Graco 226816 Instructions-Parts List Manual page 10

Determining the Proper Fluid Temperature
CAUTION
Use the lowest temperature setting needed, for
maximum heater life. Operating the heater at its
highest setting – over 82_C (180_F) – for long peri-
ods of time decreases the heater life.
Higher than necessary temperatures also causes the
fluid to dry out, resulting in a poor finish and clogging
the heater.
The chart in Fig. 6 is used on determining the Under–
Boilr temperature. It also shows the effect of tempera-
ture on reducing viscosity. Notice that most of the
viscosity reduction occurs by 55_C (130_F).
Under–Boil is the Graco method of hot, airless spray-
ing in which the fluid is heated to a temperature just
under the boiling point of its most volatile solvent.
To find the Under–Boil temperature of your fluid:
1. Pour a small sample into a heat–proof container.
2. Measure and record the temperature and viscosity
of the fluid. Use a No. 2 Zahn cup.
3. Heat water in a large container to 93_C (200_F).
Place the sample in the water.
Effect of Temperature in Reducing
Two Fluids to a Sprayable Viscosity
The chart in Fig. 7 shows the effect of tempera-
ture in reducing two fluids to a sprayable vis-
cosity – in the range of 20 to 34 seconds using
a No. 2 Zahn cup.
Notice that temperature has more of an effect
on high solid fluids than on thin enamels. That
is, for the same 10_ temperature rise, more
viscosity reduction occurs in the high solid fluid
than the enamel. This shows that high solid
fluids are "temperature sensitive," which needs
to be taken into consideration when planning
your system.
Also note that once the fluid is reduced to
about 34 on the chart, viscosity reduction starts
to level off. Therefore, high temperatures will
not significantly improve sprayability, but will
use more energy.
Fig. 7
10 307363
Operation
4. At every 10_ temperature rise, measure and
record the viscosity and temperature. Do this until
solvents start boiling off and the viscosity starts to
level off – usually 71_ to 77_C (160_ to 170_F).
5. Subtract the lowest viscosity reading from the
highest one. Multiply that result by 0.90. Subtract
the new result from the highest viscosity reading.
Find this number on your temperature and viscos-
ity records. This is the temperature to use in your
Under-Boil system.
EFFECT OF TEMPERATURE ON REDUCING VISCOSITY
VISCOSITY
TIME IN
SECONDS
with No. 2
ZAHN CUP
Fig. 6
EFFECT OF TEMPERATURE ON VISCOSITY
60
50
40
APPARENT
VISCOSITY
with NO. 2
ZAHN CUP
30
nU
1
n
U
2
20
60
UNDER–BOIL METHOD
100
HEAVY LACQUER
90
MEDIUM LACQUER
80
70
ENAMEL
60
50
40
30
20
10
0
60 80 100 120
TEMPERATURE (_F)
TYPICAL HIGH–SOLID PAINT
TYPICAL ENAMEL PAINT
80 100 120
TEMPERATURE (_F)
140 160 180
TYPICAL
SPRAY
VISCOSITIES
140