Zhuojin Pipe Fitting Co., LtdMIG Welding Process for Pure Copper Through-Flow Blast Furnace Tuyere
Literature Overview
This paper by Ma Changxuan and Sun Zhenping, published in Welding Technology (2010, Vol. 39, No. 3), addresses the welding of through-flow pure copper tuyeres used in blast furnaces. The authors identify that despite the excellent thermal conductivity and long service life of these tuyeres, their welding yield remains low due to cracking, porosity, and incomplete fusion. The study adopts MIG welding as a solution and presents experimental results demonstrating improved weld quality.
Technical Background and Challenges
Pure copper tuyeres are critical components in blast furnace ironmaking operations. The through-flow design ensures rapid water circulation through the tuyere body, providing superior cooling of the hot blast gas and protecting the tuyere from thermal degradation. However, copper presents unique welding challenges that are well-documented in metallurgical literature:
| Challenge | Root Cause | Consequence |
|---|---|---|
| High thermal conductivity | Copper's thermal diffusivity is approximately 230 W/(m·K) | Rapid heat dissipation causes incomplete fusion and cold cracks |
| Thermal cracking susceptibility | Low melting point (1085°C) combined with wide freezing range | Hot cracks in weld pool during solidification |
| Oxidation | Cu₂O formation at elevated temperatures | Brittle oxide inclusions causing porosity and reduced ductility |
| Porosity | Dissolved hydrogen and oxygen in molten copper | Gas pockets in solidified weld metal |
The through-flow geometry further complicates welding because the internal water channels create restricted access for welding operations and impose strict requirements on weld integrity to prevent water leakage into the blast furnace.
MIG Process Selection and Parameters
The authors selected MIG (Metal Inert Gas) welding, also known as GMAW (Gas Metal Arc Welding), as the primary process. The advantages of MIG for copper welding include:
- High deposition rate compared to TIG welding, compensating for copper's rapid heat dissipation.
- Continuous wire feed providing stable arc and consistent heat input.
- Shielding gas protection preventing oxidation of the weld pool.
- Positional flexibility suitable for the complex geometry of tuyeres.
The typical process parameters reported in the study include:
| Parameter | Range |
|---|---|
| Welding current | 180–260 A |
| Arc voltage | 22–28 V |
| Wire feed speed | 6–9 m/min |
| Shielding gas | Pure argon (Ar) |
| Wire diameter | 1.2 mm |
| Travel speed | 150–250 mm/min |
| Preheat temperature | 150–250°C |
The use of pure argon as shielding gas is essential because oxygen-containing mixtures would exacerbate oxide formation in the weld pool. The preheating step is critical to reduce the thermal gradient at the weld zone and minimize the risk of cold cracking.
Key Technical Insights
The study demonstrates that MIG welding can produce sound welds on pure copper tuyeres when the following process controls are maintained:
- Preheating to 150–250°C reduces the effective thermal conductivity of the base metal and slows the cooling rate of the weld pool, preventing cold cracks.
- High heat input through increased current and voltage compensates for copper's rapid heat dissipation, ensuring complete fusion of the base metal.
- Narrow groove preparation with a V-groove angle of 60–80 degrees and root gap of 1–2 mm helps maintain heat concentration in the weld zone.
- Interpass temperature control between 150–250°C prevents excessive thermal accumulation while maintaining sufficient heat for fusion.
- Post-weld heat treatment is generally not required for pure copper but may be beneficial for stress relief in heavily welded assemblies.
Engineering Practice Implications
From a practical standpoint, this work is highly relevant to blast furnace maintenance operations where tuyere replacement or repair is frequent. The following engineering considerations should be noted:
- The MIG process is significantly faster than TIG for copper, reducing downtime during furnace maintenance windows.
- Operator skill is critical; the narrow process window for copper welding requires experienced welders.
- The through-flow geometry demands thorough cleaning of the internal water channels before and after welding to prevent contamination.
- Post-weld hydrostatic testing at 1.5 times design pressure is mandatory to verify watertight integrity.
The study provides a practical foundation for developing welding procedures for copper components in iron and steel production environments.
Summary
This paper establishes that MIG welding with pure argon shielding, combined with appropriate preheating and process parameter control, can effectively overcome the traditional challenges of welding pure copper tuyeres. The process yields sound welds free from cracking and porosity, significantly improving the yield rate of these critical blast furnace components. For practitioners in the iron and steel industry, this work provides a validated approach to maintaining through-flow copper tuyeres with improved efficiency and reliability.