US2293047A - Apparatus for zone hardening - Google Patents

Description

g- 1942- F. s. DENNEEN ETAL 239 4? APPARATUS FOR ZONE HARDENING Filed Dec. 51, 1935 Fax/7 /9 24,; I 2/ VENTORS.

Patented Aug. 18, 1942 2,293,047 APPARATUS FOR ZONE HARDENING Francis S. Denneen,

Dunn, Shaker Heigh Ohio Crankshaft Co corporation of Ohio Cleveland, and William C. ts, Ohio, assignors to The mpany, Cleveland, Ohio, a

Application December 31, 1935, Serial No. 56,870

3 Claims.

The present invention, relating as indicated to apparatus for zone hardening, is an improvement in the subject matter of our invention shown and described in our copending application Serial No. 689,904 for hardened metal article and method of making same filed September 18, 1933, now Patent No. 2,170,130, issued Aug. 22, .1939.

In the present application we are disclosing means whereby the process described in the former application may be used more rapidly and with greater accuracy.

Since rapid and economical production is essential and since marked variation between successive articles of the same run is objectionable, the device should be automatic so far as practicable, free from variation or error due to the operator, and, further, should be capable of repeatedly producing articles closely duplicating each other.

In the surface hardening of articles described in the former application above referred to, we have found it is important that the heating period and the quenching period should each be held to an accuracy as close as one tenth of a second to insure both high quality and uniformity in the results obtained.

In general, we have found that best results are obtained by heating the zone to be hardened at the maximum possible rate. The hardened zone is thereby kept at minimum depth, the quantity of heat to be removed by quenching is kept at a minimum, and the flow of heat to portions of the article other than the zone to be hardened is held to a minimum. We have gone into considerable detail in .co-pending application Serial No. 718,002, filed March 29, 1934, now Patent No. 2,180,038, issued Nov. 14, 1939, regarding the metallurgical advantages obtainable by heating and quenching at high rates, and those advantages apply equally in this application.

Also the rate of power input at any instant during a heating period must be capable of accurate control and according to a predetermined value or series of values on the same or duplicate parts. Further, it has been found that the analysis of the steel or other material of which the article to be heat treated is composed. has an important influence on the resuits obtained and therefore in changing from one material to another the change must be made in a definite manner and in accordance with the material employed. To arrive at the correct set up of the apparatus, frequently test samples have to be produced and examined for their physical properties. These properties are usually readable to a marked degree in the photomicrographs of etched sections and, further, the probability of surface fractures, or flaking off of the hardened or otherwise modified shell may be found and other conditions may readily be determined from an inspection of such photomicrographs.

By employing proper adjustments in the timing of the functions of the apparatus hereinafter described to correspond with the particular analysis and the condition of the material in the article and the form of the article to be heat treated, very accurate and uniform results in the physical properties of the article thus heat treated are obtainable.

This invention has for one of its objects the provision of apparatus for surface heat treatment of metals which is adaptable to accurate duplication of parts produced thereby. Another object is to provide a device which is not wholly dependent upon the personal senses of an operator for the accuracy of its results. An additional object is to provide an apparatus which is readily adaptable for various products. A further object has been to provide apparatus for producing an article of predetermined physical properties. A still further object is to provide means for producing a series of similar articles of uniform character. Another object is to provide means for producing a number of duplicate articles rapidly, inexpensively and of high quality. Another object is to provide means for producing on an article a hardened zone of superior qualities as to some or all of the following: hardness, density, adherence to adjacent zones, ability to receive high finish, antifriction qualities, fineness of grain structure, smoothness of grain structure, low abrasive action against contacting surfaces and resistance to abrasion from contacting surfaces.

With these and other objects in view which will appear as the following description proceeds, said invention then consists of the apparatus herein described. The phraseology herein employed is for the purpose of explanation and not for limitation. Such parts of this invention as we desire to protect by Letters Patent are defined by the claims hereto appended.

In the drawing Fig. 1 is a diagrammatic representation primarily of the electric circuits employed. Fig. 2 is an enlarged view of the heating inductors in operating position over the article to be heat treated. Fig. 3 is a longitudinal view partly in section on line 3-3 of Fig. 2. Fig. 4 is a fragmentary view partly in section on line 4-4 of Fig. 2. 'Fig. 5 is'a fragmentary'view similar to Fig. 3, but showing a modification in the form of one of the inductors.

Referring now to the apparatus as illustrated,

air core type and both the primary and secondary are preferably tubular and arranged for water cooling. The primary usually is made with approximately forty turns and the secondary is composed of one turn usually made of several parallel conductors connected together.

Three bus bars I'l, I9 and 2! are provided to transmit energy to the transformer from the generator as the same ar usually spaced some distance apart. The other end coil of the primary is connected to the bus bar 2|. The generator or source of alternating current 22 supplies current to the bus bars I! and I9 usually at a voltage of about 800. A suitable switch 23 for connecting the primary I5 to the bus bars I1, I9 and 2I is provided. To compensate for the inductance of the circuit, condensers 24 and 25 are provided and are attached across the bus bars I1 and 2|. The condenser 24 is selected to provide the minimum capacity required for any given set of operations and the condenser 25 is made adjustable to provide for the variable condenser requirements above the minimum of any such given set of operations. Usually the adjustments of the variable condenser are accomplished not by varying the capacity of a single condenser, but by inserting or removing from the circuit small individual condensers or condenser elements. By the effect of resonance resulting from the presence of the inductance and condensers, these circuits may be so tuned that much more current can be supplied to the transformer primary than is supplied by the generator. Thus the bus bars I! and 2| carry much more current than bus bar I9 and must be correspondingly larger.

The generator is provided with an exciter 26 for its field 21, there being a removable resistance 28 and a readily adjustable rheostat 29 in this field circuit for the adjustment of the generator output. For the further adjustments of the field circuit, the rheostat 30 in the circuit of the field 3| of the exciter is provided, By suitable manipulation of both rheostats 29 and 30 it will be evident that the output of generator 22 can be controlled very closely and easily.

For the successful operation of this device, a given frequency of generator current being provided, several accurate adjustments are necessary and the operations must be carried out in proper sequence. After the inductor members II and I2 have been brought into enclosing relationship with the article ID to be heat treated and the contact at I3 has been assured by a suitable fastening such as clamp 32, the condenser 25 is adjusted to meet the required capacity and rheostat 29 is regulated to provide the initial current needed. Switch 23 is closed which brings the transformer primary I5 into operating connection with bus bars l1, I9 and 2|. As a very accurate duration of the heating interval is required, which has been indicated above, means must be provided for measuring this interval which means is not dependent upon the senses of the operator. This means is provided by the motor 33 which preferably is of a constant speed type and which has a very low inertia starting resistance so as to attain full speed in a minimum, and substantially constant, interval. A self starting synchronous motor meets these requirements nicely. This motor, thru suitable gearing, drives the timer comprising a contactor disc indicated at 34. After all preliminary adjustments in the condenser circuits, field circuits and switch contacts between the bus bars and transformer have been made, switches 35 and 36 which are interconnected to be closed substantially simultaneously are closed, the former bringing generator 22 across the bus bars I7 and I9 and the latter closing the circuit of motor 33, the power for motor 33 being supplied from lines 3'! and 38 as indicated. This power may be of any suitable character, but usually is low frequency current of ordinary voltage. The contactor arm 39, carried by the disk 34 and adapted to rotate therewith, starts rotating at a substantially uniform velocity upon the application of power to the transformer primary l5by the closing of switch 35,account being taken for starting lag and correction being made therefor in the position of the contactor arm 39 on disc 34. The angular movement of the contactor arm on disc 36 from its starting point determines an interval of time, the speed of the disc being known. As soon as this interval has elapsed, this disc contactor closes a circuit which derives its energy from a source indicated at 49. Power from the lines 31' and 38 is usually employed instead of the battery indicated, however. The successive closing of such circuits as have contactors which are engaged by the contactor arm 39 actuates relays or solenoids which are employed for accurately starting or terminating such functions as may be required in the cycle of operations. In the relatively simple apparatus indicated, switches 23, 35 and 3B are closed manually, and the adjustments of the condenser 25 and rheostat 29 are also made manually. For the heat treatment of a number of like articles, which are represented in the present case by the shaft I0, the adjustments of the rheostat 29 and condenser 25 are determined by previous experience with similar articles and by experiment, the analysis of the material of the article as well as its form and size having an important influence 0n the adjustments to be provided. v

In the use of the apparatus above described, the operator proceeds as follows: The adjustments of condenser 25 and rheostat 29 having been determined before hand, the inductor members II and I2 are brought into proper spaced relationship with the shaft I0 and are secured by clamp 32 so as to have good electrical contact at I3. Condenser 25 and rheostat 29 are then adjusted and switch 23 is closed which is followed immediately by the closing of switch 35, switch 36 being closed by the closing movement of switch 35. The high frequency generator 22 thru bus bars I1 and I9 delivers heating power to the transformer primary I5. Secondary I4 causes current of high density and usually low voltage to flow in the inductor members II and I2. The current in these inductor members induces high density current in the surface zones of article 10 and because of the hysteresis effect and the ohmic resistance of the article, the surface zones are brought to a high temperature in a few seconds.

Immediately upon the closing of switch 35 and the beginning of the heating interval, rheostat 29 is adjusted to provide the required power input to the transformer, it being frequently necessary to continue manipulating the rheostat thru the greater part of the heating interval because of changes in the permeability of the article being heated, changes in its resistance due to its rising temperature, or other change in the circuit, or because of varying power requirements made necessary for any other reason.

As switch 36 is closed simultaneously with the closing of switch 35, the contactor arm 39 starts to rotate at the beginning of the heating interval and continues for one complete revolution. Rotation beginning at the point A and contactor arm 39 moving in a clockwise direction as indicated, the end of this arm makes momentary contacts at points B, C, D, E and F. The contactor arm serves as a part of the conducting circuit for carrying current from the source 49. At its starting position, the outer contact end of the contactor arm 39, which is at the zero point indicated at A, is slightly clockwise beyond the point F. At the instant of closing the circuit breaker switch 35, the heating energy is applied to the heating circuit and at the same instant the contactor arm 39 starts moving clockwise from its zero position A a little beyond contact F and the heating current continues to flow during the period of travel of the contactor arm 39 from starting point A to contact point C. At the instant of reaching point C current flows from the battery 40 through contactor arm 39 into contact C, thus energizing the solenoid 4| which functions to open the circuit breaker 35, thereby cutting off the heating energy from the circuit. Atthe same instant the solenoid coil 42 (which is in parallel with solenoid 4|) is energized and this causes the quenching fluid valve 43 to open permitting free flow of coolant over the heated areas of the article l from the jacket space of the inductor through orifices in the inner inductor walls as shown in Fig. 3.

The quenching fluid valve 43 remains open during the passage of contact arm 39 from contact point C to contact point E at which time current flowing from the arm 39 into the contact E energizes the solenoid 44 which causes the valve 43 to close, cutting off flow of coolant. The contactor arm 39 continues to revolve clockwise until contact is made at F at which instant the solenoid coil 45 is energized, opening the switch 36, thereby causing the timing unit motor to stop, the contactor arm 39 having reached its stopping position at contact F and being carried a little beyond to starting point A by its inertia.

Since it is objectionable to open the circuit breaker 35 in the main circuit at the instant when current of high value is flowing, we have provided means for reducing the current just prior to the opening of this circuit breaker 35 in the following manner: Just before the contactor arm 39 reaches contact C, it makes connection at contact B energizing solenoid 46 which opens the short circuiting contact at 41, thereby inserting resistance 28 in series with the field circuit, of the generator. The resistance increment 28 when inserted in the generator field circuit just before the main circuit breaker opens, reduces the current flowing through the breaker at the instant of opening sufficiently to prevent serious damage to the breaker. It is necessary that the resistance increment 28 to be cut out from the generator field circuit before the generator is again connected to the heating circuit and this is accomplished through the contact point D which causes the solenoid 48 to be energized, drawing the member 41 into position to once more short circuit the terminals of the resistance increment 28.

It will be observed from the foregoing that the apparatus required is simple, that its operation requires no special skill and that it provides a high degree of accuracy in the duplication of the results obtained from its use.

Figs. 2, 3 and 4 illustrate on a somewhat enlarged scale, the inductor members of Fig. 1, together with their related parts and show a specific application to a crankshaft crank pin which is to be hardened. In these illustrations, the inductor members H and I2 have the jackets 49 and 49' attached by screws 50 and 50. Suitable insulation gasket 5| of rubber or other resilient material serves as means for preventing loss of the quenching medium and to confine the flow of current to the members II and I2 adjacent to the shaft. The lower inductor member I2 is attached by means of bolts 52 to the extension 53 which is supported by pin 54 and the upper inductor member II is attached to the hinge member 55 by means of bolts 56. The hinge member 55 is adapted to rotate about hinge pin 51 which is carried in the stationary hinge member 58. Extension 53 and stationary hinge member 58 are attached to bus bars 59 and 60 respectively by bolts GI and 62, these bus bars being attached preferably by fusion to the ends of the single coil secondary I 4 of the transformer. The primary turns indicated by the fragment 63 are insulated from each other and from the secondary by suitable means. To relieve the bus bars 59 and 60 from strains which would occur in the manipulation of the inductor members both pins 54 and 51 have their ends supported in the frame carrying the coils and other related parts, and which is not shown.

In applying the inductor members to the crankshaft bearing or journal l0, an insulating space 64 between these inductor members and their supports is provided. This space is usually maintained at a minimum to prevent losses and ordinarily is of the order of one sixteenth of an inch. On the other side of the journal these inductor members are brought into firm conducting contact at 13 to complete the circuit around the shaft. Usually the voltage is low and the current density is very high at this contact so that very slight diflerence in the contact resistance at different points in the contacting area will cause serious variation in the current density from one side to the other of the inductor members. This causes corresponding and objectionable variation in the rate of heating in different sections in the zone to be heated. To insure uniformly high conducting contact, we usually attach silver contact strips 63' and B4 to the inductor faces at l3. For some purposes, it is satisfactory to omit these silver strips and to use instead a piece of fine mesh hard copper or bronze gauze coated or impregnated with an amalgam containing tin, zinc, copper or other suitable metal.

As a general thing, satisfactory results may be obtained by having thersurface of theinductor members parallelto the surface tobe heated. In some cases with this parallel arrangement, however, the heating is more rapid opposite the recess theface of the inductor members bringing it further away from the surface to be heated at the-place where parallel inductor. members would tend to create excessive or objectionable depth in the hardened zone. This recessing is indicated at 51 in Fig. 3. "This provides a $111- face zone of substantially uniform depth when other related conditions are favorable. Frequently, however, neighboring elements may disturb the desired distribution of'the magnetic flux such, for instance, as the arms or cheeks 88 and the bearing. To

supply line.

mately seventy pounds per square inch in the While the water pressure required in the quenching system will, of course, vary depending upon the cooling to be accomplished, size and shape of the piece, the design and form of the heating inductor members and other conditions existing in the quench water system, we have i found that a pressure of approximately sixty pounds per square inch in the chamber communicating with the orifices in the inductor will insure proper cooling of the piece when the ori- 69 of the crankshaft. To compensate for the presence of these elements the journal I0 is placed as best shown in Fig. 4 in an eccentric position relative to the inductor members. so that the least clearance between the inductors and shaft is between the arms or cheeks. For most satisfactory results it has-been found that for journals having a diameter of approximately two and one half inches, the clearance at I0 (Fig. 4) should be of the order of: .080 of an inch, at II it should be .040 and at 12 and I3, .060. Spacers made of lava or other insulating materal as shown at 61' are usually inserted to insure the desired spacing.

Frequently it is desirable or necessary to make further modifications in the form of the inductor members to properly distribute the heating and the resulting form of hardened zone. To this end, the inductor members often assume the form shown in Fig. 5 the widths of the alter- .nate ribs and grooves being such as to accomplish the desired result. The current in the major part follows the ribs, due to proximity efiect the current induced in the shaft is of greatest den ty opposite these ribs. The grooves provide efficient means for distribution of the quench. The general contour of the face of the inductor members may assume various forms to meet the required results, but usually is ,of the general form shown, the faces of the central ribs such as 14 having greater diameters than the ribs 15 adjacent to the sides, the spacing from the shaft thereby assuming a general curved form across the width of the bearing. This is usually required since the current induced in the central part is the cumulation of inducing effects of adjacent ribs and the heated zone would therefore be too deep.

The journal to be surface hardened is enclosed in the inductor members illustrated at H and I2 in Fig. 2 and power, usually at about the maximum rate that may be practically applied to the particular article being heated, is supplied for the necessary period, at the termination of which period the heating is interrupted and quenching is accomplished by projecting a cooling fluid through orifices in the faces of the inductor members onto the journal thus heated. For journalsup to 3" in diameter the heating period is usually somewhere between 2 and 7 seconds. When water is used as a quenching medium, this is preferable at temperatures between 70 and 90 F. and-at a sufficiently high pressure which we have found should be approxifices are approximately in diameter and number: approximately 12 or 15 per square inch in the inductor face. By projecting the quenching liquid through these orifices under sufficient pressure, all incipient vesicles or bubbles of steam or gas which tend to form on the hot surface of the shaft are dislodged and their harmful quench retarding efiect due to their insulating qualities is obviated. For journals up to 3 inches diameter this quench is usually applied for a period of from five to seven seconds depending somewhat uponthe size of the shaft and the amount of heat which has been delivered to it. However, the depth of the heated zone varis somewhat depending upon a number of conditions and thus effects to a marked degree the amount of heat which must be absorbed by the quench and consequently the amount of quench which must be delivered and the duration of the quenching period. Frequently, it is desirable to cut oil the cooling action at some point, thereby taking advantage of the tempering action that results if all the heat is not immediately removed. Greatly improved physical qualities are thus frequently obtained.

Attention is directed to the quenching effect of the inner or core portion of the journal which has remained cool (usually not over 240 F.) during the heating interval. The quench which is applied through the orifices in the inductor members thus does not have to absorb all the heat as a portion of this is rapidly absorbed by the cooler metal of the coreof the journal. The amount, however, absorbed by this core is not sufiicient to materially affect the physical properties imparted by previous process or heat treat ment. This cooling effect of the core is of considerable advantage in preventing the formation of free ferrite below the demarcationline or bonding zone. r

Numerous other modes of applying the principle of our invention may be employed instead of the one explained, changebeing made as regards the mechanism herein disclosed provided such change comes within the scope of the appended claims.

We, therefore, particularly point out and distinctly claim as our invention:

1. In apparatus for surface hardening by induction, an inductor in spaced relation with the surface to be hardened, a generator source of periodically varying current including a field winding, a separable connection to make and break connection between said inductor and said source, control means to vary the degree of excitation in the generator field winding, a timing mechanism operatively connected to said connec tion and said excitation control means, a power connection to said mechanism, a separable con- Motion in said power connection and means operated by said timing mechanism after the termination of the heating cycle to, stop the action of said timing mechanism.

2. In apparatus for heating by induction, an inductor in spaced relation with the surface to be hardened, a generator source of periodically vary ing current, a separable connection to make and' break connection between said inductor and said source, means to vary the degree of excitation in the generator field winding, a control mechanism operatively connected to said connection and said excitation control means to first decrease the generator excitation, second to open said separable connection and then increase said generator excitation.

3. In apparatus for heating by induction, an inductor in spaced relation with the surface to be hardened, a generator source of periodically varying current, a separable connection to make and break connection between said inductor and said source, means to vary the degree of excitation in the generator field winding, a control mechanism operatively connected to said connection and said excitation control means to first decrease the generator excitation, second to open said separable connection and then increase said generator excitation and terminate operation of said control mechanism.

FRANCIS S. DENNEEN. WILLIAM C. DUNN.

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