Triwall siding apparatus

摘要

Highly uniform three-layer extrusions generally of flat siding or panels, preferably of PVC are extruded in an apparatus having a flow block in which lateral extruders supply the upper and lower layer streams to respective curved flow passages running to outlets of a flow block while a main extruder supplies the foam PVC to the central outlet. The outlets are aligned with orifices of a flow plate connected by respective channels to outlet orifices arranged within a common circle and communicating with a die. The outlet orifices include a pair of elongated kidney-shaped orifices encircling and straddling an ovoid central orifice.