Hydrogen Bell Jar Furnace

This Hydrogen Bell Jar is housed in one space saving enclosure and features an automatic electric actuator with air operated locking clamps for easy and complete access to the loading area. A molybdenum retort is supplied with an independent gas line to keep binders and outgassing products away from the hot zone materials, while at the same time improving temperature uniformity.

Major components:

1. Chamber and hot zone
2. Power supply & controls
3. Gas & vacuum system
4. Water cooling
5. Utilities

Chamber and hot zone

The furnace chamber is cylindrical in shape and is manufactured from double-walled stainless steel. The whole chamber is welded together and polished for vacuum integrity and a nice appearance. The whole chamber with shields and heating elements will be lifted by an electric actuator to give full and easy access to the loading area.

There are two instrumentation feed through ports (for thermocouples) and a gas ported quartz sight window is provided for viewing.

The hot zone is made from Tungsten and Molybdenum, with a minimum of 7 layers of shields as required to reduce power loss. A Molybdenum retort is supplied that will lift up and down with the Bell Jar.

Power connections to the heating elements are on the top cover of the chamber and are water cooled. The water-cooled flexible power cables will be attached to these copper feed throughs.

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Power supply & Controls

Power to the heating elements is supplied with a three phase, SCR controlled transformer package. All of the furnace controls will be mounted on the front face of this power supply thus saving valuable floor space. This includes the circuit breakers, contactors, SCR controller, volt & amp meters, a three phase Main Stepdown Transformer matched to meet the heating element resistance, etc. This transformer has 2 secondary voltage taps, to match the element resistance for each hot zone.

The furnace temperature will be controlled through a Honeywell Digital Controller with setpoint programming. This controller has several segments of programming available with
ramp and soak, to be used to create a temperature profile as required. These segments are used to ramp the furnace up to operating temperature, then hold the temperature for as long as
necessary. The controller will read and display the furnace temperature up to 2000C from a type "C" thermocouple (optical pyrometer available). This loop sends a controlling signal to the SCR which will modulate the power to the furnace.

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Gas & vacuum system:

This furnace system was designed to operate in several gas environments and a light vacuum (partial pressure), Hydrogen/Nitrogen. The positive pressure is 5 PSIG. A relief valve, 30/30 compound gauge and a H² burn-off are located on the top chamber of the furnace body. A second Hydrogen line is located on top of the moly retort. This will be plumbed with the chamber gas line. The N² purge line valve will automatically open in case of an alarm condition.

This Gas System comes with several solenoid operated inlet valves and two exhaust valves. The H² gas lines and components in this line will be stainless steel and copper. A Hydrogen Gas Manifold System, explosion-proof pressure switch, hydrogen flow meter, explosion proof solenoid valve, blow-off port and a gas igniter system on the gas out line are all standard components and meet NFPA requirements.

The pumping system will evacuate the furnace into the 10^-3 Torr vacuum range. The purpose of this pumping system is to quickly remove most of the oxygen from the inside of the furnace
and back fill with your desired inert gas, or to make furnace run in a vacuum atmosphere.

This is done with the use of the following:

• A Rotary Vane Pump with an exhaust filter.
• A electropneumatic vacuum valve to isolate the chamber from the pump for operation in process gas.
• A vacuum relief valve (back to atmosphere) is provided for the purpose of releasing the pressure or to conveniently leak check the system.
• Switches and status lights are provided to monitor and operate the pumping system.
• A Vacuum Gauge Controller is being offered that will indicate the furnace pressure through the use of a vacuum thermocouple gauge tube.
• The power to the heating elements is interlocked with the vacuum system through the use of the process control relays on the Vacuum Gauge Controller in the event that a vacuum run is being made.

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Water system:

The water system is designed to adequately cool all the furnace components so no exterior surfaces will ever exceed 120F (45C). To insure proper flow, a water flow interlock will be installed for visual indication and to allow power to be applied to the heating elements only when this switch is satisfied. In the event water flow is interrupted for more than 5 seconds when the furnace is at operating temperature, the power will be disconnected to the heating elements.

The water manifold has several circuits supplying water to the various parts of the furnace. Each one of these can be manually adjusted to allow each circuit just the proper amount of flow to minimize heat and energy losses.

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Utilities:

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