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This invention concerns a method and an apparatus for making a spirally-wound tube from a hollow thermoplastic profile (1) having a substantially rectangular cross-section, which method comprises the steps of: winding the thermoplastic profile (1) around a drum (2) and joining adjacent loops togethe

This invention concerns a method and an apparatus for making a spirally-wound tube from a hollow thermoplastic profile (1) having a substantially rectangular cross-section, which method comprises the steps of: winding the thermoplastic profile (1) around a drum (2) and joining adjacent loops together by welding, and smoothing the outer weld joint (13) by means of extra heat and a smoothing body resting against the weld joint (13). The invention is characterized in that the thermoplastic profile (1), when fed to the drum (2), comes onto a stationary first section (3) comprising spaced sliding means (5) arranged along the periphery, on which section welding is performed, after which an inner weld joint (11) thus formed is arranged to run along a spiral groove (14) running around the stationary first section (3), whereby the inner weld joint (11), as well as the outer weld joint (13), are treated by using extra heat and a stationary smoothing body (10) resting against it, and that the tube, once both of the welded surfaces (11, 13) have been smoothed, is transferred to a rotary driven drum section (4) causing the tube to rotate and generating the winding motion of the thermoplastic profile (1).

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1. A method for making a spirally-wound tube from a hollow thermoplastic profile having a substantially rectangular cross-section, wherein the method comprises:feeding the thermoplastic profile to a drum such that the thermoplastic profile comes onto a stationary section of the drum, wherein a space

1. A method for making a spirally-wound tube from a hollow thermoplastic profile having a substantially rectangular cross-section, wherein the method comprises:feeding the thermoplastic profile to a drum such that the thermoplastic profile comes onto a stationary section of the drum, wherein a spaced sliding means is arranged along a periphery of the stationary section;winding the thermoplastic profile around the drum;welding adjacent loops of the thermoplastic profile together on the stationary section so as to form the spirally-wound tube, wherein an inner weld joint and an outer weld joint are formed by the welding of adjacent loops, and wherein the inner weld joint and the outer weld joint are arranged to run along a spiral groove running around the stationary section;smoothing the inner weld joint by using extra heat and a stationary body resting against the inner weld joint;smoothing the outer weld joint by using extra heat and a stationary body resting against the outer weld joint;transferring the tube to a rotary driven section which causes the tube to rotate and pulls the thermoplastic profile around the stationary section; andfeeding the spirally-wound tube axially forward by means of freely rotating, radial press rolls influencing the thermoplastic profile during an initial winding around the drum.2. The method of claim 1, wherein the welding is performed by means of a welding keel that enables simultaneous welding of the outer weld joint and the inner weld joint.3. The method claim 1, wherein the outer weld joint and the inner weld joint are formed by separate welding means.4. An apparatus for making a spirally wound tube from a hollow thermoplastic profile having a substantially rectangular cross-section, the apparatus comprising;a cylindrical drum around which the thermoplastic profile is to be wound;radially oriented, freely rotating press rolls arranged along a periphery of the cylindrical drum at an incoming end of the cylindrical drum;welding means for joining adjacent loops of the thermoplastic profile together; andheating and smoothing means for a weld joint formed on the outside of the tube;wherein the drum is divided into a stationary section and a rotary driven cylindrical section;wherein the stationary section comprises a sliding means for the thermoplastic profile distributed over a periphery of the stationary section;wherein the stationary section comprises heating and smoothing means for a weld joint formed inside the tube;wherein a spiral groove is disposed around the stationary section for a newly made inner weld joint on the tube; andwherein the rotary driven cylindrical section is arranged to provide the tube and the thermoplastic profile energy needed for movement.5. The apparatus of claim 4, wherein the sliding means comprises a number of axially oriented, freely rotating sliding rolls with a length corresponding to a length of the stationary section, and wherein the spiral groove is an annular groove made in each sliding roll, which annular grooves are mutually axially spaced forming a spiral.6. The apparatus of claim 5, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.7. The apparatus of claim 4, wherein the stationary first section comprises a steel shell having openings for the sliding means and for the heating and smoothing means for the weld joint inside the tube, and wherein the spirally running groove for a newly made inner weld joint is made in the steel shell and in the sliding means of the section.8. The apparatus of claim 7, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.9. The apparatus of claim 7, wherein the sliding means is an axially oriented roll having a peripheral annular groove that coincides with the spiral groove in the steel shell.10. The apparatus of claim 9, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.11. The apparatus of claim 7, wherein the sliding means is a polytetrafluoroetylene slide plate into which a groove coinciding with the spiral groove in the steel shell is formed.12. The apparatus of claim 11, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.13. The apparatus of claim 4, wherein the welding means, the heating and smoothing means for the inner weld joint and the heating and smoothing means for the outer weld joint are arranged spirally one after another along the periphery of the stationary section.14. The apparatus of claim 13, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.15. The apparatus of claim 13, wherein the heating and smoothing means for the inner weld joint comprises a hot-air blower accompanied by a sole of polytetrafluoroethylene that is arranged to rest against the inner weld joint and the heating and smoothing means for the outer weld joint comprises a hot-air blower accompanied by a sole of polytetrafluoroetlhylene that is arranged to rest against the outer weld joint.16. The apparatus of claim 15, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.17. The apparatus of claim 4, wherein the stationary section and the frame with the radial press rolls form a replaceable unit of the apparatus.