Laser cleaning method for surface of metal part

Abstract

The invention discloses a laser cleaning method for the surface of a metal part. The laser cleaning method comprises the following steps that the material characteristics of a to-be-cleaned part are obtained; determining a cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the to-be-cleaned component; and protective gas is introduced into the laser cleaning equipment, the laser cleaning equipment is used for cleaning the surface of the to-be-cleaned component, and cleaning is completed when the cleaning area shows metallic luster. According to the laser cleaning method for the surfaces of the metal parts, the surfaces of the different metal parts of a thermal power plant are cleaned by selecting different cleaning modes, patent skins and oxide skins on the surfaces of the metal parts can be cleaned, and the problem that domestic multi-mode laser cleaning equipment can only clean the patent skins and is difficult to clean the oxide skins is solved; and after cleaning, the metallographic structure of the material is not changed, meanwhile, the cleaning efficiency is higher than that of a traditional mechanical polishing cleaning and shot blasting technology, the relative cost is lower than that of a traditional cleaning technology, and the cleaning effect of cleaning, high efficiency and low cost is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of laser cleaning and relates to a laser cleaning method for the surface of a metal part. Background Art

[0002] On-site cleaning of large metal parts in thermal power plants is difficult, time-consuming and laborious. Commonly used methods include mechanical grinding and sandblasting. The mechanical grinding cleaning method mainly uses various special tools to adopt physical contact and friction methods, and repeatedly rubs to remove the dirt layer. However, since this method involves direct physical contact and high collision intensity, it has low work efficiency and a harsh environment, is prone to damage the surface of the workpiece, and cannot meet the requirements of high cleanliness and high precision cleaning. This brings difficulties to the cleaning of large parts in thermal power plants, such as turbine partitions and pipelines. Therefore, a green, low-carbon, efficient and substrate-free cleaning method is needed to more effectively replace traditional cleaning methods and be applied to the surface cleaning of large monitored metal parts of thermal power units.

[0003] Laser cleaning is an effective method to remove dirty particles and films of different materials and sizes on solid surfaces. Laser cleaning is to use high-brightness and good-directional continuous or pulsed lasers, which are formed into lasers with specific spot shapes and energy distribution through optical focusing and spot shaping, to irradiate the contaminated material to be cleaned. After the contaminant materials attached to them absorb the laser energy, they will vibrate, melt, burn, and even gasify, and a series of complex physical and chemical processes will occur, and finally the contaminants will be separated from the material surface without damaging the material itself.

[0004] The essence of laser cleaning is actually the complex physical and chemical action of laser and dirt layer, that is, the continuous or pulsed laser overcomes the binding force between dirt and substrate surface, so that dirt is separated from substrate surface to achieve the purpose of cleaning. The main methods of laser cleaning are: laser dry cleaning and laser wet cleaning. Laser dry cleaning is to directly radiate laser on the surface of substrate, while wet cleaning is to coat a layer of liquid medium on the surface of the workpiece to be cleaned and then irradiate with laser. In addition, under special working conditions and cleaning conditions, there are also laser + inert gas cleaning and laser + chemical reagent cleaning methods. Laser cleaning technology has been developed for more than 30 years, but due to the limitations of early laser technology and equipment development level, the early development speed was slow, but in the past ten years, it has moved from the laboratory to various fields of application development, including cleaning oil and rust or oxide scale on metal surfaces, paint stripping, cleaning of rubber and non-rubber molds, cleaning of microelectronics industry, art protection and building cleaning, etc. The application of laser cleaning technology in the power field is still blank.

[0005] In summary, the existing technology has the problem of low cleaning quality and cleaning efficiency of metal equipment on-site in thermal power plants. Summary of the invention

[0006] The purpose of the present invention is to provide a laser cleaning method for the surface of metal parts, which solves the problems of low cleaning quality and cleaning efficiency of metal equipment on site in thermal power plants existing in the prior art.

[0007] The technical solution adopted by the present invention is a laser cleaning method for the surface of a metal part, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0008] The present invention is also characterized in that: The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0009] Parts to be cleaned include flanges, pipes, heating surface tubes, and baffles; The types of materials of the parts to be cleaned include carbon steel, low alloy steel, martensitic steel, austenitic steel; The surface characteristics of the parts to be cleaned include paint and oxide scale.

[0010] Laser cleaning equipment includes handheld single-mode laser cleaning equipment. The light source of the handheld single-mode laser cleaning equipment is a single-mode laser, the optical fiber core diameter is less than 15μm, the rated power is 1500W, and the peak power is not less than 2000W.

[0011] The cleaning modes include low-power cleaning mode, medium-power cleaning mode and high-power cleaning mode; the cleaning parameters include cleaning power, swing amplitude and number of cleaning times.

[0012] When the surface characteristic of the material characteristics of the parts to be cleaned is paint leather, the cleaning mode of the laser cleaning equipment is a low-power cleaning mode, the cleaning power ranges from 500W to 1000W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times.

[0013] When the material type of the parts to be cleaned is carbon steel or low alloy steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power range is 1000W-1300W, the swing amplitude range is 0-15mm, and the cleaning times range is 1-4 times.

[0014] When the material type of the parts to be cleaned is martensitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is to first use the high-power cleaning mode and then use the low-power cleaning mode; when using the high-power cleaning mode, the cleaning power ranges from 1200W to 1500W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times; when using the low-power cleaning mode, the cleaning power ranges from 1100W to 1500W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times.

[0015] When the material type of the parts to be cleaned is austenitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power ranges from 1100W to 1400W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 4 times.

[0016] The protective gas is an inert gas, which includes nitrogen with a purity of 99.999%, and the flow rate of the inert gas is 5L / min-20L / min.

[0017] The beneficial effects of the present invention are as follows: the present invention completes the cleaning of the surfaces of different metal parts in a thermal power plant by selecting different cleaning modes of a single-mode laser cleaning device, and can clean the paint and oxide scale on the surfaces of the metal parts at the same time, overcoming the problem that domestic multi-mode laser cleaning equipment can only clean the paint but has difficulty in cleaning the oxide scale. The laser cleaning equipment and technology can completely clean the oxide scale with a thickness of up to 200 μm on the surface of the part, and after cleaning, the metallographic structure of the material is not changed. At the same time, the cleaning efficiency is higher than that of traditional mechanical grinding cleaning and shot peening technology, and the relative cost is also lower than that of traditional cleaning technology, with a clean, efficient and low-cost cleaning effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of a laser cleaning method for a metal component surface according to the present invention; Figure 2 Schematic diagram of the metallographic structure of the uncleaned area of ​​the flange in an embodiment of the present invention; Figure 3 Schematic diagram of the metallographic structure of the flange cleaning area in an embodiment of the present invention; Figure 4 is a schematic diagram of the metallographic structure of the uncleaned area of ​​the pipeline in an embodiment of the present invention; Figure 5 is a schematic diagram of the metallographic structure of the transition area of ​​the pipeline in an embodiment of the present invention; Figure 6 is a schematic diagram of the metallographic structure of the pipeline cleaning area in an embodiment of the present invention; Figure 7Schematic diagram of the metallographic structure of the uncleaned area of ​​the heating surface tube in the embodiment of the present invention; Figure 8 Schematic diagram of the metallographic structure of the transition area of ​​the heating surface tube in the embodiment of the present invention; Fig. 9 Schematic diagram of the metallographic structure of the heating surface tube cleaning area in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Laser cleaning methods for metal parts surfaces, such as Figure 1 As shown, the following steps are included: Step 1: Obtain the material characteristics of the parts to be cleaned; The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0021] Parts to be cleaned include flanges, pipes, heating surface tubes, and baffles; The types of materials of the parts to be cleaned include carbon steel, low alloy steel, martensitic steel, austenitic steel; The surface characteristics of the parts to be cleaned include paint and oxide scale.

[0022] Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Laser cleaning equipment includes handheld single-mode laser cleaning equipment. The light source of the handheld single-mode laser cleaning equipment is a single-mode laser, the optical fiber core diameter is less than 15μm, the rated power is 1500W, and the peak power is not less than 2000W.

[0023] The cleaning modes include low-power cleaning mode, medium-power cleaning mode and high-power cleaning mode; the cleaning parameters include cleaning power, swing amplitude and number of cleaning times.

[0024] When the surface characteristic of the material characteristics of the parts to be cleaned is paint leather, the cleaning mode of the laser cleaning equipment is a low-power cleaning mode, the cleaning power ranges from 500W to 1000W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times.

[0025] When the material type of the parts to be cleaned is carbon steel or low alloy steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power range is 1000W-1300W, the swing amplitude range is 0-15mm, and the cleaning times range is 1-4 times.

[0026] When the material type of the parts to be cleaned is martensitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is to first use the high-power cleaning mode and then use the low-power cleaning mode; when using the high-power cleaning mode, the cleaning power ranges from 1200W to 1500W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times; when using the low-power cleaning mode, the cleaning power ranges from 1100W to 1500W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times.

[0027] When the material type of the parts to be cleaned is austenitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power ranges from 1100W to 1400W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 4 times.

[0028] Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0029] The protective gas is an inert gas, which includes nitrogen with a purity of 99.999%, and the flow rate of the inert gas is 5L / min-20L / min.

[0030] The present invention utilizes a handheld single-mode laser cleaning device, and according to the material characteristics of different metal parts in a thermal power plant, adopts different cleaning modes, cleaning powers and cleaning times to perform laser cleaning on the paint and oxide scale on the surface of each part; during the cleaning process, the laser cleaning device is passed with nitrogen protective gas, and after cleaning, the cleaning effect, surface morphology and metallographic structure are tested; after cleaning, the metallographic structure of each part does not change, and the service performance of each part is not affected.

[0031] Example 1 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0032] Example 2 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0033] The parts to be cleaned include flanges; the material types of the parts to be cleaned include carbon steel; and the surface characteristics of the parts to be cleaned include paint leather.

[0034] Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0035] The protective gas is an inert gas, which includes nitrogen with a purity of 99.999%, and the flow rate of the inert gas is 20L / min.

[0036] Example 3 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0037] The parts to be cleaned include pipes; the material types of the parts to be cleaned include low alloy steel; and the surface characteristics of the parts to be cleaned include oxide scale.

[0038] Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0039] The protective gas is an inert gas, which includes nitrogen with a purity of 99.999%, and the flow rate of the inert gas is 5 L / min.

[0040] Example 4 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0041] The parts to be cleaned include heating surface tubes; the material types of the parts to be cleaned include martensitic steel; and the surface characteristics of the parts to be cleaned include oxide scale.

[0042] Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Laser cleaning equipment includes handheld single-mode laser cleaning equipment. The light source of the handheld single-mode laser cleaning equipment is a single-mode laser, the optical fiber core diameter is less than 15μm, the rated power is 1500W, and the peak power is not less than 2000W.

[0043] The cleaning modes include low-power cleaning mode, medium-power cleaning mode and high-power cleaning mode; the cleaning parameters include cleaning power, swing amplitude and number of cleaning times.

[0044] Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0045] Example 5 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0046] Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; The cleaning modes include low-power cleaning mode, medium-power cleaning mode and high-power cleaning mode; the cleaning parameters include cleaning power, swing amplitude and number of cleaning times.

[0047] When the surface characteristic of the material characteristics of the parts to be cleaned is paint leather, the cleaning mode of the laser cleaning equipment is a low-power cleaning mode, the cleaning power value range is 1000W, the swing amplitude value range is 15mm, and the cleaning times range is 3 times.

[0048] Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0049] Example 6 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

[0050] Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; When the material type of the parts to be cleaned is low alloy steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power range is 1300W, the swing amplitude range is 15mm, and the cleaning times range is 4 times.

[0051] Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0052] Example 7 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; When the material type of the parts to be cleaned is martensitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is to use the high-power cleaning mode first and then the low-power cleaning mode; when using the high-power cleaning mode, the cleaning power value range is 1500W, the swing amplitude range is 15mm, and the cleaning number range is 3 times; when using the low-power cleaning mode, the cleaning power value range is 1200W, the swing amplitude range is 15mm, and the cleaning number range is 3 times.

[0053] Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0054] Example 8 This embodiment provides a laser cleaning method for the surface of a metal component, comprising the following steps: Step 1: Obtain the material characteristics of the parts to be cleaned; Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; When the material type of the parts to be cleaned is austenitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power range is 1200W, the swing amplitude range is 10mm, and the cleaning times range is 4 times.

[0055] Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

[0056] In the embodiment of the present invention, when the part to be cleaned in which a part of the area has been cleaned is a flange, samples are taken from the cleaned area and the uncleaned area to perform a metallographic structure experiment. The metallographic structure of the uncleaned area is as follows: Figure 2 As shown, the metallographic structure of the cleaned area is Figure 3 As shown in the figure, the paint on the flange surface has been completely removed, and the metallographic structure of the surface has not changed. According to the surface morphology and metallographic structure test results after cleaning, the cleaning effect is good.

[0057] In the embodiment of the present invention, when the component to be cleaned is a pipe, samples are taken from the cleaned area and the uncleaned area to perform metallographic structure experiments. The metallographic structure of the uncleaned area is as follows: Figure 4 As shown, the thickness of the oxide scale on the pipe surface is about 200 μm, and the metallographic structure of the transition area is as follows Figure 5 As shown in the figure, the oxide scale on the surface of the pipe in the cleaned area has been completely removed, while the oxide scale on the surface of the pipe in the uncleaned area still exists; the metallographic structure of the cleaned area is as follows Figure 6 As shown, the oxide scale on the surface of the pipeline has been completely removed, and the metallographic structure of the surface has not changed. According to the test results of the surface morphology and metallographic structure after cleaning, the cleaning effect is good.

[0058] In the embodiment of the present invention, when the component to be cleaned is a heated surface tube, samples are taken from the cleaned area and the uncleaned area after cleaning to perform a metallographic structure test. The metallographic structure of the uncleaned area is as follows: Figure 7 As shown, the thickness of the oxide scale on the tube surface is about 100 μm, and the metallographic structure of the transition zone is as follows Figure 8 As shown in the figure, the oxide scale on the surface of the pipe in the cleaned area has been completely removed, while the oxide scale on the surface of the pipe in the uncleaned area still exists; the metallographic structure of the cleaned area is as follows Fig. 9 As shown in the figure, the oxide scale on the surface of the tube has been completely removed, and the metallographic structure of the surface has not changed. According to the test results of the surface morphology and metallographic structure after cleaning, the laser cleaning effect is good.

Claims

1. A laser cleaning method for the surface of a metal part, characterized in that: The following steps are involved: Step 1: Obtain the material characteristics of the parts to be cleaned; Step 2: Determine the cleaning mode and cleaning parameters of the laser cleaning equipment according to the material characteristics of the parts to be cleaned; Step 3: Pass the protective gas into the laser cleaning equipment, and use the laser cleaning equipment to clean the surface of the parts to be cleaned. The cleaning is completed when the cleaned area shows a metallic luster.

2. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: The material properties of the parts to be cleaned include the material type and surface properties of the parts to be cleaned.

3. The laser cleaning method for the surface of a metal part according to claim 2, characterized in that: The parts to be cleaned include flanges, pipes, heating surface tubes, and baffles; The material types of the parts to be cleaned include carbon steel, low alloy steel, martensitic steel, and austenitic steel; The surface characteristics of the parts to be cleaned include paint skin and oxide skin.

4. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: The laser cleaning equipment includes a handheld single-mode laser cleaning equipment, the light source of the handheld single-mode laser cleaning equipment is a single-mode laser, the optical fiber core diameter is less than 15μm, the rated power is 1500W, and the peak power is not less than 2000W.

5. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: The cleaning modes include a low-power cleaning mode, a medium-power cleaning mode and a high-power cleaning mode; the cleaning parameters include cleaning power, swing amplitude and cleaning times.

6. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: When the surface characteristic of the material characteristics of the part to be cleaned is paint leather, the cleaning mode of the laser cleaning equipment is a low-power cleaning mode, the cleaning power ranges from 500W to 1000W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times.

7. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: When the material type of the material characteristics of the parts to be cleaned is carbon steel or low alloy steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power ranges from 1000W to 1300W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 4 times.

8. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: When the material type of the material characteristics of the parts to be cleaned is martensitic steel and the surface characteristics are oxide scale, the cleaning mode of the laser cleaning equipment is to first use the high-power cleaning mode and then use the low-power cleaning mode; when using the high-power cleaning mode, the cleaning power ranges from 1200W to 1500W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times; when using the low-power cleaning mode, the cleaning power ranges from 1100W to 1500W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 3 times.

9. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: When the material type of the material properties of the parts to be cleaned is austenitic steel and the surface properties are oxide scale, the cleaning mode of the laser cleaning equipment is the intermediate power cleaning mode, the cleaning power ranges from 1100W to 1400W, the swing amplitude ranges from 0 to 15mm, and the number of cleaning times ranges from 1 to 4 times.

10. The laser cleaning method for the surface of a metal part according to claim 1, characterized in that: The protective gas is an inert gas, which includes nitrogen with a purity of 99.999%, and a flow rate of the inert gas is 5L / min-20L / min.

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