CA1079753A

CA1079753A - Process for repairing basic refractory linings

Info

Publication number: CA1079753A
Application number: CA286,595A
Authority: CA
Inventors: John Damiano
Original assignee: Quigley Co Inc
Current assignee: Quigley Co Inc
Priority date: 1976-09-27
Filing date: 1977-09-13
Publication date: 1980-06-17
Also published as: DE2743374C2; BR7706269A; AU2907577A; GB1565118A; FR2365768B1; JPS5737557B2; JPS5342211A; NL7710113A; IT1086497B; DE2743374A1; FR2365768A1; SE7709752L; BE859043A; SE430883B

Abstract

ABSTRACT OF THE DISCLOSURE

An improved process for repairing and prolonging the life of basic refractory linings of metallurgical vessels which comprises using a gunning mix consisting essentially of olivine in combination with up to about 15 weight per cent of dead-burn-ed magnesia based on the total solids content. A plasticizing clay or a water-soluble binder, each in amounts up to about 10 weight per cent based on the total solids content, may be included if desired.

Description

1~79753 This invention relates to an improved process for re-pairing and prolonging the useful life of basic refractory linings of metallurgical vessels.
Basic refractory linings, usualLy constructed of magnesia, dolomite or chrome-magnesia, are employed in metallurgical vessels such as ~teelmaking furnaces like ~he basic oxygen ~urnace and electric arc ~urnace. ~t is well known that ~hese refractory linlngs, although constructed o~ material having high temperature ~tability and resistance to attack by basic slags are nonetheless subject to erosion and wear by exposure to the high temperatures and basic slags present in the steelmaking operation. Efforts to prolong the life of these basic refractory linings and to repair cracks or other defects resulting from operation have primarily consisted of applying a particulate refractory material to the lS surface o~ the lining and building up a coating or deposit thereon.
Most commonly the particulate r~ractory material is applied by the gunning technique which consists of conveying the particulate refractory material in a stream of air to a nozzle where it is mixed with water and the resulting mixture is pneumatically pro- -pelled onto the refractory lining to form a coating or patch.
Alternatively, the particulate refractory material can be premixed with water and thereafter conveyed to the nozzle and applied as previously described.
The particulate refractory materials used in the prior art in gunning mixes for the purposes described above have been

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J 0~9753 based on magnesia, chrome-ore and dolomite. These materials have been chosen for the same reasons that they are used as materials of construction of the refractory linings themselves, that i5 high temperature stability and slag resistance. These materials suffer from some disadvantages, particularly that they are relatively expensive in view of the large volumes of mzlterial employed, and they exhibit a tendency to hydrate. This latter problem leads to cracking and structural failure of the deposited coating, parti-cularly when applied to cold furnace linings, and limits the utility of these materials.
United States Patent No. 3,201,501 provides for an asbestos-filled gunning mix based on magnesia or chrome-ore but wherein materials such as forsterite or olivine can be substituted or up to about 35 weight per cent of the magnesia or chrome-ore content. However, there i9 no suggestion therein that gunning mixes which are based on olivine or related materials such as forsterite as the ma~or component are desirable or would have properties suitable for applications in the repair and malnten-ance of refractory linings exposed to the extreme conditions of steelmaking operations. In fact, the prior art considered as a whole teaches to the contrary. Thus, brick employing olivine, u~ually in the form of forsterite formed by firing mlxtures of olivine and magnesia, has been limited to use in the lower tempera-ture parts of furnaces and is not used in applications where ex-posure to basic slags is required. This is considered to beprimarily due to the lack of slag resistance and to the lowering of refractoriness of the forsterite phase by the presence of other oxides, particularly iron oxides, at temperatures above 1650C.
See J.H. Che~ter3, ~Refractories Production and Properties", The Iron and Steel Institute, London, 1973. Olivine has also been

-3-~079753 used to form foundry casting molds and as a ladle lining product.
Olivine is also used in steelmaking operations as a flux-ing agent, such use of necessity requiring the olivine to dissolve in the molten slag. A commercial material for this use is marketed by International Minerals and Chemicals Corporation under the Registered Trademark "Oliflux".
There is a need to provide an improved process for re-pairing and prolonging the life of basic refractory linings of metallurgical vessels by use of a gunning mix based on more economical raw materials.
It is a further need to provide a process for xepairing and prolonging the lie of basio re~ractory linlngs by use of a gunning mix which while providing economy of raw materials and improved hydration resistance has durability, tempera~ure stability and slag resistance comparable to the prior art gunning mixes.
According to the present invention there is p~ovided an improved process for repairing and prolonging the life of basic - refractory linings which comprises gunning a particulate refractory material in water on to at least a part of said lin1ng and drying the resulting deposit, said refractory material consisting essen-tially of olivine which may optionally contain up to about 15 weight per cent dead-burned magnesia based on the total 801~ ds content of the mixture. Further, the mixture may optional~y con-tain a plasticizing clay in an amount up to about 10 weight per cent of the total solids content, and/or a water soluble binder in an amount up to about 10 weight per cent of the total solids content. The materials are mixed with water and gunned onto the surface of the basic refractory linings using equipment and techniques known in the art. The improved process provides signifi-cant economy of raw materials while giving good durability,

-4-~' 1 ' '' ~07~753 temperature stability ! slag resistance and improved hydration resistance.
In contrast to the results expected by consideration of the prior art and previous uses of olivine it has unexpectedly been found that gunning mixes based on a particulate refractory material consisting essentially of olivine can be used as a maintenance and repair material for basic refractory linings in steelmaking applications. The deposited coatir.g resulting from the use of the present process shows durability, temperature stability and slag resistance comparable to the magnesia and dolomite based mixes and offers the advantages of economy of raw materials and better hydration resistance.
Olivine is an abundant na~urally occuring miner~l con-sisting of a mixture o~ magnesium orthosilicate, or forsterite, and ferrous orthosilicate, or fayalite. The forsterite and fayalite content of the olivine can vary in the naturally occur-ing minerals over the range of about 70% to about 95% by weight as the forcterite phase. The olivine can also contain from about 2 to about 15 weight per cent of impurities, mainly in the form of enstatite, magnetite, talc and small amounts of other materials.
These impurities are no~ detrimental to the pre~ent proce3s and in this description the term olivine is intended to include all natural and synthetic minerals classified as olivine, i.eO ~ those being predominantly mixtures of forsterite and fayalite. Where reference is made to percentages of materials in the gunning mixes the weight of olivine is to be taken as the total weight of the mineral material including impurities.
The particle size distribution of the olivine is not critical to the invention and the variation of this parameter to conform to the needs of the particular application and to impart

-5-~0797~3 suitable handling characteristics to the gunning mix is known to those skilled in the art. Generally, however, the particLe size is 3 mesh United States sieve size or smaller. The olivine may for example contain a fraction having a particle siæe between 3 and 16 mesh United Sta~es sieve size and a second fraction smaller than 16 mesh.
While gunning mixes based on olivine alone can be used in accordance with the present inventio~ it ~s preferred to use olivine in combination with up to about 15 weight per cent of dead-burned magnesia based on the total solids content of the mixture. Most preferably, from about 5 to 10 weight per cent of dead-burned magne~ia is added to the ollvine in a suitably sized ~orm. By dead-burned magnesia i8 meant magnesia tha~ has been ~ormed by heating the hydroxide, carbonate or other salt to high temperature, u~uaLly in excess of 1700~C., such that the material is essentially magne~ium oxide in the periclase form. The parti-cle size is not criticai, but the dead-burned magnesia will not normally be present in a particle size larger than that of the olivine component of the gunning mix, and prefeLabLy is inc~ded as a pulverized form where~n at least about 50% of the material will pass through a 325 mesh United States sieve. When the gunning mix contains no added magnesia, up ~o about lS weight per cent of the olivine i~ preferably ;ncluded as such a p~lve~ized form.
While not necessary for the sa~isfactory performance of the gunning mixes of the present invention, other modifying mate-rials can be added. Thus, a plasticizing clay can be added in an amount up to about 10 weight per cent based on the total solids ; content of the mixture, preferably in an amount from about 1.0 to about 7.5 weight per cent. The clay acts to improve the process-

-6-, ability of the gunning m x and tO impro-.e adherence of the result-ing deposited coating to the refractory lining sub trate. Suit-able clays for this purpose are well known in the art and are readily available commercially. These include but are not limited S ~o such materials as bentonite, ball clay and mixture~ thereof.
It is also desirable but not essential to include a binder in the gunning mix composition such tha~ the adherence to the refractory lining substrate and the structural integrity of the deposited coating are enhanced. Th~ b~nder employed can be any which is compatible w~th the other materials in the composition but is preferably a water-soluble binder such as, but not limited to, alkaLi metal silicAtes, phosphates, chromates and borates as well as chromlc acid and boric acid, or mixt~res of th~se materials.
Pxeferred b~nder~ are ~od1um silicate, phosph~te, chromate and borate. The water-soluble blnder can be added in an amount up to about 10 weight per cent based on the total sol-ds cont~nt but is preferably added ir. an amount be~ween about 1 and S weight per oent based on the total solids contentO
The gunniny mixes of the present invention can be applied to the refractory linings of the steel furnace when the linings are either hot or cold. The practice ~n the industry is to app1y the mixes while the furnace i9 still hot to m~nimi~e down tim~ between heats. However, the improved stability to hydration of the ol vine based gunning mixe~ of the present nverltion compared tO prior magnesia and particularly dolomite based mixtures allows appllca~
tion to cold walls. When applied to hot lining~ the coa~lrlg is self-drying due to residual heat, but when applied to cold walls it is necessary to dry the coating by heating the furnace or al~owing a period for air drying.
The novel gunning mixes of the presenk invention are

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~79~S3 applied to the basic refractory lining of the steel furnace using gunning equipment conventional to the industry~ The dry gunning mix is either mixed with water or another ~uitable liquid at the nozzle of the gunning apparatus or i~ premixed with water to form a slurry and thereafter gunned onto the lining. The amount of water to be used in the resulting mixture that is gunned onto the lining should be sufficient to form a gunnable mixture which can be easily applied to the refractory linir.g but w'nich will be thick enough to adhere to that lining without flowing or slumping. The amount of water to be added is a variable understood by those skilled in the art and such persons will be able to use amounts of water to give gunning mixes appropriate for the particular application. Generally however, the water con~ent will be between about 10 and 20 weight per cent o~ the mixture applicd to the refractory lining.
In evaluating the performance of gunning mixes lt has been found advisable to conduct field tests in steelmaking furnaces since laboratory te~ts to determine s$ag resistance and other properties do not correlate well with actual field performance.
The rea30ns for this are not fully understood but it is considered that the environment o~ the steelmaking furnace and the condition o~ the basic refractory linlng after expo~ure to steelmaking opera-tions may contribute to affect the physical or chemical nature of the gunned deposited coating in a manner advantageous to its per-; 25 formance.
The present invention is il7ustra~ed by the following examples. It should be understood, however, that the invention i~ not limited to the specific details of these examples.
EXAMPLE_I
An olivine based gunning mix was prepared by intimately 107~37S3 mixing the following materials:
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Olivine, (-7 +16 mesh) 44.0 Olivine, (-16 mesh) 38.0 Dead-burned magnesia, pulverized (60 to 80% -325 mesh) 10.0 Ball Clay, Air Floated 5.0 Sodium Silicate, Powder ~.5 Sodium ~orate, Anhydrous Granular 0O5 The resulting gunning mix was gunned onto the high magnesia brick refractory llning of an Electric Arc Furnace used for steelmaking, the lining being at red-heat at the time of gunning. Application was made alongside a magnesia ba~ed gunning mix ~84~ magnesia) conventlonal to the industry for comparative purposes. ~Eter the next heat in making a degasser-ca~ter grade ~teel, where the tap temperature was about 1675~., the ollvine based deposit wae inspected and compared to the conventional magnesia based materlal. This inspection showed the olivine based material had durability, temperature stability and slag re-0 si~tance comparable to the conventional magnesia mix.EXAMPLE II
The gunning mlx de~cribed in Example I above was gunned into a hole in the magnesia brick ~ining of a Basic Oxygen Furnace and used to coat khe trun~ons. After eight hea~ inspection show-ed that the material remained in the hole and showed good durability,temperature stability and slag resistance~
EXAMPLE III
An olivine based gunning mlx was prepared by intimately mixing the following materials:

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~ILai7~753 w~. %
Olivine (-3 mesh, 30% t7 mesh, less than 15% -40 mesh) 89.5 Magnesia, pulverized (60 to 80% -325 mesh) 6.0 Ball Clay, Air Floated 2.0 Sodium Silicate, Powder 2.5 EXAMPLE IV
An olivine based gunning mix can be prepared by intimate-ly mixing the following m~terials:
Wt.
Olivine, (-3 mesh, 30~ +7 mesh;
less than 15% -40 mesh) 89.5 Olivine, pulverized t60 to 80~ -325 mesh) 6.0 Ball Clay, Air Floated 2.0 Sodium Silicate, Powder 2.5 EXAMPLE V
An oiiv.ne based gunning m~x can be prepared by intlmate-ly mixing the foliowing materials:
W~. %
Olivine, (-3 mesh, 30% +7 mesh, less than 15% -40 mesh) 84.0 Olivine, pulverized t60 to 80~ -325 me~h, 10.0 Sodium Sil1cate, Powder 6.0 .

Claims

The embodiments of the invention in which an ex-cluxive property or privilege is claimed are defined as follows:

1. A process for repairing and prolonging the life of basic refractory linings of metallurgical vessels which com-prises gunning a particulate refactory material in water onto at least a part of said lining and drying the result-in deposit, characterized by using as said particulate refractory material a mixture consisting essentially of olivine optionally in combination with 0 to 15 weight per cent of dead-burned magnesia based on the total solids content of siad mixture.

2. A process according to claim 1, characterized in that said mixture contains from 5 to 10 weight per cent of dead-burned magnesia based on the total solids content of said mixture.

3. A process according to claim 1, characterized in that said mixture contains up to about 10 weight per cent of a plasticizing clay based on the total solids content of said mixture.

4. A process according to any one of claims 1, 2 and 3, characterized in that said mixture contains up to about 10 weight per cent of a water-soluble binder based on the total solids content of said mixture.

5. A process according to any one of claims 1, 2 and 3, characterized in that siad mixture contains up to about 10 weight per cent based on the total solids content of said mixture of a water-soluble binder selected from the group consisting of sodium silicate, sodium phosphate, sodium chromate and sodium borate.

6. A process according to any one of claims 1, 2 and 3, characterized in that said mixture contains from 5 to 10 weight per cent dead-burned magnesia, 1.0 to 7.5 weight per cent of plasticizing clay and 1 to 5 weight per cent of a water-soluble binder based on the total solids content of said mixture.

7. A process according to any one of claims 1, 2 and 3, wherein said mixture contains from 5 to 10 weight per cent of dead-burned magnesia, 1.0 to 705 weight per cent of a plasticizing clay and 1 to 5 weight per cent of a water-soluble binder selected from sodium silicate phophate, sodium chromate and sodium borate based on the total solids content of said mixture.

8. A process according to claim 2, characterized in that said mixture contains up to about 10% by weight of a plasticizing clay based on the total solids content of said mixture.

9. A process according to either of claims 2 and 8, characterized in that said mixture contains up to about 10%
by weight of a water-soluble binder based on the total solids content of said mixture,