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Applying Xylan - Flashing & Curing
Applying
Xylan - Flashing & Curing
The
process of achieving a tough, continuous film on the surface of
a part begins with the application of the coating, moves through
a flashing process in which the carrier is vaporized by brief
exposure to an elevated temperature (but lower than the cure temperature),
then concludes with curing, a process in which the coating particles
link into a continuous film.
Xylan coatings can be
cured several ways: convection ovens, infrared ovens,
and, with a few formulations, at ambient temperature. The curing
process is a time/temperature relationship: in all cases, the
higher the temperature, the shorter the curing time required
(see chart below). Note: Altering the time/temperature relationship
may affect the amount of cure.
Convection
systems: These use heated air to cure the coatings.
They are, by far, the most common type used to cure Xylan. Sophisticated
production ovens which employ conveyors to move parts usually
have at least three heat zones within them: a warm-up zone,
a bake zone and a heat-extraction zone.
Infrared
systems: These are less effective for coatings (such
as Xylan) because the heating elements tend to become glazed
by the fumes given off during the process. As the elements become
covered, they radiate less energy and become ineffective. Further,
parts hidden behind other parts do not cure. However, these
systems are effective for flat or shallow parts.
Curing
schedules: These vary for different Xylan formulations,
depending on the resin binder employed and other factors. However,
these coatings permit wide latitude in the selection of cure
temperatures so that cure can be compatible with the part. For
instance, you may want to limit the cure temperature of a die
cast part to 180°C/350°F, or that for a formed aluminum
part to 235°C/450°F.
Note:
Cure time is the period that begins when parts reach and remain
at cure temperature, not oven dwell time (the entire period
during which the parts are in the oven).
Caution:
Entrapped air in such parts as rollers or insulated/jacketed
vessels may create a "bomb" and explode when heated
to cure temperatures. An air relief hole or pressure relief
valve must be a part of the assembly.
Note:
Definitions of any technical terms used on this page
can be found in our
glossary.
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