Cascade Sciences CVAC-9.3, Installation & Operation Manual

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OPERATION
T
HEORY OF
O
PERATION
The CVAC-9.3 is intended for use in closed cycle under vacuum applications such as drying.
Vacuum
Vacuum is supplied to the oven chamber by a vacuum pump or building system. The vacuum supply
is connected to one of two vacuum fittings on the oven: A KF-25 fitting on the back of the oven or a
KF-25 fitting located inside the vacuum plumbing cabinet and controlled by the Vac valve control on
the front of the oven. Vacuum levels obtained in the oven chamber are dependent on pump
performance, valve settings, and the nature of the application or process, including the volume of
material outgassed.
The chamber must be sealed and evacuated at the start of a vacuum baking application. The oven is
not built to operate with the chamber exposed to free atmosphere. Running the oven with the door
or the vent open may risk destroying the vacuum pump and damaging the integrity of the oven
chamber.
Vacuum pumps and door gaskets should be selected based on the application or process.
The vacuum gauge on the control panel displays the chamber atmospheric pressure in torr and
mTorr (millitorr).
Gas Backfill
A gas supply can be connected to the vent intake port (backfill inlet) inside the vacuum plumbing
cabinet. This inlet is controlled by the Vent control on the front of the oven. Nitrogen or another inert
gas or clean air may be used to backfill the oven chamber to avoid particulate contamination,
oxidation, or introducing humid air into the chamber. The maximum allowed backfill pressure is 15 psi
of delivery at the inlet port.
Heating Options
The oven can either heat to and run at a constant temperature set point or execute automated
multistep heating profile recipes with ramp up, heat soak, and ramp down steps. Heating recipes are
programmed as profiles by the end-user.
Heating in a Vacuum
In conventional ovens, powered elements transfer heat into the chamber air. The heated air then
circulates by natural convection or blower fan action, and surrounds the product on the shelves,
gradually bringing it to temperature. In a vacuum oven, heat transport takes place primarily by
conduction. The oven heating elements are located inside the chamber walls, which in turn transfer
heat to the shelves. Each shelf then transports heat to the products or samples resting on it.
Direct radiant heating through infrared emission in a vacuum environment provides poor
temperature uniformity compared to conductive heating.