RU2227167C1 - Method of control and an inter-electrode gap adjustment in process of a vacuum arc melting and a device for its realization - Google Patents

Abstract

FIELD: special metallurgy. SUBSTANCE: the invention presents a method of control and an inter-electrode gap adjustment in process of a vacuum arc melting and a device for its realization. The invention is dealt with a special metallurgy, that is with a vacuum arc remelting of the high-reaction metals and alloys and may be used in process of smelting of ingots out of m nickel and titanium alloys. The technical result is development of a method to control the process of a vacuum arc melting, that allows to exercise an efficient control and to adjust an inter-electrode gap, as well as a device for its realization. The given task is achieved due to the fact that measurement of the arc voltage is made at a sampling frequency of no less than 10 kHz, with following separation of signals of the drop short circuits and based on the signals definition and adjustment of an inter-electrode gap. The device contains a voltage gauge, a computer, a control and adjustment unit, a drive of an electrode and a device of separation of signals of the drop short circuits from the signals having other nature using data from the voltage gauge with a sampling frequency of no less than 10 kHz. EFFECT: development of the method of the high-reaction metals and alloys vacuum arc remelting with an efficient control and adjustment of the inter-electrode gap. 3 cl, 5 dwg, 2 ex

Description

The invention relates to the field of special metallurgy, namely to a vacuum arc remelting of highly reactive metals and alloys, and can be used, in particular, in the smelting of ingots from steel, nickel and titanium alloys.

A known method of vacuum arc melting ingots of titanium alloys, which includes preparing the consumable electrodes for melting, the initial melting period, after which the optimum value of the interelectrode gap is established, is about 10-60 mm, and it is supported with an accuracy of ± 5 mm until the melting of the consumable electrode by simultaneously measuring the voltage across the arc, increasing the pressure in the furnace and adjusting the values of these values to the specified values by changing the speed of movement of the fused electrode down (p Awning RF №2164957, C 22 B 9/20, Bulletin of 10.04.2001. №10).

The disadvantage of this method is that the control and adjustment of the interelectrode gap occurs according to the pronounced value of the voltage jump on the arc and the pressure in the furnace chamber, the magnitude of which can fairly objectively control the interelectrode gap, the value of which is in the range of 25-40 mm. When the interelectrode gap is in the range of 0–25 mm, errors in measuring the voltage across the arc are introduced by short droplet faults and short-circuit surges that have a different nature and are associated with processes at the cathode and anode (hereinafter referred to as “noise”). In this case, the arc voltage and the pressure in the furnace chamber do not correlate with the magnitude of the interelectrode gap.

A device is known in the method of vacuum arc remelting of ingots with maintaining the magnitude of the interelectrode gap according to the frequency parameters of the droplet short circuits of the melting metal (US patent No. 4578795, Н05В, from 03.25.1986) - prototype. The control device includes a voltage sensor, including an analog-to-digital converter, a comparator, a microprocessor, a controller-controller and a drive.

A disadvantage of the known method is the possible errors in the evaluation of the interelectrode gap due to “noise” that are superimposed on the SCC signals and cause errors in the assessment of the interelectrode gap.

The aim of the present invention is to provide a method for monitoring and regulating the process of vacuum arc melting, which makes it possible to effectively control and maintain the interelectrode gap, including within the distance from 0 to 25 mm, and a device for its implementation.

The problem is solved in that in the method of monitoring and regulating the interelectrode gap in the process of vacuum arc melting, which includes measuring the voltage on the arc to obtain a controlled voltage signal, analyzing its change, determining from it the actual value of the interelectrode gap and adjusting the position of the consumable electrode relative to the cast ingot, voltage measurement is carried out with a frequency of not less than 10 kHz, with the subsequent isolation of short-circuit short-circuit signals, determined Ie and regulation of the interelectrode gap along them.

The specified technical result in the implementation of the invention is achieved by the fact that in the device for monitoring and regulating the interelectrode gap during the vacuum arc melting, including a voltage sensor, a computer, an electrode drive with a controller-controller, an additional filter device for filtering signals of short droplet short circuits from signals having a different nature, using a voltage measurement sensor with a polling frequency of at least 10 kHz.

In accordance with the invention, the device for filtering short drip signals is additionally equipped with blocks: filtering the high-frequency component, a threshold device, a comparator and a device for generating output pulses, and the voltage signal on the arc is fed to the input of the filtering unit, the output of this unit is connected to the input of the threshold device, the output of which connected to a comparator, the output of which is connected to the input of the droplet pulse generating device.

Vacuum arc melting of the consumable electrode includes a process for controlling the crystallization of the alloy. The control is carried out by directly changing the energy introduced into the melt, and the distribution of this energy affects the melting rate, the flows in the melt pool and, accordingly, the volume of the liquid bath.

One of the main parameters affecting the energy distribution is the interelectrode gap (the distance between the consumable electrode and the smelted ingot). With its increase, the arc energy, which could be used for melting, will be dissipated due to direct radiation to the wall of the cooled crystallizer. Therefore, a particularly important factor is the ability to control the interelectrode gap to ensure the efficiency of the vacuum arc melting of the consumable electrode.

With a decrease in the interelectrode gap of less than 5–8 mm, an increase in the SCR frequency to 10–15 Hz occurs, which leads to the extinction of the arc and, as a result, to the destabilization of the melting mode of the metal.

In the process of vacuum arc melting, sharp surges in voltage are observed on the arc, which have a different physical basis.

Two processes dominate:

- the first is the so-called “noise”,

- second - drip short circuit (KKZ).

Their essence is illustrated by graphic materials, where their parameters are given: FIGS. 1 and 2 are diagrams of recording arc voltage corresponding to noises; FIGS. 3 and 4 are diagrams of a short-circuit protection circuit.

Noise arises when gas vapors are released during the smelting process: mainly hydrogen, chlorine, and nitrogen. A sharp change in the electrical conductivity of the arc. Within 1 ms, there are 5-10 voltage surges from the average value (20 -25 V) to zero, or up to 50-60 V and higher at a speed of 5 · 10 ⁵ V / s, after which the voltage stabilizes (Fig. 1 and 2). These voltage surges are little dependent on the magnitude of the inter-arc gap.

KCH shown in FIG. 3 (hereinafter type A), occurs at small interelectrode gaps of 8-15 mm, as a result of the formation of a liquid metal bridge at the end of the consumable electrode and its subsequent closure to the liquid metal bath mirror. At the moment of contact, a sharp change in voltage on the arc to a level of 0-7 V for a period of 1-10 ms due to its shunting by liquid metal occurs. After the termination of shunting, the voltage drop across the arc is restored to the previous value of 20-25 V (figure 3).

KKZ depicted in figure 4 (hereinafter type B), occurs at small interelectrode gaps of 3-10 mm, as a result of the formation of an arc between a drop of liquid metal at the end of the consumable electrode and a mirror of the liquid metal bath. At the moment of closure, a sharp decrease in the voltage across the arc to the level of 0-7 V for a period of 1-10 ms or more (figure 4). When current flows through the bridge, a liquid conductor explodes due to the development of MHD processes, which is accompanied by the appearance of voltage peaks of 50 - 70 V.

Thus, the frequency of short-circuit type A and B depends on the magnitude of the interelectrode gap.

The proposed method is implemented by means of a device, a block diagram of which is shown in figure 5.

The device comprises: block 1 — arc voltage sensor, block 3 — a low-pass filter for isolating the low-frequency component of the signal, block 2 — a high-pass filter for isolating the frequency component of the signal characterizing the KKZ type, blocks 4a and 4b — threshold operation devices with a given setpoint threshold, blocks 5a and 5b - a comparator, block 6a - a signal conditioning device KKZ (type A), block 6b - a signal conditioning device KKZ (type B), a computer processing system consisting of a control controller 7 and industrial th computer display 8. The controller controls the speed of the consumable electrode and functions as a regulator of the interelectrode gap 9 -elektroprivod moving consumable electrode, 10 - vacuum arc furnace.

The device operates as follows.

When a voltage signal arrives at the arc, block 3 filters the high-frequency component of this signal and provides a constant component of the voltage signal. Block 2 selects the high-frequency component of the voltage across the arc, and also filters out noise.

Next, the signal after block 2 enters the threshold operation devices (blocks 4a and 4b), where the signal is compared with a predetermined threshold. Block 4a has a setting from -10% to -30% of the original signal, and block 46 has a setting from + 10% to + 30% of the original. If the constant component of the voltage signal has exceeded the threshold in block 4a, then a signal is output to block 5a. If the constant component of the voltage drop signal turned out to be less than the threshold, then a signal is output to block 5b.

After that, the signals are sent to the comparator (block 5a), where the signals from block 4a and the signal from block 3 are compared. After comparing these signals in block 6, a type KKZ signal is generated. In the same way, signals from block 46 and block are sent to block 5b 3, and after comparing them, a type B drip closure signal is generated. Next, the signals in the form of short pulses of a given amplitude and duration enter the computer processing system (blocks 7 and 8). The system processes the signals and issues a command to the electric drive to move the consumable electrode 9 of the vacuum arc furnace 10.

The method is implemented as follows.

The voltage is measured on an arc with a frequency of at least 10 kHz. This is due to the transience of the processes causing noise and KKZ, the duration of which is in the range of 0.1-10 ms. Next, the signals are classified according to their characteristics and the KKZ type A and type B signals are extracted. The KKZ type A signals are recorded by a voltage drop of approximately 20 V and by the corresponding period. KKZ type B is recorded by increasing voltage by 20 - 40 V and the period. KKZ signals are fed to a computer processing system, which determines the magnitude of the interelectrode gap from the frequency of the signals and statistical models. For each specific alloy, the dependence of the number of SCC signals on the interelectrode gap is determined individually, experimentally. Then this data is entered into the computer memory. After calculating the value of the actual interelectrode gap, it is compared with the required gap value and a signal is formed that characterizes the difference between these values. The signal is processed and, on its basis, an executive command is transmitted to the drive for moving the consumable electrode.

Consumable electrodes were melted in a DTV-8.7-G10 vacuum electric arc furnace equipped with a melting control system.

Example No. 1

A consumable Inconel 718 alloy electrode with a diameter of 500 mm and a length of 2100 mm was loaded into a mold with a diameter of 600 mm. After loading and centering the electrode, it was welded to a cinder mounted on the electrode holder. The furnace was evacuated, the power source was turned on, and a bath of molten metal was introduced using serial technology. After deposition of an ingot with a height of 200 mm, the arc current was reduced to 6.5 kA (operating current) and the voltage on the arc was 25.2 V. The interelectrode gap was established on the order of 8-10 mm - the optimal gap for this alloy. The consumable electrode is melted at the flat end of the electrode. As the electrode lowered at a constant speed, the electrode warmed up, as a result of which the melting rate of the metal increased, which led to an increase (stretching) of the interelectrode gap to 20 mm. A type B drip closure signal appeared. The controller controller increased the electrode feed rate down by 0.1 mm / min, type B drip closure frequency signal decreased to zero.

Example No. 2

Melting of the electrode was carried out as in example No. 1. The difference lies in the remelting of the titanium alloy 10V-2Fe-3Al. Arc current 8.5 kA; voltage drop on an arc of 26.1 V; arc gap 12 mm. Melting is carried out with a flat end of the electrode. The signals after the droplet closure is highlighted are fed to the controller F.ALLEN-BRADLEY, which serves as a regulator of the speed of the electrode. During a vacuum arc remelting, when type A droplets appeared, with a frequency of 5-10 Hz, the electrode speed automatically decreased until this signal disappeared, and type B droplet frequencies were maintained at a frequency of 4-7 Hz. Thus, a constant interelectrode gap of 12 mm was maintained over the entire cross section of the electrode. With sufficient heating of the electrode during melting, the melting rate increased, there was an increase in the interelectrode gap. This led to an increase in the task of the speed of movement of the melting electrode automatically by the controller by 0.1 mm / min. The end of the melting process was carried out according to known technology. The obtained ingot was with a well-melted side surface, without streaks, and was commissioned without machining.

Claims (3)

1. A method of monitoring and regulating the interelectrode gap in the process of vacuum arc melting, including measuring the voltage on the arc to obtain a controlled voltage signal, analyzing its change, determining from it the actual value of the interelectrode gap and adjusting the position of the sacrificial electrode relative to the investment cast, characterized in that the measurement voltage is produced with a frequency of not less than 10 kHz, with the subsequent isolation of short-circuit short-circuit signals, determination and regulation I eat on them the interelectrode gap. 2. A device for monitoring and regulating the interelectrode gap during a vacuum arc melting process, comprising a voltage sensor, a computer, an electrode drive with a controller-controller, characterized in that an additional device for filtering short-circuit short-circuit signals from signals of a different nature using a sensor is installed voltage measurements with a sampling frequency of at least 10 kHz. 3. The device according to claim 2, characterized in that the device for filtering short drip signals is additionally equipped with a filtering unit for the high-frequency component, a threshold device, a comparator and a device for generating output pulses, the voltage signal on the arc being fed to the input of the filtering unit, the output of this unit is connected with the input of a threshold device, the output of which is connected to a comparator, the output of which is connected to the input of the droplet pulse generating device.

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