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Case Study: Optimising Heat Treatment Furnaces with Thermal Ratio Cascade Control


people working in a furnace factory


Heat treatment furnaces are vital in industries such as metallurgy, aerospace, and automotive, where precise temperature control ensures material quality and performance. A case study based on work done by Tempcon (Temperature Controls) in South Africa highlights an innovative solution using thermal ratio cascade control to enhance furnace efficiency and precision. This blog explores the system, its operation, and the benefits it delivers.


The Challenge: Precision in Heat Treatment

Heat treatment processes require precise temperature management to achieve desired material properties. Traditional control systems often struggle with thermal lag, the delay between heater and load temperature changes, leading to overshooting or inconsistent temperatures. This can compromise product quality and energy efficiency. The challenge was to design a system that ensures rapid warm-up, prevents overshooting, and maintains steady-state control despite external disturbances like voltage fluctuations.


The Solution: Thermal Ratio Cascade Control

Tempcon implemented a thermal ratio cascade control system for a heat treatment furnace, leveraging RKC controllers and thyristor packs. The system integrates two key components:

  • Main Controller RKC PF900 or FB900: Monitors the load temperature, the material being treated, and adjusts the overall process to achieve the desired temperature profile.

  • Remote Set Point Controller RKC FB400: Controls the heating element or gas burner, managing the atmosphere temperature in the furnace.

  • Thyristor Pack RKC THV or THW series: Provides precise power regulation to the heating elements, supporting outputs like 4 to 20 mA DC, voltage pulse, or relay signals.


The system operates in a cascade configuration, where the FB400 acts as a heater temperature controller in a ratio cascade with the PF900 or FB900 load controller. Here is how it works:

  1. Initial Warm-up: The FB400 is set to a higher temperature than the PF900, as the heater must be hotter than the load. Full power is applied, but the load temperature lags due to thermal inertia.

  2. Proportional Control: As the load temperature enters the PF900s proportional band, control region, the PF900 reduces its output. This signal adjusts the FB400s remote set point, proportionally lowering the heater temperature.

  3. Equilibrium: As the load approaches the target temperature, the heater set point is suppressed, preventing overshoot and achieving equilibrium at the desired load temperature.

A variable proportional band on the FB400 allows fine-tuning of how much the load controller influences the heater set point, optimising responsiveness.


System Benefits

The thermal ratio cascade control system offers several advantages:

  • Rapid Warm-up Without Overshoot: By dynamically adjusting the heater set point based on load temperature, the system ensures fast heating while avoiding temperature spikes.

  • Steady-State Precision: The cascade technique links heater and load set points, maintaining consistent temperatures even under disturbances like voltage changes.

  • Robustness to Disturbances: The FB400s local control loop quickly corrects heater temperature variations, minimising their impact on the load due to thermal lag.

  • Flexibility: The FB400 supports multiple output types, 4 to 20 mA for thyristor packs, voltage pulse for solid-state relays, or relay for contactors, making it adaptable to various furnace setups.



furnace releasing


Real-World Impact

Implemented in South Africa, this system demonstrates how advanced control strategies can transform heat treatment processes. The cascade approach eliminates the limitations of non-cascade systems, where thermal lag could cause significant temperature deviations. By integrating the PF900 or FB900 and FB400 controllers with RKC thyristor packs, Tempcon achieved:

  • Enhanced product quality through precise temperature control.

  • Improved energy efficiency by minimising overheating.

  • Reduced wear on furnace components due to stable operation.


Conclusion

The thermal ratio cascade control system showcased in this case study, based on work done by Tempcon, is a game-changer for heat treatment furnaces. By addressing thermal lag and external disturbances, it ensures rapid, precise, and stable temperature control. For industries relying on heat treatment, adopting such advanced control systems can lead to better outcomes, from superior material properties to operational efficiency. Tempcon’s implementation serves as a model for others looking to optimise their furnace operations.

Ready to enhance your temperature control systems? Contact sales@tempcon.co.za for all your temperature control needs and discover tailored solutions for your industry.


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