JP2001214868A - Vacuum degree control device in furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vacuum degree control device in a furnace capable of easily adjusting a degree of vacuum in the furnace without enlarging equipment and without increasing a burden of a vacuum pump in operation of a vacuum arc melting furnace. SOLUTION: The vacuum arc melting furnace 1 has vacuum pump equipment connected to a furnace body 6 through a suction pipeline, and a vacuum atmosphere is formed in the furnace body 6 by jointly using a mechanical booster pump 12 of a mechanical type and a rotary pump 14. A rotating speed of the pumps 12, 14 is controlled by using an inverter 24 in the operation of the melting furnace 1, and the degree of vacuum in the furnace body 6 is adjusted by varying the suction force. When feeding back a detecting signal from a vacuum gauge 28 to a controller 26, the inverter 24 is automatically operated to automatically control the pump rotating speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling the degree of vacuum in a furnace for forming a vacuum atmosphere in the furnace and controlling the degree of vacuum as desired.

[0002]

2. Description of the Related Art For example, in a vacuum arc melting furnace or a vacuum heat treatment furnace for special steel, operations such as remelting and heat treatment of steel are performed in a furnace in a vacuum atmosphere. A high vacuum atmosphere is formed in the furnace during operation by a vacuum pump.
The degree of vacuum is usually maintained at a constant high vacuum level according to the rated suction power of the vacuum pump.

[0003] Incidentally, depending on the type of steel to be operated, an effective element (for example, manganese or copper) which easily evaporates in a high vacuum may be contained. For this reason, for example, in the operation of a vacuum arc melting furnace, while forming a vacuum atmosphere in the furnace, the evaporation of the effective elements during melting of the steel is prevented, and the content is stabilized and the yield is improved. There is a need. Similarly, in the case of copper-containing steel such as stainless steel, it is necessary to effectively prevent the evaporation of copper during vacuum heating.

[0004] Therefore, in the operation of these vacuum arc melting furnaces, vacuum heat treatment furnaces and the like, conventionally, an inert gas such as argon or nitrogen is introduced into the furnace, and the degree of vacuum in the furnace depends on the amount of introduction. Has been adjusted.

[0005]

However, the above-mentioned method of adjusting the degree of vacuum requires an additional facility for introducing an inert gas into the furnace, which leads to an increase in the size of the facility and an increase in operating costs. Is also increased. On the other hand, the introduction of gas into the furnace increases the load on the vacuum pump, so that the energy loss also increases.

Therefore, in view of the above problems, the present invention has an object to provide a vacuum control apparatus in a furnace which can adjust the vacuum by a simpler method.

[0007]

In order to achieve the above object,
The in-furnace vacuum control device (claim 1) of the present invention varies the suction force of the vacuum pump using an inverter,
The degree of vacuum in the furnace is controlled as desired. That is, the vacuum pump is connected to the furnace through a predetermined suction line, and has a synchronous motor as a power source. The vacuum pump is driven by a synchronous motor to suck the gas in the furnace through a suction line to form a vacuum atmosphere. Since a vacuum pump usually exerts a constant suction force according to its rated rotational speed, in a steady state of operation, the degree of vacuum in the furnace is at a pressure level that balances the suction force according to the rated capacity of the vacuum pump. . Therefore, in the present invention, the control means controls the rotation speed of the vacuum pump using an inverter, and adjusts the degree of vacuum in the furnace by varying the suction force. In this case, it is also possible to reduce the power consumption by adjusting the degree of vacuum and lowering the rotation speed.

The control means may include a vacuum gauge for detecting a degree of vacuum in the furnace and outputting a detection signal. In this case, the control means includes a detection signal from the vacuum gauge. , The degree of vacuum can be controlled. For example, the detection signal can be used as a feedback signal for varying the suction force.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows a process for remelting steel by a consumable electrode type vacuum arc melting method (hereinafter referred to as "VAR"). Is used. As is known, the VAR furnace 1 includes a water-cooled crucible 2, the outer periphery of which is covered by a cooling water jacket 4. The jacket 4 is connected to a cooling water circulation system (not shown), and the inside thereof is filled with circulation cooling water.

A vacuum pump equipment is connected to the furnace body 6 through a suction (exhaust) pipe line 8. More specifically, a diffusion (oil diffusion) pump 10,
A mechanical booster (roots) pump 12 and a rotary (oil rotation) pump 14 are provided. A control valve 18 is interposed in the middle of the suction line 8, and bypasses the control valve 18 to bypass the control line 18.
0 is piped. The bypass pipe 20 has valves 22 near its branch and merging positions, respectively, and can be separated from the suction pipe 8 by closing these valves 22.

The above-mentioned diffusion pump 10 is interposed in a bypass pipe 20, while a mechanical mechanical booster pump 12 and a rotary pump 14 are arranged in series on a suction pipe 8. Each of these mechanical pumps 12 and 14 has a synchronous motor as a drive source. Therefore, by varying the power supply frequency using the inverter 24, the rotation speed can be controlled as desired.

The inverter 24 is connected to a controller 26, which has a control circuit for the inverter 24. Further, the vacuum gauge 28 detects the degree of vacuum in the furnace body 6 and outputs the detection signal to the controller 2.
6 is output. The controller 26 controls the operation of the inverter 24 and also has a function of operating the control valve 18 described above.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS For example, plastic mold steel (NAK55) is remelted by a VAR furnace 1 shown in FIG. The preferred manganese content of this steel type is 1.4 to 1.7% (target value =
The purpose of the following embodiments is to remove gas components by re-melting steel and to particularly effectively suppress the evaporation of manganese.

The steel ingot cast into the consumable electrode 30 is inserted into the crucible 2 while being attached to the stinger rod 32. Then, a vacuum atmosphere is formed in the furnace body 6 by a vacuum pump facility, and a stable arc is generated to re-melt the steel. At this time, the startup of the vacuum pump equipment is first performed from the rotary pump 14, and usually, the rotary pump 14
Only the operation, the inside of the furnace body 6 from the atmospheric pressure to 13.3322Pa
(= 10 ^-1 torr).

Next, the mechanical booster pump 12 is started up, and a steady operation is performed in combination with the rotary pump 14. When these mechanical booster pump 12 and rotary pump 14 are operated at a normal rated rotation speed,
According to the suction force, the degree of vacuum in the furnace body 6 is 1.33322 Pa (= 1
0 ^-2 torr) to 1.33322 × 10 ^-2 Pa (= 10 ^-4 torr).

On the other hand, if the rotation speed of the pumps 12 and 14 is controlled by using the inverter 24, the relationship between the suction force of each pump and the rotation speed is apparent in advance by a performance curve or the like. The suction force can be varied according to the speed. As a result, the degree of vacuum in the furnace body 6 is reduced to 2 × 13
3.322Pa (= 2 × 10 ⁰ torr) to 5 × 1.33322Pa (= 5 × 10 ^-2 t
orr).

The above-described specific control of the degree of vacuum is performed by, for example, monitoring the degree of vacuum in the furnace body 6 based on a detection signal from the vacuum gauge 28 and appropriately operating the inverter 24 to adjust the pump rotation speed. It can be performed by changing. Further, if a feedback control circuit is incorporated in the controller 26 and the detection signal is used as a feedback signal, the controller 26 can automatically operate the inverter 24 to automatically control the degree of vacuum in the furnace body 6.

As described above, as a result of controlling the pump suction force using the inverter 24 by the vacuum arc melting method,
As the composition of the steel, for example, C: 0.10 to 0.15%, S
i: 0.20 to 0.50%, Mn: 1.4 to 1.7%,
Ni: 3.1 to 3.5%, Al: 0.8 to 1.1%, C
u: 0.9 to 1.2%, Mo: 0.25 to 0.40%,
S: 0.08 to 0.15%, favorable high-quality results of residual Fe and impurities were obtained.

On the other hand, conventionally, the degree of vacuum was adjusted by introducing argon into the furnace body 6, so that the mechanical booster pump 12 and the rotary pump 14 always operate at their rated rotational speeds. However, in this embodiment, power consumption can be reduced because the rotation speed is reduced by the inverter 24. Needless to say, the equipment for introducing argon, which was conventionally required, is not required, so that the entire equipment can be simplified accordingly.

The vacuum control apparatus of the present invention is not limited to the above-described embodiment, but is applicable to, for example, vacuum control in a vacuum heat treatment furnace. Similarly, in the case of a vacuum heat treatment furnace, a vacuum atmosphere is formed in the furnace by using a rotary pump, a mechanical booster pump, and the like. Can be controlled as desired. In this case, by appropriately adjusting the degree of vacuum in the furnace during vacuum heating,
For example, evaporation of copper from stainless steel or the like can be effectively suppressed.

[0021]

According to the apparatus for controlling the degree of vacuum in the furnace of the present invention (claim 1), the degree of vacuum in the furnace can be easily adjusted without introducing an inert gas from the outside. In addition, the evaporation of the active component of the steel can be reliably suppressed.
Further, since the power source of the vacuum pump is operated in a power saving manner, it is effective in saving power consumption in operation of the furnace, that is, in energy saving.

Further, if the degree of vacuum is controlled by feedback control using a vacuum gauge (claim 2), the monitoring and operation burden on the operator during operation can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an embodiment in which a vacuum control device is applied to a vacuum arc melting furnace facility.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vacuum arc melting furnace 6 Furnace body 8 Suction line 12 Mechanical booster pump 14 Rotary pump 24 Inverter (control means) 26 Controller (control means) 28 Vacuum gauge

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 3H045 AA05 AA09 AA15 AA26 BA20 BA32 CA02 CA29 DA07 EA38 3H076 AA16 AA21 AA29 AA38 BB21 BB41 CC07 CC41 CC51 CC84 CC94 4K045 AA04 AA07 BA02 CA00 DA05 RA01 A02A034K06 AA04 AA16 BA02 CA01 CA03 CA06 CA08 DA19 DA33

Claims (2)

[Claims] 1. A vacuum pump connected to a furnace through a suction line and driven by a synchronous motor to generate a suction force to form a vacuum atmosphere in the furnace; and an inverter that varies a rotation speed of the synchronous motor. Control means for controlling the degree of vacuum in the furnace by varying the suction force of the vacuum pump by the inverter. 2. The apparatus according to claim 1, wherein said control means includes a vacuum gauge which detects a degree of vacuum in said furnace and outputs a detection signal, and performs said control based on the detection signal. Vacuum degree control device in furnace.