and hydroxyl groups present in the resin mixture. A slight excess, about is employed in the case of solid acid anhydrides to allow for uneven dispersion of the anhydride powders in the resin.

Anhydrides of dicarboxylic acids are well known in the art as curing agents and include phtalic anhydride, maleic anhydride, succinic anhydride, dodecenylsuccinic anhydride, and hexahydrophthalic anhydride.

Depending upon the particular anhydride curing agent used, the proportions of primary and secondary curing agents in component III may be varied within certain welldefined limits. I have found that 2 to 15 parts of pyromellitic dianhydride and 42 to 17 parts of secondary anhydride for every 100 parts of resin give satisfactory sealing materials for high temperature uses.

The manner in which component III is added to the epoxy compositions will depend upon the particular anhydrides in component III. Phthalic anhydride must ordinarily be passed with the resin through a colloidal mill to get a good dispersion. Maleic anhydride, on the other hand, is sutficiently fine to be mixed in by hand.

When it is desired to shorten the curing time, various well-known cure accelerators may be added to the composition. Among these are alphamethylbenzyl dimethyl amine, n-butyl amine, pyridine and N-methyl pyridine. These are used in catalytic amounts, from 0.5 to 3% of the weight of the resins in the composition.

In addition to the above basic ingredients it is advantageous to add various fillers to the composition to add body, adjust viscosity, increase thermal conductivity and hence achieve more even cure and lower the coefiicient of the thermal expansion. Among the fillers which can be used are atomized aluminum, iron, copper, aluminum oxide, silica powder, mica, and asbestos. Fibrous materials such as fine asbestos tend to bind the resin together and counteract differences in thermal expansion between the resin and the bonded metal. The quantity of filler may be varied from a few percent to three or four times the weight of the resin. The compounding manipulations are well-known to those skilled in the art.

The following examples illustrate the preparation of the compositions of my invention.

Example I A commercial epoxy resin, Epi-Rez 510" with the following properties was employed as component I:

Viscosity 12,000 cps. at 25 C Specific gravity 1.15.

Color 3 (Gardner Scale). Epoxide equivalent 185.

Hydrolyzable Cl 0.1%.

Component II is also a commercial epoxy resin, Epi- Rez 507 which is the condensation product of component I and ethylene glycol in the previously described ratios. It has the following properties:

Viscosity 550 cps. at 25C. Specific gravity 1.14.

Color 2 (Gardner Scale). Epoxide equivalent 385. Hydrolyzable Cl 0.15%.

Twelve parts of component I was blended with 88 parts of component II and 43 parts of phthalic anhydride and passed through a colloid mill to reduce the particle size of the phthalic anhydride to 0.025 mm. or less. Care must be maintained to keep the temperature below about 50 C. during passage through the mill. After cooling to room temperature 2.5 parts of pyromellitic dianhydride was added together with 55 parts of micronized silica, 35 parts of atomized aluminum, and 350 parts of short fiber asbestos. The mixture was thoroughly blended while maintaining the temperature of the mix below about 25 C. and 0.3 part of pyridine were added to the mixture to act as a cure accelerator. The composition was applied to two steel rods about 2.5 cm. by 1.25 cm. by 30 cm. and the steel rods were pressed together end to end. These rods were heated to 205 C. for 15 minutes to cure the composition. The rods were then raised to 315 C., allowed to cool to room temperature and heated again to 345 C. The resin bond remained strong with no cracks or thermal decomposition noticeable.

As a further test of the ability of the composition of Example I to withstand high temperatures, a sample of the composition which had been cured at 205 C. for 15 minutes was placed in contact with a surface at 315 C. for a period of eight hours. There was no evidence of serious charring or decomposition, and the sample retained its normal compressibility.

Example II Component I was prepared in the manner described in US. Patent No. 2,682,515, column 6 under the heading Polyether A.

Component H was prepared by adding 46.5 grams of ethylene glycol to 180 grams of component I. The reaction mixture was maintained at C. for 1 hour. Upon cooling there resulted a clear, low viscosity monofunctional-epoxy flexibilizer.

Sixteen parts of component I was mixed with 84 parts of component II and blended well at 25 C. To the mix was added 13.8 parts of pyromellitic dianhydride, 19.4 parts of maleic anhydride, 75 parts of micronized silica, 25 parts of atomized iron, and 150 parts of short fiber asbestos. After mixing well a homogeneous blend of milk-like consistency was produced. To this was added 0.4 part of N-methyl pyridine to act as a cure accelerator.

The composition was spread on steel rods and baked for 20 minutes at C. After carrying out the heating and cooling steps of Example I, the bond was found to retain its strength.

Though in the foregoing examples component II was in each case a condensate of component I and ethylene glycol, this need not be the case. Component II of Example I could have been substituted for component II of Example II and vice versa. It is only necessary that component II be approximately a 50% condensate of a glycol and a glycidyl polyether epoxy resin having a molecular weight between about 350 and 450, an epoxide equivalent of 175-225, between 1 and 1.5 aromatic radicals per polyether chain and a viscosity between 5,000 and 20,000 cps.

Also, though I have shown component I to be made from Bisphenol A and epichlorohydrin for purposes of illustration, other dihydric phenols are suitable. These include resorcinol; 1, l-bis (4-hydroxphenyl) ethane; 1, l-bis (4-hydroxyphenyl) propane; l, 1-bis (4-hydroxyphenyl) butane; 2, 2-bis (4-hydroxyphenyl) butane and l, l-bis (4-hydroxyphenyl) 2-methyl propane.

In operation, the mold and basket are assembled as shown and air is evacuated from the mold cavity and conduit section to provide a suitable vacuum. This vacuum is maintained in effect and hot metal M of the unkilled class referred to above is poured into the metal containing section 10a from the ladle 22. The heat of this molten metal melts the closure member 14 and the molten metal starts to flow through the passageway 12. As the hot metal enters the degassing chamber 20, it is instantly sub jected to disruptive forces produced by the vacuum described and the stream of entering metal is separated into a multiplicity of small metal droplets.

In this dispersed droplet state, gases such as hydrogen, nitrogen and oxygen, in the form of carbon monoxide, are drawn off by the vacuum forces. At the same time, the molten metal, as it collects in the ingot mold, is caused to continuously ebbulate and, in the course of this agitation, a further additional and important removal of gases takes place and especially there may be removed small quantities of carbon monoxide. The percent of gases in the metal may, I find, be desirably reduced in both of these ways, i.e., from the dispersed material and the collected material, and a highly significant reduction in carbon content may occur when the initial carbon content is low. This removal of carbon monoxide serves both as a deoxidation treatment for high carbon steels and as a decarburization treatment and deoxidation treatment for very low carbon content steels.

In accordance with a further important feature of the invention, I provide for further removal of gases for a short period after the actual pouring operation has terminated. I accomplish this novel step by introducing into the basket 10 special closure means for sealing the pouring aperture 12 from the upper side thereof at a point just before the last portion of molten metal leaves the basket so that the vacuum is either maintained or renewed and a secondary degassing takes place.

I find that, by means of this secondary or extended vacuumizing, I may produce a very low carbon steel of a type now exceedingly difficult to produce by conventional furnace practice. For example, I may provide for a carbon content as low as .05 and lower, as will be evident from an inspection of the following table.

Vacuum Material Convention- Casting by al Casting thetlnvenion Unkilled 10% 0. Steel Unkilled 20% 0. Steel I The period during which a required amount of metal suitable for filling the ingot mold will flow is of limited duration. In this short time interval, the heat which flows toward the sealing compound 30 does not reach a maximum intensity until the desired vacuumizing has been accomplished. This usually requires about twenty minutes after all of the metal has passed into the mold. This also allows sufiicient time for the solution of any alloy additions. At this point, the heat flow reaches an intensity causing the compound to decompose and become charred or volatilized.

In addition to removal of gases by connecting a vacuum member into the conduit section, I am also enabled to realize other advantages. For example, I may introduce alloying additions into the molten metal as it passes through the conduit section into the ingot mold. As shown in FIG. 2, I may provide for this purpose a second tubular member 36 having a feed inlet suitably closed when not in use and through which additives may be passed. This tubular member is connected into the conduit section wall and may also include at its outer end a viewing piece 39. This viewing piece 39 enables an operator to observe conditions at the point where the metal is subjected to vacuum and dispersed and also permits a limited view of portions of the mold cavity.

It is pointed out that, by means of this arrangement, reactive materials which produce oxides or sulphides may have their reaction products removed by vacuum. By introducing material in the manner noted, there is an opportunity for the additives to combine with materials in the molten metal producing objectionable gases which are carried off in the vacuum stream. One chemically reactive material which I may add consists of misch-metal which acts to combine with sulphur in deoxidizing metal. Other materials which may be added for the purpose of alloying include titanium, vanadium, chromium and the like. It will be observed that, in thus introducing an alloying additive such as noted, there is found an opportunity to first remove undesirable substances present in the molten metal as it is poured and then the alloying additive may be dropped into the mass at a time when it can be most effectively employed.

From the above disclosure, it will be evident that I have discovered a new and desirable method of degassing which may also be carried out in conjunction with adding reactive materials as well as alloying additives. By means of these procedures, it is possible to produce better alloys of known type, as well as some new alloys.

It is pointed out that, by means of this vacuum sealing means described, it becomes possible to carry a highly simplified and efficient vacuum casting operation with saving in cost of handling, time consumed and equipment used. The two principal components are readily assembled and just as readily separated from one another when desired. It is pointed out that, with the vacuum effect exerted through the basket, there is eliminated the need of a special housing to form a vacuum chamber and, yet, a high efficiency may be realized.

While I have disclosed preferred embodiments of the invention, it will be understood that various modifications may be practiced within the scope of the appended claims.

This application is a continuation, in part, of my copending application, Serial No. 656,228, filed May 1, 1957 now abandoned.

Having thus described my invention, what I claim is:

1. In a method of vacuum casting the steps which include positioning an uncured plastic fiowable sealing material between the surface of a cast iron casting mold and the surface of a vacuum chamber having an upper sealable opening supported on the mold, subjecting the sealing material to heat conducted through the casting mold to provide a cured solid, elastic vacuum tight sealing mass extending around the line of junction of the casting mold and chamber conforming to the surfaces thereof, sealing said vacuum chamber and evacuating air from the chamber to provide a high vacuum, flowing molten metal through said upper sealable opening and through the evacuated chamber into the casting mold while simultaneously maintaining the sealing mass in sealing relationship between said surfaces for a period at least as long as the flowing interval, and subjecting said sealing mass to heat of increasing intensity which is transmitted from the molten metal through the casting mold to said sealing mass, said sealing relationship of said mass between said surfaces thereafter being destroyed.

2. A method as claimed in claim 1, wherein said mold is provided with a continuous well extending around said line of junction for receiving said surface of said 1 1 vacuum chamber, with said sealing material being positioned in said well against said surfaces.

3. A method according to claim 1 in which the heatresistant sealing mass includes a low molecular weight glycidyl polyether, a condensation product of a low molecular weight glycidyl polyether and ethylene glycol and a curing agent.

4. A method according to claim 1 in which the heatresistant sealing mass includes a low molecular weight glycidyl polyether, a condensation product of a low molecular weight glycidyl polyether and ethylene glycol and a curing agent composed of pyrometllitic dianhydride mixed with the anhydride of a dicarboxylic acid selected from the group consisting of phthalic anhydride, maleic anhydride, succinic anhydride, dodecenylsuccinic anhydrided, and hexahydrophthalic anhydride.

5. A method according to claim 1 wherein the destruction of said sealing relationship is caused by thermal decomposition of said sealing mass.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Epoxy Resins their Application and Technology by Henry Lee Kriss Nelville (1057), pages 260-270 relied upon.

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