Note: Descriptions are shown in the official language in which they were submitted.
131S~OO
PLUG FOR USE IN A STEEL CONVERTER TO MINIMIZE TAPPING
OFF OF SLAG
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The invention relates to a plug of refractory
material for use in a steel converter to minimize
tapping off of slag from the converter, and also to a
method of tapping a steel converter using such a plug.
2. DESCRIPTION OF THE PRIOR ART
Counteracting the slag which comes out at the
end of tapping the steel from the converter, known as
the end slag, is a long-standing problem. Various
methods are known for tackling this problem.
The simplest method is to observe the flow of
steel and to stop tapping at the first appearance of
slag.
Another method is to use a spherical ball
which is introduced into the converter before tapping.
The specific gravity of the ball is such that it floats
on the steel but not on the slag. When the slag
threatens to emerge, the ball closes the opening of the
tap hole of the converter. A disadvantage of this
method, however, is that this closing frequently occurs
so early that much steel still remains behind in the
converter. This is undesirable. For this reason,
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plugs are used which are not spherical, but for example
take the shape of a cube. This kind of plug does not
close the tap hole completely. The remain-ng steel may
still run out of the converter, but at a lower
velocity. At the point when slag threatens to emerge,
tapping off is stopped. The article "Ladle metallurgy
and clean steel production", S.C. McPherson, "Steel
Times", vol. 214, 1986-5 (May), page 220 etc.
illustrates such spherical and cubic plugs. EP-A-94241
describes a cubic plug for the same purpose.
When the cubic plug is positioned well, its
use provides better control because of the reduced
tapping velocity at the end of tapping. However, non-
spherical plugs of this kind require very accurate
positioning in the converter because they do not
automatically find the tap hole at the end of tapping.
This is because, in contrast to spherical plugs, their
ability to roll is insufficient. As a result the
closing of the tap hole is sometimes so poor that the
flow of end slag is insufficiently counteracted. With
non-spherical plugs, improvement in the probability of
achieving a good closing off is sought by providing
them with a long shank which is introduced into the tap
hole of the converter. This holds the plug at the
desired place so that the probability of
accurate positioning is equivalent to that of the
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spherical plug. However, positioning the plug with a
shank is considerably harder than positioning the
spherical plug.
SUMMARY OF THE INVENTION
The object of the invention is to provide a
plug which avoids the defects of the spherical plug and
the cubic plugs described above, as well as those of
the plugs with a shank. The plug of the invention is
of the shankless type and has a polyhedral shape with
a plurality of generally flat faces. Each face joins
at least one adjacent face at an obtuse angle. In some
embodiments at least one end point of each intersecting
line of two ad~acent faces lies on an imaginary sphere
enveloping the plug. This plug does not close the tap
hole completely so that towards the end of tapping the
flow of steel is reduced but not completely blocked.
Moreover, this plug has sufficient ability to roll so
that it does not need to be provided with a shank for
positioning at the tap hole. As a result using the
plug in accordance with the invention is as simple as
using the known spherical plug.
A preferred shape of the plug is one in which
it has symmetrical upper and lower halves meeting at a
common plane which has a larger area than any parallel
sections of the upper and lower halves. The plug then
fits releasably in the mould in which it is cast and
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can be removed from it without its shape being lost.
In view of the large number of plugs needed in practice
(per converter charge one plug is consumed), this
represents an important cost advantage.
In practice a simple embodiment has been found
to be a plug of which the common plane between the
lower and upper halves has essentially a rectangular
e.g. square shape. It is particularly desirable that
the plug has a top plane and a base plane which are
parallel to the said common plane of the lower and
upper halves.
BRIEF INTRODUCTION OF THE DRAWINGS
Embodiments of the invention will be described
by way of non-limitat~ve example with reference to the
drawings, in which:-
Fig. 1 shows a first embodiment of the plug inaccordance with the invention; and
Fig. 2 shows a further embodiment of the plug
in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The plugs shown in Figs. 1 and 2 consist
essentially of refractory material of appropriate
density to float at the steel slag interface. This may
be for example a suitable type of refractory concrete.
Fig. 1 shows an embodiment in which the plug
has fourteen flat faces, of which six large faces 5
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intersect each other at 90 and eight small triangular
faces 6 form bevels at the corners. There are thus
twenty four angles, each angle being the meeting point
for three intersecting meeting lines of the faces. For
example angle l is formed by the intersecting lines 2,3
and 4. The plug may be lifted or tippe.d into a
converter using an eye 7. Each of the faces 6
intersects each of the three adjacent larger faces 5 at
an obtuse angle. The shape of the plug enables it to
roll easily to lodge in the taphole of the steel
converter.
Fig. 2 shows a further lmproved plug with
edges bevelled off more. The shape of this plug
redices the risk of the angles crumbling away and
improves its ability to roll.
In this case the plug is a body of polyhedral
shape having a rectangular central plane of symmetry 10
and mutually symmetrical upper and lower halves 8,9 on
each side of this central plane. Each half 8,9 has
four large planar faces 8a,9a meeting the central
plane of symmetry lO and extending away from it at an
angle less than 90, specifically 75 and a planar end
face 11,12 meeting all the first planar faces 8a,9a and
lying parallel to the central plane of symmetry lO. At
each meeting point of two of the first planar faces
8a,9a and one of the second planar faces 11,12 there is
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a small bevel face 13 at an obtuse angle to all three
adjoining faces. There are rounded surfaces 14 at
meeting zones of each adjacent pair of the first planar
faces 8a,9a.
Both the lower half 8 and the upper half 9
have a tapering shape. This has the advantage that the
mould or die which is used for making the plug may be
re-used. This reduces the production costs of the plug
to a significant degree.
To give an example of dimensions, the plugs
illustrated are each 205 mm high and have maximum
widths of 205 mm.
