US2107513A - Centrifugal cast - Google Patents

Description

w. SWOGER CENTRIFUGAL CAST Filed Oct. 21, 1935 2 heets-Sheet 1 &

Feb. 8, 1938. w. SWOGER 2,107,513

CENTRIFUGAL CAST Filed Oct. 21, 1935 2 Sheets-Sheet 2 221 IEQENTgR. BY a/rasfl,

2 ATTORNEZ Pate ted Feb. 8, 1938 UNITED STATES PATENT OFFICE ommrucar. css'r William 8mm, Mich. Application octobcr 21, 1935, Serial No. 45,934 comma, (c1. 22,-)

This invention relates to foundry practices in the casting of metals, more particularly the casting of steel in which the molten metal is subjected to centrifugal forces during the freezing period.

, The use of centrifugal force in the casting of metal has been known and used as a foundry practice for many years, especially in the formation of hollow castings, such as lamp posts and the like. This method of casting has the general advantage of placing a constructive force on the metal during the molten stage and allowing the -force to act during the freezingperiod, so that the heaviest material, viz., the molten metal is forced against the wall of the mould by the centrifugal forces induced by inertia in the molten metal by the rotation thereof, and the lightest materials, such as gas, slag, inclusions, etc.,' are forced inwardly, because they are lighter and therefore are not influenced to as great an extent by the centrifugal forces.

This method has also been used in theformation of solid castings, which, after the croppage .has been cut away and the castings cut into billets, have been placed directly into the rolling mill without resorting to the usualintermediate steps, such as reheating, etc. 'As the metal that is formed by this method of casting is extremely dense and clean. many of the intermediate passes through the rolls are avoided, and instead of passing the billet through numerous forming '1 rolls, only a few passes are necessary to give the metal the desired form. Therefore much time and expense is saved bythe use of this method of forming the billeta Furthermore, the metals, especially steel, that are cast by this method, have a greater density and consistency than metals formed in the usual manner, as the metals are more likely to be free from pipes, blowholes, cavities, etc. The steel formed by this method is free from dendritic structures, and other forms of segregation found in steel made in the usual practice. Inclusions ,and. other impurities are prevented from vitiating, the steel because they are in general lighter than the molten steel and are displaced toward the center by the centrifugal force where the may be cutaway in the croppage.

A shallow depth of the mould is that the paththat the gases and other impurities must travel to a concentration, point is relatively short, and as-there is a constrictive force applied 'to the hot metal, there is great certainty that these extraneous materials will have ample opalso easily ob tainable'by the use of a mould of this type, so

portunity to concentrate, whereby a cleaner metal is attained in the casting.

These advantages are inherent in the use of centrifugal force in the casting process, but in' the past these advantages have not been available to the foundry worker because cenain practical difllculties have intervened to prevent their full utilization. For example, great difficulty has been experienced in maintaining an open path to the atmosphere through which the gases in the casting form are able to escape during the pouring and freezing period of the molten metal. Difficulty has also been experienced in keeping the metal hot enough during the freezing period for a sufilcient length of time to give the centrifugal forces induced by rotation in the molten metal an opportunity to act, hence the metal freezes solid before the advantages outlined above have been attained. The method of introducing the hot metal into the mould has also been inexpedient, so that much'dross is collected in the process of pouring. In this way the croppage to be. cut away becomes extremely large, in some cases exceeding fifty percent, making the known process very wasteful and expensive.

The present method of pouring the hot metal into a centrifugal cast has the further disadvan tage of being dangerous to the foundry worker, as. the hot metal has been impinged against a refractory surface from which the metal has splashed with violence. This spl ng of the hot metal also causes oxidation of the particles of metal due to contact with the air, the oxidized particles being carried into the mould, where they tend to cause segregation in the cast, the oxidation increasing the percentage of dross to be removed by the centrifugal forces. It is these disadvantages of the present methods of using the centrifugal cast that the present invention overcomes and solves with a high degree of efficiency. There is provided a means which gives the gases in the molten metal in the mould a free path to the atmosphere during the freezing period, and at the same time insulates the heat in the mould so that the centrifugal forces will have ample opportunity to fulfill their ber of surfaces, and those surfaces which come into contact with the hot metal, are clean so that there is a minimum opportunity to collect impurities. Furthermore, the pouring process is madefabsolutely safe for the foundry workers,

because the molten metal and the cast move in a convergent direction at approximately the same speed, so that there will be a minimum of disturbance at the pouring point.

As there is no disturbance at the pouring point during the pour, there is little opportunity for oxidation of the molten metal, which results in It is a further object of this invention to provide a method of casting metals in which the molten metal is moved in such a manner as to induce centrifugal forces therein during the freezing period, the centrifugal forces causing a constrictive action in the molten metal whereby extraneous materials are displaced to a concentration point, thereby insuring the completed casting to be free from pipes, cavities, blowholes, segregation, inclusions, etc.

It is a further object of this invention to provide'a mechanism to rotate a casting form in which molten steel is to be moved to induce centrifugal forces therein during the freezing period, which will insure greater efficiency in the pouring method by directing the metal stream from the ladle directly into the cavity of the mould under the influence of gravity, thereby preventing the molten metal from contacting extraneous surfaces to collect impurities therefrom, and also to prevent undue splashing of the metal which endangers the operators.

It is a further object of this invention to provide a flux material toform an insulating cover or hottop for the molten metal while it is under the influence of centrifugal forces in order that the metal will have sufficient time to attain a stable condition and to allow the imprisoned gases in the metal to escape before the freezing process solidifies the metal.

It is a further object of this invention to provide a mechanism to form cast steel ina billet of standard cross-sectional dimensionwhich will be suitable for rolling without. distorting-the grain of thesteel by asymmetrical attenuation.

. It is a further object, of this invention to provide amechanism for casting metal which will form a billet "of symmetrical cross-section for rolling-or milling after an extension for croppage has been cut away.

It is a further object of this invention to provide a means to cast'metal in the form of a billet by theuse of centrifugal force in which the croppage is reducedto a minimum, viz., aboutfive percent "or less of the billet.

It isa further object of this invention to provide a centrifugal cast'for metal in whichthe rotating plane of-the cast is angular with the horizontal 'plane so that molten metal can be conveniently directed into a concentric gate under the influence of gravity, the speed of the cast being approximately equal to the speed of the molten metal at the pouring point in order that the disturbance at the point of contact, of the metal and the cast will be as small as possible.

.It is a further object of this invention to provide a rotating cast for metal having its rotating time when the speed of the molten metalis approximately the same as that of the mis d. at

a point where the movements of the metal and the cast are converging.

It is a further object of this invention to provide a centrifugal cast having retaining walls to enclose the molten metal, so as to form the metal into billets having a uniform shape.

It is a further object of this invention to provide a centrifugal cast in which provision is made for the expansion and contraction of the metal during the pouring and freezing periods, so that an enclosing mould may be used to define the dimensions of the billet.

It is a further object of this invention to provide a centrifugal cast in which an enclosing mould is used to define the dimensions of the billet, the mould having a pouring gate in commetal to insure a longer freezing period at the point where the pouring gate communicates with the mould, thereby giving the molten metal an open path to the atmosphere through which it may'discharge gases, 'etc. v

It is a further object of this invention to provide acentrifugal cast in which the retaining walls of the mould can be readily repaired and made smooth by simple operations, so that the mould may be used numerous times to form billets, thereby insuring a low unit cost per billet in the foundry.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification, wherein Figl 1 is an elevational view of my cast, having parts thereof cut away to show the details of construction.

Fig. 2 is a sectional view of my cast taken at the pouring point.

Fig. 3 is a plan view of the cast.

Fig. 4 is a perspective view of the completed ingot or billet formedin the cast.

Fig. 5 is a sectional view of the ingot showing the relation between the ingot, the pouring gate, and the application of the centrifugal force.

Fig. 6 is anelevational view of the cast (cutaway) showing the wedge arrangement to compensate for theexpansion and contraction of the ingot.

Fig. 7 is a plan view of the wedge shown in Fig. 6. 7

Before explaining the invention-in detail it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also it is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation, and it is not intended to limit the invention claimed beyond the requirements of the prior art.

Referring to Fig. l of the drawings an embodiment of my invention is illustrated. A rotating table I!) of any suitable dimension is pro.- vided, the table being mounted by means of a shaft H into a bearing l2. The bearing I2 is in turn firmly held in position by means of a suitable material. Upon the rotating table the v to fit the Shaft ll.

cast I4 is mounted, which will be described in detail later.

The rotating table if] comprises a ribbed face plate 15 mounted ona hub l6, which is journalled The exact design of this mechanismis optional with. the builder, but it must be made suificiently strong to bear the stresses incident to its use in the casting of metal under the conditions to be outlined in detail later in this specification.

In order that the table l may be rotated to induce centrifugal forces in the cast l4 mounted thereon, any convenient motor means may be harnessed to the face plate in any conventional manner, as for example the use of the pinion l'l mounted on the shaft 18, which is directly connected for driving to the motor means (not shown), the pinion l1 cooperating with a gear formation Ilia on the periphery of the hub I5. It is desirable to have the motor means under control so that the table in may be rotated at varying speeds or be stopped by brakes at the will of an operator. If the motor means is an electric motor, for example, this variable speed may easily be attained through rheostatic control, and

braking by a loaded feed-back.

The table II] as shown in Fig. 1 is mounted at an angle with the horizontal plane to attain advantages in pouring'the molten metal into the cast id, but the table, if desired or convenient, may also be placed in a horizontal position. This angle of inclination may vary over wide ranges, depending upon attendant circumstances varying 'the design, such as the size of the table, the

dimension of the ingot, the magnitude of the centrifugal forces, etc.

A peripheral flange i9 is provided for the table In, it being attached to the face plate I5 of the table by any convenient means, as for example, by a peripheral angle-iron 20, which may be held in position by rivets or studs 28, or by welding, if desired. The flange l9 has a shielding function to prevent hot metal from being thrown outwardly by the induced centrifugal force during a pour, and for this purpose itmay be made any desired height, as for example in Fig. 1, the flange is made approximately as high as the mould M. Furthermore, the flange has a centering function which will be described later.

On the face plate l5, there is positioned the cast or mould M, which is divided into an upper and a lower segment, designated by the characters 30 and 3| respectively. The lower segment 3| has a base of considerable area which contacts the face plate I5, being held in position by gravity in the embodiment shown in Fig. 1. The dimensions of the cast l4 may be varied to suit the needs of the billet to be formed therein, and is preferably made in such a manner as to be readily repaired on its inner' surface. In like manner it may be fastened to the face plate in anyv convenient manner, for example bolts and studs may be used to fasten it to the face plate instead of using gravity as suggested above.

The peripheries of both the upper and lower segments are provided with outwardly extending flanges 33, which cooperate with each other to form a peripheral rib around the-mould I4, the rib serving as a barrier between the main body of the mould and the shield l9. formed between them which serves as a cache for the hot metal that may escape from the mould during a pour. The upper segment 3i] is w A pocket is concentric with the lower segment 3| so that a mould or cast of toric shape is formed between them. The two segments cooperate with one another at their outer portions where the upper segment rests in position on the lower through action of the force of gravity. Mechanical fastening means may be employed to hold the segments in their relative position, if desired.

The segments 30 and 3| are made of any suitable material, preferably they are made of high grade cast iron, with such dimensions as to fulfill their function. The dimensions of the segments are dependent upon the size of the ingot,

the speed of rotation, the factor of safety, etc.

The segments are easily repaired after their inner surfaces have become pitted under the action of the hot metal. The upper segmentis removed from the lower for this purpose, and by a simple turning process in a lathe, the pitted portion is cut away, and the segmentsare again in condition for use.

At a point relatively nearer the center of the table In, the two segments of the mould I4 00- operate to form an annular pouring gate 32 whose inner edge is large enough to allow molten metal from a pouring ladle L to be directed thereinto with ease and whose outer edge, where the gate is in communication with the space between the segments, is constricted to some extent, not sufficient, however, to prevent the molten metal from entering the mould readily. It is desirable to have the pouring gate in such form that the molten metal enters the cavity of the mould by touching as few surfaces of the mould as possible, and the gate preferably communicates with the mould at the point where the least dense of the poured material is located and concentrated after relative displacement by the centrifugal force has occurred, that is, the pouring gate entrance is preferably on the inner annular line of the toric mould so that the line on which the centrifugal forces act will substantially pass through the entrance.

The reason for placing the pouring gate in this relation with the mould is that at this inner point of the mould all the dross in the metal will tend to concentrate under the constrictive force of the centrifugal forces, and will form an extension at this point of the impurities in the metal. the extension being easily cut away as croppage, leaving the ingot pure and clean. At the same time, this relation between the pouring gate and the mould provides a space into which the operator can place insulating and fluxing material to form a hottop to keep the molten metal in fluid con dition for a long period of time, thereby allowing the gases in the metal in the mould to escape into the pouring gate, and thence through the fluid hottop into the atmosphere. In this way, a clear path for gaseous material is maintained so that it may effect its escape into the atmosphere from the interior of the mould. If

.the gases were allowed to remain in the mould they combine with the hottop to form a slag, which will subsequently be cut away from the ingot in the croppage.

The croppage or trimming that is out way from the ingot under this method of casting metal is very small, as it consists largely of the neck or extension formed by the material forced into the pouring gate under the action of the centrifugal force, the uniform cross-section of the ingot itself being not materially disturbed. Better conditions in the rolling mill are gained thereby, as the uniform dimensions of the billets entering the mill will give more uniform finished products. The uniformity of the billets before their entrance to the rolling mill will also insure more equal attenuation of the metal in the processof rolling, as it will not be necessary to shape the metal more in one axis than in the other.

To make the pouring of the molten metal'from a ladle into the pouring gate more convenient, and to keep the danger of contact between the hot metal and the mould as remote as possible,

for reasons given above the cut on the upper in the casting of steel, but as stated before it segment 30 which defines one wall of the pouring gate, is made substantially vertical, no matter at what angle the rotating table lfl is inclined. The cut on the lower segment 3| is made in proper relation to the cooperating cut on'the upper segment 30, so that the mouth of the pouring gate is of convenient size for the operator, and thence converging to form the relatively narrow inlet to the mould as has already been described.

The space into which the molten metal is poured for casting, called hereinbefore as the mould, is designated by the reference character 40, and has been described as being in the shape of a torus. As shown in Figs. 1 and 2, the crosssection of the toric ingot (shown in Fig. 4) is substantially in the form of a square, being rounded at the corners, with one of the diagonals of the square substantially coincident with the line of action of the induced centrifugal forces,

while the other diagonal of the square is sub-' stantially at right angles to the rotating table It). The concentric pouring gate communicating with the toric space at the inner corner of the square, as has already been described indetail above. I

The cross-sectional contour of this space in the mould is optional and may be varied to suit conditions. The instant contour was selected oecause it makes the problem of crop-page more simple and at the same time tends to compensate for stresses caused by the expansion and contraction of the contacting metals during the freezing period, or for any stress that arises due to changes in temperature.

To compensate for the expansion and contraction of the parts under changes in temperature, there are provided cam surfaces and wedges 50 at spaced intervals along the peripheral flanges 33. Cam-surfaced notches 5| are cut away in the cooperating surfaces of the flanges into which are fitted the wedges 50. The bases of the wedges abut against the shield l9, as shown in Fig. 7, so that as the segments 30 and 3| expand outwardly, the wedges 5|) will be driven inwardly with reference to the cam-surfaced notches 5|, thereby forcing the upper and lower segments of the mould l4 apart. This separation will ease the stress and is self-compensating to give the metal castan opportunity to expand and contract tothe demands of temperature.

The hottop which to be placed into the pouring gate afterthe cast has been poured ismade of fire clay and borax in the following proportions:

Parts Fire clay... "s 2 Borax 1 material that is to be used in any given pour depending upon the size of the gate into which it is to be placed, sufficient hottop must be used to form a good insulating cover for the hot metal in the gate opening. A long cylinder is usually utilized for conveniently dashing this material into the gate. The mixture given above is suitable for all metals except those known as sulphur steel, in which case he borax or" the hottop is displaced in the sam rcportion by sulphur.

The centrifugal cast is described as being used may be used with advantage in the casting of all metals. The process follows these steps:

First the interior of the mould is carefully cleaned and examined for faults. done by lifting the upper segment from the iow er throughthe use of the ears provided for this purpose. The upper segment is then replaced into concentric position upon the lower segment, and the complete mould carefully centered on the rotating table by the use of the centering bolts in the shield. After the centering is perfect, the centering bolts are loosened and wooden blocks are placed between the mould and the shield, so that the mould may expand under an increase in temperature without causing undue strain.

The mould is then heated to a temperature of approximately one-hundred and fifty degrees and rotated to attain a uniform speed before the ladle for the pouring of the steel is moved into position over the pouring gate. The speed of rotation of the mould is preferably such that the speed of the pouring gate as it moves past the orifice of the ladle is approximately equal to the average speed of the molten steel as it issues from the orifice of the ladle to enter the pouring gate. This uniformity of speed of the metal and the mould at their point of contact will tend to decrease the disturbance between them, thereby giving better resuits as pointed out above.

The orifice of the ladle is moved into position with regard to the pouring gate, so that the molten metal issuing from theorifice moves in a direction convergent with the movement of the gate. The position best qualified to fulfill these conditions is a quartering position from the bottom on the leading side with regard to the rotation. At this point, the metaland the gate are moving in a converging downward direction, which will give a minimum of disturbance during the pouring period.

Assuming that the ladle is in pouring position and the mould rotating at the proper speed, a weighed quantity of steel is poured into the mould, the amount being determined either by calculated orempirical means. A suflicient quantity of steel is poured into the mould to fill the cavity therein completely, with a small amount flowing into the pouring gate as shown in Fig. 5. This additional amount creates aflange-like protrusion of steel on the ingot whichis usually contaminated by dross and slag from the steel in the This may be.

ingot and also from the hottop. This protrusion will be cut away in the trimming or croppage.

The moment the steel has been poured into the mould, the hottop is dashed into the pouring gate, which immediately forms a flux and forms a protecting cover for the whole of the concentric gate. The speed of rotation of the mould is then increased to the highest point that the factor of safety allows, so that the centrifugal force induced in the molten steel in the mould may be a maximum during the freezing period. During the pouring period, the centrifugal forces have already been acting due to the rotation of the mould, but the additional force due to the increased speed is desirable because it will tend to further constrict the steel, thereby giving a better ingot.

In Fig. 5 there is shown a cross-sectional view of the ingot, showing the" successive stages that the steel may take during the pouring period.

The lines drawn'showing imaginary steps as to the way in which the hot metal may fill the mould cavity, it is not intended to illustrate the final state of the ingot. In the final state, .the steel in the ingot is perfectly homogeneous. From the illustration, it is apparent that the gases and other .inclusions of. the molten steel approximately follow the line of action of the centrifugal forces in their displacement toward the concentration point in the pouring gate. The concentration is forced into a very restricted area. As the path which the gas and dross in the molten metal must traverse to be concentrated in the pouring gate is comparatively short, and the constricting force is relatively great, a very short time interval is suflicient to cause the concentration. The steel in the pouring gate has meanwhile been kept molten through the insulating action of the hottop, thereby keeping the path clear for complete concentration.

The rotation of the cast is stopped as soon as the steel has frozen, at which time the ingot is removed from the mould by the removal of the upper segment, and then the croppage. is out 45 away. The toxic ingot' shown in Fig. 4 is the completed product of the mould, after which it may be immediately cut into billets of proper size and placed into soaking pits preparatory to the rolling mill.

I claim:

1. In a centrifugal casting machine, a rotating ring of large diameter having an annular internal slot therein into which molten metal is poured, the slot being of uniform cross ,section, which cross section is such as to define and divide the slot into a plurality of different and distinct portions, one of which, nearest the center of rotation of the ring, is a mouth portion, and another of wl ich, furthest from the center of rotation of the ring, is an ingot-shape defining portion, and a third of which, a gate portion, connects these two portions, the axis of rotation of the ring being at an angle of substantially 45 from the horizontal, and the lowest portion of the slot mouth being substantially vertical whereby molten metal dropped vertically into the said lowest portion of the slot mouth can flow into the gate portion of the slot without touching the walls of the mouth.

2. In a centrifugal casting machine, a rotating ring of large diameter having an annular internal slot ,therein into which molten metal is poured, the slot being of uniform cross section, which crosssection' is such as to define and divide the slot into a plurality of different and distinct portions,

and another of which, furthest from the center of rotation of the ring, is an ingot-shape defining portion, and a third of which, a gate portion,

one of which, nearest the cen-- 'ter of rotation of the ring, is a mouth portion,

connects these two portions, the axis of rotation of the ring being at an angle of substantially 45 from the horizontal, and the lowest portion of the slot mouth being substantially vertical whereby molten metal dropped vertically into the said lowest portion of the slot mouth can flow into the gate portion of the slot without touching the walls of the mouth, the gate being substantially perpendicular to the axis of rotation of the ring.

WM. SWOGER.

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