US1614862A - Method of casting - Google Patents

Description

' -higher fusin Patented Jan. 18, 1927.

UNITED STATES PATENT OFFICE.

I DOUGLAS '1. BEATTY, OF BIRMINGHAM; ALAFAMA, ASSIGNOR TO SAND SPUN PATENTS CORPORATION, OF WILMINGTON, DELAWARE, A CORPORATION OF DELAWARE.

METHOD OF CASTING.

No Drawing. Application filed May 15, 1925, Serial No. 30,609, Renewed June 25, 1926.

This invention is an improvement in methods of casting hollow bodies centrifugally, and more particularly in methods to prevent defacing of the inner surface of the casting through deposits of scruff and other impurities.

One of the problems involved in casting .hollow metallic bodies, such as pipe, centrifugally is the tendency to the deposit of impurities, of specific gravity lower than that of the metal, which collect on the inner surface of the casting, usually near the ends.

(kids to a greater or less degree in accordance with the nature of the metal, are continually forming on the surface while the molten metal is exposed to the atmosphere, and these together with other impurities, such as sand, slag and the like, because of their low specific gravity collect on the inner surface of the casting, in the form of scurf, scruff or scoria. There is an especial tendency toward the formation of oxids during the rotation of the casting about its axis. As the fluid metal is carried up in the rotation, small particles are detached, and fall back into the molten metal at the bottom. In their fall through the mold atmosphere, which contains oxygen, a film of oxid forms on the surface, and since the fusing point of the metallic oxid is higher than that of the metal, the particles are not reincorporated in the molten bath into which they fall.

The impurities of low specific gravity, which under the combined influence of gravity and centrifugal force eventually attain the inner surface of the casting form a film, the fusing point of which like that of .the film on the particles is higher than that of the metal, and the molten interior of the particles which is relatively pure metal, when it reaches the molten bath of similar metal, is separated therefrom by two films of a point. Hence the relatively pure metal 0 the particle does not meet the relatively pure metal of the bath, to be reunited therewith in intimate union.

Such particles, or a relatively large proportion thereof, do not wholly penetrate the 'lining film of the casting, which film when cooled is scruff or scoria, but aggregate ithemselves with the same, greatly increasing the specific gravity of the film, so that it more nearly approaches that of the metal in the casting.

Because of this approach to thesame specific gravity of scruff and casting, there is not the clear separation between the two that is desirable. The union between the scruff layer and the casting wall is relatively intimate, the scruff bedding itself somewhat deeply into the casting wall, with a consequent weakening thereof, and pitting of the wall when the scruff is removed.

Many attempts have been made to remedy the conditions, which lead to the formation of scruff, and to the conditions above noted. It has been proposed to envelope the metal in a deoxidizing atmosphere, such for instance as carbon monoxide, hydrogen, steam or the like. This however is a process of some difficulty, requiring special machinery, and if entirely successful in the prevention of oxid formation, it does not in any way affect the other impurities which may be 75 present, and which have a part in the formation of the scruff.

It has also been proposed to introduce at a suitable stage in the casting, an enameling material, in the endeavor to limit to some extent the formation of the scruff, and cover and concealthe imperfections it causes with a coating of enamel on the interior of the casting. V

This process however, does not prevent the increase in specific gravity of scruff by the aggregation therewith of metallic iron, and

the consequent blurring of the line of separation between the scruff and the casting wall. The coat of enamel also materially alters the appearance of the inner surface of the casting, so that it no longer presents the desirable natural iron color.

One of the primary objects of the present invention is the provision of a method of casting, wherein the impurities of the molten metal are converted into an extremely fluent slag with a very low melting point, which forms a coating on the surface of the molten metal, cooling into a superficial loo soluble facing on the inside of the casting.

Another object is the provision of a method, wherein the means for converting the impurities into slag is of such nature and so introduced that a non-oxidizing atmosphere is established and maintained in of demarcation betweenthe scruff and the metal, thus facilitating the removal of the scruff, and eliminating pitting.

Other objects will be in part obvious, and in part pointed out in the detail description, it being understood that many changes may be made in the materials used, in the proportions and in the time and order of their introduction, within the scope of the apl for the mold atmosphere.

pended claims. Inthe usual procedure of casting hollow bodies centrifugall the molten metal in a desired state of fluidity is introduced into a refractory mold of any suitable character, such as sand, and the mold may be, either inclined at the commencement of the introduction, or otherwise placed, as maybe desired.

During the introduction, and for a time afterwards, the pipe is rotated at selected speeds, the rotation causing the metal to flow circumferentially of the mold, and to distribute itself evenly and uniformly over the mold surface, from end to end thereof.

The impurities, such as oxids, sand, slag, and the like, are of lower specific gravit than the metal, and as a 'conse uence they collect on the inner surface of t e casting usually near the ends, cooling into stiff, heavy, viscous facing of scruff or scoria, more or less intimately attached to the metal of the casting. The coating is somewhat difficult tov remove, and because the line of demarcation between the coating and the metal is not uniform, pitting and weakening of the casting wall may result.

I have discovered that by introducing any selected one or more of a number of materials of the character known as fluxes into the mold while the metal is still fluid, and preferably at some period of the pouring operation, a number of very desirable ends may be attained, among which may be mentioned the scavenging of impurities from the molten metal and the scavenging of oxidizing gases from the mold.

The fluxes have a very lowfusing point,

' and immediately they strike the molten enging the mold, and establishing and main-' taining an atmosphere which is at least inactive, so-that nofurther oxidization of the surface metal will take place.

Because of thelow specific gravity of the slag, it remains on the surface of the molten metal, picking up the impurities as they are moved under the influence of gravity and centrifugal force to the interior of the mold, and because of its low fusing point, it remains liquid until long after the metal'is set, continuing to evolve inactive gases, and to, function as scavenger for the metal and There is a wide divergence in specific gravity between the slag produced by the flux and the metal,so that there is no tend ency toward an intimate union between the two, and the line of demarcation is well defined, and substantially uniform, thus enabling the easy separation and removal of the slag, leaving a clean iron surface of the natural color.

The coating of slag is wholly superficial, with none embedded in the casting wall. When the casting is cooled, the coating is easily removed, adhering but loosely to the wall, and detached by jarring or scraping. The coating is.in fact soluble in water, and may be removed by water treatment if desired.

The fluxing or slagging material may be introduced in any suitable manner, and at any stage while the metal is fluid. Obviously, however, the earlier it is introduced and the nearer to the ladle the point of introduction, the less opportunity there will be for the formation of oxids, and the longer time for the performance of the intended function.

Preferably the introduction of the said material is simultaneous with the introduction of the molten metal into the mold. When casting in an inclined mold, the flux may be delivered in a suitable stream onto the metal as it flows into the mold. When casting in molds'otherwise arranged, the

' point and time of introduction will be governed by conditions, and the ends to be attained.

Any suitable fiuxing compound may be used, such as sodium-tetraborate (common borax), sodium chloride (table salt) or crude sodium carbonate (soda ash). In some "respects, the last is preferable.

The quantity used depends to some extent upon the character of the metal, and the ends sought. With soda ash, the quantity for a 12 foot length of i to 6 inch pipe-will vary from A,, to 1 pounds. Usually about (pound is sufiicient. Soda'ash in pulverize form is preferably placed on the metal in the ladle just prior to casting. The soda ash fuses or melts down and becomes fluid at a relatively low temperature, so that it is almost immediately converted to a fluid .state, floating on top of the molten iron, and

running into the mold with the iron, while retaining its surface position. i

The gases given off during the slagging procedure, which is not entirely complete when the met-a1 enters the mold, provide an inactive atmosphere in the mold. The slag floats on the inner face of the pipe, and works its way toward the ends of the pr'pe or casting, just as thescruif has always done, and it may be easily removed after the cooling of the casting.

It will be evident from the description that the flowing molten metal is surface coated with a fluxing or slagging material during charging of the mold. The slag formed collects to itself the scruff, foreign material such as sand, and the oxidized iron, holding them in suspension on the surface of the iron. The formation is a true slag containing no metallic iron, and leaving beneath it a smooth surface when removed.

The desirable results attained by the use of the fluxing or slagging material, introduced at the time, and in the manner described are manifold. Considered merely as a blanket of fusible material lying on the molten surface, the slag prevents access of air to the metal, and the consequent formation of oxids. ever, there is in addition an evolution of inactive gas, produced by the reaction of the fused sodium carbonate with such silica as may be present, represented by the formula,

1 iron. Metal particles falling back from the top of the moldinto the metal below are not oxidized in their fall, and pass readily through the thin slag blanket into theclea-n pool of metal, and are integrally incorporated therewith. After cooling, the slag may be dissolved in water, and the entire deposit will be superficial, with none embedded in the metal. When entirely cooled, the slag is brittle like glass, and when removed exposes the natural clean face of the metal.

The castingsproduced in accordance with the method are of exceptional soundness, and homogeneity and free from all foreign materials. These desirable characteristics, are

With the material used howdue to the fact that the molten iron is in condition of exceptional fluidity, enabling castings of greater tensile strength are obtained than by the usual methods, and with economy of operation. There is a saving of fuel, in that the desired temperatures are more easily obtained with the use of the slagging material. That is the metal can be poured at a lower temperature than former ly, on account of the lack of resistance from scruff.

Because of the fact that the metal is purified in the practice of the method, iron with a relatively low carbon content may be used in the casting and perfect distribution obtained, which permits the making of castings of greater tensile strength without sacrifice of ability to resist bending stress, since the tensile strength of cast ironis controlled by the carbon content.

No claim is made in the resent application to the product produced by the method, the product being the subject matter of a separate application filed on June 10th, 1926, Serial No. 115,117.

I claim:

1. The step in the method of centrifugally casting= hollow bodies, which consists in evolving inactive gas within the mold during the introduction of the molten metal, thereby to eject oxidizing gases which may be already present.

2. The step in the method of casting hollow bodies centrifugally, which consists in introducing with the molten metal a material forming when fused with silica a non-oxidizing gas thereby to eject oxidizing gases which may be present.

3. The step in the method of casting hollow bodies centrifugally, which consists in introducing with the molten metal a fluxing or slagging material forming when. fused with silica a non-oxidizing gas thereby to eject oxidizing gases which may be present.

4. The step in the method of casting hollow bodies centrifugally, which consists in introducing into the'mold while the metal is still fluid a fluxing material capable of evolving a non-oxidizing gas during fusion with silica, and capable of forming withoxids and other impurities which may be present in the molten metal a slag.

. 5. The step in the method of casting hollow bodies centrifugally, which consists in introducing into the mold while the metal is fluid a material forming when fused with silica a non-oxidizing gas and combining with the impurities of th metal to form a slag thereby to simultaneously scavenge the mold and the metal. 7

6. The step in the method of casting hollow bodies centrifugally which consists in introducing a flux with the molten metal.

7 The step in the method of casting hollow bodies centrifugally, which consists in introducing into the mold a flux, while the metal is fluid.

8. The step in the method of centrifugally casting-hollow bodies, which consists in floating a fluxing or slagging material on the flowing metal while the mold is being charged.

- 9. The step in the method of centrifugally casting hollowbodies, which consists in surface coating the flowing molten metal with a fiuxing or slagging material.

10. The step in the method of centrifugally casting hollow bodies which consists, in slagging the impurities while the metal is flowing.

11. The method of centrifugally casting hollow bodies which consists in slagging the impurities while the metal is flowing with a material evolving a non-oxidizing gas during fusing with silica.

12-. The step in the method of centrifugally casting hollow bodies, which consists in surface coating the flowing metal with a flux evolving a non-oxidizing gas during fusing with silica;

prises surface coating the molten metal dur- 10 ing the charging of the mold with a flux to convert scrufl forming im urities into slag, and1 removing the slag w en the casting is coo a 15. The step in the method of centrifugally casting hollow metallic bodies in refractory molds, which consists in adding to the flowing metal a flux capable of forming with the impurities thereof a fluent slag to blanket the surface of the metal in the mold against oxidization by the air.

16. The step in the method of centrifugally casting hollow metallic bodies in refractory molds, which consists in adding to the flowing metal a flux capable of forming with the impurities thereof a fluent slag to blanket the surface of the metal in the mold against oxidization by the air, and capable of evolving when fused with silica an inactive gas to drive out the gases in the mold, thereby to establish and maintain a non-oxidizing atmosphere.

Signed at Birmingham in the county of Jefferson and State of Alabama, this 5th day of May, A. D. 1925.

DOUGLAS T. BEATTY.