Refractory lining for ladles and process for the production thereof

Abstract

 This invention relates to the production of a refractory lining for steel plant ladies, consisting of a number of prefabricated ring-shaped elements, placed one above the other within the ladle fitted onto the metal wall of said ladle. Each ring element is made of basic refractory material mainly dolomite and or magnesite or other similar material.

Description

[0001] It is known that the refractory lining for steel plant ladles is particularly important in the iron industry. It must in fact withstand, as long as possible, the strong thermal wear to which it is subjected by the liquid steel and slag, which normally reach temperatures in the region of 1620-1650^oC.

[0002] Thermal wear is, furthermore, coupled with mechanical wear due to the movement of the liquid steel contained in the ladle, and this occurs both at the time when the ladle is filled, and as a result of the modern treatment and processing techniques in the ladles.

[0003] Aluminous bricks and/or silicious material mixtures are used normally for the production of refractory ladle linings. As known, while aluminous bricks with high alumina content are most suitable for this purpose, they nevertheless entail very high costs. On the other hand, if suitably rammed silicious material is used, whether in powder and/or in grains, undesirable impurities are brought into the steel.

[0004] More recently, basic materials such as dolomite and/or magnesite - and, precisely, dolomite or magnesite calcinated at 1750-1850°C - have been used. This material is used both in powder and/or in grains to be rammed on site, and in bricks. Thus, the aforementioned drawbacks have been overcome in part, even though some inconvenience is caused by the formation of a dolomite-slag scull on the refractory wall, which must be removed periodically.

[0005] Besides the above drawbacks, which are essentially of thermal- chemical nature, the refractory ladle linings based on current technical knowledge present a further drawback, in that they require extremely slow production processes; obviously, this results in a great outlay of skilled labour, as well as in considerable dead times in ladle use.

[0006] The object of this invention is to obtain a ladle lining allowing to overcome the aforementioned drawbacks and apt, on one hand, to be manufactured more easily and quickly, while having on the other hand, features such as to improve its resistance to chemical-physical wear.

[0007] This result is achieved mainly due to the fact that the lining is formed of a number of ring-shaped prefabricated refractory elements, each provided with at least one housing and/or supporting outer jacket, the elements being superposed inside the ladle so as to cover its entire wall.

[0008] Other characteristics and advantages of this invention will anyhow result evident from the following description of some preferred embodiments thereof, which are also illustrated on the basis of the accompanying drawings, in which:

fig. 1 is a schematic axial cross-section view of a ladle provided with the refractory lining in accordance with the invention;

fig. 2 is a cross-section view similar to that shown in fig. 1, but relating to a ladle having a different shape;

fig. 3 shows one way of obtaining a refractory, ring-shaped element in accordance with the invention;

figs. 4 and 4A show two different ways of obtaining the housing walls of a refractory, ring-shaped element, directly in expendable material and, respectively with a retrievable form;

figs. 5 and 5A show two different types of reinforcement and support cages, which are to be incorporated into the refractory ring-shaped elements;

fig. 6 shows an iron rod cage for transferring a set of superposed ring-shaped, prefabricated elements into a ladle;

fig. 7 shows schematically how to form the ladle lining with prefabricated ring-shaped elements combined with a layer of safety fire--bricks.

[0009] As shown in figure 1, few prefabricated elements are used to form the refractory lining within the metal wall 1 of a ladle: that is, starting from the bottom, a base element or hearth 2 and three superposed ring-shaped elements 3, 4 and 5, forming the wall lining.

[0010] In the case of the ladle shown in figure 1, the side wall of which is flared upwardly, also the ring-shaped elements 3, 4, 5, have a frustoconical shape, with an upwardly increasing diameter.

[0011] Moreover, the mutually contacting horizontal surfaces of elements 2, 3, 4 and 5 may be provided with dap or labyrinth profiles 3¹, 4^t, 5¹ ensuring a better seal. In any case, when these elements are positioned for their final arrangement, a layer of basic or chemically neutral refractory mortar is placed between each of said elements.

[0012] Figure 2 shows instead a ladle which is essentially drum-shaped. In this case, obviously, also the ring-shaped elements 3, 4, 5, are cylindrical. In accordance with another characteristic of the invention, these elements increase in thickness starting from the top down, in order to provide better resistance to the stronger thermal shocks occuring in the lower part of the ladle.

[0013] Also another characteristic of this invention can be seen in figure 2, where the lowest ring-shaped element 3 is shown to be in one piece with the base element 2. In fact, even though manufacturing elements 2, 3₎ in one piece entails some added difficulty during the stage of prefabrication, it nevertheless has the advantage of ensuring perfect insulation especially in highly critical bottom angle positions.

[0014] Naturally, both arrangements described above with reference to figure 2 - namely, the increasing thickness of the ring-shaped element walls, starting from the top down, and the manufacture in a single piece of the bottom elements 2, 3 - can be adopted also in a frustoconical ladle such as the one shown in figure 1.

[0015] An opening 6 is provided, furthermore, in the lining of the bottom element 2: this opening precisely houses the standard, specially constructed refractory blocks defining the nozzle sprue (not shown).

[0016] Figure 3 illustrates the method followed for producing a single ring-shaped element: for this purpose, side walls or housing jackets 7, 8 are employed, between which a ring-shaped cavity is formed, the refractory material being cast and/or poured and rammed into the latter, as better explained hereinafter. The filling may be executed with the so-called "slinger" machines, which hurl the granulated, binder--enriched, refractory material.

[0017] The jackets 7 and 8 may be made in expendable material, such as sheet-metal, so as to be no longer reclaimed once the refractory ring-shaped elements have been placed into the ladle; in particular the inner jacket 7 melts as soon as the ladle is filled for the first time.

[0018] If expendable sheet-metal is used, at least the outer jacket 8 should be formed - as shown in figure 4 - of a ring-wrapped sheet, the ends of which 8, 8', partly overlap and are secured to each other for instance simply by means of a clamping wire rod (not shown). In this arrangement, the sheet-metal can in fact freely follow the expansions of the refractory material and of the metal wall of the ladle, under high working temperatures.

[0019] The inner jacket 7 presents no such problem since, as pointed out hereinabove, it melts as the ladle is filled for the first time.

[0020] In the foregoing, we have referred to expendable sheet-metal jackets; however the jackets 7 and 8 can be made of other material, for instance plywood. If the plywood is coupled with reinforcement structures - for instance wires or wire nets - such jackets may be capable of withstanding the ramming pressure.

[0021] Alternatively, as shown in figure 4A, the jackets 7 and 8 may be made of any light material, and the refractory ring-shaped elements are moulded in forms - for instance made of sheet 9 - into several pieces connected to one another by means of bolts 9a, which are removed and recovered just before the final positioning of the refractory element. These forms can also be made of wood or of any other properly reinforced suitable material.

[0022] Where forms are used - which only have to withstand the pressing and ramming actions of the refractory material - the jackets may be made, depending also on the kind of refractory material employed, of pierced sheet-metal, of cardboard or strong paper and/or wire net.

[0023] For handling the prefabricated ring-shaped elements - which, obviously, due to their size, may also reach considerable weight - brackets may be used, in the shape of hooks or of half rings 10, fixed to reinforcement metal cages (such as those shown in figures 5 and 5A) embedded in the ring-shaped elements, and /or eventually welded to the sheet-metal housing jackets.

[0024] The use of such reinforcement cages, or even of simpler reinforcement units - for instance in the form of L- or U- bent iron rod or plate crop ends embedded in the rammed refractory material - may be recommendable in any case, in order to provide greater stability for the ring-shaped element.

[0025] In the case of large ladles having a capacity of e.g. 250 to 350 tons of steel - the refractory ring-shaped elements would reach such a size as to make their handling or transport practically impossible. In this case, each ring-shaped element may be made up of two or three ring sector units, each with its reinforcement and lifting hooks. These units may then be reassembled on the floor at the foot of the ladle, tied to one another - for instance by means of a steel wire rod or strip - hence lifted by a crane and let down into the ladle as a single element. It is also possible, however, to reassemble these units directly within the ladle.

[0026] The assembly of the refractory ring-shaped elements in the ladle may be carried out by simply placing them one on top of the other inside the ladle, as mentioned previously, or else - in the case of smaller ladles - setting them one on top of the other within an iron rod framework such as the one shown in figure 6, and then lowering them all together into the ladle, almost as if it were a single piece lining.

[0027] As shown in figures 1 and 2, the outside wall of each ring-shaped element is directly in contact with the inside face of the wall 1 of the ladle. This makes the assembly extremely simple and quick; but it requires the size of the prefabricated elements to be very precise, so as to match both the size and the shape of the ladle which is to be lined.

[0028] Alternatively, the prefabricated ring-shaped elements may be produced in a range of standard sizes - which obviously facilitates mass prefabrication - and the ladle lining may be formed of ring-shaped elements of smaller outer dimensions than the inside dimensions of the ladle; in this case, at the time of placing the elements in the ladle, a hollow space - its thickness varying between e.g. 30 and 60 mm - is formed between the ring-shaped elements and the wall of the ladle, in which further refractory material can be rammed easily.

[0029] Another advantage offered by this hollow space is to make it possible to produce ring-shaped elements with an outer polygonal surface; in some cases, this simplifies the construction and use of external forms made up of several parts.

[0030] The aforementioned hollow space is normally filled with refractory material in powder and/or grains or, possibly, with a semifluid mixture of refractory, castable material. However, it is also possible to use said hollow space - to the extent that is deemed desirable, and especially in the case of larger hollow spaces - to house a layer 11 of suitably juxtaposed and superposed fire-bricks (see figure 7).

[0031] As to the kind of refractory material used for the prefabrication of these ring-shaped elements, preference is given to the use of basic mixtures, essentially containing dolomite calcinated at 1750°C, and/or magnesite calcinated at 1850-1950^oC. Besides these main products, one may use - in quantities prefarably not exceeding 10-35% - olivine, chromite, serpentine, and extra aluminous cement (with a 60 to 80% alumina content) variably blended.

[0032] In particular, the following may be used as additive material: 3-8% of sodium aluminate, 4-10% of chromite, 4-8% of aluminous cement, 2-4% of magnesium sulphate, 2-6% of sodium hydroxide, or mixtures of the above with water.

[0033] It has also been found possible to use an interesting refractory mixture based on dolomitic and/or magnesium ore at its natural state (i.e. crude, uncalcinated), especially dolomitic limestone, mixed with up to 30-35% of the following materials: chromite, olivine, serpentine, extra aluminous cement and iron oxides. With the addition of these materials, at the high temperature existing in the ladle, the dolomite and/or magnesite lead to the formation of complex calcium and magnesium oxide salts, combined with chromite, alumina and iron oxides. Thus, calcium and magnesium ferrates are formed (MgO. Fe₂O₃ and CaO.Fe 0 ) with orthosilicates and basic silicates; though slightly depressing the melting point, these chemical combinations result in a substantially strong ceramic bond at the temperature (1620-1650°C) of the liquid steel contained in the ladle.

[0034] Naturally, the usual silicious and/or silico-aluminous mixtures can be used too.

[0035] The refractory material may be employed either in fine powder of a diameter not exceeding 0.5 mm, or 1 to 3 mm diameter grains. This material is poured into moulds and then tamped, possibly with the aid of vibrating means.

[0036] It is also possible, however, especially in the case of the larger ring-shaped elements, to pre-mould the refractory material into pressed bricks or blocks - weighing, for instance, 4 to 20 kg. - then set these bricks suitably juxtaposed and superposed within the mould, finally filling the interstices with powdered material (as shown schematically in figure 7).

[0037] The refractory material can be used dry and tamped within the mould in the way described hereabove. It can also be mixed, however, with liquid or semiliquid binders. In this case, a semifluid refractory material mixture can be prepared beforehand and then poured into the mould.

[0038] Suitable binders for the above purpose include: molasses, pitch, self-hardening oily binders, magnesium sulphate binders with sodium aluminate or hydroxide, lactose solutions with natural or synthetic fats, casein emulsions or other similar binders. Other known binders may be employed, besides the ones mentioned: binders based on aluminium and chromium phosphates, binders based on vegetable oils, binders based on ethylene, ethanol, glycol and methanol, as well as binders based on silicone resins or polyacrylamic resins, etc.

[0039] Thus prefabricated, the ring-shaped elements can then be fitted directly into the ladle, or be previously subjected to a baking or stabilizing treatment at 600-800°C,

[0040] It is anyhow understood that the invention is not limited to the particular embodiments herein described, especially as far as the shape and size of the prefabricated refractory elements is concerned - since it is also possible, for instance in the case of smaller ladles, to manufacture the entire lining as a single prefabricated unit - and that many modifications may be made to the same, all within reach of the skilled in the art and all falling within the scope of the invention itself.

Claims

1) Refractory lining for metallurgical ladles, characterized in that it consists of several prefabricated, essentially ring-shaped elements, each provided with lateral housing jackets and superposed inside the ladle so as to cover at least the entire side wall.

2) A lining as in claim 1, in which the entire side wall of the ladle is covered with three or four prefabricated refractory ring--shaped elements, placed one above the other.

3) A lining as in claim 1 or 2, in which the outer surface of the prefabricated refractory ring-shaped elements is in direct contact with the inner surface of the metal wall of the ladle.

4) A lining as in claim 1 or 2, in which a hollow space is formed between the inner surface of the metal ladle wall and the outer face of the prefabricated refractory ring-shaped elements, said hollow space being filled with further refractory material forming a safety lining.

5) A lining as in claim 1, in which each refractory ring-shaped element is provided with cylindrical inner and outer surfaces.

6) A lining as in claim 1, in which each refractory ring-shaped element is provided with frustoconical inner and outer surfaces.

7) A lining as in claim 1, in which the outer surface of each refractory ring-shaped element has a polygonal profile.

8) A lining as in claim 1, in which said housing jackets of each refractory ring-shaped element are made of expendable material.

9) A lining as in claim 1 or 8, in which said housing jackets are made of thin sheet-metal, if necessary at least partially pierced.

10) A lining as in claim 1 or 8, in which said housing jackets are made of plywood, if necessary with metal reinforcements.

11) A lining as in claim 1 or 8, in which said housing jackets are made of a sheet of strong paper or cardboard and/or sealing wire net.

12) A lining as in any one of the preceeding claims, in which the refractory ring-shaped element corresponding to the lowest portion of the ladle wall is prefabricated-in a single piece with the refractory lining at the bottom of the ladle.

13) A lining as in claim 12, in which said refractory element forming the wall and the bottom of the ladle is provided, at the bottom, with an opening housing the refractory pieces forming the nozzle.

14) A lining as in anyone of the claims 1 to 11, in which each refractory ring-shaped element, apt to form the lining of large (200 to 250 ton) ladles, is made into at least two prefabricated, ring sector units, which are assembled only just before their introduction into the ladle.

15) A lining as in claim 1, in which brackets are associated to each refractory ring-shaped element for the support and handling thereof.

16) A lining as in claim 15, in which said brackets are in one piece with one or both metal housing jackets, and/or with a reinforcement cage embedded in the prefabricated ring-shaped element.

17) A lining as in claim 1, in which said refractory ring-shaped element incorporates a reinforcement cage.

18) Process for the production of a lining for ladles as in anyone of the preceeding claims, characterized in that a refractory material is poured and/or cast and rammed into a die having a substantially ring-shaped cavity, 50-90% of said material being made up of dolomite and/or magnesite and 10-50% being: chromite, olivine, serpentine, extra aluminous cement and/or mixtures of these.

19) Process as in claim 18, in which 65-90% of said refractory material is formed of calcinated dolomite and/or magnesite and the remaining part is made up of: 3-8% sodium aluminate, 4-10% chromite, 4-8% aluminous cement containing 80% alumina, 2-4% magnesium sulphate, 2-6% sodium hydroxide, or mixtures of same with water.

20) Process as in claim 18, in which 50-70% of said refractory material is dolomitic and/or magnesium ore and/or dolomitic limestone at its natural state, and 30-50% is chromite, olivine, serpentine, extra aluminous cement and/or iron oxides, which lead to the formation of complex calcium and magnesium salts.

21) Process as in claim 18, in which the refractory material rammed into the die is formed essentially of powder with particles of less than 0.5 mm, and of grains having a size between 1 and 3 mm.

22) Process as in claim 18 or 21, in which the rammed refractory material further includes blocks or bricks, weighing between 4 and 20 kg., if necessary aligned and/or piled up in the die.

23) Process as in anyone of claims 18 to 22, in which the refractory material is enriched with liquid binders, in particular molasses, pitch, self-hardening oily binders, magnesium sulphate binders, sodium aluminate, sodium hydroxide, extra aluminous cement, lactose solutions with natural or synthetic fats, casein emulsions as well as other well-known binders of the following group: binders based on aluminium and chromium sulphates, binders based on vegetable oils, binders based on ethylene, ethanol, glycol, and methanol, binders based on silicone and polyacrylamic resins, either alone or blended.

24) Process as in claim 23, in which the binders are pre-blended with the refractory material in order to form a slurry which can be cast into the forming _die.

25) Process as in anyone of claims 18 to 24, in which the prefabricated refractory ring-shaped elements are subjected to a baking or stabilizing treatment at 600-800°C, before their introduction into the ladle.

Drawing