US2178163A - Method of and apparatus for centrifugally casting metals - Google Patents

Description

Cet. 31, 1939. A.c. nAvlnsoN' A METHOD 0F AND APPARATUS FOR CENTRIFUGALLY CASTING METALS Filed oct. s1, 193e Patented Oct. 31, 1939 UNITED STATES METHOD OF AND APPARATUS FOR CEN- TRIFUGALLY CASTING METALS Arthur C. Davidson, Canton, Conn. Application -October l31, 1936, Serial No. 10S-,627

s'claims.

My invention relates to methods of and apparatus for centrifugally'casting metals.

It has heretofore been proposed 'to cast metals y by centrifugal motion, but the products produced f by such casting without the use of feed means or shrink heads have been seriously defective as, for this and other reasons, have also been the methods and apparatus used in producing the same. More particularly, the inner surfaces of such castings heretofore produced, i. e. those exposed on the inside of the rotating mold, have contained surface shrink cavities `or shrink cracks, while the'metal inside the inner surface of the casting and extending therefrom into'the axial d area, has also contained cavities, these defects ,being such as either to produce a casting dangerous or useless for many purposes, or to require expensive additional operations to make the castings marketable for other purposes. Further, prior processes and apparatus have required the use of feed means or shrink heads or other mechanical appliances for the purpose of feeding the metal to be cast continuously throughout the casting process and until solidication takes place. Such feeding sections or appliances are objectionable as the same causemetallographic disturbances as Well as physical irregularities of the structure directly underlying the same. In addition, the removal of the appliances entails costly operations as well as disturbance of the surface designs. Y

My invention has among its objects to provide an improved method of centrifugally casting metals whereby. without the use of feeding means or feed or shrink heads, and while the metal is in the rotating mold, it is made possible to obtain an improved product, substantially free from the defects which heretofore have characterized products obtained by centrifugal casting. A further object of my invention is to produce an improved and simplified apparatus whereby such an improved product may be produced, and such an improved apparatus whereby, at the same time that it is made possible to produce this improved product While the metal is in the mold, it is also made possible to eliminate any such mechanical feeding means or shrink heads as heretofore required. A still further object of my invention is to produce while the metal is in the casting apparatus, an improved product not only free from the defects above set forth, but having substantially uniform outer and inner wall surface density and a substantially uniform density between the axis and outer surfaces of the'casting. 55 These and other objects and advantages of my improved construction will, however,hereinafter more fully appear.

In the accompanying drawing, I have shown for purposes of illustration, certain forms of apparatus which may be used in carrying out my 5 improved method and my improved article produced thereby.

In the drawing:

Figure lis a vertical sectional view of a. rotating mold adapted to be used in accordance with my invention in centrifugally casting a tube, the mold being shown in position ready to receive from a ladle a charge of moltenmetal to be cast;

Fig. 2 is a similar view but showing the molten metal in the mold ready to be acted upon by l5 axially disposed air delivery means delivering to the exposed surface thereof; v

Fig. 3 is a like view showing the mold in open position and the solidied casting being -removed therefrom;

Fig. 4 is` an end elevation of the mold showing a movable end flange thereon disposed in closed and open positions;

Fig. 5 is a detail side elevation of a modified form of the air delivery means shown in Figure 2;

Fig. 6 is an enlarged ure 5;

Fig. '7 is a View similar to Figure 2 but showingA a modified form of sectionalmold adapted to use in casting a tubular member of varying cross section;

Fig. 8 is a view similar to Figure 2 but showing a modified construction including a roller acting on the metal in the mold;

Y Fig. 9 is a sectional view on line 9-9 of Figure 8 utilizing a roller and an air supply associated therewith as in the preferred form 0f my invention;

`Fig. 10- is a longitudinal sectional view of a modified form of centrifugal mold adapted to use in casting bars;

Fig. 11 is a sectional view on line Il-ll of' Figure l0;

Fig. 12 is a diagrammatic view showing the 5 travel of the mold during the casting operation,

and

Fig. 13 shows at the left a diagrammatic representation of a micrograph of my improved product as it leaves the mold, an'd at the right, a like view of the product of the prior art at the same stage.

Infcarrying out my improved method with the apparatus shown in Figures 1-4 inclusive,'it will be noted that I provide a suitable rotatable mold,

view on line 6--6 of Figpreferably rotatable on a horizontal axis and generally indicated at M, having an axial opening such as shown in which the metal is cast, and also having improved means acting on the exposed surfacer of the metal in the mold for controlling the crystal formation and solidiflcation of the metal in an improved manner to produce my improved product, all as hereinafter more fully described.

Herein, I have illustrated a rotatable mold having an outer metal shell or rotating drum I of cast metal or the like and having within the same a relatively deep lining 2 of refractory material,

such, for example, as brick, fire clay, or refrac-A tory metal such as the chrome-nickel mixtures and the like, capable of standing the elevated temperatures. Further, I provide on opposite ends of the drum I, steel flanges 3 and having like axial apertures 5 therein, these apertures being of smaller diameter than the inside diameter of the lining 2 and adapted to confine the metal to be cast between the same and the refractory material 2. Thus, a rotating mold is provided which, as the drum I is suitably rotated, is adapted to rotate therein, a tubular charge of metal engaging the refractory material 2 and the inside surfaces of both flanges 3, 4, and of a maximum depth approximating the depth of the portions'of these flanges which project inward beyond the refractory material, while having the entire continuous inner surface of the metal exposed to the atmosphere.

In practicing my invention with a mold of the construction set forth, the first step is the pouring into the mold of a charge of molten metal sufficient torproduce the desired depth in the mold. Preferably, the mold is rotated at a speed suitable to produce the desired centrifugal action on the molten metal to retain it in the mold, before the metal is poured into the mold, and this rotation is continued during pouring and throughout the remainder of the casting process hereinafter described. Experience has shown that the speed should be 600 feet per minute to 6000 feet per minute, depending upon the wall thickness of the casting and the mixture being cast. Preferably also, the ladle 6 is tilted as quickly as required to insure rapid lling up of the mold to the desired height on the flange or other gage; the ladle during ythis operation projecting into the adjacent aperture 5 through the aperture 5 in the flange 4 and, after delivering its charge, ,being quickly withdrawn to its normal position, sho vn in Figure 1. If desired, the ladle may remain stationary in this position during the remainder of the casting operation and be refilled while stationary, or also move through a predetermined path and be refined during its passage therethrough, while returning to the posi-f tion shown in Figure 1 relative to the. mold illustrated therein, or another mold in a series of molds, when the mold in question is ready to receive another charge.

Immediately upon the completion of pouring,

preferably within a short period of a few seconds thereafter and before the metal has reached the plastic state, a cooling flow of air under pres-` surejis played on the exposed surface of the g metal, i. e. the surface thereof left exposed by the mold or not in contact therewith, herein the entire inside or inner peripheral surface of the molten metal charge, as the latter is rotated i'n the mold. The air temperature and volume utilized may vary within relatively wide limits depending upon the size, shape and temperature of the casting or mold and the mixture oi' the metal to be cast. For example, on a casting having a heavy wall, a temperature of 150 ll'. will cause rapid plasticity of the inner surface, vthus resisting shrinkage and avoiding cavities. -For thinner walled castings, the temperature should be lowered and can be as low as 32 F. For castings containing copper, steam works admirably. The pressures also may be varied from 1 ounce to pounds or more, depending upon conditions and so long as the pressure is not so excessive as to disturb the surface contour of thecast. However, in all cases I utilize a flow oi' such proper temperature, volume and pressure as to control the formation of the crystals and thereby prevent or counteract the drawing away of the fluid or plastic `metal from the inner portion of the cast to any outer portion thereof which has heretofore occurred and results in the defects in the prior castings mentioned above. 'Ihis cooling air flow is continued until the metal has reached an advanced plastic state, or, if desired, until the casting has been completely solidified.

Herein, the air is supplied to the molten metal in large volume and uniformly over the entire inner surface of the casting through a pipe 1. This pipe is of a substantially smaller diameter than the inside diameter of the casting and maintained axially disposed within the mold throughout pouring and casting as shown, or, preferably, projected into that position in the mold immediately upon the completion of pouring. As shown, lthis pipe 'l has an outlet portion of at least the length of the casting and comprising outlet apertures 8 disposed uniformly around the pipe, preferably in spiral form as shown. Further, when, as herein, the pipe is adapted tobe projected into the mold from the end opposite the ladle after the ladle has moved out of pouring position, the pipe, as herein, is preferably provided with a closed frontend 9.V However, if desired, instead of the spirally disposed apertures 8, I may use longitudinal slots I0, likewise extending throughout the length of the casting and preferably spaced by distances slightly wider than the width of the slots and disposed entirely around the pipe, a closed end 9 also beingfused in thisconstruction. While air at atmospheric temperature; or even higher temperatures may be used under certain conditions, the air supplied to the casting is preferably refrigerated. It is found that by thus suillciently lowering the temperature of the air,

both the usual direction of progressive crystalformation and the usual order of crystal formation at the opposite sections is reversed thereby,

l and that better results are thereby obtained.4 More particularly, as a result of playing refrigerated air at a proper pressure on the inner surface I am'thereby `able to cause more rapid crystal formation therein than in the outer sections and thus not only to reverse the previous direction of progressive crystal formation, but alsolto control the location of the merging point, or axis. as desired and obtain a better and more uniformly dense product. Here, also, it is found that refrigerating the air reduces the dimensions of the ter results than a pressure of 100 lbs. at room temperature. v

By varying the pressure of the air and its temperature, it is also possible to control the crystal formation and to predetermine the crystal and/ or grain size and the solidification of the casting in an accurate manner. Further, if the drum is heated, for example, to say, from a temperature of 400 F. to 1250o F., and the metal then poured therein, it is found that sudden chilling at the outer area of the casting is reduced and that consequently the need for extreme rapidity of inner solidication is modified, the needed speed `varying conditions.

of chilling the inner area being proportionately reduced as the temperature of the drum is increased. Thus the air blast or pressure of the air may be moderated or reduced somewhat and the-refrigeration of the air may bemoderated or omitted under certain conditions.

In any event, the ratio of cooling for the inside and outside should be closely similar to insure uniform cooling of the metal through its plastic state. However, it should be noted that the inner surface thereof should be cooled at a faster speed at the start in order to insure immediately crystal formation at as near as possible the instant that pouring is completed. Thereafter, the speed of the cooling eect may be varied depending upon the chemical analysis of the metal and its wall thickness.` As an example, a'high alloy steel is vcooled at the start for a period of say five seconds rapidly, whereupon the pressure and temperature of the air is moderated to permit slower cooling to avoid cracks. If, on the other hand, it

is desired to speed. up production and keep the drum cool, it is only then necessary to apply proportionatelyvcooler air or a greater volume of air or air at greater pressure to compensate for the increased rapidity of cooling of the outer periphery of the casting.

As a result of thus properly proportioning the cooling effect of the air supplied to the inner surface as above set forth, as by reducing the temperature of the air vsupplied thereto or varying the pressure or volume of the air, or utilizing these controls while also heating the drum, it is made possible to provide an effective control of the formation of crystals and to predetermine the crystal size and the solidity of structure under widely More particularly by suitably controlling the cooling ratio of all exterior surfaces, it is made possible to prevent one area from continually feeding on or drawing the uid .or plastic metal away from another section and thus to avoid shrink cracks, cavities, or sponginess, which results from such metal movement and produces a casting which is unsound orv metallographically defective. On the contrary, by expediting the formation vof crystals under the action of the air supplied to the inner surface and thereby controlling solidiflcation, it is made possible to produce a casting having, a substantially uniform structureatl its vaxis and substantially uniform density between the axis and the outer and inner wall sections:

My invention is adapted not only` to use in centrifugally casting, tubes of uniform wall section but also casting tubes of varying cross section. For example, in casting a tube having a flange thereon as shown at II in Figure 7, I provide a suitable correspondingly shaped flange forming mold or channel I2 in the refractory material! with suitable drawsurfaces, and utilize a drum -of split construction comprising two complementary parts and horizontally split as indicated at I 3 and adapted to be suitably connected together and quickly detached in any well known manner to permit removal of the casting. Further, in supplying air to such a casting it will be noted that I dierently size the apertures 8 opposite the sections of the casting of different cross section, enlarging these apertures opposite the portion II of the casting as illustrated in Figure '7. As shown therein, similar enlargement of the apertures may also be used at the ends of the apertured portion of the pipe, and this feature may also be used in the pipe shown in Fig. 2, to expedite and control. crystal -formation in molten metal adjacent the anges, which otherwise Would cool more quickly due to contact with the flanges. i

Even better results than those obtainable with the use of air alone, as heretofore described, are

obtained by the application of a rolling pressure to the inside surface of the casting while supplying air to that surface. In carrying out this form of my invention, a roll is applied to the inside surface quickly after pouring the casting and while the casting is rotating in the casting appliance, and the rolling action is continued as long as the metal is malleable. Obviously the time of applying the roll will depend upon the cross section and analysis of the metal and the temperature of the metal. Further, the air supply when used .during rolling, is preferably applied close to the casting surface and the rolland behind the latter rather than vat a point ahead of the same, a1- though the latter arrangement may be used, or I 'may use such an axially disposed airsupply as previously described. Further, in a preferred form, the roll is also preferably cooled before and during rolling, as by circulating through the same a flow of fluid at a suitable temperature, and it will be understood that the pressure, volume and temperature of the air supplied to the air supply located outside theroll may be varied, as hereto# fore described.

Referring more particularly to Figures 8 and 9, wherein I have illustrated apparatus for use in carrying out this phase of my invention, it will be noted that I have shown therein a roll I4 extending through the axial aperture in the mold and having cooling or refrigerated air, orcooling water, circuit means I5 connected to the opposite endsv thereof to enable cooling. This roll I4 is carried in suitable vertically adjustable journal supports I6 .at opposite ends of the drum and adapted to be lowered into engagement with the inner surface of the casting, as shown in Figure 8, to exert the desired pressure, and to be raised out of contact with the casting when desired. As .shown in Figure 9, a tube I1 corresponding vto Y tube I is also disposed in rear of the roll I4 and closer to the inside surface of the casting in such manner as to play on the roll and on the adjacent -area ofl said inner surface, and thus cooperate of course, it will vbe obvious that a plain roll may be used where `lonly smoothing is desired, or rolls of other special shapes may be used.

As a result of using a cooled roll and exterL nallyapplied cooling air in combination, it is made possible to obtain a better product vas regards grain refinement, this being believed to be due to the-action of the roll in producing somewhat more equal solidincation and pressure, and hence, avoidance of shrink cavities. For example, assuming the outer wall density to be 100%, I am able to obtain at the axis when rolled with a cooled roll and while cooled air is also being applied, a density which may be correspondingly rated at 95%, as compared with a density of 90%, obtained when not rolling and using air only. Moreover, such rolling eliminates the need for boring or machining preparatory to fabrication and also prepares the casting to withstand further hot or cold reductions without surface tears and fractures. Further, if desired, I may, under certain conditions use a cooled roll without using externally applied air and thus obtain certain advantages obtained by the air and roll or the air alone but to a lesser extent,

the density at the axis then being approximately 80% of the outer wall surface density. However, better control of crystal formation is obtainable by the use'of externally applied air with a cooled roll, while also obtaining the advantages of rolling. Thus combined rolling with a cooled roll and an externally supplied controlled air supply is preferred with suitable control of `the ternperature, pressure and volume of the air to provide the desirable further flexibility of control and the markedly highrpercentage ,of density at the axis, both of which are incident to this combination. In connection with this density, note further that the axial condition becomes quite as true in density' as entirely hot rolled steel.

#while it will further be noted that the structure is superior to that of rolled sheets or hot pierced or cold. drawn sheets in view of the iact that the usual elongated laminatlons in such worked metal are not. formed in my improved process.

My invention is further adapted to use in centrifugally casting bars, if desired, while controlling the crystal formation and solidiilcation of the metal as previously described. In casting such bars, I provide longitudinal parallel grooves Il, corrsponding to the desired bar section and in the refractory material and spaced around the same substantially as shown in Figures 10 and 11, while providing suitable partitions It between these grooves. Further, it will be evident that if desired, instead of relatively long slender bars, sheet and plate bars may be produced by correspondingly varyingv the cro section of the lrooves Il. Also. 'in' carrying out this phase of my invention, it will be understood that air may be supplied by a `'suitable axially disposed air supply. with the air supply controlled 'as to temperature. pressure and volume, in order to control the crystal formation .and solidication as previously described.

In carrying out my invention, it will further be understood that the same may be applied to use as a continuous process, i. e. with the mold M travelling through a circuit and rotating as it travels past diil'erent stations, as diagrammatically illustrated as a straight line movement in Figure l2. Further, the ladle may also be movable in timed relation thereto and into and out of nlling and discharging positions. Further, it will be evident that the air supply 'means may move with the mold and either be fixed constantly in axial position,l or prolected into the mold upon completion of pouring and withdrawn from the mold upon the completion of solidiilcation, all as the mold travels. Also, the solidified casting may be removed from the mold in the course of its travel. Similarly, in the form of my invention utilizing a roll, and an external air supply, these may be connected for movement together as the former moves into and out of engagement with the metal, and both also may stay in the mold as the latter travels, or be projected into and out of operative relation in the mold, as desired, one of the bearings i8 therein being in the form of a detachable connection. However, the apparatus used in connection with these phases of my invention for eecting relative movement of the various component elements forms no part of the present application.

While I have herein referred to the use of air as a cooling agent, and ordinary atmospheric air may be used advantageously under certain conditions I am not limited to the use of the same. Instead, I find that in operating upon metals with a tendency to scale or oxidize, such, for example, as those containing copper, lead or iron, it is desirable to use a nitrogeneous gas sumciently free of oxygen to avoid the formation of oxides, such, for example, as used commercially for the purpose of bright annealing, and that when the same is used as a cooling agent with the temperature and pressure under control as above set forth, the productionof scale is eliminated. 'Ihus it is possible not only to control crystal formation within the metal, but also to produce a casting having asmooth external surface, as distinguished from the rough or pitted surface produced by cooling as above described in the presence of an oxidizing element.

In Figure i3 I have, moreover, shown my improved product produced as a result of the use of my improved method and apparatus described above in connection with Figures 1 to 1l. In the portion of my improved article, indicated at the left, it will be noted that the substantiallyuniform density on the opposite exteriors or surfaces and in the axial area, is indicated by stippling substantially as shown by a micrograph; while at the right a similar showing appears of an article made by previous processes and apparatus and containing the various defects previously mentioned. From a comparison of these two showings, the marked advantages of my improved method and apparatus and my markedly improved iproduct are believed to be clearly apparent.

As a result of my invention, it is made possible to obtain the desired improvement in the product while centrifugally casting any metal. Thus, for example, the same is adapted to use with any of the usual iron or steel mixtures and further to the same. Such expensive additional operations as forging or rolling may be eliminated as a result of my improvements. Further. whereas in ysand casting with a sand core, it has only been possible to obtain an exterior density of approximately 9 5% with an axis density of 50% to 70%, asfa result of my improvements. it is made possible vnot only to improve the exterior density, but also very substantially to improve the axial density. Over all such prior processes, it has also armies f been made possible very materially to reduce the expense and time required. For example, in making an ordinary steel casting containing aplproximately .30% carbon, solidiflcation may be 5 completed in three seconds after air refrigerated to34 F. is applied. These and other advantages of my improvements will, however, be clearly apparent to those skilled in the art.

While I have in this application specically described certain embodiments of my invention,

' it will be understood that these are chosen for purposes of illustration, and that the invention may be modied and embodied in other forms without departing from its-spirit or the scope of the appended claims.

What I claim as new and desireto secure by Letters Patent is: l

l. 'I'he steps in centrifugal casting which consist in, pouring molten metal into a mold while rotating the-latter, and cooling the inner exposed surface of 'the poured metal suiiciently rapidly and in accordance with the requirements of. the particular casting toextract heat therefrom substantially as rapidly as heat is being extracted from the outer surface which is in contact with the mold, to produce a casting having substantially uniform density in the portions adjacent said inner and outer surfaces.

2. The steps in centrifugal castingwhich consist in, v pouring metal into a mold while rotating the latter, and cooling the inner exposed surface of the poured metal sufficiently rapidly and sumciently early in the feeding and crystal formation stages of the casting to extract heat therefrom at least as rapidly as heat is being extracted from the outer surface which is in contact with the mold, to produce a casting having substantially uniform crystal formation and substan? tially uniformrdensity on opposite sides of the center of a radial cross section through one wall of the casting.

l 3. The stepsin centrifugal casting which consist in, pouring molten metal into a mold while includes the steps of, cooling the surface of the rotating the latter, and cooling the inner exposed surface .of the poured metal sufhciently early in the feeding and crystal formation stages of the metal and while the latter is still. in a molten state before final crystal xation, and suillciently rapidly to extract heat from saidinner surface- 59 more rapidly than heat is being extracted from the outer surface of the metal by the mold, to

control the rate of heat extraction and produce a casting having substantially uniform density in the portions thereof adjacent said inner and outer surfaces. v f

4. The steps in centrifugal casting which consist in. pouring molten metal ntoa mold while 5 `rotating the latter, and cooling the inner exposed surface of the poured metal by directing a flow of cooling :duid into'direct contact with the exposed surface of the metal before the metal in the mold has passed through the plastic state m the portions adjacent .said inner and outer sur- 15 faces. f

5. The step in centrifugal casting which con# sists in, applying while the metal is `passing through its feeding and crystal formation stages in the mold, cooling fluid ows of different volgg ume toexposed surfaces of metal bodies of different thickness and which cool at different rates, to control crystal formation therein, the flow of greater volume being applied to the body of greater thickness. 25

6. Apparatus for centrifugal casting compris ing a rotatable mold, a roller movable into contact with the exposed metal in said mold dui-ing rotation of the latter, and supply meansA for also supplying cooling fluid to the exposed .sur-A 30 face of the metal.

7.- The step in. controlling crystal formation during centrifugal casting 'which consists in, bringing under control relative crystal formation in the exposed and unexposed metal in the rotat-I 35 ing mold during feeding to lower the temperature ofthe exposed metal at a rate above thevnormal rate of solidification of the unexposed metal due Y to contact with the mold, by rolling the exposed surface of the metal with a roll while cooling o the latter and applying a cooling flow of cooling uid directly to said surface.

8'.' The method of centrifugal casting which exposed metal rapidly for the rst few seconds 45 of the feeding and crystal formation stages and while rotatingin the mold, and then reducing the cooling effect on the surface of the exposed metal during continued rotation to prevent formation of shrinkage cracls b y too rapid 50 cooling'.

ARTHUR C. DAVIDSON.

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