WO2000047783A1

WO2000047783A1 - Aluminium shapes as deoxidants for steelmaking

Info

Publication number: WO2000047783A1
Application number: PCT/GB2000/000437
Authority: WO
Inventors: Stephen David Bray
Original assignee: Qual-Chem Limited
Priority date: 1999-02-11
Filing date: 2000-02-11
Publication date: 2000-08-17
Also published as: AU2451400A

Abstract

Shaped aluminium bodies for use as an agent (such as a deoxidant) in steelmaking processes are produced by compressive forming using specific forming materials (including aluminium materials) and/or specific forming techniques to ensure tailoring of properties to end user requirements or to enhance the process of manufacturing the shaped bodies.

Description

ALUMINIUM SHAPES AS DEOXIDANTS FOR STEELMAKING

The present invention relates to steelmaking .

In certain steelmaking processes (particularly processes for producing "killed" steel, such as continuous casting processes) it is required to add aluminium materials to certain process stages for example for de-oxidising or reheat process stages. 'Conditioning' of steel at various stages in steelmaking processes often requires the introduction at relevant process stages of various additives or conditioning agents.

Presently, cast aluminium shapes such as dabs or ingots are utilised in the required process stage and work satisfactorily. Such cast dabs or ingots are (due to cost considerations) typically manufactured by remelting and casting aluminium scrap material . Such scrap material often includes other materials which are not suitable for inclusion of the dabs or ingots for steelmaking, and there is a material loss in the conversion process from scrap aluminium to cast dab or ingot which results in a metal yield loss.

It has been proposed to add aluminium material to various process steelmaking stages in other forms such as briquettes or the like. JP-A-709034 describes the compressive formation, in a forming die, of dis-continuous bodies including aluminium for use as a deoxidising agent in steelmaking. US-A-3841861 also discloses the use of aluminium material which may be pressure packed into containers, the packed containers subsequently being added to ferrous melts.

Improvements have now been devised.

According to a first aspect, the invention provides a steelmaking process in which aluminium material is added to molten steel and/or iron in a steelmaking process stage, characterised that the aluminium material is introduced into the relevant process stage in the form of self-supporting shaped bodies of compressed material, which compressed material includes aluminium material .

According to a further aspect, the invention provides a shaped body comprising compressed material, which compressed material includes aluminium material, the shaped, body being for use as an agent added to molten steel and/or iron in steelmaking.

The compression of materials should be understood as encompassing compaction and agglomeration.

It is greatly preferred that a respective shaped body includes compressed divided aluminium material in at least a first material form and a second material form, the first and second aluminium material forms differing in one or more of : i) aluminium content or purity of the divided material ;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

It is particularly preferred that a first aluminium material form comprises a higher purity aluminium material and a second aluminium material form comprises a lower purity aluminium material .

The shaped bodies may be introduced (typically as a batch comprising a multiplicity of shaped bodies) at a steel making . process stage at which metal conditioning is required (for example de-oxidisation or re-heating of molten steel) .

In an important embodiment, compressed bodies for use in slag conditioning have been devised comprising a first, higher purity al material (typically comprising aluminium foil) and a second lower purity al material (typically comprising sieved grindings) . The higher purity material desirably has a purity substantially in the range 96% al and above; the lower purity material desirably has a purity substantially in the range 86% to 94% al . Desirably the lower purity al material form is in greater proportion to the higher purity al material form. The ratio between the higher purity form and the lower purity form material is substantially in the region of between : 6 and 3:7.

The formulation as defined for the compressed body in this embodiment makes the formation of the body in tablet form utilising tableting equipment technically and economically viable. The target aluminium content is approximately 88- 90% for current user specifications (and therefore preferred) , although lower aluminium content may become industry accepted. The formulation utilises higher purity material preferably at substantially 12 ^"to 18 mesh size, the lower purity material preferably being at a size of approximately 20 mesh. The material prior to compression is therefore free flowing.

The high purity material present in desired proportion reduces tool wear and being ductile deforms readily during compression of the body to act to bind the body and provide adequate structural integrity for the body without the necessity to use additional binder material. This effect is also common to other embodiments of compressed bodies according to the invention.

Prior to compression the first and second aluminium material forms are beneficially mixed/blended to form an intimate mixture/blend of the first and second aluminium material forms. This stage is beneficial in the production of other embodiments according to the invention. In another specifically preferred embodiment particularly suited for use as a deoxidant, the compressed body preferably further comprises a third material form of aluminium differing from the first and second aluminium material forms in one or more of :

i) aluminium content or purity of the divided material ;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

One of the first, second or third forms of aluminium material preferably comprises an alloy having a hardness greater than the hardness of aluminium. The relatively hard alloy is beneficially present in a proportion less than the proportions of either of the other aluminium material forms. The relatively hard alloy is desirably present in a proportion substantially in the range 15% by weight or less of the body.

In this embodiment it is preferred that the body comprises proportions of:

a) a higher purity aluminium material (preferably aluminium foil) desirably having a purity of substantially in the range 98% al and above;

b) a middle purity aluminium material form (preferably aluminium sawings) desirably having a purity of substantially in the range 94-98% al ; and,

c) a lower purity aluminium material form

(preferably relatively harder smaller divided form such as aluminium grindings including hard alloying metals such as silicon or iron) of a purity substantially in the range 86%-94% al . It is envisaged that this material may be specifically manufactured for inclusion in the formulation.

The proportion of the lower purity/harder/smaller divided size material is preferably substantially less than the higher and middle purity materials by weight. The higher and middle purity aluminium material forms preferably have divided material size approximately in the range 0.5-5mm

(more preferably l-3mm) ; the lower purity/harder aluminium material form preferably has a divided size substantially in the range 10-40 mesh (more preferably approximately 15-

25 mesh) .

The formulation proposed in this embodiment gives a self supporting compressed body substantially without the requirement for an additional binder. The higher purity foil material, being malleable/ductile acts as an effective binder during compressive deformation. The middle purity material gives bulk and structure. User requirements currently dictate an overall aluminium content of approximately 97% al ; the relative proportions can be tailored to reduce the proportion of higher purity material should the user requirements relax. In the present embodiment a ratio of approaching 1:1 has been effective.

In order to produce the required quantities of compressed bodies for use, for example, in molten steel deoxidation, the bodies are preferably formed as shaped bodies between shaped compressive formers (preferably rotary circumferentially adjacent formers) arranged to produce a series of spaced bodies interconnected by a body- interlinking web of compressed material. The bodies are subsequently broken from the body-interlinking web into the individually formed compressed bodies. This is particularly important and prior art rotary briquetting of materials (such as aluminium for use in re-smelting) has not required such a break-up into individual shaped bodies. Instead, slabs of web-linked briquettes have been produced by such presses when processing materials such as aluminium.

Accordingly, the starting material composition and properties need to be tailored to ensure sufficient frangibility of the web. This may be achieved by means of, for example, using finely divided refractory materials as a frangibility inducing inclusion in the starting material . Indeed it may be advantageous to produce a mixture for use in such a forming technique from a single aluminium material form in combination with a finely divided non-aluminium material frangibility inducing material such as a refractory material. The frangibility inducing divided material is compressed in the web between formed briquettes increasing the frangibility of the web and aiding the breaking up of the briquettes from the web. This has heretofore been a problem in producing briquettes from such rotary briquetting apparatus which is known in the prior art for producing briquettes of other materials or formulations as mentioned above. Examples of such rotary forming apparatus are agglomeration/briquetting presses produced by Hosokawa Bepex GmbH and Maschinenfabric Koppern GmbH of Germany. Such apparatus typically include a pair of contra-rotating circumferentially adjacent cylinders having respective forming surfaces provided with an array of aligned pockets for producing an array of briquettes interlinked by a web.

It is preferred that the shaped bodies comprise intimate mixtures of swarf, chippings, grindings, powder or other divided aluminium material compressed (either alone or with other materials) to form self supporting shaped bodies. Differing aluminium waste products are of differing purities and typically have physical properties depending upon the quantity and nature of the alloying metals.

For other less specific embodiments the formulation, mix and relative proportions of aluminium material forms comprising the shaped body may vary and be tailored depending upon the metal conditioning required in the object stage in the steelmaking process. Metal conditioning additives and agents may be included in selected proportions and quantities depending upon the intended induced change in the metal chemistry at a particular process stage during steelmaking.

The proportion of aluminium may vary from being a minority constituent of the shaped body to approaching lOOper cent. The balance of the material may comprise one or more metal conditioning agents or additives (described in more detail below), incidental ingredients and impurities.

The shaped body may be compressed to form a self supporting body from an amorphous entanglement or other substantially non-coherent body or grouping of divided material. The shaped body is therefore preferably substantially more coherent than the divided starting material . A preferred formulation includes an aluminium material form of divided material effectively forming a binder for another aluminium material form.

The shaped bodies are preferably formed in compressive apparatus such as a press or rotary compacting apparatus. For example the shaped bodies may comprise briquettes formed in a briquetting process, or tablets formed in a tableting process depending upon the starting material, and/or dimensions and/or density of the shaped bodies required. Pellets of compressed material my also be formed in this way. The shaped bodies are preferably of geometric configuration, and may for example be circular, square or rectangular in cross section.

The starting material including the aluminium material (prior to being compressed to form the shaped body) is preferably subject to one or more of the following process stages :

i) breaking down into a more free flowing material

(preferably in an attritional or comminution step) ;

ii) a heating and or drying stage to reduce overall moisture content (where heating occurs it is preferred that a heating temperature sufficient to effect flaring off of oil or other hydrocarbon material is attained) ;

Where a heating process stage is provided, it is preferred that it takes place prior to compressing the material to form the shaped body, the shaped bodies being formed whilst the material is at a temperature elevated relative to ambient. This improves the malleability of the material.

By utilising shaped bodies formed of compressed aluminium material it is possible to avoid the melting losses that occur in dab/billet casting of aluminium from scrap. Furthermore compression forming processes such as briquetting, tableting or pelletizing enable divided material including divided aluminium waste (such as swarf or grindings from industrial machining processes) to be used in steelmaking. Such waste is typically economical to buy and provides supplies of more consistent quality material than the general scrap used for melting and casting of aluminium dabs/ingots.

A further technical feature is that the density of the compressed shaped bodies can be tailored, manipulated and controlled to suit particular steelmaking process stage requirements. Tailoring the density enables the sink rate through molten material (such as through slag and molten metal) to be controlled and also enables the sink depth reached by the shaped body within the molten material to be controlled. A particularly important depth within the molten material is the slag/metal interface. The invention enables the density of the shaped body to be tailored to ensure that it settles and therefore acts at, above or below the slag/metal interface.

Furthermore, because the material of the shaped body (including the aluminium material) is compressed from divided material, it will be less dense and have a greater effective surface area than correspondingly cast dabs/ingots and so have different characteristics when introduced into the relevant steelmaking process stage.

The shaped bodies may be supplied in many different physical sizes and specifications. For example, shaped bodies formed by briquetting may have a density in the range 2.2 - 2.8 Kgπr³; shaped bodies formed by tableting may have a density in the range 1.4 - 4 Kgrrr³.

As mentioned earlier, the shaped bodies may include one or more additive materials, preferably arranged to have a conditioning influence upon molten steel, iron or slag. For example the shaped bodies may include slag conditioning additives and/or metal conditioning additives for improved process control (for example de- sulfurisation) . Typically such additives are introduced into relevant process stages as free flowing materials with consequent evolution of dust in the steelmaking environment and consequent health and safety implications.

One or more of the following additives may be included in the shaped bodies, depending upon user requirements: lime, magnesia, alumina, flourspar, Millscale (FeO or Fe₂0₃) , or steel (typically in the form of steel turnings) . Each of these materials is commonly used in steelmaking processes in order to aid process control, and it should be apparent that the list is non-exhaustive . Incidental ingredients and impurities may also be present, although deleterious quantities of impurities are preferred absent.

The additives and conditioning agents desirably comprise the material compressed to form the bodies, and are typically provided in powder or divided form and mixed with the aluminium material for compression as the shaped bodies. The relative proportions of conditioning additives and agents may therefore be predetermined and dosed/tailored according to end user requirements.

The additives may be bound in the shaped bodies as divided material (fine or coarse) distributed throughout with body aluminium material comprising the shaped body. In this case the additive material may be introduced and mixed with the aluminium material prior to compression into the required shaped configuration.

Because the shaped bodies are formed from divided material by a compressive shaping technique, it is relatively easy to introduce the required additives before or at the stage of shaping (for example during a briquetting/tableting process or a mixing stage prior to the compressive shaping stage) ._. This is a further benefit of the invention over prior art techniques of using cast aluminium dabs or ingots .

Accordingly, the invention may further provide a method of producing a product for use in steelmaking, the method comprising compressing divided material including at least a proportion of divided aluminium material to produce a self supporting shaped body, wherein the divided aluminium material includes at least a first aluminium material form and a second aluminium material form, the first and second aluminium material forms differing in one or more of:

i) aluminium content or purity of the divided material; ii) size of the divided material;

iii) hardness or ductility of the divided material.

In certain circumstances it may be advantageous to provide a water resistant barrier around the shaped body. For example, where the shaped body includes lime a waterproof barrier or coating for the body (protecting the lime from contact with moisture) is particularly preferred.

As mentioned above, for high volume production it is advantageous to produce an array of shaped bodies in a pressed web arrangement, even where only a single aluminium form is present. Existing difficulties in achieving this have been overcome and according to a further aspect, the present invention provides a method of producing compressed formed bodies including aluminium material for use as an agent added to molten steel and/or iron in steelmaking, the method comprising:

i) feeding starting material, including at least one aluminium material in divided form, to compressive forming apparatus;

ii) operating the forming apparatus to produce a substantially continuous out-feed of spaced compressed bodies interconnected by a body- interlinking web of compressed material, the composition/condition of the starting material being such that downstream of the forming apparatus the compressed bodies are broken from the web material to provide substantially entirely individual bodies separated from the web .

The invention will now be further described in specific embodiments by way of example only.

A batch of aluminium sawings of purity 94%-98% al is received as waste from an industrial operation and tipped into a holding area. In the arrival condition, the waste aluminium material is likely to have an unacceptably high moisture content (for steelmaking use) and also be surface contaminated with grease or oil or other machining lubricants.

The waste aluminium material is fed into a chipping machine where the material is broken down into finely divided material of a more uniform size, typically 2-3 mm. In this condition the material is more free flowing.

An Archimedes screw arrangement next transfers the finely divided aluminium material to a rotary oven in which the internal temperature is elevated to approximately 200 Celsius. The temperature elevation dries the aluminium material and heating gas flame jets cause flashing off of oil and other contaminating surface residues.

Following the heating stage the finely divided aluminium material sawings are mixed with a second aluminium material form in the form of finely divided aluminium foil commutated to a size of 1-2 mm (purity 98%-99% al) and also finely graded sieved aluminium grindings of size 20 mesh approximately (and purity 88%-92% al) . A typical proportional mix is typically approximately 47% sawings, 47% foil, 6% grindings. Any required additives or steel conditioning agents may also be mixed in. The additives or conditioning agents will vary in nature and dosing quantity depending upon the steelmaking process stage and finished steel requirements. One or more of the following additives may be included in the shaped, depending upon user requirements: lime, magnesia, alumina, Flourspar, Millscale, steel turnings. Each of these materials is commonly used in steelmaking processes in order to aid process control and steel conditioning. The list is not exhaustive and other additives or agents may be introduced depending upon requirements. For tableting a binder (such as lime) may be added at this stage.

The aluminium material mixture/blend and additive/conditioning agents, where present is next fed to a rotary briquetting press where the mixture is mechanically/hydraulically compressed (compacted or mechanically agglomerated) to the final form of the shaped body (briquette) determined by the rotary surfaces mould. For densities and dimensions required a typical operating regime for an hydraulic press may be an application force of 150 tonnes. The briquettes produced to the formulation specified and in the manner described are extremely economically produced and suited for use as a deoxidant for molten steel .

Alternatively, products in accordance with the invention may be formed m a tabletmg press for producing shaped bodies (tablets) of generally smaller size than the shaped bodies (briquettes) from the briquetting press. The choice of briquetting or tableting will depend upon the ultimate end use for the shaped body. Typical tableting production is at a rate of 500-5000 tablets per minute. Tablets for slag conditioning may be produced in such a manner having the following composition:

40% comminuted foil - 98% min al @ 12 to 18 mesh 60% sieved grindings - 88-90% al @ 20 mesh

Target aluminium content is 88-90% al but foil is required at higher levels to aid manufacture and reduce tool wear at the current time. Adopting hard surfaced tooling such as tungsten carbide tooling will permit an increase the proportion of grindings in the mix.

After blending, the foil and grinding mixture is milled for a few seconds to fluidise and aerate the material just prior to production. This greatly improves flow and reduces fluctuations in process control due to variations in tablet density.

A tablet size of approximately 12-14 mm is believed to be optimum. In accordance with the invention, for certain applications the mixing of additives is not necessarily required or desirable and the briquettes or tablets may comprise the compressed aluminium material substantially entirely (or alternatively compressed conditioning additive or agent material, with or without incidental ingredients).

Claims

Claims :

1. A shaped body comprising compressed material, which compressed material includes aluminium material, the shaped body being for use as an agent added to molten steel and/or iron in steelmaking.

2. A shaped body according to claim 1 including compressed divided aluminium material in at least a first material form and a second material form the first and second aluminium material forms differing in one or more of :

i) aluminium content or purity of the divided material;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

3. A shaped body according to claim 2, wherein a first aluminium material form comprises a higher purity aluminium material and_; a second aluminium material form comprises a lower purity aluminium material.

4. A shaped body according to claim 3, wherein the higher purity material has a purity substantially in the range 96% al and above and the lower purity material has a purity substantially in the range 92% and above .

5. A shaped body according to claim 3 or claim 4, wherein the higher purity material has a divided size smaller than the lower purity material.

6. A shaped body according to claim 3 , wherein the higher purity material has a purity substantially in the range 96% al and above and the lower purity material has a purity substantially in the range 86% to 94%.

7. A shaped body according to claim 3 or claim 6, wherein the higher purity material has a divided size significantly larger than the lower purity material.

A. shaped body according to claim 7, wherein the divided particle size of the lower purity material is in the range 10 to 30 mesh (preferably substantially 20 mesh) .

A shaped body according to claim 2, wherein the first and second aluminium material forms differ in two or more of :

i) aluminium content or purity of the divided material ;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

10. A shaped body according to any of claims 2 to 9, further comprising a third material form of aluminium differing from the first and second aluminium material forms in one or more of:

i) aluminium content or purity of the divided material ;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

11. A shaped body according to claim 10, wherein one of the first second or third forms of aluminium material comprises an alloy having a hardness greater than the hardness of aluminium.

12. A shaped body according to claim 11, wherein the relatively hard alloy is present in a proportion less than the proportions of either of the other aluminium material forms .

13. A shaped body according to claim 12, wherein the relatively hard alloy is present in a proportion substantially in the range 15% by weight or less of the body.

14. A shaped body according to claim any preceding claim, wherein the shaped body includes aluminium material forms selected from the group comprising swarf, chippings, grindings foil sheet (commutated) or other divided aluminium material .

15. A shaped body according to any preceding claim, wherein the aluminium material forms are compressed into the self supporting shaped body from an amorphous entanglement or other less coherent body or grouping of divided material comprising the plurality of aluminium material forms .

16. A -shaped body according to any preceding claim, of geometric configuration.

17. A- shaped body according to any preceding claim, including one or more (non- aluminium) additives or agents for the conditioning of molten material in a steelmaking process.

18. A shaped body according to claim 17, wherein the shaped body includes slag conditioning additives.

19. A shaped body according to claim 17 or claim 18, wherein one or more of the following additives are included in the shaped bodies: lime, magnesia, alumina, Flourspar, Millscale, steel.

20. A shaped body according to any of claims 17 to 19, wherein the additive material is bound in the shaped bodies as divided material (fine or coarse) distributed throughout the body aluminium material comprising the shaped body.

21. A shaped body according to any of claims 17 to 20, wherein the additive material is introduced and mixed with the aluminium material prior to compression into the required shaped configuration.

22. A shaped body according to any of claims 17 to 21, wherein one or more layers of additive material are compressed (or otherwise bound) onto the exterior of the shaped body.

23. A shaped body according to any preceding claim, wherein a water resistant barrier is provided for the shaped body.

24. A method of producing a product for use in steelmaking, the method comprising compressing divided material including at least a proportion of divided aluminium material to produce a self supporting shaped body, wherein the divided aluminium material includes at least a first aluminium material form and a second aluminium material form, the first and second aluminium material forms differing in one or more of : i) aluminium content or purity of the divided material ;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

25. A method according to claim 24, wherein the divided aluminium material further includes a third material form of aluminium differing from the first and second aluminium material forms in one or more of :

i) aluminium content or purity of the divided material;

ii) size of the divided material;

iii) hardness or ductility of the divided material.

26. A method according to claim 24 or 25, wherein the shaped bodies are formed in a press apparatus.

27. A method according to any of claims 24 to 26, wherein shaped bodies are formed between shaped compressive formers arranged to produce a series of spaced bodies interconnected by a body-interlinking web of compressed material.

28. A method according to claim 27, wherein the bodies are subsequently broken from the body- interlinking web .

29. A method according to claim 27 or claim 28, wherein the compressive formers comprise rotary circumferentially adjacent formers.

30. A method according to any of claims 24 to 29, wherein aluminium material is subjected to one or more of the following process stages prior to compressive forming into shaped bodies:

i) breaking down into a more free flowing material;

ii) a heating and/or drying stage to reduce overall moisture content;

iii) mixing/blending of the plurality of aluminium material forms in dosed quantities;

iv) fluidising/aeration of . blended aluminium material forms (where the aluminium material forms comprise powder forms - typically 30 mesh or less) .

31. A method according to claim 30, wherein the heating process stage is provided prior to compressing the material to form the shaped body, the shaped body being formed whilst the material is at a temperature elevated relative to ambient.

32. A method according to any of claims 24 to 31, wherein one or more additive materials/steel conditioning agents are included in the compressed material shaped body.

33. A method according to claim 32, wherein the additive materials/conditioning agents comprise one or more of, lime, magnesia, alumina, flourspar, Millscale, steel.

34. A steelmaking process in which aluminium material is added to molten steel and/or iron in a steelmaking process stage, the aluminium material being introduced into the relevant process stage in the form of shaped self supporting compression formed bodies, characterised in that respective compression formed bodies include compressed divided aluminium material in at least a first material form and a second material form the first and second aluminium material forms differing in one or more of:

i) aluminium content or purity of the divided material ; ii) size of the divided material;

iii) hardness or ductility of the divided material.

35. A method of producing compressed formed bodies including aluminium material for use as an agent added to molten steel and/or iron in steelmaking, the method comprising:

i) feeding starting material, including at least one aluminium material in fine'ly divided form, to compressive forming apparatus;

ii) operating the forming apparatus to produce a substantially continuous out-feed of spaced compressed bodies interconnected by a body- interlinking web of compressed material, the composition/condition of the starting material being such that downstream of the forming apparatus the compressed bodies are broken from the web material to provide substantially entirely uniform individual bodies separated from the web.

36. A method according to claim 35, wherein the starting material includes a further material in finely divided form, said further material promoting break up of the bodies from the web.

7. A method according to claim 36 or 37, wherein the apparatus comprises a rotary compressive forming means including a first and second contra-rotating cylinders having respective forming surfaces provided with respective arrays of pockets for forming the array of bodies therebetween.