Molten metal transfer channels

Abstract

 A transfer channel which in use is contacted by molten ferrous metal has a protective inner replaceable lining (5,6) of bonded refractory, heat-insulating material which comprises at least 75% by weight of particulate refractory material. The inner replaceable lining (5,6) is reusable for a plurality of molten ferrous metal transfers. The lining (5,6) can be a plurality of pre-formed slabs (5,6) or one or more pre-formed, self-supporting essentially U-shaped lining sections. The lined channel can be used to transfer molten metal e.g. steel from a vessel e.g. a furnace to another vessel e.g. a ladle.

Description

[0001] This invention relates to channels for transferring molten ferrous metal from one vessel e.g. a furnace to another e.g. a ladle.

[0002] Such channels are particularly useful for transferring molten iron away from blast furnaces and cupolas, these channels sometimes being termed blast furnace troughs and cupola runners respectively and for transferring molten steel away from electric arc furnaces, in this case the channel sometimes being termed a launder or spout. It is known to provide such channels within a refractory support or metal casing.

[0003] The channels leading from a blast furnace to e.g. a torpedo ladle, are generally sited in the cast house floor and are lined with one or more layers of permanent refractory brick and/or cast refractory cement together with one or more safety linings, located behind the metal contacting lining. Such lined channels are capable of withstanding the flow of up to 4000 tonnes per day according to the output of the blast furnace for up to 28 days or more. The working, molten ferrous metal contacting layer of refractory material may be patched from time to time during this period, e.g. by gunning or the like. However it is uneconomic in terms of material cost and application time to replace the entire lining at shorter intervals.

[0004] Analogous economic considerations also apply to the launder of an electric arc furnace and a cupola runner but in these cases it is customary to replace the permanent refractory lining after approximately 7 to 14 days use. The lining is inspected e.g. daily and repaired as required.

[0005] The dense, highly refractory materials used although having the advantage of being long lasting have the disadvantage that they provide little or no heat insulation for the metal flowing therethrough which in the case of a blast furnace distribution trough may be the relatively long distance of 50 metres or more. Accordingly, chilling of the metal occurs with the risk of premature freezing with concomitant risk of damming of the metal with spillage onto the cast house floor'which is both dangerous and inconvenient for the blast furnace operators.

[0006] According to the invention a molten ferrous metal transfer channel has an outer, permanent refractory lining, or a metal casing, or both, and an inner replaceable lining (as hereinafter defined) of refractory, heat-insulating material comprising at least 75% by weight-of particulate refractory material and an inorganic binder and/or an organic binder, the inner replaceable lining being reusable for a plurality of molten ferrous metal transfers.

[0007] The inner replaceable lining is defined as one which may be in the form of a number of slabs which may be flat or otherwise or it may be in the form of one or more preformed, self-supporting channel sections having a generally U-shaped cross-section.

[0008] According to another aspect of the invention there is provided a pre-formed, self-supporting molten ferrous metal transfer channel lining section of refractory, heat-insulating material having a generally U-shaped cross-section comprising at least 75% by weight of particulate refractory material, and an inorganic binder and/or an organic binder.

[0009] The feature wherein the inner replaceable lining may be used for a plurality of molten ferrous metal transfers is a significant and remarkably advantageous property especially having regard for the thermal cycling that the lining undergoes between each reuse. From a cold (ambient) temperature the lining is immediately subjected to temperatures in the range of 1400°C to 1700°C, allowed to cool, sometimes to ambient temperature, and resubjected to high temperatures stated above. This process is repeated for each reuse. The consequent thermal shock and thermal degradation, i.e. the contact with molten metal for periods of from several minutes to an hour or more, is a severe test of endurance especially as the metal and accompanying slag are mobile. The ability to withstand such conditions of use provides the blast furnace iron producer and arc furnace steel maker with a valuable contribution to increase his productivity, and reduce his material and energy costs.

[0010] The same contribution could not be afforded by the so-called replaceable linings which it has been suggested might be used for the transfer of molten iron from a blast furnace but which would be capable of only one molten ferrous metal transfer before replacement of the channel lining was required.

[0011] As the inner lining of a channel of the invention is of heat-insulating material, the loss of heat from molten metal in contact with the lining is reduced as compared with the case where the channel merely has a conventional lining of refractory material, cast refractory cement or refractory bricks, sometimes with an overlying layer of refractory cement, all of which typically have poor heat-insulating properties and in some cases are highly conductive. In the case of conventional linings, the loss of heat from the molten metal is often such that the lining has to be pre-heated before the channel is used, although sufficient heat may be retained that pre-heating is not necessary again before the channel is used on the next occasion, whereas pre-heating can be avoided in the case of channels of the invention. As the channels are commonly large, avoidance of pre-heating saves a considerable amount of energy and also saves the considerable time required for pre-heating.

[0012] The inner lining of the invention is refractory as well as heat-insulating and is well able to resist the high temperatures of molten metal in contact with it and the erosive effect of the metal and any accompanying slag. The inner lining is such that it can satisfactorily survive use of the channel for a plurality of molten ferrous metal transfer cycles. The inner lining is replaceable i.e. when, after a number of uses it is judged to be unsuitable for further use, it can readily be removed without damage to the permanent lining and a new inner lining provided in its place. In order that the used inner lining may be more easily removed a layer of unbonded sand or the like may be provided as a parting layer between the permanent lining and the inner lining.

[0013] The outer permanent lining may be of refractory brick and/or cast refractory cement and provides a refractory support for the inner lining and may also serve as a safety lining. The inner lining protects the permanent lining and, whilst the permanent lining requires occasional repair or renewal, the permanent lining lasts over the lifetime of a number of the reusable inner linings. In the case of conventional linings for blast furnace troughs, cupola runners and electric arc furnace launders, damage to the lining necessitates periodic complete renewal of the lining and more frequent repair and each of these tasks is difficult and time- consuming.

[0014] In the case of refractory brick linings long installation times are needed and prolonged heating is required to drive off water from the refractory cement used in the joints between the bricks and from any layer of refractory cement overlying the bricks. Moreover, conventional linings tend to become contaminated with slag, that is difficult to remove, and this can contaminate the molten metal on a subsequent use.

[0015] As mentioned above, the inner lining of the invention may be _'in the form of a number of slabs, which may be flat or otherwise shaped. Typically, where the base of the channel is distinct from the sidewalls, the base and each sidewall is each lined with a succession of slabs. The slabs may be joined together by means of a refractory cement and/or by means of mating joints at the edges of the slabs. Provision of the lining in the form of a number of slabs enables a new inner lining to be put in place quickly after removal of an inner lining judged to be unsuitable for further use. Moreover, unlike the case with conventional linings of refractory bricks jointed with refractory cement or of refractory cement alone, extensive pre-heating of the lining to reduce the water content to an acceptable level is not needed before the lining is ready for use. Instead of using slabs, the inner lining may be provided by use of one or more preformed, self-supporting generally U-shaped channel sections. Furthermore, slabs held together by a flexible member e.g. wire mesh may be used, the set of slabs having, for example, a central slab for lining the base of the channel and lateral slabs for lining the sides of the channel. Such sets of slabs may conveniently be packed and transported in flat condition and moved into channel configuration at the time the lining is being fitted.

[0016] As already stated, the inner lining contains at least 75% of particulate refractory material. In accordance with the invention it has been found that if a smaller proportion of particulate refractory material is present the lining has insufficient resistance to the effects of molten metal, especially ferrous metal, and slag. Preferably the proportion of particulate refractory material is from 80 to 95% by weight. It is preferred that a major proportion by weight of the particulate refractory material should be provided by one or more basic or neutral refractory oxides e.g. magnesium oxide or alumina, e.g. in the form of a high alumina aluminosilicate. Basic or neutral refractory oxides as the particulate refractory material enhance the resistance of the lining to the effects of molten metal and slag.

[0017] The particulate refractory material may include a proportion of a clay, e.g. a fireclay, and, if present, is preferably present in an amount of 3 to 10% by weight of the inner lining. Although the inclusion of a clay enhances the strength of the lining when hot, it is to be understood the necessary hot strength may be obtained using linings which do not contain clay.

[0018] It is also preferred that the particulate refractory material should contain a proportion of carbon, e.g. crushed graphite electrode scrap, or silicon carbide or nitride, preferably in an amount of 3 to 20% by weight of the inner lining. The inclusion of such materials makes the lining less readily wetted by molten metal or slag, and thereby more resistant to attack by these, and reduces the risk of an adherent skull being formed.

[0019] The inner lining may contain a proportion of refractory fibre in addition to the particulate refractory material but it is preferred that this proportion should not exceed 6% by weight of the inner lining. Refractory fibres are commonly used in refractory, heat-insulating materials for lining metallurgical vessels and their inclusion generally enhances the heat-insulating properties but in accordance with the present invention it has been appreciated that the inclusion of a substantial proportion of refractory fibre has a marked adverse effect on the erosion resistance of the inner lining.

[0020] An inorganic and/or an organic binder may be present in the inner lining. The organic binder may be, for example, a resin e.g. a urea-formaldehyde resin or a phenol-formaldehyde resin or a starch and mixtures of organic binders may be used. The amount of organic binder is preferably 3 to 8% by weight. An organic binder is particularly beneficial in reducing any tendency of the molten metal contacting face of the inner lining to spall in use due to initial thermal shock.

[0021] The inorganic binder is preferably a sodium silicate in which the weight ratio Na₂O:SiO₂ is from 1:2.5 to 1:3.7. The amount of inorganic binder is preferably 4-10% by weight of the dry inner lining. In some instances owing to the absence of an inorganic binder the inner lining may have insufficient strength after it has cooled from its temperature of use and tend to become powdery and to crumble thereby rendering the lining unsuitable for further use. Accordingly, in such cases it is preferable for the inorganic binder to be present. Alternatively, a part or all the sodium silicate may be replaced by a corresponding amount of a phosphate binder such as aluminium orthophosphate.

[0022] The density of the inner lining may be in the a range of 1.3 to 2.2 g/cm preferably within the range of 1.5 to 1.9 g/cm

[0023] Many heat-insulating lining compositions for metallurgical vessels are known that contain a proportion of particulate organic filler and/or organic fibre. The inner lining in accordance with the present invention is preferably substantially free of such matter as it adversely affects the resistance of the lining to the conditions of use.

[0024] By adopting suitable compositional features as described above for the inner lining the working life of the inner lining can be long enough for it to be used on a considerable number of successive occasions thereby reducing the time and cost involved in maintaining a suitably lined channel. Moreover, the compositional features enable the risk of troublesome impurities being picked up by the molten metal from the lining to be reduced as compared with this risk in the case of conventional channel linings.

[0025] The inner linings of the present invention may be made by dewatering an aqueous slurry of the ingredients of the lining and oven drying the resultant shape or by hand or mechanical ramming, pressing, jolting or squeezing methods. In the case of the latter methods it is preferable to use a damp mixture of the ingredients and dry the resultant shape before use.

[0026] The invention includes not only the lined channels but also pre-formed self-supporting shapes for providing the inner lining and a method of transferring molten metal comprising supplying the metal from a vessel to one end of the channel and allowing the metal to run along the channel into another vessel.

[0027] The invention is further described with reference to the accompanying drawings wherein Figure 1 is a vertical cross-section through a lined blast furnace distribution trough, Figure 2 is a part-sectioned view of an electric arc furnace launder and, Figure 3 is a part-sectioned view of an alternative construction of an electric arc furnace launder.

[0028] In Figure 1 the distribution trough has outer sidewall and base portions 1, 2 and 3 and a permanent refractory lining 4. Within the permanent lining 4 is an inner, replaceable lining of refractory, heat-insulating slabs 5 and 6 lining the sidewalls and base respectively. To line the full length of the trough a number of the slabs 5 are positioned end to end to line each of the sidewalls and of the slabs 6 to line the base.

[0029] In Figure 2 an electric arc furnace launder assembly has an outer metal shell 7 (part shown cut away), a permanent refractory lining 8 and an inner, replaceable lining of pre-formed self-supporting channel sections 9.

[0030] In Figure 3 an alternative arc furnace launder assembly is shown which has an outer permanent refractory supporting channel 10. Within the channel is a pre-formed self-supporting channel base portion 11 having partial integral sidewalls 12 and rebates 13. Sidewall slabs (only one of which is shown) are adapted to matingly joint with the partial sidewalls 12 by means of depending tongue 15.

[0031] The following examples also serve to -illustrate the invention.

EXAMPLE 1

[0032] A composition suitable for the reusable lining slabs of a blast furnace trough is as follows:

[0033] The composition was formed into slabs by making an aqueous slurry of the ingredients, dewatering the slurry in a permeable mould, removing the damp slabs so obtained and heating them to dry them and to harden the binders.

EXAMPLE 2

[0034] 

[0035] Water was added to the above composition to provide a damp consistency and the damp mixture was sequentially added to a mould box with continuous jolting/vibration of the mould box. The "green" shapes so obtained were removed and dried by heating them in a drying oven for 4 hours at 180°C to remove the residual moisture and to harden the binders. By this means were made U-shaped reusable self-supporting channel sections, the sidewalls of which were 75 mm thick and the base 150 mm thick. The density of the dried channel sections a was 1.9 g/cm .

[0036] The reusable self-supporting channel lining sections were installed in the launder of a 10 tonne electric arc furnace directly onto the permanent cast refractory underlying layer of the launder. The reusable lining was subjected to 37 heats of low carbon steel which were tapped at a temperature between 1660°C and 1700°C. The tapping time was approximately 1 to 3 minutes per heat and the time between taps averaged 3 hours. It was observed that the reusable channel lining sections performed most satisfactorily. When removed the underlying permanent refractory of the furnace launder was found to be undamaged.

EXAMPLE 3

[0037] 

[0038] The above composition was formed into 30 mm thick slabs in the manner described in Example I.

[0039] 3 The density of the dried slabs was 1.5 g/cm .

[0040] The slabs were installed on the base and against the sidewalls of a refractory lined launder of a 2.5 tonne electric arc furnace. The joints between the slabs were sealed with a refractory cement. The lining was subjected to 18 heats of molten steel tapped at an average temperature of 1625°C. The tapping time was 1 to 2 minutes and the time between taps averaged 4 hours. On removal of the reusable lining, the underlying permanent refractory layer of the furnace launder was undamaged.

[0041] This represents a good result.

EXAMPLE 4

[0042] 

[0043] The composition was formed into 75 mm thick slabs by mechanically vibrating the composition in a suitably dimensioned former. The "green" slabs so obtained were removed from the former and cured by heating them in an oven for 3 hours at 180°C to remove any residual moisture and to harden the binder.

[0044] 3 The density of the dried slabs was 1.75 g/cm .

[0045] The slabs were installed in a 110 tonne arc furnace launder in the manner described in Example 2. The reusable launder lining so formed was subjected to 12 heats tapped at an average temperature of 1675°C. The tap time was 2 to 4 minutes and the time between taps averaged 2 hours.

[0046] This was a satisfactory result.

[0047] The benefits of the reusable linings of the present invention are further demonstrated below with reference to comparison Example 5 using the results obtained from a laboratory sized, blast furnace trough/ electric arc furnace launder, simulation furnace.

EXAMPLE 5

[0048] A slab 1 was made using the recipe of Example 3 by ramming the composition into a former measuring 25 x 25 x 3 cms (nominal). The green shape was dried for 4 hours at 180°C.

[0049] A second slab 2 was made from the recipe of Example 3 by vacuum dewatering an aqueous slurry in a permeable mould 25 x 25 x 3 cms and then dried as above.

[0050] A third slab 3 was formed by ramming a recipe comprising 17% sawdust, 61% clay and 22% sodium silicate. This composition has been proposed as being suitable for forming blast furnace runner units of predetermined life time. As for slabs 1 and 2, slab 3 was dried for 4 hours at 180°C.

[0051] The slabs were cut into test-pieces and their thickness accurately measured (see column "a" of Table 1) and placed around the periphery of the chamber of the simulation induction furnace. 100 kg of steel was melted in the furnace and once molten, was stirred to represent the flow of metal through a blast furnace trough or arc furnace launder. The samples were subjected to this test for 47 minutes at a temperature of 1650°C. At the end of the test the furnace was drained of steel and the test-pieces allowed to cool and the thickness of the test-pieces was remeasured at the junction with the surface of the steel i.e. the slag line (see column "b" of Table 1) and at the foot of the test-piece (see column "c" of Table 1).

a = original thickness (mm)

b = depth of erosion (mm)

c = shrinkage/erosion (mm)

[0052] On examination it was clear that slabs 1 and 2 of the invention were in good condition and capable of reuse. However slab 3 was upto 50% eroded from the juncture with the molten steel surface upto 100% erosion at the bottom of the test-piece. It was clear that slab 3 was not capable of being reused.

Claims

1. A molten ferrous metal transfer channel having an outer, permanent refractory lining, (4, 8, 10) or a metal casing, (7) or both, characterised by an inner replaceable lining of refractory heat-insulating material which comprises at least 75% by weight of particulate refractory material and an inorganic binder and/or an organic binder, the inner replaceable'lining being reusable for a plurality of molten ferrous metal transfers.

2. A molten ferrous metal transfer channel according to claim 1 characterised in that the inner replaceable lining is in the form of a plurality of pre-formed slabs (5, 6).

3. A molten ferrous metal transfer channel according to claim 2 characterised in that the channel has a base portion (3) distinct from the sidewalls (1,) wherein the inner replaceable lining is in the form of a succession of slabs. (5, 6) lining the said base and the said sidewalls.

4. A molten ferrous metal transfer channel according to claim 2 characterised in that the slabs (5, 6) are joined together by means of a refractory cement.

5. A molten ferrous metal transfer channel according to claim 2 characterised in that the slabs (5, 6) are joined together by means of mating joints at the edges of the slabs.

6. A molten ferrous metal transfer channel according to claim 2 characterised in that the inner replaceable lining is in the form of one or more sets of slabs held together by means of a flexible member.

7. A molten ferrous metal transfer channel according to claim 1 characterised in that the inner replaceable lining is in the form of one or more pre-formed self-supporting channel sections (9, 11) having a generally U-shaped cross-section.

8. A molten ferrous metal transfer channel according to any preceding claim characterised in that the major proportion by weight of the particulate refractory material comprises one or more basic or neutral refractory oxides.

9. A molten ferrous metal transfer channel according to any preceding claim characterised in that the particulate refractory material comprises a proportion of fireclay.

10. A molten ferrous metal transfer channel according to claim 9 characterised in that the fireclay comprises 3 to 10% by weight of the inner lining.

11. A molten ferrous metal transfer channel according to any preceding claim characterised in that the inner replaceable lining contains a proportion of one or more of graphite, silicon carbide or silicon nitride.

12. A molten ferrous metal transfer channel according to claim 11 characterised in that the graphite, silicon carbide or silicon nitride comprises 3 to 20% by weight of the inner lining.

13. A molten ferrous metal transfer channel according to any preceding claim characterised in that the inner replaceable lining contains upto 6% by weight of refractory fibre.

14. A molten ferrous metal transfer channel according to any preceding claim characterised in that the inorganic binder is a sodium silicate having a weight ratio of Na₂0 to Si0₂ of from 1:2.5 to 1:3.7.

15. A molten ferrous metal transfer channel according to claim 14 characterised in that the inorganic binder comprises 4 to 10% by weight of the inner lining.

16. A molten ferrous metal transfer channel according to any preceding claim characterised in that the organic binder is one or more of urea-formaldehyde resin, phenol-formaldehyde resin or starch.

17. A molten ferrous metal transfer channel according to claim 16 characterised in that the organic binder comprises 3 to 8% by weight of the inner lining.

18. A molten ferrous metal transfer channel according to any preceding claim characterised in that the density of the inner replaceable lining is in the range of from 1.3 g/cm to 2.2 g/cm .

19. For use in a molten ferrous metal transfer channel according to claim 7 characterised by a pre-formed, self-supporting lining section (9, 11) having a generally U-shaped cross-section and formed from a refractory, heat-insulating material comprising at least 75% by weight of particulate refractory material and an inorganic binder and/or an organic binder.

20. A lining section according to claim 19 characterised in that the major proportion by weight of the particulate refractory material comprises one or more basic or neutral refractory oxides.

21. A lining section according to claim 19 characterised in that the particulate refractory material comprises a proportion of fireclay.

22. A lining section according to claim 21 characterised in that the fireclay comprises 3 to 10% by weight of the lining section.

23. A lining section according to any of the claims 19 to 22 characterised by a proportion of one or more of graphite, silicon carbide or silicon nitride.

24. A lining section according to claim 23 characterised in that the graphite, siiicon carbide or silicon nitride comprises 3 to 20% by weight of the lining section.

25. A lining section according to any of the claims 19 to 24 characterised in that the lining section contains upto 6% by weight of refractory fibre.

26. A lining section according to any of the claims 19 to 25 characterised in that the inorganic binder is a sodium silicate having a weight ratio of Na₂0 to Si0₂ of from 1:2.5 to 1:3.7.

27. A lining section according to claim 26 characterised in that the inorganic binder comprises 4 to 10% by weight of the lining section.

28. A lining section according to any of the claims 19 to 27 characterised in that the organic binder is one or more of urea-formaldehyde resin, phenol-formaldehyde resin or starch.

29. A lining section according to claim 28 characterised in that the organic binder comprises 3 to 8% by weight of the lining section.

30. A lining section according to any of the claims 19 to 29 characterised in that the density of the lining 3 3 section is in the range of from 1.3 g/cm to 2.2 g/cm .

31. A method of transferring molten ferrous metal from a blast furnace, cupola or an electric arc furnace to a metallurgical vessel characterised by supplying the metal to one end of a molten ferrous metal transfer channel according to any of the preceding claims and allowing the metal to run along the channel into the metallurgical vessel.

Drawing