In order to improve the wear resistance of copper mould tube and prolong its service life, we coat the mold copper tube with wear-resistant materials. Different materials have different effects on mold parameters.
For small squarecopper mould tube, generally using deoxidized phosphorous as coating material, chromium-zirconium is generally better for big square copper mould tube, and chromium-zirconium copper is better for unequal rectangular billet copper mould tube. At present, the plating layer is mostly hard chromium.
For combined square billets and small-section steel strip mold copper plates, silver copper and cold-rolled silver copper are generally used, and the plating layer is mostly chromium; large section slab molds generally use chromium zirconium copper, and the plating layer is Ni-Cr , Ni-Fe, Ni-Co and other alloy coatings.
The choice of coatingmaterial is related to the system parameters of the continuous casting machine. Such as pulling speed, water cooling strength, steel grade and so on.
- Generally, under the premise of satisfying product quality, the copper mould tube forsmall square billet, squarebilletand rectangular billet is a one-time consumable part in use. So considering the operating rate of the casting machine, the maintenance rate, the maintenance cost, the quality of the cast slab, etc, silver copper and deoxidized phosphorous copper should be used more;
- Chromium-zirconium copper is more economical for large section, appropriate one-time investment, and lower unit output cost;
- Combined billet, strip billet, ultra-low head continuous caster, etc. Continuous casting furnaces are not high or the output is limited, and the drawing speed is low, generally, cold-rolled silver-copper chromium plating is used.
- If the drawing speed is higher and the continuous casting furnaces are more frequent, the chromium-zirconium-copper alloy plating is more economical and reliable; Large slab casters generally use chromium-zirconium-copper alloy plating to be more economical and reliable. Although the one-time investment is large, the cost per ton of steel is greatly reduced, the maintenance cost is less, the operation rate and other indicators are significantly improved, and there is a greater comprehensive benefit.
The following table shows the mold parameters corresponding to different coating materials:
|Material||Cu-DHP||Cu – Ag||Cu – Cr – Zr|
|High Phosphorus Deoxidized Copper||Cu – Ag ( Cu – 0.1Ag )||Cu-Cr-Zr ( Cu – 0.6 Cr – 0.15 Zr )|
|Properties||Normal Deoxidized copper||Through the addition of about 0.1% silver, strength is significantly enhanced with no loss in thermal conductivity||Cr and Zr precipitation hardening provides this alloy with high strengh, high resistance to heat, and thermal conductivity|
|Coefficient of thermal expansion at 20°C||1.68×10-5||1.68×10-5||1.70×10-5|
|Thermal||340 W/(m·K)||377 W/(m·K)||325 W/(m·K)|
|Hardness at 20°C||Min. 85 HB||Min. 90 HB||Min. 120 HB|