Filter
Top Products
Installation
12 309524N
Determining Proper Fluid
Temperature
Use the lowest temperature setting possible for maxi-
mum heater life. Use the chart in F
IG. 9 to determine the
Under-Boil
®
temperature. FIG. 9 also shows the effect of
temperature on reducing viscosity. Note that most of the
viscosity reduction occurs by 130°F (55°C).
Under-Boil is the Graco method of hot, airless spraying
where the fluid is heated to a temperature just under the
boiling point of its most volatile solvent.
To find your fluid’s Under-Boil temperature:
1. Pour a small sample into a heat-proof container.
2. Measure and record the fluid temperature and vis-
cosity using a No. 2 Zahn cup.
3. Heat water in a large container to 200°F (93°C).
Place the sample in the water.
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 160-170°F (71-77°C).
5. To find the temperature to use in your Under-Boil
system:
a. Subtract the lowest viscosity reading from the
highest one.
b. Multiply the result by 0.90.
c. Subtract the result from the highest viscosity
reading. Find this number on your temperature
and viscosity records.
CAUTION
Operating the heater at its highest setting, over 180°F
(82°C), for long periods of time decreases the heater
life and can cause fluid to dry out; which can clog the
heater and result in a poor finish.
FIG. 9: Reducing Viscosity: Under-Boil Method
0
10
20
30
40
50
60
70
80
90
100
20 30 40 50 60 70 80
o
C
(70)
(
o
F)
(80) (90) (100) (110) (120) (130) (140) (150) (160) (170) (180)
Viscosity: seconds with #2 Zahn cup
Temperature
Heavy Lacquer
Medium Lacquer
Enamel