A METHOD FOR MANUFACTURING A JOINT PIPE

Abstract: The present invention relates to a method for manufacturing a joint pipe (1) from a spirally wound thermoplastic profile (7) at an end of a thermoplastic pipe (4). The invention is characterized in that the end of the pipe (4), which will be furnished with a joint pipe (1), is pushed onto a rotatably driven, weakly conical mandrel (2), after which a melt profile (7) of thermoplast is spirally extruded with a certain overlapping around the mandrel (2) and the pipe end (4), starting farthest away from the pipe (4), until the desired overlapping between the joint pipe (1) and the pipe end (4) is obtained, the joint pipe (1) is cooled and the end surface of it is cut uniform, after which the pipe (4) furnished with the joint pipe is removed from the mandrel (2).

Description: A method for manufacturing a joint pipe The present invention relates to a method for manufactu¬ ring a joint pipe from a spirally wound thermoplastic profile at an end of a thermoplastic pipe. The invention is characterized by the following steps: - the pipe end is pushed onto a rota ably driven, heated mandrel comprising a mainly cylindrical end section cor¬ responding to the inner diameter of the pipe end, which end section transfers via a radial stop surface corres¬ ponding to the wall thickness of the pipe end into a weakly conical section, - a melt profile made of thermoplast is extruded spirally with an overlapping around the conical section of the mandrel exiting from that end of the mandrel, which is turned away from the pipe end, and continuing inside against and over that, - when a desired overlapping degree between the extruded joint pipe and the pipe end is reached, the extruder is stopped while the mandrel and pipe continuously rotate, - cooling water is sprayed from the outside over the extruded joint pipe, - the free end of the joint pipe is cut uniform by means of a rotating knife, and - the pipe end with the completed joint pipe are removed from the mamdrel. The remaining characteristics of the invention are presented in the accompanying claims 2-8. The invention is next described in more detail with reference to the accompanying drawings, in which Fig. 1 shows a scheme of principle of a joint pipe manufactured according to the present invention, Fig. 2 shows another example of a joint pipe manufactured according to the invention, and Fig. 3 and 4 show alternative applications of the joint pipe of Fig. 2. When manufacturing a joint pipe 1, a rotatably driven, heated mandrel 2 with a mainly cylindrical end section 3 is used, through which a pipe end 4, which is to be provided with the joint pipe 1, is applicable. The cylindrical end section 3 has an outer diameter, which mainly corresponds to the inner diameter of the pipe end 4. The cylindrical end section 3 transfers via a radially directed stop surface 5 into a weakly conical main section 6. The end surface of the pipe end 4 is intended to be located against this stop surface 5 during the entire manufacturing process, because of which the width of the stop surface 5 preferably corresponds to the wall thickness of the pipe end 4 so that a transition as uniform as possible is obtained between the outer surface of the pipe end 4 and the conical main section 6 of the mandrel 2. After the pipe end 4 is applied onto the cylindrical section of the mandrel 2, the mandrel 2 is continuously maintained in rotation and heated up to at least ca. 100°C. When the mandrel 2 has reached t a desired tempe¬ rature, a melt profile 7 of thermoplast is extruded on the main section 6 of the rotating mandrel, starting at that end of the mandrel 2, which is located farthest away from the pipe end 4. The extrusion is preferably carried out with an extruder nozzle 8 of a mainly rectangular cross-section, which extruder nozzle 8 may be transferred in an axial direction along the mandrel 2. The transfer¬ ring of the extruder nozzle 8 in a direction against the pipe end 4 occurs synchronically with the rotational speed of the mandrel 2 such that the extruder nozzle 8 for each rotation the mandrel 2 rotates transfers in the direction against the pipe end 4 by a distance slightly less than the width of the melt profile such that a certain overlapping is obtained. In this way, a spiral winding of the melt profile 7 around the mandrel 2 and pipe end 4 is obtained, where limiting winding turns are located tightly one above the other such that a welding- together of the melt profiles is obtained. For improving the welding together and for obtaining a more uniform surface on the joint pipe, the overlapping is pressed down with a rotating roll 11, which follows the extruder head. The extrusion continues until a desired overlapping between the melt profile 7 and the pipe end 4 is obtained, after which the extruder is stopped, while the rotation of the pipe end 4 and the mandrel 2 may conti¬ nue. Thus, a uniform transition in the material thickness between the mantle of the pipe end 4 and the joint pipe 1 is obtained. When the extrusion is stopped, the thermoplastic material in the joint pipe 1 is cooled down by spraying cooling water from the outside upon the extruded joint pipe 1. When the thermoplast material has set, the free end of the joint pipe 1 is cut uniform with a rotating knife 9, whereby an absolutely uniform surface is obtained. Finally, the pipe end 4 with the completed joint pipe 1 are removed from the mandrel 2, after which the manufacturing of next joint pipe may be started. Heating of the mandrel 2 may e.g. be performed with a gas blower from the inside or the outside, or in an inductive way from the outside. For ensuring the fixing between the pipe end 4 and the mandrel 2 during the different manufacturing steps, the cylindrical section 3 of the mandrel 2 may suitably be of an expansive construction, whereby the mantle of the section 3 is divided by a number of axially directed gaps 10, and the expansion is achieved in a hydraulic, pneumatic or solely mechanical way via toggle joints. The welding-together of the spiral wound melt profiles 7 may be intensified by applying a weak mechanical loading on the melt profiles 7 e.g. by means of a rotating roll 11 affecting the melt profiles 7 located close to each others on the mandrel 2, immediately after the nozzle 8. The rotating knife 9 comprises preferably a freely rotatable circular blade, which may be pressed in a hydraulic or mechanical way against the joint pipe 1 extruded on the mandrel 2. The pipes 4, which can be provided with a joint pipe 1 according to the present invention, are thermoplastic pipes of different types, such as entirely conventional polyethylene pipes or spirally wound pipes of some other type. The removal of the pipe end 4 with the completed joint pipe 1 from the mandrel 2 is carried out by blowing pressurized air between the mandrel 2 and joint pipe 1, preferably via small gaps or holes contained in the conical section 6 of the mandrel 2, at the same time as a push force is directed onto the joint pipe 2 in a direc¬ tion against the pipe 4. In Fig. 2 to 4 a preferable embodiment of the joint pipe 1 is shown. In connection with the manufacturing of this joint pipe, the conical section 6 of the mandrel has a mainly cylindrical end section with an increased diameter so that the joint pipe 1 manufactured obtains a cylindri¬ cal end section 11 extended in a corresponding manner. In joining- ogether of pipes by means of such a joint pipe 1, the joint pipe may be used, depending on the applica¬ tion area, as such, or, when higher requirements are set on the sealing, a rubber seal 12 according to Fig. 3 or a welding ring 13 according to Fig. 4 may be used. As a result of this possibility, the application range for the joint pipe 1 manufactured according to the invention increases significantly.

Claims: Claims : 1. A method for manufacturing a joint pipe from a spirally wound thermoplastic profile (7) at an end of a thermoplastic pipe (4), characterized by the following steps: - the pipe end (4) is pushed onto a rotatably driven, heated mandrel (2) comprising a mainly cylindrical end section (3) corresponding to the inner diameter of the pipe end (4), which end section (3) transfers via a radial stop surface (5) corresponding to the wall thickness of the pipe end (4) into a weakly conical section (6), - a melt profile (7) made of thermoplast is extruded spirally with an overlapping around the conical section (6) of the mandrel (2) exiting from that end of the mandrel (2), which is turned away from the pipe end (4), and continuing inside against and over that, - when a desired overlapping degree between the extruded joint pipe (1) and the pipe end (4) is reached, the extruder (8) is stopped while the mandrel (2) and pipe (4) continuously rotate, - cooling water is sprayed from the outside over the extruded joint pipe (1), - the free end of the joint pipe (1) is cut uniform by means of a rotating knife (9), and - the pipe end (4) with the completed joint pipe (1) are removed from the mamdrel (2). 2. A method according to Claim 1, characterized in that the mandrel (2) is heated into at least 100°C before the extrusion. 3. A method according to Claim 1 or 2, characterized in that the pipe end (4) may be fixed around the cylindrical section (3) of the mandrel (2) by temporarily extending this section (3). 4. A method according to any of the preceding Claims, characterized in that the extruded melt profile (7) is subjected to a weak mechanical loading by means of a rotating roll for intensifying the welding-together of the melt profile windinds (7) overlapping each other. 5. A method according to any of the preceding Claims, characterized in that the rotating knife (9) comprises a freely rotating circular blade, which is pressed against the thermoplastic material of the joint pipe (1) in connection with the cutting of the end of the joint pipe (1). 6. A method according to any of the preceding Claims, characterized in that the pipe (4) is a conventional polyethylene pipe or a spirally wound thermoplastic pipe. 7. A method according to any of the preceding Claims, characterized in that the pipe end (4) with the completed joint pipe (1) are removed from the mandrel (2) by blowing pressurized air between the mandrel (2) and the joint pipe (2) at the same time as a push force is directed onto the joint pipe (1) in a direction against the pipe (4). 8. A method according to any of the preceding Claims, characterized in that the conical section (6) of the mandrel has a mainly cylindrical end section with an increased diameter, whereby the joint pipe manufactured obtains an end section (11) extended in a corresponding manner, which makes the application of a sealing ring (12) or a welding ring (13) possible.

Inventors: BLOMQVIST GUNNAR, SUNDQVIST KRISTIAN, BLOMQVIST, GUNNAR, SUNDQVIST, KRISTIAN
Applicants: KWH PIPE AB OY, OY KWH PIPE AB
Application year: 1992
Main classification: B29C53
IPC codes: B29C33, B29C35, B29C53, B29C65, B29C70, B29L23, F16L47