Multi-Zone Thyristor Heater Control Panel Solution for Various Heat Treatment Processes/Furnaces
Custom Control Panel Integration with
Libratherm Products
A Strand Annealing Furnace changes a material's strength and hardness, relieves internal stress and increases ductility. This is achieved through a heat treatment process known as annealing. This process alters a material's physical and sometimes chemical properties, increasing its ductility and decreasing its hardness to make it more workable.
Annealing is a repetitive procedure during the wire drawing process. The wire drawing involves pulling a rod through a conical die, reducing its diameter and increasing its length. This results in a thinner and longer wire.
To develop and implement a multi-zone control panel solution to precisely regulate the temperature of the Strand Annealing Furnace. This involves accurate temperature monitoring, control, and reporting to ensure product quality and process efficiency.
Requirements Analysis
Initial Assessment:
The material's metallurgical properties change during the wire drawing process and become non-uniform. As the process continues, the material regains its hardness. In order for the metal to become ductile again and be reworked, it needs to undergo heat treatment.
The strand annealing furnace is utilised to increase the ductility of the material. This furnace consists of four zones with different temperature settings that are adjusted based on the specific metal or material used. The control panel for the strand annealing furnace is responsible for accurately controlling the temperature of each of the four zones.
Key Requirements:
- Accurate multi-zone temperature control.
- Temperature monitoring and feedback
- Safety features
Solution Design
Libratherm Product Selection
- Thyristor Power Regulator
(POW-12-PA-CL / POW-3-PA-CL)
The three-phase thyristor power regulators POW-12-PA-CL and POW-3-PA-CL are designed to provide a smooth and adjustable voltage output proportional to the low-level input control signal. The input control signal can come from an external controller in the form of (0-5) VDC, (0-10) VDC, or (4-20) mADC, or it can be generated using a potentiometer.
The controller's output regulates the current drawn by the resistive heater load. Additionally, the card includes a built-in regulated +5 VDC supply at its terminal to connect an external potentiometer for manual control of the thyristor power controller output voltage. This card also includes various built-in settings, such as soft start and stop and minimum and maximum power limit. The POW-3-PA-CL thyristor controller has a current range from 50A to 1000A, and the POW-12-PA-CL model has a range from 10A to 48A.
- Advanced PID Temperature Controller
(PID-966)
The PID temperature controller produces a (0-5) VDC signal, which is the control input for the three-phase thyristor power regulator. Output Relay 1 in the circuit safeguards the thyristor from excessive temperatures. The K-type thermocouple serves as the input for PID-966, and there is also an RS-485 connection available.
- Safety Controller
(DPC-903)
The input fed to the DPC-903 is the signal from a K-type thermocouple. To ensure the proper and safe functioning of the control panel, Output Relay 1 is used. The safety controller turns off the power to the heater in case the furnace temperature exceeds the safety limit.
Design Consideration
- Bus Bar Design:
The control panel uses a bus bar design for power routing instead of cables, which is colour-coded for three-phase supply.
- Terminal block:
Terminal blocks are used in the control panel for field connections to keep the wiring organised and neat and provide secure and insulated connection points for wires, preventing short circuits and ensuring safe operation.
- Digital Multifunction Meter:
A digital multifunction meter in the control panel indicates various electrical parameters, such as voltage, current, frequency, power factor, and energy.
- Isolation Transformer:
An isolation transformer with an On-delay timer is provided and mounted inside the panel. This isolation transformer offers an isolated supply to the PID-966 and DPC-903 with an adjustable delay time.
- Switch Gears:
Superior-quality switch gears control the thyristor power regulator, isolation transformer and cooling fans fitted inside the panel, providing short-circuit protection.
- Auto-OFF-Manual Switch:
The Auto-OFF-Manual Switch selects the respective modes. This switch comes in handy while testing the control panel, as a fail-safe if the PID controller fails, or as a backup for controlling the power regulators.
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Auto Mode: In this mode, the PID-966 controller is used to control the Heater Load
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OFF Mode: In OFF mode, the control action is in the Off condition, with no output.
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Manual Mode: In this mode, the power to the heater can be manually adjusted in terms of percentage through the 10K potentiometer mounted on the front panel.
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Forced Cooling Fans with Filter:
The fan cools the control panel to prevent its temperature from exceeding. A filter restricts dust particles from entering the control panel and allows the flow of cold outside air.
System Architecture
Closed Loop System
The control panel employs a closed-loop control system for regulating a furnace through a thyristor power regulator connected via a transformer. Two sensors continuously monitor the furnace temperature.
Sensor 1 provides data to the PID temperature controller. When the temperature deviates from the set point, the PID controller processes the data from Sensor 1. This processed signal is then fed to the thyristor power regulator as a 0-5VDC signal. The thyristor power regulator accepts three-phase AC input supply. The regulator provides a proportional control output to the heater load through a transformer, thereby adjusting the heater's temperature accordingly.
Sensor 2 is linked to a safety controller. In the event of a PID controller failure, the safety controller takes over the regulation of the thyristor power regulator. If the furnace temperature exceeds the predetermined limit, the safety controller activates a contactor to turn off the thyristor, ensuring safe operation.
Benefits
- Heater Life :
By regulating the voltage to the heater through the transformer, the control panel prevents excessive wear and tear on the heating elements. This leads to a longer lifespan for the heater, reducing the frequency of replacements and associated costs.
- Life of Switch Gears:
Using solid-state switches and a transformer to step down the voltage reduces the stress on the switchgear components. Lower voltage operation reduces electrical stress and heat generation, prolonging the life of switches and other control panel components.
- Low Maintenance:
The closed-loop control system and the safety features provided by the secondary sensor and safety controller ensure reliable and stable operation. This reduces the likelihood of breakdowns and the need for frequent maintenance, saving time and costs for the user.
- Energy Saving
The precise control provided by the PID temperature controller ensures that the furnace operates efficiently, reducing energy consumption by avoiding overheating and minimising energy waste.
Key Takeaways
Developing and implementing the Multi-Zone Control Panel Solution for the Strand Annealing Furnace has demonstrated significant advancements in the precision and efficiency of temperature regulation for heat treatment processes. Through careful selection of high-quality components and custom integration with Libratherm products, we have successfully addressed the critical needs of wire drawing industries, ensuring enhanced product quality and process efficiency.
- Summary
The Strand Annealing Furnace control panel's primary goals were to guarantee precise multi-zone temperature control, careful observation, and strong safety measures. Using Libratherm products, we modified the panel by incorporating safety controllers, thyristor power regulators, advanced PID controllers, and supporting components. The heater load was connected via a transformer for the best voltage regulation, and the design used a closed-loop system for accurate management and contained necessary safety precautions.
- Future Prospects
The Multi-Zone Control Panel Solution offers exciting opportunities for expansion and adaptation in the future. The system is designed to be scalable, allowing for the addition of more zones as necessary, which can be advantageous for larger or more complex heat treatment processes. Furthermore, the principles and technologies employed in this project can be extended to other heat treatment applications such as Hardening, Carburizing, Nitriding, Tempering, Soft Annealing, and many more, making the control panel a versatile solution for various industrial needs.
- Success Rate:
With over 100 panels already successfully deployed, we have established a track record of reliability and performance. This experience not only reinforces the effectiveness of our solution but also provides a strong foundation for future innovations and improvements.
The Libratherm Multi-Zone Control Panel Solution offers a proven, customizable, and efficient option for businesses seeking to enhance their heat treatment processes. Please contact Libratherm for more information or a consultation. Our team of experts is ready to assist in designing and implementing a control panel tailored to your specific needs, ensuring optimal performance and quality in your operations.
