WO2016174152A1

WO2016174152A1 - Breaker element, screenchanger arrangement, extrusion line and method of extruding an extrusion part

Info

Publication number: WO2016174152A1
Application number: PCT/EP2016/059520
Authority: WO
Inventors: Giorgio Luca GUERRINI; Andrea DE MATTEI; Paolo DENTI
Original assignee: Fabbri, Alessandro
Priority date: 2015-04-29
Filing date: 2016-04-28
Publication date: 2016-11-03

Abstract

The present invention pertains to a breaker element for a belt type screenchanger of an extrusion line, in particular for thermoplastics extrusion, the breaker element comprising: a rotational axis; a perforated breaker wall, which is configured to support a belt type filtering screen inside a melt channel; wherein the breaker wall is, at least in part, curved around the rotational axis, and wherein the breaker wall is configured to be rotated around the rotational axis while supporting a belt type filtering screen inside a melt channel. The present invention furthermore pertains to a screenchanger arrangement comprising such a breaker element. Additionally, the present invention pertains to an extrusion line comprising such a screenchanger arrangement and to a corresponding method of extruding an extrusion part.

Description

Breaker element, screenchanger arrangement, extrusion line and method of extruding an extrusion part

The present invention pertains to a breaker element, a screenchanger arrangement, an extrusion line comprising such a screenchanger arrangement and to a method of extruding an extrusion part.

TECHNICAL BACKGROUND

Although applicable to any kind of extrusion technology, the present invention and the problem on which it is based will be explained in greater detail with reference to thermoplas- tics extrusion.

A screenchanger is a machine to be part of a complete extru^¬ sion line, in particular for thermoplastics. A screenchanger is equipped with a filtering net (filtering screen) , which is intended to retain any impurities contained in the molten material to be extruded. In particular in the field of ther^¬ moplastics extrusion, often recycling thermoplastics materi^¬ al is used. Therefore, retaining impurities is important to achieve a desired product quality.

A screenchanger is intended for filtering screen replacement inside a melt channel. A screenchanger known by the appli^¬ cant is shown in Fig. 1. This screen changer 30 comprises a melt channel 31 in which melt (molten process material) can flow through a housing 32 of the screen changer 30. The mol^¬ ten material is filtered by a belt type filtering screen 33 made of metal, which extends inside the housing 32 and crosses the melt channel 31. Screenchangers 30 of the belt type make the filtering screen 33 advance by inserting a clean and fresh net (screen) section, while the dirty sec^¬ tion is pushed or pulled onwards, out of the melt channel 32.

In the most common extrusion lines, operating pressure val^¬ ues range from 50-60 bar minimum to 450-500 bar maximum. Ac^¬ cordingly, the pressure difference before and after (up^¬ stream and downstream) the filtering screen can reach hun^¬ dreds of bars, depending on the screen mesh as well as on the amount of dirt deposits on the screen - factors that dy^¬ namically determine a change in filtration levels. Standard filtration levels range from 75 to 500 microns. Filtering screens featuring higher filtration levels up to 20 microns are available.

Without support, the filtering screen 33 would immediately break due to the pressure difference, generated by the screen resistance to the melt flow. The filtering screen 33 is therefore laid on a perforated plate, a so called breaker plate 34, as shown by a sectional view in figure 2. The breaker plate 34 allows for melt conveyance through the breaker plate 34 while supporting the filtering screen 33 inside the melt channel 31. Therefore, the breaker plate 34 is perforated by plurality of drillings 35, through which the molten material can pass.

In the screenchanger 30, the belt type filtering screen 33 is made slide on the flat perforated surface of the breaker plate 34. Disadvantageously, due to the pressure difference upstream and downstream the filtering screen 33, the filter^¬ ing screen 33 itself is pushed onto the breaker plate 34. Thus, the dragging force required to make the filtering screen 33 slide on the breaker plate 34 must be higher than the static friction generated by the pressure difference acting on the filtering screen 33 inside the melt channel 31.

The force required to drag the filtering screen 33, which means to exceed the static friction between the filtering screen 33 and the breaker plate, can be up to several dozens of tons per screen cm. Furthermore, the higher the dirt lev^¬ el on the filtering screen 33 is, the harder it is to drag the filtering screen 33. As soon as operating conditions get harder, e.g. pressure difference peaks due to increased fil^¬ tration or higher contamination level, the static friction can become so strong that the filtering screen 33 cannot be dragged without breaking it, since sliding of the filtering screen 33 is prevented by the static frictional force. As a result, the screenchanger 30 stops working.

Belt type screenchangers 30 known by the applicant therefore stop the melt flow for dragging the dirty filtering screen section out and inserting a clean filtering screen section, thus causing a pressure drop and eliminating the static friction on the filtering screen 33. Disadvantageously, this type of screenchanger 30 and/or such methods cannot be used in production systems requiring a continuous and steady flow, e.g. pipe manufacturing. Furthermore, such types are extremely complex from a mechanical and automation point of view . SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to pro^¬ vide for an improved breaker element, an improved screen- changer arrangement and an improved method of extruding an extrusion part.

This object is solved by a breaker element for a belt type screenchanger of an extrusion line, in particular for ther^¬ moplastics extrusion, the breaker element comprising: a ro^¬ tational axis; a perforated breaker wall, which is config^¬ ured to support a belt type filtering screen inside a melt channel; wherein the breaker wall is, at least in part, curved around the rotational axis, and wherein the breaker wall is configured to be rotated around the rotational axis while supporting a belt type filtering screen inside a melt channel .

Furthermore, the object is solved by a screenchanger ar^¬ rangement for an extrusion line, in particular for thermo^¬ plastics extrusion, the arrangement comprising: a melt chan^¬ nel; a perforated breaker element, in particular a breaker element according to the invention, arranged in the melt channel; a screen dragging means for dragging a belt type filtering screen; wherein the melt channel, the dragging means and the breaker element are arranged such that a belt type filtering screen dragged by the dragging means is sup^¬ ported by the breaker element, and wherein the breaker ele^¬ ment comprises a rotational axis and is configured to rotate around the rotational axis while supporting the belt type filtering screen. Furthermore, the object is solved by an extrusion line, in particular for thermoplastics extrusion, the extrusion line comprising: an extruder; a screenchanger arrangement accord^¬ ing to the invention; and an extrusion head; wherein the screenchanger is installed downstream the extruder and up^¬ stream the extrusion head.

Additionally, the object is solved by a method of extruding an extrusion part, in particular by thermoplastics extru^¬ sion, the method comprising the following steps: Continuous^¬ ly conveying melt from an extruder to a screenchanger, in particular to a screenchanger arrangement according to the invention; Conveying the melt through a belt type filtering screen, which filtering screen is supported by a perforated breaker element; dragging the belt type filtering screen along the breaker element for screen changing; and rotating the perforated breaker element around a rotational axis.

One idea of the present invention is to provide a rotating breaker element for a belt type screenchanger, which is able to rotate in such a manner, that the screen does not have to slide on the breaker element in order to change the screen. This eliminates the problem of static friction between fil^¬ tering screen and breaker element, in particular the problem of the static friction becoming stronger at higher dirt lev^¬ els on the screen.

With the rotating breaker element there is no more need to overcome static friction between filtering screen and break^¬ er wall. In contrast, the breaker wall of the breaker ele^¬ ment is moved together, in particular synchronous, with the belt type filtering screen by rotation of the breaker ele^¬ ment. In particular the breaker wall moves together with the filtering screen until a region with less or without a pres^¬ sure difference pushing the filtering screen on the breaker wall is reached.

Thus, according to the present invention, the pressure dif^¬ ference acting on the screen, which keeps the screen pressed against the breaker wall of the breaker element, does not limit the screen dragging any longer. This leads to the chance of increasing the filtration level in an essential way. Furthermore, as another big advantage, the dragging means, can be equipped with reduced size of motors, since working forces/resistances are much smaller. Additionally, the filtering screen can be designed/constructed irrespec^¬ tive of or with less respect of tensile strength. Addition^¬ ally, the present invention offers the benefit of changing the belt type filtering screen with no pressure surges, both downstream and upstream the filtering net. Thus, final prod^¬ ucts requiring top stability (pipes, threads, thin film, etc.) can be achieved continuously.

Changing the screen according to the present invention takes place during continuous conveying of molten process material (melt) through the melt channel, the filtering screen and the breaker element, while the filtering screen is supported by the breaker element.

In particular, the filtering screen covers a curved angular section (angular segment) of the breaker element which is located in the melt channel. Clean belt type filtering screen is fed from one side of this section onto the exter^¬ nal surface of the breaker element. Dirty belt type filter^¬ ing screen is removed to the same extend from the breaker element on the other side of the section. The breaker ele- ment preferably rotates synchronously with the feeding of filtering screen.

To separate the filtering screen from the breaker wall at a dividing point, a separating wedge or a small rotating cyl^¬ inder may be provided.

Advantageous embodiments and improvements of the present in^¬ vention are found in the subordinate claims.

According to an embodiment of the breaker element, the break^¬ er element is cylindrically formed and the breaker wall forms a cylinder barrel of the breaker element. Therefore the breaker element can rotate around its own axis and, ad^¬ vantageously, endless rotation of the breaker element is possible .

According to a further embodiment of the breaker element, the rotational axis is formed collinearly with a cylinder axis of the cylindrically shaped breaker element. Thus, advanta^¬ geously, a very stiff construction of the breaker element is provided and only one pair of bearings is necessary for bearing the breaker element. In particular, the rotational axis additionally can serve as clamp axis for clamping to^¬ gether to parts of a screenchanger housing in order to with^¬ stand the high pressures of the molten process material. For example, the screenchanger housing is clamped together by nuts provided at both ends of the rotational axis, the nuts loading the housing and thus providing for pretension of the housing, which helps to withstand the pressures. Preferably, the nuts further include bearings, in particular roller bearings, for bearing the rotational axis. According to an embodiment of a screenchanger arrangement, the breaker element is configured to support a belt type filtering screen for retaining impurities contained in melt (molten process material) passing the melt channel. In par^¬ ticular, the breaker element completely crosses the melt channel with its outer surface supporting the belt type fil^¬ tering screen. Advantageously, a belt type filtering screen thus can be easily changed just by rotating the breaker ele^¬ ment .

According to yet another embodiment of the screenchanger ar^¬ rangement, the breaker element is configured to rotate to an extend that the peripheral speed corresponds to the dragging speed of the dragging means. Therefore, advantageously, friction between the breaker element and the filtering screen is avoided.

According to a preferred embodiment of the screenchanger ar^¬ rangement, the rotation of the breaker element is driven by the belt type filtering screen dragged by the dragging means. The screen dragging makes the breaker element rotate around its own rotational axis and the filtering screen moves combined with the breaker element up to the point where it separates from the breaker element. Advantageously, the force required to drag the filtering screen is much smaller with a rotating breaker element compared to the force required to exceed static friction between the filter^¬ ing screen and the breaker element. There is only a compara^¬ bly small force necessary to "cut" the melt flow by rotating the breaker element. Therefore, advantageously, the existing static friction force between the filtering screen and the breaker element even can be used to rotate the breaker ele^¬ ment by means of the dragging means dragging the filtering screen. Additionally or alternatively, the breaker element can be driven by a separate motor. E. g. such a separate mo^¬ tor may be provided for driving the rotational axis.

According to another embodiment of the screenchanger ar^¬ rangement, the melt channel continues through the breaker element such that melt passing the melt channel passes the breaker wall at an inlet side and at an outlet side. There^¬ fore, an inner volume of the breaker element forms part of the melt channel. The inlet side is situated downstream an extruder of an extrusion line the outlet side is situated upstream an extrusion head of an extrusion line. Therefore, advantageously, the screenchanger arrangement is well inte^¬ grated into an extrusion line.

According to a further embodiment of the screenchanger ar^¬ rangement, the belt type filtering screen is dragged such that it is supported by the breaker wall at the inlet side. Therefore, advantageously, pressure forces can be abutted by the breaker element, in particular via the rotational axis. Additionally or alternatively, a control unit is provided to control the screen dragging means such that the belt type filtering screen is dragged onwards if predetermined parame^¬ ters, in particular inlet pressure and/or outlet pressure of the melt and/or a predetermined time period, are met. Pref^¬ erably, the filtering screen is dragged onwards in steps and remains in its position as long as said parameters are not met. If the parameters are met, the filtering screen is dragged onwards to the extent necessary to provide the melt channel with a clean filtering screen section of the belt type filtering screen. With stepwise dragging the filtering screen, advantageously, the filtering screen is used very efficiently. Therefore, filtering screen coils can be used for a longer process time and considerable cost for the fil^¬ tering screen can be saved.

According to an embodiment of the method of extruding an ex^¬ trusion part, the perforated breaker element is rotated while the belt type filtering screen being supported by the perforated breaker element. Therefore, advantageously, the conveying process of the melt material does not have to be interrupted for changing the belt type filtering screen in^¬ side the melt channel. Alternatively or additionally, the perforated breaker element is rotated with a peripheral speed corresponding to a dragging speed of the filtering screen. Therefore, advantageously, the filtering screen and the outer surface of the breaker element, in particular the breaker wall, are moved at the same speed. Thus, there is no friction between the breaker element and the filtering screen. In order to achieve a peripheral speed corresponding to a dragging speed, the rotation of the breaker element preferably is driven by the dragging means dragging the belt type filtering screen. In this case, the driving force is transmitted from the filtering screen to the breaker element via the static frictional force between them due to the pressure difference between the inlet and outlet side. Al^¬ ternatively or additionally, a motor may be provided to ro^¬ tate the breaker element.

According to yet another embodiment of the method, the breaker element is cylindrically formed and the rotation takes place around a cylinder axis of the cylindrically shaped breaker element. Therefore, advantageously, endless rotation of the breaker element is possible. According to another embodiment of the method, a perforated breaker wall forms the cylinder barrel of the breaker ele^¬ ment and the melt is conveyed through the breaker element such that melt passes the breaker wall at an inlet side and at x an outlet side. Therefore, advantageously, the step of rotating the breaker element in order to change the filter^¬ ing screen is easily integrated into the extrusion method. In particular, the filtering screen is supported by the breaker wall at the inlet side of the breaker element.

Therefore, the melt can be conveyed continuously through the melt channel and through the breaker element while changing the filtering screen by rotation of the breaker element.

According to a preferred embodiment of the method, the belt type filtering screen is dragged onwards if predetermined parameters, in particular inlet pressure and/or outlet pres^¬ sure of the melt and/or a predetermined time period, are met. Preferably, the belt type filtering screen is dragged onwards in steps. In one step, the filtering screen is dragged onwards to the extent that the melt channel is pro^¬ vided with a clean filtering screen. A next step takes place, when the predetermined parameters are met again. With stepwise screen dragging, advantageously, the filtering screen is used very efficiently, which saves costs for the filtering screen.

All features of the breaker element, the screenchanger ar^¬ rangement and the extrusion line also belong to the method of extruding an extrusion part and vice versa.

The invention will be explained in greater detail with ref^¬ erence to exemplary embodiments depicted in the drawings as appended . The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and to^¬ gether with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The ele^¬ ments of the drawings are not necessarily to scale relative to each other. In the figures, like reference numerals de^¬ note like or functionally like components, unless indicated otherwise .

CONTENT OF THE FIGURES

Fig. 1 shows a perspective view of a belt type continuous screenchanger .

Fig. 2 shows a sectional view through a breaker plate.

Fig. 3 schematically illustrates a perspective view of a breaker element according to an embodiment of the invention .

Fig. 4 shows a perspective view of a screenchanger ar

rangement according to an embodiment of the inven tion .

Fig. 5 shows a sectional view through the screenchanger arrangement of Fig. 2. Fig. 6 shows a top view on the screenchanger arrangement of Fig. 2 and 3 with hidden rotational axis and hidden top part;

Fig. 7 shows a perspective view of a screenchanger ar^¬ rangement according to another embodiment of the invention .

Fig. 8 shows a sectional view through the screenchanger arrangement of Fig. 7.

Fig. 9 shows a detail perspective view on the screenchang^¬ er arrangement of Fig. 7 and 8.

Fig. 10 schematically illustrates a perspective view of a breaker element according to another embodiment of the invention.

Fig. 11 shows a perspective view of a screenchanger ar^¬ rangement according to yet another embodiment of the invention.

Fig. 12 shows a sectional view through the screenchanger arrangement of Fig. 11.

Although specific embodiments are illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent imple^¬ mentations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. Generally, this application is intended to cover any adaptations or variations of the specific em^¬ bodiments discussed herein. Fig. 3 schematically illustrates a perspective view of a breaker element 1 according to an embodiment of the inven^¬ tion. The breaker element 1 comprises a rotational axis 2 and a breaker wall 3. The breaker element 1 is formed cylin^¬ drically with the breaker wall 3 forming a cylinder barrel. A cylinder axis 4 of the cylindrically formed breaker ele^¬ ment 1 is coaxial with the rotational axis 2.

The breaker wall 3 is perforated with a plurality of drill^¬ ings or holes. Furthermore, the breaker element 1 is hollow inside. Therefore, melt can flow through the breaker wall 3 into the inside of the breaker element 1 and exit the break^¬ er element 1 through the breaker wall 3. Accordingly, the perforated breaker wall 3 is configured to support a belt type filtering screen inside a melt channel.

The rotational axis 2 is configured to abut forces on the breaker element 1. Therefore, radial discs 5 forming a top and bottom side of the cylinder form of the breaker element 1, are provided. The rotational axis 2 rotatably bears the radial discs 5, on which the breaker wall 3 is circumferen- tially mounted. In particular, pressure forces introduced at the breaker wall 3 due to a filtering screen (not shown) laid on the exterior of the breaker wall 3 and high pres^¬ sures applied to one side of the filtering screen can be transmitted via the radial discs 5 to the rotational axis 2.

Fig. 4 shows a perspective view of a screenchanger arrange^¬ ment 10 according to an embodiment of the invention, the screenchanger arrangement 10 comprises a melt channel 11 and dragging means 12. The melt channel 11 is formed in a housing 13 which houses the breaker element 1. The melt channel 11 crosses the hous^¬ ing 13 from an inlet side 14 to an outlet side 15.

The dragging means 12 comprises two spindles 16 and 17, which are configured such that a filtering screen coil (not shown) can be mounted on them. The spindles 16 and 17 each comprise an adjusting motor 18 and 19. The adjusting motors 18, 19 each are connected to a tensioning device 20, 21, re^¬ spectively. The tensioning devices 20, 21 are configured to span a filtering screen between the spindles 16, 17 with a desired, predetermined tension. Furthermore, a dragging mo^¬ tor 22 is provided on one side of the housing 13, which is configured for dragging the filtering screen and at the same time rotating the breaker element due to static friction be^¬ tween the filtering screen and the breaker wall 3.

The housing 13 has an inlet slot 23 and an outlet slot 24. A filtering screen spanned between the spindles 16, 17 enters he housing 13 through inlet slot 23, crosses the melt chan^¬ nel inside the housing 13 and leaves the housing 13 through outlet slot 24. The inlet slot 23 and the outlet slot 24 re^¬ spectively are formed with a separate cooling block attached to the housing 13.

Fig. 5 shows a sectional view through the screenchanger ar^¬ rangement 10 of Fig. 2, in particular through housing 13.

As can be seen from Fig. 5, the rotational axis 2 crosses the housing 13 through a bottom part 25 and through a top part 26 of the housing 13. On an external side of the top part 25 and an external side of the bottom part 26, a nut 6 including bearings 7 fixes the rotational axis 2 to the housing 13, respectively. In particular, the nuts 6 are fas^¬ tened to the top and bottom parts 25, 26 by means of bolts 8.

Fig. 6 shows a top view on the screenchanger arrangement 10 of Fig. 2 and 3 with hidden rotational axis 2 and hidden top part 26. Therefore, the breaker wall 3 of the breaker ele^¬ ment 1 is shown. In particular, from the perspective of Fig. 6, an inner side of the breaker wall 3 is depicted.

Furthermore, a screen channel 27 crossing the housing 13 comprises an inlet slot 23 and an outlet slot 24. The screen channel enters the housing 13 at the inlet slot 23 and ex^¬ tends in a direction tangential to the cylindrically formed breaker wall 3. From a point 29 on, where the screen channel 27 reaches the cylindrically formed breaker wall 3, the screen channel 27 extends circumferentially over a section of the breaker wall 3 until a dividing point 28, at which the filtering screen is separated from the breaker wall 3 by a separating wedge. Along this section of the breaker wall 3, the melt channel 11 crosses the breaker wall 3.

In a working state, molten material flowing through the melt channel 11 passes a filtering screen extending through the screen channel 27 and passes the breaker wall 3 supporting the filtering screen at the inlet side 14. The molten mate^¬ rial then passes the interior volume surrounded by the breaker wall 3 and leaves the breaker element 1 through the breaker wall 3 at an opposite outlet side 15.

The molten material reaches the inlet side 14 at a high pressure. Furthermore, the filtering screen has a predeter^¬ mined flow resistance, which increases with the level of contamination of the filtering screen. This results in a pressure difference between the inlet side 14 and the outlet side 15 leading to a pressure force against the filtering screen and the breaker wall 3 supporting the filtering screen. This pressure force is transmitted to the rotational axis 2 of the breaker element 1 via the radial discs 5 and abutted by the nuts 6.

The pressure force leads to a static frictional force be^¬ tween the breaker wall 3 and the filtering screen. This static frictional force is used for rotating the breaker el^¬ ement 3 synchronously together with the filtering screen when the filtering screen is dragged by the dragging means 12.

In a complete extrusion line, such as screen changer ar^¬ rangement 10 is installed downstream of an extruder and up^¬ stream an extrusion head.

The extruder provides for pressurized flow of molten materi^¬ al in that the process material is fed into the extruder through a feed hopper. The material is then molten to be conveyed by an endless screw towards the output barrel end, from which it is pushed out.

After leaving the screenchanger arrangement 10, where the molten material is filtered by the filtering screen, the ex^¬ trusion head imparts the required shape to the final prod^¬ uct, e.g. shapes of film, pipes, strands, granules, or the like .

Fig. 7 shows a perspective view of a screenchanger arrange^¬ ment 10 according to another embodiment of the invention. Fig. 8 shows a sectional view through the screenchanger ar^¬ rangement of Fig. 7.

Fig. 9 shows a detail perspective view on the screenchanger arrangement of Fig. 7 and 8

The general structure and function of the screenchanger ar^¬ rangement according to this embodiment is similar to the screenchanger arrangement of Figs. 4 to 6. In the following, only differences will be explained.

One difference lies in the design of cooling blocks compris^¬ ing the inlet and outlet slots 23, 24. According to this em^¬ bodiment, cooling blocks are now much smaller and partially machined directly on the housing 13 instead of separate cooling blocks as of Figs. 4 to 6. The small design of cool^¬ ing block has the advantage of less blocking tendency of the screen .

Another difference is that the rotational axis 2 does not cross the housing 13 through the bottom part 25 and through the top part 26, but is beared inside the housing 13. The rotational axis therefore abuts in the bottom part 25 and the top part 26.

As a result, bearings 7 on the outside are omitted. In this way, a much simpler and more compact design with closed top and bottom part 25, 26 can be realized. Such a design is in particular suitable for applications where no additional mo^¬ tor acting on the breaker element 1 is needed. Fig. 10 schematically illustrates a perspective view of a breaker element according to another embodiment of the in^¬ vention .

The breaker element 1 according to this embodiment is adapted to the screenchanger arrangement 10 of Figs. 7 and 8. Accordingly, the breaker element 1 compared to the break^¬ er element of Fig 3 has a much shorter rotational axis 2.

Besides the different rotational axis, the breaker element 3 is designed similar to the embodiment of Fig. 3.

Fig. 11 shows a perspective view of a screenchanger arrange^¬ ment 10 according to yet another embodiment of the inven^¬ tion.

Fig. 12 shows a sectional view through the screenchanger ar^¬ rangement of Fig. 11.

This embodiment mixes the alternative cooling block design of the embodiment of Figs. 7 to 10 with the bearing concept for the breaker element 1 of the embodiment of Figs. 4 to 6.

Accordingly, this embodiment comprises a breaker element 1 as of Fig. 3, the rotational axis 2 of which crosses the housing 13 through the bottom part 25 and through the top part 26. On the external side of the top part 25 and on the external side of the bottom part 26, a nut 6 including bear^¬ ings 7 fixes the rotational axis 2 to the housing 13, re^¬ spectively . Furthermore, the cooling blocks forming the inlet and outlet slots 23, 24 are designed small and partially machined di^¬ rectly on the housing 13.

This embodiment is particularly suitable for application, when a stronger force/torque needs to be exerted. In partic^¬ ular, an additional motor acting on the breaker element 1 can be installed.

Although the present invention is completely describes by the above preferred embodiments, the invention is not lim^¬ ited to these embodiments, but may be modified in many ways.

For example, optionally or additionally to driving the rota^¬ tion of the breaker element 1 by the dragging means 12 via the belt type filtering screen, the breaker element 1 may be driven by an additional motor.

Furthermore, for separation of the filtering screen from the breaker wall, alternatively or additionally a rotating cyl^¬ inder may be provided at the dividing point. In particular, such a rotating cylinder may extend in parallel to the rota^¬ tional axis of the breaker element.

Another modification that could be done is to provide addi^¬ tional or to eliminate any rollers at an exit of the screen, e. g. near the outlet slot 24, to move the screen exiting from the housing 13. For some applications, it could be suf^¬ ficient to just draw the screen on a winder with the drag^¬ ging motor 22 without any roller. In case rollers remain, an open area between the housing 13 and the rollers could be closed to have the rollers not in the open air. List of reference signs reaker element

otational axis

breaker wall

cylinder axis

radial disc

nut

bearing

bolt

screenchanger arrangement melt channel

dragging means

housing

inlet side

outlet side

spindle

adjusting motor

tensioning device

dragging motor

inlet slot

outlet slot

bottom part

top part

screen channel

dividing point

point continuous screenchanger melt channel

housing

filtering screen

breaker plate

drillings

Claims

1. Breaker element (1) for a belt type screenchanger of an extrusion line, in particular for thermoplastics extrusion, the breaker element (1) comprising: a rotational axis (2); a perforated breaker wall (3) , which is configured to sup^¬ port a belt type filtering screen inside a melt channel

(ID ; wherein the breaker wall (3) is, at least in part, curved around the rotational axis (2), and wherein the breaker wall (3) is configured to be rotated around the rotational axis (2) while supporting a belt type filtering screen inside the melt channel (11) .

2. Breaker element according to claim 1,

wherein the breaker element (1) is cylindrically formed and the breaker wall (3) forms a cylinder barrel of the breaker element ( 1 ) .

3. Breaker element according to claim 2,

wherein the rotational axis (2) is formed collinearly with a cylinder axis (4) of the cylindrically shaped breaker ele^¬ ment ( 1 ) .

4. Screenchanger arrangement (10) for an extrusion line, in particular for thermoplastics extrusion, the screenchanger arrangement (10) comprising: a melt channel (11); a perforated breaker element (1), in particular a breaker element (1) according to one of the preceding claims, ar^¬ ranged in the melt channel (11); a screen dragging means (12) for dragging a belt type fil^¬ tering screen; wherein the melt channel (11), the dragging means (12) and the breaker element (1) are arranged such that a belt type filtering screen dragged by the dragging means (12) is sup^¬ ported by the breaker element (1), and wherein the breaker element (1) comprises a rotational axis (2) and is configured to rotate around the rotational axis (2) while supporting the belt type filtering screen.

5. Screenchanger arrangement according to claim 5,

wherein the breaker element (1) is configured to support the belt type filtering screen for retaining impurities con^¬ tained in melt passing the melt channel.

6. Screenchanger arrangement according to claim 4 or 5, wherein the breaker element (1) is configured to rotate to an extend that the peripheral speed corresponds to the drag^¬ ging speed of the dragging means (12) .

7. Screenchanger arrangement according to claim 6,

wherein the rotation of the breaker element (1) is driven by the belt type filtering screen dragged by the dragging means (12) and/or by a separate motor.

8. Screenchanger arrangement according to one of the preced^¬ ing claims 4 to 7,

wherein the melt channel (11) continues through the breaker element (1) such that melt passing the melt channel (11) passes a breaker wall (3) of the breaker element (1) at an inlet side (14) and at an outlet side (15) .

9. Screenchanger arrangement according to claim 8,

wherein the belt type filtering screen is dragged such that it is supported by the breaker wall (3) at the inlet side (14) and/or wherein a control unit is provided to control the screen dragging means (12) such that the belt type fil^¬ tering screen is dragged onwards, in particular in steps, if predetermined parameters, in particular inlet pressure and/or outlet pressure of the melt and/or a predetermined time period, are met.

10. Extrusion line, in particular for thermoplastics extru^¬ sion, the extrusion line comprising: an extruder; a screenchanger arrangement (10) according to one of the preceding claims 4 to 9; and an extrusion head; wherein the screenchanger arrangement (10) is installed downstream the extruder and upstream the extrusion head.

11. Method of extruding an extrusion part, in particular by thermoplastics extrusion, the method comprising the follow^¬ ing steps :

Continuously conveying melt from an extruder to a screen- changer, in particular to a screenchanger arrangement (10) according to one of the preceding claims 4 to 9;

Conveying the melt through a belt type filtering screen, which filtering screen is supported by a perforated breaker element ( 1 ) ; dragging the belt type filtering screen along the breaker element (1) for screen changing; and rotating the perforated breaker element (1) around a rota^¬ tional axis .

12. Method according to claim 11,

wherein the perforated breaker element (1) is rotated while the belt type filtering screen being supported by the perfo^¬ rated breaker element (1) and/or with a peripheral speed corresponding to a dragging speed of the filtering screen.

13. Method according to claim 11 or 12,

wherein the breaker element (1) is cylindrically formed and the rotation takes place around a cylinder axis (4) of the cylindrically shaped breaker element (1) .

14. Method according to claim 13,

wherein a perforated breaker wall (3) forms a cylinder bar^¬ rel of the breaker element (1) and the melt is conveyed through the breaker element (1) such that melt passes the breaker wall (3) at an inlet side (14) and at an outlet side (15) ,

the filtering screen in particular being supported by the breaker wall (3) at the inlet side (14) of the breaker ele^¬ ment ( 1 ) .

15. Method according to one of claims 11 to 14,

wherein the belt type filtering screen is dragged onwards, in particular in steps, if predetermined parameters, in par^¬ ticular inlet pressure and/or outlet pressure of the melt and/or a predetermined time period, are met.