US3672429A

US3672429A - Method for the centrifugal casting of metal in a rotating horizontal shell

Info

Publication number: US3672429A
Application number: US858057A
Authority: US
Inventors: Pierre Lajoye
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-09-17
Filing date: 1969-09-15
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27
Also published as: DE1946745A1; NL6914030A; FR2056046A5; DE1946745B2; FR1587187A; AT297240B; BE738760A; GB1288622A; CH514379A; FR1587403A; CA920769A

Abstract

A process for centrifugal casting of metal components in a mold revolving around a vertical axis by supplying liquid metal into a cavity in the mold and rotating the mold to cause the liquid metal to be transferred radially outwardly in the cavity by centrifugal force, while simultaneously applying a vacuum to the cavity for degassing the molten metal during casting thereof to prevent oxidation of the molten metal while it is being supplied into the cavity through radial channels formed in the bottom there.

Description

Lajoye 1 June 27, 1972 [54] METHOD FOR THE CENTRIFUGAL CASTING OF METAL IN A ROTATING HORIZONTAL SHELL [72] Inventor: Pierre Lajoye, 40 rue de la Vacquiniere,

Montigny les Metz Moselle, France [22] Filed: -Sept. 15, 1969 [211 Appl. No.: 858,057

[30] Foreign Application Priority Data Sept. 17, 1968 France ..6850397 Oct. 11, 1968 France ..6850493 Aug. 25, 1969 France ..6928972 [52] US. Cl ..164/63,164/65,164/114-, I 164/118, 164/286, 164/337 [51] Int. Cl ..B22d 13/04 [58] Field ofSearch ..164/253,254, 256, 258,337, 164/286, 114, 118, 115, 338, 63, 65

[56] References Cited UNITED STATES PATENTS 1,095,230 5/1914 Rockwell ..l64/ll4 1,944,460 l/l934 Pike ..164/286 2,450,832 10/1948 Kuhlman... ..164/293 X 1,807,536 5/1931 Keup ..164/1 15 FOREIGN PATENTS OR APPLICATIONS 240,492 12/1945 Switzerland 1 64/292 615,484 l/1949 Great Britain. ....l64/63 519,835 12/1955 Canada 1.164/286 Primary Examiner-Robert D. Baldwin Attorney-Sughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT A process for centrifugal casting of metal components in a mold revolving around a vertical axis by supplying liquid metal into a cavity in the mold and rotating the mold to cause the liquid metal to be transferred radially outwardly in the cavity by centrifugal force, while simultaneously applying a vacuum to the cavity for degassing the molten metal during casting thereof to prevent oxidation of the molten metal while it is being supplied into the cavity through radial channels formed in the bottom there.

7 Claims, 24 Drawing Figures PATENTEDJUHZY ISYZ SHEET 10F 6 PATENTEUJUHZT m2 SHEET 5 OF 6 METHOD FOR THE CENTRIFUGAL CASTING OF METAL IN A ROTATING HORIZONTAL SHELL The present invention relates to a new process to obtain metallic bodies, preferably made from particularly oxidizable alloys, by centrifugal casting.

It is known that to introduce a liquid alloy containing oxidizable elements into a mould turning at high speed about its axis produces eddies, turbulences and atomization particularly detremental to obtaining a sound component, exempt from macro or from microinclusions of non soluble oxides. In static casting these disadvantages are remedied by bottom flowing the liquid metal into the foundry moulds. On the other hand, as regards centrifugalcasting, it is commonly admitted that it cannot be used for certain types of very oxidizable alloys.

The present invention has the aim of avoiding these disadvantages by using a new process which allows the centrifugal casting of even very oxidizable liquid metal alloys to be carried out. Thus there are obtained all the advantages of centrifugal casting, improved mechanical and metallographic properties in the finished components, whilst eliminating the risks of oxidization. The process according to the invention for the centrifugal casting of metal components in a horizontal shell able to turn around a vertical axis, and into the center of which the liquid metal is poured, is characterized in that a central cavity which receives the liquid metal is heated, the metal then being transferred without turbulence into the mould of the revolving shell, by the effect of centrifugal force.

According to a first possible method of application, the shell is left immobile during after pouring, until the surface of the bath is smooth and still, after which the oxides which are floating on the top are skimmed off, then finally the shell is set in rotation.

Thus, after skimming but before the shell is set in rotation, there is available all the time necessary to subject the liquid metal to any known treatment, whilst the central cavity remains permanently heated. This treatment may thus be carried out in the best possible conditions. It may be a question, for example, for chemical refining, of bubbling through a neutral gas, or of de-gassing under vacuum.

Following another variant, the shell is revolved whilst the liquid metal is fed in, and this feeding is carried out from the bottom through the center of the heated cavity. For this, the metal may be fed through a movable vertical tube, of which the lower end projects into the central cavity whilst the bottom of the mould has channels or vanes radiating around the center in the direction of the peripheral mould. Likewise this feed from the bottom may be carried out by sending the metal up through a central hollow tube, the shell of the mould being surmounted at its center by a metal sleeve lined inside by refractive wallsto form a sullage piece where the oxides gather at the end of centrifuging, which allows a solid metallic plate to be centrifugally cast, there being finally on the bottom of the mould channels or vanes radiating in the direction of the peripheral mould.

In all cases, it is advantageous to keep the top of the mould connected by a revolving joint to a breathing and de-gassing channel during all the casting time.

Following a preferred method of application, the central cavity is permanently heated during casting to a temperature equal to or higher than that of the metal when it penetrates into this cavity, so that it is possible to flow from the bottom at a minimum temperature while the metal is heated in the cavity, which ensuresthat the metal is fed to the periphery of the revolving mound at a suitable temperature, and is at a higher temperature for the bore of the component to be made. In addition, to govern at any time the speed of transfer of the metal from the cavity to the peripheral mould, the speed of rotation of the mould is varied by a-programmer, while the central cavity is shaped so that the walls are steep. This, in particular, allows the metal to be poured rapidly in a single flow into the central cavity, after which the filling device is removed, the speed of rotation of the already loaded mould then being modified in one direction of the other according to a fixed program.

In a first case, the mould is fed at the bottom by a rising channel is a vacuum which is as complete as possible, then this vacuum is applied to the metal to disengage it completely before and during the commencement of rotation of the mould, after which the metal injection channel is plugged and the mould is set into rotation whilst the vacuum is maintained.

In a second case, the feed is from the bottom by making the molten metal rise by a complete vacuum, the metal being degassed during its ascent, after which the vacuum is broken which causes the fall of a valve previously recessed in the center of the cavity, the mould being finally set in rotation.

The device according to the invention for carrying out this process is characterized in that the bottom of the filling cavity has vanes, ribs or channels which radiate around the central axis in the direction of the peripheral mould, which they gradually join.

The attached drawing, given by way of non-limiting example, will allow the characteristics of the invention to be better understood.

FIG. 1 is an axial section of a shell according to the invention, which is still motionless after the metal has been poured,

FIG. 2 is a corresponding view after setting in rotation,

FIG. 3 is a variant in which the central filling cavity carries vanes totally submerged in the liquid metal,

FIG. 4 is a section along IV--IV (FIG. 3),

FIG. 5 shows another variant with vanes which emerge,

FIG. 6 shows an additional variant in which the filling cavity in annular, to allow large diameter flanges to be cast,

FIG. 7 is an axial section of a device according to the invention, in which feeding from the bottom is carried out through the lower part of the shell in order to obtain a centrifuged metal plate,

FIG. 8 illustrates the variation in the transverse section of one of the radial channels,

FIG. 9 is a plan view of these channels,

FIG. 10 is a plan view of a variant in the possible arrangement of the channels on the bottom of the shell,

FIG. I 1 shows a possible manufacturing variant of the crosssection of the radial channels,

FIG. 12 shows another variant in which the channel is made in a detachable clay capping,

FIG. 13 shows the method of filling with metal during feeding in order to case a plate,

FIG. 14 shows a method of feeding from the bottom with vacuum suction in the upper part,

FIGS. 15 and 16 show two successive phases when feeding from the bottom is carried-out through the upper part of the revolving shell,

FIG. 17 illustrates more particularly the case of the centrifugal casting under vacuum of a hollow component with feeding from the bottom through the base,

FIG. 18 shows a device designed to carry out from below the filling from the bottom of the mould under vacuum,

FIG. 19 is a perspective view of a recessed valve which may be used in the case of FIG. 18,

FIG. 20 shows another variant for feeding at the bottom from below,

FIG. 21 shows the process according to the invention for the casting of a centrifuged flange feeding at the bottom from above,

FIG. 22 shows the principle according to which the inven tion allows the instantaneous casting speed to be controlled by varying the speed of rotation of the mould,

FIG. 23 is a sectional view of a flangecast according to the invention, for example, in the case of FIG. 21,

FIG. 24 shows by way of comparison a heavy flange centrifugally cast with rapid transfer of the metal into the mould.

In the example shown in FIG. I and 2, use is made of a metal shell 1 carried by a lower shaft 2. The assembly is designed to revolve about its vertical axis 3.

The bottom of the shell 1 is shaped with a central cavity of revolution 4 the wall of which is covered with a layer 5 of an insulating and refractive material.

The bottom of this cavity 4 slopes gradually upwards and it joins smoothly into a mould 6 above it. This mould is capped by a horizontal cover 7 in the center of which there is a large opening 8.

The process according to the invention consists of pouring the liquid metal 9 into the shell 1 while it is at rest (FIG. 1). The metal 9 collects on the bottom of the central cavity 4 which is preferably heated. In this way the quantity of metal 9 necessary to obtain the required component 10 is poured, (FIG. 2). In order to pour the liquid metal 9 (FIG. 1), the normal precautions for decanting oxidizable alloys are observed. If, in spite of everything, some turbulences producing oxides are then caused, these oxides which float on the top are skimmed until the surface of the bath 9 is smooth.

The shell is then set in rotation (FIG. 2), and the liquid alloy, carried by this rotation, is subject to the effects of centrifugal force, and moves outwards filling the mould 6 without turbulence. After solidification the cast component 10 is ob tained.

Naturally, the surface of revolution of the bottom 5 of the initial filling cavity 4 is joined in a smooth fashion to the mould 6 of the shell 1, its central section being in a curve designed so that the mould 6 is filled without turbulence.

To avoid the setting in rotation of the liquid alloy 9 causing, because of its inertia, eddies resulting from from a slipping of the bottom 5 of the cavity below the alloy, this cavity 4 may be provided with vanes 11 spread all around the circumference. These vanes 11 may or may not pass through the axis of rotation, may or may not be inclined to the horizontal, and may or may not be rectilinear (FIGS. 3-6).

In particular the vanes 11 may not reach the axis of rotation, thus leaving a central free space which allows the liquid metal 9 easily to find on initial filling the same level in all the compartments they form. They may not project above the surface of the liquid after filling (reference 11a, FIGS. 3 and 4), thus allowing the easy skimming of floating oxides. On the contrary, they may emerge from the surface of the liquid (reference 11b, FIG. 5), if it is feared that they would cause eddies in the liquid 9 after setting in motion.

A complementary advantage of this method of casting lies in the fact that the alloy penetrates rapidly, uniformly around the whole circumference, and at one time into the mould 6. Therefore there is not an rolling of successive layers the ones on to the others, layers between which there sometimes remain micro-segregations of oxides which give rise to external flaking.

If the diameter of the components to be cast is large, the initial filling cavity 12 may have an annular shape (FIG. 6) so as to limit the exposed surface of the alloy 9, that is to say, its superficial oxidization and cooling before it is set in rotation.

This annular cavity 12 may likewise be furnished with driving vanes which emerge 11b, or do not emerge 11a.

In the example shown in FIG. 7, use is made of a plate 101, the revolving vertical shaft 102 of which is carried by

bearings

103 and 104. On the plate 101 is placed a metal shell which comprises a bottom 105, an external rim 106, and a cover 107. This cover carries at its center an opening surmounted by a cylindrical sleeve of revolution 108 of which the side and top walls 109 are insulating and refractive. At its top, the sleeve 108 is pierced with an opening 110.

A vertical central conduit 111 co-axial with the shaft 102, passes through the bottom 105. The joining of this conduit and the flat bottom of the shell is carried out by a bell-mouth 112 of the conduit 111. Into this bell-mouth 1 12 there open several feed channels 113. These channels are grooves cut in the bottom 105 of the shell; they go from the central bellmouth 112 to the periphery 106, and are disposed regularly about all the circumference.

Finally, the vertical conduit 111 is preferably lined with a tubular lining 114 of insulating and refractive material. This lining is conical both on the interior and the exterior, so that if the cast component does not disengage from the central conduit 111, the lining 114 disengages easily with the metal solidified in the conduit, after which it is replaced for the manufacture of the following component. This lining is continued downwards by a refractive metal tube 1 15 used to draw off the liquid metal.

There is thus obtained a centrifuging machine (FIG. 7) in which the liquid metal is fed upwards to the bottom through the tube (arrow 116).

The operation is as follows:

After the machine and, in consequence, the

shell

105, 106, 107 is set in rotation at a suitable speed, by various processes which will be dealt with later the rising from the bottom of the molten liquid alloy in the central conduit 111 (arrow 116) is brought about. The liquid arrives in the upper bell-mouth 112 and the combination of weight and centrifugal force makes it penetrate, then flow, in the radial channels 113. The mould formed by the internal face of the rim 106 is filled progressively from the periphery towards the center, while the alloy is subject to centrifugal force and the air escapes from the mould by the upper hole 110 ofthe sleeve 108 (arrow 117).

In proportion as filling is carried out, the bore diminishes and the metal arrives in the

sleeve

108, 109 above the central orifice of the cover 107. Owing to the combination of weight and centrifugal force, the surface of the liquid metal passes successively through the

shapes

118, 119, 120, 121, 122, 123, 124, 125, 126, 127 shown schematically in FIG. 13. So long as the shape 124 has not been reached, the metal keeps the profile 1 18b. The flow is stopped when the sleeve 108 is on the point of overflowing through its upper central orifice 110, which corresponds to the profile 127.

The co-axial conduit 11 1 is then blocked in its lower part to prevent the liquid metal from falling again and the rapid solidification of the cast component 128 (FIG. 7) is awaited, the

shell

105, 106, 107 being usually made from a conducting material. The central part 129 having been the last to be fed, while the periphery is already practically solidified, it is the insulating

sleeve

108, 109 which will serve as a sullage piece for the feeding of the contraction of the component at its center. In addition, if some oxides have appeared in spite of the nonturbulent flowing of the piece, they have been constantly thrown up to the paraboloid form of the surface of the bore (profiles such as 125 or 126), so that these oxides are finally brought together at the end of casting at the level of the upper zone of the insulating

sleeve

108, 109 which forms a sullage piece.

In the final stage, the rotation may be stopped so that the exposed surface in the sullage piece 129, which is still liquid, may remain flat, during the contraction phase, as the surfaces of isolated sullage pieces generally are.

After cooling, the component 128 is removed from the mould. The cover 107 and the insulating sleeve 109 being detachable, the plate 128 is grasped by the central sullage piece 129 and drawn vertically upwards. One of the essential characteristics of the process which has just been described, results from the fact that, in spite of the liquid metal being fed whilst the

shell

105, 106, 107 is rotating, the filling of the latter is carried out absolutely without eddies and without causing any turbulences. To reach this result, the speed of rotation as well as the shape and distribution of the channels 1 13, is suitable chosen. Each of these channels is a groove cut in the bottom 105 of the shell, and its depth diminishes from the central bell-mouth 112 in the direction of the peripheral zone 106. This is shown particularly in FIGS. 7 and 8 for three different sections 113a, 1131: and 1130 of the same channel. In this case, the vertical walls 130 have a draw upwards.

The channels 113 may leave the central bell-mouth 112 radially and reach the exterior of the shell perpendicularly to the circumference of the zone 106 (the case of FIG. 9). Equally well use could be made of channels 113 which leave the central bell-mouth 112 tangentially (the case of FIG. 10) and curve so as to arrive perpendicularly at the exterior circumference.

It is imperative that, during the flow, the channels 113 which are uncovered should not overflow. It this occurs, there would appear the turbulences and the spraying which it precisely sought to avoid. The central feeding of the mould through the conduit 111 must therefore be varied in consequence. The speed of rotation of the

machine

101, 102, 105, 106, 107 must likewise be varied in a corresponding way. This speed must be increased in proportion as the bore diminishes (

profiles

118, 119, 120 etc. FIG. 13) in order to retain an appreciable centrifugal acceleration.

It has been seen (FIGS. 8, 9 and 10) that the cross-section of the channels 1 13 can diminish towards the periphery, which is normal since the speed of flow of the metal increases with the centrifugal force, given that the distance from the axis of rotation increases during the flow. This section, which is deep and narrow on leaving the bell-mouth 112 of the central channel 111 (section 113a) must widen and become shallower towards the exterior (section 1130) to avoid turbulences on arrival on the exterior wall 106 of the shell. In addition, this makes it cheaper to remove later by machining the ribs formed by these channels under the component 128 when it is removed from the mould.

To ensure that the channels 113 do not overflow, they may be given a special conformation corresponding to a U-section inclined at an angle to the horizontal (FIGS. 11 and 12). In this case, the direction of rotation is chosen so that the tangential speed 131 of the bottom 105 (FIG. 11) is consequently opposed to the inertia of the liquid metal when this latter flows out of the section 1l3b of the channel. Since these channels with an inclined section are cut directly in the bottom 105 of the shell, the solidified plate 128 must be removed from the mould by giving it a twisting movement intended to disengage the rigid metal from the channels.

If this conformation is used (FIG. 11), it is necessary to make the medial line of the

channels

113, 113a pass through the axis of rotation 132 of the machine, or else removal from the mould would be impossible. In order to avoid this disadvantage, the

channels

113, 113d may be cut in a lining 133 made from refractive clay which is itself inserted in wider channels 134 out with a symmetrical upward draw into the bottom 105 of the shell. In this case, the linings 133 are destroyed each time a part is removed from the mould.

Whether it is a question of channels 113 (FIG. 8) or oblique section channels 113d (FIGS. 11 and 12), the easy penetration without turbulences of the metal from the central bell-mouth 112 will be facilitated by arranging these channels as shown in FIG. 10, the direction of their leaving the bell-mouth 112 tangentially corresponding to a direction of rotation 135 of the machine. The liquid alloy is thus brought into the mould 106 with a speed of rotation equal in tangential projection to that of the shell, and this simultaneously at several points, so that the metal has no tendency to slide through inertia on the wall of the mould. This guarantees a feed spread over all the circumference of the zone 106, which is favorable to obtaining a sound casting.

It will likewise be noticed that the method of casting described, which is akin to the type known as bottom casting", presents, however, the advantages of poured" casting, filling being carried out from the outside of the mould towards the sullage piece 129.

The feeding of the

central channel

111, 115, by liquid metal from the bottom may be carried out in several different ways.

Following the variant of FIG. 14, the

shell

105, 106, 107 is made relatively airtight and the central hole of the sleeve 108 is surmounted by a tube 149 connected by a revolving joint 150 to a vacuum pump, not shown. Metal previously introduced into a supply pocket or furnace is drawn in.

There is then obtained, besides the advantages due to the non-division of the metal, a centrifugal casting under vacuum, that is to say, without oxidization. The depression in the tube 149 is ceased when the insulating

sleeve

108, 109 serving as a sullage piece 'is filled, which allows the effect of weight to facilitate the feeding of the component. For an alloy of density 2.7, for example, the total possible vacuum suction height is about 3.7 meters, which is amply sufficient to use only a partial vacuum, taking account of the height of the shaft and tooling to be provided as a general case.

There is illustrated in FIGS. 15 and 16 another variant in which a false bottom-feed of the centrifuging

shell

105, 106, 107 is carried out. There is no co-axial conduit in the revolving shaft 102 of the machine. A flow-tank 136 is placed above the central insulating

sleeve

108, 109 and a fall, or flow-tube 151, passes through the hole of the sleeve 108 and ends in a central depression 152 hollowed in the bottom of the shell in the zone from which leave the radial channels 113. The tank 136 is filled with the metal 137 to be poured; the quantity of metal admitted to the shell is measured by operating a stopper-rod 138 of which the action is sufficiently precise for the outflow to be measured exactly.

This adjustment is such that after the shell is set in rotation and the stopper 138 is opened, the level in the central depression 152 remains constantly suited to the correct flow of the metal in the radial channels 113, the lower end of the feed tube 151 being constantly below the exposed surface in the central depression and even below the bottom the feed channels. In this way the whole of the component is supplied and the tube 151 is withdrawn by raising the flow-tank 136 before the metal has started to solidify in the central part of the plate 128 (FIG. 16). This arrangement is economical the only risk of the turbulent production of oxides taking place at the moment when the metal arrives at the bottom of the central depression 152.

In FIG. 18 there is shown a horizontal shell 201 which turns by known methods around a vertical axis 202. The peripheral rim 203 of this shell forms a mould 204 in which it is proposed to centrifuge the liquid metal. The whole is capped with a cover 205 fitted with a sealing joint 206. The shell 201 has a central cavity 211. The bottom of this cavity 211 slopes gradually in the direction of the peripheral mould 204, while radial ribs 212 prevent the formation of eddies during the transfer of the liquid metal.

Following a characteristic of the invention, the bottom of the cavity 211 is formed by a sheet 213 of refractive steel below which there is a layer of refractive clay 214. Within this clay there are embedded electrical heating resistors 215 supplied at all times whether stopped or rotating by revolving sliprings fixed to the shaft 208 of the machine, and rubbing on appropriate contacts 209.

The walls of revolution of the cavity 21 1 are very steep. The lining 214 and the heating resistors 215 extend all along an axial channel 219. This channel is provided to carry out the bottom feeding of the cavity 211. It opens in the center of the latter through a seat 220 below which it extends to a ferrule 221. A detachable plug 224 ensures the blocking of the lower end of the ferrule 221 when this is required. This plug 224 turns freely on a control support 222 which may be lowered (opening) or raised (closing). The

assembly

221, 224, 222 is submerged in molten metal 223.

To facilitate removal from the mould, the refractive steel tube 219 is given a shape with a draw which widens upwards. In addition, a recessed valve 225 made from refractive alloy is used, resting by its own weight on the seat 220. The valve 225, of which details are shown in FIG. 19, comprises a disc 226 fitted with a tail formed by radial partitions 227. This tail ensures the guiding of the valve in the upper part of the tube 219, whilst allowing the liquid metal to circulate between the partitions 227 At its center, the cover 205 of the mould is surmounted by a chimney 228 connected permanently by a revolving coupling 229 to the tubing 230 of a known vacuum suction installation.

Use may be made of this device in two different ways which will be described later but using in both cases a common principle of centrifuging. This principle is as follows:

When liquid metal is contained in the heating cavity 211 which revolves with the

mould assembly

201, 205, the exposed surface of the bath of metal is hollowed out with a profile in a paraboloid of revolution. This paraboloid becomes more and more hollow in proportion as the speed of rotation increases.

There is shown in FIG. 22 a first profile corresponding to the surface of the bath of metal for a low speed of rotation of the mould. The heating cavity 211 is then practically full of molten metal. If the rotation is accelerated, the paraboloid is hollowed out and the surface of the bath finds a balance, for example, following a new profile 232. The passage from the profile 231 to the profile 232 is carried out by the evacuation from the cavity 211 of a certain quantity of metal which is which is centrifuged towards the mould 204 to supply the component 233 which is being cast. So long as the speed of rotation remains at this new value, the bath remains stable following the profile 232. If the speed of rotation is again increased, the profile is further hollowed out, for example, to the paraboloid 234, which is accompanied by a fresh drawingoff of metal by centrifuging from the cavity 217 to the component 233. By accelerating again, the cavity 211, the walls of which correspond to a paraboloid 235, is emptied completely.

It will be seen therefore that the liquid metal having been rapidly poured all at once into the central cavity 211 at a relatively low temperature, the pouring equipment becomes immediately available to pour into another mould. However, in the mould already loaded the resistances 215 may carry out an additional heating of the liquid metal, then, by programming and varying the speed of rotation of the mould, the law according to which the speed of flow of the liquid metal varies during the transfer from the cavity 211 to the mould 204 may be decided at will. For example, at first a rapid speed of flow towards the mould 204 may be ensured, and on the contrary a slow speed of transfer towards the end, that is to say, when the component 233 is already in course of solidifying.

This method allows of obtaining particularly sound components, as is shown in FIGS. 23 and 24. In FIG. 24 there is shown a metal flange 236 obtained by centrifuging when the casting is carried out in a single transfer. In is known that there appears on the internal face of this flange a deep shrinkage hole 237, sometimes matched by underlying shrinkage holes 238. In addition, the marked turbulences observed during the centrifuging diffuse the oxides and impurities 239 over a relatively thick zone 240 in the internal part of the flange 236. This zone 240 must be eliminated to obtain a sound component. I

On the other hand, the process according to the invention allows of obtaining a flange 233 (FIG. 23) on the internal face of which the zone to be eliminated 241 is much thinner. This arises on the one hand from the fact that the absence of turbulences brings together in a layer deposited at the last moment the oxides 239 which could have been produced in spite of the precautions taken, and on the other hand, from the fact that the variation of the speed of feeding the metal into the mould 204 allows the shrinkage hole to be filled in proportion as it has a tendency to appear, so that finally the solidified component shows a very shallow shrinkage hole 242. During its stay in the cavity 211, the liquid metal constitutes a sort of internal sullage piece which fills the shrinkage hole.

It has been indicated above that the equipment according to FIGS. 18 and 19 may be used with this principle of programmed variation of the speed of rotation in two difierent methods.

First method.

With the mould 201,205 motionless, the vacuum is applied through the tube 230. It must be understood that it is not a question of simply applying the depression once and for all. The tube 230 ensures a permanent vacuum as complete as possible and a constant de-gassing of the material in the mould. The flow is then carried out by opening the plug 224, the vacuum causing the metal to rise in the tube 219 and the raising of the valve 225. The heated cavity 211 fills with liquid metal. The vacuum is allowed to be applied to this metal for complete de-gassing. The

mould

201, 205 is then set in rotation, then the feed channel 221 is blocked by means of the plug 224. As previously, the speed of rotation is varied at will, whilst the vacuum is allowed to remain through the tube 230 until the component is completely solidified.

Second method.

As previously, the metal is made to rise into the cavity 211 by the action of the vacuum, while the mould 201,205 is stopped. The metal is de-gassed during its ascent in the course of which it raises the valve 225. The vacuum is cut off at the level of the tube 230 and the valve 225 falls back on its seat 220. Rotation is then started according to a programmed speed until the component has solidified. This method therefore consists of carrying out the filling of the cavity 211 under vacuum, followed by centrifuging towards the mould 204 with the vacuum which remains trapped in the mould.

To cast large components centrifugally, use may be made of a heated central cavity 211 of which the volume is smaller than that of the component to be cast. It is then necessary constantly to continue the supply of metal, under vacuum or under load, into this cavity 211 whilst the mould 204 is being filled.

There is shown in FIG. 20 a variant in which the feeding of the tube 219 from the bottom is carried out through a revolving joint 250, by means of a fixed tube 251 and a flow tank 252. This tank, placed to give a gravity feed, contains the liquid metal 243, the outflow of which is controlled by raising a stopper-rod 253 to a greater or lesser extent. The cover 205 here may still be connected to a de-gassing tube 230.

There is shown in FIG. 21 another variant in which the feed at the bottom by means of a tube 210 from above allows of obtaining a particularly sound flange 233, of the kind already described in FIG. 23. Since the shrinkage hole 242 is particularly shallow, the zone 241 which has to be eliminated, remains small.

I claim:

1. A process for the centrifugal casting of metal components in a horizontal shell adapted to revolve about a vertical axis, comprising the steps of:

a. providing a cavity below a mold and in communication therewith for receiving molten metal to be cast;

b. forming generally radial channels in the bottom of said mold for distribution of the molten metal from said cavic. heating said cavity to maintain molten metal supplied thereto in a liquid state; supplying liquid metal into said cavity at a rate of flow to prevent overflow of the generally radial channels;

e. rotating said mold and said cavity at a speed sufficient to cause the liquid metal contained in said cavity to be transferred to said mold by centrifugal force and conform to the configuration of said mold while preventing overflow of the generally radial channels to provide smooth radial transfer of the molten metal to the mold and preventing undesirable turbulence in the molten metal.

2. The process as claimed in claim 1 further comprising the steps of simultaneously supplying the molten metal to said cavity while rotating the shell and discharging the molten metal into said cavity at the bottom and in the center of said cavity.

3. The process as claimed in claim 2, further comprising the steps of supplying a molten metal to said cavity through a vertical tube having one end attached to the center of the bottom of said cavity and in communication with said cavity and its other end in communication with a source of molten metal.

4. A process as claimed in claim 1 further comprising the step of providing a metal sleeve having an internal refractory lining above and at the center of the mold for forming a cavity in which the oxides are gathered at the completion of a centrifuging operation.

5. A process as claimed in claim 1 further comprising the step of connecting the top of the mold to a vacuum source during rotation of the shell for performing a de-gassing operation on the molten metal during casting thereof.

6. A process as claimed in claim 1, further comprising the step of varying the speed of rotation of the mold to progressively fill the shrinkage hole which tends to be formed in the cast part as the metal solidifies.

Claims

1. A process for the centrifugal casting of metal components in a horizontal shell adapted to revolve about a vertical axis, comprising the steps of: a. providing a cavity below a mold and in communication therewith for receiving molten metal to be cast; b. forming generally radial channels in the bottom of said mold for distribution of the molten metal from said cavity; c. heating said cavity to maintain molten metal supplied thereto in a liquid state; d. supplying liquid metal into said cavity at a rate of flow to prevent overflow of the generally radial channels; e. rotating said mold and said cavity at a speed sufficient to cause the liquid metal contained in said cavity to be transferred to said mold by centrifugal force and conform to the configuration of said mold while preventing overflow of the generally radial channels to provide smooth radial transfer of the molten metal to the mold and preventing undesirable turbulence in the molten metal.

7. A process as claimed in claim 2, further comprising the step of providing a vertical filling tube means extending downwardly into the cavity for feeding molten metal into the bottom of the cavity.