A conventional mandrel of an extruder head used in extruding double wall plastic pipe is made of a plurality of concentric mandrel tubes which are centered and stabilized relative to one another through the use of a device known in the industry as a spider. The spider provides a spacer to allow the flow of plastic along the tubes past the spider.
The existing spider has spider legs which have an extended diamond shape generally symmetrical to the upstream and downstream sides of the widened center of the spider leg. The front edge of the diamond shape divides the flow of plastic along the mandrel to the spider such that the plastic flows as split streams around the center of the spider leg. The split streams gradually rejoin with one another after they pass the downstream end of the spider leg. The slower the streams rejoin and the less they intermingle with one another adversely affects the ability of the streams to bond to one another.
USPTO Backgrounds
USPTO Backgrounds