GB1575124A

GB1575124A - Tundishes and lining slabs therefor

Info

Publication number: GB1575124A
Application number: GB39134/77A
Authority: GB
Original assignee: Foseco Trading AG
Current assignee: Foseco Trading AG
Priority date: 1976-10-08
Filing date: 1977-09-20
Publication date: 1980-09-17
Also published as: JPS5346310A; BE859506A; SE7711284L; FR2366902A1; AT358753B; SE436844B; DE2745271A1; CA1075724A; ES463027A1; BR7706717A; FR2366902B1; DE2745271C2; ZA776026B; ATA720077A; IT1091429B

Description

(54) IMPROVEMENTS IN OR RELATING TO TUNDISHES AND LINING SLABS THEREFOR (71) We, FOSECO-TRADING A.G., a Swiss Company of Langenjohnstrasse 9, 7000 Chur, Switzerland, 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 tundishes and lining slabs therefor and in particular to tundishes used in continuous casting of steel having an outer metal casing, a permanent refractory lining in the metal casing and an expendable inner lining made of refractory heat insulating material.

Tundishes of this general type are described in British Patent Specification 1364665. During continuous casting, molten steel is poured into the tundish and flows from the tundish through one or more nozzles set in the base of the tundish into a mould. The presence of a tundish keeps the flow of molten steel into the continuous casting mould substantially constant and any non-metallic inclusions in the molten metal tend not to be entrained in the stream or streams of molten metal leaving the nozzle(s). The permanent lining may be made of refractory brick or may be cast of refractory concrete while the inner expendable lining, which is removed and thrown away whenever the tundish is emptied of metal, its usually made of a composition comprising refractory fibre, refractory filler and binder.

One advantage of using a heat insulating refractory inner lining is that preheating of the whole interior of the tundish prior to pouring molten metal steel therein, necessary with tundishes which are simply metal casings lined with refractory bricks, is avoided. Instead, only the nozzle(s) and areas of the interior of the tundish adjacent to the nozzle(s) need to be preheated.

The use of an expendable inner lining as described in the above noted specification has become widespread in recent years on account of the various advantages such a lining affords. As well as the avoidance of preheating the entire tundish, the inner expendable lining reduces the amount of heat lost from the molten metal and acts to protect the permanent lining of the tundish.

Because the molten metal is kept relatively hot, the amount of skull left behind when the tundish has been emptied is reduced and such skull can easily be removed together with the expendable lining.

Although the adoption of an inner expendable lining has been widespread, there are certain difficulties encountered in certain areas of continuous casting using such a technique. First of all, there is a growing tendency to extend the length of time of a single continuous casting cycle by successively feeding the tundish from each of a plurality of ladles. As soon as one ladle is empty, another is moved into place and molten metal tapped from the new ladle into the tundish. Working in this way, continuous casting runs of seven or eight hours duration have been achieved. Such long runs place very severe strains on the durability of inner liners for tundishes. The problem is particularly severe in the case of certain steel types, e.g. high manganese steel, leading to rapid deterioration of expendable lining materials.

A further disadvantage of known expendable lining materials resides in their poor resistance against slag attack. This can lead to erosion about a specific horizontal level with subsequent penetration of metal and slag to the permanent lining of the tundish with adverse effects. Also, the known materials have poor resistance to erosion caused by turbulence in the molten metal, particularly in the region where molten metal enters the tundish in a stream.

According to the present invention there is provided a tundish comprising an outer metal casing, a permanent lining of refractory material and an expendable inner lining formed of a set of slabs of refractory heat insulating material of a composition comprising by weight 60 to 920/n refractory filler, 2 to 16% binder, 1 to 10% fibre and 5 to 30% non-fibrous carbonaceous material.

The carbonaceous material increases the life of the slabs when exposed to molten metal. Slabs of the composition first noted are novel and constitute a further feature of the invention.

We have found that such compositions in the form of tundish lining slabs are resistant to attack by molten steel for a sufficient length of time to enable sequence casting to take place without damaging the lining slabs to such an extent that substantial damage to the permanent lining can take place. This advantage is obtained both for normal steels and special steels such as high manganese steel.

The carbonaceous material improves the resistance of the composition to erosion by basic slag which may be present in the tundish and also resistance to erosion caused by turbulence of molten metal in the tundish particularly in the region where the molten metal enters the tundish as a stream.

At the same time all of the advantages achieved by the use of an inner expendable lining, explained in the specification referred to above, are maintained.

The reason for this remarkable improvement in performance is not fully understood though it is believed that the principal effect of including a carbonaceous material in the composition of the inner expendable liner is substantially to diminish the rate of chemical attack between the slag on top of the molten metal surface and the usually siliceous filler constituting a principal ingredient of the lining.

The refractory filler which constitutes the principal component of the composition for the inner liner may be any highly refractory particulate filler material known for use in refractory heat insulating compositions, for example silica sand, quartz, alumina, magnesia, magnesite, chamotte, grog, mullite, chromite and zircon. The composition should contain at least 60% by weight refractory filler since if the amount of refractory filler is less the lining slabs tend to be too porous and become impregnated with molten steel and slag, which is disadvantageous and can shorten the life of the inner lining.

The carbonaceous material consists substantially or wholly of elemental carbon.

Among the materials which may be used are coke, graphite, carbon electrode scrap, pitch, tar, carbon black, anthracite dust and charcoal powder. The materials of choice are graphite and carbon electrode scrap.

The content of carbonaceous material in the composition of the expendable inner lining is at least 5% by weight in order to ensure an increase in durability relative to a similar composition but comprising wholly noncarbonaceous filler. It is undesirable to incorporate more than 30% by weight of such material into the inner lining composition since it reduces the strength of the composition and its heat insulation value. There is also a risk, particularly in the case of low carbon steel and other steels where the carbon content is critical, of carbon pickup by the molten metal, which is undesirable.

The binder used may be organic, inorganic or a mixture of the two.

Preferably the binder is wholly organic or a mixture of organic and inorganic binder, the organic binder contributing 2 to 10% by weight. Less than 2% of organic binder is insufficient to give the slabs adequate strength. As organic binders there are preferred thermosetting resins, particularly phenol formaldehyde resins, urea formaldehyde resins and furane resins.

Inorganic binders which may be used in admixture therewith are for example colloidal silica sol, colloidal alumina sol, various phosphate binders, hydraulic and refractory cements, bonding clays such as ball clay and bentonite.

The inclusion of a proportion of fibre in the composition of the slabs leads to a number of advantageous properties of the slab. It improves the heat insulation value, it raises the strength of the slab and it additionally. lowers the density of the slab.

The fibre used may be all organic, all inorganic, or a mixture of the two. Suitable inorganic fibres which may be used are for example asbestos, glass wool, aluminium silicate fibre and calcium silicate fibre. The latter may be used in their commercially available impure forms of slag wool and rock wool. Preferably the composition of the slabs includes not more than 6% by weight of inorganic fibre. This is because of the relatively low melting point of any of these inorganic fibres compared with the casting temperature of molten steel. During long casting periods, such fibres may melt and the molten material thereby generated may form a complex system with other ingredients of the composition, notably siliceous filler, also of melting point lower than the casting temperature of the molten metal. This would lead to progressive erosion of the composition which is undesired. These adverse effects may be avoided by ensuring that the composition contains not more than 6% of inorganic fibre.

Suitable organic fibres which may be used include paper pulp, either natural or formed of waste paper, and a wide variety of natural and synthetic fibrous materials. Cotton and various synthetic fibres such as rayon, nylon, polyacrylonitrile and polyethylene terephthalate fibre may be mentioned.

Preferably the content of organic fibre in the composition does not exceed 4% by weight since quantities above that percentage tend to lead to substantial porosity in the lining slab which tends to reduce the erosion resistance of the slab over a long period of time.

The slabs of refractory heat insulating material of the composition specified above may be made by any method convenient and methods for making such materials are known and widely practiced. The preferred method is to form an aqueous slurry of the ingredients of the slab and then to dewater portions of this slurry in an appropriate mould to leave a damp slab of the required shape and size. On drying such a slab, e.g. in an oven, a rigid, strong bonded shape is obtained which may be assembled in the tundish in known fashion to form the expendable lining. Drying is usually carried out at 150 to 2000C for a sufficient length of time to drive off substantially all of the water.

The following examples will serve to illustrate the invention. All percentages are by weight.

EXAMPLE I The composition for the slabs was: silica sand 63% asbestos fibre 3% paper pulp 2% crushed graphite 26% phenol formaldehyde resin 3% colloidal silica sol 3% These ingredients in the proportions stated were mixed with sufficient water to form a slurry of appropriate consistency.

Portions of this slurry were poured into patterns the base of which was formed by metal gauze through which the slurry was dewatered to leave shapes of thickness 30 mm. The shapes were thereafter dried at 150 to 2000 C, various shapes being produced in order to constitute a complete lining for a tundish when assembled.

Slabs so made were used to line a 6-tonne capacity tundish consisting of a metal casing lined internally with a permanent lining of fire-brick. The lining slabs were used to line the floor and sidewalls of the tundish save for the immediate vicinity of the nozzles.

After lining, the nozzles were heated for 30 minutes by gas burners. Thereafter the tundish was put to use in continuous casting plain carbon steel. Sequence casting was employed, 6 ladlefuls, each of 60-tonnes, being passed through the tundish over a time of 6 hours. At the end of casting, which had been troublefree, the tundish was allowed to empty and the tundish then visually inspected. The quantity of skull remaining in the tundish was substantially less than normal for the steelworks in question. On inversion of the tundish, the little skull present fell out together with the remains of the expendable lining. There was substantially no damage to the permanent fibrebrick lining.

EXAMPLE 2 30 mm thick lining slabs were made using the method of Example I but using a composition as follows: silica sand 80% crushed waste paper 1% phenol formaldehyde resin 4% graphite particles (crushed electrode scrap) 13% carbon black 2% The lining was used inside a 5-tonne capacity tundish which had a permanent monolithic lining formed of a cast refractory composition. The tundish was put to service casting plain carbon steel over a period of 7.5 hours. During this time eight 40-tonne ladlefuls of steel were passed through the tundish.

Results were satisfactory and similar to those obtained in Example 1.

EXAMPLE 3 35 mm thick liner slabs were made using the method of Example I but using the following composition: magnesia 73% asbestos fibre 2% aluminosilicate fibre 2% particulate graphite 14% coke powder 4% phenol formaldehyde resin 4% colloidal silica sol 1% The slabs so made were used to line a tundish having a permanent lining of firebrick and a capacity of 8 tonnes. High manganese steel (11.5% manganese) was then cast through this tundish for a period of 6 hours 20 minutes. During this time 5 ladlefuls each of 100 tonne were passed through the tundish. After casting, it was observed that little erosion of the liner had taken place and that the little skull present and expendable liner could be removed easily from the tundish. During casting molten metal flow was maintained through all the nozzles without difficulty at all times.

EXAMPLE 4 A mixture was made up of silica sand 88% asbestos fibre 1% particulate graphite 6% phenol formaldehyde resin 5% The mixture was formed to a thick paste by the addition of one part by weight water per 5 parts by weight mixture. The paste was then pressed into slab shapes each 40 mm thick and the shapes subsequently dried. A tundish of the type noted in Example 3 was then lined with such slabs and used for casting low carbon (0.2%) steel for 6 hours.

During this time 5 ladlefuls each of 100 tonnes of metal were passed through the tundish.

After casting, the expendable lining was examined and found to be substantially of the original thickness prior to casting. The expendable lining and skull were easily removed from the tundish and no difficulty was experienced during casting with nozzle blockages.

EXAMPLE 5 Tundish lining slabs were made of the following composition: silica flour 57.1% silica sand 26.0% urea formaldehyde resin 1.0% phenol formaldehyde resin 3.0% paper pulp 2.9% carbon electrode scrap (particle size less than 0.25 mm) 10.0% The slabs were made by forming an aqueous slurry of the above ingredients and dewatering portions of that slurry on to a metal former to form damp slabs. These slabs were then dried in an oven.

Dry slabs were then used to form an inner lining on the walls of a refractory brick lined tundish for a two-strand bloom casting machine. In the area of the walls which, when the tundish was in use, would be adjacent the stream of molten metal entering the tundish, the slabs were used as a replacement for high alumina refractory bricks which would normally be used to withstand the highly erosive effects of the impinging molten metal stream.

The so lined tundish was used for casting 0.6 manganese steel for 2 hours 20 minutes.

During this time, three 80-tonne ladlefuls of molten steel were passed through the tundish, the steel being at 15600C in the ladles and 1525"C in the tundish.

After the end of casting, the lining was examined and it was found that the lining slabs according to the present invention had suffered no significant erosion, even adjacent the area of the incoming molten metal stream.

Identical slabs were also used to line a tundish used for 1 hour 38 minutes to cast two 60-tonne ladles of normal steel. Ladle temperature was 15700C and tundish temperature 15300C. Similar results were obtained in that after use the lining slabs showed no significant erosion. In both cases, it was particularly noticeable that very little sintering of the material of the slabs had taken place.

WHAT WE CLAIM IS: 1. A tundish comprising an outer metal casing, a permanent lining of refractory material and an expendable inner lining formed of a set of slabs of refractory heat insulating material of a composition comprising by weight 60 to 92% refractory filler, 2 to 16% binder, 1 to 10% fibre and 5 to 30% non-fibrous carbonaceous material.

2. Atundish according to claim 1 wherein the darbonaceous material consists of elemental carbon.

3. A tundish according to claim 1 wherein the carbonaceous material is graphite.

4. A tundish according to any one of claims 1 to 3 wherein the composition comprises 2 to 10% by weight organic binder and 0 to 6% by weight inorganic binder.

5. A tundish according to claim 4 wherein the organic binder is a thermosetting resin.

6. A tundish according to any of claims 1 to 5 wherein the composition comprises a maximum of 6% by weight of inorganic fibre and a maximum of 4% by weight of organic fibre.

7. A tundish according to any one of the preceding claims wherein the composition of the slab comprises siliceous refractory filler, elemental carbon, organic and inorganic binding agents and organic and inorganic fibre.

8. A tundish according to claim 1 and substantially as hereinbefore described with reference to any one of the foregoing Examples 1 to 4.

9. A tundish according to claim 1 and substantially as hereinbefore described with reference to Example 5.

10. A tundish lining slab formed of a refractory heat insulating material of a composition comprising, by weight, 60 to 92% refractory filler, 5 to 30% non-fibrous carbonaceous material, 2 to 16% binder and 1 to 10% fibre.

11. A slab according to claim 10 wherein the carbonaceous material is elemental carbon.

12. A slab according to claim 10 wherein the carbonaceous material is graphite.

13. A slab according to any one of claims 10 to 12 and including 2-10% by weight organic binder and 06% by weight inorganic binder.

14. A slab according to claim 13 wherein the organic binder is a thermosetting resin.

15. A slab according to any of claims 12 to 14 and comprising at most 6% by weight inorganic fibre and at most 4% by weight of organic fibre.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The mixture was formed to a thick paste by the addition of one part by weight water per 5 parts by weight mixture. The paste was then pressed into slab shapes each 40 mm thick and the shapes subsequently dried. A tundish of the type noted in Example 3 was then lined with such slabs and used for casting low carbon (0.2%) steel for 6 hours. During this time 5 ladlefuls each of 100 tonnes of metal were passed through the tundish. After casting, the expendable lining was examined and found to be substantially of the original thickness prior to casting. The expendable lining and skull were easily removed from the tundish and no difficulty was experienced during casting with nozzle blockages. EXAMPLE 5 Tundish lining slabs were made of the following composition: silica flour 57.1% silica sand 26.0% urea formaldehyde resin 1.0% phenol formaldehyde resin 3.0% paper pulp 2.9% carbon electrode scrap (particle size less than 0.25 mm) 10.0% The slabs were made by forming an aqueous slurry of the above ingredients and dewatering portions of that slurry on to a metal former to form damp slabs. These slabs were then dried in an oven. Dry slabs were then used to form an inner lining on the walls of a refractory brick lined tundish for a two-strand bloom casting machine. In the area of the walls which, when the tundish was in use, would be adjacent the stream of molten metal entering the tundish, the slabs were used as a replacement for high alumina refractory bricks which would normally be used to withstand the highly erosive effects of the impinging molten metal stream. The so lined tundish was used for casting 0.6 manganese steel for 2 hours 20 minutes. During this time, three 80-tonne ladlefuls of molten steel were passed through the tundish, the steel being at 15600C in the ladles and 1525"C in the tundish. After the end of casting, the lining was examined and it was found that the lining slabs according to the present invention had suffered no significant erosion, even adjacent the area of the incoming molten metal stream. Identical slabs were also used to line a tundish used for 1 hour 38 minutes to cast two 60-tonne ladles of normal steel. Ladle temperature was 15700C and tundish temperature 15300C. Similar results were obtained in that after use the lining slabs showed no significant erosion. In both cases, it was particularly noticeable that very little sintering of the material of the slabs had taken place. WHAT WE CLAIM IS:

1. A tundish comprising an outer metal casing, a permanent lining of refractory material and an expendable inner lining formed of a set of slabs of refractory heat insulating material of a composition comprising by weight 60 to 92% refractory filler, 2 to 16% binder, 1 to 10% fibre and 5 to 30% non-fibrous carbonaceous material.

12. A slab according to claim 10 wherein the carbonaceous material is graphite.

16. A slab according to any one of claims

10 to 15 and comprising siliceous refractory filler, elemental carbon, organic and inorganic binding agents and organic and inorganic fibre.

17. A slab according to claim 10 and substantially as hereinbefore described with reference to any one of the foregoing specific Examples 1 to 4.

18. A slab according to claim 10 and substantially as hereinbefore described with reference to the foregoing specific Example 5.

19. A method of continuous casting in which molten metal is passed through a tundish, wherein the tundish used is according to any of claims 1 to 9.

20. A method according to claim 19 wherein successive ladlefuls of molten metal are passed through the tundish in sequence casting.

21. A method according to claim 19 or 20 wherein the molten metal is a manganese steel.