GB1562818A

GB1562818A - Carrier for introducing vapourising reactants into a metal melt

Info

Publication number: GB1562818A
Application number: GB42992/76A
Authority: GB
Original assignee: Foseco Trading AG
Current assignee: Foseco Trading AG
Priority date: 1975-10-15
Filing date: 1976-10-15
Publication date: 1980-03-19
Also published as: AU1875776A; FR2328050A1; BR7606896A; JPS5257010A; CA1079529A; SE7611368L; AU504073B2

Description

(54) CARRIER FOR INTRODUCING VAPOURISING REACTANTS INTO A METAL MELT (71) We, FOSECO TRADING AG, a Swiss company, of Langenjohnstrasse 9, 7000 Chur, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a carrier for introducing vapourising reactants into a metal melt, wherein the reactants are embedded in a heat insulating composition containing a filler, a fibrous substance and a binder.

Since the properties of metallic materials such as iron, cast iron and steel depend on their composition and particularly on the presence and proportion of certain impurities, it is as a general rule necessary to add to melts of the respective metals particular treatment agents such as alloying and/or refining agents. Thus for example desulphurising agents are added to melts of pig iron and desulphurising/deoxidising and alloying agents are added to steel melts. Furthermore it is often necessary to introduce particular additives into molten metals such as oxides or carbides or fluxing agents such as fluorides.

When treatment agents i.e. additives and reactants are introduced, particularly difficulties arise if the material in question is of lower density than the molten metal to be treated and/or if it has, at the temperature of the molten metal, a very high vapour pressure. The high vapour pressure can indeed lead to explosive evaporation of such treatment agents on their introduction in view of the normally high bath temperature e.g. of 1150 to 17500C for iron and steel melts. The result of this is not simply a substantially great loss of treatment agent, but also in addition there is substantial danger to the personnel from metal and slag being thrown out of the treatment vessel.As well as this, if there is an explosive evaporation, the desired reactions between the melt and the reactant or additive do not take place properly, since these reactions are time dependent and require the most even distribution possible of reactant and addtive in the melt.

A typical example of these difficulties on introducing a reactant with a low specific gravity and high vapour pressure at the temperature of the molten metal is the manufacture of spheroidal graphite cast iron with the aid of magnesium. The vapour pressure of pure magnesium is so large at the temperature of molten iron that magnesium itself simply cannot be introduced into an iron melt under normal conditions. The introduction of magnesium accordingly requires special apparatus, such as pressure vessels or injectors and/or the use of a magnesium master alloy on the basis of a carrier metal such as nickel, silicon or copper in order to diminish the vapour pressure of the magnesium and evenly to dilute the magnesium with the carrier metal.There are normally used magnesium contents of 4 to 17%, in particular in special cases up to 32%, and the specific gravity of the master alloy can be up to about 6 g/cmS depending upon the proportion of the carrier material. Despite all these measures, the yield of magnesium does not normally exceed 40%.

The introduction of magnesium in the form of a master alloy introduces on the one hand additional costs for the carrier metal, for example nickel in the case of a nickel magnesium master alloy, and on the other hand the presence of an undesired, or at least not definitely necessary, additional metal in the cast iron.

As well as this there are difficulties which result from the fact that the treatment agent generally has a lower specific gravity than the metal melt to be treated, so that the particular treatment agent floats on the surface of the bath and reacts with the slag thereon and/or with the oxygen in the atmosphere. In this fashion, substantial losses take place which adversely affect the results.

Similar disadvantages arise if the treatment agent is introduced into a metal melt in the form of briquettes or tablets, since the bfiquettes or tablets, in order to give the greatest possible diminution of the vapour pressure and increase of the specific gravity must contain a substantial proportion of high specific gravity matrix. The matrix can be heat insulating and gas permeable, as is the case with magnesium impregnated coke. Seen from the point of view of its low specific gravity, the manufacture of magnesium impregnated coke is difficult and dangerous, since the pieces of coke must be dipped into molten magnesium. Additionally the capillary forces are insufficient in order to take up large quantities of magnesium.

The introduction of magnesium and other low specific gravity reactants which evaporate at the temperature of the melt in the form of a master alloy or a briquette or tablet or impregnated coke in molten iron is difficult and accordingly requires special measures.

Thus the master alloys or briquettes can in some cases be introduced into a special pocket in the floor of a ladle and covered with steel sheet scrap before the molten metal to be treated is poured into the ladle. Another known process makes use of an expensive pressurised ladle, in which the pressure is adjusted to correspond to the vapour pressure of magnesium, or a plunging bell is used with the aid of which the treatment agent is dipped deeply into the melt. Furthermore, blowing in processes are known in which the magnesium containing additive is blown into the melt with the aid of an injector and a carrier gas.

In this, the carrier gas is unnecessarily warmed to the temperature of the melt and automatically diminishes the partial pressure of the magnesium and thereby the activity thereof. The previously mentioned processes are very cumbersome and accordingly make tlle manufacturing costs of spheroidal graphite cast iron substantially higher.

Analogous difficulties as in the manufacture of spheroidal graphite cast iron, can also arise in the desulphurisation and deoxidisation of metal melts with alkali and alkaline earth metals or rare earth metals, in the deoxidation and denitrogenisation with the aid of aluminium and boron, as well as in the introduction of treatment agents in the form of chemical compositions such as borates as fluxing agents or carbides.

The present invention provides a carrier body which enables treatment agents such as alkali and alkaline earth metals, rare earth metals and, if desired, additives such as fluorides, carbides, borates, alumina, calcium oxide and silica to be used and to give high yields i.e. with little loss, without introducing the above mentioned difficulties, particularly when these agents are to be introduced into iron and steel melts.

According to the present invention there is provided a device for treating molten metal comprising a treatment agent, which vapourises at the temperature of the molten metal to be treated, in the form of particles set in a carrier body comprising a refractory filler, a binder and a fibrous substance which forms a reinforcing rericular structure within the body and which makes the body sufficiently porous co enable release of the treatment agent from the body.

The pore forming network may be of organic and/or refractory or inorganic fibre, and preferably organic fibre is the sole fibrous substance used. The fibres can give rise to the pores themselves or as a result of a reaction or decomposition at high temperature. The use of a fibrous material gives the advantage that the components of the carrier body can be measured out in the correct proportions without difficulties, mixed and then formed into any desired shape. A further advantage consists in the fact that the fibrous material simultaneously gives strength and porosity to the carrier body; it substantialiy surrounds the granular or powdery treatment agent and in this way hinders balling together or any undesired local concentration differences rhereof.Accordingly, the treatment agent is located, after a thorough mixing, forming to shape and drying or hardening of the binding agent, in the matrix of the carrier body and within the pore forming network in a homogeneous and, if desired, highly dispersed distribution. The result of this is that the treatment agent can leave the carrier body without the carrier body thereby being disintegrated.

Tests have shown that the carrier body, after the treatment agent has been released, can be removed from the molten metal essen tlally undamaged. This is the case even if the network consists ot paper, wood shavings, sawdust or textiles. This is accordingly of particular importance, since these fibrous materials are available as waste products in large quantities and at exceptionally favourable prices.

Using the carrier bodies according to the invention, it is not a question as in the use of master alloys, briquettes, tablets or even impregnated coke of any impurities being introduced into the melt. Rather only the treatment agent remains in the melt. The yield is accordingly high, since the heating, liquefying and evaporation of the treatment agent is slow and advances progressively from the exterior to the interior of the treatment device; i.e. the treatment agent is liberated in dosed fashion over a period of time. The advantage connected with this is that the treatment agent comes into the melt in the form of little drops or bubbles. As a result of this, there is a large reaction surface between the treatment agent and the melt and long reaction times.Furthermore even difficult to separate sulphide or oxide inclusions can be taken up by the drops and bubbles of the treatment agent, by which they are swept up to the surface of the bath.

Finally, the heat losses when using the carrier body according to the invention are substantially smaller than those occurring on the introduction of treatment agents with the aid of special devices, a carrier gas, or a master alloy, since in the carrier body according to the invention, only the heat insularing matrix with the fibrous network is warmed up, and only the heat for melting and evaporating the treatment agent is used. In the known processes in contrast, large quantities of heat are lost, since the introduction devices as well as the carrier metal and the carrier gas are automatically warmed to the temperature of the molten metal, and in the case of the alloy carrier of a masker alloy heat is wasted on the heat of solution of the alloy carrier.

The network can in addition to organic fibres also contain inorganic fibres such as for example asbestos, glass wool and slag wool individually or together in order to impart to the carrier body a certain rigidity. In order to improve the coherence of the carrier body, the starting mixture can contain binding agents which harden in the cold or on heating such as resins, synthetic resins or sodium silicate.

A quite particular advantage of the carrier body according to the invention consists in that, on account of its network consisting of fibrous material, it can be pressed or cast into a desired shape without difficulty. In this way, for example, carrier bodies can be made with a central opening in order to enable them to be plunged into the melt to be treated with the aid of a rod engaging in the central opening and also to enable them to be pulled out again. The necessary openings can however also be made by boring. Furthermore, a carrier body comprising a matrix having a fibrous network can also be shaped to a particular size. The carrier body however can also be nailed to a ladle base or wound round a rod for introduction into a melt on account of its fibrous network.On the other hand, however, pressed carrier bodies can also be divided into given lengths by sawing or cutting without difficulty. Easy dosing is possible having regard to the homogeneous distribution of the treatment agent in the carrier body.

The treatment device according to the present invention can also have a heat insulating covering layer in order to delay the beginning of reaction between the treatment agent and the molten metal. The treatment device can also consist of alternating layers containing and not containing the reactant.

Although the fibres of the matrix of the carrier body corresponding to the particular conditions of manufacture surround the particles of the matrix more or less closely, and thereby constitute hollow spaces and channels, it can be that the porosity thereby arising IS not sufficient for the emergence of the molten or evaporated treatment agent. This can be counteracted if the carrier body comprises channel forming material, for example materials which shrink on heating or which collapse with a reduction in volume such as strands of natural or synthetic fibres, yarns, straw, pieces of fabric or wood chips.Under rhe influence of the temperature of the molten metal, directional or random distribution channels form, the total cross-section and distribution of which can be adjusted in order to secure a dosed release of the treatment agent by adjusting the quantity of channel forming material in the starting mixture. As channel forming materials there are suirable not only fibres connected togerher into fabrics or yarns, but also optionally perforated tubes, collars and rings, for example made of plastics, metal or a refractory material.

In so far as rhe carrier body must have a certain strength, it can contain reinforcing inserts, for example, metal or textile fabrics.

According to its type it can be a permanent or temporary strengthening insert, for example, one which decomposes in use.

Tests have shown that the carrier body can contain up to 40 to 50% by weight of reactant, e.g. 10 to 40%, by weight of magnesium, without too violent reactions taking place in the molten metal, for example, in molten iron, and also without leading to any disintegration of the carrier body. This is the more surprising since the normal magnesium master alloys in general contain at most about 17% of magnesium, in exceptional cases at most 30 to 32% magnesium. In the carrier body according to the invention, the reactant may be a granular or powdered alkali metal, alkaline earth metal or rare earth metal, a mixture of two or more of them or an alloy comprising one or more of them, and the reactant is preferably magnesium. The magnesium content can amount to up to 35% by weight e.g. 5 to 25% or 25 to 35% by weight.The particle size of the magnesium preferably lies within a range of 0.05 to 2.0 mm, but more preferably is at least 0.1 mm and does not exceed 0.5 to 1.0 mm in order that the particles occur in a finely dispersed distribution with the fewest possible points of contact with one another. Points of contact constitute bridges for the transport of heat and adversely affect the desired dosed release and reaction of the reactant.

Furthermore the carrier body can consist of up to 10% by weight paper, for example 1 or 2 to 6% by weight paper and up to 6% for example 1 or 2 to 4% by weight of organic binding agent. The remainder consists of a filler material, for example a filler inert to the molten metal or an additive such a.

alumina, magnesium oxide, calcium oxide, silica and one or more fluorides, borates or carbonates individually or in admixture. Preferably, the reactant and/or the additive material are present in the form of particles that are separate from one another and the additive may be located in a hollow space within the body.

The invention is subsequently further illustrated by way of exemplary embodiments with reference to the accompanying drawings in which: Figure 1 shows in schematic section a carrier body with a treatment agent finelv distributed therein, Figure 2 shows a treatment device according to the invention having a heat insulating covering layer, Figure 3 shows a treatment device built up of layers, Figure 4 is a schematic section of a treatment device ready for introduction into molten metal, Figure 5 is a photographic reproduction of a treatment device according to Figure 4, and Figure 6 is a photograph of the device of Figure 5 after having been plunged into molten iron and allowed to react wholly therein.

The carrier body 10 illustrated in Figure 1 consists of a matrix 11 with a fibrous network in which a glandular reactant 12 is embedded with the granules not contacting one another, as well as a likewise granular additive 13 as a filler, each in finely dispersed distribution.

Furthermore, for diminution of the transfer of heat the carrier body 23 can also be provided with a heat insulating but gas permeable covering layer 24 and a fabric type of strengthening insert 25 (Figure 2).

Referring to Figure 3, the treatment device consists of a carrier body 26 having alternate reaction agent free-layers 27 and reaction agent 28 containing layers 29.

Referring to Figure 4, in order to introduce a cylindrical carrier body 30 into a melt, the carrier body 30 can have a central bore 31 and be fixed between two perforated plates 32, 33. A threaded bolt 35 passes through the holes in plates 32, 33 and the central bore 31 registered therewith and is screwed into a plunging rod 34. Such a plunging body is of no substantial expense and is suitable particularly for dipping the carrier body into molten metal. During such a process, the carrier body does not undergo any substantial decomposition, even when it is often necessary that it remains several minutes in the molten metal in order to secure full release of the reactant.

Tests have shown that, in the manufacture of spheroidal graphite cast iron or in the desulphurisation of pig iron, the dwell time necessary to obtain a magnesium content of 0.02 to 0.08% by weight of a carrier body of the type shown in Figures 4 and 5 with a magnesium content of 35% by weight in a matrix having a network of paper fibres and with a bath temperature of 16000C, can amount to about 4 minutes to full release of the magnesium. After this time, the carrier body appeared as evident from Figure 6; i.e.

the carrier body had essentially its original shape, which is a clear indication that with the exception of rhe magnesium treatment agent, no other components of the carrier body had been taken into the molten metal.

In the framework of a test, several carrier bodies 2 to 5 according to the invention were made having the compositions evident from the following table. In their manufacture the respective proportions of the components given were formed to a slurry with water. The respective slurries were cast into a mould with a mesh floor and lid and dewatered by the application of a vacuum. The dewatered slabs were then dried at about 200"C in an oven.

From the dried slabs in each case discs were cut with a diameter of 46 mm and these were inserted between two perforated plates as shown in Figure 4.

In the test, a plunging body disc identified as number 1 in the table below and which was made in the same fashion but magnesiumfree was plunged into a 15 kg melt of pig iron with a sulphur content of 0.02% by weight, a magnesium content of 0.007% by weight and an oxygen content of 70 ppm, and after an immersion or reaction time of 170 seconds was removed from the melt substantially undamaged. Thereafter an iron sample was taken and analysed from which it was evident that the composition of the melt had not changed.

Then, consecutively, the plunging body discs identified as numbers 2 to 5 in the table below, each of which contained magnesium with a particle size of 0.06 to 1 mm but in varying quantities, were dipped into the same melt and were allowed to remain in the melt for the immersion or reaction time evident in each case from the table. The individual plunging bodies were in each case removed from the melt when no further reaction was evident. The immersion time given in the table accordingly corresponds to the period of time from immersion to the end of the reactions.

For comparison purposes, a plunging body "a" of 35% by weight magnesium impregnated coke was immersed in the melt between immersing the immersion bodies identified as numbers 4 and 5 in the table below. As is evident from the table, the immersion or reaction time in this case amounted to only 90 seconds i.e. after 90 seconds no further magnesium was released from the coke while the immersion or reaction times of the two immersion bodies 4 and 5 according to the invention, with a somewhat lower and the same magnesium content respectively, amounted to more than double and more than three times respectively. From this comparison the desired dosing obtained with the plunging bodies according to the invention is clearly evident i.e. the release of magnesium extending over a longer period of time.All the plunging bodies had their original shape after being withdrawn.

In summary it is evident from the analysis values for sulphur, magnesium and oxygen that it is possible with the plunging bodies according to the invention to diminish the content of sulphur and oxygen in dependence upon the quantity of magnesium introduced and, on the other hand, to increase the magnesium content.

Fibrous Surface Immersion Filler- substance- Binding active time Plunging Mg MgO Paper agent agent in Temperature (S) (Mg) (O) body (%) (%) (%) (%) (%) seconds ( C) (%) (%) ppm 1 0 95.7 1.9 1.9 0.5 170 1590 0.02 0.007 70 2 10 85.7 1.9 1.9 0.5 95 1590 0.018 0.012 27 3 20 75.7 1.9 1.9 0.5 250 1590 0.007 0.018 35 4 30 65.7 1.9 1.9 0.5 260 1600 0.005 0.016 10 a 35 90 0.002 0.026 24 5 35 60.7 1.9 1.9 0.5 300 1600 0.002 0.038 10

The treatment devices according to the invention provide a guarantee of not contaminating the molten metal which they are used to treat. This is of importance insofar as the treatment devices according to the invention give rise to the possibility of replacing the deoxidation and desulphurisation agents leading to undesired inclusions such as alumina, silicates or sulphides by highly reactive alkali, alkaline earth and rare earth metals.

The low heat capacity and low volume additionally give the smallest possible heat losses. Finally, the quantity of treatment agent can be adjusted exactly without any difficulty with the aid of standard bodies of the type illustrated in Figures 4 and 5; it is only necessary to place the required number of carrier bodies on the front end of a plunging rod.

On the other hand, the carrier bodies on account of their network of fibrous materials can be divided without difficulty in order to enable an exact dosing of the treatment agent.

WHAT WE CLAIM IS: 1. A treatment device for the introduction of a treatment agent into molten metal con slsting of a treatment agent, which vapourises at the temperature of the molten metal to be treated in the form of particles set in a carrier body comprising a refractory filler, a binder and a fibrous substance which forms a reinforcing reticular structure within the body and which makes the body sufficiently porous to enable release of the treatment agent from the body 2. A treatment device according to claim 1 wherein the carrier body comprises paper and/ or sawdust.

3. A treatment device according to claim 1 or 2 wherein the carrier body comprises one or more asbestos, glass wool and slag wool.

4. A treatment device according to claim 1 or 2 wherein the carrier body comprises organic fibre as the sole fibrous substrate.

5. A treatment device according to any of claims 1 to 4 wherein the reactant is a granular or powered alkali metal, alkaline earth metal or rare earth metal, a mixture of two or more of them or an alloy comprising one or more of them.

6. A treatment device according to any of claims 1 to 5 wherein the carrier body comprises one or more additives selected from alumina, magnesia, calcium oxide, silica, fluorides, borates and carbides.

7. A treatment device according to any of claims 1 to 6 wherein the reactant/and or the additive material are present in the form of particles that are separate from one another.

8. A treatment device according to any of claims 1 to 7 wherein the additive is located in a hollow space within the body.

9. A treatment device according to any ol claims 1 to 8 and having a heat insulating covering layer.

10. A treatment device according to any of claims 1 to 9 and formed of alternating layers containing and not containing reactant.

11. A treatment device according to any of claims 1 to 10 wherein the carrier body comprises channel forming materials.

12. A treatment device according to claim 11 wherein the channel forming materials consist of fibres connected to one another.

13. A treatment device according to claim 11 wherein the channel forming materials consist of tubes, collars or rings.

14. A treatment device according to any of claims 1 to 13 wherein the carrier body comprises strengthening inserts.

15. A treatment device according to any of claims 1 to 14 and containing up to 50% by weight of reactant.

16. A treatment device according to claim 13 and comprising 10 to 40% by weight magnesium.

17. A treatment device according to claim 15 and comprising 25 to 35% by weight magnesium.

18. A treatment device according to claim 16 or 17 wherein the particle size of the magnesium is at most 2 mm.

19. A treatment device according to claim 18 wherein the particle size of the magnesium is 0.1 to 1.0 mm.

20. A treatment device according to any or claims 15 to 19 wherein the carrier body comprises a network consisting of up to 10% by weight of paper.

21. A treatment device according to claim 20 wherein the network consists of 1 to 6% by weight of paper.

22. A treatment device according to any of claims 15 to 21 and comprising up to 6% of organic binding agent.

23. A treatment device according to claim 22 and comprising 1 to 4% by weight of organic binding agent.

24. A treatment device for treating molten metals according to claim 1 and substantially as hereinbefore described with reference to any of the specific plunging bodies numbers 2 to 5 herein.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. The treatment devices according to the invention provide a guarantee of not contaminating the molten metal which they are used to treat. This is of importance insofar as the treatment devices according to the invention give rise to the possibility of replacing the deoxidation and desulphurisation agents leading to undesired inclusions such as alumina, silicates or sulphides by highly reactive alkali, alkaline earth and rare earth metals. The low heat capacity and low volume additionally give the smallest possible heat losses. Finally, the quantity of treatment agent can be adjusted exactly without any difficulty with the aid of standard bodies of the type illustrated in Figures 4 and 5; it is only necessary to place the required number of carrier bodies on the front end of a plunging rod. On the other hand, the carrier bodies on account of their network of fibrous materials can be divided without difficulty in order to enable an exact dosing of the treatment agent. WHAT WE CLAIM IS:

1. A treatment device for the introduction of a treatment agent into molten metal con slsting of a treatment agent, which vapourises at the temperature of the molten metal to be treated in the form of particles set in a carrier body comprising a refractory filler, a binder and a fibrous substance which forms a reinforcing reticular structure within the body and which makes the body sufficiently porous to enable release of the treatment agent from the body

2. A treatment device according to claim 1 wherein the carrier body comprises paper and/ or sawdust.