Ultra-clean process for closed steel drum

Abstract

The invention provides a closed steel drum ultra-clean process which comprises the following steps: S1, preparing raw materials and equipment, namely cutting a drum body material, a cover material and a backing material; s2, processing of a barrel body material, processing of a cover material and processing of a bottom material; s3, the machined barrel body material, the machined cover material and the machined bottom material are subjected to final assembly, and testing is conducted; and S4, the exterior of the qualified steel drum is subjected to surface protection layer spraying, baking and sealer installing, the baking temperature ranges from 150 DEG C to 200 DEG C, and mixed gas replacement is conducted on the steel drum in a closed space. Through low-temperature powder coating and reasonable baking temperature control, the damage of high temperature to the surface protection layer of the plate is reduced, and the anti-rust performance of the steel drum is enhanced through chemical anti-rust treatment on the seam welding position. By means of mixed gas replacement in the production process, the problem that the content of silicone in the steel drum exceeds the standard is effectively solved, and pollution of silicone to stored objects is avoided.

Description

Technical Field

[0001] The invention mainly relates to the technical field of steel drum clean process, and in particular to an ultra-clean process for closed-mouth steel drums. Background Art

[0002] Closed steel drums are a common packaging container, usually made of metal sheets, with the characteristics of good sealing, high strength, and corrosion resistance. It is widely used in many fields such as chemical, petroleum, food, and medicine to store and transport various liquids, solids, and powdered substances. However, during the production process of closed steel drums, silicone will contaminate the closed steel drums in various production links. Silicone contamination may come from many aspects, such as impurities in raw materials, impurities carried by personnel (skin care products, grease, contaminated gloves and rags on hands), residues on production equipment (lubricants used for maintenance, rust removers, silicone oil on the sealing ring of quick-release connector valves, leakage of liquid in pressure gauges, or silicone oil on O-rings), dust in the construction environment, etc.

[0003] For example, in the automotive manufacturing industry, closed steel drums are often used to store automotive paint. However, if the cleanliness of the closed steel drum does not meet the requirements, that is, if there is an excessive amount of silicone in the drum, it will have a serious impact on the quality of the paint. Silicone has a low surface tension, and when it is present in a coating system, it will form local low surface tension areas on the coating surface. During the drying process of the paint, the areas with higher surface tension will flow to the surrounding areas with lower surface tension, resulting in depressions on the coating surface, i.e., shrinkage holes. Even trace amounts of silicone contamination can have a significant effect on the coating surface, leading to the appearance of shrinkage holes. Specifically, when closed steel drums containing excessive silicone are used to store automotive paint, shrinkage holes will appear on the paint surface during painting operations in the paint shop. Summary of the invention

[0004] 1. Technical problem to be solved by the invention: The present invention provides a closed-end steel drum ultra-clean process to solve the technical problems existing in the above-mentioned background technology.

[0005] 2. Technical solution: To achieve the above object, the technical solution provided by the present invention is: a closed-end steel drum ultra-clean process, comprising the following steps: S1. Preparation of raw materials and equipment, including cutting of barrel body material, cover material and bottom material. The surfaces of the barrel body material, cover material and bottom material are coated with DOS oil film, and the cut barrel body material, cover material and bottom material are wiped with ethanol; S2, processing of barrel body material, processing of cover material and processing of bottom material, welding of the joints of the barrel body material after rolling, and artificial coating of chemical anti-rust material after welding; S3. The processed barrel body, cover and bottom materials are assembled, and a sealing test is performed after the assembly test. After the test is qualified, the inner and outer surfaces of the barrel are dusted with a brush, and then the barrel is purged with compressed air; S4. Spray a surface protective layer on the outside of the tested steel drums, bake them and install a closure device. The baking temperature is 150℃ to 200℃, and the temperature fluctuation is within ±2℃. The steel drums are replaced with mixed gas in a closed space. The mixed gas used for replacement is a mixture of nitrogen and carbon dioxide in a ratio of 8:2 or 7:3.

[0006] Preferably, the S4 step comprises: S4.1. Spray the surface protective layer. Use the spraying equipment to evenly spray the low-temperature powder coating on the outside of the steel drum that has passed the test. After spraying the surface protective layer, perform mixed gas replacement; S4.2, baking, the steel drum after spraying the surface protective layer is placed in the baking equipment, the baking temperature is between 150℃ and 200℃, and the mixed gas replacement is also carried out during the baking; S4.3. After the steel drum has been sprayed and baked, install the closure.

[0007] Preferably, at the beginning of the replacement, the initial flow rate of the mixed gas is set at 1.5 to 2.5 cubic meters per minute to quickly replace most of the original gas in the steel barrel, and the replacement time is t1; In the middle stage of replacement, when gas detection is required, the flow rate is reduced to 0.8-1.2 cubic meters per minute to accurately control the gas composition in the steel drum. The replacement time is t2; In the final stage of replacement, when the replacement is nearly completed, the flow rate is further reduced to 0.3-0.6 cubic meters per minute, and the replacement time is t3.

[0008] Preferably, the total time of mixed gas replacement is T, T=t1+t2+t3, and T is calculated based on the following formula: T=nV / Q; Where: n is the replacement multiple, that is, the total volume of the mixed gas filled is n times the volume of the steel drum; V is the volume of the steel drum (L); Q is the initial flow rate (L / min); t1=(40%~50%)T; t2=(30%~40%)T; t3=(10%~20%)T.

[0009] Preferably, the intake pressure of the mixed gas is 0.2-0.5 MPa. During the replacement process, the steel barrel should maintain a positive pressure state with a pressure range of 1.02-1.1 times the atmospheric pressure. Pressure sensors are installed at the air inlet and inside the steel barrel to monitor the pressure changes in real time and control the intake flow rate through a regulating valve.

[0010] 3. Beneficial effects: Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects: The present invention reduces the damage of high temperature to the surface protective layer of the plate through low-temperature powder coating and reasonable baking temperature control, can avoid volatilization of the surface protective layer due to over-baking, thereby preventing the plate from rusting and extending the service life of the steel drum.

[0011] The chemical anti-rust treatment of the seam welding position of the present invention protects the surface protective layer from damage caused by high welding temperature, and further enhances the anti-rust performance of the steel drum.

[0012] The mixed gas replacement in the production process of the present invention effectively solves the problem of excessive silicone content inside the steel drum, avoids the contamination of stored items by silicone, meets the strict requirements for the cleanliness of the steel drum, and solves the requirements for the inner cleanliness and color of the steel drum.

[0013] The steps of the present invention are clearly divided into different parts, and the processing from raw material preparation to the final product is carried out in an orderly manner, thereby improving production efficiency. Multiple leak tests, cleaning treatments, and ethanol wiping ensure the sealing of the steel drum and the cleanliness of the inner and outer surfaces, thereby improving the stability of product quality. The present invention is widely used in storing various items with high requirements for cleanliness, such as automobile paint, etc., and has strong versatility and market competitiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the process of the present invention; Figure 2 It is a schematic flow chart of step S4 of the present invention. DETAILED DESCRIPTION

[0015] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0016] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "page", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0017] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0018] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed", "provided with", etc. should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be internal communication between two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] It should be noted that the structures not introduced in the present invention are the same as the prior art or can be implemented by using the prior art, and are not described in detail here because they do not involve the design points and improvement directions of the present invention.

[0020] Example: Refer to the attached Figures 1-2 , a closed steel drum ultra-clean process, comprising the following steps: S1. Preparation of raw materials and equipment, including cutting of barrel body material, cover material and bottom material. The surfaces of the barrel body material, cover material and bottom material are coated with DOS oil film, and the cut barrel body material, cover material and bottom material are wiped with ethanol; S2, processing of barrel body material, processing of cover material and processing of bottom material, welding of the joints of the barrel body material after rolling, and artificial coating of chemical anti-rust material after welding; S3. The processed barrel body, cover and bottom materials are assembled, and a sealing test is performed after the assembly test. After the test is qualified, the inner and outer surfaces of the barrel are dusted with a brush, and then the barrel is purged with compressed air; S4. Spray a surface protective layer on the outside of the steel drums that have passed the test, bake them and install a closure device. The baking temperature is 150℃ to 200℃, and the temperature fluctuation is within ±2℃. The steel drums are replaced with mixed gas in a closed space. The mixed gas used for replacement is a mixture of nitrogen and carbon dioxide in a ratio of 8:2 or 7:3.

[0021] The S4 step includes: S4.1. Spray the surface protective layer. Use the spraying equipment to evenly spray the low-temperature powder coating on the outside of the steel drum that has passed the test. After spraying the surface protective layer, perform mixed gas replacement; S4.2, Baking, put the steel drum with the surface protective layer sprayed on it into the baking equipment, the baking temperature is between 150℃ and 200℃, if the baking temperature is 150℃, the temperature fluctuation is ±2℃, and the temperature curve is kept in a continuous horizontal state. This precise temperature control ensures the stability and reliability of the baking process, provides a stable thermal environment for the entire production process, and helps to ensure the consistency of product quality. Whether it is for changes in the physical properties of materials or for the control of chemical reactions, this high-precision temperature control can meet strict production requirements and enable the product to achieve the best effect in the baking process. In addition, mixed gas replacement is also carried out during baking; S4.3. After the steel drum has been sprayed and baked, install the closure.

[0022] At the beginning of the replacement, in order to quickly replace most of the original gas in the steel barrel, the initial flow rate of the mixed gas is set at 1.5 to 2.5 cubic meters per minute, and most of the original gas in the steel barrel is quickly replaced. The replacement time is t1, and most of the air can be replaced in a relatively short time. In addition, when the flow rate exceeds 2.5 cubic meters per minute, the pressure in the steel barrel will rise sharply, which will cause potential risks to the structure of the steel barrel, such as deformation or even damage to the steel barrel. At the same time, too fast a flow rate will cause uneven mixing of the gas, affecting the replacement effect, and may cause more original gas to remain in some areas of the steel barrel, and fail to achieve the expected replacement purpose.

[0023] In the middle stage of replacement, when gas detection is required, the flow rate is reduced to 0.8-1.2 cubic meters per minute to accurately control the gas composition in the steel drum. The replacement time is t2. During this stage, the gas composition needs to be detected multiple times for fine adjustment. The flow rate and replacement time are adjusted according to the test results to ensure the thoroughness of the replacement. A lower flow rate helps to more accurately control the gas composition. In the final stage of replacement, when the replacement is close to completion, in order to make the gas in the steel barrel more stable, the flow rate is further reduced to 0.3-0.6 cubic meters per minute, and the replacement time is t3. This helps to reduce gas disturbances, make the final gas composition distribution more uniform, and make the gas composition more stable, ensuring that the final replacement requirements are met.

[0024] The total time for mixed gas replacement is T, T=t1+t2+t3, T is calculated based on the following formula: T=nV / Q; Where: n is the replacement multiple, that is, the total volume of the mixed gas filled is n times the volume of the steel drum; V is the volume of the steel drum (L); Q is the initial flow rate (m 3 / min); This calculation method can accurately determine the total time required for replacement according to different production conditions (such as steel drum size, required replacement mass), providing a quantitative basis for production planning and process control, making the entire mixed gas replacement process more scientific and operational.

[0025] t1=(40%~50%)T;t2=(30%~40%)T;t3=(10%~20%)T。This time allocation method matches the flow setting and replacement target of each stage. In the initial stage, more time (t1) is used for rapid and large-scale replacement, in the middle stage (t2), appropriate time is spent on fine adjustment, and in the final stage (t3), less time is spent on stabilizing the gas composition. Such allocation ensures that most of the gas can be replaced efficiently during the entire replacement process, while the precise control of the gas composition and the final stability can be guaranteed, thereby improving the replacement quality and efficiency.

[0026] Calculation example: displacement multiple n=3, the volume of the steel drum is V=0.5L, and the initial flow rate is Q=2m 3 / min, Theoretically, the total replacement time T = (0.5 × 3) ÷ 2 = 0.75 min = 45 s Then t1=50%T=22.5s; t2=30%T=13.5s; t3=20%T=9s.

[0027] The inlet pressure of the mixed gas is 0.2-0.5MPa. During the replacement process, the steel barrel should maintain a positive pressure state, with a pressure range of 1.02-1.1 times the atmospheric pressure. Pressure sensors are installed at the air inlet and inside the steel barrel to monitor the pressure changes in real time and control the air intake flow rate through the regulating valve. The inlet pressure of the mixed gas is 0.2-0.5MPa. During the replacement process, the steel barrel is kept at a positive pressure of 1.02-1.1 times the atmospheric pressure, which can effectively prevent the outside air from flowing back into the steel barrel. If the outside air enters the steel barrel, it will reintroduce impurities such as moisture and oxygen, destroying the replacement effect. At the same time, the positive pressure state helps to ensure the uniform distribution of gas in the steel barrel, making the replacement process more stable and reliable, and further ensuring the gas quality and process environment in the steel barrel.

[0028] Pressure sensors are installed at the air inlet and inside the steel drum, and the air intake flow is controlled by a regulating valve, which enables real-time monitoring and precise control of the pressure. This can timely detect abnormal pressure conditions, such as pressure changes caused by flow fluctuations or other factors, and timely adjust the air intake flow through the regulating valve to ensure that the pressure in the steel drum is always within the appropriate range, maintain a stable replacement environment, and ensure that the entire mixed gas replacement process is carried out safely and stably.

[0029] In step S4, mixed gas replacement is added, and gas replacement is performed in a confined space. The nitrogen used for replacement is replaced after being proportioned with carbon dioxide and heated. The heated mixed gas has better heat transfer performance in a confined space. The thermal physical properties such as thermal conductivity of carbon dioxide and nitrogen work synergistically under the heating state, which can make the heat more evenly distributed in the space, which is very important for process processes that require uniform heating, such as drying and curing of materials, to avoid product quality problems caused by local overheating or uneven temperature. Stabilize the temperature field. Compared with a single mixed gas, the temperature stability of the mixed gas after heating is better. This is because the thermal properties such as the specific heat capacity of carbon dioxide complement the mixed gas, so that the temperature fluctuation is smaller during the heat exchange process. In processes such as baking that require precise temperature control, a stable temperature environment can be better maintained to ensure the consistency of product quality. After carbon dioxide is mixed with the mixed gas, the diffusion performance of the gas is improved under heating conditions. This allows the gas to more quickly and completely replace the original air or other gases in a confined space. This mixed gas can better penetrate into every corner, achieving a more thorough gas replacement and reducing the impact of residual gas on the process.

[0030] Before applying chemical anti-rust materials, clean the surface of the steel drum seam welding position. Use sandpaper, wire brushes and other tools to remove rust, oil and other impurities on the surface to ensure that the surface is clean and dry. According to the type of chemical anti-rust materials and the shape of the steel drum seam welding position, choose the appropriate coating tool. For anti-rust paint and anti-rust agent, brushing, spraying or dipping can be used for coating.

[0031] After the final assembly is completed and tested, the overall structure of the steel drum has been determined. At this time, mixed gas replacement can be carried out to discharge the air inside the steel drum, reducing factors such as moisture and oxygen in the air that may have adverse effects on subsequent processes. After the replacement, the next step of internal spraying and other operations can be carried out to reduce the risk of contamination inside the steel drum and ensure the effect of the ultra-clean process.

[0032] The S4 step includes: S4.1. Spray the surface protective layer. Use the spraying equipment to evenly spray the low-temperature powder coating on the outside of the steel drum that has passed the test. After spraying the surface protective layer, add mixed gas replacement; S4.2, baking, put the steel drum with the surface protective layer sprayed on it into the baking equipment, the baking temperature is between 150℃ and 200℃, and the temperature curve is kept horizontal. This precise temperature control ensures the stability and reliability of the baking process, provides a stable thermal environment for the entire production process, and helps to ensure the consistency of product quality. Whether it is for the change of physical properties of materials or the control of chemical reactions, this high-precision temperature control can meet strict production requirements and achieve the best effect in the baking process; in addition, when baking, increase the replacement of mixed gas; S4.3. Install the closure after the steel drum has been sprayed and baked.

[0033] In the spraying process of products such as steel drums, traditional powder coatings often require higher baking temperatures to achieve good curing effects. However, high-temperature baking brings problems: the plates of steel drums and the like usually have some surface protective layers during the production process, such as anti-rust layers, passivation layers, etc. High-temperature baking may cause these protective layers to undergo chemical changes, decompose, or lose adhesion. For example, some components in the anti-rust layer may react with oxygen in the air at high temperatures, thereby losing the anti-rust effect; the passivation layer may crack at high temperatures, making the plate more susceptible to corrosion.

[0034] Advantages of low temperature powder: Low temperature powder coating is specially designed for curing at lower temperatures. Compared with traditional powder coating, it can achieve good curing effect at lower temperatures, usually reducing the baking temperature by dozens of degrees or even hundreds of degrees. For example, traditional powder coating may need to be baked at a temperature above 200℃, while low temperature powder coating only needs to be cured at 150℃ or even lower.

[0035] Due to the lower baking temperature, the damage to the protective layer on the surface of the plate is greatly reduced. This can ensure that the protective layer remains intact during the spraying process and continues to play its role in preventing rust and corrosion.

[0036] Spraying the surface protective layer will form a solid protective film on the outer wall of the steel drum, effectively blocking the corrosion of the steel drum by external corrosive substances such as moisture, oxygen, and chemicals, and extending the service life of the steel drum. This protective film plays a key role in anti-corrosion and anti-rust. First of all, it can isolate moisture in the air from contacting the outer wall of the steel drum to a great extent. Moisture is one of the important factors leading to metal corrosion, and the protective film is like a tight waterproof wall, preventing moisture from penetrating into the surface of the steel drum, thereby effectively preventing the occurrence of rust. Secondly, the protective film can also play a good barrier role for oxygen in the air. The oxidation reaction between oxygen and the surface of the steel drum will gradually destroy the structure of the steel drum, and with this solid protective film, the contact between oxygen and the steel drum can be greatly reduced, reducing the risk of oxidation corrosion. Furthermore, when the steel drum may be exposed to various chemicals in different environments, the protective film can resist the erosion of these chemicals with its good chemical stability, provide reliable protection for the steel drum, and ensure that the steel drum can maintain a good condition in various complex environments. In addition, the surface protective layer can give the steel drum different colors and gloss, improve the appearance quality of the steel drum, and enhance the market competitiveness of the product. Moreover, the surface protective layer material has high wear resistance, which can reduce the wear of the steel drum during transportation, loading and unloading and storage, maintain the structural integrity of the steel drum, and further provide strong protection for the corrosion and rust prevention of the steel drum.

[0037] Baking can speed up the curing speed of the surface protective layer material and improve production efficiency. Baking can make the surface protective layer more solid, wear-resistant and corrosion-resistant, and improve the overall performance of the steel drum. The baking process can remove moisture and solvents in the surface protective layer to avoid bubbling, peeling and other problems during use. The closure can effectively seal the steel drum to prevent leakage of the contents and the influence of the external environment.

[0038] There may be a certain amount of air inside the steel drum, and the air inside the steel drum may carry trace amounts of silicone, such as silicone oil, silicone grease and other mobile fluorinated products and surfactants. After spraying the surface protective layer, during baking, the high temperature environment may cause silicone to adhere to the inner wall of the steel drum. Mixed gas replacement at this stage can effectively remove the air in the steel drum. Expelling air through mixed gas replacement can greatly reduce the possibility of silicone being brought into the steel drum, thereby reducing the risk of silicone contamination of subsequent stored items. In addition, oxygen and moisture may react with certain substances in the steel drum under high-temperature baking to generate or promote the formation of silicone. After mixed gas replacement, oxygen and moisture are reduced, which also reduces the reaction conditions that may lead to the production of silicone, effectively preventing the generation of new silicone.

[0039] When storing items that require high cleanliness, such as automotive paint, the silicone in the steel drum will reduce the quality of the paint and cause shrinkage holes on the paint surface when spraying. Reducing silicone by replacing it with mixed gas can effectively prevent the stored items from being contaminated by silicone, thus ensuring the quality and use effect of stored items such as paint.

[0040] Working principle: The DOS oil film can form a continuous protective film on the outer surface of the steel drum, effectively blocking oxygen, moisture and other possible corrosive gases (such as sulfur dioxide, etc.) in the air from contacting the surface of the steel drum. Oxygen and moisture are the key factors that cause steel to rust. Through the isolation of this oil film, the corrosion rate of the steel drum can be greatly slowed down and its service life can be extended. The DOS oil film itself may contain some anti-rust components or have a corrosion inhibition effect. These components can react chemically with the surface of the steel drum to form a passivation film or adsorption layer on the surface, further improving the anti-rust ability of the steel drum. This anti-rust effect is particularly important for steel drums that are stored and transported for a long time, which can ensure that the steel drum maintains a good appearance and structural integrity for a long time. During the handling, loading and unloading and transportation of steel drums, friction with other objects is inevitable. The DOS oil film can play a lubricating role and reduce the friction coefficient between the surface of the steel drum and external objects (such as transportation equipment, loading and unloading tools, etc.). This can reduce scratches, wear and other damages on the surface of the steel drum caused by friction, and maintain the appearance quality and structural strength of the steel drum.

[0041] The present invention cleans the production equipment regularly to remove silicone residues on the surface of the equipment. A special cleaning agent or solvent (ethanol) can be used for cleaning to ensure the cleanliness of the equipment. For example, the shearing machine is thoroughly cleaned before and after each production to prevent silicone from accumulating inside the equipment. In the production process, avoid using auxiliary materials such as lubricants and protective agents containing silicone. If it must be used, products with low silicone content should be selected and the amount used should be strictly controlled.

[0042] The finished product is strictly tested for silicone content to ensure that the product meets the quality standards. The same methods and equipment as the raw material testing can be used to sample the finished product. The silicone testing method is as follows: 1. 50% butyl acetate + 25% isobutyl alcohol + 25% n-butanol are mixed into a solvent; 2. Take 150ml and put it into the bucket; 3. Shake fully up and down and left and right; 4. Remove the solvent and transfer 8 grams of solvent to a clean glass container; 5. Bake at 145 degrees for 10 minutes; 6. After cooling, add 3 ml of naphtha; 7.Put into small bottles; 8. Vibrate for 15 seconds and observe with the naked eye. If there are no bubbles, there is no silicone. 9. Observe with the naked eye. If there are no bubbles, there is no silicone.

[0043] The second method is to directly use naphtha as solvent, and the method and steps are the same.

[0044] By using a specific proportion of mixed solvents (butyl acetate, isobutyl alcohol, n-butyl alcohol) or directly using naphtha as a solvent, the possible silicone can be effectively dissolved, making the test results more accurate. The multi-step operation process, including shaking, baking, cooling, adding naphtha and vibration, can fully extract and visualize the silicone in the steel drum, reducing the possibility of missed detection.

[0045] Through strict silicone content testing, it can be ensured that the finished steel drums meet the quality standards and avoid the performance and use effect of the steel drums affected by excessive silicone content. For storing items with high cleanliness requirements such as automotive paint, silicone-free steel drums can ensure the quality of the stored items and prevent quality problems such as shrinkage holes in the paint.

[0046] The above-described embodiments only express a certain implementation mode of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A closed steel drum ultra-clean process, characterized in that: The following steps are involved: S1. Preparation of raw materials and equipment, including cutting of barrel body material, cover material and bottom material. The surfaces of the barrel body material, cover material and bottom material are coated with DOS oil film, and the cut barrel body material, cover material and bottom material are wiped with ethanol; S2, processing of barrel body material, processing of cover material and processing of bottom material, welding of the joints of the barrel body material after rolling, and artificial coating of chemical anti-rust material after welding; S3. The processed barrel body, cover and bottom materials are assembled, and a sealing test is performed after the assembly test. After the test is qualified, the inner and outer surfaces of the barrel are dusted with a brush, and then the barrel is purged with compressed air; S4. Spray a surface protective layer on the outside of the tested steel drums, bake them and install a closure device. The baking temperature is 150℃ to 200℃, and the temperature fluctuation is within ±2℃. The steel drums are replaced with mixed gas in a closed space. The mixed gas used for replacement is a mixture of nitrogen and carbon dioxide in a ratio of 8:2 or 7:

3.

2. The closed-end steel drum ultra-clean process according to claim 1, characterized in that: The S4 step includes: S4.

1. Spray the surface protective layer. Use the spraying equipment to evenly spray the low-temperature powder coating on the outside of the steel drum that has passed the test. After spraying the surface protective layer, perform mixed gas replacement; S4.2, baking, the steel drum after spraying the surface protective layer is placed in the baking equipment, the baking temperature is between 150℃ and 200℃, and the mixed gas replacement is also carried out during the baking; S4.

3. After the steel drum has been sprayed and baked, install the closure.

3. The closed-end steel drum ultra-clean process according to claim 2, characterized in that: At the beginning of the replacement, the initial flow rate of the mixed gas is set at 1.5-2.5 cubic meters per minute to quickly replace most of the original gas in the steel drum. The replacement time is t1; In the middle stage of replacement, when gas detection is required, the flow rate is reduced to 0.8-1.2 cubic meters per minute to accurately control the gas composition in the steel drum. The replacement time is t2; In the final stage of replacement, when the replacement is nearly completed, the flow rate is further reduced to 0.3-0.6 cubic meters per minute, and the replacement time is t3.

4. The closed-end steel drum ultra-clean process according to claim 3, characterized in that: The total time for mixed gas replacement is T, T=t1+t2+t3, T is calculated based on the following formula: T=nV / Q; Where: n is the replacement multiple, that is, the total volume of the mixed gas filled is n times the volume of the steel drum; V is the volume of the steel drum (L); Q is the initial flow rate (L / min); t1=(40%~50%)T; t2=(30%~40%)T; t3=(10%~20%)T.

5. The closed-end steel drum ultra-clean process according to claim 4, characterized in that: The intake pressure of the mixed gas is 0.2~0.5MPa. During the replacement process, the steel barrel should maintain a positive pressure state with a pressure range of 1.02~1.1 times the atmospheric pressure. Pressure sensors are installed at the air inlet and inside the steel barrel to monitor the pressure changes in real time and control the intake flow rate through a regulating valve.

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