Zhuojin Pipe Fitting Co., LtdRetrofitting of Electrode Strip Automatic Overlay Welding Equipment
Overview of the Literature
This paper, published by Jiang Yunchen from Harbin Boiler Works Co., Ltd. in the journal Welding (2006, Vol. 2, pp. 76-77), documents a practical engineering project involving the retrofitting of an electrode strip automatic overlay welding system. The work is classified under TG439.2, which pertains to welding equipment and apparatus. The author addresses the challenges encountered when adapting existing equipment for continuous rotation overlay welding applications, incorporating automatic control systems and control boxes. The keywords highlight the dual focus on equipment modification and the process requirements inherent to strip electrode overlay welding.
Core Technical Content
The fundamental challenge addressed in this study is the adaptation of conventional welding equipment to perform continuous rotary overlay welding, a process commonly required for large cylindrical components such as boiler drum liners, heat exchanger tubesheets, and pressure vessel interiors. The retrofitting work involved several critical modifications:
- Conversion of the welding head to accommodate electrode strip feed mechanisms
- Integration of a continuous rotation table or fixture to allow the workpiece to rotate beneath the stationary welding head
- Installation of an automatic control box to regulate welding parameters including current, voltage, strip feed rate, and rotation speed
- Adaptation of the boring machine (镗床) as the base platform for the welding system
The control box serves as the central nervous system of the retrofitted equipment, managing the synchronization between the strip electrode feed rate and the workpiece rotation speed. This synchronization is critical because any mismatch results in either excessive dilution (if the strip feeds too fast relative to rotation) or insufficient deposition (if the strip feeds too slowly).
Process Requirements and Engineering Analysis
Strip electrode overlay welding, also known as submerged arc strip welding, offers deposition rates typically ranging from 8 to 15 kg/h, significantly exceeding those of conventional single-wire submerged arc welding which typically achieves 4 to 8 kg/h. The dilution rate in strip electrode SAW is generally between 15% and 25% for the first pass, decreasing to 5-10% for subsequent passes.
| Parameter | Typical Range | Engineering Significance |
|---|---|---|
| Deposition rate | 8-15 kg/h | Determines production efficiency |
| Dilution rate (1st pass) | 15-25% | Affects alloy composition of weld |
| Dilution rate (subsequent passes) | 5-10% | Ensures adequate alloy protection |
| Strip width | 12-25 mm | Determines weld bead width |
| Rotation speed | 5-15 rpm | Must synchronize with strip feed |
| Welding current | 400-800 A | Depends on strip width and material |
The retrofitting approach described by Jiang reflects a pragmatic engineering philosophy: rather than procuring entirely new equipment at substantial capital cost, existing boring machines and welding power sources can be modified to serve overlay welding functions. This approach is particularly attractive for workshops that require periodic but not continuous overlay welding operations.
Engineering Practice Implications
From my experience with large-scale overlay welding operations, the success of such retrofitting projects depends heavily on the precision of the control system integration. The automatic control box must maintain tight tolerance on the strip feed-rotation speed ratio, typically within ±5%. In practice, this requires:
- Calibration of the strip feed motor encoder against the rotation table encoder
- Implementation of feedback loops to correct for strip tension variations
- Pre-programming of welding sequences for multi-pass overlay builds
- Safety interlocks to prevent equipment damage during parameter adjustments
The use of a boring machine as the base platform is an elegant solution, as boring machines inherently provide precise rotational control and heavy-duty structural rigidity. However, the spindle bore and tool post geometry must be modified to accommodate the welding head and wire feed mechanisms.
Study Insights
This paper exemplifies the Chinese engineering tradition of resourceful equipment adaptation. In an era when capital expenditure is carefully managed, the ability to retrofit existing equipment for new applications represents a significant competitive advantage. The paper, while concise, captures the essential engineering challenge: achieving the process precision required for overlay welding through mechanical and electrical modifications to general-purpose equipment. For engineers facing similar constraints, the key takeaway is that systematic analysis of the process requirements, followed by targeted modifications to existing assets, can yield production systems that rival purpose-built equipment at a fraction of the cost.