EP0235124A1

EP0235124A1 - Extrusion process for the manufacture of plastic products and arrangement for the performance of the process

Info

Publication number: EP0235124A1
Application number: EP85903653A
Authority: EP
Inventors: Erich Weichenrieder
Original assignee: RECYCLOPLAST AG
Current assignee: RECYCLOPLAST AG
Priority date: 1985-07-17
Filing date: 1985-07-17
Publication date: 1987-09-09
Also published as: WO1987000480A1

Abstract

De la matière plastique est plastifiée dans une presse à rouleaux exprimeurs (10) et transmise à l'état ainsi chauffé et plastifié à une extrudeuse (29) où elle est soumise à la pression d'extrusion requise et extrudée par la filière d'extrusion de l'extrudeuse.Plastic material is plasticized in an expressing roller press (10) and transmitted in the thus heated state and plasticized to an extruder (29) where it is subjected to the required extrusion pressure and extruded by the extrusion die of the extruder.

Description

Extrusion process suitable for the production of plastic products and arrangement for carrying out the process.

The invention relates to an extrusion process suitable for the production of plastic articles, in which the plasticized plastic is pressed through the outlet nozzle of an extruder, and to an arrangement for carrying out the process.

In the extrusion of plastics, the plastic is plasticized and called at high pressure through an extrusion die, here extrusion pressed, so that the plastic material leaves the extruder as a strand having a cross section corresponding to the extrusion die ^'comparable. The strand can be divided into pieces as a semi-finished or finished product, or can be processed in a plastic state immediately after extrusion as a blank in a blow molding process.

A high pressure is required for the extrusion, and it is also important for the quality of the product to be produced that the plastic is extruded in as uniform a condition as possible. A consistently high pressure is generated in continuously operating screw extruders in which the plastic is plasticized and degassed, the plastic being added as granules with a lens size that is as constant as possible. The granulate is produced from powdered plastic in a separate operation, which is usually done by the plastic supplier takes place because it is unprofitable for normal extrusion operation to produce the granulate itself.

The granulate is much more expensive than the powdered plastic material. Attempts have therefore already been made to process powdered plastic in an extruder instead of granules; However, it has been shown that this is only possible with increased mechanical outlay through the use of twin-screw extruders, although a drop in performance can still be accepted, so that the processing of powdered plastic in the extruder has not hitherto proven to be economically attractive .

The invention is based on the tasks of making the production of extruded plastic products more cost-effective, in particular the energy expenditure being to be reduced. The aim here is to enable the processing of powdered plastic without loss of performance, which saves the granulation process and the costs for the plastic to be processed can be reduced.

The solution to the problem is that the plastic to be plasticized is plasticized in a heated squeeze roller press and transferred from the squeeze roller press in the heated, plasticized state to the extruder and subjected to the pressure required for the extrusion.

It has been shown that the energy expenditure for plasticizing plastic material in a nip roller Press, as is known for example from DE-OS 30 23 163, is considerably less than the energy expenditure in an extruder. On the other hand, however, the pressures required for the extrusion cannot be built up at the outlet of a nip roller press. Durcl ^* . The connection of the squeeze roller press and the extruder proposed according to the invention results in a very economical mode of operation because the plasticization is carried out under the more favorable conditions of the squeeze roller press and the plasticization work in the extruder is thus omitted, so that the energy expenditure in the extruder only serves the required extrusion pressure to create.

A particular advantage arises from the fact that very different plastic materials in a Quetschwalzenpresse, also waste plastics and insbe¬ sondere also powdered plastics material for connection ^• works may be, the different materials can also be mixed in any proportion.

It has been shown that the more reliably the material is introduced into the squeezing zone, the greater the performance of the squeeze roller press, ie the more trouble-free and without congestion this occurs. The squeeze roller is covered with a thin film of plasticized material. It has proven to be effective if the material to be introduced adheres or is melted onto this layer, specifically as a tightly closed, uniform layer. There is therefore an advantageous embodiment in that the plastic is sprinkled at least approximately continuously as a uniformly and coherently distributed material layer that can be melted onto the squeeze roller from the outlet of a metering device in free fall over the entire length of the squeeze roller.

By supplying the material in free fall, it is avoided that material adheres to the boundary and guide surfaces, which can build up and break down in an uncontrolled manner, in particular when processing powdered plastic material, and which on the one hand closes a temporary reduction in the material flow and, on the other hand, can lead to a sudden oversupply with the risk of blockages.

A particularly advantageous embodiment consists in that the plastic is applied at least approximately continuously as a thin, evenly distributed over its at least approximately the axial length of the nip roller 'width material layer on a horizontally and evenly guided conveyor belt and from the discharge end of the conveyor belt in free fall onto the nip roller thrown off. On the one hand, this opens up the possibility of influencing the material flow by changing the belt speed, on the other hand, the device used for uniform material delivery can be removed from the area directly above the loading shaft of the nip roller press, where the rising hot vapors could cause the device to malfunction.

This at the same time opens up the possibility of maintaining a uniform material flow when processing material mixtures, for which purpose, according to a further advantageous embodiment, different plastic materials are each formed at least approximately continuously in accordance with a predetermined, adjustable mixing ratio at successive positions in the conveying direction for formation superimposed, thin layers are applied to the conveyor belt.

When processing plastic waste, attempts are being made to remove metal bodies or particles from the plastic material, for which purpose metal detectors and / or magnetically acting metal separators are used. It has been shown in practice, however, that it cannot be ruled out that the shredding devices, for example cutting mills, are still supplied with metallic parts which, together with metal particles resulting from the wear of these shredding devices, for example broken parts of cutting edges , can also be found in the spreadable material intended for feeding the squeeze roller press. In order to avoid costly damage to the squeeze roller press and / or the extruder and also to improve the quality of the plastic products produced, these metal particles should be removed as completely as possible before loading the squeeze roller press become. For this purpose, the formation of a thin material layer on the conveyor belt offers a particularly good opportunity because the distance between the magnets and the metal particles that may have to be removed is kept very small and therefore the magnetic forces can be optimally effective and because the material particles to be overlaid can be expected Resistance is correspondingly low with a small layer thickness. It is therefore a particularly advantageous embodiment of the method that on the

Material located on the conveyor belt is freed of metal particles by a magnetically acting metal separator.

An object of the invention is an arrangement for

To carry out the method according to the invention. The solution is that in an arrangement with an extruder suitable for extruding plasticized plastic through an extrusion nozzle, between the plastic inlet of the extruder and the plastic outlet of a squeeze roller press suitable for plasticizing plastic material, a connection for transferring the plasticized plastic from the Squeeze roller press exists in the extruder.

In order to be able to meter powdery material and to be able to dispense it, alone or mixed with other plastic materials, at least approximately continuously to the squeeze roller press, a metering device is required which can meter powdery material at least approximately continuously and which after Possibility of changing the material composition to be processed can also be used for dosing granular material. According to a further advantageous embodiment, this is achieved in that, in the material flow cross section of each metering device, between a dispensing opening, two cell rollers are arranged between each of the dispensing opening, which are arranged in parallel and fill the material flow cross section and synchronously countercross the axes of the material flow cross section consecutive in the circumferential direction separated from each other by extending obliquely to Zellenwalzenach.se webs, which opens to the extent that flat, trough-shaped cells are provided, that the webs have both cells rollers in the manner of a helical gear together abwälzbare flanks and in that the center distance and _^ the angular position of Cell rollers are adjustable to each other in the circumferential direction.

This makes it possible for the metering of powdery materials to completely block the material flow cross-section against the trickling of material by adjusting the one of the two rollers in the circumferential direction to roll the web flanks against one another, while for metering granular material a distance between the webs corresponding to the maximum grain size is also maintained in the engagement position. The oblique course of the cells, in addition to the correspondingly large number of cells on the circumference of the cell rollers, means that a continuous flow of material emerges from the metering device. Another advantageous embodiment is that a magnetic metal separator is assigned to the material transport area between the metering device or the metering devices and the discharge end of the conveyor belt.

The metal separator can be designed as a construction that crosses the belt and is optionally provided with a cleaning device. A belt crossing the conveyor belt can also be provided, which is either itself magnetically designed or is guided on the side of a magnet facing the conveyor belt . There is also the possibility of magnetically designing the deflecting roller assigned to the discharge end in order to guide metal particles over the discharge region; karin also form or equip the conveyor belt magnetically and provide a scraper on the lower run behind the discharge end.

Further advantageous or expedient refinements result from the description in conjunction with the subclaims.

The following description of an embodiment of the invention shown in the drawing will explain this in more detail.

It shows:

1 shows a schematic, partially sectioned side view of an arrangement according to the invention for plastic extrusion, FIG. 2 shows a section along the line II-II in FIG. 1, 3 shows a schematic section through a metering device,

4 shows a plan view of the metering device according to FIG. 3 and FIG. 5 shows a schematic section through a coupling device arranged in a cell roller of the metering device.

In the drawing, a screw extruder 29 is shown schematically in addition to a squeeze roller press designated by 10 in total. This is not to exclude the fact that the squeeze roller press and screw extruder can be combined to form one structural unit.

The squeeze roller press 10 known per se for processing plastic, in particular also plastic waste, consists of a housing 12 in which a roller chamber 14 with a horizontal axis is formed, in which the roller chamber 14 is at a radial distance from the wall 16 a cylindrical, heatable squeeze roller 18 is rotatably mounted. In the annular space 20, shown to scale in the drawing, between the squeeze roller 18 and the wall 16 of the roller chamber 14, a filling shaft 22 opens from above, via which the materials to be processed can be entered. In the annular space 20, for example, three squeeze segments 24a, 24b and 24c are arranged at the mouth of the filling chute 22, each narrowing the annular space 20 to a narrow gap, as a result of which the filled plastic material is subjected to severe crushing. Following the last squeeze segment 24c, the annular space opens through an outlet channel 26, in - 10 -

which the plastic mass plasticized by heat and pressure is pushed off by a scraper 28. The plastic discharged via the exit channel 26 is subjected to a sufficient pressure in an extruder 29 to carry out an extrusion process and extruded through an extrusion nozzle arranged in an extruder head 31, for which the squeeze roller press 10 itself cannot build up the required pressure .

For reliable feeding of the squeeze roller press and compliance with the desired quality, it is necessary that the plastic material with a constant mixture ratio is distributed over the entire axial length of the squeeze roller 18 as a relatively thin layer because the power increases when the layer thickness of the material decreases and because, on the other hand, there is a risk of a material jam at the inlet gap 38 of the annular space 20 if the layer thickness is too large. That fluctuations in the

Mixing ratio have a quality-reducing effect, requires no further explanation.

In order to be able to supply the squeeze roller press 10 with a layer of plastic materials that is as thin as possible in a predetermined and adjustable mixing ratio, the system is equipped with a mixing system designated as a whole with 29, in the example shown, to simplify the illustration, only the mixture of two starting materials is assumed and accordingly there are only two dosing devices 32 for these two materials. Become If several different materials are mixed, then a number of metering devices 32 corresponding to the number of materials is required, but the basic arrangement and ^" mode of operation do not change compared to the example shown.

The starting materials are each introduced into the feed chute 22 of the associated metering device 32. The metering devices 32 are successively arranged vertically in the conveying direction above a horizontal and level conveyor belt 34, the discharge end 35 of which is located above the filling shaft 22 of the squeeze roller press 10. The width of the material discharge openings 36 of the metering devices 32, the width of the conveyor belt 34 and the width of the filling shaft 22 are dimensioned such that the material emerging from the discharge opening 36 and deposited on the conveyor belt 34 as a thin layer over the entire length axial length of the squeeze roller 18 is sprinkled thereon, where the material is gripped and pulled along by a film of plasticized, sticky plastic covering the squeeze roller 18.

Each of the metering devices 32 produces a thin layer of material on the conveyor belt 34, the layer thickness of which is dependent on the one hand - as will be explained in more detail later - on the working speed of the metering device 32 and on the other hand on the running speed of the conveyor belt 34. According to the number of dosing devices 32 following one another in the conveying direction of the conveyor belt 34 until the end 35 of the conveyor belt 34 is ejected, a plurality of layers of material are placed on top of one another, the thickness of which can be kept different by appropriate adjustment of the metering device and set to a predetermined mixing ratio, while the absolute layer thickness can be maintained by changing the speed of the while maintaining the mixing ratio Volume 34 can be adjusted.

So despite the change in the belt speed

Shedding curve 40 of the material at the discharge end 35 to be supplied ^• further processing point, in this case, the squeegee roller 18, is incident in the desired manner, the discharge end can be adjusted in the conveying direction 35th For this purpose, the conveyor belt 34 is arranged in a frame 41 which can be adjusted in the conveying direction along a guide 38. In a substructure 42 carrying the guide 38, an adjusting spindle 44 is mounted, which is provided with a handwheel 46 and is guided by a nut 48 attached to the frame 41, so that by rotating the handwheel 46 the position of the frame 41 and thus the discharge end 35 of the conveyor belt 34 is adjustable.

In order to maintain the uniform distribution of the material discharged from the metering devices 32 onto the conveyor belt 34 up to the belt end 35, the conveyor belt 34 is arranged horizontally - and in addition its upper run 50 intended for receiving material is supported by a support plate 52 which the upper run 50 also holds flat transversely to the running direction, so that the danger is prevented, that the material is compressed due to an otherwise possible transverse curvature of the upper run 50 against the center of the band or against the band edges. Since the belt is essentially covered with material over the entire width, lateral shielding strips 54a and 54b, which bridge the gap between the lower end of the metering devices 32 and the conveyor belt 34 and on the inside of the belt from near the side edges of the conveyor belt, prevent it 34 arranged lateral ribs 56a and 56b overlap these ribs so that material emerging from the metering devices 32 reaches the belt 34.

A specially designed metering device 32 is provided so that powdered plastic can be fed continuously and in the required amount and, if necessary, also in the desired mixing ratio with other plastic materials, the squeeze roller press 10, which is suitable both for the metering of powdered and also suitable for granular material.

Between the feed chute 30 and the discharge opening 36, an essentially rectangular housing 86 delimits the material flow cross section, which is interrupted for the dosing process by two cell rollers 58a and 58b which can be driven synchronously in opposite directions and are arranged in parallel. The roller 58a shown on the left is mounted in a stationary but rotatable manner in the housing 86, while the right roller 58b is rotatably mounted in bearings 59 which are adjustable in the horizontal guides 61 in the housing 86. For this purpose with the bearings 59 rotatable, but fixed in the axial direction, threaded spindles 63 are connected, which are guided by nuts 65 arranged on the housing 86 and are provided at the free end, for example with a square 67 for attaching a crank.

The cell rollers 58a and 53b are provided on their circumference with a number of relatively flat, rounded cells 60 separated from webs 62, the webs 62 and thus the cells 60 running obliquely to the axis of the cell rollers 58a and 58b provided with them, webs 62 and cells 60 of the two cell rollers 53a and 58b are assigned to one another in the manner of a helical toothing for mutual engagement. The flanks of the webs 62 are shaped in such a way that they can roll against each other when the center distance is set appropriately and the angular position of the two cell rollers 58a and 58b is set accordingly.

In order to enable such an adjustment of the two cell rollers 58a and 58b, not only the adjustment of the cell wheel roller 58b in the horizontal direction by means of the threaded spindles 63 is necessary, but also a corresponding adjustment of the cell wheel roller 58b with respect to its own rotation ¬ axis are carried out. To this end, as shown in Figure 5 only schematically as a possible design, the cells roller 58b by: a Konus¬ clutch 69 is connected with its axis 71 ^'. The axis 71 is hollow and contains an adjusting spindle .73, which has a square 75 at its outwardly projecting end is provided for attaching a crank. In the area of the cone coupling, the axis 71 is provided with a slot 77, through which a gripper .79 protrudes outwards, which is provided within the axis 71 with a threaded bore through which the adjusting spindle 73 passes. The gripper 79 interacts with a clamping cone 81 which is axially adjustable with respect to the axis 71 and which, as part of the cone coupling 69, interacts with a cone 83 connected to the cell roller 53b.

If, by rotating the spindle .73, the gripper .79, which is prevented from rotating, is moved to the right in FIG. 5, the conical coupling 69 is relieved, which can be supported by a spring (not shown) and the cell roller 58b can be moved relative to the axis 71 be rotated. The adjusting spindle 73 is then rotated in the opposite direction and the gripper 79 firmly clamps the two parts 81 and 83 of the cone coupling together, so that the cell roller 58b is connected to the axis 71 in a rotationally fixed manner.

If necessary, a coupling can be provided at both ends of the cell roller 58b, for which purpose the adjusting spindle must pull the axis 71 through to a corresponding length.

A chain drive for the synchronous, counter-rotating drive of both cell rollers 58a and 58b is located in a gearbox 101 arranged on one end face of the housing 86. A sprocket 103 or 104 is assigned to each of the rollers and the drive chain 102 crosses those through the axes of both cell rollers - 16 -

53a and 53b extending plane, so that the sprockets 103 and 104 are driven in opposite directions. The chain 102 is guided over two deflection wheels 105 and 106, of which the deflection wheel 105 can be adjusted vertically, 5 which is indicated schematically by a guide 107 and an adjusting spindle 109 provided with a square 108 (FIG. 2). Changes in the center distance of the cell rollers 58a and 58b can thus be compensated for, while on the other hand a reversal of the running direction of the cell rollers 58a and 58b is possible if, for example, cleaning is desirable.

The upper Gehäu≤eteil for easy removal of optionally incorporated ^¬ clamping system material from the area of cells rollers 58a and 58b 5 can be folded around a hinge 91st

The cell rollers 58a and 58b are driven, for example, via the shaft stub 94

In a for dosing granules or small plastic particles e.g. from a cutting mill suitable setting, the angular position of the cell roller 58b is selected such that in the engagement zone

25 of the rollers of the web .62 of one roller projects exactly into the center of the cell 60 of the other roller, the flanks of the webs 62 not touching one another; Rather, a gap corresponding to the maximum permissible particle size remains free. Thereby the

30 center distance of both rollers 58a and 58b set so that the circumferential boundary of the - 1 -

Web of one roller maintains a corresponding distance from the bottom of the cell 60 of the other roller. If particles exceeding the maximum dimension reach the engagement area, they are squeezed to the maximum dimension by the pressure of the rollers 53a and 58b.

The device can optionally be adjusted to other particle sizes by changing the angular position and the center distance.

In order to also enable the metering of powdery material, the two cell rollers are set so that the flanks of the webs 62 roll against each other in the engagement area, so that powdery material is prevented from trickling freely through gaps in the teeth.

The approach of the cell rollers .58a and 58b required for the metering of powdery materials would open a gap between the area of the cell roller 53b adjacent to the housing wall .86 and the housing wall, which in turn would allow the material to trickle through, even if the material directed upwards there Movement of the cell roller 58b counteracts this somewhat. It is therefore expedient to provide in this area an inner wall element ^' 72' which is connected to the bearings 59 and adjustable together with these and the cell roller 58b, which is arranged closely adjacent to the circumference of the cell roller 58b. In front of the discharge end 35 of the conveyor belt 34, a schematically indicated, magnetically acting metal separator 23 crosses the conveyor belt 34. As already mentioned, this is only one of the many options that are relatively thin on the conveyor belt 34 Material layer with a reliability not previously achieved in plastics processing plants to extract any metal particles still present. The deflecting roller 37 could also be equipped with magnets in the region of this discharge end in order to hold the metal particles on the conveyor belt 34 beyond the discharge region, with a deflecting roller 37 still resting against the conveyor belt 34 in the direction of travel of the belt could connect to a stripper extending magnet so that the

Stripper can be arranged further away from the discharge end 35. But you could also form the tape 34 itself magnetically, e.g. by embedded permanent magnets in order to hold the metal particles beyond the discharge end 35 up to a stripper on the conveyor belt 34.

Claims

Expectations:

1. An extrusion process suitable for the production of plastic articles, in which the plasticized plastic is pressed through the outlet nozzle of an extruder, characterized in that the plastic to be plasticized is plasticized in a heated squeeze roller press and from the squeeze roller press in the heated, plasticized state transferred into the extruder and subjected to the pressure required for the extrusion.

2. The method according to claim 1, characterized in that the plastic is sprinkled at least approximately continuously Lich as a uniformly and coherently distributed material layer meltable onto the squeeze roller from the outlet of a metering device in free case in its entire length onto the squeeze roller.

3. The method according to claim 2, characterized in that the plastic is at least approximately continuously Lich applied as a thin, over its at least approximately the axial length of the nip roller correspondingly evenly distributed material layer onto a horizontal and evenly guided conveyor belt and from the discharge end of the conveyor belt is thrown onto the squeeze roller in free fall.

4. The method according to claim 3, characterized in that different plastic material ^'ien each case at least approximately continuously according to a predetermined adjustable mixing ratio at successive in conveying direction positions for the formation of overlapping, thin Schich¬ th are applied to the conveyor belt.

5. The method according to any one of claims 3 or 4, characterized in that the material found on the conveyor belt is freed from metal particles by a magnetically acting metal separator. - 21 -

6. Arrangement for performing the method according to one of claims 1 to 5, with an extruder suitable for extrusion of plasticized plastic through an extruder nozzle, characterized in that between the plastic inlet of the extruder (29) and the Plastic outlet (26) of a squeeze roller press (10) suitable for plasticizing plastic material, there is a connection for transferring the plasticized plastic from the squeeze roller press (10) into the extruder (29).

7. Arrangement according to claim 6, characterized in that above a horizontally and flat conveyor belt (34) at least one for at least. approximately continuous, metered dispensing of plastic material suitable metering device (32) is arranged.

8. Arrangement according to claim 7, characterized in that the speed of the conveyor belt is adjustable bar.

9. Arrangement according to claim 8, characterized in that the discharge end (35) of the conveyor belt (34) is adjustable in the conveying direction.

10. Arrangement according to one of claims 7 to 9, characterized in that in the material flow cross-section of each metering device (32) between a loading opening (30) and a delivery opening (36) two parallel, the mate- Cell rollers (58a, 58b) which fill the radial flow cross section and synchronously countercurrently pass through the material flow cross section are arranged, each with webs (62) which follow one another in the circumferential direction and are separated from one another by webs (62) which run obliquely to the cell roller axis and which open to the circumference , flat, channel-shaped cells (60) are provided that the webs (62) of both cell rollers (58a, 58b) have flanks that can be rolled against one another in the manner of a helical toothing and that the center distance and the angular position of the 'cell rollers (58a , 58b) are mutually adjustable in the circumferential direction.

11. The arrangement according to claim 10, characterized in that the beginning and end of each web (62) are offset from one another in the circumferential direction by the web spacing.

12. The arrangement according to claim 10, characterized in that the cells (60) have a rounded cross section.

13. Arrangement according to one of the claims 2 to 12, characterized in that a magnetic metal separator (23) is assigned to the material transport area between the metering device or the metering devices (32) and the discharge end (35) of the conveyor belt (34) is.