DE3207193C2 - Extruder barrel section in a multi-screw extruder for plastics - Google Patents

Abstract

The invention relates to a device for extruding thermoplastic materials, in particular a multi-screw extruder with an extruder cylinder element for intermeshing screws. A simplified extruder cylinder segment is proposed which has internal and external heat exchanger devices. The cylinder segment contains a cylindrical housing through which at least two intersecting screw spaces are bored. An outer tube carrying a heat exchanger medium is provided, an inner cylinder area having at least one closed heat exchanger bore which also carries the heat exchanger medium. With such a cylinder segment, the heat transfer can be controlled in accordance with the actual cylinder housing temperature.

Description

The invention relates to an extruder barrel section for intermeshing extruder screws in a multi-screw extruder, with an elongated cylinder housing, through soft at least two intersecting snap chambers are drilled, with an inner cylinder portion which is divided in two by a longitudinal plane which is defined by radii of the cylinder housing, which by the Intersections of the screw spaces run with at least one heat transfer hole for the medium with a closed end, and with an inlet channel and an outlet channel which connect to the heat transfer bore are connected.

In order to extrude thermoplastic materials on an economical scale, it is known that the material must be kept in a plastic state within a comparatively small temperature range. Within this range, the material is sufficiently fluid to flow through the extrusion die or nozzle, the distance to the temperature at which the material chemically collapses being sufficiently large to avoid defects in the structure or in the surface of the end products. In the case of PVC, the acceptable temperature range is 175-215 ^C C. As the material enters the extruder at room temperature, the critical temperature control is typically achieved in the section of the extruder barrel, which is closest to the output. In this area, the combined effects of externally driven convection heating and self-heating from material shear must be balanced out by a large number of cooling devices in order to achieve the desired temperature control.

Multi-screw extruders with intermeshing screws have peculiarities in terms of heat transfer in the area of the intersection of the screw bores, where large thermal masses and the self-heating of the material combine and temperature control is extremely difficult design. Known generic extruder cylinder sections according to the prior art according to DE-GM 72 06 521 already have the advantage that in the area of the greatest heat density, i.e. in the area of the cutting edges the screw chambers, where the two bores merge, good temperature control options exist. On the other hand, it has been shown that the as a result, the temperature control options available are not sufficient in all cases to achieve the to achieve desired temperature control.

The present invention is therefore based on the object of the generic extruder barrel section to develop according to the prior art so that a compared to the known prior art Technology results in significantly improved temperature control options, while at the same time a special Inexpensive arrangement is to be created.

This Avigabe is achieved according to the invention in that on the outer surface of the cylinder housing a helical groove is provided that in this groove a heat-transferring, medium-carrying Tube is arranged, and that the media-carrying tube with the heat transfer bore via the inlet channel and the outlet channel is connected.

From DE-OS 20 61 700 an extruder for plastics is known in which at least part of the The cylinder surrounding the extruder screws is surrounded by a jacket, with the space between A temperature control medium flows through the cylinder and jacket. To have sufficient stability of the cylinder to ensure, this has ribs running in the circumferential direction, which are primarily used as reinforcement or stiffening ribs, in addition, also serve to improve the temperature control.

After the ribs merge into one another, is also in this prior art on the circumference of Cylinder formed a circumferential groove, which, however, not the technical underlying the invention Task, namely picking up a media-carrying pipe, solves. Otherwise, the one described above Compared to the solution according to the invention, the arrangement is much more expensive to produce, since in the case of the prior art, an outer jacket must also be provided, which defines the outer boundary for the temperature control medium

The US-PS 42 35 581 shows a screw extruder in which the cylinder housing a plurality of in having grooves extending in the axial direction, in which a number of media-carrying pipes are serpentine are led. In this prior art, which is not designed as a multi-screw extruder, there is a large number of pipes with a corresponding number of connections required, which is technically in terms of production expensive way requires a large number of connections.

In the following the invention is illustrated by way of example in the drawings embodiments explained in more detail. It shows

1 shows a side view of a twin screw extruder with a cylinder section according to the invention;

Fig. 2 is an end view of the extruder barrel section; which the relative arrangement of the screw

shows bores and the inner media-carrying bores;

F i g. 3 shows a partial longitudinal section of the cylinder section along line 3-3 of FIG. 2;

F i g. Figure 4 shows a detail of the heat transfer tubes and the grooves in the outside of the cylinder section according to FIG. 3;

5 shows an alternative embodiment of the flow guide device for the inner heat exchanger bores and

F i g. 6 a schematic view of the recirculation system of the heat exchange medium and the heating control of the cylinder section.

For the purpose of illustrating the invention, a twin screw extruder will be used for manufacture of PVC pipes described in some detail.

In Fig. 1, the twin screw extruder 1 is shown in side view and contains a machine base 2 and the extruder drive including a drive motor 14 of a motor speed reducer 10 of a gear box 8 for diverting the screw drive and extruder screws 6. The extruder cylinder 4 is shown partially through a section of the cover 12 and is shown in FIG the machine base 2 supported by bearings 22 and 24 The PVC raw material for the extrusion is fed into the machine at a feed hopper 15 and from here passed through the feed pipe 16 to the entrance of the extruder cylinder 4 the feed drive 18 is driven in rotation, which in turn is driven by the motor 20. The feed hopper and the feed drive are held on an extension of the worm drive frame 42 by a bearing 26.

The cylinder section 30 at the output or extrusion end is mounted on the extruder cylinder 4 by means of a flange 32 which is screwed to the flange 40. Following this cylinder section, the extrusion die 50 is attached to a mold inlet adapter 36. The cylinder section is held on the machine base 2 and the bearing 22 by the bearing part 28. Heating strips 38 and 39 are distributed over the length of the cylinder section 30. Thermocouples 34 are inserted into the cylinder housing near the top along its length.

The raw material entering through the feed tube 16 is fed along the length of the extruder barrel 4 through the inner intermeshing augers (not shown) advanced. These snails serve at the same time to process the material within the screw holes and thereby the Convection heating of the material due to the heat supplied from the outside of the heating strips 38 'and 39 heat, while at the same time the self-heating of the material is supported by material shear.

F i g. 2 shows the end view of the cylinder section 30 in the direction of the flange 32. The inner, tapered screw bores 104 and 106 intersect along the line 62. In this view, pipe plugs 100 and 102 for closing the inner heat exchanger bores 66 and 68 are illustrated and lie on top of one another Section line 62. The line 62 forms the projection of an imaginary longitudinal plane which is defined by the cylinder housing radii which run through the intersection points of the screw bores 104 and 106 , the plane intersecting the inner area of the cylinder housing 60 in two parts. In this view are in dashed lines the inlet channels 74 and 76 to the heat transfer bores 66 and 68 illustrated. Furthermore, the outlet channels 70 and 72 are shown in dashed lines Longitudinal level are divided into two.

ίο In F i g. 3 is a partial view in longitudinal section showing the cylinder section 30 along line 3-3 of FIG F i g. 2 shows in the view of FIG. 3 is partially broken the surface, so that the groove 64 in the Surface is visible In dashed lines, sectional views of the heating strips 38 and 39 are also shown, which enclose those areas of the cylinder section 30 in which the groove 64 is formed.

In Fig. 3, the tube 110 conducting the heat exchanger medium is illustrated in a sectional view as it sits in the groove 64 of the cylinder section 30. As can be seen from the partially broken-away surface view, the groove 64 extends continuously and helically over the outer regions c of the cylinder housing and is surrounded by the heating strips 38 and 39. Inside the cylinder housing 60, the inner heat transfer bores 66 and 68 are illustrated. As shown in FIG. 3, these bores are arranged in such a way that their longitudinal center lines intersect the center line 44 of the cylinder section 30. The heat transfer bores 66 and 68 are arranged in such a way that they follow the tapering of the screw bores 104 and 106. Open-ended, media-conducting tubes 86 and 88, which are held by bearing rings 78, 80 or 82 and 84, are mounted in the heat transfer bores 66 and 68. These bearing rings 78 to 84 form seals between the interior of the heat transfer bores 66 and 68 and the exterior of the guide tubes 86 and 88. It is evident that medium entering the inlet channels 74 and 76 is conducted through the guide tubes 88 and 86 to the outlet holes 90 and 92 from where it flows to the outlet channels 70 and 72. The heat exchanger medium is guided by this media guiding device over the length of the interior of the heat transfer bores 66 and 68 in order to maximize the heat transfer between the inner regions of the cylinder housing 60 and the heat exchanger medium.

From FIG. 4 it can be seen that the tube HO, which carries the heat exchanger medium, is fitted into the groove 64 of the cylinder housing 60 in such a way that an effective heat exchanger surface is formed between the tube HO and the cylinder housing 60. In particular, the groove 64 is formed with an undercut 65, which serves to hold the tube 110 in place.

■> =; th.

Furthermore, from FIG. 4 that the outer section of the tube 110 carrying the heat exchange medium, which is shown in its original state by the dashed line, has been deformed in order to form a continuous surface on which the heating strips 38 and 39 are arranged. In this way, maximum heat transfer between the heating strips 38 and 39 and the cylinder housing is achieved, while at the same time maximum heat

b5 mcober.ragung between the heat exchanger medium in the tube 110 and the cylinder housing 60 is guaranteed. With reference to FIGS. 1 and 6 it can also be seen that the tube 110 from one end of the

Cylinder section 30 is formed continuously to the other.

In Fig. 5 is an alternate embodiment of FIG Media guiding device in its installation location in the heat transfer hole 66 illustrates. As with the media control device described above, this occurs Heat exchange medium at the inlet channel 76 and is prevented by means of a bearing ring 124 from entering the Heat transfer bore 66 enter as this ring forms a seal between the open-ended guide tube 122 and the heat transfer bore 66 forms. The heat exchange medium is then within the Guide tube 122 passed to its end, where it enters the heat transfer bore 66. In this case it is a tape 126 is wrapped around the exterior of the guide tube 122 and forms a seal between the tube 122 and the heat transfer bore 66 so that in the Heat exchange medium a turbulence is generated, while this over the length of the heat transfer bore 66 flows back to the outlet channel 70. This generation of a turbulent flow of the heat exchanger medium within the heat transfer bore 66, the effective heat transfer between the cylinder housing 60 in the inner section and the heat exchange medium is maximized.

In Fig. 6 is the cylinder section 30 together with the heat exchange medium recirculation system and the control of the heating tapes shown. The heat exchange medium is pumped 150 through the conduit 172 on the outlet side and a pressure relief valve 148 to a heat exchanger 152 and through a Control valve 144 led to feed line 140 in the circuit. From the feed line 140 the cooled is Heat exchange medium to the tube UO and the inlet channels 74 and 76 of the heat transfer bores 66 and 68 out. The heat exchange medium is through the outlet channels 70 and 72 and the pipe 110 to Return line 142 passed. From the return line 142, the heat exchange medium is through the heat exchanger 152 and passed from here to line 170 of pump 150.

The recirculation system is controlled by thermocouple 34 and control circuit 156. If that Heat exchanger medium, a reduction in the temperature in the inner regions of the cylinder housing 60 has performed, the thermocouples 34 generate a signal which is proportional to the sensed temperature is. This signal is received by control circuit 156 to produce control signals on output line 158 to generate, which close the control valve 144 so that the pressure relief valve 148 must open. In this The state of heat is absorbed by the Pump 150 via pressure relief valve 148 to heat exchanger 152 and back to pump 150 via the Return flow line 170 is circulated when the thermocouples 34 have a temperature rise in the interior areas of the cylinder housing 60 detect, lead the detected signals in the lines 154 to the fact that the Control circuit 156 in turn generates a control signal on line 158 to open control valve 144, which then causes a pressure drop in line 172, through which the pressure relief valve 148 is closed so that the heat exchanger medium in turn through the tube HO and the heat transfer holes 66 and 68 is performed.

At the same time, the control circuit 156 depending on the in the lines 154 through the thermocouples 34 generated signals activate and deactivate the heating bands 38 and 39. If the sensor signals in the lines 154 indicate that the temperature of the interior of the cylinder housing 60 is below a The threshold value have fallen, the control circuit 156 consequently generates a control signal on the output line 162, to activate the heating bands 38 and 39. However, if the sensor signals on lines 154 from the Thermocouples 34 indicate that the temperature of the interior of the cylinder housing 60 is a preset temperature Have exceeded the limit value, the control circuit 156 generates a control signal for switching off or Deactivating the heating cables 38 and 39.

Referring again to FIG. 2 it will be apparent to those skilled in the art that the large Amount of material within the immediate area of the intersection of the screw bores 104 and 106 forms a large thermal mass at the same time. When the thermocouples 34 determine that the temperature of the inner areas have exceeded the upper limit, the external cooling is therefore via the heat exchanger tube 110 alone is insufficient to cause a rapid drop in temperature within the interior areas perform. As a result, heat exchange medium must both the pipe 110 and the heat transfer holes 66 and 68 are fed to thereby overheating of the material along the To prevent the cutting plane of the screw bores 104 and 106.

It should be noted that an extruder barrel portion which has the above-mentioned inner and has external heat exchanger devices, can also be used on sections of an extruder cylinder, which is not the starting section. It should also be noted that although the preferred embodiment is based on the use of a heat exchange medium is directed for cooling, the combination of the heat exchanger medium leading tube and the Heat exchanger bores can also be suitable for performing alternative heating or cooling processes, in order to achieve an optimal temperature control of the material. It is also pointed out that that according to the respective volumes of the inner areas also a plurality of heat transfer bores can be used.

For this purpose 2 sheets of drawings

Claims (2)

Patent claims: 1. Extruder barrel section for intermeshing extruder screws in a multi-screw extruder, with an elongated cylinder housing through which at least two each other intersecting pelvic chambers are drilled with a inner cylinder section which is divided into two by a longitudinal plane, which is defined by the radii of the cylinder housing is defined, which run through the intersections of the screw spaces, with at least one heat transfer hole for the medium with a closed end, and with one Inlet channel and an outlet channel, which are connected to the heat transfer bore, characterized in that on the outer Surface of the cylinder housing (60) a helical groove (64) is provided that in this groove a heat-transferring, medium-carrying one Tube (110) is arranged, and that the media-carrying tube (110) with the heat transfer bore (66, 68) is connected via the inlet channel (74, 76) and the outlet channel (70, 72). 2. extruder cylinder section according to claim 1, characterized in that the media-carrying Tube (110) and the groove (64) are arranged so that the outer surface of the tube (110) with the outer Surface of the cylinder housing (60) is flush.