US3550206A

US3550206A - Rotational casting apparatus

Info

Publication number: US3550206A
Application number: US720700A
Authority: US
Inventors: Elmer J Von Der Heide
Original assignee: Fabricators Inc
Current assignee: Fabricators Inc
Priority date: 1968-04-11
Filing date: 1968-04-11
Publication date: 1970-12-29
Anticipated expiration: 1987-12-29

Description

1970 E. J. von DER HEIDE 3550,206

ROTATIONAL CASTING' APPARATUS 7 Sheets-Sheet 2 Filed April 11, 1968 FIG. 3

1'74 m 1'55 Q Tk l 52 INVEN'TOR. ELMER J von der HE!DE '20 BY/%A W 4aau'aqfw. ewme 67 rmlon ATTORNEYS FIG. 4

1970 E. J. von DER HElDE 30 ROTATIONAL c1xsnne APPAR'IUS 1 Filed April 11. 1968 7 Sheets-Sheet 5 FIG. 5 25 f 24 FIG. 6

INVENTOR. ELMER J.von der HE!DE ATTORNEYS 1970 E. .1Qvou DER HEIDE 3550205 BOTATIONAL CASTING' APPARATUS 7 Sheets-Sheet 4.

' Fild April 11, 1968 INVENTOR. ELMER J.von der HEIDE ATTORNEYS Dec. 29, 1970 E. J. von DER HEIDE 3550205 ROTATIONAL CASTING APPARATUS 7Sheets-Sheet s Filed April ll 1968 HEAT EXCHANGER RES INVENTOR. ELMER J. von der HEIDE BY/Wc/1mty,

peanae 8 Gnaden ATTORNEYS Dec. 29, 1970 E. J.VON DER HEIDE 3550205 ROTATIONAL CASTING APPARA'I'US Filed April 11, 1968 7 Sheets-Sheet 7 FIG. I3

- INVENTOR. ELMER J.von der HEIDE ATTORNEYS United States Patent O 3550206 ROTATIONAL CASTING APPARATUS Eimer J. von der Heide, Hudson, Ohio, assignor to Fabricators, Inc., Ravenna, Ohio, a corporation of Ohio Filed Apr. 11, 1968, Ser. N0. 720,700

1 Int. Cl. B29c 5/04 U.S. C1. 1826 19 Claims ABSTRACT OF THE DISCLOSURE A machine and method for rotationally molding or casting thermoplastic or thermosetting resinous compositions. The machine includes a rotatable turret on which at least one mold-rotating spindle and a pair of motor drives therefor are mounted as a removable unit With the spindle projecting radially outwardly from the turret. The spindle includes means for removably mounting a pair of molds on the outer end thereof for simultaneous rotation about a pair of perpendicular axes at the same or ditferent speeds as determined by the speeds of the motot drives, which are independently variable. The turret has provision for mounting additional spindle and motor drive units thereon with equi-angular spacing of the spindles about the turret to satisfy varying output and/01' process requirements. The machine further includes treating stations through which the molds on the spindle or spindles are successively indexed. The nurnber, type, and location of the treating stations may be varied to suit a number of different molding processes. Inert gas may be fed into each mold cavity, and maintained therein at a predeterrnined positive pressure during any predetermined portion of the mold processing cycle after loading and closing the molds and until they are to be opened for rernoval cf the molded or cast article. Separate ovens With independent temperature controls may be provided at successive stations. Cooling at a cooling station is two stage, first with a wet stearn spray and second with a. liquid coolant spray.

BACKGROUND OF THE INVENTION Various machines and methods have been proposed for forming hollow articles by rotationally casting or molding liquid or particulate (solid) thermoplastic and thermosetting resins, such as vinyl plastisols, particulate polyethylene, polypropylene, and the like, and numerous other classes of resins. Hereinifter, the term molding will be used generically to include casting. The machines developed for such molding operations employ molds cornprising cooperating hollow mold sections which, when closed, define the external surface of one or more articles to be molded A measured amount of resinous molding material in liquid or fusible solid forrn is placed within each mold cavity, and the mold is closed and rotated about a plurality of axes to cause the molding material to be distributed over and coat the interior of the mold cavity. While being rotated for that purpose, the mold is subjected to heat to convert the molding material to a settable fluid condition. In either case, the mold is then cooled and opened for removal of the finished article.

Prior art molding machines have usually been designed to perform a particular molding process or technique, depending upon the particular plastic material and size of the articles to be molded. For example, if the material ice to be molded is a vinyl plastisol, a suitable molding machine would be provided with a conveyor mechanism (such as an indexing table or a loop conveyor) which successively conveys the mold frorn a mold loading station to an oven which heats the vinyl plastisol to a temperature suflicient to gel the plastisol while the mold is rotating and then to a cooling station where the molds are cooled by spraying water thereon t0 solidify the resin, sometimes While continuing the mold rotation. If the plastic is a particulate thermoplastic, the sequence of steps is the Same, but the oven heats the molds to a temperature sufiicient to liquefy the solid plastic.

Such molding operations have been performed heretofore with turret-type machines having a mold carrying spindles radially extending from an indexing table. The mold carrying spindles are indexed through treating stations, such as ovens, cooling chambers, and loading and unloading stations. However, such machines have generally been provided by the manufacturers with the required number of spindles, molds, and processing stations for operation according to a predetermined process and tirne cycle With little flexibility. Thus when a plastic molder had fluctuating or radically differing production requirernents, he often found it uneconornical to operate a large volume rotational casting machine during periods of low production or 10 apply a. low volume machine to a high volume molding Operation, or he often was unable to adjust a machine t0 vary the processing conditions as required by different molding jobs. Since most prior art rotational molding machines cannot readily be modified to accornrnodate such varying production requirements, the plastic molder faced obvious problems in equipping bis plant and using bis equipment efliciently and economi cally.

SUMMARY OF THE INVENTION The machines and processes cf the present invention enable a plastic molder to modify the machine and/er the method or process performed by the machine to suit drastically different plastic molding operations and widely varying production requirements with a high degree of process control.

According to this invention, a molding machine includes a rotating turret having one or more mold carrying spindles and motor drives therefor With eaeh spindle and its motor drives being mounted as a separate unit on an indexing table. Bach spindle has an outer, hollow, rotatable shaft or sleeve which both supports and rotates a mold or group of molds about a first axis and a second shaft within the outer sleeve which drives the mold or molds about a second axis angularly related to the first axis without being required to perforrn a mold supporting function. Separate motor drives are provided for each spindle for independently driving the outer sleeve and immer shaft thereof throughout the molding and cooling operations. The outer sleeve of each spindle is mounted within and supported by bearings which are removably attached to the indexing table, so that the drive means for the outer sleeve and inner shaft of the spindle are wholly independent of the spindle supporting bearings and perform no spindle supporting function.

A molding machine according to this invention may be easily modified by relatively unskilled plant persorinel to perform different molding operations by adding, removing, and/or rearranging the positions of mold carrying spindles, oven, and/er cooling chambers. A plastic meldet may, therefore, initially acquire a machine having, for example, only one mold carrying spindle, one oven, and one cooling chamber for pilot operations, and thereafter add on to his machine as production requirements increase. Moreover, he may rearrange mold carrying spindles, oven, and/er cooling charnbers to perform different plastic molding o erations with the same molding machine and/or obtain the desired production rate with optimum efficiency and quality control.

Thus, the present invention provides a versatile and inexpensive molding machine which Will accomrnodate a Wide variety of production techniques and volurne requirements for plastic molding operations.

The invention further contemplates a molding machine and method which controls degradation of the resin being molded at elevated temperature and also controls shrinkage and distortion of the molded articles during cooling. T this and, the apparatus includes means for feeding inert gases into molds to scavenge air frorn the molds, Which might tend to oxidize and degrade the resin at elevated temperatures, and to rnaintain a predetermined inert gas pressure inside the articles being molded until they have been cooled for removal frorn the molds. The latter function not only serves to control shrinkage and distortion but, also, prevents excessive pressure build-up in the molds during the heating cycle while avoiding the use of conventional mold vents and the problem of preventing a cooling liquid from entering the molds through such vents during the cooling operation. In accordance with this aspect of the invention, there is provided a gas passageway from inside a mold to and along a spindle axis to a point adjacent a spindle support location. One and of the passageway opens inside the mold and inside the article being molded therein and the opposite end of the passageway opens adjacent the spindle support.

With or without employing an inert gas supply and pressure relief system for controlling mold pressures and minimizing shrinkage and distortion, the shrinkage and distortion can also be reduced by controlling the cooling of the molds. It has been customary in the past to cool the molds by spraying them with water 0r other liquid coolant, sometimes after a preliminary quench by blasting the molds with air at room temperature. Such techniques usually cause differential shrinkage and product distortion, since a part only of the mold that is inevitably first contacted by the water spray cools faster than the remaining part of the mold. According to this invention, the molds may be initially cooled by wet steam, uniformly and rapidly, to a point only slightly below the setting temperature of the plastic. Although the wet steam is hotter than the water heretofore sprayed on the molds, the steam movement and scrubbing efi?ect of the wet stearn on the mold surface, together with the greater ease of contacting the entire outer surface of the mold substantially simultaneously With the cooling medium, combine to give a more rapid initial cooling With greater uniformity so as to avoid difierential shrinkage. The prelirninary steam quench may then be followed by a water spray cooling step to reduce the temperature of the molds to a convenient handling temperature and an air blast to dry the molds. The apparatus of the invention permits the use of any other desired sequence of air, steam, and Water cooling steps.

DESCRIPTION OF VIEWS OF THE DRAWINGS FIG. 1 is a partly schematic plan view of a rotational molding machine in accordance with this invention.

FIG. 2 is a cross-sectional view of the machine of FIG. 1, the plane of the section being indicated by the line 22 in FIG. 1.

FIG. 3 is an enlarged, fragmentary, cross-sectional view similar to FIG. 1, showing in somewhat more detail a heating oven employed in the machine and the flow of heating fluid relative to mo ds whin the o en.

FIG. 4 is a fragmentary plan view of the oven shown in FIG. 3.

FIG. 5 is an enlarged plan view of the drive means for each mold carrying spindle illustrated in FIG. l.

FIG. 6 is a plan view of an indexing table upon which different numbers of mold carrying spindles may be mounted in accordance With this invention.

FIG. 7 is an enlarged, fragmentary, cross-sectional view of the san1e machine, the plane of the section being indicated by the line 77 in FIG. 5.

FIG. 7A is a fragmentary transverse section of the machine taken as indicated by the line 7A7A in FIG. 7 and showing a control switch assernbly for the power circuit to a spindle driving motor.

FIG. 8 is an enlarged cross-sectional view of the mold carrying end of the spindle illustrated in FIG. 7, showing that portion in greater detail.

FIG. 9 is a schematic plan view of a fluid supply system for the mold cavities.

FIG. 10 is an enlarged fragmentary, elevational view of the same machine, the view being taken as indicated by the line 1010 in FIG. 7.

FIG. 11 is a fragmentary cross-sectional view of the same machine, the plane cf the section being indicated by the line 11-11 in FIG. 10.

FIG. 12 is a partly schematic plan view of a rotational casting machine having three mold carrying spindles and treating stations according to a further aspect of this invention.

FIG. 13 is a partly schematic plan view of another rotational casting machine having four mold carrying spindles and treating stations according to a still further aspect of this invention.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to FIGS. 1 and 2 a rotational casting machine 20 according to one aspect of the present invention includes an intermittently driven turntable 21 upon which four radially projecting, mold carrying spindles 22 are removably mounted. Bach spindle 22 carries a mold or group of molds at the outer and thereof. In the drawings, the mold or mold group is generally indicated by hantom outline 23, which outline also delineates the envelope traced by the mold 01' group cf molds during their rotation about two axes. Such biaxial rotation, as will be explained in greater detail, is provided by independent drive means for each axis of each spindle 22. For this purpose, each spindle 22 is provided with first and

second drive motors

24 and 25.

The machine illustrated in FIGS. 1 and 2 is provided With four treating or process stations for performing a two-stage heating operation and a single-stage cooling operation. T0 this end, there is provided a first oven 26, a second oven 27, and a cooling chamber 28 at successive stations, the fourth station being employed to ernpty and reload the molds. As further explained below, the two

ovens

26 and 27 may be connected by a shroud to conserve heat and avoid chilling the molds while being indexed from the first oven to the second oven.

The character and arrangement of the four stations illustrated in FIGS. 1 and 2 a1e suitable, for example, for the rotational molding of vinyl plastisols. When using such a molding composition, the sequence of operations would involve loading the molds at a first station (the lowermost station illustrated in FIG. 1, heating the rotating molds at a second station in the oven 26 to gel the material being molded, continued heating of the molds at a third station in the oven 27 to complete the molding of the resin (with or without further raising its temperature) while continuing to rotate the molds, cooling the molds at a fourth station in the cooling chamber 28 to solidify and cool the molded articles while still continuing the mold rotation, and then unloading and reloading the molds at the first station.

The machine shown in FIGS. 1 and 2 may also bo employed to mold any of a variety of liquid, thermosetting resin com-positions. for exarnple, various phenolic or melamine resins, dispersions of acrylonitrile-butadienestyrene resins, and the like may be cured during the molding operation to a final, thermoset condition. Sirnilarly, meltable solid or liquid resin mixtures, or mixtures of resins and cross-linking agents, may be heated during the molding Operation to efl'ect a cross-linking of the resin molecules and produce thermoset, molded, plastic end roducts. In such cases, the heating of the rotating molds successively in the

ovens

26 and 27 at the second and third stations may be regulated as required by the particular resin or resin mixtures chargcd to the molds at the first station The molded and solidified articlcs would then be cooled by cooling the molds in the cooling chamber 28 at the fourth station and would be unloaded from the molds at the unloading and reloading station. Obviously, if desired, a single oven 26 at the second station could be followed by two cooling chambers or by a single elongated cooling chamber at the third and fourth stations.

Most of the above processes may also be carried out in the Single oven machines of FIGS. 12 and 13, the only procedural change required in some cases being that 01 repeatedly raising and lowering the oven temperature for holding a particular molding cornposition at a plurality f curing temperatures for predetermined time periods.

As may be seen in FIG. 13, the same four-spindle molding machine may readily be modified to employ a single oven 26 at one station, a cooling charnber 28 at the next station, and separate unloading and loading operations at the other two stations. This is advantageous in molding operations that involve mold loading and unloading steps that are slow and cannot both be perforrned at a .single station within the predetermined tin1e period allocated for each dwell 0f the mold assemblies at the successive stations. This may occur, for exarnple, when each mold involves a number of cavities, each containing complex arrangements of inserts.

Alternatively, as may be seen in FIG. 12, a threespindle molding machine may be assernbled on the same indexing table 21 and employ the Single oven 26 and the cooling chamber 28 by placing the single oven and cooling chamber one-hundred twenty degrees apart. As still further alternatives, only two spindles or only one spindle may be used on the indexing table With the station arrangement of FIG. l, FIG 12, 01' FIG. 13.

A plastic molder may begin pilot plant operations using a Single mold carrying spindle 22 and associated

drive motors

24 and 25 and mounting them on an indexing table 21 for movement through the stations of any FIGS. 1, 12, or 13. This may be done with a modest investment in equipment. As the table 21 is indexed, the mold assembly on the single spindle 22 will successively move frorn station to station according to the particular cycle determined for molding a particular article while using the particular station arrangement selected.

T0 increase production as business may require, the plastic molder may first acquire only one or more additional spindles 22 and add thernto the original table 21 while using the same station arrangement as before o1 a modified station arrangernent. If he started with the three-station arrangement of FIG. 12, for example and requires four spindles 22 to meet production requirements, he may simply rearrange the oven 26 and cooling charmber 28 as shown in FIG 13. Alternatively, by also adding a second oven unit 27, he may convert bis machine to one having the dual oven arrangernent of FIG. 1. Obviously, by reversing such evolution of the machine, the high capacity machine of FIG. 1 may be turned into an efficient low capacity machine.

It should be appreciated from the foregoing that this invention permits a plastic molder to modify bis machine according to production requirements, both as regards production volume and processing operations, to perform a wide variety of difi?erent plastic molding operations with the basic machine elements 0f this invention.

T0 facilitate the kinds 0f conversions just described, the turntable 21 may beprovided with a plurality of sets of mounting

holes

30a,

30b 30c

30a, 30e, and 30f arranged as shown in FIG. 6 so the turntable 21 may carry from one to four spindles 22. One set of

holes 30a

30b,

30c

30d, 30e, or 30 may be employed to mount a single spindle; any two opposite sets of

holes

30a and 30d or 30b and 30 may be employed to mount two spindles; the three sets 0f

holes

30a, 30c and 30e may be employed to mount three spindles; and the four sets of

holes

30a, 30b, 30d, and 30f may be employed to mount four spindles.

Referring now to the details of the spindle and mold assemblies and drives therefor as shown in FIGS. 5 and 7-11, the spindle 22 is a unit which include a hollow outer sleeve 40 and an inner shaft 41. The outer sleeve 40 extends through a supporting bearing box or spindle housing 42 and has a substantial portion of its length comtained within the box and supported by

bearings

43 and 44 at each end thereof. One end of the sleeve 40 extends radially inwardly bcyond the bearing 44 and is provided with a spur gear 45 which is keyed to the sleeve 40. The spur gear 45 is driven by a spur gear 46 which is keyed to the output shaft of the drive motor 25. The drive motor 25 is mounted on top of the box 42 to conserve space.

The inner shaft 41 is mounted within the hollow sleeve 40 for independent axial rotation relative thereto by a bearing 47 at the radially inward end thereof. The radially outward end of the shaft 41 is keyed to the hub of a bevel gear 48. As may be seen most clearly in FIG. 8, the bevel gear 48 and its hub have a bore 49 which receives the radially outer end of the shaft 41 and is provided with a key 50 which cooperates with a slot 51 in the shaft 41. The bevel gear 48 is rotatably mounted within a gear box 01' housing 52 by

bearings

53 and 54. The housing 52 is removably secured to a flanged end portion 55 of the outer sleeve 40 by bolts 56. The housing 52 is thereby rotated With the outer sleeve 40, and the bevel gear 48 is driven by the inner shaft 41 relative to the outer sleeve 40 and the housing 52.

The inner shaft 41 and its bevel gear 48 are driven by the motor 24 through a spur gear 57 connected to the drive shaft of the motor 24 and a cooperating spur gear 58 which is keyed to a projecting end of the shaft 41.

The housing 52 is provided with axially aligned, transverse bores 59 and 60, which are respectively provided with an inner housing mernber 61 and a bearing 62. Another bearing 63 is mounted within the inner housing rne'rnber 61. A cross shaft 64 is rotatably mounted with respect to the housing 52 by the

bearings

62 and 63 and projects in both directions beyond the bores 59 and for the attachment of mold assernblies as described below. The housing 52 is closed at its outer end by a plate 65, at one side by a cap 66, and at its diametrically opposite side by a cap 67. As shown (FIG. 8) the shaft 64 projects in opposite directions through the

caps

66 and 67 and is journaled therein.

A bevel gear 68 is keyed to the shaft 64 within the housing 52 and is driven by the bevel gear 48 so that the shaft 64 is driven about its axis relative to the housing 52 by the drive motor 24.

The

bearings

62, 63, 53, and 54 and the bevel gears 48 and 68 are enclosed and sealed in a chamber defined by the housing 52 and housing member 61, by oil seals 7 and 71 on the shaft 64, and by an oil seal 72 between the bevel gear 48 and the flange 55. That chamber forms a lubricant reservoir so that those bearings and bevel gears are immersed in lubricant, which may be adrnitted through a plug 73 in the end plate 65.

Each end of the transverse shaft 64 is provided With a mold mounting plate 74. A suitable mold or mold assembly (FIG. 7) is mounted on each of the plates 74 (only one such assernbly being shown). The mold assembly 75 may include a plurality of subassemblies 76 defining separate mold cavities, each cavity being formed by two

separable mold section

77 and 78. Bach mold section 77 is mounted on a frarne 79, and each mold section 78 is mounted on a fra'me 80. The frame 79 and its mold sections 77 may be removed from the frame 80 and its mold sections 78 by uncoupling suitable quick-disconnect clarnps (not shown). The frame 80 is attached to its mold mounting plate 74 by a plurality of bolts 81.

Bach spindle 22 and its mold assembly 75 is provided with means for feeding inert gas into each mold cavity to purge air therefrom which might tend to oxidize and degrade the resin being cast. T this end, there is provided a source of pressurized inert gas, such as the reservoir 82 (FIG. 9). The reservoir 82 delivers its inert gas through a constant pressure reguhting valve 83, a heat exchanger 84, and a supply line 85 to a distributor manifold 86 (FIG. 7) which is connected to the supply line 85 by a rotatable coupling 87. The manifold 86 is fixed to the table 21 and has a plurality of branch conduits 88 which are respectively connected to a corresponding lurality of on-off valves 89. The valves 89 are successively turned on lay a cam operated switch 122 which engages a cam 123 (FIG. 7) as the spindle 22 is indexed from the mold loading position. One of the valves 89 is provided for each spindle 22, and eaeh valve 89 has an outlet conduit 90 connected to its spindle 22 by a rotatable coupling 91.

Bach rotatable coupling 91 is in fluid communication With the radially inner end 0f a delivery tube 92 which extends through an axial bore 93 in the shaft 41. The tube 92 is suitably journaled in the bore 93 for independent rotation relative to the shaft 41. The outer end of the tube 92 is threadedly engaged with and, therefore, driven by the housing member 61 that rotates with the outer sleeve 40. The tube 92 communicates With a chamber 94 Within the housing mernber 61 that surrounds the transverse shaft 64 therein, opposite ends of the charnber 94 being closed by seals 95 and 96 acting between the shaft 64 and the mernber housing member 61. The chamber 94 is, in turn, in fluid communication with a transverse bore 97 and an axial bore 98 in the shaft 64.

The axial bore 98 is coupled at 99 (FIG. 7) to a passageway 100 in the frame 80, and the passageway 100, in turn, communicates with the cavity of each mold subassembly 76 through a tube 101 that projects well into the mold cavity to near the center thereof so that its open end will not be covered or plugged with resin during the molding operation.

After a measured amount of resin material to be molded is deposited in each mold cavity at the mold loading station and those molds are closed, the valve 89 on the associated spindle 22 is opened upon indexing of the table 21 and actuation of the switch 122 thereon to adrnit presurized inert gas to the closed mold. The inert gas pressure causes leakage of the molds at their parting planes and scavenges air from the molds which would otherwise tend to oxidize and degrade certain molding resins when heated. When liquefied resin has coated the interior of the molds as a result of their rotation in the oven 26, the resin seals the molds against further leakage at their parting planes, and the inert gas pressure established by the regulating valve 83 is maintained inside the articles being molded during the balance of the molding and mold cooling operations.

The gas supply t0 the molds on a given spindle is cut off as the molds are moved from the cooling chamber toward the unloading station by further indexing of the table 21. This may be done by means of another appropriately located cam (not shown), like the cam 123, for again actuating the switch 122. For this purpose, the switch 122 may be a step switch or the like for alternately closing, opening, and closing a circuit 011 succes sive operations.

By setting the valve 83 to establish and maintain a predetermined positive gas pressure in the molds, shrinkage and distortion of the molded articles during the cooling step (when a partial vacuum inside the hollow articles would otherwise be created) can be materially reduced and more nearly pe1fect products can be made with greater consisteney and less scrap loss. Generally, that predetermined gas pressure should be from around 2 p.s.i. gauge up to as high as 10 p.s.i. or so as limited primarily by the strength of the mold assembly.

If it is not desirable or necessary to admit gas to the molds, the gas supply and regulating systern 01 FIG. 9 from the reservoir 82 to the rotatable joints 91 011 each spindle tube 92 may simply be omitted o1 disconnected from the spindle tubes. Thus, the several mold cavities are still vented to the atmosphere at the center of the turret so that moisture from the cooling chamber 28 will never be drawn into the mold cavities during the cooling Operation.

After the molds are loaded and elosed at the loading Station, the

motors

24 and 25 on the associated spindle 22 are energized to rotate the mold assemblies about two axes. Rotation about one such axis is caused by the motor 24 which drives the inner shaft 41 about its axis. Such rotation of the shaft 41 drives the bevel gears 48 and 68, and, therefore, the shaft 64 about its axis. Rotation of the shaft 64 about its axis causes the mold assembly 75 to be rotated about the -axis 0f the shaft 64 in the direction of the arrow (FIG. 9).

As the mold assembly 75 is rotated about the axis of the shaft 64 in the dixection of the arrow 110 by the motor 24, the motor 25 rotates the outer sleeve 40 about its axis. Rotation of the sleeve 40 about its axis causes the shaft 64 to be rotated about the axis of the sleeve 40. The mold assernbly 75 is thereby also rotated about the axis of the sleeve 40 in the direction of the arrow 111 (FIG. 9).

The relative speeds of the

motors

24 and 25 may be independently varied to suit a particular molding operation. These relative speeds are preselected and are primarily dependent upon the shape of the article to be molded. This mold rotation, like the flow of inert gas (when used), is started and stopped automatically by suitable cam and switch controls (not shown) actuated by indexing of the table 21. Such rotation is continued during all of the treating operations performed on the molds and during the indexing operations between treating stations so that once the

motors

24 and 25 are energized they are not deenergized until the mold assembly 75 returns to the mold unloading station.

The loaded and rotating mold assemblies 75 are in dexed to the oven 26 (FIGS. 1, 2, 12, and 13) by driving the table 21 in a clockwise direction. T he drive means for the table 21 comprises a drive motor 112 (FIGS. 2 and 7) which is mounted on a pedestal base 113. A pinion gear 114 on a power input shaft 115 of the drive motor 112 drives a ring gear 116 in a clockwise direction with respect to the base 113. The inner surface of the ring gear 116 cornrpises a bearing race which cooperates with ball bearings 117 and a stationary bearing race 118 which is fixed to the pedestal base 113. The table 21 is connected t0 the ring gear 117 by bolts 119 so that the table is driven in a clockwise direction by the ring gear 116. The motor 112 is started and stopped according to any preselected time cycle of operation by any conventional tirner control (not shown).

Upon rotation of the table 21, the mold assemblies 75 on the outer end of a spindle 22 enter the oven 26. T0 permit such entry into the oven 26, a door 120 is raised by a suitable door opening mechanisrn (not shown). The inner face or Wall of the oven 26 is provided with a horizontal slot 121 to provide clearance for the spindle 22, the slot 121 preferably being largely closed by a depending curtain 122 that is simply deflected upwardly by the spindle as shown in FIG. 3. When the mold carrying spindle 22 positions the mold assembly 75 within the oven 26, the motor 112 is stopped by a suitable control means (not shown) for a predetermined heating period.

The oven 26 provides a heating chamber 124 which is defined by a top Wall 125, an inner sidewall 126, a heat directing bafile assembly 127, a darnper 128, the entrance door 120, and an exit door 123. The oven 26 further includes a fuel delivery chamber 129 which is defined by the baffle assembly 127, the damper 128, the top wall 125, sidewalls 130, and a rear Wall 131. A burner nozzle 132 extends through the top wall 125 into the fuel delivery chamber 129 and may be a natural gas burner which heats air in the charnber 129. The heated air is delivered by a centrifugal fan or blower 133 into the bafile assembly 127 which forms a distribution charmber 134. The baflle assembly 127 has a multiplicity of outlet openings 135 which are preferably adjustable in size and are distributed over a vertical Wall portion 136, an oblique Wall section 137, and a horizontal wall portion 138 of the assernbly 127, so that heated air will be distributed around the rotating molds within the heating charnber 124 for uniforrnly heating the molds and the plastic material contained therein. As indicated by ararrows in FIG. 2, the heated air is directed so as to flow over all surfaces 01': the rotating molds by the distribution of the baflle openings, including the opposed surfaces of the two mold assemblies which are swept by the hot air directed axially toward the mold supporting end of the spindle 22 between the mold assemblies. The damper 128 controls the total volume of air which is admitted to the delivery chamber 129, and its distribution can be regulated by adjusting the sizes of the bafile openings.

The Wall 131 of the delivery chamber 129 is provided With an eleetrically controlled and powered, quick Opening, panic door 139, which may be quickly opened as a safety precaution if a mold carrying spindle 22 cannot be indexed from the heating chamber 124 at the proper tirne. By opening the panic door 139 and turning 011 the fuel nozzle 132, cool air Will be drawn through the opening provided by the door 139 and directed around the rotating molds within the chamber 124. At the same time that the panic door 139 is opened by an appropriately located panic control button (not shown) the

main oven doors

120 and 123 are also opened. This may be eilected automatically by any suitable interlock system (not shown) for opening the rnain oven doors in response to operator actuation of the panic button, as well as by indexing of the table 21. Thus, whenever indexing of the table 21 is delayed by mold unloading or loading problems, for example, the machine operator, by actuating the panic button, may rapidly cool the oven 26 and thereby avoid charring the resin in the molds within the oven and the mold cleaning problems that would result.

When the predetermined treating time in the oven 26 has elapsed, the motor 112 is again energized to open the oven exit door 123 and index the rotating molds from the oven 26 to the oven 27 (FIG. l) or to the cooling chamber 28 (FIGS. 12 and 13) if the process does not require a second heating operation. The oven 27 may be joined to the oven 26 by an enclosure 140 to minimize the loss of heat and chilling of the molds during their transfer from the first oven to the second oven. The oven 27 in FIG. 1 and the ovens 26 of FIGS. 12 and 13 may be identical With the oven 26 of FIG. 1 and, therefore, will not be shown or described in detail.

The

doors

120 and 123 for the oven or ovens are neoessarily simultaneously actuated if the machine employs as many spindles as processing stations (FIGS. 1, 12, 13), and this is most suitably done in response to indexing of the table 121 by the controls mentioned above. Otherwise a separate control for each door is required.

A temperature dilferential may be maintained between the

ovens

26 and 27, by appropriate setting of conventional, separate, burner and damper controls (not shown) for the two ovens, as process requirernents may dictate.

Commonly, a higher temperature Will be maintained in the first oven 26, well above the temperatures reached by the molds and their contents during the dwell of the molds in that oven. In that Gase, the temperature in the seeond oven may be held at a level to maintain or only slightly raise the temperatures of the molds and their contents above the temperatures created in the first oven. On the other band, when the resin being molded is of a thermosetting type, for example, a first stage reaction temperature may be developed in the first oven maintained at one oven temperature, and a second stage reaction temperature may be developed in the second oven maintained at a second, higher, oven temperature. Various other heating cycle requirernents are satisfied more readily and with better control by employing the dual oven arrangement of FIG. 1 than would be possible With a single, elongated oven charnber enclosing a plurality of heating stations.

After completion of the heating operation in the second oven 27 (FIG. l), or after cornpletion of a singlestage heating operation in a single oven 26 (FIGS. 12 and 13), the spindle 22 and its mold assemblies are indexed to the cooling chamber 28 in all forms of the machine. The cooling chamber 28 (FIGS. 1 and 2) is defined by a top Wall 150, an outer sidewall 151, and an inner sidewall 152. The inner sidewall 152 is provided with a horizontal opening 153 (FIG. 2) to permit the spindle 22 to move the mold assembly 75 into position within the cooling chamber. The entrance and exit (radial) sides of the cooling chamber may be open to perrnit the entrance and exit of the mold assembly 75 or may be provided with automatically controlled doors to prevent outward splashing of a cooling liquid or an objectionable flow of cooling steam into a room in which the machine is located.

Within the cooling charnber, the mold assernblies may -be first cooled with wet stearn at about 5 to 50 pounds p.s.i. gauge and at a temperature of about 225 F. or somewhat higher, depending upon the solidification temperature of the particular resin if the resin is therrno plastic. T0 this end, there is provided a plurality of steam nozzles 154 which are directed toward the rotating mold assembly 75. A fan 155 is provided to eflect rapid air circulation over all surfaces of each mold 76, either as a. separate cooling step before cooling with stearn or water, or as a means for accelerating drying of the molds after a water cooling step. The steam temperature is selected to provide rapid cooling to a point only slightly below the solidification temperature of a thermoplastic resin (generally around 300 F.) or to a comparable tempera ture if a thermosetting resin is being molded. After the mold temperature has been initially lowered by a stearn spray cooling water is sprayed through the same nozzles 154, or through separate nozzles if desired, to further cool the mold assembly to a temperature which Will permit handling at the mold unloading and loading station. After the mold assemblies have been cooled in the cool 1ng charnber 28, the table 21 is again indexed to rnove the cooled molds to the next station for unloading and, optionally, also for reloading. T0 facilitate unloading of the molds, it is desirable to stop the spindle rotation by the tirne the molds arrive at the unloading station and to do this so that the molds have the desired orientation -for convenient unloading and reloading. T0 this end, a magnetically permeable (iron) disc-shaped vane (FIGS. 7 and 7A) is concentrically mounted on the outer sleeve 40 of each spindle 22 for turning within a slot 161 of a vane switch 162 mounted on the outer end of the spindle housing 42. The vane 160 is notched at 163 to provide an interruption of a magnetic flux path across the switch slot 161 through the vane 160 when the molds are in their desired loading and unloading orientation. In addition, for each spindle, two additional cams (not shown), like the cam 123, and another step switch (not shown), like the switch 122, are respectively mounted on tl21e table 21 and pedestal 113 at suitable locations for coaction to close and open the power circuits for the

drive motors

24 and 25 associated with that spindle. This step switch and the vane switch 160 are connected in parallel in the motor ower eircuits so that both must open to stop the motors. Thus, after the step switch in the motor power circuits has been opened, the switch 162 is also opened the next time the notch 163 in the disc 160 arrives in the position shown in FIG. 7A so as to deenergize the drive motors for that spindle and stop the spindle rotation with the desired orientation of the molds. By using

motors

24 and 25 having conventional dynamic breaking that stopping is substantially instantaneous.

As Will be appreciated from the foregoing, this invention provides elfective apparatus for carrying out a number of advantageous process steps which result in more efficient production of improved molded articles. One of these process steps in the feeding of inert gas to the molds, as described above, to minimize oxidation and degradation of the resin and to reduce shrinkage and permanent distortion of the molded articles by supporting them internally during cooling.

Another of these process steps is the above-described two stage heating of the molds and their contained resin, one stage at one of the process stations and the second stage at the succeeding process station. Since each dwell of the rotating table is necessarily of the same duration in a multiple spindle machine of the character shown in FIG. 1, such two stage heating at two stations makes more etlicient cycling of the machine possible since most molding operations require a longer heating time than cooling time. The output of a machine having a given number of spindles may be increased as much as 100% by such use f two ovens and two heating stations, while providing greater processing flexibility as pointed out above.

Still another of these process steps is the two-stage cooling of the mold and molded article therein, first with a relatively high temperature fluid, such as wet steam, to quickly and uniformly lower the temperature of the molded article only slightly below the temperature at which a thermoplastic resin is completely solidified, and then With a liquid coolant, such as water, to complete the cooling operation. Despite the relatively high temperature of the wet steam, the water droplets therein flash into vapor when they contact the hotter molds, thus rapidly extracting heat while obtaining the greater surface scrubhing action of the stearn spray and more rapid and complete envelopment of the molds by the cooling fluid. The result is rapid cooling at a more uniform rate over the entire surface of each mold and less product distortion from difierential cooling. Though such two-stage cooling is relatively rapid, it is not quite as rapid as when the molds are initially contacted with a water spray and, therefore, reduces the cooling shock while the procluct is under going solidification.

Shock during the initial cooling may be still further reduced merely by delaying the steam cooling step and running the fan 155 (FIG. 2) to eifect initial cooling in a current or room temperature air, then stopping the fan during the successive steam and water cooling steps, and finally restarting the fan to accelerate drying of the wet molds before they are indexed to the next station for unloading and reloading. As previously mentioned, any number and sequence of the air, steam, and water cooling steps described herein may be used to adapt the cooling operation to the particular job. Also, of course, other cooling media may be substituted for steam or for water.

What is claimed is:

1. Apparatus for rotationally casting plastic articles comprising at least one mold carrying spindle assembly, indexing means for rnoving said spindle assembly along a path from a mold loading station to at least one heating station and then to at least one cooling station and for stopping said spindle for a predetermined period at each station, said indexing means having a table on which said spindle assembly is mounted, fastening means fixing said spindle assembly to said table, said fastening means being releasable t0 permit removal of said spindle assembly from said table as a unit, said spindle assembly comprising (a) a hollow outer sleeve mounted for axial rotation in bearing means and being substantially entirely supported by said bearing means, said bearing means being removably mounted on said table, (b) a shaft mounted for coaxial rotation Within said outer sleeve, (c) a mold snpport extending transversely from one end of said spindle assembly, (d) driving connections between (l) said sleeve and said shaft and (2) said mold snpport for rotating said mold snpport about angularly related axes upon rotation of the sleeve and shaft about their common axes, and (e) separate drive means for independently rotating said sleeve and shaft.

2. Apparatus for rotationally casting plastic articles as set forth in claim 1 wherein said mold snpport is supported by said outer sleeve.

3. Apparatus for rotationally casting plastic articles as set forth in claim 1, wherein said spindle assembly includes passage means from the interior of each mold in said mold assembly to a vent spaced outside of said cooling station when the mold assembly is at said cooling station.

4. Apparatus for rotationally casting plastic articles as set forth in claim 3, wherein said spindle assembly is provided with means for delivering gas to the interior of each mold in said mold assembly through said passage.

5. Apparatus for rotationally casting plastic articles as set forth in claim 4, wherein said passage means is provided with valve means which is responsive to move ment of a spindle assembly from said mold loading station to a heating station for admitting said gas through said passage means when said movement obtains.

6. Apparatus for rotationally casting plastic articles according to claim 1, wherein said heating station comprises an oven, said oven being located in the path of said spindle assembly so that said mold assembly is surrounded by said oven when the spindle assembly is stopped at the heating station, said oven having first and second door means which are respectively opened to permit the mold assembly to enter the oven and to leave the oven, means defining a heating chamber and a fuel delivery chamber in said oven, said heating chamber and said fuel delivery chamber being separated by a baflle assembly having a multiplicity of outlet openings which direct heat from the fuel delivery chamber in two directions toward said mold assembly and about a substantial portion of the envelope traced by the mold assembly as it is rotated.

7. Apparatus for rotationally casting plastic articles according to claim 6, wherein said heating chamber is provided with door means which is openable to the atmosphere to draw cool air into the oven if a mold carrying spindle cannot be indexed from the oven.

8. Apparatus for rotationally casting plastic articles according to claim 6, wherein said mold snpport comprises at least two mold groups, each of said groups being mounted on a mold group carrying arm which extends radially from said shaft, and wherein said two directions are (1) axial with respect to said shaft and (2) transverse With respect to said shaft.

9. Apparatus for rotationally casting plastic articles as set forth in clairn 1, wherein said cooling station comprises a cooling chamber having means to deliver cooling stearn to the mold assembly to rapidly cool the mold assembly and to deliver water to the mold assembly to further cool said assembly.

10. Apparatus for rotationally casting plastic articles comprising at least one mold carrying spindle assembly, indexing means for moving said spindle assembly along a path from a mold loading station to a heating station and then to a cooling station and for stopping said spindle assembly for a predetermined period at each station, said indexing means having a table on which said spindle assembly is removably mounted as a unit, said spindle assembly comprising a hollow outer sleeve rotatably mounted in and extending through a mounting box having bearing means therein rotatably mounting said sleeve, said sleeve being substantially entirely supported by said bearing means, said mounting box being mounted on said table, fastening means fixing said box to said table, said fastening means being releasable to permit removal of said box and, therefore, said spindle assembly from said table as a unit, a shaft mounted for coaxial rotation within said sleeve, a mold support extending transversely from one end of said arm, gear means between said shaft and said mold support to rotate said mold support about a first axis normal to the axis of said shaft andthe axis of said sleeve, linkage means between said sleeve and said mold asernbly to support and rotate said mold support about a second axis angularly related to said first axis, housing means enclosing said gear means, and separate drive means for independently rotating said sleeve and shaft.

11. Apparatus for rotationally casting plastic articles according to claim 10, wherein said spindle assembly includes assage means frorn the interior of each mold in said mold support to a vent spaced outside of said cooling station when the mold support is at said cooling station.

12. Apparatus for rotationally casting plastic articles according to claim 11, wherein said passageway extends axially through said shaft and is provided With means for delivering gas to the interior of each mold in said mold support through said passage.

13. In apparatus for rotationally casting plastic articles comprising at least one mold carrying spindle assembly mounted on an indexing means which moves said spindle assembly along a path from a mold loading station to a heating station and then to a cooling station and which stops said spindle assembly for a predetermined period at each station, the improvement wherein said heating station crnprises an oven having a fuel delivery charnber, a heating chamber, and a distribution chamber separating said fuel delivery charnber and said heating charnber, means to deliver heated fuel to said fuel delivery chamber, blower means t0 force heated atmosphere from said fuel delivery chamber to said distribution chamber, said distribution chamber extending vertically between said fuel delivery chamber and said heating chamber and then horizontally along the bottorn of said heating charnber and having outlet openings along its vertical and horizontal extent for directing heated atmosphere in two directions toward the center of said heating chamber and around substantial portions of molds positioned in said heating chamber.

14. In apparatus for rotationally casting plastic articles comprising at least one mold carrying spindle assembly, indexing means for moving said spindle assembly along a path frorh a mold loading station to a heating station and then to a cooling station and for stopping said spindle assembly for a predeterrnined period at each station, the improvernent wherein said cooling station comprise a cooling chamber having inwardly directed steam nozzles therein for delivering wet cooling stearn to mold positioned within said cooling charnber and for delivering water to said molds after delivery of said wet steam.

15. In apparatus for rotationally casting plastic articles comprising a mold carrying spindle assembly for mounting a mold or group of molds at one end of the spindle assembly and for rotating the mold or molds about two angularly related axes, said spindle assembly comprising an outer sleeve, an immer shaft rotatably mounted within said sleeve and drive means for rotating the shaft and sleeve about their axes, the improvement which comprises a housing fixed to the end of said sleeve, a mold carrying shaft extending transversely with respect to the axis of said sleeve, through said housing, and rotatably mounted for axial rotatim by bearing means in said housing, gear means between said inner shaft and said mold carrying shaft and completely enclosed within said housing for rotating said mold carrying shaft about its axis upon rotation of said inner shaft.

16. Apparatus for rotationally casting plastic articles comprising at least one mold carrying spindle assembly, indexing means for moving said spindle assembly along a path from a mold loading station to at least one heating station and then to at least one cooling station and for stoppi-ngsaid spindle for a predeterrnined period at each station, said indexing means having a table on which said spindle assembly is removably mounted as a unit, said spindle assembly comprising (a) a hollow outer sleeve mounted for axial rotation in bearing means and being substantially entirely supported by said bearing means, said bearing means being mounted on said table, fastening means fixing said bearing means to said table, said fastening means being releasable to perrnit rernoval of said bearing means and, therefore, said spindle assembly frorn said table as a unit, (b) a shaft mounted for coaxial rotation Within said outer sleeve, (c) a mold support extending transversely from one end of said spindle assembly, (d) driving connections between (l) said sleeve and said shaft and (2) said mold support for rotating said mold support about angularly related axes upon rotation of the sleeve and shaft about their cornmon axes, and (e) separate drive means for independently rotating said sleeve and shaft, means for arresting the rotation of said mold support at a mold unloading station so that molds carried by said mold suport are arrested at a predetermined orientation for unloading and reloading.

17. Apparatus for rotationally casting plastic articles as set forth in claim 16, wherein said mold arresting means comprises a disc-shaped vane concentrically mounted on said hollow outer sleeve, means defining an opening through said vane, switch means responsive to the position of said opening when said mold is in said predetermined orientation to perrnit said separate drive means to be deenergized, and means to de-energize said separate drive means only when said orientation obtains and said switch means is operated.

18. Apparatus for rotationally casting plastic articles as set forth in clairn 1, wherein said separate drive means includes independent drive means for rotating said mold support about each of said angularly related axes.

19. Apparatus for rotationally casting plastic articles comprising at least one mold carrying spindle assembly, indexing means for moving said spindle assembly along a path from a mold loading station to at least one cooling station and for stopping said spindle for a predetermined peirod of time at each station, said indexing means having a table on which said spindle assembly is removably mounted as a unit, said spindle assembly comprising (a) a hollow outer sleeve mounted for axial rotation in bearing means and being substantially entirely supported by said bearing means, said bearing means being removably mounted on said table, (b) a shaft mounted for coaxial rotation within said outer sleeve, (c) a mold support extending transversely from one end of said spindle assembly, (d) driving connections between (l) said sleeve and said shaft and (2) said mold support for rotating said mold support about angularly related axes upon rotation of the sleeve and shaft about th'eir cornrnon axes, and (e) separate drive means for independently rotating said sleeve and shaft, means for arresting the rotation of said mold support at a mold unloading station so that molds carried by said mold support are arrested at a predeterrnined orientation for unloading and reloading, said mold arresting means comprising a disc-shaped vein concentrically mounted on said hollow outer sleeve, means defining an opening to said vein, switch means responsive to the position of said opening when said mold is in said predetermined orientation to permit said separate drive means to be de-energized, and means to de-energize said separate drive means on1y when said orientation obtains and said switch means is operated.

References Cited UNITED STATES PATENTS Blue 1826 Chiya 1826 Eggert et a1. 1826 Schott et a1. -1 1826 Barnett 1826X WILLIAM S. LAWSON, Primary Examiner