US1893847A - Method of and means for controlling temperature - Google Patents

Description

5am. l0, w33. e. L.. Simpsons METHOD 0F AND MEANS FOR CONTROLLING TEMPERATURE Filed June l. 1951 '4 Sheets-Sheet 1 hmmag aan. m, i933.

G. l.. SIMPSON METHOD OF AND MEANS FOR CONlfROLLING TEMPERATURE Filed June l. 1931 4 Sheets-Sheet 2 gmc/nio@ Bane w, E933. G. n... slMPsoN lg? METHOD oF AND MEANS FOR CONTROLLING TEMPERATURE Filed June 1. 1931 4 Sheets-Sheet 3 @sorge L 515m )7.50m

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METHOD 0F AND MEANS FOR CONTROLLING TEMPERATURE n Filed .June 1, 1931 4 sheets-sheet 4 WJQMM ZUN- GEORGE I.. SIMPSON, or oo RAOPOLIs, PENNSYLVANIA, AssIGNonro PITTSBURGH RESEARCH CORPORATION, OF

PITTSBURGH, `IEINNSYI-IV'ANIA METHOD :MEANS FOR 'CONTROI-LING TEMPERATURE Application ld June 1,

This invention relates to the art of;heat treating metals and the like. The invention includes both an improved method of heat treating thin sheets, more particularly steel sheets, and automatic means for regulating the temperatureA of a furnace in accordance with such method.

In the annealing of metal sheets and coiled strips, it hasbeen found in practice that if the heat is turned on the furnace and the temperature raised too rapidly, warpage of the sheets or strips and burning of the edges thereof often occurs. y

While, of course, these undesirable results can be avoided by raising the heat -very slowly, it is obvious that, for the sake of economy,

efliciency and rapid production, it is desirable to heat the furnace up just as quickly as possible' and run it at as high a temperature as can be employed without damage to the charge.

I have discovered that the important factor in this connection is not so much the actual temperature or rate of rise of temperature of l the furnace itself as it is the difference in temperature between the edges and the center of the charge.

I have found that objectionable warpage and burning of the edges of the sheets can be avoided by so regulating the heat input to the furnace that the temperature difference or gradient between the edges and center of the charge may approach but shall never exceed a certain predetermined maximum. In the case of ordinary steels and other metals of relatively high heat conductivity,

the temperature difference or gradient be-` tween the outside and the center of the charge is not so important as in the case ofhigh silicon sheets, because the thermal conductivity of the latter is so low that heat is not readily transferred from one part of the charge to the other and consequently,' too rapid rise intemperature around the e ges of the charge is very apt to result in burning and warpage.

I have also found that in the earlier stages of a heat, whilecthe charge is relatively cool, 'the permissible temperature differencp or gradient may be much higher, without damaging the charge,.than itmay be durlng the 1931. Y lSerial No. 541,451. 4

ture has been reached.

In carrying out my improved method in a manually controlled furnace, I employ a pair of pyrometers operated by thermocouples or other temperature responsive devices, located one at the edge and one nearthe center of the charge, and so regulate the supply of energy to the furnace that the difference in temperaturf between the inner and outer portions of the charge, as indicated by these pyrometers, does not exceed a predetermined amount, bearing in mind that the'permiss'ible temperature difference becomes less and less as the furnace heats up.

As regards automatic temperature regulating apparatus for performing the above described method, the primary object of the invention lis the provision of means for controlling the rate of heat input to a furnace in such a way that a predetermined temperature difference or gradient between separated points'of the charge, such as the edge and center thereof, will be maintained but not Y exceeded.

y A' further object is' to provide automatic means for progressively reducing the permissible temperature difference or gradient as the temperature of the charge increases.

While .capable of application with either fuel fired or electrically heated furnaces, my improved automatic controlling apparatus i will be illustrated and described as applied to the latter type. Also, while my improved automatic controlling apparatus is particularly useful in connection with the annealing of metal sheets and the like, it,ma y, of course, be l employed generally in connection with furnaces or heated chambers of othervtypeS.

' In carrying-out this part of the invention, I employ, as in the manual methodtwo thermocouples or other heat responsive deinces located at separated points, and I control the heat input to the furnace by the differentiall tion of the other two devices in accordance with the act-ual temperature existing in the furnace.

In order that the invention may be readily understood, reference is had to the accompanying drawings, forming part of this specification, and in which I have illustrated several examples of different ways in which the principles of the invention may be carried out, the drawings showing the invention as applied' to an electrically heated furnace. In these drawings:

Fig. 1 is a vertical sectional view through an annealing furnace, showing temperature responsive devices disposed therein in accordance with the invention;

Fig. 2 is a circuit diagram conventionally showing the furnace and temperature responsive devices as illustrated in Fig. 1, and also showin g the automatic controlling means actuated by said devices;

Fig. 3 is a diagram similar to Fig. 2, but showing," in addition, manual means by which any desired predetermined temperature gradient may be selected, and also showing a third temperature responsive device for automatically reducing such gradient as the temperature of the furnace increases;

Fig. 4 is a similar diagram showing a somewhat ditferent method by which the third temperature responsive device serves to modif v the control exerted by the other two devices, and also illustrating a thermionic amplifier for increasing the sensitiveness of the control system and Y Fig. 5 is a conventional diagram illustrating in section a furnace such as shown in Fig; 1 and also showing still another method by which the differential. action of the two temperature responsive devices may be caused to cont-rol the heat input.

Referring to Fig. 1, 1 designates a con ventional annealing furnacev of the hood type having on its inner walls the usual orr any suitable electric heating elements or ribbons 2. On the base or hearth 1EL of this furnace rests the charge 3 which may be a stack of steel sheets or the like.

Referring to Fig. 2, the heating elements 2 are connected through leads 4, power transformer 5, automatic switch 6. and leads 7 with lthe power supply line 8. The automatic switch 6, commonly known as a contacter, is operated bymeans of asolenoid 9, from which extend conductors 10 to the contacts of another automatic switch 11, operated by means of a solenoid 19. The switch 11 and solenoid 19 constitute a relay or auxiliary contactor.

The `upper switch blade 11 is connected by..V

meansof wire'12 with one side of the power line and through a resistance 13 to a wire 14` which extends from lone end of the solenoid lwinding 19 to a galvanometer contact 16, hereinafter more fully described. Associated withthe contact 16 is a contact 15, and

this contact is connected by means of wires 7 and 18 with the other side of the solenoid Another pair of contacts 20 and 21 are disposed opposite the contacts 15 and 16, the contact 2O being connected with the wire 17 and the contact 21 being connected by a wire 22 with the other side of the power line and by wire 23 with the lower switch blade 11.

In order to maintain the solenoid 19 energized, a third switch blade 24 is provided, and this is connected by means of a wire 26 with the wire 22. A wire 25 also connects the contact of the switch blade 24 with the wire 18.

The control apparatus illustrated embodles a pyrometer or galvanometer 28 of the serves to close the circuit between the con-v tacts 15 and 16 on the one hand and the contacts 20' and 21 on the other hand, in accordance with its position. The movable coil of this galvanometer is connected by wires 29, 30 and 31, with the two temperature responsive devices or thermocouples 32 and 33. One of these thermocouples such as 32 is placed adjacent the center of the charge 3 and the other, such as 33, is placed adjacent the edge of such charge, as clearly shown in the drawings.

From an inspection of Fig. 1, it will be seen that I lead the wires 29, 30 and 31 into the furnace through specially formed passages in the base or hearth 1a. Thus the use of the thermocouples 32 and 33 does not interfere with the free removal of the furnace hood.

As illustrated in Fig. 2, the positive sides of the two thermocouples are connected together by wire 30 and the negative sides are connected to wires 29 and 31 leading to the galvanometer or pyrometer, the thermocouples being thius opposed to each other.

The operation of the control apparatus, asshown in Figs. 1 and 2, will now be briefly described. Normally, when the #furnace is cold, the galvanometer arm is in its left hand that the solenoid 19 picks un its armature and closesv the switch, a holding circuit is established through'the solenoid 19 by way of wire 25, switch 24, and wire 26, independent of the contacts 20 and 21, so that thearm 27 may move awayfrom these contacts without affecting the relay. Closure of the switch blades 11 establishes a circuit of wires 12, 10, 22 and 23, through solenoid 9 of the main contacter which thereupon closes and sup# plies power to the heating element 2 of the furnace.

As the furnace heats up, it is obvious that the outer portions or edges of the charge, being nearer the heating elements, will become hot before the temperature of the center of the charge has 'risen to any appreciable eX- tent. Therefore, the thermocouple 33 will generate an electromotive force'much greater than that generated by the thermocouple 32, and, being connected in opposition, the thermocouple 33 will predominate and will cause a current to flow over the wires 30, 31, and 29, through the coil of the galvanometer, the direction of this current being such as to cause the pointer or arm 27 to move toward the right. When the difference in temperature to which the thermocouples 32 and 33 are subjected at the center and edge of the charge, res etively, reaches a predetermined amount, tiie current flowing through the Wires 29 will be suiicient to move the arm or pointer 27 over against the contacts 15 and 16, as shown in dotted lines. When these contacts are engaged by the arm, a circuit including these `contacts .and the wires 14, 17

and 18, and the coil 19, is closed, thus completely short circuitingl the coil 19 and depriving it of current. Thereupon, the switch blades 11 dropv away from their contacts, as

shown in dotted lines, thus deenergizing' the solenoid 9 and opening the main contactor switch, cutting power olf from the furnace.l

Power will thus remain cut olf until either the outer portion of the charge has cooled down or the inner portion has heated upto such an extent that the resultant current, due to the dilferential action of the thermocouples, is insufficient to keep the arm 27 away from the contacts 20 and 21. This arm, being biased toward these contacts, therefore comes into engagement with them again, thus again causing the rela 19 to become energized and power to be again supplied to the furnace.

' From the foregoing, it will be seen that my A improved control apparatus operates to cut the power oi from the furnace whenever the temperature difference between the edge and center of the charge exceeds a predetermined amount, and to turn the power on again, when this temperature difference or gradient has returned to a permissible ligure.

Referringnow to Fig. 3, I have illustrated an arrangement in which the predetermined temperature gradient may be manually adjusted as desired and also in which automatic means are provided for decreasing this gradient as the temperature of theY furnace increases. In this figure, the same reference numerals designate the same parts as in Figs. 1 and 2, and it is unnecessary to repeat a description of the` arrangement and operation of these parts. An alternative arrangement as regards the arm 27 is, however, illustrated, in that the wire 18, instead of being connected directly with the thermocouples,

as in Fig. 2, has one terminal connected with the thermocouple 32, and the other terminal connected by a wire 38, to a movable contact 39, adjustablealong a resistance 36, after the manner of a potentiometer. The other side of the thermocouple 32 is connected by a f wire 34 with one side of the thermocouple 33, the other side of the latter being connected by a wire 35 with the resistance 36. It will thus be seen that the two thermocouples 32 and 33 are connected in a series circuit with the galvanometer coil and the resistance 36,

the polarities of the two thermocouples being such that their voltages oppose or buck eachy I other, as in Fig. 2.

lA battery 42 has one terminal-40 connected` by a wire 41 in such a way as to be adjustable along the resistance 36, and its other v terminal is connected to a Wire 43, the respective polarities of the battery and of the thermocouples being, as indicated, by the plus and minussigns on the drawings.

Assuming, for the moment, as might well be the case, that the wires 35 and 43 are directly connected, it will beseen that by virl tue of the potential drop through theresstance 36, a certain voltage is impressed by the battery 42, upon the terminals of the galvanometer coil, and that this voltage may be adjusted to any desired value within the range of the instrument by shifting the contacts 39 and 40 along the resistance 36. Thus, when no voltage is being generated in the thermocouples 32 and 33, the' current flowing through the galvanolneter coil may be so 'adj usted that the biasing means of the instrument is just able to overcome the torque due to this curre'nt and maintain the arm 27 lin its left hand position, it being understood that the current tends to move the arm 27 toward the right.

As the furnaceheats up, a higher voltage I @is generated in the thermocouple 33 than in the thermocouple 32, and the former therefore predominates, and sets up an electromotive force in the same direction as that impressed by the battery 42, so that the current flowing through the galvanometer coilis to be increased. As the temperature rises, the' current, due to the joint action of the battery 42 and the predominating thermocouple continues to increase until it becomes strong enough to move the arm 27 over against coutact 16, whereupon power is cut oli' from the furnace, as above described. 1

stages, and I therefore find it desirable to provide means for automatically reducing the permissible temperature gradient as the heat progresses. To this end, I have illustrated, in Fig. 3, a third temperature responsive device or thermocouple 47, and I connect this as by wires 46 with the movable coil of a galvanometer 45, having an arm or pointer 44. This arm is flexibly connected with the wire 43 leading to the battery 42.

I also arrange in cooperative relation'with the arm 44 an arcuate series of contacts 48, between which are connected sections of re' sistance 49, the last contact being connected to the wire 35.

When the furnace is cold, the arm 44 is in its upper extreme position, as shown'in dotted lines, so that the entire resistance 49 is included between the wires 43 and 35 and is ini series with the resistance 36. Thus, it will be understood that the adjustment of the contacts 39 and 40, to bring the arm 27 to its d esired initial position, is made with the resistance 49 in circuit. As the` furnace heats up, an electromotive force is generated in the thermocouple 47 and this causes a current to fiow through the coil of galvanometer 45 in such a direction as to tend to move the arm 44 downwardly to some such position as s1 own in full lines. 4Thus, the hotter the furnace becomes, the further the arm 44 moves and the more the resistance 49 is cut out of circuit. Other factors remaining constant, it' will be seen that the cutting out of the resistance 49 tends to increase the current fiowing from the batter 42 through the coil of galvanometer 28, so that as more and more of the resistance 49 is cut out, less and less additional electromotive force is required to be impressed uponthe circuit 29, 38, in order to move the arml 27 into engagement with the contact 16. It isl therefore clear that as the furnace heats up, and as the thermocouple 47 1s subjected to progressively higher temperatures, the possibletemperature difference or gradient between the thermocouples4 32 and 33, before the power is cut off, progressively decreases. For example, during the early stages of a heat, a temperature difference of three or four hundred degrees may be permitted, while after a critical temperature has been reached, this is automatically reduced to, say, one hundred degrees, in order. to prevent burning or warping of the sheets constituting the charge.

ness, I have illustrated the arm 44 as moving over the contacts 48, it will be understood that in practice, a more delicate and complicated arrangement is necessary, because the currents generated by the thermocouple 47 are too minute to actually loperate a rheostat vas shown. The drawings, however, serve t illustrate the principle and the necessary changes will be readily understood by those skilled in the art.

While Fig. 3 shows both manual and automatic means for Varying the gradient or temperature difference between the two portions of the charge, it will, of course, be understood that the manual adjusting means is capable of use independent of the automatice means embodying the galvanometer 45, since, as above explained, the wires and 43 may be directly. connected together, and the galvanometer and its related parts omitted.

In Fig. 4, I have illustrated a somewhat modified arrangement in which a thermionic amplifier and two auxiliary contactors or relays are employed, but in which the corresponding parts have been given the same referenc'e characters as in the preceding figures. In this figure, the wire 30 connects thepositive sides of the two thermocouples 32 and 33, as in Fig. 2, and the wire 31, leading from the negative side of one of the thermocouples is connected to the grid of an amplifier tube 53. The filament of the tube is connected with an A-battery 54, and with the wire 30a connecting with the negative side of the other thermocouple. In the plate circuit of the tube is connected a B-battery and a high resistance'56 across whichis shunted, by means of wires 29, the movable coil of the galvanometer 28. f

A transformer 5 is shown as having its primary windings connected by wires with leads 8 extending from the power li-ne 8, and its secondary windings, as connected, one to the Wire 12 including the resistance 13 and the other to the wireA 14 extending to the contact 16.

The galvanometer 28 is controlled by the differential action of the two opposed'thermocouples 32 and 33, as before, operating in this case through the amplifier tube 53 in a well known manner.

It is desirable, in sonic. cases, instead of providing lmeans for varying the permissible temperature 'gradient as the furnace heats up, as in Fig. 3, to provide means for preventing the temperature of the furnace vfrom exceeding a predetermined value. This, I have illustrated in Fig. 4, and I haveshown a -third temperature responsive deyice r thernmocouple 47 for this purpose. In e rryin out this feature of the invention, I ,provide an additional galvanometer or pyrometer 28 having an arm 27", which by means of contacts'2`1a and 16, controls the energization of I/Vhile, for the sake of simplicity and clearthe coil 1,9a of a second auxiliary contacter or relay., lCurrent is'supplied to this control apparatus by means of a transfprmer 5a having4 its primary winding connected by wires 50a with the leads 8 and its secondary winding connected at one side to, the wire 12a including the resistance 13,f`and at the other iede to the wire 14 extending to the contact The solenoid 9 of the main contactor is connected by a wire 10 withV one power lead and by a wire 10 with the switch 11 of relay 19. From this switch extends a wire 51 to one side of the switch 11 of the relay 19, the -other side of this switch being connected by a wire 52 with the other power lead; thus the circuit of the main contactor 9 is controlled jointly'by the two relay switches 11 and 11 in series.

The galvanometer 28a is controlled bv the thermocouple 47, as illustrated in the following manner. One side of the thermocouple 47 is connected" by wire 29a to one side of the galvanometer -coil and the other side of the thermocouple 47 is connected by a. wire 57 to a terminal 57a which engages a point between two, of the arms -of a Wheatstoue bridge arrangement 58, the opposite point of the bridge being connected by a wire 38* with the other side of the galvanometcr coil. 'lhe other two points of the bridge are connected to the opposite poles of a battery 59, an adjustable resistance device 60, 61 being included in this connection. It will be understood without further discussion that the Wheatstone bridge arrangement illustrated and described is fork the purpose of permitting manual adjustment and making it possible to setthe galvanometer 28a so that the thermocouple 47 will cause the relay 1921 to be deenergized and the power shut 'off from the furnace when the temperature has reached any desired predetermined value. v

Thus, in the arrangement shown in Fig. 4, power will be shut off from the furnace either when the temperature difference or gradient between the edge and center of the charge reaches a certain predetermined amount, or when the furnace itself attains a predetermined temperature- Thus, damage to the charge is revented..

n will be un erstma that the third am perature responsive device 47 may be located at any desired point soas to respond either to the heat of the furnace itself or of the charge.

Referring finally to Fig. -5, I have illustraced still another method in which the differential action oftwo temperature responsivedevices may be caused to control the power input to a furnace. In this figure,

I have illustrated the same furnace, the same Y' with the movable coil of one galvanometer while the thermocouple 33 is connected by wires 63 with the movable coil vof the other galvanometer, it being understood that the direction of current flow from the thermocouples in these two circuits is such as to tend to move the shaft 66 in opposite directions. The shaft`66 carries a contact arm 67, arranged to vibrate between the two contacts 16 and 21, as before, this arm 67 being connected through the shaft 66 with the wire 18, as in Fig. 3. The arrangement ,is such that when the current generated in the thermocouple 33, due to its temperature, is high enough to produce the torque necessary to overcome that produced by the lesser current generated in the thermocouple 32, due to the lower temperature of. the latter, the arm 67 will be movedinto engagement with the contact 16 and the power thus shut off from the furnace.

What I claim is 1. In the heat treatment of a furnace charge the method of heating which comprises applying heat to the furnace to progressively raise its temperature, and so regulating the heat input that the temperature difference between two separate points of the 'charge approaches but does not exceed a predetermined amount.

2. In the heat treatment of a ack of metal sheets the method of heating whlch comprises gradually applying heat thereto and so regulating the rate of application that the difference in temperature between the edges and center of the pack approaches but never exceeds a predetermined amount.

p 3. In the annealin of a mass of metal the method of heating which comprises applying yheat thereto to progressively raise its temperature, and so regulating the rate' of application that the temperature gradient between lou two different portions thereof shall approach f but not exceed a predetermined maximum duri/rig one stage, and shall not exceed a lesser amount during another stage.

4. In a temperature regulator for annealing furnaces, means for heating the charge in the furnace, a plurality of temperature responsive devices located adjacent different portions of the charge, and automatic means controlled jointly by said devices for preventing the .temperature gradient between said portions of theicharge from exceeding a predetermined amount during a part of the operation, and from exceeding' a different predetermined amount during another part of the operation.

5. In a temperature regulator Zfor furl naces, the combination with a furnace, and heating meanstherefor, of a plurality of temperature responsive devices located at different points in the furnace, and means controlled bysaid devices for preventing the temperature gradient between two separated points of the furnace from exceeding a predetermined amount during one temperature range, and from exceeding a different predetermined amount during another temperature range.

6. In a temperature regulator for furnaces, the combination with a furnace, and heating means therefor, of automatic means for preventing the difference in temperature between two separated points of the furnace from exceeding a predetermined amount, and means controlled by the temperature of the furnace for automatically and progressivelyY varying such predetermined difference.

7. In a temperature regulator for furnaces, the combination with a furnace, and heating means therefor, of a plurality of temperature responsive devices in said furnace, means controlled by one of said devices for automatically shunting off said heating means when'the temperature of a given point of the furnace,

4exceeds a predetermined value, and means controlled by'other of said devices for shutting off said heating means when the difference in temperature between two given points in the furnace exceeds a predetermined amount.

8. In a temperature regulator for furnaces, the combination with a furnace, and heating means therefore, a pair of temperature responsive devices, means governed by the differential action of said devices for controlling said heating means, a third temperature responsive device, and means whereby said third device modifies the effect of the differential action of said pair of devices on said controlling means.

9. In a temperature regulator for furnaces,

the combination with a furnace, and means for progressively heating the same, of a plurality of temperature responsive devices in.

said furnace, and automatic means controlled jointly by said devices for continuously maintaining the difference in temperature between two separated points of the furnace substantially inversely proportional to the temperature of a certain selected part of the furnace.

10.v In heat treating a metallic mass, the

said sheets, and so controlling the application of heat that the difference in temperature between said edges and the central portion of the pack shall at no time exceed a predetermined maximum.

13. In the heat treatment of sheets of metal of relatively low thermal conductivity, the method of preventing warpage and burning thereof which comprises assembling the sheets into a pack, applying heat to the edges of the sheets, and so governing the rate of heating that the difference in temperature between such edges and a point in the interior of the pack shall not exceed a predetermined amount.

14. In a temperature regulator for furnaces, the combination with a furnace, and

means for supplying heat thereto, of a pluralityA of temperature responsive devices in said furnace, means controlled by one of said devices for preventing the temperature of a given point of the furnace from exceeding a predetermined value, and means controlled by other of said devices for preventing the difference in temperature between two given points in the furnace from exceeding a predetermined amount. t

In testimony whereof I alix my slgnature.

GEORGE L. SIMPSON.

method of heating which comprises progressively applying heat to the mass, controlling the application of heat in such manner that the difference in temperature between the edge and center of the mass shall not exceed a given maximum, and gradually lowering the value of such difference as the temperature of the mass rises.

11. In heat treating a metallic mass, the I method of heating which comprises progressively applying heat to the mass, and controlling such application of heat in accordance with the difference of temperature exist-

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