US3806690A

US3806690A - Case hardening arrangement utilizing high q tuned circuit

Info

Publication number: US3806690A
Application number: US00300287A
Authority: US
Inventors: F Frungel
Original assignee: Individual
Current assignee: Impulsphysik GmbH
Priority date: 1972-02-12
Filing date: 1972-10-24
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23
Also published as: DE2206816A1; JPS5517473B2; JPS4889811A; DE2206816B2; CH568394A5; DE2206816C3; CA954193A

Abstract

Heating pulses are applied to body to be case hardened through a heating inductor coupled to a high Q tuned circuit through a low resistance, low inductance coupling loop. Tuned circuit is pulsed by high energy pulse. Short fall time of pulse causes increased self-cooling. A photoelectric arrangement indicates when body is properly positioned relative to heating coil and initiates heating pulse. Suitable heating inductor construction and arrangement for preventing voltage breakdown between heating inductor and body to be case hardened are described.

Description

United States Patent [191 Frungel 5] Apr. 23, 1974 1 1 CASE HARDENING ARRANGEMENT UTILIZING HIGH Q TUNED CIRCUIT [76] Inventor: Frank Frungel, Glockenocker 2,

' Zurich, Switzerland 7 [22] Filed; Oct. 24, 1972 211 Appl. No; 300,287

[30] Foreign Application Priority Data Feb. 12, 1972 Germany 2206816 3,259,527 7/1966 Beggs 148/165 2,930,724 3/1960 Rudd.... 148/150 3,398,444 8/1968 Nemy 148/165 2,462,903 3/1949 Romander 219/1075 3,118,999 l/1964 Dreyer 219/1075 3,622,138 11/1971 Kostyal 266/5 E 1,909,982 5/1933 Parker 219/1079 X 2,482,493 9/1949 King 219/1077 X Primary Examiner-Bruce A. Reynolds Attorney, Agent, or Firm-Michael S. Striker 5 7 ABSTRACT Heating pulses are applied to body to be case hardened through a heating inductor coupled to a high Q tuned circuit through a low resistance, low inductance coupling loop. Tuned circuit is pulsed by high energy pulse. Short fall time of pulse causes increased selfcooling. A photoelectric arrangement indicates when [56] References Cited body is properly positioned relative to heating coil and UNITED STAT S PATENTS initiates heating pulse. Suitable heating inductor con- 3,637,970 1/1972 Cunningham 219/10.75 Struetion and arrangement for preventing voltage 3,375,468 3/ 1968 Porterfield 219/10.75 breakdown between heating inductor and body to be 2,799,760 7/1957 Fruengel 219/1075 case hardened are described 2,416,172 2/1947 Gregory et a1 219/1077 3,403,241 9/1968 Kauffman 2l9/l0.79 46 Claims, 7 Drawing Figures 16 r 220 21 f 1 I PATENTEU APR 2 3 I974 FIGA ZYIIIIIIIIIIIIIIA FIG.7

CASE I-IARDENING ARRANGEMENT UTILIZING HIGH Q TUNED CIRCUIT BACKGROUND OF THE INVENTION The present invention relates to methods and arrangements for creating very hard surfaces having an extremely finely grained structure on metal bodies and particularly on steel. The so-created surfaces are highly corrosion resistant. More particularly, it relates to methods and arrangements for case hardening steel structures or bodies by means of applied pulsed high frequency oscillations, wherein the pulses have a very steep trailing edge and the pulse duration is generally less than 0.1 second. As criteria for the steep, trailing edge a fall time of less than 1 percent of the pulse duration has proved to yield proper results.

It is known that carbon steels and particularly modern martensitic steels can be case hardened by use of a rapidly applied high heat which heats the steel to a temperature as close to the melting point as possible, the application of said heat being followed by self cooling resulting from the heat conductivity of the body being case hardened. By such methods and arrangements hardnesses of 64Rc have been reached. However, use of conventional high frequency generators has to date resulted in a surprisingly low efficiency.

The present invention constitutes an improvement of the known method and arrangement which improves said efficiency and results in an improved product of having increased hardness.

SUMMARY OF THE INVENTION The present invention comprises an arrangement for case hardening of a metallic body.

In particular, the present arrangement comprises high frequency oscillator means having a high Q tuned circuit means and low internal impedence amplifier means connected to said high Q tuned circuit means. It comprises pulsing means for pulsing said high frequency oscillator means and terminating means for terminating said pulsing of said high frequency oscillator means after a predetermined heating time interval. Further comprised are heating inductor means forapplying heat to a predetermined portion of the surface of said body. Low resistance, low inductance coupling loop means couple said high frequency oscillator means to said heating inductor means.

In a preferred embodiment of the present invention the heating time interval is less than 0.1 second. The pulse of less than 0.1 second created by said pulsing and terminating means has a F all time less than 1 percent of the pulse width. This results in a high utilization of the self-cooling effect in carbon steels.

The novel features which are considered as characteristic for the invention are set forth in particular in theappended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a circuit diagram of an induction heater in accordance with the present invention;

FIG. 2 shows wave forms at selected points of the circuit of FIG. 1;

FIG. 3 shows an arrangement for initiating the pulses in the circuit of FIG. 1;

FIG. 4 shows the construction of a heating inductor suitable for use in the circuit of FIG. 1;

FIG. 5 shows a heating inductor partially surrounded by ferrite material;

FIG. 6 shows an arrangement for terminating the pulses generated in the arrangement of FIG. I; and,

FIG. 7 shows a curve of heating current as a function of time using the arrangement of FIGS. 1 and 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS:

A preferred embodiment of the present invention will now be described with reference to the drawing.

FIG. 1 shows a circuit in accordance with the present invention. A known high freuqency oscillator with a frequency for example in the region between 20 and 40 MHz is used. However, the Q of the oscillator must be much higher than that used in conventional generators employed, for example, in the welding of plastic sheeting. The Q of the circuit should be at least and may for example be in the range of between 100 and 300. The high Q was found to be necessary afterexperimentation with conventional high frequency oscillators showed surprisingly poor results when used for the case hardening of a body in accordance with the present invention. This may'be explained as follows: the inductivity of the heating inductor is only of the order of several nH. Thus when such a heating inductor is introduced into the tuned circuit'of conventional type, its inductivity is only an extremely small fraction of the total inductivity of the circuit, thus allowing only a small percentage of the total energy to become available at the surface of the body. Thus, the present induction hardening apparatus must be of extremely large size and is commercially unfeasible. Use of a tuned circuit with a very high Q, for example a Q of 100 and an oscillator power of IOkW can result in a l MVA oscillation in the tuned circuit. When the heating inductor is supplied from a tuned circuit with such a high reactive power, a very high degree of utilization of the available power can be achieved. In order to achieve such a'high degree of utilization, a small coupling loop is introduced into the oscillating cavity of the high Q circuit,and the actual heating inductance is connected in parallel to this coupling loop. A tuning capacitor of high capacity is connected in parallel to the two inductors in-order that an exact resonant frequency corresponding to the resonant frequency of the main oscillating circuit can be achieved. Reference numeral 1 in FIG. I indicates a cavity resonator having a very high O. For example the cavity may have a volume of one quarter cubic millimeter and may be constructed from copper sheeting with possibly some silver plating. The cavity is tuned by means of an air condenser 2 to a convenient frequency, for example 27.l2 MHz. The cavity resonator is supplied by an oscillator tube 3 herein also referred to as amplifier means in conventional fashion, the anode of tube 3 being connected to the circuit via a coupling capacitor 4. Feedback is achieved by means of a small loop 5, a conventional grid capacitor 6 and grid resistance 7.

It is now possible to directly apply rectangular pulses to the anode of tube 3, via, for example, choke 8, or alternatively, a special differential pulse transformer may be used. The primary winding 10, the secondary winding 9 and the iron core 11 are comprised in this pulse transformer. A small, low inductance capacitor. 12 serves to short-circuit the high frequencies. Also shown in FIG. I is the source of electrical energy 15, and connected in parallel thereto a high capacitance capacitor 13 which is connected in series with the primary winding of the pulse transformer and also with electronic switch means (first switch means) 14. Switch means 14 may be a large thyristor, an ignitron or even a conventional switch. When switch 14 changes from the nonconductive to the conductive state, capacitor 14 discharges through primary winding 10, causing a current as shown in curve a of FIG. 2 to flow through primary winding 10. This current in turn causes a voltage proportional to the first derivative thereof to appear across secondary winding 9. This voltage is shown in curve b in FIG. 2. Since the rate of increase of current is substantially linear, a substantially rectangular induced voltage pulse b results. It thus becomes possible to operate with very high operating voltages, for example, l0,000 volts at the anode of tube 3. For such high operating voltages no semiconductor switching means such as thyristors are available at the current state of the art. Thus if it is desired that a thyristor be used for switching, the circuit location in the primary circuit of the transformer as is shown for element 14 is very desirable. Here the thyristor does not undergo potential differences of more than one kV, but is subjected to very high currents. Thus, the thyristor need only have an operating voltage of 1,000 volts, while capacitor 13 under these conditions has 100 times the capacity but is charged to only l/lO of the voltage of capacitor 12. The charging of capacitor '13 from the stabilized voltage source 15 must take place sufficiently rapidly so that the capacitor is charged in time for the next subsequent heating pulse. Since the so-required rate is approximately pulses per second, such circuits are well known and their constructions present no difficulty.

As mentioned above, it is desired in accordance with the present invention that the oscillations generated in the tuned circuit 12 are supplied to the heating inductor with a high efficiency. For this purpose, the coupling loop 16, which has a low resistance and a low inductivity, is inserted into the resonant cavity 1. The Q of the tuned circuit and the geometry of the insertion of the coil are interrelated. The higher the circuit Q, the smaller must be the surface enclosed by loop 16 within tank circuit 1. The enclosed area of labelled 16a in FIG. 4. Heating inductor 17 is connected in parallel with coupling loop 17 and positioned very closely to the surface of the body.

The circuit including the heating inductor is tuned via a capacitor 18, which may for example be a ceramic capacitor, to approximately the oscillating frequency of the high frequency oscillator. The exact frequency adjustment is carried out by means of a trimming capacitor 19 connected in parallel with capacitor 18. Capacitor 19 may be a parallel plate air capacitor. Under these conditions reactive powers of up to l MVA or more can appear in the tuned

circuit comprising elements

16, 17 and 18. Under such high reactive powers, voltage in the order of kilovolts can appear across the heating inductor loop 17 which may under some conditions comprise only a single small straight section of wire or a single small loop. Under such conditions voltage breakdown between the loops of inductor l7 and the body to be case hardened may be prevented by use of an insulating foil 21 positioned either between the body and the heating inductor or actually pasted around the body. Foils with a temperature characteristic extending to 1200C are commercially available. Use of such foils enables very high hardening temperatures to be generated at the surface of the body 20 while still maintaining adequate electrical insulation.

It is further possible to cool the body by means of blown carbon dioxide or nitrogen, or, for lower requirements, air and for higher requirements, argon, the appropriate gas being blown in the direction of arrow 22. This movement of gas also removes ions which may have formed in the air. Thus in this case the blown air does not serve primarily for the cooling of the surface, but serves for the removal of ions which are formed during the time of the pulse and through which a voltage breakdown can take place. Care must be taken that the velocity of gas 22 is very high. It may for example be necessary to use Laval nozzles for operating near the velocity of sound. When such rapidly flowing gas is used, the cooling effected by the gas is of the same order of magnitude as the self-cooling which results through the internal heat conductivity of the body 20 and takes place in the direction of arrows 23 in FIG. 1.

It has also been found rather surprisingly that plain tap water has a very high breakdown characteristic for the short pulses employed in this invention. The breakdown strength is approximately 200 killivolt per centimeter. Thus, instead of the gas indicated at reference numeral 22, the surface of the body can be insulated relative to inductor 17 by use of streaming water and, in particular, plain tap water. In this case isolating foil 21 is not required. The insulating effect of water is approximately the same as could be obtained by the use of air at a pressure of approximately 7 atmospheres between the body 20 and the inductor 17. The cooling effect of the water is here a secondary effect, the primary purpose of the water being the insulation.

Of course, if it is desired to manufacture an extremely oxidation-free surface, a cooling medium other than water can be used. For example methanol which has strongly reducing characteristics and leaves a smooth metallic surface after hardening may be employed. Use of propane, hydrogen or methane as cooling medium applied in the direction of arrow 22 will also prevent tarnishing of the surface. It must be stressed that in no case can the self-cooling due to the thermoconductivity of the object itself be dispensed with. In general, carbon steel has a heat conductivity which is at least I000 times that of a good cooling gas. It is, of course, important for the manufacture of the so-called white layers (very hard surfaces) that not only does a spontaneous heating to a very high temperature to just below melting point take place but also that after the application of the heating pulse a very rapid cooling takes place. This can in practice only be obtained due to the self-cooling of the object, although of course the gas or the liquid described above can be an additional aid.

It should further be noted that the cooling by water or oil or methanol can further result in a slight product improvement when layers of 0.2 millimeter thickness are to be hardened. In this case pulses having a relatively long pulse width of approximately 10 millisecends are used. When such wide pulses are used, the self-cooling effect is stronger for the layers which are more internal to the body, while the very external layers of the heated surface remain hot longer since the heated layers underneath prevent the rapid conduction of heat from the outer surface towards the interior of the object. Thus, it has been found by measurement that the outer layers are actually less hardened than the inner layers, so that the additional cooling of the outer surfaces under moving air, gas or liquid will aid in the hardening of these outer surfaces. Then a uniform hardness can be reached for a thickness of from 0.2 to 0.3 millimeters. For example, hardnesses of 950 kp/mm over a whole hardened section can be achieved in the production of band saws from carbon steel. Further, the method of the present invention does not require the subsequent heating that is usual in spontaneous quenching processes to prevent embrittlement, since the so-manufactured layers are very elastic and not subject to failure by brittleness. Thus, further thermal treatment is not required. The case hardened structures manufactured in accordance with the present invention are so stable that microscopic observation shows that they decompose into the martensitic base material only after an application time of approximately six hours and at a temperature of 450C.

To increase the production speed, it is of course desirable to have the body to be hardened either rotated steadily or moved past the heating coil at a definite rate and to initiate the pulse when the body is correctly positioned relative to heating inductor 17. Here a circuit as shown in FIG. 3 can be used. Reference numeral 30 in that Figure refers to a neon-helium laser of the conventional type which sends a fine beam 31 through the body 32 which may, for example, be the toothed profile of a saw. The beam impinges upon a photodiode 33 j which transforms it into an electrical signal which in per second can be used and an average anode loss of only 2 kW results. The peak anode voltages may range between 10,000 and 15,000 volts and the reactive power in the tuned circuit may reach 5 MVA.

Further shown in FIG. 1 is a special circuit arrangement for permitting the initial tuning of the circuit. A switch 24 is shown whereby the anode of tube 3 may be connected directly to the output of the relatively low voltage source through a resistance 25. Under such conditions the tuned circuit only contains about one one-hundredth of its normal power. In order to effect the correct tuning, a small antenna 26 is positioned near the tuned

circuit comprising elements

16, 19 and 17. This antenna may, for example, comprise a small length of wire 26 connected to a glow lamp 27 and having at the other side of the glow lamp an additional length of wire as a counterweight. The circuit is then tuned for maximum brightness of the glow lamp, thereby assuring that it is properly tuned when full power is applied.

Particularly good results may be obtained when the resonant frequency at the heating inductor is trimmed in such a way that the full resonance is only available when the Curie temperature and higher temperatures are reached on the surface of the body. It is known that steel has a high permeability below the Curie temperature, while having only a permeability comparable to air above the Curie temperature. Thus, the tuning described above may be carried out by using a body of copper or other substance having a low ferromagnetic permeability. In this way, the full power of the heating pulse is not applied to the body at the beginning of the pulse, that is in the first few microseconds thereof. However, during the remainder of the pulse width, and at crossing of the Curie temperature, a spontaneous and very sudden increase in the heating results, since as soon as the Curie temperature is passed, the circuit is correctly tuned to convert the reactive power almost completely into real power. In accordance with the present invention it is very important that the trailing edge of the pulse is very steep (i.e. that the fall time is very short); under the above conditions a heating impulse of substantially needle shape results which causes the hardening of a particularly thin surface, the exact depth of which may be determined in accordance with the equation for the depth of penetration of high frequency signals into steel. If a hardening to a depth deeper than such a thin layer (which may only be several thirty thousandths of a millimeter) is desired, then pulses having a longer width, for example, 50 millisec onds, may be employed and the conductivity of the body causes a corresponding deeper layer for example 0.2 millimeters from the surface, to be heated also.

FIG. 4 shows a particular preferred embodiment of the heating inductor. The inductor itself in this particular embodiment is a hollow tube with a very thin opening 41 which may have substantially conical terminations 42 which in turn are adjacent to the jaws of the contact clamp 43. A high pressure pipe 44. which is situated within the jaws 43 can be used for supplying the high pressure water required for cooling. Clamp 43 may comprise two flat conducting portions which are rigidly clamped together and whose

inner surfaces

19a and 19b are insulated from each other by a thin dielectric 40. The contact clamp can be so designed that capacities of an order of magnitude of pF are realized so that

capacitors

19 or 18 may be smaller capacitors than would otherwise be required. Because of conical portions 42 the inductors, if damaged or destroyed, may be easily interchanged. The water under high pressure flows in the direction of the arrow 45 through the bore 41 and flows out in the direction of the arrow 46. Either distilled water or tap water which is free of lime may be used. The pressure to be used here should be more than the pressure of three atmospheres, and preferably as high as 40 atmospheres, while the pipe used for inductor 17 may be very thin, as for example 2/10 mm. A good material for the manufacture of the inductors is silver piping. Surprisingly, drawn steel tubing can also be used if it is copper plated and if possible also silver plated. Of course, the higher the velocity of the cooling medium the higher the pulse rate that may be used and correspondingly, the higher the thermal requirements set for inductor 17.

It is of course desirable that the power available in inductor 17 be transferred to the body to the greatest extent possible. For this purpose the inductor may be surrounded in part by a ferrite material 47 as shown in FIG. 5. Commercial high frequency ferrites are available which have permeabilities of the order of magnitude of 600 to 1500 and, therefore, represent a substantial magnetic shortcircuit of the air space which lies outside of the body. Thus the body 20 can be heated with very high field strength and at very low losses even through insulating foil 21. If the correct type of magnetic material 47 is chosen, a decrease in permeability for increasing currents in inductor l7, and a corresponding decrease of inductivity can be achieved, while for decreasing currents in inductor 17 the permeability can increase. All manufacturers of such ferrite materials furnish curves of permeability versus magnetization. When the Curie temperature is passed at that portion of the surface which is being hardened, causing an increase in the real power and a decrease in the reactive power, then the permeability of the material 47 will inv crease. Thus the permeability of the ferrite material 47 compensates for the change in permeability in the body resulting from the passing of the Curie temperature, thereby allowing approximately the same power to be applied to said body both below and above the Curie temperature.

Because of variations in the body to be casehardened, it is often difficult to maintain the optimum hardening temperature in mass production runs. For this purpose the circuit of FIG. 6 may be used. The body to be casehardened hereis a saw having reference numeral 20. Inductor I7 is to harden a predetermined portion of the surface of the sawteeth. The loops of the inductor may enclose the teeth of the saw from each side, one loop on each side. As the blade of the saw moves past the inductor, the arrangement of FIG. 6 is used to terminate the pulse. In this case the circuit is adjusted in such a manner that the pulse is merely initiated by the circuit of FIG. 3 and has a pulse width which is arbitrarily chosen to be longer than the maximum desired pulse width. The pulse is to be terminated by electronic terminating means which, for example, may comprise means connected in parallel with the oscillator circuit for shortcircuiting the latter when the desired temperature is reached, thereby preventing any energy from reaching inductor 17. The switch means (herein referred to as second switch means) may, for example, be an ignitron or a high voltage thyratron. Referring again to FIG. 6, the heat waves which emanate from the body 20 are focused onto a photodiode 54 via a lens 52 and a filter 53. The photocell 54 is connected in series with a resistance 56 and a battery 55 in the conventional fashion. The pulses resulting when the sofocused heat waves strike photodiode 54 are amplified by an amplifier 57 which may for example be a threshold amplifier which furnishes a pulse on line 58 to the control grid of a thyratron 59 (FIG. 1), whenever the voltage at its input exceeds a predetermined threshold voltage. It will be noted that thyratron 59 has an anode connected to the anode of the oscillator tube 3 via a choke 8 and a cathode connected to ground. Thus when the thyratron becomes conductive it substantially shortcircuits the high frequency oscillator thereby absorbing the energy that would normally be furnished thereto and thereby preventing this energy from reaching inductor 17. The pulse is thus actually shortcircuited by thyratron 59 prior to the natural termination thereof. If a hydrogen thyratron is used which has a current carrying capacity of more than 300 amps and can withstand peak voltages of to kV, it can readily be accomplished that the remaining current of the pulse is completely absorbed by the thyratron instead of the oscillator tube. Filter 53 may, for example, be a light blue filter which emits light only after the predetermined portion of the surface of the body has reached a temperature of more tha 1200C. When this temperature is reached, which is the particular temperature regarded as an optimum hardening temperature, then a very rapid rise in current in photodiode 54 results and the pulse is abruptly terminated at the correct temperature, regardless of the structure of the body. It is simply required that a small but representative part of the heated portion of the body in FIG. 6) is correctly focused through the optical arrangement onto the photodiode 54. A great selection of filters 53 is available in the present state of the art. Orange, green and blue filters are available, so that the correct filter for a desired temperature is readily found.

The heating pulse is again shown in FIG. 7. At time a the pulse starts, for example, initiated by the circuit of FIG. 3 in conjunction with thyristor 14. The pulse would normally have a trailing edge as pictured in curve b. However, because of the temperature measured by photocell 54, thyratron 59 is ignited at time c, so that the pulse decreases to zero vary rapidly at time c which of course preceeds the time at which it would normally collapse. It is further possible to introduce delay means following amplifier 57 so that thyratron 59 is not fired until a time d following the reception of the heat pulse at time c. In this case, a selected amount of time can elapse, so that the body (workpiece) is heated to a greater depth than would be the case if the pulse collapsed immediately at the time that the outermost surface reached the desired temperature.

It is seen that the use of a circuit such as that shown in FIG. 6 in conjunction with a shortcircuiting switching element such as thyratron 59 very readily decreases the trailing edge of the heating pulse after the correct temperature has been reached. As stated above the switching element used need not be a thyratron. High voltage ignatrons as well as other components may be used.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means for applying a substantially rectangular pulse to said high frequency oscillator means over a determined heating interval, said pulsing means comprising first switch means for initiating said pulse and second switch means for terminating said pulse; heating inductor means for applying heat to a predetermined portion of the surface of said body; and low resistance, low inductance coupling loop means for coupling said heating inductor means to sai high frequency oscillator means.

2. An arrangement as set forth in claim 1, wherein said predetermined heating interval is a time interval of less than 0.l second.

3. An arrangement as set forth in claim 1, further comprising ferrite material partially enclosing said heating inductor means, said ferrite material having a permeability exceeding 100 and low high frequency losses at frequencies higher than MHz.

4. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means including cavity resonator means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means connected to said high frequency oscillator means for initiating the oscillations thereof and terminating said oscillations after a determined heating interval of less than 0.1 seconds; heating inductor means for applying heat to a predetermined portion of the surface of said body; and low resistance, low inductance coupling loop means extending into the cavity of said cavity resinator means for coupling said heating inductor means to said high frequency oscillator means.

5. An arrangement as set forth in claim 4, wherein said coupling loop means extends into the cavity of said cavity resonator means for a distance corresponding to said-Q of said tuned circuit means.

6. An arrangement as set forth in claim 5,, wherein said O of said tuned circuit means exceeds 100.

7. An arrangement as set forth in claim 6, wherein said cavity resonator means comprise copper sheeting enclosing a volume of approximately one quarter cubic meter.

8. An arrangement as set forth in claim 4, further comprising tuning capacitor means connected in parallel with said heating conductor means and said coupling loop means.

9. An arrangement as set forth in claim 8, wherein said tuning capacitor means comprise variable capacitor means.

10. An arrangement as set forth in claim 9, wherein said variable capacitor means comprise parallel plate air capacitor means.

11. An arrangement as set forthin claim 10, further comprising circuit means for operating said high frequency oscillator means at decreased power during initial adjustment; further comprising glow lamp means positioned near said heating inductor means, meximum glow of said glow lamp indicating correct adjustment of said tuning capacitor means.

12. An arrangement as set forth in claim 4, further comprising electrical insulating means insulating said metallic body from said heating inductor means.

13. An arrangement as set forth in claim 4, further comprising means for blowing gas under pressure through the space between said body and said heating inductor means, for removing of ions formed therebetween.

14. An arrangement as set forth in claim 13, wherein said gas is nitrogen.

15. An arrangement as set forth in claim 13, wherein said gas is air.

16. An arrangement as set forth in claim 13, wherein said gas is argon.

17. An arrangement as set forth in claim 13, wherein said means for blowing gas comprise Laval nozzles.

1 18. An arrangement as set forth in claim 4, further comprising liquid insulating means flowing between said body and said heating inductor means, said liquid insulating means having a breakdown voltage substantially higher than that of air.

19. An arrangement as set forth in claim 18, wherein said breakdown voltage of said liquid insulating means is at least seven times that of air.

20. An arrangement as set forth in claim 18, further comprising reducing means flowing between said body and said heating inductor means simultaneously with said liquid insulating means.

21. An arrangement as set forth in claim 20, wherein said reducing means comprise methanol.

22. An arrangement asset forth in claim 20, wherein said reducing means comprise liquid hydrocarbon.

23. An arrangement as set forth in claim 18, wherein said liquid insulator means further constitute means for cooling the outermost surface of said body.

24. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval, said pulsing means comprising electronic switch means having a control electrode and having a conductive state in response to a control signal at said control electrode, connected to said high frequency oscillator means in such a manner that said switch means shunt said high frequency oscillator means when in a conductive state, thereby terminating said oscillations; heating inductor means for applying heat to a predetermined portion of the surface of said body; low resistance, low inductance coupling loop means for coupling said heating inductor means to said high frequency oscillator means; and control signal furnishing means for furnishing said control signal to said switch means at the end of said heating interval.

25. An arrangement as set forth in claim 24, wherein said control signal furnishing means comprise temperature measuring means measuring the temperature of said predetermined portion of said surface of said body and furnishing said control signal when said someasured temperature is a predetermined temperature.

26. An arrangement as set forth in claim 25, further comprising delay means interconnected between said control signal furnishing means and said control electrode of said electronic switch means.

27. An arrangement as set forth in claim 26, wherein said delay means comprise adjustable delay means.

28. An arrangement as set forth in claim 24, wherein said electronic switch means comprise thyratron means.

29. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval; heating inductor means for applying heat to a predetermined portion of the surface of said body; low resistance, low inductance coupling loop means coupling said heating inductor means to said high frequency oscillator means; and ferrite material partially enclosing said heating inductor means, said ferrite material having a permeability exceeding and low high frequency losses at frequencies higher than l5MHz.

30. An arrangement as set forth in claim 29, wherein said ferrite material comprises material having a decreasing permability in response to increasing magnetization thereof.

31. An arrangement as set forth in claim 29, wherein said permeability of said ferrite material increases when the temperature at said selected portion of said surface of said body reaches the Curie temperature.

32. An arrangement as set forth in claim 31, wherein said increase of permeability of said ferrite material compensates for the decrease of permeability of said body upon reaching said Curie temperature.

33. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval; heating inductor means for applying heat to a predetermined portion of the surface of said body, said heating inductor means comprising thin, hollow metal pipe means having a first and second conical termination; low resistance low inductance coupling loop means coupling said heating inductor means to said high frequency oscillator means; contact clamp means having conical jaws for receiving said conical terminations of said metal pipe means; and means for circulating high pressure liquid cooling means through said contact clamp means and said metal pipe means.

34. An arrangement as set forth in claim 33, wherein said contact clamp means comprise first and second contact clamp means respectively receiving said first and second conical termination, said first and second contact clamp means each having an inner surface closely spaced to the corresponding inner surface to the other of said contact clamp means; further comprising insulator plate means positioned between said sofacing inner surfaces, for effecting electrical insulation therebetween.

35. An arrangement as set forth in claim 34, wherein said first and second contact means and said insulator plate means form electrical capacitance means having a high capacity.

36. An arrangement asset forth in claim 33, wherein said high pressure liquid cooling means comprises water.

37. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means, said tuned circuit means comprising cavity resonator means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval; heating inductor means for applying heat to a predetermined por- 12 tion of the surface of said body; and low resistance low inductance coupling loop means for coupling said heating inductor means to said high frequency oscillator means, said coupling loop means extending into the cavity of said cavity resonator means.

38. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency 0scillator means having a high Q tunedcircuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval, said pulsing means comprising energy storage means, pulse transformer means having a secondary winding connected to said high frequency oscillator means and a primary winding,

and first switch means for connecting said primary winding of said pulse transformer means to said energy storage means when in a conductive state; heating conductor means for applying heat to a predetermined portion of the surface of said body; and low resistance low inductance coupling loop means for coupling said heating inductor means to said high frequency oscillator means.

39. An arrangement as set forth in claim 38, wherein said energy storage means comprise capacitor means.

40. An arrangement as set forth in claim 39, wherein said first switch means comprise thyristor means.

41. An arrangement as set forth in claim 40, wherein the discharge of energy from said capacitor means through said primary winding of said pulse transformer means creates a current through said pulse transformer means having a substantially constant rate of increase with respect to time, thereby creating a substantially rectangular voltage across said secondary winding of said pulse transformer means.

42. An arrangement as set forth in claim 41,- wherein said thyristor means has a gate, said thyristor means having a conductive state in response to a voltage at said gate; further comprising means applying said voltage to said gate when said body is correctly positioned relative to said heating inductor means.

43. An arrangement as set forth in claim 42, wherein said means applying said voltage to said gate comprise photoelectric means.

44. An arrangement as set forth in claim 43, wherein said photoelectric means comprise a light source; and photoelectric transducing means receiving light from said light source intermittently in dependence on the position of said body relative to said heating inductor means.

45. An arrangement as set forth in claim 44, wherein said light source is a neon-helium laser.

46. An arrangement as set forth in claim 45, wherein said photoelectric transducing means is a photodiode.

Claims

1. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means for applying a substantially rectangular pulse to said high frequency oscillator means over a determined heating interval, said pulsing means comprising first switch means for initiating said pulse and second switch means for terminating said pulse; heating inductor means for applying heat to a predetermined portion of the surface of said body; and low resistance, low inductance coupling loop means for coupling said heating inductor means to said high frequency oscillator means.

2. An arrangement as set forth in claim 1, wherein said predetermined heating interval is a time interval of less than 0.1 second.

3. An arrangement as set forth in claim 1, further comprising ferrite material partially enclosing said heating inductor means, said ferrite material having a permeability exceeding 100 and low high frequency losses at frequencies higher than 15 MHz.

5. An arrangement as set forth in claim 4, wherein said coupling loop means extends into the cavity of said cavity resonator means for a distance corresponding to said Q of said tuned circuit means.

6. An arrangement as set forth in claim 5, wherein said Q of said tuned circuit means exceeds 100.

11. An arrangement as set forth in claim 10, further comprising circuit means for operating said high frequency oscillator means at decreased power during initial adjustment; further comprising glow lamp means positioned near said heating inductor means, meximum glow of said glow lamp indicating correct adjustment of said tuning capAcitor means.

14. An arrangement as set forth in claim 13, wherein said gas is nitrogen.

15. An arrangement as set forth in claim 13, wherein said gas is air.

16. An arrangement as set forth in claim 13, wherein said gas is argon.

18. An arrangement as set forth in claim 4, further comprising liquid insulating means flowing between said body and said heating inductor means, said liquid insulating means having a breakdown voltage substantially higher than that of air.

22. An arrangement as set forth in claim 20, wherein said reducing means comprise liquid hydrocarbon.

25. An arrangement as set forth in claim 24, wherein said control signal furnishing means comprise temperature measuring means measuring the temperature of said predetermined portion of said surface of said body and furnishing said control signal when said so-measured temperature is a predetermined temperature.

29. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval; heating inductor means for applying heat to a predetermineD portion of the surface of said body; low resistance, low inductance coupling loop means coupling said heating inductor means to said high frequency oscillator means; and ferrite material partially enclosing said heating inductor means, said ferrite material having a permeability exceeding 100 and low high frequency losses at frequencies higher than 15MHz.

34. An arrangement as set forth in claim 33, wherein said contact clamp means comprise first and second contact clamp means respectively receiving said first and second conical termination, said first and second contact clamp means each having an inner surface closely spaced to the corresponding inner surface to the other of said contact clamp means; further comprising insulator plate means positioned between said so-facing inner surfaces, for effecting electrical insulation therebetween.

36. An arrangement as set forth in claim 33, wherein said high pressure liquid cooling means comprises water.

37. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means, said tuned circuit means comprising cavity resonator means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval; heating inductor means for applying heat to a predetermined portion of the surface of said body; and low resistance low inductance coupling loop means for coupling said heating inductor means to said high frequency oscillator means, said coupling loop means extending into the cavity of said cavity resonator means.

38. Arrangement for casehardening of a metallic body, comprising, in combination, high frequency oscillator means having a high Q tuned circuit means and low internal impedance amplifier means connected to said tuned circuit means; pulsing means coupled to said high frequency oscillator means for initiating the oscillations thereof and for terminating said oscillations after a determined heating interval, said pulsing means comprising energy storage means, pulse transformer means having a secondary winding connected to said high frequency oscillator means and a primary winding, and first switch means for connecting said primary winding of said pulse transformer means to said energy storage means when in a conductive state; heating conductor means for applying heat to a predetermined portion of the surface of said body; and low resistance low inductance coupling loop means for coupling said heating inductor means to said high frequency oscillator means.

42. An arrangement as set forth in claim 41, wherein said thyristor means has a gate, said thyristor means having a conductive state in response to a voltage at said gate; further comprising means applying said voltage to said gate when said body is correctly positioned relative to said heating inductor means.