WO2010029142A2 - Device and method for cooling plastic profiles - Google Patents

Abstract

The invention relates to an extrusion line for producing plastic profiles, preferably plastic tubes, comprising at least one extruder (1), a tool (2), a calibrator (3) and additional post-processing devices (4, 5). According to the invention, at least the tool (2) has at least one passage (8) and a suction device (6) is arranged upstream of the tool (2) when seen in the direction of extrusion (7), said tool (2) having several functional areas with separate melt channels. The invention also relates to a method for increasing the cooling power of an extrusion line for extruding a plastic profile, in particular a plastic tube, said method consisting of the following steps: a) the plastic is melted in an extruder (1); b) a plastic strand is formed and is fed to a tool (2); c) a plastic profile is formed by the tool (2) and d) the profile is calibrated and hardened by cooling in a calibrator (3). The profile (9) is externally cooled in the calibrator (3) as well as internally cooled. According to the invention, air is suctioned by the suction device (6) counter to the direction of extrusion (7) for cooling the inside of the profile (9), and the plastic strand is divided into several partial strands in the tool (2) and the temperature of the melt is reduced prior to exiting the tool (2).

Description

 Apparatus and method for cooling plastic profiles

Description:

The invention relates to an extrusion line for the production of plastic profiles, preferably plastic pipes, comprising at least one extruder, a tool, a calibration and further downstream devices.

Furthermore, the invention relates to a method for increasing the cooling performance of an extrusion line for extruding a plastic profile, in particular a plastic tube comprising the steps of: a) melting plastic in an extruder, b) molding a plastic strand and feeding the plastic strand to a tool, c) forming a plastic profile by means of the tool, d) calibrating and curing by cooling the profile in a calibration, wherein in addition to the external cooling in the calibration, the profile is cooled in the interior.

Possibilities of internal pipe cooling are known from the prior art. Thus, for example, DE 69 403 693 proposes to provide the inner wall of the tube with a spray and thereby to achieve evaporation of the liquid on the inner wall of the tube and thus cooling. However, such cooling has not proved to be practical since the hot steam is carried along in the extrusion direction and thus aids in the cooling of the pipe in the calibration, but then at the end of the extrusion line, for example in the area of the saw, the pipe keeps a temperature, so that this is dimensionally stable, but too soft for the separation process. For the production of pipes, plastic is melted in an extruder and pressed by a corresponding tool. In a subsequent calibration, the outer diameter produced in this way is frozen and, in water spray baths or full baths, the heat is removed from the plastic via the outer surface. The entire heat must be conducted through the plastic wall to the outside, where it is then derived from the cooling water. With increasing pipe wall thickness, the cooling length is disproportionately longer, since the plastic is a poor conductor of heat. In addition, the temperature inside the tube remains at a high level for a long time and the plastic has sufficient time to roll down due to gravity. The consequence is that the pipe wall thickness in the upper area is always smaller than in the lower area.

So this process has two Nachtei- Ie with increasing tube wall thickness. The cooling length is disproportionately longer and the plastic runs off the inner wall, the result is an uneven wall thickness distribution. To reduce these disadvantages, several systems of internal pipe cooling are known from EP 795 389. However, these systems are very limited in their mode of action. Since the tube is cooled both outside and inside, both the outer contour and the inner contour is frozen. Now, if the melt solidifies in the middle of the pipe wall by heat dissipation to the outside and inside, created by the strong volume reduction in the transition from the melt-shaped to the solid state voids. This danger is greater with thickening pipe wall thicknesses.

From JP 56-005 750 A a device for the extrusion of plastic profiles is known, the plasticized plastics material can be supplied and has a plurality of annular channels, which are combined to form a common melt channel. Cooling channels are arranged around these ring channels. From DE 10 2005 031 747 Al a method for internal cooling of hollow plastic profiles and an extruder for producing hollow plastic profiles are known. In this case, the internal cooling is achieved in that a cooling gas is passed into the interior of the hollow profile, wherein the cooling gas is generated in a Ranqueschen vortex tube.

The object of the present invention is to provide an extrusion line and a method in which the heat can be dissipated as uniformly as possible over the entire wall thickness of the pipe, the cooling capacity being increased in the extrusion line, with the aim of increasing the output or to shorten the cooling section, or increased in the process, the cooling capacity and thus either increases the output or the cooling section can be shortened.

The solution of the object with respect to the extrusion line is characterized in that at least the tool has at least one opening and, viewed in the extrusion direction, an extraction is arranged in front of the tool, by means of which air is exchanged inside the plastic profile can and the tool consists of several functional areas with separate melt channels, by means of which the plastic melt can be divided into partial melts and the temperature of the melt can be reduced. Through this breakthrough, it is achieved that an extraction against the extrusion direction is made possible and the existing heat inside the profile heat can be removed from the process. Depending on the nature of the tool and several breakthroughs may be present. This countercurrent principle has the advantage that in comparison to the tube temperature at the end of the extrusion line colder air is sucked through the inside of the tube counter to the extrusion direction. This air warms up on the way through the tube on the tube inner wall, wherein the tube temperature also increases counter to the extrusion direction. Thus, there is always a temperature difference between the air and pipe inner wall, resulting in a permanent heat flow from the pipe into the air.

In principle, blowing in the direction of extrusion is also possible.

The breakthrough can be formed by means of a guided through the tool tube. So that a temperature separation between the actual tool and the breakthrough, ie the inserted tube, is formed, it is provided according to the training that there is an air gap between the tube and the tool. Depending on the nature of the tool and several breakthroughs may be present.

This breakthrough now makes it possible to conduct air in countercurrent mode. This results in the heat exchange between the air and the extruded tube, which is then sucked through the inside of the tool. Ideally, this dissipated heat is used for energy recovery. As a field of application is more conceivable. It can e.g. the plastic raw material is preheated or a Stirling engine driven.

The above-mentioned functional areas are not necessarily to be regarded as closed areas, they can flow smoothly into one another and thus also overlap.

According to the training is provided that the breakthrough is also in the extruder, wherein the suction viewed in the extrusion direction is arranged in front of the extruder. The further extension of the Breakage from the tool and in the extruder allows a more flexible design of the suction device itself, since the suction can be arranged in the relatively free space of the extrusion line and does not have to be placed between the extruder and the tool. Alternatively, it is possible to arrange the extruder transversely to the extrusion direction and thus to carry out the feeding of the plastic melt to the tool laterally.

Advantageously, the volume flow is regulated and / or controllable. It is thus possible to adapt the suction device to the respective extrusion conditions. The corresponding strength of the suction process can thus be adapted to the respective temperature conditions and thus the cooling requirement during the process. The more cooling capacity is required, the larger or stronger the flow rate is.

As a further alternative or supplement, it is proposed that the extraction system can be operated intermittently. It is thus sucked a time tl air, possibly in the turbulent range, followed by a period t2, where not sucked off (annealing time). The heat can thus migrate from the middle of the pipe wall to the inside again, which makes the pipe on the inside warmer again. This is followed again by a time interval t 1 in which the heat is extracted. The entire process can be repeated several times.

This method is advantageous in order to extrude very thick-walled tubes void-free.

The solution of the problem with respect to the method is characterized in connection with the preamble of claim 7, characterized in that for internal cooling of the profile, the air against the extrusion Onsrichtung is sucked by means of suction and supportive of the plastic strand is divided into several partial strands in the tool and so the temperature of the melt is reduced before exiting the tool.

In order to achieve the highest possible cooling capacity by means of the suction device in the interior of the profile is provided according to further development that at least one flow velocity is achieved by means of the suction, which is located in the turbulent region. Through this turbulent flow the best possible turbulence of the air is achieved in the interior of the profile, resulting in a high exchange of air on the inner wall of the profile and thus draws a good cooling performance.

The temperature can be reduced by at least 1O ⁰ C to 5O ⁰ C Thus, it being provided that the temperature is at least 2O ⁰ C and 4O ⁰ C, preferably at 3O ⁰ C, lowered.

Thus, the temperature of the plastic melt is lowered at least in the transition region between the melt state and partially crystalline state in semicrystalline plastics or in the transition region between the melt state and glass state in amorphous plastics, it being important to ensure that the decrease in temperature takes place only to the extent that a weld between the individual layers is ensured.

This reduction in temperature can be assisted by a countercurrent process, in which the heat generated inside the tube is sucked through the tool.

According to the invention, it is provided that the plastic melt flows through three functional areas, with the three functional areas flowing into one another in a flowing manner. Thus, the melt or a melt Particles, on the one hand still in the distribution area but also already in the cooling area. The same applies to the transition between the cooling area and the shaping area.

The proposed method and the device according to the invention are particularly suitable for producing thick-walled tubes.

In a further development, it is procedurally provided that the air volume between the suction and the end of the extrusion line is exchanged at least once, preferably twice per minute. It is therefore proposed that the volume of air within the entire pipe area within the extrusion line, ie from the extraction via the extruder or the tool along the calibration and the trigger or other downstream equipment to the separation device at which the entire profile strand is cut to length, accordingly often replace it to achieve optimum cooling performance.

In a further training is intended to operate the suction intermittently. It is thus sucked a time tl air, possibly in the turbulent range, followed by a period t2, where not sucked off (annealing time). The heat can thus migrate from the middle of the pipe wall to the inside again, which makes the pipe on the inside warmer again. This is followed again by a time interval t 1 in which the heat is extracted. The entire process can be repeated several times, the control of the intermittent suction can be done either temperature, time or volume flow dependent.

For such an embodiment, it is necessary for the separating device, at least in the region of the wall thickness in which it cuts the plastic pipe in its entirety, to perform a non-cutting separation in order to prevent chips from being sucked in the direction of the tool by means of the suction then these shavings inside the tube in the Area in which the pipe is still too warm on the surface can adhere.

The proposed extrusion line and the proposed method are particularly suitable for thick-walled plastic pipes and pipes with large to very large diameters, the residence time is within the extrusion line in the hour range, so it is relatively large.

By means of the proposed invention, the cooling capacity is increased in an extrusion line, which is associated with two significant advantages. On the one hand, the overall cooling length is shortened if one leaves an existing output power unchanged, or one can increase the output power if the entire cooling length is maintained.

Output and cooling length are physically related to the cooling time. The cooling time depends on the cooling capacity. By increasing the cooling capacity and thus reducing the cooling time, as described above, with constant output, the cooling section can be shortened or the output can be increased while the cooling section remains the same.

As a rule, an extrusion line is offered for a certain output. At constant output, the extrusion line according to this invention is then shorter than a line known in the art (Example A). Conversely, if two equal length extrusion lines are compared, one of the prior art and one according to this invention, a higher output can be achieved on the inventive line (Example B).

Comparing two lines with the same size extruder according to Example A, then the according to the prior art would build longer than the line according to the present invention. In Example B, two lines with the same cooling distance are compared, those that are the same According to the prior art, has a smaller extruder, that corresponding to the invention has a larger extruder.

In the drawings, two embodiments of the invention are schematically illustrated, it shows

1 an extrusion line,

2 shows a section through the tool,

Fig. 3 shows the article according to Figure 2 in an alternative embodiment and

Fig. 4, the individual temperature ranges.

1 shows schematically an extrusion line, wherein the extruder 1 is arranged laterally on the extrusion die 2. Viewed in the direction of extrusion 7, the tool 2 is followed by the calibration 3, which in turn follows the trigger 4. Calibration 3 comprises a vacuum tank with built-in calibration sleeve. The calibration can also be followed by additional cooling baths.

Another follower, here a separator in the form of a saw 5, follows. In the extrusion line shown by way of example, a tube 9 is manufactured. The suction 6 is arranged directly on the tool at the beginning of the extrusion line. The corresponding suction direction is indicated schematically by the arrow.

The tool 2 has an opening 8, the opening 8 communicates with the suction 6 in connection, so that the suction 6 the air Volume in the interior of the tube 9 can suck through to the end of the extrusion line in the region of the separator 5.

In this embodiment, in which the extruder 1 is arranged laterally on the tool 2, it is not necessary that the extruder 1 also has an opening 8 for the suction of the air from the interior of the tube 9.

FIG. 2 shows a tool 2 according to the invention. The actual melt channel 10, by means of which the plastic profile is extruded, forms the final part of an overall tool. The middle part of the tool 2 consists of a plurality of annular channels 13, which unite at a confluence point 12 and form the beginning of the common melt channel 10. The individual annular channels 13, which communicate with supply channels 14, are supplied with plasticized plastic material from the extruder 1, which is not shown in this figure. Between the annular channels 13 cooling channels 11 are arranged, which are in communication with a cooling circuit, also not shown. The cooling channels are arranged so that they can extract heat from the existing material mass of the tool as evenly as possible. The tool thus divides into the three functional areas distribution area 15, to which the melt from the extruder or extruders at the points A, B, C is supplied to the feed channels 14, and is divided into the annular channels 13, cooling area 16, in which the annular channels 13 are provided with cooling channels 11, and the shaping area 18, in which the pre-cooled melt merges, on. In order to dissipate the heat from the interior of the tube, an opening 8 is provided in the tool 2 by means of a tube. Between the tube 8 and the actual tool 2, an air gap 18 is provided for temperature separation. FIG. 3 shows an alternative embodiment of the invention. It differs from the execution gem. Figure 2, characterized in that the supply of the melt centrally, that is, only via an extruder. It is thus shown a section through the tool 2, in which again the actual melt channel 10 can be seen, by means of which the plastic profile is extruded. It also forms the final part of a complete tool. Again, the central part of the tool 2 consists of a plurality of annular channels 13, which unite at the confluence point 12 and form the beginning of the common melt channel 10. The individual annular channels 13 are connected to the feed channels 14 in connection. It can clearly be seen that the feed channels 14 are centrally impinged by an extruder 1, not shown, and then split between the three spiral distributors. Again, 13 cooling channels 11 are arranged between the annular channels, which are in communication with a cooling circuit, also not shown. Of course, the cooling channels are again arranged so that they can extract heat as evenly as possible from the existing material mass of the tool. Here, too, the tool 2 divides into the three functional areas distribution area 15, cooling area 16 and shaping area 18. Also in this embodiment, an opening 8 is provided by means of a tube in the tool 2 for dissipating the heat from the interior of the tube. Between the tube 8 and the actual tool 2, an air gap 18 is again provided for temperature separation.

It should be noted that both gem. the execution of Figure 2 and gem. Execution of Figure 3 each annular channel 13 can be acted upon with one and the same plastic compound or with different plastic masses. For this purpose, only the feed channel 14 is to be modified so that each feed channel is associated, for example, with its own extruder 1. It can thus be produced, for example, different color layers in the pipe or two materials with different properties can be made. It is Thus, for example, possible to apply to the middle part with a recyclate, which is then enclosed in the finished part from both sides with higher quality material.

FIG. 4 schematically shows a curve of a semicrystalline and an amorphous plastic, the specific volume v being shown above the temperature T. The illustrated solid line 22 is an example of the semi-crystalline material and the dashed line 23 for an amorphous plastic. During cooling, it is therefore to be ensured that the temperature of the melt state, represented in the region 21, is cooled at least into the transition region 20, but the cooling does not take place so strongly that the solids region 19 is reached. In the solids region 19, a partially crystalline state prevails in semicrystalline plastics and a glass state in the case of amorphous plastics.

With the proposed method and the proposed device, it is thus possible in a simplified manner to dissipate heat evenly over the entire wall thickness of the pipe.

With the proposed method and the proposed device, it is thus possible in a simplified manner to dissipate heat uniformly over the entire wall thickness of the pipe.

List of reference numbers:

1 extruder

2 tools

3 calibration

4 deduction

5 separating device

6 suction

7 extrusion direction

8 breakthrough

9 plastic profile

10 melt channel

11 cooling channel

12 confluence point

13 ring channel

14 supply channel to 13

15 distribution area of 2

16 cooling area of 2

17 forming area of 2

18 air gap

19 solids area

20 transition area

21 melt state

22 curve semi-crystalline plastic

23 curve amorphous plastic

v - specific volume

T - temperature

Claims

Claims: 1. extrusion line for producing plastic profiles, preferably plastic pipes, comprising at least one extruder (1), a tool (2), a calibration (3) and further downstream devices (4, 5), characterized in that at least the tool (2) has at least one opening (8) and in the extrusion direction (7) seen in front of the tool (2) an extraction (6) is arranged, by means of the air inside the Kunststoffprofiis (9) is interchangeable, wherein the tool (2) consists of several functional areas with separate melt channels, by means of which the plastic melt can be divided into partial melts and the temperature of the Melt is reducible. 2. Extrusion line according to claim 1, characterized in that the opening (8) is also in the extruder (1), wherein the suction (6) in the extrusion direction (7) viewed in front of the extruder (1) is arranged. 3. extrusion line according to claim 2, characterized in that the volume flow of the suction (6) is regulated and / or controllable and / or intermittently operable. 4. extrusion line according to one of the preceding claims, characterized in that as a separating device (5) at least in the region of the wall thickness, in which it cuts the plastic pipe in total, a non-cutting separation device (5) is used. 5. extrusion line according to one of the preceding claims, characterized in that the opening (8) by means of a tool (2) guided tube is formed and between the tube and the tool (2) an air gap (18) is present. 6. extrusion line according to one of the preceding claims, characterized in that the plurality of functional areas overlap. 7. A method for increasing the cooling capacity of an extrusion line for extruding a plastic profile, in particular a plastic tube, comprising the steps of a) melting plastic in an extruder (1), b) forming a plastic strand and feeding the plastic strand to a tool (2) c) shaping a plastic profile by means of the tool (2) and d) calibrating and curing by cooling the profile in a calibration (3), wherein in addition to the external cooling in the calibration (3) the profile (9) is cooled inside, characterized in that for internal cooling of the profile (9), the air is sucked against the extrusion direction (7) by means of a suction (6), wherein the plastic strand in the tool (2) is divided into several sub-strands and the temperature of the melt before exiting the tool (2) is reduced. 8. The method according to claim 7, characterized in that the air is sucked by means of the suction (6) at least at a flow rate which is turbulent. 9. The method according to claim 7, characterized in that the air volume between the suction (6) and the end of the Extrusi- onslinie (10) at least once, preferably twice per minute is replaced and / or the air extraction takes place intermittently. 10. The method according to any one of claims 7 to 9, characterized in that the temperature of the plastic melt is lowered at least in the transition region between the melt state and partially crystalline or glassy state. 11. The method according to any one of claims 7 to 10, characterized in that the plastic melt flows through three functional areas, wherein the three functional areas blended into each other. 12. Plastic pipe, in particular thick-walled plastic pipe, produced by the method according to claim 7 and with an extrusion line according to claim 1.