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How the Precision Mix™ Works
The standard Graco Precision Mix™ can blend most
two-component epoxy or polyurethane paints.
Precision Mix™ is not for use with "quick-setting" paints
(those with a pot life of less than 15 minutes).
information on handling quick-setting paints or abrasive
fluids, contact your Graco representative or Graco
Technical Assistance (see back page).
The system can be set up to mix components supplied
from pressure vessels, from feed pumps transferring the
materials from their original containers, or from a central
paint recirculating line.
The standard Precision Mix™ is designed to operate an
air spray or air-assisted airless system with a capacity
of up to 2000 cc/min.
This manual describes the electronic controller module,
which takes information from the fluid flow meters,
installed in the fluid stream, and sends signals to control
valves to reliably proportion the two component
coatings. All ratio calculations are by volume. Other
inputs and outputs are provided to control the flushing
process, provide alarm annunciation, and interface with
the operator.
Operating Cycle
To begin operation, the spray gun operator enters the
desired ratio and other parameters through the pendant
and energizes the MIX input.
normal operation of the Precision Mix™ is controlled by
the operation of the spray gun.
When the gun is triggered, the two components enter
the Precision Mix™ through separate paint lines and
check valves, then are precisely monitored by flow
meters.
When the spray gun is triggered, the two components
are introduced into the integrator chamber one at a time.
Their entry into the chamber is controlled by a dispense
valve for each component. The flow meters monitor the
exact quantities being dispensed, and send electrical
pulses to the controller. The controller monitors these
pulses and turns the dispense valves on or off
accordingly (based on the target volumes calculated by
the controller).
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The following is a typical ratio cycle:
The
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For
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The components are pre-mixed in the integrator, then
given a homogeneous blending as they pass through a
static mixer tube. Output from the mixer tube to the
spray gun may be controlled by a fluid pressure
regulator.
The two components continue to be alternately fed into
the mixing block as long as the gun is triggered. When
the trigger is released, the system idles. Operation can
be stopped at any time by energizing the STANDBY
input, or shutting off the main power switch.
From that point on,
Adaptive Overrun Correction
The actual volume of fluid dispensed each cycle can
vary slightly from the calculated target. However, the
controller monitors this variance and compensates on
the next cycle. At each cycle, the controller calculates
the proper component A (resin) volume based on the
desired ratio, the actual previous component B
(Catalyst) volume, and the desired tolerance.
Whenever the fluid overrun is greater than the
calculated tolerance volume, a relevant message is
displayed on the pendant, the pendant alarm light
blinks, the alarm annunciator closes, and the system
stops.
First, the component A (resin) dispense valve
opens, and the fluid begins to flow into the
integrator chamber. When the correct quantity has
been dispensed (based on the calculated target
value), the component A dispense valve closes.
See Fig. 1.
Next, the component B (catalyst) dispense valve
opens. The fluid begins to flow into the integrator
chamber and is lined up proportionately with the
previously-dispensed component A sample, then
the B dispense valve closes. See Fig 2.
The process repeats itself as long as the spray gun
is triggered.
When the trigger is released, the
Precision Mix™ idles; it will continue where it left off
when the gun is triggered again.
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