Method and apparatus for forming a double walled thermoplastic tube with integral bells
First Claim
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1. A method of forming a double walled thermoplastic tube by extruding a first tube into travelling mold, molding the first tube in the mold to form a corrugated outer wall, and extruding a second tube into the first tube to form a smooth inner wall, the method being characterized by the steps of:
- molding integral bell sections into the outer wall;
piercing one of the tubes between the ends of each outer wall bell section so as to allow the escape of air from between the inner and outer walls; and
pressing the inner wall into continuous contact with the outer wall along each outer wall bell section.
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Abstract
Double walled thermoplastic tubes, with corrugated outer walls and smooth inner wall are formed with integral bell sections spaced along the tube. The outer, corrugated wall is formed with a bell section. One of the walls is pierced between the ends of the bell section to allow the escape of air, and the inner wall is pressed outwards into engagement with the bell section of the outer wall.
54 Citations
10 Claims
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1. A method of forming a double walled thermoplastic tube by extruding a first tube into travelling mold, molding the first tube in the mold to form a corrugated outer wall, and extruding a second tube into the first tube to form a smooth inner wall, the method being characterized by the steps of:
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molding integral bell sections into the outer wall; piercing one of the tubes between the ends of each outer wall bell section so as to allow the escape of air from between the inner and outer walls; and pressing the inner wall into continuous contact with the outer wall along each outer wall bell section. - View Dependent Claims (2, 3)
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4. An apparatus for forming a double walled thermoplastic tube with a corrugated outer wall and a smooth inner wall, the apparatus including a travelling mold with a corrugated cavity, extruder means for extruding a first tube into the mold cavity and a second tube into the first tube, means for molding the first tube to form a corrugated outer wall and means for forming the second tube into a smooth inner wall, the apparatus being characterized by means for forming integral bells in the double walled tube, comprising the combination of:
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means for molding integral bell sections into the outer wall; piercing means for piercing one of the tubes between the ends of each outer wall bell section; and pressing means for pressing the inner wall into continuous contact with each bell section of the outer wall. - View Dependent Claims (5, 6, 7, 8, 9, 10)
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Specification