US3212309A

US3212309A - Automatic temperature regulating system

Info

Publication number: US3212309A
Application number: US299419A
Authority: US
Inventors: Norman A Wilson
Original assignee: Morgan Construction Co
Current assignee: Siemens Industry Inc
Priority date: 1963-08-01
Filing date: 1963-08-01
Publication date: 1965-10-19
Anticipated expiration: 1982-10-19

Description

Oct. 19, 1965 N. A. WILSON 3,212,309

AUTOMATIC TEMPERATURE REGULATING SYSTEM Filed Aug. 1, 1963 ERROR v0 LTAG 5 POWER SUPPLY o 86 Ar SERVO AMP 2 Sheets-Sheet 2 Fig.3

REF'ERE.NCE

VOLTAGE REGULATED VOLTAGE INVENTOR. flormam H. Wilson EX/Mg WL W United States Patent 3,212,309 AUTOMATIC TEMPERATURE REGULATING SYSTEM Norman A. Wilson, Westboro, Mass, assignor to Morgan Construction Company, Worcester, Mass. Filed Aug. 1, 1963, Ser. No. 299,419 4 Claims. (Cl. 72-8) This invention relates to wire drawing machines, and more particularly to a wire temperature regulating system for wire drawing machines.

It is well known in the wire making industry that the plastic deformation involved in drawing wire will induce internal heat and that the amount of heat thus generated will be a function of the wire analysis, the physical characteristics of the wire including wire diameter, the reduction in cross-sectional area, the shape of the die and to a lesser extent the speed at which the wire is drawn. Although the induced heat should be removed as rapidly as possible from any type of wire to avoid adversely affecting the physical properties of the wire, the problem of deformation induced increased wire temperature is especially acute when drawing high-carbon wire of a high tensile strength requirement on continuous machines. The temperature of the high-carbon wire must be controlled and maintained at as low a level as possible during the drawing process to avoid deleterious changes in the toughness and uniformity of the wire. However, the desideratum of a uniformly low wire temperature is difficult to achieve because the wire heating during continuous drafting tends to become cumulative thus producing temperatures which are frequently in excess of the desired processing temperatures, and hence, are detrimental to the quality of the drawn wire.

Several methods have been employed ot restrict this rise in wire temperature including the use of water-cool dies and air or water cooling of the wire drawing capstans or blocks. The rate at which the induced heat is removed from a continuously drawn wire is a function of ambient temperature, wire drawing speed, the accumulation of wire between successive drafts, the diameter of the wire, the coolant applied to the wire and other variables relating to wire block design and heat transfer. As an approximation or general rule, it can be said that it is desirable to keep the temperature of the wire from exceeding 400 F. or to cool the wire to within 200 F. within 15 seconds after leaving the die. Since many of the above-mentioned factors which influence the heating and cooling of the wire are fixed by the design of the wire machine or are dictated by the desired final physical properties of the wire, the only factors which can be easily varied during the drawing process are the drawing speed and the application of a coolant to the wire. Within the latter factor are included such variables as the type of coolant e.g. air or water, the initial temperature of the coolant, the mass or volume of the coolant applied to the wire and the rate of application.

Although these variables, as well as the wire drawing speed, can be adjusted by human control, it is preferable to utilize an automatic system which will regulate wire temperature within a predetermined temperature range while permitting maximum drawing speed consistent with uniform qualilty. Accordingly, it is an object of the present invention to provide an automatic wire temperature regulating system for a wire drawing machine which will maintain wire temperature at a predetermined level.

It is another object of the invention to provide an automatic wire temperature regulating system which controls wire temperature by varying the wire coolant.

It is still another object of the invention to provide an automatic Wire temperature regulating system which varies Patented Oct. 19, 1965 the drive speed of the wire drawing machine to control w1re temperature.

These and other objects of the invention will be apparent from the following written description and drawings, in which:

FIG. 1 is a schematic and partial block diagram of an embodiment of the automatic wire temperature regulating system;

FIG. 2 shows the operation of a temperature sensing device output relay plotted against time and wire temperature; and,

FIG. 3 is a schematic and partial block diagram of another embodiment of the automatic wire temperature regulating system.

Turning now to the drawings, it will be helpful to preface the detailed description of the circuitry shown in FIGS. 1 and 3 with a few general remarks directed to the operation of the automatic temperature regulating system. The regulating system is designed to control wire temperature by adjusting the previously mentioned variables of wire drawing speed and coolant application. A temperature sensing device 2 is positioned so that it will measure the temperature of a drawn wire 4 at a point corresponding to the distance that wire 4 will have traveled during some specific period of time after leaving the die (not shown) for example the distance covered in 15 seconds at normal drawing speed. The temperature sensing device 2 produces an output which represents the wire temperature at the location of sensing device 2. As the temperature of wire 4 varies from a reference temperature dialed into the temperature sensing device 2, the output from the sensing device 2 automatically adjusts the amount of coolant applied to wire 4, and hence maintains the wire temperature within a narrow range bracketing the preset temperature. Although the temperature control system is equally applicable to either a gaseous or a liquid coolant e.g., air or water, respectively, the embodiments shown in FIGS. 1 and 3 employ a gaseous coolant. However, it should be understood that it is within the spirit of the invention to regulate either ,a gaseous or liquid coolant or a combination of both.

If the wire temperature continues to increase despite the application of coolant to the wire, increased cooling will be required beyond the capacity of the available air flow or water pressure. In this situation, the temperature regulating system reduces the speed of the wire drawing machine until the temperature drops to the preset reference temperature. On the other hand, if the available cooling provided by the coolant .is more than adequate, the temperature regulating system increases the wire drawing speed thereby permitting an increase in finishing speed without sacrificing the control of finishing temperatures.

Referring now to FIG. 1, the amount of coolant applied to the drawn wire 4 is regulated by a motor driven damper 6 located within a coolant delivery pipe (not shown). The position of damper 6 in the delivery pipe is adjusted by actuating a damper motor 8 mechanically connected to damper e. Electrical power for the damper motor 8 is controlled by a damper close relay 10 and a damper open relay 12 which are alternately energized in response to variations in wire temperature. The damper control relays 1i) and 12 reverse the polarity of the applied voltage to damper motor 8 thereby rotating the damper motor 8 alternately in opposite directions so that the damper 6 opens and closes to maintain the preset wire temperature. If the damper 6 reaches either of its limits of travel, i.e., fully open or fully closed, a motor operated rheostat 14 in the main drive electrical circuit (not shown) adjusts the speed of the wire drawing machine to bring the wire temperature back within the range of temperature control provided by the damper 6.

The variations in wire temperature are detected by the temperature measuring device 2 which is positioned to measure the temperature of the wire at a predetermined distance from the die (not shown). Although the temperature sensing device 2 can be any one of the conventional temperature measuring devices such as thermocouples, heat-balanced thermopiles, pyrometers, etc., the preferred embodiments shown in FIGS. 1 and 3 employ an infrared radiation thermometer because it provides both an accurate measurement of wire temperature and a relatively high response rate to fluctuations in wire temperature. These two features of the infrared radiation thermometer facilitate the remote installation of the temperature sensing device and permit a practical and fully automatic wire temperature regulating system.

The infrared radiation thermometer 2 is essentially a transducer unit which converts the radiational heat energy from wire 4 into an electrical output which represents the temperature of wire 4. The electrical output from thermometer 2 energizes an output relay 16, but only under certain temperature conditions hereinafter described and shown graphically in FIG. 2. These temperature conditions are established by initially adjusting the radiation thermometer 2 to provide an electrical output i.e., to energize output relay 16, whenever the wire temperature equals or exceeds a predetermined reference temperature e.g., 200 F. A temperature differential is also selected to provide a lower temperature limit below which the output relay 16 is always de-energized. For example, with a 200 F. reference temperature and a F. temperature differential, relay 16 would be de-energized whenever the wire temperature was below 190 F. If the wire temperature is within the differential range i.e., between 190 F. and 200 F. and decreasing from the preset reference temperature or above, output relay 16 is energized. Conversely, if the wire temperature is increasing from below the differential range the output relay 16 is de-energized.

The output relays control of the temperature regulating system can best be understood by examining in sequence the operations performed by the various components of the system in response to the energization and deenergization of output relay 16. Assuming that the wire temperature starts out cold i.e., below the differential temperature range, the output relay 16 will be de-energized as shown in FIG. 2. Furthermore, assuming that damper 6 has not reached either of its limits of travel so that the wire drawing speed remains constant, the close damper relay CDR 10 is energized by means of a normally closed output relay contact 18, a normally closed damper close limit switch 20 and a normally closed open damper contactor 22. With the CDR 10 energized, the relays normally open

close damper contactors

24 and 26 are closed thus completing the circuit to damper motor 8. The polarity of the voltage applied to damper motor 8 through CDC 24 and CDC 26 is such that damper motor 8 will rotate in a direction which closes damper 6. If the desired preset reference temperature, i.e., 200 F., is reached before damper 6 becomes fully closed, the output from infrared radiation thermometer 2 energizes output relay 16 thus opening relay contact 18 and closing relay contact 28. The reversal of

relay contacts

18 and 28 de-energizes CDR relay 10 and energizes open damper relay 12 through a normally closed damper open limit switch 30 and a normally closed close damper contactor 32.

Contactors

22 and 32 ,are cross-connected to their

respective relays

10 and 12 to prevent an accidental shorting of the damper motor power supply in the event that output relay contact 28 closes before contact 18 opens.

Energization of CDR relay 12 closes normally open

relay contactors

34 and 36 thereby reversing the polarity of the voltage applied to damper motor 8, and hence, reversing the direction of rotation of damper motor 8 and damper 6. As damper 6 opens, more coolant is applied to the drawn wire 4 and consequently the wire temperature begins to drop. When the wire temperature has fallen below the lower level of thetemperature differential i.e., F., output relay 16 de-energizes thus reversing the direction of rotation of damper motor 8 and damper 6. As damper 6 closes, the wire temperature will again increase until the preset reference temperature is reached, at which point the automatic temperature regulating system repeats the previously described sequence.

In order to avoid excessive hunting and fluctuations in wire temperature, the temperature differential and damper motor speed must be adjusted to compensate for the inherent delay between a change in damper setting and the resulting change in wire temperature. With the proper initial adjustment of both the temperature differ ential and damper motor speed, the wire temperature can normally be maintained within a relatively narrow temperature range by damper control of the applied coolant.

As long as the damper 6 does not fully open or fully close, the normally closed damper limit switches DCLS 20 and DOLS 30 remain closed while the normally open damper limit switches DCLS 38 and DOLS 40 remain open. Wire temperature, therefore, is regulated only by controlling the position of damper 6 within the coolant delivery pipe. However, if damper 6 reaches either end of its full travel before the desired reference temperature is achieved, power is removed from damper control motor 8 by opening either DCLS 20 or DOLS 30 depending upon the direction of rotation of damper 6. Assuming that damper limit switches DCLS 38 and DOLS 40 remain relay 16 is energized, DOLS 30 opens thereby de-energizing ODR relay 12 and breaking the power circuit to damper motor 8. When DOLS 30 opens to interrupt the damper motor circuit, DOLS 40 closes energizing a decrease speed relay 42 through a now closed normally open output relay contact 44 and a normally closed increase speed contactor 46. With DSR relay 42 energized, the relays normally open

decrease speed contactors

48 and 50 are closed thus completing the circuit to a rheostat control motor 52 which is mechanically connected to the trimming rheostat 14. The polarity of voltage applied to the rheostat control motor 52 turns the motor and trimming rheostat 14 in a direction which decreases the speed of the wire drawing machine.

As the wire drawing speed decreases, the measured temperature also decreases because the drawn wire has a longer cooling period before it reaches the temperature measuring device 2. When the wire temperature reaches the lower level of the temperature ditferential i.e., 190 F., as shown in FIG. 2, output relay 16 de-energizes opening relay contact 44 and de-energizing DSR relay 42. The de-energization of DSR relay 42 breaks the power circuit to rheostat control motor 52 and stops the rotation of trimming rheostat 14. The de-energization of output relay 16 also closes relay contact 18 thus energizing CDR relay 10 which in turn completes the damper motor power circuit causing damper motor 8 to rotate in a direction which will close damper 6. Since the temperature of the wire is now within the range of control provided by damper 6, damper 6 will alternately open and close, as previously described, to maintain the wire temperature within a narrow temperature range.

If the wire temperature does not reach the reference temperature with damper 6 fully closed, DCLS 20 opens thus removing power from the damper motor 8. Since the output relay 16 is de-energized at this temperature, as shown in FIG. 2, output relay contact 54 will be closed thus energizing increased speed relay 56 through the now closed DCLS 38 and a normally closed decrease speed contactor 58. Power is therefore applied with reverse polarity to the rheostate control motor 52 through the now closed norm-ally open increase speed contactors 60 and 62 thus rotating motor 52 and rheostat 14 in a direction which will increase the Wire drawing speed. By increasing the wire drawing speed, the wire temperature is raised until it reaches the preset reference temperature at which point the temperature sensing device 2 energizes the output relay 16 thus breaking the speed control circuit and actuating the damper motor circuit. The wire temper .ature is now regulated by adjusting the position of damper 6 within the coolant delivery pipe and will continue to be regulated by damper 6 until the wire temperature changes sufficiently to drive the damper 6 to either of its limits of travel at which point the appropriate sequence described above Will be repeated.

Although the embodiment shown in FIG. 1 provides an automatic regulation of wire temperature, it is limited in application by the very nature of its on-off control system. For example, the system does not provide an extremely precise control of wire temperature because the damper motor speed is constant regardless of the magnitude of the temperature error. The damper therefore has a tendency to oveshoot the proper setting and hence overcorrect with each swing. As mentioned previously, excessive hunting can be avoided by the proper adjustment of the temperature differential and damper motor speed, however, even these adjustments do not provide a continuously correcting system wherein the amount of correction is a direct function of the magnitude of the temperature error. The automatic temperature regulating system shown in FIG. 3 is designed to accomplish this type of continuous feedback correction.

Referring to FIG. 3, the embodiment shown therein employs a servo control loop to adjust the damper 6 and the main drive trimming rheostat 14, both of which function in the same manner to control the temperature of the wire as previously described with regard to the embodiment shown in FIG. 1. Both the damper motor 8 and rheostat control motor 52 are driven by the output voltage from a servo amplifier 64, however, the rheostat control motor 52 is actuated only when damper 6 has reached either of its limits of travel i.e., fully open or fully closed.

The servo amplifier 64 is a conventional type with a reference voltage and error voltage applied to the balanced inputs of the amplifier. The reference voltage, representing the desired Wire temperature, is derived from a potentiometer 66 connected across a source of regulated voltage (not shown). The error voltage is obtained from the infrared radiation thermometer 2 and represents the measured temperature of wire 4-. It is obvious that to one skilled in the art the thermometer 2. with appropriate circuitry can produce an error signal in various forms e.g., a DC. voltage the magnitude of which varies in accordance with wire temperature or an AC. signal with variations in phase discriminator and amplifier can be employed to obtain the necessary voltage to drive the damper and rheostat motors.

The operation of the servo controlled temperature regulating system is relatively simple and can be easily understood by examining the operation of the system under varying conditions of wire temperature and damper position. Assuming that the wire temperature is below the desired temperature, and damper 6 has not reached either of its limits of travel, the input voltages to the servo amplifier 64 will be unbalanced thus producing an output voltage at the servo amplifier output terminals marked A and B. The magnitude and polarity of the output voltage are a function of the error between the infrared radiation thermometer voltage obtained from potentiometer 66.

Assuming that under these circumstances, the output at A is positive with respect to B, the damper motor 8 will rotate in a direction which closes damper 6. As the actual wire temperature increases toward the desired wire temperature, the amount of error between the reference voltage and the voltage produced by the infrared radiation thermometer 2 decreases with a concomitant decrease in the magnitude of the servo output voltage. Since the damper motor speed is directly related to the magnitude of the servo amplifier output voltage, the damper motor 8 will slow down as the actual wire temperature approaches the desired wire temperature. The feedback loop between wire temperature error and damper motor speed thus permits an accurate positioning of the damper 6 within the coolant delivery pipe without an excessive amount of hunting.

If the actual wire temperature is above the desired wire temperature, the polarity of the servo amplifier output voltage will be reversed i.e., terminal B positive with regard to terminal A, and the damper motor 8 will rotate in a direction which opens damper 6.

In the two situations described above, it was assumed that damper 6 had not reached either of its limits of travel. However, if damper 6 fully opens or fully closes, the appropriate normally closed damper limit switch DOLS 68 or DCLS 70, opens thereby removing power from damper motor 3 and actuating the main drive speed control circuit. The main drive speed is regulated by adjusting the motor driven trimmer rheostat 14. The power circuit for the rheostat control motor 52 is through

switches

72 and 74 or

switches

76 and 78 depending upon the position of the damper 6 within the coolant delivery pipe.

Switches

72 and 74 are ganged with DOLS 68 and close whenever damper 6 opens the damper limit switch DOLS 68. Similarly, switches 76 and 78 are mechanically connected to DCLS 7 i) and close whenever the limit switch 70 is opened by damper 6 reaching its fully closed position.

Assuming that the actual wire temperature is above the desired wire temperature and damper 6 has reached its fully open position, DOLS 68 opens thereby interrupting the servo amplifier output voltage applied to damper motor 8. Since

switches

72 and 74 are closed when the damper 6 trips DOLS 68, the output voltage from servo amplifier 64 is applied to the rheostat control motor 52. The polarity of the applied voltage i.e., terminal B positive with respect to terminal A, drives the rheostat control motor 52 and hence the trimming rheostat 14 in a direction which decreases the speed of the wire drawing machine.

Since the actual wire temperature is a direct function of the wire drawing speed, both the measured wire temperature and diiference between the error voltage and the reference voltage will decrease with the decrease in drawing speed. The decrease in temperature error reduces the magnitude of the servo output voltage applied to the rheostat control motor 52 thereby decreasing the rate of change in wire drawing speed, and although the decrease in actual wire temperature follows the decrease in drawing speed, the two events do not occur simultaneously because of the time lag required to produce a change in wire temperature. The speed control, therefore, will overshoot th proper setting with the result that the actual wire temperature will also overshoot the desired wire temperature. When this occurs, the measured wire temperature will be below the desired wire temperature and the polarity of both the error voltage and the servo amplifier output voltage will be reversed with output terminal A now positive with respect to terminal B. With A positive, current flows through a unilateral conductive device which may be a crystal rectifier completing the power circuit for damper motor 8. The polarity of the voltage thus applied to damper motor 8 rotates the motor in a direction which will close damper 6. The closing of damper 6 releases damper limit switch DOLS 68 thereby opening

switches

72 and 74 in the power circuit of rheostat control motor 52. With DOLS 68 now closed and switches 72 and 74 open, the wire temperature control is returned to the damper motor circuit and will remain with the damper motor 52 until damper 8 once again exceeds its limits of travel in either direction.

If damper 6 closes fully as a result of too low a wire temperature, a similar sequence of operations takes place utilizing the normally closed damper limit switch DCLS 70, rheostat control motor switches 76 and 78 and crystal rectifier 82.

I claim:

1. In a wire drawing machine, a wire temperature regulating system comprising: means for sensing Wire temperature, said sensing means producing an electrical output having a characteristic representative of wire temperature; variable speed drive means for said wire drawing machine; adjustable means for applying coolant to a drawn wire, said means having selected operational limits; means for controlling said coolant applying means operable by and responsive to the output from said temperature sensing means; and means for varying the speed of said drive means whenever said adjustable coolant applying means reaches either of said operational limits whereby the speed of said drive means is adjusted to bring the wire tempera ture within the temperature range controlled by said coolant applying means.

2. In a wire drawing machine, a wire temperature regulating system comprising: variable speed drive means for said wire drawing machine; adjustable means for applying coolant to a drawn wire, said means having selected operational limits; means for sensing wire temperature, said sensing means producing a voltage which varies in accordance with wire temperature; a reference voltage source; a servo amplifier having the inputs thereof coupled to said temperature sensing means and said reference voltage source, said servo amplifier producing an output which varies in magnitude and polarity in accordance with the difierence between said temperature sensing means output voltage and said reference voltage; means for controlling said adjustable coolant applying means operable by and responsive to the output of said servo amplifier; means for varying the speed of said drive means operable by and responsive to the output of said servo amplifier; and means for coupling the output from said servo amplifier to said coolant control means whenever said coolant applying means is within its operational limits and to said drive speed varying means whenever said coolant applying means reaches either of its operational limits.

3. In a wrie drawing machine, a wire temperature regulating system comprising: variable speed drive means for said wire drawing machine; adjustable means for applying coolant to a drawn wire including a damper, said damper being operatively connected to a first electric motor and having an open and a closed operational limit; means for sensing wire temperature, said sensing means producing a voltage which varies in accordance with wire temperature; a reference voltage source; a servo amplifier having the inputs thereof coupled to said temperature sensing means and said reference voltage source, said servo amplifier producing an output across first and second output terminals which varies in magnitude and polarity in accordance with the difference between said temperature sensing means output voltage and said reference voltage; means for varying the speed of said drive means, said means being operatively connected to a second electric motor; a normally closed damper close limit switch and a first semiconductor diode in parallel-series connection between said first output terminal and said first electric motor; a normally closed damper open limit switch and a second semiconductor diode in parallel-series connection between said second output terminal and said first electric motor; a first normally open switch in series connection between said first output terminal and said second electric motor, said switch being actuated by said damper close limit switch, a second normally open switch in series connection between said second output terminal and said second electric motor, said switch being actuated by said damper open limit switch; and a fourth normally open switch in series connection between said second output terminal and said second electric motor, said switch being actuated by said damper open limit switch.

4. In a Wire drawing machine, a wire temperature regulating system comprising: variable speed drive means for said wire drawing machine; means for varying the speed of said drive means, said means being operatively connected to a first electric motor; adjustable means for applying coolant to a drawn wire including a damper, said damper being operatively connected to a second electric motor and having an open and a closed operational limit; means for sensing wire temperature, said sensing means producing an electrical output; an output relay actuated by said electrical output; a source of electrical energy; a first normally closed switch and a first normally open switch connected to said source of electrical energy, said switches being actuated by said output and having connected thereto in series, respectively, a normally closed damper close limit switch and a normally closed open damper limit switch, a normally closed open damper contactor and a normally closed close damper contactor, and a close damper relay and an open damper relay, said relays actuating respectively, said close and open damper contactors; first and second normally open close damper contactors in series connection with said second electric motor across said source of electrical energy, said close damper contactors being actuated by said close damper relay; first and second normally open open damper contactors in series connection with said second electric motor across said source of electrical energy, said open damper contactors being actuated by said open damper relay; a second normally closed switch and a second normally open switch connected to said source of electrical energ said switches being actuated by said output relay and having connected thereto in series connection, respectively, a normally open damper close limit switch and a normally open open damper limit switch, a normaly closed decrease speed contactor and a normally closed increase speed contactor, and an increase speed relay and a decrease speed relay, said relays actuating respectively, said increase and decrease speed contactors; first and second normally open increase speed contactors in series connection with said first electric motor across said source of electrical energy, said increase speed contactors being actuated by said increase speed relay; and first and second normally open decrease speed contactors in series connection with said second electric motor, said decrease speed contactors being actuated by said decrease speed relay.

References Cited by the Examiner UNITED STATES PATENTS 1,023,316 4/12 Hurwitz 2051 2,291,540 7/42 Fearn 207-1 2,863,557 12/58 Munker 207-16 CHARLES W. LANHAM, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,212,309 October 19, 1965 Norman Ac Wilson It is hereby certified hat error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 69, for "CDR" read M ODR column 4, lines 27 to 29, strike out "Assuming that damper limit switches DCLS 38 and DOLS 40 remain relay 16 is energized," and insert instead Assuming that damper 6 has reached its fully open position and output relay 16 is energized, column 7, line 40, for "wrie" read wire column 8, lines 43 and 44, for "normaly" read normally H Signed and sealed this 5th day of July 1966 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attcsting Officer Commissioner of Patents

Claims

1. IN A WIRE DRAWING MACHINE, A WIRE TEMPERATURE REGULATING SYSTEM COMPRISING: MEANS FOR SENSING WIRE TEMEPERATURE, SAID SENSING MEANS PRODUCING AN ELECTRICAL OUTPUT HAVING A CHARATERISTIC REPRESENTATIVE OF WIRE TEMPERATURE; VARIABLE SPEED DRIBVE MEANS FOR SAID WIRE DRAWING MACHINE; ADJUSTABLE MEANS FOR APPLYING COOLANT TO A DRAWN WIRE, SAID MEANS HAVING SELECTED OPERATIONAL LIMITS; MEANS FOR CONTROLLING SAID COOLANT APPLYING MEANS OPERABLE BY AND RESPONSIVE TO THE OUTPUT FROM AID TEMPERATURE SENSING MEANS; AND MEANS FOR VARYING THE SPEED OF SAID DRIVE MEANS WHENEVER SAID ADJUSTABLE COOLANT APPLYING MEANS REACHES EITHER OF SAID OPERATIONAL LIMITS WHEREBY THE SPEED OF SAID DRIVE MEANS IS ADJUSTED TO BRING THE WIRE TEMPERATURE WITHIN THE TEMPERATURE RANGE CONTROLLED BY SAID COOLANT APPLYING MEANS.