FIELD OF THE INVENTION

The present invention relates to a stave protection system for a metallurgical furnace, for example a blast furnace.

BACKGROUND

A conventional blast furnace comprises several sections and components including a stack, belly, bosh, tuyere, hearth and taphole. The internal shell of the blast furnace may be protected with water-cooled cooling plates, called staves, which protect the shell from overheating during the reduction process taking place within the furnace. Modem staves are typically constructed from copper or copper alloy although other materials may be used, for example steel or cast iron.

The staves can be susceptible to abrasive wear from the solid raw materials charged into the furnace as they make their descent through the furnace. Wearing or thinning - either locally in one or a number of positions or across the whole surface of the stave - can occur due to abrasion caused by the descending burden materials and the outward pressure exerted on the stave face by the materials. Coke in particular is very abrasive. In some circumstances, the severity of the wear has resulted in the requirement to replace the staves before their planned service life has completed. This is costly due to furnace downtime.

Thus efforts have been made to design staves with prolonged service life.

It is known that wear of the staves is reduced by forming a frozen accretion layer on the front face of the stave during operation. To this end the stave has a machined front face, or hot face, comprising ribs and grooves which hold the accretion onto the stave. A portion of an exemplary copper stave of this type is shown in Figure 1.

A refinement of this concept has been the addition of a front-face protective material or cladding, which is harder than the copper base material but which still allows a protective accretion layer to form by freezing on the face. For example, the applicant’s publication WO/2019/175244 describes a stave protection system comprising inserts that are attached to the face of a stave. The inserts are shaped to distribute the burden material between the inserts over the front face of the stave and/or trap the burden material between the inserts, thereby forming a frozen accretion layer on the front face of the stave during operation.

The applicant’s publication CN214470084 also describes inserts or “accretion bodies” for attachment to the face of a stave. Figure 2 herein is taken from the publication and shows a multi-piece insert configured to be conveniently attached in a groove (formed between ribs of the stave) from the front of the stave, without requiring access to the edge of the stave in order to slide the inserts laterally into the groove.

While the inserts described by CN214470084 are effective in prolonging the service life of the stave, the applicant has found that the attachment between the insert and the groove/ribs of the stave can eventually weaken over time so that the insert may become detached from the stave. One reason for this is that the copper alloy material of the stave tends to expand more than the steel material of the insert when the furnace temperature is increased, causing the insert to lose its frictional grip on the surfaces of the stave. Accordingly the insert may become loose in the groove so that the insert may move relative to the ribs of the stave under the pressure exerted on the insert by the burden material. Prolonged and repeated movement of the harder steel insert tends to wear away the softer copper alloy of the ribs, causing the insert to loosen further and eventually to detach from the groove entirely. Furthermore, the applicant has observed that this loosening of the insert typically occurs at an earlier stage when the insert is fitted to a stave having partly worn ribs, rather than to a new (or reconditioned) stave with unworn ribs.

The present invention aims to alleviate at least to some extent the problems of the prior art. SUMMARY OF INVENTION

According to an aspect of the invention, there is provided a stave protection system for a metallurgical furnace, comprising: a stave comprising upper and lower ribs projecting forwardly from a front face of the stave and spaced apart from each other so as to define a transverse groove; at least one insert partially located in the groove and fixedly engaged with the upper and lower ribs so as to project forwardly thereof; and a brace located between a front surface of the lower rib and an opposing rear surface of the insert, such that in use the brace opposes a force applied to the insert so as to resist displacement of the rear surface of the insert toward the front surface of the lower rib.

As used herein, “burden material” refers to one or both of (i) iron-bearing materials in the blast furnace, for example iron-ore or iron-ore pellets, and (ii) blast furnace slag, i.e. slag which is formed when iron-ore or iron pellets, coke and a flux (e.g. limestone or dolomite) are melted together in the blast furnace and then solidified.

As will be described in more detail later herein, in use of the furnace the insert may be subjected to downward (vertical) and lateral (horizontal) forces, or a combination thereof, which are exerted on the insert by the burden material. The burden material has an abrasive effect on the lower rib, while the forces applied to the insert by the burden material tend to try to move (e.g. turn) the insert such as to displace the insert toward the lower rib. Over time, the effect of the abrasion and the movement of the insert is to cause wear to the lower rib, which may eventually cause the insert to work loose from the stave and to become detached therefrom.

The brace of the claimed invention effectively extends the lower rib forwardly to the opposing rear surface of the insert. In this regard the brace “refurbishes” the partly worn lower rib. Thus the brace is arranged to oppose (i.e. react against) the forces that are applied to the insert in use, thereby to resist displacement of the rear surface of the insert toward the front surface of the lower rib. The brace therefore serves to reinforce or strengthen and also to stabilise the lower rib, in order to prevent (or at least limit) movement of the insert due to the forces exerted thereon. Accordingly the insert is retained in the groove on the face of the stave. Due to the retention of the protective insert, the rate of wear of the ribs is reduced and the service life of the stave is prolonged.

Furthermore, the brace is an inexpensive “retrofit” item that may be conveniently produced in a wide variety of sizes to suit any given size of gap, between the front surface of the lower rib and the opposing rear surface of the insert (the size of the gap being dependent on the extent of the wear of the ribs of the stave in any given case). Moreover, installation of the stave protection system and the brace thereof is both simple and time-efficient, thus minimising furnace downtime and thereby cost.

The claimed invention therefore provides an effective and efficient solution, to a problem of how to prolong the service life of a partly worn stave.

The brace may extend fully between the front surface of the lower rib and the opposing rear surface of the insert.

The brace may extend partially between the front surface of the lower rib and the opposing rear surface of the insert.

The brace may be further located between a front surface of the upper rib and the opposing rear surface of the insert, such that in use the brace opposes a force applied to the insert so as to resist displacement of the rear surface of the insert toward the front surface of the upper rib.

The brace may comprise a plurality of discrete brace elements arranged face-to- face.

The brace may comprise a single brace element having a unitary structure.

The insert may comprise: a wedge-shaped attachment part that is at least partially received between opposing sloping walls of the upper and lower ribs such as to form a dovetail joint therewith; and a projection part that projects forwardly of the upper and lower ribs and comprises said rear surface of the insert, the attachment part and the brace being configured to engage each other to locate the brace between the front surface of the lower rib and the opposing rear surface of the insert.

The brace may be received in a slot provided in the attachment part.

An upper part of the brace may be configured to engage with the attachment part so as to prevent the brace from dropping out of the slot.

The rear surface of the insert may comprise a generally flat formation that extends into the slot; and the brace may comprise a planar sheet part and parallel ribs extending perpendicularly therefrom to form a channel between the parallel ribs, the brace being selectively reversible between: a first orientation wherein the planar sheet part faces the flat formation and the parallel ribs face the front surface of the lower rib; and a second orientation wherein the planar sheet part faces the front surface of the lower rib and the flat formation is received in the channel between the parallel ribs, the brace thereby spanning a greater distance between the front surface of the lower rib and the flat formation when in the first orientation than when in the second orientation.

A lateral width of the attachment part may be smaller than a lateral width of the projection part; and the brace may comprise first and second upright members being laterally spaced apart from each other and joined by a cross member, the cross member extending laterally along an upper surface of the attachment part and being supported thereby, each of the first and second upright members depending from a respective end of the cross member so as to extend along a respective side of the attachment part.

The lateral spacing between the upright members may be substantially equal to the lateral width of the attachment part, so that an inner edge of each of the upright members is in contact with an outer edge of said respective side of the attachment part, thereby to inhibit lateral movement of the brace relative to the insert. The stave protection system may comprise: a plurality of the inserts; and a plurality of the braces each located between a front surface of the lower rib and an opposing rear surface of a respective one of the plurality of inserts.

According to another aspect of the invention, there is provided a kit of parts for a stave protection system as described herein above, comprising: at least one of said inserts for said engagement with the upper and lower ribs of the stave; and at least one of said braces for disposing between the front surface of the lower rib of the stave and the opposing rear surface of the at least one of said inserts.

According to another aspect of the invention, there is provided a method of installing a stave protection system as described herein above, the method comprising: fixedly attaching the insert to the upper and lower ribs of the stave; selecting a brace of suitable thickness according to a distance between the front surface of the lower rib and the opposing rear surface of the insert; and disposing the brace between the front surface of the lower rib and the opposing rear surface of the insert.

Disposing the brace between the front surface of the lower rib and the opposing rear surface of the insert may comprise arranging the brace to extend fully between the front surface of the lower rib and the opposing rear surface of the insert.

Disposing the brace between the front surface of the lower rib and the opposing rear surface of the insert may comprise arranging the brace to extend partially between the front surface of the lower rib and the opposing rear surface of the insert.

The method may further comprise disposing the brace between the front surface of the upper rib and the opposing rear surface of the insert.

BRIEF DESCRIPTION OF DRAWINGS

Examples will now be described with reference to the accompanying figures, in which: Figure 1 shows a portion of a conventional stave of a furnace, the stave being in a new condition such that the ribs of the stave are unworn;

Figure 2 shows a conventional insert fitted to the stave of Figure 1 ;

Figure 3 shows a portion of a stave for use in a stave protection system, in accordance with the invention;

Figure 4 shows a plurality of inserts attached to the stave of Figure 3;

Figure 5 shows details of an exemplary one of the attached inserts of Figure 4;

Figures 6a and 6b show the insert of Figure 4 in combination with a brace, in accordance with an example of the invention;

Figures 7a-d show an exemplary one of the attached inserts of Figure 4 in combination with a reversible brace, in accordance with another example of the invention; and

Figure 8 shows another configuration of a brace, in accordance with an example of the invention.

DETAILED DESCRIPTION

Referring to Figure 3, a rectangular cooling plate or stave 100 comprises a front face (or hot face) 102, a rear face 104, and edges 306a-d (the bottom edge 306d is not shown in Figure 3). The stave 100 is intended to be one of a plurality of similar staves for use in a blast furnace.

In this example, the stave 100 has a width (in the X direction in the sense of Figure 3) of about 1 .0 m, a height (in the Y direction in the sense of Figure 3) of about 1 .5 m, and a maximum thickness or depth (in the Z direction in the sense of Figure 3) of about 120 mm. It will be understood that the X, Y, Z denotion of width, height and depth respectively is for convenience of reference only and is not limiting for the claimed invention. The interior of the stave 100 comprises water-cooling passages 110. The stave 100 body is otherwise generally solid.

In this example, the stave 100 is constructed from copper alloy. Alternative materials include, but are not limited to, copper, steel, and cast iron.

The front of the stave 100 comprises a plurality of similar grooves 112 which are arranged in rows and are separated from one another by projecting ribs 114. In this example, there are 12 grooves 112 and 13 ribs 114 (only some of which are visible in Figure 3, which shows only a portion of the stave 100). Each groove 112 extends across the entirety of the width of the stave 100 such as to have an open end at each of the side edges 106a, 106c of the stave 100. Each one of the grooves 112 has a long axis L which extends between the ends of the groove (in the X direction in the sense of Figure 3).

In this example, the grooves 112 are formed by machining. Alternatively the grooves 112 may be formed by casting.

Each one of the grooves 112 comprises a flat base or floor 112a. Each one of the grooves 112 further comprises a pair of opposing walls 112b. Each one of the opposing walls 112b is a surface of one of the two adjacent ribs 114 which define the groove 112. Each one of the ribs 114 includes a rib face 114a. The rib faces 114a are parallel with the floors 112a of the grooves 112 (at least when the rib faces 114a are in an unworn condition). The front face 102 of the stave 100 may therefore be regarded as comprising two parts, that is: a front-most part which comprises the rib faces 114a of the projecting ribs 114 and a recessed part which comprises the flat floors 112a of the grooves 112.

Each one of the two opposing walls 112b of each one of the grooves 112 is inclined, such as to provide each one of the grooves 112 with a convergent taper from the floor 112a of the groove 112 to the respective faces 114a of the ribs 114 which define the groove 112. Thus each one of the grooves 112 presents a wedge-shaped profile (when viewed from a side edge 106a, 106c of the stave 100), the thickest section of the wedge being located at the floor 112a of the groove 112 and the thinnest section of the wedge being located at the faces 114a of the ribs 114.

Referring next to Figure 4, a plurality of inserts 200 is attached to the front face 102 of the stave 100. Each one of the inserts 200 is generally as described in CN214470084, which is hereby incorporated by reference in its entirety. However, it should be understood that the claimed invention is not limited to inserts of this type. The inserts 200 are arranged on the front face 102 of the stave 100 so as to distribute burden material between the inserts 200 over the front face of the stave 100 and/or trap the burden material between the inserts 200, as described in WO/2019/175244, which is hereby incorporated by reference in its entirety.

Turning now to Figure 5, an exemplary one of the inserts 200 of Figure 4 is shown (in profile) attached to the front face 102 of the stave 100. Exemplary upper and lower ribs 114 of the stave 100 are in a partly worn condition (worn down in the Z direction, from right to left in the sense of Figure 5), such that the ribs 114 extend perpendicularly from the flat floor 112a of the groove 112 (in the Z direction, from left to right in the sense of Figure 5) a lesser distance than would the ribs of a new stave in an unworn condition. It will be understood that the front face 114a of the upper rib or the lower rib 114 may be worn along the entire length of the rib 114 (in the X direction in the sense of Figure 5) or along only a portion thereof.

In this example, the insert 200 is constructed from steel. Alternative materials include, but are not limited to, copper, copper alloy, and cast iron. The insert 200 may comprise an abrasion resistant refractory material. The abrasion resistant refractory material may comprise silicon carbide or alumina. The insert 200 itself is suitable for installation to a new stave or a stave in a partly worn condition, as will be described herein below.

The insert 200 is formed by upper and lower half-pieces that are arranged to pivot about a pin 202 located in a groove formed by the half-pieces. Each of the upper and lower half-pieces comprises a rear part 204 including a surface for engagement with the respective upper or lower wall 112b of the groove 112, the surface being configured to complement the angle of inclination of the wall 112b. Thus the rear parts 204 of the upper and lower half-pieces together form a wedge- shaped attachment part 206 of the insert 200. In this example, the engagement surfaces comprise serrations provided thereon.

Each of the upper and lower half-pieces further comprises a front part 208 that projects forwardly (in the Z direction, from left to right in the sense of Figure 5) so as to be capable of receiving and distributing flowing burden material when the furnace is in use. Thus the front parts 208 of the upper and lower half-pieces together form a projection part 210 of the insert 200.

The insert 200 further comprises a clamping nut and bolt (not visible in Figure 5) which passes through the front parts 208 (in the Y direction, from top to bottom in the sense of Figure 5) and is configured for adjusting the half-pieces.

The installation of the insert 200 to the front face 102 of the stave 100 (as shown in Figure 5) will now be described.

Initially the nut and bolt are in a loose condition, so that the upper and lower halfpieces can be rotated relative to each other back and forth about the pin 202. The insert 200 is offered up the stave 100 immediately in front of the upper and lower ribs 114. The front parts 208 are grasped by hand and are rotated in opposite directions so as to move the rear parts 204 closer to each other (the upper rear part 204 thus being rotated in a counterclockwise direction and the lower rear part 204 being rotated in a clockwise direction, in the sense of Figure 5). The insert 200 is then moved toward the flat floor 112a of the groove 112 (in the Z direction, from right to left in the sense of Figure 5). As the ends of the rear parts 204 reach the flat floor 112a, the front parts 208 are rotated back again so as to move the rear parts 204 away from each other (the upper rear part 204 thus being rotated in a clockwise direction and the lower rear part 204 being rotated in a counterclockwise direction, in the sense of Figure 5) until each of their engagement surfaces come into contact with a respective wall 112b of the groove 112. The nut and bolt are then tightened so as to further drive the rear parts 204 away from each other, thereby to exert an outward clamping force on the walls 112b of the groove 112. The serrations on the engagement surfaces of the steel rear parts 204 penetrate or “bite” into the copper alloy material of the walls 112b so as to provide a slip-resistant contact therewith. It will be understood that the rear parts 204 together form a wedge that locks into the groove 112 in the manner of a dovetail joint. Thus the insert 200 is rigidly attached or fixed to the stave 100. The nut and bolt may be tack-welded in order to prevent them from working loose during service in the operative furnace.

It will be recalled that the upper and lower ribs 114 of the stave 100 are in a partly worn condition. Accordingly a gap G exists between the front faces 114a of the ribs 114 and a rear surface 212 of the projection part 210 of the attached insert 200, as can be seen in Figure 5.

As has been mentioned herein above, during furnace operation burden material flows downwards over the stave 100 (generally in the Y direction, from top to bottom in the sense of Figure 5) under gravity and comes into contact with the projection part 210 of the insert 200. Thus the burden material applies a downward force FD to the insert 200 (as shown by the arrow in Figure 5). Furthermore, burden material will tend to apply a lateral force FL (or a force having a lateral component) to the projection part 210 in the direction of the stave 100 (as shown by the arrow in Figure 5). The lateral force FL may be caused by dynamic impacts on the insert 200 by moving burden material, and/or by static loads applied to the insert 200 by burden material that has accumulated in front of the insert 200.

During use of the furnace, the insert 200 may be subjected to either of the downward force FD and the lateral force FL in isolation, or both of these forces in combination. In practice, the forces are typically applied in combination and the resultant force FR (as shown by the arrow in Figure 5) tends to try to move the insert 200 such as to displace the rear surface 212 of the projection part 210 toward the front face 114a of the lower rib 114, for example by rotation or turning T of the insert 200 (as shown by the arrow in Figure 5) about a pivot point P located at an edge of the lower rib 114 where the wall 112b intersects the front face 114a. Thus the resultant force FR applied to the insert 200 by the burden material typically has a lever effect on the insert 200 which tends to move the rear surface 212 of the projection part 210 toward the front face 114a of the lower rib 114.

Over time, the effect of the movement of the insert 200 is to cause wear to the edge of the lower rib 114, especially at the pivot point P. Furthermore, the above- mentioned differential, between the expansion of the copper alloy of the stave 100 and the steel of the attachment part 206 of the insert 200, may cause loss of contact between the engagement surfaces of the rear parts 204 and the respective walls of the 112b of the groove 112, allowing further rotation of the insert 200. As a result, the insert 200 may work loose from the stave 100 and may eventually become detached therefrom.

Turning now to Figure 6a, in accordance with the invention a rigid brace 300 is located between the front faces 114a of the upper and lower ribs 114 and the rear surface 212 of the projection part 210 of the insert 200. In this example, the brace 300 extends downwardly beyond the lower rib 114 (in the Y direction, from top to bottom in the sense of Figure 6a).

In this example, the brace 300 comprises a plurality of discrete rigid brace elements arranged face-to-face. An outer (rear) surface of a first brace element (the left-most brace element in the sense of Figure 6a) is in contact with the front faces 114a of the ribs 114, while an outer (front) surface of a second outer brace element (the right-most brace element in the sense of Figure 6a) is in contact with the rear surface 212 of the projection part 210. Thus the gap G is filled or eliminated by the brace 300.

As can be seen in Figure 6b, the brace elements pass through slots provided in the rear parts 204 of the insert 200. The brace elements are installed by dropping the brace elements into the slots from above, either before or after the nut and bolt are tightened to secure the insert 200 in the groove 112. If necessary, the brace elements may be lightly tapped into place using a mallet or other suitable tool. An upper end of each brace element comprises a T-shaped feature to prevent the brace element from dropping out of the slots under gravity. The brace elements may all be of the same thickness (in the Z direction in the sense of Figure 6a) or they may vary in thickness. The number and thickness of the brace elements is selected as appropriate to fill or bridge the gap G. While in this example multiple brace elements are used to fill the gap G, in other examples a single brace element of suitable thickness may be used.

In this example, each one of the brace elements comprises sheet steel. Alternative materials include, but are not limited to, copper, copper alloy, and cast iron. The brace elements may comprise an abrasion resistant refractory material. The abrasion resistant refractory material may comprise silicon carbide or alumina. The brace elements may all comprise the same material, or the material may vary between the brace elements. For example, the brace element that is in contact with the front faces 114a of the ribs 114 (the left-most brace element in the sense of Figure 6a) may comprise a material which is harder than the copper alloy of the stave 100 but softer than the steel of the insert 200.

Referring again to Figure 6a, the brace 300 reduces the lateral distance (in the Z direction, from left to right in the sense of Figure 6a) from the front faces 114a of the ribs 114 to the rear surface 212 of the projection part 210 of the insert 200, such as to bridge the gap G. The brace 300 effectively extends the ribs 114 forwardly to reach the rear surface 212. Thus the brace 300 is arranged to oppose (i.e. react against) the above-mentioned resultant force FR applied to the insert 200 by the burden material, so as to resist the displacement of the rear surface 212 of the projection part 210 toward the front face 114a of the lower rib 114. The brace 300 therefore prevents, or at least limits, movement of the insert 200 relative to the lower rib 114, thereby reducing wear of the lower rib 114.

Furthermore, the configuration of the brace 300 means that the pivot point P is effectively moved forwardly (in the Z direction, from left to right in the sense of Figure 6a), so as to be located at the lower end of the outer (front) surface of the second outer brace element, immediately adjacent to the rear surface 212 of the projection part 210. Accordingly a perpendicular distance, from the pivot point P to a line of action of the resultant force FR, is reduced, thereby reducing the magnitude of a turning moment M (which is the product of the resultant force FR and the perpendicular distance to the pivot point P) in comparison with the case where the brace 300 is absent (as in Figure 5). That is, the lever effect of the burden material on the insert 200 is reduced by the presence of the brace 300, thereby reducing the risk of the insert 200 becoming separated from the ribs 114 of the stave 100.

Thus the provision of the brace 300 reduces the rate of wear of the ribs 114 and the service life of the stave 100 is therefore prolonged.

Figures 7a-d show another example, which differs from the above-described example with respect to the form of the brace. In this example, a single, rigid, reversible brace 400 is provided between the front faces 114a of the ribs 114 and the rear surface 212 of the projection part 210 of the insert 200.

Referring to Figure 7a, the reversible brace 400 comprises a planar sheet part 402 and a pair of parallel ribs 404 extending perpendicularly therefrom to form a channel 406 between the ribs 404. An upper end of the reversible brace 400 comprises a T-shaped feature. At the opposite, lower end of the reversible brace 400 the ribs 404 progressively reduce in height so as to form a taper at the lower end. The reversible brace 400 may comprise any of the materials discussed herein above in connection with the brace 300 of Figures 6a and 6b.

Referring next to Figure 7b, each of the slots in the rear parts 204 of the insert 200 comprises a formation 214 which extends inwardly into the slot and which has a generally flat face. The width of the formation 214 is substantially the same as the width of the channel 406 of the reversible brace 400. The width of the slot is substantially the same as the width of the planar sheet part 402 of the reversible brace 400. The depth of the slot (i.e. in a direction perpendicular to the width) is substantially the same as the thickness of the reversible brace 400.

Referring now to Figures 7c and 7d (the latter being a view from the bottom of the insert 200), the reversible brace 400 is installed in the slots in a first direction. The taper at the lower end of the reversible brace 400 eases entry of the reversible brace 400 into the slots, while the T-shaped feature prevents the reversible brace 400 from falling through the slots. In the first direction, the planar sheet part 402 of the reversible brace 400 is in contact with the generally flat faces of the formations 214, which themselves form a rear surface of the projection part 210 of the insert 200. The parallel ribs 404 of the reversible brace 400 are in contact with the front faces 114a of the ribs 114 of the stave 100.

In another arrangement (not shown in the Figures), the reversible brace 400 is installed in the slots in a second or reversed direction. The second direction is obtained by rotating the reversible brace 400 through 180 degrees about its longitudinal axis in comparison to the first direction. Thus in the second direction the planar sheet part 402 of the reversible brace 400 is in contact with the front faces 114a of the ribs 114 of the stave 100, while the parallel ribs 404 are in contact with the rear surface of the projection part 210 of the insert 200, the formations 214 being received in the channel 406 (as can be easily understood by envisaging a 180 degree reversal of the reversible brace 400 in Figure 7d).

Since the formation 214 is received by the channel 406 when the reversible brace 400 is in the second direction, the size of the gap filled by the reversible brace 400 when the reversible brace 400 is in the second direction is smaller than the size of the gap filled by the reversible brace 400 when the reversible brace 400 is in the first direction. Thus the reversible brace 400 advantageously provides an efficient means for dealing with gaps of differing size, allowing an operator to select the most suitable direction of the reversible brace 400 for any given size of gap.

It will be understood that the reversible brace 400 functions to oppose or react against the resultant force FR applied to the insert 200 by the burden material, so as to resist the displacement of the rear surface 212 of the projection part 210 toward the front face 114a of the lower rib 114, as has been described herein above.

While in the above-described examples the brace 300, 400 is located between the front face 114a of the upper rib 114 and the rear surface 212 of the projection part 210 of the insert 200, as well as between the front face 114a of the lower rib 114 and the rear surface 212, in other examples this is not the case. In such examples, the brace 300, 400 is located only between the front face 114a of the lower rib 114 and the rear surface 212.

In further examples, two separate braces are provided, a first brace being located between the front face 114a of the lower rib 114 and the rear surface 212, and a second brace being located between the front face 114a of the upper rib 114 and the rear surface 212.

While in the above-described examples the brace 300, 400 completely fills the gap G between the front faces 114a of the ribs 114 and the rear surface 212 of the projection part 210 of the insert 200, in other examples this is not the case. In such examples, the brace 300, 400 is arranged to extend only part of the way between the front faces 114a and the rear surface 212, the brace 300, 400 therefore being a loose fit in the gap G. In these examples, the insert 200 may be moved to a limited extent by the resultant force FR, exerted on the insert 200 by the burden material, so as to cause the rear surface 212 of the projection part 210 to come into contact with the brace 300, 400, thereby arresting the movement of the insert 200 and fully closing the gap G. The brace 300, 400 will then oppose the resultant force FR, as has been described herein above.

While in the above-described examples the brace 300, 400 comprises a generally solid piece of material, in other examples the brace takes a different form. In one such example, the brace comprises a resilient element, for instance a spring, which is held in compression between the front face 114a of the lower rib 114 and the rear surface 212 of the projection part 210 of the insert 200. Energy stored in the compressed spring causes the spring to try to expand toward the rear surface 212 such as to apply a force thereto, said force acting in opposition to the resultant force FR exerted on the insert 200 by the burden material. All such arrangements and configurations of the brace are within the scope of the claimed invention, provided that the brace opposes the resultant force FR so as to resist displacement of the rear surface of the insert toward the front surface of the lower rib (and optionally the upper rib). While in the above-described examples the brace has a generally rectangular form and is arranged in a vertical fashion, in other examples the brace is shaped and/or arranged differently. For example, the brace may be C-shaped or horseshoeshaped and may be installed by moving the brace laterally (horizontally) into the gap G. All such arrangements and configurations of the brace are within the scope of the claimed invention, provided that the brace is located between a front surface of the lower rib (and optionally the upper rib) and an opposing rear surface of the insert.

Referring to Figure 8, in another example a brace 500 is shaped to resemble “goalposts”. Thus, the brace 500 comprises a pair of vertically arranged, upright members 502 that are spaced-apart from each other and joined together at their upper ends by a horizontally arranged, cross member 504. The brace 500 may comprise a plurality of discrete rigid brace elements arranged face-to-face, or may comprise a single brace element having a unitary structure. The brace 500 may be constructed from a variety of materials, as has been discussed herein above in connection with other forms of brace.

Still referring to Figure 8, the brace 500 is installed by lowering the brace 500 over the wedge-shaped attachment part 206 of the insert 200 until the cross member 504 comes into contact with the upper surface of the upper rear part 204 of the attachment part 206.

As can be seen in Figure 8, in this example the attachment part 206 is narrower than the projection part 210 of the insert 200 in the transverse direction, so that portions of the rear surface 212 of the projection part 210 are exposed on each side of the attachment part 206. Thus, in the installed position, the upright members 502 are located between the front face 114a of the lower rib 114 and the rear surface 212 of the projection part 210. Preferably (as shown in Figure 8), the lateral spacing between the upright members 502 is substantially equal to the lateral width of the attachment part 206, so that an inner edge of each of the upright members 502 is in contact with an outer edge of a respective side of the attachment part 206. In this way, the brace 500 is prevented from moving side- to-side in the transverse direction during its service life. As can also be seen in Figure 8, in this example the cross member 504 rests on the upper surface of the upper rear part 204, so as to be located between the front face 114a of the upper rib 114 and the rear surface 212 of the projection part 210. In another example (not shown in Figure 8), the cross member 504 is accommodated within a shallow transverse groove provided in the upper surface of the upper rear part 204. Accordingly, in this other example, the cross member 504 is not located between the front face 114a of the upper rib 114 and the rear surface 212 of the projection part 210, i.e. because it is “hidden” in the groove. Whether the cross member 504 rests on the upper surface of the upper rear part 204, or is alternatively accommodated within a shallow transverse groove provided therein, the cross member 504 is supported by the upper rear part 204 to prevent the brace 500 from dropping out of the assembly under gravity.

While in Figure 8 the attachment part 206 of the insert 200 is shown including a vertical slot (as has been described herein above in connection with other forms of brace), it will be understood that the slot is not essential for the function of the goalposts-shaped brace 500 and may therefore be omitted.

While the brace 500 has been described herein above as comprising straight upright members connected by a straight cross member in a perpendicular fashion, it will be understood that the cross member and even the upright parts could instead be curved, such that the brace 500 would resemble an inverted U or an inverted horseshoe.

While in the above-described examples the engagement surfaces of the rear parts 204 comprise serrations for biting into the copper alloy of the walls 112b of the groove 112, the serrations are not essential for the invention and in other examples they are omitted.

It should be understood that the invention has been described in relation to its preferred embodiments and may be modified in many different ways without departing from the scope of the invention as defined by the accompanying claims.