GB2083896A - Refractory blocks for metal pouring vessels - Google Patents

Abstract

A well block (30) for a metal pouring vessel is a unitary body having a passage (32) therein for molten metal flow from the vessel; the body (30) is a cementitious composite made from at least two different concretes (37, 39) which are successively cast one in contact with the other followed by curing to bond them together. The concrete (39) forming part of the well block including its discharge end is of low thermal conductivity and heat capacity and is less highly refractory than the concrete (37) forming the part of the well block which in use is exposed to the metal contained in the vessel. <IMAGE>

Description

SPECIFICATION Refractory blocks for metal pouring vessels The present invention relates to refractory blocks for metal pouring vessels Vessels such as ladles, tundishes and other molten-metal pouring vessels employed e.g. in the steel industry commonly have pour openings in or adjacent their bottoms. Such vessels have refractory linings in which well blocks are seated in juxtaposition to the openings, such that the well blocks and associated bore or nozzle liners guide and define the stream of melt as it pours from the vessel. The pouring rate can be controlied by sliding gate valves. In some cases a special purpose well block may coact with a stopper rod to control flow rate, the well block providing a seating for the stopper rod.

Other special purpose blocks of design and shape similar to well blocks may be incorporated into vessel bottoms, in recesses or wells therein. Such blocks may be used as carriers for gas-permeable bricks which frequently serve as means for introducing gases into the molten metal. If gases and particulate matter are to be introduced into the molten metal, such blocks can be used as mounts for gas/particle conduits or lances.

Well blocks are of quite considerable size and weight, and for convenience of installation have often been multipart constructions. In practice, components of the known well blocks have been cemented together during their assembly in their vessel linings. Assembly is relatively-speaking time consuming and, more seriously, freedom from defects cannot be guaranteed. The presence of cement joints between well block components introduces a significant risk of dangerous break-out i.e. leakage and escape of molten metal.

Manipulation of heavy well blocks need not, in our view be particularly bothersome for lifting equipment suitable for this purpose or adaptable to suit abounds.

An object of this invention is therefore to provide a well block which is unlikely to be the cause of breakout, and which is easy and economical to manufacture.

According to the present invention, there is provided a well block for a molten metal pouring vessel, which is a unitary refractory body having a flow passage extending therethrough from a passage entry, the body being cast cementitious composite made from at least two different refractory material masses adjoining and bonded to each other, the refractory mass in the region of the entry being of higher duty than the refractory mass in the region of the opposite end of the well block, the latter mass having lower heat capacity and thermal conductivity than the higher duty refractory mass.

The well block entry can be flared, e.g. frusto-conically. If the well block is to co-operate with a stopper rod, a curved flare, in the manner of the bell of a trumpet, can form the passage entry.

Also according to the present invention, there is provided a refractory block to form means for admitting substances to molten metal in a molten metal pouring vessel, said block being a unitary refractory body consisting of a cast cementitious composite and made from at least two different refractory material masses adjoining and bonded to each other, the refractory mass at one end of the block, which in use is the end to be exposed to the molten metal in the vessel, being of higher duty than the refractory mass forming the remainder of the block the latter mass having lower heat capacity and thermal conductivity than the higher duty refractory mass. Such a block has a passage therein, e.g.

shaped to receive a gas-porous plug; externally pressurised gas applied to the plug permeates therethrough to enter the molten metal. Alternatively, a lance pipe may be mounted in the passage for conveying gas/particulate mixtures into the molten metal.

In the simplest form, blocks according to the invention are made from only two successively-cast refractory masses, although three or more such masses could be used if warranted by manufacturing or service conditions.

High and low duty, as these terms are used herein, refer to the relative ability of the refractory materials to withstand the rigrous of the molten metal environment to which they are exposed, and are related to the refractoriness of the said materials. In a well block, the entry end is the portion exposed to the highest temperature, since it is contacted by molten metal within the vessel, and is the portion most likely to be eroded by molten metal as it sluices into the flow passage. Extremes of temperature may be encountered by the entry end, too, on occasions when frozen metal in the pour opening region has to be burned free by oxygen lancing. All these conditions require that high duty material be used to form the upstream portion of the well block.

The conditions existing at the opposite, downstream end of the well block are less severe and for this reason it is possible to economise by using cheaper, lower duty refractories of lower thermal conductivity. Using such refractories minimises heat losses from the pouring metal stream to the ladle casing and surroundings, and helps to mitigate against freezing of metal or metal oxides in the flow passage. Deleterious freezing can be especially troublesome when pouring certain steels, notably aluminium-killed steels. When pouring rate is to be controlled by undermounted sliding gate valves, use of low conductivity refractory at the downstream end of the well block is considered to be advantageous, since it may lead to less stringent valve cooling needs.

The refractory masses are advantageously chemically, e.g. phosphate, bonded concretes although hydraulically bonded concretes could be used. Such materials need no high temperature firings to bond them into coherent bodies, and so substantial saving in energy and hence in manufacturing costs can be realised.

The invention comprehends a molten metal pouring vessel, e.g a ladle, embodying a block according to the invention. To control metal flow from the vessel, a sliding gate valve may be fitted thereto in registry with a well block according to the invention.

There will now be described, by way of example only with reference to the accompanying drawings, a preferred embodiment of the invention. In the drawings: Fig. 1 shows in cross-section a portion of a metal pouring ladle mounting a sliding gate valve, the ladle incorporating a known well block structure: and Fig. 2 is a longitudinal sectional view through a ladle well block assembly incorporating a well block according to the invention.

The illustrated metal pouring vessel 10, see Fig. 1, is a ladle having a metal casing 11 and a refractory brick lining 12. A pour opening 1 4 of the ladle 10 is occupied by a well block structure 1 5 seated in the lining and defining a passageway 16 through which molten metal may teem from the ladle, The well block structure conveys molten metal to a gate valve 1 7 which, by appropriate shifting of a valve slide plate 1 8 relative to a stationary valve plate 19, is opened or closed to control metal flow from the ladle. The illustrated valve is of known type commercially available from Flogates Limited, under the FLO-CON registered trade mark and will not be described in detail here. However, the type of valve employed is not a limiting factor to the use of the invention.

The well block structure 1 5 is known, and comprises several refractory elements cemented to one another and to the lining 11 to wit: an upper well block 20, a lower well block 21, a spigot 22 and in this case a nozzle sleeve 23. The spigot 22 registers with an aperture in a metal mounting plate 24 for the valve 1 7 and seats in a groove in the stationary plate 19, and the sleeve 23 abuts the same plate. All internal joints of the well block structure, joints between the said structure and the lining 12, and joints between the spigot and sleeve and the plate 19, should be safe against leakage of molten metal, but are potential sources of extremely dangerous break-out.

The foregoing well block is in two parts, 20 21 and it is proposed to replace it by a unitary cast composite body according to the invention. The preferred well block is shown in Fig. 2 of the accompanying drawings. Well block 30 is an elongated structure predominantly square or possibly rectangular in transverse cross-section and terminating in a downstream end portion 31 of circular cross-section. Portion 31 is dimensioned to pass through the aperture in an adapter plate 34 secured to the ladle bottom. The well block 30 is used in conjunction with a spigot 35 and sleeve 36 as described above, though it may be preferred to omit these latter items. When the well structure comprises parts 30, 35 and 36, these parts can be joined one to another by cement as is common practice.

The external shape of the well block is determined by the form of the ladle lining adjacent the pour opening, and the rectangular configuration just described is not necessarily the best form for all applications. Other shapes may therefore be preferred. For example, the well block could be right cylindrical throughout its length and of uniform diameter; it could however be of stepped shape, with a smaller diameter downstream end portion.

The well block assembly 1 5 has a central metal flow passage 32 extending therethrough.

The well block 30 is a unitary refractory cast composite body comprising, in this case, two successively-cast, refractory concretes. The concretes are self-bonded to one another where they adjoin at an irregular, or non-smooth interface 38. The concretes are of different compositions, one being a high duty concrete and the other a lower duty concrete.

The high duty concrete 37 is one which is capable of withstanding the conditions in the bottom of the ladle and erosion by molten metal entering the well block passage 32, and forms the upper part of the well block body. The high duty concrete 37 can be allumina-based having at least 60% Awl203 % by weight, the normal upper limit for Awl203 being 93% or 95% by weight. Exemplary concretes have 70 to 85% Awl203 by weight. Alumina/chromite and zircon/aluminosilicate high duty concrete formulations could be employed instead, if desired.

The low duty concrete 39 is one which has a low thermal conductivity and low heat capacity, and forms the lower part of the well block body. The chosen low conductivity material is incidentally of relatively low cost compared with concrete 37. Concrete 39 reduces loss of heat from the pouring metal stream to the ladle casing, the ambient atmosphere and the valve, and inter alia acts as a safeguard minimising the likelihood of metal freezing in the passage 32. Concrete 39 can again be alumina-based and have an Awl203 content of 50% by weight or less, but could be essentially siliceous, containing up to 95% SiO2.

Concretes 37 and 29 can be chemically, e.g. phosphate, bonded or hydraulically bonded.

As shown, the well block 30 comprises two superposed refractory concrete masses but it could be made from more than two successively-cast concretes.

Instead of the different concretes meeting and bonding directly to one another at interface 38, there may be a cementitious junction band, consisting of a concrete blend comprising a mixture of the respective formulations of concretes 37, 39 between the adjoining masses thereof.

In principle the lower duty concrete 39 could be confined to the well block region most likely to suffer from heat loss. Thus, concrete 39 could be confined to end portion 31. However, since the concrete 37 is substantially more costly than concrete 39, the latter should occupy a significantly greater portion of the well block 30 than just portion 31. The concrete 39 in the illustrated block 30 therefore extends about half the length of the block 30 from the lower, discharge end and could extend even further.

The well block 30 can have the following exemplary dimensions: overall length 21" (53.4 cms); end portion 31 of 12-" (32.4 cms) diameter and length 4" (10.1 cms); main portion of square section 15" sides (38.1 cms); weight 150 kg. The foregoing dimensions are, of course, not limiting and will depend on the particular ladle/valve combination.

The passage 32 is of ciruclar cross section and as normal its major portion defined here by the sleeve and spigot is shown parallel-sided, but could be tapered and of increasing or decreasing diameter towards the lower discharge end; the diameter of the passage 32 at its discharge end should match the orifice size of the stationary plate 1 9 of the valve which it may be intended to use to control metal flow.

The passage 32 could be defined by the moulded cementitious materials 37, 39, sleeve and spigot being omitted. As shown, however the passage and its form are defined by a fired refractory liner sleeve 36. The sleeve and possibly the spigot can either be cemented in place or incorporated in situ in the well block during moulding thereof.

Manufacture of the elongated well block is a straightforward moulding operation. After pouring one concrete formulation into an appropriately shaped mould so as to part-fill the mould, the mould and contents are vibrated to consolidate the concrete. After vibrating, the concrete has a somewhat rough exposed surface. Another concrete formulation is then poured on top of the first-poured concrete and vibration repeated. Where only two concrete masses are to form the well block, this completes the moulding operation. The moulded shape is then cured at a modestly-elevated temperature, e.g. in the range of 3000 to 4000C for phosphate-bonding concretes. The curing time will depend on the dimensions of the well block, and for the above-quoted dimensions will be 10 to 12 hours.

EXAMPLE 1 Two phosphate-bonded high duty concretes have the following compositions: Parts by Weight (a) Calcined Bauxite, 4 mm and finer 60 Calcined Alumina, finer than 45 microns 20 Kyanite, 0.4 mm or finer 6 Refractory Ball Clay 2 Phosphate Binder 8 Setting Agent 1 Acid Inhibitor 0.1 Water 3 (b) Bauxite, 4 mm and finer 40 Calcined Alumina, finer than 45 microns 1 8 Chromite, 0.5 mm and finer 30 Refractory Ball Clay 3 Phosphate Binder 8 Setting Agent 1 Acid Inhibitor 0.1 Water 3 Suitable phosphate binders include aluminium orthophosphate, orthophosphoric acid, mono aluminium phosphate and any acid phosphate which will not adversely affect refractory properties.The setting agent can be selected from fused- magnesia, periclase and calcined magnesia instead of fused magnesia, and should be ground finer than 1 50 microns. The acid inhibitor is added to minimise or eliminate chemical reaction between the acidic phosphate binder with trace metallic iron picked up during the crushing process undergone by the refractory aggregates used. A suitable acid inhibitor is described in British Patent Specification No. 1 41 6,079.

EXAMPLE 2 A phosphate bonded low duty concrete has the following composition: Parts by Weight Graded Chamotte 4 mm and finer 81 Kyanite 0.4 mm and finer 5 Refractory Ball Clay 3 Phosphate Binder 8 Setting Agent I Acid Inhibitor 0.1 Water 3 Chamotte may be calcined china clay, calcined flint clay, calcined ball clay and calcined fireclay, but naturally occurring alumino silicate minerals could also be used, e.g. andalusite and sillimanite.

EXAMPLE 3 An hydraulically-bonded high duty concrete has the following composition: Parts by Weight Graded Bauxite 4 mm and finer 80-85 Calcium Alumina Cement 15-20 An hydraulically-bonded low duty concrete has the following composition: Parts by Weight Graded Chamotte 4 mm and finer 80-85 Calcium Aluminate Cement 1 5-20 Sufficient water is added to the above mixes to make them suitable for vibration casting (usually around 10%) but this can widely vary depending upon the amount and type of calcium aluminate cement and refractory aggregate present. The percentage of calcium aluminate cement present in the mixes can vary. 1 5-20% is usually considered normal but, depending on type refractory aggregate used, a higher or lower amount could be used. Graded refractory aggregates 9.6 mm and finer can be used. The mixes can incorporate additives (say 0.1 < 5% by weight) to improve certain properties. Such additives can be refractory ball clay, sodium silicate and steel fibres.

The foregoing description has been directed to well blocks, but the teaching is applicable to other special purpose blocks as mentioned hereinbefore; the higher duty concrete of such blocks will, of course, in use be located where the most adverse conditions exist.

Claims (12)

1. A well block for a molten metal pouring vessel, which is a unitary refractory body having a flow passage extending therethrough from a passage entry, the body being a cast cementitious composite made from at least two different refractory material masses adjoining and bonded to each other, the refractory mass in the region of the entry being of higher duty than the refractory mass in the region of the opposite end of the well block, the latter mass having a lower thermal conductivity than the higher duty refractory mass.

2. A refractory block to form means for admitting substances to molten metal in a molten metal pouring vessel, said block being a unitary refractory body consisting of a cast cementitious composite and made from at least two different refractory material masses adjoining and bonded to each other, the refractory mass at one end of the block, which in use is the end to be exposed to the molten metal in the vessel, being of higher duty than the refractory mass forming the remainder of the block, the latter mass having lower heat capacity and thermal conductivity than the higher duty refractory mass.

3. A block according to claim 1 or claim 2, wherein the lower duty refractory mass occupies at least half the length of the block.

4. A block according to claim 1, 2 or 3, wherein the juncture between each adjoining mass comprises a band of cementitious material which is a mixture of the refractory materials of which the masses are composed.

5. A block according to claim 1, 2, 3 or 4, wherein the refractory materials are chemically or hydraulically bonded concretes.

6. A block according to claim 5, wherein the concretes are phosphate bonded.

7. A block according to any of claims 1 to 6, wherein the higher duty refractory mass comprises an alumina-based concrete of at least 60% All03 by weight.

8. A block according to any of claims 1 to 6, wherein the higher duty refractory mass comprises an aluminaichromite or zircon/alumino-silicate concrete mix.

9. A block according to any of claims 1 to 7, wherein the lower duty refractory mass comprises an alumina concrete of 50% or less Al203 by weight.

10. A well block according to claim 1 or any of claims 3 to 9 when dependent on claim 1, wherein the well block is an elongated body of square or rectangular cross-section which terminates in a discharge end of circular cross-section.

11. A well block substantially as herein described with reference to and as shown in Fig. 2 of the accompanying drawings.

12. A molten metal pouring vessel having a refractory lining and a well block as claimed in any preceding claim secured therein and defining a metal discharge passage from the vessel.