AT401031B - DEVICE FOR REGULATING THE WALL THICKNESS - Google Patents

Description

AT 401 031 B

The invention relates to a device for regulating the wall thickness of a pipe or profile made of thermoplastic plastics by extrusion, with an extrusion gap formed by a nozzle and mandrel body, the nozzle of which is preferably divided into a number of sectors with heating devices that can be controlled separately in terms of their heating power, and a downstream one Calibration form, the inner walls of which determine the outer shape of the extruded tube or profile and can be tempered by means of a temperature control device.

EP 0 153 511 B1 discloses a method and a device for extruding a plastic tube with a controlled wall thickness, the temperature in each of a plurality of temperature-controlled sectors arranged over the extrusion gap of the extrusion die being regulated as a function of the wall thickness measurements, which is carried out on a wall thickness measuring device Number of measuring points to be carried out. The wall thickness is measured in several points in a measuring sector, the mean value is determined and compared with the mean value measured in all measuring sectors, and the temperature is regulated by heating as a function of the difference found, in order to eliminate the measured difference, the heating devices only measuring the temperature influence a surface of the plastic tube body in the shaping end.

Furthermore, EP 0 287 551 A1 specifies a method for regulating the thickness of an extruded plastic article, the extrusion gap comprising a plurality of sectors with a controllable heating source and a temperature measuring device. The temperature of each sector is regulated and adjusted to effect a change in the wall thickness corresponding to the respective sector, so that a desired wall thickness distribution is achieved.

In such known methods, the wall thickness of the extruded tube or profile is regulated by changing the temperature in the region of the extrusion gap. The extruded profile or tube is then placed in a calibration mold on its cooled inner walls by a negative pressure generated in the area of the inner walls or, in the case of hollow profiles, by an overpressure generated in the interior of the hollow profile and thus the outer shape of the profit is calibrated.

The aim of the invention is now to provide a method of the type mentioned in the introduction, in which the predetermined wall thickness of an extruded profile can be manufactured more precisely than before.

According to the invention, this is achieved in that the inner wall of the calibration mold is divided into sections or sectors which are adjacent to one another in the circumferential direction and are thermally decoupled from one another, the individual sectors or sections being assigned temperature control devices which can be controlled independently of one another.

This makes it possible to control the temperature of the individual peripheral sections of the calibration mold independently of one another, as a result of which the wall thickness of the extruded profile or tube can be influenced within wide limits.

The cooling of the calibration mold, which differs in circumferential areas, causes the extruded profile to solidify at different rates, with a greater wall thickness being obtained in the areas in which less cooling is carried out, with the same rate of withdrawal of the extruded profit or tube. This is due to the fact that in these areas even more plastic material can be applied to the already more solidified and therefore tougher layer, which is in direct contact with the cooled wall of the calibration mold. This makes it possible to produce profiles, in particular hollow profiles, with a wall thickness that largely corresponds to the desired value.

Experiments have shown that if the temperature of the wall of the calibration mold changes in its individual sections or sectors by approximately 40 ° C., the wall thickness can be changed by approximately 10%. A wall temperature of the calibration form can e.g. between 10 * and 50 ’C are observed, with the latter still having a sufficient cooling effect.

Another advantage of the device according to the invention is that there is usually no possibility of forced cooling in the tool or in the area of the extrusion gap and it is possible for a thick point to be formed in the area of the extruded profile formed by this area of the extrusion gap. In this case too, the wall thickness of the calibration mold can be correspondingly influenced and thus corrected by correspondingly influencing the temperature of the wall of the calibration mold.

In the conventional devices, the calibration mold is cooled in its entirety, which usually takes place via a central water supply, in which no temperature control is provided. This also has the disadvantage that the temperature fluctuations of the cooling water cause fluctuations in wall thickness. These problems can also be avoided in a simple manner by the device according to the invention, in which the temperature of the wall of the calibration mold is regulated in sections.

A solution that is particularly simple in terms of design results if the individual sections or sectors are assigned chambers through which a temperature control medium flows and one with 2

AT 401 031 B have the common wall of the inner wall of the calibration mold, and that each chamber is also assigned a separately controllable control valve for controlling the flow of the temperature control medium.

In this way, when the device is installed with a substantially constant temperature cooling medium, e.g. Water that can be found. It is also not necessary to ensure that the temperature of the cooling medium is constant, but rather that the temperature fluctuations occurring in a central water supply can be easily coped with.

According to a further feature of the invention, it can be provided that the wall thickness measuring device is arranged in the area of the calibration mold and temperature sensors are arranged in the individual sections or sectors of the inner wall of the calibration mold, which, like the wall thickness measuring device and the control valves, are connected to a control circuit having a computer are.

These measures make it possible to quickly correct any deviations in the wall thickness from the specified target value, since the deviation is recorded practically in situ and therefore there are very short dead times in the control. This is practically given only by the thermal inertia of the calibration form, which can, however, be kept relatively small.

Furthermore, it is also possible to take into account the marginal zone influence despite the thermal decoupling of the individual sectors or peripheral sections of the calibration mold - the sectors can be separated by air gaps and only closed in the area of the inner wall of the calibration mold or completely separated by thermal insulation - because a temperature change in a circumferential section also affects the edge zone of the adjacent sections. This influence can be taken into account by means of the computer.

Furthermore, it can be provided in a device for the production of pipes that the wall thickness measuring device is formed by a number of sensors held in a ring, the ring being able to oscillate about an angular amount corresponding to a sector of the inner wall of the calibration mold.

These measures make it possible to record the wall thickness practically over the entire circumference and to compensate for any deviations in the wall thickness by changing the temperature of the corresponding sector of the calibration mold and / or the extrusion gap.

Furthermore, it can also be provided that the extrusion gap and the calibration mold are thermally decoupled from one another, for example by means of thermal insulation or an air gap.

This prevents mutual influence between the extrusion gap and the calibration mold.

In this context, it is advantageous if thermocouples are arranged in the individual sections or sectors of the extrusion gap, which are connected to the control circuit and which are assigned to the individual sections or sectors of the calibration mold, which are separated and by means of actuating devices acted upon by the control circuit can be regulated independently of one another.

This enables closed control loops for controlling the temperature of the individual peripheral sections of the extrusion gap and the calibration form. In addition, the computer also allows the influence of the temperature change of an adjacent section on the edge zones of the respectively adjacent sections of the calibration mold and of the extrusion gap to be taken into account.

Furthermore, these measures have the advantage that there are options between different operating options. For example, the correction of the wall thickness of the extruded profile can be controlled exclusively by influencing the individual circumferential sections of the calibration mold, or an additional influencing of the temperature distribution over the individual circumferential sections or sectors of the extrusion gap can be provided. In this way, it is still possible to correct thick spots in the extruded profile when the temperature in the extrusion gap can no longer be reduced. In this case, the temperature must be increased in the corresponding section of the calibrating mold, the section of the extrusion gap whose temperature can no longer be increased. Likewise, in the case of thin spots, when the maximum temperature in the extrusion gap is reached, the temperature in the corresponding area of the calibration mold can be lowered, as a result of which the thin spot can be corrected.

Experiments have shown that even when the individual sections of the extrusion gap are heated, a variation range of approximately 40 ° C. is available, the temperature in the region of the extrusion gap being in the range of approximately 190 to 230 ° C. for most thermoplastic materials lies and this variation range enables a change in the wall thickness of approx. 10% with the same cooling over the scope of the calibration form. By combining it with the variation of the temperature of the cooled calibration mold over its circumference, there is therefore a very extensive possibility of influencing the wall thickness in individual circumferential sections or sectors of the extruded profile or tube.

The invention will now be explained in more detail with reference to the drawing.

Show: 3

AT 401 031 B

Fig. 1 shows schematically a device according to the invention;

2 and 3 are schematic oblique views of two embodiments of an inventive

Facility;

4 and 5 a longitudinal and cross section through the extrusion gap of an inventive

Facility;

6 to 8 flowcharts and

9 and 10 cross sections of the calibration device.

1 has an extrusion tool 30, the extrusion gap 3 of which is divided into a plurality of peripheral sections or sectors 4, the temperature of which can be regulated separately from one another.

Separated from this extrusion tool by an air gap 16 which serves for thermal decoupling, a calibration mold 1 is arranged, on the inner wall of which the extruded profile or tube is cooled and fixed in this form and which is also divided into peripheral sections or sectors 2, the temperature of which can be regulated essentially independently of one another.

At the end of the calibration mold 1 there is a wall thickness measuring device 5 which uses ultrasound to measure the wall thickness of the extruded profile or tube. However, it can also be provided to provide wall thickness measuring devices both in the area of the extrusion die 30 and in the area of the calibration mold 1, the signals of which are processed in the control circuit 12.

Furthermore, a withdrawal device 41 is provided for the already cooled profile or tube, which is formed essentially by the extruded tube surrounding substantially synchronous revolving conveyor belts 42, which act distributed over the circumference of the extruded tube on its outer surface and pull it off via the frictional engagement . The drives of the conveyor belts 42 are regulated by the control unit 43, which in turn receives the control signals from the control circuit 12.

The control circuit 12 receives signals from the wall thickness measuring device 5 and the temperature sensors 17 and, apart from the control unit 43 of the extraction device 41, controls the heating devices 6 arranged in the sectors 4 of the extrusion tool 30, which, as can be seen from FIGS. 4 and 5, are designed as heating rods . Furthermore, the control circuit 12 also controls a temperature control device 8 which, as can be seen from FIG. 2, regulates the flow of a temperature control medium through chambers arranged in the sectors 2 of the calibration mold 1 by means of control valves 10. Further temperature sensors 11 are arranged in the sectors 2 of the calibration mold 1, which also supply signals to the control circuit 12.

In the embodiment of the device according to the invention according to Fig. 2, which is provided for the production of pipes, the wall thickness measuring device is provided by a number of sensors 14, not shown, e.g. Ultrasonic measuring heads, which are held in a ring 13. This ring can be pivoted in the direction of the double arrow 15, oscillating about the angular amount over which a sector extends, so that the wall thickness measurement can take place over the entire circumference. These measured values are averaged over the respective sector 2 in the control circuit.

The embodiment according to FIG. 3, which is intended for the production of non-circular profiles, differs from that according to FIG. 2 only in that both the extrusion tool 30 and the calibration mold 1 in sections 4 or 2 adjoining one another in the circumferential direction 2, which, like the sectors 4 and sectors 2 according to FIG. 2, are thermally decoupled from one another, the decoupling being provided by corresponding incisions into which insulating material can optionally be inserted.

2 and 3, it should be noted that the air gap 16 for the thermal decoupling of the extrusion die 30 from the calibration mold 1 is exaggerated for reasons of better clarity.

FIG. 4 shows, on an enlarged scale, a cross section of the outer jacket of the extrusion die 30, which is divided into corresponding sections 4 by sectors, which are largely thermally decoupled from one another by the cuts and which can be heated by two heating elements 6. The heating power for each segment 4 can be regulated separately and independently of one another, the heating power being regulated by the control circuit 12.

Furthermore, a temperature sensor 17, which is connected to the control circuit 12, is arranged in each of the sectors 4 of the extrusion tool 30.

5, the heating elements 6 run essentially in the longitudinal direction of the extrusion die, whereas the temperature sensors 17 are installed radially.

FIG. 9 shows a cross section through the calibration mold 1 according to FIG. 3. In this calibration mold 1 too, the individual sections 2 adjoining one another in the circumferential direction are thermally decoupled from one another by corresponding incisions. In addition, in the areas of the walls 7 of the mold that come into direct contact with the extruded profile, a temperature-control medium flows 4

AT 401 031 B

Chambers 9 arranged so that the temperature of the walls 7 coming into contact with the extruded profile can be regulated accordingly.

In the walls 7 coming into contact with the extruded profile, temperature sensors 11 are arranged, which are connected to the control circuit 12. The temperature of the chambers 9 through which the temperature control medium can flow separately and independently of one another is regulated by the control circuit 12 via the temperature control device 8.

FIG. 10 shows a cross section through a calibration mold according to FIG. 2, which is provided for the production of pipes. This calibration form also has chambers 9 lying next to one another in the circumferential direction, through which a temperature control medium flows and which can be regulated in temperature independently of one another. For this purpose, the flow through the individual chambers 9 is controlled by means of control valves 10. The number and arrangement of the chambers, which simultaneously form sectors 2 of the calibration mold 1, is selected such that they are aligned with the sectors of the extrusion tool or its extrusion gap 13.

In the wall or walls 7 that come into contact with the extruded tube, a temperature sensor 11 is arranged in each of the sectors 2, all of which are connected to the control circuit.

The possible modes of operation with the device according to the invention are shown in the flow diagrams according to FIGS. 6 to 8.

Fig. 6 shows a flow chart for thermal centering using the control of the temperature in the extrusion gap.

The results S; the wall thickness measurement in the individual circumferential sections Uj of the extruded profile are used to calculate the mean wall thickness smittei of the entire profile and to determine the difference between the measured minimum smin and maximum value smax. The values Si, in particular in the case of pipes, can be values averaged over a sector.

If the value smjn is not within a certain tolerance range around a predetermined value S limit. the take-off speed is changed accordingly and the process is started again.

If the value smin lies within the tolerance range and the withdrawal speed therefore remains constant, the point or the peripheral section Uk at which the value smin occurs is located and the temperature increase T required to increase the wall thickness to the predetermined target value Ssoh in the corresponding peripheral section 4 (Circumferential section Uk) of the extrusion gap 3 is calculated.

It is then checked whether a predetermined maximum temperature T limit should be exceeded. This value tenter depends on the material to be processed and is around 230 * C for the most frequently used materials. If such an excess was required for centering, an alarm is triggered to cause manual pre-centering.

If the temperature required for centering is below this value, the calculated temperature increase T is carried out in the corresponding peripheral section 4 of the extrusion gap.

The wall thicknesses are then measured again and it is checked whether the currently determined difference smax-smin of the wall thickness is below a predetermined difference value. If this is the case, the control process is complete, if not, the entire control loop is run through again.

With this adjustment mechanism, the average wall thickness is brought up to the target value and the different wall thickness distribution is compensated.

Fig. 7 shows a flow diagram for the thermal centering of the wall thickness with the aid of the calibration form in connection with the trigger control.

After this, the take-off speed is regulated in the same way as according to the flow chart according to FIG. 6.

After setting the take-off speed, that circumferential section or sector Uk is determined in which the maximum wall thickness Smax occurs and the temperature increase T necessary to achieve the desired wall thickness in this area is calculated in that chamber 9 of the calibration mold 1 which is the temperature of this area of the extruded profile forming circumferential section or sector 2 determined.

In a further step, it is checked whether the temperature in this circumferential section or sector 2 of the calibrating mold 1 would have to be increased to above T limits (e.g. 50 * C). In this case, an alarm is triggered which can cause the device to be pre-centered manually.

If this is not the case, the temperature increase T is now carried out in that chamber 9 of the calibration mold 1 which determines the temperature of the peripheral section Uk.

Then, analogously to FIG. 6, the difference between the maximum and minimum wall thickness over the circumference of the extruded profile is determined and checked whether it is below a predetermined limit value. If this is the case, the control process has ended, if not, the described loop is run through again. 5

Claims (6)

AT 401 031 B FIG. 8 shows a flow chart for the thermal centering of the wall thickness of an extruded profile using the calibration mold and the extrusion tool in connection with the control of the take-off speed. The flow diagram consists of two parts, the first of which essentially corresponds to the sequence according to FIG. 6 and the second essentially corresponds to that according to FIG. 7. The setting of the take-off speed is carried out in the same way as in FIGS. 6 and 7. The The first part of the control corresponds to the sequence in FIG. 6, with the difference that if a temperature increase T in the extrusion nozzle is required which would exceed the predetermined limit value Tlim1 (eg 220 ° C.), the alarm is not triggered, but now this temperature limit value first is set in this peripheral section 4 of the extrusion gap 3. Then, in the second part, another regulation is carried out using the temperature setting in the calibration form as in Fig. 7. For this purpose, the wall thicknesses are measured again, smittei, smax, smjn, and smax - smin are calculated and checked whether the minimum wall thickness smm is outside the tolerance range. If this is the case, the system branches to the very beginning of the first part and smjn is corrected by the deduction rule. Otherwise, as in FIG. 7, the maximum wall thickness is then located. The temperature increase T2 in the peripheral section 2 of the calibration mold 1, in which the maximum wall thickness occurs, is then calculated in order to reduce the difference between the maximum and the minimum value smax, smin of the wall thickness. In a further step, it is checked whether the temperature in this circumferential section 2 has to be raised above Tgren22 (e.g. 50 ° C). If this is the case, an alarm is triggered which requests manual pre-centering. If this is not the case, the temperature in chamber 9 of this peripheral section 2 is increased accordingly. Then, as in FIG. 7, it is checked again whether the current difference between the maximum and the minimum wall thickness is below a predetermined limit value or not. In the first case, the control is finished, in the second case the lower loop for the trigger control and the thermal centering is run through again with the help of the calibration nozzle from the first wall thickness measurement. 1. Device for regulating the wall thickness of a pipe or profile made of thermoplastic plastics by extrusion with an extrusion gap formed by a nozzle and mandrel body, the nozzle of which is preferably divided into a number of sectors with heating devices that can be controlled separately in their heating power, and a downstream calibration mold , the inner walls of which determine the outer shape of the extruded tube or profile and can be temperature-controlled by means of a temperature control device, characterized in that the inner wall of the quenching mold (1) is divided into sections (2) or sectors which are adjacent to one another in the circumferential direction and are thermally decoupled from one another , The individual sectors or sections (2) being assigned independently controllable temperature control devices. 2. Device according to claim 1, characterized in that the individual sections or sectors (2) are assigned chambers (9) which are flowed through by a temperature control medium and have a wall common with the inner wall of the calibration mold (1), and that each Chamber is also assigned a separately controllable control valve (10) for controlling the flow of the temperature control medium. 3. Device according to claim 1 or 2, characterized in that the wall thickness measuring device (5) is arranged in the region of the calibration mold (1) and in the individual sections or sectors of the inner wall of the calibration mold (1) temperature sensors (11) are arranged, which just as the wall thickness measuring device (5) and the control valves (10) are connected to a control circuit (12) having a computer. 4. Device according to claim 3, for the production of pipes, characterized in that the wall thickness measuring device (5) by a number of in a ring (13) held sensors (14) is formed, the ring around a sector of the inner wall of the Calibration form (1) corresponding angle amount can be pivoted in an oscillating manner. 5. Device according to one of claims 1 to 4, characterized in that the extrusion gap (3) and the calibration mold (1) are thermally decoupled from one another, for example by means of thermal insulation or an air gap (16). 6 AT 401 031 B device according to one of claims 1 to 5, characterized in that in the individual sections or sectors (4) of the extrusion gap (3) thermal sensors (17) are arranged, which are connected to the control circuit (12), and which are assigned to the individual sections or sectors (4) of the calibration standard (1), which can be regulated separately and independently of one another by means of actuating devices (8) acted upon by the control circuit (12). Including 8 sheets of drawings 7