US2091172A

US2091172A - Apparatus for heating

Info

Publication number: US2091172A
Application number: US33965A
Authority: US
Inventors: Wilson Lee
Original assignee: Individual
Current assignee: Individual
Priority date: 1935-07-31
Filing date: 1935-07-31
Publication date: 1937-08-24
Anticipated expiration: 1954-08-24

Description

Aug. 24, 1937.

1 WILSON APPARATUS FOR HEATING Filed July 31, 1935 2 Sheets-Sheet l INVENTOR Aug. 24, 1937. L, WILSON i 2,091,172v

APPARATUS FOR HEAT ING Filed July 51, 1935 2 Sheets-Sheet 2 INVENTOR Patented Aug. 24, 1937 Uur/TED STATES PATENT OFFICE 2 Claims.

My invention relates broadly to the art of heating and, particularly, to the heating of metallurgical furnaces, such as those for the heat treatment of Various materials, for example,

sheet steel.

Heating, normalizing, and annealing furnaces of the continuous or tunnel type have been used for a considerable period. In the so-called roller hearth furnaces, the material is passed through an elongated heating chamber on a roller conveyor and heated as it moves therethrough. The earliest method of heating fuelfired furnaces of this type was to provide burners extending through the side walls thereof, and supply them with fuel for combustion within the heating chamber and in direct contact with the material passing therethrough. Several objections to this method were experienced. In the rst place, the temperature throughout the furnace was not uniform but varied according to the distance of the point under observation from the nearest burner. The direct contact of the combustion gases at considerable velocity, with the material being treated, sometimes has a deleterious effect on the latter. Where the combustion gases have direct contact with the material, furthermore, they constitute the atmosphere in which the heat treatment takes place and it is not possible to provide a. special atmosphere which is desirable in some cases. In an attempt to overcome the aforementioned disadvantages of the original method of direct firing continuous or tunnel type furnaces, it was proposed to place the burners in special combustion chambers or pockets alongside the furnace and communicating with the main body thereof, whereby the combustion took place in a zone slightly removed from the path of the material and the hot gases passed into the furnace proper and around the material being heated. While this expedient resulted in a slight improvement on the previous practice, it did not provide absolutely uniform temperature throughout the furnace and, in addition, prevented the application of a special atmosphere to the treating zone.

I have invented an apparatus for heating, specically, heating metallurgical furnaces, which overcomes the objections to the previous prac- 50 tice described above. In accordance with my invention, I provide a heating chamber with a plurality of heat-exchange tubes extending thereinto, each tube having a burner adjacent one end and an exhaust at the other. By sup- 55 plying fuel and air to the burners, hot combustion gases are delivered to the heat-exchange tubes and the latter heat the furnace chamber by convection and radiation. I prefer to employ U-shaped or hairpin-loop tubes extending through the walls of the furnace from opposite sides, although the specific arrangement of the tubes is susceptible of wide variation. In a specic example, the tubes extend through the side walls of the furnace and are disposed above the level at which the material being treated is located. The method of my invention thus provides for the delivery of hot combustion gases in a predetermined direction through a zone adjacent the material being treated, and the diversion of the gases to an opposite and substantially parallel direction, while confining the heating gases out of contact with the material being treated at all times. As a further step of the invention, I prefer to circulate the atmosphere surrounding the tubes and the material being heated to maintain a uniform temperature in all parts of the furnace. The invention is applicable not only to stationary furnaces of the continuous or tunnel type, but also to portable furnaces of the cover or bell type, such as shown in my U. S. Patent No. 1,952,402.

The accompanying drawings illustrate preferred embodiments and practice and method of my invention. In the drawings:

Figure 1 is a central longitudinal section through a continuous furnace, in accordance with the invention;

Figure 2 is a sectional view taken substantially along the line II--II of Figure 1; and

Figure 3 isa transverse sectional view to enlarged scale along the line III-III of Figure 2.

Referring now `in detail to the drawings, a furnace I0 comprises a hearth II, side walls I2, a roof I3 and end Walls I4 having entrance and discharge openings I5 therein. Transverse partition walls I6 having ope irigs therethrough for the passage of material, olvide the furnace into a preheating zone I'I, a heating zone proper I8, and a soaking zone I9. The walls of the furnace arekcomposed of refractory brick assembled in the usual structural framework, indicated at 20, the furnace walls being built up on a foundation 2|.

A plurality of conveyor rolls 22 extend through the side walls I2 and are journaled in suitable bearings 23 mounted exteriorly thereof. The rolls 22 define the so-called roller hearth, and are of the dry or hot shaft type, being composed of heat-resistant alloy capable of withstanding continued exposure to the high temperatures involved in metallurgical operations. Any desired type of drive may be provided for the rolls 22, as an example of which I have shown the rollers provided with sprockets 24 adapted` to be actuated by a driving chain (not shown). 'Ihe invention is obviously not limited to .roller hearth" furnaces, and any suitable type of conveyor other than that shown may be substituted therefor.

For heating the furnace, I provide a plurality of heat-exchange tubes 25. In the particular form illustrated, these tubes are U-shaped, or hairpin-like in conformation and extend through each side wall toward the opposite wall. The

tubes are distributed along the interior of thev furnace and may be mounted therein in any desired manner. In the `illustrated example of the invention, the tubes are disposed above the roller hearth on which the material traverses the furnace. Each tube is provided with a burner 26 having a. connection 21 including a valve 28 to a fuel main 29. Air is supplied to the burner through a connection 30 from a header 3l. The main 29 and the header 3| extend along both sides of the furnace for connection to each' burner and are themselves connected to any suitable source of fuel and air. As will be apparent from the drawings, the two ends of each tube extend outwardly through a side wall of the furnace adjacent each other. The end not provided with a burner has an exhaust pipe or stack 32 connected thereto for discharging the products of combustion to the atmosphere after they have traversed the portion of the tube within the furnace.

A plurality of inlet ports 33 is disposed in the side walls I2 of the furnace adjacent the hearth II to permit the introduction and maintenance of a predetermined atmosphere within the furnace. While the entrance and discharge doors I permit the leakage of. a certain portion of the furnace atmosphere, the entrance of air from the outside maybe prevented by maintaining in the furnace a pressure slightly above that of the outer atmosphere.

Circulating fans 34 are mounted in the various zones of the furnace for causing the continuous movement of the furnace atmosphere between the heat-exchange tubes and the work passing therethrough on the roller hearth. Each of the fans has a driving motor 35 which is preferably mounted as shown, above the furnace roof on Y suitable supports. By thus circulating the furnace atmosphere, I am able to maintain a substantially uniform temperature throughout the space enclosed thereby. If desired, different temperatures maybe maintained in the several zones of the furnace by'varying the adjustment of the burner valves of the heat-exchange tubes heating that particular portion, and while the circulation of the atmosphere in any one zone maintains the temperature throughout the latter substantially uniform, this does not preclude the maintenance of different temperatures in the various zones, if desired.

A roller conveyor 36 is provided for feeding material toward the entrance door I5. A quenching chamber 3'I is disposed adjacent the discharge door and provided with cooling means, such as water sprays 38. A discharge conveyor 39 delivers material from the quenching chamber to any desired point.

While the operation of the apparatus described so far will probably be apparent, a brief review thereof will be included here. Assuming that the various burner valves have been properly adjusted and the various zones of the furnace brought up to their proper temperatures, material such as steel sheets to be normalized, is fed into the preheating zone I1 through the entrance I5 by the conveyor 36. In traversing the preheating zone, the material`is heated gradually to the desired temperature. Ina specic example, the heating zone was 21 ft. long and the U- shaped heat-exchange tubes were spaced on 18" centers. As the material traverses the preheating zone, the heat-exchangetubes radiate heat thereto and the circulation of the furnace atmosphere also conveys heat from the tubes to the material.

As ythe material advances to the heating zone proper I8, it is similarly heated to the maximum desired temperature. In the aforementioned specific example, the heating zone was l5 ft. long, with the same spacing of heating tubes. After being brought up to the maximum desired temperature, the material passes into the soaking zone, in which it is maintained at that temperature. 'Ihe soaking zone was 6 ft. long in the example mentioned. The dimensions of the various zones, of course, are susceptible of Wide variation, depending on the nature of the operation to be" carried on and the rate of travel of the material thereon. On emerging from the soaking zone, the material is quenched in a quenching chamber 31 and is then ready for further nishing operations. If quenching is not desired the material may be cooled slowly.

The advantages of the apparatus of my invention have already been indicated. Among them, is the fact that the combustion gases employed for heating are maintained out of direct contact with the material being treated. It is possible to maintain a substantially uniform temperature within the furnace or the various heating zones thereof. It is` also possible to maintain an atmosphere within the furnace different from that which would be provided if the combustion gases were discharged directly into the furnace. The U-shaped tubes, furthermore, have an. advantage over the straight tubes anchored at both ends, shown in my prior patent, in that the bent end is free or floating so that expansion and contraction of the tube could not set up any destructive forces in the furnace walls. The tubes themselves are preferably made of heat-resistant alloy, to give them a. long life.

Although I have illustrated and described herein but two present preferred embodiments and practice of .the apparatus and method of my invention, it will be apparent that many changes therein may be made without departing from the spirit of the linvention or the scope of the appended claims.

I claim:

l. A furnace comprising an elongated heating chamber, having side walls, a roof, and a conveyor for passing material therethrough, heatexchange tubes disposed adjacent the conveyor, said tubes extending through opposite sides of the chamber alternately, being bent back on themselves in a horizontal plane and then passing out through the same side wall through which they entered.

2. A furnace as defined by claim l characterized by said tubes being disposed above the conveyor.

yLEE WILSON.