DE102006013008C5 - Method for producing a butt-welded connection of protective jacket pipes - Google Patents

Abstract

Method for producing a butt-welding connection of the tube ends of protective jacket tubes by means of butt-welding with a polyethylene core tube and a protective jacket applied on the inside of the core tube by coextrusion with a wall thickness of ≥ 0.5 mm and a post-extruded protective jacket on the outside a polypropylene with a wall thickness of ≥ 1 mm, wherein the core tube and the outer protective jacket have different thermal conductivity and melting behavior, such that the protective jacket melts slower than the core tube, by heating the ends of the tube ends together with the protective shells to the melting temperature of the core tube by subsequently compressing the tube ends with a predetermined pressing force, by filling the gap between the butt ends of the protective sheaths with polyethylene, by forming a Schweißwulst from herausgedrücktem polyethylene and the polyol efins of parts of the protective jacket and by removing the outer weld bead after cooling the weld.

Description

The invention relates to a protective jacket tube suitable for butt welding, consisting of a polyethylene core tube with a protective jacket made of another pure or modified polyolefin, preferably a polypropylene, and a method for producing a butt-welded connection of such protective jacket tubes.

Protective jacket pipes are usually produced by extruding the polyethylene core tube (PE core tube) and coextruding the protective jacket in one step with a tool or by subsequently extruding the protective jacket, ie in two steps. Such protective casing pipes are preferably used for trenchless laying methods (no-dig). The protective jacket located on the core tube has only the function, the core tube during installation or other handling against external damage, eg. B. notches to protect.

The problem with such tubes, however, that for connecting the pipes by butt-welding, first the protective jacket in the welding area must be removed by peeling. That is, the protective jacket must be cut with a suitable cutting device and then removed manually.

Thereafter, the ends of the tubes may be joined together by butt welding. For this purpose, the pipe ends are heated with a suitable heating device to the melting temperature and then pressed together butt. In this process, plastic material in the welding area is pushed outwards and outwards out of the weld seam, whereby a bead is formed on both sides of the weld seam, ie inside the pipe and outside.

Then then the missing protective coat by applying a protective layer, for. B. by wrapping with a suitable plastic material, be restored. This step is unavoidable, otherwise there would be a considerable risk of damage to the core tube during installation in this area.

Welding the core tube without removing the protective jacket is at least problematic because polyethylene and polypropylene have different welding parameters.

However, the butt welding of a protective jacket tube with coextruded protective jacket has become known. Such a plastic pipe is produced by a so-called "hot in hot" extrusion of core tube and protective jacket in one operation. It should be prevented that can form an oxide skin on the core tube.

The protective jacket is here very thin (<0.5 mm), in order to carry out a welding of the tubes with standardized welding jaws (butt welding) - the welding jaws hold the tube during the welding process on the outside diameter. A disadvantage of such a tube is the low wall thickness of the protective jacket and the low protection against abrasion and scratching, and that by coextruding core tube and protective sheath from a tool core tube can be characterized neither by colored stripes nor by a pipe lettering. In addition, it can be assumed that the weld seam area is less protected, since the small wall thickness of the protective jacket carries more PE melt into the weld seam area and thus a larger area remains unprotected.

From the EP 0 869 304 A2 is a tube made of a thermoplastic material, in which the inner tube of a high density polyethylene (HDPE) and a cover layer of a cross-linked polyethylene (VPE) produced by co-extrusion and the cover layer is then crosslinked. The tube dimensions correspond to a standard tube, so that the welding with standard electric welding sleeves is possible.

Butt welding of the pipe ends is excluded here.

Furthermore, goes from the DE 82 32 202 U1 a pipe for underfloor heating, in which the core tube of polyethylene or polypropylene and a substantially oxygen diffusion-inhibiting coating has been applied by extrusion. Information on the weldability of such pipes are not made, especially since it can be assumed that pipes for floor heating are connected by means of conventional fasteners to a heating circuit.

Finally, in the DE 36 40 105 A1 a method for butt welding of pipe ends thermoplastic pipes described in which at the weld inside a Dehnkörper is positioned to prevent the formation of a weld bead on the pipe inside.

Also from the DE 29 23 205 A1 is a method for seamless joining of thermoplastic hollow plastic profiles, in which during the butt welding of the profile ends within the profiles a support element, for. B. a rubber bellows, is introduced.

The invention is now based on the object to provide a method for producing a butt-welding connection of a protective jacket tube, which allows the simple production of butt welds and in which the protective jacket runs in the welding area almost without interruption.

The object underlying the invention is solved by the features of the claim.

Further embodiments of the invention will become apparent from the accompanying dependent claims.

It has surprisingly been found that butt welding is easily possible with a protective jacket tube made of a PE core tube with a subsequently extruded protective jacket, if the protective jacket has a minimum wall thickness of ≥ 1 mm. The gap formed between the two abutting protective sheaths, which is filled with the material of the core tube, is minimal, so that no further operations to protect the welding zone are necessary. At the same time excess material of the protective jacket is pushed outwards with. The result is a quasi-continuous protective sheath and a butt weld well protected by the protective sheath, so that the interconnected pipes can be laid immediately.

The prerequisite is that the protective jacket has an at least slightly different thermal conductivity and thus a different melting behavior than the material of the core tube, d. H. The protective jacket must melt slightly slower than the material of the core tube.

If a protective jacket is also applied to the inside of the core tube, it must have a minimum wall thickness of ≥ 0.5 mm. The weld bead which also forms on the inside during welding dissolves just as easily as that on the outside. However, it is not possible to manually remove the welding bead inside. This then takes place during the solid transport in the pipe, so to speak automatically, so that then forms a perfectly smooth inner wall.

The invention will be explained in more detail below using an exemplary embodiment.

The starting point is a finished extruded polyethylene tube as a PE core tube, which then a protective jacket of a pure or modified polyolefin, preferably a polypropylene was extruded. The protective jacket is applied by post-extrusion onto the PE core tube with a wall thickness of ≥ 1 mm. The material of the protective jacket should have a different thermal conductivity and a different melting behavior than the material of the PE core tube in such a way that the protective jacket melts somewhat slower than the material of the core tube. This ensures that during the joining of two pipe ends with each other by a butt welding process no mixing of the melted material of the core tube with the material of the protective jacket and that forms a Schweißwulst in the welding area by pushing together the abutting ends of the PE core tube, easily removable is. At the same time during the welding process, the gap between the ends of the protective jacket is filled by molten material of the core tube and excess material of the protective jacket pressed to the outside.

In addition, the inside of the PE core tube can be equipped by coextrusion with a protective jacket of pure or modified polyolefin, preferably a polypropylene. It is understood that only coextrusion of the protective jacket is possible on the inside of the tube. The inner protective jacket should have a wall thickness of ≥ 0.5 mm and should otherwise have the same properties as the outer protective jacket.

The inner protective sheath serves to protect the core tube against damage when passing solids, such as sand, flour, etc. The welding bead forming here during butt welding can not be removed manually, but it is released automatically during the transport of solids through the protective sheath tube.

The butt-welding operation of the two tube ends is carried out by heating them to the required melting temperature of the PE core tube and pressing the tube ends together with a predetermined pressure force. The typical Schweißwulst is formed by pushing out material of the PE core tube, wherein the gap between the ends of the protective jacket is filled with material of the PE core tube. The excess material of the protective jacket is located after the butt welding process in the weld bead, which can be easily removed after cooling the weld, so that a completely smooth pipe outside.

Completely new to the protective jacket tube according to the invention is that welding, especially after the heating element butt welding process can be carried out without prior removal of the protective jacket from the welding area. It is also essential that due to the choice of material of the protective jacket and the selected thickness, the protective jacket does not adversely affect the welding quality, ie. H. the strength of the compound, affects.

During welding, the protective jacket softens only, so that it is pushed away by pushed out material of the PE core tube. Due to the almost butt ends of the protective jacket abutting a post-treatment of the welded joint of the pipe is unnecessary.

The particular advantages are a significant time and cost savings, since no peeling of the protective jacket before butt welding is required and after butt welding no additional protection system is needed.

There is a user-independent full protection of the welding area.

Furthermore, the Schweißwulst is easily removable, so that a trenchless installation of the protective jacket tube according to the invention is possible.

Claims (1)

Method for producing a butt-welding connection of the tube ends of protective jacket tubes by means of butt-welding with a polyethylene core tube and a protective jacket applied on the inside of the core tube by coextrusion with a wall thickness of ≥ 0.5 mm and a post-extruded protective jacket on the outside a polypropylene with a wall thickness of ≥ 1 mm, wherein the core tube and the outer protective jacket have different thermal conductivity and melting behavior, such that the protective jacket melts slower than the core tube, by heating the ends of the tube ends together with the protective shells to the melting temperature of the core tube by subsequently compressing the tube ends with a predetermined pressing force, by filling the gap between the butt ends of the protective sheaths with polyethylene, by forming a Schweißwulst from herausgedrücktem polyethylene and the polyol efins of parts of the protective jacket and by removing the outer weld bead after cooling the weld.