Horizontal Centrifugal Casting Method

Abstract

A horizontal centrifugal casting machine is described wherein a sectionalized mold for casting a cylindrical structure, e.g., a finned motor frame, is assembled, the structure cast and the mold sections stripped from the cast structure in an entirely automated process. The casting machine includes a plurality of arcuately shaped mold sections mounted upon jaws capable of being secured to pistons of pulling cylinders. With the pistons extended, the mold sections form a substantially cylindrical structure and dual annular rings having a tapered radially inner face are traversed axially along a tapered outer portion of the jaws to fixedly secure the mold sections in position. After disengagement of the pistons, the mold is rotated by a high speed drive motor whereafter a ladle containing molten metal is inserted axially within the mold and the ladle is tilted to pour the molten metal into the mold. The ladle then is withdrawn and a mandrel assembly supporting the ladle, an expandable arbor and a mold coating device is rotated to register the expandable arbor with the mold. The high speed drive motor then is de-energized and the mold stopped at a predetermined angular position using a low speed drive motor. After the expandable arbor is inserted axially within the mold and the arbor expanded to engage the interior of the cast cylindrical structure, the pistons of the pulling cylinders are driven radially inward to engage the outer surface of the jaws and the annular rings are released to permit the pistons to strip the mold from the cast structure. The cast then is removed from the interior of the stripped sections and the open jaws are coated with casting lubricant permitting the casting cycle to be repeated. To obtain optimum quality in casting finned aluminum motor frames, the rate of rotation of the ladle during the pour should vary to effect a more rapid rate of angular displacement at the initiation and termination of pouring metal from the ladle than at the middle of the pour to produce a constant flow of metal from the ladle.

Parent Case Text

This is a division of application Ser. No. 277,920, filed Aug. 4, 1972, now U.S. Pat. No. 3,825,057.

Description

This invention relates to a horizontal centrifugal casting machine for casting finned cylindrical structures and in particular, to a casting machine wherein a sectionalized mold is assembled into a cylindrical configuration, the structure is centrifugally cast within the mold and the mold stripped from the structure in a substantially automated process.

In the manufacture of dynamoelectric machines, a number of diverse techniques heretofore have been proposed and/or utilized to fabricate machine frames dependent upon such diverse factors as the size and number of frames to be cast. For example, high pressured die casting techniques have been employed to produce cylindrical frames below approximately 10 inches in diameter on a high volume basis while maachine frames above 10 inches in diameter generally have been formed commercially by sand casting or extrusion techniques.

While centrifugal casting has been known for many years, centrifugal casting machines primarily have been limited to casting structures having a smooth outer surface, such as metal pipes, or for applying interior linings to preformed objects, e.g., casting brake linings along the interior of brake drums. For example, a centrifugal casting machine is described in U.S. Pat. No. 1,917,872 for casting brake drum linings by inserting a ladle into a metal drum retained in position within a plurality of arcuately shaped segments and gradually tilting the ladle to pour metal at a uniform rate into the drum. Because the mold is separate from the centrifugal casting machine and forms a part of the finished product, there is no need to strip the mold from the centrifugally cast metal. A highly automated centrifugal casting machine for producing smooth surfaced pipes also is shown in U.S. Pat. No. 3,457,986 wherein a plurality of molds are mounted along the periphery of a rotatable turret and the turret is revolved to register the individual molds with circularly disposed stations, i.e., a centrifugal casting station, a spray cooling station, a pipe withdrawal station, etc., to effect the sequential steps of the casting process. Such machine, however, is specifically designed for smooth surfaced objects and would not be suitable for casting finned structures because of the use of expandable tongs to withdraw the cast pipe from the mold.

It also has been proposed (i.e., in Baumann et al U.S. Patent applications, Ser. No. 220,285 entitled "Horizontal Centrifugal Casting Machine" and Ser. No. 220,286 entitled "A Dismemberable Mold For Centrifugally Casting Finned Structures," both filed Jan. 24, 1972), that a sectionalized mold be seated upon horizontal rollers of a centrifugal casting machine to permit substantially automated casting of finned cylindrical structures. Because the mold is not fixedly secured to the casting machine, the mold can be lifted from the rollers by a crane and transported to a stripping machine (such as is described in LaBahn et al U.S. Patent application, Ser. No. 220,280, entitled "Method and Apparatus For Automatically Stripping A Sectionalized Mold From A Cast" and Baumann et al U.S. Patent application, Ser. No. 220,279 entitled "Automated Method Of Manufacturing Finned Machine Frames," both filed Jan. 24, 1972) to strip the sectionalized mold from the underlying centrifugally cast structure. While the centrifugal casting equipment and casting methods disclosed in the foregoing applications are highly suitable for casting large diameter finned cylindrical structures, the production rate is somewhat limited by the necessity for transferring the mold from the casting machine to the stripping machine. Moreover, because the crane required to transfer the mold from the casting machine to the stripping machine normally is under the control of an operator and because the heat of the mold makes manual assistance in the transfer difficult, substantial labor is required to complete the process notwithstanding the automated nature of each individual machine utilized for casting.

It is therefore an object of this invention to provide a highly automated centrifugal casting machine wherein the mold is assembled, the structure cast and the mold stripped from the cast in a single machine.

It is also an object of this invention to provide a centrifugal casting machine capable of producing a large quantity of cast finned structures on a substantially automated basis.

It is a further object of this invention to provide a centrifugal casting machine having a mold locking assembly capable of securely fastening the individual mold sections into a composite unit for casting while permitting ready disengagement from the mold for stripping the mold sections from the cast structure.

It is a further object of this invention to provide an automated method of casting finned cylindrical structures and stripping the mold from the cast structures.

A horizontal centrifugal casting machine for casting cylindrical structures in accordance with this invention generally includes a plurality of arcuate mold sections having interlocking edges and means connected to the mold sections for moving the sections into juxtaposition to form a cylindrical mold capable of confining the liquid material to be cast. Means also are provided for connecting a rotary drive to the cylindrical mold for rotation of the mold at a predetermined speed and suitable means within the machine pour molten material into the mold during rotation to cast the cylindrical structure. After solidification of the cast structure, suitable means strip the individual mold segments from the cast structure to produce a cylindrical structure independent of the mold into which the molten material was poured. To assure complete stripping of all mold sections from the cast and to prevent fracturing of the cast structure during stripping, the casting machine preferably also includes means for inserting an arbor within the cast cylindrical structure and means for expanding at least a portion of the arbor in a radial direction to contact the interior of the cast structure prior to stripping the mold sections from the cast. When the molten material is poured into the rotating mold from a ladle, suitable means desirably are included within the machine to tilt the ladle at a variable rate during the pour, i.e., a more rapid angular displacement of the ladle is desirable at the beginning and end of the pour than at the middle of the pour, in order to produce constant flow of metal from the ladle and high quality in the finished cast product.

Although this invention is described particularity in the appended claims, a more complete understanding of the invention may be obtained from the following detailed description of a specific centrifugal casting machine formed in accordance with this invention when taken in conjunction with the appended drawings wherein:

FIG. 1 is an elevation of a centrifugal casting machine in accordance with this invention,

FIG. 2 is a plan view of the mandrel assembly utilized in the stripping machine of FIG. 1,

FIG. 3 is a view of the apertured plate utilized in the speed sensing and mold positioning assembly,

FIG. 4 is an enlarged sectional view of the speed sensing and mold positioning assembly,

FIG. 5 is a sectional view taken along lines 5--5 of FIG. 1 to illustrate the T-shaped groove wherein the gripping jaws slide,

FIG. 6 is an enlarged view of the lock rings utilized to secure the mold in position for casting,

FIG. 7 is an isometric view of the mold in a machine mounted assembly,

FIG. 8 is a view depicting the serial connection of the coolant hoses to the mold sections,

FIG. 9 is a sectional view of the mold pulling assembly,

FIG. 10 is a sectional view of the ladle rotation mechanism,

FIG. 11 is a view of the variable pour rate control of the ladle rotation mechanism,

FIG. 12 is a graph illustrating the variation of rate of angular displacement of the ladle with the quantity of aluminum poured from the ladle,

FIG. 13 is a sectional view of the expandable arbor,

FIG. 14 is a view of the arbor taken along lines 14--14 of FIG. 13,

FIG. 15 is a sectional view of the lubricant spray mechanism of the casting machine,

FIG. 16 is an elevation view of the main turntable,

FIG. 17 is a plan view of the main turntable to illustrate the speed control and positioning mechanism of the turntable,

FIG. 18 is a view of the main turntable rotary drive,

FIG. 19 is a sectional view of the mechanical registration piston of the main turntable,

FIG. 20 is a sectional view taken along lines 20--20 of FIG. 17 to illustrate the limit switches controlling table rotation,

FIG. 21 is a flow chart showing the sequential operation of the casting machine, and

FIG. 22 is an electrical diagram of a circuit suitable for controlling the operation of the machine.

A horizontal centrifugal casting machine 10 in accordance with this invention is shown in FIG. 1 and generally comprises a drive and transmission unit 11, a mold assembly and stripping unit 12 and a mandrel assembly 13. The mandrel assembly (illustrated also in FIG. 2) is rotatable to axially register ladle 14, expandable arbor 15 or lubricant spray head 16 with the mold and the entire mandrel assembly is mounted upon a carriage 17 axially traversable along rails 18 to permit insertion of the registered mandrel component axially into the mold.

DRIVE AND TRANSMISSION UNIT

The main drive for horizontal centrifugal casting machine 10 is provided by drive motor 19, e.g., a solid rotor motor such as is described in G.M. Rosenberry, Jr. U.S. Pat. Ser. No. 3,582,696 speed regulated by the control circuit taught in Rosenberry et al U.S. Patent Ser. No. 3,582,737 (both of which patents are assigned to the Assignee of the instant invention). Typically the drive motor is operated at a rotary speed of approximately 900 rpm to produce a speed of approximately 500 rpm in rotary face plate 20 to which the arcuate sections of centrifugal mold 21 are secured. Because the drive and transmission unit are subject to multiple starting and stopping during operation, motor 19 desirably is cooled by a blower unit 23 which includes fan 24 driven by motor 25 and suitable ducting 26 communicating the drive motor interior with the external environment.

The drive end 27 of main drive motor 19 rotates a pulley 28 driving flexible belts 29 to apply torque to a larger diameter pulley 30 to obtain the desired reduction in speed between the drive motor and centrifugal mold 21. Because the belt load is too great for direct application to main shaft 31 of the drive and transmission unit, torque transmitted through belt 29 is transferred to the main shaft through a conventional bearing block assembly 32 and standard coupling unit 33. As is shown in FIG. 1, the outer housing 34 of bearing block assembly 32 is fixedly secured to base 35 of the casting machine to support the belt load while a pair of bearings 36 permit rotation of shaft 37 within the bearing block assembly to transmit rotary force through coupling unit 33 to main shaft 31. The torque applied to main shaft 31 through coupling unit 33 then is transmitted to rotary face plate 20 secured to the hollow main shaft by bolts 38 to permit rotation of centrifugal mold 21 mounted to the face plate (as will be more fully explained hereinafter).

The speed of main shaft 31 is monitored by a speed sensing and mold positioning assembly 39 (illustrated in FIGS. 3 and 4) which includes a selectively apertured wheel 40 mounted upon the shaft to pass between three proximity switches 41-43 secured to supports 44 mounted to block 45 on base 35. Uppermost proximity switch 41 is radially registered with six arcuately spaced apertures 46 in wheel 40 to measure the rotary speed of shaft 31 by counting the number of actuations of proximity switch 41 within a fixed period of time while lower proximity switch 42 registered with radially outer semicircular lip 47 of wheel 40 is employed to determine whether shaft 31 is rotating by sensing continued actuations of the proximity switch. The third proximity switch 43 serves to position rotary face plate 20 (and mold 21 mounted thereon) at a particular angular orientation with pulling assembly 48 (illustrated in FIG. 1) of the casting machine by aligning the proximity switch with protrusion 49 extending axially outward from wheel 40. Proximity switches, to achieve the foregoing results, are well-known in the art and can be obtained commercially from the General Purpose Control Department of the General Electric Company.

To obtain the desired registration between protrusion 49 and proximity switch 43 (and the resultant registration between centrifugal mold 21 and pulling assembly 48), a small drive motor 50 (illustrated in FIG. 1) is connected to the opposite drive end of the shaft of main drive motor 19 through a gear reducer 51 and an electric clutch 52 to permit slow rotation of main shaft 31 after termination of mold rotation at the end of a cast, as observed by proximity switch 42. Thus, with drive motor 19 stationary after the completion of a centrifugal cast, electrical clutch 52 is engaged and small drive motor 50 is energized to slowly rotate shaft 31 through main drive motor 19 until protrusion 49 is registered with proximity switch 43 at which time energization of the small drive motor is terminated and the motor electric brake is engaged to stop rotation of the mold. Clutch 52 then is disengaged, and the tapered piston of hydraulic cylinder 22 is inserted into a slot in rotary face plate 20 to lock the plate in position.

Main shaft 31 is utilized not only to transmit torque to rotary face plate 20 but also as a conduit to transmit fluid coolant to mold 21 mounted upon the face plate. The fluid coolant, typically water, enters axially outer annular chamber 53 through aperture 54 in water jacket 55 surrounding the end of shaft 31 remote from the mold and the coolant flows through bore 56 in the shaft to a central pipe 57 for axial transmission along the shaft. The fluid coolant then advances into annular chamber 58 formed between partition 59 and plug 60 whereafter the coolant flows radially outward through aperture 61 in the shaft and flexible hoses 62 to pass serially through the four individual sections forming mold 21 (as will be more fully explained hereinafter with reference to FIG. 8). The coolant then returns through aperture 63 to axial flow channel 64 between shaft 31 and pipe 57 to return to annular chamber 65 by way of radial bore 66 in shaft 31. From annular chamber 65, the coolant flows through aperture 67 within water jacket 55 to return to a heat exchange and pumping unit (not shown) for recirculation through the mold. A partition 68 serves to separate the streams of circulating coolant in the adjacent annular chambers at the end of shaft 31 while conventional face seals 69 inhibit leakage of coolant adjacent the shaft.

Main shaft 31 is supported at the driven end of the shaft by a spherical bearing 70 while a tapered roller bearing 71 is situated at the drive end of the shaft to absorb both radially and axially directed shaft loads. In conventional fashion, tapered roller bearing 71 is positioned between shaft 31 and housing assembly 72 at a fixed axial location while spherical bearing 70 is axially slidable between the shaft and housing assembly to inhibit axial loading of the bearing. Both bearings are lubricated by oil circulating between the rotating shaft and the stationary housing assembly by way of oil intake and exhaust orifices 73 and 74, respectively, within the housing assembly.

MOLD ASSEMBLY AND STRIPPING UNIT

A pair of hydraulic cylinders 75 mounted on plate 76 fixedly secured to base 35 serve to reciprocally drive mold locking unit 77 in an axial direction thereby securing mold 21 in position for casting. To effect locking of the mold, pistons 78 within cylinders 75 reciprocally drive annular plate 79 and the reciprocal motion of the plate is transmitted through the radially outer raceway of tapered roller bearing 80 to axially traverse the rotary bearing members and the inner raceway of the bearing along shaft 31. Because the inner raceway of bearing 80 also forms an integral part of back plate 81, the back plate and rods 82 fixedly secured along the periphery of the back plate also are traversed in an axial direction by actuation of pistons 78. Axial movement of rods 82 draws the tapered annular face 83 of lock rings 84 against the tapered radially outer faces 85 of mold gripping jaw 86 to radially slide the jaws within a T-shaped aperture 87 (shown in FIG. 5) of rotary face plate 20 thereby locking the four mold sections secured to the respective ones of orthogonally disposed jaws 86 into a composite cylindrical unit. Limit switches 88 are mounted upon the exterior of housing assembly 72 to measure the outward extent of pistons 78, i.e., by actuation of the limit switches by vanes 89 carried upon rod 90 mounted on plate 79.

Because the axially outer and inner lock rings, identified by reference numerals 84a and 84b, respectively, of the mold locking unit may not contact tapered faces 85a and 85b of mold gripping jaws 86 with equal force due to unequal thermal expansion of the jaws during casting, axially outer lock ring 84a is driven by an individual spring biasing means, such as the Bellville washers 92, shown in FIG. 6, to compensate for the effects of thermal expansion. Thus, although rods 82 produce an equal axial advancement of tapered lock rings 84a and 84b upon actuation of hydraulic cylinder 75, thermal expansion of gripping jaw 86 may produce a higher clamping force between one ring, i.e., inner ring 84b, and tapered face 85b of the gripping jaw then occurs between outer ring 84a and the gripping jaw. By dimensioning the inner radius of ring 84a to engage the gripping jaw before ring 84b, Bellville washer 92 situated adjacent ring 84a on rod 82 can absorb the axial load as axially inner ring 84 b is driven into firm contact with the associated tapered face on gripping jaw 86 to equalize the force distribution at axially opposite ends of the assembled mold.

A sectionalized centrifugal mold 21 preferred for utilization in this invention is depicted in FIG. 7 in a machine mounted configuration, i.e., with associated gripping jaws 86 of the casting machine. The mold preferably is formed of four arcuate sections 21a-21d having interlocking axial edges 93 to mate upon juxtaposition of the sections thereby forming a composite mold capable of retaining molten metal therein. The interlocking edges 93 of mold 21 are similar to the edge configuration of the mold disclosed in Baumann et al U.S. Patent application, Ser. No. 220,286 (the disclosure of which is incorporated herein by reference). The edges of mold 21, however, are designed to be disengaged or engaged upon simultaneously moving all four sections along perpendicularly oriented axes. To obtain the ready dismemberment of the mold while inhibiting leakage of molten metal from the mold, two diametrically opposite mold sections, i.e., sections 21a and 21c, are provided with longitudinal edges having an angular, preferably orthogonal, step 93a which functions as a seat for the longitudinal edges 93b of the adjacent mold sections. The radially inward extending lips 94 at the axial ends adjacent mold sections also have edges 94a with a complimentary angular taper, preferably radial, to snugly mate upon juxtaposition of the mold sections. When the mold is employed to cast frames for dynamoelectric machines, the interior or each mold sections preferably is notched, in conventional fashion, to form a plurality of triangular grooves 91 extending in a substantially parallel direction into each mold section to produce the cooling fins desirable for the cast frame without substantially inhibiting stripping of the mold sections from the frame. To effect such result, the width of the grooves should taper at a suitable anglel, e.g., 0.030/in. n 2..degree.30', with penetration into the sidewall of the mold.

Each mold section is individually secured to a mold gripping jaw of the casting machine by bolts 95 and a suitable fluid connector, preferably a commercially available quick disconnect connector 96 and an elbow 97 (shown in FIG. 8) admits fluid coolant from flexible hoses 62 to the region between the mold section and the jaw fixedly secured thereto. Preferably, the coolant is circulated in dual streams serially through the composite mold jaw units (as shown in FIG. 8) before returning to flow chamber 64 in shaft 31 for return to the heat exchange and coolant pumping unit associated with the machine.

Because lock rings 84 clamp the mold sections into a composite unit, no provision (other than tapered face 85 on the mold gripping jaws) is required along the outer periphery of the mold sections to secure one mold section to the other. Four ears 99, however, (shown in FIG. 7) are provided on each mold section to maintain the sections in juxtaposition in order to facilitate changing molds within the casting machine. Thus, to change the mold for a new frame size, pins 98 can be inserted through the ears of the mold sections to maintain the sections in juxtaposition whereafter the composite unit may be supported upon arbor 15 of mandrel assembly 13. Mandrel assembly carriage 17 then is moved axially into the machine permitting the mold sections to be bolted to gripping jaws 86 of the machine. The pins retaining the mold sections in juxtaposition then can be manually removed and the arbor withdrawn axially from the mold to permit the initiation of casting.

As was stated earlier, each gripping jaw 86 to which the individual mold sections are secured has a tapered radially outer face 85 at axially opposite ends of the mold to permit the application of a radially inward force to the mold sections upon the axial traversal of lock rings 84 across the faces. One edge of the jaw, the axially inner edge, has a T-shaped protrusion 100 to be slidably received within T-shaped aperture 87 of rotary faace plate 20 to permit the jaw to slide in a radial direction. The radially outer face of each jaw also has a pulling bracket 101 for engagement with pistons 102 (shown in FIG. 1) of hydraulic pulling assemblies 48 fixedly secured to the stationary main back plate 104 of the centrifugal casting machine.

The pulling assembly utilized to position the mold sections for engagement by lock rings 84 and for stripping the mold sections from the cast is illustrated more clearly in FIG. 9 and generally comprises a large hydraulic pulling cylinder 105, e.g., a 6 inch diameter cylinder, fixedly secured to back plate 104 by brackets 106 and angles 106a. Piston 102 of the pulling cylinder has a tapered bifurcated member 107 threadedly engaged at the forward end of the piston to engage pulling brackets 101 along the radially outer face of gripping jaws 86 while an elongated bracket assembly 108 extends outwardly from bifurcated member 107 to support small diameter piston cylinder 109 which drives dual lockpins 110 through aligned apertures 111 in the bifurcated member and the pulling brackets of the jaws upon admission of hydraulic fluid to the small diameter cylinder. Dual limit switches switches 112 and 113 also arae mounted along the outer housing of small diameter cylinder 109 to be engaged by lockpins 110 to indicate the position of the lockpins relative to bifurcated member 107. Similarly, piston 102 of the large pulling cylinder also carries a lower platform 114 having dual guide rods 115 mounted thereon to actuate limit switches 116 and 117 by vanes 118 mounted on the guide rods to indicate the extent of piston 102 toward the mold. In order to permit both the positioning of the four arcuate sections of mold 21 into a cylindrical structure prior to casting, and the stripping of the mold sections simultaneously from the cast, four pulling cylinders 105 are mounted at 90.degree. intervals about main back plate 104 to radially align bifurcated members 107 with pulling brackets 101 of gripping jaws 86.

To assure that the four pulling pistons operate simultaneously during stripping of the mold from the cast, the four pulling cylinders are fed hydraulic fluid through commercially available flow dividers (not shown) to synchronize the pulling of the mold sections from the cast notwithstanding differing adhesive forces between the cast and the separate mold sections. Flow dividers to achieve this result typically include four hydraulic pumps having a single interconnected shaft to assure the pumping of equal quantities of hydraulic fluid to each of pulling cylinders 105. Thus, all the pulling pistons are withdrawn into their respective cylinders at a uniform rate and there is substantially no withdrawal until all mold sections are broken loose from the cast.

Should the slip rate of the pumps forming the hydraulic fluid flow divider become excessive, two flow dividers can be connected in series in the hydraulic lines, e.g., a flow divider capable of pumping seven gallons per minute per cylinder could be serially connected with a flow divider capable of pumping 35 gallons per minute per cylinder. The lower volume flow divider then functions to reduce the slip between pulling pistons until the mold sections are disengaged from the cast whereafter a suitable valve by-passing the lower volume flow divider could be actuated to permit a more rapid synchronized withdrawal of the pulling pistons into their respective cylinders under the control of the higher volume flow divider.

MANDREL ASSEMBLY

As was heretofore mentioned with respect to FIG. 2, mandrel assembly 13 is formed of a ladle 14, an expandable arbor 15 and a lubricant spray head 16 protruding outwardly from an upwardly extending centerpost 120 at angulary displaced locations, shown at 90.degree. intervals, to permit axial registration of each of the outwardly extending components with the assembled mold upon rotation of the centerpost. Ladle 14 is substantially identical to the ladle described in heretofore cited Baumann et al U.S. Patent application Ser. No. 220,285 (the disclosure of which is incorporated herein) and generally includes a cylindrical vessel 121 having a ceramic lining 122 and a metallic outer sheathing 123. In conventional fashion, a rectangular opening 124 is provided along the top of the ladle to admit and remove molten metal from the ladle and the ladle is secured to a rotatable shaft 125 to permit tilting of the ladle when discharge of molten metal from the ladle is desired. A back plate 126 also is mounted between the ladle and rotatable shaft 125 to mate with opening 127 in hood assembly 128 to entirely enclose the rotating mold during the pouring of molten metal into the mold.

Tilting of the ladle to pour molten metal therefrom is accomplished utilizing ladle rotating mechanism 129 (illustrated in FIG. 10 and 11) which mechanism generally includes a hydraulic cylinder 130 fixedly secured within the mandrel assembly for driving rack 131 meshed with gear 132 fixedly mounted upon rotatable shaft 125 of the ladle. The hydraulic cylinder itself is actuated by a hydraulic pressure source 133 through a commercially available, electromagnetically operated control valve 134. However, in order to obtain optimum quality in the finished cast, theh rate of angular displacement of the ladle must be varied during pouring of the molten metal into centrifugal mold 21. This variable displacement rate is obtained by a tapered cam 135 (shown in FIG. 11) which engages control unit 136 of valve 134 to vary the orifice within the valve to produce a faster rate of angular displacement of the ladle at the initiation and termination of a pour than at the middle of a pour (as is shown in the graph of FIG. 12). Thus, rather than utilizing a continuous rate of angular displacement for the ladle, the casting machine of this invention employs a rapid ladle tilt rate at the initiation of the pour of molten metal from rectangular opening 124 and the tilt rate of the ladle is gradually decreased along line a until approximately one-half of the molten metal within the ladle is discharged into the rotating mold. The rate of tilt of the ladle then is increased along line - b - to return the tilt rate at termination of the pour to approximately the rate of tilt at the initiation of the pour.

By varying the ladle tilt rate in the foregoing manner, the volume of metal per unit time discharged from the ladle is substantially constant throughout the pour cycle and the quality of the cast structure is improved relative to cast structures formed by tilting the ladle at a uniform rate. In general, the maximum rate of ladle displacement and the change in rate of ladle displacement will vary, i.e., dependent upon such factors as the size of the rectangular opening the ladle, the height of the molten metal in the ladle, the interior configuration of the mold, etc., and best is determined empirically for each frame size to be cast by a particular ladle.

Expandable arbor 15 is similar to the structure disclosed in heretofore cited Baumann et al U.S. Patent application Ser. No. 220,285 and generally includes four arcuate segments 137 (illustrated in FIGS. 13 and 14) mounted on jaws 138 having lips 138a slidably engaged within tapered slots 139 of a cruciform centerpost 140. Each of the spokes 140a - 140d of the centerpost, however, are individually driven by the respective pistons of four hydraulic cylinders 141 to securely engage each of arcuate segments 137 with the internal surface of the cast structure before a pressure switch (not shown) in the hydraulic line of each piston cylinder terminates radial extension of the arcuate segments. A tapered nose 142 also is provided at the end of the arbor remote from center-post 120 to be secured within socket 143 in face plate 20 during pulling of the mold sections from the cast. In such manner, both ends of the arbor are supported and centilever bending of the arbor produced by an unequal force distribution from pulling assembly 48 is inhibited.

In order to prevent undue adhesion between the cast and the overlying mold sections, the mold sections should be sprayed with a commercially available lubricant prior to each cast. Spraying preferably is accomplished in the automatic casting machine of this invention by rotating spray head 16 into registration with the mold sections and longitudinally traversing the spray head into the interior of the mold sections to spray the sections while the sections are in an open position, i.e., with the mold sections drawn radially outward by withdrawal of pistons 102 into cylinders 105. Air valve 144 (illustrated in FIG. 15) controlling the pressure on lubricant reservoir 145 is opened by limit switch 169b along path of carriage and the spray head sprays the interior of the mold sections upon entry therein to assure complete coverage of the mold interior. It generally has been found necessary to spray the mold sections in an open position in order to adequately cover the axially confronting edges of the mold sections and inhibit undue adhesion between the mold sections and any molten metal leaking therein during casting. Although the spray head for coating the internal surface of the mold sections with lubricant preferably is mounted on mandrel assembly 13 to obtain complete automation of the casting process, it will be appreciated that lubricant coating of the mold sections also could be accomplished, if desired, by manually directing a spray along the mold sections or by brushing the mold sections with a suitable lubricant applicator.

As can be seen in FIG. 16, centerpost 120 is axially supported upon main turntable 146 while a plurality of gussets 147 disposed about the lower end of the centerpost serve both to support the centerpost against cantilever type forces and to provide a ledge for mounting cam 148 to control the speed of the turntable (as will be more fully explained hereinafter). An annular ring 149 secured to the lower periphery of the turntable serves both as a support for the turntable and a bearing surface for the application of torque to the turntable from hydraulic motor 150 (illustrated more clearly in FIG. 18) to rotate the turntable upon bearings 151 situated between the annular ring and adjacent annular bracket 152. The bracket is substantially L-shaped to provide an enlarged surface for fixedly securing the annular shaped bracket to platform 153 of carriage 17 while a radially outward extending portion of the bracket provides a lip 154 to maintain annular ring 149 in fixed radial position. Composite bearings of the foregoing type are commercially available and may be purchased from Rotek, Inc. in Ravenna, Ohio.

The speed of main turntable 146 is controlled by valve 155 (shown in FIG. 17) regulating the flow of hydraulic fluid to hydraulic motor 150 of conventional design fixedly secured in vertical position by bracket 156. As can be seen from FIG. 17, cam 148 controlling valve 155 is shaped into three arcuate segments to gradually increase the speed of hydraulic motor 150 from stanstill to a maximum speed by control of valve 155 until the desired outwardly extending component on centerpost 120 approaches registration with the mold whereupon the flow of hydraulic fluid to the motor is gradually terminated to bring the motor to a stop. To assure precise registration of the mandrel component with the mold, three brackets 157 having angularly shaped grooves 158 are mounted along the outer periphery of the turntable to accept the tapered nose 159 of the piston of hydraulic cylinder 160 mounted along carriage 17 at a position to register the mandrel assembly with the mold. Thus, as the forward end of the tapered nose is inserted within the triangularly shaped groove in bracket 157, precise mechanical registration is obtained between the outwardly extending component on the centerpost and the mold. A pair of limit switches 161 (illustrated in FIG. 19) actuated by the piston of hydraulic cylinder 160 serves to indicate the position of tapered nose 159 relative to the grooved bracket. Tapered cam 148 also serves as a support for three vanes 162 (illustrated in FIGS. 17 and 20) disposed along the periphery of the turntable at differing elevations to actuate three limit switches 163 in conventional fashion to indicate the degree of rotation of the turntable.

As can be seen in FIGS. 1 and 16, the entire mandrel assembly is mounted on carriage 17 supported upon longitudinally extending rails 18 by commercially available bearings 164. To impart motion to the carriage, the front end of the carriage is fixedly secured through a bracket 165 to the forward end of piston 166 of hydraulic cylinder 167 fixedly secured upon base 35. A vane rod 168 also is secured along one side of the carriage assembly to trigger a plurality of limit switches 169a - 169c disposed along the length of the carriage traversal to control the length of travel of the carriage assembly and to initiate sequential operation in the machine (as will be more fully explained hereafter).

OPERATION devices mold 110

The sequential operation of casting machine is illustrated in the flow chart of FIG. 21 and initially includes the filling of ladle 14 by means of a suitable metering device (not shown) with a quantity of molten metal proportional to the size of the frame being cast. Metering devides to measure the amount of molten metal passing to a ladle are well known in the art and generally work upon a positive displacement of the molten metal utilizing gravitational flow or by the pumping of molten metal from a lower molten metal reservoir to the more elevated ladle. It will be appreciated, however, that any known type of liquid metal transfer system can be utilized to fill ladle 14. Pulling assembly cylinders 105 also are actuated at this time to move mold sections 21a - 21d radially inward into an approximately cylindrical configuration whereupon hydraulic cylinders 75 are actuated to pull lock rings 84 axially across the tapered faces of mold gripping jaws 86 to securely lock the moldl to face plate 20. Hydraulic cylinders 109 controlling lockpins 10 of the pulling assembly then are actuated to disengage bifurcated member 107 from the mold sections and, after retraction of the pulling pistons into cylinders 105, main drive motor 19 is energized to rotate the mold at a speed of approximately 500 rpm. The flow of liquid coolant through the mold assembly also is initiated at this time to insure that the molten metal is rapidly solidified upon subsequent pouring of the metal into the mold.

After filling of the ladle with the desired quantity of molten metal has been completed (as determined by a conventional weight actuated switch or a timing switch, not shown), the valve controlling admission of hydraulic fluid to hydraulic cylinder 167 is actuated to drive ladle 14 axially into the mold whereafter hydraulic fluid is admitted to cylinder 130 controlling rack 131 to dump the molten metal into the rotating mold. After rotation of the mold for a fixed period of time to permit centrifugal casting of the molten metal, e.g., approximately one minute for a 250 diameter motor frame, mold 21 is stopped by dynamic braking of main drive motor 19 whereafter small drive motor 50 is energized to slowly rotate the mold until protrusion 49 is registered with proximity switch 43. The mold then is locked in position by advancement of the tapered piston of hydraulic cylinder 22 into a suitable notch in rotary face plate 20. Mandrel assembly 13 next is retracted by hydraulic cylinder 167 along rails 18 to remove the ladle from the mold and the mandrel assembly is indexed to a position registering arbor 15 with the mold by admission of hydraulic fluid to motor 150 until the corresponding limit switch 163 mounted along the periphery of the turntable terminates the flow of hydraulic fluid to the hydraulic motor. After precisely indexing turn-table 146 by extension of tapered nose 159 into the angularly shaped groove in bracket 157, hydraulic cylinder 167 is again actuated to move the mandrel assembly towards the mold and insert expandable arbor 15 axially within the mold. The arbor then is expanded radially by admitting hydraulic fluid to cylinders 141 controlling the longitudinal traverse of centerpost 140 to abut arcuate segments 137 against the interior surface of the cast. After the pressure switches within the hydraulic lines of hydraulic cylinders 141 indicate contact between each of the arcuate segments on the arbor and the internal surface of the cast, hydraulic cylinders 105 of the pulling assembly are actuated to move bifurcated members 107 into registration with pulling brackets 101 along the outer face of the stripping jaws whereupon lockpins 110 are driven through the aligned apertures in the pulling brackets and the bifurcated members to lock pistons 102 of the pulling assembly to the individual mold sections. Lock rings 84 then are disengaged from jaws 86 by admission of hydraulic fluid to cylinders 75 to drive pistons 79 outward and the pistons of the main pulling assembly are drawn radially outward, i.e., into hydraulic cylinders 105, to simultaneously strip all four mold sections from the cast (with the cast being supported in position by the expanded arbor within the cast). Mandrel assembly 13 next is withdrawn by hydraulic cylinder 167 and hydraulic motor 150 is again actuated to index spray head 16 with the axis of the separated mold sections. After precise registration of the spray head with the mold sections by insertion of tapered nose 159 into bracket 157 and removal of the cast frame from the arbor, the mandrel assembly again is driven toward the mold sections to insert the spray head therein. As the spray head enters the mold sections, valve 144 is opened by limit switch 169b to pressurize lubricant reservoir 145 to spray lubricant along the internal surface of the mold sections. The spray head then is removed from the mold interior and, after indexing the mandrel assembly to register the ladle with the mold, a second cast can be initiated by the process heretofore described.

ELECTRICAL CONTROLS

Electrical control of the centrifugal casting machine to perform the process of FIG. 21 can be achieved utilizing any commerically available sequential switching control, e.g., a commerically available stepping switch or a wired program control. A particularly preferred control system for the casting machine, however, is illustrated in FIG. 22 in simplified form and generally comprises a sequencing circuit utilizing latching relays to inhibit loss of sequence upon a loss of power to the system. The system utilizes a 120 volt DC source applied across terminals 200 and 201 to permit energization of all the sequencing circuits and the casting cycle is initiated by depressing start button 203 to energize relay coil 1K if all preliminary conditions are functioning (e.g., assuming the hydraulic system is operating to close contacts H, liquid coolant is flowing in main shaft 31 to close contacts C, lubricating oil is circulating in housing assembly 72 to close contacts L, the aluminum pump is energized to close contacts A, et cetera. Energization of relay coil 1K then closes contacts 1K1 (contacts operated by coils are identified by a designation containing the first two identifying characteristics of the controlling relay coil) to energize coil 2K. Diodes D1 and D2 across coils 1K and 2K, respectively, provide a time delay for each coil so that contacts 1K1 remain closed approximately 35 milliseconds after release of start button 203 while contacts 2K1 remain closed about 35 milliseconds after contacts 1K1 de-energize relay coil 2K. The interval after the de-energization of coil 1K and before relay coil 2K drops out, i.e., when contacts 1K2 and 2K1 are both in their closed positions, relay coil 1LKL is energized to initiated automatic operation of the pour cycle. Energization of coil 1LKL closes contacts 1LK1 to energize relay coils 2LK1, 3LK1 and 4LK1 (through diodes D3-D5 inhibiting circulating currents) to admit hydraulic fluid to hydraulic cylinders 105, 75 and 160, respectively, to withdraw pistons 102 into cylinders 105, to drive lock rings 84 toward face plate 20 and to lock the mandrel assembly into position. After limit switches 116, 88 and 161 (measuring the piston extent from hydraulic cylinders 105, 75 and 160) are closed, main drive motor 19 is energized to rotate the mold by energization of relay coil 5LKL and aluminum is pumped into ladle 14 by energization of coil 6LKL controlling the metering unit employed to pump the molten aluminum into the ladle. Energization of coil 6LKL also closes contacts 6LK1 to energize coil 1LKV through diode D6 to open latched relay coil 1LKL. After timing switch TS (set at the interval required for aluminum to flow from the pipes into the ladle) closes, relay 7LKL is energized through closed contacts 6LK1 and the timing switch to open the valve admitting hydraulic fluid to hydraulic cylinder 167 to drive mandrel assembly 13 along rails 18 and insert the ladle within the rotating mold. When the ladle has reached the end of its traversal, as measured by limit switch 169c, relay coil 8LKL is energized through closed contacts 7LK1 and limit switch 169c to admit hydraulic fluid to hydraulic cylinder 130 controlling rack 131 to dump the molten aluminum from the ladle into the rotating mold. Closure of contacts 8LK1 by coil 8LKL also delatches coil 7LK1 by energization of coil 7LKV through diode D7. Although each sequential operation of a coil in FIG. 22 closes contacts to delatch a previously energized coil, such delatching coils function similar to the operation of coils 1LKV and 7LKV (previously described) and will be omitted from the remainder of the circuit for purposes of clarity. After completing dumping of the molten aluminum into the rotating mold (as determined by limit switch 170 actuated by rack 131), relay coils 9LKL, 10LKL and 11LKL are energized to operate a timer (not shown) controlling the energization period of drive motor 19, to rotate the ladle to the initial upright position and to retract the ladle from the mold interior by the admission of hydraulic fluid to hydraulic cylinder 167. Hydraulic cylinder 160 controlling the insertion of tapered nose 159 into angularly grooved bracket 157 then is actuated to unlock main turntable 146 by the energization of relay coil 12LKL through closed contacts 11LK1 and limit switch 169a at the end of the carriage traversal path. Simultaneously, relay coil 13LKL1 is energized through closed contacts 10LK1 and limit switch 169a to withdraw lockpins 110 from bifurcated members 107 of the pulling jaws. After radial retraction of the expanded jaws on arbor 15 (i.e., by closure of contacts 13LK1 to energize coil 14LKL controlling the admission of hydraulic fluid to cylinders 141), contacts 13LK2 and pressure switches P within the hydraulic lines of cylinders 141 are closed to energize coil 15LKL controlling the admission of hydraulic fluid to hydraulic motor 150 and mandrel assembly 13 is rotated to index the expandable arbor with the rotating mold. Energization of coil 15LKL also closes contact 15LK1 and, after closure of the associated limit switch 163 by vanes 162 on the main turntable, coil 16LKL is energized to admit hydraulic fluid to cylinder 160 to drive the tapered nose of the cylinder piston into the tapered groove of bracket 157 on the turntable. Energization of coil 16LKL also closes contacts 16LK1 and relay coil 17LKL controlling the braking of the main drive motor is energized by the closure of timing switch TS1 at the expiration of the mold rotation cycle. After mold rotation has stopped (as determined by proximity switch 42), relay coil 18LKL is actuated to initiate energization of small drive motor 50 until an output signal is generated from proximity switch 43 to energize relay coil 19LKL thereby terminating energization of the small drive motor. In a commercial embodiment of the invention, it generally is desirable to provide circuitry (not shown) to assure at least one-half cycle rotation of the mold by drive motor 50 to inhibit actuation of the pulling pistons by the stoppage of protrusion 49 adjacent, but not in precise registration with, proximity switch 43. After locking of the drive motor in position to prevent any further rotation of the mold, i.e., by energization of relay coil 20LKL through contacts 19LK1 and timing switch TS2, mold pulling pistons 102 are extended by the admission of hydraulic fluid to cylinders 105 by energization of coil 21LKL through closed contacts 20LK1 and a limit switch LS monitoring locking of the main drive shaft by hydraulic cylinder 22. Simultaneously with the extension of the mold pulling pistons 102, relay coil 22LKL is energized to admit hydraulic fluid to cylinder 167 thereby driving mandrel assembly 13 forward at high speed to position arbor 15 within the cast. Upon actuation of limit switch 169c at the end of the mandrel assembly traversal, coil 23LKL is actuated through contacts 22LK1 and the limit switch to admit hydraulic fluid simultaneously into the four hydraulic cylinders 141 to expand the arbor. Pulling pistons 102 then are locked to pulling brackets 101 of gripping jaws 86 by energization of coil 24LKL to admit hydraulic fluid to cylinders 105 upon closure of pressure switches P' within the hydraulic lines of cylinders 141 controlling the expandable arbor. Energization of coil 24LKL also closes contacts 24LK1 and, when limit switch 117 is actuated to a closed position by vane 118, hydraulic fluid is admitted to cylinder 109 (by energization of coil 25LKL controlling the valve admitting fluid to the cylinder) to drive lockpins 110 through the aligned apertures in bifurcated member 107 and pulling bracket 101. Limit switch 112 then is closed by the lockpins 110 securing the pulling cylinder to the mold and relay coil 26LKL is energized to admit hydraulic fluid to cylinder 75 disengaging lock rings 84 from gripping jaws 86. After the closure of the respective limit switch 88 on housing assembly 72, relay coil 27LKL is energized through closed contacts 26LK1 and limit switch 88 to admit hydraulic fluid to pulling cylinders 105 to strip the mold sections from the cast. Upon the closing of limit switch 116 by vanes 118 carried by guide rods 115 on the piston platform, coil 28LKL is energized to admit hydraulic fluid to hydraulic cylinder 167 withdrawing the mandrel assembly and cast from the interior of the stripped mold sections. At the end of the mandrel assembly traversal, as determined by limit switch 169a, coil 29LKL is energized through contacts 28LK1 and 169a to unlock rotatable turntable 146 by withdrawal of the tapered nose piston into cylinder 160. When the piston has been withdrawn, as determined by appropriate limit switch 161, relay coil 30LKL is energized through closed contact 29LK1 and the limit switch to admit hydraulic fluid into hydraulic motor 150 to rotate the mandrel assembly 90.degree. clockwise to position spray head 16 in registration with the stripped apart mold sections. Upon closure of the appropriate limit switch 163 by vanes 162 on the main turn-table, relay coil 31LKL is activated through closed contacts 30LK1 and hydraulic fluid is admitted to cylinder 160 to advance nose 159 into groove 158 locking the mandrel assembly into position. Energization of coil 31LKL also retracts the arbor, i.e., by closing contacts 31LK1 to energize coil 32LKL controlling the admission of hydraulic fluid to cylinders 141 to permit the cast frame carried upon the mandrel to be withdrawn by suitable means such as a conveyor (not shown). With the turret locked in a position to register spray head 16 with the stripped mold sections, limit switch 161 is closed to energize relay coil 33LKL through closed contacts 32LK1 admitting fluid to hydraulic cylinder 167 to again drive the mandrel assembly toward the mold sections. Upon closure of limit switch 169b, coil 34LKL is energized to pressurized lubricant reservoir 145 (by actuating valve 144) to spray lubricant upon the faces of the mold sections as the spray nozzle is traversed therein. At the end of the mandrel traversal (as determined by limit switch 169c), relay coil 35LKL is energized through closed contacts 34LK1 admitting fluid to hydraulic cylinder 167 to withdraw the mandrel assembly from the mold sections. At the end of the mandrel withdrawal, as determined by limit switch 169a, relay coil 36LKL is energized through closed contacts 35LK1 and the limit switch to admit hydraulic fluid to pulling cylinders 105 to drive pistons 102 radially inward thereby closing the mold. Relay coil 37LKL also is energized at this time to unlock main turntable 146 by withdrawal of the tapered piston into cylinder 160. Upon closure of limit switch 117 indicating juxtaposition of the mold sections by the pulling cylinders, coil 38LKL is energized to admit hydraulic fluid to hydraulic motor 150 to rotate the turntable to again position ladle 14 in registration with the assembled mold. When the registration has been accomplished (as determined by the appropriate limit switch 163), coil 39LKL is energized through closed limit switch 163 and contacts 38LK1 to admit hydraulic fluid to cylinder 160 to drive the tapered piston into the groove of bracket 157. After locking the rotatable turntable in position, as determined by limit switch 161, coil 40LKL is energized through closed contacts 39LK1 and the limit switch to admit hydraulic fluid to cylinders 75 to draw tapered lock rings 84 over the tapered faces of gripping jaws 86. When the lock ring is fully seated upon the gripping jaws, as determined by limit switch 88, relay coil 41LKL is energized through closed contacts 40LK1 and the limit switch to admit hydraulic fluid to piston cylinder 108 unlocking the mold pulling cylinders from the jaws. Pulling pistons 102 then are withdrawn, i.e., by energization of coil 42LKL controlling the admission of hydraulic fluid to piston cylinders 105, upon closure of limit switch 113. The system then is ready to begin a repeat cycle by re-energization of coil 1LKL1 through contacts 42LK1 unless frame counter FC remains open indicating completion of the desired number of frames to be cast.

Claims

What we claim as new and desire to secure by Letters Patent of the United

1. A method of centrifugally casting finned cylindrical structures comprising juxtaposing a plurality of arcuate sections to form a horizontally disposed cylindrical mold, rotating said mold at a predetermined speed, pouring molten material into said mold to centrifugally cast said finned cylindrical structure, registering said cast structure with a horizontally disposed arbor, obtaining relative movement between said arbor and said cylindrical structure to insert said arbor within said structure, expanding at least a portion of said arbor into contact with the interior surface of said cast structure, applying a radially outward force to each said arcuate section to strip said section from said cast cylindrical structure, removing said cast structure from the interior of said stripped mold sections and applying a radially inward force to said sections to reassemble said horizontally disposed

2. A method of centrifugally casting finned cylindrical structures according to claim 1 wherein pouring of said molten material into said mold is accomplished by pouring a quantity of molten material proportional to the size of the cylindrical structure to be cast into a ladle, inserting said ladle axially into said mold, tilting said ladle to pour said molten material into said mold, axially removing said ladle from said mold and further including rotating said ladle and said expandable arbor upon a common mandrel to axially register said arbor with the cast cylindrical structure prior to insertion of said arbor in said structure.

3. A method of forming cylindrical cast objects comprising juxtaposing a plurality of mold sections to produce a cylindrical mold, centrifugally casting a cylindrical structure within said juxtaposed mold sections by inserting a ladle within the mold and tilting the ladle to pour molten material from said ladle to said mold, axially removing said ladle from said mold, registering said mold with a horizontally extending arbor, inserting said arbor within said mold, extending at least a portion of said arbor to engage the interior of said cast structure, stripping said mold sections from said cast structure to insulate a structure formed entirely of molten material, removing the cylindrical structure from the interior of said stripped mold sections, spraying the interior surface of said stripped sections while in an open position, and subsequently moving said mold sections radially inward to form a cylindrical mold for subsequent casting.