Ransburg Aerobell (Std.) Rotary Atomizer A12381 - Manual (Page 30)

AIR HEATER
REQUIREMENTS
Turbine drive air expands as it moves through
the turbine wheel cavity and as it exits the turbine
from the exhaust port. This expansion will cause
cooling of the exhaust air and the surfaces it
contacts. This same expansion cooling can occur
across the shaping air exit ports. This cooling
effect can cause surface temperatures to fall
below the dew point of the booth, which will result
in condensation on the interior and exterior of the
atomizer, machine, and its components. It is even
possible that the temperature of the supply air
may be below the booth dew point, even without
additional expansion cooling.
Condensation is especially probable in waterborne
applications when booth temperature and relative
humidity levels are typically maintained very high.
This condensation will allow sufficient conductivity
of the surfaces such that they act as an erratic
ground source potential. This can cause damage
to the equipment.
It is therefore, a requirement that turbine exhaust
air temperature be maintained above the booth
dew point to prevent condensation from forming
on atomizer surfaces. Doing so will eliminate
moisture as a potential defect in painted surfaces
as well as extending equipment life. Thus, it is
recommended that air heaters be installed into the
atomizer air supply lines, i.e. shaping air. The air
heaters must be of sufficient capacity capable of
raising the incoming air temperature at least 40°F
(4.4°C) at a flow rate of 60 SCFM per applicator.
The actual air heater process setting depends on
applicator fluid flow rate load, booth conditions,
turbine airflow settings, and incoming air
temperature. The heater should be set as low
as possible, sufficient to maintain the applicator
surface temperatures above the dew point in the
booth.
Example: With the incoming air temperature at
72°F (22.2°C), an Aerobell with 70mm bell cup
rotating unloaded at 60 krpm has a turbine outlet
temperature drop of approximately 28°F (-2.2°C)
(@ 40 krpm unloaded, ∆T ~ 14°F (-.10°C).
Referring to the ASHRAE Psychrometric chart,
the saturation temperature range (dew point) of
a spray booth maintained at 70-75°F / 65-70%
RH is 62-68°F (21.1-23.9°C / 65-70° RH is 16.7-
20°C). Thus it is almost certain that the surface
temperatures of the applicator will fall below the
dew point of the booth, and an air heater will be
needed in this case.
To prevent condensation, an air heater assembly
should be assembled after the air filters. (Reference
the current "Air Heater Assembly" service manual
for further information.)
> Failure to use an air heater may cause
damage to equipment or ruin the finished
component being processed.
NOTE
Figure 4: A11065-05 Air Heater
Aerobell - Installation
26 LN-9264-08.2
Ransburg