Solving rejects in pipe extrusion

A new Xaloy® screw designed by Nordson Corporation put an end to a long series of troubles on a pipe extrusion line that had defied numerous attempts at a solution. 

 

The line, operated by diversified pipe manufacturer Polyethylene Technology Inc., would exhibit wide fluctuations in throughput caused by surging and, for heavy-wall HDPE pipe, consistently exhibited variation from the target wall thickness of 0.097 in (2.46 mm). “We tried all sorts of solutions,” said Brad Williams, senior manufacturing manager. Polyethylene Technology looked for problems with the motor drive and the puller, tested 4 or 5 alternate resins, and finally got a new screw and relined barrel—all with no success. Its gravimetric extrusion control showed fluctuations occurring every 5 or 10 seconds. An additional trouble with the extrusion line was poor mixing of carbon black, whose required addition level was 2%. The company could not get a good mix and there were always areas of the pipe with too little carbon black.  

 

 

Polyethylene Technology turned to Nordson within months of receiving the screw from another supplier. “We recommended our Xaloy Efficient™ barrier screw with a Nano™ mixer in the metering section,” said Brad Casale, Nordson regional sales manager. “By preventing premature break-up of solids and increasing melting rates, the Efficient screw has enhanced mixing and increased throughput in the Polyethylene Technology extrusion line. The Nano mixer has provided intensive dispersionary mixing of the carbon black.”

 

Besides solving the surging problem and delivering a homogeneous melt, the new Xaloy screw increased the output of the extrusion line. As a result of using the new Xaloy screw, Polyethylene Technology's target output rate has increased by 12%, according to Mr. Williams.

 

Founded in 1980, Polyethylene Technology Inc. manufactures polyethylene pipe for municipal water, geothermal, pump and well, and irrigation applications.