Ransburg RMA Indirect A11600 - Manual (Page 30)

Figure 4: A11065-05 Air Heater
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 cool-
ing 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 condensa-
tion 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 be-
low 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. turbine drive air,
shaping air, and seal 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 tempera-
ture. The heater should be set as low as possi-
ble, 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 RMA-303 with 65mm 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)). Re-
ferring 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
(A11065-05) 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
> Connect Air heater to turbine air tubing.
NOTE
RMA-303 Indirect Charge - Installation
Ransburg
26 LN-9252-06.4