BACKGROUND OF THE INVENTION

This invention relates to insulating and/or metallurgical composites, and in particular to composites which are utilised as fluxes in pelletised or granular form for iron and steel manufacture.

During the processing of ferrous melts, for example in ladles or tundishes, it is necessary to maintain a flux cover over the melt. The cover can perform a number of functions, ranging from one extreme of purely acting as a insulating flux, to the other extreme of purely acting as a metallurgical flux, or, an intermediate function of simultaneously acting as an insulating and a metallurgical flux.

The purpose of an insulating flux is to minimise the heat loss, through radiation, from the surface of a ferrous melt. To be effective, an insulating flux must readily spread over the melt surface, remain predominantly in a solid form, (ie. powder/pellet form, a non-liquid) at 1500 to 1800°C and not react adversely with the ferrous melt or furnace refractory.

To work effectively as an insulant, the cover should ideally consist of a thin liquid flux layer (approximate depth 5-30mm) and non liquid layer whose approximate depth is 20-200mm. The liquid flux layer retards re-oxidation of the melt by atmospheric oxygen and the non-liquid layer reduces heat lost (through radiation) from the melt surface.

The role of a metallurgical flux is to absorb various impurities (such as sulphur, phosphorus, alumina and oxygen), to prevent atmospheric oxidation of a ferrous melt,

to modify inclusions whose" presence is detrimental to the properties and processing of ferrous metals etc. Metallurgical flux generally sits on the surface of a ferrous melt and in this application it must form a deep liquid layer at the ferrous melt temperatures. Typically, the melting point of a metallurgical flux (low temperature phase) should be within the range of 1100-1400°C. Typically metallurgical flux is comprised of calcium oxide, alumina, silica and magnesium oxide.

To work effectively, a metallurgical flux should provide a deep liquid flux layer in contact with the ferrous melt and a non-liquid layer in contact with the liquid flux layer. The liquid layer through turbulent mixing, reacts with the impurities contained in the ferrous melt and thus causes these impurities to be transferred from the ferrous melt to the molten liquid flux layer. The non-liquid layer, with time, dissolves into the liquid flux . layer thus replenishing it with active metallurgical components.

Typically, insulating and metallurgical fluxes have in the past been in very fine powder form. However, such powder forms are undesirable as their use results in a dusty « environment which can cause health and safety problems for plant operators, particularly due to the reactive nature of the powder.

It is known to pelletise insulating flux utilising fly ash as the major proportion as disclosed in Republic of Korea Patent Publication No. 88-2456 published 14 November 1988. This known pellet being formed by plastic working and having the proportions of 60-80%wt fly ash, 15-20%wt of bentonite (binder) , 10-15%wt of powdered coke and <_ 5%wt of sawdust.

According to the disclosure of the abovementioned Korean publication the composite pelletised insulant is possible by the use of bentonite (binder) in the range of

15-20%wt where bentonite is-principally used for its binding properties. A disadvantage of this is that the bentonite significantly reduces the insulating properties of the composite and promotes unfavourable reactions such as intersintering betwen pellets when they are being used, and also lowering of pellet refractoriness. This results in solidification of the flux layer which is undesirable during pouring and handling of molten metal.

SUMMARY OF THE INVENTION

It is therefore desirable to provide an insulanting and/or metallurgical composite which can be manufactured in pelletised or granular form, which requires a relatively small amount of binder or no binder at all.

With little or no binder present the composite can be made up of more of the effective components which are required, thus improving the effectiveness of the composite.

In a first aspect of the present invention there is provided a composite for providing a metallurgical and/or insulating flux to a molten metal, comprising: aluminosilicate material; calcium and/or magnesium bearing material; and, carbonaceous raw material.

Preferably, said aluminosilicate material is selected from one or any combination of: kaolin, flint clay, china clay, calcined flint clay, fly ash, boiler house ash, or molten slags, and/or sillimanite.

Also preferably, said calcium and/or magnesium bearing material is selected from one or any combination of: calcium oxide (burnt lime), calcium carbonate, calcium hydroxide, magnesium oxide, dolomite olivine, fosterite and/or vermiculite.

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Also preferably, saic carbonaceous raw material is selected from any one or combination of: carbon black, coke/graphite and/or exfolliating graphite.

Preferably, to obtain optimum metallurgical properties, the specific reactivity of the flux is varied by addition of raw materials selected from any one or combination of: calcium fluoride, barium fluoride or sodium fluoride, calcium carbide, sodium carbonate, barium oxide, alimina, aluminium or a deoxidising agent similar to aluminium.

Most preferably, said composite is provided in the form of pellets, granules, or the like.

Also most preferably, said composite in pellet, granule or like form, is either, placed at the bottom of a tundish or ladle prior to pouring a ferrous melt therein, injected into the melt, and/or, placed into the pouring stream or on top of the molten metal.

In a first preferred embodiment of the invention, the proportion of said materials are varied to yield a metallurgical flux composition comprising: silica (Si0 ₂ ) 0-50 %wt; alumina (Al-O,) 0-40 %wt; calcium oxide (CaO) 30-70 %wt; calcium carbonate 0-20 %wt; calcium hydroxide (Ca(OH) ₂ ) 0-20 %wt; magnesium oxide(MgO) 0-20 %wt; aluminium (Al) 0-10 %wt; carbon (C) 0-10 %wt; calcium cardide 0-5 %wt; calcium fluoride 0-10 %wt; sodium carbonate 0-10 %wt; barium oxide 0-20 %wt.

Preferably, also, said metallurgical composite in this composition further comprises:

binder material, such 'as bentonite, sodium silicate or other binder material 0-15 %wt.

Preferably, also the metallurgical composite further has insulative properties provided by variation of the proportion of raw materials to yield a metallurgical/ insulative composite, comprising: silica. (Si0 ₂ ) 5-40 %wt; alumina (A1 ₂ 0 ₃ ) 0-40 %wt; magnesium/calcium oxide 0-20 %wt; magnesium/calcium carbonate 0-50 %wt; calcium hydroxide 0-50 %wt; carbon (C) 0-36 %wt.

In a second preferred embodiment, the proportion of said materials are varied to yield an insulating composite, comprising: silica (Si0 ₂ ) 10-70 %wt; alumina (A1 ₂ 0 ₃ 0-50 %wt; calcium oxide (CaO) 0-20 %wt; calcium carbonate 0-20 %wt; calcium hydroxide (Ca(OH) ₂ ) 0-20 %wt; carbon (C) 0-26 %wt.

Preferably, said insulating composite in this composition further comprises binder material, such as bentonite, sodium silicate or other binder material in the range 0-15 %wt.

In a preferred embodiment, the insulation composite further has metallurgical properties provided by variation of the proportion of said materails to produce a metallurgical/ insulating composite, comprising: silica (Si0 ₂ ) 10-55 %wt; alumina (A1 ₂ 0_) 0-50 %wt; magnesium/calcium oxide 0-20 %wt; magnesium/calcium carbonate 0-50 %wt; calcium hydroxide 0-50 %wt; carbon (C) 0-36 %wt.

Preferably, also, the proportion of said raw materials are varied to yield a metallurgical/ insulative composite, comprising: silica (Si0 ₂ ) 5-40 %wt; alumina (A1 ₂ 0 ₃ ) 0-40 %wt; magnesium oxide/calcium oxide 0-20 %wt; magnesium/calcium carbonate 0-50 %wt; calcium hydroxide 0-50 %wt; carbon (C) 0-36 %wt.

In yet a further aspect, the present invention provides processes for manufacturing insulating and/or metallurgical composite in the form of pellets or granules or the like, comprising the steps of: mixing the components in a dry powder form; adding water or other like fluid to the components whilst mixing such that the moisture level is substantially in the range of 15-35%; feeding the resultant moistened mix into a pelletising mill in a controlled manner for formation into pellets; and drying said pellets to remove all the moisture.

In a further aspect, the present invention provides a process for manufacturing an insulating and/or metallurgical composite, comprising the steps of: (i) briquetting a wet composite; (ii) removing moisture and hardening same; and (iii) crushing the briquette to create granules of predetermined size.

In yet a further aspect, the present invention provides a process for manufacturing an insulating and/or metallurgical composite, comprising the steps of: (i) supplying a moist premixed powder, by means of a screw feeder or the like at the base of a hopper onto an inclined rotating disc (or dish) ; (ii) simultaneously supplying fine water sprays to further

wet said mix; and

(iii) drying and hardening said mix to form granules.

Preferably, one or more of the following characteristics may be varied:

(a) Inclination angle of the disc.

(b) Angle and position of mixer blades

(c) Rotation speed of the disc.

(d) Feed rate of moist powder onto disc.

(e) Positioning of moist powder feed on to the rotating disc.

(f) Position of water sprays.

(g) Flow rate of sprayed water.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

The insulant and/or metallurgical composite in pellet form will now be described by way of example. It should however be appreciated that the present invention is not limited to the examples specified hereinafter. Variations and modifications thereto will become obvious to persons skilled in the art.

Metallurgical Pellets

The composition ranges, together with typical examples thereof, is shown in the following table.

chemical entity range typical example %wt %wt

(a) (b) silica (Si0 ₂ ) 0-50 13 11 alumina (A1 ₂ 0 ₃ ) 0-40 30 34 calcium oxide (CaO) 30-70 48 45 calcium carbonate 0-20 0 0 calcium hydroxide (Ca(OH) ₂ ) 0-20 0 0 magnesium oxide(MgO) 0-20 6 6 aluminium (Al) 0-10 3 3 carbon (C) 0-10 0 1 binder 0-15 0 0 calcium carbdide 0-5 0 0 calcium floride 0-20 0 0 sodium carbonate 0-10 0 0 barium oxide 0-20 0 0

The metallurgical flux composition can be achieved by using a mixture of pure components or a mix of pre-melted components such as aluminosilicate or slag and pure components.

Magnesium oxide and calcium oxide can be added as pure oxides or as carbonates or as a mixture of oxides, carbonates and hydroxides.

Whilst two specific examples have been given, the composition can be varied in the general range to produce a flux suitable for different processing conditions or for different grades of ferrous melt etc. Further components such as calcium carbide, calcium flouride, barium fluoride, sodium fluoride, sodium carbonate, barium oxide, aluminium and similar deoxidising agents can be added in small

quantities to provide fluxes" having different characteristics.

When such metallurgical fluxes are used, their primary role is to remove impurities from the molten metal to modify inclusions and to inhibit oxidation of the melt by oxygen in the atmosphere.

A metallurgical composite in the form of pellets or granules has the advantage of being able to be placed in the bottom of a tundish or a ladle before the ferrous melt is poured therein and not create dust (airborn particles) and/or fume when the molten metal is poured on top of it. The purpose of placing a metallurgical flux on the bottom of a ladle or a tundish is to remove impurities from the molten metal (which is poured on top of it); to create a liquid barrier between the molten metal and the ladle/tundish lining; to minimise contaminations of the melt by the tundish/ladle lining refractory; and to absorb powder/aggregate which may have accumulated at the bottom of an empty tundish/ladle. With the known powder form metallurgical fluxes it is unacceptable, from environmental and occupational health safety viewpoints, to pour molten metal onto powder flux placed at the bottom of a ladle or tundish as this would create unacceptable amount of dust (airborn particulate could be above the allowable limit). Whereas the pelletised or granular form minimises the amount of dust generated, it is easier and safer to handle and therefore more suitable for this application.

Therefore, another aspect of the invention involves a method of placing a metallurgical flux composite in pellet or granular form at the bottom of a tundish or ladle before pouring the ferrous melt or optionally injecting the flux into the melt.

Another form of the invention involves placing the metallurgical granule into the pouring stream or on top of molten metal.

Metallurgical/Insulating Pellets

Typical composition ranges and specific examples are shown in the following table.

chemical entity range %wt typical silica (Si0 ₂ ) 5-40 27 alumina (Al-O-) 0-40 12 magnesium/calcium oxide 0-20 8 magnesium/calcium carbonate 0-50 15 calcium hydroxide 0-50 15 carbon (C) 0-36 23

The raw materials which may be utilised to constitute the pellets may include kaolin, flint clay, china clay, calcined flint clay, fly ash, boiler house ash, molten slag and/or silliminide, calcium oxide (burnt lime), calcium carbonate, calcium hydroxide, magnesium oxide, dolomite, olivine, fosterite, vermicullite, carbon black, coke, graphite, exfolliating graphite, calcium fluoride, barium fluoride, calcium carbide, sodium carbonate, barium oxide, alumina, aluminium and/or a similar deoxident to aluminium.

Whilst insulating/metallurgical pellets can be formed with no binder, relatively small amounts of binder ie. less than 15% can be added to the raw materials.

Where binder is used, then the binder may be any suitable type of binder such as bentonite, sodium silicate, organic binders or cellulose based binders such as carboxy methyl cellulose, cement and gypsum.

Insulating Pellets

Typical composition ranges and examples are shown in

the following table.

chemical entity rraannggee typical example typical example %wt without binder with binder silica (Si0 ₂ ) 1 100--7700 45 47 alumina (A1 ₂ 0 ₃ ) 0 0-- -5500 24 25 calcium oxide

(CaO) 00-- -2200 5 0 calcium carbonate 00-- -2200 0 0 calcium hydroxide

( (CCaa((OOHH)) ₂₂ )) 00-- -2200 0 0 carbon (C) 00-- -2266 26 25

The ingredients of insulating pellets containing binder comprises the same ingredients as the binderless insulating pellets, however, the burnt lime (Calcium Oxide) calcium carbonate and/or Ca(OH)_ do not need to be included. The binder is less than 15% wt.

The raw materials making up the above composition may include kaolin, flint clay china caly, calcined flint clay, fly ash, boiler house ash, silliminide, calcium oxide (burnt lime), olivine, fosterite, vermicullite, carbon black, coke, graphite, exfolliating graphite, aluminium.

Pelletising process

A process similar for pelletising the composites, is as follows. The constituent powders are weighed according to the appropriate formulation and transferred into a screw mixer. An appropriate amount of water is added in the form of a fine spray to moisten the powder, typically the moisture level is in the range of 15-35%.

The moistened powder is fed into the pelletising mill in a controlled manner, ie. by fixing the speed and size of a screw feeder. Additional moisture can be introduced through

steam/mist jets which are located near the disc cavity of the pelletising mill.

On passing through the pelletising mill, the moist powder is formed into pellets. The pellets are typically cylindrical in shape, with a diameter typically in the range of 2-8mm and a typical length of 3-15mm. The pellet size being dependent on the sizing holes of the mill.

Once formed the pellets are transported by a conveyor belt into a moving belt drying oven, where the pellets are heated to remove all the moisture. The advantage of this process is that it yields pellets which exhibit good strength and are relatively free of fines.

The ability to produce strong pellets, without binder or with relatively small amounts of binder is achieved by selecting the appropriate amounts of constituents of the composition. The composition is such that on drying a reaction occurs within the pellet between the constituent components causing bonding and thus yielding a strong pellet.

Granulation Process

Alternatively the insulating composites can be granulated instead of pelletised. One suitable granulation process is as follows.

The process consists of taking a moist premixed powder and feeding this in a controlled manner, for example by means of a screw feeder at the base of a hopper onto an inclined rotating disc (or dish), where fine water sprays further wet the mix and granulation occurs.

The initial moisture, is typically in the range 15-35 wt ^β -

The rotating disc has numerous variable which

contribute to the granulation process. The variables are as follows:

(a) Inclination angle of the disc.

(b) Angle and position of mixer blades

(c) Rotation speed of the disc.

(d) Feed rate of moist powder onto disc.

(e) Positioning of moist powder feed on to the rotating disc.

(f) Position of water sprays.

(g) Flow rate of sprayed water.

By varying the abovementioned, the density and size of granules produced can be varied. Once formed the granules are hardened by a drying process.

A second granulation process is to initially form a hard composite, dry the composite to remove moisture and harden same, and then crush to create granules of the required size. This can typically be achieved by briquetting moist composite, drying and crushing.

Other pelletising/granulating techniques such as drum granulation, concrete mixer granulation (this is used for iron ore granulation), screw extrusion, mechanical extrusion through perforated grills or spray drying could be used.

It will be noted that particular examples and description of the composites and the process for production therefor have been hereinbefore described.

It should be obvious to persons skilled in the art that numerous variations and modification could be made to the composite material and process of the present invention. All such variations and modifications should be considered to fall within the the scope of the invention.