Luoyang Judian Metal Hot Processing Equipment Co., LTD is mainly engaged in the manufacture of complete sets of equipment in the metal thermal processing industry and the integration of the entire production line.
Learn how slab reheating technology evolved in modern hot strip mills. Explore induction slab heating systems, production capacities, energy consumption, temperature uniformity, and continuous rolling applications for steel manufacturing.
Modern hot strip production has increasingly adopted continuous casting slabs as a replacement for traditional ingot-based rolling processes. As steelmakers pursue higher productivity, lower energy consumption, and improved product quality, slab reheating technology has become a critical part of the rolling line.
A notable development occurred in 1965 when McLouth Steel Corporation in the United States explored new methods for reheating continuously cast slabs before rolling. These efforts ultimately contributed to the development of advanced induction slab heating systems capable of handling cold, warm, and hot slabs in continuous production environments.
This article summarizes the principles, design requirements, and operating performance of induction reheating systems for steel slabs.
Why Secondary Reheating of Slabs Is Necessary
Before entering the rolling mill, continuously cast slabs typically require secondary reheating. Depending on their condition, slabs may be:
Cold slabs
Warm slabs (approximately 200–500°C)
Hot slabs directly from continuous casting (typically 500–700°C)
The objective of secondary reheating is to:
Achieve uniform rolling temperature
Improve deformation characteristics
Reduce rolling forces
Enhance product quality
Support continuous rolling operations
Early studies investigated pusher-type reheating furnaces and walking-beam furnaces. However, these systems encountered limitations when processing mixed batches containing cold, warm, and hot slabs simultaneously. Operational complexity and high costs encouraged the search for alternative technologies.
Development of Induction Slab Reheating
To overcome these challenges, Ross of Ajax Magnathermic proposed a reheating method based on a large rectangular induction coil.
Working Principle
The system operates as follows:
Slabs are positioned vertically.
Mechanical handling equipment lifts the slabs.
The slabs pass through a fixed rectangular induction coil.
Electromagnetic induction generates heat directly within the slab.
The slab reaches the required rolling temperature before entering the mill.
Because steel slabs may warp during heating, sufficient clearance must be maintained between the slab and the induction coil. While this reduces the power factor slightly, it allows safe and reliable operation.
Design Requirements for the Slab Heating Installation
The installation was designed according to the following production objectives:
Production Capacity
Annual production target: approximately 2,200,000 tons
Slab Thickness
Maximum slab thickness: 300 mm
Available Slab Widths
0.9 m
1.1 m
1.3 m
1.5 m
Operational Requirements
The system was expected to:
Process slabs of varying widths.
Achieve an average throughput of 276 tons/hour for general operation.
Reach 550 tons/hour when processing 1.5-meter-wide slabs.
Handle mixed charging of cold, warm, and hot slabs.
Support fully continuous production.
Provide high operational flexibility.
Be compatible with computerized process control.
Deliver large-scale production capability.
Minimize plant floor space requirements.
Reduce labor requirements.
According to reported results, the final installation successfully met all these design objectives.
Induction Heating Line Configuration
When processing the largest slabs:
Thickness: 300 mm
Width: 1.5 m
Length: 8 m
The plant employed:
6 heating lines
Production rate per line: 100 tons/hour
Each line contained three induction heating sections:
Heating Section
Rated Power
Section 1
20,000 kW
Section 2
10,000 kW
Section 3
5,000 kW
Total Power per Line
35,000 kW
Total System Power
210,000 kW
These values represent maximum rated capacities. In actual production, simultaneous operation at full power across all heating sections is rarely required.
Energy Consumption and Heating Performance
Published operating data indicated excellent performance characteristics.
Power Consumption
Energy consumption remained below:
358 kWh per ton
regardless of slab dimensions.
Oxidation Loss
Scale formation was controlled below:
0.25%
This represents a significant advantage over many conventional fuel-fired reheating furnaces.
Temperature Uniformity
The induction heating process achieved:
Excellent temperature consistency
Uniform slab heating
Reduced thermal gradients
Improved rolling quality
Advanced Coil Design
To accommodate different slab widths, the induction coils were designed with adjustable sections.
Key features included:
Modular coil construction
Adaptability to multiple slab dimensions
Improved heating efficiency
Reduced energy waste
Power regulation was achieved through specially designed controllable switching systems. The switching devices connected or disconnected power at the zero-crossing point of the AC waveform, minimizing electrical stress and improving system reliability.
Advantages of Induction Slab Reheating
Compared with traditional reheating furnaces, induction slab heating offers several important benefits:
Higher Productivity
Continuous processing
Rapid temperature rise
Reduced waiting time
Improved Energy Efficiency
Direct internal heating
Lower heat losses
Reduced fuel consumption
Better Product Quality
Uniform temperature distribution
Lower oxidation rates
Reduced scale formation
Greater Automation
Easy integration with computer control systems
Real-time process monitoring
Reduced operator intervention
Smaller Footprint
Compact installation
Reduced plant space requirements
Environmental Benefits
Lower emissions
Cleaner production process
Improved workplace conditions
Conclusion
The adoption of induction reheating technology marked a significant advancement in hot strip mill operations. By enabling efficient reheating of cold, warm, and hot continuously cast slabs, induction systems provide exceptional flexibility, productivity, and energy efficiency.
The McLouth Steel installation demonstrated that large-scale induction slab reheating can successfully support annual production exceeding two million tons while maintaining low oxidation losses, excellent temperature uniformity, and energy consumption below 358 kWh per ton.
Today, induction slab heating remains an important technology for steel producers seeking higher efficiency, improved product quality, and more sustainable manufacturing practices.
