US1777657A

US1777657A - Method of forming ingots for working

Info

Publication number: US1777657A
Application number: US338955A
Authority: US
Inventors: Theron D Stay; Holzhauer William
Original assignee: Aluminum Company of America
Current assignee: Alcoa Corp
Priority date: 1929-02-11
Filing date: 1929-02-11
Publication date: 1930-10-07
Anticipated expiration: 1947-10-07

Description

. 6 5 1 7 7/ J c. b. a. m. 1/ /1 1 fa/A7 t 3 3 3 w 0 9 u m 2 2 2 a I 1 Oct. 7,, 1930. T. D. STAY ET METHOD OFFORMING INGOTS FOR WORKING Filed Feb. 11

Patented Oct. 7, 193

UNITED STATES PATENT OFFICE TEERON STAY, 01 CLEVELAND, AND WILLIAM HOLZHAUER, OF LAKEWOOD,

onro, assrenoas 'ro Ammnftm comumr or AMERICA, or PITTSBURGH, 2mm

BYL VANIA, A CORPORATION 01 PENNSYLVANIA 7 METHOD OF FORMING INGO'IS FOR WORKING Application filed February 11, 1829. Serial No. 338,955.

The invention relates to the formation of in ots which are subsequentl worked by ro ling, forging, extrusion, an the like, and has particularly to do with the formation of ingots of aluminum base alloys, with reference to which it is herein described.

In the production of aluminum base alloy ingots for working, it is desirable to JIVOlCl piping at the tops which necessitates cropping and corresponding scrap loss, and to avoid. segregation, liquation, and. porosity which ma arise from the variations in the solidification temperatures of eutectic and other constituents of non-homogeneous alloys or from other causes. On the other hand, it is desirable to produce such a gram structure throughout the ingots as Wlll best meet the requirements of the particular ma ner of working to which they are to be su jected, and such a grain structure as will result in the best physical properties of the worked metal.

Prior to our invention, as far as is known to us, the best results in the production of alumlnum base alloy ingots have been obtained by progressively cooling the molten metal from the'bottoms of the ingot molds upwardly, either by gradually lowerlng the molds into bodies of water, or by spraying water upon the molds beginning at their hottoms and advancing the spray upwardly upon the molds or the molds downwardly through the spray. As compared to natural cooling of the ingots accompanied by heading the molds with additional metal as the ingots solidify and shrink, this progressive cooling materially reduces the piping, lessens the tendency to segregation and liquatlon', and eliminates a part of the gas-occlusion porosity, as well as that due to shrinkage. However, the grain' structure of the ingots progressively cooled in the manner explained 1s unsatisfactory. It is unsuitable for some forms of metal working, and does not lend itself to the attainment of the best physical properties of the worked metal.

B cutting from end. to end many full size aluminum base alloy ingots thus progi'essively cooled, and pollshing and etching t e cut surface, we have found that they have rather coarse grain structures of irregular sizes, and elongate dendrite forms extending upwardly and inwardly from the outer faces to the centers of the ingots. In the commercial forging of such ingots corner and surface cracks frequently develop rendering the forged articles unsuitable for purposes where strength is required, for example for articles, such as airplane propellers, which in use are subjected to very rapid alternating stresses. Aside from this loss of strength due to such cracks, such worked metal ossesses substantially less tensile strength t an that produced according to our invention, and as will presently be explained by descriptions of comparative tests. Furthermore, due to the segregation, liquation and porosity characteristics of the ingots thus progressively cooled, metal at different parts of the ingots did not have uniform physical properties.

The object of our invention is to rovide a methodof forming, particularly 0 aluminum base alloys, ingots for working, the ingots having such grain structures, and such freedom from segre ation, 1i nation, and porosity that the wor ed metal I as high and uniform physical characteristics and does not develop surface and corner cracks while being worked.

Our invention is predicated on our discovcry that its stated object is attained by progressively. gradually and rapidly solidifying a. body of molten alloy metal in an ingot mold from its bottom to its top, while applying heat to the unsolidified portion of the metal above its progressively rising plane of solidification.

In the practice of our invention as appliedto the formation of aluminum base alloy ingots for working, an ingot mold of suitable form is suppliedwith molten metal at a temperature best suited to the formation of the lidifidd from the bottom to the top of the mold while heat is applied to the bed of the metal above its progressively rising p ane of solidification. Such solidification the metal may be accomplished-by gradually lowering the mold through a burner or series of burners which apply heat to its walls to keep the upper portion of the metal molten and at its desired temperature, and through a s ray or s rays of water applied to the mol below the burners to progressively cool the metal substantially in that portion of the mold lying in the horizontal plane passing through the s ray. In a simiar manner, the mold ma he gradually lowered through a burner or burners into a body of water below the burner, the body of water bein aised instead of spraying water upon the mo ld. As a further alternative, the mold may remain stationary within a series of alternating water sprays and burners which are individually controlled to cause the metal to progressively solidif in a gradually rising general plane while eing maintained molten above such plane. While gas or other fluid fuel burners are preferably used for heating the upper ortion of the mold and its contained metal, 1t will be understood that such heating may be effected electrically or otherwise.

Apparatus which may be and has been used in the practice of the invention in the several ways just explained is illustrated in the accompanying drawings, of which Fig. 1 is a vertical central sectional view of a mold passing downwardly through a heater and a water spray; Fig. 2 a similar view of a mold assin downwardly through a heater and into a ody'of water; and Fig. 3 a similar view of a stationary mold surrounded by alternately arranged burners and sprays.

The apparatus shown in Fig. 1 comprises a vertically disposed shaft 1 of refractory material suitably supported by posts 2 and rovided at its bottom with a gas or other uid fuel burner 3 preferably extending on all sides of the shaft. Below burner 3 there is a spray pipe 4 which also preferably extends on all sides of the shaft, or in other words, completely surrounds the mold. In the course of being lowered through the superposed heater and cooler, there is an ingot mold here shown as consisting of a tubular side wall member 5 which is preferably square in cross section, and a removable bottom 6 attached to the side wall member by straps 7, the lower edge of the wall being suitably luted in a groove formed in the upper face of the bottom 6. The top-of the mold is provided with lu s 8 engaged by hooks U attaehed to a cable 10 which is paid out at a predetermined rate by means of any of the variouswell known mechanisms for doing this. As the mold is lowered through cooling spray 4, the metal in the mold solidifies in a general plane lying substantially in that of the spray, and the metal above this ilane of solidification is maintained in its mo ten condition by heat from burner 3 the flames of which rise between the wall of the mold and shaft 1. u

The up aratus shown in Fig. 2 is similar to that o Fi 1, the water spray 4 of Fig. 1 being displaced by a vessel 15 provided with a body of water, which, if desired may be circulated and kept at a definite horizontal level by means of inlet and outlet pipes16 and 17. The mold 18, shown in Fig. 2 as being lowered through the heater and into the cooler, is of the closed bottom integral type, and may be suspended and lowered in the game manner as explained with reference to In the apparatus shown in Fig. 3, a mold 20 of the same form as that shown in Fig. 1 is indicated as resting upon a base 22, and as being surrounded by a series of

water spray pipes

23, 23, 23 and'23, each connected to water supply line-24 from which flow of water to each of the several spray pipes is independently controlled by

valves

25, 25, 25 and 25. Between adj aeent water spray pipes there are

burners

26, 26 and 26*, each connected to a fuel supply pipe 27 from which flow of fuel is independently controlled by

valves

28, 28 and 28 In the operation of the apparatus of Fig.

3, valve 25 is first opened to cause water to spray from pipe 23 upon the lower portion of the mold, and burner 26 is lighted to maintain molten the metal in the upper portion of the mold. At the beginning of the cooling operation sprays 23', 23 and 23 are not used, but where necessary the

upper burners

26 and 26 may be used, this being determined by a suitable pyrometer placed in the molten metal. As the plane of solidification of the metal rises, burner 26 is turned off by closing valve 28, and spray 23 is brought into play by opening valve 25*, burner 26' being then lighted if not previously in use. This procedure is followed until the rising plane of solidification reaches the top of the metal in the mold. In the use of this apparatus heat is effectively abstracted from the molten metal through the lower solidified portion of it and through the lower cooled portion of the mold wall, and accordingly in some cases, depending upon the size of the ingot being solidified. it is unnecessary to use the upper a hammer or a press if shrinkagehas notbeen sufficient to permit the mold to readily strlp from the ingot. When the metal is cooled by lowering the molds into the body of water in the manner illustrated in Fig. 2, it is I struction and operation of the ap aratus which may be, and which in point of act has been, used in the practice of our invention and in the attainment ofits object, it will be noted that the gradually rising plane of solidification of the metal is not a geometrically true plane, this term being used in the specification and in the claims to describe and define a solidification. stratum which is flat as compared to the rior somewhat conicalv solidification strata incident to the solidification of metal proceeding from the side walls as well as the bottom of a mold. The

chilling of the mold at and below the point of plication of a cooling medium being rapi and the mold being maintained at an elevated temperature above the plane of a plication of the cooling medium, the metal in the mold above such plane does not chill upon the upper side wall of the mold, and accordingly upwardly and inwardly extending elongate dendrite crystallization of the metal is precluded.

In the practice of each of the several described ways of progressively cooling the metal various advantageous grain structures may be produced. By maintaining that portion of the metal above the rising plane of solidification at a temperature materially higher than its melting point, we have found that the grain. structure is of an elongated form extending parallel to the vertical axis of the ingot, which is in the direction of working the metal by rolling. By maintaining, as is preferred, the unsol'idified portion of the metal at a temperature slightly above its melting point, there results an ingot having a fine equiaxed grain structure substantially uniform from end to end, and which may be forged or otherwise worked without developing. corner and surface cracks. It is inherent in both of these procedures that the metal solidifies simultaneously throughout its substantially horizontal rising plane of solidification. as distinguished from solidifying progressively fromthe wall .of a mold towards the center of the metal in it, such simultaneous solidification being due -to the continual and uniform extraction of heat by and from the solidified metal which is beneath the molten metal. Also, ingots formed by both of these procedures have substantially uniform compositions throughout.

/ As a specific example of the practice of our porosity characteristics.

invention in the formation of ingots having fine equiaxed grain structures, we have found that in forming ingots 8 x 8 x 22 inches from an aluminum base allo containing from about 4 to 5% co per, a out 0.75% manganese and about 0. 5% silicon, and by the use of the apparatus of F i 1, the best grain structures, coupled with reedom from preju- "sdicial segregations, 1i nation and porosity characteristics, are pro mgot mold at a rateof nnnute while spraying of water per minute under a pressure of about 6 lbs. per square inch, and while maintaining the unsolldified metal at a temperature of from about 1200 to 1250 F., preferably at or near the lower part of its temperature range.

The advanta e of this invention in the improved physica properties of metal worked from ingots-having equiaxed grain structures uced by lowering the about 1 inches per on it twenty gallons 'produced in the manner explained in the forele, and being substantially free going exam from preju icial segregation, porosity characteristics, tensile strength of the liquation and is apparent from the worked metal as compared to metal of the same composition worked from ingots having the coarser grain structures which characterize the formation of m'gots according to prior practice. Test bars cut from an ingot formed of an aluminum base alloy of the above described composition, the metal having been reduced 37.7% by forging, showed an average tensile strength of 57 ,125 lbs. per square inch, and an average elongation of 7.4%, while test bars of metal of the same analysis cut from an ingot formed according to prior procedure and having a consequent coarser grain structure, the metal having-been reduced 43.7% by forgin showed an average tensile strength 0 47,813 lbs. and an average elongation of 3.9%. Although the metal of the coarser grained ingot had been given a greater reduction, and, other factors being the same, wouldaccordingl have a higher tensile strength and elongation, nevertheless the metal of the fine equiaxed grain structure ingot produced according to this invention had a tensile strength nearly 10,000 lbs. greater than, and a percentage of elongation nearly double that, of the coarser grained ingot. This specific example of the advantage .of this invention in worked aluminum base alloys is typical of a large number of similar test which we have made, and of which detailed descriptions would be merely a cumulative showing of the advantage of this invention.

Ingots formed according to this invention have the well known advantages incident to the elimination of pipes at their tops, and have also the advantages of being free from prejudicial segregation, liquation and These advantages are substantial, and important in the production of aluminum base alloy ingots for work ing. Another marked advantage of the invcntion resides in the grain structure of the ingots, which structure very substantially improved physical properties, but also eliminates ingots to develop corner and surface cracks when worked.

According to the provisions of the Patent Statutes, we have explained the principle and mode of operation of our invention, and

have given specific directions concerning the However, we demanner of practicing it.

within the sire to have it understood that, scope of the appended claims, may be practiced otherwise than as specifically described, and with the use of apparatus other than that illustrated.

lVe claim as our invention:

1. The method of forming in a mold from a molten body of an aluminum base alloy an ingot for working having a readily workable grain structure and of substantially uniform composition throughout, COIIIPIIS-I ing solidifying said body in and simultaneously throughout a substantially horizontal plane rising gradually and progressively from the bottom to the top of the body of metal, and maintaining in its molten condition the portion of the body of metal above its said rising plane of solidification.

2. The method of forming in a mold from a; molten body of an aluminum base alloy an ingot for working having a fine equiaxed grain structure and of substantially uniform composition throughout, comprising solidifying said body in and simultaneously throughout a substantially horizontal plane rising gradually and progressively from the bottom to the top of the body of metal, and maintaining at a temperature slightly above its freezing point the portion of the body of metal immediately above its said rising plane of solidification.

3. The method of forming in a mold from a molten body of an aluminum base alloy an ingot for working having a grain structure of elongated form extending parallel to the vertical axis of the ingot as formed and of substantially uniform composition throughout, comprising solidifying said body in and simultaneously throughout a substantially horizontal plane rising gradually and progressively from the bottom to the top of the body of metal, and maintaining at a temperature materially higher than its freezing point the portion of the body of metal above its said rising plane of solidification.

In testimony whereof, we hereunto sign our names.

THERON D. STAY. WILLIAM HOLZHAUER.

not only results in.

the tendency of the the invention