US3233287A - Apparatus for casting hollow bodies - Google Patents

Description

Feb. 8, 1966 E. B. BLUE ETAL 3,233,287

APPARATUS FOR CASTING HOLLOW BODIES Filed March 9, 1962 4 Sheets-Sheet 1 Feb. 8, 1966 E. B. BLUE ETAL 3,233,287

APPARATUS FOR CASTING HOLLOW BODIES Filed March 9, 1962 4 Sheets-Sheet 2 INVENTORS L OWAAD d 494 (/5 BY @664440 A flay/42745 wzwuua m u. Un tin @QK x i m N 2 -imlm IIK J Jm wn uq uwuw h n lllllll 1 fit L -mm f www Pp mw v N y: H

Feb. 8, 1966 E. B. BLUE ETAL 3,233,287

APPARATUS FOR CASTING HOLLOW BODIES Filed March 9, 1962 4 Sheets-Sheet 5 g T WMMMWW I I Feb. 8, 1966 E. B. BLUE ETAL 3,233,287

APPARATUS FOR CASTING HOLLOW BODIES Filed March 9, 1962 4 Sheets-Sheet 4 j w m 4% m w m M /2 1 /09Z /09a ATTORNEY United States Patent 3,233,287 APPARATUS FOR CASTING HOLLGW EQDEES Edward B. Blue, 9 Kimberly Place, New Canaan, Conn., and Richard A. Nonweiler, ()shhosh, Wis, said N onweiler assignor to said Biue Filed Mar. 9, 1962, Ser. No. 178,749 2 Claims. (Ci. 1826) This invention relates to apparatus for casting of articles in hollow molds, and is a continuation-in-part of copending application S.N. 72,907, filed December 1, 1960 and now abandoned.

While this invention is not limited to any particular casting composition, at the present time polyvinyl chloride compositions are usually employed and are mentioned herein as a specific application of the invention, but other casting compositions including polyethylene powders are also being used.

The terms casting and molding are used herein interchangeably.

Polyvinyl chloride compositions usually include stabilizers such, for example, as barium salts and cadmium salts. Because of the presence of stabilizers the vinyl plastisol remains stable up to 350 F., whereas, without a stabilizer the polyvinyl would degrade at temperatures between 300350 F.

In the casting of articles in hollow molds the liquid casting composition is supplied into molds of the desired shape in an amount which, when distributed over the entire interior surface of a mold and transformed from liquid to solid phase will give a product of the desired thickness. If the molds are not heated uniformly the thickness of the casting will not be uniform. In order to cover the entire inner surface of the mold evenly with the casting composition, and to heat all of the casting composition uniformly, it is customary to rotate the molds simultaneously through two different planes while the casting material is being heated and jelled and cured, if a plastisol, or fused if initially in powder form. This double rotation of the molds stirs and distributes the casting material while it remains in liquid phase thus preventing a portion of the liquid from becoming overheated by remaining in contact with the inner surface of the mold, and also distributes the composition evenly over the entire inner surface of the mold so that when the material jells or fuses it will form an article coextensive with the inner surface of the mold.

The prior art methods are unsatisfactory because they are too time consuming, or produce articles which are unsatisfactory in quality, or have both of these objections. The chief difficulty in the prior art methods has been in the heating of the molds.

Heretofore, molds have been subjected to an atmosphere of steam while being rotated in two planes, but this is unsatisfactory since it subjects the outer surface of the molds to a temperature of substantially 212 F. Unless this operation is continued for a long time the interior of a mold is heated to a temperature somewhat less than the outside of the mold, and even for a composition which is heat setting at a temperature below 212 F. the operation is inefficient because of the time consumed in heating the casting composition in the molds sufficiently to cause it to set. superheated steam requires more expensive equipment, and steam is not an efi'icient heat transfer medium.

It has been proposed to heat the molds by immersing them in a body of heated liquid. However, it is difficult to maintain a double rotation operation while the molds are immersed in liquid.

It has been customary to heat the molds by directing a stream of heated air against them but even under the best conditions air is not an efiicient heat transfer medium.

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It is therefore an object of this invention to overcome the deficiencies of the prior art and obtain a better distribution of heat on the mold surfaces, and thereby to perform the molding operation in less time than has been heretofore required, While at the same time obtaining cast articles of uniform high quality.

The invention will best be understood if the following description is read in connection with the accompanying drawings in which:

FIGURE 1 is a front elevation looking into a treatment chamber.

FIG. 2 is a front elevation detail view illustrating one form of double rotation means which may be employed including mold support and mold carrier means.

FIG. 3 is a detail view showing in perspective means which may be employed for locking a mold carrier on its support.

FIG. 4 is a side elevation of the locking means showing how it may be used in conjunction with a finger carried by a sliding panel to prevent starting of the apparatus unless the locking means is in locking position.

FIG. 5 is a modification of FIG. 1 showing apparatus preferred when using a liquified salt as the heat transfer medium but not necessarily limited in use to any particular liquid heat transfer medium, and

FIG. 6 is a view similar to FIG. 5 but showing a second fluid conduit leading to the shower header means above the tank within the housing, or alternatively to other spray heads.

In practicing our method we supply the desired amount of casting composition into molds which are clean both on the inner and outer surfaces, and then move the molds into a heating chamber, Where we direct against the entire surface of the molds a rain or shower of heat transfer medium so that the casting material may be speedily fused or converted to a plastic stage while keeping the temperature of the heating medium within a range at which the rate of decomposition of the medium is so low there will be no discoloration during the fusion cycle.

The terms rain and shower are used herein interchangeably.

We have had excellent heat transfer results using a heat transfer liquid having high specific heat, and a boiling point and flash point substantially above the molding temperature of the vinyl plastisol or other casting material, and heating it to a temperature substantially above the molding temperature and substantialiy below its boiling point, and directing a shower or rain of heat transfer liquid onto the entire outside surfaces of the molds while they are continuously rotating. After the heating operation, and before opening the molds, the heat transfer medium is washed off, using a liquid solvent for the heat transfer medium. Desirably, to reduce cost, the mixture is collected and the heat transfer medium decanted for repeated use.

Examples of liquid heat transfer media having the above characteristics which we have used successfully are:

(1) A salt composition comprising:

Percent Sodium nitrate 1050 Potassium nitrate 1050 Sodium nitrite 550 (2) A liquid hydrocarbon having one or more hydroxy groups, as for example: Polyalkylene Glycerine Glycol Polyethylene glycol Chlorinated bisphenol An eutectic mixture of diphenyl and diphenyl-oxide We have had particularly good results using a polyalkylene glycol which is commercially available under the trade designation Ucon SOHBZSOX (a product of Union Carbide Company), which is completely soluble in water at room temperature, i.e., within a range of 65- 90 F., and becomes 80% insoluble in water when raised to a temperature of 160180 E, and so separates from water within said temperature range and can easily be decanted and recovered.

We have found that a heated shower or rain of any of the above directed over the entire outer surfaces of the molds wets the mold surfaces, which results in very efficient heat transfer through the mold to the inner surfaces of the molds. Good results are obtained when the casting composition inside the molds is heated evenly to a temperature approximately within the range of 300-375 F. The temperature to which the heat transfer liquid should be heated in order to obtain the desired temperature within the molds depends upon the thickness of the molds and the material of which they are made, the composition of the casting material, the heat within the space through which the sprays are directed upon the molds, and the distance between the spray heads and the molds.

We have successfully used a liquid hydrocarbon heat transfer medium, supplied from a single tank or two tanks. When a heat transfer medium is supplied from a single tank, we prefer to start the molds rotating and to wet the molds for a short timed period to jell the plastisol, and then stop the flow of the medium and allow the molds to rotate for a timed interval before turning on the flow of the medium again to wet the molds for a longer timed period of time to effect the curing of the plastisol, and then to drain off the-molds before removing them from the housing. For example, we have wetted the molds with a shower or rain of the liquid heat transfer medium for a period of eight seconds, and then turned off the shower and allowed the molds to continue to rotate without the shower for a half minute. We have then turned on the spray and wetted the molds for from 1 to 4 minutes to effect fusing of the gelled plastisol. The period between the two wetting steps seems to be beneficial in causing the plastisol to gell evenly over the entire inner surface of the molds.

If the liquid heat transfer medium is supplied from two tanks the liquid in one may be heated to a temperature desirable for the gelling step and the liquid in the other may be heated to a different temperature desirable for the curing step.

We have found that the molds commercially available at the present time are not always completely tight when closed and that if an oily heat transfer medium seeps into the mold interior it may cause some undesirable discoloration of the material in the mold if the contents of the mold are of a light color, and we prefer to use a liquified salt medium where the contents of the molds have a light color. Because the salt reverts to its solid phase when its temperature is reduced it is desirable to collect and reheat it as soon as possible after its contact with the molds, and to reduce as much as possible the extent of its travel from its storage chamber to the shower or rain heads. When using a liquified salt heat transfer medium we prefer to start the mold support means rotating for a short timed period and then turn on the rain of medium to wet the molds and heat them for a timed period long enough to cause both gelling and curing, or fusing, of the casting composition, and then to drain off" the molds within the housing, with or without a washing off step within the housing.

It will be understood that desirable time control means of any suitable kind are employed for each step of the operation. Timer means for the pump by which the heat transfer medium is supplied to the header N8 is shown in FIG. 6. The number of steps may vary. As indicated above it may be desirable to divide the operation into more steps when using a liquid hydrocarbon as the heat transfer medium than when using a liquified salt.

Various means may be used for supporting the molds and moving them for even heating, and to distribute the casting material over the inside surface of the molds when the molds are not entirely filled and the resulting article is a hollow article.

Very good results have been obtained employing double rotation apparatus of the kind described in U.S. Patent No. 3,016,573 issued January 16, 1962. As shown herein in FIG. 2 the rotation apparatus is enclosed in a housing 12 having an access opening or window 14, which may be opened and closed by sliding panel 15 through which mold carrier frames 46 may be inserted in a slideway S on a support member 28 and removed after the casting operation, and the apparatus is stopped while a mold carrier frame is being loaded onto a support member or unloaded from it.

A desired amount of a selected plastisol is poured into one or more molds M (usually several are employed) of known kind, which are secured on a mold carrier frame id. The individual molds are closed and the frame is slid through the window 14 into the slideway S of a support member 23. The locking means is then positioned to hold the carrier frame on the support during the time the double rotation apparatus is operating, and the power means (not shown) is actuated. When a casting operation is completed, the locking means is released and the mold carrier frame 49 is slid out of the slideway S on its support means and withdrawn through the window. The moids M are then cooled and opened and the cast products are withdrawn. The molds are then cleaned if required, in readiness for being refilled and employed again as described.

A drive shaft 17 extends through wall 11 of housing 10 and is rotated by.-any suitable means such as an electric motor (not shown). Drive shaft 117 comprises a first part 17a which enters the housing through the sleeve 1'8, and a second part 17b which extends through a bearing 19 provided in wall 12. The shaft parts 17a and 17b are aligned with their inner ends spaced apart. Bridging the space between the shaft parts and interconnecting them is the collar means 170. A cross support shaft 2%, which is a double headed bolt, extends at a right angle to shaft 17, between the opposed ends of shaft parts 17a and 17b, and through the collar 170 to which it is secured in any suitable way as by welding.

A first pair of gears 21 and 2.2 are mounted for rotation on cross shaft 2t) on opposite sides of shaft 17. On the inner end of stationary bearing sleeve 18 a bevel gear 23 is mounted. Gear 23 is stationary and with bevel gear 24, which is loosely mounted on shaft 17. forms a second pair of bevel gears which mesh with gears 21. and 22. When the drive shaft 17 and cross shaft 20 are revolving around the axis of the drive shaft the gears 2i and 22 are caused to travel on and around the stationary gear 23 and they are thus also rotated around the axis of cross shaft 2%). If desired gears 22; and 2:4 may be eliminated and a counterbalancing disc used in place of gear 22 and keyed to cross shaft 20.

The support members 28 are mounted on the outer surfaces of gears 21 and 22; (or on gear 21 and a counterbalancing disc used in place of gear 22), respectively and may be integral with said gears or fixed to them in any suitable way, as for example by welding. Accordingly, when shaft 17 is rotated the support members 28 are caused to rotate simultaneously around the axis of shaft 17 and the axis of cross shaft 20.

Each of the support members 38 is an open frame member with means 32 along its side edges defining a slideway S and with the 2-sided angle stop member 34 along its rear edge. Its front edge is defined by the cross pieces 36 and 38 (FIG. 4) which form part of a lock and stop assembly. Members 28 each comprise the crossed channel members 32a and 35. A bore or hole 33 extends through the portions of 32a and 35 which cross one another, and the double headed bolt 20 projects through this aperture. Washers W are provided around ends of member 20 on the outer surface of the support members respectively, and are held in place by the nuts N which are screwed onto the ends of cross shaft 20 respectively.

Member 34 serves as a stop against which an end of a mold carrier abuts when it is in home position in a slideway S on a support.

Each mold carrier 40 comprises a rectangular frame. The horizontally extended perimeter of each mold carrier is perforated with a number of small apertures 42, the purpose of which is to receive the threaded stems respectively, of molds, such for example as the molds M shown in FIG. 2.

In order that a single carrier may support a greater number of molds cross pieces such as 44, 46 and 48 may be provided each having a number of said openings or perforations 52. It will be understood that the molds employed may vary considerably in size and shape, and the perforations 42 are only illustrative of many possible means which can be used to engage and positively hold the molds on an air pervious carrier while they are subjected to double rotation.

Cross pieces 36 and 38 at the front end of a support member are spaced apart by the spacing blocks 39 leaving a space from Within which there projects outwardly a locking guide member 52 which is mounted on the rotatable shaft 50 which extends through said cross pieces 36 and 38. In locking guide member 52 the hole 53 is provided to receive and act as a bearing for the locking finger 54 which projects rearwardly from the lock-andstop member 56 which is mounted on the rotatable shaft 50 in front of cross piece 38. Around the rear end of rotatable shaft 50, between the flange 58 thereon and the rear end of sleeve 68 which surrounds shaft 50 just to the rear of cross piece 36, is a spring 62 which tends to retract shaft 50 and therefore cause locking finger 54 to pass into and through the bearing 53 in locking guide member 52 when rod 50 has been rotated to bring member 56 into upright position. With member 56 in upright position and finger 54 extending through bearing 53 a fixed stop is provided on the front end of the mold carrier support which prevents the inadvertent dislodgment of a mold carrier from its support as will be more fully explained. However, when shaft 50 is pulled forwardly against the force of spring 62, thereby withdrawing finger 54 from the bearing 53, and, the said members 54 and 56 and member 53 are rota-ted counterclockwise through approximately 90", the finger 54 will be received in the re-entry slot 64 in cross piece 38, with its free end abutting against the cross piece 36 and therefore positioning lock-and-stop member 56 further outwardly from cross piece 38 than is the case When finger 54 is inserted through the bearing 53 in the locking guide member 52. In this unlocked position of lockand-stop member 56, it is positioned in the path of movement of a finger member 65 which is carried on the inner surface of the sliding window panel 15, and prevents the panel 15 from being closed and thereby completing an electric circuit (not shown), for energizing the power means for actuating the drive shaft 17.

As shown herein, FIG. 1, there are two tanks (or reservoirs) 76 and 78 in which a liquid heating medium may be stored and heated to the desired temperature by any suitable means. From tank 76 a supply pipe 77 leads into housing 12 and to a header or spray head 80. A pump 82 and return pipe 84 are provided for returning liquid medium from the housing to tank 76. From tank 78 a supply pipe 79 leads into the housing 12 and to the header or spray head 86. A pump 88 and return pipe 90 are provided for returning liquid medium to tank 78.

After the molds have been charged and loaded onto the double rotation apparatus, they are preferably but 'tisol over the entire inner surface of the molds.

not necessarily rotated for a short period at room temperature during which time the plastisol, which is in liquid phase, wets and is distributed over the entire inner surface of the molds.

A shower or rain of the liquid heat transfer medium having a temperature sufficient to heat the contents of the mold and cause it to gel is introduced into the housing, as for example from a first tank 76, and directed against the molds while the molds are rotated to distribute the plas- Because of the efficient heat transfer accomplished by use of a liquid heat transfer medium of the kind described herein, the rate of gelation of the plastisol may be controlled more exactly than has been possible with the heat transfer media previously employed. This results in a more uniform film or layer of the casting material being deposited over the inner surface of the mold.

After the casting material is gelled, a shower of a liquid heat transfer medium having a temperature sufficient to heat the contents of the mold to cure it is introduced into the housing, as for example, from a second tank 78, and directed against the molds. By the use of a liquid heat transfer medium of the kind described herein, the speed with which the plastisol or casting material can be cured after the gelation step has been completed is much faster, and more easily controlled, than by the use of hot air at the same temperature.

After each of the steps of heating the molds by means of a rain or shower of liquid heat transfer medium as described above, it is desirable, although not essential, to discontinue the shower while continuing the movement of the molds for a short interval prior to the next step. During each of these intervals the recovery of the liquid heat transfer medium employed may be continued and substantially completed by draining it from the treatment chamber and returning it to the appropriate tank.

In PEG. 5 heat transfer heating and circulating apparatus is shown which is preferred when using a liquified salt as the heat transfer medium. A tank is provided within the treatment chamber 12 below the double rotation apparatus. It is heated, as by gas jets 98, to keep the salts from reverting to solid phase and also to heat the heat transfer medium to the desired temperature. Within the tank 100 is a pump 102 which sucks in the liquefied salt and, depending upon the position of slide valve 104, either delivers the liquified salt through pipe 106 to the perforate header 108, from which it is rained down on molds supported on the double rotation means, or returns it through orifice 110 directly into the tank 189. The slide valve 104 may be actuated by an air valve 112 controlled by an electric circuit including a timer 114 and a solenoid valve 116. Obviously only a single supply tank and its pump and return pipe need be used when the same temperature is employed for effecting both the gelling and the curing of the plastisol. Timer and slide valve control means such as is shown in FIG. 5 may of course be used with either or both of the tanks 76 and 78.

After the material in the molds has been gelled and cured, the molds are washed with a solvent for the heat transfer medium employed, and cooled, after which the molds are opened and the cast products are removed. The wash water may be collected and the heat transfer medium it contains separated and recycled. In the case of polyethylene powders the phases of liquifying and adhering to the mold surface, and partially hardening, correspond to the phases of gelling and curing of a liquid hydrocarbon heat transfer medium.

When using a liquified salt as the heating medium in apparatus of the kind shown in FIG. 5 the salt may desirably be washed from the outer surface of the molds, preferably with water, and returned to tank 100 While the molds are within housing 12. -In this way the salt is conserved and the water or other washing agent employed for washing does not substantially dilute the liquified salt 7 since the water is soon evaporated from the heated tank Washing the salt or other heat transfer medium off the molds while they are within housing 12 has an added. advantage when polyethylene plastic resin powder is used as the molding composition since the washing step can also be used to lower somewhat the temperature of the plastic resin within the molds which facilitates the setting of the plastic resin.

For washing or partially cooling the molds while they are within housing 12 a conduit 109 for water or other suitable liquid is shown (FIG. 6) connected to the header 108, and may be opened by suitable valve means preferably automatically to provide a washing and a tempering rain when pump 1102 is idle. A conduit 109 may be connected to spray heads 109:: if spray orifices differing in size or location from those of header 108 are desired.

Providing a rain of water or other suitable liquid on the molds to Wash them off within the housing is desirable when using a liquified salt as the heat transfer medium for otherwise the salt left on the surface of the molds may revert to solid. form before the molds have been removed from the housing and washed. With the apparatus disclosed herein the heat transfer to the casting material in the molds is accomplished so rapidly that when stabilizers and plasticizers are employed the amount may be substantially reduced. Since these materials are expensive, this results in a substantial reduction in the cost of raw materials.

A correlated advantage is that when plastisols are used they may be more easily formulated. for casting in the manner, and with the use of a heat transfer medium of the kind described above.

One of the chief advantages of the methods disclosed herein i in the more precise temperature control provided during the gelation, or fusing in the case of powders, of the casting material. Many casting compositions go through many physical changes as temperatures are increased. Non-uniformity in the temperature imparted to the casting material in a mold. results in non-uniformity in the time required for distribution and deposit of the material over the inner surface of the mold.

It is desirable to have all casting compositions deposit at the same rate. In the past when using a casting material such as a polyvinyl plastisol it has been left to the supplier of the material to change the gellatin rate through the use of slow or fast acting plasticizers to conform to relatively fixed heating conditions. With the more exact control of the temperature of the casting material in the mold obtainable with the apparatus which is the subject of this divisional application and is described above, it is possible to make all plastisols deposit at substantially the same rate by raising or lowering the temperature of the heat transfer medium, as may be required. The ability to more exactly transfer heat to the casting material in a mold and thus better control its ternperature also has the advantage that the supplier of plastisols may choose plasticizers on a basis other than whether they are fast or slow gelling. For example, he may choose them on a basis of cost and storage life at room temperature. It happens that plasticizers of very slow gelation (175195 F. gel point) normally have by far the best storage life at room temperature. Under the fixed or less exactly controlled heat transfer conditions of the prior art, it has not been considered possible to use these plasticizers. Now, by means of the apparatus described above, it is possible to use any of a large number of different type plastisols, including those of very slow gelation.

By using apparatus of the kind described above, fused plastisol articles of improved quality may be produced at significantly lower temperatures and shorter fusion cycles and lower compounding costs.

For example, in casing a plastic hobby horse which Liquid shower Hot air transfer transfer medium medium Temperature range 550 650" F. Cold rotation 30 seconds. Gelation of total distribution l1% minutes. 25 minutes.

at about 200 F. Fusiquraiter gelation at about 1 minute 2-10 minutes.

We have found in the manufacture of the hobby horse with a hot air transfer medium that the total time for cold rotation plus the periods of gelation and curing after gelation require from 9 to 14 minutes and only about 4 minutes when using a liquid shower heat transfer medium of the kind disclosed above. At a temperature of from 150 F. lower the liquid transfer medium produces curing to faster. There is a raw material saving on the order of 10% due to better distribution of the plastisol.

Furthermore, the lower temperature used with a liquid shower heat transfer medium is easier on the molds and mold carriers and results in a prolongation of their useful life. The lower temperature also extends the useful life of the cast product which, because of being exposed only to the lower temperatures, retains its physical properties and original color for a substantially longer period of time.

There has thus been disclosed an apparatus for casting articles from heat setting materials in which the above mentioned objects are accomplished in a thoroughly practical manner.

What is claimed is:

1. Apparatus for casting a plastic composition which comprises Within an enclosure, one or more closable molds adapted to be partly filled with the composition, an open-work carrier for supporting said one or more molds, means for rotating the carrier in a plurality of planes, means for introducing the carrier into the enclosure and removing it therefrom, spray means within the enclosure for a thermal liquid and another liquid, means for collecting the thermal liquid and returning it to said spray means for the thermal liquid and for heating it, and means for supplying another liquid to said spray means for the other liquid.

2. The apparatus of claim 1 in which separate spray means are used for the thermal liquid and the other liquid.

References Cited by the Examiner WILLIAM J. STEPHENSON, Primary Examiner.

ROBERT F. WHITE, Examiner.

Claims (1)

1. APPARATUS FOR CASTING A PLASTIC COMPOSITION WHICH COMPRISES WITHIN AN ENCLOSURE, ONE OR MORE CLOSABLE MOLDS ADAPTED TO BE PARTLY FILLED WITH THE COMPOSITION, AN OPEN-WORK CARRIER FOR SUPPORTING SAID ONE OR MORE MOLDS, MEANS FOR ROTATING THE CARRIER IN A PLURALITY OF PLANES, MEANS FOR INTRODUCING THE CARRIER INTO THE ENCLOSURE AND REMOVING IT THEREFROM, SPRAY MEANS WITHIN THE ENCLOSURE FOR A THERMAL LIQUID AND ANOTHER LIQUID, MEANS FOR COLLECTING THE THERMAL LIQUID AND RETURNING IT TO SAID SPRAY MEANS FOR THE THERMAL LIQUID AND FOR HEATING IT, AND MEANS FOR SUPPLYING ANOTHER LIQUID TO SAID SPRAY MEANS FOR THE OTHER LIQUID.

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