High-Temperature Vacuum Furnaces VHT with Graphite, Molybdenum or MoSi2 Heating

The compact furnaces of the VHT line are available as electrically heated chamber furnaces with graphite,
molybdenum or MoSi2 heating. A wide variety of heating designs as well as a complete range of accessories
allow optimal furnace configuration for technically demanding customer processes. The vacuum-tight retort
enables heat treatment processes either in protective and reaction gas atmospheres or in a vacuum,
depending on the application, all the way to 10-5 mbar. With the appropriate safety technology,
the furnaces are also suitable for operation with hydrogen.

Heating Concepts

Graphite – VHT ../GR

• Suitable for processes under protective and reaction gases or under vacuum
• Tmax 1800 °C and 2200 °C
• Graphite felt insulation
• Temperature measurement using type B thermocouple (version to 1800 °C)
• Temperature measurement using optical pyrometer (version to 2200 °C)

Molybdenum – VHT ../MO

• Suitable for processes under highly pure protective and reaction gases or under a high vacuum up as much as 10-5 mbar
• Tmax 1600 °C
• Insulation made of Molybdenum steel sheets

MoSi2 – VHT ../KE

• Suitable for processes under protective and reaction gases or in air or under vacuum
• Tmax 1800 °C
• Insulation made of high purity aluminum oxide fiber

Basic Version VHT (All Heating Concepts)

• Standard furnace sizes 8, 40 and 100 liters
• A water-cooled stainless steel process reactor sealed with temperature-resistant o-rings
• Frame made of stable steel profiles, easy to service due to easily removable stainless steel panels
• Casing of the VHT 8 model on castors for easy repositioning of furnace
• Cooling water manifold with manual stopcocks in supply and return lines, automatic flowmeter monitoring, open-loop cooling water system
• Adjustable cooling water circuits with flowmeter and temperature indicator and overtemperature fuses
• Switchgear and controller integrated in furnace housing
• H 700 PLC control with clearly laid out 5.7" touchpanel control for program entry and display, 10 programs each with 20 segments
• Over-temperature limit controller with adjustable cutout temperature for thermal protection class 2 in accordance with EN 60519-2
• Manual operation of the process gas and vacuum functions
• Manual gas supply for one process gas (N2 or Ar) with adjustable flow
• Bypass with manual valve for rapid filling or flooding of furnace chamber
• Manual gas outlet with overflow valve (20 mbar relative)
• Single-stage rotary vane pump with ball valve for pre-evacuating and heat treatment in a rough vacuum to 5 mbar
• Pressure gauge for visual pressure monitoring

Additional equipment

• Housing, optionally separable, for passing through narrow door openings
• Manual gas supply for second process gas (N2 or Ar) with adjustable flow and bypass
• Molybdenum or carbon-fiber-carbon retort with direct gas supply for clean atmosphere and improved temperature uniformity in the furnace chamber
• Charge thermocouple with display
• Two-stage rotary vane pump with ball valve for pre-evacuating and heat-treating in a vacuum to 10-2 mbar
• Cooling unit with closed-loop cooling water circuit

The use of automatic valves for process gas or exhaust air management and the powerful H3700
controller allow the entire heat treatment process to be run fully automatically. The entry of all
process data (temperatures, ramps, gas supply and vacuum) is easily controllable from a large,
12" graphic control panel. System status with all process-related data are clearly shown on a
process control diagram. All valves and the vacuum pump can also be operated manually from
here as well. The system has an automatic pre-program and post-program for purging the
furnace chamber and also features automated leak testing.

• Features the same as basic version of VHT, plus:
• Automatic gas supply for one process gas (N2 or Ar) with adjustable flow
• Bypass for rapid filling or flooding of furnace chamber
• Automatic gas outlet with check valve and pressure relief valve (20 mbar)
• Single-stage rotary vane pump with check valve for pre-evacuating and heat treatment in a rough vacuum to 20 mbar
• Transducer for absolute and relative pressure measurements
• H3700 controller (10 programs with 20 segments each)
• Operation with 12" graphical control panel (touchpanel)

Additional equipment

• Mass flow controller for varying flow volumes and generating gas mixtures (with second process gas)
• Furnace pressure control with position-controlled exhaust valve (partial pressure control)
• Electric or gas-heated exhaust gas torch for process gas post-combustion
• Water-cooled exhaust gas cooler
• Condensate traps for separation of large amounts of binder
• Two-stage rotary vane pump with check valve for pre-evacuating and heat treatment in a vacuum to 10-2 mbar
• Pump stand with turbo-molecular pump and slide valve for pre-evacuating and for heat
• treatment in a vacuum to 10-5 mbar (only for molybdenum model) including electric pressure transducer and booster pump
• PC control via NCC with enhanced optional documentation and possible connection to customer LAN

When hydrogen is used as a process gas, our systems come equipped with additional safety technology.
Only certified and industry proven safety sensors are used. The furnaces are always controlled using a
fail-safe controller (S7-300F/safety controller). The controller and documentation are carried
out using Nabertherm Control Center NCC (see page 42).

Two Temperature-Dependent Concepts Available for Safe Operation with Hydrogen:

• Partial pressure operation: H2 infeed under controlled negative pressure (partial pressure)
• in the process reactor starting from 750 °C furnace chamber temperature
• Atmospheric operation: H2-purging of process reactor starting from room temperature at controlled over pressure (50 mbar relative)

Automatic Version VHT for Operation with Hydrogen

• Features as found with automatic version of the VHT without hydrogen operation, plus
• Redundant process gas valves for hydrogen
• Monitored pre-pressures of all process gases
• Bypass for safe purging of furnace chamber with inert gas
• Pressure-monitored emergency flooding with automated solenoid valve opening
• Electric or gas-heated exhaust gas torch for H2 post-combustion