IL33085A

IL33085A - Furnace for molten metal

Info

Publication number: IL33085A
Application number: IL33085A
Authority: IL
Original assignee: Glaverbel
Priority date: 1968-10-04
Filing date: 1969-09-29
Publication date: 1973-01-30
Also published as: DE1950006A1; FR2032262A1; DK138090B; ES393254A1; PL80279B1; GB1289175A; DE1950006B2; IE33897B1; US3655356A; AT314125B; DK138090C; BR6912972D0; IE33897L; NL6915048A; FI50615C; CA939146A; JPS4823328B1; SE373350B; FI50615B; DE1950006C3

Description

F U R H A 0 I FOR MOLTEN METAL ronn1? V 3 The invention relates to a furnace having walls made of refractory blocks.

Current practice requires a lot of time for the construction of a furnace wall made of refractory blocks, particularly when the blocks have to be individually secured to a supporting structure, e.g. a skeletal framework or metal walls. When the furnace is intended to contain a bath of liquid material having a higher density than that of the refractory blocks, each of the blocks must be firmly anchored to prevent it from becoming detached from the supporting structure by the buoyancy forces. This applies inter alia to tank furnaces containing molten metal. To make sure that the blocks are secured, it has been proposed to form them with one or more recesses, in each of which one end of an attaching member, for instance a clamp or a tie-rod, is inserted and cemented with a refractory cement; the projecting ends of the attaching members are connected to the furnace supporting structure, for instance, by bolting or welding.

This practice has the following disadvantage: the cement bonds between the blocks and the attaching members are weak points which are liable to deteriorate under working conditions, e.g. the heat. If any of the blocks becomes detached the furnace structure is exposed and may be seriously damaged by the direct contact with the furnace contents, e.g. molten metal. This situation can arise in a furnace containing a bath of molten metal such as tin, in which flat glass is produced by the float process.

Even after attaching the refractory blocks the construction of the furnace is not yet complete, since as a rule thermal conditioning systems must be installed which usually include components which have to be disposed inside the furnace. These members extend through the furnace walls and their installation gives rise to hermetic sealing problems. In the particular case of a float glass furnace, the atmosphere of the float tank must be carefully insulated from the outside atmosphere to prevent the metal bath from becoming oxidised and spoiling the surface quality of the glass ribbon formed.

The present invention enables at least some of these disadvantages to be obviated.

According to the invention at least one wall of the furance is formed at least in part by a refractory block having at least one passageway through which fluid medium can be conveyed through said block, said passageway being traversed by at least one member by which such block is anchored to a supporting structure. By means of this invention, furnace erection can be simplified and accelerated. Reliance on a cement bond between an attaching member and a block is obviated.

Preferably at least one wall of the furnace is formed at least in part by an assembly of refractory blocks which are traversed by at least one passageway through which fluid medium can be passed, and which is also traversed by at least one said anchoring member common to the blocks of said assembly. Furnace erection is in that case particularly simple.

Refractory blocks can readily be manufactured (e.g., cast) with a hole or channel ready to serve as a passageway or part of a passageway for fluid medium and an anchoring member. Alternatively the required hole or channel can be formed in a solid refractory block after its manufacture.

Any given wall of a furnace can comprise a plurality of blocks or block assemblies traversed by anchoring members as above referred to. For example the bottom of a furnace may be composed of a plurality of such assemblies of blocks arranged side by side and extending transversely of the furnace.

If desired one or more refractory blocks may be moulded or cast onto the anchoring member or members to form a structural unit. This is appropriate if the refractory blocks and anchoring member or members are not liable to undergo appreciable expansion. Constructional work is facilitated however if the block or blocks is or are merely "threaded" onto the anchoring member or members or the latter member or members is or are threaded through the block or blocks. There may be substantial clearance between the walls of the passageway or passageways through the block or blocks and the anchoring member or members. Thus it is not essential for the anchoring member or members to entirely prevent movement of the block or blocks. It suffices if the said member ormembers serve(s) to prevent the block or blocks from coining adrift from its proper place, or from their proper places, in the structure. The block or blocks may be held by supplementary means, e.g., cementing, but the anchoring member or members make reliance on any such supplementary means unnecessary.

The construction of a furnace wall can be greatly speeded up by using assemblies of blocks as specifed, since there is no longer any need to secure each block individually to the furnace structure. In some cases the assembly can be fixed simply by its ends to the supporting structure of the furnace.

The or each block or assembly of blocks may be held to the support structure of the furnace at the ends of the anchoring member or members. In the case of a block assembly of appreciable length, connecting members may extend between neighbouring blocks and couple the support structure to points of the anchoring member or members intermediate the ends of the assembly. Only a few such connecting members are required, even with a long span, and a single such connecting member at a central region of the assembly will often suffice.

The invention also affords another substantial advantage, namely that thermal conditioning can be effected by conveying fluid medium along at least one passageway through the block or blocks. Such passageway may be defined by the block or blocks. Thus, the block or blocks may have a passageway there-through which is traversed by an anchoring member of cross-sectional dimensions such that fluid medium can flow.along the block or blocks between such anchoring member and the wall of the passageway. Alternatively the passageway may be traversed by an anchoring member which is itself of tubular form and serves as a conduit to convey thermal conditioning medium. Such a conduit need not extend along the full length of the block or block assembly. A conduit or passageway or means associted with it may be designed to permit thermal conditioning to be applied selectively or differentially along the block or block assembly, e.g. , for regulating the temperature in a float tank both longitudinally and transversely, in accordance with the required temperature curves.

At least one conduit or passageway may have differential conditioning elements which can be formed by localised heat insulations disposed in the conduit or passageway of the block or block assembly; and/or by electrical resistances and/or coolers disposed therein.

The invention includes a process for thermally conditioning an interior face of at least one part of a furnace wall comprising one or more refractory blocks with a passageway or passageways as hereinbefore defined, such process being characterised in that there is circulated in said passageway or passageways a fluid having temperatures substantially different from those of the boundary faces of the said passageway or passageways so as to exert a thermal action which is substantially non-uniform along the length of such passageway or passageways. Advantageously,, substantially more heat is transferred in the central zone of the furnace wall than in the lateral zones.

In a float glass process wherein molten glass floats and cools on a liquid, it is particularly advantageous for the sole of the float tank to be thermally controlled by fluid exercising a non-uniform cooling action along the length of the fluid flow passageway or passageways as above referred to.

In a simple embodiment, the thermal conditioning element comprises at least one duct formed by an anchoring member providing a fluid-circulating conditioning conduit. In a variant, at least one duct formed by an anchoring member contains a fluid-circulating conditioning conduit extending over some or all of the length of the block or block assembly. Such a conduit can be hairpin-shaped when the thermal conditioning must be differential, In an advantageous embodiment, a passageway in the block or block assembly contains a fluid-circulating tube which extends over some or all of the length of the block or block assembly and is formed with fluid-blowing orifices. For differential conditioning, the distance apart of the orifices, measured along the tube axis, may diminish from the ends of the block or block assembly towards its centre, so that more heat can be extracted at the centre of the block or block assembly than at its ends. Moreover, a perforated tube of the kind specified can have at least one mobile orifice-masking member, e.g., a sleeve, enabling the amount of fluid discharged through the orifices to be controlled.

Thermal conditioning enables the temperature of the refractory blocks and therefore their behaviour to be controlled. Moreover furnace chamber thermal conditioning elements can be dispensed with or their number can be reduced. This is particularly of importance if the interior of the tank has to be sealed from the outside atmosphere, as in the case of a float glass tank* More particularly in the case of a float tank, a thermal conditioning system using passageways in one or more assemblies of refractory blocks can be employed instead of the coolers usually situated above the glass ribbon. That is an important advantage because cooling, when achieved by such upper coolers, has to be restricted in order to obviate the occurrence of defects in the glass such as wave and drawn-out wave (discontinuous lines) which sometimes spoil the optical quality of longitudinally drawn thin glass. One effect of thus restricting the cooling is a tendency for highly vitreous drops of glass, which has a composition very different from that of the float glass product, to form at the internal faces of the refractory blocks from vitreous phases within the blocke, and to rise and become drawn out into fine fibres between the refractory blocks and the float glass. Thermal conditioning elements disposed in at least one passageway traversing the blocks also obviate the need for locating thermal conditioning elements in the tin bath. The location of elements within the bath is a disadvantage because of the need for the tubes to be made of special metal to resist corrosion and the need for the bath depth to be appreciably greater than is otherwise required, merely to accommodate the said elements. When thermal conditioning is achieved by means of cooling medium traversing at least one passageway in the blocks, the temperature of the tin bath can be readil regulated both longitudinally and transversely as will hereafter be exemplified, and the tank can be shortened. The cooling can be made greater to\vards the longitudinal central zone of the tank so that compensatory heating at the side regions to avoid excessive cooling of the sheet edges is avoided.

Clearly, although the blocks of an assembly can be mounted on a single anchoring member, two or more such members may traverse such blocks. In the latter case, the cross-section of each of the anchoring members can be smaller than if a single member is used. The holes extending through the blocks can therefore be of smaller sections with the result that there is less mechanical weakening of the blocks.

Advantageously, at least one anchoring member for the or each block or assembly of blocks is in the form of an angle iron. The section of the angle iron can e.g., be of U-shape or a saltire cross. For accommadating such an angle iron the or each block may have a hole shaped so as to leave one or more passageways between the angle iron and the wall of the hole for the conveyance of fluid medium. As a result, the conditioning fluid can be brought into direct contact with the refractory block or blocks. The block or blocks can be satisfactorily located by an angle iron. For instance, a U-shaped angle iron will satisfactorily locate blocks with holes of rectangular section, if, e.g., the base of the "U" lies against one wall of the hole while the parallel limbs of the "U" are close to the adjacent parallel walls of the hole and prevent the blocks from tilting around the anchoring member.

Instead of using an angle iron as an anchoring member, a tubular member may be used, as already referred to. The tube may be imperforate so that a conditioning fluid can circulate through the tube without contacting the refractory block or blocks. This is required when a liquid conditioning medium is used which must not come into contact with the refractory block or blocks. This feature is also advantageous, because if a block becomes cracked while the furnace holds a bath of molten metal, the metal cannot enter the conditioning system.

The block or blocks need not actually have holes for accommodating an anchoring member. As an alternative, the or each block may have a channel or passageway which is open at one side of the block and which is of angled cross-section to provide an internal branch, and the anchoring member may traverse such branch so that the block or any of them can be disengaged from such member by successive movements of the block in different directions. The anchoring member may in this case be installed first, during the construction of the furnace, and connected, e.g., by its ends, to the furnace support structure, and the block or blocks can then be fitted to the anchoring member.

For instance, if the or each block has a channel of inverted L-section, the or each block is fitted to the anchoring member by a first vertical translation movement in which the said member moves along the vertical arm of the L, and a second horizontal translation movement to engage such member in the horizontal arm of the L.

In the case that the anchoring member anchors a plurality of blocks, it is not necessary for the blocks of the assembly to be identical or to be connected to the anchoring member or members in the same way. For example, end blocks of an assembly can be moulded onto an anchoring member while intermediate blocks are simply threaded onto such member or interlocked with it in the manner just described.

Advantageously, the block or block assembly is mounted on an anchoring member, e.g., a tube, which has a polygonal section. An arrangement of this kind completely prevents the refractory block or blocks from rotating around the anchoring member.

If a block or blocks traversed by an anchoring member in accordance with the invention forms part of the bottom wall of a furnace containing a molten material of higher density than the refractory block or blocks, at least the ends of the anchoring member are advantageously secured to the wall-supporting structure. Also advantageously, more particularly for block assemblies having a long span, the assembly is provided with one or more attaching members which anchor the assembly to the supporting structure at various places along the span. For instance, the assembly can have an attaching member in the centre of its span. If the blocks are cast or moulded onto the anchoring member, one or more attaching members, e.g., in the form of a clamp, can be fixed beforehand to the anchoring member so that in the final assembly, the attaching member or members is or are embedded in one or more refractory blocks.

Alternatively the or each attaching member can be an attaching claw one end of which is welded, screwed or riveted to the anchoring member, the other end being made unitary with the structure by a foot retained by members which are welded to the furnace-supporting structure and allow the assembly a certain amount of clearance to take up the displacements of the assembly perpendicular to itself as a result of the expansion of the refractory blocks. In another example, an attaching member may comprise a collar surrounding the anchoring member and having a stem with a screwthreaded end which is engaged in a slot in the furnace-supporting structure, also to allow the assembly some clearance, the collar being attached by a packing bolt. Clearly, these are only examples of methods of attachment and other methods may be employed.

Advantageously, the face of at least one refractory block adapted to come into contact with at least a portion of the contents ' of the furnace is clad or covered with at least one member having a thermal conductivity and/or a density greater than that of the refractory block. This is particularly useful in the case of a block or block assembly forming the whole or part of the bottom of the furnace. Such a lining can serve to i-fiprove the thermal homogeneity of a tin bath and/or act as a ballast to the block or blocks and/or to protect the joints between adjacent refractory blocks.

Preferably tungsten plates are used for this purpose.

In some cases there may be a layer of blocks (e.g. thermally insulating blocks) between the block( s) held by the anchoring member or members and the exterior of the furnace. A combination of silico-clay ( insulating) blocks and carbon ( anchored) blocks is an example. The carbon blocks promote the carrying away of heat when required from the molten metal in the furnace towards the exterior of the furnace through the intermediary of the fluid cooling medium flowing through the passageway( s) in such blocks whereas the insulating blocks permit high heat retention in the furnace at other times.

In a furnace according to the invention two or more block or block assemblies as hereinbefore referred to can be disposed side-by-side to form the whole or a portion of a wall of the furnace and/or a number of such blocks or block assemblies can be arranged in a number of superimposed layers. When the furnace wall comprises two or more layers of blocks, blocks traversed by anchoring members according to the invention may be used for all or only one of the layers, preferably the layer which is best able to stand up to the forces ( gravity, Archimedean force, etc.). For walls of furnaces having a large span, at least two blocks or block assemblies can be disposed end to end, the corresponding anchoring members being joined.

The refractory block or blocks anchored according to the invention_ can be of any refractory material, for instance, carbon or silico-aluminous blocks.

Although the invention will be described hereinafter with particular reference to float Hanks, it clearly also applies to other furnaces used either in the glass-making industry or the foundry and metallurgical industries.

A number of embodiments of the invention will now be described with reference to the accompanying drawings, wherein.

Fig. 1 is a longitudinal section through a float tank] Fig, 2 is a partial longitudinal vertical section, on a larger scale through the bottom wall of a float tank, on line II-II in Fig. 3; Fig. is a vertical section of the same bottom wall, on line III-III in Fig. 2; Figs.4-6 are sections similar to Fig. 3> of walls of other furnaces according to the invention; and Figs. 7-12 show various forms of refractory blocks and anchoring members.

Fig. 1 is a simplified diagrammatic longitudinal section through a float glass apparatus. The apparatus comprises a melting tank 1, a float tank 2 and an annealing lehr 3· The float tank is formed by a bottom 1+, a crown 5> side walls 6 and end walls 7> 8 separated from the crown 5 *>y slots.9, 10. All these members of the float tank 2 are made of refractory materials. A metal wall 11 hermetically encloses the bottom and the side walls 6 and end walls 7J 8 of the tank, which contains a bath of molten material 12.

Molten glass from the bath of glass 13 in the melting tank 1 is cast therefrom over a casting lip 1 between casting rollers 15> 16 which shape a glass ribbon 17. The glass ribbon 17 is then conveyed by a series of transporting rollers 18 to slot 9 of the float tank, and is deposited on the bath of molten material 12 while continuing to move in the direction indicated by the arrow X. The glass ribbon is given a fire polish on the bath of molten material 12. The bath of molten material 12 can be formed by a molten salt but is advantageously formed by a metal, such as silver or tin.

The glass ribbon moves towards slot 10 of the float tank, and is conveyed by rollers 19 to an annealing lehr 3· Figs, 2 and 3 illustrate a wall construction which can be used in making a float tank, as illustrated in Fig. 1.

Refractory blocks 33 are disposed in rows of side by side blocks over a metal wall 31 covered with cementing 32, the rows extending transversely of the float tank. Figs. 2 and 3 show one row of blocks. A hole 3 forming a duct of rectangular section extends right through each block. The end blocks of the lines back up against metal side walls 35 , 36 covered with cementing 37. A rectangular section tube 38 extends through the ducts of the aligned blocks, leaving a small clearance around the tube. The tube 38 thus forms an anchoring member for the blocks of the row. The ends of the tube 38 extend through "the side walls 35> 36 via holes 39 , 40 therein. The tube 38 is supported at its ends outside the tank by fixing members, shown diagrammatically at 41 and 42, which permit axial elongation of the tube consequent upon its thermal expansion.

Refractory blocks 46, 47 are disposed on the end blocks of the row3 against the corresponding side walls 35, 36. The blocks 46, 47 and the blocks 33 of the assembly form a tank for a bath of molten material 48 on which a glass ribbon 49 floats and sl ides in the direction indicated by the arrow X.

Tungsten plates 50, which are denser than I e bath of molten material 48, are disposed on the blocks 33 of the assemblies. The plates 0 have higher thermal conductivity than that of the refractory blocks, and promote the thermal homogenisation of the bath 8. The plates also act as ballast, for the assembly, and protect the joints between -the refractory blocks 33 · A fluid-circulating conduit 43 is disposed inside the tube 38 serving as anchoring member for the blocks. The conduit 43 is formed with orifices 44 via -which the fluid is discharged on to the inner surface of the tube 38. The orifices 44 are orientated towards the upper portion of the tube 38, i.e. the portion which is nearest to the bath 48. At the central portion of the span, the orifices are more closely spaced than at its ends, so as to reduce or control temperature gradients transversely of the bath 48.

Moreovera displaceable heat-insulating sleeves 45 can be provided on the conduit 43 > preferably at the end portions of the conduit. The sleeves 45 limit the discharge of fluid at the places where the sleeves are disposed; they enable the transverse temperature gradient to be regulated as required. Moreover, the temperature gradient along the float tank can be very effectively controlled, thus reducing the length of the tank, by controlling the temperature and/or the flow of fluid in -the tubes 43 traversing the juxtaposed rows of blocks.

Each row of blocks and its anchoring member can be assembled at the site where ihe tank is installed. In that case the refractory blocks 33 > •which have already been formed with holes 34 J are placed in parallel rows on the tank bottom 31 covered with the cementing 32. The side walls 35, 36, formed with holes 39 , 40 , are then placed against "the end blocks with the interposition of the cement 37, -whereafter a tube 38 acting as anchoring member is passed endwise through each hole 39 in the side wall 3 through the holes 34· in the aligned blocks, and through the hole 40 in the other side wall 36 of the tank. Attaching members 41» 42 are then fitted onto the projecting portions of the tubes 38. The thermal conditioning conduits 43 and their heat insulating sleeves 45 can then readily be slid into the tubes 38. Lastly, refractory blocks 46, 47 are placed on the end blocks of each assembly. The assemblies thus built up form tiie bottom and side walls of the tank.

Alternatively, the assemblies can be formed prior to transportation of the components to the site of "the float tank, for instance in an assembly shop. For example, the blocks may be disposed in rows, and the tubes 38 then slid through the holes in the blocks. Alternatively the blocks can be threaded on to the tubes which are to serve as anchoring members. In another possible way of applying the invention, a single refractory block is moulded on the tube 38. Such a construction is useful for small spans. After being made up in the assembly shop, the combinations of anchoring members and blocks can be stored ready for transportation to the erection site where they are used to form a tank wall as above described.

Reference is now made to Fig. 4» in. which parts corresponding with parts of the Fig. structure are denoted by the same numerals as in that figure. These parts are the tank metal bottom 31> the cementing 32, the refractory blocks 33, the hole 34 i the blocks, the tank side wall 35 > the cementing 37 of the side wall 35» the tube 38 acting as an anchoring member, the refractory block 46 placed on the end block of the assembly, the bath of molten material 48 and the glass ribbon 49.

As shown in Fig. , the side wall 35 is not unitary with the metal bottom 31. A compensating system 55 shown diagrammatically, and formed, for instance, by resilient elements, such as springs or resilient washers, takes the thrust on the side wall 3 caused by the expansion of -the refractory blocks. A washer 6 separates the side wall 35 from the compensating system 55. The tube 38 serving as anchoring member is supported by an attaching member 57, also shown diagrammatically, such attaching member being unitary with the tank metal bottom 31.

In the embodiment shown in Fig. 4> the thermal conditioning system for the bath 8 comprises tubes 58 through which water is circulated, these tubes extending through the tubes 38. Sleeves 59 which can move over the tube 8 are provided to enable the thermal gradient transversely of the bath to be controlled. The sleeves 59 form a heat insulation which controls the transmission of heat between the water circulating in the tube 58 and the ti bath.

Fig. 5 is an analagous partial view showing a member for attaching the assembly to the tank metal bottom 31; the attaching member can be advantageously disposed at various places over the span, for instance in its centre. Fig. 5 shows cementing 32, two refractory blocks 33 disposed side by side (the space between them is exaggerated to make the drawing clearer) , a bath of molten material 8, a glass ribbon 49j the hole 34 in "the blocks and the tube 38 serving as anchoring member.

The hole 3 and the tube 38 are of circular section. The attaching member disposed between two adjacent blocks comprises a - ' collar 61 surrounding the tube 38 and having a stem 62 with a screw-threaded end 3 which extends through a slot 64 in the metal bottom 31 and is fitted with a nut 65 bearing against a washer 66. The slot 6 allows movement of the assembly perpendicularly to itself, i.e. in the longitudinal direction of the tank. The adjoining faces of the two refractory blocks 33 are formed with recesses 67 to accommodate the attaching member.

Pig. 6, which is similar to Pig. 5> shows an alternative system for attaching the assembly to the metal bottom 31. Pig* 6 shows the cementing 32> two adjacent refractory blocks 33 the bath of molten material 8, the glass ribbon 49» the hole 34 in the blocks, and the tube 38 serving an anchoring member. In this case the attaching member disposed between two adjacent blocks comprises an attaching lug 70 welded as at 71 to the lower face of the tube 38. The attaching lug 70 has a foot 72 which is retained by two angle irons 73 of appropriate shape welded to the tank metal bottom. The attaching system 70 , 72 also allows free displacement of the assembly perpendicularly to itself.

Pigs. 7-12 show various possible sections of "the holes 34 in the refractory blocks 33* an of ihe anchoring members. In the embodiment shown in Pig. 7> the sections of the hole and the anchoring tube are circular and there is clearance between the anchoring tube and the wall of the hole in the block. In the Pig. 8 embodiment, the sections are square and again there is clearance around the tube. In the form shown in Pig. 9 the block has a channel with a bend, In this case, each refractory block is fitted onto the Square anchoring tube by a vertical translation movement in -which the tube enters the channel in the direction X , followed by a horizontal translation movement to cause the tube to move in the direction Y relative to "the block. This method of ■ attachment is advantageous when a block of the assembly is to be replaced or the assembly is to be mounted without displacing the anchoring tube. In the embodiment shown in Fig. 10 , the block has three holes 82-¾. of smaller section than ttie holes in the blocks previously described. The holes 83 , 84 do not house anchoring members but a conditioning fluid, such as air, can circulate therein. The hole 82 houses an anchoring tube 38 in this case the upper portion of the blocks is conditioned more satisfactorily.

In the form of assembly shown in Fig. 11, the hole in the block is of rectangular section. An angle iron 80 in ty form of a sal tire cross is disposed in the hole to produce four ducts 81 through which the conditioning fluid can circulate.

In the form shown in Fig.12, the angle iron 80 is U-shaped and defines with the wall of the block a fluid-circulating duct.

Clearly, the invention is not limited to these embodiments , which have been given simply by way of example.

Claims

WHAT IS CLAIMED IS:

1. A furnace having at least one wall comprising at least one refractory block, which is traversed by at least one passageway through which fluid medium can be conveyed through said block, said passageway being traversed by at least one member by which such block is anchored to a supporting structure, characterized thereby that the said passageway comprises also means for circulating a thermally conditioning fluid medium across said block.

2. A furnace according to Claim 1, characterized in thfct at least one wall of the furnace is formed at least in part by an assembly of refractory blocks traversed by at least one passageway through which fluid medium can be conveyed through such blocks and which passageway is traversed by at least one member by which such blocks are anchored to a supporting structure.

3. A furnace according to Claim 1 or 2, characterized in that there is a said anchoring member in the form of a tube.

4. A furnace according to any of Claims 1 or 2, characterized in that there is a said anchoring member in the form of an angle iron.

5. A furnace according to any preceding claim, characterized in that there is at least one said refractory block which has been moulded onto a said anchoring member.

6. A furnace according to any preceding claim, characterized in that a said anchoring member traverses at least one block with clearance.

7. A furnace according to claim 6, characterised in that there is a said anchoring member which traverses at least one block with clearance, the passageway and the said member having polygonal cross-sections of such dimensions that turning movement of such blocks is prevented or restricted.

8. A furnace according to any of claims 1 to 7, characterised in that there is at least one said refractory block having a passageway which is open at one side of such block and which is angled in cross-section to provide an internal branch, and said branch is traversed by a said anchoring member from which such block can be disengaged by successive movements of the block in different directions.

9. A furnace according to any preceding claim, characterised in that there is a plurality of refractory blocks traversed by a said anchoring member and at least one connecting piece extends between neighbouring blocks of such assembly and connects said anchoring member to a supporting structure.

10. A furnace according to any preceding claim, characterised in that there is at least one said passageway with which inermal conditioning means is associated.

11. A furnace according to claim 10, characterised in that there is at least one said passageway with which differential thermal conditioning means is associated.

12. A furnace according to claim 11, characterised in that there is at least one said passageway in which heat-insulating means is disposed.

13. A furnace ac<∞rding to claim 10 or 11, characterised in that there is at least one said passageway with which electrical resistance heating means is associated.

14. A furnace according to any preceding claim, characterised in that there is a said anchoring member of tubular form and means is provided for circulating fluid through such member for thermal conditioning purposes.

15. A furnace according to any of claims 1 to 13, characterised in that there is a said anchoring member of tubular form which accommodates a conduit extending along the whole or part of the block or block assembly, and means is provided for circulating fluid through such conduit for thermal conditioning purposes.

16. A furnace according to claim 15, characterised in that said conduit has fluid discharge orifices at positions within the block or block assembly.

17. · A furnace according to claim 16, characterised in that the block or block assembly forms part of the bottom of the furnace and extends transversely thereof and there is a series of said orifices arranged so that the spacing between successive orifices diminishes from the ends of the block or block assembly towards its centre,

18. A furnace according to claim 16 or 17, characterised in that said conduit is fitted with an orifice-masking member which is displaceable along the conduit for controlling the discharge of fluid from the conduit.

19. 1 . A furnace according to any preceding claim, characterised in that at the interior of the furnace at least one block is covered by a member having a thermal conductivity and/or density greater than that of such block.

20. A furnace according to claim 19, characterised in that a said covering member composed of tungsten is present.

21. A furnace according to any preceding claim, characterised in that said block or assembly of blocks traversed by an anchoring member is one of at least two such blocks or block assemblies disposed side by side and/or superimposed.

22. A furnace according to any preceding claim, characterised in that said block or assembly of blocks traversed by an anchoring member is one of at least two such blocks or block assemblies disposed in mutual alignment and having their anchoring members joined together.

23. A furnace according to any preceding claim, characterised in that there is at least one said block or block assembly forming at least part of the bottom of the furnace and the latter holds molten medium with a density greater than the densities of said block or blocks.

24. 2 . A furnace according to claim 23 , vshen used for the manufacture of flat glass by the float process.

25. A furnace having at least one wall which is formed at least in part by a block or assembly of blocks as specified in claim 1 or 2 and which is substantially as herein described with reference to the accompanying drawings.

26. A furnace constructed substantially as herein described with reference to the accompanying drawings.

27. A process for thermally conditioning an interior face of at least one part of a furnace wall constituted according to any preceding claim, characterised in that there is circulated in the said passageway or passageways a fluid having temperatures substantially different from those of the boundary faces of the said passageway or passageways so as to exert a thermal action substantially non-uniform along the length of the said passageway or passageways.

28. , A process according to claim 27» characterised in that substantially more heat is transferred in the central zone of the furnace wall than in the lateral zones.

29. A process for tiie production of flat glass by floating and cooling molten glass on a liquid characterised in that the temperatures of at least one part of the sole of the float tank are controlled according to the process claimed in claim 27 or 28. tto rney s f o r A p p l i c a n t