US2940141A - Centrifugal casting of tubular metallic bodies in hot, permanent molds, and method of manufacturing such molds - Google Patents

Description

June 14, 1960 R. H. VON SETH 2,940,141

CENTRIFUGAL CASTING OF TUBULAR METALLIC BODIES IN HOT, PERMANENT MOLDS, AND METHOD OF MANUFACTURING sucH MOLDS Filed April 16. 1957 @umwz HENR/K vo/v 55/77 IN VGA/7'01? ATTOR/VEX United States Patent CENTRIFUGAL CASTING 0F METAL- LIC BODIES IN HOT, PERMANENT MOLDS, AND METHOD OF MANUFACTURING SUCH MOLDS Rutger Henrik von Seth, Alters Styckebruk, Sweden, as-

signor to Aktiebolaget Akers Styckebruk, Akers Styckebrnk, Sweden, a corporation of Sweden Filed Apr. 16, 1957, Set. N0. 653,081

' Claims priority, application Sweden, Apr. 17, 1956 4 Claims. c1. 22-1135 manner, that is through a runner pot whichis inserted in one end of the mould. Under theefiect of the centrifugal forces the metal is then spread along the entire inner surface of the mold.- 1

Even if the mold is furnished with the above men 7 tioned lining it has nevertheless proved diflicult to entirely protect the inner surface of the mold at the spot where the molten metal strikes the mold during casing. The mold gradually develops a network of cracks or fissures into which the metal penetrates at every casting. Corresponding irregular protuberances are formed on the outside of the case body and cause long scratches in the mold when the body is extracted. During the next casting operation these scratches in the mold naturally cause corresponding ribs on the cast body and thus give it an unsatisfactory surface.

Finally, the mold must be discarded or rebored to a larger diameter. The damage to the mold would of course be still greater if it were not lined with the above mentioned coating.

To avoid these disadvantages it has been suggested that an exchangeable collar or sleeve of suitable material be attached coaxially to the casting end of the mold and, either inserted into or aifixed to the end of the mold so that the molten metal first strikes this part of the mold and not the mold proper. The fact that the sleeve gradually develops a damaged surface does not, of course, affect the surface of the mold proper or the surface of the cast body. The sleeve can easily be replaced by a new one when required.

In practice, however, the sleeves give rise to serious difficulties however well they may be fitted. It is very difficult if not impossible in practice to atn'x the sleeve inside the mold, or at its end, without a certain space occurring between the wall of the mold and the sleeve. Even if the space or gap is very small, the molten metal will force its way into it under the influence of the very high centrifugal forces and form.thin fins at the end of the cast body. If the metal has once forced its way into the gaps theywill become larger and larger'in subsequent castings, and consequently larger fins will be formed on the castings. 'When these castings are extracted the fins score the inner surface of the mold, and if the fins become very large they may cause the tubular body to shrink off in two halves after the casting, as it is sometimes locked at the casting end and cannot shrink freely. In casting a metal such as cast iron which owing to the rapid cooling inthe said gaps solidifies to hard, white iron, the scratches in the mold will be still more serious.

If the sleeve is placed inside the mold, other difliculties are also encountered. Even if it is fitted as carefully as possible, it will during casting become overheated in relation to the surrounding mold, and as it cannot ex-' pand freely, be exposed to shrinkage stresses which will sooner or later give rise to a gap between the sleeve and the mold. The metal will penetrate into this gap durin casting.

If such sleeves are not employed as protection for the: mold, the casting end of the mold is generally closed with a ring which'limits the length of the cast body. Even when using such a ring it is very diflicult in practice to prevent the formation of a gap between the ring and the mold into which molten metal can penetrate during casting, with the result that fins will be formedon the cast body so that the mold will be scratched on extraction.-

The main object of the present invention'is to eliminate these drawbacks and to increase the life of the mold by lengthening the same with an extension, made in onepiece or integrally with the mold without any joints with; any spaces between the extension and the mold proper.

into which metal can penetrate during casting.

A fu her object of the invention is to provide a simple; and eifective method of manufacturing'such a mold by lengthening the mold proper, in conjunction with its"- manufacture, with an extension located outside the mold and made in one piece with the mold proper without:

. joints withany spaces between them;

One embodiment of a mold according to the invention is shown in the accompanying drawing, in which Fig. 1 is a longitudinal section of the mold, and

Fig. 2 is a sectional perspective view of the same mold. In the drawing, 1 indicates the mold which gives the tubular body its outer shape,'2 is the extension at one end of the mold and 3 indicates-a socket or other type? ofstop at the otherend of the mold. The difference;

between the internal diameters, A of the mold, and B at the inner end of the extension, should be at least equal to double the wall-thickness of the cast tubular body. The outer diameter of the extension 2 is suitably made as large as the external diameter of the mold, so that the extension is kept hot, thereby preventing too much of the molten metal remaining there. The extension can, however, be given a smaller external diameter if for example it is desired to make the whole mold as light as possible.

The internal diameter C of the outer end of the extension should not be larger than the internal diameter B of its inner end as the metal will otherwise tend to spray out during casting. Diameter C should preferably be smaller than diameter B in order to facilitate the running of the iron into the mold. The inner surface of the extension 2 will be scored during use and this can give rise to difiiculties. It is therefore advisable in manufacturing a new mold to make the taper, that is to say, the difference between diameters B and C, larger than necessary for the inflow of the iron. When the inner surface has become too scored this can be removed by turning, still leaving suflicient taper for the inflow of the iron. The extension 2 should be at least long enough for the metal to strike the inner surface of the extension and not the inner surface of the mold proper during casting. It has, however, been found advisable and of great im-' portance for the life of the mold to make the extension longer from the beginning. The reason for this is that the gradual development of serious heat cracks in the inner surface of the mold socket 3 can hardly-be avoided so that the mold can no longer be used without these cracks being removed by machining. This can only be effected by moving the socket or hub profile further into the mold, thus making the cast body shorter than before, which is usually undesirable. Thus, it is obviously of value to be able to increase the inner length of the mold proper in the direction of the casting end by shortthe: extension so that PIQDQI have the same length internally as it had before the cracks in the hub were removed. The extension will then be shorter and should therefore from he beginning be made longer than necessary according st e'aboves a a 7 for; somereason it is not desired or possible to make the extension as long. as is ppropriate, or if, according to what has: been said above, it has been shortened so much that the metal would strike the-inner surface of the mold proper during. casting, a further extension can fitted stolthe 'extension 2 at its outer end. The fact that there Will-Jpossibly'. be a space in the joint betweenthe twoextensions is of little significance. The important-point isrtha't there must be no space thejoint extension and the" mold proper. a What I ela'imisz? r a V 7 1. In the method of manufacturing a hot permanent mold-used forcentrifu'ga'l casting of tubular metal-he bodies-anti for restoring said mold after it hasbecomethe actual bore of the mold F having a conical bore therethrough co-axial with respect to said bore oi said mold portion,- said conical bore forming an integral continuation of said bore of said mold portion, said conical bore converging in a direction away from said 'bore'of said moldrportion and having its greatest diameter less thanthe diameter of said bore of saidmold portion; a T f l x I 3. vfor the l ifie' ofj a hot' permanent mold centrifugal casting of tubular metallic bodies extension length ening the 'niold acme "end where the metal is: pouredin so'fthat metal stpike'theinside of said extension but not the inside of the mold proper, said extension being formedv'tith semis-atinremarsurrace having the e -dia e er th t)? at s" wetland; e

greatest internal diameter of said extension being less than the interna f di ainefii: of- 'said ni'old proper, wherein at least the inner part of said extension is ade intone V a damaged. byusafthosest'eps which comprise lengthen-i11g a r r meld .propen -in' conjunction, with its nianufactnre; i

by-zfonnihg anin'tegral extension thereon inter;

. a nal pouring Mace at: the inlets-end of the) mold," and} 'afterthe' endoi! the rnold opposite to saideXtension has 7 been.shortened "by:v machining necessitated by damages" caused during the use of the' mold, eflectively shortening" tlie'length oiE sa'id extension by machining out a portion thereof adjoining said mold to give said portion the same inner diameter-as the inner diameter of themold proper, '2'. A hot permanent mold for the centrifugal casting of tubular metallic"bodies which comprises; "a mold port-ion and an entrant'extensionportion, said mold port-ion tion= being formed for theintroduction ofmolten metal 1 formed as' an elongated tubular' member an I V internal bore" extending therethrough, said extension porinto' said bore of said mold portion, said extension pore being formed integrally said mold; portion and a 4 a from 'penetra V proper.

workingmargin is $p'rovide 'f=for"ren1ovi said internal surfiace wh1le:1getaiiiih piece said mold; said internatsurfac'eiof satdex-V tension continuing integral-1y the interior: snrtace' of saidEmold proper with a viewto preventing, thefcasti'metall I j'l m.-

between said extension an 4-. Arrangement' 'a fccbrdmf 3 whereini'th tenet of 'saidinternal. surface of "fns'ionj misnewry introduction" of metal intoi the ntold fprdper whereby a References Giteif in?thefileiofthis gate ntj I s fFo msi n'irs t- 728,1:26' Great: Britain a -A ri' is, 759,581 Great-Brita n Anrpli 19-5-7; 762,5.24- Great Britain new-- Apr; is, 1954- {Sch ting f o mfeifnafi irface'

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