CA1036305A - Pelletizing apparatus with lubricated pervious orifice wall - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Apparatus for extruding thermoplastic material comprising an extrusion die having an extrusion orifice having thermoplastic material conducted thereto, the orifice having a fluid pervious wall. Coolant is supplied under pressure through the pervious wall into contact with the outer surface of the material, part of the coolant evaporating immediately on contacting the outer surface of the liquid and the residue of the coolant remaining liquid to provide lubrication along the inner wall at the orifice to facilitate passage of the material therethrough.

Description

~ACKGROUND OF THE INVENTION
In the plastic molding industry, there is a large demand for pellets of synthetic plastics of the thermoplastic type. In many of such machines, an extrusion die is used ha~ing a plurality of orifices through which the plastic while hot is extruded. As the extruded plastic emerges from the die face, one or more moving knives cut the emerging plastic into small pellets. In some of these machines~ the plastic is extruded into a fluid bath (generally water) to solidify the plastic as it emerges from the die orifices and thus facilitate cutting by the knives. The water bath may also be used as a means to extract the pellets from the casing which surrounds both extrusion die and the cutting knives.
One of the difficulties encountered in the prior art machines is that, regardless of whether the die face is curved ~such as cylindrical) or flat, as the plastics emerge from the die orifices and the knife passes over them to cut the pellets, the plastic has a tendency to smear under the knife. The result i9 that in a short time, sufficient plastic has been built up on the die face to require the stopping of the machine in order to clean off the die face. This smearing action is a minimum for some plastics, but on plastics such as poly-urethane and polypropylene, the smearing takes place very rapidly and thus the down-time of such machines may be excess-i~e.
Accordingly, one of the unsolved problems in the prior art is to obtain a machine which will make pellets from all kinds of thermoplastics without the smearing effect.
t Another difficulty with the prior art machines is that in order to make clean cuts, the kni~es are pressed against the die face by spring means or hy a direct mechanical fastening, i so that the knife edge bears with considerable pressure against :. - . ,, : . .
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the die face. As a result~ wear occurs~ both on the knife and the die face which requires rather expenslve regri`nding and down time of the machine.

SUMMARY OF THE TN~IENTION
Accordingly, it is the general purpose of this invention to provide solutions to the above problems by providing an extrusion die apparatus and the dies therefor for making pellets rom synthetic thermoplastics without the above smearing, and which therefore minimizes the down time o the machine, and of providing an extrusion type apparatus and die therefor which has a reduced amount of wear, thus again to minimize the down time of the machine. In addition, the invention includes what is deemed to be a novel and inventive method of extruding materials for the above purposes.
Accordingly, among the several objects of the invention may be noted the provision of apparatus for making pellets from thermoplastic material which is so constructed as to minimize the build up of plastic material at the extrusion orifices beneath the die face and the cutting knife.
2Q Another object of the invention is the pro~ision of a ;
machine for making pellets from thermoplastic material, in ~hich the wear of the die face caused by the cutting knife has been -~
practically eliminated.
A still further object of the invention is to provide apparatus for making pellets from synthetic thermoplastic material in ~hich, as the plastic material is being extruded through the die orifice, the material is cooled ~hile within the orifice and simultaneously lubricated to assist its passage therethrough.
Another object of the invention is the provision of apparatus of any of the aboYe kinds ~hich has the desired features-of reduced cost of manufacture and of operation, as ~ell as reduced maintenance, while maintaining a high output -3~
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Another object of the inve,ntion is the provision of methods for making pellets of thexmoplastic synthetic resins, in which the material, while being fed through an extrusion orifice is both chilled while in the orifice and lubricated in its passage therethrough.
Other objects and adYantages will be in part pointed out hereinafter~ and In part obvious, Accordingly, the invention comprlses the elements and combinations of elements, arrangements of parts, and features of construction of the apparatus, as well as steps and sequence of steps and features of operation of the methods, all of which will b.e exemplified in the structures and in the methods hereinafter described, and the scope of the application of which will be indicated in the appended claims.
More particularly, there is provided apparatus for extruding thermoplastic material comprising an extrusion die having at least one extrusion orifice, means for forcing said thermoplastic material through said orifice, said oriflce having a ~luid pervious wall portion, supply means connected to a source of liquid coolant under pressure and operable to deliver said pressurized liquid coolant to said pervious wall portion, said pervious wall portion being constructed to permit passage of said liquid coolant therethrough and into contact with said material within said orifice at such a rate that a part of the coolant e~aporates immediately upon contacting the outer surface of said material within said orifice and a residue of the coolant remains liquid to provide a lubricant on said wall portion of said orifice adjacent to said material to facilitate passage of the material therethrough~ and means spaced from and operable with said die for severing said material after passa~e through.said orifice, "
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103630s In the accompanying drawnngsr in which'several of possible em~odiments of the invention are illustrated:
Fig. 1 is a generalized ~iew showing one embodiment of the apparat-ls of the present invention coupled to a conver,, tional machine for m~xing and extruding synthetic thermoplastic ~ -, materials; ' Fig. 2 is a sectional elevation of the Fig. 1 embodiment;
Fig. 3 is an end eleYation~ partly in section, of the F~g. 1 embodiment;
Fig. 4 is a cross-sectional view of a portion of one embodiment of an extrusion die which is an invention and which forms part of the die assembly of Figs. 1 and 2;
Fig, 5 is an enlarged view showing in greater detail a single die orifice of Fig. 4, taken in the direction of sight lines 5-5 of Fig. 3;
Fig. 6 i9 a view similar to Fig. 5, but showing ~ ' another embodiment of the die orifice of this invention;
Fig. 7 is a view showing a cutting knife arrangement for this in~ention;
Figs. 8~ 9 and 10 are ~iews showing the cutting knife , utilized in Fig, 4;
Fig. 11 is a sectional elevation of another embodiment of this invention; and ' Fig. 12 is an end view of the Fig. 11 embodiment, taken in the direction of-sight lines 12-12 thereon.
Throughout the-dra~ings, like parts will be designated '' by liXe reference numerals. Dimensions of certain of the parts as shown in the drawings may ~ave heen modifi~d and~or exag- `~
gerated for the purposes of clarit~ of illustration and under- `' -standing the ànvention.
~ eferring now to Fig. 1, there is shown a combination of elements as follows, the view sho~ing a ~orka~le assembly :,......... :. . . . . . . ~ . : .. - :: :, . . . .

of parts, some of which are ~ell kno~n and others of ~hich are new and fall within t~e purview of this inYention.
A conventional extruder indicated generally- by numeral

2 is shown having the feed hopper 4, the drive mechanism 6 for the extruder screw,and an outlet end 8~ These parts are all conventional, and are not part of this invention.
Mounted on a base 10, which is shown on suitable rollers 12 for ease of moving the assembled structure, is one embodiment of the apparatus of this invention indicated gener~
ally by numeral 14 and comprising a casing 16, means 18 for coupling the casing to the outlet 8 of extruder 2, a drive shaft 20 extending into the interior of casing 16, a pulley 22 mounted on the drive shaft for coupling the latter to an electric motor (not shown), a pipe 24 in the shaft 20 for feed-ing water into the interior of the casing, and an outlet 26 through which water is forced out of the casing carrying with it cut pellets. A sealed port of heavy glass 28 is provided in both sides of the casing 16 in order to see what is taking place therewithin.
Referring now to Fig. 2~ there is shown partly in cross-section, the casing 16 and the elements therewithin. One end of the casing is closed ~y means of a plate 30 welded to the case perimeter and to which is removably fastened by bolts 33 a plate 32 which holds a ~earin~ and water sealing mechanism indicated generally by numeral 34, the bearings 136 rotata~ly supporting the dri~e shaft 20.
At the other end of the casing 16 is the die assembly of this invention indicated generally by numeral 38, mounting being as follows: A mounting plate 40 is fastened against the left~hand end of casing 16 by means of clamping studs 42 whose supports 44 are pivoted to the casing. In order to supply a suitable bearing surface for the plate 40, a steel ring 46 ~ 6 -, .,: ~ , -. , ,. ~
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- ' 1036~305 is welded around the inner end of the casing 16 against which the plate 40 is firmly held by means of the bolts 42~ suitable sealing means 48 being provided Fastened to the mounting plate 40 by means of bolts (not shown) in conventional manner is a coupling or adaptor 52 having at the left-hand end thereof the coupling means 18 by which the adaptor is fastened to the outlet 8 of the extruder 2. The adaptor has an entrance opening 54 which communicates with the extruder orifice when the parts are clamped together.
This clamping means may also structurally support the adaptor 52 and die assembly 38 ~hen the casing 16 is disengaged from plate 40 for access into the interior thereof and to die face 154.
A plurality of interior bores or conduits 56 are provided in the adaptor, each of which communicates at i~s one end with the opening 54, and at its other end with a manifold 58 which is ;-provided in a cylindrical surface 60 provided on the adaptor.
The cylindrical extrusion die 38 which is in the shape of a torus is mounted by a slidable fit onto the cylindrical surface 60 of the die body, mounting being by conventional means such a9 bolts 50 which pa99 through the die body and thread into die r;ng 64. ~
The extrusion die 38 in this embodiment is, as ~-indicated above, a torus which fits onto the cylindrical surfaces ~ ;
60. It is comprised of the inner and outer rings 64 and 66 ; -which fit upon each other and which lsee Fig. 5) are welded together. The inner die ring 64 is composite, and comprises a ring 68 whose cross-section is spool-shaped and has flanges 70, together with outer annuli 72 and 74 which fit within the flanges 7a~ Shoulders 76 are provided so that when annuli 72, 30 74 are welded in place~ as at edges 78 (see Fig. 5), manifold channels 80 are formed to receive d~e heating oil. A plurality ~ of radially extending extrus~on bores 82 are provided spaced - around the composite die ring 64. Bores 84 are provided which ,: . . ~ . . - . . :
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are coaxial with and continguous with the bores 82. sores 82 and 84 communicate with eacfi other hy means of a short bore 86 of reduced diameter which has a shoulder 88.
It will be observed that the channels 80 lie on each side of the entering bores 82 of the extrusion die. The channels 80 are inter-connected between the bores by a plurality of cross channels ~0. See Figs. 3 and 4 An inlet 92 (see Figs. 3 and 4) is provided for one of the mani~olds 80 and an outlet 94 for the other. Suitable baffles may be placed in these manifolds to direct the heating fluid back and forth from one channel to the other for even heating. By means of the inlet and outlet, heating oil is conducted through manifolds or channels 80 to maintain the inner portions of the bores 82 heated, thus keeping the plastic entering these bores hot while therein.
The outer ring of the extrusion die proper is provided with an inner peripheral groove which when ring 66 is positioned on ring 64 and welded thereto, forms a manifold 98. Extending radially from manifold 98 are bores 100 each o which is aligned axially with one of the bores 84 in the inner die ring 64. Each of the bores 100 is provided with a reduced ~ ;
diameter portion 102 and an enlarged end port~on 104 which is threaded to receive a plug 106. A shoulder 105 is provided, and each of plugs lQ6 is provided with a central bore 108 axially aligned with its respecti~e bore 104, and can seat on shoulder la5.
Inserted in each of the composite bores (as shown in Figs. 4 and 5~ is a metallic sleeve 110 which is pervious to fluid, and has a central bore 120. The sleeve, in its preferred embodiment, is a sintered material of open cell construction, -the cell pores being (for examplel in the order of 20 microns diameter. It is po;`nted out that the pore size can be changed, ~ut the 20 micron pore size has been found to work satisfactor-C

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ily. The sleeve 110 is preferably made of type 316 stainless steel, but other comparable materials may be used.
Each of sleeves 110 has the neck 112 which is a sliding flt in the short ~ores 86, and an O~ring sealing member 114 (or other suitable sealing means) is provided which seals the neck 112 as to the surface of bore 84. At the other end of the bushing or sleeve 110 there is provided a portion 116 which is a sliding fit in the bore 102 in which an O-ring sealing member 118 is provided, At the upper end (as viewed in Fig. 5) there is provided a gasket or sealing washer 119 which surr~unds the neck 112 and bears against the shoulder 88. It will be observed that the bottom end (as viewed in Fig. 5) of the sleeve 110 is provided with the neck 121 of reduced diameter which enters a suitably enlarged portion of the bore of plug 106. ~hen plug 106 is screwed into place and bears against shoulder 105 and the O-ring 118, it forces the sleeve 110 against the gasket 119 and expands O-ring 118, thus sealing the entire structure together.
It is to be noted that the manifold 98 as well as the 2Q indi~idual hores laO surround each of the sleeves 110.
It is thus to be noted that once the molten plastic has entered the entering bore 82, thereafter the sleeves 110 -~
with the bores 120 become the extrusion dies proper, the sleeves receiving hot plastic from their associated inlet bores 82.
The preferred embodiment of the invention is shown in Fig. 5, to the extent that if a sleeve 110 should become plugged, then all that is necessary in order to replace the sleeve is to remove the respective plug 106, withdraw the sleeve and insert a replacement therefor, In the event that it is desired to make a simplified for~ of composlte die rlng, a non-insertable type is shown in Fig. 6, ~n which there is shown one of a pluralit~ of pervious _ g _ ~,i .
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103630s sleeyes or bushings 122, each sleeYe haying hore 123 and being permanently bra~d at the outer end ~nto a suitahle recess 124 provided in the inner face of a cylindrical ring 125 surrounding the outer die ring 126. As in the Fig. 5 embodiment, a water manifold 127 and ind~v~dualbores 128 surround slee~es 122 as in Fig. 5. The upper ends of the sleeves are brazed into suitr able bores 129 proYided in the torus 130, which is somewhat like torus 68, the bores 129 communicating with inlet bores 132.
The inlet die ring comprises the torus 130 and the annuli 133 to provide heating manifolds 134.
After the cylindrical ring 125, torus 126, torus 130 and annuli 133 are welded together, the sleeves 122 are inserted with properly located braz ng compound, and brazing is done in a furnace, Into the manifolds 98 and 127 (ie., in both embodiments) there is provided the inlet 135, the purpose of which is to provide a fluid under high pressure which will pass through the sleeves or bushings 110 or 122 and into the interior ~ores 120 or 123 thereof. In view of the fact that the egress rom the channel is to be through the sleeYes 110 or 122, no exit nipple or connection for the channels ~8 is necessary.
Referring to Fig. 2, fixedly mounted on the inner end of the shaft 20, the latter being supported conventionally by , the bearings 136 plus whatever additional bearings are necessary is the drive plate or coupling plate 137. It will be noted that the mounting plate 32 also contains the water tight seal 138 for the shaft. A sleeve 13~ is provided which is supported on bearings 140, the inner races thereof being mounted on the stationary bearing member 142 which is anchored on the adaptor 52 as indicated. Anchoring is done by means of the support plate 144 which is mounted on the right~hand face of the adaptor by means of the bolts 146, the plate oYerlapping and sealing the die 38 in place. Slee~e 139 is provided with a bore 145 which communicates with pipe 24.
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Mounted on sleeve 13~ is driven sleeve 147 which is fixed thereon by suita~le means such as set screws and key, Plate 137 is attached to sleeve 147 as shown using conventional means. Attached to the inner (or left-hand end as shown2 of the sleeve 147 is a knife support plate 14a on which, near the upper edge thereof, are mounted knife holders 150. The knife plate itself is attached to the drive slee~e 147 in conventional manner by means of the shoulders indicated in Fig. 2, and the mounting screws or bolts 182, Referring now to Figs. 7-10, there is shown in detail the knife holders and the knives, The die face 154 of the outer die ring 66 is shown in part, and one of the knife holders 150 attached thereto.
Each knife holder 150 comprises a body 156 which is `
provided with the channel 158 adapted to receive in sliding relationship the body portion 160 of a cutting knife. A clamping member 162 is provided which bears against the body in order to lock it securely in the body 156 and hold it in adjusted position.
Clamping member is forced against body 156 by means of the bolts 164 in customary manner. At the rear end of the body portion 160 i5 provided a plate 166 fastened to the body by means of the bolts 168, the function of the plate being to support adjusting screw 170 with its lock nut 172. By means of the latter construction, the knife is securely adjusted in its ~ -proper relationship to the die face 154.
Each of the knives is provided with the cutting edge 174 and it will be noted that the cutting edge does not make contact with the die face 154. The reason why this is not necessary will be explained below, However~ at this point it is to he noted that because the knife edge does not make engagement with the d~e face~ there is no wear caused by the blade on the die face 154, The gap between the knife edge and the die face may be, for example 0.002 to 0.004 inches.

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If desired, a channel 176may be provided in the body 160 of the knife which cooperates with the outstanding shoulder 178 on the pressure plate 162 to assist in safely holding the knife within the holder 150.
As shown, see Fig. 3, a plurality of knives is pro-vided. The number of knives is not critical, and six to twelve can be used, as examples. Each of these knives is mounted on the perimeter of the knife plate 149 by means of bolts, for example, 180.
In the operation of the apparatus thus shown and described, it will be noted that the manifolds 80 are used to heat the entering portion of the die orifices, that is, the bores 82. To this end, hot oil or other suitable heating medium is forced through these manifolds or channels to supply con-tinuous heat thereto and thus to a portion of each die orifice which is adjacent thereto. By this means, the plastic entering the composite orifice of the die ring is maintained in a heated condition.

However, and this is quite co~trary to the teaching of the art, after the plastic being extruded has progressed within the sleeves or tubes 110 or 122, it therein encounters a cooling .~ . .
liquid, preferably, which is ~J thin the sleeve bores. Water is supplied to the manifolds 98 or 127 (and thus to counter bores 100 or 128) at approximately 800 lbs. per square inch pressure, -and as a result of the pressure and the perviability of the : sleeves 110 or 122 to water, the water if forced through the sleeve wall and into the bores 120 and 123 of the respective ~ -sleeves. Assuming that plastic is already in these sleeves in the hot condition, most of the water immediately evaporates (the system being hydraulically open). A considerable amount of heat is withdrawn from the plastic due to the heat of ;,'C
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-. - : : , :, evaporation of the water. As a result of this, at least the surface of the plastic becomes solidified. In addition, the cooling fluid (water for example) is constantly being forced under pressure through the walls of the sleeves with the result that a continuous film of water surrounds the interior surface of the bores of each extrusion sleeve 110 or 122. This film of water acts as a lubricant for the cylindrical rod of -plastic which is being forced through the extrusion sleeve by the pressure of the heated plastic in the bore 82. As a result of this combined action, it is believed, the plastic does not freeze in the die orifice and it emerges therefrom in the form -of a plastic cylinder having a solidified outer wall. When it emerges, one of the k~ives 174 encounters the plastic cylinder and immediately shears it off. No smearing of the die face 154 takes place, with the result that no plastic is built up thereon.
Furthermore, pelletization takes place successfully even though the knife does not contact the die face. The result is that no wear takes place on the die face or, for that matter, on the knife edge itself because of any contact against the die face. If wear takes place against the knife, it is solely due to the abrasive action of some plastics, but not otherwise.
The above explanation of what happens in the die orifice sleeve 110 or 122 is what is believed to take place. However, there may be other more accurate explanations for what happens~
and applicant does not wish to be bound in the description of the invention by the above explanation of what is believed to take place. ~;
In order to remove the pellets from the casing 16 as they are cut off at the die face by means of the revolving knives 150, water is forced through the entrance pipe 24 and thence .~, . . .. . .
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through bore 145, from which it flows through holes 254 in member 142 and through suitable spacings 190 between the knife supporting plate 149 and the bearing support plate 144. Water flows across the cylindrical face 154 of the extrusion die proper and in so doing carries the pellets, as they are cut, away from the path of the respective knives. The pellets then enter the chamber formed by t~he casing 16, and are carried therefrom by the flow of water out the exit tubing 26. From tubing 26 the pellets and wAter go into a suitable separation device where the pellets ànd water are separated, the pellets being collected by separate means (not shown) and the water being recycled through casing 16.
In respect to the perviousness of the bushings or sleeves 110 or 122, tests have been run successfully with the sleeves being made of Type 316 stainless stell, with the porosity of the sleeves being in the order of 20 microns. The tests were successful with a water pressure of 800 lbs. per square inch. Of course, it is possible to change the pervious-ness of the sleeves, for example, to either ten microns or five microns, but the pressure required to obtain the suficient in-flow of water will be raised. Such other parameters are well within the realm of the person skilled in the art in view of the teaching of this invention.
In regard to the lubricating film, it is believed that this is probably a mixture of water and steam but this is not certain. The fact that chilling takes place is well indicated by the fact that on examination, it is observed that the plastic cylinder, as it emerges from the respective extru- -sion orifices or sleeves in this invention comprises a stiffened crust of chilled plastic and an inner soft core. It is believed that the presence of the firm surface is what enables one to ~`~

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10;~6305 use a knife edge which is separated from the die face, and that it also prevents smearing of the plastic. - -In the machines which have been constructed and which ;
have operated successfully, the diameter of the bores 120 and -123 have been in the order of magnitude of 0.110 inches inside diameter and approximately one inch long. . -It is also to be noted that during operation of the apparatus, shrinkage and distortion of a material such as '~ ;
polypropylene is minimized, and the pellets are more uniform ' in configuration.
Referring now to Figs. 11 and 12, there is shown another embodiment of the invention in which the die face ;
is flat rather than being cylindrical. Means 188 are provided ;~
for feeding a toroidal manifold structure 190 attached to die body 196 and enclosing ai,manifold 192. The feeding means may be, for example, a coupling plate such as that illustrated by numeral 18 in Fig. 1 and Fig. 2, and conduits 188 extending from the inlet of the coupling means to the manifold 190. This part of the description is purposely made somewhat schematic, because it is not part of the invention and is within the skill of the art to provide a suitable apparatus for feeding the mani-fold 190.
A die assembly is shown and is indicated generally by numeral 194, the assembly comprising the die body 196 in which are provided a plurality of extrusion bores 198 ~e axes of which are parallel to the axis of the die body itself and which communicate ~ith manifold 192. A channel 200 is provided in the die body of such size as to receive a die ring indicated generally by numeral 202. The cross-sectional structure illustrated for die ring 202 is somewhat like that shown for ~' the extrusion die 38, except that in this instance the individual extrusion orifices are positioned so as to be , .,,; .. . . , : . , -~ ~036305 parallel to the axis of the die body, with the exit face 204 of the die being perpendicular to the die body axis. As before, the die ring 202 is composite in structure, and is made of the -two separate toroidal annuli 206 and 208. The torus 206 is made in composite form, for example, following the general idea of section 64 of the first embodiment, thus to provide the heating oil manifolds or channels 210. The outer part 208 of the die ~ -ring is provided with the circular channel 212 which communi- ~-cates with the individual enlarged outer bores 214 which surround the individual extrusion sleeves 216. Each of the extrusion sleeves is fastened into its respective bore in the composite ~`
die ring 202 by means of the plugs 218 and suitable shoulders and sealing means just as in the first embodiment. The bores ;
in the rings 206 and 208 are coaxial not only with each other, but with the initial extrusion bores 198. The entire die ring is thus assembled and welded together, is locked into the die body by means of shoulders 220 provided on the periphery of part 208, and locking annuli 222 and 224 which are fitted into place in a suitable circular recess provided in the right-hand face ~as viewed in Fig. 11) of the die body so as to engage the shoulders 220. Thus, by means of locking screws or bolts 226 the die ring is securely locked into the die body. It will thus be apparent that with this embodiment, a flow of fluid plastic through the die plate is coaxial in direction with the axis of the die itself, and thus is coaxial with the drive shaft for the cutting mechanism which will now be described. -A drive shaft 230 is provided, which is driven by suitable motor means (not shown). The drive shaft enters through the right-hand end of the casing 232 having an inlet 234 and outlet 236 for a ~luid bath such as water. A seal 238 is provided of conventional nature where the shaft enters the closure at the right-hand end of casing 232. The drive shaft 230 ~, ,. ~ ,: - - - , -10363~5 terminates in a suitable bearing 240 in the body of the die.
Mounted on the drive shaft 230 are a pair of knife arms 242, for example, it being realized that instead of having individual arms a circular cup-shaped plate such as circular plate 149 of the Fig. 2 embodiment may be used.
At the extremities of the knife arms 242 there are mounted holders 244 for the knives 246. As in the Fig. 2 embodiment, the knives are made adjustable using conventional means, and again it will be noted that the knife edges do not bear against the die face 204. As in the Fig. 2 embodiment, wear on the face of the die ring is thus avoided.
Hot oil inlets and outlets 248 and 250 are indicated in Fig. 11. By this means, hot oil is passed through the manifolds 210 to keep the entrance portion of the extrusion orifices hot. A water inlet 252 is provided which communicates with the manifold 212 and the counter bores 214 in order to surround the individual sleeves 216 with a fluid which can pass through these sleeves. Water is the preferred fluid, the latter being at about aoo lbs. per square inch pressure or thereabouts.
~he operation of this device is basically the same as that shown in Fig. 2 with the exception that in this embodiment a flat die face is used insteàd of a cylindrical die face as in the Fig. 2 embodiment.
The operation of the apparatus and the method of pelletizing plastic therewith are as follows, reference being ~ -to the Fig. 5 embodiment. (The operatiDn will be for poly-propylene since this plastic is one of the difficult ones to - pelletize on conventional pelletizers).
The polypropylene to be pelletized is put into hopper 4 and is heated in its passage through extruder 2. From the extruder it enters the adaptor, see Fig. 2, and flows by the channels 56 to the manifold 58. As the polypropylene emerges . . .

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103630s from the extruder it is preferably at a temperature of approxi-mately 425F. (The adaptor 52 will have been heated by the flow of heating oil or other medium at a temperature of 475-500F. ~-through suitable manifolds in the adaptor.) After the viscous plastic reaches manifold 58, extrusion is continued until the plastic enters the extrusion bores 82, and passes through the 7 extrusion sleeves 110, and emerges from the die face 154 of the apparatus. The die 38 is maintained in heated condition by the pasSage of the heating oil through the manifolds 80.
It will be noted that at the start up, the adaptor 52 and die 38 are first heated, and the plastic is extruded through the die. No water as yet has been forced into the manifold 98.
After the plastic is extruding satisfactorily through the bushings or sleeves 110 which have been heated by the temperature of the adaptor 52 as well as the heating fluid in the manifolds 80, water is then introduced at 800 lbs. per square inch pressure into manifold 98, (this having been found suitable for polypropylene) which soli,difies at least the sur-face of the plastic. Drive shaft 20 is now rotated at approxi-mately 800 rpm to move the knives around the face 154 of the -~
extrusion die 38. At the same time, water is being introduced at conventional pres~ure (such as 100 lbs per square inch) into the pipe 24 which will flow through the bore 145, through the holes 254, between the spacing 190 and across the face of the die. This will further chill the plastic, thus facilitating the proper pelletizing thereof. At the same time, the in-flow o water will fill the casing 16, and as it emerges via outlet pipe 26, it carries with it the pellets of plastic.
The combined water and pellets are then processed to separate them, and the pellets are transferred to a drying chamber, while the water is then returned to the case 16 via , -, :. . , , -- . - :::- , - , the pipe 24, a suitable type of water pump being provided for ~ -this purpose. ~
This pelletizing operation is continued so long as -plastic is being supplied from the extruder to the adaptor 52 and to the die 38.
It is believed that when the plastic enters the orifices for extrusion, it will be at approximately 425F.
There may be a small temperature drop from the plastic tempera-ture of 425 at the entrance to the adaptor, but this loss will not be substantial, and it can be corrected by regulating the temperature of the heating medium in the adaptor and in the manifolds 80.
Other parameters which have worked successfully for ~;
polypropylene are as follows: the inlet water temperature used in the manifold 98 may be approximately 80F. The water pressure of 800 lbs. per square inch has been found to work satisfactorily with polypropylene which is being extruded at a temperature of approximately 400-425F. The water in the casing 16 can be at an approximate temperature o 80F. The knives may be rotated at approximately 800 rpm, but this can be varied somewhat since the speed is not critical. While not shown in the drawings, the speed of 800 rpm may be obtained by suitable gear reduction unit which in turn is driven by a conventional motor.
It will alsa be noted that because the plastic is first extruded through the orifices without any water being present in the manifold 98, the entire die is permitted to heat up to a proper extrusion temperature for the plastic. Once this point has been reached, then the introduction of water in the manifold 98 will not be sufficient to cool the extrusion die to the point the plastic will not flow therethrough. As indicated ~.. ' .
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abov~, what seems to happen is that the outer surface of the plastic within the extrusion sleeves 110 becomes chilled while being extruded, and a solidified wall forms around what seems - '' to be a much softer central core. In addition, it seems that water lies between the inner wall of the extrusion sleeves and the plastic, thus lubricating the passage, of the latter therethrough. ~' While the operation thus described has been directed particularly to the Figs. 1-5 embodiment, the embodiments shown in 6 and 11-12 operate in the same manner, the apparatus of Fig. 6 being the same as that of Fig. 5 except that the sleeves 122 are p,ermanently fastened in place. As to the Figs. 11-12 embodiment, the hot viscous plastic is conducted from the extruder through the conduits 188 and into the manifold 192 from which it enters die 194. Hot oil or other suitable medium , ., is passed through the mainfolds 210 in order to keep th'e die hot, and therefore to keep the plastic in its fluid state. The start up of the Figs. 11-12 apparatus is the same as described above for the former embodiments, and from the former description it will be obvious how this'latter embodiment is thereafter operated. The hot plastic is extruded completely through the sleeves 216 until the extrusion is taking place properly for the particular plastic, and thereafter the cooling liquid is introduced into the manifold to pass through the walls of the sleeves to the interior extrusion bores thereof, with resulting formation of the hardened or solidified plastic outer wall on the plastic being extruded. At the time that the water is introduced into the manifold 212, the knives 246 of this embodiment are rotated to pelletize the plastic as it extrudes.

Cooling and conveying water is introduced into casing 232 via inlet 234, which passes across the die face to emerge through - ~ . ...
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. ~ - , ~036305 the outlet 236 carrying the pellets with it to the proper separation medium.
In view of the above it will be seen that the several objects of the invention are achieved and other advantageous results attained. , It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or aarried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.
As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent vari-ations as come within the true spirit and scope of the invention.

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Claims (8)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Apparatus for extruding thermoplastic material comprising an extrusion die having at least one extrusion orifice, means for forcing said thermoplastic material through said orifice, said orifice having a fluid pervious wall portion, supply means connected to a source of liquid coolant under pressure and operable to deliver said pressurized liquid coolant to said pervious wall portion, said pervious wall portion being constructed to permit passage of said liquid coolant therethrough and into contact with said material within said orifice at such a rate that a part of the coolant evaporates immediately upon contacting the outer surface of said material within said orifice and a residue of the coolant remains liquid to provide a lubricant on said wall portion of said orifice adjacent to said material to facilitate passage of the material therethrough, and means spaced from and operable with said die for severing said material after passage through said orifice.

2. Apparatus as set forth in claim 1, wherein said die includes a plurality of said orifices, each said orifice being connected with said passage means, each said orifice having a fluid pervious wall portion, said coolant supply means being arranged to supply said coolant to all of said walls, and said severing means being operable to sever the material passage through said plurality of orifices.

3. Apparatus as set forth in claim 2, wherein said coolant supply means is operable to deliver said coolant through said walls at a pressure greater than the pressure of the material passing through said orifices.

4. Apparatus as set forth in claim 2, including means for heating at least a portion of said orifices during passage of the material therethrough.

5. Apparatus as set forth in claim 2, wherein each said orifice is defined by a bushing pervious to said coolant.

6. Apparatus as set forth in claim 5 wherein each bushing is detachably positioned in a bore.

7. Apparatus as set forth in claim 1 including means for conveying said material to a locus remote from said die after said material is severed.

8. Apparatus as set forth in claim 1 wherein said severing means is rotating knife means operable to move in a path to engage said material after passage through said orifice.