초록 ▼

Physical properties of extruded amorphous thermoplastic pipe are improved by a method of extrusion which allows for relaxation of internal stress introduced during the processing. The stress is relieved by using an extrusion die having an inner and outer diameter which is smaller than the final prod

Physical properties of extruded amorphous thermoplastic pipe are improved by a method of extrusion which allows for relaxation of internal stress introduced during the processing. The stress is relieved by using an extrusion die having an inner and outer diameter which is smaller than the final product inner and outer diameter. The extruded pipe is allowed to expand as a result of melt swell and thereby permit relaxation of internal stresses within the extruded pipe. The expansion brings the inner and outer diameter to approximately the size of the final pipe. The further introduction of internal stress is avoided by pulling the extruded pipe from the extruding apparatus at a rate which is approximately the same as the rate of extrusion. The pipe can undergo a final sizing step to bring the extruded pipe to the final product size.

대표청구항 ▼

A process for the production of a hollow product having a final inner diameter and a final outer diameter to define a final wall thickness therebetween and a cross-sectional shape, said product being formed from amorphous thermoplastic comprising polyvinyl chloride and/or chlorinated polyvinyl chlor

A process for the production of a hollow product having a final inner diameter and a final outer diameter to define a final wall thickness therebetween and a cross-sectional shape, said product being formed from amorphous thermoplastic comprising polyvinyl chloride and/or chlorinated polyvinyl chloride, said method comprising the steps of (1) charging said thermoplastic into an extruding apparatus including a processing portion and die means and processing said thermoplastic through said processing portion; (2) discharging said thermoplastic through said die means at a rate of N feet per minute to form an extrudate, said extrudate having a cross-sectional shape corresponding to the cross-sectional shape of said product, and having an inner diameter and an outer diameter to define wall thickness therebetween; (3) allowing said extrudate to freely expand as a result of melt swell and thereby permit relaxation of internal stresses within said extrudate resulting from said processing, said expansion bringing the extrudate inner diameter to within about 110 percent of the final inner diameter and bringing the extrudate outer diameter to within about 110 percent of the final outer diameter; (4) drawing said extrudate from the die from within plus or minus 10 percent of N feet per minute; and (5) bringing said inner diameter to said final diameter and said outer diameter to said final outer diameter.