TECHNICAL FIELD

[0001] The present invention concerns glass fibre man ufacturing plants comprising a forehearth forming a passage for conveying molten g lass from a melting furnace to a series of bushings. Said forehearth comprises longitudinal walls made of a refractory mason ry including a number of support blocks for supporting a burner, a pressure or temperature measurement device, a peep hole or camera, a gun for injecting a fluid into the passage, an atmospheric beam, and the l ike. The gist of the present invention is that the su pport blocks can be reversibly inserted and removed from the masonry of the long itudinal walls without having to cool the forehearth, and without having to destroy part of the masonry surrounding the support blocks.

BACKGROUND OF THE INVENTION

[0002] A glass fibre manufacturing plant comprises a melter or furnace for melting pre-mixed and pre-dosed batch materials to form a molten (i .e., liquid) glass composition. The molten glass composition is fiberized by drawing the glass melt th rough a n umber of bushings distributed in a forehearth, sometimes referred to as front end, both terms being considered herein as synonyms. As descri bed in DE2961 2683 , a forehearth consists of at least one passage, generally divided into several passages, for conveying molten glass from the melter to the bushings and comprising a first and second opposite longitudinal walls, a ceiling, a bottom floor, and an end wall. The pressure and thermal conditions within the forehearth must be carefully controlled in order to ensure that the molten g lass reaches each bushing at the right temperature, pressure, and composition, required for a successful formation of the glass fibres.

[0003] For this reason , forehearths are equipped with burners for ensuring an opti mal temperature of the glass melt, with temperature and pressure measurement devices for monitoring the temperature and pressure within the forehearth, with peepholes or cameras for an optical control of the forehearth, with flu id injection gu ns for locally controlling tu rbulences or temperature peaks, and even with atmospheric beams extend ing across the passages defined by the forehearth for controlling the gas flows with in the forehearth. In order to provide all this equipment to the forehearth, the longitudinal walls and end walls, sometimes even the ceiling, are equipped with support blocks integrated in the masonry of said walls, wh ich are specifically designed for receiving the foregoing equipment. The support blocks are integ rated into the mason ry during the building of the forehearth and cannot be removed easily during use, without interrupting production and dismantling the mason ry surrounding a support block to be removed. Such operation can paralyse the activity of a passage of forehearth during more than a week.

[0004] Bu rners are distributed along the longitudinal walls, at regularly spaced, predefined positions. A support block supporting a burner is called a burner block, and burners can easily be mounted in and removed from a burner block. Burner blocks, however, can wear during service. In particular when oxygen-fuel burners, often referred to as oxy-burners, are used instead of traditional air-fuel burners, because the temperature of the flame of oxy-burners is substantial ly higher than the one of traditional air-fuel burners. If a burner block is damaged, it must be replaced, yield ing an interruption of production of at least one week. [0005] Measu rement blocks for supporting measurement equipment, peep hole blocks and camera blocks for supporting a camera of a peeping window, injection blocks for supporting a fluid injection gun, and atmospheric blocks for su pporting an atmospheric beam do not wear off during service as rapidly as burner blocks which are exposed to particularly high temperatu res. Their positions, however, determined before the building of the forehearth may reveal not to be optimal during use of the forehearth, at which point it is d ifficult to change their positions without interrupting production for a considerable period of time. The decision to interrupt the production for a long ti me must therefore be justified by a substantial advantage in moving the position of a support block. If such is not the case the forehearth must be operated with equipment which is not located at optimal positions. [0006] Providing a removable block in a masonry seems prima facie pretty obvious, as it suffices to provide a cavity between two blocks of the masonry, and to reversi bly insert said support block into the cavity without seal ing it with mortar. If this solution applies to a "normal" wall exposed to room temperature, it does not work with a forehearth longitudinal wall built at room temperature and exposed to service temperature, hT, temperatures greater than 1 000°C, generally of the order of 1 200°C, since the blocks of the masonry undergo considerable thermal expansion, thus reducing the di mensions of the cavity, and thus clamping the support block in the cavity. The gap to be left at room temperature between the support block and the surround ing blocks defining the cavity would be too large to ensu re that the gap has the requ ired size to allow the removal of the su pport block at service temperature, hT, of about 1 1 50°C + 1 50°C, and someti mes hig her.

[0007] There therefore remains a need in the art for a more flexible forehearth construction allowing support blocks to be exchangeable within the masonry of the longitudinal wall at service temperature, hT, of at least 1 000°C. This allows the replacement of damaged burner blocks, and opti mization of the position of support blocks for supporting other equipment such as pressure or temperature measu rement devices, a peep glass or camera, a gun for i njecting a fluid into the passage, an atmospheric beam, and the like. [0008] The present invention proposes a solution for providing exchangeable support blocks in the masonry of the walls of a forehearth, which can be reversibly inserted and removed at service temperature greater than 1 000°C, and yet ensuring the required seal between the support blocks and the adjacent blocks surrou nding it. This and other advantages of the present invention are presented in continuation. SUMMARY OF THE INVENTION

[0009] The present invention is defined in the appended independent claims. Preferred em bodiments are defined in the dependent clai ms. In particular, the present invention concerns a glass fibre manufacturing plant comprisi ng a forehearth formi ng a passage for conveying molten glass and defined by: - a first and second opposite longitud inal walls having a hot longitudinal wall surface facing said passage and extending along a longitudinal direction, XI , having a longitudinal wall thickness extending along a first transverse d irection, X2 , normal to XI , and having a longitudinal wall height extending along a second transverse direction , X3, normal to both XI and X2 ,

- a ceiling,

- a bottom floor and

- an end wall.

[0010] Each longitudinal wall is made of a refractory masonry comprising : (a) a series of refractory base bricks forming a base wall comprising a top surface for su pporting,

(b) two spacer bricks lying on the top surface of the base wal l and separated from one another at the level of the hot longitudinal wall surface by a distance, Wc, measured at room temperature (RT) along the longitudinal direction , XI , each spacer brick having a cuboid geometry comprisi ng a hot su rface (23H) forming a portion of the hot longitudinal wall surface, wherein,

(c) a lintel (25) of length, WL > Wc, measured along the longitudinal direction, XI , at room temperature and comprising two opposite ends, each resting on one surface of one of the two spacer bricks, thus defi n ing with the top surface of the base wall and the two spacer bricks,

(d) a cavity (28) of width, Wc, and height, H l c, measured at the level of the hot longitudinal wall surface at room temperature along the longitud inal d irection, XI , and along the second transverse axis, X3, respectively, and of depth, Dc, measured at room temperature along the first transverse axis, X2 ,

(e) a support block (20) comprising a hot cuboid portion having a cuboid geometry of width, w, and height, h, measured along XI and X3, respectively, at the level of the hot longitudinal wall surface at a service temperature, hT, of the forehearth of at least 1 000°C, and of depth measured along X2 at least eq ual to D, wherein w < Wc, and h < H l c, said hot cuboid portion being reversi bly inserted in the cavity, and

(f) a gap surround ing the hot cuboid portion of the support block when positioned in the cavity, said gap being filled with a resilient material,

[0011] According to the present invention, the masonry com prises a spacing element hindering the thermal expansion of the two spacer bricks, such that the distance, Wc, between said two spacer bricks measured at room temperature along the longitudinal direction, XI , at the level of the hot longitudinal wall surface cannot be reduced below a predetermined hot cavity width, W, at said service temperature, hT, wherein said predetermined distance, W, is larger than the width, w, of the hot cuboid portion of the support block. [0012] In a preferred embodi ment,

(a) The top surface of the base wall forms a planar surface along a base plane (XI , X2),

(b) The two spacer bricks are characterized in that,

• two opposite edges remote from the base plane and extending in the fi rst transverse direction , X2 , are cut off to form a rig ht step at each of said two opposite edges, defining a recessed surface (23 R) parallel to the base plane, and a steppi ng surface extending parallel to X3,

• at the service temperature (hT) the hot surface has a height, H2 , measured along the second transverse direction, X3, and a height, H I , measured up to the recessed surfaces, the stepping surfaces (23S) of the steps thus having a height, HS = H2 - H I ,

(c) the two opposite ends of the lintel each rests on one recessed surface of one of the two spacer bricks,

[0013] In this embodi ment, the spacing element is formed by the lintel resting on the recessed surfaces and resisting the thermal expansion of the stepping su rfaces of the two spacer bricks.

[0014] Alternatively or additionally, the glass fibre manufacturing plant of the present invention may comprise a base spacer of length equal to the predetermined distance, W, measu red at said service temperature, hT, along the first longitudi nal direction , which lies on the top surface of the base wal l between the two spacer bricks, such that the distance, H I , measured at the service temperature along the second transverse direction, X3, between said base spacer and the li ntel is larger than the height, h, of the hot cuboid portion of the support portion, said base spacer thus forming the spacing element. [0015] In an alternative embodi ment, the top surface of the base wall forms a merlon of length equal to the predetermined distance, W, measured at said service temperature, hT, along the first longitudinal direction, said merlon separating the two spacer bricks, said merlon thus forming the spacing element. [0016] In yet an alternative embodi ment,

(a) The two spacer bricks are characterized in that,

• two opposite edges adjacent to the top surface of the base wall and extend ing in the first transverse di rection, X2 , are cut off to form a right step at each of said two opposite edges, defining a recessed surface parallel to XI , and a stepping surface extending parallel to X3,

• measured along the second transverse direction, X3, at the service temperature (hT), the hot surface has a total height, H2 , and a height, H I , measu red down to the recessed surfaces, the step thus having a height, HS = H2 - H I ,

(b) the top surface of the base wall forms a merlon of height, HS, measured along the second transverse di rection, X3, and of length such that when the merlon contacts the stepping surfaces of the two spacer bricks, the distance between said two spacer bricks measured along the longitudinal direction, XI , at the level of the hot longitudinal wall surface at said service temperature, hT, is equal to the predetermined distance, W.

[0017] In this embodi ment, the spacing element is formed by the merlon supporting the recessed surfaces of the two spacer bricks and resisting the thermal expansion of the stepping su rfaces of the two spacer bricks. [0018] In any of the previous embodiments, the support block can be selected among one of the following :

(a) a burner block for supporting a burner, preferably an oxy-burner;

(b) a measurement block for supporting a pressure or temperature measuring device ;

(c) a peep hole block for supporting a viewing device for observing the passage;

(d) a camera block for supporting a camera for taking pictures or videos of the passage,

(e) an injection block for supporting a gun for injecting a fluid at a predetermined location of the passage; or

(f) an atmospheric beam, for controlling the gas flows within the passage [0019] The gap at the level of the hot longitudinal wall surface preferably has an average width, wg l = ½ (W - w), measured at service tem perature, hT, along the longitudinal direction, XI , comprised between 1 and 5 mm, and is preferably equal to 3 + 1 mm. The gap preferably has an average height, hg = ½ (H I - h), measured at service temperature, hT, along the second transverse axis, X2 , comprised between 1 and 5 mm, and is preferably equal to 3 + 1 mm.

[0020] In order to facilitate the insertion and withdrawal of a support block, in a preferred embodiment, the cavity has tapered walls, with a width, Wt, and /or with a height, H i t, measured at room temperature at the level of a cold surface of the spacer bricks, opposite the hot su rface, along the long itudinal direction, XI , and along the second transverse axis, X3, respectively, which are larger than the width, Wc, and height, H l c, measured at the level of the hot longitudinal wall surface, Wt > Wc and /or H i t > H l c

[0021] IN one embod iment, the support block is a burner block comprising a cold surface and a hot surface opposite the cold surface, the cold surface being connected to the hot surface by a through-passage extending along a passage axis, Xp, said th rough-passage comprising three portions :

(a) A burner portion, open ing at the cold surface, and having a cross-section suitable for accommodating a burner having a body and a downstream end portion characterized by a large base adjacent to the body, and ending at a small base having a cross-section smaller than the cross-section of the large base;

(b) A flame portion, opening at the hot surface and converging along the passage axis, xp, in the direction of the cold surface until meeting

(c) A joining portion, fluidly joining the flame portion with the burner portion in wh ich it opens with a cross-section of di mensions com prised between the one of the large base and the one of the small base, and wherein in a top view along a plane (XI , X2), the passage axis, Xp, forms an angle, a, with the longitudinal direction , XI , comprised between 30 and 90°, preferably, between 45° and 90°, more preferably, a = 90°, such that the passage axis, Xp, is parallel to the first transverse d irection, X2.

[0022] In this embodi ment, the burner block preferably further comprises a cold cuboid portion comprising the cold surface and adjacent to the hot cuboid portion, wherein the cross-sectional area normal to the first transverse axis, X2 , of the hot cuboid portion is smaller than the one of the cold cuboid portion. An oxy-burner is preferably used with the burner block. An oxy-burner comprises a body extending along the passage axis, Xp, and encloses a fuel line and an oxygen line separate from the fuel line, both fuel line and oxygen line having a separate outlet at or adjacent to a downstream end of the body of the oxy-burner. The downstream end of the oxy- burner body has a trunco-conical geometry which is mounted in the burner portion of the burner block, with the downstream end bei ng located partly in, or adjacent to the joining portion and being oriented towards the passage.

[0023] Each longitudinal wall usually comprises at least two cavities, each cavity containing a support block reversibly engaged therein , said at least two cavities being alig ned horizontally and separated from one another by at least one spacer brick. The at least two cavities of the first longitudinal wall facing the at least two cavities of the second longitudinal wal l preferably in a staggered arrangement. In a practice, a longitunal wall comprises several dozen of cavities. The end wall can also be provided with a cavity containing a support block reversibly engaged therein

[0024] The present invention also concerns a method for reversibly load ing a support block in a forehearth of a glass fibre manufacturing plant as defined supra, said method comprising :

(A) building a forehearth as defined supra, forming a passage for conveying molten g lass, wherein building each longitudinal wall comprises:

(a) laying a series of refractory base bricks to form a base wal l comprising a top surface,

(b) laying two spacer bricks onto the top surface of the base wal l, separated from one another at the level of the hot longitudinal wall surface by a distance, Wc, measured at room temperature (RT) along the long itudi nal direction, XI , each spacer brick having a cuboid geometry comprising a hot surface (23 H) forming a portion of the hot longitudinal wall surface,

(c) providing a lintel of length, WL > Wc, measured along the long itudinal direction, XI , and comprising two opposite ends, and laying each of the two opposite ends onto one of the two spacer bricks, thus defin ing with the base wal l and the two spacer bricks a cavity (28) of width, Wc, and height, H l c, measured at the level of the hot longitudinal wall surface at room temperature along the longitudinal direction, XI , and along the second transverse axis, X3 , respectively, and of depth, Dc, measured at room temperature along the first transverse axis, X2 ,

(d) providing and installing a spacing element that hinders the thermal expansion of the two spacer bricks, such that the distance, Wc, between said two spacer bricks measured at room temperature along the longitudinal d irection, XI , at the level of the hot long itudinal wall surface cannot be reduced below a predetermined d istance, W, at a service temperature, hT, of the forehearth of at least 1 000°C, ,

(B) provid ing a support block (20) comprising a hot cuboid portion having a cu boid geometry of width, w, and height, h, measured along XI and X3 , respectively, at the level of the hot long itudinal wall surface at a service temperature, hT, of the forehearth of at least 1 000°C, and of depth measured along X2 at least equal to D, wherein w < W < Wc, and h < H I c < H I , said hot cuboid portion comprising four peri pheral surfaces meeting two by two at ridges extending transverse to the first longitudinal d irection , XI ,

(C) coating the four peripheral surfaces of said hot cuboid portion with a layer of resilient material, and

(D) reversibly inserting into the cavity the hot cuboid portion of the support block, which peripheral surfaces are coated with the resi lient material.

25] The method of the present invention may further comprise the steps of:

(E) removing the support block from the cavity by sliding the hot cuboid portion along the first transverse axis, X2 ,

(F) removing any resilient material left in the cavity,

(G) reversibly inserting into the cavity the hot cuboid portion of a new support block as defined in (B), which peripheral surfaces are coated with the resilient material. BRIEF DESCRIPTION OF THE FIGURES

[0026] For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in wh ich :

Fig ure 1 : shows a front view of a longitudinal wall provided with support blocks according to an em bod iment of the present invention.

Fig ure 2 : shows a front view of a longitudinal wall provided with su pport blocks according to an alternative embodi ment of the present invention. Fig ure 3 : shows a front view of a longitudinal wall provided with su pport blocks according to an alternative embodi ment of the present invention.

Fig ure 4: shows a front view of a longitudinal wall provided with su pport blocks according to an alternative embodi ment of the present invention.

Fig ure 5 : shows a front view of a longitudinal wal l provided with support blocks according to an alternative embodi ment of the present invention.

Fig ure 6: shows a front view of a longitudinal wal l provided with support blocks according to an alternative embodi ment of the present invention.

Fig ure 7: shows (a) a cross-section, and (b) a top view of a portion of forehearth according to the present invention. Fig ure 8: shows a perspective view of a support block being inserted into a cavity provided in the masonry of a forehearth longitud inal wall according to an embodi ment of the present invention.

Fig ure 9: shows (a) a perspective, partly exploded view of a support block being inserted into a cavity provided in the mason ry of a forehearth longitudinal wall according to an alternative embodi ment of the present invention, and (b) a top view of a cavity accord ing to the embodi ment of Figure 8 compared with the one of the em bodiment of Figu re 9(a). Fig ure 1 0 : shows a burner block suitable for the present invention , (a) perspective cross-sectional view, (b) and (c) top cross-sectional views of two embodi ments of burner blocks suitable for the present invention.

Fig ure 1 1 : shows a top cross-sectional view of (a) a burner block suitable for the present invention, and (b) the same burner block with a burner mounted therein.

Fig ure 1 2 : Compares the variation , L α ΔΤ, of a section of the longitudinal wall of a forehearth according to the prior art measured along the longitudinal direction, XI , (a) at room temperature (RT), and (b) at service temperature (hT).

.Figu re 1 3 : Compares the variation, L α ΔΤ, of a section of the longitudinal wall of a forehearth according to the present inventiont measured along the longitudinal direction, XI , (a) at room temperature (RT), and (b) at service temperature (hT).

DETAILED DESCRIPTION OF THE INVENTION

[0027] As illustrated in Figure 7, a glass fibre manufactu ring plant according to the present invention comprises a forehearth (31 ) forming a passage for conveying molten glass (30) and defined by:

- a first and second opposite longitudinal walls (31 L) having a hot longitudi nal wall surface facing said passage and extending along a longitudinal direction, XI , having a longitudinal wall thickness extending along a first transverse d irection, X2 , normal to XI , and having a longitudinal wall height extending along a second transverse direction , X3, normal to both XI and X2 ,

- a ceiling (31 T),

- a bottom floor (31 B) and

- an end wall (31 E).

[0028] As can be seen in Figures 1 to 6, each longitudinal wall is made of a refractory mason ry comprising :

(a) a series of refractory base bricks (32) forming a base wall comprising a top surface for su pporting, (b) two spacer bricks (23) lying on the top surface of the base wall and separated from one another at the level of the hot longitudi nal wall surface by a distance, Wc, measured at room temperature (RT) along the longitudinal direction, XI , each spacer brick having a cuboid geometry comprisi ng a hot su rface (23 H) form ing a portion of the hot longitudinal wal l surface, wherein,

(c) a lintel (25) of length, WL > Wc, measured along the longitudinal direction, XI , at room temperature and comprising two opposite ends, each resting on one surface of one of the two spacer bricks, thus defining with the top surface of the base wall and the two spacer bricks,

(d) a cavity (28) of width, Wc, and height, H l c, measured at the level of the hot longitudinal wall surface at room temperature along the longitud inal d irection, XI , and along the second transverse axis, X3, respectively, and of depth, Dc, measured at room temperature along the first transverse axis, X2 ,

(e) a support block (20) comprising a hot cuboid portion having a cuboid geometry of width, w, and height, h, measured along XI and X3, respectively, at the level of the hot longitudinal wall surface at a service temperature, hT, of the forehearth of at least 1 000°C, and of depth measured along X2 at least eq ual to D, wherein w < Wc, and h < H l c, said hot cuboid portion being reversi bly inserted in the prismatic cavity, and

(f) a gap surround ing the hot cuboid portion of the support block when positioned in the cavity, said gap being filled with a resilient material (29).

[0029] A cuboid geometry is defined as a convex polyhedron bounded by six quadrilateral faces, whose polyhedral graph is the same as that of a cube. A cuboid bounded by six rectangular faces, with each pair of adjacent faces meeting in a right angle is herein referred to as a "rectangular cuboid." This more restrictive type of cu boid is also known as a. " right cuboid." In other words, if not rectangular, a cuboid may for example be bounded by two or more trapezia. A support block su itable for the present invention preferably has a hot cuboid portion wherein each pai r of adjacent faces meet in a right angle. The hot cuboid portion is preferably, but not necessarily, of rectangular cuboid geometry. Indeed, it may also have a slightly tapered geometry with smallest dimensions at the level of the hot longitudinal wall surface, with width, w, and height, h, With such tapered geometry, the insertion into and withdrawal out of a cavity simi larly tapered of a su pport block can be facilitated.

[0030] The g ist of the present i nvention consists of a spacing element provided in the mason ry which hinders the thermal expansion of the two spacer bricks, such that the distance, Wc, between said two spacer bricks measured at room temperature measured along the longitudinal direction, XI , at the level of the hot longitudinal wall surface cannot be reduced below a predetermined hot cavity width , W, at said service temperature, hT, wherein said predetermined hot cavity width, W, is larger than the width, w, of the hot cuboid portion of the support block. The gap left between the hot cu boid portion of the support block and the walls defining the cavity is filled with a resilient material (29) made of refractory material .

[0031] In an embodiment illustrated in Figure 1 ,

(a) The top surface of the base wall forms a planar surface along a base plane (XI , X2),

(b) The two spacer bricks (23) are characterized in that,

• two opposite edges remote from the base plane and extending in the fi rst transverse direction , X2 , are cut off to form a rig ht step at each of said two opposite edges, defining a recessed surface (23 R) parallel to the base plane, and a steppi ng surface (23S) extending parallel to X3 ,

• at the service temperature (hT) the hot surface has a height, H2 , measured along the second transverse direction, X3, and a height, H I , measured from the base plane (XI , X2) up to the recessed surfaces, the stepping surfaces (23S) of the steps thus having a height, HS = H2 - H I , (c) the two opposite ends of the lintel (25) each rests on one recessed surface (23R) of one of the two spacer bricks.

[0032] A "right steri' is defined herein as a step characterized by two planar surfaces, a recessed surface (23 R) and a stepping surface (23S), normal to each other. The recessed surface (23 R) is substantially parallel to (XI , X2) and the stepping surface (23S) is substantially parallel to (X2 , X3).

[0033] In this configuration , the spacing element is formed by the lintel (25) resti ng on the recessed surfaces (23R) and resisting the thermal expansion of the two spacer bricks which stepping surfaces abut against the lintel.. The width, WS, of a right step on either side of a spacer brick is therefore about ½ (WL - Wc), measured along the longitudinal axis, XI , at room temperature.

[0034] As illustrated in Figures 1 2(a) and 1 3(a), the masonry of a longitudinal wall is built at room tem perature (RT). Figure 1 2 illustrates a longitudinal wall section of a traditional forehearth of the prior art and Figure 1 3 illustrates a corresponding longitudinal wall section of a forehearth according to the present invention. Upon heating the forehearth to service temperature, hT, of at least 1 000°C, generally of the order of 1 1 50° + 1 50°C, all the bricks, lintels, etc. of a longitudinal wall (collectively referred to a longitudinal wall components) expand along the three directions, XI , X2 , and X3. The most critical expansion component for maintaining the removability of a support block from the longitudinal wall at service tem perature, hT, is the longitudinal expansion, ΔΙ_, along the longitudinal direction, XI . As illustrated in Fig ures 1 2(b) and 1 3(b), the longitudinal expansion, AL = L α ΔΤ, wherein a is a mean coefficient of expansion of the longitud inal wall's components. The longitudinal wall must be allowed to expand relatively freely, lest pressure concentrations may develop leading to the misal ignment of the longitudinal wall's components, which would form an arched longitudinal wall or, worse, the collapse of some of the longitudinal wall's components. Open joints are usually distributed at regular intervals along the longitudinal wall to "absorb" the longitudinal expansion, AL, of the order of 5 to 20 mm, of sections of the longitudinal wall. [0035] As can be seen in Figure 1 2(b), as the longitudinal wall components expand, they will absorb any gap of width, wgO, left during the building at room temperature between two adjacent bricks, and start pushing chai n-wise the adjacent components, reducing such gaps to a width at service temperature, wg l ^ 0. As a result, the longitudinal walls components which are adjacent to one another along the longitudinal direction are in tight contact with one another forming a compact line of components with substantially no gap between two components. The same applies to the support blocks (20) which are sandwiched in tight contact between two adjacent spacer bricks (23) and cannot be removed from the longitudinal wall at service temperature (hT). [0036] By contrast, as can be seen in Figure 1 3 illustrati ng an em bodiment of a longitudinal wall according to the present invention, the thermal expansion of the spacer bricks (23) does not bring them into contact with the su pport blocks sandwiched therebetween , because the expanding spacer bricks contact the spacer elements first (in Figu re 1 3(b) the lintels (25) act as spacer elements), It follows that the gaps, wgO, between a su pport block (20) and adjacent spacer bricks (23) at room temperature are not reduced to a gap width , wg l , at service temperatu re (hT), which is close to zero, as is the case in the prior art (cf. Figu re 1 2(b)), but are merely reduced to a positive gap width, 0 < wg l < wgO (cf. Figure 1 3(b)). It follows that the support blocks (20) can be withdrawn from between two spacer bricks (23) even at service temperature (hT). As discussed later, the resil ient material (29) serves here inter alia to seal the gaps, wg l , left at service temperature (hT) between a support block and adjacent spacer bricks.

[0037] This has an enormous advantage in that it is not necessary to cool the forehearth, nor to dismantle the masonry surrou nding a support block to exchange an old support block with a new one, operation that may last at least one week d uring which time the forehearth activity is interrupted . The support block in a forehearth according to the present invention can be exchanged at service temperature, without any dismantling of the bricks forming the masonry surrounding the support block. The exchange of a support block in a forehearth of the present invention can be completed in half a day. Although the replacement of the support block per se may be completed in less than an hou r, it is necessary, prior to resuming a full volume production rate, to allow time for the forehearth to recover stationary thermal and pressure conditions, and to remove all dust of masonry and resilient material which may have fallen into the glass melt during the exchange.

[0038] A second embodi ment of the present invention , showing an alternative spacing element, is illustrated i n Figures 2&3. In this embodiment, which can be used instead of (cf. Figure 2), or in combination with (cf. Figure 3) the embodi ment illustrated in Fig ure 1 and discussed supra, comprises a base spacer (26) forming the spacing element. Said base spacer has a length equal to the predetermined distance, W, measured at said service temperature, hT, along the first longitudinal direction, and it lies on the top surface of the base wall between the two spacer bricks, such that the distance, H I , measured at the service temperature along the second transverse direction, X3, between a top surface of said base spacer and the lintel is larger than the height, h, of the hot cuboid portion of the support portion. In this embodiment, the top surface of the base wall preferably forms a planar surface along a base plane (XI , X2).

[0039] In a variation of the embodiment illustrated in Fig ure 2 , an alternative em bodiment illustrated in Figu re 4, the top surface of the base wall does not form a planar surface, but is crenelated, forming merlons (27) of length equal to the predetermined d istance, W, measured at said service temperature, hT, along the first longitudinal direction. Said merlons separating two spacer bricks actually correspond to a base spacer (26) which is an integral part of the base wall, instead of being laid on top of said base wall. In this embodi ment, the spacing elements are formed by the merlons (27), which abut against the lateral walls of the flanking space bricks.

[0040] In yet an alternative embodiment, illustrated in Figure 5 , the two spacer bricks (23) have a geometry similar to the one discussed with reference to Figure 1 , but upside down. They are characterized in that,

• two opposite edges adjacent to the top surface of the base wall and extend ing in the first transverse di rection, X2 , are cut off to form a right step at each of said two opposite edges, defining a recessed surface (23R) parallel to XI , and a stepping surface (23S) extending parallel to

X3 ,

• measured along the second transverse direction, X3, at the service temperature (hT), the hot surface has a total height, H2 , and a height, H I , measu red down to the recessed surfaces, the step thus having a height, HS = H2 - H I ,

[0041] As shown in Figure 5 , the top surface of the base wall forms a merlon (27) of height, HS, measured along the second transverse direction, X3, and of length such that when the merlon contacts the stepping su rfaces of the two spacer bricks, the distance between said two spacer bricks measured along the longitudinal direction, XI , at the level of the hot longitudinal wall surface at said service temperature, hT, is equal to the predetermined d istance, W. Alternatively, a base spacer (26) can form a merlon on top of a planar top surface of the base wall (not shown). [0042] In this embodi ment, the spacing element is formed by the merlon supporting the recessed surfaces (23 R) of the two spacer bricks and resisting the thermal expansion of the two spacer bricks by abuting against the stepping surfaces (23S).

[0043] The embodi ment, illustrated in Figure 6, is a combi nation of the embod iments of Figu res 1 and 5 , wherein the four edges extending in the second transverse direction, X2 , of the spacer bricks are cut off to form a right step at each of said four edges, defining two top recessed surfaces (23R) and two bottom recessed su rfaces (23R), each parallel to XI , and corresponding to two top stepping surfaces (23S) and two bottom stepping surfaces (23s) each extending substantially parallel to X3. The thermal expansion of the two spacer bricks flanking the two lateral sides of the cavity is hindered , on the one hand, by the lintel resting on the two top recessed surfaces of the top edges and pressing on the top stepping surfaces and, on the other hand, by the merlon (27) formed at the top surface of the base wall and pressing on the bottom stepping surfaces.

[0044] Hindering the thermal expansion of the spacer bricks (23) both at the level of the lintel and at the level of the base wal l (cf. for example, Figures 3 and 6) is advantageous as it ensu res a better control of the cavity dimensions as a function of temperature. But prel imi nary tests have shown that excellent results were obtained also when thermal expansion was hindered only at the level of the lintel (cf. for example, Fig ure 1 ) or of the base wall (cf. for example, Fig ures 2 , 4, and 5). [0045] At service temperature, hT, of at least 1 000°C, the gap surrounding the hot cu boid portion of the support block when positioned in the cavity has an average width, wg l , defined as wg l = ½ (W - w), measured along the longitudinal di rection, XI , which Is preferably comprised between 1 and 5 mm, and is preferably equal to 3 + 1 mm. This means that once the spacer bricks flanking either sides of the cavity have thermally expanded as the temperature reached the service temperature, hT, the cavity has a width ; W, at the level of the hot longitud inal wal l surface, which is still approximately 6 + 2 mm larger than the width, w, of the hot cuboid portion of the support block, at sevice temperature, hT ((w + 4 mm)≤ W≤ (w + 8 mm)). The support block may be slightly misaligned with a gap on one side of the support block being wider than the gap on the other side of the support block. To en hance alignment of the support block in the cavity, guiding ridges may be provided either on the surfaces of the hot cuboid portion of the support block, or on the walls defin ing the cavity. Alternatively or additionally, match ing surfaces may be provided at the level of the cold surfaces (23C) of the spacer bricks, which are substantially colder, between the spacer bricks, lintel and support block, to ensure that the support block is well aligned , as shown for example in Figure 1 1 .

[0046] Similarly, at service temperature, hT, the gap surrounding the hot cuboid portion of the support block when positioned in the cavity has an average heig ht, hg, defined as hg = ½ (H I - h), measured along the second transverse axis, X2 , which Is preferably comprised between 1 and 5 mm, and is preferably equal to 3 + 1 mm. This means that once the whole masonry defining the cavity as well as the spacer block have thermally expanded as the temperature reached the service temperature, hT, the cavity has a heig ht, H I , at the level of the hot longitudinal wall surface, which is still approximately 6 + 2 mm larger than the height, h, of the hot cuboid portion of the support block, ((h + 4 mm)≤ H I ≤ (h + 8 mm)). It is clear that if the hot cuboid portion of the support block simply rested on the bottom floor of the cavity, the gap height above the block would be substantially larger than the gap height below the block. Even with the presence of resi lient material filling the gap, it is to be expected that resilient material would be pressed by the weight of the support block, which would eventually move down closer to the floor of the cavity. This is of course undesirable, as the position of the support block must not change during operation. Again, guiding edges may be provided on the floor of the cavity, or matching su rfaces may be provided at the level of the cold surfaces (23C) of the spacer bricks, which are substantially colder, between the spacer bricks, lintel and support block, to ensure that the support block is well aligned.

[0047] In a preferred embodi ment illustrated in Figure 9, the cavity (28) has tapered walls, with a width, Wt, and /or with a height, H i t, measu red at room temperature at the level of a cold surface (23C) of the spacer bricks, opposite the hot surface (23H), along the longitudinal direction, XI , and along the second transverse axis, X3 , respectively, which is larger than the width, Wc, and height, H l c, measured at the level of the hot longitudinal wall surface, Wt > Wc and /or H i t > H l c. Figure 9(b) compares top views of a cavity having parallel lateral walls as shown in Fig ure 8 (top drawing) with a cavity having tapered lateral walls as shown in Figure 9(a) (bottom drawi ng). At room temperature (RT), the spacer bricks (23) are separated from one another at the level of the hot longitud inal wall surface by a distance, Wc, regardless of whether the lateral walls of the cavity are parallel or tapered. At the opposite side of the hot longitudinal wall surface, however, defined by the cold surfaces (23C) of the spacer bricks, the spacer bricks are separated from one another by a distance, Wt, in case of tapered walls, wherein Wt > Wc. The tapered walls allow an easier and self-centred introduction of a support block into the cavity both at room temperature, RT, and at service temperature, hT. As shown in Figure 9(a), the l intel may have a tapered surface defining a cavity height at the level of the cold surfaces of the spacer bricks wh ich is larger than the heig ht, H I , measured at the level of the hot longitudinal wall su rface. [0048] As shown in Figures 8 and 9, the resi lient material (29) is preferably provided in the form of a sheet, which is wrapped around the four peripheral surfaces of the hot cu boid portion of the support block. The resi lient material is preferably made of refractory fibres, typically alumina fibres, or fibres comprising at least 90 wt.%, more preferably at least 95 wt.%, most preferably at least 99 wt.% alu mina. The resil ient fi bres preferably do not comprise more than 2 wt.% silica, and more preferably comprise no silica, as silica may form an eutectic with oxides of adjacent refractory bricks, which could contaminate the glass melt by subli mation at high temperatures. An example of resi lient material supplied as a sheet which is suitable for the present invention comprises ceramic fibre paper such as supplied by Morgan Thermal Ceramics.

[0049] The resilient material contributes to the proper al ig nment of the support block with in the cavity, but its principal task is to thermally insulate and fluidly seal the hot longitudinal wall surface from the opposite side of the wall defined by the cold surface of the spacer bricks. Absent the resilient material filling the gap, heat from the forehearth passage would be lost th rough the gaps of the nu merous cavities flanking said passage, creating an unacceptable thermal draft throug h the gaps in the longitudinal walls and disrupting the temperature and pressu re control of the passage.

[0050] The support block may be anyone among one of the following :

(a) A burner block for supporting a burner, preferably an oxy-burner;

(b) A measurement block for supporting a pressure or temperature measuring device ;

(c) A peep hole block for su pporting a viewing device for observing the passage;

(d) A camera block for supporting a camera for taking pictures or videos of the passage,

(e) An injection block for supporting a gun for injecting a fluid at a predetermined location of the passage; or

(f) An atmospheric beam, for controlling the gas flows within the passage

[0051] Of all the above types of support blocks, burner blocks are of particular interest because a typical forehearth may comprise several hundred of such burner blocks alig ned on each longitudinal wall. As shown in Figu res 8 to 1 1 , a burner block suitable for the present invention may comprise a cold surface (20C) and a hot surface (20H) opposite the cold surface. The cold surface is connected to the hot surface by a th rough-passage extending along a passage axis, Xp. As shown in Fig ure 1 0(a), the th rough-passage comprises three portions: (a) A burner portion (2 I B), opening at the cold surface, and having a cross- section suitable for accommodating a burner (1 ) having a body and a downstream end portion (1 D) characterized by a large base adjacent to the body, and ending at a small base having a cross-section smaller than the cross-section of the large base;

(b) A flame portion (2 I F), opening at the hot surface and converging along the passage axis, xp, in the direction of the cold surface until meeting

(c) A joining portion (21J), fluidly joining the flame portion with the burner portion in which it opens with a cross-section of dimensions comprised between the one of the large base and the one of the small base.

[0052] A support block and, in particular a burner block, is preferably made of a refractory material composed of at least 95 wt.% alumina, more preferably of at least 99 wt.%. The refractory material of the support block preferably comprises less than 1 0 wt.% silica, more preferably comprises less than 5 wt.% silica, most preferably comprises less than 2 wt.% silica. The bricks surrounding the cavity may be made of mullite, preferably of alumina enriched mullite.

[0053] As shown in the top views along a plane (XI , X2) of Figure 1 0(b)&(c), the passage axis, Xp, forms an angle, a, with the longitudinal direction, XI , comprised between 30 and 90°, preferably, between 45° and 90°. In Figure 1 0(b), a burner block having a passage axis, Xp, forming an angle, a = 90°, is illustrated, such that the passage axis, Xp, is parallel to the first transverse direction, X2. In Figure 1 0(c) an alternative embodiment with a angle, a < 90°, is illustrated, the burner preferably pointing in the direction of the flow of molten glass.

[0054] A support block suitable for the present invention and, in particular, a burner block preferably further comprises a cold cuboid portion comprising a cold surface (20C) opposite the hot surface (20H). The cold cuboid portion is coupled to the hot cuboid portion. The cross-sectional area normal to the first transverse axis, X2, of the hot cuboid portion is smaller than the one of the cold cuboid portion. The cold cuboid portion is adjacent to the cold surfaces of the flanking spacer blocks and they are not exposed to high temperatures. Consequently their geometries remain more stable during the heating u p of the forehearth and can be controlled more accurately to ensure that the cold cu boid portion of the support block matches the cavity surfaces adjacent the cold surfaces of the spacer blocks. This way, a support block can be fixed to its predefi ned service position with a better control of the gap width and height around the hot cuboid portion of the support block.

[0055] The cold cuboid portion of a support block may comprise one or several surfaces which are coplanar with peripheral surfaces of the hot cuboid portion. For example the burner block represented in Figure 1 0(a) comprises three surfaces coplanar with the hot cuboid portion : the bottom surface and the two lateral surfaces. The cold cuboid portions of the burner blocks represented in Figures 8 and 9(a) only have the bottom surface which is coplanar with the bottom surface of the hot cu boid portion. In yet an alternative embodiment, none of the surfaces of the cold cuboid portion is coplanar with any of the peripheral surfaces of the hot cuboid portion.

[0056] As shown in Figu re 1 0(b)&(c) and in Figure 1 1 (b), an oxy-burner is a burner comprising a body extending along the passage axis, Xp, and enclosing a fuel line (I F) and an oxygen line (l Ox) separate from the fuel line, both fuel line and oxygen line having a separate outlet at or adjacent to a downstream end (I D) of the body of the oxy-bu rner. The downstream end of the oxy-burner body has a cross section decreasing with the d istance from the body; often the downstream portion has a conical or trunco-conical geometry. The downstream end can be mounted in the burner portion (21 B) of the burner block, with the downstream end being located partly in , or adjacent to the joining portion (2 I F) and being oriented towards the passage of the forehearth. The present invention is particularly adapted for burner blocks supporting an oxy-burner (1 ) because since the flame of an oxy-burner reaches temperatures much higher than trad itional air-burners, the burner blocks wear more rapid ly and need changing more reg ularly. To date, the only two options available when a burner block is damaged is either to condemn it and let one spot without burner during production with the consequent temperature drop at the area su rrounding the condemned burner block, or stop production i n the forehearth passage concerned, dismantle the wall surrounding the condemned burner block, build a new wall section with a new burner block, and re-heat the forehearth passage to service temperature, hT, The latter option requires production to be interrupted for at least one week.

[0057] The downstream ends of the oxi-burners are usually partially engaged into the joining portion (2 1 F) of the burner blocks and thus exposed to the service temperature, hT, in the forehearth . As long as fuel and oxygen flow th rough the corresponding lines, the downstream ends of the oxy-burners are cooled and kept at a safe temperature. In case of an accidental disruption of the flow of either fuel or oxygen, however, the downstream ends are not cooled anymore and they can get thermally degraded by exposure to the service temperature, hT. For this reason, the downstream end of an oxy-bu rner can be fl uidly cooled with a cooling unit (3). As illustrated in Figure 1 1 (b). such cooling un it (3) may comprise :

• a cooling plate made of a thermally conductive material, defined by a fi rst and a second main surfaces separated by a thickness of said cooling plate, and by an aperture extending through said thickness and having a geometry match ing the geometry of the downstream end of the oxy-bu rner to form a thermal contact therewith ; and

• a cooling chan nel defined by walls and comprising an in let and an outlet for circulating a refrigerating fluid, in thermal contact with the cooling plate.

[0058] Generally, each longitudinal wall comprises at least two cavities (28), each cavity containing a support block (20) reversibly engaged therein. In case of burner blocks, each longitudinal wall comprises dozens, even hundreds of burner blocks. The at least two cavities are alig ned horizontally and separated from one another by at least one spacer brick (23). It is preferred that the at least two cavities of the first long itudinal wall face the at least two cavities of the second longitudinal wall in a staggered arrangement. The end wall is likely preferably also provided with a cavity containing a support block (20) reversibly engaged therein.

[0059] A forehearth according to the present invention is greatly advantageous over forehearths of the prior art. As discussed above, i n case a burner block is thermal ly damaged , instead of at least one week of interruption of the production in a forehearth of the prior art, a burner block can be changed in a forehearth according to the present invention with less than half a day interruption of the production : about a quarter of to half an hour to remove the damaged burner block, clean the cavity and replace the burner block by a new one, and a couple of hours to restore the thermal and pressure conditions d isrupted during the change, as well as to give time to the glass melt to evacuate any dust from the refractory bricks and resilient material that may have fallen into the melt du ring the changing operation.

[0060] Other kinds of support blocks, such as a measurement block, a peep hole block or camera block, an injection block; or an atmospheric beam, for controlling the gas flows within the passage, may not be numerous and may not be exposed as intensely to thermal damages as bu rner blocks, in particular for supporting oxy-firing burners, but their positions may be required to vary more often depending on the actual behaviour of the forehearth, which may deviate from the expected behaviour, and thus may req uire such support blocks at other positions than in itially planned. Of course, with an interruption of at least one week with prior art forehearths, it would be excluded to change the position of a support block on ly to get a hopefully better position . With a forehearth according to the present invention , on the other hand, the position of such su pport blocks may be changed more easily.

[0061] A support block can be reversi bly loaded in a forehearth of a glass fibre manufacturing plant as d iscussed supra, by a method comprising :

(A) building a forehearth as defined supra and illustrated in Figure 7, formi ng a passage for conveying molten glass (30) and defined by:

- a first and second opposite longitudinal walls (31 L) having a hot longitudi nal wall surface facing said passage and extending along a longitudinal direction, XI , having a longitudinal wall thickness extending along a first transverse d irection,

X2 , normal to XI , and having a longitudinal wall height extending along a second transverse direction , X3, normal to both XI and X2 ,

- a ceiling (31 T),

- a bottom floor (31 B) and

- an end wall (31 E), wherein building each longitudinal wall comprises:

(a) laying a series of refractory base bricks (32) to form a base wall comprising a top surface,

(b) laying two spacer bricks (23) onto the top surface of the base wall, separated from one another at the level of the hot longitudinal wall surface by a distance, Wc, measured at room temperature (RT) along the longitudinal d irection , XI , each spacer brick having a cuboid geometry comprising a hot surface (23H) forming a portion of the hot longitudi nal wall surface,

(c) providing a lintel (25) of length, WL > Wc, measured along the longitudinal direction, XI , and comprising two opposite ends, and laying each of the two opposite ends onto one of the two spacer bricks, thus defin ing with the base wal l and the two spacer bricks a cavity (28) of width, Wc, and height, H l c, measured at the level of the hot longitudinal wall surface at room temperature along the longitudinal direction, XI , and along the second transverse axis, X3 , respectively, and of depth, Dc, measured at room temperature along the first transverse axis, X2 ,

(d) providing and installing a spacing element that hinders the thermal expansion of the two spacer bricks, such that the distance, Wc, between said two spacer bricks measured at room temperature along the longitudinal d irection, XI , at the level of the hot long itudinal wall surface cannot be reduced below a predetermined d istance, W, at a service temperature, hT, of the forehearth of at least 1 000°C, ,

(B) providing a support block (20) comprising a hot cu boid portion having a cu boid geometry of width , w, and height, h, measured along XI and X3, respectively, at the level of the hot longitudinal wall su rface at a service temperature, hT, of the forehearth of at least 1 000°C, and of depth measured along X2 at least equal to D, wherein w < W < Wc, and h < H l c < H I , said hot cuboid portion comprising four peripheral surfaces meeting two by two at ridges extend ing transverse to the first longitudinal direction, XI ,

(C) as illustrated in Figures 8 and 9(a), coating the four peripheral surfaces of said hot cuboid portion with a layer of resilient material (29), preferably in the form of a sheet, and

(D) reversibly inserting into the cavity the hot cuboid portion of the support block, which peripheral surfaces are coated with the resilient material .

[0062] Fig ure 8 illustrates the method defined supra with a burner block seen from the passage of the forehearth, i.e., looking at the hot surfaces of the spacer bricks (23), whilst Figure 9(a) illustrates the same method seen from the opposite side of a longitudinal wall, looking at the cold surfaces (23C) of the spacer bricks (23). The cavity illustrated in Figure 9(a) has tapered walls as discussed supra, to facilitate insertion and removal of a support block.

[0063] Once in place in a cavity, a su pport block can easi ly be removed therefrom as 5 follows:

(E) removing the su pport block from the cavity by sliding the hot cuboid portion along the first transverse axis, X2 ,

(F) removing any resilient material left in the cavity,

(G) reversibly inserting into the cavity the hot cuboid portion of a new support 10 block as defi ned in (B), which peripheral surfaces are coated with the resilient

material.

REF DESCRIPTION

1 burner or oxy-burner

I D downstream end of oxy-burner

I F Fuel line of oxy-burner

l Ox oxygen line of oxy-burner

20 bu rner block

20C cold surface of burner block

20H hot surface of burner block

21 B burner portion of th rough-passage

21 F flame portion of through-passage

21J joining portion of throug h-passage

23 spacer brick

23C cold surface of spacer brick

23H hot surface of spacer brick

23R recessed surface of spacer brick

23S stepping surface of spacer brick (parallel to X3)

25 lintel

26 base spacer

27 merlon formed by top surface of base wall and separating the spacer bricks

28 cavity

29 resilient material

30 molten g lass

31 passage

31 B passage bottom floor

31 E passage end wall

31 L passage longitudinal wall

31 T passage cei ling

AW = ½ (Wc - W) = restrained thermal expansion

5