US2041612A - Metallurgical furnace - Google Patents

Description

May 19, 1556.

R. L. LEVENTRY METALLURGI-CAL FURNACE 2 Sheets-Sheei 1 Filed June 3, 1933 Zimaentor Boy L ZEyE-Nr/E'X 'Gttorneg Patented May 19, 1936 2,041,612 METALLURGICAL. FURNACE Roy L. Leventry, Youngstown, Ohio, assignor to TheRepublic Steel Corporation, Youngstown, Ohio, a corporation of New Jersey 1 Application June 3, 1933, Serial No. 674,250

- 4 Claims. (01. 266-43) This invention relates to improvements in metallurgical furnaces and more particlarly metallurgical furnaces of the open-hearth type.

The general nature and operation of openhearth steelfurnaoes are well understood in the art. The most widely used furnace of this character is the one which is known as the basic open-hearth furnace. In these furnaces the charge i. e. the metal in process of treatment, is subjected to the action of radiated heat, the flame necessary for this purpose being produced by the combustion of streams of combustible gas and air. It is customary in such furnaces to have them provided with a chimney draft suflicient to catch the flame about in the middle of the laboratory and drag it out through the ports on the opposite side from which it entered without allowing it either to drop down and. touchthe bath or to impinge upon the roof, and the draft l or has also to do thework of overcoming the friction of the outgoing regenerators and fines, such regenerators and fines being provided as a means for assuring that the entering air and combustion gases, when subsequently allowed to flow through such regenerators and fines, on entering the laboratory, will have the requisite temperature. It is obvious that under the stated requirements the draft through such a furnace during its operation is very considerable. The gas and air are given a velocity which causes them to enter the. furnace with some force and the construction of the ports directs the streams in the desired manner. In passing through the labora-v tory the gas should be spread out all over the width of the hearth beneath the air as the latter must be kept away from direct contact with the bath. The products of combustion of the flame together with any materials which may have been picked up in passing through the furnace are drawn along the furnace walls and into the exit flues with considerable power. It is well known that during the operation of the furnace particles of slag, dust, and dirt are carried over 45 with the outgoing gases and because of this the so-called slag pockets or dirt pockets are ordinarily provided as a part of the structure of such furnaces. In spite of the presence of such slag pockets, however, the space between the bricks 50 of the checker-work of the regenerators becomes partially choked, and for this reason, as well as because the deposit of the slag, dust, and dirt particles makes the surface of the bricks rough,

the total area between the bricks must be much to larger than the area of the ports, so that the open-hearth furnaces was discarded and disvelocity of the gas will not be lessened. These conditions indicate that there is a very considerable amount of foreign material picked up and carried along by the high velocity of the gasstreams passing through the laboratory. 5 In the construction of open- -hearth furnaces ithas been customary to use magnesite as a lining for the bottom of the furnace as it is well re- I sistant to basic slag which contains iron oxide, silica dioxide and lime but the topmost layer .or working bottom and the repairs put in during the intervals of the furnace life, are usually made of dolomite. The sides and roof of the furnace are generally made of silica bricks.

Magnesite is the most expensiveof the several 15 materials made use of in the construction of an open-hearth furnace and a cheaper equally good substitute material has long been sought for. Substances such as chromite and dolomite have been tried but have not been found the equal of burnt magnesite although dolomite has proved itself to be a very desirable material for use as a patching substance 'in filling up the holes made in the magnesite during the operation of the furnace; Several years ago a suggestion was made to the eflect that olivine rock, inasmuch as it possessed properties enabling large pieces or blocks of the rock to be heated to very high temperatures while retaining its mechanical strength at high temperatures, might be available in the construction of metallurgical furnaces to replace magnesite. Experiments were made with olivine but they proved to be failures with the result that the use of olivine as a lining material for credited.

I have now discovered that the, cause for the failure of olivine in metallurgical furnaces is to be found chiefly in its incapacity to resist the ef- 40 feet of the action of lime. In the presence of lime such as exists in the molten metal bath as the result'of the addition of dolomite patching material olivine disintegrates. This disintegrating effect is most active in those regions where most lime exists, 1. e. at or near the immediate vicinity of the slag line. Accordingly, inasmuch as the slag is itself in contact with the lining of the bottom of the furnace and is also subjected at its surface to the vigorous sweeping action of the gas currents passing through the furnace and in v more highly refractory. Thus, although olivine does not resist the basic slag in the bath, it does well resist the effect of iron oxide and silica dioxide while such lime or lime-bearing substances 7 as may be physically carried into contact with olivine by a flame of such fierce velocity and constitution as passes through a basic open-hearth furnace seems to be ineffective on the olivine.

Based on these foregoing discoveries, it occurred to me that beneficial effects might result if, instead of attempting to use olivine as a material to replace the magnesite lining of the bottom of the furnace, it were used at least partially to replace or to form a surfacing layer for the silica bricks used for the sides of the open-hearth furnace. Iron oxide is very active on silica brick and tends to slag it, while, as above stated, olivine resists the action of iron oxide. Even the most refractory silica bricks can be melted by the intenseheat of the direct impact of the flame. The silica brick walls constituting the side walls of an open-hearth furnace are usually thin, which results in great radiation of heat from the furnace chamber but as one authority puts it This has to be endured, as thicker walls produce endless trouble by expansion and contraction.

Based on the foregoing considerations and in order to put my discovery to practical use I designed a 'basic open-hearth furnace in which, although the bottom was lined as usual with magnesite, patchable and repairable at will by the introduction of dolomite, the end walls, at least at those parts thereof which are affected by the impingement of the .gas flow, and those portions of the front and rear walls of the furnace which were above the slag line and within the region affected by the flame and the gas draft were constituted of olivine. Furnaces of this design wereput into practice and use and found to constitute a material improvement over furnaces of like nature constructed in accordance with the fundamentals of practice theretofore followed. The. term olivine applies to a mineral of varying degrees of constitution, not every one of which can be satisfactorily employed forthe purposes under consideration.

I have however found that certain grades of olivine, which occur in extensive. deposits in the United. States and which are therefore relatively cheap and readily obtainable, may be used satisfactorily for lining parts of metallurgical furnaces and will satisfy the requirements.

Olivine is an anhydrous silicate of magnesium. and iron. Altho the composition varies somewhat, a formula which may be considered more or less typical is (MgFe) 2Si04. An average theoretical composition of olivine may include about 48% of MgO, 42% of S102 and 10% of iron calculated as FeO. The iron content ranges from a low amount such as 2% or 3% to as high as about 20% in different forms of olivine.

Olivine containing between about 4% and about 15% of iron, calculated as FeO, may be used satisfactorily as a lining material for metallurgical furnaces when arranged as hereinabove set forth. Another way of describing the com position-of olivine within the preferred range, is

on the basis of the ratio of magnesium to iron. This ratio varies in different types of olivine from as low as 2 to 1 to as high as 16 to 1. I prefer a ratio of not less than 3 to 1 and not more than about 8 to 1, and more especially prefer a ratio of between 5 to 1 and 8 to 1. As a result of extended tests and experiments in actual use, I have found that olivine within the foregoing composition range and conditions of use above specified has been entirely satisfactory and is favorably comparable with the more expensive and high grade furnace lining materials, such as chrome ore.

A preferred olivine for the foregoing uses contains between about 7% and about 10% of iron, calculated as FeO.

When olivine of the foregoing composition range is used as a lining material for walls which are-within the gas flow region but above the slag rendering olivine of the foregoing composition highly refractory when used and positioned in the described manner and places. Moreover, I believe that such high temperatures and highly oxidizing atmospheres tend to produce a bond between contacting pieces of olivine. At any rate, such olivine when highly heated in the oxidizing atmosphere of an open hearth furnace, becomes stronger and more highly refractory and endures long continued use. Such olivine stands up well under high furnace temperatures, has good load carrying strength, is not materially eroded even after many heats of steel have been made in a furnace lined above the slag line with it, and the contacting pieces are, after sometime, actually glued or fitted together and thus bonded to each other. Olivine within the stated composition range may be used as 'a lining material either in the form of suitably shaped blocks or in the form of lumps of different sizes, made up my invention to a conventional open hearth furnace and wherein similar. reference characters denote corresponding parts and wherein:

Fig. 1 is a horizontal sectional view taken on a plane through the mid portion of an open hearth furnace.

Fig. 2 is a vertical section taken on line 2-2 of Fig. 1. I I

Referring to the drawings there is illustrated a conventional open hearth furnace having certain portions thereof constructed of a refractory; made in accordance With my invention. The open hearth furnace shown generally at I includes a foundation grillage indicated at 2, having transverse members 2' to which are secured at their I9 and 20 and a gas port 2|.

lower ends, vertically extending buckstays 3, and rear buckstays 3. The rear buckstays 3' are located opposite front buckstays 3 and. the opposite buckstays are connected together at their upper ends by tie rods 4.

Each of the rear buckstays 3', however, includes a substantially vertically extending lower strut 5 and a substantially vertical upper strut 6, outwardly offset from the lower strut and being connected at its lower end with the upper end of the lower strut by a substantially horizontal ledge supporting beam 8,. A diagonal brace 9 is provided for connecting the outer end of the beam 8 with the lower end of the strut 5. Within the structural frame work thus formed the refractory materials of the furnace are supported which includes a furnace bottom l preferably made of conventional refractory brick and a vertically extending refractory brick front wall I l, abutting the buckstays 3.

Opposite the front wall and abutting the lower vertical strut of the buckstays 3 is provided a vertically extending brick wall 12. The brick walls II and 12 are made of any suitable refractory such as silica brick now in common use. These walls made of silica brick extend upwardly as far as the slag line which is designated as at l3. Suitable vertical extensions. 14 and I5 of the front and rear walls II and I2 respectively are provided. These extensions are connected by roof I6 of any usual construction. The walls l4 and I5 being disposed above the slag line are constructed of a refractory olivine material.

Furnace ends I6 and I! may be provided of any usual construction and include the air ports The walls defining these ports being out of contact with the slag disposed on thebath disposed in the furnace are constructed of olivine refractory.

Having thus-described my invention so that those skilled in the art may practice the same,

what I desire to secure by Letters Patent is defined in what is claimed.

What is claimed is:

1. An open-hearth steel furnace, the lining whereof is subjected at high temperatures to the effects of a basic slag, said furnace comprising a bottom adapted to support a molten metallic bath, a hearth lining for said bottom composed of refractory material capable of withstanding the action of a basic slag, said lining covering the bottom of said furnace and extending up the walls thereof to a point above the line where the slag on the bath contacts with said lining, and a lining for portions of the walls of said furnace ar anged to form contact surfaces for the hot gases passing through the furnace, said last mentioned lining being composed of olivine containing approximately from 4 to 15% of iron calculated as FeO and being resistant to the hot gases passing at high velocity through the furnace and overthe slag of the bath and laden with foreign material picked up in the furnace.

2. In a basic open hearth steel furnace where the lining thereof is subjected at high temperatures to the effects of a basic slag containing appreciable amounts of lime, a lower lining composed of basic refractory material capable of withstanding the action of a basic slag, said lining covering the bottom of said furnace and extending up the walls thereof to a point above where the slag on the bath will contact with the lining of the furnace, and an upper lining covering upper portions of the walls of said furnace and being in contact with the hot gases passing through the furnace, said upper lining being composed of olivine containing approximately from 4 to 15% of iron calculated as FeO, the contacting pieces of which have been formed into bonded and partially sintered masses at the high heat in the oxidizing atmosphere and are resistant to the hot gases passing at high velocity through the furnace and over the slag of the bath and laden with foreign material picked up in the furnace.

3. In a basic open hearth steel furnace, a lining comprising basic-slag-resisting refractory material for the bottom and lower side walls up to a point slightly above the slag line, and a lining for the upper side walls in contact with the hot gases extending from the lower walls to the roof of the furnace, said lining for the upper side walls consisting of olivine containing between about 4% and about 15% of iron calculated as FeO and being resistant to the hot gases passing at high velocity through the furnace and over the slag of the bath and laden with foreign material picked up in the furnace.

4. In a basic open hearth steel furnace, a lining comprising basic-slag-resisting refractory material for the bottom and lower side walls up to a point slightly above the slag line, and a lining for the upper side walls in contact with the hot gases extending from the lower walls to the roof of the furnace, said lining for the upper side walls consisting of olivine containing about 10% iron calculated as FeO and being resistant to the hot gases passing at high velocity through the furnace and over the slag of the bath and laden ROY L. LEVEN'I'RY.

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