MXPA97005618A - Method to produce a tubular metropolistic profile and internal cooling unit tal met - Google Patents

Abstract

The present invention relates to a method for producing a tubular profile made of thermoplastic material, wherein the tubular profile is extruded during normal production using an extruder which comprises an internal mandrel, the tubular profile exiting the extruder is externally cooled and internally, respectively, downstream of the extruder with the aid of an external cooling device and an internal cooling device, comprising an internal cooling unit mounted on the internal mandrel of the extruder, and a tension force is exerted on the tubular profile downstream of the external cooling device through a traction device, which acts externally on the tubular profile, characterized in that the method a starting procedure comprises the following steps: the fixing during the operation of the extruder without the unit of internal cooling being mounted on the internal mandrel of the extr the extrusion of the tubular profile and the coupling of the traction device with the tubular profile, which is optionally cooled by the external cooling device, and when the traction device is coupled with the tubular profile, the introduction of the internal cooling to the tubular profile at a point located downstream of the traction device and joining it to the internal mandrel of the extrus

Description

METHOD TO PRODUCE A TUBULAR PROFILE THERMOPLASTIC AND INTERNAL COOLING UNIT FOR SUCH METHOD DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a tubular profile from a thermoplastic material, wherein the tubular profile is extruded during normal production, using an extruder comprising an internal mandrel, the tubular profile exiting the extruder is cooled externally and internally, respectively, downstream of the extruder with the aid of an external cooling device and an internal cooling device, comprising an internal cooling unit mounted on the internal mandrel of the extruder, and a tension force is exerted on the tubular profile downstream of the external cooling device through a traction device, which acts externally on the tubular profile. Such a method is described, for example, in NL-A-7605758. The use of internal cooling in the extrusion of tubular profiles made of thermoplastic material, has the important and also generally known advantage that the necessary cooling of the tubular profile leaving the The extruder proceeds much more conveniently and quickly than if the tubular profile were to be cooled exclusively from the outside. As a result, the occurrence of an unfavorable internal stress distribution in the synthetic material of the tubular profile can be avoided, particularly in the case of profiles with thick walls. The use of internal cooling during the production of thermoplastic tubular profiles is also described in WO 94/05482. Both in the case of the method described in this publication and in the method according to NL 7605758, use is made of internal cooling of an internal cooling unit that can be coupled to an internal mandrel of the extruder, and which has external dimensions that they are smaller than the internal dimensions of the extruded tubular profile. Therefore, a gap remains free between the internal cooling unit and the tubular profile to be cooled, circulating through such hollow cold air, which removes the heat from the tubular profile and releases it to a cooling system incorporated in the internal cooling unit and being cooled by a liquid. In these known methods, the presence of a gap between the tubular profile to be cooled and the internal cooling unit is not only required to establish the air flow. The gap is also provided to overcome the typical problem related to the use of internal cooling. Such a problem occurs during practice when starting the method according to the preamble. The problem for initiating an extrusion process with internal cooling is that the tubular profile exiting the extruder has to be passed over the internal cooling unit mounted on the extruder. WO 94/05482 describes how the extruder is initially set in operation during startup without the internal cooling unit being mounted on the extruder, and how the internal cooling unit accessory is delayed until the extrusion process has been stabilized. The smooth tubular profile is then cut immediately downstream of the extruder head and the internal cooling unit is mounted on the extruder. The tubular profile then slides over the internal cooling unit as a result of the progress of the extrusion. Provided that the cooling is not operative, the tubular profile in the region that joins the extruder is only slightly cooled, particularly in the interior, and consequently it is soft and has very little or no shape retention. As a result, there is an appreciable risk that the still soft tubular periphery will come into contact with the relatively cold internal cooling unit and will stick to or adhere to it, possibly with the consequence that the tubular profile will break in that point or that it no longer passes through the internal cooling unit. After all, at the moment in which the internal cooling unit has to be passed, the tubular profile has not reached the traction device and no force can be exerted by the traction device to assist the tubular profile on the internal cooling unit. GB 1 422 325 describes an extrusion process, wherein the extruded tube exits vertically down from the extruder. The extruded tube is cooled internally by an internal cooling unit mounted on the internal mandrel of the extruder. The intercooling unit has sealing elements located at a distance from each other, which act in a sealing manner on the inner wall of the extruded tube. Water is circulated in the cavity bounded by the inner wall of the extruded tube and the sealing elements. As described in Example 1 of GB 1 422 325, the extruder is activated with the internal cooling unit mounted on the extruder. To prevent the hot and soft extruded tube from sticking to the internal cooling unit, a pressurized gas is introduced into the space within the tube between the extruder and the adjacent seal element. This known actuation procedure is not effective when the extruded tube exits horizontally from the extruder, which is the common position for an extruder. In particular, a pressurized gas will not be able to prevent the soft tube from collapsing before it reaches the sealing element adjacent to the extruder. The object of the present invention is, therefore, to eliminate the aforementioned disadvantages by describing measures that can perform a problem-free drive of the possible production. For this purpose, the present invention provides a method according to the preamble, which is characterized in that the method has a starting procedure comprising the following steps: the fixing in operation of the extruder without the internal cooling unit mounted on the mandrel of the extruder, the extrusion of the tubular profile and coupling the traction device with the tubular profile, which is optionally cooled by the external cooling device; and when the traction device is coupled with the tubular profile, introduce the internal cooling unit into the tubular profile at a point located downstream of the traction device and attach it to the internal mandrel of the extruder. In this starting procedure, the contact between the tubular profile and the internal cooling unit when fixed to the latter is not a problem. This is due, on the one hand, to the fact that the external cooling device can already be operative during the fixing of the internal cooling unit, as a result of which, the tubular profile already has some shape retention. In addition, the tubular profile is, as it were, securely maintained by the traction device when the internal cooling unit is inserted into the tubular profile. An important advantage of the method according to the invention is that it is now possible to use, without problems, an internal cooling unit, which has parts that make contact with the internal wall of the tubular profile to be cooled during normal operation. These can be, for example, seal elements, which are conventional in the case of internal cooling with the help of the direct contact of the tubular profile by circulating liquid cooler. Preferably, an auxiliary tool, which can be coupled to the internal cooling unit, is used to insert the internal cooling unit into the tubular profile, and, after the internal cooling unit has been mounted on the extruder, the Auxiliary tool is removed from the tubular profile. The present invention also relates to an internal cooling unit for carrying out the method involving internal cooling through a direct contact of the tubular profile with the liquid cooler (in most cases water) and an auxiliary tool for fixing the internal cooling unit. The invention will now be explained in more detail with reference to the drawings. In which: Figure 1 diagrammatically shows an illustrative embodiment of the installation for carrying out the method according to the invention, and Figure 2 diagrammatically shows a unit of internal cooling according to the invention. In Figure 1 the reference number 1 indicates an extruder for thermoplastic synthetic material having an extruder head 2. An external dimensioning and cooling device 3 is disposed downstream of the extruder 1 and a traction device 4 is located downstream of the device 3. Figure 1 further shows an internal cooling unit having seals 5a and 5b, which make seal contact with the internal part of the extruded tubular profile 7, when the internal cooling unit 5 is located in the tubular profile 7. An auxiliary tool 6 for fixing the internal cooling unit 5 is also shown. In the method according to the invention, the procedure is as follows.

The extruder 1 is first put into operation, as a result of which, the tubular profile 7 made of thermoplastic material is forced outwardly from the extruder head 2. In this connection, it is pointed out that sometimes it is desirable to use a different synthetic material. to the synthetic material finally intended to produce tubular profiles of synthetic material during the initiation process of an extrusion process, the "starting material" has a better stabilidaid at high temperatures. As time elapses, the tubular profile 7 exiting the extruder 1 reaches a length, which is such that the tubular profile 7 reaches the traction device 4. Up to that point in the start-up procedure, use is preferably made of an element elastic such as a cable or rope, which is fixed between the punching end of the tubular profile 7 and a pipe (not shown) placed in the pulling device 4. As a result of the fastening of the pulling device 4 during operation, the tubular profile 7 after it is pulled. The external cooling and dimensioning device 3 is preferably already in operation when the tubular profile 7 reaches the device 3. When the tubular profile 7 is sufficiently advanced, the pulling device 4 comes into contact with the tubular profile 7 and Fixed in operation. The invention then provides that the internal cooling unit 5 is inserted into the open end (at 8) of the tubular profile 7 at a point downstream of the pulling device 4. In this connection, it will usually be necessary to remove the front part of the tubular profile 7 as it compresses on itself or twists. In order to insert the internal cooling unit 5 into the tubular profile 7 up to the extruder head 2, use is made of the bar-shaped auxiliary tool 6. Preferably, during the insertion of the internal cooling unit 5 into the tubular profile 7, the extruder 1, the external cooling device 3 and the traction device 4 normally remain in operation. The internal cooling unit 5 can then be mounted on the extruder head 2. In this example, the internal cooling unit 5 is provided with a thread (in 9) and the extruder head 2 is provided with an associated hole having an internal thread (not shown) the internal cooling unit 5 is screwed to the extruder head 2 by rotating the auxiliary tool 6, which is in separate form coupled to the internal cooling unit 5. The extruder 1, the head of The extruder and the cooling unit 5 are designed so as not to show the supply and removal of the cooler, so that a circulation of the cooler can be maintained in the cavity, which is limited during operation by the seals 5a and 5b of the internal cooling unit 5 and the tubular profile 7, with this cooler, the heat can be removed from the tubular profile 7. Preferably, the cooler is water. The insertion of the internal cooling unit 5 in 8 towards the tubular profile 7 is not a problem, since the tubular profile 7 may already be cold at this point to such an extent that it has adequate shape retention and is rigid. The force that is exerted on the tubular profile 7 during the insertion of the internal cooling unit 5 in the latter is also not a problem since the tubular profile 7 is now being transported by the traction device 4. After the unit of internal cooling 5 has been mounted on the extruder 1, the auxiliary tool 6 is removed and the internal cooling of the tubular profile 7 is started with the help of the internal cooling unit 5. Figure 2 shows another embodiment of a cooling unit internal suitable for carrying out the method according to the invention. This internal cooling unit 20 has a rigid body that can be assembled from 3 parts 21, 22 and 23. The first part 21 is provided with two seals 24 and 25, the second part 22 is provided with a seal 26 and the third part is also provided with a seal 27. Seals 24, 25, 26, 27 make seal contact with the internal wall of the tubular profile during the production of the tubular profile with internal cooling. The parts 21, 22 and 23 are provided with diagrammatically indicated coupling means, the coupling means 21a serve to couple the internal mandrel of the extruder, and the coupling means 21b, 22a and 22b, 23a serving to mutually couple the parts 21, 22 and 23. In the method according to the invention, it is first possible to insert the part 21 into the tubular profile 7 and to couple it to the extruder 1, then to couple the part 22 to the part 21 and finally the part 23 to the part 22. This simplifies the fixing of the internal cooling unit 20. Figure 2 does not show the fact that a plurality of pairs of conduits, which each belong to a cavity between two seals, are incorporated in the internal cooling unit. 20. Such ducts are connected to associated ducts in the extruder, through these ducts it is possible to regulate exactly the degree of cooling in each cavity.

Claims (6)

1. A method for producing a tubular profile made of thermoplastic material, wherein the tubular profile is extruded during normal production using an extruder 1, which comprises an internal mandrel, the tubular profile exiting the extruder is externally and internally cooled, in the form respective, downstream of the extruder with the aid of an external cooling device and an internal cooling device, comprising an internal cooling unit mounted on the internal mandrel of the extruder, and a tension force is exerted on the downstream tubular profile of the external cooling device through a traction device, which acts externally on the tubular profile, characterized in that the method an initiation process comprises the following steps: the fixing during operation of the extruder without the internal cooling unit being mounted on the internal mandrel of the extruder, the extrusion of the profile bular and the coupling of the traction device with the tubular profile, which is optionally cooled by the external cooling device, and when the device; The traction is coupled with the tubular profile, the introduction of the internal cooling unit to the tubular profile at a point located downstream of the traction device and joining it to the internal mandrel of the extruder.

2. The method according to claim 1, characterized in that an auxiliary tool, which can be coupled to the internal cooling unit, is used to insert the internal cooling unit into the tubular profile and, after the internal cooling unit has been mounted on the internal mandrel of the extruder, the auxiliary tool is removed from the tubular profile.

3. An internal cooling unit; adapted to be mounted on an internal mandrel of an extruder to produce a tubular profile made of thermoplastic material, the extruded tubular profile exiting the extruder being pulled by a traction device downstream of the extruder, the internal cooling unit comprising a body elongate rigid provided with coupling means, to form a detachable coupling with the inner mandrel and with seal elements, which are located at a distance from each other, and which are adapted to act in a sealing manner on the inner wall of the extruded tubular profile, so that a cavity is formed limited by two seal elements and the internal wall of the extruded tubular profile, the internal cooling unit further comprises conduit means which, during normal operation, are connected to the conduit means in the internal mandrel of the extruder to maintain a circulation of liquid cooler in each cavity, c characterized in that the coupling means are adapted to mount the internal cooling unit on the internal mandrel after the internal cooling unit has been inserted at the point downstream of the traction device, in the extruded tubular profile exiting the extruder.

4. The internal cooling unit according to claim 3, further characterized in that the number of sealing elements is three or more, in order to form a plurality of cavities in sequence in the extrusion direction.

5. The internal cooling unit according to claim 4, characterized in that the conduit means comprise a supply conduit and a separate removal conduit for each cavity.

6. The internal cooling unit according to a further JD of claims 3-5, characterized in that the rigid body comprises a plurality of component bodies, which are provided with separable interaction couplings for inserting the component bodies in the tubular profile one by one.