JPS5856034B2 - Glow discharge stabilization control method in metal surface treatment - Google Patents

Description

Detailed Description of the Invention For example, in the ion nitriding method, which is a surface hardening method for steel, the material to be treated (iron) is generally placed in a vacuum container, and the pressure inside the vacuum container is reduced to a predetermined value. From a state in which the remaining atmosphere is nitrogen or a gas containing nitrogen, a DC voltage is applied with the object to be treated as a cathode and the reduced pressure container as an anode, and the nitrogen in the atmosphere is cationized by the glow discharge generated accordingly, The collision energy of the nitrogen ions against the workpiece is converted into thermal energy and used to heat the workpiece, while the nitrogen ions and iron are reacted to form iron nitride on the surface, and the heat also causes internal nitridation. proceed.

By the way, the most important point in this ion nitriding method is to maintain stable glow discharge and protect the object to be treated from damage caused by arc discharge.

In other words, if there is dirt or the like on the surface of the material to be treated during the nitriding process, the glow discharge will turn into arc discharge, and the arc will damage not only the material to be treated, but also the jig and electrode supporting the material. A situation occurs.

Therefore, it is necessary to stabilize the glow discharge by some kind of electrical control means.

The conventional method for stabilizing a suspended discharge is to detect the arc discharge current value (abnormal discharge current value) when an arc discharge occurs, to cut off the energization state using an electrical current valve such as a silicon-controlled rectifier, and then to energize it again. starts and reaches a glow discharge.

If you look at this as a current waveform, it will look like Figure 1.

In the figure, IO is the stable discharge current value during glow discharge, ■A
When is the abnormal discharge current detection level value during arc discharge,
The current value rises as soon as the current starts flowing, resulting in a stable discharge current■.

As a result, the glow discharge is stabilized.

When arc discharge occurs at time To, the occurrence of arc discharge is detected at arc detection time T1 when the abnormal discharge current detection value ■A is reached.

The current supply is cut off at peak value detection time T2 when the current value further increases.

The reason why a slight time lag t1 occurs between the arc detection time T and the peak value detection time T2 is due to the characteristics of the silicon-controlled rectifying element.

Immediately after the current is cut off in this manner, the current is re-energized, the current value rises, and the state shifts to a glow discharge state.

Although it is certainly possible to stabilize glow discharge to a certain degree using this conventional method for stabilizing glow discharge, however, if the current is restarted immediately after the current is cut off after detection of arc discharge, the atmospheric gas conditions and Since the temperature of the workpiece is high enough for arc discharge, it is easy to switch to arc discharge, and as a result, a repeated phenomenon of hanging discharge and arc discharge occurs, and the nitriding process of the workpiece is completely delayed. There are some difficulties in making progress.

The present invention was developed in view of this point, and as a result of various experiments, instead of immediately re-energizing the current after it has been cut off upon detecting arc discharge, the present invention pauses the discharge without applying voltage for a certain period of time. If, after the pause time has elapsed, the current is re-energized and the glow discharge discharge current is gradually increased to reach a stable discharge current value IQ, the repetition of glow discharge and arc discharge can be eliminated and the damage caused by arc discharge can be eliminated. It is popular based on the fact that damage to the workpiece, jig and electrodes is eliminated.

In other words, in order to transition from arc discharge to glow discharge again, a certain period of time is provided for the discharge body to stop, and after the pause time has elapsed, the glow discharge current is gradually increased to a stable discharge current value required for nitriding. The purpose of this invention is to provide a glow discharge stabilization control method by adjusting the time width, the purpose of which is to reach the following.

In this case, the power supply F is a full-wave rectified signal, and in order to maintain normal glow discharge, the silicon-controlled rectifying element control unit 10 side controls the silicon-controlled rectifying element every time the current drops to O level every half wave. A trigger is applied to the gate of the rectifying element 5 to maintain conduction of the element 5, but these mechanisms are well known and will not be described in detail.

Hereinafter, one embodiment of the present invention will be described based on the drawings. In Fig. 2, 1 indicates a reduced pressure container, in which a table 2 serving as a cathode electrode and an anode electrode 3 are installed, and these are connected to a DC power source E. ing.

4 is a workpiece supported on the table 2;

5 is a control rectifier element interposed between the anode electrode 3 and the DC power source E, 6 is a temperature detector for the object to be treated, 1 is a discharge current detector, and the outputs of both detectors 6 and 7 generate control signals. Sent to vessel 8.

Reference numeral 9 denotes an operational amplifier that calculates the outputs of both the control signal generator 8 and the discharge current detector 7, and the output of the operational amplifier 9 is sent to a silicon-controlled rectifier control unit 10.

Furthermore, the control signal generator 8 includes a detection level setter 11, a pause time setter 12, a rise time setter 13, as shown in FIG.
The power is derived from a comparator 14, a memory circuit 15, an integrator 16, 17, an arithmetic unit 18, 19 and a pause width pulse generator 20.

Next, the circuit operations of FIGS. 2 and 3 will be described in detail with reference to the time chart of FIG. 4.

The glow discharge current detection value from the discharge current detector 7 (FIG. 4A) is constantly compared with the detection level of the detection level setter 11 (FIG. 4B) by the comparator 14.

The detection level in this case corresponds to the abnormal discharge current detection value IA.

When arc discharge occurs, the glow discharge current detection value exceeds the above detection level, so the comparator 14 outputs an output signal (FIG. 4C), which is sent to the memory circuit 15 to write the arc discharge occurrence state. .

Correspondingly, a signal (
FIG. 4D) is sent to apply the necessary integral action, and the integral signal (FIG. 4E) is input to the pause width pulse generator 20.

This rest time width pulse generator 20 includes a rest time setting device 1.
A current signal of a constant value (FIG. 4F) is inputted from 2, and a rest time width pulse (FIG. 4G) with a pulse width corresponding to the rise width of the above-mentioned integral signal (FIG. 4E) is output. , the Hals are input to the negative terminals of the computing units 18 and 19, respectively.

On the other hand, the detection signal of the temperature detector 6 (H in FIG. 4) is
Since it is input to the positive terminal of 9, the calculation output of both the positive and negative terminal signals (Fig. 4 ■) is input to the integrator 17.
is input.

Since this integrator 17 is supplied with a setting signal from the rise time setter 13, the calculation output signal (■ in FIG. 4) undergoes an integration operation, and becomes a waveform signal as shown in FIG.
It is input to the positive terminal of 8.

This input signal is calculated with the output of the rest time width pulse generator 20, and is inputted to the positive terminal of the operational amplifier 9 as a side signal having a waveform as shown in FIG.

The detection signal from the current detector 6 is input to the negative terminal of this operational amplifier 9, and therefore, the operational amplification output signal is applied to the silicon-controlled rectifier control unit 10, and the signal output of this unit 10, the silicon-controlled rectifier Control element 5.

If these operations are viewed in terms of the current waveform detected by the current detector 7, it will be as shown in FIG.

In other words, when arc discharge starts at time T0, the occurrence of an arc is detected at time T1, the current is stopped at time T3, the current is kept in the stopped state for a period of time T2, and the current is restarted at time T4, and the current is gradually turned off. The current value increases and reaches a constant glow current value at time T5.

The pause time T2 at this time corresponds to the pulse width of the pause time width pulse (FIG. 4G) from the pause time width pulse generator 20, and the rise time t3 of the glow current corresponds to the rise time by the integrator 17. That's what I do.

Furthermore, if this current control is explained by the control operation of the control unit 10 in relation to the silicon-controlled rectifying element 5,
The trigger for the element 5 is stopped at time T1, the element 5 is turned off at time T3, and this state is maintained until T4.

At time T4, the trigger for element 5 is started again, but
At this time, the phase of the trigger applied to the gate is changed and the conduction angle is changed to control the output of the element 5 at 8*, increasing it from T4 to T.

For example, an RC phase circuit may be used to change the phase of this trigger.

Next, the experimental results according to the present invention are shown in Table 1 below.

This experiment was conducted in a 600φ x 20001 container with a degree of vacuum of 1 to 10 TORR1 atmosphere gas N2 + H2 (1:1)
, gas flow rate 0.5 l/min, applied voltage 500V
, nitriding steel is used as the workpiece, and the density of the workpiece is 43
The test was carried out at 0°C.

Also, tl is 8~10m5ec1t2 is 20m5ec'1
0 sec, t3 to 100 m5ec ~10 sec
The condition was set as c.

According to experiments conducted by adjusting the set detection level values shown in Table 1 above, arc discharge detection frequency is high at 1.5 times the glow discharge current, but this is because the detection accuracy is too sensitive and even small arcs are detected. It is from.

At the optimal 2x and 3x, the number of subsequent occurrences was almost non-existent.

Furthermore, the reason why arc discharge is not detected when the magnification is 10 times is that the detection accuracy is too insensitive.

Further, Table 2 below shows experimental results obtained by adjusting the rest time setting value, and Table 3 shows experimental results obtained by adjusting the rise time setting value.

According to this experiment, the downtime is 50m5ec~1 sec.
The optimum rise time was between 50 m5 ec and 1 sec.

Furthermore, although the present invention has been applied to the ion nitriding method in the above description, it is of course possible to use the present invention for other metal surface treatments using glow discharge such as sputtering.

As described in detail above, according to the present invention, in order to interrupt the current flow due to the occurrence of arc discharge, instead of immediately reenergizing after the interruption, a certain pause time is provided, and after the pause time has elapsed, the glow discharge current value increases. , thereby eliminating repeated occurrences of arc discharge.

This is because the atmospheric gas conditions and the temperature conditions of the workpiece return to the state before the arc discharge occurs due to the above-mentioned downtime, and by gradually increasing the discharge current, the discharge progresses stably. Due to the reason.

[Brief explanation of drawings]

Fig. 1 is a discharge current control waveform diagram according to a conventional glow discharge stabilization control method, Fig. 2 is an electric circuit diagram showing an embodiment of the present invention, and Fig. 3 is a circuit diagram of the control value generator shown in Fig. 2. , FIG. 4 is a time chart of each part in FIG. 3, and FIG. 5 is a discharge current control waveform diagram of the present invention. Explanation of symbols, 1... Decompression vessel, 2...
Table, 3...Anode electrode, 4...Workpiece, 5...Silicon controlled rectifier, 6...
. . . Processing object temperature detector, 7 . . . Discharge current detector, 8 . . . Control signal generator, 9 .
- Operational amplifier, 10...Silicon controlled rectifier, 11...Detection level setter, 12...
- Rest time setter, 13... Rise time setter, 14... Comparator, 15... Memory circuit, 16, 17... Integrator, 18.19...
. . . Arithmetic unit, 20 . . . Rest time width pulse generator.

Claims (1)

[Claims] 1 Compare the glow discharge current detection value of the discharge current detection means and the setting level of the abnormal discharge current detection level setting means with a comparator, and when an abnormal current is detected, the discharge body stop circuit suspends energization for a required time, and the suspension A glow discharge stabilization control method in a metal surface treatment method using glow discharge, characterized in that the glow discharge current is re-energized by a current control circuit that gradually increases the glow discharge current after a lapse of time.