NL1016456C2 - Method for manufacturing an accessory as well as a pipeline. - Google Patents

Description

Method for manufacturing an accessory as well as a pipeline

The invention relates to the manufacture of an accessory from plastic. Traditional thermoplastic fittings are usually made by injection molding. In the design of an accessory used as a branch, account is taken of the fact that the opening to which the branched-off pipe section is connected constitutes a major weakening of the wall of the through-pipe. Such an attenuation can be absorbed in the case of an injection-molded attachment by increasing the edge of the hole as well as the wall thickness of the attachment 10 itself.

Especially with larger pipe diameters, however, there is a problem that the injection molding of fittings is hardly economically justified anymore. In such cases, the attachment must be made up of individual pieces. In order to achieve the required strength and to compensate for the negative influence of the hole in the continuous wall 15, additional reinforcements must be provided. This is a cumbersome and expensive method.

The strength of such an accessory could also be achieved by starting from a pipe piece with a larger wall thickness. It is precisely in the case of pipes with large diameters that the position of the extrusion technique does not allow the wall thickness to be increased indefinitely. If a thicker wall were to be extruded, the cooling process may proceed too slowly. This entails undesired oxidation phenomena, which have a negative effect on the quality of the end product

The object of the invention is therefore to provide a method with which these problems can be circumvented, and a pipe piece with improved strength properties can be manufactured economically.

That object is achieved by means of a method for manufacturing a pre-stressed pipe section from plastic, comprising the steps of: - providing a first plastic pipe section, - providing a second plastic pipe section with an internal diameter of 30 which is smaller than the external diameter of the first pipe part, - changing the cross-sectional dimensions of at least one end of a first of the pipe parts, such that the end of the second pipe part can be brought around the end of the first pipe part, 7 o 1 6 4 Sliding the pipe parts onto each other, such that tensile stresses are generated in the first (inner) pipe part, and tensile stresses are generated in the second (outer) pipe part.

With such a prestressed pipe section, there is a tensile pre-stress in the outer layer and a pressure pre-stress in the inner layer. Such a bias distribution is favorable for conduit tubes in which a medium is transported under excess pressure. The pressure bias in the inner layer ensures that no or only tensile stresses occur there. As a result, the occurrence of cracks due to internal stresses in the inner wall (stress cracking) can be largely avoided.

The method according to the invention can be based on pipe sections with standard dimensions. Preferably, a pipe part is chosen that is identical to the pipe parts that are used in the rest of the pipe, so that the desired connection is ensured.

The most obvious advantages are obtained if the first and the second pipe section have identical cross-sectional dimensions. By sliding such identical pipe sections onto each other, first of all, the desired bias and thus the desired improvement of the strength properties are obtained in a simple manner, while furthermore the correct connection to the rest of the pipe is guaranteed.

Sliding the pipe parts onto each other can be facilitated by pumping one of them. Alternatively, one or both pipe sections can be made with a conical end surface. By means of end surfaces thus formed, one pipe part can be widened and the other slightly compressed, to such an extent that they can then be pushed over one another.

The pipe parts can be manufactured from all kinds of plastics, for example semi-crystalline plastics such as polyethylene or polypropylene.

Sliding on top of each other can be further promoted by heating the sliding surfaces over each other. In the case of polyethylene, a temperature of up to 60 ° C can be selected for this. On the one hand, at such a temperature, the cohesion of the polyethylene material is retained, and with it the pre-stress 70 1 6 456 3 in the pipe section, while on the other hand an important reduction of the friction coefficient and hence of the shear forces is obtained.

To reduce the shear forces, a fluid can also be pressed between the pipe sections.

The pipe sections can be used in various ways. First of all, such pipe sections can be used to manufacture accessories, for example T-shaped taps or bends. Secondly, such pipe sections can be used as complete pre-stressed pipes.

When manufacturing an accessory, such as manufacturing a reinforced branch piece or a bend piece, for a pipeline, the method according to the invention comprises the following steps: - providing at least a first and a second reinforced line piece as described above, - applying an end surface 15 inclined with respect to its axis to at least one end of both pipe sections, - heating said obliquely shortened end surfaces of both pipe sections, and - welding the two pipe sections together by pressing the pipe sections together heated end surfaces thereof.

The invention furthermore relates to a prestressed pipe section manufactured according to the method as described above, wherein both pipe sections have the same length and completely overlap each other.

The invention also relates to an accessory made according to the method described above, wherein each pipe section with an end surface perpendicular to the axis thereof, comprises only one pipe part over the part adjacent to that end surface, and that the other pipe part ends at a distance from that end surface.

The invention will be explained in more detail below with reference to a few exemplary embodiments shown in the figures.

FIG. 1 shows a tubular piece of starting material for a prestressed pipe piece according to the invention;

FIG. 2 shows a piece of starting material, divided into two parts, just before sliding onto each other; * 0 ^ 6 456 4

FIG. 3 shows a cross section through the finished prestressed pipe section;

FIG. 4 to 6 show the steps of manufacturing a T-shaped attachment:

FIG. 7 shows the finished T-shaped attachment;

FIG. 8 shows a bend; FIG. 9 shows a variant.

The conduit 1 with a circular cross-section shown in fig. 1 forms the starting material for manufacturing a prestressed conduit piece according to the invention. This line 1 is divided by means of a cut 2 into two line parts 3,4, which must be pushed onto each other.

As shown in Fig. 2, the one pipe part 3 is flared up at its end 5 for this purpose. The end 6 of the other pipe part that faces the flared end 5 can have the original dimensions. As shown in Fig. 2, these pipe parts 2, 3 are then moved towards each other, the end 6 of the pipe part 2 penetrating into the raised end 5 of the pipe part 3. The pipe parts 2, 3 can thus be pushed completely over each other after which a pipe piece 7 is obtained with the cross-section shown in fig. 3.

As a result of the compression of the pipe parts 2 and 3, a compressive stress is created in the inner pipe part 2, while a tensile stress has been created in the outer pipe part 3. Such a bias distribution is favorable for transporting medium under pressure. In the case of non-prestressed pipe sections, that medium will generate a tensile stress over the entire thickness of the pipe section wall. The tensile stresses are concentrated in the inner wall of the tube. With pipe section 7 according to the invention, up to a certain overpressure of the medium, no tensile stresses occur in the inner pipe section 2, since first the pressure stress therein should be reduced to zero. As a result, cracks and fractures will occur less rapidly in the pipe piece according to the invention which could result from tensile stresses.

The pipe piece 7 according to the invention can be used for various applications. First of all, such a pipe piece can be used as a complete pre-stressed pipe, in which case the pipe parts 2, 3 have the same length and are fully pushed together. Such pipe sections can then be welded together at the end edges to the desired length.

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According to a second possibility, with such a pipe piece 7 according to the invention, an auxiliary piece can be manufactured, for example the T-shaped auxiliary piece 8 shown in Fig. 7. This T-shaped auxiliary piece 8 requires three pipe pieces 7 which according to the weld seams 9, 10 (see fig. 8) are attached to each other.

Such a T-shaped accessory is manufactured according to the steps shown in Figs. 4 to 6. First of all, three pipe sections 7 are manufactured for this purpose. The shaded part 12, 13 is removed from these pipe sections according to cuts extending at 45 ° to their center line. As shown in Fig. 6, these pipe sections 7 are then attached to each other with their end surfaces 14, 15 determined by these cuts, whereby an L-shaped connection 12 is obtained. Finally, a T-shaped accessory can be obtained by means of the third pipe section 7 by removing the shaded parts 16, 17 from the L-shaped connection and the third pipe section 7, respectively. The L-shaped connection 11 and the third pipe piece 7 are then attached to each other according to their end surfaces 18, 19 running at 45 ° to the respective center lines, whereby the K-shaped accessory according to FIG. 7 is obtained.

The variant of Fig. 9 relates to a bend piece that is made up of four pipe pieces 7, which are welded together by means of end surfaces (21) with a suitably chosen angle relative to the associated center lines.

With the pipe sections 7 located at the ends of that bend, the outer pipe section 3 ends at some distance from the end surface 20. The normal pipe can be welded to said end surface 20.

In the variant of Fig. 9, the first (inner) pipe part 2 has an outwardly directed conical end surface 22, and the second (outer) pipe part 3 has an inwardly directed conical end surface 23. Through these pipe parts 2, 3 with these end surfaces 22 23 to press against each other, the second pipe part 3 is slid over the first pipe part 2. In this case it is not necessary to first inflate the second pipe part 3.

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Claims (18)

Method for manufacturing a pre-stressed pipe section (7) from plastic, comprising the steps of: - providing a first plastic pipe section (2); - providing a second plastic pipe part (3) with an internal diameter that is smaller than the external diameter of the first pipe part (2); - changing the cross-sectional dimensions of at least one end (5) of the pipe sections, such that the end (5) of the second pipe section (3) can be brought around the end (6) of the first pipe section (2); - sliding the pipe parts (2, 3) onto each other, such that tensile stresses are generated in the first (inner) pipe part (2) and in the second (outer) pipe part (3). 15 Method according to claim 1, wherein the cross-sectional dimension of the pipe sections (2, 3) is identical. 3. Method according to 1 or 2, wherein the end (5) of one of the pipe parts (3) is widened by pumping on. Method according to claim 1 or 2, wherein the end of one of the pipe sections (2) has a conical cut (22). A method according to claim 4, wherein one end of the other conduit part (3) has a corresponding cone-shaped cut (23) such that if the conduit parts (2, 3) with their cone-shaped cuts (22, 23) face each other, the imaginary tips of those cuts (22, 23) point in the same direction. Method according to any one of the preceding claims, wherein the pipe parts (2,3) consist of semi-crystalline plastic. * 0 1 6 456 Method according to claim 6, wherein the pipe sections (2,3) consist of a polyolefin, such as polyethylene or polypropylene. A method according to any one of the preceding claims, wherein the pipe parts (2, 3) consist of an amorphous plastic. Method according to claim 6, 7 or 8, wherein at least one of the pipe parts (2,3) is heated to a maximum of 60 ° before they are pushed onto each other. The method according to claim 9, wherein at least one of the surfaces of the pipe sections (2,3) to be slid onto each other is heated. A method according to any one of the preceding claims, wherein during the sliding of the pipe parts (2, 3) a fluid is pressed between them. 15 Method according to one of the preceding claims, wherein pipe sections (2, 3) are pushed onto each other by an overlap length that is at least equal to the external diameter of the pipe section (7). A method for manufacturing a reinforced attachment, such as a branch piece (8) or a bend piece (21) for a pipeline, comprising: - providing at least a first and a second reinforced line piece (7); applying an end surface 25 inclined with respect to its axis to at least one end of both pipe sections (7); - heating said obliquely shortened end surfaces of both pipe sections (7); welding the two pipe sections together by pressing the heated end surfaces thereof together. 30 A method according to claim 13 for manufacturing a branch piece (8) for a pipeline, comprising: providing three pipe pieces (7), each with an end surface oriented obliquely with respect to the axis thereof; - applying to a pipe piece a flat end surface (19) directed at 45 ° with respect to the axis thereof; 5. arranging on the other two pipe sections of two end surfaces (14, 18; 15, 18) each forming a pointed end, each of which is directed at 45 ° with respect to its axis and encloses an angle of 90 ° with each other; - welding the three pipe sections together such that the flat, obliquely directed end surface (19) of the pipe section is welded to one of the end surfaces (18) of the pointed pipe sections and the other end surfaces (14, 15) of the pointed pipe sections are welded together. 15. Method according to claim 13 for manufacturing a bend piece, comprising providing at least three pipe pieces, two of which have a flat end surface (21) directed obliquely with respect to the axis thereof, and an end surface (20) directed perpendicularly to said axis. and of which each other pipe section has two obliquely directed flat end surfaces (21), the obliquely directed end surfaces (21) being welded together. A method according to any one of claims 13, 14 or 15, wherein each pipe section with an end surface (20) directed perpendicular to the axis thereof comprises only a single pipe part over the part adjacent to that end surface, and that the other pipe part ends at a distance of that end surface (20). A prestressed accessory manufactured according to the method of any one of claims 1-16, wherein each pipe section (7) with an end surface (20) directed perpendicularly to the axis thereof comprises only one pipe part (2) over the part adjacent to that end surface, and that the other conduit part (3) ends at a distance from that end surface (20). 30 A prestressed pipe section made according to the method of any one of claims 1-12, wherein both pipe sections (2, 3) have an equal length and completely overlap each other. 10 1 6 456