Patent ID: 6399002
Filing Date: 2002-06-04
Classification: F16L

Abstract:
A method of extruding a plastic pipe having a pipe wall construction made from first and second streams of plastic, the first stream of plastic being formed into an interior part of the wall construction, the second stream of plastic being formed into a covering wall part over the interior wall part of the wall construction, the covering wall part being shaped into first and second corrugations with the interior wall part being flat where covered by the first and second corrugations, the wall construction further including a bowed wall region where the first and second steams of plastic are extruded lying against one another, the first corrugations and the bowed wall region being formed with consistent outside diameters and the second corrugations being formed with an outside diameter less than that of the first corrugations and the bowed wall region, the first corrugations, the bowed wall region and the second corrugations all being formed continuously along the pipe with the bowed wall region being located between the first corrugations and the second corrugations, the first corrugations comprising a major part of the pipe and the bowed wall region and the second corrugations comprising a minor part of the pipe.