GB1565118A

GB1565118A - Gunning process for basic refractory linings

Info

Publication number: GB1565118A
Application number: GB39173/77A
Authority: GB
Original assignee: Quigley Co Inc
Current assignee: Quigley Co Inc
Priority date: 1976-09-27
Filing date: 1977-09-20
Publication date: 1980-04-16
Also published as: DE2743374C2; DE2743374A1; BE859043A; FR2365768A1; AU2907577A; IT1086497B; BR7706269A; CA1079753A; NL7710113A; FR2365768B1; SE430883B; JPS5342211A; JPS5737557B2; SE7709752L

Description

(54) GUNNING PROCESS FOR BASIC REFRACTORY LININGS (71) We, QUIGLEY COMPANY INC., a corporation organized under the laws of the State of New York, United States of America, of 235 East 42nd Street, New York, New York, United States of America do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to refractories and particularly to an improved process for repairing and prolonging the useful life of basic refractory linings of metallurgical vessels.

Basic refractory linings, usually constructed of magnesia, dolomite or chome-magnesia, are employed in metallurgical vessels such as steel making furnaces like the basic oxygen furnace and electric arc furnace. It is well known that these refractory linings, although constructed of material having high temperature stability and resistance to attack by basic slags are nonetheless subject to erosion and wear by exposure to the high remperatures 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 surface of the lining and building up a coating or deposit thereon.Most commonly the particulate refractory 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 propelled 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 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 is 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 material employed, and they exhibit a tendency to hydrate. This latter problem leads to cracking and structural failure of the deposited coating, particularly when applied to cold furnace linings, and limits the utility of these materials.

U.S. Patent No. 3,201,501 provides for an asbestos-filled gunning mix based on magnesia or chars me-ore but wherein materials such as forsterite or olivine can be substituted for up to about 35 weight percent of the magnesia or chrome-ore content. However, there is no suggestion therein that gunning mixes which are based on olivine or related materials such as forsterite as the major component are desirable or would have properties suitable for applications in the repair and maintenance 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. usually in the form of forsterite formed by firing mixtures of olivine and magnesia, has been limited to use in the lower temperature parts of furnaces and is not used in applications where exposure to basic slags is required.

This is considered to be primarily 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 16500C. See J. H. Chesters. "Refractories Production and Properties", The Iron and Steel Institute. London, 1973. Olivine has also been used to form foundry casting molds and as a ladle lining product.

Olivine is also used in steelmaking operations as a fluxing agent, such use of necesslty 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".

It is an object of this invention to provide an improved process for repairing 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 object to provide a process for repairing and prolonging the life of basic refractory linings by use of a gunning mix which while providing economy of raw materials and improved hydration resistance has durability, temperature stability and slag resistance comparable to the prior art gunning mixes.

The present invention accordingly provides a method for repairing and prolonging the life of basic refractory linings of metallurgical vessels which comprises gunning a particulate refractory material which is a mixture consisting essentially of olivine optionally in combination with up to 15 weight percent of dead-burned magnesia based on the total solids content of the mixture in water onto at least a part of said lining and drying the resulting deposit. Further, the gunning mixture may optionally contain a plasticizing clay in an amount up to 10 weight percent of the total solids content, and/or a water soluble binder in an amount up to 10 weight percent 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 significant economy of raw materials while giving good durability, 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 coating resulting from the use of the present invention 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 naturally occurring mineral consisting of a mixture of magnesium orthosilicate, or forsterite, and ferrous orthosilicate, or fayalite. The forsterite and fayalite content of the olivine can vary in the naturally occurring minerals over the range of about 70% to about 95% by weight as the forsterite phase. The olivine can also contain from about 2 to about 15 weight percent of impurities, mainly in the form of enstatite, magnetite, talc and small amounts of other materials. These impurities are not detrimental to the present process and in this description the term olivine is intended to include all natural and synthetic minerals classified as olivine, i.e. 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 suitable handling characteristics to the gunning mix is known to those skilled in the art.

Generally, however, the particle size is 3 mesh U.S. sieve size or smaller. The olivine may for example contain a fraction having a particle size between 3 and 16 mesh U.S. 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 invention it is preferred to use olivine in combination with up to about 15 weight percent of dead-burned magnesia based on the total solids content of the mixture. Most preferably, from about 5 to 10 weight percent of dead-burned magnesia is added to the olivine in a suitably sized form. By dead-burned magnesia is meant magnesia that has been formed by heating the hydroxide, carbonate or other salt to high temperature, usually in excess of 1700 C, such that the material is essentially magnesium oxide in the periclase form.The particle size is not critical, 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 preferably is included as a pulverized form wherein at least about 505? of the material will pass through a 325 mesh U.S. sieve. When the gunning mix contains no added magnesia. preferably up to 15 weight percent of the olivine has a particle size so as to pass through a 325 mesh U.S.

sieve.

While not necessary for the satisfactory performance of the gunning mixes of the present invention, other modifying materials can be added. Thus. a plasticizing clay can be added in an amount up to 10 weight percent based on the total solids content of the mixture, preferably in an amount from 1.0 to 7.5 weight percent. The clay acts to improve the processability of the gunning mix and to improve adherence of the resulting deposited coating to the refractory lining substrate. Suitable clays for this purpose are well known in the art and are readily available commercially. These include but are not limited to such materials as bentonite, ball clay and mixtures thereof.

It is also desirable but not essential to include a binder in the gunning mix composition such that the adherence to the refractory lining substrate and the structural integrity of the deposited coating are enhanced. The binder employed can be any which is compatible with 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 chromic acid and boric acid, or mixtures of these materials. Preferred binders are sodium silicate, phosphate, chromate and borate. The water-soluble binder can be added in an amount up to 10 weight percent based on the total solids content but is preferably added in an amount between 1 and 5 weight percent based on the total solids content.

The gunning 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 in the industry is to apply the mixes while the furnace is still hot to minimize down time between heats. However. the improved stability to hydration of the olivine based gunning mixes of the present invention compared to prior magnesia and particularly dolomite based mixtures allows application to cold walls. When applied to hot linings the coating 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 allowing a period for air drying.

The novel gunning mixes of the present invention are 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 suitable liquid at the nozzle of the gunning apparatus or is 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 lining but which 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 content will be between 10 and 20 weight percent of the mixture applied to the refractory lining.

In evaluating the performance of gunning mixes it has been found advisable to conduct field tests in steelmaking furnaces since laboratory tests to determine slag resistance and other properties do not correlate well with actual field performance. The reasons for this are not fully understood but it is considered that the environment of the steelmaking furnace and the condition of the basic refractory lining after exposure to steelmaking operations may contribute to affect the physical or chemical nature of the gunned deposited coating in a manner advantageous to its performance.

The present invention is illustrated by the following examples. It should be understood, however, that the invention is not limited to the specific details of these examples.

Example I An olivine based gunning mix was prepared by intimately mixing the following materials: Wt;C/o Olivine, (7 +16 mesh) 44.0 Olivine, - 16 mesh) 38.0 Dead-burned magnesia. Pulverized 10.0 (60 to 80% -325 mesh) Ball Clay, Air Floated 5.0 Sodium Silicate, Powder 2.5 Sodium Borate, Anhydrous Granular 0.5 The resulting gunning mix was gunned onto the high magnesia brick refractory lining 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 based gunning mix (84% magnesia) conventional to the industry for comparative purposes.After the next heat in making a degasser-caster grade steel, where the tap temperature was about 1675"C, the olivine based deposit was inspected and compared to the conventional magnesia based material. This inspection showed the olivine based material had durability, temperature stability and slag resistance comparable to the conventional magnesia mix.

Example II The gunning mix described in Example I above was gunned into a hole in the magnesia brick lining of a Basic Oxygen Furnace and used to coat the trunions. After eight heats inspection showed that the material remained in the hole and showed good durability, temperature stability and slag resistance.

Example III An olivine based gunning mix was prepared by intimately mixing the following materials: Wt.% Olivine 89.5 (-3 mesh, 30% +7 mesh, less than 15%-40 mesh) Magnesia, Pulverized 6.0 (60 to 80% -325 mesh) Ball Clay, Air Floated 2.0 Sodium Silicate, Powder 2.5 Example IV An olivine based gunning mix can be prepared by intimately mixing the following materials: Wt.% Olivine 89.5 (-3 mesh, 30% +7 mesh, less than 158Sc- -40 mesh) Olivine, Pulverized 6.0 (60 to 80% -325 mesh) Ball Clay, Air Floated 2.0 Sodium Silicate, Powder 2.5 Example V An olivine based gunning mix can be prepared by intimately mixing the following materials:: Wit.50 Olivine 84.0 (-3 mesh, 30% +7 mesh, less than 15% -40 mesh) Olivine, Pulverized 10.0 (60 to 80% -325 mesh) Sodium Silicate, Powder 6.0 WHAT WE CLAIM IS: 1. A method for repairing and prolonging the life of basic refractory linings of metallurgical vessels which comprises gunning a particulate refractory material which is a mixture consisting essentially of olivine optionally in combination with up to 15 weight percent of dead-burned magnesia based on the total solids content of the mixture in water onto at least a part of said lining and drying the resulting deposit.

2. A method as claimed in claim 1 wherein the mixture contains from 5 to 10 weight percent of dead-burned magnesia.

3. A method as claimed in either claim 1 or claim 2 wherein the mixture contains up to 10 weight percent of a plasticizing clay based on the total solids content of the mixture.

4. A method as claimed in claim 3 wherein the mixture contains from 1.0 to 7.5 weight percent of the platicizing clay.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Example II The gunning mix described in Example I above was gunned into a hole in the magnesia brick lining of a Basic Oxygen Furnace and used to coat the trunions. After eight heats inspection showed that the material remained in the hole and showed good durability, temperature stability and slag resistance. Example III An olivine based gunning mix was prepared by intimately mixing the following materials: Wt.% Olivine 89.5 (-3 mesh, 30% +7 mesh, less than 15%-40 mesh) Magnesia, Pulverized 6.0 (60 to 80% -325 mesh) Ball Clay, Air Floated 2.0 Sodium Silicate, Powder 2.5 Example IV An olivine based gunning mix can be prepared by intimately mixing the following materials: Wt.% Olivine 89.5 (-3 mesh, 30% +7 mesh, less than 158Sc- -40 mesh) Olivine, Pulverized 6.0 (60 to 80% -325 mesh) Ball Clay, Air Floated 2.0 Sodium Silicate, Powder 2.5 Example V An olivine based gunning mix can be prepared by intimately mixing the following materials:: Wit.50 Olivine 84.0 (-3 mesh, 30% +7 mesh, less than 15% -40 mesh) Olivine, Pulverized 10.0 (60 to 80% -325 mesh) Sodium Silicate, Powder 6.0 WHAT WE CLAIM IS:

1. A method for repairing and prolonging the life of basic refractory linings of metallurgical vessels which comprises gunning a particulate refractory material which is a mixture consisting essentially of olivine optionally in combination with up to 15 weight percent of dead-burned magnesia based on the total solids content of the mixture in water onto at least a part of said lining and drying the resulting deposit.

5. A method as claimed in any one of claims 1 to 4 wherein the mixture contains up to

10 weight percent of a water-soluble binder based on the total solids content of the mixture.

6. A method as claimed in claim 5 wherein the mixture contains 1 to 5 percent of the water soluble binder.

7. A method as claimed in either claim 5 or claim 6 where said water-soluble binder is selected from sodium silicate, sodium phosphate, sodium chromate or sodium borate.

8. A method as claimed in any one of claims 1 to 7 and substantially as hereinbefore described.

9. Basic refractory linings whenever treated by the method claimed in any one of claims 1 to 8.