These gastight retort furnaces are equipped with direct or indirect heating depending on temperature. They are perfectly suited for various heat treatment processes requiring a defined protective or a reaction gas atmosphere. These compact models can also be laid out for heat treatment under vacuum up to 600 °C. The furnace chamber consists of a gastight retort with water cooling around the door to protect the special sealing. Equipped with the corresponding safety technology, retort furnaces are also suitable for applications under reaction gases, such as hydrogen or, in combination with the IDB package, for inert debinding or for pyrolysis processes.

Different model versions are available depending on the temperature range required for the process:

Models NRA ../06 with Tmax 650 °C

• Heating elements located inside the retort
• Temperature uniformity up to ∆T 6 K inside the working chamber from 100 °C - 600 °C
• Retort made of 1.4571
• Gas circulation fan in the back of the retort provides for optimal temperature uniformity

Models NRA ../09 with Tmax 950 °C

• Outside heating with heating elements surrounding the retort as well as an additional door heater
• Temperature uniformity up to ∆T 6 K inside the working chamber from 200 °C - 900 °C
• Retort made of 1.4841
• Fan in the back of the retort provides for optimal temperature uniformity

Models NR ../11 with Tmax 1100 °C

• Outside heating with heating elements surrounding the retort as well as an additional door heater
• Temperature uniformity up to ∆T 10 K inside the working chamber from 200 °C - 1050 °C
• Retort made of 1.4841

Basic version

• Compact housing in frame design with removable stainless steel sheets
• Controls and gas supply integrated in the furnace housing
• Welded charging supports in the retort or air-baffle box in the furnace with air circulation
• Swivel door hinged on right side with open cooling water system
• Multi-zone control for 950 °C and 1100 °C version, separated by furnace chamber and door. Depending on furnace chamber additionally subdivided into one or several heating zones
• Temperature control as charge control with temperature measurement inside and outside the retort
• Gas supply system for one nonflammable protective gas with flow meter and solenoid valve, switchable via the control system
• Operation under vacuum up to 600 °C with optional single-stage rotary vane pump
• Port for vacuum pump for cold evacuation
• PLC controls with touch panel H 700 for data input (resp. P 300 for 650 °C-version)

Additional equipment

• Upgrade for other nonflammable gases
• Automatic gas injection, including MFC flow controller for alternating volume flow, PLC controlled with touch panel H 3700
• Vacuum pump for evacuating of the retort up to 600 °C, attainable vacuum up to 10-5 mbar subject to selected pump
• Cooling system for shortening process times
• Heat exchanger with closed-loop cooling water circuit for door cooling
• Measuring device for residual oxygen content

When hydrogen is used as a process gas, the furnace is additionally equipped with the required safety technology. Only certified and industry proven safety sensors are used. The furnace is controlled by a fail-safe PLC control system (S7- 300F/safety controller).

• H2 supply at controlled overpressure of 50 mbar relative
• Certified safety concept
• PLC controls with graphic touch panel H 3700 for data input
• Redundant gas inlet valves for hydrogen
• Monitored pre-pressures of all process gases
• Bypass for safe flushing of furnace chamber with inert gas
• Torch for thermal afterburning of exhaust gases
• Emergency flood container for purging the furnace in case of failore

• Process control under monitored and controlled overpressure of 50 mbar relative
• Certified safety concept
• PLC controls with graphic touch panel H 1700 for data input
• Monitored gas pre-pressure of the process gas
• Bypass for safe flushing of furnace chamber with inert gas
• Torch for thermal afterburning of exhaust gases

Compared with the VHT models (page 56 ff), the furnaces of the SVHT product line offer improved performance data with regard to achievable vacuum and maximum temperature. Due to the design as pit-type furnace with tungsten heating, processes up to max. 2400 °C even in high vacuum can be implemented with models of the SVHT..-W product line. Models of the SVHT..-GR product line with graphite heating, also in pit-type design, can be operated in an inert gas atmosphere even up to max. 3000 °C.

• Standard sizes with a furnace chamber of 2 or 9 liters
• Designed as pit-type furnace, charged from above
• Frame construction with inserted sheets of textured stainless steel
• Double-walled water-cooled stainless steel container
• Manual operation of process gas and vacuum functions
• Manual gas supply for non-combustible process gas
• A step in front of the furnace for an ergonomic charging height
• Retort lid with gas-charged shock absorbers
• Controls and switchgear as well as gas supply integrated in furnace housing
• Further standard product characteristics see description for standard design of VHT models

Heating options

SVHT ..-GR

• Applicable for processes:
  • under protective or reaction gases or in the vacuum up to 2200 C
  • under inert gases (argon, helium) up to 3000 C
• Max. vacuum up to 10-³ mbar depending on the type of pump used
• Heating: graphite heating elements in cylindrical arrangement
• Insulation: graphite felt insulation
• Temperature measurement by means of an optical pyrometer

SVHT ..-W

• Applicable for processes under protective or reaction gases or in vacuum up to 2400 °C
• Max. vacuum up to 10- mbar depending on the type of pump used
• Heating: cylindrical tungsten heating module
• Insulation: tungsten and molybdenum radiant plates
• Temperature measurement with optical pyrometer

• Additional equipment such as automatic process gas control or design for the operation with flammable gases incl. safety system see VHT models

The compact furnaces of the VHT product 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 provide for optimal furnace configurations even for sophisticated applications.

The vacuum-tight retort allows heat treatment processes either in protective and reaction gas atmospheres or in a vacuum, subject to the individual furnace specs to 10-5 mbar. The basic furnace is suited for operation with nonflammable protective gases or under vacuum.

The H2 version provides for operation under hydrogen or other flammable gases. Key of the specification up is a certified safety package providing for a safe operation at all times and triggers an appropriate emergency program in case of failure.

For debinding applications under vacuum, we recommend the VDB version, which besides the corresponding safety technology has an additional debinding retort in the heating chamber and prevents the exhaust gases from contaminating the furnace chamber. The exhaust gases are channelled from the debinding retort into the exhaust gas torch.

The following heating systems are available for the different application temperatures:

VHT ../GR with Graphite Insulation and Heating

• Suitable for processes under protective and reaction gases or under vacuum
• Tmax 1800 °C or 2200 °C
• Max. vacuum up to 10-2 mbar depending on pump type used
• Graphite felt insulation
• Temperature measurement using type B thermocouple (version to 1800 °C)
• Temperature measurement using optical pyrometer (version to 2200 °C)

VHT ../MO or ../W with molybdenum or tungsten heating

• Suitable for high-purity processes under protective and reaction gases or under high vacuum
• Tmax 1200 °C, 1600 °C or 1800 °C (see table)
• Max. vacuum up to 5 x10-5 mbar depending on pump type used
• Insulation made of Molybdenum steel sheets
• Temperature measurement with thermocouple, type S for models with 1200 °C
• Temperature measurement with thermocouple, type B for models with 1600 °C and 1800 °C

VHT ../KE with Fiber Insulation and Heating through Molybdenum Disilicide Heating Elements

• Suitable for processes under protective and reaction gases, in air or under vacuum
• Tmax 1800 °C
• Max. vacuum up to 10-2 mbar (up to 1300 °C) depending on pump type
• Insulation made of high purity aluminum oxide fiber
• Temperature measurement by thermocouple type B

Basic version

• 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
• Housing 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, openloop 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 manual reset for thermal protection class 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

• Tmax 2400 °C
• Housing, optionally divisible, for passing through narrow door frames (VHT 08)
• Manual gas supply for second process gas (N2 or Ar) with adjustable flow and bypass
• Inner process box made of molybdenum or CFC, especially recommended for debinding processes. The box is installed in the furnace with direct gas inlet and outlet and provides for better temperature uniformity. Due to a change in gas supply direction after debinding a clean process atmosphere for sintering is achieved.
• 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
• Temperature measurement at 2200 °C with pyrometer and thermocouple, type S with automatic pull-out device for precise control results in the low temperature range (VHT 40 and larger)
• Turbo molecular pump with slide valve for pre-evacuation and for heat treatment in a vacuum to 10-5 mbar including electric pressure transducer and booster pump (only VHT…/MO)
• Heat exchanger with closed-loop cooling water circuit
• Automation package with graphic touch panel H 3700
  • 12" graphic touch panel H 3700
  • Input of all process data like temperatures, heating rates, gas injection, vacuum at the touch panel
  • Display of all process-relevant data on a process control diagram
  • Automatic gas supply for one process gas (N2 , argon or forming gas) with adjustable flow
  • Bypass for flooding and filling the chamber with process gas controlled by the program
  • Automatic pre- and post programs, including leak test for safe furnace operation
  • Automatic gas outlet with bellows valve and overflow valve (20 mbar)
  • Transducer for absolute and relative pressure
• MFC flow controller for alternating volume flow and generation of gas mixtures with second process gas (only with automation package)
• Partial pressure operation: protective gas flushing at controlled underpressure (only with automation package)
• PC control via NCC with corresponding optional documentation and connection to customer PC networks

In the H2 version the furnaces of the VHT…/MO or VHT…/GR product line can be operated under hydrogen or other reaction gases. For these applications, the systems are additionally equipped with the required safety technology. Only certified and industry proven safety sensors are used. The furnaces are controlled by a fail-safe PLC control system (S7-300F/safety controller).

• Certified safety concept
• Automation package (see additional equipment above)
• Redundant gas inlet 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
• Atmospheric operation: H2-purging of process reactor starting from room temperature at controlled over pressure (50 mbar relative)

Additional equipment

• Partial pressure operation: H2 flushing at underpressure in the process reactor starting from 750 °C furnace chamber temperature
• Retort in the process chamber for debinding under hydrogen

Certain processes require debinding under protective gases or in vacuum. For these processes the models VHT…/MO-VDB or VHT…/GR-VDB are perfectly suited. They are equipped with the necessary safety technology for debinding. The furnace chamber has an additional debinding retort with a direct discharge into the exhaust gas torch. This system ensures that exhaust gases during debinding do not get into and contaminate the furnace chamber.

• Adapted safety concept for debinding
• Automation package (see additional equipment above)
• Exhaust gas torch for burning the exhaust gases
• Debinding retort in the furnace chamber with direct discharge of the exhaust gases into the exhaust gas torch
• Bypass for safe flushing of furnace chamber with inert gas
• Dry-running vacuum pump

Additional equipment

• Condensate trap for separation of large binder volumes during vacuum debinding
• Heated exhaust gas discharge to prevent condensate deposits in the exhaust gas section
• Exhaust gas treatment depending on the process with binder trap, washer or exhaust gas torch