Upward continuous casting defies gravity ?

Discussion in 'Furnaces and their construction' started by metallab, Dec 6, 2021.

  1. metallab

    metallab Silver

    I have seen several videos about continuous casting of copper wire where a tank of liquid copper is inside an induction furnace and the metal is (magically ?) pushed / pulled upwards to form a wire.
    But in such a situation, at the interface where the metal freezes it would break up when the frozen metal moves upward as gravity pulls the still (partially) liquid metal downward. But, obviously this does not happen, otherwise it would not be commercially viable.

    How do they do that ?



     
  2. 0maha

    0maha Silver

    My guess is the process relies on surface tension and has to be very carefully calibrated.

    It's interesting to me that when you look close, the 'pull' is not smooth and continuous. They pull it up a little, then pause, then pull again.
     
  3. This video shows the start of a run with a long straight steel bar and a short length of sacrificial bar that the molten copper solidifies and attaches to before being drawn out. It looks like the inlet for the copper is 30 cm or so under the molten copper surface. So they must have enough cooling of the metal in the graphite dies for some jaws to drag it up a short distance and grab the bar again.

     
    Last edited: Dec 10, 2021
    0maha likes this.
  4. metallab

    metallab Silver

    Looks nice, but I would expect that the pulling action detaches the interface between liquid and solid (the freezing zone) ? There should be enough overpressure (sucking pressure) to overcome the hydrostatic pressure of the column of liquid copper (which is 1 bar per 1.25m as Cu is 8 times heavier than water).

    Weird that the steel industry does not use this. Not particularly upward, but continuous casting of such narrow objects. They continuously cast bars of 20cm thickness for sheet which are hot rolled down to 1 cm sheet, the latter ending up in the coiler to 2m diameter x 1.5m width toilet rolls.
    Why not continuously casting 1-3cm thick sheet blank (or 1-3cm thick bar for rebar blank) ? That saves a lot of energy needed for another reheating step and the roughing mill.
     
    Last edited: Dec 11, 2021
  5. Smoking Shoe

    Smoking Shoe Silver

    Made me think about this enough to do some research. The actual solidification takes place under the surface of the molten pool. It just looks like it happens at the top of the cooling/withdraw stack in the videos.
    Think of it as a continuously filling open riser?

    Cast.jpg
     
  6. metallab

    metallab Silver

    That's the trick. as long the freezing zone is below the surface, it would work. Then the hydrostatic pressure pushes it upward until the surface which is at the same level as the neighboring vessel(s) as long as there is an open connection between them. Just like having two open tubes (different shape does not care) in a container with water, the surface level is the same in the tubes and the container.
    Why are steel bars (e.g. rebar) not made that way ? Just such an upcast device pulls the bar from the tundish (which normally distributes the steel over the downward continuous caster). The only postprocessing of rebar is rolling ribs in the bars. That is much more energy efficient than the current method of continuously casting 100x100mm or even larger slabs which have to be reheated to roll them to the centimeter size with an energy hogging roughing mill.
     
    Last edited: Dec 12, 2021

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