DE2357275A1 - Extruded pipes of synthetic thermoplastics and rubber - stretched mono- or biaxially on arbor determining inside diameter using hydraulic lubricant to prevent seizing - Google Patents

Abstract

In an extrusion machine with a ring-section die ejecting the semi-fluid thermoplastic material on to an arbor determining the inside dia. of the tube, a hydraulic lubricant is introduced without press. into a cavity immediately in front of the die where the extrusion is still semi-fluid, to be drawn along the arbor by the tube in a layer which becomes progressively thinner as the radial forces caused by cooling and/or a conical increase in dia. of the arbor, act on the extrusion.

Description

Method and system for the internal calibration of a plastic pipe.

The invention relates to a method for internal calibration a pipe made of plastic, in particular thermoplastic plastic, wherein the Tube as a quasi-liquid in a highly viscous state from a spray head with a mandrel and removed via a calibration cylinder connected to the mandrel as well as being cooled from the outside and thereby from the quasi-liquid state a soft plastic state is solidified until the pipe containing the caliber. the The invention also relates to a system for carrying out such a system Procedure. - The term plastic here also includes rubber. The following will only ever talked about plastic, although mainly the usual thermoplastics Plastics are addressed. - The term pipe also includes hoses, as far as these are sufficiently thick-walled to be calibratable. Of the Cross-section can be round or quasi-round, e.g. B. be elliptical. The calibration cylinder is a solid mandrel or a hollow cylinder. Ouasi fluid means the state of the preform geometrically already corresponding to the pipe to be produced, with the the pipe leaves the spray head, but in which the pipe is subjected to internal and external pressure loads is not yet able to absorb due to a lack of solidification. It is as it were around a highly viscous flow of liquid emerging from the spray head of a plastic screw press exit. The pipe is only solidified and increasingly solidified by increasing cooling thus keeping its shape and, after calibration, keeping its caliber.

Caliber denotes the fact that the barrel, except for controlled Has thermal expansion, defined inner diameter.

In known processes of the type described (compare Schenkel, Kunststoff-Extrudertechnik, 1963, pages 333 to 338 # is the calibration cylinder a more or less large extension of the mandrel in the spray head, the internal cooling, mostly as water cooling. Without cooling, the plastic, the alE Quasi-liquid emerges from the spray head, on which the mandrel resp.

Adhere to the calibration cylinder, at least in the layer.

The known measures are more or less expensive in terms of devices. If the calibration cylinder is cooled, the spray head must be used as a cross spray head or offset injection head. This requires a diversion of the liquid Plastic in the spray head and the storage is restricted to plastics that contain them Allow redirection. For example, hard polyvinyl chloride cannot be processed. If the spray head is designed as a straight spray head, then the coolant inlet is difficult. It could at most take place via the webs that are regularly used in such an extrusion head hold the mandrel. At the same time, this also requires cooling of these webs, cooled ones Bars produce weak points in terms of strength in the finished pipe. Furthermore the cross-section of the webs is hardly sufficient for considerable cooling. It is often, even with intensive cooling, it is not possible to place the tube on the calibration cylinder to solidify up to the caliber-containing molding, as this is too long a calibration cylinder and thus very high frictional forces and excessive pull-off forces would trigger.

If the withdrawal forces are to be controlled, must be within the framework of the known measures are used with a relatively short calibration cylinder, Furthermore, uncontrolled changes in the pipe must be carried out with this method after deduction from the calibration cylinder, the achievable tolerance must be accepted adversely affect the calibration. That doesn't change much, though the calibration cylinder is tapered conically for the purpose of reducing the pull-off forces. executes.

Often the pipe emerging from the spray head also sticks in the quasi-liquid area on the calibration cylinder, even if only on a part. It creates one In addition, the drag flow determined by the outlet pressure at the spray head, which the molecular Structure, orientation and texture, depending on the material, not favorably influenced. This is all the reason why e.g.

Pipes made from flexible materials such as soft PVC or from low-viscosity materials Materials such as polyester resins or made of highly adhesive materials are not included Internal calibration can be calibrated. External calibration is possible here (compare Schenkel, l.c.), however, it is very much in terms of devices and facilities much more complex and does not deliver the smooth one or even extreme smooth inner surface, which has numerous uses in thermoplastic pipes Plastic is required. - In a procedure of a completely different kind, it is known the pipe with considerable pressure between a hollow cylindrical outer tool and to press out using a suitable internal tool. Here are internal tools and Outer tool extended to such an extent that there is also cooling between the tools he follows. With the pressure between the tools, on the other hand, even higher pressure a hydraulic lubricant is introduced between the tool and the pipe, which acts as a hydrostatic cushion. This cannot be done with mere internal calibration Realize, because the pipe, especially in the quasi-liquid area, inflate would.

For external calibration with the calibration hollow cylinder connected to the spray head # and supporting air introduced into the pipe to be calibrated (in front of the plug or drag plug) it is known (see Schenkel, l.c.) between the pipe and the calibration hollow cylinder lubricating air to introduce. That may be the friction between the outer wall of the pipe and the inner wall of the calibration hollow cylinder but did not affect the internal calibration problems and does not eliminate the problems described there.

The invention is based on the object of the internal calibration method of the genus described at the outset so that it can be further developed without difficulty Raw materials made from all common plastics, in particular from flexible or low-viscosity plastics thermoplastic materials can be calibrated very precisely and with low tolerances.

The invention relates to a method for the internal calibration of a pipe made of plastic, with the pipe as a quasi-liquid in the highly viscous state an extrusion head with a mandrel and connected to the mandrel via a Calibration cylinder removed and thereby cooled from the outside and thereby out of the State of the quasi-liquid through a soft plastic state to the caliber-containing state Pipe is solidified. The area in which the described highly viscous state prevails, is referred to as the quasi-liquid area. The invention consists in that in Quasi-liquid area between the pipe and the calibration cylinder practically unpressurized a hydraulic lubricant is introduced, the molding having a lubricant entrainment layer dragged along between the calibration cylinder and the blank, and that this layer of lubricant on the calibration cylinder by radial forces to a lubricant drag wedge is degraded in the longitudinal section with decreasing thickness in a wedge shape. According to a preferred embodiment of the invention, the radial forces are generated by shrinkage, # the z. B. by Cooling is controlled.

- In the context of the invention, hydraulic lubricant refers to any (practically incompressible) liquid, the viscosity of which is lower than that of the Quasi-liquid that forms the pipe when it emerges from the spray head. The entry there is practically no pressure between the pipe and the calibration cylinder. In general, can can be worked with a conventional hydraulic lubricant. The statement that the hydraulic lubricant is broken down into a lubricant drag wedge also a quantity. The lubricant drag wedge surrounds the calibration cylinder, it can, depending on what is caused by the cooling of the pipe on the calibration cylinder Pressure in longitudinal section outwards more or less arcuate run when the pipe wall bulges a little. - The invention uses the surprising fact that (after the introduction of a hydraulic lubricant between Tube and calibration cylinder in the quasi-liquid range) with the withdrawing tube acting radial forces a drag flow of special geometry, namely one which decreases in thickness in a wedge shape towards the end of the calibration cylinder and therefore as it were, can suck in the drag flow known as lubricant drag wedge, if you ensure that the cooling-based shrinkage of the pipe in the The range of the calibration cylinder does not become too large. On the hydrostatic pressure in the lubricant drag wedge, the pipe wall rests as if on an inclined plane or on a corresponding pad.

The friction is practically zero. It is enough despite the proportionately small extrusion speed the viscosity-dependent pressure in the drag flow at every point to compensate for the radial shrinkage stress, however so that the lubricant is dragged along. Of course the hydraulic one is Lubricant wedge thin everywhere. The temperature dependence of the viscosity of the lubricant is taken into account. All of this can be done by choosing an appropriate lubricant and always achieve and through appropriate design of a surrounding cooling bath requires a relatively large calibration cylinder that is considerably longer than with the known version. A slight conical extension of the calibration cylinder towards the end of the trigger (in contrast to the usual conical tapering of such Calibration cylinder) supports the effect. In the method according to the invention a real drag flow arises from the hydraulic lubricant around the calibration cylinder around with that for a wake typical speed profile (with decreasing thickness in a wedge shape). This has the consequence that the pipe wall on the calibration cylinder no longer adheres at any point and in the pipe wall itself, even in the quasi-liquid area, no more wake flows. As a result, the molecular Structure, orientation and texture of the finished pipe positively influenced. With a pneumatic medium - similar to the lubricating air described at the beginning - can be too low a viscosity a more effective and effective in the sense of the above explanations Do not generate the entrainment wedge, not even when the pressure is applied pneumatic medium.

In addition, a pressure feed of the lubricant because of the character of the pipe emerging from the spray head as a quasi-liquid in the area of the outlet is not possible at all. It would cause annoying bloating and inflation of the tube enter in the quasi-liquid area.

In detail, the process according to the invention can be applied in various ways Wise-further training and shaping. In the embodiment in which the pipe (depending on the material) In the quasi-liquid area, when exiting the spray head, there is initially a relief expansion experiences, which forms a relief gap between the pipe and the calibration cylinder, The invention recommends that the lubricant is immediately behind the spray head and is introduced distributed over the inner circumference - and practically without pressure. in the The scope of the invention is to use the lubricant drag wedge for the purpose of increasing its viscosity and thus the pipe to cool from the inside, so what a Requires cooling of the calibration cylinder. In general, such cooling is as is explicitly emphasized, but not necessary and not even wanted. At least it should the tube in the area of the end of the calibration cylinder be subjected to particularly intensive cooling from the outside, so on this Place a stuffing box effect through the shrinkage of the pipe, which prevents that the withdrawing pipe entrains too much of the hydraulic lubricant.

In the method according to the invention, as already mentioned, the hydraulic lubricant to adjust its viscosity so that the lubricant drag wedge absorbs the pressure loads described. The smaller the gap, the larger is the internal pressure that is created in the lubricant drag wedge against the shrinkage pressure of the pipe to be calibrated acts. There is an analogy to the hydrodynamic one Lubricant Friction Theory.

The advantages achieved can be seen in the fact that when implemented of the method according to the invention practically for any plastic, in particular A perfect internal calibration is carried out for each thermoplastic material can be. For this it is not necessary to have a cross-head on the extruder to work, especially since cooling of the calibration cylinder is regularly out of the question comes. The supply of the lubricant via the mandrel of the spray head and consequently through the mandrel holding webs through is problem-free, since only one is relatively A small amount of lubricant is required, which does not have a cooling effect and, if necessary, increases it May have temperature. Even materials that have hardly been calibrated so far thes, such as soft PVC and highly adhesive synthetic resins in particular, can be calibrated will. This enables the manufacture of completely new products. The length of the calibration cylinder is chosen so that the calibration is complete on the calibration cylinder closed is. As a result, very accurate inside diameters can be guaranteed. Disruptive frictional forces are not caused by an extremely long calibration cylinder, # because it is open everywhere the sliding friction is replaced by lubricant friction in the calibration cylinder. Of particular advantage is finally the fact that the method according to the invention inherently very easily can be realized that I knew with opposite Plants of vastly improved performance works.

In terms of the device, the invention is based on a screw extruder with extrusion head and mandrel and calibration cylinder connected to the mandrel. the In terms of device, the invention consists mainly in the fact that between the mandrel and the calibration cylinder a device for introducing a hydraulic lubricant is arranged and the calibration cylinder from a heat exchanger to achieve the radial forces is surrounded by shrinkage. The device to introduce the hydraulic According to a preferred embodiment, there is lubricant between the calibration cylinder and the tube of the invention from a ring roughening mandrel and calibration cylinder, wherein the ring space Via bores in the mandrel or in the extrusion head to a lubricant reservoir connected.

A return line for the lubricant can be connected to the annulus be, which at the same time causes a pressure relief of the annulus. The annulus is expediently via a conical section on the calibration cylinder in the withdrawal direction of the tube tapers in a wedge shape. According to a preferred embodiment of the invention the calibration cylinder has a smooth surface everywhere. As within the scope of the invention a vote of cooling and thus the shrinkage forces Formation of the lubricant drag wedge is required, according to the preferred embodiment the invention of the heat exchanger designed in a special way. You just come result when the heat exchanger consists of a coolant tank with several longitudinal of the calibration cylinder consists of distributed chambers that can be adjusted to different cooling temperatures are. The means for introducing the hydraulic lubricant are generally provided with a simple storage container, the lubricant is not supplied negative pressure. It can even be useful to connect the storage container to relieve with a vacuum pump, at the same time possibly on the hot pipe sucking off evaporating lubricant.

In the following the invention is based on only one embodiment Illustrative drawing explained in more detail.

In a schematic representation, FIG. 1 shows a longitudinal section through a system for carrying out the method according to the invention, FIG. 2 the enlarged Section A from the object according to FIG. 1 and FIG. 3 shows a graphic representation to explain the pressure behavior in the lubricant drag wedge in the figures The system shown serves for the internal calibration of a pipe 1 made of thermoplastic in the exemplary embodiment Plastic, with the tube 1 as a quasi-liquid in the highly viscous state from the Injection head 2 with mandrel 3 of a plastic screw extruder 4th expressed and withdrawn via a calibration cylinder 5 connected to the mandrel 3 as well as being cooled from the outside and thereby from the state of quasi-liquid is solidified via a soft plastic state up to the caliber-containing pipe 1. In particular from FIG. 2 it can be seen that between the mandrel 3 and the calibration cylinder 5 a device 6 for introducing a hydraulic lubricant 7 is arranged and the calibration cylinder 5 is surrounded by a heat exchanger 8. Here is the Arrangement made so that this device 6 for the introduction of a hydraulic Lubricant 7 between the calibration cylinder 5 and the quasi-liquid pipe 1 from a Annular space 6 exists, this annular space 6 via bores 9 in the mandrel 3 or extrusion head 2 is connected to a lubricant reservoir 10. Here is that hydraulic lubricant 7 pressureless. The bore 9 for the supply of the lubricant 7 goes through a web 11 with which the mandrel .3 in the extrusion head 2.

is kept as usual. Incidentally, it can be seen in FIG. 2 that the Annular space 6 via a conical section 12 on the calibration cylinder 5 in the withdrawal direction of the tube 1 is designed to be tapered in a wedge shape. Here the calibration cylinder can be equipped with a distributor groove.

The heat exchanger 8 consists of one. Coolant container with several along the calibration cylinder 5 distributed chambers 13, which by the supply of coolants different temperature can be set to different temperature. the The temperature is set so that initially in the quasi-liquid range of the pipe 1 between tube 1 and calibration cylinder 5 in the exemplary embodiment over the inner circumference the pipe 1 distributed a hydraulic lubricant 7 is entrained. This forms # under the Influence of radial forces due to shrinkage mentioned lubricant drag wedge 14. Fig. 3 makes it clear that the tube 1 on removed from this hydraulic drag wedge 14 and on the lubricant drag wedge 14 is solidified until the pipe 1 containing the caliber. The pressure P is above it as a curve applied. It can be seen that the pipe 1 as it were on a wedge-shaped hydraulic Padding. The tube 1 is one in the region of the end of the calibration cylinder 5 subjected to particularly intensive cooling, so that at the end of the calibration cylinder 5 a stuffing box effect arises through shrinkage, which causes the lubricant drag wedge 14 reduced to a minimal, almost vanishing thickness. At the beginning of cooling shouldn't this be too strong.

Claims (11)

Expectations: Method for the internal calibration of a pipe made of plastic, wherein the pipe as a quasi-liquid in a highly viscous state from a spray head with a mandrel pressed out and pulled off via a calibration cylinder connected to the mandrel as well as being cooled from the outside and thereby from the state of quasi-liquid is solidified via a soft plastic state up to the caliber-containing pipe, d a d u r c h e k e n n -z e i c h n e t that in the quasiflUELgkeitsbereich between A hydraulic lubricant was introduced into the tube and calibration cylinder practically without pressure is, whereby the molding has a layer of lubricant between the calibration cylinder and Molding with it, and that this layer of lubricant on the calibration cylinder by radial forces to a lubricant drag wedge with a wedge-shaped in the longitudinal section decreasing thickness. 2. The method according to claim 1, characterized in that the radial Forces generated by shrinkage. -3. Method according to claims 1 and 2 in the embodiment in which the pipe is initially in the quasi-liquid area when it emerges from the spray head undergoes a relief expansion that creates a relief gap between the pipe and Forms calibration cylinder, characterized in that the lubricant directly is introduced behind the spray head and distributed over the inner circumference, namely practically pressureless. 4. The method according to claims 1 to 3, characterized in that that the lubricant drag wedge and thus the pipe are also cooled from the inside. 5. Process according to claims 1 to 4, characterized in that that the tube is particularly intense in the area of the end of the calibration cylinder Is subjected to cooling. 6. Plant for carrying out the method according to claims 1 to 5, consisting of screw extruder, extrusion head with mandrel and to the mandrel connected calibration cylinder, characterized in that between the mandrel (3) and calibration cylinder (5) a device (6) for introducing a hydraulic Lubricant (7) arranged and the calibration cylinder (5) from a heat exchanger (8) is surrounded. 7. Plant according to claim 6, characterized in that the device (6) for introducing a lubricant (7) between the calibration cylinder (5) and the tube (1) consists of a ring space (6) between the mandrel (3) and the calibration cylinder (5) and the annular space (6) via bores (9) in the mandrel (3) or extrusion head (2) to one Lubricant reservoir (1Q) is connected. 8. Plant according to claims 6 and 7, characterized in that the annular space (6) via a conical section (12) on the calibration cylinder (5) in the withdrawal direction of the tube (1) is designed to be tapered in a wedge shape. 9. Plant according to claims 6 to 8, characterized in that the heat exchanger (8) consists of a coolant tank with several along the calibration cylinder (5) consists of distributed chambers (13) which can be adjusted to different cooling temperatures are. 10 system according to claims 6 to 9, characterized in that the calibration cylinder (5) is in turn designed so that it can be cooled. 11. Plant according to claims 6 to 10, characterized in that the calibration cylinder (5) has a smooth surface. Blank page