Title of Invention

A DIE FOR THE PRODUCTION OF A PLASTIC PIPE

Abstract

A DIE FOR THE PRODUCTION OF A PLASTIC PIPE A die for the production of a plastic pipe of length X in the centrifugal process, comprising : a cylindrical casing (26), an internal diameter > 1 metre, a length > 3 metres, two ball races (22, 24) for the rotational guidance of the die on corresponding bearings (30.1, 30.2; 30.3, 30.4), the ball races (22, 24) are arranged at opposite ends of the die outside a die section (10, 12, 14) corresponding to pipe length X, characterized in that at least one ball race (24) has a peripheral face (24u), which has at least a first portion which runs at an angle > 0 and < 90° to the axial direction (M-M) of the die. Figure 2.

Full Text

The invention relates to a die for the production of plastic pipes in a centrifugal process. The production of plastic pipes in the centrifugal process is described for example in CH 684 326 A5. CH 688 765 A5 shows a known die (also called: mould or matrix) By means of an arm (so-called "feeder") movable back and forth in the axial direction of a die, the raw materials, in particular curable resins, sand, glass fibres and fillers, are flung (thrown) into the rotating die, for which reason one speaks of the centrifugal process. EP C 360 758 Bl gives examples of a material selection and the construction of one such pipe with different layers. Although the curing of the synthetic resins used is an exothermic process, the die is additionally temperature-regulated from the exterior with warm air or warm water in order to accelerate the curing of the plastic material and thus to increase the cycle time. This applies in particular to relatively thick-walled pipes with a larger diameter and greater length. These are pipes with an internal diameter of at least 1 metre and a length of at least three metres, whereby the internal diameter of the die can be > 2 metres, > 2.50 metres, but also > 3 metres, and the die length can also amount to 4, 5 or 6 metres, if need be even more. With such large-format dies the bearing arrangement is extremely difficult. CH 688 768 A5 already makes reference to this, although dies are described there that are intended to have a diameter of only 0.15 m. In the case of large-format dies of the type mentioned above, it is known from DE 29 21 652 Al to arrange support rings (ball races) on the outside of the die, said support rings rolling off on corresponding bearings (rollers, in some cases driven rollers). For static reasons, these ball races are arranged at a distance from the respective end of the die. According to DE 29 21 652 Al, the support rings are arranged on longitudinal ribs which run in the axial direction on the die casing. If warm (hot) air is blown from the exterior onto such a die or if such a die is sprayed from the exterior with warm/hot water, this has the drawback that, wherever the die casing is mechanically reinforced, i.e. in the region of the longitudinal ribs and support rings for example, the heat transfer to the internal wall of the die is delayed. The effect of this is that the temperature on the internal wall of the die in the immediate vicinity of the ball races/longitudinal ribs is often lower than in the regions in between where the die casing is relatively thin. The result is a different duration or even type of curing reaction of the resin. This gives rise to problems in the production of the pipe and with regard to its quality. For example, the time for the heating of the die has to be extended in order to establish temperature equalization. But even then there remains, considered over time, a temperature gradient inside the wall of the pipe to be produced, with the consequence of possible quality differences along different sections of the pipe. The object of the invention is to solve this problem and in particular for large-format pipes which are produced in the centrifugal process. No drawbacks should arise for the bearing arrangement of the die. The invention is based on the following knowledge: Special reinforcements of the die and special bearing parts for the die, such as the aforesaid support rings or longitudinal ribs, are to be avoided as far as possible, in order to avoid different wall thicknesses of the die. Dies of the size mentioned, however, are for the most part unusable without mechanical reinforcements, at least in the region of their bearing faces. There follows from this the idea according to the invention of displacing these troublesome, but necessary parts into regions of the die that lie outside the die zone along which the pipe to be produced is formed. In other words: the ball races for example are to be displaced to theends of the die, more precisely in a region that lies outside the technically relevant length of the pipe to be produced. For the production of a pipe with a length of 6 metres, for example, the die necessarily has to be longer. For example, it has a length of 6.50 m. By means of the aforesaid feeder, a pipe with a length > 6.00 and The idea according to the invention aims to displace the ball races either into these regions, i.e. at the end of the die in regions in which the construction of a pipe (pipe jacket) does not take place at all, or in die regions which are adjacent to the end regions of the pipe to be produced, but which after production of the pipe are cut off. In this way, the die casing (jacket) is designed for the most part homogeneous over the whole technically relevant length in particular, there are no large-volume ball races or such like present. The heat transfer from the exterior to the interior (onto the pipe to be produced) is now for the most part constant over the whole extent of the die. A pipe with very homogeneous material properties can thus be formed. In its most general embodiment, the invention relates to a die for the production of a plastic pipe of length X in a centrifugal process, comprising the following features: a cylindrical casing, an internal diameter > 1 m, a length > 3 m, two ball races for the rotational guidance of the die on corresponding bearings, - the ball races are arranged at opposite ends of the die outside a die section corresponding to pipe length X. For example, one ball race is arranged at one free end of the die, the other ball race at the other free end. The casing of the die can be formed at least at one free end with a radially projecting flange, to which a ball race is fixed. This means that, with a desired pipe length of 6 m for example, the die needs to be only a little larger, for example 6.10 m. The ball races are then fixed, as it were in the extension of the die, at both ends to the aforesaid flanges. The die together with the two ball races can then have a length of, for example, 6.30 or 6.40 m. Precisely with this form of embodiment it becomes clear that the ball lie outside the die section that is relevant for the pipe production (the finished pipe). At least one ball race can project axially beyond the casing i.e. at the end face. It is however also possible for at least one ball race to project radially beyond the casing. This can be arranged for example by the disposition of the aforesaid flange. The length of the die can clearly be over 3 m, for example > 4 m, > 5 m or even 6 m and thereover. The internal diameter can also be > 2m, > 2.5 m or 3 m or thereover. The larger and a longer the die is selected, the more expedient it is to produce the die from several cylinders following on from one another in the axial direction of the die. For this purpose, the cylinder (pieces) can be welded together at the end face. It is also possible to design the cylinder pieces with (relatively narrow) flanges at the end faces. Adjacent flanges of adjacent cylinder pieces can thus be bolted together or connected in some other way. It is true that a material reinforcement arises at these points compared with neighboring zones of the die casing. These material reinforcements, however, are much smaller than those in the region of a ball race, so that they do not in fact interfere with the pipe manufacture. At least one ball race can have a cylindrical peripheral face. The axes of associated bearings then run in particular parallel to the axis of the die. Any tolerances can be compensated for by the use of pendulum bearings. The peripheral face of a least one ball race can however also be designed differently. According to one form of embodiment, at least one ball race has a peripheral face, which has at least a first portion that runs at an angle > 0 and According to a further form of embodiment, the peripheral face is designed with two inclined faces having different inclination, and preferably in a mirror-inverted design. In the simplest case, the peripheral face has a V-shape in cross-section. In this way, the die can be guided in the region of this ball race by a total of four bearings, whereby in each case two bearings in an inclined position act on the ball race on a side of the die, as is represented in the following description of the figures. Additional guide rollers can also be provided that guide the die in the axial direction. Further features of the invention will emerge from the features of the sub-claims as well as the other documents of the application. The invention will be explained below in greater detail with the aid of an example of embodiment. The figures of the accompanying drawings show the following: Figure 1 : is a perspective view of a die according to the invention, Figure 2 : a longitudinal section through the die according to figure 1, Figure 3 : a plan view onto the bearing end of the die according to figure 1. Identical or identically acting components are shown with the same reference numbers in the figures. Figure 1 shows a cylindrical die comprising three cylindrical pieces Q 0) (T2M 4 J welded together. All the cylindrical pieces Qo) (1^(14) have the same wall thickness w. The internal diameter amounts uniformly to 3.00 m. The total length of the three cylindrical pieces is 6 m. It goes without saying that the three cylindrical pieces a continuous, smooth, cylindrical internal wall ft 6) Whilst flange(l^) is welded to the free end of cylindrical piece(ity a corresponding flange at the free end of cylindrical sectional 4}bears reference number(20} A ball race(22\is bolted to this flange(2& Ball race(22)has a cylindrical peripheral facefe2iu A second ball race £4] is bolted to flange(j8| Ball race^24)has a peripheral face(24ia V shaped in cross-section. The overall length of the die including flanges 18, 20 amounts to approx. 6.10 m; including ball races 22, 24, the overall length is approx. 6.50 m. It is important to point out once again that the pipe to be produced is formed solely it the die section which is specified by cylindrical pieces 10, 12, 14. Insofar as the total length of the pipe is longer after removal from the die this does not cause any inconvenience, because the pipe is in any case subsequently cut to the desired length, whereby the pipe is trimmed at both sides. During the manufacture of the pipe, the die is sprayed, as described, around the periphery with hot water, for example. This takes place on the whole peripheral face of the die, i.e. especially on the peripheral face of cylindrical sections 10, 12, 14. But spraying of ball races 22, 24 is also harmless, because the ball races lie outside the region in which the pipe is produced. Since wall thickness w is in fact constant over the whole axial length of the die, a uniform temperature distribution also results and therefore uniform heating or uniform cooling over the whole of die casing (loS The special design of ball race (24) creates the possibility represented in fig. 3 of arranging obliquely set bearing wheels 30.1, 30.2 and 30.3, 30.4 respectively on opposite sides of the die and thus of creating not only a rotational bearing arrangement for the die, but at the same time an axial guide (in the direction of centre longitudinal axis M-M of the die) WE CLAIM: 1. A die for the production of a plastic pipe of length X in the centrifugal process, comprising 1.1 a cylindrical casing (26), 1.2 an internal diameter > 1 metre, 1.3 a length > 3 metres, 1.4 two ball races (22, 24) for the rotational guidance of the die on corresponding bearings (30.1, 30.2; 30.3, 30.4), 1.5 the ball races (22, 24) are arranged at opposite ends of the die outside a die section (10, 12, 14) corresponding to pipe length X, characterized in that 1.6 at least one ball race (24) has a peripheral face (24u), which has at least a first portion which runs at an angle > 0 and 2. The die as claimed in claim 1, wherein the casing (26) whereof has at least at one free end a radially projecting flange (18, 20) to which the ball race (22, 24) is fixed. 3. The die as claimed in claim 1, wherein at least one ball race (22, 24) projects axially beyond the casing (26) at the end face. 4. The die as claimed in claim 1, wherein at least one ball race (22, 24) projects radially beyond the casing (26). 5. The die as claimed in claim 1, comprising the cylinders (10, 12, 14) which are welded together at the end faces and/or are bolted together via flanges. 6. The die as claimed in claim 1, wherein a second portion of the peripheral face (24u) of the ball race (24) runs at an angle > 0 and with opposite inclination to the first portion. 7. The die as claimed in claim 1, with a cross-section of the peripheral face (24u) of the ball race (24) that is V-shaped in cross-section.

Documents:

0639-chenp-2005-abstract.pdf

0639-chenp-2005-claims.pdf

0639-chenp-2005-correspondnece-others.pdf

0639-chenp-2005-correspondnece-po.pdf

0639-chenp-2005-description(complete).pdf

0639-chenp-2005-drawings.pdf

0639-chenp-2005-form 1.pdf

0639-chenp-2005-form 18.pdf

0639-chenp-2005-form 26.pdf

0639-chenp-2005-form 3.pdf

0639-chenp-2005-form 5.pdf

0639-chenp-2005-pct.pdf