A METHOD FOR JOINING SPIRALLY WOUND THERMOPLASTIC PIPES TOGETHER

Abstract: The present invention relates to a method for joining spirally wound thermoplastic pipes (1, 2) of a hole profile together, characterized by the following steps: working the end surfaces (3, 4) of the spirally wound thermoplastic pipes (1, 2) into a smooth step-formed surface; setting two thermoplastic pipes (1, 2) end against end such that a smooth step-formed gap is formed between the end surfaces (3, 4); applying a stainless steel band (5) over the gap and heating the steel band (5) to ca. 100 DEG C; applying an extruder (6) with a rotating extruder head (6) and a cooled slide and smoothing organ (8) cooperating therewith inside the pipes (1, 2) to be joined together; heating the end surfaces (3, 4); extruding a weld seam of a melted thermoplastic (9) into the gap between the two end surfaces (3, 4); as well as stopping the heating of the steel band (5) and removal of the steel band (5) from the joining place after cooling.

Description: A METHOD FOR JOINING SPIRALLY WOUND THERMOPLASTIC PIPES TOGETHER The invention relates to a method for joining spirally wound thermoplastic pipes of a hole profile together. According to earlier methods, the joining-together of spirally wound pipes of the above-mentioned type usually occurred by means of extruder welding from the outer and inner side of the pipe. Since pipes of very large diameters, 2 or more, are often concerned, this previously known technique causes considerable technical problems, and it is simultaneously very time-consuming. It was very diffucult to reach a satisfactory final result by means of the previously known technique. The object of the present invention is to eliminate these problems, which is achieved by means of a method, which is characterized by the following steps: working the end surfaces of the sprirally wound thermoplastic pipes into a smooth step-formed surface, - setting two thermoplastic pipes end against end such that a smooth step-formed gap is formed between the end surfaces, - applying a stainless steel band over the gap and heating of the steel band to ca. 100°C, - applying an extruder with a rotating extruder head and a cooled slide and smoothing organ cooperating therewith inside the pipes to be joined together, - heating the end surfaces, - extruding a weld seam of a melted thermoplastic into the gap between the two end surfaces, as well as - stopping the heating of the steel band and removing the steel band from the joining place after cooling. The remaining characteristics of the invention will be apparent from the enclosed claims 2-7. The invention will next be described in more detail with reference to the accompanying drawing, wherein Fig. 1 shows the oining-together of two spirally wound pipes according to the present invention, seen from the outside in a radial direction, and Fig. 2 shows the joining- ogether of Fig. 1, seen in an axial direction. The joining-together of spirally wound thermoplastic pipes 1, 2 made of a hole profile occurs according to the invention as follows. The ends of the two thermoplastic pipes 1, 2 to be joined together are worked such that an end opening of the corresponding hole profile is closed and two smooth step-formed end surfaces 3, 4, which fit together, are obtained, whereafter the two pipes are placed end against end and set such that a uniformly wide step- formed gap forms between the end surfaces 3 and 4. The gap width is to be fitted according to the radial dimension of the hole profile, of which the spirally wound pipe 1, 2 is comprised. In connection with the most usual pipe dimensions, the gap width varies in the range of 10-40 mm. A stainless steel band 5 is applied over the gap between the two thermoplastic pipes 1, 2 and is heated to ca. 100 °C. In order to avoid that the melted thermoplastic material will adhere to the steel band 5, it is preferably teflon coated. An extruder 6 with a rotating extruder head 7 and a cooled slide and smoothing organ 8 cooperating therewith are applied inside the pipes 1, 2 to be joined together. The end surfaces 3, 4 are heated e.g. with warm air coming from a warm-air blower 12. A weld seam of melted thermoplastic 9 is extruded into the gap between the two end surfaces 3, 4, whereby the slide and smoothing organ 8 brings about the fact that the melted thermoplastic 9 completely fills the gap and a weld pressure is obtained. In this way, a weld seam with a smooth inner surface is formed. After the extrusion of the whole gap is completed, the heating of the steel band 5 is stopped and the extruded thermoplastic seam is cooled, whereafter the steel band 5 is removed from the joining place. A very smoooth seam may then be observed, which is nearly invisible to the naked eye. According to a preferred embodiment, the heating of the steel band 5 occurs electrically, preferably by short- circuiting. For setting the temperature of the steel band 5 to the desired level, it may preferably be provided with a temperature sensor coupled to a regulating circuit, which is arranged to regulate the electricity supply to the steel band. The joining place, after the steel band 5 has been applied, has preferably to be surrounded with an insulation layer, as well as a felt cloth 10, which is in turn surrounded with a rubber sleeve 11, which prevents moisture and wetness from coming into contact with the steel band 5, which may detrimentally affect the heating cycle.

Claims: Claims 1. A method for joining spirally wound thermoplastic pipes (1, 2) of a hole profile together, characterized by the following steps: - working the end surfaces (3, 4) of the sprirally wound thermoplastic pipes (1, 2) into a smooth step-formed surface, - setting two thermoplastic pipes (1, 2) end against end such that a smooth step-formed gap is formed between the end surfaces (3, 4), " - applying a stainless steel band (5) over the gap and heating of the steel band (5) to ca. 100°C, - applying an extruder (6) with a rotating extruder head C6) and a cooled slide and smoothing organ (8) cooperating therewith inside the pipes (1, 2) to be joined together, - heating the end surfaces (3, 4), - extruding a weld seam of a melted thermoplastic (9) into the gap between the two end surfaces (3, 4), as well as - stopping the heating of the steel band (5) and removing the steel band (5) from the joining place after cooling. 2. A method according to Claim 1, characterized in that the steel band (5) is heated by short-circuiting. 3. A method according to Claim 2, characterized in that the steel band (5) is provided with a temperature sensor, which in cooperation with a regulating circuit is arranged to maintain the temperature of the steel band at a desired level. 4. A method according to any of the preceding Claims, characterized in that a ca. 10-20 mm wide gap is left between the end surfaces (3, 4) of the two pipes (1, 2). 5. A method according to Claim 4, characterized in that the steel band (5) is teflon coated. 6. A method according to Claim 5, characterized in that the steel band is coated from the outside with a felt cloth (10) and a rubber sleeve (11) surrounding the felt cloth (10). 7. A method according to any of the preceding Claims, characterized in that the end surfaces (3, 4) are heated with warm air coming from a warm-air blower (12), before the extrusion of the weld seam is initiated.

Inventors: BLOMQVIST GUNNAR, BLOMQVIST, GUNNAR
Applicants: KWH PIPE AB OY, OY KWH PIPE AB
Application year: 1992
Main classification: B29C65
IPC codes: B29C53, B29C65, B29L23, B29L24, F16L47