CA1041718A - Method and apparatus for extruding melted plastic mixtures - Google Patents

Abstract

IMPROVED METHOD AND APPARATUS FOR
EXTRUDING MELTED PLASTIC MIXTURES

ABSTRACT OF THE DISCLOSURE

An improved method and apparatus for extruding plastic materials provides for processing a mixture of plastic particles, additives, dyes, and the like by means of an extruder screw to form a melted mass which is moved in a helically-directed stream in a confined space. At a predetermined point, flow-diverting means in said confined space abruptly changes the flow pattern.
Portions of the helically-directed melted mixture advanced by the extruder screw and coming into contact with the flow-diverting means, undergo a contin-uous shearing action and sheared-away portions of the melted material are constantly turned over upon themselves and forced through restricted passage ways of short axial length in a highly turbulent flow pattern. After leaving the restricted passageways, the melted material again moves in a helical path flow. Turbulency thus induced at one or more points in the flow line brings together melted and unmelted particles more effectively and rapidly, and there is further accomplished an improved mixing together of the melted mixture and the additives and other components.

Description

~0~17~
This invention relate~ to an improved method and apparatus for extruding plastic mater~als including mixtures of plastic materials, addi~ives, dyes and the like, and more particularl~, the invention is concerned with processing mixtures of plastic material and other components wherein mel~ing of the materials is accomplished by generating suitably high melting temper-, ,:
atures through frictio~ and compression exerted by means of an extruder screw - in a cylindrical body of the class commonly referred to as an "extruder barrel".
- It is found that processing of plastic materials in this manner may ~ -develop difficulties in bringing together melted and unmelted particles in a satisfactory manner, and in accomplishing a degree of mixing which provides for the incorporation of additives, dyes and other substances distributed in a ; substantially uniform manner in the molded product.
: It is an object of the invention, therefore, to provide an improved method and apparatus for extruding plastic materials and to devise a mixing -~ technique for more effectively bringing together and mixing melted and unmelted plastic materials in the presence of additives, dyes and the like. The invention provides an improved extruder screw apparatus for processing plastic ~ , i mixtures, and for inducing a turbulent 10w pattern at one or more points in ' the path of flow of a melted mixture.
i 20 The invention also relates to an improved method of constructing ~j and assem~ling an extruder screw apparatus.
The quality and appearance o extruded plastic products will thus be improved.
The nature of the invention and its other objects and novel features will be more fully understood and appreciated from the following description of a preferred embodiment of the invention selected for purposes of illustra- ' ~ tion and shown in the accompanying dra~ings, in which:
;;~ FIGURE 1 is a cross sectional view showing a plastic extruding :", -, . ..
~crew apparatus and illustrating flow-diverting means of the invention com-bined therewith;

` FIGURE 2 is another cross sectional view illustrating the flow-diverting ring means of the inventlon on a somewhat larger scale;

FIGURE 3 i8 a cross sectional view taken on the line 3--3 of , -FIGU~E 2. ~ ~ 4 ~
~IGURE 4 is a cross section taken on the ~ine 4--4 of PIGURE 5;
FIGURE 5 is a ~ragmentary cross-sectional view of the flow-divert-ing means of the invention;
FIGURE 6 is a cross-sectional view taken on the line 6--6 of ; FIGURE 5;
FIGURE 7 located on the same sheet as FIGU~E l, is a detail per- ;-spective view of the diverter rin~ means shown in FIGURES 1--5 inclusive;
FIGURE 8 is a diagrammatic view illustrating a helically directed flow of plastic material passing through the flow-diverting means of the invention;
FIGURE 9 is a detail view illustrating diagrammatically a shearing flow pattern set up in melted material in accordance with the method of the :
invention;
FIGURE 10 is a detail vie~ of a ring member having reversely formed - vanes;
FIGURE 11 is a sectional vie~ illustrating a~other form of exeruder apparatus; ! .,^ ' , FIG~RES 12, 13 and 14 illustrate a modified form of diverter ring means in which diverter vanes are formed ~ith a helical shape;
FIGURES 15 ana 16 illustrate diverter vane means associated ~ith an extruder barrel by a clamping device;
FIGURES 17 and 18 illustrate a further modification in ~hich the ' ' diverter vanes are formed integrally on a diverter ring member;
FIGURE 19 is still another detail modification in which diverter vane meanq extend both inwardly and outwardly of the ring member.
I have found that the ob~ectsnoted above may be reali~ed to a vsry satisfactory degree by inducin~ a region of turbulency in a flow o mel~ed material. In the invention methods, a melted mixture of plastic materialj additives, dyes a~d tha like is moved throu~h an extruder screw apparatus in a helically directed stream in the conventional manner. At a predeterminea point or point9, however) the flow pattern i9 abruptly interrupted by flow- , divertin~ means. Portlon~ of the melted mixture advanced by the extruder ' ~' . , screw and comlng in~o contact with the flow-diverting mec~ns undergo a contin-- uous shearing action.
; Sheared-away portions of the me:Lted material are constantly turned over upon themselves and forced through restricted passageways of short axial - length to induce a highly ~urbulent fl~w pattern. Turbulency thus induced a~ .
one or more separated points in the flow line brings together melted and unmelted particles more effectively and rapidly and there is further accom-plished a significantly improved mixing together of tke melted ma*erial9 additives, dyes and the lika.
In carrying out the method of the invention, I have devised a ... .
: special ~orm of extruding apparatus which includesg in combination, an extruder barrel, an extruder screw specially formed with stepped-~own .
portions of restricted.diameter, and flow-diverting means located around the extruder screw portions of restricted diameter and held in stationary.relationship.to.the.inner.peripheral surface of tne extruder ~`
barrel.
The flow-diverting means may, for example, comprise a plurality of flow-diverting blades or vanes supported in a stationary position inside of the -extruder barrel by means of an annular retaining body or ring which is located around the screw portions of reduced diameter. It should be understood that the invention is not limited to the use of an annular retaining body, and stationary vanes may be associated with the extruder barrel in other ways, and the method of diverting flow to induce turb`ulence may be carried out with other vane structures, as hexeinafter described.
Referring more in detail to the method and apparatus illustrated in - ~IGURES 1 through 9, numeral 2 denotes an extruder member formed with cylindri-cal barrel having a hopper portion 4 into which plastic material is introduced together with additivesl dyes3 and the like. An extruder screw member 6 is rotatably mounted in the barrel and driven by suitable power driving means, for example, through the pulley 8. At the outer end of the barrel 2 is located a die member 10, through which melted material may be extruded to form an extruded body 12 of some desired shape.

In accordance with one form of the invent~on9 the extruder screw 6, - 3 ~

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as best sho~m in FIGURES 2 and 5, i6 ~o~med with stepped-down portions 6a, 6b, 6c, 6d and 6e of progressively smaller diameters.
In combination with this spPcially formed ext~uder screw con-struction, I further provide fl~7-diverting means consistlng of one or more annular supporting bodies or retaining rings on which are mDunted a plurality of flow-diverting vanes. In FIGUR~ l, two retaining rings have been shuwn and indicated by the nu~erals 14 and 160 These retalning rings are all si~ r,and as noted in FIGURES 1 through 7, the retaining ring 14 is constructed and arranged to encircle the extruder screw portions of restricted diameter. It is pointed out that the inner diameter of rin~ 14 is greater than the diameter of the stepped-down portions 6a, 6b, 6c, 6d, so that the inner peripheral portion of the ring portion 14 is located in ~lightly spaced relation to the adjacent stepped-down extruder screw surfaces, and the ring is, therefo~e, loosely supported and can be moved a short distance along the screw in either direction. It will be understood that this lDose fitting may be desirable in some types of extruding. ~7ever, it should be further observed that the inner diameter of ring portion 14 at one end, i.e., the left hand end as viewed in FIGU~E 1, ls less than the diameter of those portions of the ;
extruder screw which have been reduced at 6a, so that the ring may be displaced -rearwardly only a short distance before being engaged and held by the portion 6a.
At its opposite end, i.e., the right hand, as viewed in FIGUR~ 1, the ring portion 14 is formed with an annular abutment part 14c which projects ,. ~
radially inwardly and is of a diameter only slightly ~reater than the diameter of portions 6d and is of a diameter less tha~ 6e. This si7e relationship provides for the abutment part 14c solidly engaged against adjacent relleved sicrew surface 6f, thus preventing any ~or~7ard displacement beyond this engaged position. , ',,"
As one method of assembling ring 14 around the extruder screw with the reduced diameters described above, the ring 14 may be made from ~70 half sections whloh are ~oined together, for example, by lines of welding 14a and 14b, as is most clearly sh~7n in FIGURE 7. This provides for the half . ~ ;
sections and vanes being separately constructed and secured around the ''" : . ; ., ' ", ' , , ' ' .,'. .; '. '' , ' , " "1 ' ''. ~' .' ' ' ' ' ' ' ~ ' ".

` i(~4~7~8 restricted porkions of a screw at a des~xed point. Thereafter, the extruder screw and ring assembly can be introduced into the barrel 2 as a single u~it.
The flow-diverting vanes earlier referred to are located around the outer peripheral surface of the ring member 14 in circumferentially spaced apart relatlon and are denoted by numerals 18, 20, 22, 24, 26 and 28. These vanes are of generally rectangular shape and may be solidly attached to the ring by welding or they ~ay be formed as an integral part of the ring 14.
Each o~ the vanes is further positioned in an an~ularly disposed manner to facilitate flexing in a circumferential direction inside the barrel 2. ~ach ~ane is also chosen of a len~th such that the outer edges of the vanes all lie in a circle, of a diameter slightly exceeding the diameter of the barrel 2.
' It will be understood that the ring body and vanes are preferably ; made of a metal such as spring steel, and also, the outer edges oE each vane may be slightly beveled as indicated i~ ~IGVRE 7 at 18a, 20a, 22a, 24a, 26a and 28a. With such an arrangement, the extruder screw and ring member may be introduced into the barrel 2 and by slightly rotating the screw in the barrel i ~
and forcing it inwardly, the beveled edges of the vanes may be progressively engagad against inner peripheral surfaces of the barrel with the vanes becoming flexed a~d compressed very slightly. When all of the vanes are compressed and engaged inside the barrel, they become held in tight fr~ctional engagement with the inner peripheral surace of the barrel 2 to constitute stationary flow~
diverting surfaces with the extruder screw being free to rota~e inside of the ring member 14.
In operation9 a mixture of plastic particles, additives, dyes and the like is introduced through the hoppe~ 4. Heating takes place with heat being externally applied or generated by frictional pressure of the extruder screw 6 turning in the barrel 2. Ihere is thus induced a helical flow of the melted mixture indicated at F in FIGU~E 8 wherein a flow path of generally helical configuration has been indicated diagram~atically. It will be observed ~hat at a predetermined point, this helical flo~ is brought in~o contact with the flow-diverting vanes described as will be evident from an inspection of the dotted line in FIGURE 8. As suggested in this fig~re9 fully melted particles mixed with partially melted particles approach the ~-anes, and por~ions of the .: .

~ mixture are continuously ~e~re~ a~a~ h t~e sheared~away portions being ; turnea over and forcedthrough short angularly dlrected passageways defined by the spaced apart vaneæ. In thus abruptly chan~ing t~e directi~n of flow of the mass, a highly turbulent flow pattern is induced which is found to provide an intense mixing action at a locali~ed region with ~nmelted particles becom-; ing more rapidly fused and mixed with already melted particles.
In additi~n, the additives, dyes and th~ like ara found to be dis-` persed and distributed throughout the mass in a highly uniform manner not here-- tofoTe realized in extruding processes, and the effect of this is evidenced by significantly improved quality and appearance o the product thus extruded.
.' . . . .
As the helical flow of melted mixed material is diverted a very large ~-part of the flow passes between the vanes- ~oWever, small quanities may en~er ; between the stepped-down portions of the screw and the inner periphery of the ring 14. I provideoutlets 31, 33, etc. which are formed through the ring walls -. : .
and through which material may emerge and be mixed together with other portions ; passing through the axial passageways. A second set of outlets is also pro-vided at the forward end of the ring as indicated in the dxawing by numerals -35, 37, etc. to provide for outward flow of material forced against the screw surface 6e. In FI~URE 9, lines are shown in crossed relatio~ship to illustr-ate diagrammatically the diverted flow pattern of sheared material.
In carrying out the method ~f the invention, I have determined that I may control the ex~ruding operation in various ways to obtain different results, depending on the materials to be processed. Thus I may vary the spacl~g of the scre~ flights and their angularity. I may also increase the number of ring and diverting vane units employed, as ~or example, two units such as 32, 34 and 36 in a barrel 2' on a screw 6', as illustrated in FIGU~E
11. FIGURE 11 is also intended to illustrate a screw with a single restricted diameter portion as indicated at 38, 40 and 42. In FIGURE 10 there is Illustr-ated a ring me~ber 37 having reversely curved vanes as 37a, 37b, etc.
In FIGVRES 12 and 13, a modification o~ the invention illustrates a barrel 2" having a screw 6" on which a ring body 14' is provided with vanes as 18l, 20', 22'3 etc. curved, as shown, to extend part way around the outer ring periphery ln an interrupted helical-like manner. This vane arrangement .
provides passageways which tend to wInd around the ring instead of extending linearly. FIGURE 13 also shows the vanes~ curving in a direction from left to right, while FIGURE 14 illustrates vanes as 18", 20", 22", etc. in which the vanes curve from right to left on a ring 14".
In FIGVRES 15 and 16, there is illustrated an extruder screw barrel 50 in which is received an extruder screw 52, having a reduced portion 54. Formed in the barrel 50 are openings as 56, 58, 60, etc. through which are located vanes 62, 64, 66, etc. which are formed as an integral part of ring sections 68 and 70, adapted to be clamped together by means of vanes as 72 and 74 around the ope~ings in the barrel to provide projecting vane ends which lie in spaced relation to the reduced section 54 o~ the screw 52.
This arrangement provides another means of assembling vanes with a ring which is applied externally of the barrel and with the vanes being ~ormed to ex~end radially inwardly~ `
FIGURES 17 and 18 illustrate another arrangement in which a ring member 80 formed in half sections and welded together is provided with vanes 82, 84, 86, etc. This ring member may also be combined with a reduced section 88 of a screw 90 received in a barre~ 92.
In FIGURE 19, still another arran~ement of ring member is shown in which a ring 94, made in half sections and welded together, is co~structed with radially outwardly extending vanes 96a~ 96b, 96c, etc. and also with radially inwaxdly extending yanes as 98a, 98b, 98c, etc.

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Claims (11)

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

1. An apparatus for extruding a mass of melted plastic material, including, in combination, a cylindrical enclosure body for receiving the plastic material, an extruder screw mounted for rotative movement in the enclosure body for advancing melted material along the enclosure body in a helical path of flow, and flow-diverting means located within the cylindrical enclosure body for interrupting the helical path of flow and moving the melted mass through short restricted passageways in a turbulent flow pattern.

2. An apparatus according to claim 1 in which the flow-diverting means is held in fixed relation to the enclosure body.

3. An apparatus according to claim 1 in which the flow-diverting means consists in a plurality of circumferentially spaced-apart vanes.

4. An apparatus according to claim 1 in which the flow-diverting means consists in a plurality of circumferentially spaced-apart vanes and the vanes are supported in a ring member and extend radially-outwardly therefrom.

5. An apparatus according to claim 1 in which the flow-diverting means consists in a plurality of circumferentially spaced-apart vanes and the vanes are supported on a ring member and extend radially inwardly and out-wardly therefrom.

6. An apparatus according to claim 1 in which the flow-diverting means consists in a plurality of circumferentially spaced-apart vanes supported on a ring member and the vanes are formed with a helically curved shape.

7. An apparatus according to claim 1 in which the flow-diverting means consists in a plurality of circumferentially spaced-apart vanes and the vanes are supported on a ring member and the vanes are formed with a reversely curved shape.

8. A structure according to claim 1 in which the extruder screw is formed with an intermediate portion of reduced diameter and said flow-diverting means comprises a ring body located around the reduced diameter portion of the extruder screw, and a plurality of vanes extending between the ring body and the inner peripheral surface and the enclosure body in fixed relationship thereto.

9. In a method of extruding a mixture of plastic particles and additives, the steps which include placing the mixture in a confined space, subjecting the mixture to heat and pressure to provide a melted mixture which is travelled in a helically-directed stream in the confined space, moving the melted material into contact with flow-diverting surfaces, subjecting the melted material to a continuous shearing operation in which sheared-away portions of the melted material are moved through restricted passageways of short axial length to blend the additives and the melted plastic together in a uniformly dispersed relationship.

10. A method according to claim 9 in which diverted material leaving the restricted passageways is thereafter advanced in a helical path of travel.

11. A method of extruding according to claim 9 in which the sheared-away portions are moved in inner and outer streams occurring in concentrically separated relationship.