US3754852A

US3754852A - Apparatus for rotational casting

Info

Publication number: US3754852A
Application number: US00482198A
Authority: US
Inventors: D Rempel
Original assignee: DODDS T Inc
Current assignee: REMPEL ROTO-CAST CORP; DODDS T Inc
Priority date: 1965-08-24
Filing date: 1965-08-24
Publication date: 1973-08-28
Anticipated expiration: 1990-08-28

Abstract

This invention relates to improved apparatus for rotational casting in hollow molds and a method of operating the same; more particularly, this invention relates to apparatus in which liquid materials are solidified or powdered materials are fused to a solid material while being rotated to distribute the material over an inside mold wall surface and to a method of supply and/or removing heat from the molds during such casting operations.

Description

United States Patent 91 Rempel 1 1 APPARATUS FOR ROTATIONAL CASTING [75] Inventor: Dietrich G. Rempel, Akron, Ohio [73] Assignee: Thomas M. Dodds, lnc., Lakewood,

Aug. 24, 1965 221 Filed:

[21] Appl. No.: 482,198

[52] US. Cl....- 425/429, 425/435 [51] Int. Cl. B29c 5/00 [58] Field of Search 18/26 R, 26 M; 425/429, 435

[56] References Cited UNITED STATES PATENTS 803,799 11/1905 Voelke... 18126 R 1,501,338 7/1924 Henry. 18/26 R UX 1,812,242 6/1931 Jensen... 18/26 UX 2,536,692 l/1951 Miller 18/26 R X 2,659,107 11/1953 DeBell 18/26 R X 2,834,986 5/1958 Bailey et a1. 18/26 R Aug. 28, 1973 3,095,260 6/1963 Ferriot 1 8/26 R X 3,104,423 9/1963 3,117,346 l/1964 Bertin et a1.

3,275,733 9/1966 Schule et a1.

3,337,662 8/ 1967 Spencer 3,173,175 3/1965 Lemelson 18/26 R Primary Examiner-H. A. Kilby, .li'.

Attorney-Ely and Golrick 57 ABSTRACT 5 laims, 8 Drawing Figures Patented Aug. 28, 1973 6 Sheets-Sheet 1 m T m V m DIETRICH G. REMPEL ATTORNEYS 6 Sheets-Sheet 2 FIG.2

In In INVENTOR DIETRICH G. REMPEL Y z? aw 4M ATTORNEYS I Patented Aug. 28, 1973 6 Sheets-Shoot 3 'IIHHHI INVENTOR.

DIETRICH G. REMPEL ATTORNEYS Patented Aug. 28, 1973 6 Sheets-Shoot 4 INVENTOR.

DI ETRICH G. RE MPEL FIG.6

ATTORNEYS Patented Aug. 28, 1973 6 Sheets-Sheet 5 RUE m. R v

I H 7 m ATTORNEYS Patented Aug. 28, 1973 I 6 Sheets-Sheet 6 3oz i f t 9 F wziosz wziw E 8 8 fi A P. 53 68 2282 For J o 8 @Qm 3 INVENTOR.

DIETRICH G. REMPEL BY ZZ I ATTORNEYS APPARATUS FOR ROTATIONAL CASTING The process of casting hollow articles without the use of cores has long been accomplished by variations of the generic process known as slush casting.ln recent years, the art has tended to subdivide the generic process into two groups, drain or in-and-out casting [in which the mold cavity is filled with the material to be cast (usually liquid or molten) which material is then poured out after a desired thickness has solidified or commenced to be immobilized on the mold walls] and rotational casting" (in which less than the entire mold cavity is filled with the material to be solidified and then the mold is oscillated or rotated about one or more axes to distribute the material over the mold walls). in some instances, the species of the process have been combined, i.e., after material has been poured into a mold cavity, solidification has commenced, and the majority of the unsolidified material drained out, the mold is rotated or oscillated to distribute over the solidified or solidifying material any residual material that has not yet solidified; this is done in order to shorten draining time and either minimize unwanted runs on the inside of the hollow article or distribute such residual material in specific locations. Such a combined drain and rotational casting method may be considered a rotational casting method for which this invention may be adopted.

Although rotational casting of certain materials, such as waxes, chocolate, low melting lead and lead alloys, plaster, and clay slips have apparently been practiced by hand for centuries and machines for rotating molds have been available for several decades, and means for heating and cooling the molds during the casting operation have been employed, the demand for rotational casting equipment has increased with the increased availability and introduction of various synthetic organic materials such as heat-setting latices, plastisols and organisols, and thermoplastic resins having fairly sharp melting, gelling, or fusing points. These resins and resinous materials may be introduced in the molds as liquid or molten material or as solids (usually in the form of powders); heat is applied during the initial rotation either to maintain a liquid condition of molten material during distribution, or to cause the materials which set in response to heat, such as latices, plastisols and organisols, to gel] and/or fuse as distribution takes place, or to melt and/or fuse the distributed material, in the case of powdered or solid resinous thermoplastic materials. At such elevated tempeatures, the molds and cast articles are too hot to be handled conveniently by the machine operators. Also, the cast articles are usually too weak and tender at such elevated temperatures to be safely removed from the molds; accordingly, prior to opening the molds and removing the articles, it has been conventional practice to cool the molds and their contained cast articles to temperatures sufficient to develop strength sufficient to permit handling.

Heretofore, the rotational casting machines employed in the art have essentially merely conveyorized, by means of lineal conveyors or by mounting on arms carried on a turntable or spindle, mechanisms for turning the molds simultaneously about a plurality of axes. So far as heating and cooling the molds is concerned, the machines commercially available to the prior art retained essentially the same methods and means as employed in hand-manipulation of the molds. That is, to heat the molds, the molds and at least part of their turning mechanisms have been placed in an oven or dipped in hot oil or salt baths; thereafter the molds and associated mechanisms have been cooled in spray chambers or cooling tanks prior to return to a station where an operator removes the cast articles and loads the molds for a repetition of the cycle.

The above described prior art rotational casting machines have many faults, some of which have been long appreciated but tolerated in the art because nothing better was available commercially; other faults and deficiencies are less obvious and appreciatedby only a few in the art.

Among the more obvious faults are these: When the molds and associated apparatus, including drive and mold closing apparatus, are conveyed from a cooling spray chamber or tank to an unloading station, unless the cooled molds (usually assembled in gangs on spiders or plates for simultaneous opening and closing) and their associated apparatus are relatively dry, any cooling water which drips on the hot cast articles may spot or otherwise spoil the articles as well as provide a maintenance problem at the unloading station. In the heating phase of the cycle performed by prior rotational casting machines, the molds and their supports and associated gearings were generally rotated in gasfired hot air ovens, in preference to the quicker and thermodynamically more efficient heating electrically or by submersion in oils or salt solutions which may be heated to the requisite temperature that may have to be well in excess of 200 F. (thereby excluding the use of steam heat in chambers which, for rapidity in transfer of the molds in and out of the chambers, cannot be maintained at pressures in excess of atmospheric pressure). Electrically heated molds were both expensive to make and operate and, unfortunately, hot liquid baths present the problem of loss of some of the liquid each time the molds are transferred to the cooling chamber; if not removed in the cooling chamber, any residual oil remaining in the molds and associated apparatus at the unloading station further complicated problems of product spoilage and plant maintenance. Also, theoretically, the gearing associated with the mold supports in prior art machines can be designed and lubricated to withstand the repetitive heating and cooling; in actual practice such mechanisms break down or require continual maintenance, resulting, in either case, in considerable downtime.

Another obvious problem is encountered in the prior art machines which carry the multi-axial rotating molds on arms supported on a central shaft or a rotating turntable which carries the arms from a loading and unloading station to an oven, thence to a cooling chamber, and thence back to the loading and unloading station. In such machines, the arms swing the mold assemblies eccentrically during the rotation of the molds and mold assemblies. Stitfening the arms to withstand such eccentric loads (in addition to increasing the cost of the machines), increases their weight and, thus, increases the inertia loads on the mechanisms for indexing the arms or the arms themselves as they pass from one position to the next. The prior art solution to this problem has been to accelerate and decelerate the indexing movements slowly; this either lengthens the cycle time (thereby reducing output) or shortens the dwell at each position (thereby, because the molds are most efficiently unloaded and reloaded with material to be cast while the molds are stationary, limiting the capacity of the machine, particularly for smaller articles).

Among the less obvious problems of prior art machines are these:

To overcome the loss in articles which have to be scrapped and the production of excessive flash caused by the warping of thin-walled shell molds in the heating phase and the consequent escape of casting material into or through the mold parting lines, the art had heretofore gone to sturdier molds having thicker walls to resist such warping, fully realizing that such molds were not only more expensive and required more massive mold-supporting spiders and, thus, more heating and cooling capacity to heat and cool the greater masses of metal; that the more expensive molds would have to be scrapped eventually because of growth of the metal by repetitive heating and cooling; and that cast articles aften exhibited weak spots attributable to under-curing as the machine was brought up to equilibrium conditions after a plant shut-down or the machines were shut down to allow for mold changes or maintenance. What the art apparently failed to realize was that the heavier bosses required on the heavier molds for attachment to the requisite sturdier mold supports constituted heat sinks that caused relatively cooler spots on the mold surface during the heating phase and relatively warmer spots during the cooling phase and, thus, were a substantial contributing factor to uneven curing of portions of cast articles. Further, the so-called growth of the metal in the molds and supports was largely due to permanent warping caused by repeated uneven contraction and'expansion of the molds and their supports. Still further, in many castable plastics, the development of optimum strength and other derivable physical properties in the cast material is often not merely a matter of bringing the material of the cast article up'to a requisite temperature and then cooling it to a temperature at which it can be handled in removing it from the molds, but in doing so at fairly closely controlled rates, including cooling at a controlled rate down to or near room temperature; the heat sinks provided by the means for attaching molds to a mold support in prior art machines can be sufficient to prevent requisite controlled rates of heating and cooling of all the material in a cast article.

Still another-serious, but seldom appreciated, objection to prior art machines is the cost of flexibility of product mix as themachines are increased in capacity to obtainincreased operating efficiency (for a single size and type of cast article). Thus, in a lineal conveyor type of prior art machine, in which the individual molds or small sets of molds'are each mounted on a mechanism for rotation of the molds simultaneously about two axes, which mechanisms are, in turn, mounted on a chain conveyor and driven by the movement of the conveyor through an oven and cooling chamber, the lengths of the oven and cooling chamber are fixed relative to the time required for heating and cooling the most massive molds which the machine is designed to handle. Smaller, less massive molds, requiring less time to heat and cool to requisite temperatures, can be substituted for the largest molds in such lineal conveyor machines, if the-conveyor is speeded up-within the limits of the capacity of the operations at the loading and unloading stationsto shorten the length of time the less massive molds remain in the fixed length oven and cooling chamber. Such mold changes, however,

not only require extensive down time, but a satisfactory curing of substantially different size articles simultaneously in such machines is obviously impossible. The spindle or turntable type machine has the advantage of permitting somewhat simpler mold changes and permits one arm to carry a set of molds of one size while other arms each carries a set of molds, all of the same size within the set but different from the size of the molds in other sets. This flexibility of product mix is limited, however, to mold sets which are each of the same total mass of metal and content of material to be cast, since all arms must heat and cool (and be unloaded and reloaded) in an equal period of time at each phase. The mixing of different size molds in any one set, or mixing sets of different mass on different arms would result in improper curing of at least some of the cast articles The simultaneous curing in one machine not only of different size articles but of different casting materials requiring different heating and cooling ranges and rates was obviously inconceivable in prior art machines.

The object and advantage of a machine made and operated according to this invention is that it overcomes or minimizes the foregoing faults of prior art machines. A particular advantage is that it eliminates the ovens and cooling chambers heretofore employed; thus, its general construction is simpler and less expensive and operating and maintenance costs are lower. Initial mold costs may be somewhat higher but, due to longer mold life and reduction of scrap through controllable rates of heating and cooling of individual molds or set of molds, the ultimate mold costs are considerably less. Also, due to the controllable rates and ranges of heating and cooling temperature obtainable by this invention, a wider variety of casting material may be cast. A still further advantage is the enormously greater flexibility of product mix obtained; molds may be changed quickly and simply; not only may different size molds be employed in one machine, but different materials, requiring different heating and cooling temperature ranges and rates, may even be cast simultaneously in one machine.

Other object and advantages of this machine will be apparent from the following specification, claims, and drawings, in which:

FIG. 1 is a front elevation, partly in section, of a machine made according to this invention shown prior to mounting the molds in which articles are cast.

FIG. 2 is a detail horizontal section, taken along the line 2-2 of FIG. 1, but showing molds mounted in the machine.

FIG. 3 is a detail vertical section of a closed mold as attached to the machine, taken along the line 3-3 of FIG. 2.

FIG. 4 is an enlarged fragmentary view of a modified construction of the spindle as shown in FIG. 1.

FIG. 5 is an enlarged fragmentary view, similar to FIG. 4, showing another modified spindle construction.

FIG. 6 is a detail elevation, partlyinsection, showing a modification of the frame support and drive, bearing and piping shown at the left of FIG; 1.

FIG. 7 is a detail elevation, partly in section, showing a modification of the central spindle drive, bearing, and piping shown in the lower center of FIG. 1.

FIG. 8 is a schematic showing of a heating and cooling fluid system for a machine made according to this invention and for practicing the mold heating and cooling method of this invention.

Fundamentally and basically, this invention minimizes or eliminates the above outlined faults of the prior art rotational casting machine and achieves many of its advantages through the technique of bringing the heating and cooling mediums to molds while they are rotated simultaneously about a plurality of axes, rather than conveying the molds successively through heating ovens or baths and through cooling chambers or baths, the molds being double walled or jacketed molds in which the heating and cooling medium is circulated in the jacket cavities or spaces between inner and outer molds walls. Jacketed molds capable of being used in a machine according to this invention are, per se, broadly old in other molding and curing equipment not requiring the circulation of heating and cooling mediurns in the molds while they are being rotated and neither requiring the means to conduct such mediums from suitable reservoirs to the rotating molds nor embodying a circulation system as described more fully below.

Referring to FIG. 1, showing one embodiment of a machine made according to this invention, a frame is fixed to and symmetrically mounted on a pair of spaced and axially aligned hollow stub shafts l1 and 12, each journaled in the pillow blocks 13. The pillow blocks 13 are supported by a pair of spaced stanchions 14. As shown, the stanchions 14 support the pillow blocks so that the horizontal axis is at substantially a I counterheight. Thus, the molds carried within the frame 10 may be opened, a cast article removed, and casting material loaded into the mold and the molds closed at the most convenient working height for the operator. This simple construction alone provides substantial advantage over prior art rotational casting machines which, by necessity, often presented the molds in a position where the operator had to stoop or reach during the loading and unloading operations. Each hollow stub shaft 11 and 12 is received at its outer end in a conventional rotary seal 15, the stub shaft 11 being thereby connected to a fixed inlet pipe 16 and the stub shaft 12 to a fixed outlet pipe 17 so that a heat-transfer fluid (i.e., heating or cooling) may flow into the stub shaft 11 and out of the stub shaft 12 as the frame 10 is rotated (or oscillated) about the horizontal axis by the gear head motor 20 connected to the shaft 11 through the drive comprised of the pinion l8 and the gear 19 fixed to the shaft 11.

The shaft 11 within the frame 10 is connected to the piping 21 carried by the frame 10, which piping is connected to a rotary seal 22 similar to the rotary seal 15. The rotary seal 22 is connected to a hollow spindle shaft 31 of the spindle assembly 30. The spindle assembly includes a hollow spindle shaft 32, similar to and axially aligned with the spindle shaft 31, both

shafts

31 and 32 being journaled in a pair of bearings 33 carried by the frame 10 so that the spindle assembly 30 may rotate within the frame 10 about an axis perpendicular to the horizontal axis of the frame 10. The spindle shaft 32 is connected by the rotary seal 23 to the piping 24 leading and connected to the hollow stub shaft 12 by a flxed connection (not shown) similar to the connection of the piping 21 to the shaft 11. This permits the spindle assembly 30 to be rotated in the bearings 33 and frame 10 by the gearhead motor 25 mounted on the frame 10 and driving the spindle shaft 31 through its gear 26 and the motor pinion 27, while heat-transfer fluid passes into the shaft 31 from the piping 21 and out of the shaft 32 into the piping 24.

The spindle assembly 30 comprises a mounting plate 34 carried by the shaft 31 and a corresponding mounting plate 35 carried by the shaft 32, the two mounting plates being connected to be driven as a unit by the mold-supporting

channels

36 and 37. The two moldsupporting channels are shown in this embodiment, it being understood, however, that any necessary number of such channels may be employed. To permit fluid to pass into the fluid distribution assembly 40, the plate 34 is-provided with an opening leading from the hollow shaft 31 to a distributor cap 38 secured to the plate 34. Similarly, a distributor cap 39, secured to the plate 35, collects fluid from the assembly 40 and allows it to pass through an opening in the plate 35 to the hollow spindle shaft 32.

The distribution assembly comprises, in this instance, two inlet riser tubes 41 tapped into the cap 38 and extending nearly to the cap 39, the outer ends of the tubes being plugged. A corresponding set of outlet riser tubes 42, plugged at their outer ends, are connected to the cap 39. Tapped into the riser tubes are a plurality of flexible connections (not shown in FIG. 1) to the several molds normally carried by the

channels

36 and 37. One inlet tube 41 and one outlet tube 42 are normally connected, as a pair, to one mold or a set of molds which is opened and closed 'at the same time. For purposes of illustration, only two pairs of inlet and outlet riser tubes are shown in this embodiment; just as the number of mold-supporting

channels

36 and 37 may be varied to suit the number of molds or sets of molds that may be carried within the mold rotating volume (indicated by the phantom block 50 in FIG. 1), so the number of pairs of riser pipes, serving as manifolds for distributing heat exchange fluid to and collecting it from the several molds, may be varied as needed. To change molds in this machine, they may be either quickly bolted and unbolted from the

channels

36 and 37 and their flexible connections to the riser tubes in the assembly 40 changed, or, where a sufficient inventory of molds has been acquired for scheduled production of product mix, sets of molds, pre-assembled on spindle assemblies 30, each with its appropriate distribution assembly 40, may be even more quickly changed by simply switching spindle assemblies within the frame 10.

To supply electrical power to the spindle motor 25, circuits for controlling mold inlet or outlet valves (and even for supplying electric current to electrically heat the molds, if desired) the frame 10 carries commutator disks 45 'to which electrical connections are made by brush blocks 46 mounted on the stanchion 14. Electrical connections (not shown) from the disk 45 to the motor 25 control the operation of the motor 25. Additional electrical connections from the brush blocks 46 to the disks 45 on the frame 10 to a commutator disk 47 on the spindle assembly 30 through brush blocks 48 on the frame 10 provide the optional circuits for controlling optional mold valves, electrical mold locking means, and/or mold heating.

The mold rotating volume 50 is the solid of revolution generated by the simultaneous rotation about the axis of the spindle assembly and the axis of the coaxial stub shafts 11 and 12 by the largest molds which may be mounted on the spindle assembly and rotated with safe clearance within the frame 10. It is to be noted that center of the volume 50 will coincide with the intersection of the two axes of rotation, thereby minimizing the eccentric load of the molds on the machine and permitting use of lighter weight structural elements in the machine. The height of the stanchions 14 or the support therefor is selected to position the center of the mold rotating volume at a height to permit the molds to be unloaded and'loaded by an operator without undue stooping or reaching.

During simultaneous rotation of the molds about the axes of revolution, the ratio of the rotational speed of the frame 10 about the axis of the stub shafts 11 and 12 with respect to the rotational speed of the spindle assembly 30 may be varied by adjusting the speeds of the

motors

20 and 25 to provide the optimum distribution of material within the mold cavity. This optimum ratio may vary according to the material being cast and the shape of the internal mold cavity. Both rotational speeds are normally low enough to cause the material to distribute itself within the mold cavity under the influence of gravity, rather than by centrifugal force. However, when a particular mold cavity has recesses or deep sockets into which it may be desirable to force the casting material by centrifugal force, this may be accomplished by acceleration of one of the motors, usually while the other is stopped. Other variations of the motor speeds from a fixed ratio during the casting operation, including momentarily stopping or even reversing the direction of rotation about one or both axes, may be employed to distribute the casting material so as to provide localized wall-thicknesses in the cast article differing from those which would be obtained by simultaneous rotations at a fixed ratio.

When the rotation of the molds is stopped for unloading and recharging, the gear-head drive of the motor 20 may be provided with a suitable indexing detent to stop the frame 10 in a vertical plane or other position which presents the opened mold for the most convenient unloading and recharging. Similarly, the independently driven motor 25 may be provided with an indexing detent to present each mold so that the frame 10 will not interfere with the opening of the mold. In the absence of such detent means for automatically presenting the molds to an operator in a position for convenient unloading and recharging of an opened mold, each motor is preferably provided with manual controls which permit the frame 10 and spindle assembly 30 to be independently jogged backwards or forwards, after coni tinuous rotation has stopped, to present the molds in the most convenient positions for opening, unloading, recharging, and closing.

One manner of mounting jacketed molds on the spindle assembly 30 and connecting the mold jackets to the distribution assembly 40 is shown in FIGS. 2 and 3.

A pair of molds 50 are bolted to the mold-supporting

channels

36 and 37. In this instance, to demonstrate the simplicity of mounting even relatively large and complex molds (in comparison with the two-part molds customarily handled in prior art machines) the molds 50 are three-part molds for hobby-horse bodies, Each such mold 50 (see FIG. 3) comprises a fixed jacketed section 51, bolted to a mold support channel, and jacketed upper and lower pivoted

sections

52 and 53 pivoted to the channels by pivot pins 54 and locked to each other and the fixed section'Sl by suitable means, such as the doweled locking tab sets 55. (Locking clamps mounted on the tab sets 55 are omitted from the drawings for simplicity of illustration; these locking clamps may be simple conventional hand-operated C-clamps, but are preferably electrically operated clamps in order to speed mold opening and closing). Sets of flexible inlet tubes 611, 62, and 63 are tapped into each inlet riser 4] and into one end of the jackets of the

mold sections

51, 52, and 53, respectively; similarly, sets of

flexible outlet tubes

64, 65, and 66 are tapped into the opposite ends of the jackets of the

mold sections

51, 52 and 53, respectively, and into the outlet risers 42.

MOLD TEMPERATURE CONTROL AND OPERATION Various means may be employed to insure equal heating and cooling of the several mold sections at predetermined rates. As an example, one may install, in either the inlet or outlet tubes connected to each mold section,

valves

67, 68, 69 (shown in phantom in FIG. 3 to indicate their optional use and location). Such valves .are preferably electrically operated and controlled by remote external timers acting in combination with thermocouples located in the jackets or on the inside mold walls for extremely precise control; for established production, such thermocouples may be located either in the flexible inlet or outlet tubes 61 to 66 or in the

risers

41 and 42. Acting .in conjunction with the valves controlling the change in temperature of the heat-exchange liquid circulated through the machine, such timed valves control the duration of the heating and cooling phases of each casting cycle in any given mold.

Merely controlling the duration of flow of the heattransfer medium of the desired temperature through the jacketed mold sections, however, is not necessarily sufficient to insure equal rates of heating and cooling of the casting material. Good mold design indicates that each section of a multi-section mold be of substantially the same mass of metal and that each mold section heat and cool substantially the same mass of material on the cast article; in such cases the equal internal diameter of the flexible tubes 61 to 66 will insure, under the pressure drop between an inlet riser and outlet riser serving the same mold or set of molds, an equal volumetric flow of heat-transfer liquid in each section. However, product configuration or design for the most desirable location of parting lines often prohibits such balance of mass in multi-sectional molds. For example, in the mold 50 as shown in FIG. 1, the

sections

52 and 53 are of equal mass and also moldequal masses of the plastic cast against their inside mold surfaces; the section 50, which molds the under-belly of the hobby horse body and the inside surfaces of the leg sections is smaller in mass and a smaller mass of plastic is cast against its inside mold surface. To obtain an equal rate of input and output of Btus per square inch of casting surface per second, the mold is initially installed with petcocks interposed in each of the flexible inlet tubes 61, 62 and 63 and thermocouples are installed to measure the temperatures of the liquid flowing through the

outlet tubes

64, 65, and 66. Without rotating the molds but causing the heat transfer liquid to flow through the molds at operating pressures and temperatures, the petcocks are then adjusted until the temperatures of the liquid flowing through the outlet tubes rise and fall at equal rates in each tube. With the rates of fow in the mold sections thus determined, the flow for production operations may be fixed by inserting appropriately sized flow-restricting orifice disks in a tap fitting of any inlet tube requiring restriction. Any substantial difference in flow between mold sections of equal mass and casting surface, such as the

equal sections

52 and 53, will generally indicate incomplete removal of core material or other blockage of the jacket cavity in the mold section requiring greatest flow; a substantially greater flow requirement in the smaller section 51 from that required by similar sections in duplicate molds likewise indicates a jacket cavity blockage which should be corrected before the mold is placed in production.

From the foregoing it should be evident that, instead of single cavity molds 50 being supported on the channel members of a spindle assembly 30, either a mold having a number of similar cavities or a gang of equal molds may be assembled on suitable spiders or plates and substituted for the single cavity mold 50. Also, more than one mold or set of molds may be supported on a channel of a spindle assembly provided they are sufficiently spaced to permit the mold section to be opened (as indicated by the arrows in FIG. 3) to remove cast articles and load the cavities with a charge of casting material for the successive cycle.

In prior art machines; optimum operating efficiency was obtained when all molds in the machine were casting identical articles; under such circumstances all production at any given period could be geared to the phase (usually the heating phase) requiring the longest period in the cycle. In machines as shown in FIGS. 1 to 3, the limitation on optimum production efficiency for any given group of molds mounted on the spindle assembly, is only that each mold cavity is, in the same period of time, heating and cooling its cast material to the required temperatures at the fastest rates for proper curing. This, by no means, requires that all mold cavities be for identical articles. For example, in products cast from the same plastic with the same wall thickness, optimum rates of heating and cooling, regardless of size of the article, will require equal delivery (or extraction) of an equal number of Btus/second/square inch of mold surface. Thus, just as the optimum rate of heating and cooling the smaller mold section 51 in the mold 50 is obtained by restricting the volume of flow of the heat exchange liquid to the section 51 with respect to the volume of flow of the liquid to the

larger sections

52 and 53, so, for example, may a series of molds for smaller articles replace one of the large molds 50 as shown in FIG. 3; by regulating the flow of fluid to the molds, articles may be cast in the smaller molds simultaneously with the casting of a large hobby horse body in the remaining mold 50.

In order to simplify production logistics, production scheduling should normally avoid the casting of articles of different castable materials in the same machine at the same time. However, the product mix at certain times may permit such separation of materials only at the expense of idle machine time and labor. Fortunatcly, with machines made and operated according to this invention, such sacrifices in plant efficiency may be eliminated or minimized. Thus, for example, if the product mix should require that the article east in one mold of FIG. 2 be of one material and that the article east in the other mold be of a different material requlr= ing different temperature ranges and rates, the problem is no longer insurmountable. Due to the fact that the rise or fall of temperature in any given mold is determined by the combination of temperature differential between the mold and the fluid and the volume of fluid supplied to the mold, by supplying the heating liquidat the maximum temperature appropriate for either of the materials and the cooling liquid at the minimum temperature appropriate for either of the materials, the combination of valves or orifices for controlling the rate of flow between the risers and the molds and a remote control valve to one mold for stopping flow at the end of the requisite cooling period and starting flow sufficiently in advance of the change from hot to cool liquids sent through the distributor assembly during the requisite heating period, two different plastics having different casting temperature ranges and rates maybe cast simultaneously. Such simultaneous casting of differentmaterials is usually at the expense of an increase in the dwell time between the heating and coolingphases beyond that required for loading and unloading but may represent a very substantial gain over the loss in idle machine time and labor which might otherwise be incurred.

MODIFICATIONS OF SPINDLE ASSEMBLIES ANI) SPINDLE BEARINGS The spindle and

distributors

30 and 40 of the proto type shown in FIG. 1 are preferably designed to permit the mounting of molds so that the open molds are presented laterally outwardly of the frame 10 as well as vertically from the floor at a convenient position for an operator to load and unload the molds; also, the assembly of pairs of

risers

41 and 42 permits one mold or set of molds carried on one channel, together with the associated flexible tubing and risers to be interchanged with another without disturbing other molds on the other channel or channels or the heat insulation (not shown) which may be packed around their risers. Because the

risers

41 and 42 serve as manifolds for the flexible tubing connecting them to the mold sections, they permit the shortest lengths of flexible tubing to be used with a minimum of tangling between sets of tubing leading to different molds served by the same pair of risers. Thus, because locations of the tappings for the sets of flexible tubing into a riser are generally peculiar to the particular mold or sets of molds it serves, when a mold or sets of molds are interchanged, it is usually practical to change the associated risers as well.

When the machine must rotate large molds, the central space occupied by a spindle assembly 30 may have to be reduced to permit the molds to clear the frame 10. An alternate spindle assembly 40', as shown in FIG. 4, accomplishes this result. The assembly comprises a pair of axially aligned, structurally strong pipe sections 41' and 42' joined end-to-end by a central plug 43' (preferably of non-heat-conducting strong material such as reinforced plastic). The sections 41 and 42' are secured respectively to

plates

34 and 35 having openings through which inlet fluid from the spindle shaft 31 may pass into the section 41' and outlet fluid in the section 42' may pass into the outlet spindle shaft 32. The sections 41' and 42 may thus serve both as supports for molds supported thereon and as manifolds into which flexible tubing for the mold sections may be tapped.

When an extremely large mold, as for a seat or chair, boat, tank, or the like is to be rotationally cast in the machine, the central spindle assembly may be omitted altogether and the mold simply fastened to the

plates

34 and 35, as indicated fragmentarily in FIG. 5.

The machine as above described is suitable for easting operations in which the mold rotation is accelerated or decelerated sufficiently slowly to avoid heavy inertial loads on the bearings and also in which temperature differential of the heating and cooling fluids passing through the stub shafts l1 and 12 is insufficient to affect significantly either the operation of the

bearings

13 and 14 or the heat economy (due to loss of heat by conduction to the structural elements of the machine and the pick-up of heat by the cooling fluid from such structural elements). Where such a temperature differential between the heating and cooling fluids adversely af-' fects either the bearing operationor the heat economy of the machine, and when it is desirable to shorten cycle times by starting and stopping rotation of the machine quickly, an embodiment as shown in detail in FIGS. 6 and 7 is preferred.

Referring to FIG. 6, showing the detail of mounting a frame 110 (generally corresponding to the frame 10 of FIGS. 1 to the stanchion 114 supports a bearing 113 in which a hollow stub shaft 111 is journaled. Instead of functioning both as a frame'supporting shaft and as a connecting conduit between the rotary seal connected to an inlet pipe 16 and the fluid piping of the frame (as the stub shaft 11 in the embodiment shown in FIG. 1), the stub shaft 1 11 merely supports the frame 110. Inlet piping 121 carried by the frame 110 (and supported therein by heat-insulating bushings 124) extends through the bore of the stub shaft 111 and is directly connected to a rotary seal 115, preferably of a high-temperature type, as shown, to accommodate higher temperature fluids supplied by the inlet pipe 16. The piping 121 is spaced from the shaft 11 1 throughout its length to provide air insulation between the shaft and piping and, thereby, avoid transfer of heat at this point between the fluid conduit means and other structural elements of the machine, particularly the bearing 113.

To permit the gear-head motor 120 to start and stop the frame 110 quickly, the motor is mounted lower on the stanchion 114 to permit the motor pinion 118 to engage a large gear 119 mounted directly on the frame 1 10. As shown, the gear 1 19 is of the type which is built up from a bent rack or roller chain fixed on a suitable ring, so that its periphery extends well outwardly toward the periphery of the frame 1 large radius of the gear provide a greater moment for coping with the larger inertial forces involved in starting the rotation of the frame about its horizontal axis.

It is to be understood that a similar mounting may be provided for the frame 110 at its opposite end to an outlet pipe 17. Also, at either or both ends the frame 110 may carry a commutator disk 145 to which electrical connection may be made by a brush block (not shown). It is also to be understood that, instead of a commutator disk 145, one may provide commutator rings on the shaft 111, preferably on its outboard end, to provide electrical connections to the frame 110.

To effect similar heat economy of this modification and provide a capability of handling large inertial loads where a spindle assembly 130 is rotatably mounted in the frame 110, as shown in detail in FIG. 7, a bearing 133 is mounted on the center of one side of the frame, in which bearing a hollow shaft 131 is journaled. A mounting plate 134 is carried by the shaft 131 and both are provided with enlarged bores to receive a spaced tube 129 connecting the piping 121, through a rotary seal 122, to the lower plate of a distributor box 138. The distributor box is mounted onthe plate 134 by means of suitable brackets, which also space the box from the plate toprovide air insulation. As in FIG. 1, the mounting plate 134 may carry suitable moldsupporting channels, but in this embodiment a moldsupporting column 136 is shown mounted on the distributor box, being insulated therefrom by a suitable insulating disk 137. A fluid distributing assembly 140 comprises inlet riser tubes 141 and outlet riser tube 142.

A similar arrangement is, of course, provided at the opposite end of the spindle assembly to permit the rotation of the molds mounted on the column 136 within the frame 110 and to permit connection of the outlet riser tubes to piping leading to an outlet pipe 17.

Rotation of the spindle assembly 130 is obtained by a gear head motor 125 through a pinion 127 driving gear teeth carried in the periphery of the plate 134 similar to the gear 119. Electrical connections for the operation of valves, mold clamps, or heating the molds (if desired) is supplied to the spindle assembly through a commutator disk 147 and brush block (not shown).

HEATING AND COOLING FLUID SYSTEM 'For materials which may be cast at temperatures less than approximately 2002l0 F., the heating fluid for the molds may be hot water or steam at substantially atmospheric pressure and cooling fluid may be water from the plant supply. However, most plastics or other synthetic materials which may be cast in a machine made and operated according to this invention usually require heating to higher temperatures which may be in the order of 350 to 400 F., or higher. Jacketed molds and piping with the casting machine capable of withstanding the pressure of super-heated steam at such higher temperatures would necessarily be mas sive. Such massive molds and piping'are not only expensive but would necessitate the dissipation of a substantial proportion of the heating and cooling fluid solely for the purpose of heating and cooling the molds and piping, rather than the plastic being cast. Accordingly, the preferred heating and cooling fluids are liquids having high boiling points and relatively low vapor pressure at the requisite curing temperatures such as buffered salt solutions, various oils, and other liquids available under proprietary names, such as the various Dowtherms, which have a wide spread between a freezing point or thickening range at or below room temperature and a boiling point or relatively low vapor pressure ranges at or above the maximum temperature required for curing the cast plastic.

As shown diagrammatically in FIG. 8, a preferred system for supplying a requisite heating and cooling liquid comprises a reservoir made up of a series of tanks connected by a collecting manifold 71 to a pump 72 which, in turn, is connected to the inlet piping 16 of the casting machine. After passage through the casting machine and its molds, the fluid is then returned to the reservoir 70 through a distributing manifold 73 connected to the outlet piping 17 of the machine.

The tanks in the reservoir 70 comprise at least two, a tank 75 for the hottest fluid supplied to the machine, and a tank 76 for the coolest; improved heat economy is obtained by employing at least one tank 77 for liquid of intermediate temperature.

When employing a three-tank system as shown in FIG. 8, the operation of the system is as follows:

assuming the molds in the machine are cooled sufficiently to allow cast articles to be removed and have been reloaded with charges of the material to be cast, liquid from the medium temperature tank 77 passes from the tank 77 through its associated valve87 to the manifold 7i; the liquid is thereby forced by the pump 72 through the casting machine and molds to begin to heat up the molds and thence to the distributing manifold 73. As the temperature guage T in the outlet pipe 17 indicates the initial heating of the molds, the valve 87 is closed and the valve 85 leading from the hot tank 75 is opened to allow the hottest liquid to pass through the machine and molds into the distributing manifold 73. After the molds have been brought to temperatures (as again indicated by the guage T) and held for the requisite period, the valve 85 is closed and the valve 87 is opened for a period to allow the medium temperature liquid to commence cooling and is then closed; the valve 86 is then opened to allow the coolest liquid to pass through the machine and molds into the distributing manifold 73 until the molds are cooled sufficiently to allow the molds to be opened, whereupon the cast articles to be removed and the'molds are recharged, concluding the cycle.

From the foregoing, it is apparent that as the fluid passes into the distributing manifold 73 it will generally range in temperature from slightly less than the highest temperature maintained (by heating means, now

- shown) in the tank 75 to slightly more than the temperature maintained (by cooling means, not shown) in the coolest tank 76. In a two tank system, the valve 95 leading from the distributing manifold to the tank 75 and the valve 96 leading to the tank 76 are simply opened and closed alternately to allow the warmer liquid in the' distributing manifold to discharge into the hot tank 75 and the cooler liquid to discharge into the cool tank 76, the flow being balanced to maintain substantially equal volumes of flow through the tanks. When a system of three or more tanks (intermediate tanks being represented by the tank 77 and its associated valves 87 and 97) is employed, however, the flow is distributed approximately equally among them, according to the temperature changes in the distributing manifold 73 and the heat economy of the system is improved. That is, when liquid from the medium temperature tank, after initially warming the molds is thereby cooled and is first discharged into the cool tank, some of the preceding cooling of the molds is recovered; likewise, when liquid from the medium tank, after commencing the cooling of the mold is thereby heated and is first discharged into the hot tank 75, heat is recovered. By utilizing the preferred medium tank 77, not only are the loads on the heating and cooling means in the reservoir 70 lessened, but only usually one heating means in the hot tank 75 and one cooling means for the tank 76 are required.

The above-described and functioning system of circulating the heating and cooling fluid is particularly advantageous with the casting machines made and operated according to this invention because of the unidirectional flow of the fluid through the casting machine,

I which unidirectional flow also permits precise control of the mold temperatures and their heating and cooling rates.

warranted by the economy of operation. Likewise, if

the cost warrants the improved increase in heat economy, each tank may deliver its contents through its own individual pump and the actual physical length of the manifolds may be no more than the connections of the several tanks to the inlet and outlet piping of the casting machine.

A further advantage of the design of a rotational casting machine made according to this invention, in which the heat-transfer fluid passes to a jacketed mold from a spindle assembly and supporting frame by means of fittings which allow the fluid to pass axially through bearings about whose divergent axes the mold is rotated is this: Simple extensions of the members of the frame andpiping'permit the enlargement 'of the machine to accommodate, within a wide range, larger molds. For'the machine manufacturer this permits machines to be readily custom-built from stock sub-'- assemblies; especially when the frame is of a bolted construction, the users may also enlarge the machines when, as frequently occurs, it becomes necessary to use molds or mold assemblies larger than originally contemplated. Such ready enlargement is impossible, as a practical matter, in prior art machines requiring oven and cooling chambers or heating and cooling tanks for heating and cooling the molds by submersion, due to the expense of rebuilding such heating and cooling equipment. In equipment made according to this invention, the reservoir and pumping system are seldom seriously overloaded by such enlargements, particularly when, as may be frequent, one reservoir for heating and cooling the heat-transfer fluid or fluids serves several machines.

It is to be understood, therefore, that those skilled in the art may devise other and further embodiments and modifications of this invention and, accordingly, this invention is not limited to the specific embodiments disclosed by the appended claims.

What is claimed is:

l. A machine adapted to cast hollow articles rotationally comprising a mold having a hollow cavity and a passage through the mold for heat-transfer fluid to vary the temperature of the mold cavity surface, a spindle assembly upon which said mold is mounted, a-

frame, inlet and outlet fluid conduit means in said frame, a pair'of axially aligned bearings carried by said frame, on which bearings said spindle assembly is mounted, means, including a rotary seal at each of said spindle bearings, for conducting fluid from said inlet conduit means substantially concentrically through one of said spindle bearings to said mold passage and from said mold passage substantially concentrically through the other of said spindle bearings to said outlet fluidv conduit means, bearing means in which said frame is rotatably mounted, means for supporting said frame bearing means, means to rotate said frame and said spindle assembly in their respective bearings, said frame bearing means being supported so that an extension of its axis lies within and intersects the solid of revolution generated by said mold when said frame and spindle means are simultaneously rotated, means, including rotary seals, for connecting said, inlet and outlet conduit means to a reservoir of heat-transfer fluid, whereby heat-transfer fluid may be circulated through said mold passage to vary the temperature of said mold cavity while said mold is capable of being simultaneously rotated about two diverse axes, and in which means to rotate said spindle assembly and frame include a motor mounted on said frame and connected to said spindle, and commutator means carried by said frame whereby said spindle motor may be controlled to rotate said spindle assembly independently of the rotation of said frame, and in which at least one of the structures (frame or spindle assembly) supported on a bearing is supported by a hollow stub shaft journaled in such bearing and the tube passing through said bearing for conducting heat-transfer fluid to said inlet and outlet conduit means in said frame is spaced from said stub shaft to insulate said tube from said shaft and minimize the conduction of heat between the heat-transfer fluid in said tube and said bearing and the structural elements of said machine mechanically connected with said bearing and the shaft journaled therein.

2. In a spindle assembly for a machine of the class described, means for supporting a jacketed mold through which heat-transfer fluid passes to vary the temperature of the mold and for conducting said fluid to and from said mold, tubing connecting said means to inlet and outlet openings in said mold, and means in such spindle assembly to control the flow of fluid to said mold and thereby control the rate of heat transfer between said mold and said fluid, including means for supporting a multi-sectional jacketed mold, the mass of whose sections are different and which sections define different areas of a mold cavity enclosed by said mold and also including a distributing assembly for distributing heat-transfer fluid through tubing connected therewith to and from the jacket of each of said mold sections, and said flow control means controls the flow of heat-transfer fluid to said mold sections to provide a substantially uniform rate of heat-transfer per unit of area of mold cavity surface.

3. In a spindle assembly as defined in claim 2 in which said distributing assembly is spaced from said mold supporting assembly to insulate and minimize the conduction of heat from said heat-transfer fluid to said mold supporting means.

4. In association with a rotational casting machine of the class described, a reservoir system for recirculating heat-transfer liquid through such a machine, including pumping means for forcing heat-transfer liquid into said machine and withdrawing the same from said machine for return to said reservoir system, a hot tank maintaining said liquid at at least the hottest temperature at which said liquid is circulated through said machine and a cool tank maintaining said liquid at no more than the coolest temperature at which said liquid is transferred through the machine, means providing for the circulation of the liquid at intermediate temperatures through said machine, and valving means allowing the withdrawal of liquid from said hot tank into said circulated liquid when it is desired to raise the temperature of the liquid circulated through said machine and to allow the withdrawal of liquid from said cool tank into said circulated liquid when it is desired to lower the temperature of said circulated liquid.

5. In a system as defined in claim 4 in which said means allowing circulation of the liquid at intermediate temperatures includes an intermediate tank for receiving liquid (of intermediate temperature) which has been heated or cooled by a mold in said machine and said valving means includes a valve for distributing to the hot tank the liquid in the uppermost range of temperatures of liquid returned from said machine, to the cold tank the liquid in the lowermost range of temperatures of liquid returned from said machine, and to said intermediate tank some of the liquid of an intermediate range of temperatures which is returned from said machine, said temperature ranges of returned liquid being selected to distribute liquid in the warmest, intennediate, and coolest ranges in substantially equal volumes of liquid to each of the hot, intermediate, and cool tanks, respectively, whereby some of the heating and cooling imparted by said circulated liquid to said mold is recovered by the liquid returned to an intermediate tank.

Claims

1. A machine adapted to cast hollow articles rotationally comprising a mold having a hollow cavity and a passage through the mold for heat-transfer fluid to vary the temperature of the mold cavity surface, a spindle assembly upon which said mold is mounted, a frame, inlet and outlet fluid conduit means in said frame, a pair of axially aligned bearings carried by said frame, on which bearings said spindle assembly is mounted, means, including a rotary seal at each of said spindle bearings, for conducting fluid from said inlet conduit means substantially concentrically through one of said spindle bearings to said mold passage and from said mold passage substantially concentrically through the other of said spindle bearings to said outlet fluid conduit means, bearing means in which said frame is rotatably mounted, means for supporting said frame bearing means, means to rotate said frame and said spindle assembly in their respective bearings, said frame bearing means being supported so that an extension of its axis lies within and intersects the solid of revolution generated by said mold when said frame and spindle means are simultaneously rotated, means, including rotary seals, for connecting said inlet and outlet conduit means to a reservoir of heat-transfer fluid, whereby heat-transfer fluid may be circulated through said mold passage to vary the temperature of said mold cavity while said mold is capable of being simultaneously rotated about two diverse axes, and in which means to rotate said spindle assembly and frame include a motor mounted on said frame and connected to said spindle, and commutator means carried by said frame whereby said spindle motor may be controlled to rotate said spindle assembly independently of the rotation of said frame, and in which at least one of the structures (frame or spindle assembly) supported on a bearing is supported by a hollow stub shaft journaled in such bearing and the tube passing through said bearing for conducting heattransfer fluid to said inlet and outlet conduit means in said frame is spaced from said stub shaft to insulate said tube from said shaft and minimize the conduction of heat between the heattransfer fluid in said tube and said bearing and the structural elements of said machine mechanically connected with said bearing and the shaft journaled therein.

5. In a system as defined in claim 4 in which said means allowing circulation of the liquid at intermediate temperatures includes an intermediate tank for receiving liquid (of intermediate temperature) which has been heated or cooled by a mold in said machine and said valving means includes a valve for distributing to the hot tank the liquid in the uppermost range of temperatures of liquid returned from said machine, to the cold tank the liquid in the lowermost range of temperatures of liquid returned from said machine, and to said intermediate tank some of the liquid of an intermediate range of temperatures which is returned from said machine, said temperature ranges of returned liquid being selected to distribute liquid in the warmest, intermediate, and coolest ranges in substantially equal volumes of liquid to each of the hot, intermediate, and cool tanks, respectively, whereby some of the heating and cooling imparted by said circulated liquid to said mold is recovered by the liquid returned to an intermediate tank.