Thermal Process Technology /
Hot-Wall Retort Furnaces up to 1100 °C

Hot-Wall Retort Furnaces up to 1100 °C

Schematic presentation of a hot-wall retort furnace with additional equipment 1 Retort 2 Heating 3 Insulation 4 Gas management system 5 Vacuum pump 6 Fan for indirect cooling 7 Outlet indirect cooling 8 Exhaust torch 9 Fan for gas circulation (NRA models) 10 Charging frame 11 Emergency flushing container

Inside heating in retort furnace NRA ../06

These gas tight 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 gas tight retort with water cooling around the door to protect the special sealing. 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 :

Models NRA ../06 with Tmax 650 °C

  • Heating elements located inside the retort
  • Temperature uniformity up to +/- 5 °C inside the work space
  • Retort made of 1.4571
  • Gas circulation fan in the back of the retort provides for optimal temperature uniformity
  • Insulation made of mineral wool

Models NRA ../09 with Tmax 950 °C

  • Design like models NRA ../06 with following differences:
    • Outside heating with heating elements around the retort
    • Retort made of 1.4828
    • Only fiber materials are used which are not classified as carcinogenic according to TRGS 905, class 1 or 2

Models NR ../11 with Tmax 1100 °C

  • Design like models NRA ../09 with following differences:
    • Retort made of 1.4841
    • Without gas-circulation

Retort furnace NRA 25/09 Retort furnace NRA 150/09 with controls H1700 and bayonet door lock

Vacuum pump for cold evacuation of the retort

Process control H3700 for automatic version

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 resp. air-baffle box in the furnaces with atmosphere circulation
  • Swivel door hinged on right side
  • Open cooling water system
  • Depending on furnace volume for 950 °C- and 1100 °C-models the control system is divided in one or more heating zones
  • Furnace temperature control with measurement outside the retort
  • Gas supply system for one non-flammable protective or reaction gas with flow meter and magnetic valve
  • Port for vacuum pump for cold evacuation
  • Operation under vacuum up to 600 °C with optional vacuum pumps
  • Defined application within the constraints of the operating instructions
  • NTLog Basic for Nabertherm controller: recording of process data with USB-flash drive

Additional equipment

  • Upgrade for other non-flammable gases, H2 version for flammable gases
  • Automatic gas injection, including MFC flow controller for alternating volume flow, controlled with process control H3700, H1700
  • Vacuum pump for evacuating of the retort up to 600 °C, attainable vacuum up to 10-5 mbar subject to selected pump
  • Indirect cooling
  • Direct cooling
  • Heat exchanger with closed-loop cooling water circuit for door cooling
  • Measuring device for residual oxygen content
  • Door heating
  • Temperature control as charge control with temperature measurement inside and outside the retort
  • Retort, made of 2.4633 for Tmax 1150 °C
  • Process control and documentation via VCD software package or Nabertherm Control Center (NCC) for monitoring, documentation and control

Retort furnace NRA 400/03 IDB with thermal post combustion system
IDB Version for Debinding under Non-flammable Protective Gases or for Pyrolysis Processes

The retort furnaces of the NR and NRA product line are perfectly suited for debinding under non-flammable protective gases or for pyrolysis processes. The IDB version of the retort furnaces implements a safety concept by controlled inerting the furnace chamber with a protective gas. Exhaust gases are burned in a termal post combustion. Both the purging and the torch function are monitored to ensure a safe operation.

  • Process control under monitored overpressure
  • Process control H1700 with PLC controls and graphic touch panel for data input
  • Monitored gas pre-pressure of the process gas
  • Bypass for safe flushing of furnace chamber with inert gas
  • Thermal post combustion of exhaust gases

Retort furnace NRA 300/09 H2 for heat treatment under hydrogen
H2 Version for Operation with Flammable Process Gases

When a flammable process gas like hydrogen is used, the retort 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).

  • Supply of flammable process gas at controlled overpressure of 50 mbar relative
  • Certified safety concept
  • PLC controls with graphic touch panel H3700 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 post combustion of exhaust gases
  • Emergency flood container for purging the furnace in case of failore
ModelTmaxModelTmaxWork space dimensions in mmUseful volumeElectrical
 °C °Cwdhin lconnection*
NRA 17/..650 or 950NR 17/111100225350225173-phase
NRA 25/..650 or 950NR 25/111100225500225253-phase
NRA 50/..650 or 950NR 50/111100325475325503-phase
NRA 75/..650 or 950NR 75/111100325700325753-phase
NRA 150/..650 or 950NR 150/1111004507504501503-phase
NRA 200/..650 or 950NR 200/11110045010004502003-phase
NRA 300/..650 or 950NR 300/1111005909005903003-phase
NRA 400/..650 or 950NR 400/11110059012505904003-phase
NRA 500/..650 or 950NR 500/11110072010007205003-phase
NRA 700/..650 or 950NR 700/11110072013507207003-phase
NRA 1000/..650 or 950NR 1000/111100870135087010003-phase
*Please see page 89 for more information about supply voltage

Manual or Semi-Automatic Tempering Plants for Hardening in Protective Gas with Subsequent Quenching outside the Furnace

Semi-automatic annealing plant with retort furnace NR 50/11 and water quenching bath on rails

NR 50/11 with charging rack for manual removal at high temperatures for quenching in an external bath

Processes such as hardening of titanium or hardening/carburization, carburizing of steel, which require a controlled gas atmosphere with a subsequent quenching process, can be carried out with protective gas quenching and tempering plants. Such a system consists of a hot-wall retort furnace and an external quenching bath. Depending on the arrangement and design of the components, quenching delay times of up to 10 seconds can be achieved, so that the components are exposed to air for a short time only. Chamber retort furnaces or pit-type retort furnaces can be offered for heavy components, where the batch is removed by crane after heat treatment and transferred to the quenching bath. Depending on the requirements, the degree of automation can range from a purely manual version to a fully automated system with manipulator. The quenching medium shall be selected taking into account the material to be treated and may be water, polymer, oil or a salt. Additional equipment required for the process, such as cooling or heating or circulation of the medium, can be offered as well. In a manual quenching and tempering plant, the process control is carried out by means of a Nabertherm controller. For more complex requirements, the controller is replaced by a PLC control. Process documentation in accordance with current standards such as the AMS 2750 E (NADCAP) is also possible.


Retort Furnaces for Catalytic Debinding also as Combi Furnaces for Catalytic or Thermal Debinding

Retort furnace NRA 40/02 with cupboard for the acid pump

Acid pump for nitric acid

Retort with internal heating

The retort furnaces NRA 40/02 CDB and NRA 150/02 CDB are specially developed for catalytic debinding of ceramics and metallic powder injection molded parts. They are equipped with a gastight retort with inside heating and gas circulation. During catalytic debinding, the polyacetal-containing (POM) binder chemically decomposes in the oven under nitric acid and is carried out of the oven by a nitrogen carrier gas and burned in an exhaust gas torch. Both retort furnaces have a comprehensive safety package to protect the operator and the surrounding. Exectuted as combi furnace series CTDB these retort furnace can be used for either catalytic or thermal debinding incl. presintering if necessary and possible. The presintered parts can be easliy transferred into the sintering furnace. The sintering furnace remains clean as no residual binder can exhaust anymore.

  • Retort made of acid-resistant stainless steel 1.4571 with large swiveling door
  • Four-side heating inside the retort through chromium steel tube heating elements for good temperature uniformity
  • Horizontal gas circulation for uniform distribution of the process atmosphere
  • Acid pump and acid vessel (to be provided by the customer) accommodated in the furnace frame
  • Gas-fired exhaust gas torch with flame monitoring
  • Extensive safety package with redundantly operating safety PLC for safe operation with nitric acid
  • Large, graphic process control H3700 for entering data and for process visualization
  • Emergency tank for flushing in case of a failure
  • Defined application within the constraints of the operating instructions

Version NRA .. CDB

  • Tmax 200  °C
  • Automatic gas supply system for nitrogen with mass flow controller
  • Adjustable acid volume and correspondingly adjusted gas spply volumes

Version NRA .. CTDB

  • Availabel for 600 °C and 900 °C with atmosphere circulation

Additional equipment

  • Scale for the nitric acid vessel, connected to the PLC monitors the acid consumption and visualizes the fill level of the acid vessel (NRA 150/02 CDB)
  • Lift truck for easy loading of the furnace
  • Cupboard for acid pump
  • Process control and documentation via Nabertherm Control Center (NCC) for monitoring, documentation and control
ModelTmaxInner dimensions in mmVolumeOuter dimensions in mmHeating power inElectricalWeightAcidic quantityNitrogen
 °Cwdhin lWDHkW2connection*in kg(HNO3)(N2)
NRA 40/02 CDB200300450300401400160024002,03-phase1800max. 70 ml/h1000 l/h
NRA 150/02 CDB20045070045015016501960285020,03-phase11650 max. 180 ml/hmax. 4000 l/h
1Heating only between two phases *Please see page 89 for more information about supply voltage
2Depending on furnace design connected load might be higher

Bottom Loading Retort Furnaces up to 1100 °C

Bottom loading retort furnace LBR 300/11 H2 with safety technology for operation with Hydrogen as process gas Gas management system at bottom loading retort furnace LBR 300/11 H2

The bottom loading retort furnaces of the LBR series are suitable for production processes that are carried out in protective/reaction gas atmosphere. With regard to the basic performance data, these models are constructed like the SR models. Their size and design with electro-hydraulically driven lifting bottom make it easier to load heavy duties. The retort furnaces are available in different sizes and designs.

Basic version (all models)

  • Tmax 650 °C, 950 °C or 1100 °C
  • Frame-mounted housing with stainless steel sheets
  • Charging from the front
  • Electro-hydraulically driven furnace bottom
  • Gas supply system for a non-flammable protective gas or reaction gas with flow meter and solenoid valve
  • Temperature control designed as furnace chamber control
  • Connection possibility for an optional vacuum pump (cold evacuation or operation up to 600 °C under vacuum)
  • Defined application within the constraints of the operating instructions
  • NTLog Basic for Nabertherm controllers: recording of process data with USB flash drive
  • Additional equipment, H2 version and IDB version see models NR and NRA

Pit-Type Retort Furnaces up to 1100 °C

Retort furnace SRA 300/06 with charging basket Retort furnace SRA 200/09

Front made of textured stainless steel

The retort furnaces SR and SRA (with gas circulation) are designed for operation under non-flammable or flammable protective or reaction gases. The hot-wall retort furnaces are loaded from above by crane or other lifting equipment provided by the customer. In this way, even large charge weights can be loaded into the furnace chamber.

Depending on the temperature range in which the furnace be used, the following models are available:

Models SRA ../06 with Tmax 600 °C

  • Heating inside the retort
  • Gas-circulation with powerful fan in the furnace lid
  • Temperature uniformity up to +/- 5 °C inside the work space
  • Single-zone control
  • Retort made of 1.4571
  • Insulation made of high-grade mineral wool

Models SRA ../09 with Tmax 950 °C

  • Design like models SR…/06 with following differences:
    • All-around heating from outside of the retort
    • Only fiber materials are used which are not classified as carcinogenic according to TRGS 905, class 1 or 2
    • Retort made of 1.4828

Models SR .../11 with Tmax 1100 °C

  • Design like models SR…/09 with following differences:
    • Without gas-circulation
    • Top down multi-zone control of the furnace heating
    • Retort made of 1.4841

Standard Equipment (all models)

  • Design like standard equipment of models NR and NRA with following differences: see control alternative page 87
    • Compact housing in frame construction with inserted stainless steel sheets
    • Charging from above with crane or other lifting equipment from customer
    • Hinged lid with opening to the side
    • Welded charging frame resp. gas-guiding box for furnaces with circulation
    • Gas-supply system for one non-flammable protective or reactive gas with flowmeter and magnetic valve
    • Furnace temperature control
    • Possible connection of an optional vacuum pump (for cold evacuation or for processes up to 600 °C under vacuum)
    • Defined application within the constraints of the operating instructions
    • NTLog Basic for Nabertherm controller: recording of process data with USB-flash drive
  • Additional equipment, H2 version or IDB version see models NR and NRA
ModelTmaxInner dimensions of alloy retortVolumeOuter dimensions in mmElectricalWeight
 °CØ in mmh in mmin lWDHconnection*in kg
SR(A) 17/.. 250350171300170018003-phase600
SR(A) 25/.. 250500251300190018003-phase800
SR(A) 50/.. 400450501400200018003-phase1300
SR(A) 100/..600,4008001001400200021003-phase1500
SR(A) 200/..9506007002001600220022003-phase2100
SR(A) 300/..or60010003001600220025003-phase2400
SR(A) 500/..110080010005001800240027003-phase2800
SR(A) 600/.. 80012006001800240029003-phase3000
SR(A) 800/.. 100010008002000260028003-phase3100
SR(A) 1000/.. 1000130010002000260031003-phase3300
SR(A) 1500/.. 1200130015002200280033003-phase3500
*Please see page 89 for more information about supply voltage

Forced Convection Pit-Type Retort Furnaces up to 850 °C

Pit-type furnace SAL 30/65 with alternating retort for defined inert gas atmosphere and two retort cooling stations

Retort with vacuum and protective gas line, cooling water connections as well as thermocouples and pressure sensors

Cooling station without forced cooling with exchangeable retort

The forced convection pit-type furnaces of the SAL series (technical data see page 66) can be upgraded by the use of gas tight retorts for processes with defined atmospheres. These systems are very well suited for the heat treatment of bulk materials. By means of an additional retort and cooling station, the retort can be removed after completion of the heat treatment process and cooled in a cooling station. In the case of sensitive components, further flushing with protective gas can also be carried out during the cooling phase. The cooling station can be designed with or without forced cooling by means of a powerful fan. When equipped with a vacuum pump, the retort is evacuated outside the furnace in cold state and then flushed with protective gas. This procedure is particularly suitable for heat treatment of bulk solids as well as for non-ferrous and precious metals. Residual oxygen is much better and faster removed by means of pre-evacuation. Up to a maximum working temperature of 600 °C, the furnaces can also be operated under vacuum by connecting a vacuum pump depending on the type of pump, a vacuum of up to 10-5 mbar can be achieved. The furnaces can be equipped with gas supply systems for non-flammable protective and reaction gases, as described on pages 74 - 75. A gas supply system for operation under hydrogen, including safety technology, is also available as an additional equipment.


Pit-Type Furnace with Exchangeable Retort

Pit-type furnace SRA 450/06 with exchangeable retort Retort furnace SR 170/1000/11 with changeable retort and cooling station

Exchangeable retorts with supply and measuring lines

Main advantage of the pit-type furnace design is that the retort can be taken out of the furnace by crane, in order to cool down outside the furnace while the inert gas flushing is still switched on. Cooling can be carried out naturally outside the furnace on a separate cooling station or forced in a cooling station with powerful cooling fan. The throughput can be increased by using a second exchangeable retort, which is loaded and inertised before the first retort is removed.