JPH06624A - Method and apparatus for automatic control plasma melting and casting - Google Patents

Abstract

PURPOSE:To stabilize a continuous plasma melting and casting operation by calculating the area ratio of melting surface having the fixed temp. value or more and controlling the charging speed of raw material. CONSTITUTION:In a plasma melting and casting apparatus composed of a plasma torch 1, atmospheric control melting chamber 2, water cooled mold 3, raw material continuously charging device and cast block continuously drawing-down device, the temp. of the melting surface is measured with an infrared ray thermosensor 6. An analyzer 7 for calculating the area ratio occupied with the range having the fixed temp. value or more and a sequenser 8 for deciding the charging speed of the raw material based on the area ratio are provided and further, the plasma voltage is measured, and by changing the automatic drawing-down speed of the cast block, the condition of approaching to the setting voltage is given to a controller 9. By this method, the observation for long time and the manual operation are made unnecessary, and the automation can be executed and the operation is stabilized and product quality is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for performing continuous plasma melting and casting of metal under automatic control, and a plasma melting and casting apparatus capable of automatic control operation. The present invention is particularly significant when applied to the primary melting of Ti or a Ti alloy.

[0002]

VAR is used for refining Ti or Ti alloys.
(Vacuum arc remelting) is usually performed and this VA
The primary dissolution to produce the electrode used for R is PPC (Plas
ma Progressive Casting (plasma continuous melting casting) technology.

As is well known, plasma melting casting is performed by plasma arc melting and solidifying a metal in a water-cooled mold under an Ar gas atmosphere, continuously charging raw materials and lowering the solidified metal. Consists of obtaining a continuous ingot. A drum feeder is used for continuous charging of raw materials, and usually two feeders are provided and they are switched and used.

The above-mentioned work has been performed manually until now. The operator constantly monitors the condition of the melting site by CRT and changes the rotation speed of the drum feeder according to the condition. That is, if there are many unmelted and low-temperature parts, the charging speed is slowed down, and if the high-temperature parts are widened, the charging speed is increased. On the other hand, since the height of the melted portion is closely related to the plasma voltage, the continuous pulling speed of the ingot must be manually adjusted while balancing the raw material charging speed so that the voltage is always constant. To control. The switching of the drum feeder described above is also performed manually while monitoring the remaining material (displayed at the drum pitch) in the feeder on the operation panel. In addition, the operator must constantly monitor for abnormalities such as arc breaks, raw material falling defects (“shelf hanging”), ingot lowering defects, and take appropriate measures.

In a typical operation in which one charge of melt casting requires 10 to 11 hours, the amount of manual work of the operator is 8.3 person hours, and in particular, during melting, it is continuously monitored for about 6 hours. There is a need. Moreover, a high degree of skill is required for this operation.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned complications in plasma melting casting, and to perform melting casting by automatic control and therefore without the need for constant monitoring of the operator. To provide a device.

[0007]

According to the method of automatically controlling plasma melting and casting of the present invention, a metal is melted and solidified by a plasma arc in a water-cooled mold in an Ar gas atmosphere, and raw materials are continuously charged and solidified. In a melting and casting method consisting of pulling down the metal obtained to obtain a continuous ingot,
The temperature of the melting site is measured with an infrared heat sensor and taken out as an infrared thermal image, data processing is performed, the area ratio of the melting site belonging to a prescribed temperature level is calculated, and the rate of raw material charging is determined according to that value. It is characterized by making a decision.

When a drum feeder is used as the raw material charging means, the raw material charging speed can be controlled by changing the rotation speed of the drum feeder.

It is preferable to use two drum feeders alternately. When the raw material of the running drum is running low, start the idle drum operation at low speed,
When the former raw material is exhausted, the latter is operated at a constant speed to prevent a decrease in the raw material charging amount and realize a desired charging speed.

The basis of the operation control is the charging rate of the molten raw material, but the rate of ingot lowering is also important. This is because, as described above, the height of the melting portion is closely related to the plasma voltage. Therefore, it is preferable to add control to monitor the plasma voltage and change the pulling speed of the ingot so as to return to the set voltage when the plasma voltage fluctuates from the set voltage over a predetermined value.

An automatic control plasma melting and casting apparatus of the present invention for carrying out the above-mentioned method comprises a plasma torch (1), an atmosphere-controllable melting chamber (2), as shown in FIG.
Plasma consisting of a water-cooled mold (3), means for continuously charging raw materials into the melting chamber, here a means for continuously pulling down the drum feeder (4) and the ingot from the water-cooled mold, here a hydraulic cylinder (5) In the melting and casting equipment, an infrared heat sensor (6) for monitoring the melting portion, an analyzer (7) for processing the output of the sensor to calculate the area ratio of the melting portion belonging to a predetermined temperature level, the calculated area It is characterized by comprising a sequencer (8) for determining a raw material charging rate according to the ratio and a controller (9) for controlling the raw material charging means based on the output of the sequencer.

In addition to the above basic structure, this apparatus has
The sequencer (8) is provided with a function of monitoring the plasma voltage and detecting a difference from the set voltage, and when the voltage difference exceeds a predetermined value, the speed of the ingot lowering means is changed to approach the set voltage. Is preferably given to the controller (9).

[0013]

[Function] The image obtained by the infrared thermal sensor can be obtained as a slightly tilted image because the raw material charging port is located directly above the melting site and the sensor is located outside it, but the plasma torch is used. The portion immediately below (there are six in a typical device) is naturally the highest temperature, and the portion where the new raw material falls is the lowest temperature. Therefore, when the ratio of the area reaching a specific temperature level in the field of view exceeds a certain value, the temperature of the melting site has risen too much, so the rate of raw material charging should be increased. When the temperature falls below a certain value, the temperature has dropped, so the feed rate should be slowed. This is controlled by the rotation speed of the drum feeder as shown in FIG. This is shown in the graph of FIG. The characteristic broken line shown in the figure is an example, and it goes without saying that it can be arbitrarily set.

Control of the ingot lowering speed based on the plasma arc voltage is performed by turning on and off a hydraulic cylinder, which is a lowering means, as shown in FIG. FIG. 5 is a chart showing the operation.
In the operation according to this chart, when the actual arc voltage is Vx, when Vx is lower than V-ΔV, the pull-down output is O.
It is set to N and kept in that state, and is turned off when Vx reaches V + ΔV. If the ingot continues to be melted while the ingot is stopped, the melting point rises and the arc voltage decreases. If Vx is lowered to V-ΔV and turned on again, the above cycle is repeated.

As is known in the art of plasma melting and casting, in order to obtain an ingot having a uniform density, it is desired that the area ratio of the portion of the melting portion exceeding a specific temperature is as constant as possible. In order to realize this, it is necessary to change the rotation characteristics of the drum feeder depending on whether the solubility of the raw material is good or not, specifically, to adjust the relationship between the area ratio and the feeder rotation output. For example, T
When titanium sponge having poor solubility is used as a raw material in the melt casting of i, the rotation characteristic of the drum feeder is selected as shown in FIG. 6 according to the amount of the compounding amount.

The ingot lowering speed is controlled so that the arc voltage becomes constant as described above. Even if the voltage becomes constant, the charging of the raw materials is too fast with respect to the melting speed, and complete melting is achieved. If not secured, an ingot with a low density at that portion may be formed, and the ingot length for one charge may be varied. To prevent this, the maximum reduction amount should be monitored and controlled. In particular,
For example, the pull-down amount pulse is taken out as 1 mm / pulse, the pull-down result for the past 1 minute is monitored (checked every 12 seconds), and when the pulse exceeding the set value is accumulated,
Turns down output temporarily off. An example of implementing this is the chart of FIG.

[0017]

EXAMPLES Ti was melt-cast by using the apparatus having the structure shown in FIG. Depending on the ratio of the area occupied by the area of 1200 ° C or higher in the infrared thermal image,
It was converted to a 20mA analog signal and output to the sequencer. On the other hand, the rotation output of the drum feeder corresponding to this is 0-10V (1V corresponds to approximately 0.4 rpm)
Was output to the controller according to a preset characteristic broken line as shown in FIG.

The changes over time in the area ratio output and the drum feeder rotation output are shown in FIGS. For comparison, the case of conventional manual operation (volume control by the operator) is shown above each figure.

In the case of the present invention, the area ratio of the region having a temperature of 1200 ° C. or higher is stable in the range of about 40 to 60%, and the corresponding rotary output of the drum feeder is
Responsiveness is obtained according to the feeder rotation characteristics.
On the other hand, in the manual operation, it is inevitable that the area ratio fluctuates greatly, and the feeder rotation output fluctuates.

The lowering of the ingot was controlled by setting the arc voltage (average of six plasmas) at 68V and ΔV = 1V. At the same time, the operation of monitoring the maximum pulldown amount and temporarily turning off the pulldown output was added. Plasma torch No. The time change of the arc voltage of the three wires 1, 3 and 5 is shown in FIGS. 10A to 10C in comparison with the case of the conventional manual operation. In addition, the length of the ingot was examined and shown in FIG. 11 in comparison with the conventional case.

By controlling the arc voltage to be constant, the ingot can be accurately pulled down at short intervals, so that the fluctuation of the voltage becomes small and the output becomes stable.

A shorter ingot length according to the invention means a higher density. The length of all 1.8 ton ingots is controlled within 3150 mm.

[0023]

EFFECTS OF THE INVENTION Plasma melting casting under automatic control in accordance with the present invention relieves the need for lengthy monitoring and manual operations. No skill in operation is required. This allows a significant reduction in ingot manufacturing costs. The operation is more stable than that of the manual operation, and a product of superior quality is obtained.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing the overall configuration of an automatic control plasma melting and casting apparatus of the present invention.

FIG. 2 is a diagram showing a main part of FIG. 1 for explaining the principle of automation of raw material charging in the present invention.

FIG. 3 is a characteristic broken line chart of a drum feeder for automatically feeding the raw material shown in FIG.

FIG. 4 is a view similar to FIG. 2 for explaining the principle of automation of ingot lowering in the present invention.

FIG. 5 is a hydraulic cylinder ON-OFF chart for performing automatic ingot lowering of FIG.

6 is a polygonal line chart showing another example of the rotation characteristics of the drum feeder shown in FIG.

FIG. 7 is an ON / OFF chart of an operation in which maximum pulling amount monitoring is added to automatic ingot lowering.

FIG. 8 is a graph showing data of an example of the present invention, showing a temporal change of an area ratio of a region having a temperature equal to or higher than a certain value in an infrared thermal image, compared with a conventional example.

FIG. 9 is a graph showing data relating to FIG. 9 and showing a temporal change in rotation output of a drum feeder, as compared with a conventional example.

FIG. 10 is also data of an example of the present invention,
3A to 3C are graphs showing changes with time in arc voltage of three of the six torches of the plasma melting and casting apparatus, as compared with the case of the conventional manual operation.

FIG. 11 is also data of an example of the present invention,
The bar graph showing the distribution of the length of the obtained ingots in comparison with the conventional manually operated product.

[Explanation of symbols]

 1 Plasma torch 2 Melting chamber 3 Water-cooled mold 4 Drum feeder 5 Hydraulic cylinder 6 Infrared heat sensor 7 Analyzer 8 Sequencer 9 Controller

Claims (7)

[Claims] 1. A melting process in which a metal is melted and solidified by a plasma arc in a water-cooled mold in an Ar gas atmosphere, a raw material is continuously charged, and the solidified metal is pulled down to obtain a continuous ingot. In the casting method, the temperature of the melted portion is measured with an infrared heat sensor, extracted as an infrared thermal image, data processing is performed, and the area ratio of the melted portion belonging to a predetermined temperature level is calculated. An automatically controlled plasma melt casting method characterized by determining the rate of charge. 2. The plasma melting and casting method according to claim 1, wherein the metal to be melted and cast is Ti or a Ti alloy, and the obtained ingot is an electrode for vacuum arc remelting. 3. The plasma melting casting method according to claim 1, wherein a drum feeder is used as a raw material charging means, and the raw material charging speed is controlled by changing the rotation speed thereof. 4. Use two drum feeders alternately,
When the raw material of the running drum is running low, the operation of the drum that was paused is started at a low speed, and when the raw material of the former is exhausted, the latter is operated at a constant speed to prevent a decrease in the raw material charging amount. The plasma melting and casting method according to claim 1, which is carried out. 5. The plasma according to claim 1, wherein the plasma voltage is monitored, and control is performed to change the ingot lowering speed so as to return to the set voltage when the plasma voltage fluctuates from the set voltage over a predetermined value. Melt casting method. 6. A plasma melting casting apparatus comprising a plasma torch, a melting chamber capable of controlling an atmosphere, a water cooling mold, means for continuously charging raw materials into the melting chamber, and means for continuously pulling down an ingot from the water cooling mold. , An infrared heat sensor that monitors the melting area, an analyzer that processes the output of the sensor to calculate the area ratio of the melting area that belongs to a predetermined temperature level, and determines the raw material charging rate according to the calculated area ratio An automatic control plasma melting and casting apparatus characterized by having a sequencer for controlling the raw material charging means based on the output of the sequencer. 7. A sequencer for monitoring a plasma voltage to detect a difference from a set voltage, and a controller for changing the speed of a means for pulling down an ingot to bring it closer to the set voltage when the voltage difference exceeds a predetermined value. The automatic control plasma melting and casting apparatus according to claim 6, further comprising: