Welding Principle and Technical Analysis of Used Pipe Welding Machines

In modern industrial production, pipe welding machines are one of the core equipment for manufacturing metal pipes. Used pipe welding machines, with their cost advantages and high cost-effectiveness, have become popular choices for small and medium-sized enterprises and start-up factories. This article will delve into the working mechanism of used pipe welding machines from the perspectives of welding principles, equipment composition, technical characteristics, and precautions for using used equipment.

1. Basic Welding Principles of Pipe Welding Machines

The core function of a pipe welding machine is to process metal strips into seamless or welded steel pipes through forming, welding, and sizing. The welding process primarily relies on high-energy heat sources such as high-frequency current or lasers to fuse metal materials.

1. High-Frequency Induction Welding (Mainstream Technology)
   Most used pipe welding machines employ high-frequency induction welding technology. The principle is as follows: after the metal strip is gradually coiled into a tubular shape through multiple rollers, a high-frequency current (typically 100–500 kHz) is applied to the seam of the tubular blank. When the current passes through the edges of the blank, the "skin effect" generates dense eddy currents on the surface of the seam, rapidly heating the metal to a molten state. Subsequently, pressure is applied via squeeze rollers to bond the molten metal and form a dense weld.

2. Supplementary Applications of Contact Welding and Laser Welding
   Some older used pipe welding machines may use contact welding technology, where current is directly conducted through electrodes to heat the seam. Newer equipment might incorporate laser welding modules, but such machines are rare in the used market.

2. Typical Structure and Workflow of Used Pipe Welding Machines

Used pipe welding machines generally consist of the following core components:

• Uncoiler: Unrolls and feeds metal coils into the production line.

• Forming Unit: Gradually bends the strip into a tubular shape using multiple sets of rollers.

• Welding Device (High-Frequency Generator/Electrodes): Provides energy for welding.

• Sizing Unit: Calibrates the diameter and roundness of the pipe.

• Cooling System: Rapidly cools the weld to prevent oxidation.

• Cutting Device: Cuts pipes to required lengths.

Workflow Example:
Metal strip → Leveling → Forming → Welding → Deburring → Sizing → Cooling → Cutting → Finished product.

3. Technical Features and Challenges of Used Equipment

1. Significant Cost Advantages
   The procurement cost of used pipe welding machines is typically only 30%–60% of new equipment, making them suitable for businesses with limited budgets. They remain reliable for producing mid-to-low-end products such as carbon steel pipes and low-pressure fluid pipes.

2. Technical Limitations

   • Aging High-Frequency Generators: Efficiency loss in high-frequency oscillators or transformers may reduce welding speed or increase energy consumption.

   • Forming Accuracy Deviation: Roller wear from prolonged use may lead to increased roundness errors in pipes.

   • Lower Automation Levels: Older equipment may lack modern PLC control systems, relying on manual parameter adjustments.

3. Maintenance and Upgrade Requirements
   Key considerations for using used pipe welding machines include:

   • Electrical System Overhaul: Replacing aging capacitors, insulation materials, etc.

   • Mechanical Component Calibration: Repairing or replacing worn rollers and guides.

   • Weld Quality Optimization: Compensating for performance degradation by adjusting current frequency (e.g., reducing from 300 kHz to 200 kHz).

4. Key Technical Parameter Adjustments for Used Pipe Welding Machines

To ensure welding quality, the following parameters require precise adjustments:

1. Matching Welding Speed and Power
   Example parameters for producing Φ50mm×2mm carbon steel pipes:

   • Welding speed: 20–30 m/min

   • High-frequency power: 120–150 kW
     (Note: Specific parameters depend on actual equipment conditions.)

2. Control of Squeeze Force
   Squeeze roller pressure must balance: Insufficient pressure causes porosity in welds, while excessive pressure may thin the pipe wall. Empirical formula:

   P=k×t×σsP=k×t×σs​

   Where tt is material thickness, σsσs​ is yield strength, and kk is a correction coefficient (0.8–1.2).

3. Cooling System Optimization
   Segmented cooling: Air-cooling first reduces weld temperature to below 500°C, followed by water cooling to room temperature, minimizing residual stress.

5. Purchasing and Usage Recommendations

1. Equipment Evaluation Criteria

   Test high-frequency generator output stability (fluctuation < ±5%).Measure roller wear (radial runout < 0.1 mm).Evaluate weld joint tensile strength (≥90% of base material strength).

2. Common Issue Resolution

        Weld Cracks: Adjust parameters and preheat materials if caused by insufficient squeeze force or rapid cooling.Excessive Pipe Ovality: Replace No. 3–4 sizing rollers or adjust roller spacing.

3. Upgrade Directions
   Retrofitting modern sensors (e.g., infrared thermometers) and PLC control systems can enhance automation and quality control capabilities.

Conclusion

Used pipe welding machines, with proper maintenance and technical optimization, can still meet the production needs of most conventional pipes. Users must fully understand their welding principles and technical characteristics to balance cost control and quality assurance. As remanufacturing technology advances, the performance potential of used equipment will continue to expand, offering cost-effective solutions for manufacturing industries.

For more information, please pay attention to the website of Jinyujie Mechanical and Electrical Used Pipe Mill Supplier：www.usedpipemill.com

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