Method and apparatus for forming continuous thermoplastic pipe having corrugated segments

Claim 2

Apparatus for forming continuous thermoplastic pipe which has spaced corrugated wall portions along the length of the pipe comprising: a. continuous pipe forming means for forming pipe of a predetermined diameter and wall thickness and for cooling the formed pipe; b. heating means for selectively heating spaced portions of the formed pipe after it leaves the pipe forming means; c. corrugation forming means for engaging the heated spaced portions of the continuously advancing pIpe, and forming discrete corrugated sections; and d. coordinating means for coordinating movement of the heating means and corrugation forming means to the travel of the pipe including means for moving the heating and corrugating means with the continuously advancing pipe.

Claim 3

The apparatus specified in claim 1, wherein the heating means comprises a ring shaped heater freely slidable axially along the formed pipe and wherein said coordinating means includes means for advancing the heating means with the advancing pipe and for selectively moving the heating means along the advancing pipe in the direction opposite that of the advancing pipe.

Claim 4

The apparatus specified in claim 1, wherein the heating means comprises generally half-cylinder shaped mating portions which are reciprocally movable together into mating relationship about the pipe, and movable away from the pipe and wherein the coordinating means includes means for advancing the heating means in synchronism with the advancing pipe when the mating portions are in mating relationship about the pipe and for selectively moving the heating means along the advancing pipe in the direction opposite to that of the advancing pipe when the mating portions are moved away from said pipe.

Claim 5

The apparatus specified in claim 1, wherein the corrugation forming means comprises mating mold portions which are reciprocally movable into mating relationship about the pipe, and away from the pipe and wherein said coordinating means includes means for advancing the corrugation forming means with the advancing pipe when the mating mold portions are in mating relationship about the pipe and for selectively moving the corrugation forming means in the direction opposite to that of the advancing pipe when the mating mold portions are moved away from the pipe.

Claim 6

The apparatus specified in claim 4, wherein the mating mold portions have a corrugated interior wall surface, and wherein the mating mold portions include a vacuum manifold with the corrugated interior wall being permeable whereby the pipe can be formed against the corrugated interior wall as a result of maintaining a partial vacuum in the manifold and on the exterior of the pipe.

Claim 7

The apparatus specified in claim 1, wherein the heating means and corrugation forming means are reciprocably mounted and movable on elongated support rods which extend parallel to the direction of pipe travel.

Claim 8

The apparatus specified in claim 1, wherein the coordinating means includes a common carriage on which the heating means and the corrugation forming means are mounted and which is movable in synchronism with the advancing pipe, said heating means and corrugation forming means being spaced apart on said carriage in the direction of pipe movement a distance corresponding to the desired distance between corrugations.

Claim 9

The apparatus as specified in claim 1 including sizing means for calibrating the diameter of the formed pipe and puller means for aiding in passing the formed pipe through the sizing means being disposed successively between said continuous pipe forming means and said heating means, said puller means being selectively operative to pull those portions of the pipe to be corrugated at a speed faster than the speed at which the formed pipe leaves the pipe forming means to stretch those selected portions of the pipe, whereby the selected portions of the pipe to be corrugated are strengthened through the molecular alignment of the thermoplastic resulting from the stretching.

Claim 10

The apparatus specified in claim 1, including a reciprocally movable elongated rigid tube extending through the pipe forming means along the central axis of the formed pipe, a source of pressurized gas for selectively pressurizing said tube, a pair of inflatable collars axially spaced along the rigid tube inside the pipe on either side of externally disposed corrugation forming means, said collars being inflatable by the pressurized gas in the tube through first apertures in the tube Walls to engage the interior walls of the formed pipe and to thereby define a pressure chamber within the formed pipe between said inflatable collars, additional apertures in the rigid tube between the collar means to permit pressurization of the pressure chamber by the pressurized gas in the tube and thereby press the pipe wall intermediate said inflatable collars against the externally disposed corrugation forming means, and reciprocation means for advancing the rigid tube along the axis of the pipe to maintain said pressure chamber in alignment with the corrugation forming means as it advances with the formed pipe.