Tuyere Formed By Cementing A Ceramic Liner In A Metal Tube

Abstract

A method of bonding a high density, low-porosity, abrasion-resistant, ceramic liner in a metal tube, such as a tuyere or an oxygen lance. The method comprises applying a sodium silicate-refractory aggregate cement to one of the surfaces to be joined, and inserting the liner in the tube. The cement need not be dried, as it does not run. Therefore, the tube can be used immediately, even in high-temperature applications.

Description

In bottom blown oxygen steelmaking processes, dual concentric tuyeres are often installed in a removable bottom which is then installed in a furnace prior to charging of a heat. The inner and outer tubes of the tuyere are usually made of stainless steel, but can be made from a number of other materials such as ordinary carbon steel, special alloy steels or even copper. Oxygen is injected into the steelmaking furnace through the central tube of the tuyere, and a jacket gas, which can be an inert gas such as argon or nitrogen or a hydrocarbon such as propane, butane, methane or natural gas is injected through the annular space formed by the central and outer tubes. When lime or other flux is to be injected with the oxygen, either in a bottom blown or a top blown process, it is desirable to provide a ceramic liner to prevent erosion of the central tube by granular particles of flux.

Such flux particles are entrained in oxygen and are blown either into the bath of molten metal through a tuyere in a bottom blown converter or onto the surface of the bath through an oxygen lance in a top blown converter. The term "tuyere" is used in this specification to mean "tuyere or lance." These flux particles can cause early erosion of the tuyere. It is, therefore, desirable to include a liner of a low-porosity, high-density, abrasion-resistant ceramic material within the tuyere.

Heretofore, in bottoms manufactured for the bottom blown oxygen steelmaking process, an alumina tube has been installed in the metal tube of the tuyere and bonded thereto with a colloidal silica adhesive. Use of this adhesive necessitated placing the colloidal silica under pressure. Further, the adhesive must have been completely dried before the tuyere was used. If the adhesive was not completely dried, this adhesive, which is a flowable material, would flow from between the ceramic liner and the metal tube, leaving the ceramic liner free to be blown into the furnace when the oxygen was turned on.

We have invented a method of cementing ceramic liners in metal tubes, which avoids the problems that were attendant with the prior method.

It is an object of our invention to provide a method of cementing ceramic liners in tuyeres after the tuyeres have been installed in a furnace bottom and the bottom has itself been installed in the furnace, and the parts are at a relatively high temperature.

It is also an object to provide a method of cementing ceramic liners in tuyeres which does not require drying the cement mixture prior to use of the tuyere.

It is a further object of our invention to provide a method of cementing ceramic liners in tuyeres that will enable the tuyere to be used immediately after the liner is installed.

It is another object to provide a method of cementing ceramic liners in tuyeres that does not require any special equipment, either to handle the cement or to dry the cement after it is applied.

These and other objects will become more apparent by reference to the following detailed specification and the appended drawing in which:

FIG. 1 is a longitudinal sectional view of a dual concentric tuyere taken along line I--I of FIG. 2.

FIG. 2 is a cross-sectional view of a dual concentric tuyere having a ceramic liner in the central tube of the tuyere, taken along line II--II of FIG. 1.

The drawings show a dual concentric tuyere which comprises a stainless steel outer tube 10 having nipples 12 which act as spacers, and stainless steel inner tube 13. The inner tube has a ceramic liner 14 of a low porosity, abrasion resistant ceramic material, such as alumina or mullite. These materials have a very low porosity approaching zero. The liner is held in tube 12 by a layer of cement 16.

We prepare a cement which by weight consists essentially of about 1 to 10 percent alkali metal silicate mixture and 90 to 99 percent refractory aggregate. The preferred range of alkali metal silicate is from 3 to 6 percent, the balance being refractory aggregate. The preferred alkali metal silicate is sodium silicate, although we can use lithium or potassium silicate. In the example of sodium silicate, the sodium oxide content by weight may be in the range of about 19 to 51 percent, and the silica content about 24 to 80 percent, the balance water of crystallization and incidental impurities. The preferred range is about 22 to 32 percent sodium oxide and 50 to 60 percent silica, and the optimum about 27 percent sodium oxide and 55 percent silica. The sodium silicate is water soluble, and it may be either in powdered or liquid form, i.e., water glass. The sodium silicate is mixed with an alumina-silica refractory aggregate, such as calcined clay, raw clay, kyanite, mullite, bauxite, alumina, and mixtures thereof. The aggregate should have a thermal expansion that approximates that of the ceramic liner. The particle size of the refractory aggregate must be -20 mesh and preferably will be -100 mesh. Next we add sufficient water to sodium silicate - refractory aggregate cement to obtain a trowelable consistency. The percentages of sodium silicate and aggregate are on a water free basis, that is, are measured prior to adding water to obtain a trowelable consistency.

Ceramic liner 14 is installed in tube 12 by applying an excess of the prepared cement to one of the two surfaces to be joined, that is, to the exterior surface of the ceramic liner or to the interior surface of the metal tube. The ceramic liner is then inserted into the tube in a manner to effect substantially complete contact of the cement with both of the surfaces being joined. We have found that insertion with a rotary motion will effect such substantially complete contact. The consistency of the cement being such that it does not run, the tuyere may be used immediately after it is installed in a furnace, or the liner may even be installed in a tuyere which has already been installed in a furnace, and used immediately, even at high temperatures. However, inasmuch as there is no requirement that the tuyere be used immediately, it may first be dried, if desired.

One of the advantages of our invention is that the external diameter of the ceramic liner need not be within any particularly close tolerances. The cement layer can be as thick as or even thicker than the thickness of the ceramic liner.

It is readily apparent from the foregoing that we have invented a method of cementing ceramic liners in tuyeres before or after such tuyeres are installed in a furnace, which method requires neither special cement handling equipment nor cement drying apparatus, and which method provides a resulting ceramiclined tuyere that can be used immediately without drying the cement.

Claims

We claim:

1. A composite tube comprising a metal tube, a high-density, low-porosity, abrasion-resistant ceramic tube substantially concentric with said metal tube, a refractory cement layer between said tubes bonding said tubes together, said cement consisting essentially by weight of:

about 1 to 10 percent of water-soluble alkali metal silicate mixture having an alkali metal oxide content of about 19 to 51 percent and a silica content of about 24 to 80 percent, balance water of crystallization and incidental impurities; and

about 90 to 99 percent of an alumina-silica refractory aggregate which has a particle size of about -20 mesh and is selected from the group consisting of calcined clay, raw clay, kyanite, mullite, bauxite, alumina and mixtures thereof.

2. A composite tube according to claim 1 wherein said metal tube is steel.

3. A composite tube according to claim 1 wherein said metal tube is stainless steel.

4. A composite tube according to claim 1 wherein said metal tube is copper.

5. A composite tube according to claim 1 wherein said ceramic tube is alumina.

6. A composite tube according to claim 1 wherein said ceramic tube is mullite.

7. A composite tube according to claim 1 wherein said alkali metal is sodium.

8. A composite tube according to claim 7 wherein said sodium silicate mixture has a sodium oxide content of from 22 to 32 percent and a silica content of from 50 to 60 percent.

9. A composite tube according to claim 7 wherein said cement consists essentially of about 3 to 6 percent of said sodium silicate mixture and about 94 to 97 percent of said refractory aggregate.

10. A composite tube according to claim 7 wherein the particle size of said refractory aggregate is -100 mesh.

11. A tuyere comprising:

a composite tube according to claim 1,

an outer tube surrounding said composite tube and forming an annular space therebetween, and

spacing means between said tubes to maintain said tubes in substantially concentric relation.

12. A tuyere according to claim 11 wherein said outer tube is steel.

13. A tuyere according to claim 11 wherein said outer tube is stainless steel.

14. A tuyere according to claim 11, wherein said outer tube is copper.