DE2437410A1 - Abrasion resistant magnesium contg. briquettes - used for introducing magnesium into a metal bath - Google Patents

Abstract

Briquettes comprise 10-90 wt. %, (pref. 30-70 wt. %) matrix of calcined dolomite particles and 10-90 wt. %, (pref. 30-70 wt. %) Mg and, opt. alloying elements such as Cr, Mn, Si, C, Ca or rare earth metals. Mg is present in finely dispersed form obtd by thermal diffusion. The briquettes are added to liq. iron from a shaft furnace or to liq. pig iron using a bell. They are used for desulphurisation of Fe or ferronickel, and the prodn of spheroidal graphite cast iron.

Description

ABRASION RESISTANT BRIQUETTES The invention relates to non-breakable, novel Briquettes containing magnesium, a method for their production and a method for desulfurization of molten fan shaft furnace iron for the production of ductile Iron or for desulfurizing other molten metals.

Magnesium additives to molten iron as a means of desulfurization, Deoxidizing and spheroidizing are well known and have been numerous Methods for carrying out these additions were developed. As is well known, poses Magnesium is a light reactive metal that at temperatures considerably below boils at the temperature of a molten iron bath.

There are therefore considerable difficulties in introducing it of magnesium below the surface of the molten metal and it is required by injecting finely divided magnesium or a magnesium alloy into a stream of inert gas to remedy the situation, or magnesium or a magnesium alloy in specially designed S made of graphite or refractory materials Immerse diving bells. These known methods have disadvantages fraught with difficulties in terms of safety factors, high Capital expenditures, extremely heavy smoke generation, little recovery of the metal and high material costs. In general, it has been found that diving bells provide the best solution to this problem, and they are therefore generally applied. However, several difficulties remain. First there must be the release of magnesium vapor are precisely controlled and carefully depending on the Training of the bell can be regulated, otherwise it is under the bell can develop dangerously high vapor pressure, which makes it difficult to control of the procedure and possible threats to safety. aside from that the magnesium or magnesium alloy present in the bell must be complete used to leave a clean bell that can then be reused without the need for excessive cleaning or plastering.

The invention is therefore based on the object of providing an additional safe and less expensive way of supplying magnesium accessible to make, in which magnesium is added in a form that is suitable for direct Introducing a diving bell for metal melting and which is clean without Leaving behind annoying adhesive residues or slag dissolves.

The term "molten metals" used here is primarily intended to but not limited to molten fan shaft furnace iron or pig iron relate. Under certain circumstances it may be possible to use other ferrous metals such as steel, or non-ferrous metals such as ferronickel.

According to the invention, this object is achieved by abrasion-resistant briquettes, consisting essentially of 10 to 90% by weight of a matrix from calcined Dolomite particles and 90 to 10 wt .-% magnesium and optionally alloy elements contain the chromium, manganese, silicon, carbon, calcium and / or rare earth metals could be.

According to the present invention, it was found that it achieved an excellent effect can be when 10 to 90 wt .-% of magnesium powder or magnesium grains with a Diameters of about 3.18 mm to 1.09 mm (1/8 to 1/16 inch) in one relative hard abrasion-resistant or non-fragile briquette are dispersed, the calcined Contains dolomite or limestone as a carrier and / or modifier for the magnesium.

It has been found that calcined dolomite or, in certain less preferred cases, calcined limestone with finely divided magnesium can be briquetted in almost all proportions, so that stable briquettes can be formed without the use of any external binder. In general the briquettes contain 10 to 90% by weight CaOMgO and the remaining portion Iiagnesium. However, the magnesium content of the briquettes is preferably between 30 and 70% by weight. and, more preferably, between 50 and 60 weight percent. The so educated Briquettes are hard and sufficiently wear-resistant to withstand normal handling and handling Resist transportation without further treatment, provided that care is taken is worn that the briquettes are stored in a moisture-free atmosphere will. This is usually done by enclosing the briquettes tightly once They are made in airtight steel drums that hold 45.36 to 68.04 kg (100 to 150 lbs) of the briquettes. The steel drums can be poured directly into a conventional diving bell made of ceramic or graphite can be used.

If the briquettes contain less than 30% by weight magnesium, there is the tendency to have a sluggish response, a slight one Exploitation the magnesium and to stick the partially melted material in the holes and around the holes of the diving bell. In addition, in order to achieve a fixed Magnesium dosage an excessively high amount by weight of the briquettes may be added. If the briquettes contain more than 70% magnesium, the reaction tends to to get too violent and there will be special precautions and a special one Formation of the bell necessary, as there is generally an insufficient amount of dolomite is present to moderate the release of magnesium from the briquettes or rules. In the preferred proportion by weight of 50 to 60% by weight, magnesium is found the release of magnesium takes place sufficiently rapidly to allow good mixing and To ensure turbulence in the molten metal without disruptive splashing takes place and it is also guaranteed that the entire residue is clean melts so that contamination of the diving bell is avoided.

The size of the briquettes and the particle size of the magnesium and dolomite or lime is not critical and can vary within wide limits. It is However, take into account that large briquettes, on the order of four inches x 10.16 cm x 7.62 cm, take a much longer time to be consumed, as small briquettes, especially for low magnesium concentrations.

For this reason, it is preferred to use briquettes about 7.62 in size 3 "x 1" x 3/4 "(3" x 1 "x 3/4") to make a clean to ensure rapid consumption.

The invention will be explained in more detail below with reference to the following examples made clear.

Example 1 Calcined dolomite of high purity was made up to one smaller particle size than corresponding to a Tyler sieve with 10 meshes (mesh size 1.651 mm) crushed so that the particles following Sieve analysis showed: mesh mesh weight width, mm number 0.417 + 35 8.8 0.295 + 48 7.6 0.208 + 65 12.2 0.147 + 100 18.2 0.074 + 200 25.0 0.074 - 200 28.3 Magnesium was mechanically comminuted and resulted in the following values in the sieve analysis: Mesh - mesh - Weight width, mm number 5 '1.651 + 10 1.8 1.168 + 14 24.6 0.833 + 20 34.8 0.589 + 28 20.2 0.417 + 35 10.0 0.417 - 35 8.8 The crushed magnesium and the crushed Dolomite was mixed in a ratio of magnesium to dolomite of 60:40 and at a rate of 544.31 kg / h of the mixture on a Komarek-Greaves ™ roller briquetting press fed, which had 22.86 cm wide rollers with a diameter of 52.07 cm. The rollers were provided with 3 rows of recesses, so that briquettes of one size 7.62 cm x 2.54 cm x 1.905 cm. It wasn't a binder necessary, to make strong, non-fragile briquettes that would not break even when they have been dropped from a height of up to approximately 183 cm. They were instantly at 45.36 kg steel barrels packed and tightly welded.

Example 2 45.36 kg of the briquettes (6056 mg) made in Example 1 were placed in a ceramic diving bell and in 138 tons of hot-blower shaft furnace metal submerged that was contained in a torpedo ladle. The sulfur content of the Metal was determined before and after treatment: S before treatment 0.026% S after adding 0.181 kg Mg / ton 0.019 5 '.

Example 3 136.08 kg of the briquettes produced in Example 1 (60% Mg) were immersed in 3 consecutive amounts of 45.36 kg each in 160 tons Hot-blower shaft furnace metal immersed, as in Example 2, in a torpedo ladle -Template. The sulfur content of the metal before and after the treatment was determined: S before treatment 0.040% S after immersion of 0.499 kg Mg / ton 0.0105 '.

From Examples 2 and 3 it can be seen that even 0.181 kg of magnesium caused a considerable reduction in the sulfur content per ton and that at With a value of 0.499 kg Mg / ton, a high degree of sulfur removal is achieved became.

When firmer briquettes are required for special purposes, was stated that these can be made using those described above Briquettes are subjected to a heat treatment before use. When the briquettes to a temperature above the melting point of magnesium, i.e. on one Temperature in the range of 650 to 900 ° C, in an inert atmosphere such as argon, at one positive pressure; qfon heat about 0.211 kg cm2 (3 psi) for a sufficient period of time to distribute the metallic magnesium throughout the matrix high-strength briquettes are produced. The atmosphere is because of the presence of Strongly reducing magnesium, since the vapor pressure of magnesium is between 6000C and 10000C increases from 0.001 to more than 0.4 atmospheres to prevent magnesium losses To avoid the briquetted mixture, an open container can be provided 9 which contains additional free magnesium. When the briquettes are over 9000C When heated, they appeared to become brittle on contact with air, and when they were heated to a temperature below 6500C did not become essential Increases in their strength compared to that of the untreated briquettes were observed. Between 650 and 900 ° C the magnesium seems to melt and through the whole Diffuse CaO-MgO matrix. Heating to any temperature between 6500C and 9000C led to the diffusion of magnesium through the CaO "MgO matrix9 see above that at a ratio of 15% magnesium and 85% CaOMgO (and at a temperature of more than 8500C) the cross section had the appearance of a single phase while two phases occurred at quantitative ratios above and below this optimum value - none of which resembled any of the original ingredients.

Example 4 13.61 kg of magnesium were mechanically crushed into particles, whose largest diameter was about 1909 mm, and one with 31.5 kg CaOMgO Particle size corresponding to a Tyler sieve with 200 mesh (mesh size 0.074 mm) mixed0 The mixture was a single punch press with a capacity of 20 Tons fed in the briquettes with a diameter of 2.54 cm and a length 1.905 cm.

The briquettes obtained were placed in a heated muffle furnace brought, in which a positive argon pressure of + 0.211 kg / cm² was maintained, to prevent the entry of air and in what some pure magnesium in one open container was arranged. The charge was heated to 850 ° C. for 5 hours. The resulting briquettes were resistant to handling damage and against breaking when dropping Individual particles of CaOMgO could on cut or broken surfaces are observed, but there was one metallic bond through the entire briquette.

Example 5 22.68 kg of magnesium were mixed with 22.68 kg of CaOMgO and processed in the same manner as in Example 4, with satisfactory briquettes with a correspondingly higher magnesium content.

The briquettes produced in Examples 4 and 5 were used for desulfurization Used of iron containing 3.9, carbon and 0.064% sulfur. Desulfurization was carried out in a treatment pan with a capacity of 226.80 kg, which was equipped with a weighted pan lid through its center a rod was guided, on whose e a graphite diving bell was provided, which perforated warr to allow magnesium vapor to escape. The whole arrangement was designed so that the diving bell dipped into the molten iron when the lid was on the edge of the pan. The iron was drawn off at 15250C and transferred to the treatment pan, in which the temperature during an experiment Was 1360 ° C. A sufficient amount of the briquettes was placed in the diving bell. so that it contained a total of 0.113 kg of magnesium and became the diving bell for a period of one minute during which the temperature dropped to 1310 ° C, dipped in the iron. In a second Attempt reached the Pan temperature 14300C and was after the treatment at 1285 ° C for 2 1/2 minutes please.

The sulfur removal was 0.034%. The reaction was calm and the briquettes left after the treatment remained intact and floated on the surface of the melt.

Example 7 A mixture of 50 parts of CaOMgO and 50 parts of magnesium was briquetted in a roller press, -which notches for the formation of almond-shaped Pellets 2.54 cm long and about 1.59 to 1.9 cm thick. These pellets were used to treat iron in the same manner as in Example 3 used. This was 0.054 56 sulfur-containing metal withdrawn at 15800C had been treated at 14700C, the temperature rising for 2 1/2 minutes 13500C fell. The final sulfur content was 0.025 5 'which is a decrease vDn more than 50%.

From the above examples it can be seen that the particle size of magnesium and CaOMgO is not critical, but that it is preferable To use particles of a size which mix without separation and which can be produced in an economical manner. Preferably. should therefore the magnesium has a particle size between 100 mesh (Tyler sieve) and -1/8 inch (between 0.147 mm and -3.18 mm) and the calcined CaOMgO a size between -200 meshes (Tyler sieve) and - 3/16 inch (between -0.074 mm and - 4.76 mm).

It must be taken into account that the composition of the briquettes changes can be to achieve a more rapid evolution of magnesium vapor and how has been previously carried out, solid briquettes can be made up to about Contains 90% magnesium. Since the insulating effect or regulating effect of the CaOMgO great is enough to put in the molten iron whose temperature is well above the boiling point of magnesium is to ensure a quiet development of magnesium vapor, the reactivity can be increased by increasing the proportion of magnesium or by part of the CaOMgO by a neutral substance with higher thermal conductivity, like iron, or by varying the size of the briquettes.

It must also be taken into account that the binding effect of CaOMgO-Mg is so strong that other alloying additives, such as chromium, manganese, silicon or carbon in the form of crushed iron alloys or powdered coke or graphite can be added to the briquette mixture in the mixing stage, while still being sufficient solid briquettes are formed, which are used for the simultaneous alloying and removal of the Sulfur can be used without contamination from other binders entry. Also other additives with a strongly reducing character, such as metallic Calcium, or rare earth metals, can be added.

Claims (14)

Claims 1. Abrasion-resistant briquettes, consisting essentially of 10 to 90 wt. 5 ' a matrix of calcined dolomite particles and 10 to 90% by weight magnesium and optionally alloy elements, the chromium, manganese, silicon, carbon, calcium or rare earth metals. 2. Briquettes according to claim 1, d a d u r c h g e k e n n -z e i c h not that they contain 30 to 70 56 magnesium and 30 to 70 5 'calcined dolomite. 3. Briquettes according to claim 1 or 2, d a d u r c h g e -k e n n z e i c h n e t that the magnesium in a by thermal diffusion in the matrix distributed form. 4. Process for the production of abrasion-resistant briquettes according to a of claims 1 to 3, in which finely divided magnesium, calcined dolomite carbonate and optionally alloying elements mixed with one another and with the formation of green briquettes are briquetted, that the green briquettes in an inert atmosphere at a temperature range between ohms 6509C and 9500C are heated for a time that allows diffusion of the magnesium through the entire briquette is sufficient. Se method according to claim 4, d u r c h g e n n -z e i c h n e t that one can finely divided magnesium with a particle size between 0.147 mm mesh size and -3.18 mm (100 nose Tyler sieve and -1/8 inch) and calcined dolomite particles a size between 0.074 mm and -4.76 mm (200 mesh Tyler sieve and -3/16 inch) used. 60 The method according to claim 4 or 5, d a d u r c h g e -k e n n z e i n e t that one can heat treat the green briquettes up to about 5 hours performs. 7. The method according to any one of claims 4, 5 or 6, d a -d u r e h it is not noted that the inert atmosphere is a noble gas, preferably Argon, is used. 8. The method according to claim 7, d a d u r c h g e k e n n -z e i c h n e t that one maintains an argon pressure of 0.211 kg / cm2. 9. The method according to any one of claims 4 to 8, d a d u r c h g e k It is noted that during the thermal treatment by providing of additional free magnesium maintains a reducing atmosphere. 10. Method of treating molten metal by addition from magnesium to the molten metal, d u r c h g e k e n n z e i c h n e t that the magnesium is in the form of briquettes according to one of the claims 1 to 3 used. 11. The method according to claim 10, d a d u r c h g e k e n n -z e i c This does not mean that the molten metal is subjected to a desulfurization treatment. 12. The method according to claim II, d a d u r c h g e k e n n z e i c It does not mean that the desulphurisation of molten iron or ferronickel is carried out. 13. The method according to claim 10, d a d u r c h -g e k e n n -z e i n e t that the spheroid formation of GaBeisen is carried out. 14. The method according to any one of claims 10 to 13, d a d u r c h g It is not shown that the briquettes are placed in a dipping bell in the molten metal immersed.