Application of Frequency Converters (VFDs) in Metallurgical Equipment

Frequency Converters (Variable Frequency Drives, VFDs) are extensively and critically applied in metallurgical equipment, serving as a core electrical drive device for modern metallurgical industry to achieve efficient, energy-saving, precise, and automated production.

I. Main Application Areas and Equipment

The metallurgical process mainly includes ironmaking, steelmaking, rolling, and auxiliary processes, with VFDs involved throughout.

1. Raw Material Handling and Ironmaking Process

Blast Furnace Charging System: Controls the main hoist and stock rod, enabling smooth startup, precise stopping, and speed control of the skip car to ensure uniform burden distribution in the blast furnace.

Blast Furnace Blower: Precisely regulates air volume and pressure, representing one of the most significant applications for energy savings. Replacing traditional damper/valve control with VFD speed regulation can drastically reduce energy consumption.

Dust Removal Fans: Given the extreme dust in plants, these fans adjust air volume based on operating conditions. VFD operation leads to significant energy savings.

Pig Casting Machine: Controls the speed of the conveyor chain to accommodate different molten iron temperatures and cooling requirements.

2. Steelmaking and Continuous Casting Process

Converter/Electric Arc Furnace: The tilting mechanism and lance hoist require smooth and precise positioning control, which VFDs provide via accurate torque and speed regulation.

Ladle Car/Slag Pot Car: Speed regulation and start/stop control for the travel mechanism, requiring smooth operation to prevent molten metal splashing.

Continuous Caster:

Mold Oscillation: Requires extremely high-precision frequency and waveform control (e.g., sinusoidal, non-sinusoidal) to improve the surface quality of the cast strand.

Withdrawal Straightener Machine/Dummy Bar: Controls casting speed, synchronized with mold oscillation and secondary cooling to achieve constant or variable speed casting.

Segment Drives: Multi-motor synchronous control ensures the strand is pulled out uniformly.

3. Steel Rolling Process (Core Application Area)
This is the most demanding and complex area for VFD performance.

Roughing Mill, Finishing Mill: Main drive motors were traditionally DC but are now widely replaced by high-power AC VFD drives (e.g., vector control for synchronous motors). They require extremely high dynamic response speed, torque control accuracy, and overload capacity for a stable rolling process.

Downcoiler/Uncoiler: Require constant tension control. The VFD automatically adjusts speed and torque as the coil diameter changes, ensuring tight and flat coil shape.

Loopers: In continuous rolling mills, the looper's height control requires fast and precise torque response to maintain constant micro-tension, preventing pile-up or stretching of the material.

Transport Roller Tables: Numerous roller table motors are controlled in groups by VFDs to achieve speed synchronization and soft start/stop, reducing impact and scratches on the steel surface.

4. Auxiliary and Public Facilities

Various Pumps (Circulating water pumps, cooling water pumps, hydraulic station pumps): Adjust flow according to actual demand, achieving significant energy savings.

Compressed Air System: Controls compressor speed to stabilize pipeline pressure, avoiding frequent line-start/stop cycles.

Hoisting Equipment (Overhead cranes, metallurgical cranes): Hoisting, long travel, and cross travel mechanisms all require VFD speed control to achieve extreme smoothness, precision, and safety when handling molten metal, preventing load swing.

II. Core Benefits Brought by VFD Application

• Outstanding Energy Savings: The most direct economic benefit. For fan and pump loads, using VFDs for speed control can save 20%-50% compared to traditional valve/damper control. For cyclical loads, it reduces no-load energy consumption.
• Improved Process Control Accuracy and Product Quality:

Enables precise speed, torque, and tension control.

Ensures speed cascade and constant micro-tension in continuous rolling mills.

Improves dimensional accuracy (thickness, profile) and surface quality of rolled products.

Soft Start and Smooth Speed Regulation:

Eliminates the electrical (5-7 times rated current) and mechanical (gears, bearings) shock of direct-on-line starting, extending equipment lifespan.

Provides wide, smooth, and stepless speed regulation.

Enhanced Automation and Intelligence:

As an execution unit, integrates seamlessly into PLC/DCS systems for full-process automated control.

Facilitates remote monitoring, fault diagnosis, and predictive maintenance.

High Reliability and Adaptability:

Modern VFDs incorporate comprehensive protection functions (overcurrent, overvoltage, overload, phase loss, etc.).

Feature specialized designs or protective measures for harsh metallurgical environments (high temperature, dust, conductive metal dust, vibration).