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Title:
METHOD OF MANUFACTURING REFRACTORY STRUCTURE AND REFRACTORY STRUCTURE FOR LINING OF METALLURGICAL VESSEL
Document Type and Number:
WIPO Patent Application WO/2007/096469
Kind Code:
A1
Abstract:
A method of manufacturing a refractory structure for lining a metallurgical vessel, the method comprising casting and drying of the structure, whereby particles of refractory material are included in a cast mass, is characterised in that at least 10 volume percent of the particles of the cast mass are large particles the size of which is more than 50 millimetres and within the range of 1/3 to 1/2 of the thickness of the structure, the rest of the particles has at least in the size range of 0 to 6 millimetres a distribution providing dense package, and the amount of formation water in the structure before drying is not more than 5 weight percent, for producing a structure the relative density (the relation of the density of the structure to the density calculated from the densities of the constituents according to the composition) of which is at least 0.87 and preferably at least 0.90. A lining manufactured according to the invention is remarkably more durable than conventional linings, and also costs are often lower.

Inventors:
RUOTANEN KYOESTI (FI)
Application Number:
FI2007/050088
Publication Date:
August 30, 2007
Filing Date:
February 20, 2007
Export Citation:
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Assignee:
BET KER OY (FI)
RUOTANEN KYOESTI (FI)
International Classes:
C04B35/66; B22C1/00; B22D41/02; F27D1/00
Domestic Patent References:
WO1998039608A11998-09-11
Foreign References:
JPH09278545A1997-10-28
EP0857704A11998-08-12
JPS5926979A1984-02-13
EP0915069B12002-03-13
EP0857704B12001-01-24
EP0965024B12002-07-24
US5681786A1997-10-28
US5506181A1996-04-09
EP1170267A12002-01-09
Other References:
See also references of EP 1993973A4
Attorney, Agent or Firm:
LAURINOLLI, Tapio (Patenttitoimisto Tapio Laurinolli, P.O. Box 258, Oulu, FI-90101, FI)
Download PDF:
Claims:

CLAIMS

1. Method of manufacturing a refractory structure for lining a metallurgical vessel, the method comprising casting and drying of the structure, whereby particles of refractory material are included in a cast mass, characterised in that: at least 10 volume percent of the particles of the cast mass are large particles the size of which is more than 50 millimetres and within the range of 1/3 to 1/2 of the thickness of the structure, the rest of the particles has at least in the size range of 0 to 6 millimetres a distribution providing dense package, and the amount of formation water in the structure before drying is not more than 5 weight percent, for producing a structure the relative density (the relation of the density of the structure to the density calculated from the densities of the constituents according to the composition) of which is at least 0.87 and preferably at least 0.90.

2. Method of claim 1, characterised in that the particles have a distribution providing dense package in the range from 1/3 to 1/2 of the thickness of the structure to zero.

3. Method of claim 1, characterised in that the large particles are brought into the cast mass separately during the casting.

4. Method of claim 1, characterised in that the cast mass is first mixed without large particles, and the large particles are brought into the cast mass thereafter in another mixing phase before carrying out the casting.

5. Method of claim 1, characterised in that the casting comprises one or more vibration phases.

6. Method of claim 1, characterised in that the material of the large particles is sintered bauxite or fused corundum.

7. Refractory structure for lining a metallurgical vessel, the structure being manufactured by casting and drying from cast mass in which particles of refractory material are included, characterised in that: at least 10 volume percent of the particles of the cast mass are large particles the size of which is more than 50 millimetres and within the range of 1/3 to 1/2 of the thickness of the structure, and the rest of the particles has at least in the size range of 0 to 6 millimetres a distribution providing dense package, for producing a structure the relative density (the relation of the density of the structure to the density calculated from the densities of the constituents according to the composition) of which is at least 0.87 and preferably at least 0.90.

8. Refractory structure of claim 7, characterised in that the particles have a distribution providing dense package in the range from 1/3 to 1/2 of the thickness of the structure to zero.

9. Refractory structure of claim 7, characterised in that the material of the large particles is sintered bauxite or fused corundum.

Description:

METHOD OF MANUFACTURING REFRACTORY STRUCTURE AND REFRACTORY STRUCTURE FOR LINING OF METALLURGICAL VESSEL

FIELD OF THE INVENTION The invention is related to a method of manufacturing a refractory structure and a refractory structure for lining of a metallurgical vessel, the method comprising casting and drying of the structure.

BACKGROUND OF THE INVENTION Refractory structures are manufactured for e.g. bottom, wall and lid linings of metallurgical vessels, like casting, handling and transport vessels.

Replacement and maintenance of the refractory lining form a very remarkable proportion of the use costs of a steel ladle, for example. The lining should be replaceable as quickly as possible and it should withstand use as long as possible, so that it needs as few inspection and maintenance operations as possible, which operations also cause breaks in the use of the ladle. Naturally, also savings in material and labour costs are always sought, i.e. an object is to use materials and methods which bring cost savings while a lining with as good quality as possible is produced.

So called monolithic refractory linings may be manufactured by casting, and cast masses contain water. After casting, a structure is dried, and the amount of water affects essentially both the drying time and the properties of the formed structure, like wear resistance.

The publication EP 0915069 Bl presents a method for improving the wear resistance of a lining and for cost savings, in which method wreckage material containing MgO/C and having the diameter between 50 and 100 millimetres, is embedded into the matrix of refractory concrete. The publication considers in more detail only the properties of said wreckage material but does not present any examples about the properties of the cast structure manufactured by the method.

The publication EP 0857704 Bl presents a method for manufacturing refractory structures, in which method a mould is first filled with dry relatively coarse material having a particle size within the range of 1 to 60 millimetres, to form a body comprising 50 to 90 percent of the volume of the mould, and then the space between the particles is filled with liquid cast mass containing binder, water and fine filler materials. In our opinion, the method defined in the publication can not work in any case if 90 percent of the volume or a volume close to that is filled with said kind of coarse particles. If a mould is filled with the above defined coarse material (1 to 60 millimetres), then a cast mass having a particle size

within the range of 0.001 to 1.0 millimetres, as defined in the publication, is no more able to infiltrate to fill the interstitial voids between the coarse particles. As an advantage of the method it is mentioned that small amount of water is reached in a cast structure and so the drying time is short, whereby the structure may be manufactured very quickly. As to the amounts of water, only desirable percents are given in the publication without even saying if weight or volume percents are concerned. No examples of carrying out the method as well as no information about the properties of manufactured structures are presented in the publication.

The publication EP 0965024 Bl presents essentially the same method as above. Also there, the description of the method is indefinite and, on the basis of our experience and knowledge, defective in many points. No examples of carrying out the method or information about the properties of manufactured structures are presented in this publication, either.

The publication US 5681786 presents a special composition of a castable refractory material which contains 41 to 100 parts of weight aluminium oxide particles, the diameter of which is from 10 to 50 millimetres. An object of the solution is to improve the corrosion resistance, strength and, especially, resistance to high temperatures. Much the same is presented in the publication US 5506181. Due to the materials and required special compositions, the solutions are expensive and therefore suitable for special purposes, primarily.

The publication EP 1170267 Al presents a refractory concrete based on using conventional body material of the size not more than 10 millimetres and including additionally larger particles of the size up to 60 millimetres. The proportion of the particles of the size from 10 to 60 millimetres may be not more than 60 percent. The solution is considered to decrease the amount of water needed in concrete manufacturing, to facilitate even heating, to produce a more dense structure and to prevent fractures from spreading as well as to improve wear resistance. No examples of carrying out the method or information about the properties of manufactured structures are presented in this publication, either.

SUMMARY OF THE INVENTION

An object of the invention is to present such a method of manufacturing a refractory structure by casting and drying from cast mass, by which method e.g. the wear resistance of a replaceable lining of the most widely used metallurgical vessels, like a steel ladle, is improved significantly while at the same time the replacement of a lining is speeded up and the manufacturing costs are reduced.

To achieve these objects, a method of manufacturing a refractory structure for lining a metallurgical vessel, the method comprising casting and drying of the structure, whereby particles of refractory material are included in a cast mass, is characterised in that: at least 10 volume percent of the particles of the cast mass are large particles the size of which is more than 50 millimetres and within the range of 1/3 to 1/2 of the thickness of the structure, the rest of the particles has at least in the size range of 0 to 6 millimetres a distribution providing dense package, and the amount of formation water in the structure before drying is not more than 5 weight percent, for producing a structure the relative density (the relation of the density of the structure to the density calculated from the densities of the constituents according to the composition) of which is at least 0.87 and preferably at least 0.90.

In an embodiment the particles have a distribution providing dense package in the range from 1/3 to 1/2 of the thickness of the structure to zero.

In an embodiment, the large particles are brought into the cast mass separately during the casting. In another embodiment, the cast mass is first mixed without large particles, and the large particles are brought into the cast mass thereafter in another mixing phase before carrying out the casting. The casting may comprise one or more vibration phases.

The material of the large particles may be sintered bauxite or fused corundum, for example.

To achieve these objects, a refractory structure for lining a metallurgical vessel, the structure being manufactured by casting and drying from cast mass in which particles of refractory material are included, is characterised in that: at least 10 volume percent of the particles of the cast mass are large particles the size of which is more than 50 millimetres and within the range of 1/3 to 1/2 of the thickness of the structure, and the rest of the particles has at least in the size range of 0 to 6 millimetres a distribution providing dense package, for producing a structure the relative density (the relation of the density of the structure to the density calculated from the densities of the constituents according to the composition) of which is at least 0.87 and preferably at least 0.90.

In an embodiment the particles have a distribution providing dense package in the range from 1/3 to 1/2 of the thickness of the structure to zero.

The material of the large particles may be e.g. sintered bauxite or fused corundum.

DETAILED DESCRIPTION OF THE INVENTION

In the following, some examples of the method of the invention and structures realised by the method are presented in comparison with conventionally produced structures.

Example 1

Table 1 here below is related to experiments in which the method of the invention and structures manufactured by it are compared with a conventional method in which a structure is manufactured from spinel-forming cast mass in which the size of body material particles is in the range of 0 to 6 millimetres. In the structure according to the invention, 20 volume percent sintered bauxite particles, the size of which is within the range of 520 to 1800 cm , are added into conventional spinel-forming cast mass.

Table 1

The manufacturing method includes casting and drying and, if necessary, heat treatment. When manufacturing structural elements, the drying is made according to a

certain program and is lasting e.g. 1 to 4 days. First, the aim is to evaporate interstitial and crystallisation water at a lower temperature (e.g. 100 to 200 °C) and then so called hydration water at a higher temperature (e.g. about 350 0 C). At least when manufacturing structural elements, heat treatment may be necessary for a mass so that good enough binding is provided in it. A heat treatment may be combined with the drying e.g. so that the temperature is increased higher than what is needed for drying.

The test pieces are manufactured by using vibration compacting for being used as structural elements in the bottom of a steel ladle. The conventional cast mass, called here the basic mass, is made by adding formation water into conventional dry matter having the particle size of 0 to 6 millimetres in a pan mixer run for about 4 minutes. A batch in the mixing has been 500 to 550 kg.

The conventional structure is cast from two batches so that the cast mass, in which the particle size is 0 to 6 millimetres, is transferred through a spout at the bottom of the mixer directly downwards into a mould, and the mould is vibrated after disposal of the both batches for compacting the cast mass.

The structure of the invention is cast in the same way as the conventional structure, but between the batches, after the disposal of the first batch, remarkably large refractory particles comprising the proportion of sintered bauxite having the particle size of 520 to 1800 cm 3 presented in Table 1 is added on the layer of the basic mass. During the vibrating, the particles of the sintered bauxite sank partly into the basic mass. After that, the other batch of the basic mass was added and the casting was compacted by vibration.

In the both cases, the mould was disassembled in the next day and the structural elements were transferred for being dried after 30 to 100 hours from the casting. After drying, a structural element is free from interstitial and crystallisation water and possibly also from chemically bound water. The costs of evaporating the water by drying are smaller with the material of the invention than with the material of comparison.

No further heat treatment were made for the structural elements. After the drying phase, the structural elements were cooled and packed and transported to a customer for being used. In the process of the customer, the structural elements have been installed at the bottom of the steel ladle as a wear lining, and the ladle is heated to a temperature of at least 800 0 C before taking it into use.

During the period of use, a steel ladle must be cooled for some maintenance operations, e.g. for changing a well block. Then also a structural element at the bottom is cooling down almost to the room temperature. After maintenance operations the ladle is heated again and taken into use. There are no observations of the negative effects of this cooling operation on the durability of the structural element.

When the steel ladle has come to the end of the lining campaign life time, the structural element at the bottom of the ladle has been broken into parts by using a strong hydraulic hammer driven by an excavator.

From the used structural element of the invention it has been found that the particles of sintered bauxite are vertically relatively evenly distributed. As the density of sintered bauxite is close to the weighted density of the basic mass, the observed even distribution of the particles of sintered bauxite is natural.

Additionally, it has been found that steel has penetrated hardly at all into the material in the structural element of the invention. The penetration of steel is clearly more effective when using the conventional structure of Table 1, to say nothing of the case in which conventional cast mass is cast directly on the bottom of a ladle to form a wear lining.

Slag is not penetrating into the material of the structure of the invention as much as into the material of comparison, either. The interpretation is that this is caused by a lower porosity and decreased reacting surface area. For the same reason, the resistance to the chemicals added to the slag is improved. The improvement of the wear resistance is of the order of 30 percent. This is contributed by better resistance to slag and metals and erosion resistance as well as obviously better resistance to temperature changes which is affected by a better thermal conductivity.

The solution of the invention reduces remarkably the material costs. In the example of Table 1, the cost savings were of the order of 30 percent. Also drying costs and labour costs are reduced, and the reliability of the manufacturing process is improved. The invention makes possible also to use thinner wear linings, whereby the utilisation capacity of a ladle is increased.

Example 2

Table 2 compares with each other structures manufactured of ultra-low cement refractory cast mass including calcined bauxite as a body material, the structure of comparison including no large particles and the proportion of them being 23 volume percent in the structure of the invention. The test pieces manufactured in the experiments are equivalent to bottom lining structure of a steel ladle and there dimensions are: length 1200 millimetres, width 250 millimetres and thickness 280 millimetres. The span length used in the bending tests is 1060 millimetres.

The difference of the materials of Table 2 in relation to the materials of Table 1 is that the cast mass including calcined bauxite is used as the cast mass having the body material particle size in the range 0 to 6 millimetres. Additionally, in the material of the invention in

Table 2, the proportion of the sintered bauxite particles having the diameter of 93 to 140 millimetres is 23 volume percent.

In the case of Table 2, the raw material costs of the material according to the invention are hardly smaller than in the material of comparison because the cost of sintered bauxite in relation to calcined shaft-kiln bauxite is high. Savings are obtained primarily due to the better durability of the material of the invention and lower labour costs resulted from this.

Table 2

In the structures of the invention the materials of both the small particles of the size 0 to 6 millimetres and the large particles may vary. For example, one or more of the following materials are possible: burnt bauxite (especially as homogenised before burning), fused bauxite, fused corundum, various sintered corundums, fused magnesia, sintered magnesia,

sintered magnesia, fused mullite, olivine or silicon carbide. Also raw materials obtained from refractory bricks or other structural elements by crushing are possible.

As a binder may be used, for example, aluminate cement, Portland type cement, hydratable aluminas, aluminium hydroxides, calcium hydroxide, alkaline phosphates, phosphoric acid, colloid silica, colloid alumina, magnesium oxide or magnesium hydroxide.

Various additives may be used in the masses, like dispersing and deflocculation chemicals and other materials, like steel needles.

An advantage of the invention is that by means of it and by using efficiently vibration compacting structures with high quality properties may be manufactured from relatively low cost raw materials.

It is advantageous to restrict the maximum of the particle size to 1/3 of the thickness of the structure e.g. if fresh mass is transferred vertically in a mould structure. On the other hand, if fresh mass is not essentially transferred in a mould but is only compacted by means of vibration and the own weight of the mass, then the maximum particle size may be of the order of 1/2 of the thickness of the structure. That kind of application may be e.g. casting of a horizontal plate shaped piece, like a bottom lining of a ladle.

In many applications, the proportion of the large particles is of the order of 30 to 40 volume percent, but it may be increased even to a level of 50 volume percent if desired. To achieve the effects aimed by the invention, the proportion of the large particles must be at least 10 volume percent, and it is preferable at least of the order of 20 volume percent. In practice, the extreme maximum which could be reached is of the order of 70 volume percent. The proportion of the large particles and the properties of a structure may be affected by using a suitable size distribution of the particles, by modifying the manufacturing techniques at need and by material selections, for example. The advantages achieved by the solution of the invention have already been considered above in connection with the described examples. Additionally, also the resistance of a structure against thermal shocks is improved. The reason is possibly that when a starting fracture in the matrix meets a large particle, its propagation is stopped on condition that the contact between the matrix and the particle is good. As the fire resistance of the binder and fine materials is normally worse than that of the body materials, also the fire resistance of the structure is improved as the volume or weight proportion of the body material in the structure is increased.

The applications of the solution of the invention may be e.g. structural elements manufactured for wear lining of metallurgical vessels. The vessel may be a ladle, melting furnace or converter used in manufacturing of iron, steel, copper, nickel, ferrochrome or

aluminium, for example. The vessel may be also a foundry ladle, melting furnace, converter, spout or trough.

A factor affecting essentially the advantage of the manufacturing method and the good properties of the structures produced by it is the proportion of the formation water in the cast structure before drying. In the solution of the invention, a starting point is that said proportion of formation water is not more than 5 weight percent. Preferably, it is not more than 4 weight percent, and it may be even 3,5 or 3 weight percent.

The remarkably large particles included in the cast mass are in the solution of the invention advantageously also irregularly shaped, i.e. not spherical, cubic or otherwise regular and provided with even surfaces. The maximum thickness of a lining is in practice of the order of 600 millimetres.

The invention may vary within the scope of the accompanying claims.