EP2205769B1

EP2205769B1 - Metallurgical impact pad

Info

Publication number: EP2205769B1
Application number: EP08837773.4A
Authority: EP
Inventors: Donald Zacharias; John Morris; Gerald Nitzl
Original assignee: Foseco International Ltd
Current assignee: Foseco International Ltd
Priority date: 2007-10-08
Filing date: 2008-10-03
Publication date: 2013-10-02
Anticipated expiration: 2028-10-03
Also published as: UA100863C2; ZA201003162B; EP2205769A1; WO2009048810A1; AR071250A1; HRP20140001T1; SI2205769T1; AU2008311108B2; TWI450777B; CA2704622A1; ES2437594T3; EP2047928A1; TW200927333A; PL2205769T3; KR101539793B1; EP2205769A4; PT2205769E; AU2008311108A1; KR20100088134A

Description

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.
US-A1-2004/135298 discloses an impact pad according to the preamble of claim 1.
Whereas 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 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°.
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 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 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

Particular embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figures 1A 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 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 1A 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 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 1A 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 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 4^th 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 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 72 extends to approximately 30% of the height of the sidewall portions 14, as per example 3. In a 7^th 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 planar 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 1A 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 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 10A 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 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 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 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.

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.

Table 1

Impact Pad Configuration	Example	DEAD	PLUG
Open Box		31.6	14.5
Embodiment 1	1	29.4	16.0
Embodiment 4	5	27.2	23.3
Embodiment 5	7	25.2	23.3
Embodiment 3	4	15.4	26.7
Embodiment 3	3	28.7	20.4
Embodiment 7	9	12.6	30.1
Embodiment 8	10	3.8	34.9

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).
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.

Claims

An impact pad (20), formed from a refractory material capable of withstanding contact with molten metal, comprising a base (12) serving in use as an impact surface for molten metal, and a sidewall (14) extending generally upwardly therefrom, said sidewall (14) terminating at an upper surface (16) which is above the base (12) in use such that the base (12) and sidewall (14) define a receptacle for receiving molten metal, wherein the sidewall (14) contains therein at least one channel (22), said at least one channel (22) having first and second ends (24, 26), the first end (24) being relatively closer to the base (12) at its intersection with the sidewall (14) than the second end (26), characterized in that said at least one channel (22) is open ended at the second end (26) or is tapering such that said at least one channel (22) has zero depth at its second end (26).
An impact pad (20) according to claim 1 wherein the first and second ends (24, 26) of the at least one channel (22) are vertically aligned in the plane of the sidewall (14).
An impact pad (20) according to claim 1 wherein the first and second ends (24, 26) of the at least one channel (22) are vertically displaced in the plane of the sidewall (14).
An impact pad (20) according to any preceding claim wherein the sidewall (14) is inclined relative to the base (12).
An impact pad (20) according to any preceding claim wherein the at least one channel (22) has a depth which increases, decreases or otherwise varies between its first and second ends (24, 26).
An impact pad (20) according to any preceding claim wherein the at least one channel (22) has a width which increases, decreases or otherwise varies between its first and second ends (24, 26).
An impact pad (20) according to any preceding claim wherein the at least one channel (22) has a cross-section which varies between its first and second ends (24, 26).
An impact pad (20) according to any preceding claim wherein the first end (24) of the at least one channel (22) is spaced from the base (12).
An impact pad (20) according to any of claims 1 or 3 to 8, wherein at least a pair of channels (22) is provided and wherein the pair either converge or diverge towards their second ends (26).
Assembly of a tundish for holding a volume of molten metal, the tundish having a floor and sidewalls enclosing a region of impact and a drain, and an impact pad (20) according to any of the preceding claims, the impact pad (20) being provided on the floor of the tundish in the region of impact.