Note: Descriptions are shown in the official language in which they were submitted.
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METALLURGIC IMPACT PAD
Field of the Invention
This invention relates to a metallurgic impact pad. Particularly, but not
exclusively, the
invention relates to a metallurgic impact pad for use in a tundish.
Background to the Invention
An impact pad is the general term for a pad of erosion resistant material that
is
commonly positioned on the floor of a tundish to receive an incoming stream of
molten
metal poured into the tundish from a ladle. It helps to minimise wear of the
tundish
itself whilst also allowing for improved flow characteristics of the molten
metal through
the tundish and into a mould.
U.S. patent 5169591 discloses an impact pad for a tundish for use in the
continuous
casting of steel. The impact pad comprises a base, a peripheral top surface
and a
discontinuous sidewall extending between the base and the peripheral top
surface, the
sidewall having an undercut inner surface, which may be curvilinear.
U.S. patent 5358551 discloses an impact pad which comprises a base, a sidewall
extending around the base, the sidewall having an inner surface having a
portion which
extends inwardly and upwardly and which may be concave.
Whereas both of the above, and other, types of impact pad are designed to
reduce
turbulence in the tundish, to minimise slag-entrapment, to prevent the break-
up of
tundish flux cover and re-oxidation of molten metal and to ensure a proper
flow path of
the metal within the tundish, it is an aim of the present invention to provide
an improved
impact pad.
Summary of the Invention
According to a first aspect of the present invention there is provided an
impact pad,
formed from a refractory material capable of withstanding contact with molten
metal,
comprising a base serving in use as an impact surface for molten metal, and a
sidewall
extending generally upwardly therefrom, said sidewall terminating at an upper
surface
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which is above the base in use such that the base and sidewall define a
receptacle for
receiving molten metal, wherein the sidewall contains therein at least one
channel, said
at least one channel having first and second ends, the first end being
relatively closer to
the base at its intersection with the sidewall than the second end, said at
least one
channel being open ended at the second end or tapering such that said at least
one
channel has zero depth at its second end.
The term `receptacle' is used herein in a general sense to mean a
configuration capable
of containing at least a portion of the molten metal received therein.
Specifically, the
sidewall need not necessarily be continuous or completely surround the base.
It will be understood that the at least one channel referred to herein may be
constituted
by a groove which is cut into the sidewall or may be formed indirectly: for
example by
the space between a pair of mutually spaced ridges or other projections on the
sidewall.
In a first series of embodiments, the first and second ends of the at least
one channel are
vertically aligned in the plane of the sidewall. In a second series of
embodiments the
ends are vertically displaced in the plane of the sidewall.
The sidewall itself may be inclined relative to the base. In some embodiments,
the
angle between the sidewall and the base is from 75 to 115 and most preferably
from
about 85 to 95 .
The sidewall may have a planar, convex or concave inner surface.
The shape of the at least one channel is not particularly limited and it may
be linear,
angular or curved, or a combination thereof. Preferably the channel is linear,
in which
case reference to a vertical channel (ends vertically aligned) is with respect
to its
disposition within the plane of the sidewall (i.e. if the sidewall is inclined
relative to the
base, the channel therein can still be described as vertical). Similarly, in
the case of a
linear channel, inclination (ends vertically displaced) is described without
regard to
inclination of the sidewall itself. Preferably the channel is inclined from 85
to 45
relative to the base and more preferably, at an angle of approximately 70 .
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The at least one channel may have a constant depth in the sidewall in which
case the
channel will be open ended at the second end. Alternatively, the depth of the
at least
one channel may increase, decrease or otherwise vary between its first and
second ends.
The depth may vary gradually or discontinuously, i.e. stepwise.
The at least one channel may have a constant, increasing, decreasing or
otherwise
varying width between its first and second ends. As above, the width may vary
gradually or discontinuously, i.e. stepwise. Advantageously, a discontinuous
variation
in width or depth of channel can help to create a `dead zone' in which
undesirable
inclusions tend to deposit thereby preventing them from proceeding into the
mould.
The at least one channel may have a square, rectangular, triangular, curved or
otherwise
polygonal transverse cross-section. The cross-sectional profile of the at
least one
channel may be constant or may vary along its length, e.g. it may change from
being
semi-circular towards its first end to triangular towards its second end.
Varying the
cross-sectional profile of the at least one channel can effect advantageous
changes in
boundary flow conditions.
The sidewall may be endless (i.e. extend continuously around the periphery of
the base).
Alternatively, the sidewall may extend partway around the periphery of the
base. Two
or more sidewalls may be provided, each extending partway around the periphery
of the
base, in which case each sidewall is preferably provided with at least one
channel.
The or each sidewall may have any combination of one or more straight or
curved
portions away from or along the base. In one embodiment the or each sidewall
has a
constant height and a constant profile (i.e. thickness), although it will be
appreciated
that the height and/or shape of the sidewall may vary over its length. In the
case of a
non-linear (or non-uniform) sidewall, "the plane of the sidewall" is
determined at the
relevant point on the sidewall (e.g. for a curved sidewall, the plane of the
sidewall at
any given point on the sidewall is the tangent to the sidewall at that point).
The base will normally be planar (although it may be provided with ripples,
channels, or
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protrusions) and the impact pad designed such that the impact surface lies
horizontally
in the tundish and perpendicular to the stream of metal. However, there may be
embodiments in which the base is concave, convex, rippled, steepled or
otherwise
contoured. In these cases, references to inclinations to the base should be
construed as
being to the horizontal plane, when the impact pad is orientated in use.
Moreover, when
the base comprises features disposed at different heights relative to the
horizontal,
reference to "above the base" is in respect of the highest feature on the
base.
The shape of the periphery of the base is not limited and may for example be
polygonal
(e.g. rectangular, square, trapezoidal, etc.), oval or circular.
In one embodiment, the impact pad is substantially box-shaped having a
rectangular,
flat base with a continuous sidewall having four linear sidewall portions,
each sidewall
portion extending vertically upwardly from the periphery of the base and being
connected to each adjacent sidewall at right angles.
A generally inwardly directed lip may be provided at the upper surface of the
or each
sidewall. The lip may be substantially parallel to the base or may extend in
an inwardly
and upwardly direction or an inwardly and downwardly direction.
In addition to the at least one channel, the or each sidewall may additionally
include
slots or holes therethrough.
The first end of the at least one channel may be at the intersection of the
base with the
sidewall. Alternatively, the first end of the at least one channel may be
spaced from the
base. In the latter case the spacing may be less than 50%, less than 40%, less
than 25%
or even less than 10% of the height of the sidewall at the relevant point. In
either case
the channel may be open-ended at its second end. Alternatively, the at least
one channel
may be tapered such that, at least in a region towards the second end, the
depth of the at
least one channel reduces to zero at the second end.
The second end of the at least one channel may extend to the upper surface of
the
sidewall. Alternatively, the second end of the least one channel may be spaced
from the
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upper surface of the sidewall. In the latter case the spacing may be less than
50%, less
than 40%, less than 25% or even less than 10% of the height of the sidewall at
the
relevant point.
In some embodiments, a plurality of channels is provided. Each channel may be
equidistantly spaced from each adjacent channel. The spacing between the
channels
may be, for example, from 0.5 to 5 times the width of the channels, from 0.75
to 3 times
the width of the channels or even about 1 to 2 times the width of the
channels.
Alternatively, the spacings between adjacent channels may vary. In this way,
the flow
can be influenced by providing a greater concentration of channels in one area
when
compared to another area. When the channels are linear, they may be parallel
and either
vertical or inclined. In one embodiment, the channels may be arranged in a fan-
shape,
e.g. where their first ends are clustered closely together and their second
ends are
spaced further apart.
In a particular series of embodiments, the or each sidewall (or sidewall
portion) has at
least a pair of linear inclined channels converging (but not necessarily
meeting) towards
their second ends. Where more than one pair of such channels is provided, each
pair
may be arranged adjacent to the next, in which case each channel will be
inclined in an
opposite direction to each adjacent channel (i.e. in a "zigzag" fashion).
Alternatively,
the channels may diverge towards their second ends.
In a related series of embodiments the pairs of channels may be nested i.e.
the channels
of each pair become increasingly spaced apart.
A second aspect of the invention provides a tundish for holding a volume of
molten
metal, the tundish having a floor and sidewalls enclosing a region of impact
and a drain,
an impact pad of the present invention being provided on the floor of the
tundish in the
region of impact.
The impact pad may be integral to the tundish.
Brief Description of the Drawings
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Particular embodiments of the present invention will now be described, by way
of
example only, with reference to the accompanying drawings, in which:
Figures IA and B show respectively a full and a part perspective view of a
prior art
impact pad of an open box configuration;
Figures 2A and B show respectively a full and a part perspective view of a
first
embodiment of an impact pad according to the present invention, with
vertically aligned
channels;
Figures 3A and B show respectively a full and part perspective view of a
second
embodiment of an impact pad according to the present invention, with inclined
channels;
Figures 4A and B show respectively a full and part perspective view of a third
embodiment of an impact pad according to the present invention, which is
similar to the
second embodiment (Figures 3A and B), but with the channels inclined in the
opposite
direction and spaced from the base;
Figures 5A and B show respectively a full and part perspective view of a
fourth
embodiment of an impact pad according to the present invention, which is
similar to the
second embodiment (Figures 3A and B), but with the channels being defined by
corrugations in the sidewall portions;
Figures 6A and B show respectively a full and part perspective view of a fifth
embodiment of an impact pad according to the present invention, which is
similar to the
fourth embodiment (Figures 5A and B), but with the channels spaced from the
base;
Figures 7A and B show respectively a full and part perspective view of a sixth
embodiment of an impact pad according to the present invention, with a
circular base;
Figures 8A and B show respectively a full and part perspective view of a
seventh
embodiment of an impact pad according to the present invention, with nested
converging channels in two opposite sidewall portions and nested diverging
channels in
the other two opposite sidewall portions;
Figures 9A and B show respectively a full and part perspective view of a ninth
embodiment of an impact pad according to the present invention, which is
similar to the
first embodiment (Figures 2A and B), but with channels of increasing depth
away from
the impact surface;
Figures 10A and B show respectively a full and part perspective view of a
tenth
embodiment of an impact pad according to the present invention, which is
similar to the
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first embodiment (Figures 2A and B), but with the inner surface of the
sidewall portions
inclined towards the centre of the pad;
Figures 11A and B show respectively a full and part perspective view of an
eleventh
embodiment of an impact pad according to the present invention, which is
similar to the
third embodiment (Figures 4A and B), but with channels of decreasing depth
away from
the impact surface;
Figure 12 shows a full perspective view of a twelfth embodiment of an impact
pad
according to the present invention, which is similar to the third embodiment
(Figures
4A and B), but having one open side and channels of increasing depth away from
the
impact surface;
Figures 13A and B show respectively a full and part perspective view of a
thirteenth
embodiment of an impact pad according to the present invention, with channels
having
an increasing width and depth away from the impact surface;
Figures 14A and B show respectively a full and part perspective view of a
fourteenth
embodiment of an impact pad according to the present invention, which is
similar to the
thirteenth embodiment (Figures 13A and B), but with the channels spaced from
the
base;
Figures 15A and B show respectively a full and part perspective view of a
fifteenth
embodiment of an impact pad according to the present invention, with channels
having
a decreasing width and depth away from the impact surface;
Figures 16A and B show respectively a full and part perspective view of a
sixteenth
embodiment of an impact pad according to the present invention, which is
similar to the
fifteenth embodiment (Figures 15A and B), but with the channels spaced from
the base;
and
Figure 17 shows a full perspective view of a seventeenth embodiment of an
impact pad
according to the present invention, with two opposed open sides and two
opposed
sidewall portions having vertical channels therein.
Detailed Description of Certain Embodiments
With reference to Figures IA and B, there is illustrated a prior art tundish
impact pad 10
known as an `open box'. This is included for comparative purposes only. The
impact
pad 10 comprises a square planar base 12 (i.e. impact surface) with a
continuous
sidewall constituted by four vertically upstanding sidewall portions 14
disposed around
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the periphery of the base 12. Each sidewall portion 14 is of a planar form and
has a flat
upper surface 16 which is parallel to the base 12. The heights of each
sidewall portions
14 are equal and substantially less than their lengths. Accordingly, the
impact pad 10
constitutes a relatively shallow open-topped box.
EXAMPLE 1
Figures 2A and B (example 1) show an impact pad 20 according to a first
embodiment
of the present invention. The general configuration of the impact pad 20 is
the same as
that for the open box impact pad 10 described above in relation to Figures 1 A
and B and
so like reference numerals will be used for like elements. Thus, the impact
pad 20
comprises a square base 12 with four vertical sidewall portions 14, as
described above.
However, the impact pad 20 additionally includes a plurality of linear,
vertical channels
22 formed in the inner surface of each sidewall portion 14. Each channel 22
has a first
end 24 disposed adjacent to the base 12 and a second end 26 disposed at the
upper
surface 16 of the sidewall portions 14. Each channel 22 is of a constant depth
from its
first end 24 to its second end 26 and has a rectangular cross-section.
Accordingly, each
channel 22 is open-ended at its second end 26, i.e. the rectangular cross-
section of the
channel 22 extends all the way to the upper surface 16. Each channel 22 is
spaced from
the next by approximately the width of a channel 22. It will be understood
that a similar
configuration could have been achieved by applying cuboidal spacers to the
inner wall
such that the channels 22 are defined therebetween.
EXAMPLE 2
An impact pad 40 according to a second embodiment of the present invention is
shown
in Figures 3A and B (example 2). The general configuration of the impact pad
40 is the
same as that for the impact pad 20 described above in relation to Figures 2A
and B and
so like reference numerals will be used for like elements. The main difference
between
this second embodiment and the first embodiment is that each of the channels
42 is
inclined in the plane of each sidewall portion 14 (i.e. the first end 44 and
the second end
46 of each channel 42 are relatively vertically displaced). In this particular
embodiment, the second end 46 of each channel 42 is vertically displaced in a
clockwise
direction when viewed from above the centre of the impact pad 40. Each channel
42 is
linear but has a generally U-shaped transverse cross-section. As for the
embodiment of
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Figures 2A and B, each first end 44 is disposed adjacent to the base 12 and
each second
end 46 is disposed at the upper surface 16 of the sidewall portions 14.
EXAMPLES 3 & 4
A third embodiment of an impact pad 50 according to the present invention is
shown in
Figures 4A and B (example 3). The general configuration of the impact pad 50
is the
same as that for the impact pad 40 described above in relation to Figures 3A
and B and
so like reference numerals will be used for like elements. The difference
between this
third embodiment and the second embodiment is that each of the inclined
channels 42 is
spaced from the base 12 (i.e. each of the first ends 44 are provided part-way
up the
sidewall portions 14 from the base 12). Accordingly, an undercut 51 is
provided in the
sidewall portions 14 to create a gap 52 between the base 12 and the first ends
44 of the
channels 42. In this particular embodiment (example 3), the gap 52 extends to
approximately 30% of the height of the sidewall portions 14. In a 4t' example
(not
illustrated), an impact pad according to the third embodiment has a gap 52
which is half
of that of example 3 (i.e. 15% of the height of the sidewall portions 14).
EXAMPLE 5
A fourth embodiment of an impact pad 60 according to the present invention is
shown
in Figures 5A and B (example 5). The general configuration of the impact pad
60 is the
same as that for the impact pad 40 described above in relation to Figures 3A
and B and
so like reference numerals will be used for like elements. The main difference
between
this fourth embodiment and the second embodiment is that, rather than the
channels 62
being formed in a planar sidewall portion, the inner surface of the sidewall
portion 14 is
corrugated (i.e. has a sinusoidal cross-section), the channels 62 being
defined by the
corrugations. As for the embodiment of Figures 3A and B, each channel 62 has a
first
end 64 disposed adjacent to the base 12 and a second end 66 disposed at the
upper
surface 16 of the sidewall portions 14. A further difference is that the
second end 66 of
each channel 62 is vertically displaced in an anti-clockwise direction when
viewed from
above the centre of the impact pad 60.
EXAMPLES 6 & 7
Figures 6A and B (example 6) show an impact pad 70 according to a fifth
embodiment
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of the present invention. The general configuration of the impact pad 70 is
the same as
that for the impact pad 60 described above in relation to Figures 5A and B and
so like
reference numerals will be used for like elements. The difference between this
fifth
embodiment and the fourth embodiment is that an undercut 71 is provided in the
sidewall portions 14 to create a gap 72 between the base 12 and the first ends
64 of the
channels 62. In this particular embodiment (example 6), the gap 52 extends to
approximately 30% of the height of the sidewall portions 14), as per example
3. In a 7th
example (not illustrated), an impact pad according to the fifth embodiment has
a gap 72
which is half of that of example 6 (i.e. 15%).
EXAMPLE 8
A sixth embodiment of an impact pad 80 according to the present invention is
shown in
Figures 7A and B (example 8). The general configuration of the impact pad 80
is
similar to the impact pad 50 described above in relation to Figures 4A and B
and so like
reference numerals will be used for like elements. The main difference between
this
sixth embodiment and the third embodiment is that the base 82 is circular and
the
sidewall 84 is a circular annulus. In addition, the base 82 is `steepled'
having a raised
central portion 86 with sloping sides 88. In this embodiment, the channels 90
are
inclined at an angle of 80 to the base 82. A gap 52 of approximately 40% of
the height
of the sidewall 84 is provided between the channels 90 and the base 82. The
channels
90 are mutually spaced by about the width of single channel 90. A variant of
this
embodiment (not shown) has a planer base 82.
EXAMPLES 9 & 10
An impact pad 100 according to a seventh embodiment of the present invention
is
shown in Figures 8A and B (example 9). The general configuration of the impact
pad
100 is the same as that for the impact pad 10 described above in relation to
Figures IA
and B and so like reference numerals will be used for like elements. As for
the impact
pads of the first to sixth embodiments described above, the impact pad 100
additionally
includes a plurality of linear channels 102 formed in the inner surface of
each sidewall
portion 14. However, in this embodiment two opposed sidewall portions 14 have
a first
pair of inclined channels 102 diverging from their first ends 104 disposed
near to (but
spaced from) the base 12 towards their second ends 106 disposed at the upper
surface
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16. A second pair of inclined diverging channels 108 is also provided on these
sidewall
portions 14. The second pair of channels 108 is nested around the first pair
of channels
102 to create on both sides of a centre line of each of these sidewall
portions 14 two
parallel channels diverging away from the centre line. On each of the
remaining
opposed two sidewall portions 14 a further set of two nested pairs of channels
110 and
112 are provided. However, in this embodiment these pairs of channels 110, 112
are
arranged to converge towards a centre line so that each set of channels on
each sidewall
portion 14 alternately converge and diverge from the base 12 towards the upper
surface
16. In an alternative (eighth) embodiment (not shown), each sidewall portion
14
includes only converging pairs of channels (example 10). In an alternative
embodiment
still (not shown), each sidewall portion 14 includes only diverging pairs of
channels.
Each channel 102, 108, 110, 112 is of a constant depth from its first end 104
to its
second end 106 and has a generally U-shaped cross-section. As for the
embodiments of
Figures 4A and B, 6A and B and 7A and B, the channels 102, 108, 110, 112 are
spaced
from the base 12. In this particular embodiment (example 9), a gap 114 of
approximately 30% of the height of the sidewall portions 14 is provided
between the
channels 102, 108, 110, 112 and the base 12. Also in this embodiment, the
channels
102, 108, 110, 112 are inclined at an angle of 70 to the base 12.
EXAMPLE 11
An impact pad 120 according to a ninth embodiment of the present invention is
shown
in Figures 9A and B (example 11). The general configuration of the impact pad
120 is
similar to the impact pad 20 described above in relation to Figures 2A and B
and so like
reference numerals will be used for like elements. The main difference between
this
ninth embodiment and the first embodiment is that the depth of the channels
122
gradually increases away from the base 12, i.e. the channels 122 are tapered.
EXAMPLE 12
An impact pad 130 according to a tenth embodiment of the present invention is
shown
in Figures l0A and B (example 12). The general configuration of the impact pad
130 is
similar to the impact pad 20 described above in relation to Figures 2A and B
and so like
reference numerals will be used for like elements. The main difference between
this
tenth embodiment and the first embodiment is that the inner surface 132 of the
sidewall
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portions 14 are inclined towards the centre of the base 12. The channels 22
have a
constant depth along their length and are essentially the same as those in
Figures 2A and
B but they are now provided on an inclined inner surface 132.
EXAMPLE 13
An impact pad 140 according to an eleventh embodiment of the present invention
is
shown in Figures 11A and B (example 13). The general configuration of the
impact pad
140 is similar to the impact pad 50 described above in relation to Figures 4A
and B and
so like reference numerals will be used for like elements. The main difference
between
this eleventh embodiment and the third embodiment is that the depth of the
channels
142 decreases away from the base 12.
EXAMPLE 14
An impact pad 150 according to a twelfth embodiment of the present invention
is shown
in Figure 12 (example 14). The general configuration of the impact pad 150 is
similar
to the impact pad 50 described above in relation to Figures 4A and B and so
like
reference numerals will be used for like elements. The main difference between
this
twelfth embodiment and the third embodiment is that the depth of the channels
152
increases away from the base 12. In addition, this embodiment has one open
side 154,
i.e. it comprises three, as opposed to four, sidewall portions 14.
EXAMPLE 15
An impact pad 160 according to a thirteenth embodiment of the present
invention is
shown in Figures 13A and B (example 15). The general configuration of the
impact pad
160 is similar to the impact pad 120 described above in relation to Figures 9A
and B
and so like reference numerals will be used for like elements. The main
difference
between this thirteenth embodiment and the ninth embodiment is that as well as
the
depth of the channels 162 increasing away from the base 12 they also increase
in width.
Accordingly, fewer channels 162 are provided on each sidewall portion 14.
EXAMPLE 16
An impact pad 170 according to a fourteen embodiment of the present invention
is
shown in Figures 14A and B (example 16). The general configuration of the
impact pad
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170 is similar to the impact pad 160 described above in relation to Figures
13A and B
and so like reference numerals will be used for like elements. The main
difference
between this fourteenth embodiment and the thirteenth embodiment is that a gap
172 of
approximately 30% of the height of the sidewall portions 14 is provided
between the
channels 162 and the base 12.
EXAMPLE 17
An impact pad 180 according to a fifteenth embodiment of the present invention
is
shown in Figures 15A and B (example 17). The general configuration of the
impact pad
180 is similar to the impact pad 160 described above in relation to Figures
13A and B
and so like reference numerals will be used for like elements. The main
difference
between this fifteenth embodiment and the thirteenth embodiment is that the
depth and
width of the channels 182 decrease away from the base 12 rather than increase.
EXAMPLE 18
An impact pad 190 according to a sixteenth embodiment of the present invention
is
shown in Figures 16A and B (example 18). The general configuration of the
impact pad
190 is similar to the impact pad 180 described above in relation to Figures
15A and B
and so like reference numerals will be used for like elements. The main
difference
between this sixteenth embodiment and the fifteenth embodiment is that a gap
192 of
approximately 30% of the height of the sidewall portions 14 is provided
between the
channels 182 and the base 12.
EXAMPLE 19
An impact pad 200 according to a seventeenth embodiment of the present
invention is
shown in Figure 17 (example 19). The general configuration of the impact pad
200 is
similar to the impact pad 20 described above in relation to Figures 2A and B
and so like
reference numerals will be used for like elements. The main difference between
this
seventeenth embodiment and the first embodiment is that two opposed sides 202
are
open, i.e. it comprises two, rather than four, sidewall portions 14.
In all of the above-described embodiments, the second ends of the channels
terminate in
the same plane as the upper surface 16 of the sidewall portions 14. In
alternative
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embodiments (not shown), the second ends of the channels may terminate below
or
above the upper surface 16. In the case that the channels are created by
attaching a
series of spacers to a substantially planar sidewall portion, the spacers may
be
positioned to terminate below the upper surface 16 or to extend past the upper
surface
16.
In a further embodiment (not shown), the depth of the channels may gradually
decrease
to zero at their second ends. In this case, the second ends may be
substantially in the
same plane as the upper surface 16 of the sidewall portions 14 or a distance
below the
upper surface 16.
In use, an impact pad of any of the above-mentioned embodiments is placed
inside a
tundish (not shown) in the region where molten metal is flowed into the
tundish from a
ladle. Accordingly, the molten metal will first be received within the impact
pad and
this helps to reduce wear on the tundish itself whilst also dissipating the
energy of the
incoming stream through impact with the base and sidewalls of the impact pad.
As the
stream continues to flow, the molten metal flows up and over the sidewalls of
the
impact pad and along the tundish towards a drainage hole which is usually
provided
some distance away from the position of the impact pad. This allows time for
undesirable inclusions to float to the top of the pool of molten metal to
improve the
quality of the metal flowing out of the tundish and into a mould.
The Applicants have found that the various embodiments of the present
invention help
to generate rotational or turbulent flow in the region of the impact pad in
use, which can
help to trap inclusions and encourage them to float to the surface of the
molten metal
pool sooner than normal and/or which can help to dissipate kinetic energy in
the flow of
molten metal before it travels along the length of the tundish, thereby also
reducing the
likelihood of inclusions flowing with the metal into the mould. It is noted
that beyond
the region of the impact pad, the flow of molten metal is relatively non-
turbulent.
Table 1 below shows the results of water-modelling tests performed by the
Applicants
in relation to some of the above-described embodiments. The `dead' value is a
measure
of the stagnant portion of metal in the tundish. It is desirable that this
value be low.
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The `plug' value is a measure of the quantity of metal moving along the
tundish, which
is not really mixing. It is desirable that this value be high. All of these
values are
obtained using standard techniques, the details of which can be found in
relevant
textbooks.
Impact Pad Fmmple DEAD PLUG
Configuration
Open Box 31.6 14.5
Fmbodi mnt l 1 29.4 16.0
Fmbodi mnt 4 5 27.2 23.3
Fmbodi mnt 5 7 25.2 23.3
Fmbodi mnt 3 4 15.4 26.7
Fmbodi mnt 3 3 28.7 20.4
Fmbodiment 7 9 12.6 30.1
Fmbodiment 8 10 3.8 34.9
Table 1
As can be seen from Table 1, all of the embodiments of the present invention
have an
improved (i.e. lower) `dead' value when compared to the prior art open box
configuration. In addition, all of the embodiments have an improved (i.e.
higher) `plug'
value when compared to the prior art open box configuration.
As described above, the difference between examples 3 and 4, and 5 and 7 is in
the
extent or existence of a gap between the first end of the channels and the
intersection
between the base and the sidewall of the impact pad under consideration. From
the
results for embodiment 3 it can be seen that a smaller gap (example 4)
improves the
`dead' value and the `plug' value. In addition, from the results for examples
5 and 7 it
can be seen that a small gap (example 7) improves the `dead' value and has no
effect on
the `plug' value when compared to no gap (example 5).
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It can also be seen from Table 1 that the provision of vertical channels
(embodiment 1)
has less effect than inclined channels (embodiments 3, 4, 5). Also, the
provision of
wide channels (embodiment 3) has more effect than narrow channels (embodiments
4,
5). Furthermore, the arrangement of embodiment 8 has a markedly improved
performance when compared to all other embodiments.
The Applicants also noted by observing the progress of dye introduced into the
flow
during the water-modelling that where an impact pad according to an embodiment
of
the present invention was employed, the dye remained in the vicinity of the
impact pad
for longer than when a prior art impact pad was used. In addition, it was
noted that
when the dye began to progress along the length of the tundish, it began
travelling along
the tundish close to the surface of the pool for a longer period of time than
normal
before also travelling along the bottom of the pool. This suggests that the
flow is forced
upwardly more than in previous designs, thereby encouraging more inclusions to
float
to the top of the pool.
It will be understood that the depth and size of the impact pad will depend on
the
particular configuration of the tundish in which it is used.
It will be appreciated by persons skilled in the art that various
modifications may be
made to the above-described embodiments without departing from the scope of
the
present invention. In particular, features of two or more described
embodiments may be
combined in a single embodiment and features of one or more described
embodiments
may be employed in prior art impact pads.
