JPH02258905A - Rotating electrode type powder manufacturing apparatus - Google Patents

Abstract

PURPOSE:To effectively restrain vibration while melting a billet and to stably manufacture powder at high rate by supporting a rotating shaft for rotating the billet with a magnetic bearing. CONSTITUTION:A plasma torch (electrode) 6 and the billet 7 cylindrically formed of raw material, are set with the same axis just below an electrode inserting hole 5. The billet 7 is directly connected with rotating shaft 23 in a magnetic spindle 22 arranged at lower part of a chamber 1 and freely rotated around the axis. The magnetic spindle 22 rotates the rotating shaft 23 at high velocity while holding the rotating shaft 23 to the condition without contact with an electromagnet interposed between the rotating shaft 23 and a main body 24. When plasma arc generates between the plasma torch 6 and the end face of the billet 7, the end face of the billet 7 is melted, and the molten metal is spattered with centrifugal force to manufacture the powder. Even in the case imbalance is developed in the billet, the powder can be stably manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a rotating electrode powder manufacturing apparatus for manufacturing powder of metals such as Ti and Zr to which atomization methods using ordinary gas and water are difficult to apply.

[Prior Art] Conventionally, as an apparatus for manufacturing this type of powder, there is a Birefutra, which is made by forming powder raw metal into a substantially cylindrical shape, and is mounted on a rotating shaft in a vacuum chamber (hereinafter referred to as a chamber). While rotating the billet at high speed around its axis, the billet is melted in the axial direction by the plasma arc heat generated between the billet's tip and the opposing plasma torch, and the molten metal is scattered by centrifugal force and turned into powder. A so-called rotating electrode type powder manufacturing apparatus was used.

Among such rotating electrode type powder manufacturing equipment (hereinafter abbreviated as powder manufacturing equipment), those specifically aimed at melting small-diameter billets incorporate a motor in the chamber and directly connect the rotating shaft and the motor shaft. and left to 3000 O
Those that can stably rotate at high speeds of r, p, and w have been put into practical use.

On the other hand, those applied to large diameter billets,
While a motor is provided outside the chamber, a speed increasing mechanism is installed inside the chamber, and this motor is driven at a relatively low rotational speed and transmitted to the speed increasing machine, which then increases the speed. The rotating shaft is designed to rotate at high speed.

This is because the bearings of high-output motors that are suitable for the high loads associated with melting large-diameter billets cannot be used in a vacuum due to lubrication problems, and when the speed is increased outside the chamber, the seal on the shaft that penetrates the chamber is damaged. It is difficult to ensure perfection, and if the motor is supplied with a large current commensurate with the high load in a vacuum state,
This is because arc discharge occurs in the brush portion or between the rotor and stator, significantly shortening the motor life.

[Problems to be Solved by the Invention] By the way, when producing powder using the above-mentioned conventional powder production apparatus, billet melting rarely progresses uniformly;
Billets often melt unevenly at their end faces, like a crown. In such cases, vibrations are unavoidable because the molten metal is partially scattered and the ff1ffi balance around the billet axis is disrupted, and as a result, it becomes necessary to take measures such as lowering the billet rotation speed. However, problems such as uneven particle size of the powder produced may occur.

Furthermore, since continuous heating by the plasma arc creates an axial temperature gradient at the tip of the billet, a semi-molten layer with low strength and high deformability may be generated below the molten layer on the billet surface. In this case, the semi-molten layer is greatly deformed by the centrifugal force, further worsening the weight balance, and sometimes lumps of unmelted metal partially fall off, resulting in an extreme unbalance. Vibrations sometimes occurred, forcing powder production to stop.

Furthermore, in the conventional powder manufacturing equipment mentioned above, in which the motor is installed outside the chamber, various components such as gears are interposed between the billet rotating shaft and the motor shaft, so the entire drive system is The rigidity of the structure inevitably decreases. For this reason, the vibrations generated during the above-mentioned melting process are further amplified,
Not only could this cause damage to bearings and gears, but if the vibration frequency matched the natural frequency of the drive system, it could cause irreparable and fatal damage, including bending of the rotating shaft. .

The present invention was made against this background, and an object of the present invention is to provide a powder manufacturing apparatus that can effectively suppress vibrations during billet melting and stably manufacture powder at high speed.

[Means for Solving the Problems] In order to solve the above problems, the inventors have made extensive studies and found that in order to stably produce powder, the first step is to increase the allowable unbalance of the drive system itself. We have come to find out that this is effective.

Furthermore, we discovered that by quickly dissolving and dissolving the deformed portion of the semi-molten metal layer, which is the biggest cause of billet imbalance, we could suppress the spread of billet imbalance.Based on these findings, we He invented the following powder manufacturing apparatus.

That is, in the powder manufacturing apparatus of the present invention, a rotating shaft for rotating the billet is supported by a magnetic bearing (non-contact bearing).

Further, another powder manufacturing apparatus of the present invention includes a swing drive unit that periodically swings the electrode in the radial direction of the billet, and a swing drive unit that detects an increase value in the radial displacement of the billet, and detects an increase value in the radial displacement of the billet. Based on the above electrode billet radial oscillation period,
The apparatus is provided with a swing period control section that changes the electrode so that it stays on the outer circumferential side of the billet.

In this case, by providing a plasma current control unit that increases the plasma current supplied to the electrode based on the increase value of the radial displacement of the billet, vibration can be suppressed more reliably.

Further, a lifting drive unit that lifts and lowers the electrode in the axial direction of the billet, and a fluctuation value of the distance between the electrode and the billet tip surface are detected, and the lifting drive unit is driven by an amount that absorbs this fluctuation value. Controllability can be further improved by providing an elevation control section that controls the height of the vehicle.

[Operation] According to the above configuration, the rotating shaft supporting the billet is held in a non-contact state by the magnetic bearing, so that vibrations of the rotating shaft are hardly transmitted to other components of the drive system. Therefore, the allowable amount of unbalance of the drive system is significantly improved.

In addition, in the case where the above-mentioned swing drive section and the above-mentioned swing period control section are provided, an electrode is installed on the outer circumferential side of the billet in response to the occurrence of deformation of the semi-molten metal layer, which is the biggest cause of unbalance. Since it is retained for a long time, the plasma arc is intensively irradiated to this part, and the semi-molten metal layer is quickly melted and disappeared, and as a result, the balance is quickly restored.

In this case, in the case where the current control section is added, the plasma current is increased in response to a change in the oscillation period of the electrode, so that a larger amount of heat is applied to the outer circumferential side of the billet in a shorter time. Therefore, the semi-molten metal layer is dissolved and disappeared more quickly.

In addition, in the device provided with the above-mentioned elevating drive unit and elevating control unit, the electrode is moved up and down so as to offset the change in the distance between the billet and the electrode as the melting of the billet progresses. Since the distance between the
The plasma current applied to the electrode and the amount of heat per unit time given to the billet are always constant. For this reason,
It becomes easier to calculate the increase in billet residence time and plasma current, improving controllability.

Embodiments] The present invention will be described in detail below with reference to FIGS. 1 to 4.

In FIG. 1, reference numeral 1 indicates a chamber. This chamber 1 is an airtight container in which a dome-shaped ceiling part 3 is joined to the upper part of a cylindrical peripheral wall part 2. A tube 4 is formed. Further, an electrode insertion opening 5 is formed in the center of the ceiling portion 3.

Immediately below the electrode insertion port 5, there is a cylindrical plasma torch (electrode) 6 and a raw material metal (for example, Ti, Z) for the powder to be manufactured.
A billet 7 formed by molding a substantially cylindrical shape (such as r) is arranged coaxially with the billet 7.

The plasma torch 6 is supported by an electrode drive mechanism 8 attached to the electrode insertion port 5 and suspended within the chamber 1 . This electrode drive mechanism 8 includes an elevation drive section 9 that moves the plasma torch 6 up and down in the axial direction of the billet 7, and a swing drive section 10 that swings the plasma torch 6 in the radial direction of the billet 7. It is.

The lift drive unit 9 includes a lift motor 13 connected via a first motor base 12 to a support base 11 that airtightly closes the electrode insertion port 5, and a lift motor 13 that is rotatably inserted into the support base 11 so that the tip thereof is connected to the a screw shaft 14 connected to the plasma torch 6;
The lifting motor 13 includes a drive gear 16 fitted to the motor shaft 15 of the lifting motor 13 and a driven gear 17 rotatably supported by the first motor base 12.
By transmitting the rotation to the driven gear 17 via the drive gear 16, the screw shaft 14 screwed with the driven gear 17 is moved in the axial direction, and the plasma torch 6 is raised and lowered.

The swing drive unit 10 also includes a swing motor 19 connected to the support base 11 via a second motor base 18.
and a screw shaft 21 connected to a motor shaft 20 of this swing motor 19, and by rotating the motor 19, the first motor base 12 screwed with the screw shaft 21 is horizontally moved. By moving the plasma torch 6
is adapted to swing in the radial direction of the billet 7 together with the lifting drive section 9.

The billet 7 is directly connected to a rotating shaft 23 of a magnetic spindle 22 disposed at the lower part of the chamber 1, and is rotatable around the axis. This magnetic spindle 22 rotates the rotating shaft 23 at high speed while holding the rotating shaft 23 in a non-contact state by means of an electromagnet (path shown) interposed between the rotating shaft 23 and the main body 24. A so-called active type magnet is used, which changes the magnetizing current of the electromagnet based on radial displacement.

As shown in FIG. 2, a control device 25 is disposed between the plasma torch 6, billet 7, and electrode drive mechanism 8.

This control device 25 includes a current control section 26 that controls the current applied between the plasma torch 6 and the billet 7, and a plasma voltage signal (2) outputted from the current control section 26 to control the lifting drive section 9. The above-mentioned rocking drive is performed based on the output signal SI of a lift control section 27 that controls the lift motor 13 and an eddy current gap sensor (hereinafter abbreviated as sensor) 28 that detects the radial displacement of the billet 7. Part 1
and a swing cycle control section 29 that controls the swing motor 19 of No. 0.

Here, as shown in FIG. 1, the sensors 28 are provided in a total of four pieces, one each at positions dividing the proximal end side of the billet 7 into four equal parts in the circumferential direction. It is precisely aligned with the direction.

In the figure, reference numeral 29 is a cooling plate that cools the scattered molten metal, and 30 is a collection gutter that collects the manufactured powder.

In the powder manufacturing apparatus configured as described above, the inside of the chamber 1 is first evacuated by the suction action of the vacuum pump connected to the suction port 4, and then an inert gas (for example, A , He, etc.).

Then, a predetermined plasma current A is applied between the plasma torch 6 and the billet 7 by the current control section 26, and the billet 7 is rotated at high speed around the axis by the magnetic spindle 22.

As a result, a plasma arc is generated between the plasma torch 6 and the tip surface of the billet 7, the tip surface of the billet 7 is melted, and the molten metal is scattered by centrifugal force to produce powder.

At this time, if the melting of the billet 7 does not proceed uniformly, the weight balance around the axis of the billet 7 will be disrupted and vibrations will be induced. Based on the displacement signal S1 output from the sensor 28, control is performed to uniformly progress the melting of the billet 7.

The operation of the control device 25 will be explained below. At the start of powder production, the current control unit 26 A predetermined plasma current A is output from the oscillation cycle control section 29, and a drive signal S for alternately rotating the oscillation motor 19 forward and reverse at predetermined intervals is output from the oscillation period control section 29, respectively. As a result, a certain amount of heat is applied to the tip end surface of the billet 7, and the plasma torch 6 is periodically oscillated between the center and the outer peripheral edge of the billet 7.

When powder production starts according to the above uniform dissolution mode,
First, the lift control unit 27 drives the lift motor 13 in order to prevent the distance between the plasma torch 6 and the billet 7 from changing as melting progresses and to keep the plasma current A constant.

Hereinafter, the processing in this elevation control section 27 will be explained as shown in FIGS. 2 and 3.
To explain with reference to the figure, the lift control section 27 measures the plasma voltage from the plasma voltage signal V output from the current control section 26 (Step 5Pi), and then measures the plasma torch 6 and billet 7 based on this plasma voltage. The distance between them is calculated (step 5P2). Then, calculate the amount of movement of the plasma torch 6 necessary to make this distance match the predetermined value determined in the uniform melting mode.
p3), and a drive signal S corresponding to this movement amount is output to drive the lifting motor 13.

This process by the lift control unit 26 is performed continuously during powder production, and thereby the distance between the plasma torch 6 and the billet 7 is always kept constant.

When the weight balance of the billet 7 is disturbed due to the continuation of powder production and vibration is induced, a difference occurs in the output signals S from each sensor 28 due to this vibration, and from these output differences, the oscillation period control section Vibration is detected at 29. When the difference in the output signal SI increases beyond a predetermined vibration stable region, the swing cycle control section 29 starts a swing cycle change process.

This oscillation period changing process is performed in consideration of the fact that the imbalance of the weight of the billet 7 is mainly caused by the deformation of the semi-molten metal layer that occurs at the tip of the billet 7 toward the outer circumference of the billet. be. That is, assuming that an unbalanced equivalent mass exists on the outer circumferential side of the billet 7, the above-mentioned oscillation period is This is to change the

This change process will be explained below with reference to FIGS. 2 and 4.

When vibration exceeding the stable range of the billet 7 is detected from the output signal SI of the sensor 28, the output signal S1 of each sensor 28 is first compared to measure the amplitude of the billet 7 (step 5p4), and then the amplitude of the billet 7 is measured (step 5p4). The amplitude is differentiated and the amplitude increment rate is calculated (step 5P5).

Next, the rate of increase in unbalance is calculated from the rate of increase in amplitude (step 5P6), and from this rate of increase in unbalance, the rate of increase in input heat required to reduce or even eliminate the imbalance is calculated (step 5P7).

Then, the oscillation period for applying the determined amount of heat to the outer peripheral portion of the billet 7 is calculated, and the drive signal S of the oscillation motor 19 is changed accordingly.

That is, in order to apply a predetermined amount of heat to the outer circumference of the billet 7 in a short time, the oscillation period of the plasma torch 6 is set such that it stays on the outer periphery of the billet 7 for a long time compared to the normal oscillation period. It is changed (Step 5P8). In addition,
In this case, if the amount of heat determined in step SP4 is so large that changing the oscillation period alone is insufficient, a current increase signal S4 is output to the current control section 26. Upon receiving this, the current control unit 26 increases the plasma current A to increase the output of the plasma arc so as to supplement the insufficient amount of heat and reliably eliminate the equivalent mass.

When a predetermined amount of heat is applied to the outer periphery of the billet 7 by changing the oscillation period or by changing the oscillation period and increasing the plasma current A, the amplitude of the billet 7 changes based on the output signal S from the sensor 28. It is determined whether the incremental speed has turned negative and whether the absolute value of the amplitude is smaller than the vibration stable region (step 5P9), and if these conditions are not met, it is assumed that the unbalance has not been resolved yet. , the above procedure is repeated after calculating the unbalance increase rate again.

Then, when the amplitude increment speed of the billet 7 turns negative and the absolute value of the amplitude becomes smaller than the vibration stable region, it is determined that the unbalance has been resolved, and the oscillation period or oscillation period of the plasma torch 6 changes. Both plasma currents Δ are returned to the uniform melting mode at the start of powder production (step 5 PIO), thereby ending the process.

As described above, according to the powder manufacturing apparatus of this embodiment, even if the weight balance of the billet 7 collapses as melting progresses,
Correspondingly, the oscillation period of the plasma torch 6 is changed to intensively irradiate the outer circumferential side of the billet 7 with the plasma arc, and depending on the degree of imbalance, the output of the plasma arc is also increased. The equivalent mass of the balance is quickly dissolved and disappeared, and the weight balance is quickly restored. Therefore, vibrations due to unbalance are significantly suppressed, and powder production can be performed stably at high speed.

In addition, since the distance between the plasma torch 6 and the billet 7 is always kept constant by the lift drive unit 9 and the lift control unit 27, the applied plasma current is applied to the billet 7 by plasma arc irradiation. The relationship between the amount of heat generated per unit time is always kept constant. Therefore, the melting conditions such as the amount of heat and the residence time of the plasma torch 6 when changing the oscillation period to eliminate imbalance can be calculated very easily, and as a result, controllability is improved.

In addition, since the base end side of the rotating shaft 23 that supports the billet 7 is kept in a non-contact state by the magnetic bearing, the tolerance for movement in the radial direction is lower than when using a conventional bearing that restricts movement. The amount of unbalance is significantly improved. For this reason,
The stability of the drive system against vibrations of the billet 7 is improved, and powder production can be performed stably even if some vibrations occur.

Furthermore, since the operating load on the rotating shaft 23 has been significantly reduced by employing a magnetic bearing, the operating current of the magnetic spindle 22, which is its driving source, has become smaller. Rotating axis 2
3 and billet 7 could be directly connected. Therefore, the rigidity of the drive system was improved, and the stability against vibration was further improved.

Note that the configuration of this example is just an example.
The powder manufacturing apparatus of the present invention is not limited to this.

For example, various measuring means such as a laser measuring means can be used to measure the displacement of the billet 7 and the distance between the plasma torch 6 and the billet 7.

In addition, if the rotating shaft 23 is held in a non-contact state by an independent magnetic bearing, the magnetic spindle 22 can be used as a driving means.
There is no necessity to use a motor, and a normal motor can also be used. In this case, it is considered that the allowable unbalance amount of the rotating shaft 23 will not be impaired if the rotating shaft 23 and the motor shaft are connected by means such as a flexible coupling that allows movement of the shafts.

Here, in order to clarify the effects of the above embodiment, the vibration measurement results obtained when a powder manufacturing experiment was conducted using the powder manufacturing apparatus having the above configuration and a conventional powder manufacturing apparatus are shown in FIGS. 5 to 7. Refer to and explain. The specifications of the billet used at this time are as follows.

■ Billet dimensions: φ100 x 250 C ■ Billet material: Ti alloy (experimental results) Figure 5 shows the results of powder manufacturing using a conventional powder manufacturing device.

6000r, p, m, for about 100 seconds after starting the motor.
After preheating and rotating the billet, the billet rotational speed was increased to 1400 Or, p, m almost simultaneously with plasma activation (Nt).

accelerated to Approximately 200 seconds after the start of acceleration ((1
), the billet started melting, but at the same time the billet
The vibration amplitude of the billet, which had been maintained at about m, increased significantly over time, and after about 50 seconds, the vibration reached an extremely dangerous state.

Furthermore, under the same conditions as in the above case, an attempt was made to suppress vibration by appropriately manually adjusting the plasma current, rotation speed, etc., and the results are shown in FIG. In this case, although it is possible to prevent the vibration from expanding indefinitely, the increase and decrease in amplitude is large, and the response period until the effect of manual adjustment appears is long, about 30 seconds.
It has no effect on vibrations that peak in a short period of time.

In contrast to the above results, FIG. 7 shows the results obtained when powder was manufactured using the powder manufacturing apparatus of the above example. In this case, the oscillation period of the plasma torch is 2 to 6 seconds, and the residence time of the plasma torch on the outer circumferential side of the billet is 0 to 6 seconds.
Controlled in seconds.

First, the billet rotational speed was maintained at 1200 Or, p, m, and preheating rotation was performed for about 100 seconds (0 to t).
When a plasma current of 2000 A was applied, the amplitude of the vibration did not increase by 30 μ even though the billet began to melt (t4).
It was kept at about m. From this, it was confirmed that by changing the oscillation period of the plasma torch, vibrations were suppressed and powder production could be performed stably.

Then, about 280 seconds after the start of the experiment (t), the rotation speed was accelerated to 1350 Or, p, m, and at the same time, the plasma current was controlled. As a result, the amplitude of the vibration actually decreased, and it became clear that the vibration could be further suppressed by increasing the plasma current.

[Effect] As explained above, according to the present invention, the rotating shaft is held in a non-contact state by the magnetic bearing, and its movement in the radial direction is not restricted, so the influence of vibration on the drive system is significantly reduced. This allows stable powder production to continue even if some imbalance occurs in the billet.

In addition, in this invention, even if a semi-molten metal layer is generated in the billet and vibration is induced, the oscillation driving section and the oscillation period control section change the oscillation period of the electrode in response to this, thereby generating plasma. The arc is focused on the outer circumference of the billet,
Furthermore, when a plasma current control section is provided, the plasma current is also increased, so that the unbalanced equivalent mass is rapidly dissolved and disappeared, and the weight balance is quickly restored. Therefore, vibrations due to unbalance are significantly suppressed, and powder production can be performed stably at high speed.

Furthermore, when a lift drive unit and a lift control unit are provided,
Since the distance between the electrode and the billet is kept constant, the relationship between the plasma current applied between them and the heating melon applied to the billet per unit time is kept constant.
The electrode residence time and plasma current increase value for eliminating imbalance can be easily calculated, improving controllability.

[Brief explanation of drawings]

1 to 4 show an embodiment of the present invention,
Fig. 1 is a vertical cross-sectional view of the powder manufacturing device, Fig. 2 is a block diagram of the control device, Fig. 3 is a flowchart showing the processing procedure of the elevation control section, and Fig. 4 shows the processing procedure of the oscillation period control section. The flowcharts, Figures 5 to 7, are diagrams showing the relationship between billet rotation time and amplitude when powder manufacturing is actually performed. FIG. 7 shows a case in which a conventional powder manufacturing apparatus is manually adjusted to suppress vibration, and FIG. 7 shows a case in which the powder manufacturing apparatus of the above embodiment is used. l...Vacuum chamber 6...Plasma torch (electrode), 7...
・Billet, 9... Lifting drive unit, 10...
...Swing drive unit, 22...Magnetic spindle, 2
3... Rotating shaft, 26... Current control section,
27... Elevation control section, 29... Swing period control section.

Claims (4)

[Claims] (1) Rotating a substantially cylindrical billet made of powdered raw material metal to be manufactured at high speed around its axis, and melting the tip of the billet with a plasma arc generated between opposing electrodes. A rotating electrode type powder manufacturing apparatus for manufacturing powder by scattering molten metal of the billet by centrifugal force, characterized in that a rotating shaft for rotating the billet is supported by a magnetic bearing. . (2) A swing drive unit that periodically swings the electrode according to claim 1 in the billet radial direction according to claim 1, and detects an increase value of the radial displacement of the billet, and based on the increase value. 1. A rotating electrode type powder manufacturing apparatus, comprising: a swinging period control section that changes the swinging period of the electrode in the radial direction of the billet so that the electrode stays on the outer circumferential side of the billet. (3) Based on the increase value of the radial displacement of the billet,
3. The rotating electrode powder manufacturing apparatus according to claim 2, further comprising a plasma current control section for increasing the plasma current supplied to the electrode. (4) A lifting drive unit that moves the electrode up and down in the axial direction of the billet, detects a fluctuation value in the distance between the electrode and the billet end surface, and moves the lifting drive unit by an amount that absorbs this fluctuation value. 4. The rotating electrode type powder manufacturing apparatus according to claim 2, further comprising an elevation control section for driving the powder.