Tool Type: Vinyl Extrusion Die Set
Work Material: Polyvinyl Chloride Extrusion Compound
Original Tooling Material: 420 ESR Stainless Steel RC 50-52
Problem: After production of 12,000 to 15,000 feet of 2” diameter PVC pipe, the outside diameter of the pipe begins to smear. After another 2000 to 3000 feet of pipe is produced, the smeared area begins to develop ridges and pillows on the surface of the pipe. These ridges and pillows are determined to be out of pipe specifications and the production needs to be halted. Removal of the tool set caused 6 hours of lost downtime.
Upon inspection of the vinyl extrusion die set, the
tooling manager discovers that the surface of the die has marked pitting,
corrosion and wear. He determines that the surface has deteriorated because it
lacked enough wear resistance and surface finish. The low polish of the surface
caused the surface to corrode. Once corrosion began, the surface began to wear
Solution: Upgrade to PM 420 Stainless Steel, increase the hardness to RC 56-58 and polish the surface to RMS 4 minimum. A new tool set is made from PM 420 stainless steel and heat treated to RC 56-58. The cleanliness of the PM 420 stainless steel allows the surface to be polished to RMS 4+ using electropolishing. The improved surface finish should prevent corrosion of the surface.
Results: Due to the high polish on the surface of the tool
and the added wear resistance provided by the PM 420 stainless steel, the new
die set produces more than 120,000 feet of the PVC tubing before it requires
removal from operation. Upon inspection of the tool, no corrosion or pitting is
observed, so the die set is repolished and returned to service to produce
another 50,000 feet of pipe.
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