CN115464002A - Gas diffuser shaping device and gas diffuser correction method - Google Patents

Abstract

The invention discloses a gas diffuser shaping device and a gas diffuser correction method, belonging to the technical field of gas diffuser shaping processing, wherein the shaping device is provided with a convex arc-shaped surface; the radian of the arc-shaped surface is greater than that of a standard forming surface, so that when the arc-shaped surface is attached to the standard forming surface, a gap is formed between the arc-shaped surface and the standard forming surface; the amount of the gap is equal to the amount of deformation of the gas diffuser due to internal stress or external force. The amount of clearance reserved after the shaping device shapes can offset the amount of resilience and the amount of deformation influenced by self gravity. After the offset, the forming surface of the gas diffuser is exactly in line with the standard forming surface. The shaping precision is improved.

Description

Gas diffuser shaping device and gas diffuser correction method

Technical Field

The invention belongs to the technical field of shaping and processing of gas diffusers, and particularly relates to a shaping device and a correcting method of a gas diffuser.

Background

In the manufacturing process of the liquid crystal display panel, a Chemical Vapor Deposition (CVD) process is used to deposit some functional films on the surface of the glass substrate. In the chemical vapor deposition process, the gas diffuser can uniformly diffuse the gas on the substrate.

As the gas diffuser is used for a long time, its shape is deformed, resulting in non-uniform gas diffusion. When the deformation of the gas diffuser exceeds a certain range, the film formation on a part of the whole substrate is not uniform, and at the moment, the gas diffuser needs to be detached and the flatness correction is performed.

In the prior art, the flatness of the gas diffuser is usually corrected by local thermal shaping. For example, the chinese patent publication No. CN110961489a discloses a flatness thermal shaping process for a gas diffuser in 2020, 4, 7, that is, laying cushion blocks with different thicknesses at corresponding positions of a bearing platform of an electric heating furnace, placing the deformed gas diffuser on the cushion blocks, then laying aluminum foil paper on the gas diffuser, laying counter weights with corresponding weights layer by layer on the aluminum foil paper, and heating the deformed gas diffuser into an inverted bowl shape at one time by a heating process of the electric heating furnace, thereby reducing the risk of collision damage caused by hoisting, flanging, detecting and transporting for many times in the middle, and the flatness and surface shape of the corrected gas diffuser are not easy to rebound, thereby improving the service life and reducing the maintenance cost. The heat treatment furnace is adopted in the patent of the invention, and local point position support and gravity pressing blocks are utilized for shaping, so that the problem of internal stress during shaping is solved, but the following defects and shortcomings exist:

(1) By utilizing local point position support, concave points (high contact point pressure, depression of a forming surface finished by the gas diffuser is easily caused) can be caused at corresponding support point positions, and the forming surface of the whole gas diffuser cannot form a curved surface with uniform and smooth transition.

(2) Along with temperature variation in the heat treatment process, the unsupported position on the shaping surface of the gas diffuser can produce irregular deformation, and the deformation can not be accurately controlled, so that the shaping precision is poor.

(3) After shaping, the gas diffusion surface generates deformation due to the influence of the rebound quantity and the self gravity, so that the shaping precision is poor.

Disclosure of Invention

1. Problems to be solved

Aiming at the technical problem of poor shaping precision in the prior art, the invention provides a gas diffuser shaping device and a gas diffuser correction method.

2. Technical scheme

In order to solve the problems, the invention adopts the following technical scheme:

a gas diffuser reshaping device for modifying the shape of a shaping surface of a gas diffuser, the reshaping device having a convex arc-shaped surface; the radian of the arc-shaped surface is greater than that of a standard forming surface, so that when the arc-shaped surface is attached to the standard forming surface, a gap is formed between the arc-shaped surface and the standard forming surface; the gap amount is equal to the deformation amount of the gas diffuser due to internal stress or the deformation amount of the molding surface under external force.

Preferably, the deformation amount includes a rebound shrinkage amount a after shaping of the gas diffuser and/or a gravity deformation amount b generated by the heat of the gas diffuser due to the self gravity.

Preferably, the calculation formula of the central height h of the arc-shaped surface is as follows:

h＝s-a-b；

wherein s is the standard molding surface center height.

Preferably, a plurality of counterweights are included for positioning above the gas diffuser to be shaped, applying a load for shaping said gas diffuser.

Preferably, the counterweight block is wrapped by an aluminum foil.

A method for straightening a gas diffuser is provided,

s1: inversely buckling a gas diffuser forming surface to be shaped on an arc-shaped surface of a gas diffuser shaping device;

s2: a plurality of balancing weights are placed above the gas diffuser, and the balancing weights are unevenly distributed on the top of the gas diffuser in the shaping process.

S3: and (3) integrally placing the gas diffuser, the gas diffuser shaping device and the plurality of balancing weights which are placed in the steps S1 and S2 in a heating furnace for heat treatment to eliminate the internal stress of the gas diffuser.

Preferably, the number of the weight blocks decreases from the edge of the gas diffuser to the center thereof.

Preferably, in the step S3, the heat treatment includes a temperature rise stage, a heat preservation stage and a temperature reduction stage.

Preferably, in the step S3, the cooling stage is a sectional cooling stage, and includes a first stage: completely closing the furnace door, and naturally cooling the gas diffuser to 250 ℃; and a second stage: the furnace door is not completely opened, and the gas diffuser is naturally cooled to 48 ℃; and a third stage: and completely opening the furnace door, and naturally cooling the gas diffuser to the normal temperature state.

3. Advantageous effects

Compared with the prior art, the invention has the beneficial effects that:

(1) The shaping device is provided with the convex arc-shaped surface, the arc-shaped surface shapes the shaping surface in a surface contact mode, and the problem of local depression defect of the shaping surface caused by point contact shaping is solved. On the other hand, the arc-shaped surface shaping is adopted, so that the shaping surface is always consistent with the arc-shaped surface in the shaping process of the whole gas diffuser. Therefore, the forming surface of the gas diffuser does not generate uncontrolled deformation due to temperature change in the heat treatment process, so that the forming surface of the gas diffuser forms a uniform and smooth curved surface after being shaped.

(2) In the invention, the radian of the arc-shaped surface is greater than that of the standard molding surface, so that when the arc-shaped surface is attached to the standard molding surface, a gap is formed between the arc-shaped surface and the standard molding surface; the amount of the gap is equal to the amount of deformation of the gas diffuser due to internal stress or external force. The amount of clearance reserved after the shaping device shapes can offset the amount of resilience and the amount of deformation influenced by self gravity. After offset, the radian of the forming surface of the gas diffuser is just consistent with that of a standard forming surface, and the shaping precision is ensured.

(3) In the invention, a plurality of balancing weights are unevenly distributed on the top of the gas diffuser in the shaping process. The thickness is relatively thin in the central region of the gas diffuser and relatively thick in the edge region. In order to make the load of the gas diffuser in the whole body be in a proper range (too large load easily causes the transition deformation of the forming surface, and too small load cannot play a shaping effect). Thus, a relatively small number of clump weights are arranged in the central region and a relatively large number of clump weights are arranged on both sides, as required. Load is applied to the gas diffuser through adjusting the distribution quantity of the balancing weights, and the purpose of improving the precision control shaping load is achieved.

(4) And placing the shaping device and the gas diffuser into a heating furnace for shaping. The gas diffuser is heated while applying a force shaping to the gas diffuser, which can relieve internal stresses therein. And after the gas diffuser is subjected to heat treatment, the gas diffuser enters a cooling process. The cooling process is divided into three stages. The first stage is as follows: the furnace cover is closed, the heat source is closed, the temperature of the gas diffuser naturally decreases from 450-480 ℃ to about 250 ℃, and the crystal structure is prevented from being changed due to the too fast temperature decrease in the stage. And a second stage: the furnace top cover is slightly opened, the temperature is reduced to 48 ℃, and the temperature is prevented from being reduced too fast at the stage, so that the internal stress of the gas diffuser is increased. And a third stage: the furnace top cover is completely opened, and the temperature is reduced to the normal temperature. The whole cooling process is about 48.5h, the cooling time is long, the temperature change rate is low, the influence of temperature change on expansion with heat and contraction with cold generated by the gas diffuser can be reduced, and the shaping accuracy is improved.

Drawings

FIG. 1 is a schematic cross-sectional view of a gas diffuser and its standard profile;

FIG. 2 is a schematic cross-sectional view of a gas diffuser reshaping apparatus and its arcuate surface;

FIG. 3 is a schematic cross-sectional view of a standard profile surface inverted in the arc plane;

FIG. 4 is a schematic sectional view showing the rebound amount a when the molding surface rebounds;

FIG. 5 is a schematic cross-sectional view of the amount b of deformation of the molding surface after the molding surface is deformed by the influence of the dead weight;

FIG. 6 is a schematic diagram showing the relative positions of the weight, the gas diffuser and the shaping device during shaping;

FIG. 7 is a graph of the change in gas diffuser temperature during heat treatment;

FIG. 8 is a view of the detection of the local flatness of the molding surface before reshaping;

FIG. 9 is a view of the inspection of local flatness of the shaped surface after shaping;

in the figure:

1. a gas diffuser; 11. standard molding surface;

2. a shaping device; 21. an arc-shaped surface; 22. a base;

3. a balancing weight;

4. the amount of play.

Detailed Description

The following detailed description of exemplary embodiments of the invention refers to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration exemplary embodiments in which the invention may be practiced. Although these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that various changes to the invention may be made without departing from the spirit and scope of the present invention. The following more detailed description of the embodiments of the invention is not intended to limit the scope of the invention, as claimed, but is presented for purposes of illustration only and not limitation to describe the features and characteristics of the invention, to set forth the best mode of carrying out the invention, and to sufficiently enable one skilled in the art to practice the invention. Accordingly, the scope of the invention is to be limited only by the following claims.

In order to solve the above problems, the following description is made with reference to the accompanying drawings:

examples

1. A shaping device:

(1) Arc surface 21

In order to address the deficiencies of the prior art, the present invention provides a gas diffuser reshaping apparatus 2, as shown in fig. 1-3. The gas diffuser reshaping means 2 comprises a base 22. The base 22 is cylindrical, but is not limited to being cylindrical. A protrusion is fixedly connected to the center of the base 22. The convex surface is an arc-shaped surface 21. The specific shape and size of the arc-shaped surface 21 are determined according to the standard forming surface 11 of the gas diffuser 1 (forming surface: concave surface for working on the gas diffuser 1. Standard forming surface 11: forming surface of the gas diffuser 1 according to the design standard and meeting the production requirement).

The arc of the arc surface 21 is larger than the arc of the standard molding surface 11. When the standard forming surface 11 is turned over on the arc-shaped surface 21 (no load is applied to the forming surface), since the radian of the arc-shaped surface 21 is greater than that of the standard forming surface 11, a gap amount 4 (a gap between the forming surface and the arc-shaped surface) exists between the standard forming surface and the arc-shaped surface, and the gap amount 4 is equal to a deformation amount of the gas diffuser 1 caused by internal stress or external force. Before shaping, the arc surface design radian of the shaping device 2 is larger than the 11 radians of the standard shaping surface, so that the arc surface 21 has a reserved gap amount 4 to offset the rebound amount after shaping of the shaping surface of the body diffuser and the deformation amount generated by self gravity influence. After the offset, the shaping surface of the gas diffuser 1 corresponds exactly to the standard shaping surface 11. The shaping precision is ensured.

Since the gap amount 4 is difficult to measure, we replace the gap amount detection with a height difference between the height h at the center of the arc face 21 and the standard molding face center height s. The difference in height between the two is defined as Δ t.

When the arc-shaped surface 21 is designed, the central height of the arc-shaped surface is h, the central height of the standard molding surface 11 is s, and the difference value between the central height of the arc-shaped surface 21 and the central height of the standard molding surface 11 is delta t.

The height h = s- Δ t of the center of the arc face 21 is calculated.

The gap 4 is equal to the deformed amount of the shaped gas diffuser 1 itself or due to an external force.

The deformation of the gas diffuser 1 itself or due to external force includes, but is not limited to, the rebound shrinkage amount a of the gas diffuser 1 after heat treatment and the gravity deformation amount b of the gas diffuser 1 due to its own weight. Or the deformation amount generated by the molding surface receiving external force.

1) When Δ t = a; in this case, only the influence of the molding surface rebound shrinkage a after the heat treatment of the gas diffuser 1 on the molding accuracy is considered

Calculating the height of the center of the arc surface: h = s-a;

2) When Δ t = b; at the moment, only the influence of the gravity deformation b of the forming surface of the gas diffuser 1 after heat treatment due to self gravity on the forming precision is considered;

calculating the height of the center of the arc surface: h = s-b;

3) When Δ t = a + b; only considering the impact of the rebound shrinkage a of the forming surface of the gas diffuser 1 after heat treatment and the gravity deformation b caused by self gravity on the forming precision;

calculating the height of the center of the arc surface: h = s-a-b;

(2) Rebound shrinkage a after heat treatment of gas diffuser 1:

as shown in fig. 4, in the shaping process of the present invention, the shaping surface of the gas diffuser 1 is shaped by the arc surface 21, and when the shaping surface 21 is used, a large amount of internal stress is generated in the shaping surface. Once the load is removed, the molding surface will partially recover under the influence of internal stress, thereby causing a reshaping deviation. In order to eliminate the internal stress, the forming surface in the shaping and loading process is subjected to heat treatment to eliminate the internal stress, and the deformation of the shaped forming surface due to the internal stress is reduced. However, since the surface contact molding is adopted, the entire surface of the molding surface bears a load during the molding process, which enlarges the internal stress in the gas diffuser 1, and even if the heat treatment process is adopted, it is difficult to completely eliminate the internal stress, resulting in a certain elastic deformation (deformation amount is a) of the molding surface. Therefore, in designing the height of the center of the arc surface 21, the amount of springback is reserved by reducing the height of the center of the arc surface 21 in advance (the amount of reduction is a) taking into account the amount of springback contraction a after the heat treatment of the gas diffuser 1. After the heat treatment of the forming surface, the elastic deformation is generated, which can just be used for offsetting the error, thereby improving the shaping precision. The value of a is mainly influenced by the material of the molding surface, the shaping applied load, the heat treatment, and the like.

The measurement mode of a is as follows:

1) Preparing a gas diffuser 1 with a standard forming surface 11 and a gas diffuser shaping device 2 (the arc-shaped surface 21 of the shaping device 2 is the same as the center height of the standard forming surface 11);

2) Reversely buckling the forming surface of the gas diffuser 1 on the arc-shaped surface 21 of the shaping device 2;

3) Applying and maintaining a load above the gas diffuser 1;

4) Placing the gas diffuser 1 and the shaping device 2 into a heating furnace for heat treatment;

5) Taking out after the heat treatment is finished, and detecting the central height a1 of the standard forming surface 11;

6) Calculate a = a1-s.

The value of a is an initial value, and the value of a is continuously corrected according to the production process by using quality inspection parameters (comparing the measured central height of the forming surface of the gas diffuser 1 after being shaped with the central height of the standard forming surface 11, and according to the difference value of the two), so as to improve the accuracy of the value of a, wherein the more accurate the value of a, the higher the accuracy of the shaping. When the value a is adjusted, the material, the shaping method and the shaping heat treatment parameters of the subsequent shaping device 2 are kept the same, and then the method can be used

(3) Amount of gravitational deformation b of gas diffuser 1 due to its own weight:

as shown in fig. 5, the amount of gravity deformation b of the gas diffuser 1 due to its own weight is an error in the profile caused by the use of the gas diffuser 1. Gas diffuser 1 adopts unsettled, the fixed mounting means of four corners in the middle of the time of using, receives its dead weight influence itself, and the profiled surface can be inwards sunken, and this deformation can lead to profiled surface radian to increase and profiled surface central height to increase. Therefore, when designing the height of the center of the arc surface 21, the arc degree of the arc surface 21 is increased in advance by reducing the height of the center of the arc surface 21 in advance (the reduction amount is b) in consideration of the amount of gravitational deformation b generated by the self-gravity of the gas diffuser 1. When the forming surface is used, the error is just offset, so that the shaping precision is improved.

b was measured as follows:

1) Taking a gas diffuser 1 with a standard forming surface 11, and enabling the standard forming surface 11 to face upwards;

2) Placing the gas diffuser 1 on a workbench, and padding reference blocks at four corners of the bottom of the gas diffuser 1 to enable the gas diffuser 1 to be horizontally placed;

3) Measuring and obtaining the central height b1 of the molding surface;

4) Calculate b = b1-s.

For the above reasons, the difference Δ t = a + b between the height of the center of the arc face 21 and the height of the center of the standard molding face 11 at the time of design; the height h = s- Δ t of the arc-shaped surface 21, preferably, h = s-a-b; when the height of the designed arc-shaped surface 21 is h, errors caused by a and b are offset, and the shaping precision is improved.

2. And (3) balancing weight:

as shown in fig. 6, the weight member 3 applies a load to the gas diffuser 1 during the shaping process by its own weight. The balancing weight 3 is cuboid and is provided with a plurality of blocks. Several weights 3 can regulate the load force applied to different parts of the gas diffuser 1. In the shaping process, the weight block 3 is positioned above the gas diffuser 1, and loads are applied to the gas diffuser 1 through the self gravity. Under the action of the gravity of the balancing weight 3, the forming surface of the gas diffuser 1 is tightly attached to the arc surface 21 of the shaping device 2 and is shaped. The counterweights 3 are distributed unevenly over the gas diffuser 1. Specifically, the gas diffuser 1 has a small number of distribution in the center region and a large number of distribution in the edge region. This is mainly because the central region has a profiled surface, resulting in a relatively thin thickness in the central region and a relatively thick thickness in the edge regions. In order to make the overall bearing load of the gas diffuser 1 suitable (too large bearing load easily causes transition deformation of the molding surface, and too small bearing load cannot play a shaping effect), relatively few counter weights 3 are arranged in the central area, and relatively many counter weights 3 are arranged on two sides. The weight 3 is made of metal iron. When in use, the material sheet which is the same as the material of the gas diffuser 1 is arranged outside the heat exchanger, so that the material of the balancing weight 3 is prevented from polluting the material of the gas diffuser 1 in the heating process. In the invention, the gas diffuser 1 is made of aluminum, so the outer surface of the counterweight block 3 is wrapped by an aluminum foil.

3. And (3) heat treatment:

as shown in fig. 7, the curved surface 21 is a uniform transition photo-thermal treatment as a key step for eliminating internal stress during the shaping process of the gas diffuser 1. Comprises a heating process, a heat preservation process and a cooling process. And placing the shaping device 2, the gas diffuser 1 and the balancing weight 3 at corresponding positions, and then placing the components into a heating furnace for heat treatment.

And (3) heating process: and closing the top cover of the electric heating furnace and starting to uniformly heat the heating furnace. The heating rate was set as: the gas diffuser 1 was heated to a temperature of 450-480 ℃ during a period of 6h at 80 ℃/h.

And (3) heat preservation: and after the highest temperature is reached, monitoring the temperature by a thermocouple of the electric heating furnace, and controlling the electric heating furnace to carry out heat preservation. The heat preservation is divided into a first stage and a second stage. In the first stage, the temperature of the gas diffuser 1 is slowly reduced from 480 ℃ to 400 ℃; and a second stage: the heating furnace is ignited, and the gas diffuser 1 is slowly heated to 450-480 ℃ for keeping. At this temperature, the gas diffuser 1 is allowed to deform sufficiently over a period of time. The heat preservation time of the first stage and the second stage is about 20.5 hours, and if the heat preservation time is too short, the diffuser is insufficiently deformed; the heat preservation time is too long, which causes the waste of energy and cost.

And (3) cooling: after the heat preservation time is finished, the temperature is automatically reduced along with the heating furnace, the temperature reduction time is slow, and the internal stress caused by deformation is eliminated. The cooling process is divided into three stages. The first stage is as follows: the furnace cover is closed, the heat source is closed, the temperature of the gas diffuser 1 is naturally reduced to about 250 ℃ from 450-480 ℃, and the crystal structure is prevented from being changed due to the too fast temperature reduction at the stage. And a second stage: the furnace roof is slightly opened and the temperature is reduced to 48 c, which avoids that the temperature is reduced too fast, so that the stress in the gas diffuser 1 increases. And a third stage: the furnace top cover is completely opened, and the temperature is reduced to the normal temperature. The whole cooling process is about 48.5h, the cooling time is long, the temperature change rate is low, the influence of temperature change on expansion with heat and contraction with cold generated by the gas diffuser 1 can be reduced, and the shaping accuracy is improved. When the temperature reaches the normal temperature, the weight of the gas diffuser 1 is firstly pressed out, and then the gas diffuser 1 after being heated and shaped is lifted out of the heating furnace.

Table 1: heat treatment temperature control parameters:

4. gas diffuser 1 straightening method

Based on the shaping device 2, the following shaping method is provided:

s1: reversely buckling the molding surface of the gas diffuser 1 to be shaped on the arc-shaped surface 21 of the corresponding gas diffuser shaping device 2;

s2: a plurality of balancing weights 3 are placed above the gas diffuser 1, and the balancing weights 3 are unevenly distributed on the top of the gas diffuser 1 in the shaping process. The number of the balancing weights 3 distributed at the center of the gas diffuser 1 is small, and the number of the balancing weights 3 distributed at the edge is large. More preferably, the number of the weight blocks 3 decreases from the edge of the gas diffuser 1 to the center thereof.

S3: and (3) integrally placing the gas diffuser 1, the gas diffuser shaping device 2 and the plurality of balancing weights 3 which are placed in the steps S1 and S2 in a heating furnace for heat treatment to eliminate the internal stress of the gas diffuser 1.

The heat treatment comprises a heating stage, a heat preservation stage and a cooling stage.

Wherein, the temperature reduction stage is divided into three sections for cooling. Comprises the following steps: completely closing the furnace door, and naturally cooling the gas diffuser 1 to 250 ℃; and a second stage: the furnace door is not completely opened, and the gas diffuser 1 is naturally cooled to 48 ℃; and a third stage: and (3) completely opening the furnace door, and naturally cooling the gas diffuser 1 to a normal temperature state.

As shown in fig. 8 and 9, comparing the forming surfaces before and after shaping, it is obvious that the forming surface of the gas diffuser 1 shaped by the method is obviously smoother and the shaping effect is good.

The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.

Claims (9)

1. A gas diffuser reshaping device for modifying the shape of the forming surface of the gas diffuser (1), characterized in that the reshaping device (2) has a convex arc surface (21); the radian of the arc-shaped surface (21) is greater than that of the standard forming surface (11), so that when the arc-shaped surface (21) is attached to the standard forming surface (11), a gap (4) is reserved between the arc-shaped surface and the standard forming surface; the gap amount (4) is equal to the deformation amount of the forming surface of the gas diffuser (1) caused by internal stress or external force.

2. The gas diffuser reshaping device according to claim 1, wherein the deformation amount comprises a rebound shrinkage amount a after reshaping of the shaping surface of the gas diffuser (1) and/or a gravity deformation amount b of the gas diffuser (1) due to its own weight.

3. Gas diffuser reshaping device according to claim 2, wherein the height h of the centre of the arc surface (21) is calculated as follows:

h＝s-a-b；

wherein s is the central height of the standard molding surface (11).

4. The gas diffuser reshaping device according to claim 1, comprising a plurality of weights for being arranged above the gas diffuser (1) to be reshaped to apply a load for reshaping said gas diffuser (1).

5. The gas diffuser reshaping device of claim 4 wherein the weight is overwrapped with aluminum foil.

6. A method for straightening a gas diffuser,

s1: the shaping surface of the gas diffuser (1) to be shaped is reversely buckled on the arc surface (21) of the shaping device of the gas diffuser;

s2: a plurality of balancing weights are placed above the gas diffuser (1), and the balancing weights are unevenly distributed on the top of the gas diffuser (1) in the shaping process.

S3: and integrally placing the gas diffuser (1), the gas diffuser shaping device and the plurality of balancing weights which are placed in the steps S1 and S2 into a heating furnace, wherein the gas diffuser (1) is loaded and shaped and heat treatment is carried out synchronously, and the internal stress of the gas diffuser (1) is eliminated during shaping.

7. The gas diffuser straightening method according to claim 6, characterized in that the number of said weights decreases from the edge of the gas diffuser (1) towards its center.

8. The method according to claim 7, wherein in the step S3, the heat treatment comprises a temperature raising stage, a temperature keeping stage and a temperature lowering stage.

9. The method according to claim 8, wherein in the step S3, the temperature reduction stage is a staged cooling stage, and comprises a first stage: completely closing the furnace door, and naturally cooling the gas diffuser (1) to 250 ℃; and a second stage: the furnace door is not completely opened, and the gas diffuser (1) is naturally cooled to 48 ℃; and a third stage: and (3) completely opening the furnace door, and naturally cooling the gas diffuser (1) to a normal temperature state.

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