Importance

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Abstract

Apparatuses and methods for simultaneously extruding two lengths of plastic tubing wherein each of said lengths includes alternate axial sections of materials having different characteristics (e.g., a harder material and a softer material). The apparatus includes two extruders which feed plastic extrudate to a dual die head having first and second dies for forming tubular lengths. Valves are operatively associated with each extruder for selectively feeding plastic extrudate from each extruder to either of the dies. The valves are intermittently operated so that during one cycle extrudate from the first extruder is fed to the first die and extrudate from the second extruder is fed to the second die, and during alternate cycles extrudate from the first extruder is fed to the second die and extrudate from the second extruder is fed to the first die. A cooling tank receives the tubular length from the dies for setting the plastic material. A take-off mechanism is associated with each die for pulling the tubular extrudate from the die and through the cooling tank. Tubular extrusions having axial sections of different lengths may be made by setting the extruders to run at different speeds and programming the take-off mechanisms to intermittently operate at different speeds so that each take-off mechanism will operate at a faster speed when the faster-operating extruder is feeding into the die with which the take-off mechanism is associated and at a slower speed when the slower-operating extruder is feeding into that die.

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First Claim