GB2045676A

GB2045676A - Improvements in or relating to methods of producing encapsulated refractory bricks

Info

Publication number: GB2045676A
Application number: GB8010367A
Authority: GB
Original assignee: SANAC SpA
Current assignee: SANAC SpA
Priority date: 1979-03-27
Filing date: 1980-03-27
Publication date: 1980-11-05
Also published as: AU5644880A; IT1124030B; ES8101976A1; DE3011268A1; ZA801309B; FR2452343A1; ES489854A0; IT7912530A0

Abstract

A method is provided of producing a refractory brick 10 in a metal casing 21. A loose mixture of granular refractory compounds and a chemical binder is placed in the casing 21. The mixture is then compressed into the casing 21 and its surface 11 projecting therefrom is flattened and ground. The refractory compounds preferably contain at least 20% of alumina. <IMAGE>

Description

SPECIFICATION Improvements in or relating to methods of producing encapsulated refractory bricks This invention relates to a method of producing an encapsulated refractory brick, which may be suitable for slide dischargers for ladles, tundishes and the like, and to refractory bricks produced thereby.

Certain refractories, in particular basic refractories, can be used without being previously fired, as they can be equally given a considerable mechanical strength by special additives which provide them with a chemical instead of the ceramic bonding obtained by firing.

In certain types of slide discharger, fired refractories are contained in metal containers the purpose of which is to increase their life in view of the fact that on the one hand they increase their overall bending strength, and on the other hand they enable the refractory brick to perform its function even when for various reasons, such as thermal shock, the brick has become cracked or broken. This is because in such a case the metal container holds together the two or more pieces of the cracked or broken brick. This occurs particularly in the case of hollow refractory bricks which constitute the two elements of a closure device of a slide discharger, these elements being mobile relative to each other.

In such types of fired refractory encapsulated in metal containers, the join between the fired refractory brick in the metal container, this being a very costly operation.

According to one aspect of the invention, there is provided a method of producing a refractory brick encapsulated in a metal casing, comprising mixing basic granular refractory compounds with a chemical binder, placing the mixture in its loose state inside a metal casing, compressing the mixture into the casing, and then flattening and grinding the surface of the refractory brick projecting from the casing, at least a fraction of the refractory compounds being constituted by alumina in a quantity not less than 20%, a preformed sleeve, preferably constituted by a refractory composition with ceramic bonding, being inserted into the casing in order to protect the casting hole before moulding the remaining part of the refractory brick.

According to another aspect of the invention, there is provided a method of producing a refractory brick, comprising mixing one or more granular refractory compounds with a chemical binder, placing the mixture in its loose state inside a metal casing, compressing the mixture into the casing, and flattening and grinding a surface of the refractory brick projecting from the casing.

It is thus possible to directly produce the pieces necessary for a slide discharger by inserting and compressing into a metal casing a refractory mixture with non-ceramic bonding, i.e. chemical bonding.

The pieces thus produced can then be machined to give the necessary flatness to the working surface of the brick encapsulated in a metal casing.

The refractory bricks used as the elements of a slide discharger are hollow or apertured at their centre and slide in contact with each other such that, when the two holes are more of less partly aligned, the discharger is open whereas, the two holes do not even partially cover each other, then the discharger is closed.

It is apparent that in both cases (discharger open or closed), the opening faces of the two bricks in question must be completely coplanar and in contact with each other. Otherwise, a seal would not be formed and the steel could seep between the opposing faces of the two bricks.

In refractory bricks of the previously fired type encapsulated in a metal casing, the working surface of the brick is ground before being positioned inside the metal casing.

Consequently the positioning of the brick inside the casing, and the casing and the brick require special care which further increases the cost of the encased brick prepared in this manner from previously fired refractories.

However, in a preferred embodiment of the invention, the flattening and grinding of the brick working surface are performed after inserting and compressing the refractory mix and attaining chemical bonding within the brick.

In order to associate the speed of manufacture of a chemically bonded basic refractory with the reliability obtained by using higher quality material requiring firing in order to provide ceramic bonding between its various components, sleeves may be inserted into the passage hole for the liquid metal. The sleeves can be formed by using material such as zirconium oxide, zirconium silicate, silicon carbide, either directly bonded or otherwise, graphite, alumina or baked magnesite (with or without tar). The sleeve of high quality material can be inserted when moulding the brick, without this operation leading to any substantial increase in the price of the final formed product.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a section through a refractory brick constituted a preferred embodiment of the invention; and Figure 2 is a section through a brick constituting another preferred embodiment of the invention.

With reference to the drawings, a refractory brick 10 is provided with a sheet metal casing 20 which encloses it on fire faces, leaving an upper face free, at which an edge 21 is bent over to provide fixing above a peripheral step provided in the periphery of the uncovered upper surface 11 of the brick 10. When speaking of "upper" surfaces of the refractory brick 10, reference is made to the position shown in the drawings. In practice, the brick can have its uncovered face 11 facing either downwards or upwards.

According to a preferred embodiment of the invention, the refractory brick is moulded after a sleeve 30 of a higher quality refractory material, in particular provided with ceramic bonding obtained by firing, has been disposed in its interior, given that the walls of the hole 40 through which the liquid metal is to pass are subjected to the greatest thermal and mechanical stresses.

In the embodiment shown in Fig. 1, the sleeve is provided with an outer cylinderical side wall.

In the embodiment shown in Fig. 2, the sleeve 30 is provided with a lower outer flange 41 which enables it to be fixed more effectively in the surrounding refractory mass, which is provided with chemical bonding by using a suitable binder.

The examples given hereinafter illustrate some preferred compositions for the covered brick.

EXAMPLE 1 A granular refractory mixture having a particle size distribution of the type usually used in moulding refractory bricks, and having the following composition: - magnesite 70% - alumina 30% is mixed with five parts by weight of tar.

The mixture is placed in an upperly open metal casing and is compressed into it after a zirconium oxide sleeve having a radial thickness of 5 cm has been disposed in the casing.

The refractory mixture is compressed in such a manner that the free surface of the refractory brick slightly projects above the edges of the metal casing.

The surface of the refractory brick projecting from the metal casing is then carefully flattened and ground, this operation also extending to the upper surface of said sleeve.

EXAMPLE 2 A granular refractory mixture having a particle size distribution of the type usually used in moulding refractory bricks, and having the following composition: - magnesite (with MgO content between 94 and 98%) 35% - chromite 5% - alumina 60% is mixed with five parts by weight of tar.

The mixture is placed in an upperly open metal casing and is compressed into it in the manner described in the previous example, after disposing in the casing a refractory sleeve formed from a mixture of zirconium silicate and silcon carbide, and having a radial thickness of 6 cm.

The free surface of the refractory brick projecting from the edges of the casing is again subsequently flattened and ground.

EXAMPLE 3 A refractory brick is prepared in the manner described in the two previous examples, but in this case using a refractory mixture of the following composition: - magnesite 20% - chromite 5% - alumina 75% In this case, the material of the sleeve, which has a radial thickness of 5 cm, is formed from a mixture of approximately equal parts of alumina and baked magnesite.

EXAMPLE 4 A refractory brick is prepared in the manner described in the previous example, but with the difference that the sleeve is formed from graphite and has a radial thickness of 4 cm.

Although for descriptive reasons the present invention has been based on the description given heretofore by way of example with reference to the accompanying drawings, many modifications can be made thereto, all of which fall within the scope of the claims given hereinafter.

Claims

1. A method of producing a refractory brick encapsulated in a metal casing, comprising mixing basic granular refractory compounds with a chemical binder, placing the mixture in its loose state inside a metal casing, compressing the mixture into the casing, and then flattening and grinding the surface of the refractory brick projecting from the casing, at least a fraction of the refractory compounds being constituted by alumina in a quantity not less than 20%, a preformed sleeve, preferably constituted by a refractory composition with ceramic bonding, being inserted into the casing in order to protect the casting before moulding the remaining part of the refractory brick.

2. A method as claimed in the preceding claim, in which the alumina is contained in the granular refractory mixture in a quantity of between 20 and 85%, the remaining fraction of refractory material being constituted by magnesite (60 - 90%); the tar content added to the refractory mixture being 3 to 7% by weight of the entire mixture.

3. A method as claimed in the preceding claim, in which the alumina is contained in the refractory mixture in a quantity of between 25 and 85%, the remaining fraction of granulated refractory material being constituted by magnesite (75 - 95%) having a MgO content of 92 - 99%, the remainder being chromite (5 - 25%); the tar content added to the refractory mixture being 3 - 7% by weight of the entire refractory mixture.

4. A method as claimed in any one of the preceding claims, in which, after moulding, the refractory brick is subjected to a hardening process at a temperature of 300 - 400"C.

5. A method as claimed in any one of the preceding claims, in which the refractory brick has a radial thickness of 1 - 6 cm, and is constituted by one of the following compounds or a mixture thereof; zirconium oxide, zirconium silicate, silicon carbide, graphite, alumina, and baked magnesite.

6. A method of producing a refractory brick, substantially as hereinbefore described with reference to any of the examples, and as illustrated in the accompanying drawings.

7. A method of producing a refractory brick, comprising mixing one or more granular refractory compounds with a chemical binder, placing the mixture in its loose state inside a metal casing, compressing the mixture into the casing, and flattening and grinding a surface of the refractory brick projecting from the casing.

8. A refractory brick produced by a method as claimed in any one of the preceding claims.