WO2014207121A1

WO2014207121A1 - Screw element of a co-rotating twin screw extruder, and corresponding screw and co-rotating twin screw extruder

Info

Publication number: WO2014207121A1
Application number: PCT/EP2014/063556
Authority: WO
Inventors: Serge Maisonny; Roland THETIER; Daniel Durand; Anne-Sophie LE CORRE-LECHEVIN
Original assignee: Clextral
Priority date: 2013-06-27
Filing date: 2014-06-26
Publication date: 2014-12-31
Also published as: FR3007685B1; FR3007685A1

Abstract

The screw element (10) according to the invention comprises a single-piece body (11) which is provided with an inner bore (12) designed to receive a drive shaft rotating about an axis (X-X), such that a plurality of screw elements (7, 8, 9, 10), including the screw element (10), is stacked on said drive shaft. In order to facilitate the production of screws for a co-rotating twin screw extruder, which screws have consecutive threads having a direct pitch and a reverse pitch, respectively, the invention provides for the single-piece body to comprise: two separate axial parts which are opposite one another along the axis, a first part (14) being provided with one or more outer threads (15) having a direct pitch only, and the second part (16) being provided with one or more outer threads (17) having a reverse pitch only; and a connecting zone (18) between the first and second parts, which zone is configured on the outside to connect, transversely to the axis, the, or at least one of the, threads of the first part with the, or at least one of the, threads of the second part.

Description

Screw element for a corotative twin-screw extruder, as well as corotating screw and twin-screw extruder

The present invention relates to a screw element for a corotative twin-screw extruder. The invention also relates to a screw and a twin-screw corotative extruder, including such a screw element.

The invention is concerned with the field of twin-screw extrusion machines, commonly called twin-screw extruders. This type of extruder has two screws, generally parallel, rotating inside an extruder sheath, whose section has the shape of an eight. In this field, there are the twin-screw corotative extruders, in which the two screws rotate in the same direction, and the counter-rotating twin-screw extruders, in which the screws rotate in opposite directions from one another. The invention relates to twin-screw corotative extruders.

For several decades now, twin-screw extruder screws have been made by stacking individual screw elements on two rotating drive shafts, typically splined shafts, which provide torque transmission to the screw elements. Each screw element is characterized by its length, pitch, number of threads and helical direction. There are thus elements of positive pitch screws, and others not negative, sometimes called "counterfeit". Other individual parts are often stacked with the aforementioned screw elements, such as mixing discs, connecting pieces, etc.

Thus, each screw element has a threaded external geometry, which serves to convey the material treated by the extruder, this geometry being of constant characteristic all along the screw element. The use of such individual screw elements has many advantages, among them the ease of their individual machining, the reduction in extruder screw manufacturing costs, and the possibility of abutting different screw elements without dead space between where they would accumulate material processed by the extruder. GB-A-1,125,775 discloses such individual screw elements. This modular structure of the screws, which is preferred for the aforementioned advantages, tends to supplant an older technical approach, which is not concerned by the invention and according to which each screw does not include such abutting elements, but is constituted along its entire length of a single monolithic threaded body, as disclosed in JP-S64 63109, US-A-3,667,733, US-A-5,527,106 and JP-H01 146723.

GB-A-1,125,775 discloses the abutment of a screw member having a direct pitch, or otherwise referred to as a positive pitch, and a screw member having a reverse pitch, or otherwise called not negative. Such abutment is generally considered to be avoided or, at the very least, causes difficulties in implementation: in fact, because one or more threads with a direct pitch of a first screw element precede or follow, directly, one or more threads in reverse pitch of a second screw element, the mechanical stresses transmitted by the treated material to the shaft of the screw and the sheath of the extruder are increased tenfold, in the sense that the stresses resulting from the action of the thread or threads of the first screw element add to those resulting from the action of the thread or threads of the second screw element. This situation typically leads to vibrations of the extruder, or even its accelerated wear, at its singularity region where the screw elements are respectively abutting direct and reverse pitch.

The object of the present invention is to propose a new screw element which facilitates the production of screws for a corotative twin-screw extruder, along which at least one net has a direct pitch and at least one net has a reverse pitch.

For this purpose, the subject of the invention is a screw element for a corotative twin-screw extruder, as defined in claim 1.

One of the basic ideas of the invention is to dissociate the geometrical junction, between at least one thread having a direct pitch and at least one thread having a reverse pitch, of the physical junction between two abutting screw elements. According to the invention, the aforementioned geometric junction is provided in a central zone of a screw element according to the invention, that is to say, more generally, in the current extent of this screw element, while that, on either side of this junction zone along the axis of the screw element, the one-piece body of the latter includes a axial portion threaded with a direct pitch and a axial portion threaded with a reverse pitch. According to the invention, the junction between the threads with direct and reverse pitch is achieved by a connection, transverse to the axis, between the aforementioned threads: in other words, this connection is formed by an external geometry of the element of screw, which projects from the one-piece body of the element in the same way as the threads of the first and second parts are projecting. Such a projecting external geometry serves to convey, from one of the first and second parts to the other, the material treated by the extruder, while avoiding the accumulation of this material between the first and second parts. In particular, according to a preferred embodiment of the invention, which will be detailed later but is not limiting, the aforementioned junction zone extends along the axis of the screw element, thus occupying a third part of this screw element, interposed directly between the first and second parts, and has substantially helical left surfaces which, together, provide the connection between the respective threads of the first and second parts. Whatever the embodiment of the invention, the constraints resulting from the singularity of junction between the respective threads of the first and second parts are supported by the current extent of the screw element according to the invention, more effectively and more stable, in particular by limiting or canceling the vibrations and wear of the extruder at this level. In addition, the screw element according to the invention makes it possible to retain the advantages associated with the constitution of the extruder screws by stacking individual screw elements, namely that the screw element according to the invention is interchangeable and can easily be abutted with other screw elements, which are either pre-existing or in accordance with the present invention.

Additional advantageous features of the screw element according to the invention are specified in the dependent claims.

The invention also relates to a screw for a twin-screw corotative extruder, and a twin-screw extruder corotative, as defined respectively in claims 14 and 15.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the drawings in which:

- Figure 1 is an elevational view, partially schematic, of an extruder according to the invention;

FIG. 2 is a view similar to FIG. 1, illustrating the extruder after its screws have rotated by 180 ° by referring to the configuration shown in FIG. 1;

- Figure 3 is a view similar to Figure 1, illustrating, in isolation, a screw member according to the invention belonging to the extruder of Figure 1;

- Figure 4 is an elevational view along the arrow IV of Figure 3;

- Figure 5 is an elevational view along the arrow V of Figure 4; and

- Figure 6 is an elevational view along the arrow VI of Figure 5.

Figures 1 and 2 show an extruder 1. This extruder 1 is called a twin-screw extruder, in the sense that it comprises two screws 2, which are identical and which, in the embodiment considered in the figures, are parallel to each other. Each screw 2 is mounted in the extruder 1 rotatably on itself about a geometric axis X-X. By means of arrangements, which are known per se and which will be somewhat detailed subsequently, the driving force generated by a unit 4 belonging to the extruder 1 is transmitted to each of the screws 2 so as to, when the extruder is in operation, drive the two screws in rotation on themselves, and in the same direction of rotation for these two screws, so that the extruder 1 is called a twin-screw extruder corotative.

Thus, FIG. 1 illustrates a first angular position of the screws 2 around their axis XX, whereas FIG. 2 illustrates a second angular position of these screws 2, achieved by rotating 180 ° about the axis XX that each of the two screws 2 from the first position.

In a manner known per se, the extruder 1 is used to treat a material to be extruded, this material being introduced, at one or more points, into the upstream part of an extruder sheath, which is not shown on the extruder. figures and inside the internal volume, eight-shaped cross section, which the screws 2 rotate. The material thus introduced into the sleeve is conveyed by the screws 2 to a downstream end of the sleeve not visible in the figures, undergoing a thermomechanical treatment resulting from the action of the screws 2 rotating inside the aforementioned sleeve and, if necessary, the action of means for heating or cooling all or part of the sheath. In FIGS. 1 and 2, the direction of flow of the material treated by the extruder 1 is indicated by the arrow 6.

As clearly visible in Figures 1 and 2, each screw 2 comprises a plurality of individual screw elements, which successively follow one another along the axis X-X. Thus, in the exemplary embodiment considered here, each screw 2 comprises a screw element 10, which is mounted alone in FIGS. 3 to 6 and which will be described in more detail later, as well as referenced screw elements. 7, 8 and 9: the screw element 10 succeeds, in the direction of the arrow 6, to the screw element 7, the rear axial end 10A of the screw element 10 being abutted at the axial end before 7B of the screw element 7, while still considering the direction of the arrow 6, the screw element 8 succeeds to the screw element 9 which itself succeeds to the screw element 10, the forward axial end 10B of the screw element 10 being abutted at the rear axial end 9A of the screw element 9, and the forward axial end 9B of the screw element 9 being abutted at the end rear axial axis 8A of the screw element 8.

It will be noted that in FIGS. 1 and 2, the screw element 7 is indicated only schematically, in the form of a block drawn in dotted lines: this illustrates the fact that, in practice, the embodiment of the screw element 7 is not limiting of the present invention, in the sense that various pre-existing screw elements can be abutted against the rear end 10A of the screw element 10. Moreover, as a variant not shown, the screw element 10 may be the most upstream screw element of the screw 2, which is to say that the screw element 10 is preceded by no other screw element.

In the same way, the embodiment of the screw element 9 abutting against the front end 10B of the screw element 10 is not limiting of the present invention. This being so, in the embodiment considered according to the figures, it will be noted that this element 9 is structurally identical to the screw element 10, while being arranged in the opposite direction, that is to say that the rear end 9A of the screw element 9 corresponds structurally at the end 10B of the screw member 10 and the front end 9B of the screw member 9 structurally corresponds to the end 10A of the screw member 10.

The remainder of the description will take a closer look at the screw element 10, in connection with FIGS. 3 to 6.

The screw element 10 comprises, or, as in the embodiment considered here, consists of a one-piece body 1 1 which connects the ends 10A and 10B of the screw element to each other and which in practice, is made of a metal alloy.

This one-piece body 1 1 is provided with an internal bore 12 indicated in bold dotted lines only in FIG. 3. This bore 12 is centered on the axis XX and axially passes through the one-piece body 1 1 from one side to the other, connecting the to one another the ends 10A and 10B of the screw element. In a manner known per se, this bore 12 is adapted to receive axially and rotate in relation to the axis XX to a complementary shaft, not shown in the figures, belonging to the extruder 1 and connected to the drive unit 4 to be rotated on itself about the axis XX. By way of known example, the internal bore 12 of the screw element 10 is provided with a plurality of axial grooves, distributed around the axis XX and designed to be engaged around corresponding grooves carried by the shaft. mentioned above of the extruder 1. Of course, other embodiments are possible for the bore 12, without being limiting to the present invention.

As indicated in FIGS. 3 to 6, the one-piece body 1 1 of the screw element 10 includes, or advantageously consists of, three parts, which follow each other along the axis X-X, each of which is traversed by a corresponding part of the bore 12, and which are distinguished from each other by the geometry of their outer face.

Thus, a first of the three aforementioned parts is referenced 14 and corresponds to the axial end portion of the one-piece body 1 1, located furthest left in Figures 3 to 6. This portion 14 carries the end 10A of the screw element 10 and extends axially from this end to the other parts of the one-piece body 1 1. The portion 14 is provided with a single helical external thread 15, which wraps around the one-piece body 1 1 with a positive pitch considering the direction of the arrow 6, and this over the entire axial extent of the part 14 In a manner known per se, the net 15 defines geometrically a first cylindrical envelope E1, which is centered on the axis XX and which contains the top of the net, as well as a second cylindrical envelope E2, which is also centered on the XX axis and which includes the bottom of the net. In other words, the envelope E2 includes the entire external surface of the portion 14, not covered by the helical structure of the thread 15, this helical structure extending transversely to the axis XX, projecting from the envelope E2, up to the envelope E1. We note 15A and 15B the opposing flanks of the net 15, each of these flanks corresponding to a helical surface which extends, transversely to the axis XX, from the envelope E1 to the envelope E2, as clearly visible, for example, in FIG.

A second part of the three aforementioned parts of the one-piece body 1 1 of the screw element 10 is referenced 16 and corresponds to the axial end portion of the one-piece body 1 1, located rightmost in FIGS. 3 to 6. This part 16 carries the end 10B of the screw element and extends axially from this end to the other parts of the one-piece body 1 1. The portion 16 is threaded similarly to the portion 14, with the difference that the thread of the portion 16 has a pitch opposite to that of the portion 14. Thus, more specifically, in the embodiment shown on the FIGS., the portion 16 is provided with a single helical external thread 17, which wraps around the part 16 with a reverse pitch considering the direction of the arrow 6, and this over the entire axial extent of the part 16. The top of the net 17 is included in the geometrical envelope E1, while the bottom of the net 17 is included in the geometrical envelope E2, as can be seen in FIGS. 3 to 6. The sidewalls 17A and 17B are noted, opposed to one another, of the thread 17, respectively correspond to helical surfaces extending, transversely to the axis XX, from the envelope E2 to the envelope E1, as clearly visible, for example, in Figure 6.

The third of the aforementioned three parts of the one-piece body 1 1 of the screw element 10 is referenced 18 and is interposed axially between the parts 14 and 16. This part 18 provides a direct connection between the parts 14 and 16, in the sense that the axial extent of the portion 18 is equal to the axial distance separating the respective axial ends, facing each other, of the parts 14 and 16.

As shown in Figures 3 to 6, the part 18 has a complex external geometry, which, in particular, is not revolution.

More precisely, in the exemplary embodiment considered in the figures, the portion 18 is, as clearly visible in FIGS. 3 and 4, provided with a first left external surface 18A, which, transversely to the axis XX, is extends from the envelope E2 to the envelope E1, and which, in the direction of the axis XX, extends over only part of the portion 18, since the axial end of the latter, facing the part 14. This left surface 18A is substantially helical, in the sense that this left surface 18A wraps around the axis XX, and in the same direction as the thread 17 to reverse the part 16. In practice, this left surface 18A does not necessarily correspond to a portion of helix in the strict geometric sense of the term, but, as an advantageous embodiment, this left surface 18A corresponds geometrically to a portion of the leading edge 17B of the net 17. At the axial end of Part 18, turned to Part 14, the left surface 18A intersects the trailing edge 15A of the net 15, forming a tip 19 which extends transversely to the axis XX, from the envelope E2 to the envelope E1.

At its axial end opposite to the tip 19, the left surface 18A is non-tangentially connected to a second left external surface 18B of the portion 18, as can be seen in FIG. 4. This left surface 18B extends transversely to XX axis, from the envelope E2 to the envelope E1. As clearly visible in FIGS. 4 and 5, this left surface 18B is substantially helical and is connected tangentially to the front flank 15B of the thread 15 at the axial end of the portion 18, directed towards the portion 14. In other words, the left surface 18B extends tangentially the front flank 15B of the thread 15 of the portion 14 on an axial portion of the portion 18, towards the portion 16.

As clearly visible in Figures 4 and 5, the portion 18 is also provided with a third left outer surface 18C extending transversely to the axis X-X, from the envelope E2 to the envelope E1. This left surface 18C is substantially helical in the sense that this left surface 18C wraps around the axis XX in the same direction as the thread 15 with a direct pitch of the part 14, and from an intermediate axial level of the part 18 to the axial end of the portion 18, directed towards the portion 16. In practice, the left surface 18C does not necessarily correspond to a portion of the helix in the strict sense of the term, although, as an advantageous embodiment , this left surface 18C geometrically corresponds to a portion of the rear flank 15A of the net 15. At the axial end of the portion 18 directed towards the portion 16, the left surface 18C intersects the front flank 17B of the net 17 of the portion 16, forming a tip 20 which extends transversely to the axis XX, from the envelope E2 to the envelope E1, as clearly visible in Figures 4 and 5.

At its axial end opposite the tip 20, the left surface 18C is non-tangentially connected to a fourth left surface 18D of the portion 18, as can be seen in FIGS. 5 and 6. This left surface 18D extends transversely to the axis XX, from the envelope E2 to the envelope E1. This left surface 18D is substantially helical, in the sense that it wraps around the axis XX in the same direction as the thread 17 in reverse pitch of the part 16, by connecting tangentially to the rear flank 17A of the net 17 at the axial end of the portion 18, directed towards the portion 16. In other words, the left surface 18D extends tangentially the rear flank 17A of the thread 17 of the portion 16 on an axial portion of the portion 18, in the direction of part 14.

In view of the foregoing explanations, it is understood that the left surfaces 18A,

18B, 18C and 18D of the part 18 serve, together, to connect the net 15 of the part 14 in the net 17 of the part 16. In this way, within the extruder 1, in other words when the screw elements 10 belonging respectively to the two screws 2 of this extruder cooperate with each other by interpenetration of the nets 15 and 17 of one of its two elements in the channel delimited by the threads 15 and 17 of the other of its two screw elements, the material treated by the extruder flows from the respective parts 14 to the parts respectively 18, via the respective parts 18. The left surfaces 18A, 18B, 18C and 18D of each portion 18 prevent the accumulation of the material treated by the extruder 1, between the parts 14 and 16. This results in a limitation of mechanical stresses resulting from the treatment of the material flowing along the screw elements 10, avoiding vibrations or accelerated wear of the extruder at these screw elements 10.

Advantageously, in order to balance the operating forces of the extruder 1 at the level of the screw elements 10, the tips 19 and 20 are situated substantially opposite each other about the axis XX, as clearly visible by comparison of Figures 3 and 5. Thus, the penetration efforts of the tip 19 in the treated material equilibrium substantially around the screw element 10, with the penetration efforts of the tip 20 in the material treated. The aforementioned efforts thus tend to cancel out vis-à-vis the screw element 10 considered as a whole.

As an advantageous option, which is also implemented in the exemplary embodiment considered in the figures, each screw element 10 is provided with at least one external machining at its part 16 and / or its portion 18, arranged across the thread 17 and / or at least one of the left surfaces 18A to 18D of the portion 18. In the embodiment considered here, the aforementioned machining consists of grooves 21, which, transversely to the axis XX, are each dug in the net 17 from the top of the latter and which, in the direction of the axis XX, each connect the flanks 17A and 17B to each other, as clearly visible in FIGS. 3 to 6. These grooves 21 allow the material pushed by the direct thread 15 of the part 14 to pass through the part 16 and / or the part 18 with a limited and, advantageously, controlled pressure drop. In practice, the geometric shape and the number of these grooves are not limited to the exemplary embodiment considered in the figures, but may be subject to variants.

Various arrangements and variants to the screw element 10 and the extruder 1, described so far, are also conceivable. As examples:

the order in which the direct-threaded portion 14 and the reverse-pitch threaded portion 16 follow one another along the screw element, considering the direction of the arrow 6 of flow of the material in the extruder is not limited to that illustrated by the screw member 10 above; this is also illustrated by the screw element 9; rather than providing a single thread for the threaded part with direct pitch 14 and for the threaded part with reverse pitch 16, one and / or the other of these parts 14 and 16 may have several threads, respectively with a direct pitch or not reverse, including two or three nets; and or

rather than extending the junction zone between the parts 14 and 16 over an axial extent of the one-piece body 1 1 of the screw element 10, as with the part 18, this junction zone can be essentially contained in a plane substantially perpendicular to the axis XX; in particular, in this case, an embodiment consists in that, in the abovementioned plane, the rear flank 15A of the thread 15 intersects the front flank 17B of the thread 17, forming a point similar to the point 19, and the flank front 15B of the thread 15 intersects the trailing edge 17A of the net 17, forming a tip similar to the tip.

Claims

1. Screw element (10) for a corotative twin-screw extruder (1),

comprising a one-piece body (1 1), which is provided with an internal bore (12) for receiving a rotary drive shaft about an axis (XX) so as to stack on said drive shaft, a plurality of screw members (7, 8, 9, 10) including said screw member (10),

characterized in that the one-piece body (1 1) includes:

two distinct axial parts (14, 16) which are opposite each other along the axis (XX) and of which a first part (14) is provided with one or more external threads (15) exclusively at a direct pitch, while the second portion (16) is provided with one or more external threads (17) exclusively in reverse pitch, and

- a junction zone (18) between the first and second parts, which is externally shaped to connect, transversely to the axis (XX), the or at least one of the threads (15) of the first part (14) with the or at least one of the threads (17) of the second part (16).

2. - A screw element according to claim 1, characterized in that said junction area extends along the axis (XX), constituting a third axial portion (18) of the one-piece body (1 1), which third part is provided with substantially helical outer left-hand surfaces (18A, 18B, 18C, 18D) which, together, connect the or at least one of the threads (15) of the first portion (14) with the or at least one of the threads (17). ) of the second part (16).

3. A screw element according to claim 2, characterized in that one (18A) of said left surfaces of the third portion (18) is wound around the axis (XX) in the same direction as the thread or nets ( 17) at opposite pitch of the second portion (16) and intersects a flank (15A) of one or at least one of the threads (15) of the first portion (14), forming a tip (19).

4. A screw element according to one of claims 2 or 3, characterized in that one (18C) of said left surfaces of the third portion (18) is wound around the axis (XX) in the same direction as the one or more threads (15) with a direct pitch of the first part (14) and intersecting a flank (17B) of one or at least one of the threads (17) of the second part (16), forming a point (20).

5.- A screw element according to claims 3 and 4 taken together, characterized in that said points (19, 20) are located substantially opposite each other about the axis (X-X).

6. A screw element according to any one of claims 2 to 5, characterized in that one (18B) of said left surfaces of the third portion (18) tangentially extends a flank (15B) of one or at least one of the threads (15) of the first portion (14) toward the second portion (16).

7.- A screw element according to claims 3 and 6 taken together, characterized in that said flanks (15A, 15B) are the opposite flanks of the same thread (15) of the first portion (14).

8. - screw element according to any one of claims 2 to 7, characterized in that one (18D) of said left surfaces of the third portion (18) tangentially extends a flank (17A) of one or to at least one of the threads (17) of the second portion (16) to the first portion (14).

9. - A screw element according to claims 4 and 8 taken together, characterized in that said flanks (17A, 17B) are the opposite sides of the same thread (17) of the second part (16).

10. - screw element according to any one of claims 2 to 9, characterized in that the second portion (16) is provided with at least one external machining (21) arranged across the threads or (17) of the second part.

1 1. - Screw element according to any one of claims 2 to 10, characterized in that the third portion (18) is provided with at least one external machining (21) arranged across at least one of the left surfaces (18A , 18B, 18C, 18D) of the third part.

12. - A screw element according to claim 1, characterized in that the junction zone is essentially in a plane perpendicular to the axis (XX).

13. - A screw element according to any one of the preceding claims, characterized by a single thread (15) for the first part (14) and a single thread (17) for the second part (16).

14. - Screw (2) for a twin-screw corotative extruder (1),

having a plurality of screw members (7, 8, 9, 10) stacked on a common drive shaft in rotation about an axis (X-X) of the screw,

characterized in that said plurality of screw members includes at least one screw member (10) according to any one of the preceding claims.

15. - Twin-screw corotative extruder (1),

having two identical screws (2) which are each rotated on themselves in the same direction, each of the two screws having a plurality of screw elements (7, 8, 9, 10) stacked on a common shaft of rotational drive,

characterized in that the plurality of screw elements of each of the two screws (2) includes at least one screw element (10) according to any one of claims 1 to 13.