US3051462A - Method and means for operating a soaking pit - Google Patents

Description

1962 A. A. FENNELL 3,051,462

METHOD AND MEANS FOR OPERATING A SOAKING PIT Filed March 12, 1959 2 Sheets-Sheet 1 PORTR MRO cnsO

umin' Aug. 28, 1962 A. A. FENNELL 3,051,462

METHOD AND MEANS FOR OPERATING A SOAKING PIT 2 Sheets-Sheet 2 Filed March 12, 1959 9n. R w W W m H i E d M m w/ m M m 5 M 0 m a WNssss QM m m x i l mm 81%. Q NN Q WWIULIS UI I 1 3% U II V U HU wwn- IIDH A W U NMQ 3,051,462 METHOD AND MEANS FOR OPERATING A SOAKING PIT Anthony A. Fennell, Homewood, Ill. 379 E. 147th St., Harvey, 111.) Filed Mar. 12, 1959, Ser. No. 799,030 7 Claims. (Cl. 263-15) This invention relates generally to furnaces for heating ingots and more particularly to an improved method of operating a regenerative-type furnace which may be employed in heating ingots.

Brick-lined, pit-type furnaces are frequently used for heating ingots in order to prepare the ingots fo-r subsequent rolling or forging. Commonly, the heating efliciency of such soaking pits is increased by the provision of checker chambers, brickwork heat exchangers built with alternate open spaces. Furnaces, so provided are called regenerative.

According to conventional practice, two checker chambers are employed so that incomping air may be heated as it passes over the brickwork in one chamber while exhaust gases passing out of the soaking pit heat the brickwork in the other chamber. The flow of air and exhaust gases are periodically reversed. Fuel, naturally, is introduced only at the burners associated with incoming air.

Heretofore, reversing of the flow of air and exhaust gases has been controlled according to the temperature differential existing between the two checker chambers, or according to a uniform, fixed, time interval. By either method, rather slow heating rates must be used in order to prevent overheating and burning of the ingots since the flames actually impinge the ingots and high flame temperatures are encouraged by preheating the incoming air in the checker chamber.

Especially with regard to steels, overheating results in an enlarged grain size and impaired physical properties. Burning is an extremely overheated condition which allows the fusible constituents to melt and run into the grain bounderies leaving voids between the grains.

Even when rather slow heating rates are used in conventional, regenerative-type soaking pits, some overheating and burning has been known to occur, particularly with regard to sensitive metals and alloys.

Therefore, a general object of the present invention is to provide an improved method of operating a regenerative-type soaking pit.

States Patent Another object of the invention is to provide a method of'operating a regenerative-type soaking pit, which method involves firing a plurality of burners in sequence according to the error between the actual temperature in the pit and the required temperature.

Yet another object of the invention is to provide an improved system for heating ingots which obviates overheating to a hitherto unknown degree.

A further object of the invention is to provide an improved system for heating ingots which is permissive of rapid heating rates.

A still further object of the invention is to provide a novel firing sequencer for regenerative-type soaking pits.

Additional objects and features of the invention pertain to the particular structure and arrangements whereby the above objects are attained.

The invention, both to its structure and mode of operation, will be better understood by reference to the following disclosure and drawings forming a part thereof,

FIG. 3 is a view of a control box incorporating parts of the firing sequencer of FIG. 2.

A system for heating ingots constructed in accordance with a preferred embodiment of the invention includes a brick-lined, pit-type furnace or soaking pit 10 provided with four ports, port A, port B, port C and port D. It is recognized, however, that a number of ports other than four may be readily utilized.

Port A communicates with a checker chamber or heat exchanger 12a by means of a passageway 14a. Checker chamber 12a terminates at one end in a flue 16a which includes a draft reversing valve 18a. Air from a blower, not shown, may be introduced between the top of the chamber 12a and the reversing valve 18a through a manifold 20a. Advantageously, manifold 20a is provided with a draft control gate 22a.

For purposes of injecting ignited fuel into the incoming air stream entering through port A, there is provided a burner 24a juxtaposed with the port A. Burner 24a is appropriately connected to a fuel valve arrangement 26a which is adapted to supply suitable fuel ingredients. As is well known, oil, natural gas, and manufactured gas have proved to be appropriate fuels. In effect, the burner 24a transduces the potential source energy of the fuel to actual heat energy in the furnace.

In one useful embodiment, fuel valve arrangement 26a is comprised of an air-operated fuel valve 28a. Appropriately, a solenoid valve 30a works fuel valve 28a through a diaphragm air motor 32a mounted on valve 28a.

Like elements associated with the ports B, C and D have been denoted by like numerals to which have been added the appropriate suflix letter.

In order to coordinate the several operating elements, there is provided a firing sequencer 34- which includes a control unit 36, a temperature measuring element 38 mounted in the wall of furnace 110 and a temperature controller 40 connected between control unit 36 and measuring element 38. So that the instantaneous condition under which furnace 10 is operating may be perceived at a glance, control unit 36 has a number of indicator lights 42 mounted to its face. As shown, the several lights 42 may be adapted to provide an indication of the condition ,of the materials being supplied to the various ports in furnace 10.

With reference to FIG. 3, the control unit 36 may be composed of a housing or enclosure 44 to which a door 46 is swingably mounted. In the instance wherein lights 42 are transformer-type lights, corresponding transformers 48 are afiixed to the back of door 46 to be connected appropriately with the lights 42. The transformers 48 are supplied with power from a suitable source by means of the connector block 50.

Other important elements of the firing sequencer 34 are contained within the housing 44. Among these elements is a shunt-wound DC. motor 52 which is adapted to rotate a camshaft 54 through a speed reducer or gear train 56 interconnected therebetween. Three groups of timing elements taking the form of segmented cams, cams 58, cams 60, and earns 62, are mounted on the camshaft 54 in order to operate respectively switches 64, switches 66 and switches 68. Switches 68 are adapted to operate a purge timer 70.

Enclosure 44 may also house purge relays 72 and a sequencing relay 74. Electrical power may be supplied to the motor 52, the switches 64, the switches 66 and the switches 68 by means of the connector block 76.

As indicated in FIG. 2, the speed at which the camshaft 54 is rotated by motor 52 is governed through temperature controller 40. In response to the output of the measuring element 38, temperature controller 40 operates a rheostat 78 which is connected in series with a DC. source 80 and the shunt field of motor 52. Thus, as the temperature within furnace =10 increases, temperature controller 40 moves to reduce the field resistance included by means of rheostat 78; and accordingly, motor 52 may be made to operate at a gradually increasing speed.

As is also shown in FIG. 2, the switches 66 operate damper reversing solenoids 82 whereas switches 64 operate pressure switches 84. Switches 84 are conditioned by the solenoids 82. As is also indicated in FIG. 2, the purge relays 72 are conditioned by the sequencing relay 74, relay 74 responding to the output of the purge timer 7 which is operated by switches 68. The output of purge relays 72 is directed to the valves 30 which are operated thereby. Specifically, a switch 64, a switch 84 and a purge relay 72 are electrically connected in series with each of the valves 30. When a switch 64 is closed by the cooperating cam 58, the corresponding switch 84 must also be closed before current will be passed to the corresponding purge relay 72. The purge relay 72 must be conditioned, i.e. its contacts must be closed as by the operation of sequencing relay 74, before any current passed by the switches 64 and 84 can be passed, in turn, to the valve 30. The switches 64 may be grouped with the switches 84 to form what may be termed a conditioning means. Similarly, the solenoids 82 and the switches 66 may be grouped to form what may be termed a conditioning means. Furthermore, the relays 72, the switches 68, purge timer 70 and sequencing relay 74 may also be grouped for convenience defining what may be termed an operating means for the valves 30.

For purposes of providing an easy understanding of the invention, it is advantageous to provide at this juncture a functional description of the mode of operation of the component parts, given with reference to Table I which traces a firing sequence for the embodiment shown in the figures.

Table I Cycle Stage Port(s) Port(s) Ex- Open Valves Closed Valves Firing hausting O and D 28a, I); 180, d 280, d; 1811, b. D and A 28!); 18d, a 28a, c,d;l b,c. D and A 281), 0; 1811, d 280, d;18b, c. A and B 281:;18 b d; l c, d. A and B 280, d; 1811, 180, d. B and 0-. 28d; 18!), c c;18d, a. B and 0-. 28d, a: 18b, c 18 d. 4purge O and D 28a; 180, d 811, b. Damper 18a.

Assuming that furnace 10 has been charged with ingots, and that the system is prepared for operation, power may be applied to the firing sequencer 34 in order to initiate heating.

Having the cams 58, 60 and 62 positioned so that stage 1 of the firing sequence will be realized, burners 24a and 24b will have fuel directed therethrough by means of the fuel valves 28a and 28b which have been actuated by the solenoid valves a and 30b respectively. Valves 30a and 30b act thus in response to the signals from the switches 64, which are closed by the appropriate segmented earns 58. These signals are passed appropriately by the pressure switches 84 and the purge relays 72.

In stage 1, air is directed through the chambers 12a and 12b from the manifolds 20a and 20b respectively, draft reversing valves 18a and 18b being closed. Furthermore, exhaust gases pass through ports C and D; and valves 18c and 18d are therefore open. The valves 28c and 28d are closed in order to prevent firing the burners 24c and 24d.

The next successive stage in the firing sequence is denoted l-purge in Table I. This condition is achieved by motor 52 appropriately rotating cam shaft 54 and thereby altering the condition of the switches 64, 66 and 68. Accordingly, valve 28b is left open in continuation of the firing of burner 24b. Valve 180 is closed in order to clear the exhaust gases from the chamber 12c and the passageway 14c prior to the subsequent firing of burner 24c. Appropriately, valve 280 remains closed.

Valve 18a and valve 28a are closed during the 1- purge stage since port A is being changed over from firing to exhausting. Valves 18d and 28d remain in their former condition as port D continues in the exhausting condition.

In similar manner the firing sequence progresses from one cycle stage to the next, stage 1 following stage 4 in continuation of the heat. When furnace 10 eventually reaches the temperature set on controller 40, the damper condition is achieved. At this stage, the entire furnace is closed down in order to allow the ingots which have been charged therein to absorb heat from the furnace walls and to equalize in temperature. This damper stage continues until the charged ingots have absorbed sufficient heat to depress the furnace temperature, as sensed by the temperature measuring element 38, thereby to initiate a new firing sequence.

It should be noted that FIG. 1 specifically illustrates cycle stage 3. It is also important to point out that the draft control gates 22 are ordinarily not varied in position during the firing sequence.

Having one firing sequence thus described, it is apparent that this firing sequence will be repeated in gradually increasing tempo as the temperature of the furnace and the ingots charged therein increases and as the temperature controller 40 gradually reduces the resistance in the field of motor 52 by means of the rheostat 78. For example, the first firing sequence might extend over a five minute interval, and the last firing sequence before the damper stage is achieved might extend over only a oneand-one-half minute interval. Thus, overheating of the ingots is obviated for, while the flames still impinge the ingots, they do so for very short periods and, as the danger of overheating increases with the increasing temperature of the ingots, the flames impinge for ever shortening periods.

The specific example herein shown and described is illustrative only. Various changes in structure and method of operation will, no doubt, occur to those skilled in the art; and these changes are to be understood as forming a part of this invent-ion insofar as they fall within the spirit and scope of the appended claims.

The invention is claimed as follows:

1. A system for heating materials comprising: a furnace; a plurality of energy transducers arranged to deliver heat energy to the interior of said furnace; regulating means for each of said transducers controllably supplying source energy thereto; rotatable shaft means external to said furnace; means for periodically and unidirectionally rotating said shaft means at a speed proportional to the temperature within said furnace; means individually conditioning said regulating means for operation; a first plurality of timing means on said shaft means individ-, ually actuating said conditioning means in sequence; means individually operating said regulating means when said regulating means have been readied for operation by said conditioning means; and a second plurality of timing means on said shaft means individually actuating said operating means in sequence, whereby to supply source energy to said transducers periodically and at selected intervals and whereby to vary said intervals according to the temperature within said furnace in order to minimize overheating of materials introduced therein.

2. A system for heating materials comprising: a furnace; aplurality of energy transducers arranged to deliver heat energy to the interior of said furnace; regulating means for each of said transducers controllably supplying source energy thereto; rotatable shaft means external to said furnace; means for periodically and unidirectionally rotating said shaft means at a speed directly proportional to the temperature within said furnace, including temperature responsive means for sensing said temperature and for providing an output indicative thereof and further including drive means operated in accordance with said output; means individually conditioning said regulating means for operation; a first plurality of timing means on said shaft means individually actuating said conditioning means in sequence; means individually operating said regulating means when said regulating means have been readied for operation by said conditioning means; and a second plurality of timing means on said shaft means individually actuating said operating means in sequence, whereby to supply source energy to said transducers periodically and at selected intervals and whereby to vary said intervals according to the temperature within said furnace in order to minimize overheating of materials introduced therein.

3. A system for heating materials comprising: a furnace structure having a plurality of ports communicating exteriorly thereto; a plurality of heat exchangers connected individually to said ports and reversibly associated with inlet oxidizing gases and outlet exhaust gases; draft reversing means arranged with each of said heat exchangers; a plurality of energy transducers arranged to deliver heat energy to the interior of said furnace, said transducers being individually arranged with said ports; regulating means for each of said transducers controllably supplying source energy thereto; rotatable shaft means external to said furnace; means for periodically and unidirectionally rotating said shaft means at a speed proportional to the temperature within said furnace; first means individually conditioning said regulating means for operation; a first plurality of timing means on said shaft means individually actuating said conditioning means in sequence; second means individually conditioning said regulating means for operation and simultaneously operating said draft reversing means; a second plurality of timing means on said shaft means individually actuating said second conditioning means in sequence; means individually operating said regulating means when said regulating means have been readied for operation by said first and second conditioning means; and a third plurality of timing means on said shaft means individually actuating said operating means in sequence, whereby to supply source of energy to said transducers periodically and at selected intervals and whereby to vary said intervals according to the temperature within said furnace in order to minimize overheating of materials introduced therein.

4. A system for heating materials comprising: a furnace structure having a plurality of ports communicating exteriorly thereto; a plurality of heat exchangers connected individually to said ports and reversibly associated with inlet oxidizing gases and outlet exhaust gases; draft reversing means arranged with each of said heat exchangers; a plurality of energy transducers arranged to deliver heat energy to the interior of said furnace, each of said transducers being arranged with one of said ports; regulating means for each of said transducers controllably supplying source energy thereto and including a solenoidoperated valve; rotatable shaft means external to said furnace; means for periodically and unidirectionally rotating said shaft means at a speed directly proportional to the temperature within said furnace, including temperature responsive means for sensing said temperature and for providing an output indicative thereof and further including drive means operated in accordance with said output; first means individually conditioning said regulating means for operation including a first plurality of electrical switches; a first plurality of timing cams on said shaft means individually actuating said first conditioning means in sequence; second means individually conditioning said regulating means for operation and simultaneously operating said draft reversing means, including a plurality of damper reversing solenoids and a. second plurality of electrical switches; a second plurality of timing cams on said shaft means individually actuating said second conditioning means in sequence; means individually operating said regulating means when said regulating means have been readied for operation by said first and second conditioning means, including a third plurality of electrical switches connected to said solenoidoperated valves through a plurality of relays individually controlled by said first plurality of electrical switches; and a third plurality of timing cams on said shaft means individually actuating said operating means in sequence, whereby to supply source energy to said transducers periodically and at selected intervals and whereby to vary said intervals according to the temperature within said furnace in order to minimize overheating of materials introduced therein.

5. The method of heating a soaking pit to a desired temperature by a plurality of burners, which method is characterized by the steps of: firing the plurality of burners in a predetermined repeated order to establish a heating cycle over a starting period of time; sensing the temperature within said pit; and reducing the period of time required to complete the repeated order of firing in the heating cycle in accordance with the approach of temperature sensed within the pit to said desired temperature.

6. A firing sequencer for a regenerative-type soaking pits comprising: a housing; a plurality of fuel control valves spaced apart from said housing; means for operating said valves; a camshaft rotatably mounted in said housing; drive means for said camshaft; means for increasing the output shaft speed of said drive means as the temperature of said pit is increased; including means sensing the temperature of said pit and means operatively connected to said sensing means for varying the input to said drive means in accordance with changes in said temperature; and a plurality of cams affixed to said camshaft and arranged to operate said valve operating means in sequence.

7. A firing sequencer in combination with a regenerative-type soaking pit and comprising: a housing; a plurality of fuel control valves spaced apart from said housing; a plurality of purge relays arranged within said housing; a plurality of pressure switches individually connected in series with said purge relays; a camshaft rotatably mounted in said housing; drive means for said camshaft; means for increasing the output shaft speed of said drive means as the temperature of said pit is increased and including means sensing the temperature of said pit and means operatively connected to said sensing means for varying the input to said drive means in accordance with changes in said temperature; a first plurality of cams affixed to said camshaft and arranged to operate sequentially said fuel control valves through said pressure switches and through said purge relays, the period over which said sequential operation occurs being reduced in proportion to the reduction in temperature error of said pit; a plurality of damper reversing solenoids adapted to condition said pressure switches; a second plurality of cams affixed to said camshaft and arranged to operate sequentially said damper reversing solenoids; a sequencing relay adapted to condition said purge relays; a purge timer connected in series with said sequencing relay; and a third plurality of cams affixed to said camshaft and arranged to operate said purge timer, whereby to minimize overheating of materials introduced into said pit.

References Cited in the file of this patent UNITED STATES PATENTS 2,095,906 Beck Oct. 12, 1937 2,163,510 Cantrell et al. June 20, 1939 2,429,880 Hays Oct. 28, 1947

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