DE3017337A1 - DEVICE FOR CHANGING SCREEN SETS IN THE OUTLET AREA OF EXTRUDER EXPRESSES - Google Patents

Description

Windmöller & Hölscher, ^ 33 470 g-su

4540 Lengerich " _{6φ May 198O}

Device for changing sets of sieves in the outlet area of extruder extrusion presses

The invention relates to a device for changing sets of sieves in the outlet area of extruder extrusion presses with a screw conveyor mounted in a surrounding housing, with a screw conveyor on both sides of the outlet channel of the Housing located guides in a plane perpendicular to the screw axis displaceable frame in which at least two sets of sieves, each displaceable in the outlet channel, are arranged, and with one of them sealing against the frame its guides in the housing pressing ring arranged on the side of the screw conveyor.

When processing thermoplastic or elastomeric materials by means of an extruder extrusion press, it is known to connect a screening device between the screw conveyor and the extrusion head forming the extruded profile in order to remove impurities withhold and, if necessary, the melting and to improve the homogenizing effect of the screw conveyor in that the melt pressure is increased by the closing resistance caused by the sieve.

In the simplest case, the sieve device, which consists of a from the filter sieves and a so-called honeycomb perforated disk that supports the sieve package formed from them Sieve set is firmly installed in the connecting flange connecting the extruder extrusion press housing to the injection head. With such a construction, it makes cleaning or renewal the filter sieves an interruption of the production and after a longer assembly time a restart of the production required to run without interrupting production during the Operation of the extruder extrusion press the required screen

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To be able to make changes are therefore already a large number been carried out by screen changing devices.

In order to enable continuous operation of the extruder-extrusion press, it is known to have at least two sets of screens to be arranged in a housing and this alternately by adjusting the valves diverting the melt flow to bring to use so that the unused sieve set can be removed, cleaned and reassembled while the melt conveyed by the extruder screw through the another set of sieves flows.

In another known screening device is transverse to In the direction of flow of the melt, a sieve belt is slowly pulled over the flow cross-section of the melt channel and wound up so that the effective screen surface is constantly renewed. This sieve belt wandering through the melt flow however, it is very expensive and the sealing of the contaminated screen belt that is fed in from the outside and withdrawn from the outside is very problematic, since the high melt pressure acts on the feed-through slots of the screen belt.

Another frequently used screen changing device the sieve sets are installed in a so-called cassette pusher, which is positioned transversely to the extruder screw axis Can be shifted by the melt flow that the dirty sieve set pushed out and instead a clean sieve set is pushed into the melt flow. To the side or pushing in the cassette slide consisting of a frame holding the sieve sets can be a hydraulic one Actuating device can be provided. Also with this so-called cassette slide, which is easy to operate,

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the sealing of the sliding frame in the extruder strand housing is problematic because of the unavoidable sliding gap the high melt pressure also has an effect.

To improve the sealing of the cassette slide, it is known to provide sealing rings that can be adjusted for a gap, which, however, are difficult to adjust and, due to the inevitable wear and tear, leak after a certain period of operation will.

In a further known screen changing device, the sealing problem is solved in that between the At the end of the extruder screw and the sieve cassette, a special sealing slide is arranged, which is replaced by an inserted thermoplastic ring with a significantly higher melting temperature than that of the processed melt, self-reinforcing depending on the mass pressure of the melt is pressed against the cassette in that this ring is made of thermoplastic Material with a higher melt temperature acts as a hydraulic cushion. There are now applications for screen changing devices known, in which, for example in extrusion coating systems, the required melt temperatures are so high that the thermoplastic pressure ring is washed out after a short period of operation due to excessive softening and the sealing sleeve is no longer pressed on sufficiently so that the screen changing device becomes leaky.

The object of the invention is therefore to provide a pressure element that is dependent on the mass pressure in a device of the type specified at the beginning to create for the frame-shaped cassette slide that can also be used in extruders with very high melt temperatures and ensures a good sealing effect.

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According to the invention, this object is achieved in that the ring consists of a metallic pipe section, the annular end faces of which are supported on the one hand on the frame and on the other hand on a shoulder of the housing, and that the jacket of the pipe section has convex curvatures in axial section with vertices facing each other. The pipe section according to the invention consists of a resilient metallic material which, due to its special shape, by utilizing the known "archway effect", converts the melt pressure acting within the pipe section into an axial pressure component that reliably counteracts the screen cassette slide formed by the frame depending on the prevailing mass pressure Seals guides. The pipe section according to the invention has a shape similar to a venturi nozzle, although the static pressure predominates so much within the slowly flowing mass that it tends to expand the central area of the pipe section and the pipe section exerts a pressure dependent on the mass pressure on the sieve cassette slide due to its resulting lengthening . ^J

The tube according to the invention can be adjusted by the choice of its different diameters, length and radius design its convexity for various maximum permissible melt pressures.

Advantageous embodiments of the invention have been described in claims 2 to 6.

An embodiment of the invention is explained in more detail below with reference to the drawing. In this shows

1 shows a longitudinal section through a screen changing device an extruder extrusion press,

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FIG. 2 shows a section through the device according to FIG. 1 along the line II-II in the level of the cassette slide and

3 shows a section through the metallic pressure ring in an enlarged illustration.

1 shows a longitudinal section through the end region of an extruder-extrusion press with a sieve cassette. With the end of the cylindrical housing 1 of the extrusion press, the housing parts 3 ¹ , 3 ¹ 'are screwed, in which the sieve cassette 4 is arranged displaceably. The screw conveyor protrudes with its mixing element arranged at its end into the housing part 3 '. In the sieve cassette 4, at least two sieve sets 5 ′, 5 ¹¹ are arranged, which support the actual sieve inserts 6. On the outlet-side housing part 3 ¹ , an extrusion head 9 is indicated schematically, which forms the melt into the desired profile.

The cartridge 4 can be through the schematically indicated hydraulic cylinders 11 operate, which displaces the cartridge, for example, from the position shown in Fig. 2 position to the dashed line position indicated 4 ^1, in which the contaminated sieve set 5 'is replaced with a clean set of sieves which, after Contamination of the sieve set 5 ″ can be withdrawn again into the position shown in FIG.

The pipe section 7 is provided as a self-reinforcing pressure element, the passage _{bore D 1 of which is} arched through to the center with the radius R in the shape of an archway. The radial thickness D _{2 of} this

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"Archway" is dimensioned so that an elastic deformation is possible without the pipe section due to a too high Melt pressure is permanently deformed and destroyed. By means of a known pressure measuring device 12 with switch contacts If the sieve set 5, 6 becomes increasingly dirty, the sieve can be changed automatically by moving the cassette 4 initiated and if the mass pressures are too high, for example if a spray head is accidentally started up that is still too cold 9, the extruder drive can be switched off automatically by a maximum pressure contact of the pressure gauge.

Hardened exchangeable wear rings 8 advantageously ensure that the sealing properties on the cassette 4 not deteriorated by surface wear.

With appropriate dimensions D ^, D-, R and L, the dimensioning of the pipe section 7 to different, maximum permissible melt pressures be interpreted.

In the drawing is a substantially symmetrical piece of pipe 7 shown with the same inlet and outlet diameter. However, it is possible to use the archway effect to use a pipe section with differently large inlet and outlet diameters, depending on the flow channel design between the end of the cylindrical housing 1 and the sieve cassette 4 and the shape of the tip of the snail. Furthermore, the radius of curvature R of the pipe section 7 is to be adapted to the respective conditions.

As a result of the curvature R, the pipe section 7 acts as an axially relatively stiff spring, the length L of which is dimensioned so that after the assembly of the screen replacement parts 3 ¹ , 3 ' ¹ , 4 and 7, the wear rings 8 rest against the cassette 4 with a certain preload, which then increases the contact pressure as a function of pressure by utilizing the archway effect with increasing mass pressure by a certain elongation effect.

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Claims (1)

PATENT CLAIMS Device for changing sets of sieves in the outlet area of extruder extrusion presses with a screw conveyor mounted in a surrounding housing , with a frame that is displaceable in a plane at right angles to the screw axis in guides located on both sides of the outlet channel of the housing? in which at least two sets of sieves are arranged, each slidable in the outlet channel, and with a ring which presses the frame sealingly against its guides in the housing and is arranged on the side of the screw conveyor, characterized in that the ring consists of a metallic pipe piece (7), whose annular end faces are supported on the one hand on the frame (4) and on the other hand on a shoulder of the housing, and that the jacket of the pipe section (7) has convex curvatures in axial section with vertices directed towards one another. Device according to claim 1, characterized in that that the ends of the pipe section (7) are widened by flange-like rings. ο Device according to claim 1 or 2, characterized in that in the area of the outlet-side cross-section of the outlet channel and on the frame (4) 130Ö46 / 0231 ORIGINAL INSPECTED facing end face of the pipe section (7) sealing rings (8) made of hard material are arranged. 4. Apparatus according to claim 3, characterized in that the sealing rings (8) are interchangeable in grooves or paragraphs are supported. 5. Device according to one of claims 1 to 4, characterized characterized in that the annular end faces of the pipe section (7) have different diameters exhibit. 6. Device according to one of claims 1 to 5, characterized in that the wall thickness of the pipe section (7) continuously decreases from its ends towards its central region. 13ÖÖ4S / 02S1