US3914575A

US3914575A - Power supplying device for the operation of a gas discharge container

Info

Publication number: US3914575A
Application number: US439872A
Authority: US
Inventors: Walter Eichler
Original assignee: Elektrophysikalische Anstalt Bernhard Berghaus
Current assignee: Elektrophysikalische Anstalt Bernhard Berghaus
Priority date: 1973-02-19
Filing date: 1974-02-06
Publication date: 1975-10-21
Anticipated expiration: 1992-10-21
Also published as: FR2218687B1; JPS49113242A; BR7401198D0; PL90222B1; AT335014B; NL7402226A; LU69416A1; ES423369A1; BE810982A; DE2346053A1; RO68758A; IT1006250B; CH561285A5; FR2218687A1; DD107192A1; ATA126874A; GB1463557A; CA1002613A

Abstract

A power supplying device for the operation of a gas discharge container for the treatment of metallic workpieces. For the provision and the adjustment of the operating voltage the power supplying device comprises a transformer, a thyratron-or thyristor full-wave rectifier located in the secondary circuit and an ignition control device for the ignition of the rectifiers. The power supplying device further comprises a device monitoring the discharge and in response to which the ignition control device further serves as a quick-action switch interrupting the discharge during a number of periods. An inductance is located in the primary circuit having such design that the increase of the operating voltage following every zero passage is retarded. Resulting is an extension of the interruption of discharge occuring at every zero passage of the operating voltage causing minor discharge disturbances on the workpiece surface to decay.

Description

United States Patent 11 1 1111 3,914,575

Eichler Oct. 21, 1975 [5 POWER SUPPLYING DEVICE FOR THE 3,593,105 7 1971 Brohaugh 321 40 x OPERATION OF A GAS DISCHARGE 3,737,763 6/1973 Chadwick 321/40 X CONTAINER 3,746,966 7/1973 Tiirok et a1.

3,781,508 12/1973 Dauer et a1 219/121 P [75] Inventor: Walter Eichler, Cologne, Germany [73] Assignee: Elektophysikalische Anstalt Bernard Primary Truhe g h Vaduz, Liechtenstein Assistant ExaminerG. R. Peterson Fl d F b 6 1974 Attorney, Agent, or FirmBacon & Thomas [21] Appl. N0.2 439,872 57 ABSTRACT A power supplying device for the operation of a gas 1 Foreign Application Priority Data discharge container for the treatment of metallic Feb. 19, 1973 Switzerland 2357/73 workpieces. For the provision and the adjustment of the operating voltage the power supplying device com- [52] US. Cl 219/121 P; 315/127; 323/123; prises a transformer, a thyratron-or thyristor full-wave 321/40 rectifier located in the secondary circuit and an igni- [51] Int. Cl B23k 9/00 tion control device for the ignition of the rectifiers.

[58] Field of Search..... 219/121 P, 131 R, 131 WR; The power supplying device further comprises a de- 315/111.1, 111.2,111.3,111.4, 111.5, vice monitoring the discharge and in response to 111.6, 111.7, 111.8, 111.9, 136, 127, 119; which the ignition control device further serves as a 323/123, 9, 20, 4; 321/40 quick-action switch interrupting the discharge during a number of periods. An inductance is located in the [56] References Cited primary circuit having such design that the increase of UNITED STATES PATENTS the operating voltage following every zero passage is 2 508 954 5/1950 Latour et al 32) X retarded. Resulting is an extension of the interruption 323/123 X of discharge occuring at every zero passage of the op- 3,205,426 9/1965 Mills 321/40 x erating voltage causing minor discharge disturbances 3,270,272 8/1966 Kurimura 321/40 x o the workpiece surface to decay.

3,579,029 5/1971 Spescha 315/127 3,582,755 6/1971 Liss et a1 321/40 x 3 Clams, 2 Drawmg Flgures 3,189,747 6/1965 Hoff, Jr

- REGULATOR CONTROL 24 AUNIT 12 2 J 15 liq 11 30 3 p 22 u ,wORK .1 B PIECE 11/ 'MONITORING/ DEVICE CONTAINER U.S. Patent 0a. 21, 1975 3,914,575

Fig.1

REGULATOR CONTROL 24/ UNIT MONITORING/ DEVICE CONTAINER POWER'SUPPLYING DEVICE FOR THE OPERATION OFA GAS DISCHARGE CONTAINER The present invention relates to a power supplying device for the operation of a gas discharge container for thetreatment of metallic workpieces, particularly for the operation of an ionitriding furnace, comprising a transformer and'rectifiers for the provision of theopcrating voltage from the alternating or three-phase current supply," with a continuously operating regulating devicefor the operating voltage, a monitoring device for the discharge process during the process, and with a quick-acting 'switch for'the brief interruption of operation when the monitoring device responds.

Several forms of such power supplying devices are known, by way of example those using a variable voltage transformer as a continuously operatingregulating device or also grid rectifiers with a regulating device for their control grid. With'all such current supplying devices designed for the operation'of gas discharge processes it is of great importance that a quick-response monitoring device is provided which causes a quick brief disconnection of the'operating voltage when irregularities in the discharge occur and which disconnection lasts anurnber of periods. Without such a brief disconnection'a disturbance in the discharge process, by way of example'a tinygas eruption from the surface of the metallic workpieces treated, would as is well known cause a transition of the gas discharge into an arc discharge, which might cause damage to the metal surface. Particularly in the operation of ionitriding furnaces with an electrical high-intensity gas discharge, which are employed on an industrial level itcannot be avoided during the starting process at the beginning of the 'nitriding operation that such imperfections in the glow discharge frequently occur which necessitate brief quick disconnection of the glow discharge process. By way of example this starting process and its control by brief interruption of the operation is disclosed in U.S. Pat. No. 2,884,511.

The monitoring device there described, however, is only one of the many known systems for monitoring the operating condition of gas and glow' discharge processes, and further types of such monitoring devices which have provided satisfactory and are disclosed for example in U.S. Pat. No. 3,579,029.

In operating a glow or gas discharge with a rectified alternating voltage from a single-phase alternating voltage network it has proved to be of advantage for the discharge to be briefly switched off beforeevery zero passage of the operating voltage in order to recommence only during the subsequentrise of the operating voltage after reaching' the so-called ignition voltage value of the discharge. These brief interruptions of the discharge process which occur at double the frequency of the alternating 'voltage employed, however, are generally so shortthat,:=in the presence of the .glow discharge, the cause ofdisturbancehas not sufficiently decayed and thus stillremains when the discharge process is resumed. YY

The present current supplying device in which the alternating currentis rectified to provide the operating voltage constitutes a particularly simple and .inexpensive design 'which'employs the effect of the-brief interruptionof the discharge atevery zero' passage of the rectified operating voltage while avoiding the-aforementioned disadvantages. a a I The power supplying device according to the invention is characterized by the combination of:

a. a full-wave rectifier located in the secondary circuit of a transformer comprising thyratron or thyristor components, an ignition control device for the continuous adjustment of the phase position for the purpose of controlling the operating voltage and by the simultaneous use of this ignition control device as said switch when said monitoring device responds,

b. an inductance located in the primaray circuit of the transformer, I

0. design of said inductance influencing the phase position of the secondary voltage applied to the rectifiers so that the increase of the operating voltage following every zero passage is retarded until minor discharge irregularities on the workpiece surfaces have decayed.

One embodiment of this invention will now be described in greater detail with reference to the drawing in which F IG. 1 shows a simplified circuit schema of the power supplying device supplying an ionitriding furnace, and

FIG. 2 shows the diagram of the curve of the operating voltage plotted against time.

In the embodiment shown a metallic underpressure container 10 with a gas inlet 11 and a gas outlet 12 accommodates the workpiece 13 which is e.g. to be ionitrided by means of a glow discharge in a nitrogenous atmosphere. The metallic workpiece 13 is connected, via a metallic coupling member 14, to the inner conductor of an insulated current lead-in 15 shown diagrammatically and of which the exterior connection 16 represents the negative pole of the power supplying device. The other pole 17 of the power supplying device is connected to the metallic container 10 and ground. The operating voltage U, is applied between the connections 16 and 17 of which the variation in time is diagrammatically shown in FIG. 2.

The voltage U, is applied via the voltage divider formed by the resistances l8, 19 to the monitoring device 20. Also the voltage drop at the series resistance 21- in the supply line to the connection 17 is applied to the device 20. The function of this monitoring device requires no detailed explanation since it is described in detail in U.S. Pat. No. 3,579,029.

Connected to the monitoring device 20 is a control unit 22 which determines, in accordance with the known phase shifting method, the switch on point of the thyratron or

thyristor rectifiers

28, 29, 30, 31 during each half period. This point can be manually set by the regulator 23 diagrammatically indicated. The

rectifiers

28, 29, 30, 31 constitute a full-wave rectification for the alternating voltage of the secondary side 27 of the transformer 26.

This device which is known in itself functions as follows: As soon as the monitoring device 20 responds because of a major irregularity in the glow discharge on the workpiece 13, the control unit 22 receives a control impulse. Thereupon the control unit 22 causes the alternating voltage in the secondary circuit to remain interrupted after the zero passage next following during the time of a predetermined number of periods as mentioned before. The starting is effected again only by a second control impulse which is automatically supplied by the monitoring device 20 after a delay time which can there be adjusted.

It was found that it is of great advantage to provide an inductance, for example an iron choke coil 24, in the primary circuit 25 of the transformer 26, between the transformer and the power supply. Filtering or suppression means for suppressing high-frequency interference by the

rectifiers

28, 29, 30, 31 may be used in addition. The action of the inductance 24 will be described below,

In principle, the power supplying device according to FIG. 1 described above would be entirely suitable, also without the iron choke coil, for the perfect operation of a glow and gas discharge process of the type described since the monitoring device' 20, the control unit 22 and the

adjustable rectifiers

28, 29, 30, 31 ensure that, when disturbances in the discharge process occur, the operating voltage U remains off after the next zero passage during the time of a predetermined number of half-waves until the

rectifiers

28, 29, 30, 31 ignite again depending on the adjusting of the monitoring device 20. Experience has shown, however, that by way of example in the industrial treatment of workpieces, particularly the simultaneous treatment of a plurality of different workpieces in a common discharge container, the number of arising disturbances is so high, particularly during the starting process at the beginning of the ionitriding operation, that this process may extend over many hours owing to the frequency disconnections. However, the utilization of the ionitriding furnace involved is undesirably reduced by the greatly extended starting period, which necessitates the installation of additional ionitriding facilities where an ionitriding operation has a predetermined capacity. The present power supplying device with the control unit 22 and the inductance 24 provided in the primary circuit removes this undesirably high extension of the starting process without involving defects in the workpieces treated.

As indicated in the diagram of FIG. 2, the discharge process is discontinued at point 33 before the zero passage of the operating voltage U, after the discharge ignition voltage U is negatively exceeded. This discharge process will normally start again as the operating voltage U increases after reaching the ignition voltage U of the discharge at point 34. The period t, of discharge interruption at the zero passage of the operating voltage U normally lasts only a millisecond or less and is too brief to enable defects on the workpiece surfaces to decay so that, when the operating voltage U has passed the point 34, such defects remain active and will result in the response of the monitoring device 20 and thus in said predetermined number of periods of disconnection of the discharge container 10. The provision of the inductance 24 in the primary circuit 25 on the one hand, however, and proper adjustment of the control unit 22 on the other make it possible that the increase of the operating voltage U after the zero passage occurs later. As it is well known an inductance causes a change of the phase position of the voltage, in the present embodiment of the voltage applied to the rectifiers 28 to 31, which effects a retardation of the reincrease of the operating voltage U,,. The ignition of the discharge occurs now only at point 35, so that a discharge interruption time is results instead of the smaller interruption time t, if no such an inductance is provided.

Although the connection of an inductance in the primary circuit of the transformer 26 may seem to be an insignificant measure, its effect on the duration of the ionitriding during a longer lasting ionitriding process is considerable. It is achieved, that a plurality of minor defects just forming, and which would remain active after the time have now sufficiently decayed in order to avoid response of the monitoring device 20 and thus avoiding a discharge interruption during a number of periods at each response. However, this results in that the response frequency of the monitoring device 20 in the starting process of a gas and glow discharge process is substantially reduced, which experience has shown to result in a considerable reduction of the total starting period required. The discharge interruption time 1 may be adjusted to the degree of purity of the workpiece surface by means of a suitable design of the inductance in combination with the monitoring device 20 and the control unit 22.

By way of example, in the operation of an ionitriding furnace with a rated power of about 40 kW and a mean operating voltage of 500 V, a starting process of up to 5 hours isfrequently observed. However, if an inductance 24 is included in the primary circuit which is in this embodiment an iron choke coil having 3, 2 mHy and 20 kVA power dissipation, the starting process for the same type of workpieces may be reduced to about k to 2 hours. With a normal nitriding period of 6 to 8 hours the saving of 2 to 3 hours starting time constitutes a substantial improvement of the efficiency of the nitriding furnace involved since the amount of products to be nitrided is increased by about 25 to 40 per cent if the facility is operated continuously. With this power supplying device the interruption time t, is adjusted during the starting process in accordance with the power requirements for heating the workpieces and kept not lower than about 6 or 7 ms. With increasing degrees of purity I, may then be reduced until about t, 2 ms is reached in normal operating condition. This value should not be negatively exceeded.

Naturally the extension'of the zero passage of the operating voltage does not by any means render unnecessary the monitoring device 20 and the quick switch-off actuated by it. Only the response frequency of this monitoring device is reduced despite unchanged sensitivity and limited to cases where the cause of disturbances has not decayed during the extended zero passage of the operating voltage. Despite the raised efficiency obtained with the power supplying device described, perfectly nitrided surfaces are obtained which are free from so-called discharge patterns or burning pits.

What is claimed is:

1. In a power supplying device for the operation of a gas discharge container, particularly an ionitriding container, containing metallic workpieces to be treated, said device being supplied from an alternating-current power source, comprising a transformer, the primary circuit of which is connected to said power source, a rectifying device comprising controlled rectifiers, the input of said rectifying device being connected to the secondary circuit of said transformer, the output of said rectifying means providing direct operating voltage between said workpieces and the housing of said container, a monitoring device connected between said workpieces and said container for monitoring said operating voltage and the operating current, the output of said monitoring device being connected to the input of a regulating and switching device for said operating voltage, the output of said regulating and switching device being connected with said rectifying device in combination, the improvement comprising:

a. said rectifying device comprising a fullwave bridge having four controlled rectifier elements,

performing across one bridge diagonal a full wave 5 direct operating voltage while the other diagonal of said bridge is connected to the terminals of said secondary circuit of said transformer, pairs of controllingelectrodes of said rectifiers being interconnected and connected to said output of said regulating and switching device; and

wherein the inductance is an iron choke coil.

Claims

1. In a power supplying device for the operation of a gas discharge container, particularly an ionitriding container, containing metallic workpieces to be treated, said device being supplied from an alternating-current power source, comprising a transformer, the primary circuit of which is connected to said power source, a rectifying device comprising controlled rectifiers, the input of said rectifying device being connected to the secondary circuit of said transformer, the output of said rectifying means providing direct operating voltage between said workpieces and the housing of said container, a monitoring device connected between said workpieces and said container for monitoring said operating voltage and the operating current, the output of said monitoring device being connected to the input of a regulating and switching device for said operating voltage, the output of said regulating and switching device being connected with said rectifying device in combination, the improvement comprising: a. said rectifying device comprisIng a full-wave bridge having four controlled rectifier elements, performing across one bridge diagonal a full wave direct operating voltage while the other diagonal of said bridge is connected to the terminals of said secondary circuit of said transformer, pairs of controlling electrodes of said rectifiers being interconnected and connected to said output of said regulating and switching device; and b. an inductance connected in series with said primary circuit such that the start of each wave of the operating voltage following every zero passage is retarded by a period of time in the range of 2 - 7 milliseconds.

2. A power supplying device according to claim 1 wherein the rectifier elements are thyristors.

3. A power supplying device according to claim 1 wherein the inductance is an iron choke coil.