CN115087185A

CN115087185A - Three-dimensional swinging mechanism of plasma gun for cold bed furnace and plasma arc length control method

Info

Publication number: CN115087185A
Application number: CN202210869434.XA
Authority: CN
Inventors: 赵博; 陈小龙; 李永华; 王健; 王红伟
Original assignee: Shangi Institute For Advanced Materials Nanjing Co ltd
Current assignee: Shangi Institute For Advanced Materials Nanjing Co ltd
Priority date: 2022-07-22
Filing date: 2022-07-22
Publication date: 2022-09-20

Abstract

The invention relates to the technical field of plasma smelting, in particular to a three-dimensional swinging mechanism of a plasma gun for a cooling bed furnace and a plasma arc length control method, which comprise the following steps: the first end surface of the first connecting seat is connected to the cold hearth furnace, and a cavity for the plasma gun to pass through is formed in the connecting seat; the second connecting seat can rotate along the X-axis direction relative to the first connecting seat and is arranged above the first connecting seat; and the third connecting seat can move along the Y-axis direction relative to the second connecting seat and is arranged above the second connecting seat. The second connecting seat and the third connecting seat can independently swing in the X direction and the Y direction, and the plasma gun can slide relative to the third connecting seat along the axial direction of the plasma gun, so that the plasma gun can compensate the end position of the plasma gun when swinging in the X-Y direction, the arc length of a plasma arc is constant, and the uniformity of a temperature field of a molten pool is ensured.

Description

Three-dimensional swinging mechanism of plasma gun for cold bed furnace and plasma arc length control method

Technical Field

The invention relates to the technical field of plasma smelting, in particular to a three-dimensional swinging mechanism of a plasma gun for a cold bed furnace and a plasma arc length control method.

Background

Plasma smelting is a metallurgical method using high-temperature plasma arc generated by electric energy as a heat source, and has the characteristics of high arc temperature (over 10000 ℃) and effective control of furnace chamber atmosphere, so that the plasma smelting method is suitable for smelting active metals, refractory metals and alloys thereof.

Plasma melting has been widely used in many countries since the beginning of the 20 th century, the beginning of the 60 th era, plasma melting is mainly applied to cold hearth furnace equipment at present, a plasma cold hearth furnace (PACHM) and an electron beam cold hearth furnace (EBCHM) are in two parallel development directions, the plasma melting is rapidly developed in industrially developed countries such as the united states, russia, germany and the like, and the plasma melting is gradually replacing the traditional melting process of a vacuum consumable arc furnace (VAR).

Plasma cold hearth furnace compares electron beam cold hearth furnace main advantage lies in: the volatilization of alloy elements is less, and the components are easy to control; the plasma arc generated by the plasma gun is high-speed and rotary, can stir a titanium molten pool and is beneficial to the homogenization of alloy components; when the plasma cold hearth furnace is used for smelting, the molten pool is large and deep, and the titanium melt can be fully diffused.

However, how to determine the uniformity of a temperature field of a molten pool in the smelting process and realize smelting and refining of materials in a cold bed becomes a problem to be solved urgently.

Disclosure of Invention

The invention provides a plasma gun three-dimensional swing mechanism for a cold bed furnace, which comprises:

the first end surface of the first connecting seat is connected to the cold hearth furnace, and a cavity for the plasma gun to pass through is formed in the connecting seat;

the second connecting seat can rotate along the X-axis direction relative to the first connecting seat, and the second connecting seat is arranged above the first connecting seat;

the third connecting seat can rotate along the Y-axis direction relative to the second connecting seat, and is arranged above the second connecting seat;

the plasma gun is assembled on the inner wall of the third connecting seat from the upper part of the third connecting seat, the first end of the plasma gun extends into the cooling bed furnace, and the plasma gun can slide along the height direction of the third connecting seat;

a flexible sleeve is arranged between the first connecting seat and the third connecting seat, so that a sealed space with variable volume is formed between the third connecting seat and the cooling bed furnace;

the plasma torch comprises a first connecting seat, a second connecting seat, a third connecting seat, a plasma torch, a first driving part, a second driving part and a third driving part, wherein the first driving part is arranged between the first connecting seat and the second connecting seat and used for controlling an inclination angle between the first connecting seat and the second connecting seat to enable the plasma arc jetted by the plasma torch to displace along the Y direction, the second driving part is arranged between the second connecting seat and the third connecting seat and used for controlling the inclination angle between the second connecting seat and the third connecting seat to enable the plasma arc jetted by the plasma torch to displace along the X direction, and the third driving part is arranged between the third connecting seat and the plasma torch and used for controlling the relative position between the plasma torch and the third connecting seat to enable the distance between the head of the plasma torch and a molten pool to be the same when the plasma arc jetted by the plasma torch displaces along the X-Y direction.

Preferably, the second connecting seat is annular, the third connecting seat is circular truncated cone-shaped, the first end of the flexible sleeve is connected to the upper end face of the first connecting seat, the second end of the flexible sleeve is connected to the lower end face of the third connecting seat, and the flexible sleeve is located on the inner side of the second connecting seat.

Preferably, the flexible sleeve comprises a vacuum bellows.

Preferably, the first connecting seat and the second connecting seat are hinged through two X-axis hinge parts which are linearly distributed, and the second connecting seat and the third connecting seat are hinged through two Y-axis hinge parts which are linearly distributed.

Preferably, the first driving member includes a first linear telescopic rod, a first end of the first linear telescopic rod is hinged to the first connecting seat, a second end of the first linear telescopic rod is hinged to the second connecting seat, and the first linear telescopic rod and the two X-axis hinged members are distributed in a triangular shape.

Preferably, the second driving part comprises a second linear telescopic rod, two ends of the second linear telescopic rod are respectively hinged to the second connecting seat and the third connecting seat, and the second linear telescopic rod and the two Y-axis hinged parts are distributed in a triangular shape.

Preferably, an axial sealing structure is arranged between the plasma gun and the third connecting seat.

Preferably, the third connecting seat is provided with a second water cooling channel at the periphery of the axial sealing structure.

Preferably, a first sealing structure is arranged between the first connecting seat and the cooling bed furnace, and a first water cooling channel located on the periphery of the first sealing structure is arranged on the first connecting seat.

The invention provides a technical scheme, a plasma arc length control method for plasma cold hearth smelting, which uses the plasma gun three-dimensional swinging mechanism and comprises the following steps:

igniting the plasma gun to form a plasma arc between the plasma gun and the molten pool;

controlling the first driving part and the second driving part to stretch and retract so that the plasma gun deflects along an X axis and a Y axis, and moving plasma arc spots emitted by the plasma gun along a preset track on the surface of a molten pool;

the extension and contraction of the third driving part are controlled, so that the arc length of the plasma arc emitted by the plasma gun in the deflection state along the X axis and the Y axis is constant.

Compared with the prior art, the invention has the advantages that:

the plasma torch is provided with three layers of connecting seats, wherein the second connecting seat and the third connecting seat can independently swing in the X direction and the Y direction, and the plasma torch can slide relative to the third connecting seat along the axial direction of the plasma torch and is used for compensating the end position of the plasma torch when the plasma torch swings in the X-Y direction, so that the arc length of a plasma arc is constant, and the uniformity of a temperature field of a molten pool is ensured; in addition, a vacuum corrugated pipe is used as a dynamic seal to ensure that the smelting atmosphere of the furnace chamber is not damaged in the swinging process.

Drawings

The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic structural diagram of a three-dimensional swinging mechanism of a plasma gun for a cold bed furnace according to the present invention;

FIG. 2 is a schematic view of the second connecting seat of the present invention deflected in the X direction;

FIG. 3 is a schematic structural diagram of an embodiment of a three-dimensional swinging mechanism of a plasma gun for the cold hearth furnace according to FIG. 1;

FIG. 4 is a side view of FIG. 3;

FIG. 5 is a schematic structural view of an axial seal arrangement according to the present invention;

FIG. 6 is a graphical representation of the trajectory of a plasma arc within the molten bath in accordance with the present invention.

Detailed Description

In order to better understand the technical content of the present invention, specific embodiments are described below with reference to all the accompanying drawings.

In plasma smelting, on the premise that a given current is not changed, the output power of a plasma gun depends on the arc length, if the plasma gun is perpendicular to the surface of a molten pool and moves to any position of the molten pool in a mode of controlling the horizontal movement of the plasma gun, the sealing state of a cooling bed is not easy to control, if the plasma gun is fixed to a certain position, the distance between the gun head of the plasma gun and the surface of the molten pool changes when the gun head of the plasma gun swings in a swinging mode, but the arc length changes no matter in X-direction swinging or Y-direction swinging.

The plasma gun is in a three-layer connecting seat structure, the plasma gun swings along the X-axis direction between the first layer connecting seat and the second layer connecting seat, so that plasma arc spots emitted by the gun head of the plasma gun move along the Y direction on the surface of a molten pool, the plasma gun swings along the Y-axis direction between the second layer connecting seat and the third layer connecting seat, the plasma arc spots emitted by the gun head of the plasma gun move along the X direction on the surface of the molten pool, the arc spots can reach any point on the surface of the molten pool, further, the plasma gun and the third layer connecting seat can move along the length direction of the plasma gun, and when the plasma gun swings along the X-Y axis, the plasma gun is controlled to extend or shorten, and the arc length of the plasma arc emitted by the plasma gun head is kept unchanged.

Therefore, the plasma arc spot can reach any point on the surface of the molten pool in the swinging process of the plasma gun, and meanwhile, the arc length of the plasma gun is kept constant, so that the output power of the plasma gun 40 is kept constant in the smelting process, and the uniformity of the temperature field of the molten pool is ensured.

Three-dimensional swinging mechanism of plasma gun for cold hearth furnace

Referring to fig. 1, a first aspect of the present invention provides a technical solution, in which a three-dimensional swinging mechanism of a plasma gun for a cold hearth furnace mainly includes three layers of connecting seats, a plasma gun 40 is connected to the connecting seat at the uppermost layer, and the connecting seat at the lowermost layer is connected to a cold hearth furnace 100, so that a plasma arc 41 emitted from the plasma gun 40 moves on the surface of a molten pool 101 by controlling the swinging of the plasma gun 40 in an X-Y plane, and the length of the arc is controlled to be constant.

Swing driving part of plasma gun

Referring to fig. 1, a first end surface of the first connection base 10 is connected to the cold hearth furnace 100, and a cavity for the plasma gun 40 to pass through is formed in the first connection base 10; the second connecting seat 20 is rotatably arranged above the first connecting seat 10 along the X-axis direction relative to the first connecting seat 10; the third connecting holder 30 is rotatably disposed above the second connecting holder 20 in the Y-axis direction with respect to the second connecting holder 20, the plasma gun 40 is assembled to the inner wall of the third connecting holder 30 from above the third connecting holder 30, and the first end extends into the cold hearth 100, and the plasma gun 40 can slide in the height direction of the third connecting holder 30.

Furthermore, in order to control the swinging and the expansion of the gun head of the plasma gun 40, the emitted plasma arc can reach any point on the surface of the molten pool, and the arc length is kept constant.

Specifically, a first driving part 11 is disposed between the first connection seat 10 and the second connection seat 20, and is used for controlling an inclination angle between the first connection seat 10 and the second connection seat 20, so that a plasma arc emitted from the plasma gun 40 is displaced along the Y direction, and a second driving part 21 is disposed between the second connection seat 20 and the third connection seat 30, and is used for controlling an inclination angle between the second connection seat 20 and the third connection seat 30, so that a plasma arc emitted from the plasma gun 40 is displaced along the X direction.

In this way, the arc spot of the plasma arc reaches any point on the surface of the molten pool in the cooling bed by controlling the combination of the swing of the plasma gun 40 along the X direction and the swing along the Y direction.

In an alternative embodiment, the first driving member 11 and the second driving member 21 are servo electric cylinders, and first and second ends of the servo electric cylinders are connected with the first connecting seat 10, the second connecting seat 20 and the third connecting seat 30 through hinge structures to ensure that the servo electric cylinders are not bent when the inclination angle between the first connecting seat 10, the second connecting seat 20 and the third connecting seat 30 is changed.

Because the arc length can be changed no matter in X-direction swinging or Y-direction swinging, a third driving part 31 is arranged between the third connecting seat 30 and the plasma gun 40 and is used for controlling the relative position between the plasma gun 40 and the third connecting seat 30, so that the arc length of the plasma arc emitted by the plasma gun 40 is kept unchanged when the plasma arc generates X-Y-direction displacement.

The third driving part 31 may be a servo electric cylinder, a first end of the servo electric cylinder is connected to the outer wall of the plasma gun 40, a second end of the servo electric cylinder is hinged to the third connecting base 30, and when the servo electric cylinder extends and retracts, the plasma gun 40 and the third connecting base 30 generate relative displacement.

Therefore, the length direction of the plasma gun 40 is defined as the Z direction, and the arc length of the plasma arc is adjusted by using the linear motion of the Z direction, so that the arc length of the plasma gun is kept constant in the swinging process, the output power of the plasma gun 40 is kept constant in the smelting process, and the uniformity of the temperature field of the molten pool is ensured.

Referring to fig. 2, the second connecting socket 20 is rotated about the X-axis to move the plasma arc of the plasma gun 40 in the Y-direction when the first driving part 11 is extended. It will be appreciated that when the second driving member 21 is extended and retracted, the third connecting socket 30 can be rotated about the Y-axis relative to the second connecting socket 20 to move the plasma arc of the plasma gun 40 in the X-direction.

In a specific embodiment, the plasma arc emitted by the plasma gun 40 can be controlled to move in the X-Y plane to reach any point on the surface of the molten pool by controlling the extension and retraction of the first driving component 11 and the second driving component 21.

Referring to fig. 6, a schematic view of the trajectory of the plasma arc moving along a broken line from one end to the other end of the cooling bed is shown.

In other embodiments, the plasma arc may be moved across the surface of the molten bath according to different predetermined trajectories while maintaining a constant arc length to ensure uniformity of the temperature field of the molten bath.

Further, a flexible sleeve 50 is arranged between the first connecting seat 10 and the third connecting seat 30, so that a sealed space with variable volume is formed between the third connecting seat 30 and the cold hearth furnace 100, and thus, the smelting atmosphere in the cold hearth furnace is ensured on the premise of not interfering the activity of the plasma gun 40.

In a specific embodiment, the flexible sleeve 50 uses a vacuum bellows, a first end of the vacuum bellows is connected to the upper end surface of the first connecting seat 10, a second end of the vacuum bellows is connected to the lower end surface of the third connecting seat 30, the vacuum bellows is located at the inner side of the second connecting seat 20, and the vacuum bellows is used as a dynamic seal to ensure that the smelting atmosphere of the furnace chamber is not damaged during the swinging process.

As shown in fig. 3-4, in an alternative embodiment, the lower end of the first connecting seat 10 is provided with a first connecting surface 13 for connecting with the upper end of the cold hearth furnace 100, the upper end of the first connecting seat 10 is provided with a first bearing seat 121, the second connecting seat 20 is annular, the outer wall of the second connecting seat 20 is provided with a second bearing seat 122, and the first bearing seat 121 and the second bearing seat 122 are connected through a rotating shaft; the first bearing seat 121 and the second bearing seat 122 constitute an X-axis hinge member 12; a third bearing seat 221 is arranged at the upper part of the second connecting seat 20, the third connecting seat 30 is in a circular truncated cone shape, a fourth bearing seat 222 is arranged at the outer edge of the third connecting seat 30, the third bearing seat 221 and the fourth bearing seat 222 are connected through a rotating shaft, and the third bearing seat 221 and the fourth bearing seat 222 form a Y-axis hinge component 22.

Preferably, the first connecting seat 10 and the second connecting seat 20 are hinged through two X-axis hinge parts 12 which are linearly distributed, and the second connecting seat 20 and the third connecting seat 30 are hinged through two Y-axis hinge parts 22 which are linearly distributed, so that the three-layer structure of the first connecting seat 10, the second connecting seat 20 and the third connecting seat 30 can flexibly and reliably rotate relative to each other.

Specifically, as shown in fig. 3 to 4, the first driving member 11 includes a first linear telescopic rod, a first end of which is hinged to the first connecting seat 10, a second end of which is hinged to the second connecting seat 20, and the first linear telescopic rod and the two X-axis hinge members 12 are distributed in a triangular shape. The second driving part 21 comprises a second linear telescopic rod, two ends of the second linear telescopic rod are hinged to the second connecting seat 20 and the third connecting seat 30 respectively, and the second linear telescopic rod and the two Y-axis hinged parts 22 are distributed in a triangular mode.

Further, a limiting structure 23 is disposed between the first connecting seat 10 and the second connecting seat 20 to prevent the second connecting seat 20 from excessively inclining relative to the first connecting seat 10, and it can be understood that a limiting structure is also disposed between the second connecting seat 20 and the third connecting seat 30 to prevent the third connecting seat 30 from excessively inclining relative to the second connecting seat 20.

Sealing structure

Preferably, as shown in connection with fig. 1-2, an axial sealing arrangement 32 is provided between the plasma gun 40 and the third interface socket 30.

Referring to fig. 5, the linear bearing 321 is installed in the central hole of the third connecting seat 30 and is pressed by the pressing cover 322, the pressing cover 322 and the third connecting seat 30 are fastened by using bolts, and a sealing ring is arranged inside the pressing cover 322 for preventing metal dust inside the furnace body from entering the bearing, so as to prolong the service life of the bearing; the gland 322 is provided with a cooling water passage therein for cooling the sealing ring to extend the life thereof, and the linear sealing member 323 is installed at the upper portion of the third connecting seat 30 and compressed by the gland.

In this way, the linear sealing assembly is used as a dynamic seal between the plasma gun 40 and the third connecting seat 30, and the reliability of the sealing member is ensured by injecting flowing cooling water into the water cooling channel.

Further, a first sealing structure is arranged between the first connecting seat 10 and the cooling bed furnace, and a first water cooling channel located on the periphery of the first sealing structure is arranged on the first connecting seat 10. Likewise, the first connection socket 10 can be cooled by the first water cooling channel to ensure reliable use of the sealing element.

In the smelting process of the plasma cold hearth furnace, the temperature in the furnace chamber far exceeds the highest service temperature of the sealing rings, and all the sealing rings must be cooled by water to ensure that the sealing rings have long enough service life; in actual operation, the cooling water channel can only be arranged around the sealing ring to indirectly cool the sealing ring.

Swing adjustment process

Wherein, the linear expansion link can be selected as servo electric cylinder, take servo electric cylinder as an example, when first drive unit 11 stretches out and draws back, plasma gun 40 swings along Y direction, plasma arc length that plasma gun 40 jetted out at this moment correspondingly increases, in order to compensate the distance that increases, control third drive unit 31 and shorten, make plasma gun 40 closer to the molten bath, furthermore, when second drive unit 11 stretches out and draws back, plasma gun 40 swings along X direction, plasma arc length that plasma gun 40 jetted out at this moment correspondingly increases, further control third drive unit 31 and shorten, make the arc length of plasma arc that plasma gun 40 jetted out keep invariable, on the contrary, in the process of swinging back again, third drive unit 31 extends, make the plasma arc length that plasma gun 40 jetted out still be the fixed value.

In a specific embodiment, the method comprises the following steps:

1. and (3) cold state independent debugging: after the assembly is finished, the X, Y, Z movement in three directions needs to be independently debugged under the condition that the plasma gun 40 is not ignited, and each servo electric cylinder is inching and running at a lower speed during independent debugging so as to find out the clamping stagnation, the shaking and other abnormal conditions of the movement mechanism in time.

2. The mechanical limit in three directions is set: the mechanical limit is set to ensure safety under the most extreme condition, and reasonable setting is carried out on the premise of safe smelting according to the actual swinging requirement of each direction.

3. Setting swing parameters: according to the size of the cooling bed, the actual motion range of the arc spot, the length of the plasma gun 40, the geometric size of the swing mechanism and the like, a functional relation between the arc spot displacement in each direction and the stroke of the servo electric cylinder is preset in a control system, and the stroke range, the speed range and other parameters related to the swing of each servo electric cylinder are preset.

4. And (3) cold state integral debugging: as shown in fig. 6, according to the required arc spot motion trajectory, the motion curves and the motion logics of the servo electric cylinders are set in the control system, so that the plasma gun is ensured to have no phenomena of jitter, pause and stagnation and the arc length is always kept constant in the whole motion process; during integral debugging, the moving speed of the arc spot is gradually increased from low to high, and the stability and the reliability of the plasma gun during high-speed movement need to be inspected.

5. Thermal state integral debugging: in the actual smelting process, the plasma gun swings according to a program preset by a control system, the arc spots of the plasma arc scan the liquid level of a molten pool in the cooling bed along corresponding tracks, and the scanning speed needs to be matched with the power of the plasma gun.

[ plasma arc length control for plasma cold hearth melting ]

The invention provides a plasma arc length control method for plasma cold hearth smelting, which uses the plasma gun three-dimensional swinging mechanism and comprises the following steps:

igniting the plasma gun 40 to form a plasma arc 41 between the plasma gun 40 and the molten pool 101;

controlling the first driving component 11 and the second driving component 21 to stretch and retract so that the plasma gun 40 deflects along the X axis and the Y axis, and moving the arc spot of a plasma arc 41 emitted by the plasma gun 40 along a preset track on the surface of a molten pool;

the expansion and contraction of the third driving member 31 are controlled so that the arc length of the plasma arc 41 emitted from the plasma torch 40 in the deflected state along the X-axis and the Y-axis is constant.

Specifically, the adjustment process is that when the first driving part 11 extends and retracts, the plasma gun 40 swings along the Y direction, the arc length of the plasma arc emitted by the plasma gun 40 correspondingly increases, and in order to compensate for the increased distance, the third driving part 31 is controlled to shorten, so that the plasma gun 40 is closer to the molten pool, and the arc length of the plasma arc 41 is kept constant;

further, when the second driving component 21 extends and contracts, the plasma gun 40 swings along the X direction, the arc length of the plasma arc emitted by the plasma gun 40 is correspondingly increased, and the third driving component 31 is further controlled to be shortened, so that the arc length of the plasma arc emitted by the plasma gun 40 is kept constant;

in contrast, during the swinging back, the third driving member 31 is extended so that the plasma arc emitted from the plasma torch 40 is still at a constant value.

The arc length variation of the plasma arc in the swinging process can be calculated in real time according to the swinging amplitude in the X direction and the Y direction and the distance between the swinging shaft and the surface of the molten pool, and the expansion and contraction of the third driving part 31 can be controlled in real time according to the arc length variation.

With the combination of the above embodiments, the invention is provided with three layers of connecting seats, wherein the second and third connecting seats can independently swing in the X direction and the Y direction, and the plasma gun can slide relative to the third connecting seat along the axial direction of the plasma gun, so that the plasma gun can compensate the end position of the plasma gun when swinging in the X-Y direction, the arc length of the plasma arc is constant, and the uniformity of the temperature field of the molten pool is ensured; in addition, a vacuum corrugated pipe is used as a dynamic seal to ensure that the smelting atmosphere of the furnace chamber is not damaged in the swinging process.

Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims

1. The utility model provides a three-dimensional swing mechanism of plasma gun for cold bed furnace which characterized in that includes:

the first connecting seat (10) is connected to the cold bed furnace (100) at a first end face, and a cavity for the plasma gun (40) to penetrate through is formed in the first connecting seat (10);

the second connecting seat (20) can rotate along the X-axis direction relative to the first connecting seat (10), and the second connecting seat (20) is arranged above the first connecting seat (10);

the third connecting seat (30) can rotate along the Y-axis direction relative to the second connecting seat (20), and the third connecting seat (30) is arranged above the second connecting seat (20);

a plasma gun (40) assembled to an inner wall of the third connecting seat (30) from above the third connecting seat (30) with a first end extending into the cold hearth furnace (100), the plasma gun (40) being slidable in a height direction of the third connecting seat (30);

a flexible sleeve (50) is arranged between the first connecting seat (10) and the third connecting seat (30), so that a sealed space with variable volume is formed between the third connecting seat (30) and the cold bed furnace (100);

a first driving part (11) is arranged between the first connecting seat (10) and the second connecting seat (20), is used for controlling the inclination angle between the first connecting seat (10) and the second connecting seat (20) to ensure that the plasma arc emitted by the plasma gun (40) displaces along the Y direction, a second driving part (21) is arranged between the second connecting seat (20) and the third connecting seat (30), is used for controlling the inclination angle between the second connecting seat (20) and the third connecting seat (30) to ensure that the plasma arc emitted by the plasma gun (40) displaces along the X direction, a third driving part (31) is arranged between the third connecting seat (30) and the plasma gun (40), the plasma gun connecting structure is used for controlling the relative position between the plasma gun (40) and the third connecting seat (30) so as to keep the plasma arc (41) emitted by the plasma gun (40) to be constant in length when the plasma gun (40) swings along the X axis or the Y axis.

2. The three-dimensional swinging mechanism of the plasma gun for the cold hearth furnace according to claim 1, wherein the second connecting seat (20) is ring-shaped, the third connecting seat (30) is truncated cone-shaped, a first end of the flexible sleeve (50) is connected to an upper end surface of the first connecting seat (10), a second end of the flexible sleeve (50) is connected to a lower end surface of the third connecting seat (30), and the flexible sleeve (50) is located inside the second connecting seat (20).

3. The three-dimensional oscillating mechanism of plasma gun for cold bed furnaces according to claim 2 is characterized in that the flexible sheath (50) comprises a vacuum bellows.

4. The three-dimensional swinging mechanism of the plasma gun for the cold bed furnace is characterized in that the first connecting seat (10) and the second connecting seat (20) are hinged through two linearly distributed X-axis hinge parts (12), and the second connecting seat (20) and the third connecting seat (30) are hinged through two linearly distributed Y-axis hinge parts (22).

5. The three-dimensional swinging mechanism of the plasma gun for the cold hearth furnace according to claim 4, characterized in that the first driving part (11) comprises a first linear telescopic rod, the first end of the first linear telescopic rod is hinged to the first connecting seat (10), the second end of the first linear telescopic rod is hinged to the second connecting seat (20), and the first linear telescopic rod and the two X-axis hinged parts (12) are distributed in a triangular shape.

6. The three-dimensional swinging mechanism of the plasma gun for the cold hearth furnace according to claim 4, wherein the second driving part (21) comprises a second linear telescopic rod, two ends of the second linear telescopic rod are respectively hinged with the second connecting seat (20) and the third connecting seat (30), and the second linear telescopic rod and the two Y-axis hinged parts (22) are distributed in a triangular shape.

7. The three-dimensional swinging mechanism of the plasma gun for the cold bed furnace according to any one of claims 1 to 6, characterized in that an axial sealing structure (32) is arranged between the plasma gun (40) and the third connecting seat (30).

8. The three-dimensional swinging mechanism of the plasma gun for the cold hearth furnace according to claim 7, characterized in that the third connecting seat (30) is provided with a second water cooling channel at the periphery of the axial sealing structure (32).

9. The three-dimensional swinging mechanism of the plasma gun for the cold bed furnace according to any one of claims 1 to 6 is characterized in that a first sealing structure is arranged between the first connecting seat (10) and the cold bed furnace, and a first water cooling channel positioned at the periphery of the first sealing structure is arranged on the first connecting seat (10).

10. A plasma arc length control method for plasma cold hearth melting, characterized in that the plasma gun three-dimensional swinging mechanism of any one of claims 1-9 is used, comprising the following steps:

igniting the plasma gun (40) to form a plasma arc (41) between the plasma gun (40) and the molten pool (101);

controlling the expansion and contraction of the first driving part (11) and the second driving part (21) to enable the plasma gun (40) to deflect along the X axis and the Y axis, wherein the arc spot of a plasma arc (41) emitted by the plasma gun (40) moves on the surface of a molten pool along a preset track;

the extension and contraction of the third driving member (31) are controlled so that the arc length of a plasma arc (41) emitted from the plasma gun (40) in a deflected state along the X-axis and the Y-axis is constant.