US3378242A - Hearth dam - Google Patents

Description

April 16, 1968 c. CONE ETAL HEARTH DAM 2 Sheets-Sheet 1 Filed July 1, 1966 INVENTORS: E. DUNE F. RHINKEH RE. PINNE'Y.

April 16, 1968 c. CONE ETAL 3,378,242

' HEARTH DAM Filed July 1, 1966 2 Sheets-Sheet 2 IIIHIH INVENTORS E. DUNE 13 BUNKER, 12-5. JMNEY ATTY.

United States Patent 3,378,242 HEARTH DAM Carroll Cone, Toledo, ()hio, Robert E. Pinney, Lambertville, Mich, and Franklin G. Rinlcer, Toledo, Ohio. as-

signors to Midland-Ross Corporation, Toledo, Ohio,

a corporation of Ohio Filed July 1, 1966, Ser. No. 562,245 8 Claims. (Cl. 263-7) ABSTRACT OF THE DISCLOSURE This invention relates to a hearth dam adapted to retain a refractory hearth layer that goes through a liquid phase. The hearth darn has a plurality of vertically extending ribs that are disposed about the perimeter of the hearth and a pad is attached to the top of each rib. These pads are disposed in an end to end relationship to form a retaining structure about the hearth and are disposed at an obtuse angle relative to the top layer of the hearth.

This invention relates to apparatus to be used during the formation of the top layer of a refractory hearth, and more particularly to a hearth dam for retaining the top layer of an annular refractory hearth during fabrication thereof, when the layer goes through a liquid phase.

In the construction of refractory hearths, problems often are encountered because of the different coefficients of thermal expansion (CTE) of the various materials and apparatus used during such construction. This is particularly true while making the top layer of an annular rotary hearth which goes through a liquid phase when heated to formation temperatures. The problem is compounded by the fact that the liquid has to be contained in addition to the requirement of compensating for expansion and contraction that occurs with changes in temperature.

It is, therefore, an object of this invention to provide a novel hearth dam for use in the construction of refractory hearths.

It is another object of this invention to provide means for constructingthe top layer of a hearth that goes through a liquid phase which means accommodates expansion and contraction occasioned by temperature changes.

it is still another object of this invention to provide a hearth dam made of heat resistant alloy.

In one embodiment of this invention, the substructure of an annular rotating hearth includes a bottom layer of insulating refractory and an intermediate layer of hard castable refractory that are received by a metal housing. Circumfereutially spaced about the inside and outside diameters of the refractory layers, are a plurality of supporting ribs which give backing strength to the housing. Extending from the upper edges of the intermediate layer, about the inside and outside diameters, are a plurality of pads, or plates, that extend radially inwardly and outwardly, respectively, at an angle of approximately 45 relative to the vertical. Each pad is supported by one of the ribs and the pads cooperate with one another to form a hearth dam about the inside and outside diameters of the annular hearth. The ends of the pads are ship lap to afford movement and to eliminate a spacing between the pads when there is limited radial movement of the hearth darn. A layer of high purity magnesium oxide is placed on the intermediate castable refractory layer to complete the hearth substructure. The magnesia layer extends radially to engage the angularly extending hearth dam, but the top of the dam is located substantially above the upper surface of the magnesia.

For the formation of the top layer of the rotary hearth, a finely divided iron ore with coal fines may be used as a raw material. The hearth substructure is rotated and 3 ,3 78,242, Patented Apr. 16, 1968 the furnace is brought to temperature. The raw material is added to the top of the substructure to form the top layer, and, as it reaches a temperature in excess of 2200 F., it forms a liquid. The top layer tends to shrink in volume as the liquid is formed, consequently, more raw matcrial is continually added until the desired thickness is reached in the liquid form. As the top layer is formed it moves up and down the incline while being contained by the dam. Since the pads of the dam are at an outward angle as seen by the top layer, when the layer experiences physical changes, it moves up and down the slope of the darn instead of drawing away from its retainer to form openings therebetween or pushing against it to exert a force thereon.

In the drawing, FIG. 1 is a vertical view in section of a rotary hearth furnace demonstrating features of this invention.

FIG. 2 is an enlarged cross sectional view of the furnace hearth of FIG. 1.

FIG. 3 is a back view of a support member of the furnace hearth taken along the line 3-3 of FIG. 2.

FIG. 4 is a side view of the support member taken along the line 4--4 of FIG. 3.

FIG. 5 is a longitudinal view of a dam pad taken along the line 5-5 of FIG. 3 and FIG. 6 is a plane view of a portion. of a rotary hearth dam of this invention.

Referring now to the drawing, the rotary hearth furnace 10 includes an annular hearth 12 having a bottom layer 16 of insulating refractory that is supported on a structural member 17 and a hard castable refractory layer 18 on top of the bottom layer, each layer being disposed in an annular metal housing 19. Heat resistant alloy ribs 14 extend about both the inside and outside diameters of the hearth layers 12 and 16 to provide backing strength to the housing 19. The ribs 14have inwardly projecting members 20 that are received between the housing 19 and the member 17 and serve as guide means to maintain the proper elevation of the ribs as they extend about the hearth 12.

The top of the rib 14 is inclined at an obtuse angle relative to the hearth 12, the preferred angle being approximately and has mounted thereon a dam pad 22. The dam pads 22 extend circumferentially in an end to end relationship about the inside and outside diameters of the hearth 12 to form, with the ribs 14, a hearth dam 26. Each dam pad 22 has interdigitating ship lap ends 24 so that adjacent dam pads are able to move relative to one another a limited distance without creating a space therebetween. Extending from each side of the ribs 14 is a buttress 28, each of which cooperates with an opposed buttress on an adjacent rib to limit the minimum distance between ribs.

Disposed on the castable refractory layer 18 is a high purity magnesium oxide layer 30 which may be either castable or prefircd shapes. The MgO layer extends radially to engage the hearth dam 26; however, the dam extends substantially above the level of the MgO layer.

Means is provided for rotating the annular hearth 12 and includes a pair of rails 32 attached to the bottom of the structural member 17 and supported by a rotatable shaft member 34 driven by a motor 36. A removable refractory cover 38 is provided to be placed over the rotary hearth 12 and the space therebetween is sealed by a conventional water seal 40. The cover 38 and hearth 12 have annular shell members 39 and 41, respectively, that extend downwardly and are received by the water seal 40 to complete the seal between the hearth and the cover. Suitable burner means 42 are placed into the vertical wall of the refractory cover 38 and the furnace enclosure is vented by flue means 44. As is well known in the art, the

burners are regulated so that different temperatures are maintained at various zones in the furnace. Thus, as the hearth is rotated, each portion thereof experiences temperature changes.

The top layer 46 of the hearth may be formed by using as a raw material a finely divided iron ore with about 5% by weight of coal fines admixed thereto. This raw material is placed upon the MgO layer to the top level of the dam 26. The hearth 12 is then rotated by actuation of the motor and the burners are lit to heat the furnace 10 so that in the hottest part thereof the raw materials experience a temperature in excess of 2200 F. At these elevated temperatures, the iron ore mixture Will form a liquid and the raw material will slowly shrink to about 1 the original thickness. As the hearth is rotated from the hot zone to the cooler zones, which may be as low as approximately 200 F., more raw material is added to the top layer 46 as this layer goes from the liquid phase to a solid phase. The added material rotates into the hot zone to become liquid and shrunk, and the process is repeated until a sufficiently thick top layer 46 is obtained. Generally, six revolutions of the hearth are required to obtain a sufliciently thick top layer.

Obviously, the primary function of the heat dam 26 is to prevent the top layer 46 from flowing away when it is in the liquid state. The hearth dam of this invention offers other advantages when used with a rotary hearth 12. The hearth dam 26 may be made of conventional heat resistant alloy steel. Normally, this type of alloy steel would be affected by the high temperature, but because of the presence of the Water seal 40, heat is radiated from the dam to the water and the metal parts of the dam are kept from being damaged by the high quantity of heat.

Normally the alloy steel dam 26 and the refractory hearth 12 would not be compatible with one another because of the difference in CTE, for the rotation through different temperature zones causes the parts of the furnace to assume different dimensions. Ordinarily, this difference in thermal expansion would lead to stresses that could cause damage and eventual destruction of the hearth.

This is particularly true of the top layer 46, which has a CTE considerably higher than most refractories, when the temperature of the furnace is reduced from operating temperatures to ambient temperature. After the top layer 46 is fabricated from raw material fines that are melted, a monolithic slab is formed that exerts tremendous force against its retainer as the furnace is cooled to ambient temperature. This force is particularly critical at the inside diameter of the annular hearth, for the shrinking monolithic slab tends to crush any normal supporting means. The hearth darn 26 of this invention not only contains the top layer 46 as it is formed, but also withstands the stresses imposed through the presence of the ship lap ends 24, the angle of the dam pads 22, and the buttresses 28.

The hearth dam 26 is constructed to move radially independently of the hearth while at the same time containing the top layer 46 when the same is liquid. The ship lap ends 24 of the darn pads 22 are able to have radial movement without a space being created between the pads through which space the liquid could flow. The dam 26 is prevented from contracting to an extent that it would damage the hearth because of the buttresses 28 that extend from the sides of the ribs 14. The buttresses 28 are particularly useful at the inside diameter of the hearth, for they act as rigid structural members which engage one another to prevent the top layer 46 from crushing the hearth dam 26. The ribs 14 have a certain amount of resiliency so that they are able to yield a slight amount under pressure from the top layer as the buttresses 23 hold fast.

The dam pads 22 are positioned at an angle relative to the hearth layers. As the dam 24 and the hearth layers, particularly the top layer, experience changes in temperature, the top layer tends to run along the su fa e o the dam, i.e. uphill and downhill instead of away or toward it. For example, when the top layer is cooled and it changes from the liquid state to the solid state, instead of pulling away from the dam, as it would from a vertically extending container, and having spaces or holes therebetween, the layer tends to slide and maintain contact with the dam. Thus, no openings are created through which objects may fall to act as a wedge which would eventually destroy the hearth as it changes its physical dimensions due to temperature changes. When the top layer 46 is heated, instead of directing a force (that results from expansion) normal to the face of the retainer, a portion of this force is diverted through the movement of the layer up the incline of the pads 22.

Having the dam pads 22 at an obtuse angle relative to the hearth it) also serves another purpose. The water seal 40 is used to prevent atmosphere from entering the furnace and this water seal is also used to cool the hearth dam components. By having the top of the ribs 14 extending over the water seal 40, these portions are able to radiate heat to the water and remain comparatively cool. The remaining portions of the ribs 22 are able to radiate heat to the water seal 4%) because of their proximity to the same.

In the above preferred embodiment, the clam pads 22 have ship lap ends 24. It is obvious that other ends may work equally Well, for example, tongue-in-groove. Flat ends that abut one another may also be used, for as they separate from one another during expansion, the liquid will freeze therein due to the pads being subject to heat loss. When the dam contracts, the frozen portions would normally break away and not create serious problems.

Although the preferred embodiment of this invention has been shown and described, changes and modifications can be made therein Without departing from the scope of this invention and it is understood that the preceding description is illustrative only and not for the purpose of rendering this invention limited to the details illustrated or described except insofar as they are limited by the terms of the following claims.

We claim:

1. A hearth dam for retaining a refractory hearth top layer that goes through a liquid phase, the combination comprising: a plurality of vertically extending ribs disposed about the perimeter of the hearth, said ribs having pads attached to the tops thereof, said pads being disposed end to end to form a retainer about the top layers and said retainer being at an obtuse angle relative to the top layer.

2. The hearth dam of claim 1 wherein said angle is between -160.

'3. A hearth darn for retaining the top layer of an annular rotary hearth furnace, having a refractory substructure that supports the top layer, the combination comprising: a plurality of pads disposed in an end to end relationship about a circumference of the substructure, said pads extending upwardly about and at an obtuse angle relative to the top layer, means supporting said pads, and means for radiantly cooling said pads.

4. The combination of claim 2 wherein said angle is between 120 and 5. The combination of claim 2 wherein the ends of said pads are ship lap and adjacent ends interlock.

6. A hearth dam for retaining a liquid forming top layer of an annular rotary hearth furnace having a refractory substructure that supports the top layer, the combination comprising: a plurality of vertically extending ribs circumferentially spaced about a diameter of the substructure, a plurality of pads attached to the top of said ribs in an end to end relationship and disposed about the top layer, said pads extending upwardly at an angle between 120 to 160 relative to the top layer, means limiting the minimum diameter bound by said ribs, and means for radially cooling said ribs and pads.

5 7. The combination of claim 5 wherein said pads have ship lap ends that interdigitate with one another.

8. The combination of claim 5 wherein said diameter limiting means comprises a plurality of buttresses that extend in an opposed, paired relationship from each side of a said ribs, each buttress being operative to engage an adjacent buttress on an adjacent rib when said minimum diameter is assumed.

6 References Cited UNITED STATES PATENTS 2,944,805 7/1960 Nesbitt et all. 263-' 3,061,295 10/1962 Martin et a1 263--4 FREDERICK L. MATTESON, JR, Primary Examiner. JOHN J. CAMBY, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,378,242 April 16, 1968 Carroll Cone et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, lines 60 and 62, the claim reference numeral 2" each occurrence,

should read 3 Column 5, lines 1 and 3, the claim reference numeral 5",

each occurrence, should read 6 Signed and sealed this 24th day of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER; JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer

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