US2479934A - Heat treating - Google Patents

Description

Aug. 23, 1949. JAGEN 2,479,934

HEAT TREATING Filed Aug. 26, 1943 3 Sheets-Sheet 1 nvvz/vroe THEODORE 4. JA af/v,

HIS ATTORNEY.

T. A. JAGEN HEAT TREATING Aug. 23, 1949.

Filed Aug. 26, 1943 3 Sheets-Sheet 2 w M N x 3% W n W 5 W wm Aug. 23, 1949. r, A. JAGEN I 2,479,934

v HEAT TREATING Filed Aug. 26, 1943 3 Sheets-Sheet 3 Fig. /4

HLS ATTO RNEY,

Patented Aug. 23, 1949 en -rag li' lo'tor'sfnflorporation', Detroit, Mich}, a;

corporation of Delaware Do tioiied arid controlled transient z'oii'e or z s of small extent. Desired results are"ol o{ tairied' by preqteiiehmg, that sjby ov'ej iat the beginning of the quench withthe erid'oft 1 Heating period. v The mveauea s disclosed for eitaTmple'by' reference to the hardening of race- 'surfac oh theinterior of airing, the v rig axially overhanging lips at the" out r'iphery' Y to be keptsOitffor" subsequentsp nn rig wane the small transition z'o'nesi are kept a y from the lips and away from theraceway sur-' face; However; the inveriti'dfiis' not necessarily liii rited to thisspecific use. v I

To these ends and also to improvegeaerany upoif ni'ethods andappa'ratus' of this character; the invention consists in the" various; matters hreinafter disclosed and claimed; In' the drawi'ngst Fig: 1 is a vertical section of theapparatus'i Fig.2 is a-plan view of Fig 1'.

Fig. 3-15 aplan view of the'ind'uctioncoil and core: 7

Fig. 4is-a front-view of Fig.3.

Fig. 5-is-a side view of Fig.4; W

Fig. 6 is a bottom plan view of- Fig. 4.

Fig; 7, is a plan view of the work carrier.

Fig 8 is a cross sectional view of Fig; 8:

Figs. 9 to 13- are diagrammatic views to indi cate the locations of various zones of lf artiness as obtained by the methods described the thicl ness of the rm'g'temgf exaggerated and the proportions beingindicated by Fig. 1 and in an ex: ample by actual drmensmns'hefema'aer" appear 14 is: a diagram of the electrical and by draulic'svstem. p I r h Theworli piece W herein" illustratdiis'ath'fi dialled outer race ring of steel fofronerbearings; The piece is externally cylindrical a'siiid dia'r riiati'c'ally in Fig. 9 and it has a cy a real rabewaifR; Before heat'treatmnt; it issoft and of uniform p earlitic structure. Beyond the raceway, the piece has a counterbore at each end formed by acylindrical surface F which extends to a shoulder S, thus leaving an overhanging lip L. When the bearing is subsequentlycompleted, end rings which are externally bevelled are in} sorted inthe counterbore against the shoulders and the lips L are spun down upon the bevelled exterior of the end rings to hold theh i. Thus the lips L and closely adjacent portions e: the ring should be kept soft for spinning whilethe raceway surface R- where the rollers run and the remainder of the piece should be hard to resist wear and-abrasion.

Prior to establishing the present practice of the invention" and'leading up to it, the greater part of the piece was heated by induction in a zoneA (Fig; 1-0') and then, with the heat turned 01f, there was adelay'before applying the Fig. 10' indicates the effect of a relatively long delay and Figpll the effect of a relatively short delay. Hardness patterns such as indicated in these figures could be secured but would vary substantially. The larger zone A represents the areahardenedentirely by induction while the intermediate or transition zones Brepresent the areas Where grain refinement occurs due to heat conduction from Zone A during the delay period. The end" zones 0 are the unaffected soft areas ofah'ard'ness of 8-10 Rockwell C to be protected from hardening. The zone A becomes entirely of a martensitic'structure with a hardness (if-64 65 Rockwell C while the transition zones B area mixture of nai'tensit'eaiid ferrite with-ahardhe'ss ranging between-that of zonesA and C.

With suchpractice using a' delayed quench, the size-of zones and 0 becomesvery variable and theinternie'diate zone may run into the lips to spoilthe piece, depending oh several-factors. One factor isf the accuracy of the time delay and this is" affected by the length of time it takes for the quench ;wa te"r to travel from its control" valve through the quench jacket to the piece. Also sn 'all timevaiiiations' would cause considerable variation in the size ol" zones B C The accuracy in the nia'chining of the physical cliinensions of thepiece is another material factor because may variation the counterborediameter causes a change in the volume of zone C which is directly proportional to; the square of the variation in; diameter, thisdiameter affectmg the thickness of the lip'L and the thinner thelipL the greater the thermal conduction and hence the" smaller the zones" C and the larger 3 the zones B. Zone A has a shape which depends on the shape of the induction coil.

It is desirable to keep both the size and variation in size of the transition zone B to a minimum to attain the required results because a constant high hardness is desired across the whole length of the raceway R while the lip L should retain its original softness for at least the full depth of thecounterbore. Transition zone variations might undesirably cause the lips to be hardened or else would unduly lower the hardness of the racewa R near its ends depending on which way the variations occurred. A large transition zone, assuming no variation in transition zone size, would not permit any variation in the heating cycle, since, to achieve the desired results, the zone A would have to be maintained exactly and this is not practicable due to combinations'oi line voltage variation as well as slight timer variations. Thus the induction heating of small thin-walled rings with small thin zones to be protected is very critical and can be successful only by keeping the transition zones small. The pre-quenching or overlapping quench and induction heating of the present invention accomplish this as indicated in Figs. 12 and 13. In Figs. 12 and 13 respectively the minimum and maximum sizes of the zones A of acceptable hardness are illustrated.

With this pre-quenching, there is very little thermal conduction from the inductively heated zone A towards the zones which are to be kept soft and such conduction can be reliably controlled. The transition zones are reduced to a very small amount, thus permitting greater variations in the quenching cycle, power input and work dimensions so that these less controllable factors do not have to be so closely maintained. Pie-quenching also results in an increase of one or two points Rockwell C hardness, this bein due to the fact that the heat is kept on longer, the end of the heating period being postponed and the beginning of the quenching cycle being advanced to overlap the longer heating period. Hence the temperature of the heated zones does not drop immediately after the quench is applied and there is an action like a soaking period while the temperature stays up.

Pre-quenching not only minimizes the size of the transition zone but will also minimize a, subsequently tempered area between any very hard area and a core hardened area as is sometimes encountered in certain objects if the body of apart is hardened throughout by the furnace method to one hardness and then a higher surface hardness is afterwards superimposed by the induction method. In such a process without .any prequenching, the subsequently applied heat from the induction heated surface will be conducted into the body of the part for an appreciable depth and will cause a general lowering inhardness, thus creating an undesired soft layer forming a transition zone of considerable size. Eliminating the delay between the heating and quenching cycles and causing them to overlap will minimize the depth of the tempered area to an appreciable extent.

A desirable apparatus for carrying out the preferred method is shown in Figs. 1 to 8. The numeral 2 indicates a semi-cylindrical guard welded to a flange 4 which is bolted to a suitable frame 6. Concentric with the guard 2 is a vertical shaft 8 which, by any suitable mechanism, can be set in rotation and raised and lowered as indicated by the arrows. The shaft has a flange ll] to which is bolted a work carrier I2 which is composed of insulating material such as Micarta. As indicated in Fig. '7, the carrier has holes H! for securing bolts and is provided with a central recess 16 from near the middle of which a series of drain openings l8 for cooling fluid slant outwardly and downwardly to register with openings in the flange l0. Other drain openings 29 in the circular side wall of the recess l6 slant outwardly and downwardly and continue through the work carrier above the flange. Vertical counterbored openings in the carrier locate a series of vertical supporting pins 22 all of exactly the same height, the pins being adapted to enter with a small clearance within the counterbore at the end of the work piece W just inside of the overhanging lip to approximately center the work piece before it is raised to operative position for heating and quenching. The ends of these pins are very hard and they provide a friction drive for rotating the work.

In its cold and unexpanded condition, the rotating piece can enter upwardly between three locating or centering screws 24 having rounded ends, the screws being carried by an annular quenching jacket 26 which is Welded to the guard 2. Two of the three screws 24 will initially be engaged by the rotating work piece due to centrifugal action and, as the piece expands, it may just make very light contact with the remaining screw 24 without any binding action which would stop rotation. Magnetic forces tend to center the piece. The screws are carefully pre-set in accordance with the known diameter of the work or by preliminary cut and try. The screws are supported in threaded openings in an outer imperforate jacket wall 23 and in an inner perforated jacket wall 39 the perforations forming quenching nozzles. The jacket also has an an-- nular botom and an annular top wall the latter having fittings 32 to which a very copious supply of quenching fluid such as water is supplied under pressure under control of a valve when the piece is heated by induction.

Heat by high frequency electromagnetic induction is applied to the piece by a one-turn copper induction coil til which is slightly tapered or frusto-conical and supported in a position concentric to the work and to the quenching Jacket. The coil has an arcuate portion extending for nearly a full circle, its ends being welded to vertical legs 42 which also extend laterally into the circle and into a recess in a frustoconical core 45. The core is supported in the coil by two little plates 2% fastened to the lower ends of the legs and unrelying the core, The core is preferably composed of powdered iron having a suitable binder. The legs 32 are extended upwardly to a shoulder i5 above which are blocks or plates 45 to be secured by bolts 48 to copper leads 55, The leads 56 are supplied with high frequency alternating current and are hollow so they can be supplied with cooling fluid through pipes 52. The Coll itself is not water cooled because to provide enclosing walls for a hollow coil would result in too much current carrying capacity in the extra metal. Between the shoulder 45 and the upper ends of the core and coil is interposed a thick washer 55 of insulating material. The core is tapered, being smaller at the top but this does not result in any asymmetry in the hardness pattern but insures symmetry. For some reason, perhaps because of the proximity of the leads, there is a tendency for a coil to heat the work more near the top and the taper compensates for this tendency.

The work piece to be treated is; placed on. the pins 22 manually and. a commercial timing unit 60 (Fig. 14') is started by a push button switch 62 which causes the master switch 64 to close. When switch 64 closes to start the timing cycle, it controls starting of a motor 66- which rotates the shaft 8 of the work carrier. At the same time, a solenoid 68 is energized tooperate a valve which causes pressure fluid from a pump to enter the front end of a pivoted cylinder 12 to cause lifting of the shaft 8. After a short interval, a switch 74 in the timer closes for an interval and energizes a solenoid 76 to. close a switch which connects a motor generator set to a step-down transformer 18 whereby the induction coil 46 is supplied with high frequency alternating current. Before the heating period is ended, a switch 80 is closed for an. interval to energize a solenoid 82 to open a normally closed valve 84 to supply quenching fluid to the quenching jacket 25, After the quenching period, the quenching fluid drains out and a switch 8'6 closes for a short interval to turn on the heating current for tempering. After the switch 86 opens, the timing unit is automatically reset ready for a new timing cycle. Since its master switch 64 is then open, the motor 66 stops and the solenoid 68 is de-energized allowing the valve 18 to spring to its normal position in which pressure fluid is admitted to the rear of the cylinder 12 to lower the shaft for unloading of the work piece and insertion of a new piece. Prior to insertion of a new work piece, cooling fluid is directed against the coil to dissipate the heat generated therein by the tempering operation. This heat would otherwise accumulate and interfere with the subsequent heating operations. The cooling fluid can be conveniently controlled by a foot treadle connected to the valve 84 since the exact time of application is not critical.

Without intending to limit the invention and to set forth a specific example of what has been found successful, it being understood that the relative size, shapes and relations of the coil and work are as indicated in Fig. 1, a race ring of SAE 1065 steel two inches in outside diameter, 1.816 inside diameter, 1.915 counterbore diameter, length 1.711 with the lip overhanging .070 inch, utilizing a power input of 40 kw. at 9600 cycles per second frequency, would have approximately the following cycle: With the timing unit 60 started at zero time, the work is brought up into operative relation to the induction coil and is rotated on its axis. At 1 seconds, the heat inducing current is applied to the coil. At 8 seconds, the quenching medium is applied and at 9% seconds the heating current is shut off thus providing a one second pre-quench or overlap. At 11 seconds the quench supply is turned off and the quench is allowed two seconds to drain completely from the jacket. The heat is turned on again for tempering at 13 seconds, lasting for 1 seconds and is discontinued at 14% seconds. The timing switch resets to zero at 15 seconds. The work is lowered to unloading position and removed by tongs.

There are so many critical factors that some of the preliminary pieces may need to be broken for observation of the hardness pattern which will show how to make any necessary corrections; Coil size and coil shape change the other factors considerably. The importance of an overlapping heat and quenching period is more pronounced 6, when the frequency is below about 20,000 cycles per second because for very high frequencies, the skin effect is more pronounced and the transition zone naturally becomes smaller. In the present example, the outer surface of the piece where the zone A intersects it is desirably hard. However, this zone A can be prevented from reaching the outer surface by shaping the coil differently, as by a concavity locating its intermediate position farther away from the bore of the piece. Zone B then extends along the middle of the outer surface between zones C.

' The degree of tempering is determined entirely by the period of the final reheating cycle. Duotility and grain structure of the inductively tempered parts heated for this short period are identical with that of parts tempered for hours in a furnace. In addition, induction tempering improves size stabilization to a considerable degree and inhibits growth or slight expansion of the work as often occurs over long periods of time at ordinary temperatures.

I claim:

1. The method of heat treating a work piece of heat hardenable metal, which consists in first applying heat alone to a portion of the work piece by high frequency electromagnetic induction for a predetermined period, then, before the piece is heated throughout to a hardening temperature, applying both a quenching medium and the induced heat together for a predetermined overlapping period, and continuing the application of said quenching medium alone from the end of the overlapping period.

2. The method of heat treating a hollow work piece of heat hardenable metal having a circular enclosing wall, which consists in supporting the work piece in concentric relation to an inductor, first applying induced heat from one side of the wall for a predetermined period, then applying a quenching medium from the opposite side of the wall together with a continued application of induced heat for a predetermined period of overlap, and continuing the application of said quenching medium alone from the end of the heating period.

3. The method of heat treating a hollow work piece of heat hardenable metal having a circular enclosing wall, which consists in supporting and rotating the work piece on its axis in con-= centric relation to an inductor, applying high frequency induced heat from one side of the wall for a predetermined first period to heat adjacent portions of the work piece to hardening temperature, then, before the remaining portions of the piece become heated to hardening temperature, applying a quenching medium from the opposite side of the wall together with a continued application of induced heat for a predetermined period of overlap, then discontinuing the supply of heat and continuing the application of said quenching medium alone during a third period beginning at the end of the overlapping period.

4. The method of hardening and tempering a hollow work piece of heat hardenable metal having an enclosing wall, which consists in supporting the work piece in concentric relation to an inductor, first applying induced heat from one side of the wall for a predetermined first period, next applying a quenching medium from the opposite side of the wall together with a continued application of induced heat for a predetermined period of overlap, continuing the application of said quenching medium alone during a third period beginning at the end of the overlapping period, and thereafter app1ying: inducedyheat from the same inductor for a tempering period while the work remains on the work support. 5. The method of heat treating a cylindrical work piece of heat hardenable metal having an overhanging lip, which consists in inducing heat to hardening temperature byelectromagnetic in.- duction in a zone including the entire length of the bore and the greater portion of the body of the piece, applying quenching medium, toathe piece before the heat can travel by conduction to the overhanginglip, said, quenchingmedium being applied after the heating period begins and before it ends to produce an overlap and .con-. tinuing without interruption after the heating period ends. v 1 THEODORE A. JAGEN.

REFERENCES CITED The following references are of recordinth'e file of this patent: i 7

Number 8 UNITED STATES PATENT Name Date Brooks Apr. 4, 1882 Newbury et a1 June 20, 1882 Koelkebuck et al. May 24, 1898 Bowser Dec; 29, 1914 Lingo Feb. 14, 1922 Davis May 7, 1929 Hulster Dec. 5, 1939 Ingalsbe Mar. 19, 1940 Denneen et a1 May 28, 1940 Denneen et a1 May 28, 1940 Somes Apr. 28, 1942 Somes 2 June 30, 1942 Somes Sept. 8, 1942 Bierwirt Mar. 30, 1943 Schackenbach Sept. 21, 1943 OTHER REFERENCES 0 Heat Treating and Forging, March 1941, page

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