DE29913316U1 - Extrusion machine - Google Patents

Description

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D-81479 Munich

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L814

Extrusion machine

The invention relates to an extrusion machine with at least one extruder screw, which is rotatably mounted in an extrusion chamber of a housing and can be driven rotatably via a drive.

Such extrusion machines are known as single-screw extruders with one extruder screw or multi-screw extruders, in which at least two extruder screws are provided, which are driven in opposite or concurrent directions. The drive is provided from one end of the extruder screw, while the other end is directed towards the extruder outlet. The radial bearing of the extruder screw is essentially provided by the surrounding housing, into which the extruder screw is inserted with a precise fit.

With this conventional bearing of an extruder screw, sliding friction inevitably occurs between the outside of the extruder screw and the surrounding housing wall. In order to reduce this sliding friction, it is well known in the art to provide suitable material pairings between the wall of the extruder chamber and the extruder screw. Usually, a sliding bush made of a high-quality material that is good for sliding friction is used over the entire length of the extruder housing.

Manufacturing such extrusion housings is particularly complex for extruder screws with a relatively large axial extension. Even with a segment-like structure of the extruder housing, precisely manufactured holes up to one meter long must be provided in individual housing segments, into which the bushings are inserted with a defined fit. This is particularly problematic with multi-screw extruders, where the outer circumference of the bushings is no longer cylindrical, but has a cross-section roughly in the shape of a figure eight.

Despite this bearing, which is very complex in terms of manufacturing technology, considerable frictional wear occurs between the extruder screw and the surrounding housing bushing during operation of the extruder. Due to this wear, it is necessary to replace the entire utility model or the worn housing bushing at certain intervals. Due to the complex activities described above, this maintenance work is associated with considerable costs and usually involves the extrusion machine being down for several days.

The invention is based on the object of creating an extrusion machine in which a simple and at the same time low-maintenance bearing of the extruder screw in the housing of the extruder is achieved.

The object is achieved according to the invention by an extrusion machine having the features of claim 1. Preferred embodiments are specified in the dependent claims.

The extrusion machine according to the invention is characterized in that at least one insert element is arranged on a partial region of a wall of the extrusion chamber, which insert element projects radially by a defined amount in the direction of the extruder screw, and that the extruder screw rests against the insert element at least during operation.

A basic idea of the invention is to keep the extruder screw at a certain distance from the wall of the extrusion chamber and to allow sliding friction only at certain, precisely defined points. To this end, according to the invention, insert elements are provided along the wall of the extrusion chamber, which protrude radially from the wall. The extruder screw can rest on the insert element in its rest position and be supported by it, or it can only come into contact with the insert element during operation of the extruder.

This achieves several advantages. Firstly, wear only occurs in certain places, namely on the insert elements. This means that an entire housing bushing is no longer exposed to sliding friction wear, but only individual insert elements, which are specifically arranged at more heavily stressed points and can be easily replaced if necessary. There is also no longer any need for complex housing bushings, which makes the manufacture and operation of an extrusion machine much easier. Secondly, the radially protruding insert elements drastically reduce the contact area between the extruder housing and the extruder screw.

A slight gap between the outer circumference of the extruder screw and the inner wall of the extrusion chamber has no significant influence on the functionality of the

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Extrusion machine. This is especially true if the defined amount of radial protrusion of the insert element preferably has a value between 0.5 mm and 1 mm. Depending on the material to be extruded, larger or smaller gap sizes are also possible.

A preferred embodiment of the invention is that the insert element comprises a particularly wear-resistant material. Since, according to the invention, only small sections of the inner wall of the extrusion chamber are provided with the insert element, relatively complex materials can also be used for this. For example, molybdenum alloys, various other hard metals, wear-resistant plastics or ceramics are suitable for the insert element. This great freedom in the choice of material also provides the advantage of great design freedom for the extrusion screw, since the material combination between the insert element and the screw material is essential with regard to wear behavior.

On the other hand, if a particularly complex extruder screw is used, it can also be advantageous according to the invention if the insert element is made of a relatively soft material. This would have the advantage that wear would then occur almost exclusively on the insert elements, while wear on the complex extruder screw would be almost completely avoided.

For particularly simple embodiments, the insert element can be welded to the wall of the extrusion chamber or formed by build-up welding. However, according to the invention, a preferred embodiment

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in that the insert element is attached to the wall of the extrusion chamber in a detachable and replaceable manner. This detachable attachment of the insert element makes it possible to quickly replace a worn insert element. In this way, the maintenance effort and the necessary interruption of production of the extrusion machine can be drastically reduced.

For this purpose, it is preferably provided that a recess is formed in the wall of the extrusion chamber, into which the insert element can be inserted with a precise fit. The recess can be essentially circular, so that it can be produced in a simple manner by drilling. However, other recess shapes such as rectangular, dovetail or prism grooves are also possible, which on the one hand are relatively easy to produce and on the other hand allow the insert element to be inserted quickly and precisely.

A further advantageous embodiment of the invention consists in that the insert element is axially and/or radially prestressed in the housing. In this way, when different materials are used for the insert element on the one hand and the housing on the other hand, different thermal expansions during operation can be compensated.

For a simple and therefore cost-effective production of the insert elements, the invention provides that the insert element is rod-shaped and arranged in the axial direction along the wall of the extrusion chamber. The insert element runs essentially axially only in a partial section or over the entire length of the extrusion chamber. Depending on the application, several insert elements can be arranged parallel or at an angle to one another.

one another. The insert elements are preferably evenly distributed over the circumference. Of course, in certain cases more complexly shaped insert elements can also be used, which can be curved or spiral-shaped, for example.

It is particularly preferred that the insert elements are arranged in pairs for each extruder screw and that the insert elements are arranged at a distance from one another in the circumferential direction and on both sides of a deflection plane of the extruder screw, the insert elements forming a two-point or two-line support for the extruder screw. In a single-screw extruder, a deflection direction or deflection plane of the extruder screw is determined primarily by its own weight. In such an extrusion machine, the insert elements would be arranged at an angular distance of preferably between 10 and 60 degrees around the cylinder bore.

Multi-screw extruders also have a preferred bending direction or plane, which is primarily determined by the operating pressure between the intermeshing extruder screws. The extruder screws are usually pressed outwards against the housing wall at an oblique angle from the intermeshing area of the extruder screws. Accordingly, these multi-screw extruders have a two-point bearing arranged approximately centrally to the preferred bending direction or preferred bending plane.

A preferred embodiment of the invention consists in that two extruder screws are arranged which are driven in opposite directions and that a two-point or two-line support is provided for each extruder screw.

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On the other hand, for a co-rotating extruder, it has been found to be advantageous according to the invention that a three- or multi-point or three- or multi-line support with three or more insert elements is provided for each extruder screw.

In addition to an axial arrangement of the insert elements, according to a further aspect of the invention, it is possible for the insert element to be ring-shaped or designed as a partial cylinder segment. Ring-shaped insert elements with a relatively small axial extension can be arranged, for example, like sealing rings on the butt joints of the individual segments in a segment-like extrusion housing. Furthermore, the insert elements can be designed as partial cylinder segments which have a circular arc-shaped support surface in cross-section. The circular arc can be, for example, an eighth, quarter, third or half of a circular arc.

In a further embodiment of the invention, it is preferred that the insert element comprises a support surface facing the extruder chamber, which is convex, concave or wave-shaped. With a convex design, a relatively small contact surface with the extruder screw results, so that relatively low friction is achieved. With an insert element with a concave support surface, this can be adapted to the radius of the outer circumference of the extruder screw, so that there is uniform contact across the entire width of the insert element. On the other hand, a particularly strong concave design can also achieve a two-point or two-line support with a single insert element. With a wave-shaped contour, a multi-point or multi-line support results accordingly.

A preferred embodiment further consists in providing cooling channels in the insert element for the passage of a cooling medium. This allows increased frictional heat occurring at the insert elements to be dissipated in a targeted manner, for example by means of cooling water.

The invention is further explained using preferred embodiments which are shown schematically in the drawings. In the drawings:

Fig. 1 is a schematic cross-sectional view through a first extrusion machine according to the invention;

Fig. 2 Cross-sectional views of various insert elements;

Fig. 3 is a schematic cross-sectional view through another extrusion machine according to the invention with counter-rotating extruder screws;

Fig. 4 is a schematic cross-sectional view of another extrusion machine according to the invention with co-rotating extruder screws,

Fig. 5 is a schematic cross-sectional view of an extrusion machine according to the invention with a partially cylindrical insert element and

Fig. 6 is a schematic cross-sectional view of another extrusion machine according to the invention comprising: an insert element with cooling channels.

A first extrusion machine 10a according to the invention with a single extruder screw 11 is shown in Figure 1. In a rectangular housing 14a, a bore

which forms an extrusion chamber 12 and in which the extruder screw 11 is accommodated coaxially with its axis of rotation 17. The outer diameter of the extruder screw 11 is smaller by a defined amount than the bore diameter of the extrusion chamber 12, so that the extruder screw is spaced from a wall 13a of the extrusion chamber 12 over its entire circumference.

For the radial mounting of the extruder screw 11 with a screw flight 16 only indicated schematically,

o a total of six strip-shaped insert elements 20a are arranged at an angular distance of 60. To detachably hold the insert elements 20a, grooves or recesses 15a are made along the entire extrusion chamber 12, into which the insert elements 20a are inserted axially with a precise fit. The position of the insert elements is fixed in the conventional manner, for example by means of clamping screws on the respective end faces of the insert elements 20a. The insert elements 20a are dimensioned such that they protrude radially inwards from the wall 13a of the extrusion chamber 12a and rest against the outer circumference of the extrusion screw 11. A contact surface 21a of the insert elements 20a is concave with a radius which corresponds to the radius of the outer circumference of the extruder screw 11.

According to the invention, the extruder screw 11 rests exclusively on the contact surfaces 21a of the insert elements 20a and is thereby supported and radially mounted during the extrusion operation. In this way, frictional wear between the extruder screw 11 and the housing 14a occurs exclusively on the contact surfaces 21a of the insert elements 20a. This has the advantage that the frictional wear is limited to the contact surfaces 21a,

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whereby the overall frictional wear is significantly reduced by the choice of a particularly wear-resistant material for the insert elements 20a. On the one hand, this reduces the maintenance cycles. On the other hand, worn insert elements 20a can be removed from the recesses 15a and replaced with new insert elements 20a without a lengthy interruption in operation. This also results in the advantage of reduced maintenance effort at relatively low costs for the insert elements 20a to be replaced.

A further advantage of an extrusion machine 10a according to the invention compared to a known extrusion machine with an inserted bushing is the possibility of better temperature control within the extrusion chamber 12. The reduced frictional contact means that less uncontrolled frictional heat is introduced into the extrusion chamber. In addition, tempering holes 18, through which a heating or cooling medium can be passed, for example, can be arranged in the housing 14a very close to the wall 13a of the extrusion chamber 12a. Compared to a conventional extrusion machine with a bushing, a more direct temperature control by a heating or cooling device is thus possible.

Figure 2 shows various alternative cross-sectional shapes for insert elements 20 according to the invention. In the alternative according to Figure 2a, the contact surface is convex, which results in a particularly small contact and friction surface.

In the alternatives according to Figures 2b and 2f, a convex contact surface is provided in a rectangular or circular output element with a radius which is smaller than the radius of the extruder screw.

In this way, two separate contact points are created on the insert element, which is desirable for a particularly favorable support function.

In the cross-section alternatives according to Figures 2c, d and e, the contact surface is designed with a radius R which corresponds to the radius of the extruder screw. A particularly simple design with a convex contact surface is shown in Figure 2g, since the insert element can be produced, for example, by hardening a rod-shaped bar material with a circular cross-section.

A so-called counter-rotating extruder, in which two extruder screws 11 are driven in an opposite direction of rotation according to the arrows P1 and P2, is shown in Figure 3. For this purpose, two holes are made in a housing 14b in an overlapping manner, which create an extrusion chamber 12e, which has the contour of the number 8 in cross section. In this extrusion machine 10b according to the invention, the extruder screws 11 are also arranged at a distance from a wall 13b of the extrusion chamber 12b. The radial bearing of the extruder screws 11 is carried out by two insert elements 20b, on which the extruder screws 11 each rest.

In the direction of rotation shown according to the arrows Pl and P2 around the respective axis of rotation 17 of the extruder screws 11, the material to be extruded is pressed against each other in the upper cutting space 9, so that a high operating pressure is created in this cutting space 9. Due to this high operating pressure, the extruder screws 11 are each pressed obliquely outwards against the wall 13b. This bending direction is indicated by the arrows P3 and P4.

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net. For a particularly good support of the extruder screws, the insert elements 20b are each arranged almost centrally to the bending direction at an angular distance of approximately

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30 to the bending direction. This achieves a very favorable 2-point or 2-line support function.

Figure 4 shows a further extrusion machine 10c according to the invention, which is constructed similarly to the extrusion machine 10b of Figure 3. In contrast to the previously described extrusion machine 10b, the extrusion machine 10c is designed as a so-called co-rotating machine, in which the directions of rotation of the two extruder screws 11 are the same as shown by arrows P5 and P6. For radial bearings, rod-shaped insert elements 20c including the contact surface 21c with an approximately kidney-shaped cross-sectional shape are provided in accordance with the alternative design according to Figure 2f. In contrast to a counter-rotating extruder, a co-rotating extrusion machine 10c does not form a single bending direction for the extruder screws. Depending on the load conditions, at least three insert elements are to be provided over the circumference of each extruder screw 11, wherein in the embodiment shown, two insert elements 20c are arranged in a lower region and two further insert elements 20c are arranged in an upper region along the extrusion space for each extruder screw.

In a further extrusion machine 10d according to Figure 5, an insert element 20d is used, which is designed as a partial cylinder segment. The contact surface 21d has the shape of a quarter circle in cross section, as can be seen from the enlarged detailed illustration. The insert element 20d can be made in one piece over the entire

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Length of the extrusion machine 10d. Alternatively, axial sections, for example with a length of about 10 cm, can be provided, from which the overall insert element is assembled.

Figure 6 shows another extrusion machine 10e with an insert element 20e in which several cooling channels 30 are introduced along the contact surface 21e. A cooling medium can be guided through these in a controlled manner in order to dissipate the frictional heat generated during operation and to avoid overheating of the insert element 20e.

Claims (13)

1. Extrusion machine with at least one extruder screw ( 11 ) which is rotatably mounted in an extrusion chamber ( 12 ) of a housing ( 14 ) and can be driven rotatably via a drive, characterized in that at least one insert element ( 20 ) is arranged on a partial region of a wall ( 13 ) of the extrusion chamber ( 12 ), which insert element projects radially by a defined amount in the direction of the extruder screw ( 11 ), and that the extruder screw ( 11 ) rests against the insert element ( 20 ) at least during operation. 2. Extrusion machine according to claim 1, characterized in that the defined amount of radial protrusion of the insert element ( 20 ) preferably has a value between 0.5 mm and 1 mm. 3. Extrusion machine according to claim 1 or 2, characterized in that the insert element ( 20 ) comprises a particularly wear-resistant material. 4. Extrusion machine according to one of claims 1 to 3, characterized in that the insert element ( 20 ) is detachably and replaceably attached to the wall ( 13 ) of the extrusion chamber ( 12 ). 5. Extrusion machine according to claim 4, characterized in that a recess ( 15 ) is formed in the wall ( 13 ) of the extrusion chamber ( 12 ), into which the insert element ( 20 ) can be inserted with a precise fit. 6. Extrusion machine according to one of claims 1 to 5, characterized in that the insert element ( 20 ) is axially and/or radially prestressed in the housing ( 14 ). 7. Extrusion machine according to one of claims 1 to 6, characterized in that the insert element ( 20 ) is rod-shaped and is arranged in the axial direction along the wall ( 13 ) of the extrusion space ( 12 ). 8. Extrusion machine according to claim 7, characterized in that the insert elements ( 20 ) are arranged in pairs for each extruder screw ( 11 ) and that the insert elements ( 20 ) are arranged at a distance from one another in the circumferential direction and on both sides of a deflection plane of the extruder screw ( 11 ), the insert elements ( 20 ) forming a two-point or two-line support for the extruder screw ( 11 ). 9. Extrusion machine according to claim 8, characterized in that two extruder screws ( 11 ) are arranged, which are driven in opposite directions, and that a two- or multi-point or two- or multi-line support is provided for each extruder screw ( 11 ). 10. Extrusion machine according to one of claims 1 to 7, characterized in that two extruder screws ( 11 ) are arranged, which are driven in parallel, and that for each extruder screw ( 11 ) a three- or multi-point or three- or multi-line support with corresponding insert elements ( 20 ) is provided. 11. Extrusion machine according to one of claims 1 to 6 or 10, characterized in that the insert element ( 20 ) is annular or designed as a partial cylinder segment. 12. Extrusion machine according to one of claims 1 to 11, characterized in that the insert element ( 20 ) comprises a support surface ( 21 ) directed towards the extrusion chamber ( 12 ) which is convex, concave or wave-shaped. 13. Extrusion machine according to one of claims 1 to 12, characterized in that cooling channels ( 30 ) for the passage of a cooling medium are provided in the insert element ( 20 ).