DE102013100123B4 - Extrusion device for producing an at least three-layered tube - Google Patents

Abstract

Extrusion device for producing an at least three-layered tube, in particular cable guide tube, wherein the tube is preferably formed of the same material with a tube inner wall (4), a foamed intermediate layer (7) and a tube outer wall (5), with at least one wall extruder (11a) and a foam extruder (11b ), characterized in that - at least the spatially extruded foam extruder (11b) from the wall extruder (11a) is equipped with a cooling element (13) such that - the melt temperature of at least the intermediate layer (7) to be produced at least on the exit side of a common extruder head (12) is located below the melt temperature of the tube walls to be produced (4, 5) and that - at least one temperature sensor (17, 18, 19) in the region of the cooling element (13) is provided.

Description

The invention relates to an extrusion device for producing an at least three-layered tube, wherein the tube is preferably formed of the same material with a tube inner wall, a foamed intermediate layer and a tube outer wall, with at least one wall extruder and a foam extruder. The tube is usually a cable guide tube and in particular cable protection tube.

An extrusion device of the structure described above, for example, in the US Pat. No. 6,176,269 B1 or even the US 4 249 875 A described. The same applies to the EP 2 477 289 A1 the applicant. Also relevant in this context is the US 3 299 192 A , To produce the foamed intermediate layer, use is typically made of chemical and / or physical blowing agents, as exemplified in US Pat US 4 249 875 A be enumerated.

As part of the US 3 299 192 A In addition, cooling of the tube during manufacture is described. This engages on the one hand on an annular nozzle assembly, which surrounds an end-side outlet head of the known extrusion device on the outside. In addition, on the other hand, there is still an internal cooling by a central air supply. As a result, the three-layered tube is cooled uniformly over its entire cross section during the manufacturing process.

In the production of three-layer pipes with foamed intermediate layer has been found that depending on the use of chemical blowing agent, the foamed intermediate layer or the adjusting cells tend to form clusters. This is the tendency to understand that individual cells are or become interconnected. This suffers the mechanical stability.

In the context of the present invention, it is not about three-layer pipes per se, but primarily to cable guide tubes made of a thermoplastic material for receiving mainly electrical cables, telecommunication cables or the like. In particular, cable protection tubes for receiving fiber optic cables with the described extrusion device are to be realized, as they are in principle in the EP 1 091 463 A1 the applicant are described. Such cable guide tubes and in particular cable protection tubes are used to protect predominantly telecommunications cable and in particular fiber optic cable in the course of their burial. For this purpose, the telecommunication cables in question are typically drawn into the cable guide tubes in question using compressed air. It is often worked with an internal pressure within the cable guide tubes of more than 10 bar (more than 1 MPa).

For this reason, cable guide tubes or cable protection tubes must be designed on the one hand pressure-tight and on the other hand have a low friction on its channel inner wall or pipe inner wall. For this purpose, in the teaching of the previously mentioned EP 1 091 463 A1 worked on the inner tube wall with sliding ribs for the telecommunications cable to be recovered. With the help of these sliding ribs, the friction between the channel inner wall or tube inner wall and the telecommunications cables to be recovered in each case is reduced.

Cable ducts and in particular cable ducts are nowadays made predominantly of polyolefins, ie of polymers which are produced from alkenes (olefins) such as ethylene, propylene, etc. by polymerization.

Polyolefins are semi-crystalline thermoplastics which are easy to process and have good chemical resistance and electrical insulating properties, which is of particular importance for the purposes described above for protecting telecommunications cables.

Within the scope of DIN 16876, pipes and fittings made of high-density polyethylene (PE-HD) are defined in more detail for buried cable conduits. This not only depends on the recyclability of such tubes, but it has particular mechanical properties such as tensile strength or the achievable modulus of elasticity and the yield stress of particular importance. The tensile strength is important against the background that, for example, when blowing telecommunications lines into the pipes, a mutual extraction of the pipes is prevented and / or the tubes are not stretched when pulling or laying the telecommunication lines in question. For this reason, it is important that the pipes and their fasteners withstand at least an internal pressure of 10 bar (1 MPa) at 20 ° C.

In order to meet the described requirements for cable guide tubes, in particular in mechanical terms, only tubes made of solid material are used in practice. Especially with three-layer pipes with foamed intermediate layer, however, there is the problem of leaks, as in the US 3 299 192 A is explained in more detail. That is, such three-layer pipes are not suitable for the application described as a rule, because they obviously do not withstand the described internal pressure of at least 10 bar during installation. Not for nothing are the plastic pipes according to the US Pat. No. 6,176,269 B1 used for thermal insulation and should also hardly meet the requirements to be placed on cable conduits. The same applies to the three-layered tubes according to the US 4 249 875 A because this is primarily about combining different plastics in the course of the realized multi-layer construction. However, such pipes are unsuitable for their eventual recycling.

That is, in the prior art three-layered tubes with foamed intermediate layer are realized so far, when it comes to providing, for example, heat insulating properties. If special mechanical loads must be absorbed by the pipes and at the same time their recyclability is required, the state of the art at this point offers no practical solutions. In addition, three-layer pipes with foamed intermediate layer are generally considered to be advantageous, as far as the material consumption of plastic granules and the recoverable weight is concerned. That is, for the sake of resource conservation, three-layer pipes with a foamed intermediate layer are to be considered positive, but so far have not achieved the mechanical properties required for, for example, cable protection pipes. Here, the invention aims to provide a total remedy.

The invention is based on the technical problem of specifying an extrusion device for producing an at least three-layered tube and in particular cable guide tube or cable protection tube, with the help of mechanically particularly durable tubes can be produced, at the same time should allow the tubes to recycle properly.

To solve this technical problem, a generic extrusion device for producing an at least three-layered tube in the invention is characterized in that at least the spatially separated from the wall extruder designed foam extruder is so equipped with a cooling element, so that the melt temperature of at least the intermediate layer to be produced at least on the outlet side of the extrusion device is located below the melt temperature of the produced pipe inner wall and / or pipe outer wall or generally the pipe walls.

The invention thus initially works with a foam extruder and at least one wall extruder, which are designed spatially separated from each other. That is, the wall extruder and the foam extruder are spatially separated from each other and are combined only on the output side in a common extruder head from which exits the desired three-layer pipe on the output side. In this extruder head open on the one hand, the wall extruder and on the other hand, the foam extruder. In principle, you can also work with two wall extruders. As a rule, however, a single wall extruder is used, with the help of both the pipe inner wall and the tube outer wall are made.

The cooling element realized according to the invention is generally arranged on the outlet side of the foam extruder and is located in a region in which the foam extruder merges into the common extruder head from the one hand the wall extruder and the other the foam extruder. As a result of this arrangement of the cooling element, the foamed intermediate layer to be produced with the aid of the foam extruder is cooled before its entry into the extruder head with respect to the respective tube outer wall and / or tube inner wall to be produced. This ensures that the melt temperature of at least the interlayer to be produced at least on the outlet side of the extrusion device and consequently also downstream of the common extruder head is below the melt temperature of the pipe inner wall and / or the tube outer wall or both tube walls.

In general, the melt temperature of the intermediate layer to be produced is located both below the melt temperature of the tube inner wall and below the melt temperature of the tube outer wall. In principle, however, it is also conceivable that, for example, the melt temperature of the intermediate layer to be produced and that of the pipe inner wall are designed approximately the same and both temperatures are settled below the melt temperature of the pipe outer wall.

As a rule, however, the tube inner wall and also the tube outer wall on the outlet side of the common extruder head have a melt temperature which is typically when using PE (polyethylene). is well above 190 ° C, usually even at 200 ° C and more settled. On the other hand, the melt temperature of the foamed intermediate layer to be produced is below the stated values and is generally about 185 ° C. and less. To set and specify these temperature differences, at least the foam extruder is equipped with the cooling element in question. In addition, this different temperature setting is achieved in that the foam extruder is designed spatially separated compared to the wall extruder, at least in the area in front of the common extruder head.

In detail, for this purpose, the cooling element can be placed on and / or in an outlet head of the foam extruder. This exit head of the foam extruder is usually located just before a connection region of the foam extruder to the end-side extruder head, which connects the wall extruder and the foam extruder, as it were. The cooling element itself can work for cooling with a cooling liquid, a cooling gas, with an electrothermal transducer, etc.

In the cases described, the cooling element is generally arranged in a cavity of the outlet head of the foam extruder. The cavity is typically a hollow cylinder. The hollow cylinder regularly surrounds a central outlet opening or passage opening for the foamed intermediate layer.

If the cooling element works with a cooling liquid for cooling, the cavity in question of the outlet head of the foam extruder is supplied with the relevant cooling liquid, which in turn is brought outside the extrusion device by a separate cooling device to the required temperature. The same applies to the case that is used as an alternative to the cooling liquid with a correspondingly designed cooling gas. Also in this case, the cooling gas may flush the said cavity or the hollow cylinder surrounding the central passage opening for the foamed intermediate layer.

Alternatively, the cooling element may also be an electrothermal converter. Such an electrothermal transducer typically generates a temperature difference at current flow. As an example of such an electrothermal transducer is called a Peltier element, which works with two semiconductors. If one conducts a current through these two materials, then on the one hand heat energy must be taken up, so that the electrons get into an energetically higher conduction band. This causes it to cool down. At the other contact point, the electron returns from the higher to the lower level, so that energy is given off here in the form of heat. As a result, the already mentioned temperature difference between the two contact points is observed, which can be exploited in the invention such that the quasi-cooled contact point of the electrothermal transducer or Peltier element is placed inside the cavity adjacent to the intermediate layer to be produced, whereas the heat-releasing Contact point is arranged facing outward.

In order to reproducibly adjust the temperature ratios already described above, at least one temperature sensor is usually provided in the region of the cooling element. Mostly two temperature sensors or even more are realized. Of these two temperature sensors, one temperature sensor is designed as a wall temperature sensor, while the other temperature sensor is a foam temperature sensor. With the help of the wall temperature sensor, the temperature of the pipe inner wall or pipe outer wall respectively the melt temperature of the molten plastic inside the associated wall extruder can be determined. In contrast, the foam temperature sensor serves to detect the melt temperature of the foamed intermediate layer to be produced.

Both temperature sensors are usually connected to a common control unit. With the aid of this control unit, the desired temperature difference between the melt temperature of the pipe wall to be produced and the melt temperature of the intermediate layer to be produced can be set and specified. For this purpose, the control unit acts on the cooling element accordingly. Alternatively or additionally, the control unit can act on individual augers on the one hand the wall extruder and on the other hand the foam extruder accordingly.

In this case, the invention is based on the fact that the melt temperature can additionally be set via the processing speed and consequently the conveying speed of the screw conveyors. Because with the help of the respective auger friction heat can be transferred to the granules for the production of the pipe inner wall or pipe outer wall on the one hand and / or the granules of the foamed intermediate layer on the other hand. That is, with the help of the speed of the screw conveyor can be alternatively or additionally the melt temperature of the pipe wall to be produced and also that of the Adjust the intermediate layer to be produced. As a consequence of this, the desired temperature difference can also be preset and set via the speed of the screw conveyors. For this purpose, the control unit may act on the individual augers in accordance with the desired temperature difference as an alternative or in addition to the cooling element.

As a result, an extrusion device is provided which is particularly suitable for producing a tube of at least three layers. In fact, the production of a cable guide tube and, in particular, a cable protection tube with a three-layer structure is particularly advantageous with the aid of the described extrusion device. The cable conduit or conduit in question typically employs up to 30% less raw material in its manufacture than a tube of solid material. This results in cost and weight advantages. In fact, at this point usually worked with a material of uniform construction tube, so such a tube, which uses one and the same plastic both for the pipe inner wall and the tube outer wall and finally the foamed intermediate layer. This not only makes the tube in question easy to produce but also benefits in terms of recycling. In addition, no temperature-related stresses occur.

Since the tube produced by means of the extrusion device according to the invention and in particular cable guide tube or cable protection tube has a lower overall density and consequently a lower weight compared to a tube made of solid material, the handling, transport and of course the installation are significantly simplified. At the same time similar mechanical properties are observed as with a cable guide tube or cable protection tube made of solid material. Thus, in the context of the invention, the cooling of the foamed intermediate layer during its manufacture in comparison to the tube wall or tube inner wall and / or tube outer wall ensures that the cellular structure of the foamed intermediate layer has an optimum geometric shape.

In fact, in comparison to the situation without cooling, particularly pronounced spherical cells are observed with relatively little statistical variance in terms of their diameter. As a result of this, defined cellular structures of the foamed intermediate layer are available and mechanical properties of the three-layered tube produced by means of the extrusion device and in particular three-layered cable guide tube or cable protection tube are achieved which correspond to those of correspondingly shaped tubes made of solid material.

This applies generally to virtually any conceivable combination of chemical and / or physical blowing agent for the production of the intermediate layer. In fact, generally 0.1 to 6% by mass of blowing agent is used based on the total mass of the pipe. In addition, the mixture of the granules and the one or both blowing agents may additionally be added up to 3% by weight of a nucleating agent, based on the total mass of the tube.

In any case, comparable mechanical properties are achieved as with a tube made of solid material. Thus, the tube produced with the aid of the extrusion device according to the invention typically has a tensile strength of more than 5,000 N, in particular even more than 8,000 N. The modulus of elasticity is usually in the range of more than 500 MPa, in particular even more than 700 MPa. The yield stress assumes values of at least 15 MPa, in particular even those of 18 MPa.

The observed mechanical properties and properties are achieved taking into account a significant material saving, depending on the proportion of the foamed intermediate layer on the produced tube in the range of about 20 wt .-% and more up to 30 wt .-% of required plastic starting material compared to a tube can be made of solid material. In addition, the pipe length-related weight can be reduced by almost 30%. A tube made of solid material typically has a tube weight of about 0.7 kg / m. In contrast, the tube produced by means of the extrusion device according to the invention can be produced with a tube weight of only 0.5 kg / m or even less. Here are the main benefits.

In the following the invention will be explained in more detail with reference to a drawing showing only one exemplary embodiment; show it:

1 and 2 the extrusion apparatus used according to the invention in an overview ( 1 ) and a detailed view ( 2 ) and

3 with the help of the extrusion device according to the 1 and 2 produced tube and in particular cable protection tube in a perspective view.

In the 3 is a three-layer pipe, according to the embodiment, a three-layer cable guide tube made of a thermoplastic material. The cable guide tube is designed as a cable protection tube and is used to hold only in the 3 indicated telecommunication cables 1 , In the telecommunication cables 1 is not limited to fiber optic cable 1 ,

The pipe or cable guide tube has a cylindrical jacket 2 in comparison to a longitudinal axis L. In fact, the cable guide tube with its jacket 2 Circular in cross-section and defined in this way a corresponding circular cable duct 3 for or for the fiber optic cables 1 at the inside. The cable guide tube or its jacket 2 has an overall rotationally symmetrical structure in comparison to the longitudinal axis L, which passes through a center M of the tube.

As already explained, the tube has an at least three-layered construction of a tube inner wall 4 , a pipe outer wall 5 and a foamed intermediate layer 7 , The pipe inner wall 4 and the pipe outside wall 5 Close between the foamed interlayer 7 as supplemented by the enlarged detail view in 3 becomes clear. The cable guide tube is constructed of the same material, so it is made of a same plastic for the realization of the pipe inner wall 4 , the pipe exterior wall 5 as well as the foamed intermediate layer 7 together.

In the exemplary embodiment comes as a material for the production of the tube polyethylene (PE) and in particular PE-HD used. Of course, variations of this are possible. Through the uniform material design of the pipe inner wall 4 made of PE, the tube outer wall 5 made of PE and finally the foamed intermediate layer 7 also made of PE or polyethylene foam, a total homogeneous thermal expansion behavior of the tube is observed.

The production of the pipe after 3 done with the help of in the 1 and 2 illustrated extrusion device. It can be seen that the extrusion device with two screw conveyors 8th . 9 is equipped, namely a screw conveyor 8th for the production of the pipe inner wall 4 and outside pipe wall 5 and another screw conveyor 9 for the realization of the foamed intermediate layer 7 , Both augers 8th . 9 are with a in 1 merely indicated funnels for supplied granular starting material 10 equipped. With this granular starting material 10 These are PE granules that are used in conjunction with the screw conveyor 8th be processed directly and essentially without additives. On the other hand comes to the realization of the foamed intermediate layer 7 a mixture of granules is used. In the example, this mixture contains about 0.1 to 3% by mass of a chemical blowing agent and additionally about 0.1 to 3% by mass of a physical blowing agent, in each case based on the total mass of granules, which is required for the production of pipes.

Overall, the extrusion device consists of a wall extruder 11a and a foam extruder 11b together. The wall extruder 11a and the foam extruder 11b have each outlet nozzles arranged concentrically to each other and open into a common extruder head 12 , The overall design is such that the foam extruder 11b leaving foamed interlayer 7 between the pipe inner wall 4 and the pipe outer wall 5 in the common extruder head 12 is included. The screw conveyor 8th is inside the wall extruder 11a arranged, whereas the auger 9 inside the foam extruder 11b place.

Both the pipe inner wall 4 as well as the tube outer wall 5 are designed here smooth surface. Also like on the pipe inner wall 4 still parallel sliding ribs 6 be provided, which have with respect to the longitudinal axis L alternating directions. For the topological arrangement of the sliding ribs 6 on the pipe inner wall 4 is referred to the introductory already mentioned EP 1 091 463 A1 the applicant and the 3 directed.

Of particular importance is the fact that the foamed interlayer 7 has a layer thickness d ₁ of about 50% to 90% of a total wall thickness s of the produced tube. In contrast, the layer thickness d _{2 of} the tube inner wall 4 and the layer thickness d _{3 of} the tube outer wall 5 taken together only 10% to 50% of the total layer thickness s. In the exemplary embodiment, the layer thicknesses d ₂ , d ₃ on the one hand of the pipe inner wall 4 and on the other hand, the pipe outer wall 5 each designed the same.

Based on the specific case, this means that the total layer thickness s of the in the 3 shown tube, for example, about 5 mm. The diameter D of the tube may be in the range of about 50 mm. As a consequence thereof arises for the pipe according to the invention according to the 3 a pipe weight of about 0.5 kg / m.

In contrast, it is observed for comparable tubes made of solid material, that is tubes made of polyethylene without a foamed intermediate layer 7 , a pipe weight of about 0.7 kg / m. Nevertheless, for the tube according to the invention with the foamed intermediate layer 7 observed comparable mechanical properties, as they are measured for polyethylene pipes made of solid material in the example and according to DIN 16876. Thus, the change in length of the pipe according to the invention according to 3 limited to ≤ 3% after heat treatment. The tensile strength of the tube is above 8,000 N. A creep internal pressure test at 35 ° C and 12 bar has led to tightness over a period of more than 2 hours (2 h) each.

Other material parameters such as the modulus of elasticity achieved, the yield stress, the tensile strength and finally the elongation at break are for a tube of solid material according to DIN 16876 and the foamed tube according to the invention with the foamed intermediate layer 7 in comparable ranges, so that practically identical mechanical characteristics and load capacities are observed. That is, the tube according to the invention with the foamed intermediate layer 7 Its mechanical strength and mechanical properties make it comparable to solid wall pipes according to DIN 16876, as the attached comparison table makes clear. Tubes according to DIN 16876 foamed pipes according to the invention tube weight kg / m about 0.7 about 0.5 Dimensional accuracy (mm) mm D = 50.0 D = 50.0 s ≈ 5 s ≈ 5 surface finish smooth inner and outer surfaces smooth inner and outer surfaces Length change after heat treatment % ≤ 3 ≤ 3 Change after heat treatment no cracks, blisters or exfoliation no cracks, blisters or exfoliation Creep internal pressure test 35 ° C / 12 bar H > 2 h > 2 h Tensile strength tube N > 8000 > 8000 Modulus of elasticity in MPa according to DIN 53457 and ISO 527 > 700 > 500 Yield stress in MPa according to DIN EN 638 ≥ 18 ≥ 15 Tensile strength in MPa according to DIN EN 638 ≥ 20 ≥ 18 Elongation at break in% according to DIN EN 638 ≥ 300 ≥ 100

The foamed tube according to the invention according to the above table, as well as the DIN-compliant tube has been made of PE (PE-HD). As a chemical blowing agent, 0.5 to 1.0% by mass of an endothermic blowing agent based on carbonate / citrate was used. Such a propellant of the company Rowa or Tramaco with the product name Tracel PO 2201 has been advantageously used. The physical blowing agent used is about 1.0% by mass. The type Tracel G6800 MS has also proved to be particularly favorable as a propellant for Tramaco. The mass fractions in each case relate to the total mass of PE-HD for the production of the inventively foamed tube.

In order to be able to produce in detail the pipe in question with the aid of the illustrated extrusion apparatus and the described specifications, in particular with regard to the mechanical characteristics, the wall extruder is first of all 11a and the foam extruder 11b spatially separated from each other. This is based on a comparative analysis of the 1 and 2 clear. In fact, the wall extruder 11a on the one hand and the foam extruder 11b on the other hand in the embodiment arranged at an angle to each other and are only in the common extruder head 12 merged. According to the invention, the foam extruder 11b with a cooling element 13 equipped, which is particularly clear on the basis of the enlarged sectional view in the 2 can recognize.

The cooling element 13 can be found on the outlet side of the foam extruder 11b immediately before a connection area 15 , in which the wall extruder 11a and the foam extruder 11b merged and to the common extruder head 12 be connected. In the context of the embodiment, the cooling element 13 in a discharge head 16 the foam extruder 11b arranged, but in principle also (outside or inside) at the outlet head in question 16 to be placed. The cooling element 13 operates within the scope of the embodiment for cooling with a cooling liquid, which has a cavity 14 the exit head 16 the foam extruder 11b applied. Instead of working with a cooling liquid at this point, it can also be ensured with a cooling gas, an electrothermal converter, etc., that the foamed intermediate layer to be produced 7 on the outlet side of the foam extruder 11b brought to a certain melt temperature.

In fact, the overall design is such that the melt temperature of the foamed intermediate layer to be produced 7 below the melt temperature both of the pipe inner wall to be produced 4 as well as the tube outer wall to be produced 5 is settled. This also applies to the exit side of the common extruder head 12 ,

To achieve this, on the one hand, the already mentioned cooling element 13 on the output side of the foam extruder 11b intended. On the other hand, the desired temperature difference across the screw conveyors 8th . 9 be set and supported, as already described in the introduction.

The cavity acted upon by the coolant 14 is formed overall as a hollow cylinder, as the enlarged sectional view in 2 makes it clear. In the center of the hollow cylinder 14 is the central outlet opening or passage opening for the foamed intermediate layer 7 or the corresponding granules 10 arranged.

In addition, you can still see at least two temperature sensors 17 ; 18 . 19 in total to a common control unit 20 are connected. At the temperature sensor 17 it is a foam temperature sensor 17 , with the help of which the temperature of the foamed intermediate layer 7 or whose melt temperature is determined. The two other temperature sensors 18 . 19 are in contrast as wall temperature sensors 18 . 19 educated. The wall temperature sensor 18 serves for temperature measurement of the melt temperature of the pipe outer wall to be produced 5 whereas the wall temperature sensor 19 the melt temperature of the pipe inner wall to be produced 4 to the common control unit 20 reports.

In addition to the temperature sensors 17 ; 18 . 19 are also the two previously described augers 8th . 9 to the control unit 20 connected and are acted upon by this. In this way, the control unit 20 a desired temperature difference between on the one hand the melt temperature of the pipe wall to be produced 4 . 5 and on the other hand, the melt temperature of the foamed intermediate layer to be produced 7 pretend.

In the context of the invention and of particular importance is now the fact that the melt temperature of the foamed intermediate layer to be produced 7 below the melt temperature of the pipe wall to be produced 4 . 5 is settled. In fact, the pipe walls like 4 . 5 or their melt temperature in the range of about 190 ° C and even more in the area of the extruder head 12 be settled. In contrast, the melt temperature of the produced foamed intermediate layer 7 to values well below 190 ° C, mostly set to values of 185 ° C and less at this point. Of course, in the processing of polyethylene (PE) in the example, the melt temperature of the produced foamed intermediate layer 7 in any case above the crystallization temperature or glass transition temperature for polyethylene (PE) of about 130 ° C.

In any case, the described temperature difference and in particular the fact that the melt temperature of the produced foamed intermediate layer 7 below the melt temperature for the pipe wall 4 . 5 settled on the outlet side of the common extruder head 12 a foamed intermediate layer 7 observed in the local expansion, which has a particularly uniform and homogeneous cell structure. This can essentially be attributed to the fact that the relatively low melt temperature of the foamed intermediate layer to be produced 7 the expansion of the foam cells due to the chemical reaction of the blowing agent and / or as a result of the expansion of the physical blowing agent due to the associated lower viscosity in some ways slows down. As a result, an overall uniform cell structure with a restricted size distribution of the cells is observed. This results in comparison with the prior art improved mechanical properties, which have already been described in the introduction.

The described temperature difference between on the one hand the melt temperature of the foamed intermediate layer to be produced 7 and on the other hand, the melt temperature of the pipe wall to be produced 4 . 5 can still be supported or adjusted by the fact that the control unit 20 the screw conveyors 8th . 9 applied differently. Here, the invention is based on the fact that a lower processing speed or feed rate of the relevant auger 8th . 9 to a reduced heat input by using the respective screw conveyor 8th . 9 produced frictional heat corresponds.

That is, the control unit 20 In addition to ensuring the temperature difference, it can ensure that the screw conveyor 9 the foam extruder 11b rotates at a slower speed than the auger 8th for the production of the pipe walls 4 . 5 , This also results in a lower heat input into the foamed intermediate layer to be produced 7 and the desired temperature difference between the melt temperatures is supported as described. That is, the control unit 20 applied in accordance with the desired temperature difference between the melt temperature of the pipe wall to be produced 4 . 5 and the melt temperature of the foamed intermediate layer to be produced 7 the cooling element 13 and / or the individual augers 8th . 9 corresponding.

Claims (9)

Extrusion device for producing an at least three-layered tube, in particular cable guide tube, wherein the tube is preferably of the same material with a tube inner wall ( 4 ), a foamed intermediate layer ( 7 ) and a pipe outer wall ( 5 ) is formed, with at least one wall extruder ( 11a ) and a foam extruder ( 11b ), characterized in that - at least spatially from the wall extruder ( 11a ) separately designed foam extruder ( 11b ) in such a way with a cooling element ( 13 ), that - the melt temperature of at least the intermediate layer to be produced ( 7 ) at least on the exit side of a common extruder head ( 12 ) below the melt temperature of the pipe walls to be produced ( 4 . 5 ) and that - at least one temperature sensor ( 17 . 18 . 19 ) in the region of the cooling element ( 13 ) is provided. Device according to claim 1, characterized in that the cooling element ( 13 ) exit side of the foam extruder ( 11b ) is arranged. Device according to claim 1 or 2, characterized in that the cooling element ( 13 ) and / or in an exit head ( 16 ) of the foam extruder ( 11b ) is placed. Device according to one of claims 1 to 3, characterized in that the cooling element ( 13 ) works for cooling with a cooling liquid or a cooling gas or with an electrothermal transducer. Device according to one of claims 1 to 4, characterized in that the cooling element ( 13 ) in a cavity ( 14 ) of the exit head ( 16 ) of the foam extruder ( 11b ) is arranged. Device according to claim 5, characterized in that the cavity ( 14 ) as a central passage opening for the foamed intermediate layer to be produced ( 7 ) surrounding hollow cylinder ( 14 ) is trained. Apparatus according to claim 6, characterized in that two temperature sensors ( 17 ; 18 . 19 ), on the one hand a wall temperature sensor ( 18 . 19 ) and on the other hand, a foam temperature sensor ( 17 ) are provided. Apparatus according to claim 6 or 7, characterized in that the temperature sensors ( 17 ; 18 . 19 ) to a control unit ( 20 ) are connected. Apparatus according to claim 8, characterized in that the control unit ( 20 ) in accordance with a desired temperature difference between a melt temperature of the pipe wall to be produced ( 4 . 5 ) and a melt temperature of the foamed intermediate layer to be produced ( 7 ) the cooling element ( 13 ) and / or individual screw conveyors ( 8th . 9 ) acted upon accordingly.

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