Gas Carburising Control Systems

  • SIMPLE to build using pre-defined building blocks
  • SCALABLE solution fits the requirements of any plant
  • The most ACCURATE atmosphere control solution available

Thermochemical heat treatments are widely used in the aircraft and automotive industry manufacturing process. Many components such as gears, shafts and bearings, as well as a host of sub-parts, are subject to some case hardening technique and there is a world-wide installed base of furnace equipment. 

Eurotherm supply a wide variety of control solutions into batch and continuous carburising furnace applications.
The scope of supply may vary but there are some key common requirements:

  • Temperature programming and control
  • Atmosphere (Carbon Potential) programming and control of case depth diffusion control
  • Atmosphere probes and atmosphere probe diagnostic features
  • Gas control (sequence and mass flow control) for some specific applications
  • Quench programming and control
  • Furnace sequence control
  • Furnace safety alarms
  • Recipe control and programme management
  • Data management
  • Power control and energy management
  • Furnace diagnostics and maintenance
  • Furnace mimics and screen navigation


Furnace Temperature Control and Programming

Optimum temperature control is achieved using an independent furnace sensor.  The heat control output can either be connected to gas burners or thyristors.  In some applications a cooling output may also be connected to a circulation fan or an exhaust damper. 

It is normal for many instances of the furnace programme to be available for operator selection against a component or batch reference.

Password protected multi-segment programmes enable an optimum profile to be achieved with full traceability.

 

Furnace Atmosphere Control

A zirconia probe is used to measure very low concentrations of % oxygen in the furnace, typically less than 1 x 10 -20.   To supply the required species carbon it is usual for the furnace to be supplied with a base endothermic carrier gas which conditions the furnace, at say 20% CO for a methane based carrier gas. 

In the atmosphere loop, the controller uses the carbon potential calculation based on the known oxygen reading to increase the carbon potential by allowing enrichment gas (ie methane) to enter the furnace.

Conversely, to decrease the carbon potential, controlled air is introduced into the furnace. Automatic probe cleaning functions ensure that the reading is accurate, while probe health and sooting alarms warn of a deterioration in the probe performance.

 

Diffusion Control

Traditionally carburising is carried out against a timed setpoint profile where the time periods for the different temperature/carbon stages are selected against empirical post-process material results. 

This method provides a steel/alloy dependent recipe, which gives good repeatable performance but heat treaters tend to process at the high end of the case depth tolerance to ensure good repeatable results.

Since the purpose of the process is to provide components with a defined effective case depth,  usually with a minimum tolerance, other methods, which allow effective case depth to be selected as the controlling setpoint, have become more widely available.

The case depth diffusion solution is available as a function block within the EyconTM  Visual Supervisor.   This uses an algorithm based on carbon potential, temperature, material specification and process factors to determine the carbon setpoint profile. 

In this case the traditional recipe hands control to the dynamic on-line diffusion calculation, which completes the carburising cycle to the required effective case depth.

Benefits

  • Optimised cycle time
  • Real time calculation of case depth profile
  • High repeatability of case depth results
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