GB2164430A - Tundishes and tundish linings - Google Patents

Abstract

A tundish comprises a metal shell (2), a refractory lining (3) bordering the metal shell and a consumable inner lining bordering the said refractory lining, wherein said refractory lining comprises a plurality of panels (4, 5, 6) having interfitting edge portions (7, 8). Typically, a first set of said panels (5) are provided to line the floor of the tundish each extending across substantially the whole width of the floor and a second set of said panels (4, 6) are arranged around the wall of the tundish each extending substantially the full height of said wall. <IMAGE>

Description

SPECIFICATION Tundishes and tundish linings The present invention relates to tundishes. In the casting of metal by the continuous casting process tundishes are used to form a reservoir of liquid metal above the solidfying sections of metal formed in the moulds below or at the side of the tundish.

The tundish casing is usually of steel inside which is a refractory lining to contain the molten metal. This refractory lining is often in two parts one part being designated the permanent lining which is placed adjacent to the steel casing whilst the second or wearing lining (also known as the replaceable or consumable lining) is placed adjacent to the permanent lining and is in direct contact with the molten metal. The wearing lining is designed to be replaceable and ideally protects the permanent lining from direct contact with the molten metal or slag. The permanent lining acts as a safety lining. The permanent lining of a tundish can be of refractory brick construction and is often of refractory castable concrete cast in situ.The wearing or replaceable lining can for example be a sprayed refractory particulate material which is applied to maintain an appropriate thickness after each tundish use or a complete replaceable inner lining of refractory insulating board construction which is changed after each tundish use. This is known as the cold tundish system.

Whilst the replaceable or consumbable inner refractory tundish lining is partly designed to protect the permanent lining from wear, the permanent lining does in practice suffer wear and damage and eventually needs replacing.

How frequently depends upon the severity of the operating conditions.

The invention is concerned with improvements in the permanent lining of the tundish.

When the permanent lining of a tundish needs replacing the tundish can often be out of service for 2 to 3 days to allow time for the old lining to be removed and the new one installed. If the lining is of refractory castable material the old lining will often need to be broken up in a laborious manner. This is partly due to the fact that the cast lining is generally attached to the steel shell of the tundish by numerous steel ties or tangs welded to the inside of the steel shell. When the old lining has been removed a new lining is cost often by placing a former inside the tundish to give the required shape. The refractory castable concrete is for the most part placed in approximately the correct position in the tundish then vibrated to give the correct density.To obtain the best strength and performance from most commercial castable materials commonly recommended practice says that they be kept damp for 24 hours after casting followed by 24 hours air drying then dried under heaters to a temperature in excess of 1 00"C for a period often exceeding 24 hours depending upon the type, density and total weight of castable material involved.

Thus a tundish requiring to be relined with in situ castable material can easily be out of service for 4 to 5 days. Often a tundish cannot be left out of the system for this length of time with the result that insufficient time is allowed between casting and using the tundish for the proper strength of the castable material to be developed. In turin this may lead to earlier deterioration of the castable lining in service than otherwise might have occurred leading to an earlier need to replace the lining once more with both the resultant increased castable lining cost involved and often increased pressure to return the relined tundish into operation again before the strength of the cast lining is properly developed.

With the differing coefficients of linear thermal expansion between steel and refractory castable materials many of the steel ties fixed to the tundish steel casing to tie the castable concrete to it become dislodged either when the tundish is in use or when the cast refractory concrete lining is being removed from the tundish casing or shell at the end of its useful life. Often then prior to casting a new permanent lining into the tundish casing many of these steel ties have to be replaced. This is a time consuming and costly procedure. Also, because of the pressure often inherent in steelmaking operations, water in excess of that recommended is added to the castable concrete which may decrease its service life.

Also the increased water content in the concrete increases the drying requirement. With the increased use of low cement refractory castables with their improved refractory and strength properties the addition of excess water has a more deleterious effect that on the normal castable concrete. Where conditions in a steelworks exist such that good control of water addition cannot be guaranteed, the decision can be taken not to take advantage of low cement castables for that reason.

In certain refractory monolith applications including the casting of refractory concrete permanent linings to tundishes, the addition of steel fibres to the mix as reinforcement has proved advantageous from a refractory wear point of view. Care has to be taken in mixing these fibres into the castable refractory mix.

The time and preferred type of mixers for the proper introduction of steel fibres into the mix may not be available in the steelworks.

The above remarks pertaining to steel fibres in steelworks conditions also apply to the use of organic fibres introduced into the refractory concrete mix for the purpose of speeding up the drying out of the concrete.

This invention is particularly concerned with the provision of precast pre-dried, sectional, refractory concrete, permanent linings for continuous casting tundishes.

The present invention provides a tundish comprising a metal shell and refractory lining bordering the metal shell and a consumable inner lining bordering the said refractory lining, wherein said refractory lining comprises a plurality of panels having interfitting edge portions.

In a second aspect, the present invention further provides a tundish comprising a metal shell, a refractory lining bordering the metal shell and a consumable inner lining border the said refractory lining comprising a plurality of panels, a first set of said panels on the floor of the tundish each extending across substantially the whole width of the floor and a second set of said panels around the walls of the tundish each extending substantially the full height of said walls.

Preferably, said panels have interfitting edge portions.

Preferably, the interfitting edge portions are tongue and rebate formations.

Preferably, some of all of the panels are fixed to the metal shell of the tundish by fixings passing through said shell.

Alternatively or additionally, some or all of the panels may be fixed in position in the metal shell of the tundish by wedges inserted between edge portions of the panels and overlying portions of the metal shell.

In particular, where said metal shell has an inwardly projecting lip, panels may be fixed in position by wedges inserted between the tops of the panels and said lip.

Preferably, joints between panels of said refractory lining are sealed by refractory mortar or other suitable refactory material.

Preferably, selected one of said panels are of a different grade or type of refractory material than other ones of said panels.

For instance ones of said panels in the tundish base may be harder wearing than others of said panels.

Some or all of said panels may comprise fibre reinforcement, e.g. steel fibre reinforcement.

The panels may also comprise organic fibres added to speed up the drying out of the panels during manufacture.

The present invention will be illustrated by the following description of a preferred embodiment with reference to the accompanying drawing, in which: Figure 1 is a plan view of a tundish according to the invention, with the consumable lining omitted.

Figure 2 is a section on the line A-A of the tundish of Fig. 1; and Figure 3 is a section on the line B-B of the tundish of Fig. 1.

As shown in Fig. 1, a tundish according to the invention comprises a steel shell 2 having adjacent thereto a so-called permanent lining 3. Lining 3 consists of refractory cement panels. A single panel 4 lines each end wall of the tundish 1 and extends substantially the full height of the tundish. Four panels 5 line the tundish floor, each extending across the whole width of the floor. Five panels 6 line each long side of the tundish, again extending substantially the whole height of the tundish.

Each panel has along a pair of opposed sides a rebate 7 adjacent a tongue 8. The tongues 8 of each of the pair of opposed sides of a panel are on the same face of the panel.

The panels are interfitted by the tongues 8 being received in rebates 7 of adjacent panels to build up the lining of the floor and longer side walls of the tundish.

Holes 9 for nozzles for controlled out-flow of molten metal from the tundish are provided in the panels 5 lining the tundish base.

The tundish shell 2 comprises an inwardly projecting lip or rim 10.

Retaining bolts 11 are passed through holes in th shell 2 to fix the panels 4 and 7 to the longer and shorter sides of the tundish shell 2.

The individual panels are designed as far as practical to interlock together. This helps maintain the integrity of the lining when the tundish is in use. The interlocking joints also make a more difficult path for metal and/or slag to penentrate than a straight joint.

In the design shown the bottom panels are placed in the tundish shell first followed by the end and side pieces 4,6. The end and side panels are held in place either by bolts 11 or other suitable fixing devices from the outside of the steel shell into each individual panel or by being wedged in place under the steel rim 10 often forming part of the tundish top or a combination of both of these methods. The firmly held in position side and end panels in turn hold in the bottom panels 5. This is necessary as most tundishes are inverted for cleaning after metal has been cast through them.

With use, tundish shells can become distorted. Where such distortions occur the result may be for example a bottom surface not good enough for the placing of the bottom panels. Suitable refractory material can be used to provide a bed between the metal tundish shell and the underside of the bottom panels. Similarly when any side or end panels butt against a distorted side, refractory material can be placed if desired between the inside of the metal shell of the tundish and the adjoining face of the pre-cast panel.

The joints between the panels can be sealed with a suitable mortar.

With the construction illustrated, the permanent lining is allowed some freedom of movement from its containing metal shell. This is aided by the existence of the joints between the panels.

Thus the lining allows for the differential expansion under temperature which occurs between the lining 3 itself and the metal shell 2 of the tundish thus alleviating any tendency for the individual panels to crack. This contrasts with the situation mentioned above with the cast in situ linings where metal ties or tangs endeavour to hold the monolithic contrete to the steel shell whilst both are cycled through a range of temperatures when the tundish is in operation. The resulting tension caused in the concrete due to the differential expansion of the concrete and the metal shell of the tundish often results in cracks occuring in the concrete lining. These cracks are a source of weakness in the lining where metal or slag penetration may lead to premature breakdown.This breakdown may be accelerated by the physical strain on the lining when the tundish is being deskulled i.e. the residue of a cast in the tundish is being removed as part of the cleaning of the tundish prior to its being prepared for a new cast. The ingress of slag and/or metal into cracks in a cast in situ lining where it solidifies on cooling can also help breakdown the lining as it is removed.

The use of panels not tied to the tundish shell helps alleviate this problem.

The panels may suitably be cast from refractory concrete of a type conventionally used to form permanent linings for tundishes.

Because the panels need not be cast at the steelworks, the conditions under which they are cast may be optimally controlled. This will assist in the use of reinforcing fibres such as steel fibres and the use of low cement content castable materials which require careful mixing. The panels may be fully dried after casting, again under the optimum conditions.

In tundishes as with many molten metal refractory lined vessels e.g. Electric Arc Furnaces, Ladles, and Blast furnaces, the refractory quality throughout the system is varied to meet the refractory demands imposed upon it.

One objective is often to so design the system that it all wears out together. Where fired refractory bricks are used to form the permanent lining of the tundish variations in the refractory quality of the brick can be used from one place to another to achieve an even wear pattern.

For cast in-situ linings it is generally not feasible to mix types of refractory concrete whilst casting. In the present invention panels can be cast in the quality of refractory concrete best suitable to the place of the panel in the overall lining. For example the molten metal impact area of the tundish often has more difficult metal erosion conditions to cope with than elsewhere in the tundish. For the Impact Area, bottom and sometimes side panels of higher refractory quality may be cast, compared with the rest of the tundish lining.

As mentioned above the stripping out after use of a pre-cast in-situ lining and the subsequent casting and drying of a new lining can take a matter of days. An advantage of the system described above is that a new lining can be installed often in a matter of hours.

After installation of the lining, the tundish can be put immediately into service if no ramming material or mortar has been used. If ramming material and/or mortar has been used a few hours drying will render the tundish available for use. At the end of the life of the permanent tundish lining, it is a relatively simple matter to knock out the lining, the individual panels not being permanently tied to the tundish shell. Thus stripping such a tundish is generally much faster than stripping a cast insitu lining.

Another advantage of the described embodiment is that with the close control possible in the manufacture of the pre-cast pre-dried sections a longer life should be achieved with these linings than with comparative cast in situ linings. The installation of the relatively small number of interfitting panels described will naturally be much less time consuming that lining a tundish with a much larger number of individually mortared in bricks.

Claims (18)

1. A tundish comprising a metal shell, a refactory lining bordering the metal shell and a consumable inner lining bordering the said refractory lining, wherein said refractory lining comprises a plurality of panels having interfitting edge portions.

2. A tundish comprising a metal shell, a refactory lining bordering the metal shell and a consumable inner lining bordering the said refractory lining, wherein said refractory lining comprises a plurality of panels, a first set of said panels on the floor of the tundish each extending across substantially the whole width of the floor and a second set of said panels around the wall of the tundish each extending substantially the full height of said wall.

3. A tundish as claimed in Claim 2, wherein said panels have interfitting edge portions.

4. A tundish as claimed in Claim 1 or Claim 3, wherein the interfitting edge portions are tongue and rebate formations.

5. A tundish as claimed in any preceding claim, wherein some or all of the panels are fixed to the metal shell of the tundish by fixing passing through said shell.

6. A tundish as claimed in any one of Claims 1 to 4, wherein some or all of the panels are fixed in position in the metal shell of the tundish by wedges inserted between edge portions of the panels and overlying portions of the metal shell.

7. A tundish as claimed in Claim 6, wherein the said metal shell has an inward projecting lip and panels are fixed in position by wedges inserted between the tops of the panels and said lip.

8. A tundish as claimed in any preceding claim, wherein joints between panels of said refractory lining are sealed by refractory mortar or other suitable refractory material.

9. A tundish as claimed in any preceding claim, wherein selected ones of said panels are of a different grade or type of refractory material than other ones of said panels.

10. A tundish as claimed in Claim 9, wherein ones of said panels in the tundish base are harder wearing than others of said panels.

11. A tundish as claimed in any one of the preceding claims, wherein some or all of said panels comprise fibre reinforcement.

12. A tundish as claimed in Claim 11, wherein the fibre reinforcement is steel fibre reinforcement.

13. A tundish substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

14. A method of lining a tundish comprising inserting adjacent a metal tundish shell a plurality of panels of refractory material to form a first lining for the shell, said panels having interfitting edge portions, and forming a consumable refractory lining within said first lining.

15. A method of lining a tundish comprising inserting adjacent a metal tundish shell a plurality of panels of refractory material to form a first lining for the shell, wherein a first set of panels on the floor of said shell extend across substantially the whole of the width of said shell and a second set of panels around the wall of said shell each extend substantially the full height of said wall.

16. A method as claimed in Claim 14 or Claim 15, wherein panels of said refractory material are first placed to line the base of said shell and panels are then placed to line the wall of said shell and to hold in place the panels lining said base.

17. A method of lining a tundish substantially as hereinbefore described with reference to the accompanying drawings.

18. A tundish produced by a method as claimed in any one of Claims 14 to 17.