US1802001A - Furnace - Google Patents

Description

F. w. BROOKE 1,802,001

FURNACE April 21, 1931.

Filed Nov. 16, 1928 3 Sheets-Sheet lw J L Wm INVENTOR April 21, 1931. F. w. BROOKE 1,802,001

FURNAC E Filed Nov. 16, 1928 3 Sheets-Sheet 2 INVENTOR QQ m iw wg Apnl 21, 1931. F. w. BROOKE 1,802,001

FURNACE Filed Nov. 16, 1928 3 Sheets-Sheet 3 I700-- I600- 27 C e f CRITICAL EMPHMMRE I400 g l -l200- ]Z E; o;|000- w a:

800- 3 g a600- E k 400- 5.

9 l I 1 I 4 a :2 I6 20 24 2a 52 as 40 44 4Q T/ME //v HouRs.

in F a Fatented Apr. 21, 1931 UNITED STATES PATENT OFFICE FRANK W. BROOKE, OF PITTSBURGH; PENNSYLVANIA, ASSIGNOR TO' WILLIAM SWIN- DELL & BROTHERS, OF PITTSBURGH, PENNSYLVANIA, CORIPQRAHION 0F PENN- SYLVANIA FURNACE Application filed November 16, 1928. Serial No. 319,825.

The present invention relates broadly to the art of furnaces and more particularly to furnaces of the so-called annealing type provided with a car bottom upon which the work being annealed is supported within the furnace and by which movement of such work into and out of the furnace is simplified and facilitated.

In the heat treating of metals-there are certain temperatures or temperature ranges, frequently referred to as critical temperatures, determined largely by the carbon content of the metal undergoing treatment, through which the temperature conditions to which the metal is subjected must be accurately controlled This is particularly true during the cooling down of the metal after treatment when varying rates of cooling are particularly desirable. Much time is lost by cooling at the natural rate of the furnace. Ordinarily as long or even a longer period] has been required for the cooling down than that required for the heating up of the metal.

The requirements of temperature control together with the necessity of maintaining a controllable atmosphere, which may be reducing, neutral or oxidizing, or an atmosphere to produce a particular reaction, has necessitated keeping a given charge or batch of work within a furnace throughout both the heating up and the cooling down period, and this in turn has obviously been one of the principal factors determining the capacity or output of a given furnace.

The present invention has for one of its objects the provision of a furnace of such characteristics that the cooling down period may be shortened considerably, and definitely controlled, thereby enabling a given furnace to treat a greater amount of metal in a given period of time, and enabling the obtaining of definite characteristics in the metal.

Another object of the invention is to provide a furnace of the general character referred to which is capable of maintaining a controllable atmosphere in contact with the metal undergoing treatment during the cooling down period.

In the accompanying drawings, I have shown for purposes of illustration only, a

preferred embodiment of the present invention, it being understood that changes in the construction, operation and arrangement of the parts therein illustrated may be made without departing from the spirit of my invention or the scope of my broader claims.

In the drawings Figure 1 is a transverse sectional view through a furnace constructed in accordance with the present invention;

Figure 2 is a partial longitudinal sectional view through the furnace construction shown in Figure 1;

Figure 3 is a side elevational view of a portion of the furnace shown in Figure 1;

Figure 4 is a detail sectional view on an enlarged scale illustrating part of the elec-,

trical connections for the furnace;

Figure 5 is a diagrammatic illustration of typical temperature conditions obtainable in accordance with the present invention; and

Figure 6 is a detail plan View, partly broken away, illustrating one type of heat- 'ing means which may be utilized in a furnace constructed in accordance with my invention.

In carrying out the present invention there may be provided a furnace herein illustrated more or less diagrammatically, in accordance with the accepted engineering principles, having side walls 2 and a top wall 3.

For supporting the work being treated, there is provided a movable bottom 4, preferably in the form of a car adapted to be moved at will into and out of the furnace. As is customary in furnaces of this type, the car may be provided with any arrangement of supporting wheels 5 cooperating with tracks 6.

' For effectively sealing the treating chamber 7 a ainst the infiltration of air during the operation of the furnace, the car 4 is preferably provided on each edge thereof with a channel 8 containing sand or other sealing material. Cooperating with the sealing material are plates 9 carried by the side walls and so arranged as to automatically seal the sides of the car during movement thereof into the furnace.

At the rear of the furnace there is provided a movable sealing member 10 preferably in terbalanced by a counterweight 13 on the opposite side of the pivotal mounting. Co-

operating with the sealing plate and counterweight is a trigger 14 so located as to be engaged by a projection 15 on the car during its movement into the furnace. As will be apparent from Figure 2 of the drawings, the engagement of the projection 15 with the trigger 14 swings the sealing plate 11 in a clockwise direction about the pivotal mounting 12 and thereby brings the sealing plate into the sealing material in the trough 16. Upon movement of the car out of the furnace the counterweight 13 serves to swing the sealing plate 11 in the opposite direction so as not to interfere with the free movement of the car.

In the front of the furnace is a vertically movable door 17 provided on its lower edge with flanges 18 adapted when the door is in position to close the furnace to cooperate with the sealing material in a trough 19 projecting outwardly from the car 4. At its upper edge the door 17 is formed with a sealing plate 20 adapted to cooperate with sealing material in a trough 21 extending transversely of the furnace roof. For sealing the side edges of the door the the side walls 20 of the furnace are formed at their front ends with sealing faces 22 adapted to cooperate with the back face of the door, the parts hein forced tightly into engagement by suitab e clamping means 23.

By reason of the construction just described, it will be apparent that the chamber 7 is completely sealed against the ingress of air, thereby ermitting a non-oxidizing atmosphere to e maintained within the furnace during any complete cycle of operations.

The present invention is adapted for use with furnaces heated, either by gaseous or liquid fuel, by electricity, or in any other manner common to the annealing industry. In the illustrated embodiment I have shown electrical heating units 24 on opposite sides of the furnace, although it will be understood that any other arrangement of units on the side walls, on the roof, or in the car itself, ma be utilized as desired.

- Kmea-ns of such units the work supported on t e car 4 is raised to the desired temperature, the application of heat being controlled in such manner as to insure the desired results, particularly at such times as the work is passing throu h critical temperatures of the character re erred to.

Heretofore it has been customary in the art of annealin furnace operation to cool the charge by etting air into the furnace chamber, or by the use of alloy ducts. The former practice destro s the desirable atmosphere, and the latter is expensive and takes up valuable room in the furnace chamber.

In accordance with the present invention, provision is made for accelerating, decelerating or otherwise controlling the cooling down period while maintaining a controllable atmosphere within the furnace. Such acceleration is obtained by the provision of a series of fines 25 and 26, preferably formed in the roof of the furnace and extending transversely thereof throughout a complete dimension of the furnace; in the illustrated embodiment from side to side thereof.

All of the fiues 25 are adapted to receive at will a supply of cooling medium through suitable header 27 having individual connections 28 to the flues whereby a cooling me dium may be passed through theflues from left to right as illustrated in Figure 1. The lines 26 are similarly connected to a common header 29 through connections 30 whereby a cooling fluid can be passed through them from right to left as viewed in Figure 1.

In order to insure against any induced circulation through the fiues during the heating up operation, they are preferably so formed that the opposite ends thereof are in a common horizontal plane. In addition to this, the discharge end of each of the flues is provided with an extension 31 terminating in the plane of the headers 27 and 29, as clearly apparent from Figure 1 so that the point of ingress and the point of egress of any circulating medium are in a common horizontal plane.

By reason of this construction, at all times except those during which a draft is produced by the actual admission of a cooling fluid, the various fines and their connections constitute in effect dead air spaces not serving to produce any cooling or non-uniform heat abstracting function. By the division of lines into two series in which alternate flues have a flow therethrough in the same direction while intermediate flues havaa flow in the reverse direction, a substantially uniform cooling action may be exerted on the entire annealing chamber. In actual practice, the supply of cooling medium may be varied during the existence of critical temperatures in the annealing chamber, to thereby give the results desired throughout the entire cooling down operation.

By reason of the fact that the fiues are entirely isolated from the chamber itself, coupled with the complete sealing of the car against the infiltration of air, it is possible to maintain a non-oxidizing or other given atmosphere within the chamber at all times.

For decelerating or otherwise controlling the cooling of the furnace and thecharge therein, I may provide one or more separate heatin units 24' which ma conveniently be locate adjacent the roof 0 the furnace, and of such order as tobe effective for substantially offsetting the natural heat loss from the furnace by reason of radiation. With such a construction, I may at any time energize the unit or units 24 and thereby hold the furnace for a given period of time at substantially a given temperature below that effected by the main heating units.

In Figure 5 of the drawings I have illustrated graphically temperature conditions within the furnace when Operated in accordance with the present invention. In this figure the ordinates represent degrees of temperature Fahrenheit while the abscissae represent time in hours. The portion of the curve a?) indicates the heating up period of the furnaces. The portion 60 of the curve represents the soaking period. The following portion 0d indicates the conditions within the furnace during artificial cooling by the passage of a cooling medium through the fines provided for that purpose, the difference between the rate of artificial cooling thus obtained and the natural cooling heretofore obtained in operation of annealing furnaces is illustrated by a comparison of the portion 0d of the curve with the dotted line curve indicated adjacentthereto.

The portion abcd of the curve thus described may be considered as comprising a typical normalizing treatment in the furnace constructed in accordance with the present invention.

The portion ole of the curve indicates the conditions within the furnaceduring such particular characteristics of the metal undergoing treatment, to increase the temperature conditions thereof, and to cause it to again pass through the recalescence zone. By the use of the unit or units 24' the charge may be held for any desired interval at a fixed temperature, this interval being indicatedby the portion efof the curve. Thereafter, the rate 'of cooling may be so controlled as to produce a condition either corresponding to an acceleration of the natural rate of cooling or a deceleration of thenatural rate of cooling. The portion fg of the curve indicates such a period in which the cooling provides an average'drop in temperature throughout the entire interval substantially equal to the natural rate of cooling but differing from a natural cooling condition in that each successive increment of time represents a definite decrease in temperature corresponding to the decrease during the preceding increment.

The portions git and hi respectively designate succeeding cooling periods, in. which the cooling has been further accelerated in accordance with the present invention.

The entire portion of the curve (Zefghz' may be considered as illustrating annealing c011- ditions typical of a furnace operated in accordance with my invention. V It will be apparent to those skilled in the art that the curve herein referred-to is illustrative only of conditions which may be obvariable rate of cooling is extremely desirable.

As a matter of'operating convenience, connections may be established to the heating units 24 through the medium of detachable connectors 32 and 32, preferably located respectively adjacent the front of the furnace and movable upwardly through openings 35 in the floor 36, and below such floor. Both terminals of theseconnections are outside any influence of heat from the furnace and are therefore not subject to deterioration. These openings are preferably formed partly or entirely in doors 37 pivotally mounted in the floor, in such manner that upon detaching any of the connectors 32 they immediately slide downwardly into the chamber 38, but are readily accessible upon opening the door 37.

I have found in actual practice that any metallic scale or similar foreign matter which may come into contact with the heating unlts in a car such as car 4 only causes short circuiting trouble when there is a considerable electric potential between the portions of the resistor that are bridged by the foreign matter. Such short circuiting has been part-icularly objectionable where it has occurred between a portion of a loop and a portion of the return conductor in such manner as to cut out the major portion of any given unit. As illustrated in Figure 6 of the drawings, I provide a car 4 with a series of units 40 each comprising successive convolutions 41, substantially the length thereof. Each unit has a lead-in conductor 42 and a return conductor 43, the return conductor being characterized by its location beneath the floor of the car in such manner as to make it impossible for any scale or any foreign matter dropping onto the car to bridge any portion of the resistor proper and the return conductor. With such a construction, it may be assumed that the voltage drop across any given convo1u tion is 2 to5 volts. It will be apparent that in short circuiting,under such conditions, of any given convolution or convolutions will not seriously interfere with the operation of the furnace. In certain cases this makes it unnecessaryto decrease the heating efliciency of the units by covering them with sheets or blocks of protective material, although such protective coverings may be utilized where a uniform supporting surface isdesirable, or where an indirect heating is of advantage.

2. In a furnace having a heating chamber, a roof for said chamber havmg parallel passages formed therein and extending transversely the full width of the chamber, said passages having their opposite termini disposed in substantially the same horizontal plane, and means for delivering a cooling medium in opposite directions to alternate passages.

3. In a furnace having a heating chamber, a roof for said chamber having a plurality of parallel passages formed therein and extendin throughout substantially one dimension 0 the chamber, saidpassages having their opposite termini disposed in substantially the same horizontal plane, and means for delivering a cooling medium at opposite ends of adjacent passages.

4. In a furnace, a heating chamber, a movable work supporting means in said chamber, means for sealing said work supporting means against air infiltration when in position within the chamber, a roof for said chamber having substantially parallel passages formed therein out of communication with the chamber, and means for delivering a cooling medium at opposite ends of adjacent passages.

5. In a furnace, a heating chamber, a roof for said chamber having parallel passages formed therein out of communication with the chamber, a header adjacent each side of the furnace common to alternate passages, and a cooling fluid connection from each passage to one of said headers.

6. In a furnace, a heating chamber, a roof for said chamber having parallel passages formed therein out of communication with the chamber, a header adjacent each side of the furnace common to alternate passages, and a cooling fluid connection from each passage to one of said headers, each of said passages having a discharge extension terminating in substantially the plane of the air supplly thereto.

7. n a furnace, a roof having parallel cooling flues formed therein with their inlet and outlet ends in substantially the same horizontal plane, and means for supplying a cooling medium in opposite directions to alternate flues.

8. In a furnace, a roof having cooling flues formed therein extending entirely across the furnace with their inlet and outlet ends in substantially the same horizontal plane, and means for supplying cooling medium to said fines and causing the cooling medium in ad- In hand.

y FRANK W. BROOKE.

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