Dispensing – Molten metal dispensing – Flow controllers or assists
Patent
1998-12-01
2000-11-28
Kastler, Scott
Dispensing
Molten metal dispensing
Flow controllers or assists
222606, B22D 4150
Patent
active
061523364
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a feed dip pipe for the continuous casting of thin slabs and more in particular a submerged nozzle for guiding in the best way as possible a molten metal or alloy from a ladle having a nearly constant head for feeding the same, without turbulence or swirling, to a level underneath the head or meniscus of a slab being formed within a cooling mould in which the slab itself takes a shape by solidification.
Thin slabs are known which are formed of four walls extending in vertical direction with horizontal cross-section having two sides of prevailing length with respect to the other two. It is also known that for introducing molten metal, especially steel, fed from a vessel above, into the inside of the mould, a connection conduit is used, being called "submerged", as its lower mouth is dipped in the molten bath within the mould and is adapted as much as possible to the thin size of the same mould in order to keep a sufficient distance from the cooling walls. Therefore dip pipes for thin slabs are usually employed in the technique as having in the lower portion horizontal cross-section of rectangular, polygonal or elliptical shape, with outlet boards directed the narrow sides and/or downwards.
However these prior art dip pipes do not solve the various problems; which are typical of this technology, as are widely described in the literature in this field and due to various reasons. In particular the fluid stream flowing out from the dip pipe has the tendency to circulate within the liquid mass in the core of the forming slab, solidified only externally, while having the attitude to re-emerge to the surface, thus generating stationary waves at the bath surface, especially in the proximity of the narrow faces of the thin mould. Thereby the lubricating slag will generally gather in the lower portions of the wave-shaped meniscus, while leaving the picks uncovered, with consequent lack of lubrication or poor distribution thereof, which gives rise to mould wear as well as a poor surface quality of the slab and incorrect thermal exchange of the forming slab with the mould, that is a cause of possible cracks.
Furthermore, the zones where the fluid swirls come back again into the liquid bath show a marked bent of the meniscus, in which the particles of powder and lubricating slag are easily entrapped in the forming slab, thus providing an additional cause of cracks and other surface defects. The turbulence at the level of meniscus in the mould is also an important cause of wear for the nozzle the life of which is then reduced.
Possible turbulence and whirlpools in the fluid stream at the outlet of the nozzle have a negative influence on the solidification process occurring within the slab, which should be progressive and as homogeneous as possible in the direction parallel to the narrow faces of the mould. On the contrary steadiness of feed and a distribution as symmetrical as possible of the flow with respect to the longitudinal axis of the slab, with the maximum of homogeneity at the horizontal cross-sections would be desirable.
Mention is made of the additional inconvenience due to the fact that oxides are present in the molden metals or alloys and have the tendency to deposit on the inner surfaces of the nozzle thus modifying its geometry and hence negatively effecting the passage cross-sections of flow.
Except for the last mentioned inconvenience, which becomes worse in case of slow flow rates in the various passage cross-sections, all the other inconveniences previously mentioned worsen as the flow rate of molten metal or alloy increases, namely in correspondence with higher speeds at which the slab being formed in the mould is withdrawn and/or larger cross-section areas of the slab, thereby higher flow rates in the various passage cross-sections, in particular at the discharge holes.
Anyhow all these mentioned inconveniences are present in whichever known shape of dip pipe or nozzle thus negatively affecting in various ways the correct trend of the casting and of the cooling of the
REFERENCES:
patent: 5681498 (1997-10-01), Poloni et al.
patent: 5716538 (1998-02-01), Poloni et al.
Arvedi Giovanni
Bianchi Andrea
Manini Luciano
Arvedi Giovanni
Kastler Scott
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