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VDL (E3.1) 10/2020 Page 37/196
Material
The inner chamber is made of especially corrosion resistant stainless steel V4A (German material no.
1.4404, US equivalent AISI 316L) micro-polished. The rack holder and all of the chamber's vacuum con-
nections and valves are made of especially corrosion resistant stainless steel V4A (German material no.
1.4571, US equivalent AISI 316Ti). The housing is RAL 7035 powder-coated. All corners and edges of the
housing are also completely coated. When operating the chamber at temperatures above 150 °C / 302 °F,
the impact of the oxygen in the air may cause discoloration of the metallic surfaces (yellowish-brown or
blue) by natural oxidation processes. These colorations are harmless and will in no way impair the function
or quality of the chamber.
The chambers are jacket-heated. The preheating chamber technique ensures a completely homogeneous
jacket temperature, ensuring uniform heat transfer into the inner chamber. The low-loss heat transfer to the
material uses the aluminum vacuum expansion racks (or optionally available in stainless steel). The elastic-
mounted safety glass window reliably compensates any overpressure or explosions that may occur. The
laminated safety glass pane ensures proven and effective splinter protection in the event of an implosion.
The chambers provide a universal connection for inert gas / ambient air, a compressed air connection for
sweeping the electrical installation area, the preheating chamber, and the controller housing, and a meas-
uring connection, e.g. serving to connect a measuring access port for the optional object temperature dis-
play.
All installable items, such as racks and rack holders, can be easily removed. The completely smooth inner
chamber with its rounded corners and internally welded seams is easy to clean.
The minimum working temperature of the vacuum drying oven is approx. 10 °C / 18 °F above room tem-
perature. The maximum temperature is 110 °C / 230 °F.
Vacuum pumps with a suction capacity of 1 m
3
/h to 30 m
3
/h are suitable for the VD vacuum drying oven.
3.1 Manufacturer's safety plan: Protective measures and equipment
The following measures were taken on the manufacturer’s side in order to prevent ignition and explosions.
• Ignition source monitored via safety temperature limiter (TL) class 1
Only solvents with an auto-ignition temperature above 200 ° C may be entered into the chamber.
There is a safety margin of 20% of the minimum permissible auto-ignition temperature of 200 °C, related
to the hottest point in the interior (where the heating is attached to the inner chamber). The maximum
surface temperature of the inner chamber is 160 °C. Therefore, when operated correctly, the hot sur-
faces are always below the auto-ignition temperature of permitted substances.
The safety temperature limiter (TL) serves to protect the vacuum drying oven, its environment and load-
ing material against exceeding the permitted temperature. It has a fixed switching threshold and pre-
vents exceeding the maximum surface temperature of the inner chamber of 160 °C in the event of a
fault. If this temperature is exceeded, the heater turns off. The TL protects the VDL vacuum drying oven,
its environment and the loading material against impermissible excess temperatures and prevents ex-
ceeding the maximum surface temperature in case of a fault.
The safety temperature limiter (TL) provides temperature monitoring through a thermal switch (bimetal
switch). If the permissible temperature is exceeded, the heating is switched off and an additional self-
holding circuit is activated, which is only reset when the power plug is removed and reconnected. This
prevents the heating from being automatically switched on again. When the TL is triggered, an alarm
message is displayed on the controller. An annual function check by the operator is recommended, for
this a controller test routine is provided (chap. 16.5).
The setpoint can only be set up to the maximum drying temperature of 110 °C / 230 °F.
Control technology ensures that there are no temperature overshoots when heating up.
The interior is hermetically sealed against the heating system. The heating elements are located pre-
heating chamber, which is swept with compressed air.
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