US2139861A - Regenerative furnace reversing means - Google Patents

Description

Dec. 13, 1938. w. E. SHENK ET AL REGENERATIVE FURNACE REVERSING MEANS Filed Oct. 5, 1955 4 Sheets-Sheet l INVENTORS W/ZL/AMESHEN/n, BY BER/IRDM fFJE/V ATTORNEYS Dec. 13,

1938. w. E. SHENK ET AL REGENERATIVE FURNACE REVERSING MEANS Filed Oct. 5, 1935 4 Sheets-Sheet 2 .OMEQSQ HE 9 INVENTORS VV/Z LIAM Z: JHENA. BE/PNA/PDMLA/PSEM ATTORNEYS Dec. 13, 1938. w. E. SHENK EfAL.

REGENERATIVE FURNACE REVERSING MEANS Filed Oct. 5, 1955 4 Sheets-Sheet 3 VNVENTORS VWLL/AMZ: .JHEN/l.

' ATTORNEYS Dec. 13, 1938. w. EJSHENK ET AL REGENERATIV E FURNACE REVERS'ING MEANS Filed dot. 5, 1955 4 Sheefs-Sheet 4 INVENTORS Patented Dec. 13, 1938 UNITED sures oFFI REGENERATIVEFURNACE REVERSHNG MEANS Application October 5,

12 Claims.

This invention relates to regenerative furnaces and more particularly to a method and means for automatically controlling the operation of the same in response to the thermal conditions attained therein.

The usual regenerative furnace'comprises a horizontally disposed hearth enclosed from the atmosphere and upon which is located the molten metal bath. The metal of the bath is melted and heated to the desired refining temperature by circulating burning gases thereo'ver. It is customary to dispose fuel burners at opposite ends of the furnace and to alternately operate the said burners so that the burning gases pass alternately in opposite directions over the bath. It is further customary to provide means to utilize the sensible heat of the outgoing gases to preheat the air used for supporting combustion. This is accomplished by disposing adjacent each end of the furnace a socalled checker chamber in which are disposed checker brick and through which the outgoing gases are circulated before passing to the stack. The sensible heat in said gases is in large part abstracted by the said checker brick. When the furnace is reversed and the opposite burner ignited, the outgoing gases from the furnace is passed through the opposite checker chamber and air to support combustion is preheated by passing the same through the first checker chamber.

During the operation of the regenerative furnace it is essential for maximum efflciency to maintain the thermal conditions attained within the checker chambers substantially equal. It is also essential to protect the checker brick work from being overheated. In the past it has been customary to reverse the furnace at determined time intervals. In reversing a certain sequence of operations must be follow.ed:--(a) the fuel supply to the ignited burner must be shut off, (1)) the fiow of preheated air interrupted through one checker, (c) the air flow must be applied to the opposite or heated checker chamber and the outgoing gases diverted into the other or cold checker chamber and (d) the opposite burner must be ignited. This sequence of operations is usually performed automatically by means of time controlled relays but means are usually provided for manual operation of the same independently of the time relay at shorter time intervals if desired.

In connection with this time controlled and manually operative reversing means many attempts have been made to provide means to de- 1935, Serial No. 43,786

termine the tnermal conditions within the checker chamber to enable the operator of the furnace to ascertain when it is necessary to reverse the furnace to protect the checker brick in the outgoing checker chamber from overheating or to regulate an unbalanced thermal condition between the two chambers.

Such means as have heretofore been proposed however have failed for one reason or another to give an accurate or as prompt a thermal determination as is desired. Hence, in the operation of regenerative furnace outside of the provision of means to automatically reverse the furnace at determined time intervals, no automatically operative means has been successfully devised to reverse the furnace in response to thermal conditions attained by the checkerbrick work within the checker chambers which ordinarily are subjected to the maximum heating by the gases of combustion passing into the chamber.

One of the objects of the present invention is to provide a means to automatically reverse a regenerative furnace in response totemperature conditions attained by the top checker brick work in the checker chamber. 7

Still another object of this invention is to provide a means for determining the thermal con-- dition of the top checker brick in a checker chamber and to utilize this determination in the automatic regulation and reversing of a regenerative furnace.

Another object is to improve the operating efficiency of a regenerative furnace by the provision of means to automatically reverse the same in response to the thermal conditions, of the top checker brick in the checker chambers superposed upon a. time reversing means, the

combined means effectively maintaining the furnace in a balanced thermal condition throughout operation.

" Other objects and advantages will be apparent" as the invention is more fully disclosed.

In accordance with these objects we have devised a means for determining the temperature attained by the top checker brick in the checker chamber of a regenerative furnace and have devised an electrically operated system and control electrical system also providing means to cut off the fuel supply tothe furnace in the event of failure of the power supply to the system to function, and means to permit manual operation of the furnace reversing means if and when desired.

We .propose to accurately measure and determine the temperatures attained by the top checker brick by means of a radiation sensitive pyrometer device which is sighted through an opening in the checker chamber wall directly upon the checker brick. The top checker brick work is subjected to the maximum heating by the outgoing gases of combustion passing into the checker chamber. We further propose to utilize the temperature measurement obtained by the said pyrometer device as a means for energizing the usual reversing means for the furnace.

In accordance with the present invention we provide means to continuously determine and record the thermal conditions of the top checker brick and to superpose this determination upon a time controlled reversing means, thereby obtaining a system for furnace reversal which is based upon a time-temperature cycle wherein a maximum and minimum time for reversal is provided and the temperature measurement of the checker brick is utilized as a means for reversing within this time cycle in the event the checker brick attains a certain maximum temperature governed by the composition of the brick or a certain minimum governed by the exigencies vnecessary to preserve a balanced thermal condition between the checker chambers.

In the operation of a regenerative furnace it is usual to initiate combustion in one direction and following a, standard time interval, to automatically reverse the furnace. After the expiration of the same time interval the furnace is again automatically reversed and such time controlled reversal is continued throughout the run. As the furnace and charge reach the maximum operating temperature it is frequently necessary to shorten the time of reversal in one or both directions to prevent overheating of the furnace and checker brick work and to equalize or balance the thermal conditions at the two ends of the furnace incident to unequal combustion conditions, periodic evolution of heat energy from bath, or unequal thermal absorption conditions within the checker chambers. This balancing of the thermal conditions at each end of the furnace is difficult to attain by manual operation or by manual operation aided by thermal measuring means disposed in the checker chambers or furnace as heretofore in the art.

By the practice of the present invention the furnace is maintained in perfectly balanced condition throughout a run and the checker brick work protected from overheating at any stage of the run.

Before further disclosure of the present invention reference should be made to the accompanying drawings wherein:----

Fig. 1 is a schematic diagram illustrating the present invention;

Fig. 2 is a schematic diagram illustrating the operation of the same;

Fig. 3 is a piping diagram illustrating the application of the present invention; and

Fig. 4 is a wiring diagram of the present invention.

Referring to Fig. 1, we provide a radiationsensitive means for determining the thermal condition attained by the top checker brick work in the checker chamber, which means comprises a radiation pyrometer device P ---P which is sighted through the top of the checker chamber C C in such position as to be affected by the radiation emitted by the top checker brick D D in the said chamber. In the usual operation of a regenerative furnace the outgoing gases from the furnace F are circulated into the top of the checker chamber 0 C and are conducted to the stacks from the bottom of the said chamber. When the furnace is reversed, the cold air enters the bottom of the chamber and passes from the top of the chamber into the furnace. Hence the top checker brick in the chambers C C are exposed to the maximum heating effect of the outgoing furnace gases and the minimum cooling by the incoming air. The temperature attained by the top checker brick accordingly must be ascertained.

Radiation pyrometers P P are devices heretofore proposed in the art and specifically form no part of the present invention. In its simplest definition it comprises a radiation sensitive element and means to focus radiation emitted from an incandescent surface on the said element. Preferably, we prefer to employ the improved pyrometer device which is disclosed and claimed in our copending application Serial No. 31,740, filed July 16, 1935, entitled Radiation pyrometer device, now issued September 15, 1936, as United States Patent No. 2,054,382.

Said preferred pyrometer device generates an electric current which is relative to the intensity of radiatio falling thereon, which current may be utilizedkenergize mechanism recording the same in values correlated in degrees of temperature.

Heretofore in the art a means for the continuous recording of the electric currents generated by pyrometer P have been devised and we propose to adapt the same to analogous use in the present invention. In the drawing, ig. 1, such a continuous recorder device R has been schematically indicated. The recorder R forming per se no part of the present invention need not be more fully described or illustrated.

The electric current generated in pyrometer P passes to the recorder R wherein it energizes mechanism operating to move recorder arm E which in moving makes a mark or.movement upon a sheet of paper (not shown) thereby forming a permanent record. Recorder R is preferably what is' known as a two point recorder in that it is adapted to alternately indicate and record in response to the current flow of two pyrometers P and P by the provision of means to alternately connect the pyrometer cir'cuits P P to therecording mechanism at determined time intervals. Pyrometer P is located in the opposite checker chamber C in identically the same position as hereinabove described with respect to pyrometer P Recorder arm E as indicated schematically is free to move to the right or left towards high (H) or low (L) temperature measurements and will respond in the same direction irrespective of which pyrometer is connected therewith. It is usual to provide means comprising an adjustable contact arm A to limit the swing of recorder arm E towards H and to provide means energized by the contact of arm E with arm A to energize mechanisms of various sorts. In the present instance arm A is adjustable as a maximum temperature limiting element and we have .utilized the contacting of arm E therewith to energize the 'the checker chambers are equal.

automatically operative reversing means M for the regenerative furnace F.

Reversing means or mechanism M per se forms no part of the present invention and is one heretofore employed in the art in combination with time control means T T which operate to reverse the furnace F automatically at determined time intervals.

In accordance with the present invention as schematically illustrated in Fig. 1, the furnace F will be reversed automatically by means M at determined time intervals regulated by means T T (depending upon which checker chamber C and C is being heated) unless before the expiration of such time interval the temperature recorded by arm E of recorder R exceeds the maximum set by adjustable arm A whereupon arm E contacting with arm A closes an electrical circuit energizing mechanism operating to actuate means M. In this manner burners X and X of furnace F are alternately operated and the direction of incoming preheated air and outgoing gases of combustion correspondingly changed in checker chambers C and C However, we have found.

well as upon the particular period of time.during any one melting operation.

It is seldom that the fuel supply to the two burners is equal; and due to structural differences, it is seldom that the thermal properties of At certain stages in the melting and refining operations the melt will absorb or will evolve heatenergy. Consequently, the sensible heat of the outgoing gases will vary materially and continuously. A balanced condition between the checkers implies that the temperature attained during any one heating up cycle is substantially the same as that attained by the preceding or following checker. Conversely, the temperature to which the checker is cooled during any preheat should approximate the temperature to which the preceding or following checker cools.-

In the normal operation of furnace F, the usual tendency is for the temperature of the outgoing gases to gradually increase as the melting down process proceeds. During the refining operation, however, the temperature of the outgoing gases may suddenly increase to a relatively high figure thereby raising the checker brick temperatures to an unsafe level in a relatively short time interval. Consequently by maintaining a fixed time of periodic reversal during the melting down period the heate checker continually attains a higher temperature than the preceding checker. This is not necessarily serious while the bath' is being melted down unless the fuel supply to the burners or the heat absorbing properties of the checker chambers are markedly out of balance. Where they are out of balance then the thermal conditions within the checker chambers become out of balance and the efficiency of the furnace during this period is markedly lowered. Furthermore, unless the checker chambers are in near thermal balance during the refining operation serious overheating of one of the checkers is In the ordinary operation of the liabl'to result unless exceedingly close watch is kepton the time interval of reversing.

It is therefore usually necessary for the furnace operators to carefully watch for and to correct the conditions leading to such an unbalanced condition during the melting down period because if it extends into the refining period the danger of overheating the checker brick is great.

We have devised therefore a means for regulating the reversal of the furnace on a minimum temperature basis as well as a maximum temperature basis, which minimum temperature is a shifting temperature which is set by the maximum temperature attained by the heating checker during the preceding period. Thus the furnace is reversed first on a maximum time basis which is operative only. when the temperature attained by the outgoing checker does not exceed a predetermined and set maximum, and when.

preceding checker was exceeded within the minimum time limit set. The maximum limit set still operates to positively protect the checker brick from overheating.

Referrin to Fig. 1, we have indicated this shifting temp rature limit as arm B operatively linked with ar E in such manner as to be moved thereby as'ar E shifts to record higher (H) or lower (L) temperatures. By such an arrangement indicated it may be seen that as the temperature recorded by the heating checker increases arm B will be carried forward by the recorder arm E. Duringthe following cycle arm E is free to move backward without changing the position of arm B to record the temperatures in the cooling checker chamber and as this cooler chamber heats up during the following cycle, arm E will approach arm B. Upon contacting with arm B, arm E closes an electrical circuit energizcontact is made before the expiration of a minimum time, means T operates to render inoperative the reversing by arm B and the arm E pushes arm B further along the scale towards H until the minimumtime period has elapsed whereupon the furnace is reversed. The cooled checker then heats similarly and as the melting down operation proceeds arm B is gradually moved to the right towards the maximum limiting temperature set by arm A. Upon the contacting of arm E with arniA thefurnace is reversed irrespective of the time control means T, T T or arm B.

Referring to Fig. 2 we have plotted out on a time-temperature basis the thermal history of the checker chambers C C obtained'by the practice of the present invention. Temperaturesare indicated along the vertical center line and time in minutes are indicated to the right and left of the vertical center line for chambers C and C respectively.

The two point recorder R indicates alternately the temperature of the heating checker and the cooling checker as it is determined by radiation pyrometers P and P We have indicated in Fig. 2 the maximum and minimum temperatures recorded during each cycle in each checker chamv her. This is shown in the drawings'by the elongated double arrow lines l, 2, 3 etc. Referring to arrow i, which indicates the initial temperature of the chambers C and C it will be noted that chamber C is approximately 2100 F. while chamber C is approximately 1980 F. Chamber C is the heating checker and chamber 0 is the cooling checker. At the conclusion of the minimum time interval set up on means T (6 minutes) checker C has heated up to a temperature approximating 2140 F. and as this is in excess of the previous temperature of chamber C the furnace is reversed automatically at the end of this minimum time interval.

Checker C during this minimum time interval has cooled to approximately 1980 F. Maximum time control means T and T in this instance is set for 12 minute reversals. Checker C then proceeds to heat up while checker C proceeds to cool down. Checker C heats up to the same temperature as previously attained by chamber C but requires a time interval of about 10 minutes and the furnace is reversed automatically when recorder arm E contacts with shifting limit arm B. During this time interval the chamber C has cooled down to about 2000? F.

During the next cycle, chamber C attains a temperature approximating 2180 F. during a time interval of about 8 minutes and chamber C cools down to a temperature approximating 1980 F. On reversal chamber C reheats to approximately the same temperature as previously attained by chamber C but requires 10 minutes to do so,while chamber C cools down to about The two checker chambers therefore appear to be thermally out of balance as regards their respective capacities to-heat and cool in the same time intervals Accordingly without the shifting limit feature and minimum time control means of the present invention even an approximate thermal balance therebetween could not be obtained.

Thermal balancebetween the checkers is obtained substantially as indicated in the drawings (Fig. 2). From the drawings, it will be apparent (arrow 4) that furnace reversal occurred at .the end of 12 minutes, the maximum time set. Reversal at the end of this maximum time interval may be due to the fact that the heating checker ature to attain, and as evidenced by the chart,

attained this temperature within a time. interval less than the minimum time interval (6 minutes) and again raised the lower temperature limit to a higher level approximating 2180 F. Reversal occurred at the end of this 6 minute minimum time interval and checker chamber C during this time interval hadcooled only to 2020 F. It required but 6 minutes to heat checker C to a temperature higher than that attained previously in C (2180 F.) and to again raise the lower temperature limit to a higher level. From this point on, each checker chamber heated and cooled to approximately the same temperatures during the same time intervals with substantially uniform raising of the lower temperature limit, until the maximum limiting temperature for reversal (2400 F.) was attained. During the operating time interval the two chambers are heated to and cooled from this maximum temperature, the furnace reversal is at substantially uniform time interval and the thermal conditions of the checkers are substantially equal.

In order to set this minimum or shifting temperature limit as above as well as to prevent too frequent reversals, we provide a minimum time limit for reversal. If the temperature of the heating checker attains or exceeds this limit before the minimum time of reversal has elapsed, the furnace is not permitted to reverse, but instead the temperature limit is increased. Thus the temperature limit will automatically be set at the highest temperature attained by the heating checker within the minimum time providing this temperature is greater than the temperature at which the preceding reversal occurred. The maximum temperature limit set still operates to positively protect the checker brick from overheating.

Referring to Fig. 3, we have indicated schematically the mechanical movements involved in the reversing of the regenerative furnace F. Referring to Fig. 4, we have indicated the wiring diagram operatively connecting the various means of the present invention into a co-operating and automatically operative control means for reversing furnace F upon a time-temperature basis. The following description should be read in connection with Figs. 3 and 4.

In the arrangement indicated in Figs. 3 and 4 checker chamber C is indicated'as the heating chamber and checker chamber C is indicated as the cooling chamber. 'Burner X therefore is ignited and at the conclusion of the determined time interval regulated by time relay device T or upon the contacting of arm E with arm A of recorder device R (Fig. 1) or upon a contacting of arm E with arm B within a time interval shorter than the maximum time interval set by time relay device T but longer than the minimum time interval set upon time relay device T,

it is desired to energize reversing mechanism M- thereby reversing furnace F. As may be hereinafter identified furnace F with burner X ignited is operating at No. 2 end and with burner X ignited is operating at the No. 1 end of the furnace.

' In its simplest definition mechanism M comprises an electrical relaydevicel which upon being energized or de-energized sets into operation a series of electrical circuitsoperating to close and open valves regulating the supply of air and oil to burners X and X and supplying the power to the mechanical means provided to shift r butterfly valve .ll from No. 1 to No. 2 position and vice versa. In the wiring diagram illustrated in Fig. 4 "when the furnace is operating at its.

No. 2 end relay device 1 is de-energized; when theelectric circuit including said relay'device 1 is energized by the time-temperature or manual means hereinabove identifiedthe relay device 1 operates to close an electrical circuit energizing the solenoid valves controlling the supply, of-fuel and air to the burner and hydraulic cylinders 9 and I0 respectively.

In the arrangement illustrated in Figs. 3 and the furnaceis operating at its No. 2 end, the

burner X ignited. Valve V is therefore open and valve V is closed. Assuming relay 1 mechanism M is energized by any of the means hereinabove identified; contact arms 20 are raised to the up position thereby completing an electrical circuit which energizes solenoid actuated valve V shutting off the oil to the ignited burner X At the same time, the valve V is operated to release the air pressure on piston l and as the relay 1 completes its motion valve V is operated to apply air pressure to the opposite side of piston '5, thereby moving hydraulic valve 8 to such a position as to release the hydraulic pressure on cylinder l and to apply it to cylinder 9 thereby moving butterfly valve H over to its No. 1 position.

As switch arm 12 moves from rest position as shown, switch i4 is opened breaking the electrical circuit to oil valve V and switch 15 closes completing the circuit to air valve V Valve V then operates to apply atomizing air to burner X When switch arm 12 has traveled to the No. 1

7 position of butterfly valve ll, it contacts with switch it completing the circuit to oil valve V through pressure switch 5. Switch closes automatically when the air pressure in the burner X accumulates to a desired pressure.

Switch arm l2 also contacts in its No. l position with switch ll to open said switch, thereby breaking the circuit to air valve V which operates to turn off atomizing air to burner X Bressure 5 then is released automatically by the fall in pressureof the atomizing air in burner X This completes the reversing operation.

To operate relay l, we have provided for optionaloperation by manual means, time controlled means and temperature controlled means.

Manual operation of relay 1 is obtained by means of momentary contact push buttons H and H The closing of either push button H or H will direct current from alternating current source (A. C.) through manually operated switch S and magnetic switch S provided with a no-voltage release safety means common in the art, into .relay 1 of reversing mechanism M, thereby closing the above described series of electrical circuits energizing and tie-energizing the various valves identified. Push button 1 controls the No. 1 side of the furnace F including burner X andpush button 2 controls the No. 2

side of the furnace F including burner X The motor circuits 2! and 22 of time controlled relays T and '1 respectively are energized from the power supply passing through relay 1 and pressure switches 5 and 6 respectively. With time relay T in operation pressure switch 6 is normally closed substantially as indicated, and relay mechanism of 'I' is operating through a selected period of time to close contact 24 thereof at the conclusion of said determined time interval.

Upon the closing of contact 24 the power supply circuit to relay 1 is closed thereby energizing relay 1 and setting in operation the closing and opening of the various circuits hereinabove described for reversing the furnace.

The closing of contact 24 operates to perform the same sequence of operations as does the closing manually operative push button H The temperature means for reversing the furnace consists of two parts; (one) means for' reversing on maximum temperature to prevent overheating of the refractories in chambers C and C and (two) a means for reversing on a shifting minimum temperature to maintain a balanced condition of temperature between the checker chambers C and C. These two means are controlled throughcontact arms A, A and B.

Referring to the maximum temperature means, as hereinabove described in connection with Fig. 2 recorder R is provided with adjustable contact arm A; The usual two point recorder is provided with two such contacts A which are identified in Fig. 4 as contacts A and A each acting separately as a maximum temperature limit for checkers C and C respectively.

With the furnace F operating on No. 2 end with burner X ignited, contact arm A is electrically connected to relay 1 to energize the relay to set in motion the above described sequence of operations to reverse the furnace F to No. 1 end, and contact arm A is electrically in circuit to operate to de-energize relay 1 when the maximum temperature is attained in checker. C

A performs the same function as does push buttom H and contact 26 of time relay T as has been hereinabove described.

In connection with the operation of push button -means H contact 28 and arm A, we provide secontacts H 24 or A will release relay 3 by deenergizing the same at the same time that the circuit to oil valve V is interrupted by relay 1. When the reversing operation is completed and oil valve V is energized selector relay 2 is also energized and operates to hold closed its contacts thereby connecting push button H and arm A in the control circuit to relay 1.

With relay 3 energized, for example, a closing of push button H or of A accidentally would not operate in the control circuit to energize relay 1. Relay 1 can only be energized by completing the circuit through a closing of push button H arm A or contact 2d.

Referring to the minimum time means B, only one time relay T is provided to control the opera tion of arm B from either end of the furnace.

In association with arm B and relay' T we provide relays 4, 5 and 6. Relays 4 and 5 determine the position of arm B through energize.- tion of reversible motor 25., As shown 25a operates to move arm B to hi her temperatures in response to the contacting of arm B before the expiration of the period of time set on .relay T has transferred arm B from the circuit of motor 25a to the controlcircuit of relay 1 running from A or A as determined by the position of relay 6.

As shown relay 6 connects the circuit of arm B to the circuit of push button H and arm A Upon closing of this contact B after the time relay T through relay 6 has connected arm B into As shown furnace F is operating on No. 2 end,

relay T is therefore in operation, and if T operates to reverse the furnace by closing contact 24,

it also opens contact 26 which breaks the control circuit of relay 4 causing contacts 28 thereof to close completing circuit to motor 25b, at the same time energizing the upper coil of relay which 'and to de-energize the upper coil of relay 5 and to energize the lower coil of relay 5, thereby transferring arm B back in to the circuit with motor 25a. Motor 25a then operates to move arm B back up to the maximum temperature attained within the time limit set on T.

Relay 6 is energized and de-energized from the circuit of oil valve V Hence for operation from No. 2' end of furnace F, it is in the de-energized position as shown.

In its present position the lower two of contacts 30 of relay 6 connects the motor circuit of time relay '1' to the circuit of oil valve V and when the time limit set on T expires the arm B will be connected through T and relay 6 and selector relay 3 to the control circuit of relay 1. Arm B then is able to reverse the furnace F from end No. 2 to end No. 1 in the same manner as push button H contact 2d of relay T and arm. A of recorder R.

The specific means hereinabove described whereby shifting limiting temperature arm B is rendered operative is the subject matter of a separate patent application filed by William E. Shenk bearing Serial No. 87,304, filed June 25, 1936.

Manually operated valves V V and V are provided in the oil line and airlines respectively I as a main volume control and as an'emergency shut-off means.

Having broadly and specifically described the present invention it is apparent that many modifications and adaptations may be made therein without departing essentially from the nature and scope thereof and all such modifications and departures are contemplated as may fall within the scope of the following claims.

What we claim is:

1. The method of operating a regenerative furnace provided with a time controlled automatic reversing means, which comprises providing means to determine and continuously record the thermal conditions of the top checker brick work in the checker chambers associated with said furnace, and providing means energized by said recording means to actuate said automatic reversing means whenever the thermal conditions of the top checker brick work approximate a determined maximum safe operating temperature and when during any one heating cycle the temperatures attained by thesaid top checker brick work in the heating checker approximate the maximum temperature attained in the previously heated checker within a time interval shorter than that determined by said time controlled reversing means but at least as long as a determined minimum time interval.

2. Ina regenerative furnace including checker chambers, means to determine the thermal conditions of the top checker brick work in said chambers which comprises a radiation pyrometer device sighted through the chamber walls upon the upper surface of said top checker brick work and aisasci a recorder device operatively connected therewith to continuously record the temperatures of said surfaces, means to automatically reverse the said furnace at determined time intervals and means energized by said recorder device to automatically reverse the said furnace during each heating cycle when the temperature attained by the top brick work in the heating checker approximates the maximum temperature attained by the preceding heating checker within or after the expiration of a minimum time interval. and means energized by said recorder device to automatically reverse the said furnace when the temperature of the said brick work in either checker approx!- mates a determined maximum.

3. The method of operating a regenerative furnace provided with a hearth enclosed from the atmosphere, fuel burners at opposite ends of said hearth, a checker chamber at each opposite end of the hearth and means to pass the gases of combustion and the air to support combustion alternately through opposite checker chambers, which comprises heating the furnace by alternately firing said burners limiting the heating by each burner to a determined maximum time interval, measuring the temperatures attained by the checker brick work subjected to the maximum heating by said gases of combustion during each heating cycle and in each chamber, reversing the firing of said burners and the circulation of said gases. of combustion and air through said chambers whenever the temperature attained during any heating cycle approximates a determined maximum safe temperature for said brick work irrespective of the expiration of said determined time interval, and reversing the said burners, gases and air also when the'temperature attained by the said brick work in the heating chamber after the expiration of a minimum time interval equals or exceeds the maximum temperature attained by the brick work of the opposite chamber during the preceding heating cycle.

4. In combination, a'regenerative furnace having a hearth enclosed from the atmosphere, a fuel burner and a checker chamber at each end of the furnace, means to pass the air to support combustion through one checker chamber into the furnace and the gases of combustion out of the furnace through the opposite checker chamber, means to alternately ignite said burners and to reverse the circulation of said air and gases at determined time intervals, means to determine the thermal conditions attained by the top checkignite the opposite burner whenever the temperature of said top checker brick work approximates a maximum safe operating temperature irrespective of said determined time interval, means energized by said thermal determining means independently of the said maximum safe operating temperature reversing means'to reverse the fiow of said air and gases and to shut off the ignited burner and to ignite the said opposite burner whenever the maximum temperature attained by said top checker brick equals or exceeds the temperature attained by the top checker brick in the opposite checker chamber during its previous heating cycle within a minimum time interval or after the expiration of said minimum time interval and before the elapse of said determined time interval.

aiaasci j 5. Means for controlling the operation of a regenerative furnace provided with fuel burners at opposite ends, checker chambers at opposite ends and means to reverse the firing of said burners and the direction of circulation of gases through said chambers at determined time intervals, said termined maximum, and means actuated by said recording means to actuate said reversing means when the temperature being recorded during any heating cycle approximates or exceeds the maximum temperature recorded during the previous heating cycle at or after the expiration of a minimum time interval.

6. In the combination of claim 5, said last mentioned means comprising a shiftable contact lever operatively connected with the said recording means to be forwardly moved thereby to the maximum temperature attained by the heating chamber during any one heating cycle, the said recording means contacting therewith on the next heating cycle operating to close an electrical circuit energizing said reversing means, and time controlled means rendering inoperative said electrical circuit during a determined time interval shorter than the said first mentioned determined time interval.

7. In a regenerative furnace, a control means therefor comprising means to automatically reverse the furnace at determined maximum time intervals to obtain alternate heating and cooling cycles for the checker chambers associated with said furnace, means including a radiation sensitive device to continuously measure and record the thermal condition of the top checker brick work in-each said checker chamber, means actuated by said thermal recording means to energize said reversing means when the tempera-' ture of the brick work in the heating checker during each heating cycle approximates a determined maximum safe operating temperature and means actuated by said thermal recording means to energize said reversing means when the tem perature of the brick work in the heating checker approximates the maximum temperature attained by the brick work of the preceding heating checker after the expiration of a determined time interval shorter than the determined time interval of said automatic reversing means.

8. In a regenerative furnace, a control means therefor comprising means to automatically reverse the furnace at determined maximum time intervals to obtain alternating heating cycles for the checker chambers associated with said furnace, and thermally responsive means disposed in each checker chamber of the said furnace to energize said automatic reversing means to reverse said furnace during any onelheating cycle when the temperature attained by the top checker brick work of the heating checker chamber approximates a determined maximum safe operating temperature for said brick work or when the temperature attained by said brick work equals or exceeds the highest temperature attained by the brick work of the preceding heating checker chamber after the expiration of a minimum time interval whichever occurs first.

9. The method of operating a regenerative furnace which comprises reversing the heating of the furnace at a determined time interval or at a determined maximum temperature whichever occurs first during any one heating cycle, and reversing the heating of the said furnace at and after the expiration of a time interval shorter than the said determined time interval when the temperature attained by the heating checker approximates or exceeds themaximum temperature attained by the previously heated checker.

10. The method of operating a regenerative furnace whichcomprises reversing the heating of the furnace at a determined maximum time interval or at a determined maximum. temperature attained by the brick work of the heating checker chamber of the furnace, or after the expiration of a minimum time interval when the temperature attained by the heating checker equals or exceeds the temperature attained by the preceding heating checker, Whichever occurs first.

11. The method of operating a regenerative furnace which comprises reversing the heating of the furnace at a determined maximum time interval or at a determined maximum temperature attained by the brick work of the heating checker chamber of the furnace whichever occurs first during any one heating cycle, said maximum tem.- perature being representative of the maximum safe operating temperature for said brick' work, or reversing the said furnace at a temperature attained by the said brick Work after the expiration of a minimum time interval, said tempera ture corresponding to the maximum temperature attained by the opposite checker during the preceding heating cycle, if said temperature should occur first.

12. The method of operating a regenerative furnace provided with time controlled means to automatically reverse the firing of the furnace at determined time intervals which comprises continuously measuring andrecording the tempera ture attained by the heating brick work in the heatin checker associated with said furnace, and reversing the furnace during each heating cycle whenever the temperature attained by said brick work approximates a determined maximum safe operating temperature and whenever the temperature attained by said brick work approxirnates the maximum temperature attained by the opposite checker chamber during the preceding heating cycle at or after the expiration of a minimum time interval whichever occurs first.

WILLIAM E. SHENK. BERNARD

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