US2220385A - Metallurgical flux and method of producing it - Google Patents

Description

Patented Nov. 5, 1940 UNITED' STATES PATENT OFFICE METAILURGICAL FLUX AND METHOD or rnonocmc rr No Drawing Application March 4,1940, Serial No. 322,108

7 Claims.

This invention relates to the production of a synthetic flux for use in metallurgical processes in substantially any circumstances requiring a fiuorspar-bearing flux 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 steellmanufacture and other metallurgical operations principally to insure the desired fluidity in the slag and thereby assist in refining the bath of molten metal but without changing the basicity or acidity of the slag, and it has been customary to employ for this purpose fiuorspar which occurs in nature in limited quantities in certain parts of the United States, since not all natural fiuorspar ores possess the degree of purity and physical characteristics requisite for the purpose.

For attainment of the best results in commercial practice, a fiuorspar flux 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 the larg-. est pieces do not exceed in size a one-inch 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; of course it is usually preferable that the pieces be more uniform in size than is the case when considerable numbers of them approximate these maximum and minimum dimensions.

Much of the fiuorspar used for fluxing is derived from deposits of fiuorspar ore in the southern Illinois-Kentucky district, the ore being usually 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 readily 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 usually been distinctly preferable, when possible, to obtain the ore for the production of metallurgical flux from a deposit in which it occursnaturally in a relatively pure state.

Asa result, but a limited number of the known fiuorspar deposits have been practically workable 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 substantially valueless for the purpose.

To the end that industry may be freed from its present dependence for its requirements upon the limited output of those districts in which there occur natural deposits of fiuorspar suitable for use as metallurgical fluxes, it is a principal object of the invention to provide a synthetic metallurgical flux of the required fiuorspar content as well as physical form produced from fiuorspar concentrate or other fiuorspar-bearing materials which because of their finely divided condition cannot be used as metallurgical fluxes.

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

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

As is well known by those familiar with the art, relatively finely divided fiuorspar such as that resulting from flotation concentration of fiuorspar ores and commonly known as fluorspar concentrate, in which the particles are usually of the order of 100 mesh, cannot be used as metallurgical flux for the reason that the spar particles are blown out through the furnace stack by the violent currents of airand 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 proposed to agglomerate spar concentrate with a tarry or other carbonaceous viscous binder and press the mixture in molds to form bri. quettes large enough to prevent their being blown out of the stack when charged into the furnace. This expedient is unsatisfactory, however, for the reason that the intense heat of the 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 while much of the remainder is quickly destroyed by chemical reaction without contributing materially to the quality of the product of the furnace or producing any other beneficial result. 1

Portland cement has also been suggested for use as a binder in the manufacture of fiuorspar concentrate briquettes as it is cheap and noncombustible but suchbriquettes 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 fiuorspar content isdiluted 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 fiuorspar fluxes hitherto proposed are entirely obviated by our invention by means of which we are able to produce from fiuorspar flotation concentrate or other finedly divided fiuorspar a fiuorspar-containing material in which the fluorspar particles are held together in fairly porous 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 fiuorspar.

As illustrative of the practice of our invention we shall initially refer to the production in accordance therewith of a fiuorspar 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 fiuorspar flotation concentrates of relatively high purity now being produced in certain parts of the United States, particularly in the Rosiclare district in Illinois. tain about 8% to 12% moisture when delivered from the filter or comparable mechanism in the flotation circuit and in accordance with our invention may be used immediately in this condition without further drying. If the damp material is to be utilized as an ingredient of the flux however, it is preferable to ascertain fairly accurately the percentage of moisture it contains if it is not to be further. dried 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. That is, with 100 parts by dry weight of the fiuorspar concentrate regardless of whether it is actually in a damp or a dry state, about 3 parts dry weight of a binder 'material hereafter more fully described and about one part dry weight of bentonite clay are thoroughly mixed in a wet mass in any suitable machine.

In accordance with the invention the binder material we preferably utilize consists of that by-product of the sodium sulphite process of paper making which is generally known as sul- Such concentrates usually conphit e liquor. This material is available in various'forms, one, for example, containing approximately 50% solids in water while another produced by substantially complete dehydration of the liquor is in powdered form; since the principal difference between these forms is in their water content, they may be used interchangeably and the amount of water supplied to the mixture adjusted accordingly. That is, the binder material is mixed with the fiuorspar concentrate and bentonite clay in such way as to produce a plastic mass neither so short that it crumbles or so wet as to be runny, its consistency being determined by the amount of water present. Consequently, it will be understood that when the liquor containing approximately 50% water is used and particularly when the spar concentrate is taken directly from the flotation circuit filter and therefore already contains an appreciable amount of water, considerablyless water will have to be added to the mixture in the mixing machine to insure production of a plastic mass of proper consistency.

Sulphite liquor, or the flour obtained by dehydration of this material, is believed to contain products of the reaction of sulfurous acid with the unsaturated carbon atoms of lignin in the wood from which paper pulp is made by the sulphite process, the ligno-sulphonic acids initially produced by this reaction probably subsequently reacting with other substances so as to be represented in the liquor or flour predominantly as calcium salts of these acids rather than as the free acids themselves; at least, these salts appear to be the most active ingredients of the sulphite- Total gf gggg Glutrin Goulac Solids 95. a9 49. 20 51. 46 91. so 11 9. 62 4. 5. 44 10. 44 4.93 2. 05 2.56 4.79

It will be observed from this table that Bin-j derene Flour and Goulacff containing substantially total solids as against 50% total solids in Binderene Liquid" and Glutrin, also contain about double the quantities of ash, CaO

and MgO respectively, beating out the suggestion that these dry materials are substantially the respective liquids reduced to dryness and ex-.

cepting for differences in water content are chemically substantially, equivalent. It is consequently a matter' of choice which of these or generally comparable binder materials is employed, while the bentonite clay which we use may also be considered as but a convenient material for promoting the handling of the plastic mass and particularly the production therefrom of the pellets which constitute our flux as the bentonite clay makes no material contribution to the chemical composition of the finished flux Typical analyses of I these materials are as follows:

from the standpoint of its effectiveness as such.

Thorough mixing of the several ingredients, however, with the addition of water if required, produces a plastic mass of substantially uniform consistency and composition and when it is in this state, the mass is introduced, either continuously or in successive batches, into a machine adapted to form it into pellets and which may preferably 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 /2" 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 011? 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 sufficient length to retain their shape until they are subjected to the succeeding drying operation.

The moist pellets are discharged from the pelleting machine preferably directly onto a moving belt arranged to convey them into a drying and curing oven where they are heated, to about ZOO-400 F., the exact temperature depending on the speed at which they are heated and the time alotted thereto. This treatment removes most of the retained excess moisture and substantially dries the pellets, causing them to become quite hard and more or less resistant to atmospheric moisture while they possess adequate structural strength to enable them to resist being broken or crushed during handling or shipment. As they are not entirely inert to the action of water, it is preferable that the pellets be kept out of the rain and therefore shipped in closed cars but they are not harmed by dampness or even wetting if dry at the time of being handled. Thus even when they have been exposed to the action of water, they can be readily restored by a simple drying operation to their normal condition and thus ready for use as a flux.

The pellets are consequently of suitable size and cohesiveness to be conveniently handled and charged into an open-hearth or other metallurgical furnace and their mass is sufiicient to prevent their being blown out the stack by the furnace draft before becoming incorporated in the slag.

, As the organic constituents of the material used latter to become incorporated in the slag, and thereafter its presence is not required for metallurgical or any other reasons.

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.

Having thus described our invention, we claim and desire to protect by Letters Patent ofthe United States:

1. A metallurgical flux consisting of pellets of approximately uniform'size and substantially devoid of uncombined water, each pellet comprising particles of fluorspar agglomerated with sulphite liquor dehydration residue and bentonite clay.

2. A .metallurgical flux consisting of pellets of approximately uniform size and substantially devoid of uncombined water, each pellet comprising particles of fluorspar and bentonite clay maintained in a cohesive solid mas by sulphite liquor dehydration residue.

3. A metallurgical flux consisting of pellets of approximately uniform size and substantially devoid of uncombined water, each pellet comprising particles of fluorspar flotation concentrate about 96% by dry weight, sulphite liquor dehydration residue about 3% by dry weight, and bentonite clay about 1% by dry weight.

4. The method of producing calcium-fluoridecontaining metallurgical flux which comprises mixing fluorspar flotation concentrate with sulphite liquor-residue'and and bentonite clay in the presence of water, forming the wet mixture into pellets, then drying the pellets to substantially dehydrate and harden them. a

5. The method of producing calcium-fluoridecontaining metallurgical flux which comprises mixing fluorspar flotation concentrate with bentonite clay and a sulphite liquor containing approximately 50% total solids, then pelleting the mixture and drying the pellets.

6. The method of producing calcium-fluoridecontaining metallurgical flux which comprises mixing fluorspar flotation concentrate with bentonite clay and a substantially dehydrated residue of sulphite liquor in the presence of water to form a plastic mass, then pelleting the mass and drying the pellets.

- 7. The method of producing calcium-fluoridecontaining metallurgical flux which comprises mixing fluorspar flotation concentrate with sulphite liquor residue containing at least about 50% total solids and bentonite clay in the presence of water to form a plastic mass, pelleting the mass and then heating the pellets to approximately 200 to 400 F. to thereby substantially dehydrate and harden them.

FREDERICK C. ABBOTT.

CARL 0. ANDERSON.