Microcomputer-Controlled Magnetic Control Device for Strip Cladding

Literature Overview

The microcomputer-controlled magnetic control device for strip cladding represents a significant advancement in the automation and precision control of strip cladding processes. This literature describes the design, development, and implementation of a magnetic control system that uses electromagnetic forces to precisely position and stabilize the strip electrode during welding. The device addresses the challenges of maintaining consistent strip electrode geometry, arc stability, and cladding quality in high-production strip cladding operations. The study is particularly relevant to submerged arc strip cladding, where the strip electrode is used to build up thick overlay layers with high deposition rates.

Technical Background

Strip cladding using submerged arc welding (SAW) offers deposition rates of 10 to 30 kg/h, significantly higher than wire electrode methods. However, maintaining the precise geometry of the strip electrode relative to the workpiece is challenging. The strip electrode must be held at a constant angle, distance, and alignment to ensure uniform arc distribution and consistent weld bead geometry. Manual or mechanical control systems often fail to maintain the required precision, leading to defects such as uneven bead width, porosity, and incomplete fusion.

Design Principles of the Magnetic Control Device

The magnetic control device operates on the principle of electromagnetic attraction and repulsion to position and stabilize the strip electrode. The system consists of an electromagnet assembly, a position sensor, a microcomputer controller, and a feedback loop. The electromagnet generates a controlled magnetic field that holds the strip electrode at the desired position. Position sensors monitor the actual electrode position and feed this information back to the microcomputer controller, which adjusts the electromagnetic current to maintain the target position.

System Architecture

Control Algorithm

The microcomputer controller implements a PID (Proportional-Integral-Derivative) control algorithm to maintain the strip electrode position. The control loop operates as follows:

1. The position sensor measures the actual electrode position at a sampling rate of 1 kHz.
2. The microcomputer compares the measured position with the target position and calculates the error.
3. The PID algorithm computes the required adjustment to the electromagnetic current.
4. The power amplifier adjusts the electromagnetic current accordingly.
5. The cycle repeats continuously to maintain stable electrode positioning.

The PID parameters are tuned for each specific application based on the strip electrode material, thickness, and the desired weld geometry. Typical PID parameter ranges include:

• Proportional gain (Kp): 2.0-8.0
• Integral time (Ti): 0.5-2.0 s
• Derivative time (Td): 0.05-0.3 s

Performance Characteristics

The magnetic control device demonstrates excellent performance in maintaining strip electrode position stability. The position accuracy is within ±0.05 mm, which is sufficient for high-quality strip cladding operations. The system can handle strip electrodes with thicknesses ranging from 0.5 mm to 3.0 mm and widths from 50 mm to 300 mm. The control response time is less than 10 ms, ensuring rapid correction of any position deviations.

Comparison with Mechanical Control Systems

Engineering Applications

The magnetic control device has been successfully applied in the production of stainless steel clad plates, nickel-based alloy overlay plates, and bimetallic pressure vessel components. In the manufacture of 304 stainless steel clad plates with 3 mm overlay thickness on 20 mm carbon steel base plates, the device achieves a dilution rate of less than 10% in the first pass and below 3% in subsequent passes. The weld bead geometry is uniform with a width variation of less than 1 mm across the entire plate length.

For hydrogenation reactor internals clad with Hastelloy C276, the magnetic control device enables consistent overlay quality over large surface areas. The uniform bead geometry ensures consistent dilution rates, which is critical for maintaining the corrosion resistance of the overlay layer. Field trials have shown that the magnetic control system reduces rework rates by 60% compared to manual control systems.

Defect Analysis

Despite the advantages of magnetic control, several defect modes can still occur. Arc blow can occur when the magnetic field from the control electromagnet interferes with the welding arc, causing deflection and uneven bead geometry. This is mitigated by carefully designing the electromagnetic field distribution to avoid interaction with the welding arc. Strip electrode vibration can occur at high travel speeds, leading to bead width variation. The control system compensates for this by increasing the PID gain at higher speeds. Flux bridging can occur when the strip electrode is positioned too close to the workpiece, causing flux to accumulate and disrupt the arc. The position sensor and control algorithm prevent this by maintaining a minimum electrode-to-workpiece distance.

Study Insights and Implications

The development of the microcomputer-controlled magnetic control device represents a paradigm shift in strip cladding technology, moving from mechanical to electromagnetic positioning with closed-loop digital control. The key advantage is the ability to maintain precise electrode positioning with minimal mechanical wear and high adjustability. For engineers involved in bimetal product manufacturing, this technology offers a path to higher production rates, better quality consistency, and reduced rework. The integration of position feedback, PID control, and electromagnetic actuation provides a robust solution for the demanding requirements of modern cladding operations. Future developments should focus on integrating multiple control loops for simultaneous control of electrode position, travel speed, and flux feed rate to achieve even higher levels of process automation.