Process and an apparatus for the extrusion of plastic pipes with composite walls

Claim 1

In a process for the manufacture by coextrusion of plastic pipe having a composite structure formed of inner and outer walls of plastic material enclosing an intermediate layer of a filling material which is synthetic plastic or polymeric in nature and which adheres to said walls comprising introducing the material constituting said pipe walls in a heated and plastic state, separating the introduced plastic material into two distinct streams, injecting the filling material in a plastic state to between the separated streams of material constituting the inner and outer walls, bringing the three streams into a contacting relation with the stream of filling material sandwiched between the streams forming the inner and outer walls to form a composite having the final structure, the improvement comprising passing the sandwiched streams through a divergent passageway to form the sandwiched streams to a dimension greater than the final dimension of the product, separating the sandwiched streams into circumferentially separated streams, passing the separated sandwiched streams through a convergent passageway and die for rejoinder of said separated streams and to form a homogeneous pipe to final dimension.

Claim 7

An apparatus for the manufacture by coextrusion of plastic pipe having a composite structure formed of inner and outer walls of plastic material with a layer of filling material in between, comprising: (a) a heated and regulated distribution head, (b) a first extruder for introduction of the material constituting the inner and outer walls in a plastic state into said head, (c) a second extruder for introduction of a synthetic plastic or polymeric filling material into said distribution head, (d) means within said distribution head for separating the material introduced by the first extruder into two distinct streams, (e) means within said distribution head for guiding the filling material into a stream between said streams of wall material, (f) means for bringing the three streams together into contacting relation to form a continuous composite stream in the form of a sandwich with the filling material and wall material in their final arrangement, (g) a divergent passageway of conical shape in communication with the outlet of said distribution head wherein the sandwiched streams increase in dimension during passage therethrough, (h) a convergent passageway as a continuation of the divergent passageway, (i) a trefoil between said divergent and convergent passageways to separate the expanded sandwiched streams into circumferential segments before passage through the convergent passageway for rewelding the segments, (j) a heated and regulated tool downstream of said passageways and in communication therewith to give the sandwiched streams their final shape and dimension.

Claim 8

An apparatus for the manufacture by coextrusion of plastic pipe having a composite structure formed of inner and outer walls of plastic material with a layer of filling material in between, comprising: (a) a heated and regulated distribution head, (b) a first extruder for introduction of the material constituting the inner and outer walls in a plastic state into said head, (c) a second extruder for introduction of a synthetic plastic or polymeric filling material into said distribution head, (d) means within said distribution head for separating the material introduced by the first extruder into two distinct streams, (e) means within said distribution head for guiding the filling material into a stream between said streams of wall material, (f) means for bringing the three streams together into contacting relation to form a continuous composite stream in the form of a sandwich with the filling material and wall material in their final arrangement, (g) a divergent passageway of conical shape in communication with the outlet of said distribution head wherein the sandwiched streams increase in dimension during passage therethrough, (h) a convergent passageway as a continuation of the divergent passageway, (i) a trefoil between said divergent and convergent passageways to separate the expanded sandwiched streams into circumferential segments before passage through the convergent passageway for rewelding the segments, (j) a heated and regulated tool downstream of said passageways and in communication therewith to give the sandwiched streams their final shape and dimension.