All these methods have their merits, and each is suitable for different applications.
If you want mainstream extrusion billet production, vertical casting is your first choice. You achieve super-smooth billet surfaces with air-slip mold technology. That’s because it minimizes the residue in the extrusion press. This also applies to rolling slabs. Here, casting in a magnetic field significantly reduces the skin zone. However, compared with the HDC process, the VDC process comes with some fundamental drawbacks.
- VDC casters are more expensive. Why? Because they need higher ceilings, overhead cranes, and foundations for the casting pit.
- The semi-continuous character of VDC casting results in lower productivity.
- The procedure involves extensive, labor-intensive set-up work per drop. In contrast, HDC commonly achieves continuous production runs of 3 to 20 days.
- It takes just one or two operators per shift to produce T-bars (two operators for cast start and stop).
- VDC plants do not feature integrated sawing. They require an additional sawing station plus operator. HDC casting wins hands-down here as well, because an automatic flying saw cuts the T-bars to length without interrupting the casting process.
- Finally, the VDC process fails to cast products with small sectional areas cost-effectively or in the required quality.
Pouring metal into open molds generates dross:
Traditionally, sows, pigs, and ingots are produced using the open-mold process. Although this technology has been improved over the years, dross formation and inclusions are still unavoidable. Cascading causes turbulence during mold filling. That exposes a relatively large surface area to the atmosphere for oxidation. What chiefly influences dross formation are the metal temperature, pouring height, and pouring rate.
Our HDC plants almost eliminate dross. You save money by avoiding metal losses and inclusions. Here is how the process works:
First, the metal flows smoothly to the mold via the launder and tundish, protected by an undisturbed oxide layer. There is no opportunity for oxides and other impurities to enter the product.
Next, the HDC-cast T-bars and foundry ingots are chilled at least ten times faster than sows and pigs. This ensures a fine and even grain structure as well as a uniform analysis throughout the cast product.
Another way of boosting the quality of remelt products is combining the HDC process with an inline degasser and ceramic foam filter (CFF). Working together, these systems produce T-bars and foundry ingots free of porosity and inclusions.
These are the advantages of HDC-cast alloy ingots compared to ingots cast in open-top molds:
- Low hydrogen and extremely low oxide inclusions
- Fine, uniform grain structure
- Consistent, uniform content and distribution of alloying elements
- No gravity segregation
- No cracks, shrink holes, or water inclusions
- Consistent dimensions, straightness, and weight
- Smooth surface that makes stacking and strapping compact bundles easy
All this means: the horizontal continuous caster genuinely deserves the attribute “universal caster”.