US2780453A - Continuous furnace for heating slabs or the like - Google Patents

Description

Feb. 5, 1957 F. B. COFFMAN ETAL 2,780453 CONTINUOUS FURNACE FOR HEATING SLABS OR THE LIKE Filed March 5, 1954 4 She'ets-Sheet few 6. COffMfl/V and' fzam &Day/5 Nm NM N mm sm w m\ & V mm Feb. 5, 1957 F. B. COFFMAN ETAL & 2

CONTINUOUS FURNACE FOR HEATING SLAB S OR THE LIKE Filed March 5, 1954 4 Sheets-Sheet 2 ?5 Inventari' FG'ED 5. (OFF/mm m/ flam 5 DHV/,

Feb. 5, 1957 F. B. COFFMAN ET AL CONTINUOUS FURNACE FOR HEATING SLABS OR THE LIKE 4 Shets-Sheet 3 Filed March 5, 1954 %aki/fam@ Feb. 5, 1957 F. B. COFFMAN ETAL 2,780453 CONTINUOUS -FURNACE FOR HEATING SLABS OR THE LIKE Filed March 5, 1954 4 Sheets-Sheet 4 F'IE- 7.

Ewan/tara: fim) B. .OFFMAW and Horo E. V/5,

%www/17 4 h be/r /%mey United States Patent O CONTINUOUS FURNACE FOR HEATING SLABS OR THE LIKE Fred B. Coifman, Crown Point, and Floyd E. Davis, Gary, Ind.

Application March 5, 1954, Serial No. 414,:&80

6 Claims. (Cl. 263-6) This application is a continuation-in-part of our copending application, Serial No. 248,422, filed September 26, 1951.

This invention relates to a continuous furnace for heating metal slabs or the like to rolling or forging temperature, usually designated a reheating furnace.

Reheating furnaces as usually constructed heretofore have had a solid hearth and have usually been fired from the discharge end, combuston occurring solely in the space above the metal to be heated, and have been provided with a down-take flue at the charging end for the escape of combustion gases. Thus the heat available at any point in the furnace adjacent the charging end is dependent on the amount produced at a point distant therefrom. p

While numerous attempts have been made to improve the construction and operating characteristics of such furnaces, they remain nevertheless subject to several serious objections. In thevfirst place, the input of heat to 'the charge is slow since the combustion gases which come in contact with the cold, freshly charged metal have already given up most of their heat. By the time the metal reaches the region of maximum temperature, therefore, it is heavily scaled and this retards further absorption of heat. A considerable soakng period is thus necessary.

A further objection to known reheating furnaces is the difliculty of adjusting them to take care of delays at the rolling mill. In case of such a delay, there is danger of overheating the metal already charged, requiring discontinuance of firing, and a likelihood that metal charged when operation is resumed will not be sufiiciently heated because the normal firing rate may not be restored until the metal previously heated is out of the furnace. In addition, the metal charged at the entrance end obstructs the down-take flue to some extent and the larger the slabs the greater the obstruction, thus reducing the heat which it is possible to generate at the very time when it should be increased. Finally, known reheating furnaces have arched roofs of varying height. This makes for costly Construction and maintenance, besides overheating of the charge at points of minimum roof height and also washing the surfaces of the slab which ca'uses the accumulation of cinder on the hearth.

We have invented a reheating furnace for metal slabs or the like which overcomes the aforementioned objections or greatly minimizes them. In a preferred embodiment, we provide a furnace divided into a number of zones with burners firing transversely so that the amount of heat available at practically any point may be controlled independently of the rest of the urnace. After traversing the width of the furnace, the combustion gases escape through down-take flues spaced along the furnace on the side opposite the burners. A bale or sill along the flue side defines a waste-gas Pocket from which the flues descend. The furnace has no hearth as such but is provided with water-cooled skids extending the full length thereof at a level above the bottom or 5 V Patented Feb. 5, 1957 'ice floor, along which slabs may slide. The burners are disposed in vertically spaced banks so that combustion of fuel takes place below the slabs as well as above whereby the latter absorb heat rapidly. The skids are carred on water-cooled beams extending through the furnace from one side to the other. The beams rest on water-cooled columns or posts extending upwardly from water boxes spaced along the furnace and disposed transversely thereof and below the bottom or floor. The furnace roof may be flat and level throughout or arched from the front side (burner side) to the back side (flue side) or fiat and sloped or arched and sloped transversely of the furnace.

A complete Understanding of the invention may be obtained from the following detailed description and explanation which refer to the accompanying drawings illustrating the present preferred embodirnent. In the drawings,

Figure l is a partial longitudinal vertical section through our improved furnace showing parts in elevation;

Figure 2 is a cross-section taken on the plane of line II--II of Figure 1; line I-I of Figure 2 indicates the plane on which the section of Figure 1 is taken;

Figure 3 is a partial horizontal section taken on the plane of line III--III of Figure 2;

Figure 4 is a partial plan view of the skids on which the slabs slide in travelling through the furnace;

Figure 5 is a partial elevation thereof showing one of the transverse beams in section;

Figure 6 is a partial section taken on the line Vl-VI of Figure 5',

Figure 7 is a View similar to Figure 4 showing a modification; and

Figure 8 is a partial section taken on line VIII-VHI of Figure 7.

Referrng in detail to the drawings and, for the present, particularly to Fgures 1 through 3, the furnace of our invention co-mprises an elongated refractory-lined chamber 10 including a floor 11, sides 12 and 13, a roof 14 and ends 15 and 16 of suitable brick. The binding (structural members and plates) enclosing and supporting the brick walls of the furnace is omitted. A charging opening 17 in end 15 is defined by a water-cooled lintel 18 and is normally closed by a vertically movable watercooled door 19. Slabs 20 or the like are charged into the opening 17 in single thickness and sidewise, i. e., with their length extending transversely of the chanber, and slide longitudinally therethrough on spaced skids 21, being pushed step-by-step by known means. The skids extend the full length of the furnace and are located at a level about halfway between the floor and roof. A discharge opening 22 in end 16 is defined by a watercooled lintel 23 and is normally closed by a water-copied door 24. The slabs, after passing through the chamber, descend a slide 25 onto a roller conveyor 26, the door 24 being opened for the exit of successive slabs.

Skids 21 are composed of pipe and are arranged in spaced pairs. A connection 27 extends from one end of each to a source of cooling water. The skids rest on beams 28 also of pipe, extending transversely of the furnace chambter and outwardly through the sides 12 and 13. The skids are not secured to the beams but are free to slide thereon as necessitated by expansion and contract ion, being confined laterally in saddles formed by short lengths of curved bar 29 welded to the beams on their upper side in spaced pairs, as clearly shown in Figures 5 and 6. Each beam is carried by tubular posts 30 extending upwardly through the floor from a water box 31 disposed therebelow and provided with a connection 32 to a source of cooling water. Posts 30 communicate with the interior of the water boxes and the beams and consequently water supplied to the boxes under pressure flows up through the posts, into the beams and outof the ends of the latter. The` water boxes may also serve as beams on which the furnace chamber is carried, in addition to supporting posts 30.

skids 21 have short lengths of round bar welded longitudinally to the top thereof forming ribs 33, with which the slabs have contact in sliding along the skids, the ribs on one skid of each pair being staggered relative to those on the other (see Figures 4 and 5). As a result of this staggered relation, the same portion of a slab is not always in contact with the supporting rib and all portions of the slab are exposed for heating during various portions of their travel through the chamber. The ends of the ribs nearer the entrance end 15 are beveled as at 34.

Transverse partitions 35 spaced along the length of chamber extend up from the floor thereof to about the level of skids 21, and divide the chamber into several zones, e. g., preheating, final heating, holding, soaking or temperature-controlling zones, and the amount of heat supplied in each may be adjusted independently of all others. The several zones are heated by flames fired t'ansversely of the chamber by mixer-type burners spaced along the length thereof and arranged in vertically spaced banks, the upper burners being designated 36 and the lower 37. The former fire above the slabs on skids 21 and the lattcr below them. Pre-heated air is supplied to the burners from a conventional recuperator through headers 38 and 39 and individual connections 40 each having a control valve 41 therein. Fuel is supplied by valved connections 3811 by which the firing rate of each burner may be adjusted to effect the independent control of the several zones as aforementionecl.

A longitudinal baflle wall 42 spaced inwardly of the side 13 of the chamber extends upwardly to about the same height as the partition walls and forms pockets 43 for receiving waste combustion gases after they have traversed the width of chamber 10. The baflle wall also guides the products of combustion from the lower burners upwardly toward the slabs on skids 21. Waste-gas down-take flues 44 spaced along the chamber extend downwardly from the pockets to a stack flue (not shown). Each flue 44 preferably is provided with a damper 44a of known Construction operable independently to control the flow of combustion gases therethrough.

The burners 36 and 37 in the several zones defined by partitions 35 and the dampers in the waste-gas flues leading from each zone are adjusted to cause each slab to be subjected to a predetermined heating cycle as it advances through the chamber. The burners and dampers of the pre-heating and final heating zones are preferably adjusted for a higher firng rate than those of subseqent zones in order to cause the slabs to absorb the maximum amount of heat possible in the early stages of the heating cycle, i. e., before the formation of a scale layer of substantial thickness, since the latter acts as an insulator and retards further heat absorption. The exterior of the slab should be at rolling temperature (about 2100 F.) by the time it has passed through the first two zones. The remaining zones are fired at a lower rate in order to permit the soaking necessary to cause the heat to penetrate the interior of the slab and become equalized throughout all portions thereof.

Figures 7 and 8 show a modified arrangement of ribs 33n on skids 21. As shown, each skid has its ribs 33a alned in a plurality of rows, the ribs of adjacent rows being staggered relative to each other. This permits the number of skids to be reduced by one-half compared to the arrangement shown in Figures 2-6, yet preserves the advantage of freedom from cool spots or skid marks on the slabs which results from alternating the lines of contact with supports, between different portions of the slabs. The reduction in the number of skids means less loss of heat from the furnace and lower initial cost as well. The corresponding ribs 33a of adjacent skids may be alined transversely of the furnace or staggered, so long as the ribs in adjacent rows on each skid are staggered.

It Will be apparent from the foregoing that the furnace of our invention is characterized by numerous advantages. In the first place, the transversely firing burners above and below the path of the slabs, and the separate, independently controllable heating zones make possible the heating of the steel at a higher rate in the early stages than possible with known reheating furnaces, thus shortening the overall heating time and reducing the opportunity for free scaling to occur. The greater flexibility in the temperature control provided by this method of zone firing eliminates the solid hearth soaking zone and soaking period. The quality of the heating is also improved, i. e., uniformity of temperature throughout the slab, avoidance of washing, and the prevention of overheating during mill delays as wel] as the occurrence of insufliciently heated slabs on resumption of operation after a delay. In other words, early and higher preheat assures faster heating and heat penetration. This in turn elminates the required soaking period at the delivery end of the furnace. The flexibility of control makes it possible to hold all steel throughout the furnace indefinitely and then to immediately deliver steel at the proper rolling temperature after the delay. The flexibility of control also makes it possible to heat without interruption steels of varying composition which require different heating cycles. The root of uniform contour (flat or arched) and height (whether sloped or level) eliminates hot spots and washing. The greater uniformity of temperature achieved, moreover, permits shortening or elimination of the soaking period. Greater efliciency of heating and lower cost thereof result directly from these advantages, and from the cheaper constructon and lower maintenance characteristic of our furnace.

Although we have disclosed herein the preferred embodiment of our invention, we intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

We claim:

1. A continuous furnace for heating slabs or the like comprising an elongated chamber, spaced parallel skids disposed therein at a level above the chamber floor and extending longitudinally thereof in a substantially horizontal plane constituting a grid adapted to support slabs during progressive movement through the furnace, a plurality of spaced partition walls extending transversely of the chamber and upwardly substantially to the level of the skids, said partiton walls dividing the chamber into a plurality of zones, a longitudinal vertical baffle wall adjacent but spaced from one side wall of the chamber, said baflle wall extending upward only to about the level of said skids, said partition walls and said baflle wall forming pockets adjacent said one side wall open at the top, one for each zone, a plurality of burners spaced along said other side wall of the chamber above and below said grid, ring transversely thereof, there being at least one burner tor each Zone, a waste-gas flue extending from each pocket and a damper in each flue whereby the flow of gases through said zones may be independently controlled.

2. A continuous furnace as defined in claim 1, characterized by tubular transverse beams spaced along said chamber and extending through the side walls thereof, supporting said skids, transverse water boxes spaced along the chamber beneath the floor thereof, one for each beam, and tubular posts extending upwardly from said boxes supporting said beams, said posts communicating with the interior of both the boxes and beams permitting the flow of cooling water from the former to the latter.

3. A continuous iurnace as defined in claim 1,' characterized by tubular transverse beams spaced along said chamber and extending through the side walls thereof, supporting said skids, saddles at the points where the skids bear on the beams, each saddle comprising a pair of short Iengths of bar welded to the beams in spaced relation so that the skids fit snugly but slidably therebetween.

4. A continuous furnace as defined in claim 3, charaeterized by said beans being cylindrical and said lengths of bar being bent to conform to the transverse contour of the beams.

S. A continuous furnace as defined in claim 1, characterized by a row of longitudinally spaced, alined, solid contact ribs welded on top of each skid, the rbs in adjacent rows being staggered thereby exposing all portions of the bottom of each slab to combustion gases at least at intervals.

6. A continuous furnace as defined in claim 5, characterized by two parallel rows of ribs on each skid.

References cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Trinks Industrial Furnaces, Volume 1, third edition, published by John Wiley and Sons, Incorporated, New York, New York, 1934, pages 289 and 290.

Images