Refractory plate

Abstract

The invention concerns a refractory plate, in particular for a system of liquid molten metal flow, comprising at least two zones when considering the main plane of the plate: a passage zone (1) with at least a passage hole (3) for said liquid metal and a composition resistant to stresses resulting from the flow of the liquid metal through the hole (3), and a manoeuvring zone (2) designed to stop the liquid metal flow, and a composition, different from that of the passage zone (1), selected to resist in particular thermal shocks when the flow stops, the zones taking up the entire thickness of the plate wherein the securing link between the passage zone (1) and the manoeuvring zone (2) results from joint pressing, in a common mould, the composition of the passage zone(s) and the composition of the manoeuvring zone (2), the compositions having previously been deposited into the mould respectively along the zones, followed by consolidating heat treatment. The invention also concerns a method for making said plate.

Description

[0001] The present invention relates to a refractory plate, in particular for a system for regulating the flow of a liquid molten metal, comprising at least two zones considering the principal plane of the said plate:

[0002] at least one passage zone

[0003] which comprises at least one passage hole for the said liquid metal, with a composition chosen to withstand in particular stresses due to contact with the said liquid metal flowing through the hole,

[0004] a manoeuvring zone intended to conduct the regulation and provide the stoppage of the flow

[0005] which is intended in particular to stop the flow of the liquid metal, with a composition different from the composition of the passage zone, chosen so as to withstand in particular thermal shocks due to the liquid metal in abutment on this manoeuvring zone in the event of stoppage of the flow, and

[0006] a connection for fixing together the said zones, in order to form a single-piece assembly in which a movement imparted for example to the manoeuvring zone is transmitted univocally to the passage zone or respectively to each passage zone.

[0007] An examination of the damage modes to known refractory plates, due to their use, reveals various types of degradation:

[0008] at the casting hole, radial cracks and a fairly strong erosion of the lips are found,

[0009] in the closure position, the plate is subjected, vertically in line with the molten metal, to a violent thermal shock which generates, under the surface, mechanical stresses which, eventually, lead to flaking.

[0010] As a result these plates must meet criteria of:

[0011] resistance to radial cracking

[0012] resistance to erosion and chemical corrosion

[0013] resistance to thermal shock

[0014] resistance to flaking.

[0015] At the present time, no solution based on a single composition for the entire plate gives full satisfaction from a technical and economic point of view.

[0016] Several documents make mention of plates for metallurgical valves calling on a combination of several materials.

[0017] Thus DE-A-1.935.424 claims a closure device provided with a plate surrounded by a refractory support element with high porosity (50-60%) and with insulating thermal properties.

[0018] EP-0832707 relates to a problem of wear at the sliding surface of the refractory plates used in a flow regulation system in a metallurgical receptacle. This document covers a multilayer refractory body consisting of a high-density wearing layer and at least one other layer with different physical characteristics, the thickness ratio between the wearing layer and the other ranging from 1:2 to 1:5.

[0019] In DE-A-1.937.742, the plate is provided with a housing which receives an insert made from high-hardness metallic material (zirconium oxide/molybdenum composite), fixed to the remainder of the plate by an elastic cement. The role of this insert is to prevent the solidification of the metal during closure by virtue of its high thermal conductivity but it has proved to be not very effective in resistance to erosion.

[0020] The technology of the insert is also set out in DE-A-3.614.730, in which a base structure of the plate surrounds and supports a ceramic insert of the oxide type, by virtue of a mortar fulfilling the role of thermal expansion joint. The basic structure itself consists of a magnesia concrete.

[0021] On the other hand, in DE-A-2.719.105, the ceramic insert is surrounded by an aluminous concrete.

[0022] In this design with insert and cement or installation mortar, the interface between the principal body of the plate and the insert constitutes a weak point which is a great nuisance since it is the subject of corrosion, infiltration of liquid metal, suction of air, etc.

[0023] The aim of the present invention is to remedy the problems which stem both from the presence of this interface and from its design which, for its part, takes up time and requires the use of a cement or mortar with the known special qualities, and in the end does not give the result counted on. For this purpose, the invention proposes a plate on which all the zones are produced simultaneously so as to be intimately interlinked in each other and connected univocally and without the possibility of interstices between them.

[0024] To this end, according to the invention, the said zones each take up the entire thickness of the plate and the fixing connection between the said different zones is the result of co-pressing, that is to say simultaneous pressing, in one and the same mould, of the composition constituting the passage zone or zones and the different composition constituting the manoeuvring zone, the different compositions previously having been disposed in the mould respectively according to the zones. The co-pressing is followed by a consolidation heat treatment.

[0025] As according to the invention the passage zone concerns the entire thickness of the refractory plate, the latter can advantageously be used successively in the recto and verso position, which is not the case in plates with an insert.

[0026] The invention also concerns a method of manufacturing the refractory plate according to the invention, in particular for a system for regulating the flow of a liquid molten metal, comprising at least two zones, considering the principal plane of the said system: at least one passage zone for a first given composition, and a manoeuvring zone for a second given composition, forming the remainder of the plate. Each zone extends over the entire thickness of the plate.

[0027] The method of the invention comprises for this purpose

[0028] the addition in a mould, firstly, of one or more volumes of the composition for the passage zone or zones and, secondly, a volume of the other composition for the manoeuvring zone, complying with the required geometric limits for each corresponding zone, the composition chosen for each zone being identical therein over the entire thickness of the plate,

[0029] simultaneous pressing of the two compositions in the mould in order to give the required shape and compactness to the pressed plate, and

[0030] consolidation heat treatment of the pressed plate.

[0031] In an aforementioned flow regulation system for molten liquid metal, the refractory plate according to the invention can be situated either in the top and/or bottom fixed position or in the bottom or intermediate movable position.

[0032] Other details and particularities of the invention will emerge from the dependant claims and from the description of the drawings which accompany the present document and which, by way of non-limiting examples, illustrate both the plate of the invention and its manufacturing method according to the invention. Amongst other things, the terms “passage” and “manoeuvring” used at the present time are used only to differentiate different types of zone in the embodiments described, without limiting the basis of the invention.

[0033] FIG. 1 shows in plan view an embodiment of a plate of the invention, in which two passage zones are enclosed in what is termed the manoeuvring zone.

[0034] FIG. 2 shows, also in a plan view, another embodiment of a plate of the invention, in which two passage zones are contiguous with a manoeuvring zone and situated on each side of this zone.

[0035] FIG. 3 shows, also in a plan view, a variant of a plate of the invention, in which the passage zone of a given composition is surrounded by a manoeuvring zone of another composition.

[0036] In the various figures, the same reference notations designate identical or similar elements.

[0037] In the design of the refractory plate according to the invention, the passage zone 1, referred to as the part 1 below, and provided with a casting hole 3, has a composition especially designed to withstand the flow of liquid molten metal and the slag which accompanies it whilst the manoeuvring zone 2, referred to as the principal body 2 below, which is not subject to the continuous flow of the molten metal, must be able to withstand the thermal shock incurred when the valve is closed and for example ensure the positioning and/or the movement of the refractory plate. Each of the zones 1 and 2 extends on each occasion over the entire thickness of the plate.

[0038] The part 1 consists of prime-grade refractory grains chosen from the family of alumina, mullites, zirconia and compounds thereof, divided carbon, which may be of the graphite, anthracite, coke or carbon black type, antioxidants and a thermosetting resin.

[0039] The principal body 2, which is fixed to the part 1, consists principally of refractory grains belonging to the silica-alumina system, such as bauxite, andalusite, kyanite and chamotte and/or refractory grains resulting from a recycling process and in particular the recycling of these same cast refractory plates, these grains being coated and bonded by a carbonaceous bonding agent compatible with that used for binding the grains of the part 1.

[0040] As a variant, when the casting conditions and the nature of the metal so require, the refractory grains of the part 1 consist of prime grades of magnesia and/or spinel MgO Al2O3, divided carbon, antioxidants and a thermosetting resin. The refractory grains of the principal body 2 consist advantageously of less noble grades belonging to the same system as those of the part 1 and/or batches resulting from a recycling process and in particular recycling of these same cast refractory plates. These grains of the body 2 are then bonded by a carbonaceous bonding agent compatible with that of the part 1.

[0041] In order to succeed with the production of the single-piece refractory plate according to the invention, it is necessary for the part 1 and the principal body 2, although of different compositions since they fulfil particular respective functions, to be compatible on the manufacturing level, in particular during the different manufacturing steps (co-pressing, stoving, baking) so that the plate has sufficient cohesion between these two constituents 1 and 2 so that in service it behaves as a single-piece assembly.

[0042] In particular, the two compositions of raw materials, special for the part 1 and for the principal body 2 respectively, must have packing densities and pressed densities which are relatively close to each other in order for the co-pressing to succeed, and hence the advantage of using, in whole or in part, in order to produce the principal body 2, recycled materials resulting from a reprocessing of masses coming from plates with the same use.

[0043] Advantageously, the same carbonaceous bonding system will be used to bond the refractory grains of the constituents 1 and 2, namely the same thermosetting resin or two resins compatible rheologically and thermally. This way of proceeding is a method for obtaining a structural bond between part(s) 1 and body 2.

[0044] Given that the part 1 and the principal body 2 undergo different thermal and chemical stresses during service, they are provided with oxidising agents or combinations of oxidising agents adapted to these respective stresses.

[0045] The advantage of the design of the plate of the invention is to reinforce, by means of highly elaborate oxidising systems, only the zones which are actually stressed, without however burdening the cost of producing the refractory plate. According to the geometry of the plate overall and according to the position of the casting hole or holes 3, a different design of the assembly formed by the different compositions will be adopted.

[0046] The part or parts 1 can be situated in an enclosed position in the principal body 2 (FIG. 1) or in an adjacent position with respect to this principal body 2, as illustrated by FIG. 2.

[0047] Likewise, when it is a question of a linear-movement plate with one or more casting holes 3, the enclosed position, shown in FIG. 3, of the part 1 may be preferred.

[0048] In one of the preferred embodiments of the invention, during the pressing operation, either in hydraulic mode or by friction, a thin but rigid accessory can momentarily represent the boundary between the part 1 and the principal body 2 during the phase of depositing of the two compositions in the mould. Once the two compositions have been put in place in their respective housings, the accessory is removed for the pressing proper in order to promote the contact and intimate interlocking of the two compositions at the interface between the part 1 and the principal body 2.

[0049] Such a way of proceeding makes it possible to obtain, both for the part 1 and for the principal body 2, physical characteristics (of density and porosity) which are as high as if they were pressed separately.

[0050] In addition, inspections by microscope and mechanical bending tests on bars sampled from composite pieces produced according to the method of the invention have shown that the interface between the part 1 and the principal body 2 does not constitute a weak point, rupture by bending usually taking place at the part which mechanically is the weakest (the part 1 or the principal body 2 according to circumstances).

[0051] In order to produce the casting hole 3 to the required diameter, either the press is provided with a core representing the said hole 3, or it is obtained by boring in the composite piece produced by pressing.

[0052] The use of a core has several advantages:

[0053] a saving with regard to the quantity of noble mix intended for the part 1,

[0054] no subsequent boring operation nor defects through pulling away or flaking which result therefrom,

[0055] better surface finish of the wall constituting the casting hole 3, favourable to resistance to erosion in service.

[0056] Once the shaping step has ended, the composite pieces are subjected to the conventional operations of stoving, baking in a protected atmosphere (subsequent impregnation with pitch if necessary) and finishing by planing.

[0057] It must be understood that the invention is in no way limited to the embodiments described and that many modifications can be made to these without departing from the scope of the claims.

[0058] Thus the passage zone or zones 1 can be provided, at each casting hole 3, with a nesting and centring system for a refractory piece (not shown) contiguous with the casting system.

[0059] A few peculiarities of the invention will now be illustrated by examples.

EXAMPLE 1 (FIG. 1)

[0060] In this example, it is wished to manufacture a rotary-movement casting plate provided with three casting holes 3.

[0061] Each hole 3 is formed by a part 1, the two parts 1 being located in an enclosed position in a principal body 2.

[0062] To produce the part 1, use was made of a mixture consisting of: 1 white corundum 1-3 mm: 35% white corundum <1 mm: 40% calcined alumina 325 mesh: 15% graphite <150 &mgr;m:  5%

[0063] and, for the balance, thermosetting resin and a set of known antioxidants.

[0064] To produce the body 2, use was made of a mixture consisting of: 2 andalusite 1-3 mm: 40% andalusite <1 mm: 30% andalusite <0.2 mm: 10% calcined alumina 325 mesh: 10% graphite <150 &mgr;m:  3% the balance consisting of the same thermosetting resin and one or more known antioxidants.

[0065] The parts 1 and the principal body 2 are co-pressed on a hydraulic press; the single-piece plate obtained has two parallel principal faces themselves consisting of the coplanar faces of the two constituents 1 and 2. After stoving and baking in a protective atmosphere, the composite refractory plate obtained has all guarantees of cohesion and has an entirely satisfactory behaviour in service.

EXAMPLE 2 (FIG. 2)

[0066] In this example, the same compositions were used as in Example 1 for the parts 1 and the principal body 2 but the parts 1 are situated in adjacent positions with respect to the principal body 2.

[0067] The composite plate according to this design also behaves very well in service.

EXAMPLE 3 (FIG. 3)

[0068] It is wished to produce a refractory plate for a linear slide where the part 1 is situated in an enclosed position in the principal body 2.

[0069] The compositions used for producing the two constituents 1 and 2 are the same as those of Example 1.

EXAMPLE 4

[0070] For this example, the general shape and the design of the plate of the invention are the same as in Example 1, FIG. 1, but this time the composition of the principal body consists of grains resulting from a plate recycling process, to which there is added a carbonaceous agent consisting of graphite to 4%, antioxidant and resin.

[0071] It is found that the chosen option of using recycled grains reinforces the compatibility between the two constituents of the plate thus obtained.

EXAMPLE 5

[0072] For the casting of special steels in which the formation of calcium aluminate is to be avoided, a plate is produced consisting of a part 1 based on magnesia for the aggregate and the fine fraction (90% of the weight), carbon in the form of graphite (5%), resin and antioxidants for the balance.

[0073] The principal body 2 is produced from magnesia aggregates resulting from a recycling process for 75% of the weight, magnesia fines of first usage for 15% of the weight, the carbonaceous agent being the same as for the part 1.

[0074] The invention has been described mainly in the context of zones, different in composition, which are contiguous in the direction of the plane of the drawings in the figures.

Claims

1. Refractory plate, in particular for a system for regulating the flow of a liquid molten metal, comprising at least two zones considering the principal plane of the said plate:

at least one passage zone (1)

which comprises at least one passage hole (3) for the said liquid metal,

with a composition chosen to withstand in particular stresses due to contact with the said liquid metal flowing through the hole (3),

a manoeuvring zone (2) intended to conduct the regulation,

which is intended to stop the flow of the liquid metal, and

with a composition different from the composition of the passage zone (1), chosen so as to withstand in particular thermal shocks due to the liquid metal in abutment on this manoeuvring zone (2) in the event of stoppage of the flow, and

a connection for fixing together the said zones, in order to form a single-piece assembly,

characterised in that the said zones each take up the entire thickness of the plate and the fixing connection between the passage (1) and manoeuvring (2) zones is the result of a co-pressing, in the same mould, of the composition constituting the passage zone or zones (1) and the different composition constituting the manoeuvring zone (2), the different compositions previously having been disposed in the mould respectively according to the zones, followed by a consolidation heat treatment.

2. Refractory plate according to claim 1, characterised in that the passage zone or zones (1) and the manoeuvring zone (2) are directly connected to each other structurally.

3. Refractory plate according to claim 1, characterised in that the casting hole or holes (3) in the passage zone or zones (1) are produced by boring the plate after the co-pressing of the compositions.

4. Refractory plate according to claim 1, characterised in that the casting hole or holes in the passage zone or zones (1) are obtained directly by the use of a core during the co-pressing.

5. Refractory plate according to claim 1, characterised in that the passage zone or zones (1) are enclosed within the manoeuvring zone (2).

6. Refractory plate according to claim 5, characterised in that the enclosed passage zone (1) comprises several casting holes (3).

7. Refractory plate according to claim 1, characterised in that the passage zone or zones (1) and the manoeuvring zone (2) are contiguous.

8. Refractory plate according to claim 1, characterised in that the passage zone or zones (1) are provided, at each casting hole (3), with a nesting and centring system for a refractory piece contiguous with the casting system.

9. Refractory plate according to claim 1, characterised in that the composition of the passage zone or zones (1) consists of

prime-grade refractory grains belonging to the family of alumina, mullite, zirconia and composites thereof,

divided carbon which may be of the graphite, anthracite, coke or carbon black type,

antioxidants, and

a thermosetting resin.

10. Refractory plate according to claim 1, characterised in that the composition of the manoeuvring zone (2) consists of

refractory grains belonging to the silico-alumina system, such as bauxite, andalusite, kyanite and chamotte, and/or

in whole or in part, refractory grains resulting from a recycling process, bonded by a carbonaceous agent compatible with that of the passage zone (1).

11. Refractory plate according to claim 1, characterised in that the composition of the passage zone (1) comprises prime-grade refractory grains of magnesia and/or spinel MgO Al2O3, divided carbon, antioxidants and a thermosetting resin, and in that the composition of the manoeuvring zone (2) comprises less noble refractory grains belonging to the same system as those of the other zone (1) and, in whole or in part, resulting from a recycling process, bonded by a carbonaceous bonding agent compatible with that of the passage zone (1).

12. Method of manufacturing a refractory plate, in particular for a system for regulating the flow of a liquid molten metal, comprising at least two zones, considering the principal plane of the said plate:

at least one passage zone (1) for a first given composition, and

a manoeuvring zone (2) for a second given composition, forming the rest of the plate,

the method being characterised in that it comprises

the addition in a mould, firstly, of one or more volumes of the composition for the passage zone or zones (1) and, secondly, a volume of the other composition for the manoeuvring zone (2), complying with the required geometric limits for each corresponding zone, the composition chosen for each zone being identical therein over the entire thickness of the plate,

simultaneous pressing of the two compositions in the mould in order to give the required shape and compactness to the pressed plate, and

consolidation heat treatment of the pressed plate.

13. Method according to claim 12, characterised in that it comprises

for the separate addition of the compositions, a partitioning of the distinct zones in the mould, and

before pressing, a removal of the partitioning.

14. Method according to one or other of claims 12 and 13, characterised in that, after the pressing of the plate, the casting hole or holes (3) are produced by boring.

15. Method according to one or other of claims 12 and 13, characterised in that it comprises, in order to make the casting hole or holes (3), the use of a moulding core.