US1688220A - Furnace lining and method of making same - Google Patents

Description

Oct. 16, 1928. 1,688,220

J. R. WYATT FURNACE LIN I NG- AND Filed Nov. 1, 1923 2 Sheets-Sheet OD OF MAKING, SAME ,Lae;

Fatented Oct. 16, I

UNITED STATES I 1,688,220 PATENT OFFICE.

JAMES R. WYATT, CAMDEN, NEW JERSEY, ASSIGNOR TO THE AJAX METAL OOM PANY, OF FHILADELPHIA, PENNSYLVANIA, Av CORPORATION OF PENNSYLVANIA.

FURNACE LINING AND METHOD OF MAKING SAME.

Application filed November A further purpose is to provide a retaining lining having relatively good heat conducting properties and to depend for heat insulation upon theouter support for this shell.

A further purpose is to avoid abrupt changes in thickness of the inner lining and, preferably, to make it of substantially un1- form thickness throughout.

A further purpose, when applied to sub merged channel furnaces, is to-form the inner lining or shell for the channel outside of the furnace casing, to back it and to form the supporting insulation and shell for the pool subsequently in position within the furnace.

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

My invention relates to the processesinvolved as well as to mechanism by which these processes may be carried out.

I have preferred to illustrate my invention by one form only and in one furnace only among the various forms and furnaces to which it may be applied, selecting a form andfurnace which have proved highly practical,

effective and reliable and which at the same time well illustrate the principles of my invention.

Figure 1 is a central vertical section upon line 1-1 of Figure 2, through the length of the channel in a submerged channel furnace to which my invention is applied. Figure 2 is a section upon line 2-2 in Figure 1. i e

Figure 3 is a section upon line 3--3 of Figure 1.

Figure 4 is a section correspondingto Figure 1 showing the inner lining for the channel as separately made and before it has been inserted within the furnace. a

Figure 5 is a top plan view of Figure 1. Figure 6 is a section taken upon line 66 of Figure 1.

In the drawings similar numerals indicate like parts.

Though my invention is of value in lining awide variety of electric furnaces I believe 1, 1923. Serial No. 672,073.

I that it will find its greatest usefulness in lining furnaces of the induction type in which there is a submerged channel. I believe it to be most needed in such furnaces because of the inaccessibility of their channel interiors for repairs, the small cross sections of their channels with thickness of lining relatively great as compared with the channel dimensions and lacking in uniformity, with consequent relatively excessive strains due to temperature changes, and the factthat the metal is constantly moving through the channel at a much higher speed than in the pools of these or of other types 'of furnaces. The temperature of the metal within the channels is also considerably higher in these furnaces than the average temperature of metal in the pools.

The invention has been illustrated in connection with the furnace invented by me and shown in my Patent No. 1,201,671. This furnace is much used in the trade for brass melting and is known as the Ajax-Wyatt furnace.

The main cause of lining trouble in the submerged'secondaries and a. serious cause of trouble everywhere when there is lining trouble lies in the cracking of the refractories, especially objectionable within the submerged secondaries. This cracking has not been confined to pre-fired blocks or linings but has been present also in those linings which have been rammed in place by the use of apower hammer and which have subsequently been baked in-position. I believe this trouble to be due almost wholly to dif ferences .in expansion due to gradients in temperature. It might therefore be viewed as essentially mechanical.

v The metal within the channeland within the furnace pool-is very hot. In prior linings the heat gradient from the metal outwardly has begun at the inner surface of the lining through the attempt to make all of the lining surrounding the metal effective as a heat insulator. As the result of this there has been an immediate and continued dif-' ference in temperature from the metal outwardly, each portion more distant from the metal being cooler than that nearer to-the metal.

Freedom from mechanical strains due to heat gradient is thus made dependent upon plastic when hot.

perature changes. Efforts along this line have met with but indifferent success. The materials forthe lining immediately adjoin ing the metal have been selected as heat insulators rather than because of their capacity to retain the metal.

In dealing with lining materials which are based upon chrome, magnesite and bauxite, for example, though they are plastic when cold and may then be rammed into homogeneous union for this reason, there has been serious difliculty when they are heated because they are hot-short. With the chrome, magnesite and bauxite, the hot-short characteristics have given difficulty because the heat gradient has resulted in a considerable difference of temperature between the outside and inside with the thickness used. As a result of the consequent difference in ex pansion and contraction the lining has fractured.

Graphite is cold-short but is somewhat lVith graphite also the thickness has been such that, with the heat gradient present, there has been excessive difference in temperature between the outside and inside, with corresponding difference in expansion and contraction and with the outside cool enough to be cold-short.

On the other handclay base linings which do not suffer to the same extent from this shortness when hot, fuse out with some met- .als because of chemical reaction between the metal or its oxides and the lining.

-One purpose of my invention isto make these linings which will not fuse out by such chemical union more available generally as well as available specificallyfor the metal with which clay base linings would not fuse.

No material is wholly inert to temperature changes and with prior constructions mechanical strains and ultimate fine cracking or even more serious fracture due to thermal changes have been inevitable. This objection has not proved so serious with metals such as yellow brass as with metals such as red brass and copper as the penetrating powers of the latter two are much greater than in the case of yellow brass.

'My invention applies-to furnaces intended for ferrous metals as well as those for nonferrous metals.

In furnaces intended for non-ferrous uses it offers the considerable advantage of being well suited not only to yellow brass but also to red brass and copper. the most difficult of these to hold, andfor which latter two most of the linings at present found to be satisfactory for yellow brass are wholly unsuited. Describing my invention in connection with the preferred embodiment shown, in illustration and not in limitation That portion 10 of the lining which comes in'intimate contact with the metal, the inner lining or shell, I make of a conductor of heat which may or may not be a conductor of electricity also. It is given just sufficient depth to reliably mechanically hold the metal when supported by its backing.

The thickness need not ordinarily be more than an inch in a furnace of the type shown and the material may, for example, be graphite or a double oxide of magnesium and aluminium or an oxide of chromium.

Three materials besides graphite are on the market which could be used for this purpose, known respectively under the trade names of diamel, thcrmolith and magnesitc. These various substances have varying electrical and heat conductivities but have in common sufficient thermal conductivity for the purpose and, when well consolidated and thoroughly backed up mechaically, are tenaceous enough and of firm enough surface to retain the metal.

This portion of the lining may be rammed in place or be made as a separate insert or block as preferred in the installation which is being made. The contour and the relative accessibility of the interior of the lining within the furnace casing must be considerable factors in determining which practice should be followed and both the character and size of the furnace being lined, affect the. detei mination.

All of the materials named lend themselves well in the case of the Ajax-lVyatt furnace above illustrated to the use of an initial block for the channel portion of thc furnace with a connecting lining 11 for the bottom and walls of the pool rammed in place and into effectively integral engagement with the block.

When the block is made separately it may be fired before insertion to eliminate shrink age as far as possible, if the character of the material and shape permit proper consolidation of the pool lining to make a good oint, free from leakage, or may be fired in place. The latter is much to be preferred. Unless the block can be made to include both the channel and the pool, with such casing shape or step-by-step building up of the casing as will permit proper ramming'of the backing for the entire unit, proportionate and cooperative shrinkage are best attained by ramming the lining of the pool into engagement with the channel lining before the latter is fired. Even where the block includes lining for the pool, if pre-fired there is danger of shrinkage of the backing away from it when the furnace is used.

The lining in any event and particularly the portion about the channel should he of as uniform thickness as possible throughout its section. If changes in thickness are desired for any special need they should be made as gradual as possible. The temperature difference between the outer and inner walls of the inner lining or shell should be a minimum;

for which as stated the thermal conductivity should be at least fair.

Because of its small thickness, of its relatively poor insulating quality and its lack of I use a rammed supporting insulation which has a cushioning effect and which rests upon a brick lining 14. This supporting and insulating rammed lining must be capable of withstanding high tei'nperature without undue shrinkage or breakage but does not need to hold the metal against the see age and, for that reason, need not be free rom" the fine lines of cracking which would be serious,

weaknesses in the inner lining. For this supporting lining I have secured very satis factory results in the Ajax-Wyatt furnace with a composition of 7 5 per cent IVoodland clay and per cent VVidemayer plastic'clay and believe this composition will be found valuable for other types also. I prefer to use a silocel brick next to the supporting lining.

Between the supporting lining and the split metal casing 15 I place a thin layer of electrical insulation in sheet form capable of withstanding the temperature of the molten metal, in order to check at this point any flow of metal which may seep through the linings near the end of the life of the linings. As-

' bestos paper willserve this purpose. My

reason for this is that though one such leakage might rest against the metal casing without interruption to the operation of the fur nace, two such leaks to the metal shell would cause a short circuit of the secondary to the shell, which short circuiting of the secondary can be avoided and the life of the lining extended by the asbestos paper or similar continuous electrical insulator having suitable heat resistance and enough cohesion to stand up against the mechanical strain placed upon it.

The lower part-of the inner lining, in the illustration (see Figure 4) conforms to previously existing types of. Ajax-Wyatt furnace. It comprises V-shaped lower channel portions, 16 united at the bottom, whose outer channel walls extend upwardly at 17 approximately vertically and whose inner channel walls curve inwardly at 18 and join below the top 19 of the channeled section (i. e., below the pool) so as to provide a groove 20 across from one channel top to the other. The channel section is narrow and the fiat channels have their greatest dimension in section parallel with the length of the middle transformer leg.

In the best provislon,

form of my invention known to me the lower section as seen in Figure 4,. is preferably made separately and is held in position within the lower part of the furnace casing after the silocel brick has been placed within this shell and before the supporting lining is rammed in place. It is dried sufficiently to-hold its shape against the necessary pressure but is not burned until the backing is in position and the full inner lining has been placed. The supporting lining is rammed in position about the block, finishing the lower part of the lining. The brick is then placed in position to outline the pool the supporting lining of the'bottom of the prliol and the sides of the pool is rammed to p ace. sides of the pool is then placed, being rammed, into amalgamated union with the section 23 for the groove and with proper if desired, for the bottom at least of the pouring spout 24 and bottom of the charging opening at 25. The upper part of the pouring spout is also shown as lined at 26 and a suitable cover 27 having opening 28 is applied. The opening is protected by a top The inner lining 22 of the bottom and within the upper casing 21 of the furnace and 29 and the charging inlet is closed by a door 30.

The casing and these several cover and closure parts are suitably protected and supported by metal, including metal brackets for any intended projection of the pouring spout and charging opening. Among these are brackets 31, ring 32, cover parts 33, 34 and 35 and band 36 presenting trunnion openings 37.

The furnace illustrated shows other supporting structure which forms no part of the present invention, including brackets 38, filler pieces 39, bottom strips 40 and retaining bolts 41 by which-in conjunction with the transformer, a portionof the lower part of the furnace below the pool is encased.

The transformer is a type old in these furnaces, having closed core 42 of which the central leg 43 passes through the opening 44 in the inner lining. The winding 45 surrounds this middle leg and is spaced from it by an insulating cover 46.

The air space 47 between the transformer winding and the tube 48 gives room for circulation of air admitted to opening 49. Tube 48 limits the backing within the interior of the inner lining. I

The edges of the transformer are protected by angle irons 50 held in by bolts 51.

The metal of the furnace casing is interrupted to avoid useless flow of induced currents into the casing.

In assemblage the transformer is ordinarily built up in place after the inner lining insert has been completed as seen in Figure 4 and permissibly after it has been put in place and the supporting lining has been packed against it.

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That portion of the brick within the transformer is directly supported by strips 52 held in place by angles 53.

The supporting lining is rammed in to, the shell between the brick and the inner lining insert or block by a power hammer. The pool is lined first with brick and the supporting lining and then with the inner lining or facing is applied and is rammed into position. I have found that the inner lining can be rammed into contact with an unbacked inner lining so effectively as to make the material practically integral with that of the lining, in that the two are of uniform strength and density throughout, homogeneous across the joint. I then bake the lining at one'operation obtaining uniform contraction and solidification.

In use, the cross section of the inner lining heats so nearly uniformly that it is substantially free from stress due to differences in expansion, with the result that it retains its mechanical strength to hold the molten metal. Since the temperature of the metal is not destructive to the backing from other standpoints than differences in expansion and the inner lining is supported by a backing of heat insulating material sufficiently thick to take care of the heat insulation between it and the shell of the furnace, both the requirements as to mechanical retention and heat insulation are completely met by the combination of the two.

Thinness of the inner lining and preferably uniform thinness for it-avoidance at least of abrupt changes in thicknessgreatly reduce the .risk of breakage of the inner lining.

Though I have treated the question of the advantage obtained from m invention from the standpoint of heat gradlent and the heat sulators.

gradient will be improved by using a separate inner lining having relatively good heat conductivity as compared with the support ing lining, it will be obvious that what I am primarily after is to reduce the difference in temperature between the inner and outer portions of the inner lining used, to reduce the difference in expansion and contraction sufficiently so as'to keep it within the safe limits of expansion and contraction difference for the material in question. A portion of my benefit is therefore obtained by using a thinner lining even where the slope of the gradient, viewed as a curve, is not improved.

However, with the relatively good heat conductivity sought it will be obvious that the heat gradient curve will be much more nearly horizontal than in the case of either poor conductors of heat or intended heat in- It will be obvious that in view of my disclosure other forms and modifications of my invention will occur to those skilled in the art, which will secure all or a part of the benefit of my invention without directly copying it, and it is my purpose therefore to cover herein all such as come within the reasonable spirit and scope of my invention.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is 1. In an induction electric melting furnace, afurnace casing, rammed heat insulation therein and an inner lining adapted to hold the molten content of the furnace, resting upon the heat insulation and'low in heat insulating quality.

2. In an induction electric melting furnace, a furnace body with a thin inner lining of substantially uniform thickness at equal heights in the furnace, a compressed heat insulation between them, the inner lining be ing adapted to rest upon the supporting lining and itself hold the molten metal and means for inducing electric current in the said furnace.

3. In an electric melting furnace, a metal casing, brick lining therefor, a heat insulating rammed lining within the brick and an inner lining, a substantial conductor of heat resting upon the supporting lining and adapted to hold the molten metal.

at. In an electric induction melting furnace, a furnace having a pool and a submerged channel connecting with the pool, in combination with a supporting rammed lining for the pool and channel having very low heat conductivity and an inner linin resting upon the supporting lining and havlng relatively high heat conductivity.

5. In an electric induction furnace of th submerged channel type, a furnace casing, a lining of brick therefor, including the channel section, a supporting rammed lining of low heat conductivity resting upon the brick and an inner lining having relatively high heat conductivit resting upon the support ing lining and a apted to retain the metal.

6. In an electric induction furnace, a furnace casing, a heat insulating rammed lining within the casing and a thin inner lining supported by the heat insulating lining providing a channel composed of a material of low heat insulating quality and which is electrically conductive when heated.

7. In an electric furnace, a furnace cas ing, a heat insulating rammed lining within the casing and a thin inner lining supported by the heat insulating lining and comprising an oxide of chromium.

8. An inner lining for the channel of an induction electric furnace comprising a lower channel section of substantially uniform channel opening and uniform small wall thickness, curving on opposite sides from the inner wall contour to join these curves, relatively diverging from these curves in the outer walls. therefrom to increase the dis tance between the inner and outer channel I walls and having substantially parallel side channel Walls.

9. A continuous heat conducting inner lining for an induction furnace channel of substantially uniform thickness throughout, in combination with a supporting heat-insulating clay backing for the lining.

10. In an induction electric furnace of the submerged channel type, a pro-formed inner channel lining of compressed material plastic under pressure. v

11. In an induction electric furnace of the submerged channel type, a preformed thin inner channel lining of compressed material plastic under pressure dried but not burned.

12. In an induction electric furnace of the submerged channel type, a pre-formed thin inner channel lining of compressed material plastic under pressure, a heat insulating and supporting backing for the pool and a thin inner pool lining thereon in homogeneous union with the channel lining.

13. In on induction electric furnace, a thin interior wall forming the lower part of the pool and the lining for the channel having an upper flare into the pool, composed of a material relatively high in heating conduction, in combination with a compressed supporting covering therefor of low heat conductive properties and means for merate lining for the channel portion, ramming a supporting lining for this inner lining into position when the inner lining is in place, in subsequently ramming in a supporting lining for the pool portion ofthe furnace and in finally ramming in an inner lining for the pool into homogeneous union with the inner lining for the channel.

15. The method of constructing a lining of an electric induction furnace of the channeltype which consists in preparing a separate lining for the channel portion, in ramming a supporting lining for the inner lining into position when the inner lining is in place, in subsequently ramming in a supporting lining for the. pool portion of the furnace, in ramming an inner lining for the pool into homogeneous union with the inner lining for the channel and in baking all of the linings in position together.

JAMES R. WYATT.

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