In the copper mould tube, the “throat” of the continuous casting machine, a seemingly ordinary flow of cooling water actually holds the power of life and death over the transformation of molten steel from a liquid to a solid initial billet shell. It is both the sculptor’s chisel and the destroyer’s blade. Even a slight difference in its flow rate directly determines whether production runs smoothly and efficiently or slides into the abyss of leaks and defects.
Core Objective: Forging a “Perfect Armor”
The fundamental mission of the copper mould tube cooling water is to precisely carve a uniformly thick and reliably strong initial solid billet shell from the molten steel in an instant, using the copper wall as a “water-cooled chisel.” This armor must be tough enough to withstand the static pressure of the internal molten steel and the friction of the external casting process; it must also be uniform enough to lay a defect-free foundation for the subsequent long solidification process. Ideally, there exists a “golden flow” range—within this range, heat is efficiently and evenly dissipated, the protective slag lubrication film is just right, and the final product is a high-quality billet shell that lays a solid foundation for subsequent processes.
Insufficient Water: Triggering a Fatal Chain Reaction of “Bonding and Steel Leakage”
When cooling water flows sparingly, a series of dangerous chain reactions quietly begin. This is the most common and most alarming nightmare in continuous casting operations.
Cooling Failure, Thermal Imbalance: The water flow rate decreases, and heat transfer efficiency drops sharply. The copper wall of the copper mould tube becomes like a persistent fever, where heat accumulates.
Weak Billet Shell, Poor Development: Insufficient heat dissipation means slow billet shell growth. It becomes thin and uneven, like a fragile armor with inherent deficiencies.
The Terrifying Birth of “Bonding”: The weak billet shell is extremely prone to tearing under stress.
At the crack, the high-temperature molten steel meets the scorching copper wall, instantly completing a fatal “remelting-rewelding”—this is bonding.
This weld point acts like a “steel nail,” hooking one end to the copper wall and the other to the billet. As the billet is pulled, it plows a longitudinal tear (adhesion mark) into the nascent billet shell.
Ultimately, when the force of the adhesion point exceeds the strength of the billet shell itself, the tear evolves into a break, and the catastrophic “adhesion leak” occurs.
The most faithful early warning signal: At this point, the temperature difference between the inlet and outlet cooling water of the copper mould tube will surge significantly. This is not only a physical manifestation of the heat not being carried away, but also the most alarming and unavoidable warning from the production line.
A single warning: Insufficient water → Cooling failure → Weak billet shell → Adhesion tear → catastrophic leak.
Excessive Water Flow: Overcooling Leads to “Hidden Cracks”
However, going to the other extreme—overcooling like “flooding the gold mine”—also fails to produce good results, only leading to another type of thorny quality problem.
“Forced Growth” Stress Disaster: Excessive cooling forces the billet shell to grow too quickly and shrink violently. This easily leads to:
Premature Air Gap Formation: The billet shell separates from the copper wall prematurely, forming uneven insulating air gaps, which in turn disrupts the uniformity of subsequent heat transfer.
Internal Cracks: The huge internal and external cooling gradients create hidden dangers of longitudinal or corner thermal stress cracks within the billet shell, creating natural weak points.
“Cold War” in the Lubrication System: Overcooled copper walls disrupt the conditions for the formation of an ideal liquid lubricating film by the protective slag. Increased friction, although not directly bonding, can induce transverse cracks in the billet shell’s “weak points” (such as corners).
The Paradox of Quality: Ironically, while overcooling can produce a thicker billet shell, uneven shrinkage and internal cracks may actually result in inferior overall toughness and uniformity compared to a moderately thick but uniformly dense shell. A “strong man” riddled with hidden flaws is more prone to fracture during subsequent bending and straightening.
In short: Excessive water flow → Overly aggressive cooling → Uneven stress → Hidden cracks → Quality hazards.
Mastering Water Flow: Collaborative Control Towards the “Optimal Window”
Therefore, mastering cooling water is not a simple art of switching on and off, but a precise science requiring multi-dimensional coordination.
Dancing with Casting Speed (Iron Rule): Cooling water flow must pulse synchronously with casting speed. Increased casting speed means increased heat to solidify per unit time, necessitating a corresponding increase in water flow. The industry-standard concept of “specific water volume” (L/kg steel) is precisely designed to accurately match this dynamic relationship.
Prioritizing “Flow” Over “Quantity”: **Flow Rate is Paramount:** Ensure a sufficiently high flow rate within the water gap (typically >8m/s) to combat localized boiling and scaling, maintaining peak heat transfer.
Uniformity is King:Uniform cooling around the copper mould tube is essential; any uneven flow is the culprit behind defects like rhomboidization and bulging.
Understanding the Language of Temperature Difference:The temperature difference between the inlet and outlet water is the most honest indicator of the cooling system’s health. A stable temperature within a reasonable range (e.g., 6-10℃) signifies perfect operation; an abnormally high temperature indicates insufficient water flow or overload; a persistently low temperature may indicate excessive flow or blockage in the heat transfer channels.
Water Quality is the Hidden Foundation: Minerals in hard water will form scale on the high-temperature copper walls, creating a deadly layer of “insulation.” Therefore, soft water or deionized water is an uncompromising prerequisite for ensuring long-term, efficient heat transfer.
Golden Flow Decision Chart:
Copper mould tube Cooling Water Flow Rate
| Insufficient flow rate (dangerous red light) | Golden flow zone (efficient green light) | Excessive flow rate (warning yellow light) |
| Poor heat transfer | Highly efficient and uniform heat transfer | Initial heat transfer too strong |
| Overheating of copper wall | Suitable copper wall temperature | Copper wall too cold |
| Weak and uneven billet shell | Uniform and strong billet shell | High risk of billet shell cracking |
| Between and exposed steel (Temperature spike alarm) | Stable and high-quality production(Optimal stable temperature difference) | Surface crack defects(Temperature difference may be too low) |
Conclusion: Seeking an Eternal Balance in the Tiniest Moments
The stability and efficiency of billet copper mould tube production essentially involve dancing with the laws of thermodynamics. Cooling water, this silent partner, must have its flow rate precisely controlled within an “optimal process window” verified through rigorous calculations and countless practical trials.
This window avoids both the “insufficient water” cliff of sticking and leakage, and the “excessive water” trap of cracks. It requires operators to not only focus on flow rate figures but also to understand the subtle nuances of flow velocity, temperature difference, and water quality. Only in this way can the ultimate victory of safety, quality, and efficiency be achieved in this art of balance, where millimeters are the minimum.
Why is there a “golden range” for the flow rate of cooling water in the copper mould tube?
A: The cooling water flow rate is not necessarily better the higher it is; it operates at a precise balance point.
Lower limit (preventing steel leakage): The flow rate must be sufficient to remove heat, allowing the molten steel to quickly solidify into an initial billet shell with a certain strength, preventing “sticking and steel leakage” caused by an excessively thin shell.
Upper limit (preventing cracks): The flow rate cannot be too high, otherwise it will cause excessive shrinkage of the billet shell, generating air gaps and severe thermal stress, thus inducing surface or internal cracks.
Ideal state: Within the “golden range,” heat is uniformly dissipated, the protective slag lubricating film thickness is moderate, and high-quality square billets without defects can be produced.
How does “sticking” occur when the water volume is insufficient, as mentioned in the article?
A: This is a fatal chain reaction. When the cooling water volume is insufficient, the heat transfer efficiency decreases, causing the initial billet shell to become extremely thin. The thin billet shell tears under drawing stress, and the high-temperature molten steel comes into direct contact with the scorching copper wall, resulting in a “remelting-rewelding” phenomenon, like a “steel nail” hanging the billet shell onto the copper wall. As the drawing machine continues to pull downwards, the tear widens, eventually causing molten steel to leak out, resulting in a catastrophic steel leakage accident.
What negative impacts does excessive cooling (excessive water volume) have on the quality of the billet?
A: While excessive cooling can produce a thicker billet shell, it can cause “hidden damage”:
Stress cracks: Violent cooling leads to excessive temperature differences between the inside and outside of the billet shell, generating huge thermal stress and creating potential longitudinal or corner cracks.
Premature air gap formation: The billet shell detaches from the copper wall too quickly due to excessive shrinkage, forming uneven insulating air gaps, which in turn leads to uneven heat transfer.
Lubrication failure: An overly cooled copper wall can damage the liquid lubricating film of the protective slag, increasing friction and inducing transverse cracks at weak points in the billet shell.
