DE2206816C3 - Device for producing extremely fine-grained metallic surface structures - Google Patents

Description

a) the high-frequency generator contains, as an oscillating circuit, a well-known pot circle (1) which is of large volume and has an fC / ice quality above 100

b) the oscillator tube feeding the pot circle (1) (3) has an internal resistance below 1000 ohms,

c) the inductor (17) used to heat the steel body is connected to a low-resistance, low-inductive double loop that goes into the interior of the pot circle (1) protrudes fed

2. Apparatus according to claim 1, wherein a Diffo entialimpulstransformator is provided for generating the pulse feeding the oscillator tube the primary side has a capacitor brought to discharge by a thyristor circuit, characterized in that one of a workpiece to be hardened (32; controlled light barrier for periodic ignition of the thyristor (14) is provided by disconnection or interruption

3. Apparatus according to claim 2, characterized in that a for feeding the light barrier fine-beam neon-helium laser (30) is provided as a light source, to which a small-area photodiode (33) is assigned as a receiver

4. Apparatus according to claim I, characterized in 4s shows that the decoupling loop (16) is connected in parallel with the heating inductor (17) and both jointly have one or more capacitors (18, 19) connected in parallel, of which at least one is an air condenser (19) (plate condenser sator) is switched to be trimmable.

5. Apparatus according to claim 4, characterized in that the inductor (17) by means of conical Clamping jaws (43), which at the same time represent a liquid seal, in a two-pole connection SS extension piece protrudes, and that the inductor (17) as a metal tube with a very thin internal width, preferably as drawn silver pipe or copper-plated-silver-plated steel pipe, and is made of water or another coolant with at least 8 atm. Overpressure is flowing through that, furthermore, the feeding pole pair at a small distance, preferably insulated from one another by a mica (40) or ceramic plate, low-inductance and with a large Capacity is formed and this capacity is part of the oscillating capacity of the coupling loop (16) and the heating inductor (17).

6. Apparatus according to claim 4 and 5, characterized

characterized in that, for trimming the device, the oscillator tube (3) is operated with reduced power and an indicator lamp (27) is capacitively assigned to the heating inductor (17) via a small HiIFs antenna (26)

7. Device according to claims 1 to 6, in which the heating inductor is partially enclosed by a ferritic material, characterized in that the ferritic material (47) has a permeability of more than 100 and small high frequency losses in the range of more than 15MHz owns

8. Apparatus according to claim 7, characterized in that the ferritic material (47) with a increasing magnetization has decreasing permeability and that by the heating inductor (17) flowing current together with this permeability has a rating at which the ferritic material (47) below the Cnrie point of the surface elements to be hardened Workpiece (20) a smaller permeability and above the Curie point and sinking through the inductor (17) flowing current has a higher permeability and thus has a compensatory effect

9. Apparatus according to claim 1 to 8, characterized in that between the workpiece (20) and Heizinduktor (17) a highly heat-resistant plastic film (21) that prevents flaps and is made of a organometallic compound is arranged

10. Apparatus according to claim 1 to 9, characterized in that for generating a neutral or reducing atmosphere and to remove in the space between inductor (17) and Workpiece (20) ions generated a stream of neutral or reducing gas (22) with high Speed, alternatively by using a Laval nozzle, is provided in this space

11. Device according to claims 1 to 9, at a laminar flowing, liquid cooling medium is provided between the inductor and the workpiece, characterized in that the cooling medium has a dielectric strength that of pulses higher than 7 times that of air.

The present invention relates to a device for producing extremely fine-grained metallic surface structures by inductive high-frequency heating with a duration of less than 0.1 seconds Pulses and subsequent self-deterrence through the use of rectangular programmed power pulses with an extremely steep trailing edge corresponding to a fall time of less than 1% of the impulse exposure time according to the previously published process according to the main patent 19 57 884.8, which is used to carry out a High-frequency generator, at least one resonant circuit and a vain inductor are required

The present invention aims at an advantageous one device-like further development of the process according to the main patent and is based on the knowledge that are laid down in the main patent. She has an inventive combination of various constructive

and structural features for the task, which, taken together, are only perfect «? Enable production of the aforementioned hardness structure on practical workpieces. Structures of this type have also become known in the literature as so-called white slips, which always have microhardness between 900 and 1700 kp / mm ² . These white layers always occur on all carbon-containing hardenable steels when a high temperature occurs spontaneously and the high temperature quickly disappears due to self-cooling.The level of this temperature must be much higher than the conventional hardening temperature and often rise to near the melting point.

According to the invention, this object is achieved by a combination of the following features:

a) the high-frequency generator has an oscillating circuit with a circular quality above 100, the is designed as a large-volume cup circle,

b) the oscillator tube feeding the pot circle has an internal resistance below 1000 ohms,

c) the inductor used to heat the steel body is via a low-resistance, nierlerindnktiv double loop that goes into the inside of the pot circle protrudes, fed

The high-frequency generator works in a manner known per se (CH-PS 4 28 821) in a high-frequency range above 5 MHz, preferably with the industrial frequency of 27.12 MHz.

The extraordinary circular quality provided according to the invention was found in the conception of the invention as required, after all working with conventional high frequency generators a surprising one showed poor efficiency on the workpiece. This can be explained by the fact that the inductance of the Heating inductor is only in the order of magnitude of a few nH and thus when they are in an oscillating circuit conventional type is involved, only a tiny one Including fraction of total inductance In this way, only an equally small fraction came up on the Work piece surface become effective. But it was precisely this that led to uneconomical, huge induction hardening devices according to the state of the art, so that the Procedure could not be naturalized in practice.

By using an oscillating circuit with a very high circular good, mar ζ is achieved. B that with a Circle quality of 100 and an oscillator vibration power of 10 kW already oscillates I MVA in the resonant circuit. If you get out of a resonant circuit with such a high Reactive power cleverly feeds the inductor, it is possible to achieve an extraordinarily high level of efficiency for ponds. To do this, a small coupling loop is raised in the oscillating cavity of the circle Quality inserted and the actual heating inductor connected in parallel to this coupling loop both have a large tuning capacitor, which causes a reasonably accurate resonance match between the main circuit and the Heating circuit is present

Regarding the state of the art, it should be pointed out in connection with the subclaims that it has already become known to partially enclose a heating inductor with a ferritic material (DE-AS 12 Il 235).

Preferred embodiments of the invention are described in detail below with reference to the drawings explained in more detail

In the drawings shows

Fig. 1 is a circuit diagram of a pot circle with an exciter circuit,

F i g. 2 Course of the current curve in the primary part and the s voltage curve in the secondary part of the generator,

3 shows a device for synchronizing the Workpiece feed,

Fig. 4 is a cross-section of a high performance suitable inductor,

ίο F i g. 5 an inductor surrounded by a ferritic jacket with an insulating film in the air gap to the Workpiece,

F i g. 6 an additional control device for taking into account different material qualities and

7 course of a hardness pulse in a according to F i g. 6 controlled device.

In a device according to the invention, a pot circle 1 with a very high quality, the z. B. with a volume of Ά m ³ made of copper sheet with silver plating can be designed by an air condenser 2 to an industrial working frequency, e.g. the working frequency 27.12 MHz or to a k & iliche lower or higher frequency tuned The circuit is fed by the oscillator tube 3 in a conventional manner Way, by connecting the anode of this tube 3 to the pot circle 1 via a coupling capacitor 4 The feedback is done by a small current loop 5 through a commonly used one Grid capacitor 6 and a grid working resistor

7. A pulse that is as precisely square as possible can now be applied directly to the anode of the tube 3, e.g. B. via a throttle 8, can be given. As a further embodiment of the invention, a special differential pulse transformer is used, with a secondary winding 9 and a Primary winding 10 encloses an iron core 11. A small, low-inductance capacitor 12 is used to divert the high-frequency or high-frequency short-circuit. If the charge of a very large capacitor 13 via an electronic switch 14, e.g. B. a large thyristor, an ignitron or even a conventional switch is placed on the primary winding 10, there is in this according to Figure 2 an increase in the current according to curve a. As a result, in the secondary winding 9 the first derivative of this current occurs as the voltage shown in curve b . As can be seen, it can be achieved that the uniform rise of curve a to an almost rectangular secondary pulse course b at the small

so capacitor 12 leads this way can with very high working voltages, e.g. B. 10,000 volts, to be worked on the anode of the tube J.

For these high working voltages there are small thyristors or similar semiconductors, so that old

ss tube circuits used which have recently been avoided. To now one To be able to use thyristor, which at very high currents in good reliability only voltages capable of switching a maximum of about 1 kV, becomes a's electronic Γ .'holder 14 a thyristor with only 1000 Volts working voltage used The capacitor 13 has in this case a hundred times the capacity, but only '/ 10 of the voltage of the capacitor * IZ The capacitor 13 is charged in a conventional manner by a stabilized high voltage generator 15, which must quickly enough charge the capacitor 13 to a fast cycle sequence, e.g. B. to accomplish 20 / s. Such Circuits are technically known and not new.

In order now to decouple the oscillation generated in the pot circle with high efficiency on one To give heating inductor 17 is a low-resistance and also low-inductance decoupling loop 16 in the Cup circle I inserted, the quality of the cup circle 1 and the geometry of the insertion of the Loop 16 connected together. The higher the resonant circuit quality of the pot circle 1, the smaller the area 16e enclosed by the loop 16 must be within the circle 1.

The actual heating inductor 17, which is very close to the surface of a workpiece 20 to be heated, is implemented parallel to the decoupling loop 16. This is by means of a fixed capacitor, e.g. B. ceramic capacitor 18, approximately to the frequency and by means of a trimmable air capacitor, preferably a plate capacitor 19, exactly süf the Arbsitsfreijuenz the To ⁿ fkr? Ls? S I ahepstimmen occur in the from the decoupling loop 16, the heating inductor 17 and the capacitor 18 existing resonant circuit also has extremely high reactive powers, which could lead to a reactive resonant power of I MVA or more flowing in the inductor 17. These high reactive oscillating powers have the consequence that the inductor 17, which under certain circumstances only consists of a single small straight piece of wire or a single small loop. Voltages in the kilovolt range occur. In order to prevent these tensions from flashing over onto the workpiece 20, it can be expedient to arrange an insulating film 21 in front of the workpiece 20 or to glue such a film 21 around it.

Films with a temperature resistance of up to 1200 ° C are recently commercially available as organometallic compounds. By means of these foils it is possible to achieve excellent Isolation to produce very high impulse hardening temperatures on the surface of the workpiece 20. Additionally the workpiece 20 can be reached by means of a gas stream of carbon dioxide, nitrogen, can also be cooled by air for lower requirements or by argon for high requirements. This gas flow also ensures that ions between the inductor 17 and the workpiece 20 be blown away. In this case, the air flow no longer primarily causes the cooling of the Surface of the workpiece 20, but the removal of ions that arise during the pulse duration want or have arisen and favor a rollover.

The speed of the gas must be very high. Under certain circumstances, Laval nozzles can even be used in order to be able to work close to the speed of sound. With gas flowing this fast, the cooling speed achieved by the gas is similar to the conduction cooling in the workpiece 20. In this way, the workpiece 20, which has just been heated by the pulse of the inductor 17, is heated both by the gas flow in the direction of arrow 22 and by the flow in the direction of arrow 23 occurring self-quenching into the interior of the workpiece 20 is cooled.

In order to obtain the above-mentioned white structure, the pulse durations are in the order of magnitude of 03 to 10 ms. It is therefore advisable, at higher production speeds, to rotate the workpiece 20 continuously or to let it move continuously past the inductor 17, as is the case with a saw, for example. The pulse is always triggered when the workpiece 20 is in the correct position with respect to the inductor 17. For this purpose, according to a preferred embodiment of the invention, a laser beam is used as a synchronization aid. One shown in FIG. 3 shown neon-helium laser 30 of conventional design sends one

S fine beam 31 through a workpiece 32, e.g. B. that Tooth profile of a saw. A photodiode 33 picks up this beam 31. It is further amplified as a signal in one small differential amplifier 34 and via a signal line 35, i. H. a control line for actuation

ίο of the electronic switch designed as a thyristor

14 headed. Signals 36 are recorded on line 35 for symbolization. In this way, with a well-trained and correctly dimensioned machine of this type, up to 20 pulses / s can be generated as hardening pulses with tubes 3 with an average anode power loss of only 2 kW. The anode peak voltage can be 10-15,000 volts and the reactive power peaks in the pot circle 1 to 5 MVA.

jo To set the device according to the invention correctly To be able to do so, a special switching measure is required. By one shown in FIG. 1 outlined Changeover switch 24, the tube 3 is switched to a small operating voltage via a resistor 25, e.g. B.

by putting them on the high voltage generator

15 switches. Then swings the whole circle with about ei ^r ~ m hundredth of its performance. To set the exact resonance by means of the capacitor 19, a small antenna 26, for. B. a wire a few centimeters in length, with an auxiliary glow lamp 27 and a small, serving as a counterweight piece of wire 28 arranged By setting the glow lamp 27 to maximum brightness, the setting can be made critical so that when switching to full power immediately correct Working is guaranteed

The result achieved is particularly good if the full resonance of the inductor 17 is only present when the Curie temperature is reached and exceeded in the workpiece 20 on the surface to be hardened. As is well known, steel below the Curie temperature has a high, upper limit the C urie temperature jciiix.ii with the normal permeability of air or other common metals. As copper or brass, carried out with a lack of ferromagnetic permeability so it generates in the hardening of steel during the beginning of the pulse, ie during the first microsecond, not the full Leistu ·· * 20 on the workpiece Upon further persistence of the pulse the Curie temperature is exceeded. At this point in time, the workpiece is heated up extremely suddenly, since the correct adjustment is available immediately after the Curie temperature is exceeded and the full reactive power is converted into active power. In this way an important prerequisite for realizing the invention is met, since the pulse is not slow

6c creeps out, but ends spontaneously. It creates an almost needle-shaped heating impulse, through which only an extremely thin surface corresponding to the known formula for the penetration depth of the high frequency in the steel is heated. SoTi the hardening is deeper than in

& 5 penetrate this thin layer, which can often be only a few 30 / thousandths of a millimeter, a longer pulse duration, e.g. 50 ms, must be selected and thermal conduction ensures that a corresponding

correspondingly deeper layer, ζ. B. 0.2 mm, the surface is heated.

An inductor 17, which is particularly effective for the required high power transmission quality, is embodied as a tube with a thin bore 41, as shown in FIG. The high pressure water can expediently be supplied through the high pressure pipe 44 located in the jaws 43. The jaws 43 can consist of two flat conductors pressed firmly onto one another as a so-called sandwich line , the inner surfaces 19a-19b of which are insulated by a thin mica film 40. In this way, capacitances of the order of magnitude of 100 pF are realized, so that the capacitors 19 and 18 can be smaller. Due to the conical configuration 42, the inductors 17 can easily be exchanged if they are occasionally to be destroyed or changed for other shaping purposes .

In the direction of arrow 45, cooling water flows at high pressure into the bore 41 and out again in the direction of arrow 46. It has proven to be useful to use either distilled water or tap water with little lime to avoid unnecessary deposits. Preferably water with a pressure of more than 8 atm., Occasionally even 40 atm. used when the bore 41 of the inductor 17 is very thin, e.g. B. ² / io mm. Drawn silver pipe has proven itself as the material for producing the inductors 17. Surprisingly, it is also possible to use drawn steel pipe that is copper-plated and, if possible, additionally silver-plated. The higher the flow rate of the cooling medium, the higher the pulse rate and thus the higher the thermal stress on the inductor can understandably be.

In order to concentrate the power of the inductor 17 as completely as possible on the workpiece 20 , ferritic material 47 can be arranged in its vicinity. There are commercially available high-frequency technical ferrites that have permeabilities in the order of 600 to 1500

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Represent air spaces that lie outside the workpiece 20. In this way, the insulating film 21 through the workpiece 20 is acted upon with a very high field strength and almost loss-free and heated.

The correct choice of the ferritic material 47 allows that when the current in the inductor 17 is high Permeability μ and thus the inductance decrease. When the current in the loop 17 decreases, the increases Permeability All manufacturers of such ferritic materials give permeability curves in comparison for magnetization. In the case of an increase in active power and a decrease in reactive power associated exceeding the Curie temperature in the hardness spot on the workpiece 20, the permeability increases In this way it can be achieved that both below and above the Curie point approximately the same high-frequency technical tuning conditions exist. Choosing the right ferrite material leads approximately to the fact that during the heating phase below and above the Curie temperature about the the same effective power through the compensation effect of the ferrite 47 heats the workpiece

Surprisingly, it has also been shown that ordinary tap water for pulses as short as they are used here, has a very good dielectric strength, which is around 200 kV / cm. Instead of of the cooling gas flow in the direction 22 can therefore also successfully affect the surface of the workpiece 20 from the inductor 17 by laminar inflowing water, namely ordinary tap water, isolated will. Insulating film 21 is then not required. The water insulates about as well as ordinary ones atmospheric air of 7 atm. Pressure between

ίο workpiece 20 and inductor 17 would be. The fact that the water also contributes to the rapid cooling of the surface as a cooling medium is a welcome addition. The primary task of the flowing water is insulation.

For certain tasks, e.g. to produce very bright surfaces without oxidation, a coolant can flow in instead of water. Methanol has z. B. strong reducing properties and leaves a shiny metallic surface after curing. If a liquid is not to be used, it is advisable to let propane or hydrogen gas or also methane flow in the direction of arrow 22 as a cooling medium. These gases ensure the metallic brightness of the surface. In no case can the heat conduction cooling of the workpiece itself, which takes place in the direction of arrow 23, be dispensed with. Normal carbon steel has a thermal conductivity that is about a thousand times that of a good cooling gas. The decisive factor for the creation of white layers is not only spontaneous heating to very high temperatures just below the melting point, but also spontaneous cooling after the application of the heating power pulse. This cooling can only practically

i <; effectively done by the self-deterrence of the workpiece 20 itself. Alternatively, it also takes place through the gas blown in or the liquid flowing into it.

It should be noted that the cooling by means of water, oil or methanol still allows a small improvement in the process. Should layer thicknesses of sth ^. 02 mm are to be hardened, impulses from a

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scm long uauvt, t » u. t \ ß iiu, autgvtsi at-iii tt * .iu \ .ii. i> \, i however, after the cessation of the Impulse, as expected, the cooling effect through the Self-deterrence is stronger in the more inner layers. The very outer layers the heated surface elements remain longer due to the highly heated layers underneath re time hot. So you will be put off more slowly. This then leads to the surprising fact that in Her microhardness test the outermost layer is a results in lower hardness than the somewhat deeper layers measured when using somewhat higher pressures.

In order to avoid this effect of decreasing hardness to the outside, the heat dissipation cooling of the Work piece 20 are supported by compressed air, compressed gas or liquid cooling from the outside. on this creates a homogeneous area of z. B.

^{6c 0.2 to 03 mm with uniform hardness, which can easily amount to 950 kp / mm 2} in series production of, for example, band saws made of carbon steel, if measurements are taken over the entire hardness cross-section. The process does not require any subsequent heating,

* s as it is otherwise necessary for spontaneous deterrence, to avoid fraudulent activities. The generated white layers are very elastic and never have the tendency to break brittle. A subsequent one

thermal treatment is therefore not recommended. That way after this The method described with the device according to the invention described here are so stable that their disintegration into the usual, the s Material own -.nartensitic basic structure, microscopically only after a period of 6 hours acting temperature of 450 "C can be observed.

A preferred embodiment of the invention ro relates to a further automation. In practice it is It is often very difficult to find the optimal hardening temperature with fluctuating workpiece quality in large-scale production to be observed. A small auxiliary device is used to automatically maintain the temperature has proven to be excellent. The workpiece 20 is intended to be a saw here. The inductor 17, the parts of the To harden saw tips, encloses z. B. on both sides with one turn each, vcrbeüstiiender; Sawtooth. That The saw blade releases by means of a light barrier, as in FIG. 3, the pulses automatically turn off. The auxiliary device only switches the by means of the light barrier Beginning of the impulse. However, the impulse is deliberately chosen too long and through an electronic one Disconnection device, e.g. B. a parallel-connected Ignitron or a high-voltage thyratron 59 short-circuited.

For this purpose, the thermal radiation emanating from the pulse-heated surface element 50 of the workpiece 20 is transmitted in a beam path 51 via a Optics 52 and a critical filter 53 imaged on a photodiode 54, which in a known manner with a Power supply source 55 and a load resistor 56 is provided. The pulses from this photodiode 54 can be processed in a special amplifier 57 so that after reaching a critical voltage a pulse is delivered in line 58. In this way the impulse at the tube 3 becomes spontaneous Brought to disappear by - purely mentally - z. B. the switch 24 is opened. In the In practice, it is better to use a short-circuited Thyraf rrm ^ Q vprwpnrtpt because it is known from the literature is. The thyratron 59 takes up the remaining current of the pulse instead of the tube 3 and is shown in FIG. 1 as Auxiliary device outlined. Through the impulse on the « Line 58 can, for example, the grid of a hydrogen thyratron 59, which has an emission of more than 300 Amp. and a peak voltage of 15 up to 20 kV can be ignited without great difficulty. In this way, the rest of the flow of the Pulse instead of through the oscillator tube 3 via the hydrogen thyratron 59.

When the filter 53, e.g. B. as a light blue filter, so it is chosen that only at a color temperature of more than 1200 ° C. that which is found to be the optimum Hardening temperature of the respective steel to be hardened corresponds to a light emission is transmitted, increases the photocurrent in the photodiode 54 very spontaneously. In this way also with this impulse increase fully automatic despite strongly fluctuating surface structures a constant hardening temperature adhered to. It is only necessary that the imaging optics 52 with the surface element 50 and the Photodiode 54 cooperates so that only a small but representative portion of the heated area is on the Photodiode 54 is imaged. The material for the filter 53 is according to the current status of orange, Green and blue filters a large selection iur Disposal; which can be selected and used according to the desired curing temperature.

The hardness pulse course is shown again in FIG. 7 as a function of the associated pulse current la. At time a) the light barrier or a contact starts triggering the pulse, e.g. B. by actuating the electronic switch 14. The pulse would fall after the normally fixed discharge time with the trailing edge b). However, the thyratron 59 is already ignited at point c ^ by the thermally measuring the temperature, so that the pulse breaks down prematurely, namely after the set temperature has been reached. A delay circuit in the amplifier 57 causes the pulse to disappear instead of c) a little later, as sketched under d). In this way, after reaching the desired surface temperature, a certain time between c and d is given to the impulse to heat up deeper surface elements by conduction.

The very rapidly disappearing, i.e. spontaneously falling, required in the preamble of the main claim trailing edge of the heating pulse can therefore with very simple switching measures by the spontaneous short circuit of the tube 3 with the help of the hydrogen thyratron 59 (instead of the hydrogen thyratron are also High-voltage signitrons usable) can be realized. With this arrangement, there are no special critical circuits for generating square-wave pulses necessary because the short-circuited tube 3 causes this effect

1 sheet of drawings

Claims (1)

Patent claims: 1. Device for generating extremely fine-grained metallic surface structures by inductive High-frequency heating rait impulses acting for less than 0.1 seconds and more Self-deterrence through the use of rectangular programmed power pulses extremely steep trailing edge corresponding to a fall time of less than 1% of the pulse application time according to the method according to patent 19 57 884.8, consisting of a high frequency generator, at least one resonant circuit and an inductor, characterized by the combination of the following features: