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Scrap Allocation

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Scrap Allocation

Chris Jowett, Alcan Primary Metal Group, Toronto, Ontario, Canada
Johnie Adams and Chris Daughetee, Magnode Corporation, Trenton, Ohio, USA
Greg Lea, MI-metals, Smyrna, Tennessee, USA
Oliver A. Huff, Rio Tinto Alcan, Sebree, Kentucky, USA
Norm Fossl, Rio Tinto Alcan, Kitimat, BC, Canada


ABSTRACT --- For many types of extruded product, the complete exclusion of
front-end and back-end defects is necessary. Front-end defect, otherwise called
transverse weld, which results from the joint between consecutive billets, is
generally taken as a function of the volume of metal remaining in the pockets and
ports left behind from the preceding billet. The length of the extrusion that needs
to be scrapped is related to this volume; however, flow through the die can be
very non-uniform and there can be significant variations in the extruded length
when this scrap material is cleared. Back-end condition, or coring, results from
flow of the billet surface into the extrusion during the latter stages of the cycle.
This flow can be sensitive to the temperature of the billet, container, and dummy
block, as well as the geometry of the extruded profile. While the location of the
completion of front-end defect/transverse weld and the onset of back-end
defect/coring can be approximated, the exact location needs to be physically
verified, usually by etching profile cross sections. This paper will look at the
validity of the simple rules that are used to estimate front-end and back-end
scrap. Nine hollow dies and four solid dies with significant production statistics
were chosen for this detailed analysis. While the causes of these two types of
scrap are quite different, they do interact depending on the specific die being
extruded. Rules are given that define the amount of scrap that needs to be taken
to eliminate both defects.

© Extrusion Technology for Aluminum Profiles Foundation (ET Foundation). All rights reserved. No part of The Proceedings may be reproduced in any form without the express written permission of the ET Foundation.