Molten steel droplet scatter regulation cylinder

In a molten steel droplet scatter regulation cylinder for use in a vacuum steel casting system, for the object of prevention of growth of molten steel droplets into a solid steel block at the lower end portion of the cylinder to subsequently drop into the molten steel, deteriorating its internal properties, the cylinder has at least its lower end portion made of a material which has a small wetting property against the molten steel, e.g. carbides such as graphite, silicon carbide, etc. or refractory materials containing carbon, carbides, etc.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for use in a vacuum steel 
casting system and more particularly to a regulation cylinder for the 
prevention of scatter of molten steel droplets which occurs when the 
molten steel is poured into a mold placed in a vacuum chamber. 
It is a well known fact that, in a vacuum steel casting system, when the 
molten steel is poured into a mold placed within a vacuum chamber through 
a nozzle provided in the bottom of a vessel which is put on the lid of the 
vacuum chamber and in which the molter steel is contained, the molten 
steel scatters thereabout to fall in a state of droplets. Therefore, in 
order that the droplets be poured into the mold properly it is necessary 
to mount in the lid a molten steel droplet scatter regulation cylinder 
directly beneath the nozzle to collect the droplets. In this case the 
molten steel which flows along the inner wall of the scatter regulation 
cylinder finally solidifies at the lower end portion of the cylinder due 
to the temperature drop to adhere there, and the solidified steel grows to 
a large block as time elapses. However, as the result of the growth, 
should the block of solidified steel thus grown drop into the molten steel 
in the mold the internal properties of the steel ingot thus produced 
deteriorate remarkably whether the drop occurs during the pouring or after 
the completion of the pouring. 
Therefore it has been a matter of utmost concern in the field of art to 
solve this difficulty inherent to the conventional molten steel droplet 
scatter regulation cylinders. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a molten steel droplet 
scatter regulation cylinder for use in a vacuum steel casting system which 
can effectively prevent the molten steel from adhering to the lower end 
portion of the cylinder to grow to solidified steel blocks there. 
It is another object of the present invention to provide a molten steel 
droplet scatter regulation cylinder for use in a vacuum steel casting 
system which can effectively eliminate all internal defectives found in 
steel ingots such as abnormal structure, non-metallic inclusion, etc. that 
are apt to be caused by the fall of the solidified steel blocks adhering 
to the lower end portion of the cylinder into the molten steel within the 
mold in which the steel ingot is cast. 
It is a still further object of the present invention to provide a molten 
steel droplet scatter regulation cylinder for use in a vacuum steel 
casting system which is simple in constitution and also allows a easy 
application to existing droplet scatter regulation cylinders with simple 
modification. 
In accordance with the present invention, molten steel droplet scatter 
regulation cylinder principally comprising a substantially conical or 
cylindrical hollow element made of a refractory material is provided in 
which at least the lower end portion of the hollow element is constituted 
from carbides such as graphite, silicon carbide, etc. or refractory 
materials containing carbon, carbides, etc. which little wet molten steel 
or have a small wetting property against the molten steel. Thus, it will 
be appreciated that according to the present invention the stay time of 
molten steel droplets at the end portion of the droplet scatter regulation 
cylinder is made small due to the contact of the molten steel droplets 
with the hollow element at the end portion made of carbides, etc. which 
little wet the molten steel, resulting in no solidification or growth to a 
block of the droplets there, so that no deterioration occurs in the 
internal properties of the steel ingot produced due to such as the 
dropping of solidified droplets into the molten steel in the mold.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Prior to entering into the detailed explanation of the preferred embodiment 
of the present invention, the phenomena of the growth of solidified steel 
at the lower end portion in a conventional molten steel scatter regulation 
cylinder will be qualitatively explained in reference to FIGS. 1 and 2. As 
shown in FIG. 1, arranged centrally on the lid 3 of a vacuum chamber 2 is 
a vessel 4 for receiving molten steel which is adapted to be poured into a 
mold 7 placed in a vacuum chamber 2 through a nozzle 5 provided in the 
bottom of vessel 4 and a molten steel droplet scatter regulation cylinder 
1 mounted to lid 3 beneath nozzle 5, the cylinder 1 functioning to guide 
or collect molten steel contained in vessel 4 into mold 7 placed within 
vacuum chamber 2 when the molten steel drops through nozzle 5 in a 
droplets state. FIG. 2 shows basically the process by which the molten 
steel adheres to the lower end portion of scatter regulation cylinder 1 
shown in FIG. 1 to solidify there. As shown in FIG. 2A a molten steel 
droplet 6 falling down along the inner wall surface of scatter regulation 
cylinder 1 remains at its lower end as a droplet 8 as shown in FIG. 2B. 
The part of the inner wall of cylinder 1 with which molten steel droplets 
come into contact 6 is generally of a refractory material, and since it 
has a large wetting property against molten steel droplet 8 i.e. it wets 
molten steel droplet 8 well, the time period during which molten steel 8 
remains there is long so that molten steel droplet 8 solidifies there as 
the result of its cooling to adhere to the surface of the refractory 
material as a solidified steel block 9 as shown in FIG. 2C. Further, as 
shown in FIG. 2D, another molten steel 6 falls down along the inner wall 
surface of scatter regulation cylinder 1 onto solidified steel 9 to stop 
at its lower end, and when the stay time is sufficiently long molten steel 
6 solidifies together with previously solidified steel 9 to become a 
larger solid steel block 10 as shown in FIG. 2E. Thus, solidified steel 
block 10 gradually grows to an even larger solid steel block 11 as shown 
in FIG. 1. Should this drop into the molten steel, whether during the 
pouring or after completion of the pouring, there arise defects in the 
internal properties of the steel ingot produced such as abnormal 
structure, large non-metallic inclusion, etc. due to the non-fusion of the 
steel block. 
Now a preferred embodiment of the present invention will be explained in 
reference to FIG. 3, the embodiment being aimed at effectively preventing 
the molten steel droplet from adhering to the lower end portion of a 
droplet scatter regulation cylinder and growing to solid steel blocks 
there. 
As shown in FIG. 3, in accordance with the present invention, the molten 
steel droplet scatter regulation cylinder comprises a hollow conical metal 
frame 20, one or more refractory rings 21 stacked within metal frame 20 
with a hollow conical passage for the molten steel being left centrally 
axially therein, and a ring 22 made of carbides such as graphite, silicon 
carbide, etc. or refractory materials containing carbon, carbides, etc., 
ring 22 being directly secured to the underside of the lowermost 
refractory ring 21 by any suitable means such as by supporting the 
underside of ring 22 with a set of metal mountings 23 which are suitably 
swingably secured at their upper portions to the outer surface of metal 
frame 20 at its lower portion. Further, ring 22 may be integral as a 
single piece or separated into several pieces so as to be assembled as a 
unit when supported on metal mountings 23. 
It will be appreciated that the molten steel droplet scatter regulation 
cylinder thus constituted according to the present invention makes it 
effectively possible to prevent solid steel blocks from forming at its 
lower end portion thanks to the provision of ring 22 made of carbides, 
etc. which do not substantially wet molten steel, letting the molten steel 
droplet fall before it solidifies or grows. Consequently, the molten steel 
droplet scatter regulation cylinder in accordance with the present 
invention can wholly eliminate the occurance of such internal defects 
found in steel ingots as abnormal structure, large non-metallic inclusion, 
etc. that have been usual in the case of conventional molten steel droplet 
scatter regulation cylinders due to the dropping of the solid steel blocks 
into molds when the molten steel is poured into the molds contained in a 
vacuum chamber. 
Following are the two examples of the present invention which proved that 
it could attain its objects as expected. They have respectively such 
dimensions as shown in FIGS. 4 and 5 in mm, the former being intended for 
use in pouring an ingot having a weight of about 75 t, the latter that of 
below 40 t. 
In both examples, refractory rings 21 are made of conventional high-alumina 
material, comprising: 
SiO.sub.2 38.28 wt%, Al.sub.2 O.sub.3 58.56 wt%, Fe.sub.2 O.sub.3 1.42 wt%, 
whereas ring 22 is made of alumina-carbon material in accordance with the 
present invention, comprising: 
C 20.5 wt%, Al.sub.2 O.sub.3 65.2%, SiC 6.0%. 
As will be readily apparent to those skilled in the art, the present 
invention may be realized in other specific forms without departing from 
its spirit or essential characteristics. The present embodiment is, 
therefore, to be considered as illustrative and not restrictive, the scope 
of the invention being indicated by the claims rather than by the 
foregoing description, and all changes which come within the meaning and 
range of equivalents of the claims are therefore intended to be embraced 
therein.