DE3242708A1 - Single shaft screw extruder - Google Patents

Abstract

A screw extruder for processing polymeric plastics is described, which consists of a screw (2) with several processing zones (10 to 15) and a cylinder (1) with several sections (3 and 7 to 9), the length of which cylinder is matched to the length of the screw (2). The combination of measures to increase especially the flow of solid materials in the feed zone (10) is essential, e.g. the use of a replaceable grooved bush (4), and a shearing and mixing zone (12), which is described in detail, at the end of the compression zone (11), in which annular elements (18; 19), which are mutually supporting at their face sides, on the screw and in the related cylinder section cooperate in a special manner. Varied shearing and dispersion of the material flow, which is under the pressure of solid transport and enters into the mixing and shearing zone in a semiplastic state, achieves complete plastication thereof and extremely fine distribution of the components contained in the material flow. Each annular element (18; 19) has a plurality of chambers (21; 27) distributed on its interior and/or exterior circumference, which chambers are enclosed by helically extending, radial shear webs and axial delimiting webs (23; 29), so that the material flow is deflected several times in an approximately sinusoidal manner with mutual overlapping of the annular elements (18; 19) in the shearing and mixing zone (12) of the extruder in the direction of flow. With opposite pitch of the groove system, i.e. directed against the transport direction, the annular elements (18; 19) act in the sense of baffle elements. Any desired combinations are possible. <IMAGE>

Description

Single-shaft screw press

The invention relates to a single screw press for Drawing in, plasticizing and pressing out of fusible, high-polymer plastics according to the preamble of claim 1.

Such screw presses, which consist of a cylinder and one in it rotatably mounted screw with a feed, a plasticizing and a Discharge zone defining screw thread, which includes a mixing zone, are known from the prior art.

A technical and economic one has existed for some time Need to define the output of a screw press with a given Increase screw cross-section or with the same cross-section and throughput the reduce the required drive line (val.

New Screw Designs Improve Extrusion Efficiency, Modern Plastics International, January 1981, pages 50 and 51).

It is known to have different types in the feed zone of a screw press To use pull-in aids, in particular grooved bushings with longitudinal grooves or helical grooves, to increase the feed rate of the screw press for granulate, powder or melt increase (like. "Kunststoffe", Volume 61, 1971, Issue 2, pages 104 to 107; H. Domininghaus "Progressive Extruder Technology", VDI-Taschenbuch T 14 (1970), pages 39 to 43); but it turns out that the subsequent snail zones in one large increase in the intake capacity and the mass flow is not sufficiently homogenized in the discharge zone to achieve a qualitative to produce high quality product. It was also found that parts of the absorbed granulate is not completely melted and solids and Melt were not properly separated.

Numerous attempts have therefore been made to add additional to the screw To arrange kneading, plasticizing or shearing elements with which not yet melted Particles should be treated on their way to the screw tip.

Sensitive plastics are, however, thermally damaged as a result. Furthermore, homogenizing sections are in correspondingly extended discharge zones to equalize the temperature of the plasticate or the melt and in particular with high quality requirements when mixing additives or fillers related. Such measures cannot prevent high volume outputs that solid particles reach the discharge zone unmelted.

In the reference mentioned at the beginning of constructions reported where the mass flow between the worm gear and one with this cooperating and slowly decreasing cross-section in the cylinder is also moved in the radial direction.

Similar considerations have already been made in GB-PS 842 692. However, such constructions have a very complex construction and are few flexible when converting to processing other materials.

The object of the invention is to provide a single-shaft screw press to create the preamble of claim 1, in which the transport and plasticizing function the screw are clearly separated and achieve a substantial increase in the mass flow and a high quality, i.e. uniformly melted and in terms of Temperature and composition of fully homogenized melt for production high quality products are produced.

The solution to this problem takes place in the characterizing part of the claim 1 specified combination of known features.

The advantage of the specified solution over the known prior art Technology lies in the fact that the screw press has a surprisingly high throughput and highest quality on the one hand very flexible to the different needs the processor can be adapted and on the other hand at the manufacturer of the screw press the components are mass-produced in larger quantities and then conform to the material or can be assembled according to the application.

The invention is for this purpose in particular by a modular Structure of cylinder and screw according to claims 2 and 3 advantageously developed.

From a technological point of view, the combination of the The advantage achieved is that the shearing and mixing device used, which is known from US Patents 4,128,342 and 4,253,771 are known in their basic structure in a similar way, at the end of the conversion or plasticizing zone ensures that this screw zone can no longer be passed over by the flow of solids from the feed zone and Solid particles no longer get into the discharge zone.

In particular, it is under the high pressure of solids pumping delivered mass flow in the semi-plastic state compulsorily in the groove systems mixed on the screw and in the cylinder and again and again at those delimiting the grooves Shear bars sheared and distributed. As a result, this leads to an extraordinary even distribution and mixing of all, even very small, proportions of the feed material before the plasticate or the melt reaches the discharge zone, without damaging the thermoplastic, as observed with conventional shear parts will.

Even small amounts of additives such as antioxidants, color pigments or additives to increase the electrical conductivity, to reduce the Flammability or the like.

are very finely distributed in the discharged melt, so that differences in concentration, especially when using several mixing rings, can no longer be determined.

The repeated shearing of the high polymer plastic on the At the end of the plasticizing zone, it sometimes has very different thermal stresses. It is therefore suggested that additional thermoplastics be used for critical processing still to provide a distributive mixer to control the melt temperature in a special homogenizing zone further to equalize and possibly radial temperature under divide completely to dismantle. Such mixers are, for example, as LTM mixing parts (Low Temperature Hixer) known (cf.

"Kunststoffe", Volume 63, 1973, Issue 6, pages 355 to 361, in particular Fig. 7). The advantage of such mixing parts is that the radial temperature equalization between the melt layers near the screw core and near the cylinder without any noteworthy Pressure losses and thus takes place without a high expenditure of energy.

Claims 3 to 11 specify preferred embodiments of the mixer integrated into the screw press as a mixing and shearing section, the from a plurality of ring elements with in the axial and circumferential directions as well as on Groove bottom closed chambers - both in the cylinder and on the screw - consists.

Due to the constantly changing flow in the radial direction - from the ring element rotating with the screw into the stationary ring element in the cylinder on the one hand and from there back into the overlapping chambers, subsequent ring element on the worm on the other hand, etc. - one takes place exactly adjustable shear stress and a distribution of all components of the material flow with easy assembly and high flexibility of the screw press.

By the arrangement of the groove systems specified in claims 7 to 11 in such a way that the circumferentially distributed shear webs on multiple helical lines are next to a conveyor or. Traffic jam effect also achieved that one Chamber of a groove system in the cylinder simultaneously with several chambers of a groove system is in communication on the screw, so that the melt flow is never interrupted and critical pressures are excluded in individual chambers.

Finally, a screw press is proposed in claim 12 with the features specified in the previous claims in the packaging of polyolefins, in particular of polypropylene, and preferably for uniformity to use the mean molecular chain length following the polymerization, whereby a previously necessary process step is carried out with less effort can be.

The invention is illustrated below with reference to an exemplary embodiment Illustrative drawing explained in more detail.

It shows; 1 shows a screw press according to the invention in longitudinal section; Fig. 2a / ring elements at the end of the plasticizing zone of the 2b screw according to Fig. 1 in Axialschnittg Fig. 3 shows the cross section of a ring element according to Fig. 2a or 2b Fig. 4a / Axial sections of ring elements at the end of the 4b plasticizing zone in the cylinder the screw press according to Fig. li Fig. 5 shows the cross section of a ring element 4a and 4b, respectively.

The screw press according to Fig. 1 is both in terms of its cylinder 1 as well as with regard to their screw 2 constructed in a modular manner. This is how the Cylinder 1 from a first cylinder section 3, in which a temperature-controlled, in particular coolable, grooved bushing 4 is arranged interchangeably. He has an opening 5 for the outlet of the material feed hopper 6. On the cylinder section 3 are on on the one hand the transmission, not shown, with the drive motor and on the other Page several other cylinder sections 7 to 9 interchangeably flanged, see above that its length can be adapted to the screw 2 if necessary. The molding tool at the end of the cylinder 1, as well as its heating and cooling, are for reasons not shown for better clarity.

The screw 2 rotatably mounted in the cylinder 1 consists of several interchangeably assembled screw sections, in particular a feed section 10, a conversion section 11 (compression zone) with decreasing screw flight volume, the dispersing shearing and mixing section 12, the discharge section 13 (metering or pumping zone) and a homogenizing section 14 with mixing cams of known design, which extends to the screw tip 15.

The individual sections can - depending on the diameter and Length-made in one piece or made individually and in a known manner by tie rods, parallel key and screw connections (e.g. DE-PS 23 40 499) or the like.

be composed.

The screw flight 17 defined by the screw flight 16 runs continuously from the intake section 10 to the end of the conversion section 11 is then in Shearing and mixing section 12 interrupted and continued again in discharge section 13, in order to build up a constant pressure there and discharge a metered mass flow.

It should be mentioned that the screw is not assembled in a modular manner must be, as it is easily accessible for processing the groove systems. but she is - More flexible, especially for trial operation and variable use than a screw that consists of a single component.

The ring elements 18 arranged in the shearing and mixing section the screw 2 and 19 in the cylinder 1 are shown enlarged in FIGS. The ring elements 18 and 19 are available in two different basic designs Figures 2a and 2b and Figures 4a and 4b, respectively.

In both cases, however, the ring elements 18 have the same inner and outer diameter and an axial groove 20 to hold them against rotation on the worm 2 secure.

On the circumference they have - as FIG. 3 shows in cross section - chamber-shaped Recesses 21, which between radial shear webs 22 on the one hand and end-face, axial shear or. Limiting webs 23 (Fig. 2) are formed on the other hand. the Recesses 22 and the laterally delimiting shear webs 22 run on the by the outer diameter of the ring element 18 defined cylinder section in of the type of a multi-start helix which, according to FIG. 2a, has a positive slope (Arrow 24) and according to Fig. 2b has a negative slope (arrow 25). The recesses 21 have a rounded, partially oval or elliptical cross-section Form (Fig. 3), the depth of which decreases towards the shear webs 23 (Fig. 2a, 2b) and then runs out completely. Depending on the type and purpose of use, several Ring elements 18 of the same construction can be arranged, i.e. that of the shear bars 22 is the defined slope (arrow 24) of the ring elements 18 lined up one behind the other running concurrently with the screw flight 16 or this slope (arrow 25) of the ring elements 18 is opposite to Fig. 2b to the screw flight .16. But it is special also possible to combine ring elements 18 according to FIG. 2a with those according to FIG. 2b in a shearing and mixing section 12 of the screw 2 to apply and so sections with to combine a conveying effect with those that cause a congestion effect.

The ring elements 19 of FIGS. 4 to 5 are in a manner analogous to that Ring elements 18 of FIGS. 2 to 3 are formed. Your inner diameter is like this dimensioned that they the ring elements 18 with an extremely small clearance (shear gap) include. They have an axial groove 26 on the outer circumference Definition the ring elements in the cylinder section 8 - by a feather key, not shown or the like - on. Distributed on the inner circumference are in analogy to the ring elements 18 2 and 3, the recesses 27, which between the radial shear webs 28 and the axial delimitation webs 29 are present as closed chambers all around. Included run - as shown in FIGS. 4a and 4b - the recesses that are only open towards the screw 27 on multiple helical lines either in the positive screwing direction (arrow 30) or in the negative screwing direction (arrow 31) .. The ring elements 19 can in Cylinder section 8 are present in such a way that! # The screwing direction of the circumferentially distributed, radial shear webs 28 in the same direction or in opposite directions to the screw web 16 or the screw groove direction of the radial shear webs 22 of the on the screw 2 is arranged ring elements 18 is. But it is also possible to alternate the ring elements 19 according to FIGS. 4a and 4b or to assemble alternately in groups, so that in cooperation with the Ring elements 18 of the mixing section 12 of the screw 2 with regard to the effects Conveyance, stowage, dispersion and shear varied as required and the one to be processed Polymers can be optimally adapted.

In one embodiment of a screw press according to the invention with a screw diameter of 90 mm, the screw had a length of L / D # 30, thus Lss 2700 mm. The screw had a feed zone 2 with a total length L = 5 D = 1350 mm. The cylinder 1 had a grooved bushing 4 to increase the solids delivery. The conversion or compression zone 11 had a length of L = 6.6 D = 595 mm.

This was followed by the shear and mixing zone of L ty 3.1 D 280 mm, a discharge section 13 with a length of L = 3.6 D = 315 mm and another one without a screw flight Homogenizing section 14 with radial mixing cams (LTM section), which has a length L = 1.7 D = 155 mm had. The shear and mixing zone consisted of three ring elements 18 and 19 respectively on the screw and in the cylinder section 8, their groove systems according to the arrows 24 and 30 in Fig.

2a or 4a in the direction of the screw flight - and thus effective for the promotion were arranged. Behind it there were three ring elements with axially parallel ones Groove systems. The outer ring elements had 12, the inner ring elements 10 Grooves. The width of the grooves was 12 mm and 16 mm, respectively.

In a comparative experiment, Hostalen PP polypropylene was used 1060 F natural, extruded with a melt index (MFI) of 8 g / 10 min. The throughput was 1,477 kg / h at a screw speed of approx. 200 min. The power consumption was determined to be 123 KW. The temperature of the melt at the exit of the extruder was approx. 2680 C. With a passage depth in the discharge section of 5 mm, the specified throughput at the entrance of the shear and mixing zone a pressure of 320 bar and a pressure of 95 bar + 0.5 bar measured at the end of the screw press. The temperature at the end of the melt channel showed a maximum gradient of ß t = + 20 C between melt layers close to the core and cylinder. The homogeneity of the extrudate achieved by the addition of color pigments was judged was excellent and showed one very good distribution of the color additives in the melt over the entire melt channel cross-section.

With a screw press of a similar design (L / D; s30 and 90 mm screw diameter) for the production of stranded wires from the plastic used in Experiment 1, which however not the inventive combination of a grooved bushing in the cylinder section the feed zone and the described shear and mixing zone are maximum only achieved throughput rates of 240 kg / h. The power consumption of the drive motor is - depending on the melt index of the polypropylene - 50 to 60 KW. At a Machine with grooved bushing, but without the described shear and mixing zone although the volume output can be increased, but the extruded mass flow contained as yet unmelted granulate and was in terms of its homogeneity and temperature constancy completely insufficient for further processing.

LIST OF REFERENCES 1 cylinder 2 screw 3 cylinder section 4 grooved bushing 5 opening 6 material feed hopper 7 cylinder section 8 cylinder section 9 cylinder section 10 feed section (feed zone) 11 conversion section (compression zone) 12 Shear and mixing section (mixing zone) 13 Discharge section (metering, discharge, Pumping zone) 14 homogenizing section 15 screw tip 16 screw flight 17 screw flight 18 ring element (for screw) 19 ring element (for cylinder) 20 axial groove 21 recess (Chamber) 22 radial shear bar 23 axial shear bar, limiting bar 24 arrow (pos. Screw direction) 25 arrow (neg. Screw direction) 26 axial groove 27 Recess 28 radial shear web 29 end area, axial shear web; Limiting bar 30 arrow (pos. Screw direction) 31 arrow (neg. Screw direction)

Claims (12)

R e p e rtio ns 1. Single-shaft screw press for drawing in, plasticizing and extrusion of fusible, high-polymer plastics, in particular thermoplastics Plastics such as polyolefins, polyamides or polyesters, consisting of an in a cylinder rotatably mounted screw with a feed, a plasticizing and a screw flight defining a discharge zone, which comprises a mixing zone by the features present in combination that 1. in the feed zone (10) a the friction between the plastic and the cylinder (1) increasing the groove system, preferably a grooved bushing (4) with axially parallel or coiled grooves, one Feed pocket or the like. Is present, and that 2. between the feed zone (10) and the Discharge zone (13), preferably at the end of the plasticizing zone (11), a shear and Mixing zone (12) is arranged, the at least one stationary, circumferentially distributed Groove system in the cylinder section (8) on the one hand and at least one with the screw (2) rotating and with. the first cooperating, similar groove system a cylindrical web-free section (12) the screw (2) on the other hand includes, through which groove systems the plastic is forced to alternate one groove system on the worm (2) in the raidial opposite groove system, which partially covers the first axially, and from there as a result of an axial Limitation of the grooves (27) radially back to the groove system following in the axial direction to flow on the screw (2) with also axially length-limited grooves (21). 2. Single-shaft screw press according to claim 1, characterized in that that the cylinder (1) of the screw press consists of several cylinder sections (3, 7, 8, 9) is put together in the form of a modular system, with in particular the length of the cylinder section (8) for the shear and mixing # one is designed to be variable. 3. Single-shaft screw press according to claim 1 or 2, characterized in that that the screw (2) of the screw press is designed as a modular screw. 4. Single screw press according to claims 1 to 3, characterized by a plurality of ring elements (18, 19) in the cylinder (8) and / or on the core of the assigned screw section (12), which include the circumferentially distributed groove systems and each by webs (23; 29) limit their axial extent. 5. Single-shaft screw press according to claim 4, characterized in that that the ring elements (18, 19) in the cylinder (8) and / or on the screw core (12) each available in two different lengths. 6. Single screw press according to claims 1 to 5, characterized characterized in that in the ring elements (18, 19) between two circumferential, in axially spaced limiting webs (23; 29) a plurality of circumferentially distributed Recesses (216 2i) are present, these recesses (21g 27) being formed by shear webs (22; '28) are separated from one another on the circumference and the radial circumferential surfaces of the with the axial limiting webs (23; 29) connected shear webs (221 28) on the Inner or outer surface of a straight circular cylinder Bore of the cylinder (1) or Envelope surface of the screw (2)]. 7. Single-shaft screw press according to claim 1 to 6, characterized in that that the recesses (21; 27) between the radial shear webs (22; 28) of the ring elements (18g 19) are circular or oval in cross-section and the Recesses (211 27) which separate from one another and extend with an axial component ßcherztege (22 2 &) lie on a multiple helix. 8. Single screw press according to claim 7, characterized in that that the helix of the shear webs (22, 28) in the direction of the slope of the screw flight (16) runs in the plasticizing zone. 9. Single-shaft screw press according to claim 7, characterized in that that the screwing direction (24, 25; 30, 31), which of the shear webs (22g 28) of the axially adjacent ring elements (18, 19) is defined on the worm (12) and in the cylinder (8) is designed to run concurrently with the screw flight (16). 10. Single-shaft screw press according to claim 7, characterized in that that the screwing direction (24, 25; 30, 31), which of the shear webs (22; 28) of the axially juxtaposed ring elements (18g 19) is defined on the worm (12) and in the cylinder (8) are formed in opposite directions to one another. 11. Single screw press according to claim 8, characterized in that that the screwing direction (24, 25; 30, 31), which of the shear webs (22; 28) of the axially adjacent ring elements (18, 19) is defined by sections is interrupted with a reversal of the screwing direction (24, 25; 30, 31), this Comprise portions of one or more ring members (18-19). 12. Use a single screw press after at least one of claims 1 to 11 for shortening the average molecular chain length during packaging and processing vows polypropylene.