US2155165A - Furnace roof - Google Patents

Description

April 18, 1939. R. P. HEUER FURNACE ROOF Filed May 28. i957 2 sheets-sheet l 'n d' 1W 2 Sheets-Sheet 2 R. P. HEUER FURNACE RooF Filedv May 28, 1957 April 18, 1939*.

Patented Apr. 18, 1939 TENT OFFICE f FURNACE ROOF l I -.ussel Pearce Heuer, lBryn Mawr, Pa.

Application May 28, 1937, Serial No. 145,357 i 5 Claims.

The invention relates to suspended basic refractory roofs for furnaces operating at high temperatures, particularly open hearth steel furnaces whose roof temperatures are in excess of 2910 F. (1600 C.).

A purpose of the invention is to improve the effectiveness of iron spacers i'n a suspended basic refractory roof operating at a temperature above the melting point of iron.

A further purpose is to use, with iron spacers in a suspended basic refractory roof, brick which have lower shrinkage than magnesia brick, but which are more resistant to sp-alling and more reactive with the iron spacers than vordinary chrome brick.

A further purpose is to employ individually hung furnace roof brick which comprise chiefly chrome ore particles Yimparting low shrinkage,

with magnesia particles bonding the chrome ore particles and rendering them more resistant to iron oxide, and to place iron spacers laterally between the brick, which spacers oxidize and comsate by growth through the use of a matrix of.

chrome Alarger particles, to obtain rapid oxidation and prevent melting notwithstanding'thatthe furnace temperature is above the melting point of iron by virtue of the thinness of the spacers and to bond the chrome matrix and render it more resistant to basic oxides, and also react with the iron oxide from the spacers to form a refractory compound by use of magnesia smaller particles of suitable size and in suitable proportions as later explained.

A further purpose is to obtain a basic suspended furnace roof ofimproved resistance to spalling, crushing, high temperatures and basic slags, and improved volume stability. V

A further purpose is to employ oxidizable metal spacers having resilient prongs which removably grip the brick and hold the spacers to the brick during storage, transport and assembly.

Further purposes appear in the specification and in the claims. Y

The invention relates both to the methods involved and to the apparatus employed.

In the drawings one main form of the invention has been shown with desirable alternate forms, choosing the main and alternate forms primarily from the standpoints of convenience in illustration, satisfactory operation and easy demonstration of the principles involved. Brick for 'suspended roofs are available in such a multitude 'showing the suspended roof after it has been exposed to furnace conditions for some time.

Figures 4 and 5 are respectively front and side elevations of one of the bricks employed in the suspended roof of Figures l to 3 inclusive.

Figure 6 is a view corresponding to Figure 1, showing a modification of the invention.

Figures 7 and 8 are respectively front and side elevations of the spacers employed between the adjoining rear faces of the bricks of Figures 1 to 6 inclusiv Figure 7a is a. plan View of Figure 7, taken on the line laf-1a.

Figures 9 and 10 are respectively front and side elevations of spacers used between the adjoining front faces of bricks in Figures 1 to 6 inclusive.

Figure 9a is a plan view of Figure 9, taken on the line StL-9a;

Figures 11 and 12 are respectively front and side elevations of spacers used between adjoining side faces of the bricks in Figures 1 to 6 inclusive.

Figure 11a is a top plan view of Figure 11.

Figure 13 is a front elevation of an alternate form of brick, showing a side spacer to be used with the alternate form.

Figure 14 is a fragmentary section of Figure 13 on the line I4-I4, showing a front spacer employed in connection with the brick of Figures 13" and 14.

In the drawings similar numerals refer to corresponding parts.

In referring to the unit used in constructing a suspended roof as a brick, it is desired, of course, to include any block or similar shape, the word brick being employed as a convenient generic term Yto cover any preformed refractory shape, regardless of whether it is preliminarily red or is subjected to furnace temperature for the first time in the furnace roof.'

'I'he present inventor has previously proposed the construction of basic suspended refractory roofs from individually hung chrome or magnesia brick laterally spaced by spacers of iron or some In accordance with this prior proposal of the -high shrinkage.

present inventor, when the roof is subjected to furnace temperature, the metallic spacers oxidize particularly at the ends toward the furnace, and, since vthe oxide occupies greater volume than the original metal of the spacer, the spacers swell or grow, filling any moderate spaces left between the brick at the time the roof is constructed and vcompensating for shrinkage which occurs in the brick when it is heated up to furnace temperature. The compensation for shrinkage by growth of the spacer has been of' primary importance where roof brick are unflred previous to being subjected to furnace temperature because the inevitable shrinkage in such unred brick is greater than that exhibited by similar bricktwhich have been prellminarily fired. y

As a result of experiments upon the brick of the prior invention, it has been discovered that certain difllculties which may be encountered in basic suspended refractory roofs may be overcome and improvements in such roofs may be made by departing in certain respects from the prior practice. Particularly where basic suspended refractory roofs are being employed in high temperature furnaces such as open hearth steel furnaces where the roof temperature (on the side toward .the interior of the furnace) is above the melting point of'iron, there is considerable danger that the spacers, suitably made of iron, will melt out before they oxidize and therefore fail to perform their function of filling the space between adjoining bricks and bonding the bricks together. Especially where vthe unflred brick of the prior art have been used, the inevitable shrinkage of the brick is so great that the spacers must necessarily be quite thick in order to be able to compensate for the shrinkage by lgrowth The relatively great thickness of the spacer, while favorable from the standpoint of compensating for shrinkage of the brick, is distinctly unfavorable from the standpoint of avoiding melting of the spacer, as an unduly thick spacer, even when it oxidizes at the surface, still has a metallic core which is likely to melt.

Where the major constituent of the brick is magnesia, a relatively high shrinkage is inevitable at temperatures such as those attained by lthe open hearth steel furnace, and relatively thick spacers are needed to compensate for the However, such relatively thick spacers do not function satisfactorily at the open hearth steel furnace temperature because they melt out between the brick. l

Brick whose chiefv constituent is chrome ore have desirably low shrinkage at the open hearth steel furnace temperature, but in prior art practice have often been objectionable from the standpoint of low resistance to spalllng and to basic oxides and failure to unite flrmly in all cases with the oxidizedfspacer. The fact as developed by the experiments of the present inventor would seem to be that magnesia chemically combines readily'with the iron oxide of the spacer,'form ing a compound, p oibly magnesium ferrite,

' which is quite refractoryv andvery strong and volume stable, whereas chrome, on the other hand, chemically unites with the iron ox'ide much less readily and does not appear to produce a union of as great strength as that formed with magnesia.

In accordance with the present invention, it is proposed to employ a suspendedA furnace roof bility equal to or superior to that of chrome brick,

thus making'it possible to employ thin spacers, the spacer thickness being preferably not greater than 3/,4ths of an inch (0.109 centimeter). In resistance to spalling and to basic oxides, the brick employed in the present invention is superior to prior art chrome brick. Due apparently to its magnesia content, the brick of the present )invention has the property .of chemically combining readily with the oxidized spacer, in a very desirable manner to form the adjoining brick into a monolithic mass.

In this way it is possible to 'produce a suspended roof which is satisfactory for furnaces operating at Very high temperatures, such as open hearth steel furnaces in which the temperature is in excess of 2910 F. (1600 C.). The spacer does not melt out objectionably under open hearth steel furnace conditionsl apparently because, dueA to its thinness, it oxidizes very quickly and combines with the refractory. Due to the small brick shrinkage, the growth of the thin spacer is suiilcient to fill the spaces left during construction and to compensate for the shrinkage. The brick are inherently` very resistant to spalling, and

spalling is further reduced by the chemical combination between the iron oxide of the spacer and the magnesia of the brick, which holds spalled fragments in place in the roof.

In order to facilitate construction of the roof, the spacers are very deslrably provided with resilient prongs by which the plates can be secured to the brick before assembling the'roof. One of the prongs may be the flange whichha's heretoforebeen used to prevent the spacer from drop-A ping out of its position between the bricks. A cooperating prong desirably has contact with the hot face of the brick. After the furnace is -brought up to temperature, the prongs exposed at the hot face will of course melt off, but by that time they will have performed their function. In conventional suspended roof constructions, the bricks hang with the longest dimension4 generally vertical, exposing the smallest f ace to the furnace interior. The bricks arepreferably indi-l vidually hung from hangers, although of course they may if desired be hung in small groups. in which case one or more bricks of each group may be supported from other bricks. This generally vused suspended roof construction may be employed in the present invention.

Where the roof is to be subjected to very high temperatures, such as those of the open hearth steel furnace, the spacers which are placed between some or preferably all of the adjoining lateral faces of the bricks will be of iron. The designation iron is intended to include alloys in which iron is the predominant constituent, such as steel. In furnaces operating at substantially lower temperatures than that of the open hearth steel furnace,\spacers of copper or aluminum may be used, but it will be. understood that iron is the preferable material for the spacers even under lower temperature conditions.

The spacers should be sheet metal of a thickness preferably not greater than 3yaths of an inch (0.109 l centimeter), the desirable spacer thickness being 15nd of an inch (0.079A centimeters). vEach spacer should preferably be a single sheet in thickness, and, if, the spacer in thickness comprises two or more sheets, it should not be hollow. The cumulative effect of the oxidation and corresponding growth of the spacers is to press the bricks firmly against one another in a lateral direction, and this tightness of interiitting between the lateral faces of the bricks will increase as more and more of each spacer .oxidizes, although in many instances the spacers will not oxidize all the way to the cold face of the bricks.

It will of course be understood that the present invention is not applicable to acid (silica) bricks, since these would flux the iron oxide of the spacer and destroy the roof.

Figures 1 and 2 show a typical fragment of a suspended roof structure of the present invention as it will appear after construction and l before the furnace has been heated. The bricks 2U have front faces 2|, rear faces 22, side faces 23, cold or top faces 24 and hot or bottom faces 25 directed toward the interior 'of the furnace.

The brick are individually suspended by hangers 26 engaging in recess 21 in the brick. The hangers are supported from any conventional overhead structure (suggested by hooks 26') on any suitable side structure, not shown. The hangers may if desired be supported in groups so that a particular section of the roof can be removed as a unit. If this is to be done, it may be advisable to omit spacers at the line of junction between the roof units, so that lateral interlocking will not take place to prevent removal of the brick units.

In the form of Figures 1 and 2, each hanger 26 has twoprojections 28 and 29 which extend in opposite directions, and each of which supports an individual brick. The projections 28 and 29 engage the downwardly directed surfaces 30 of the recess 27 while the vupwardly directed surfaces 3l of the recesses slope to provide clearance for, and permit ready insertion of, the projections 28 and 29. Each of the bricks is cut out at 32 to pass the body 33 of one of the hangers 26. The hangers 26 and the cooperating recesses in the bricks are conventional means for supporting a suspended roof.

If desired, the suspended roof may be sur- -rounded by a permanent frame structure 34, of

which part only is shown. Such a structure,

where used, confines the brick of the roof later- I ally and exerts lateral pressure against adjoining brick in the roof. The frame structure 34 as shown consists of I- beams 35 and 36 joined b y a strip 3l fastened at 38 to the respective I-beams. The lateral supports may be eliminated if desired, and are not present in Figure 6. A lateral thrust on the brick can be obtained by permanent expansion of the spacers without the use of .lateral supports, due to the tendency of the brick toremain in vertical position under the action of gravity and due to the tendency of the hangers to remain in vertical position.

The spacers 39 are preferably o-f three types, which t the peculiarities 'in shape of the respective faces of the brick. Each ofthe spacers has a ange '40, adapted to rest upon the upper face 24 of avbrick as at 4I and thus prevent the spacer from dropping out of its position between the bricks before oxidation occurs to hold the spacer in place. At their ends, the flanges 43 are desirably mitered as shown at 42 to prevent the necessity of having one iiange overlap another flange at a corner of the brick.

In order to prevent handling the spacers separately from the bricks at the time of assembly, the spacers are desirably secured to the bricks,

as by suitable prongs. The flange may be used to function as a prong at one end, while a cooperating prong 43 is placed at the opposite end of the spacer to engage the lower face 25 of the brick. The sheet iron composing the spacer is somewhat resilient so that the resilient pinching of the brick by the prongs 40 and 43 holds the spacers in place upon the brick during storage, shipment and construction of the roof. The spacer is simply snapped in place upon the brick. The prongs may if desired be roughened to prevent them from slipping off the brick ends. The prong 43 is desirably mitered at 44 at the corners of the brick.

4Figures '7 and 8 illustrate a. spacer 45 for use between the rear faces of the brick. It corresponds generally in size with the rear face 22 of the brick. Figures 9 and 10 show a spacer 46 of the same general size as the spacer 45, for use between the front faces 2| of the brick. The spacer 46 is cut away at 41 to permit ready insertion of the hanger 2B. Figures Il and I2 show a spacer 48 for use between the side faces of the brick.

In the form of Figures l to-3, the spacers will be differently applied to the bricks of different longitudinalrows, the bricks of one row carrying a front face spacer and a left side spacer, while those of another row carry a rear face spacer and a right side spacer, for example.

It will be evident that the sizes and contours of the spacers will depend very largely upon the sizes and contours of the faces of the brick, and that, while it isydesirable to have the spacers conform more or less exactly to the external outlines of the brick faces, the spacers may, if desired, differ from the external outlines of the brick faces.

It will also be evident that, while Figures 1 and 2 show spacers in contact with all four lateral faces of the bricks (with the exception of those bricks at the outer edges of the roof) some advantage rnay be obtained by using spacers between some but not all of the adjoining faces of the brick.

Figure 6 shows spacers between the front and rear faces4 2i and 22 but not between the side faces 23 of the brick.

The hanger and spacer function may be combined in a single fitting, the detail of which is not important from the standpoint of the presentV imperfectly upon the drawings. The portions of the spacers above the lower ends 49, as for example at 50, are partially converted into oxide,

with correspondingly less, but nevertheless marked, increase in volume. The upper portions of the spacers at 5l have not yet become very extensively oxidized. The effect of the oxidation upon the suspended roof has been to ll any slight free space between the bricks left at the time the roof was constructed, to compensate for the shrinkage which occurs in the brick, to exert a lateral force between adjoining bricks and to chemically react with the( adjoining brick welding one brick to another by a highly refractory and very strong compound, thus producing a 'monolithic construction. Under the pressures developed, some of the iron oxide appears to penetrate small roughnesses in the brick surface. In

kil

the great majority of the cases, all leakage openings-between the brick are'sealed by the growth of the spacers.

The bricks are held so firmly against lateral movement after the spacers oxidize that an individual brick may even break in pieces, and yet the pieces will not fall out. This is particularly important in the case of furnaces which are shut down from time to time, with the resultant tremendousI ,expansions and contractions. The spacers serve to seal the roof against leakage of combustion gases `or entrance of air into the furnace, thus improving the heat efciency and prolonging the life of the furnace.

When the roof is firsty subjected to furnace temperature, the respective brick and spacers are relatively loose andfree to move and to readjust as required by the pressure on the individual partsof the construction. Readjustment during the initial heating up of the roof is very desirable to prevent localized abnormal stresses upon individual bricks. It is only after the roof has been thoroughly heated at furnace temperature, and the action of the oxidizing atmosphere of the furnace has caused the spacers to oxidize, that the individual bricks are integrated together.

The spacers must not collapse nor compress laterally under pressure, as if they do so, they cannot by increase in volume exert lateral pressure on the bricks. Therefore each spacer should 'preferably comprise a single thickness of metal.

In order to indicate that various forms of brick may be used, Figures 13 and 14 show a different type of brick 20 having a recess 21 in which any suitable hanger may be inserted, and provided with spacers 52. Many variations of hangers may be used, and it is not desired to conne the present invention to constructions showing any particular type of hanger.

The brick employed in the present invention has the desirable properties of prior art chrome brick without some of the disadvantages of such prior' art chrome brick. The novel brick is manufacv chrome particles and using instead smaller magi tured by employing the principle of grading the size of larger and smaller particleswhile omitting intermediate sized particlesv as previously discussed by the present inventor, and in addition, rejecting'some or preferably all of the smaller Anesia particles. The use of smaller magnesia pare ticles in preference to smaller chrome particles in a brick chiefly containing chrome ore increases theresistance to spalling; to crushing, to high temperatures and to basic slags and the volume stability beyond the properties of chrome brick of the prior art, without serious loss in density or increase in porosity.

Chrome is a satisfactory basic refractoryv for many purposes because of the great strength,

hardness, resistance to crushing and volume stability of its particles and theirchemicalinertness in the metallurgical furnace. A typiml-v-'analysis of chrome ore used for refractory purposes is here from 100.00

a volume stable skeleton or matrix in the brick.4

It is important to use chrome ore rather than magnesia as the major constituent of this matrix since magnesia exhibits an excessive shrinkage at the temperatures cf an open hearth steel furnace, for example, The larger chrome particles are supplemented with additions of smaller particles of-magnesia. The magnesia particles serve as a coating upon the chrome particles, bonding the chrome particles, protecting the chrome so as to make the brick more resistant to iron oxide and any other basic oxides and reacting readily with the iron oxide of the spacer. In this Way the objectionable properties of chrome ore, such as its poor bonding qualities, its lack of resistance to iron oxide arid other basic oxides and its lack of vigorous reactivity with the iron oxide of the spacer, are overcome and objectionable features of magnesia, such as its tendency to shrink excessively at the temperature of the open hearthA steel furnace, are also not harmful.

For the smaller particles magnesia which is desirably the calcined or dead-burned magnesite or periclase of ,usual commercial grade is em'- pl'oyed. Typical analyses follow:

Percent Percent Ignition loss 0.00 0. 10 Silica 0. 67 3. 36 Ferrie oxide. 7. 13 1.46 Alumina. 0. 25 1.02 L1me 2. 29 1.11 Magnesia by dliierenc 89. 66 92. 95

'rtm1 10o. oo 10o. oc

These analyses are, of course, subject to variation within the usualI commercial range, and

and 20 mesh per linear inch, and may very desirably be more closely graded as to size, for ex,

ample ranging between-6 and 20 mesh per linear inch, between 3 and 10 mesh per linear inch, or

be 3 and 6 mesh per linear inch, etc.

urse it will be understood that no commuch as 10% or even in an extreme case 15% in the dry mix, o1 chrome particles of smaller size. Likewise, there may-be a small proportion, possibly 1% or 2% or even in an extreme case 5% in the dry mix, of chrome particles 'of-larger size.

screening process is one hundred per cent eilicient and that, notwithstanding due care,

vbrick which is suitable for use withoutprevious Based on the weight of the refractory, there may be as much as 15% of the larger particles outside the chosen size rangedue to the inefdciency of commercial screening. 'Ihis will be made clear by the following typical screen analyses of chrome particles commercially graded to be between 6 and 20 mesh per linear in'ch in one case, between 3 and 10 mesh per linear inch in another case, and between 3 and 6 mesh per linear inch in another case:

Mesh per linear inch 6 x 20 3 x 10 3 x 6 Percent Percent Percent On 3 Nil 2 Through 3 on 4 Nil 13 36 Through 4 on 6.--- l 2T .56 Through 6 on 8.--. 23 29 4 Through 8 on 10 26 18 2 Through l on 14-- 26 7 Nil Through 14 on 20 2l 5 Nil Through 20 3 Nil Nil Total 100 100 l0() The intermediate size-particles are omitted or thequantity of intermediate sized particles is maintained very low.

The magnesia smaller particles should pass 48 mesh per linear-inch. They have the following typical screen analysis:

Mesh per linear inch- It will of course be evident that the illneness of 1f' the smaller particles may be increased, using smaller -particles for example passing entirely through 65 mesh per linear inch,'or even smaller.

Of the chrome larger particles, between 65% and '75% (that is, between 65 and '75 parts in 100 parts) are employed, preferably using about '70%.

Of the magnesia smaller particles, between 35% and 25% (between 35 and 25 parts in 100 parts) are employed, preferably using about 30%.

To a slight extent chrome may be substituted for magnesia and magnesia for chrome without aiecting the special properties of the brick, although the larger particles will be chiefly or predominantly chrome and the smaller particles chieily or predominantly magnesia. This means that more than 50%, most desirablyv100%, of the larger particles will be chrome ore, and more than 50%, most desirably 100% of the smaller particles will be magnesia. The larger particles will preferably comprise in excess of 80% chrome and not over 20% magnesia, while the smaller -particles will preferably comprise in excess of 80% magnesia and not over 20% chrome. This will be understood when reference is madein the claims to larger particles of chrome and smaller particles of magnesia.

Conventional brick-making practice is used as far as the preparation of the brick mix is concerned. 'Ihe larger chrome particles and smaller magnesia particles are mixed with water, preferably adding enough water to temper the mix, desirably about 2% based on the weight of the wet mix. A

Where the brick is'to be kiln fired as later explained, it is not necessary to use a bonding substance. If it is preferred, however, to make a kiln firing, a bonding substance should be employed.

As a bonding substance, sulphuric acid may be used. One suitable mix might be bonded with about 1% of 66 Baum sulphuric acid based" upon the weight of the wet mix (the percentage is practically the same if based on the dry iinished brick). As much as 2% or even more of sulphuric acid may be used. Where sulphuric acidof another strength is used,l allowance should be made in the percentage employed. For some uses clay may be added as a bond, and as much as 2% or less desirably even 5%of clay may be added'if desired in addition to the sulphuric acid.

Other bonding substances such as\sodium acid sulphate, sodium silicate ororganic bonding substances like waste .liquorslfrom the sulphite paper process, dextrin, etc., may be used. 'I'he quantity of sodium acid sulphate, sodium silicate or organic bonding substance will most desirably be limited to 1% or permissibly 2% of the wet mix, not considering in this 2% the water which is used to dissolve the bonding substance. In any case the quantity of any such bonding substance will not exceed 5% of the wet mix. Clay, preferably not exceeding 2% but less desirably up to 5% of the wet mix, maybe used with any of the above bonding substances.

The total bonding substance will very desirably be limited to 5% of the wet mix so as not to impair the refractory properties of the brick. The bonding substance may be mixed with the tempering water before incorporating the water in the mix. l

The molstened brick mix is molded under a pressure exceeding 1000 pounds per square inch (70.3 kilograms per square centimeter), preferably exceeding 5000 pounds per square inch (351.5 kilograms per -square centimeter), and most desirably exceeding 10,000 pounds per square inch (703 kilograms per square centimeter). It is preferable to apply a Vacuum during the molding, increasing the pressure in a second step after the vacuum is applied.

The molded brick, if they are to be kiln fired, are dried preparatory to kiln ring, and then fired, suitably at a temperature such as 1830" F. (1000 C.) or above, for example 2190 F. (1200 C.) or 2730 F. (1500 C.). Where a bonding substance has been used, the brick need not be kiln red, but should be treated to develop the bond, after which they may be shipped-in unburned condition and subjected to firing temperature for the first time in the metallurgical or chemical furnace in which they are used. The preferred treatment to develop the bond is to heat the moist brick to a temperature between.

212 and 572 F. (100 and 300 C.) until 1Sub-- stantially all free moisture is removed. The dry invention when bonded and in unflred co'ndition,

after drying for.75 hours at'25'l F. (125 C.) has a bulk specific gravity in excess of 3.10, preferably about 3.20. The open pore space is less than 10%.

A very high resistance to spalling is obtained in the actual finished brick as indicated by tests under conditions of 'actual use. -The cold crushing strength of the dry unred brick exceeds 2000 pounds per square inch (140.5 kilograms per square centimeter) and often exceeds 4,000 pounds per square inch (281 kilograms'per square centimeter). Y

'I'he brick of the present invention in unilred condition is very volume stable and has excellent resistance to high temperature, as indicated by the fact that when rcheated in a testing furnace to 3300 F. (1815 C.) for 24 lhours or more the brick show a change in linear dimensions of less than 1% shrinkage.

Tests undr actual conditions of use indicate very high resistance to basic slags and other basic oxides.'

The eiliciency of the sulphurio acid bond depends of course upon the presence of magnesia smaller particles and `is slightly diminished by substitution of chrome smaller particles for magnesia. 'I'he bond, after it is once developed, is effective at ordinary room temperatures land is supplemented after the brick are heated to firing temperature during use, by a reaction between the constituents of the brick. The excellent service characteristics of the brick of the present invention, and particularly the resistance to spalling, crushing, high temperatures and basic slags, and the volume stability, are due in part to the tight intertting between particles, to the presence of an optimum size of chrome particles, to

the presence of the magnesia smaller particles.

and to the presence of 'an optimum proportion and optimum size of magnesia particles.

The magnesia in the brick is important not only from. the standpoint of the properties of the brick itself, but also in order to render the brick capable of reacting readily with the oxide of the spacer metal to unite the brick firmly to the spacer by a compound which is refractory and volume stable under the furnace conditions and which makes of the roof effectively a monolithic structure.

Where reference is made to a sulphate acid bonding substance it is intended to include both sulphuric acid and acid sulphates such as sodium acid sulphate.

The screens which have been described as possessing certain mesh per linear inch are Tyler Standard screens.'

Commercial Ascreening frequently employs screens which are inclined at an angle from the horizontal and have rectangular openings. These screens should be chosen so that the particles which -are produced, when tested by screening over standard screens, shall conform to the required grading.

'. All percentages mentioned herein arepercentotal material being analyzed.

Percentages based upon the dry mix are substantially identical for practical purposes with percentages based upon the dry nnished brick,

and one can be used as the other without change 1f desired. i

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain au or part.

of the benefits of my invention without copying the structure shown, and I, therefore, claim all such in so far as they fall within the reasonable spirit and scope of my invention.

Having thus described my invention, Whatl claim' as new and desire to secure by Letters Patent is:

l. In a refractory roof, a plurality of suspended refractory bricks positioned side by side, supported by hanging from above, having lateral faces which are adjacent and generally parallel and comprising chiey chrome ore with mag- 'nesia as the chief minor constituertkand spacers between lateral faces of the bricks, each spacer contacting the refractory material of the generally parallel faces of adjacent bricks, the spacers comprising iron part atleast of which is oxidized and iron oxide of the spacers being combined with the magnesia of the bricks on both sides of individual spacers.

2. In a refractory roof, a plurality of suspended -refractorybricks positioned side by side, supported by hanging from above, having lateral faces which are adjacent and generally parallel and comprising chiefly chrome ore in the form `of relatively larger particles with magnesia in* the form of relatively srrialler particles interspersed among and coated on the larger chrome particles, and spacers between the lateral faces of the bricks, each spacer. contacting the refractory material of the generally parallel faces of adjacent bricks, the spacers comprising iron part at least of which is oxidized and iron oxide of thev spacers being combined with the magnesia. of the bricks on both sides of individual spacers."

3. An open hearth steel furnace roof having a plurality of volume-stable chrome-magnesia suspended refractory bricks positioned side by side, supported by'hanging from above, having lateral faces which 'are adjacent and generally parallel and containing more than 50% chrome ore, yand chrome ore with magnesia as the chief minor constituent, means for individually hanging the bricks from above and spacers between lateral faces of the bricks, each spacer contacting the refractory material of the generally parallel faces of adjacent bricks, the spacers comprising iron part at least of which is oxidized and iron oxide `of the spacers being combined with the magnesia of the bricks on both sides of individual spacers. 5. In a suspended refractory roof, a plurality of dry chrome-magnesia suspended refractory bricks positioned side by side, supported by hanging from above, having lateral faces which are adjacent and generally parallel and comprising 75 tightly intertted masses of from 65 to '75 partsof larger particles consisting chiey of chrome ore and large enough to be retained 0n a 20 mesh per linear inch screen and from 35 to 25 parts of smaller particles consisting chieiiy of mag'- nes'ia and small enough to pass through a. 48 mesh per linear inch screen in combination with spacers between the lateral faces` of the bricks,

each spacer contacting the refractory material of the generally parallel faces of adjacent bricks, the spacers comprising iron part at least of which is oxidized and the iron oxide of the spacers being combined with the magnesia of the bricks on both 5 sides of individual spacers.

RUSSELL PEARCE HEUER.

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