ABOUT THE AUTHOR: Jim Frankland is a mechanical engineer who
has been involved in all types of extrusion processing for more than
40 years. He is now president of Frankland Plastics Consulting, LLC.
Contact jim.frankland@comcast.net or (724) 651-9196.
and leave polymer on the radius or above it on the die face as die
buildup. The combination of tearing along with die buildup is
often a largely invisible cause
of poor surface finish on the
extruded part. A radius as
small as 0.010 in. has been
found to result in surface
tearing and die-face buildup
with certain polymers.
Obviously dies periodi-
cally need cleaning, and if aggressive cleaning is necessary,
even what are believed to be protective materials such as brass
are hard enough to abrade a die's sharp edges, creating a radius
or chamfer. To counter this effect, the die-exit face may need
periodic resurfacing to restore the sharp edge. This can be done
by surface grinding, but requires removing and disassembling
the die, resulting in extended downtime.
Simply using only soft copper scrapers, gauze, feeler gauges and
other tools can prevent this abrasion and many surface defects.
吀栀攀 爀攀ⴀ攀渀最椀渀攀攀爀攀搀 䴀漀搀甀氀愀爀 䔀愀最氀攀 猀栀爀攀搀猀 搀漀眀渀琀椀洀攀 愀渀搀 氀愀礀猀 眀愀猀琀攀 琀漀 愀氀洀漀猀琀 愀渀礀 洀愀琀攀爀椀愀氀⸀
吀栀攀 䴀漀搀甀氀愀爀 䔀愀最氀攀 猀栀愀欀攀猀 甀瀀 琀栀攀 洀愀爀欀攀琀 眀椀琀栀 瀀愀琀攀渀琀攀搀 匀瀀氀椀琀ⴀ䄀ⴀ倀愀爀琀 愀挀挀攀猀猀 愀琀 愀 瘀愀氀甀攀ⴀ搀爀椀瘀攀渀 瀀爀椀挀攀⸀
吀漀 猀挀栀攀搀甀氀攀 愀 搀攀洀漀 挀愀氀氀 ⠀㔀 ㈀⤀ 㘀㌀㜀ⴀ㘀㜀㜀㠀
漀爀 攀洀愀椀氀 甀猀 愀琀 猀愀氀攀猀䀀爀攀瀀甀戀氀椀挀洀愀挀栀椀渀攀⸀挀漀洀⸀
刀攀瀀甀戀氀椀挀䴀愀挀栀椀渀攀⸀挀漀洀
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The die-exit face
may need periodic
resurfacing to restore
the sharp edge.
42
JUNE 2017
Plastics Technology
PTonline.com
K now How