GB2104837A

GB2104837A - Prefabricated insulating fibre composite block for furnace lining

Info

Publication number: GB2104837A
Application number: GB08126041A
Authority: GB
Inventors: Iwao Iemura; Hajime Asami; Shigeo Yoshino; Tadashi Zenbutsu
Original assignee: Shinagawa Refractories Co Ltd
Current assignee: Shinagawa Refractories Co Ltd
Priority date: 1981-08-26
Filing date: 1981-08-26
Publication date: 1983-03-16
Also published as: GB2104837B

Abstract

An insulating refractory composite block comprising a refractory fibre block 1 having one or more faces coated by a flexible refractory board 2 which consists of (a) 100 parts by weight of a refractory material such as alumina, magnesia, silica, chamotte and silicon carbide, (b) 1 to 20 parts by weight of organic and/or inorganic fibres, and (c) 2 to 50 parts by weight of a binder e.g. an aluminate, alkali silicate, phosphate or alumina cement. <IMAGE>

Description

SPECIFICATION Prefabricated insulating fibre composite block for furnace lining This invention relates to a refractory composite for heat insulating on various kinds of furnaces and vessels, and the object of the invention is to provide an insulating refractory composite block having excellent heat insulating and endurable properties, and a refractory structure in which said insulating refractory composite block is applied to the inner and outer faces of various furnaces and vessels.

These days a heat insulation of various kinds of furnaces and vessels are attempted from the viewpoints of resource saving and energy saving.

Conventionally there are used, as heat insulating materials for such purpose, insulating bricks or an inorganic, insulating fibrous material.

However, they have disadvantages in that in the former the heat insulation at high temperatures is insufficient and the shape is small thereby requiring a long time for construction while in the latter the heat insulation at high temperatures is excellent but if used for a longer period of time the fibre is caused to crystallize whereby it becomes powdery, and therefore, in case said inorganic fibrous material is applied to the inner faces of heating furnace the powderized fibre pollutes the products in the furnace. Another problem is that if the insulating bricks or the inorganic fibrous materials are applied to the inner faces of heating furnace the faces are subject to abrasion by gas flow, and erosive abrasion by erosive gas.Another attempt is to prevent the iron shell from oxidation as well as to heat insulate it by applying a heat insulating material to the inner walls of various kinds of furnaces and vessels, but said two kinds of insulating materials have greater gas permeability so that they are given heat insulation but disadvantageously they cannot be prevented from oxidation of iron shell. Alternatively it is also attempted to coat the surface of said fibrous insulating material with a refractory material but this is troublesome in constructing the furnace.

The present invention has been completed as a result of various studies made to solve the above problems. The subject matter of the invention lies in an insulating, refractory composite block which consists of a flexible refractory board based on refractory materials such as alumina, magnesia, silica, chamotte and silicon carbide, said board having a flexible refractory property and a property shrinkable under pressure, and/or a hard refractory board based on alumina, magnesia, silica, chamotte and silicon carbide, and an inorganic fibre block, and in a refractory structure in which is applied, to the hot faces of various furnaces and vessels and/or the inner walls such as in iron shells, an insulating, refractory composite block which consists of a flexible refractory board based on refractory materials such as alumina, magnesia, silica, chamotte and silicon carbide, said board having a flexible refractory property and a property shrinkable under pressure, and/or a hard refractory board based on alumina, magnesia, silica, chamotte and silicon carbide, and an inorganic fibre block, while providing an insulating refractory composite having an excellent insulating property and an excellent endurability over longer period of time.

Some insulating refractory composites of the invention will now be described, by way of example, with reference to the accompanying drawings, in which Figs. 1, 2 and 3 are respective cross-sectional views showing essential portions of some insulating refractory composites of the invention.

Fig. 1 is a cross-sectional view showing the essential portion of an insulating refractory composite which consists of a flexible refractory board 2 and a fibre block 1. The fibre block 1 is sheet-like and is soft like cotton. It is therefore small in strength, but if fibre is stacked in laminate as shown it may be easily handled with the flexible refractory board as core and in applying the block it can be easily deformed optionally to adapt to the curved faces. Further, even in a longer period of use the fibre block may be prevented from powderization due to crystallization and abrasion and erosion by gas flow thereby obtaining an endurable heat insulation over a long period of time.

Fig. 2 is a cross-sectional view showing the essential portion of an insulating refractory composite block which consists of a hard refractory board 3, fibre blocks 1 and a flexible refractory board 2.

Fig. 3 shows another example and is a crosssectional view of a prefrabricated insulating fibre composite block in which the whole six faces of the rectangular refractory fibre block 1 is covered with a hard refractory board 3.

These insulating refractory composite block are not flexible, but even in a longer period of use the fibre blocks are prevented from powderization due to crystallization when an endurability for heat insulation is obtainable over a long period of time.

Further, they can be used for lining which is brought into contact with molten metals. In case they are used for heat insulation between a refractory lining material of furnace or vessel and an iron shell they do not shrink even if subjected to the expansion of the lining material or the stress such as static pressure of the molten metal thereby to provide a furnace structure having an insulating property.

According to the invention the flexible refractory board 2 is based on powdery refractory and inorganic fibre, and preferably it has a flexible property and a shrinkable property under pressure at room temperature when constructing. Such a flexible refractory board is completely, closely adhered to the curved faces when constructing the furnace, and thanks to a composite structure with the fibre block 1 it is possible to use said board as it is without losing the natural properties even if it is used as part of an insulating refractory composite block of the invention.

As the flexible refractory board is used such one which is characterized by mixing 100 parts by weight of a powdery refractory raw material 120 parts by weight of an organic or inorganic fibre, and 3-50 parts by weight based on solid parts) of polymer emulsion as a binder, said emulsion having a flexibility after drying; and as the fibre for the flexible refractory board are used inorganic fibres such as slagwool, asbestos, glass fibre and ceramic fibre and organic fibres such as wood pulp, and flocks of hemp thread, cotton and synthetic fibres. Preferably the fibre length is shorter than 10 mm to prepare a mix for the board where fibre is uniformly dispersed.

The inorganic fibres are active to provide a strength at normal temperature or medium temperature but decrease the refractory property of said board so that preferably the additive amount of the inorganic fibre is less than 20 parts.

The organic fibres are active to provide a strength at the time of normal temperature, increase the pores thanks to the burning when used, and improve the heat insulability, but preferably the additive amount of the organic fibre is less than 5 parts by weight and with more than 5 parts there is caused a demerit such that the board texture is deteriorated owing to the burning when used.

The vinyl resin emulsion used as binder is one or more in mixture of aqueous emuisions such as poly vinyl-acetate emulsion, poly ethylenevinylacetate emulsion and poly vinylacetateacrylicester emulsion, but it is preferable that the minimum film forming temperature (MFT) of the binder is lower than 300C. If the MFT exceeds 300C the refractory board after drying may not occasionally have a sufficient flexibility.

The more the additive amount of the binder is, the more the board becomes pliable and increases flexibility, and with less than 3 parts by weight of the binder the flexibility is not sufficient so that the insulating composite block coated over the surface of the fibre block may not deform enough to the curved faces when applied, whereby cracks occur.

However, if the binder is added by more than 40 parts by weight the board texture is deteriorated due to the thermal decomposition of the binder when the temperature rises, after construction, and the board loses resistance to the abrasion and erosion caused by gas flow, etc.

The hard refractory board 3 in the invention bases on refractory powder and fibre. Preferably it does not shrink even if subjected to expansion of bricks or the stress such as static pressure of molten metal, does not decrease the heat insulability and has an endurability when brought into contact with molten metal. The composite block can be used without losing the natural properties thanks to the combination of a hard refractory board 3, a fibre block 1 and a flexible refractory board 2. As the hard refractory board there is used a mixture of 100 parts by weight of refractory materials such as alumina, magnesia, silica, chamotte and silicon carbide, 1-20 parts by weight of organic fibre and/or inorganic fibre, and 2-10 parts by weight of binder such as aluminate, alkalisilicate, phosphate and alumina cement.For the fibre of said hard refractory board there are used inorganic fibres such as slagwool, asbestos, glass fibre and ceramic fibre and organic fibres such as wood pulp, and flocks of hemp thread, cotton and synthetic fibres.

In order to prepare a mix of the hard refractory board where the fibres are uniformly dispersed it is preferable that the fibre length is shorter than 10 mm.

The inorganic fibres are active to provide a strength at normal temperature and medium temperature, but they decrease the refractory property of said board so that preferably their additive amount is less than 20 parts by weight.

The organic fibres are active to provide a strength at the time of normal temperature, increase the pores thanks to the burning when used, and improve the heat insulability, but preferably their additive amount is less than 5 parts by weight and in excess of 5 parts by weight there is caused a drawback such that the board texture is deteriorated owing to the burning when used.

Referring to the additive amount of the binder, the strength will be small if it is less than 2 parts by weight, but with the binder of more than 10 parts by weight a problem occurs in that the refractory property is lowered and the resistancy to melting down is also lowered when contacted the slag of molten steel.

The fibre block 1 according to the invention is employed in various shapes. For example, it may be in the form of felt of slagwool, ceramic fibre or glass fibre or of laminate thereof. The form can be suitably selected depending on temperature condition of the place where the composite block is used.

The insulating, refractory composite block is moulded by adhering, with a refractory adhesive, for example a fibre block with a flexible refractory board or a hard refractory board. Otherwise it is obtained in such manner that a mix for the flexible refractory board or a mix for the hard refractory board is coated over or poured onto the upper surface of the fibre block, and thereafter said mix is dried for more than 2 hours at a temperature higher than 1000C.

The insulating, refractory composite block of the invention can be applied, as it is, by fixing it with known mortar or bolts to the hot faces and/or the non-hot faces (iron shell side) of various furnaces and vessels, but to improve the working speed it may be preferable to apply a pressure sensitive adhesive at the working faces.

For example, the working speed of application of the composite unit will be further improved by backing, to the applying faces, a pressure sensitive adhesive consisting of a mixture of a powdery refractory, an inorganic binder and a synthetic resin or a rubber type adhesive, and by applying a release backing paper.

Example 1 At the walls of a heating furnace for hot rolling there were used insulating refractory composite blocks each having a structure as shown in Fig. 1 and consisting of a ceramic fibre block 1 of 50 mm thick and 55% Awl203 content, and a flexible refractory board 2 of 5 mm thick and 95% Awl203 content. As a result, the composite block of 55% Awl203 content of the same materials as said conventionally used ceramic fibre block became powdery after a three months use and there was no alternative but to replace the composite for repair, but in the insulating refractory composite block according to the invention any powderizing phenomenon was not noticed and an endurability of longer period over more than six months was ascertained.

Example 2 Between the lining refractory bricks and iron shell of ladle for molten steel there were entirely applied insulating refractory composite block, each having a structure as shown in Fig. 2, consisting of ceramic fibre blocks 1 of 30 mm thick and 55% Awl203 content, a flexible refractory board 2 of 5 mm thick and 50% Awl203 content and a hard refractory board of 30 mm thick and 75% Al2O3 content, and having a space of 150 mm between each pair of convexity.As a result it was found that on the insulation effect and the endurability the temperature of the molten metal was lowered only by 3N60C during the stay as molten metal for 3 hours and that the lowering of the temperature of molten steel could be prevented in the range 29 to 32 OC, compared with the case where the insulating refractory composite block of the invention was not used, in which case the temperature of molten steel was lowered by 350C. Further, in the flexible refractory board 2 of said insulating refractory composite block after used, the 5 mm thickness before use was decreased to 2.3 mm thereby absorbing sufficiently the expansion of the lining refractory bricks, while in the ceramic fibre block 1 and the hard refractory board 3 the dimensions and others were found unchanged as before use.

Example 3 At the iron shell of a forging furnace there was constructed, according to the same method as for ordinary bricks, a prefrabricated insulating fibre composite block which has a structure as shown in Fig. 3 and in which the refractory fibre block 1 is of a rectangular shape of 100 mm thick, 200 mm wide and 300 mm long and has 55% by weight of Awl203 content, and the six faces of said refractory fibre block 1 were coated with a hard refractory board 2 of 75% by weight of Awl203 content.

Compared with conventional structure in which a plastic refractory of 100 mm thick was applied to the iron shell and a ceramic fibre block of 55% by weight of Awl203 content was applied thereover in 100 mm thickness, it was ascertained that the insulating refractory composite block of the present invention can be very easily constructed and that the temperature of the iron shell when operating was lowered by lotto 150C.

After a six months use, in said conventional structure the ceramic fibre there was noticed, a phenomenon that the ceramic fibre was powderized, but in the present insulating composite block any abnormality was not acknowledged while ensuring a long-term endurability of more than one year.

The invention will not be limited to the above examples, thicknesses, lengths, widths and number of layers, and the modification and change within the subject matter of the invention will be included in the invention.

Claims

1. An insulating refractory composite block comprising a refractory fibre block having one or more faces coated by a flexible refractory board which consists of (a) 100 parts by weight of refractory materials such as alumina, magnesia, silica, chamotte and silicon carbide, (b) 1 to 20 parts by weight of an organic fibre and/or an inorganic fibre, and (c) 2 to 50 parts by weight of a binder.

2. An insulating refractory composite block as claimed in Claim 1, wherein the binder for said flexible refractory board consists of 3 to 50 parts by weight of a vinyl poiymer emulsion, in terms of solid parts.

3. An insulating refractory composite block as claimed in Claim 1, wherein the binder for said refractory board is a hard refractory board consisting of 2 to 10 parts by weight of at least one of aluminate, alkalisilicate, phosphate and alumina cement.

4. An insulating refractory composite block as claimed in Claim 3, wherein the refractory fibre block is coated with the flexible refractory board and the hard refractory board.

5. An insulating refractory composite block as claimed in any one of Claims 1 to 4, wherein said block is used as a refractory structure which is directly applied to the lining of hot face of various furnaces and vessels or the faces of inner walls of iron shell of these furnaces and vessels.

6. An insulating refractory composite block as claimed in Claim 2 wherein the minimum film forming temperature of said vinyl polymer emulsion is lower than 300C.

7. An insulating refractory composite block substantially as herein described in any one of Examples 1 to 3.