US1630043A - Centrifugal casting - Google Patents

Description

May 249 i192?,

C. P. WETMORE CENTRIFUGAL CASTING 2 Sheets-Shea?, 2

Filed June 5, 1925 INI/EN TOR.

Patented May 24, 1927.

UNITED srATss PTEN'T OFFICE.

CHARLES P. WETMORE, DECEASED, LATE OF MILWAUKEE, WISCONSIN; BY AUGUSTA. M. WETMORE, EXECUTRIX, OF MILWAUKEE, WISCONSIN, ASSIGNOR TO A. O. SMITH CORPORATION, OF MILWAUKEE, WISCONSIN, A CORPORATION OF NEW YORK.

cEn'rnIrUeAL CASTING.

Although centrifugal casting is a very old art, its practice is attended' by so many contlngent conditions that it is not always cerf' tain in itsresults. Time, temperatures, and apparatus used,` all are factors to be carefully determined and regulated in order to achieve success, and the control of vthese factors presents aproblem beset with difficulties. .Principal among these difficulties is that of casting in such manner that the rate at which the casting metal is converted from its fiuid to a solid state, by the abstraction of the heat therefrom, is so controlled that the article will be free from cracks, such as are formed when the casting is permitted to cool at too rapid a rate. Usually the cracks are only slight, but 'frequently they are so deep as to render the castinga total loss. In certain classes of cast tubular articles, such as pipe couplings to the production of which the present studies have been directed. even the surface cracks are objectionable.

In the course of experimentation conducted in connection with such studies, it has beenobserved that steel, among some other metals, shrinks at the time of passing from a molten to a solid state, and that 'up to a point somewhat below solidification it is very frangible and'wholly lacking in tensil-y ity. In the centrifugal casting of steel pipe 4 casting awayfrom the walls ofthe mold is opposed by the centrifugal force acting upon f the still soft metal and tending tothrow it outwardly, thus setting up .counterstrains which often destroy the cohesiveness'of .the 4metal and produce its' disintegration just'at` a time when the molecules are in the process oi: uniting and should be restrainedjfrom` couplings, the inevitable shrinking ofthe exerted evenly upon all areas of the exterior surface of the casting so as to produce a slight diametral compression, which is closely proportioned to the degree of shrinking, and thus effect a compacting of the metal of the casting at the time the latter is solidifying, and While the heat is in the course of out-Ward transference from the latter. Such compression during the cooling of the casting resists the outward movement of vthe still soft metal under centrifugal action, and contributes tothe preservation of the castlng in the state which it assumes by reason of the natural forces affecting it, so that the formation vof the crackstherein is avoided.

The invention comprises -alsocthe arrangement and confinement in the mold of a skeleton tubular lining which is kresilient in a proper -degree and is adapted -to have the diameter of its opening reduced by the ex.-

pansive action of the heat. transferred thereto from the casting while. the ,metal of the latter is solidifying, the contraction of the said lining following the shrinkage of the casting. This action may be supplemented by a mechanical operation whereinthe lining is also caused to contract soas to engage the surface of the castin To prevent the inwar radiation of the heat from the casting'and assist .in maintaining its temperature so as to avoid a too rapid cooling, a gas'burner mayv be intro duced into the mold at the conclusion of the pouring of the molten metal into the mold.

The operations whereby the results stated are effected, together with a `description of the construction lofthe means which may be employed inthe attainment of such results, will hereinafter be set forth in detail, and the novelty residing in the method and the means will be particularly'pointed out inthe appended claims.

- In the drawings:

z Figure l is a view in side elevation show ing a rotating mold and a conventional mounting therefor.

Fig. 2 is an enlarged vertical section, longitudinally of the mold, on the line 2--"2, Fig. 3, looking in the direction of the arrows, showing one form of the improved means.

Fig. 3 is a vertical sectional view transversely of the mold, on the line 3-3, Fig. 2, showing the outer end of the mold with the cap or cover removed.

Fig. 4 is an enlarged sectional view, transversely of the mold, showing a portion of one form of the liner adapted for operation by the action of the heat to cause its contraction and effect compression of the exterior surface of the cast-ing.

Fig. 5 is a similar enlarged view of a detail of construction.

Fig. 6 is a vertical section longitudinally of the mold, on the line .ri-5, Fig. 6, showing an arrangement of auxiliary devices whereby contraction of thev liner about the exterior surface of the cast-ing is produced by mechanical means.

Fi 7 is a transverse sectional view on the line 6 6, Fig. 5 looking in the direction of the arrows.

Fig. 8 is a transverse sectional view on the line 7-7, Fig. 5 showing the formation of the liner.

Referring to the drawings, the numeral 10 in Fig. 1 indicates a stand or head in which is journalled a shaft 11, provided with a driven pulley 12. The tubular mold 13 is attached to one end of the shaft 11 so as to rotate therewith. 'Ilie mold 13 may be of conventional form, and is provided with a removable ca -p or cover 14, having a central opening 15 through which the moltenmetal may be introduced into the mold while the latter isn-nder rotation.

The resilient and contractible skeleton liner in which my invention is embodied 'is formed as a casting or drum composed of two elongated rings 16 and 17, concentrically arranged, and maintained in that relation by a plurality of radial webs 18. so distributed between the rings 16 and 17 as to firmly suport thering 17 a-ainst distortion or deection by the centrifugal action of the mass of molten metal out of which the casting 19 is formed. The hollow of the ring 17 determines tlie diameter of the casting. At s aced points, the ring 17 is slitted longituinally as at 20, so as to permit contraction of the diameter thereof, and such slits may be. chamfered upon the inner surface ofthe ring to form longitudinal channels 21, Fig. 5, for the reception of a packing material 22 of asbestos, or other spongy combustion resisting substance, which will admit of compression in the contractionof the ring 17, and at the same time prevent the molten metal from passing outwardly into the said slits, so that the exterior contour of the casting will be symmetrical.

In operation, the mold is set 1n rotation and a measured quantity of molten metal is introduced thereinto through the opening 15 in the cap or cover 14. The heat of the molten metal constitutes the means for contracting the ring 17 and is quickly traiisferred to the sectors of the ring 17 and to the webs 18, causing a perceptible radial eX- pansion inwardly of the webs 'to take place immediately. with the result that the sectors of the ring 17 are moved bodily inward to reduce the diameter of the ring, and maintain engagement with the casting. In this movement, the metal in the exterior surface of the casting is compressed and condensed by the ring 17, and this action upon the surface of the casting at the time of cooling is found to iniprove'it in Such degree that the tendency to thc formation of cracks incident to the practice of the older methods of casting like articles is avoided. Iliasmuch as the liner has a close fit in the bore of the mold, the latter resists the tendency to outward expansion upon the part of the liner. n

The contract-ing action of the skeleton liner under the influence of heat transference maybe supplemented by mechanical means, as illustrated in Figs. 6, 7, and 8. In this illustrated construction, the walls of the circular rings 161 and 171 forming the liner are not parallel, as in the first instance, but the outer ring 161 is made to taper toward the bottom of the mold, so that the liner has the outline of a truncated cone. The inner ring 17 is constructed as before. and the outer ring 161 likewise is slitted at 23, so as to )rovide the necessary further resilience to lt e liner, but the slits must be' formed respectively in alternate sections of 'he rings, to preserve the integrityY of the iner.

Bell crank levers 25 are pivoted upon a ange 26'on the shaft 1l, one arm of lsuch bell cranks and links 27 forming a oggle connected to a collar 28 sliding 'on the shaft 11. Thev collar 28 is. provided with a circuinferential groove29 which receives oppositely projecting pins in the forked end of a lever 30, pivoted intermediate its ends upon a bracket 31, which latter is mounted upon the stand 10. The other arms of the bell cranks 25 have a sliding pivotal connection with links 32 working through and guided in openings in the bottom of the mold, and threaded -at their outer ends for adjusted engagement with ,threaded bores formed in a wedging ring 33 adapted for a sliding movement longitudinally in the mold. The wedging ring is provided with a tapering bore of the angularity of the conical surface of the liner. By throwing the lever 30 to the right, Fig. 6, the toggle connections are actuated. and the wedging ring is moved outwardly of the mold and into sliding engagement with the conical surface of the liner, with the result that compression of the liner takes place, through positive inechanical action. suoli action supplementing that of the contraction of the diameter of the liner due to the heat transference from the casting.` However, the mechanical construction for effecting compression of the surface of the casting may be utilized without consideration of the action due to heat transference.

To prevent a too rapid cooling of the casting, there may be introduced into the mold immediately after the molten metal has been poured thereinto, a. gas burner 34, the action of the flame of which will be to maintain in a more suitable degree 'the temperature o'f the` molten metal at the inner side of the casting, so that the latter will solidify at a lower rate of'speed. The provision will act to retard the formation of the exterior surface of the casting, inasmuch as the application of the additional heat at the inside of the casting creates an oHset to the natural radiation in that direction, and requires that a greater amount of the heat be liberated by passage through the outer surface of the casting. The time required for this to be effected contributes to the slower cooling of such surface, and consequently the retarded action results in the slower solidification of the. metal upon the exterior surface. The gas flame may be continued in play until sufficient time has elapsed for the molecules of the metal forming the exterior surfaceof the casting to adjust themselves under the compression eX- erted by the contractible lining without set-l ting up any internal strains', such as result when the cooling is not retarded. Thus, surface shrinkage cracks due to the too rapid cooling and disintegration of the metal of the casting are avoided.

My invention surmounts one of the most serious situations encountered in the centrifugal casting of metals which shrink at the time of solidilication.

Having thus described the invention, what I claim and desire to secure by Letters Patent of the United States, is:

1. rfhe process of casting tubular articles, which consists in subjecting a rotating mass of molten metal to inwardly directed surface pressure to resist disintegration of the metal under centrifugal force during solidi'- cation.

2. The process of casting tubular articles, 'which consists in providing a rotatable mold with a contractible liner having a hollow formation defining the contour of the casting, introducing molten metal into the liner, rotating the mold to form the casting, and applying pressure through the liner to the exterior surface of the casting to resist disintegration of the metal under centrifugal force during solidification.

3; The process of casting tubular articles. which consists in providing a rotatable mold \with a liner having a contractible hollow ring defining the contour of the casting,

introducing molten metal into the said ring, and rotating the mold to form the casting and effect contraction of the ring into surface engagement with the cast-ing by heat transferred from the metal to the liner, to resist disintegration 'of the metal under centrifugal action during solidification.

l. The process of casting tubular articles, which consists in subjecting a rotating mass of molten metal to inwardly directed surface pressure to resist disintegration `,of the metal under centrifugal force during solidification, and applying additional heat to the inside of the casting to retard the cooling of the latter.

5. rl`he process of casting tubular articles, which consists in placing molten metal in a rotatable mold and rotating the latter to form the casting, and applying additional heat to the inside of the castingto retard the cooling of the latter and increase the radiation of the heat outwardly of the casting.

6. In a centrifugal casting machine, a rotatable mold, a liner therein to determine the diameter of the casting, and means for effecting contraction of the liner into engagement with the casting to prevent disintegration of the metal under centrifugal action during solidification.

7. In a centrifugal casting machine, a rotatable mold, a liner therein provided with a slitted ring to determine the diameter of the casting. and means for effecting contraction of the liner into engagement with the casting to prevent. disintegration of the metal under centrifugal action during solidification.

8. In a centrifugal casting machine, a rotatable mold. a liner therein composed of two concentrically arranged rings the inner one of which determines the diameter of the casting` webs connecting the rings and eX- pansible radially inward under the heat transferred from the casting to cause such inner ring to maintain engagement with the surface of the casting and prevent disintegration of the metal under centrifugal action duringl solidification.

9. In a centrifugal casting machine, a rotatable mold, a liner therein embodying a contractible ring which determines the diam-- eter of the casting, and means as heat transference for contracting the ring into engagement with the outer surface of the casting to prevent disintegration of the metal thereof under centrifugal action during solidification.

v 10. In a centrifugal casting machine, a rotatable mold, a liner therein embodying a contractible ring which determines the diameter of the casting, and means as heat transference for contracting the ring into engagement with the outer surface of the casting to prevent disintegration of the metal thereof under centrifugal action during ill@ lZO

solidification, and supplemental means for eifeoting such contraction of the ring.

11. In a centrifugal casting machine, a rotatable mold and a oontractible liner therein, the latter comprising an elongated ring which is sltted to permit contraction in the diameter of the ring to take place, the slits being packed with a oompressible, noncombustible material to prevent the flow of the cast-ing metal into the said slits.

In testimony whereof, I have signed my name at Milwaukee, this 3d day 0f June, 1925.

AUGUSTA M. VVETMORE, Eweouzfrz' of Charles P. Wetmore, Deceased.

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