US2220384A - Metallurgical flux and method of producing it - Google Patents

Description

Patented Nov. 5,1940

UNITED STATES IPATENT OFFICE METAILURGICAL FLUX AND DIETHOD h PRODUCING IT e No Drawing. Application June 26, 1940,

Serial No. 342,448-

11 Claims.

This application is a continuation-impart of an application for U. S. Letters Patent filed by us March 4, 1940 under Serial No. 322,107, en- 'titled Metallurgical flux and method of producing it, and like it relates to the production of a synthetic fiux for use in metallurgical'processes requiring a fluorspar-bearing fiux having certain more or less specific physical and chemical characteristics, as in the production of steel in open hearth furnaces or the like.

Fluorspar fluxes are used in steel manufacture and other metallurgical operations principally to insure the desired fluidity in the slag and thereby assist in refining the bath of molten metal but v without changing the basicity or acidity of the slag, and it has been customary to employ for this purpose fluorspar which occurs in nature in limited quantities in certain parts of the United States, since not all natural fluorspar ores possess the degree of purity and physical characteristics requisite for the purpose. For attainment of the best results in commercial practice, a fluorspar fiux usually should contain not less than 85% calcium fluoride (CaFz) and not more than 5% silica (SiOz) and also, even when conforming to or excelling these chemical standards, must be available in quantity and preferably in a physical form such that thelargest pieces do not exceed in slzefa oneinch cube and the portion of the material which can be passed through a twenty-mesh screen does not exceed 25% by weight of the total, but of course it is preferable that the pieces be more uniform in size than is the case when consider- 5 able numbers of them approximate these maximum and minimum dimensions.

Much of the fluorspar used for fiuxing is derived from deposits of fluorspar ore in the southern Illinois-Kentucky district, the ore being commonly either in the form of loose to partly coherent coarse gravel associated with clay and lying near the surface or else in veins in association with. shale, limestone and silica and lying at greater depth but in either case the ore can be concentrated to the requisite degree of purity.

This concentration, however, is generally accomplished through log washing and/or jigging operations which are wasteful in that substantial losses occur in middling products and in the fine sizes so that it has been distinctly preferable,

when possible, to obtain the ore for the production of metallurgical fiux from a deposit in which it occurs naturally in a relatively pure state. As a result, but a limited number of the known fluorspar deposits have been practically available for flux production, as those in which the spar does not occur naturally in quantity with the requisite purity or with the essential physical characteristics are not satisfactory for the purpose. 5 To the end thatindustry may be freed from its present dependence for its requirements upon the limited output of those districts in which there occur natural deposits of fluorspar suitable I for use as metallurgical fluxes, it is a principal object of our invention to provide a synthetic metallurgical fiux of the required fluorspar content as well as physical form produced from fluorspar concentrates or other finely divided fluorspar-bearing materials. 15

A further object of the invention is the production of a metallurgical flux from such materials in which the particles are agglomerated in lumps or pellets having adequate physical strength and resistance to abrasion and impact,

which are readily susceptible of incorporation in the slag, and which are of sufficient mass individually to prevent their being carried out the stack of an open hearth furnace by the draft.

A still further object is to provide a novel 25 method of producing from finely divided fluorspar flotation concentrate or similar substantially pulverized fluorspar-bearing material a practical synthetic metallurgical fluorspar flux of such character, physical condition and chemical 3O purity that it may be satisfactorily employed in place of the best grade of the natural product.

As is well known by those familiar withthe art, relatively finely divided fluorspar such as that resulting from flotation concentration of fluorspar ores and commonly known as fluorspar concentrate, in which the particles are usually of the order of mesh, cannot be used as me tallurgical flux for the reason that the spar particles are blown out through the furnace stack 40 by the violent currents of air and gases in open hearth and other metallurgical furnaces before they can unite with or become incorporated in the slag layer floating on the bath of molten metal. To obviate this condition, it has been pro-posed to agglomerate spar concentrate with a tarry or other carbonaceous viscous binder and press the mixture in molds to form briquettes large enough to prevent their being blown out the stack when charged into the furnace. This expedient is unsatisfactory, however, for the reason that the intense heat of the furnace causes violent and rapid oxidation or combustion of the carbonaceous binder so that the briquettes virtually explode as soon as they are charged into it which is not only dangerous to the operatives but causes wide dissipation of the spar particles contained in the.

briquettes, so that a large proportion of them is lost in the stack gases just as when loose concentrates are used.

Portland cement"ha's also been suggested for use as a binder in themanufacture of fluorspar concentrate briquettes as it is cheap and noncombustible but such briquettes do not have adequate strength and hardness to withstand the abrasion to which they are subjected during handling and shipment unless so much cement is used that the fluorspar content is diluted to an excessive degree. Sodium silicate and similarly water soluble materials have also been utilized in briquettes but are so susceptible to the action of rain and atmospheric moisture that the briquettes cannot be economically stored and/or shipped and. such binders are therefore generally considered unsuitable for practical use in this connection.

These and other objections to the artificial fluorspar fluxes hitherto proposed are entirely obviated by our invention by means of which we are able to produce from fluorspar flotation concentrate or other finely divided fluorspar, a fluorsparcontaining material in which the fluorspar particles are held together in relatively hard lumps of suitable size which can be handled and shipped without becoming pulverized or otherwise disintegrating, which do not readily dissolve in atmospheric moisture or in other ways lose their normal physical and chemical characteristics, and which, when charged into the furnace, do not burn with undue rapidity or pass up the stack and thereby nullify in whole or in material part the desired effect of the fluorspar.-

As illustrative of the practice of our invention we shall initially refer to the production in accordance therewith of a fluorspar flux using as an ingredient fiuorspar flotation-concentrate consisting principally, if not entirely, of particles of the order of one hundred mesh and finer, this being the size of the particles of the fluorspar flotation concentrates of relatively high purity now being produced in certain parts of the United States, particularly in the Rosiclare district in Illinois. Such concentrate usually contains about 8% to 12% moisture whendelivered from the filter or comparable mechanism in the flotation circuit and in accordance with our invention may be used immediately in this condition without drying but it is preferable to ascertain fairly accurately the percentage of moisture it contains so as to afford a basis for its dry weight measurement which is the basis on which the several ingredients of the flux are compounded. Thus we mix with 100 parts of the fiuorspar concentrate by dry weight about three parts more or less of a resinous vegetable oil product, preferably one such as that generally known as tall oil or talloel, sometimes known as liquid rosin. The oily or resinous fluid'so designated is produced in commercial quantities in the United States and abroad as a by-product of manufacture of paper from pine wood and while analytical chemistry of the higher fatty acids is not yet sufficiently developed to permit unqualified statements concerning its exact composition, it is said to contain three classes of compounds, (a) rosin acids, (b) fatty acids and (c) non-acids such as sterols, higher alcohols and other unsaponiilable matter. This classification, however, is by some considered misleading as it may suggest to chemists conclusions not home out in practice and the material which we prefer to employ in carrying out our invention may therefore perhaps best be identified as that now being sold on the domestic market by the Industrial Chemical Sales Company of New York, Chicago and Cleveland under the trade name Liqro."

This substance is understood to contain about 45.8% rosin acids, 46.1% fatty acids and about 8.1% sterols etc., with but negligible moisture content of usually not more than a small fraction of 1% and ash residue on combustion as well as sulfur content likewise so-insigniflcant in quantity that they may be disregarded insofar as their effect upon the practice of our invention is concerned.

The fluorspar concentrate is thoroughly mixed with the Liqro or a comparable material in either a continuous or in a batch machine and the mixture sufficiently worked to form a plastic mass of substantially uniform consistency. This mass is then transferred to a machine adapted to form it into pellets which machine may comprise, essentially, a plate or die perforated with a plurality of holes, which may be circular, square or of any other desired shape, and preferably about in greatest transverse dimension, over one face of which heavy rollers are arranged to travel so as to force the plastic material through the holes as it is deposited on the plate and extrude it from its other face. A rotating blade cooperative with the latter may be provided to sever the material into pellets of suitable length, desirably some to as it is extruded through the holes by the pressure exerted by the rollers, or the extruded material may be allowed to simply break off by its own weight and thus form longer pieces usually some 3" in length which in the subsequent drying and handling tend to break up into shorter pieces. The pellets in either case are of sufiicient strength to at least temporarily .retain their shape.

The pellets are next dried to remove moisture carried into the mixture through the use of damp concentrate or otherwise, and after the drying the pellets are relatively hard and solid, substantially waterproof, and of sufficient strength and density for use for any purpose for which the best grades of natural fluorspar flux are adapted.

The drying may be performed in any convend ient way and at any temperature though it is preferable the latter be insumcient to partially oxidize the Liqro in the composition. Thus the pellets may be dried at atmospheric temperature, say 70 F., by merely exposing them to the air, as on a drying table, or they may be dried in suitable furnaces or the like with equally good results at temperatures running up to around 400 F. and of course in a much shorter time.

As exemplifying various temperature-time relations we have used for drying the pellets, we have found they may be satisfactorily dried at 70 F. in a period of 70 hours; at 180 F. in a period of two hours; at 276 F. in a period of one-half hour, their attainment of constant weight after exposure to these various temperatures for the approximate times stated demonproduction the longer times required for drying the pellets at the lower temperatures are not desirable from the standpoints of economy and efliciency, and we therefore prefer to dry them in such a way as to shorten the drying time to a half hour or thereabouts. This can be readily efiected by discharging the moist pellets from the pelleting machine onto a moving belt arranged to convey them into a suitable oven where they are heated for the requisite period, for example, about one-half hour at an oven temperature of 276 F. or thereabouts; while a higher temperature and shorter time might of course be employed, we prefer approximately the temperaturetime relation stated, as it is insufiicient to effectthe undesirable oxidation of the "Liqro to which we have referred although it may perhaps, similarly to drying at any temperature, result in volatilization of some of its lighter constituents. After removal from the furnace and cooling, the pellets are in condition for use without further treatment.

The Liqro remaining in the flux, being composed substantially exclusively of organic materials decomposes completely and passes out the stack when the flux pellets are subjected to the heat of a metallurgical furnace and it' therefore has no appreciable metallurgical eifect whatever upon the slag into which the flux is introduced or upon the metal bath itself. The spar concentrate thus constitutes the only ingredient of our flux which produces any noticeable metallurgi cal results in the furnace and its use therefore does not require compensation for other metallurgically active components. One of these is of course sulfur, and we have suggested that Liqro, and hence our flux, may contain some of it but not more than a small fraction of 1% of this element is likely or should be permitted to be present in Liqro, and as the Liqro constitutes only about 3% ofthe weight of the flux pellets, and some sulfur may be lost in the drying operation, the sulfur content of the finished flux obviously cannot under ordinary conditions amount to more than a very few hundredths of 1% and is usually even less. Since metallurgical processes commonly require only a few pounds of flux per ton of charged metal it is evident that the quantity of sulfur which could get into the metal from losses of it almost certain to occur through combustion or by inclusion in the slag.

While we have herein described with considerable particularity a preferred method of making our novel flux, we do not thereby desire or intend to restrict or confine ourselves specifically thereto as changes and modifications in the practice of the invention as well as in the materials utilized will readily occur to those skilled in the art and may be made if desired without departing from the spirit and scope of the invention as defined in the appended claims. c Having thus described our invention, we claim and desire to protect by'Letters Patent of the United States:

1. A=metallurgical flux composed of separate, relatively hard, water-resistant pellets each coinprising finely dlvided fiuorspar-agglomerated with this source is infinitesimal, even disregarding heating the the residue-resulting from drying a mixture of the fluorspar and tall oil.

2. A metallurgical fiux composed of separate, relatively hard, water resistant pellets each comprising the dehydration residue of a mixture of finely divided fluorspar and tall oil.

3. A metallurgical fiux composed of individual pellets, each comprising a dried mixture of finely divided fluorspar and tall oil.

- 4. A metallurgical flux composed of individual pellets, each comprising a dried mixture of fluorspar concentrate and tall oil in dry weight proportion of about 100 parts of the concentrate and about 3 parts of the oil.

5. The method of making a synthetic fluorspar flux which comprises mixing finely divided fluorspar with tall oil, forming the mixture into pel-' lets, and drying the pellets to thereby solidify and harden them.

6. The method of making a synthetic fluorspar flux which comprises mixing finely divided fluorspar with tall oil in dry weight proportions of about 3 parts of the oil to 100 parts of the fluorspar, forming the mixture into pellets, and drying the pellets to thereby solidify and harden them.

7. The method of making a synthetic fluorspar fluxv which comprises mixing fluorspar concentrate with tall oil in dry weight proportions of about 3 parts of the oil to 100 parts of the concentrate'to form a plastic mass, progressively forming the massinto individual pellets, dehydrating the pellets at a temperature insufiicient to aplets adapted for charging into a metallurgical furnace.

9. A metallurgical fiux in the form of individual pellets each comprising a plurality of particles of fluorspar flotation concentrate and, binding the particles .to each other, the residue remaining after heating tall oil to approximately 200 F. to 400 F. in contact with the particles.

10. The method of making a synthetic fluorspar flux which comprises mixing fluorspar concentrate with tall oil in dry weight proportions of about 3 parts of the oil to 100 parts of fluorspar, forming the plastic mixture into pellets, and pellets'to approximately 200 F. to 400 F. to thereby solidify-and harden them.

11. The method of making a synthetic fluorspar flux which comprises mixing fluorspar particles with tall oil in dry weight proportions of about 3 parts of the oil to 100 parts of fluorspar to form a plastic mass, progressively reducing the mass to rod-like form, severing the rods to create pellets, heating the pellets to a temperature below about 400 F. to thereby substantially dehydrate them and extract volatile constituents,

and finally cooling the pellets to set and harden them.

FREDERICK C. ABBO'I'I'. CARL O.- ANDERSON.