US2270822A - Centrifugal casting - Google Patents

Description

Jan. 20, 1942. R. H. MCCARROLL EIAL 2,270,322

CENTRIFUGAL CASTING I Filed July 31, 1959 5 Sheets-Sheet 1 I I 1 V 151 51 T Y A iSfLL H. WCJEEOLL-INVENTORS 5.06/76 CL/YQDE' JE/cz Jan. 20, 1942. R. H. MOCARROLL EpAL 2,270,822

CENTRIFUGAL CASTING Filed July 31, 1939 5 Sheets-Sheet 2 i d g (a v 2 Fig.6.

Jan. 20, 1942, MCCARROLL ETAL 2,270,822

CEN'I'RIFUGAL CASTING Filed July 31, 1939 5 Sheets-Sheet 3 Ed SSELL b. IVC/VEEM- LFINVENTORj 1942? R. MCCARROLL ETAL 2,270,822

CENTRIFUGAL CASTING 44 Cow p6 1 7- 2 Patented Jan. 20, 1942 2,270,822 I CENTRIFUGAL CASTING Russell H. MoCarroll, Dearborn, and Edgar Claude Jeter and Walter Kroy, Detroit, Mich., assignors to Ford Motor Company, Dear-born, Mich., a corporation of Delaware Application July 31, 1939, Serial No. 287,584

10 Claims.

This invention relates to methods and apparatus for centrifugal casting of ferrous metal parts in which molds are rotated for the purpose of distributing molten metal in the mold by centrifugal force thereby assuring an improved metal structure and making available a casting process for parts previously requiring more expensive and involved processes.

Developments in metallurgy in recent years have produced types of ferrous metals of physical properties such that many parts previously formed by the well-known forging process may now be formed by casting. This possibility of eliminating the relatively slow forging process,

' which comprises the forming of steel into ingots,

heating these ingots and ultimately forging the steel to a desired shape after cropping off approximately 25% of the metal, is of major importance when it is considered that an equivalent completed casting can be made by transferring molten metal directly from the furnace to the mold where'the operation of forming the part desired is accomplished in a few minutes time.

In applying the casting process to some parts, particularly irregularly shaped or small parts, the advantages of centrifugal casting in properly distributing the metal and improving the metal structure are particularly apparent. Specifically in comparison with the previously used forging process, the use of a centrifugal casting method -is known to insure: (1) an improved metal structure, (2) a higher yield of good castings as compared to back-stock, and; (3) the ability to use a less fluid metal, which means lower pouring temperatures and less damage, to the mold, with the additional possibility of more easily casting steels of lower carbon content. All of the above enumerated advantages are in addition to the admitted economy advantage of a casting process.

In any casting process it is considered an advantage both as regards economy and manufacturing efficiency to employ molds which can be used repeatedly. It is further important that mold parts he designed for ease in handling and if mo'ds cannot -be made completely permanent that replaceable parts be such as are easily and quickly assembled to the permanent parts of the molds.

It is therefore a primary object of the present I invention to make available a method and mechanism for centrifugal casting particularly adaptable for use in the manufacture of ferrous metal parts in quantity.

It is another object to provide a method and r mechanism capable of producing cast parts in quantity by utilizing molten metal taken directly from a furnace, said method replacing the former method of forging which required intermediat steps for forming ingots and subsequently forming these ingots to a desired shape.

It is a further object to provide a method and mechanism in forming metal parts whereby the most perfect metal structure is afforded in the portion of the part in which the greatest wear and stress is to be resisted.

It is another object to provide a method of forming metal blanks suitable for subsequent machining to form gears, said blanks having a structure that does not have lines of weakness at the base of teeth caused by the flow lines on the forgings as shown in etched sections.

It is a further object to provide a method for producing metal parts which will give a higher yield of satisfactory and usable parts than is possible with the forging method now commonly used.

It is another object to provide a method for forming ferrous metal parts which makes possible the use of a less fluid molten metal with the result that lower pouring temperatures and less damage to the mold is brought about with the additional possibility of using molten metal of a lower carbon content.

It is a further object to provide a centrifugal casting mechanism in which the major portions of the molds used are capable of repeated use, and which fit together in such manner as to be easily and quickly assembled and disassembled. It is another object to provide a casting method 7 and mechanism in which the major portions of the mold are permanent, in the sense that they can be'repeatedly used for a considerable time, but which also provide dry sand inserts of onceused parts positioned opposite the entrance openings provided for receiving streams of molten metal, thereby to assure satisfactory forming of metal parts with least damage to the permanent portions of the mold.

It is a further object to provide a method and mechanism for centrifugal casting of metal parts whereby the shrinkage of the metal during cooling is compensated for by suitable connecting portions between a plurality of castings formed at one time, such connections breaking apart on cooling and shrinkage of said castings, thereby to separate the individual castings without further manual operations and making possible certain advantageous design of dles.

'It is another object to make available as a new article of manufacture a. ferrous metal article molten metal carried by said conveyor line may be poured into said mold units carried by said spinner units as they move in a path adjacent to the path of the said conveyor.

It is a further object to providea means to both rotate and position a mold in a spinner unit so that said mold may be quickly and efiiciently portions thereof, but in placed in position in the spinner unit for rotation during the centrifugal casting process and easily and quickly removed from said spinner after the casting is completed.

The above and other objects of the invention will appear more fully in the following more detailed description and by reference to the accompanying drawings forming a part hereof and wherein:

Fig. 1 is a cross section through an assembled mold used for casting a ring gear by the centrifugal process.

Fig. 2 is a section taken on the line 2-2 of Fig. 1 and shows a top view of the interior of the bottom half of the mold with the sand core member positioned centrally therein to serve as a cushion for the incoming stream of molten metal.

Fig. 3 is a section taken on the line 3--3 of Fig. l and shows the cooling fins and means to allow the escape of gases from the mold.

Fig. 4 is a perspective view of a completed ring gear after machining from a blank cast in accordance with the present invention.

Fig. 5 is a mold assembly corresponding to that shown in Fig. 1 but in this case designed to cast so-called transmission cluster gear blanks.

Fig. 6 is a top view of the mold shown in Fig. 5. Fig. 'l is a section taken on the line I -l of Fig. 5. x

Fig. 8 is a perspective view of a sand core used in the mold shown in Fig. 5.

Fig. 9 is a perspective view of another sand core used in the mold shown in Fig. 5.

Fig. 10 is a perspective view of a completed transmission cluster gear, the blank for which is produced by the mold of Fig. 5.

Fig. 11 is an assembly view partly in section showing the spinner unit for rotating a mold such as shown in Fig. 1 but with its several operating parts in position to hold the mold in such relation to the spinner unit as to be easily removed by suitable lifting means. I r

Fig. 12 is also an assembly view, partly in section, of the spinner unit and differs from Fig. 11 in that the mold unit is lowered into the position it occupies when molten metal is poured into the mold and when the unit is being rotated.

Fig. 13 is a plan view showing the general assembly of a turntable which carries a plurality of centrifugal mold spinners. The adjacent 'conveyor. for carrying the molten metal for pouring into the molds is also shown. I

Fig. 14 is a section taken on the line H-H of Fig. 13 and shows a cross section through the turntable and its adjacent driving mechanism and supports.

Fig. 15A is a view showing one-half of the travel of the turntable of Fig. 13 with the successive positions of the centrifugal mold spinner units as they travel around the semi-circumference of the turntable, the particular section of the travel shown in Fig. 15A being the portion provided with a cam which lifts the molds into position to be removed from the spinner units and places the spinner units in position to receive new molds.

Fig. 153 is a view similar to Fig. 15A but shows successive positions assumed by the spinner units 'during the other one-half of the rotation of the table shown in Fig. 13.

The method and apparatus disclosed herein are particularly well adapted for the casting of certain automobile parts, for example, a gear blank for a transmission cluster gear and a gear blank for a ring gear adapted to be used in the differential. Blanks on which gears are eventually to be cut require a metal structure which can satisfactorily withstand the stresses and wear to which the gear teeth are necessarily subjected in use. It has been common heretofore to produce transmission cluster gear blanks and differential ring gear blanks by a forging process. In contrast, the present invention contemplates casting such blanks by a novel centrifugal casting process. The details of the method will be more fully brought out hereinafter, but it may be stated that a mold is provided which is continuously rotated while the molten metal is poured into the mold-the,

, centrifugal action of this rotating unit serving to throw the molten metalv to the outside of the mold. The distribution of molten metal thus provided for by the centrifugal method produces a metal structure, which is particularly adaptable for use as a gear of the metal structure in the centrifugally cast gear blank will be evident on inspection and comparison of the flow lines thereof with-,a similar blank made by forging. It will be found upon such comparison that the forged blank has flow lines formed therein in a direction parallel to the longitudinal axis of the gear blank. Thus, pronounced lines of possible cleavage orv fracture would be produced adjacent the base of the' gear teeth and would provide less resistance to breaking of the gear teeth by forces acting on the finished gear when in operation than would be the case if the grain ran at right angles or radially outward. However, upon considering the metal structure of the centrifugally cast gear blank it will be found that there are no flow lines present to form lines of weakness, and the dendrites that are present are more nearly perpendicular to the direction of force normally applied during the operation of the gears and will, therefore, be more satisfactorily adapted to resist forces without breaking the metal. It is also important that in the centrifugally cast gear blank the more dense portion of, the metal is near the circumference of the projecting portions where the gear teeth are to be cut, and less dense metal structure is confined to the central portion of the casting, a condition which entirely satisfies requirements. The fact that the metal is formed in the central region in large dendrites of no definite orientation is of no importance since this portion is removed by later machining operations, and a structure of 0 improved quality is formed in the region where the gear teeth are to be cut.

The method and its application blank. The advantages I casting a considerable number of di'iferent articles, the differential ring gear and the transmission cluster gear, discussed-above, have been found to be particularly adaptable for centrifugal casting and have been selected for the purpose of illustration, in the description herein.

.The details of mold units for producing these parts are shown in Figs. 1 to 3 and 5to 9. Speaking generally, the molds used are made up of what might be termed permanent parts except for necessary sand core inserts positioned opposite the sprue openings so that the stream of molten metal entering at the center of the rotating mold will first fall upon the sand core inserts which act as a cushion for the incoming stream of molten metal thus protecting the steel parts of the mold from the direct cutting action of the stream of hot steel. Using this method, it is possible to form molds of a permanent nature which fit together to relatively locate the parts in positive relation with each other, the sand core inserts forming the replaceable and removable parts of the molds being so positioned as not to interfere with the assembly of the separable parts, but affording suitable protection from the incoming stream of molten metal. It has been found that steel molds without protection opposite the sprue opening cannot be used a suiliciently long time to warrant the construction of such permanent molds. However, with the addition of the sand core inserts positioned as above noted the arrangement becomes a practical production implement producing great savings in time and labor. In considering the two mold units shown in Figs. 1 to 3 and Figs. 5' to 9, it is to be understood that a mechanism later to be described contin-- uously rotates the molds about their vertical axes. and that this rotation is continued while molten metal is poured in the top of the mold and for a limited time after the mold is filled with molten metal.

Ring gear mold Figs. 1 to 3 show details of the mold unit used for centrifugal casting of ring gears one at a time. As shown in the cross section view of Fig. 1,

a lower mold or die I5l which is of circular form in the top view, as shown in Fig. 2, is provided with cut out portions I52 and I53 in the bottom and top thereof, the top portion I53 forming an opening which defines the lower half of a mold for shaping a ring gear blank I54. As shown in Fig. l a top mold I55 has a cut out portion forming the upper half of the mold and is set in place upon the lower mold member I5I being positioned by a circular flange I56 on the lower mold and second circular flange I51 of larger diameter on the top mold portion I55. The top mold portion I55 has-an upper flange I58 for the purpose of lifting the top mold away from the bottom portion thereby to remove the completed casting. A central opening I59 in-the top mold is adapted to support a funnel member I60 thereby providing means to fill the mold by pouring metal into the opening I 6| of the funnel member I66. It is understood that the entire mold unit shown in Fig. 1 is supported in a suitable mechanism for rotating the mold about its vertical central axis while the metal is being poured into the opening I 6|. The top and bottom portions of the lower mold member are identical, the purpose of the two identical openings I52 and I53 being to provide a replacement for the bottom mold when the heated metal damages or wears out the mold so that it cannot be.used for forming additional castings.

In the central portion of both the top and bottom portions I52 and I53 there are drilled holes I62 and I63 located on the vertical axis of themold' and adapted to receive a sand core member I64. This sand core member- I64 is of circular form with a downwardly projecting portion, the circular form-covering a portion of the bottom surface of the mold which is formed by the top and bottom mold parts I5I and I55. It is to be noted on reference to Fig. 1 that the sand core insert I64 is positioned directly below the opening provided by the funnel IIiI for admitting molten metal, and as previously pointed out this positioning of the once-used sand core' opposite. the so-called sprue opening through which a molten metal is poured, covers the-bottom surface of the semi-permanent mold parts. If such. a removable insert were not provided to act as a cushion for the stream of molten metal, the mold could not withstand the cutting action of the stream of molten metal, and the mold would be destroyed in a very short time; in

fact, in so short a time that it would not be practical to construct such a permanent steel unit. However, with the provision of the insert I54 and by the provision of openings I52 and I53 on the top and bottom of the lower mold so that when the top portion becomes worn the mold can be reversed and the other opening used, a length of life for the entire part is assured which will be satisfactory from an expense standpoint.

As shown in Figs. 1 and 3, the mold I5I is provided with so-called cooling fins I65 constructed in such manner as to carry off the heat from the bottom mold. Suitable drilled openings are also provided to allow escape of gases. These openings are shown at I66, I61 and I68 in Figs.

1 and 3.

Transmission cluster gear mold Figs. 5 to 9 show parts necessary for casting two blanksfor a transmission cluster gear of the type shown in Fig. 10 by the centrifugal casting method. Referring to Fig. 5, the steel mold member I is formed to the shape shown and so designed as to receive five sand members, a runner core member I82, a top sand core I83, a center sand core I84, a lower sand core I85, and a bottom sand core member I86. The core member I82 is secured in place in the steel mold member I86 bymeans of a bayonet type joint I81, this construction being obvious on inspection of Figs. 5 and 6.

Referring to Figs. 5, '7 and 8, it is to be noted that the upper sand core I83 is also provided with projections I88 for a bayonet type joint and that suitable projections are provided on the interior portion of the mold as shown at I89in Figs.

5 and 7, it being understood that a similar construction is provided on both sides of the sand core mold as is shown in the drawings. The center sand core I84 is held in place by a pin I80, this core being the first member to be inserted and it is obvious on inspection .of Fig. 5 that the pin I98 is held in place by a suitable lug and bolt I9I. The lower sand core I is of identical construction to that used for the upper sand core I83, the core, however, being inverted for use as sand core I85 and is similarly secured by a bayonet type joint as shown at I92 in Fig. 5. The bottom sand member I66, as shown in Figs.

5 and 9, is also provided with bayonet type projections I93.

The mold unit shown in Fig. 5 is assembled by first inserting the center sand core I84, as previously noted, and securing it in place with. the pin I90. The sand cores I83 and I85 are next fixed in place and finally the bottom sand core member I86 and the core member I82 are assembled.

After the mold shown in Fig. 5 has beenfilled, as shown, and the metal begins to cool, the-small cross section in the central sand core I84 will break away as shown at I95 because of the shrinkage of the metal, causing separation of the two blanks at the point shown. The small opening provided at I96 by the. shape of the runner core I01 assures the breaking of the sprue from the top of the upper casting.

Spinner unit Figs. VII and 12 are views partially in section of a spinner unit showing details of the mechanism for rotating a mold and subsequently raising it from its spinning position to a position suitable for removing the casting from the mold. The spinner unit has a base member IOI which is provided with a flange I02 which rests upon a suitable supporting ring I03.

Above the base member IOI there is mounted a housing I04 which rests upon the base member IOI and is also. supported upon the ring I03. A suitable joint betweenthe housing I04 andthe base IN is shown at I06 in Fig. 11. A cover member I01 is supported from the top of the housing I04 and is pivoted at I08 so thatit may be lifted upwardly and opened by means of a handle I09.

Fig. 12 shows the mold in the lowered position with the roller 53 and the push rod 52 in the lowered position represented. In this position the mold is rotated by motor 59, and the mold is ready to receive molten metal through the opening I6I.

A further detail of the unit shown in Figs. 11 and 12 is the provision of clamps I32 near the top of the projection of the shell member I26 for the purpose of positively holding the mold unit in place, the weighted ends I33 of these clamps being forced outwardly by centrifugal force when the unit rotates thus actuating the clamp in a direction to hold the mold unit in place.

In the interior of the housing formed by the central housing I04, the base member WI and the upper and lower cover members, a shell II4 is mounted for rotation on a bearing II6 supported in the base member IOI and a hearing I I1 supported in the central housing member I04. These bearings aresuitably supported from inwardly projecting flanges numbered H8 in the base member and I I9 in the central housing. An internal gear I2I is secured to the lower projecting portion I22 of the shell member II4. For the purpose of providing power for rotationg the shell member II4 the electric motor 59 is supported in the lower section of the base member IOI and rotates the shell II4 through a pinion I24 and the previously mentioned internal gear I2I. The upper portion I26 of the shell member II4 is formed with a suitablyshaped cylindrical receptacle to receive mold parts I5I and I55 shown in Fig. 1. This mold unit, supported on a base I25, is raised and lowered in the shell by movement of a piston I21 which is connected to be reciprocated by a push rod 52 which is actuated by contactbfroller 53 with the cam track 5I later to be described. For the purpose of supporting the mold unit, three push rods I28 are provided in the example illustrated, two of which are shown in Fig. 11. These push rods are connected at their lower ends with the piston I21 and reciprocate with said piston, being guided by bearings I29 which project inwardly into the central portion of the shell II4. The operation of the spinner unit to raise and lower the mold into mold removing and mold spinning positions 'respectively will be obvious from the above description and by reference to Figs. 11 and 12, the upper or lifting position of the mold being shown in Fig. 11 wherein the piston I21 is at the top of its travel with the push rod and roller 53 contacting the highest portion of the cam track 5I thereby holding the mold unit54 in the position shown so that the top half I55 of the mold may be easily picked up by a suitable mechanical handling device. This position of the mold is maintained for a short time also just after the moldis placed in the spinner before the star of the casting process.

Provision for continuous operation of a plurality of units It is possible to provide for continuous operation of a plurality of spinner units and each marked a to r, a mold spinner unit 22, such as shown in Figs. 11, 12 and 14, being provided at each station. The turntable 20, as shown in Fig. 14, is mounted in such position as to be flush with the floor 23 adjacent thereto. A pit 24 is provided below the turntable for the purpose of housing various parts which are necessary to drive and support the turntable unit. Motor 25 and a gear box 26 are located in the central portion of pit 24 and drive the turntable through a pinion 21 and a large gear 28 secured to the turntable frame. Thecentral portion of the turntable is supported on a large bearing 29 thereby mounting the entire table for rotation on a vertical shaft 3| which extends upwardly from a suitable pedestal 32, a suitable bearing and oil retainer unit 33 being also provided. The outer circumference of the turntable is vertically supported through a plurality of roller units 34 which are secured to the under surface of the turntable, a suflicient number being distributed around the circumference to assure adequate support. The rollers 34 contact a track 35 which is circular in form and is provided with the required number of suitable supports 36, one of which is shown in Fig. 14. The necessary electrical circuits for operating individual motors to rotate each of the spinner units are connected onto the rotating table from the stationary upwardly projecting portion 31 of the shaft 3|, Fig. 14 showing three commutator connections 38 which contact rings 39 on shaft 3I thereby to connect the required number of cables with the rotationg table. A plurality of conduits 4| are used to carry the cables outwardly to connect, with the individual motors of the spinner units.

Giving further consideration to the general plan view of the unit as shown in Fig. 13, a

located as to convey ladles 43 from a furnace 44 in a path adjacent the circular path of the rotating spinner units 22 on table 20. A ladle I is shown in Fig. 13 in position for pouring molten metal into the spinner units. It is understood that a plurality of ladies are used, spaced along the conveyor so that molds carried in the spinner units will be successively poured as they pass adjacent the conveyor.

As was previously noted, a mold spinner unit is mounted at each of the stations, there being eighteen stations located near the outer circumference of the table 20 in the specific example here-' in described. Fig. 15A shows nine of the spinner units, the view being partially diagrammatic, in that the spinner units are shown in a straight line in Fig. 15A representing one-half of the circumference of the table 20. The nine spinners shown in Fig. 15A are those beginning at station n in Fig. 13 and ending with station d in said figure. Fig. 153 shows the spinner units on the other half of the rotating table and begins at the left hand and with the unit numbered e in Fig. 13 and ends with the unit numbered m. Beginning with the left hand end of Fig. 15A, it may be therefore considered that the several spinner units successively shown from left to right indicate the operations being performed at any one time by and on each at the position in the circumference of the turntable 20 which each individual unit occupies. It will be understood that on further rotation of the table 20 the cycle of operations will continue on successive spinners as such assumes a station corresponding to those shown.

conveyor 42, here shown diagrammatically, is so Each spinner unit provides means to rotate a mold which is placed therein and to lower and raise said mold into positions for spinning and for lifting the top half I55 out of the spinner unit. This raising and lowering'is accomplished by a cam track 5i positioned on the floor of the pit beneath the rotating table as shown in Fig. 14, and as shown in Fig. 15A this cam track has a raisedportion with inclined sections at each endthereof so that downwardly projecting push rods 52 with suitable rollers 53 will be raised and lowered by contact with the cam track 5i thereby to raise and lower the molds by mechanism included in each spinner unit,

Considering Fig. 15A, when an individual mold spinner is in position centrally of the raised cam track 5| the internal mechanism controlled by the previously mentioned push rod 52 and the roller 53 will be in position to hold a mold unit i5i, I55 in an outwardly projecting position, and

as shown at station a in Fig. 15A a mold lifting device 55 is positioned to lower top mold i55 into the position on the top of lower mold i5l in the spinner unit positioned at station a. The spinner located at station b shows the mold in position after the lifting device has been removed therefrom and the mold is still held in an upwardly projecting position by the action of the cam track on the roller 53 and the push rod 52. On subsequent rotation of the table the spinner next travels down the portion of the cam track 5|. labeled 20 decline. It is noted that at station 0 the roller 53 and the push rod 52 are so positioned as to lower the mold 54 into the interior of the spinner unitand also at this station a switch operating member 56 contacts a lever 51 on switch 58 which controls a motor 59 which rotates the spinner unit with the mold 54 suptained in each spinner unit The rate of move- V ment of the conveyor 2 is so timed relative to the rotation of the table 20 that the ladle 45 will be carried along at the same rate as the spinner unit positioned under it, and therefore molten metal may be poured therefrom into the opening IBI of themold as the tablerotates. It is understood that a suflicient number of ladies are positioned on conveyor 42 to 1111 successive molds during their travel from station (I to station a. As the spinner units take up positions a, h, hi, it, 1, m and n, the spinner continues to rotate and the casting operation is substantially completed at the station 11.. Between stations 11. and o the lever 51 of the'switch 58 contacts an operating arm 60 which stops motor 59 and stops rotation of the spinner unit. At position 0 m Fig. Mail. the roller 53 begins to contact the portion of cam track 5i labeled 25 use which actuates the mechanism enclosed in the spinner to lift shown in station 1). A second mold mung device 62, as is shown at station q, is then connected to the pro ecting nange I58 of the top mold I to hit the same upwardly and out of the spinner unit, the mold I55 carrying therewith the completed casting. The bottom mold I5! is then prepared to receive another top mold l55 to start another cycle at station a. a

The operation of the device is described in the description of several units. It may be noted in addition, however, that the stream of molten metal is poured into a rotating mold, the openings for mining being located substantially on the axis of rotation of the mold. The stream of molten metal entering at the center of the rotating mold is not brought directly in contact with the steel mold partsas it enters the mold, but first contacts inserts which are formed of sand and are of the general type known as sand cores. This method of treatment has been found to be necessary in the successful practice of centrifugal casting of parts of the type shown in the drawings.

It is specifically to be noted also that an arti cle cast by this method produces a structure which, by its relative characteristics of structure in its varying parts, is particularly adapted for certain uses, specifically the centrifugal casting of parts having a cross section symmetrical around an axis which may be positioned in a mold so that it will be the axis of rotation of a centrifugal casting mold and will have the most dense structure near the outer circumference of the substantially circular cross section. This Although the invention has been described by reference to a specific structure found practical in actual use, it is' to be understood thatvarious changes and modifications may be made without departing from the fundamental principles of the invention within the scope of the' following claims.

reciprocation in the lower portion of said shell,

members projecting upwardly from said piston to engage the lower face of said mold, a push rod mounted to reciprocate and project downwardly from said base member and having its upper end connected with said piston, a roller member secured to the lower end of said push rod, and a cam track below said base member whereby said mold may be raised and lowered on engagement of said roller with said cam track.

2. In a mold for centrifugal casting, a plurality of permanent metallic parts forming the major portion of the mold and adapted to fit together to form a desired interior mold shape, and

a single additional removable once-used part of refractory material adapted to be'inserted into and form a minor part of the interior surface of only one of the permanent mold parts, said part of refractory material being in such position as to act asa cushion for molten metal on its initial entry into said mold.

' 3. In a permanent mold for centrifugally casting metal articles, top and bottom metallic mold members adapted to be superposed, said top metallic mold member having an inlet opening in the central portion thereof through which molten metal may be poured, and a removable insert in said bottom metallic mold member only and positioned opposite said inlet opening, said metallic mold members being hollowed out to provide a casting of desired cross section and with a. removable insert in said bottom member only and said insert having a top surface serving as a portion of the interiorend wall of said bottom metallic mold member.

4. In a spinner and mold unit for centrifugal casting of metal parts, a base member, an inner shell supported from said base member and mounted to rotate relative thereto, an individual motor mounted on said base member and connected to rotate said inner shell, an upwardly projecting portion of said inner shell forming a receptacle/a mold of such size as to be positioned in said receptacle for rotation with said shell, automatic means to raise and lower said mold in said receptacle, said means comprising a piston member mounted for reciprocation in the lower portion of said shell, members projecting upwardly from said piston to engage the lower face of said mold, a piston operating member connected with said piston and mounted to reciprocate and project downwardly from said base member, a cam track below said base member positioned to operate said piston operating member by contact with said cam track whereby said mold may be raised and lowered relative to said base member and said shell.

5. In a spinner and mold unit for centrifugal casting of metal parts, a base member, an inner shell supported fromv said base member and mounted to rotate relative thereto, anindividual motor mounted on said base member and con nected to rotate said inner shell, an upwardly projecting portion of said inner shell forming a receptacle, a mold of such size as to be positioned infsaid receptacle for rotation 'with said shell, automatic means to raise and lower said mold in said receptacle, said means comprising a reciprocable member projecting upwardly to contact a lower portion of said mold, and a downwardly projecting operating member connected with said reciprocable member, and a cam track below said base member positioned to contact said downwardly projecting operating member whereby said mold may be raised and lowered on engagement of said cam track with said downwardly projecting'operating member.

6. A mold unit for use in-simultaneously centrifugally casting a plurality of metal parts comprising: a substantially cylindrical metallic body member adapted to be rotated upon a vertical axis, said body member being hollowed to provide symmetricalnpper and lower mold portions and having an interconnecting portion betweensaid mold portions; and a sand core member positioned in the interconnecting portion of said body member, said sand core member having an ,opening formed therein to allow flow of metal between said plurality of mold portions to form the articles to be cast, said opening being of such restricted size relative to said articles that shrinkage of said parts on cooling of said metal will cause a separation of said metal parts at said restricted opening by shrinkage of the metal of said parts after the casting operation is complete.

'7. A mold unit as defined in claim 6 in which a sand core is positioned at the lower extremity of said body member to serve as a cushion for the metal initially poured into said mold.

8. A mold for use in making centrifugal castings comprising: metallic body means hollowed to form a mold of a desired shape, said metallic body means having one end thereof constructed so that molten metal may be poured into saidmold; and a removable part of refractory material adapted to be inserted into said body means and to form a minor portion of the interior surface of the mold, said refractory part being so positioned in the mold as to act as a cushion for molten metal on its initial entry into said mold.

9. A mold for centrifugal castings comprising: a plurality of permanent metallic parts forming the major portion of the mold, said parts being hollowed to form a desired interior mold shape, one of said parts having an opening for the introduction of molten metal into said mold, the other of said parts having a surface adapted to support an insert thereon, and a once-used part of refractory material seated upon said insertsupporting surface with its marginal edges spaced from the inner wall surfaces of the mold; and means for retaining said insert in position in the mold opposite said opening, whereby said refractory insert in positioned so as to act as a cushion for molten metal on its initial entry into said mold.

10. A permanent mold for centrifugal castings, comprising: top and bottom metallic mold members adapted to be superposed, said metallic mold members being hollowed out to provide a casting of desired cross-section, said metallic top member having an inlet opening'in the central portion thereof through which molten metal may be introduced into the mold, said metallic botrespect to said metallic bottom mold member, the

' top and outer edge surfaces of said insert serving as a minor portion of the interior wall area of said mold.

RUSSELL H. McCARROLL. EDGAR CLAUDE JETER. WALTER KROY.

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