Page 35 - Platics News June 2022

FEATURE

Importance Of Tooling-Learning Heater-Band Principles For Pro le Die

Tim Groth

When a profile is not being extruded to the tolerances of previous runs, the die is often suspect—but the real problem may
be the heaters. Learn the five heater-band principles before you do any profile die work
T he pro le extrusion process has At some point an air pocket (shown in distance from the opening on the band
many variables that processors try to
red) will develop along the heater band varies with band style and manufacturer.
control, and one of the most overlooked after repeated use. is air pocket will e band style with a clamp requiring
is how heat is applied to the pro le die cause the tool to be nonuniform in tem- no tools to tighten tends to have a larger
via heat transfer from the heater band. perature. area where no heat is applied (Fig. 3). Be
Often, a pro le cannot be extruded to Openings: When more than one heater aware of the dead space on the band be-
the same tolerance as the previous run. band is used on the tool, the openings ing used
In response, work is done to the die to need to be rotated 180° to each other. If
compensate for heat not being appropri- the openings are parallel, a cold section
ately applied, or not applied in the same will develop on the tool, again causing
manner as when the tool was hung on the material to run at an inconsistent ve-
the extruder. locity. In Fig. 2 the openings are in par-
Here’s a more e cient approach to that allel, and the side of the tool with those
problem. ere are ve principles of heat openings will be colder than the other
transfer processors need to know before side. When multiple bands are required,
proceeding to tooling work. mount every other band with the open-
Contact: Heater bands tend to curl up ing on the opposite side of the tool.
away from the tooling after repeated use.
Regardless of the heater system or style
the processor uses to keep the heater in Fig. 03
contact with the tool, an air pocket will
develop at some point along the heater Band-style heaters have an opening in
band (see Fig. 1). is air pocket will the back where no heat is applied.
cause the tool to be nonuniform in tem- Wattage: Most processors tend to over-
perature. e colder tool surface will shoot the wattage required in an e ort
slow the velocity of the plastic as it goes to speed up the changeover process. Plan
through this portion of the tool, caus- Fig. 02 for 0.035 kw × in.2 as a standard. Too
ing the pro le to run out of tolerance When more than one heater band is used high a wattage will overshoot the heat
compared to the previous run. A gap as on the tool, the openings need to be ro- required. Temperature controllers must
narrow as 0.015 in. is enough to cause a tated 180° to each other. If the openings be auto-tuned to the band wattage. If
temperature variation in that area of the are located in parallel as shown above, multiple sizes of bands are used on any
tool. a cold section will develop on the tool, one extruder tool, standardize by mak-
causing the material to run at an incon- ing a ring to cover the tooling and use
sistent velocity. one standard size and wattage of band.
Heater Band Style: ere are many Location: e band’s location on the
styles of heater bands. e scope of this tooling must be duplicated each time the
article is not to ascertain what style is band is taken o . Ideally, the band open-
best but rather to make processors aware ing and position on the die will always
that not all styles apply heat equally to be the same to repeat the melt tempera-
the tool. All bands have an opening in ture across the extrudate. Use some form
which no heat is applied. e heating of locating system on the die as a stop to
Fig. 01

35 PLASTICS NEWS June 2022