When the crescent-shaped surface of the copper tube turns black and is overburned, it is not “normal wear and tear over time”, but rather an early warning from the heart of the continuous casting process.
First, observe the phenomenon: Overburning of the crescent-shaped surface, not a problem of one unit
Recently, several small square billet continuous casting bases have reported that there is a significant overburning and blackening phenomenon in the crescent-shaped surface area of the crystallizer copper tube. From the on-site pictures, we can see that the four surfaces of the copper tube have varying degrees of blackening, and the conditions on each surface are inconsistent.
It should be clear that: We can understand occasional occurrences, but we should regard repeated occurrences over a long period as abnormal.
For the buyer, this is a quality signal that must be taken seriously – it directly relates to the service life of the copper tube, the quality of the cast billet, and even the risk of leakage.
In one sentence, explain the reason: The temperature in the crescent-shaped surface area is too high
The essence of overburning of the crescent-shaped surface is that the temperature in that area is too high.
But “high temperature” is just the result; the underlying influencing factors are what the buyer needs to pay attention to:
Among them, the protective slag and slag layer is too thin, which is often one of the core causes of overburning in the crescent-shaped surface area.
| Influencing Factors | Significance to the Purchaser (Steelmaker) |
| Crystallizer working water temperature | Directly affects cooling capacity; excessively high water temperature will aggravate overheating |
| Cooling water flow and pressure | Insufficient flow or unstable pressure prevents effective cooling of the copper tube hot surface |
| Water quality | Poor water quality leads to scale buildup and water gap blockage, reducing cooling efficiency |
| Uniformity of water gaps | Uneven water gaps cause insufficient cooling in local areas, resulting in inconsistent overheating degrees across different faces |
| Excessive withdrawal speed | Molten steel stays for too short a time in the meniscus, causing heat flux concentration |
| Excessive number of heats for the copper tube | Exceeding the service life causes a decline in the inherent thermal conductivity of the copper tube |
| Insufficient mold flux addition / thin slag layer | Impaired lubrication and heat transfer lead to severe heat flux |
| Copper tube material and coating type | Material and coating determine the copper tube’s inherent resistance to overheating |
Analyzing the Essence from the Images: Four surfaces burned black, what does it indicate?
Judging from the fact that all four surfaces of the copper tube are blackened and to varying degrees:
The protective slag and slag layer is relatively thin → Intense heat transfer of high-temperature molten steel → Uneven heat flow density on each surface → Uneven growth of the billet shell → Increase in air gap volume → Heat transfer obstruction and instability → Stress concentration → Increased risk of cracking and leakage of the casting in the crystallizer.
This is not caused by a single factor, but is the result of the combined effect of cooling, protective slag, casting speed, and the state of the copper tube.
Hidden Dangers Behind the Oscillation Marks: Purchasers cannot only look at the surface
Looking at the oscillation marks in the middle of the casting surface:
Oscillation upward → Crack the casting shell → Oscillation downward → The casting shell heals → Again upward → Again crack → Again heal → Again crack…
This repetitive cracking-healing process indicates that the heat transfer and lubrication in the crescent-shaped area have reached an unstable state. For purchasers, this means:
- The copper tube works under harsh conditions, so its service life will drop significantly.
- The surface quality of the casting deteriorates, and the risk of subsequent rolling defects increases;
- The risk of leakage increases, and the downtime loss is much higher than the value of the copper tube itself.
Suggestions for Purchasers: Select copper tubes, pay more attention to “compatibility”
As a purchaser of copper tube crystallizer, you need to pay attention not only to the material and price of the copper tube itself, but also to:
- Whether the copper tube material and coating match your operating conditions – different casting speeds, different steel types, different protective slag systems, have different requirements for the copper tube;
- Whether the supplier provides usage guidance – water temperature, water quality, water gap, casting speed, protective slag addition amount, these parameters directly affect the lifespan of the copper tube;
- Check whether the crescent-shaped area repeatedly overburns — if it does, it means the copper tube does not match your continuous casting process, or the copper tube itself has quality problems.
- Comprehensive cost, not just unit price – overburning, leakage, downtime, casting grade degradation, these hidden costs are far higher than the price difference of the copper tube purchase.
Conclusion
The crystallizer is the heart of continuous casting, and the copper tube is the valve of the heart.
The crescent-shaped area overburns. This is not a trivial matter. It is the copper tube’s “overheating alarm” to you. As a purchaser, do not just compare prices. Choose a supplier who can analyze your operating conditions, optimize parameters, and provide compatible copper tubes. That is far more valuable.
Don’t let a burnt copper tube burn away your production efficiency and casting quality.
If you have any questions, please feel free to reach out.
E-mail: cykc@cykcgroup.com.cn