Apparatus for producing tubing
An apparatus for extruding tubing having axially spaced sections of different diameters, comprising: extruding die means for continuously producing a tubular extrudate, means for continuously producing molten plastic material, conduit means interconnecting said means for producing molten plastic material and sheet production extruder die for establishing a flow path for continuous delivery of said material from said means for producing molten plastic material to said die, first accumulator-injector means for withdrawing a portion of said material from said conduit means and thereafter injecting it therein, second accumulator-injector means for withdrawing a portion of said material from said conduit means and thereafter injecting it therein, and means for controlling the withdrawal and inject phases of said first and second means for producing said tubing with axially spaced sections of different diameters.
Various types of extruding apparatus have been provided in the past for producing tubing having variations in external diameter, internal diameter and wall thickness. Such extruding apparatus is designed to provide periodic and repetitive variations of the size of the tubing along the length of the extrudate so that the tubing may be thereafter cut at predetermined intervals into useable tubing products such as for the biomedical field, e.g. catheters. There are, however, a large variety of other tubing products that may be mass produced according to the apparatus of the present invention as will appear hereinbelow.
One prior apparatus for producing tubing having variations in diameter along its axial length includes a single screw extruder and die combination with a control for varying the speed of the extruder itself, thus, varying the flow from the extruder to the die in a programmed fashion.
Another twin screw extruder provided for producing tubing having variations in diameter along its axial length is that disclosed in the copending application, assigned to the assignee of the present invention. In this prior application an extruding apparatus is disclosed including an extruder that feeds molten plastic to an extruding die through a conduit having an accumulator-injector therein. The accumulator is timed and programmed so that during the withdrawal phase thereof molten plastic is delivered from the extruder to the die at a reduced rate and during the inject phase of the accumulator-injector, molten plastic is delivered to the die at an increased rate providing a larger diameter or bubble section of extrudate.