51312-01151-Fracture of a Discharge Screw Element in a Polyethylene Resin Extruder

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Product Number: 51312-01151-SG

ISBN: 01151 2012 CP

Author: Jeffrey Xie

Publication Date: 2012

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Fracture of a Discharge Screw Element in a Polyethylene Resin ExtruderJeffrey Xie NOVA Chemicals Research & Technology Center 2928 16th Street NE Calgary AB T2E 7K7 CANADA Derek Mitchell Bill Oberg Raj Noorithaya Bill Courtney NOVA Chemicals Corporation Joffre Alberta T4A 6N1 CANADA A discharge screw element in a polyethylene resin extruder was found fractured after excessive temperature excursion and main motor power spike. Investigation was conducted to understand the root causes of the failure; determine the construction materials of the discharge screw element and the barrel; and provide recommendations to prevent similar failure and for better operations. The fracture occurred at a weak section of the discharge screw element as a result of a frictional stress due to excessive adhesive wear between the discharge screw element and corresponding barrel liner. The weak section roughly 160 mm in length is where there was no spline support to transmit the torque from the main motor to the die plate. Because of the large hardness difference the metal-metal contact induced adhesive wear between the barrel liner and the discharge screw element causing excessive wear loss formation of metal particles and a temperature excursion. The adhesive wear induced such a large amount of frictional stresses that the first fracture crack propagated at a shear stress direction into the body of discharge screw element. With continuous application of the extrusion torque the discharge screw element was fractured into four pieces starting at the end of the splines where stress was concentrated. The failed screw element was constructed of three components: the outmost hard-facing was Colmonoy 56 the body was 4140 steel and the middle butter layer was stainless steel (304). The corresponding barrel was constructed of a hard facing of Ni-based cermat with WC strengthening particles and 4140 body. Recommendations were proposed for the new construction of discharge screw elements: 1) Using new hard facing material in the barrel to reduce the hardness difference thus avoiding adhesive wear; 2) Strengthening the weak section by extending the splines of the discharge screw element. Both recommendations have been incorporated into the new design for the discharge screw elements and barrels. Key words: discharge screw element barrel liner extruder fracture adhesive wear hard-facing.