Capillary Seamless Steel Tubes and Their Preparation Methods

Abstract

This invention relates to a method for preparing capillary seamless steel tubes, comprising the following sequential steps: S100. Selecting austenitic stainless steel seamless tubes as tube blanks, the outer diameter of the tube blanks being 8mm-15mm, the wall thickness being 0.5mm-1.2mm, and the wall thickness accuracy being ±0.015mm; S200. Using a drawing machine with a long mandrel, cold-drawing the tube blanks from S100, when the deformation compression rate of a single cold drawing is 30%-75%, performing internal and external surface cleaning and solution treatment; repeating the above treatment until a capillary seamless steel tube with an outer diameter of 3.8mm-4.2mm and a wall thickness of 0.125mm-0.3mm is obtained. Drawing the billet; wherein the hardness of the long mandrel is 780HV-860HV, and the diameter accuracy of the long mandrel is ±0.005μm; S300. Using a drawing machine with a moving mandrel, the moving drawing billet obtained in S200 is cold drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated; repeat the above treatment to obtain a capillary seamless steel tube with an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm, and a wall thickness accuracy of ±0.003mm; S400. The capillary seamless steel tube obtained in S300 is subjected to external grinding treatment to obtain the final product.

Description

Technical Field

[0001] This invention relates to the field of medical metal tubing processing technology, and in particular to a capillary seamless steel tube and its preparation method. Background Technology

[0002] Stainless steel capillary seamless pipes possess excellent flexibility, corrosion resistance, high temperature resistance, wear resistance, tensile strength, and water resistance, and also provide excellent electromagnetic shielding performance, making them widely used in various fields. However, in the medical device field, due to the small diameter and short length of the required tubing, a technical problem in processing is uneven wall thickness, which affects the use of medical devices and leads to low product yield.

[0003] Specifically, 304L capillary seamless steel tubes, as a common type of medical metal tubing, are typically manufactured using traditional techniques involving a combination of three-roll cold rolling and floating mandrel drawing, or a cold drawing method using a floating mandrel throughout the entire process. For small-batch production, this traditional method presents the following problems: First, the initial investment in equipment is substantial, leading to high production costs and poor economic efficiency. Second, the processing requires changing molds and dies, making the production process complex and demanding higher technical skills from operators. The increased number of steps also increases preparation time, affecting production efficiency. Third, the wall thickness uniformity of stainless steel capillary seamless tubes produced using this traditional method is unstable, resulting in a low product yield. Summary of the Invention

[0004] Based on this, the present invention proposes a capillary seamless steel pipe and its preparation method. By first drawing with a high-precision long mandrel and then by floating drawing, the initial equipment investment can be reduced and the production arrangement can be more flexible. The wall thickness uniformity of the stainless steel capillary seamless steel pipe prepared by the preparation method of the present invention is greatly improved, thereby increasing the product yield.

[0005] This invention discloses a method for preparing a capillary seamless steel tube, the method comprising the following steps performed sequentially:

[0006] S100. Select austenitic stainless steel seamless steel pipe as the pipe blank, wherein the outer diameter of the pipe blank is 8mm-15mm, the wall thickness is 0.5mm-1.2mm, and the wall thickness accuracy is ±0.015mm;

[0007] S200. Using a drawing machine with a long mandrel, the tube blank of S100 is cold-drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated. The above cold drawing, cleaning and solution treatment are repeated until a floating drawn blank with an outer diameter of 3.8mm-4.2mm and a wall thickness of 0.125mm-0.3mm is obtained. The hardness of the long mandrel is 780HV-860HV, and the diameter accuracy of the long mandrel is ±0.005μm.

[0008] S300. Using a drawing machine with a moving mandrel, the moving drawing billet obtained in S200 is cold-drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated. The above cold drawing, cleaning and solution treatment are repeated to obtain capillary seamless steel pipes with an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm and a wall thickness accuracy of ±0.003mm.

[0009] S400. The capillary seamless steel pipe obtained from S300 is subjected to external grinding treatment to obtain the final product.

[0010] In some embodiments, in step S100, the pipe blank has an elongation of more than 55%, a surface finish of less than 0.8 μm on both the inner and outer surfaces, and is made of 304L or 316 stainless steel seamless pipe.

[0011] In step S300, the inner wall smoothness of the obtained capillary seamless steel tube is less than 0.6 μm and the hardness is not less than 280 HV.

[0012] In some embodiments, in step S200, the long core rod is made of SKD11 mold steel.

[0013] In some embodiments, the drawing frequency in step S200 is 3-6Hz, and the elongation coefficient of the tube blank in cold drawing is 1.2-1.5.

[0014] In some embodiments, in step S300, the wall elongation coefficient of the floating mandrel is 1.3-1.5, and the floating mandrel drawing frequency is 20Hz-25Hz; the diameter reduction compression rate of the floating mandrel is 5%-10%, and the floating mandrel drawing frequency is 25Hz-30Hz.

[0015] In some embodiments, in step S300, the moving core is made of cermet and the drawing die is a polycrystalline die.

[0016] In some embodiments, hydrogen is used as the medium for the solution treatment in steps S200 and S300.

[0017] In some embodiments, in steps S200 and S300, the solution temperature is 1050℃-1080℃, the holding time is 15min-20min, the heating rate is 30-50℃ / min, the cooling rate is 40-50℃ / min, and the cooling rate after solution treatment is greater than 500℃ / min.

[0018] In some embodiments, the inner and outer surface cleaning methods in steps S200 and S300 include the following steps: degreasing and ultrasonic cleaning of inner and outer surfaces; cleaning and blowing air into the inner wall; ultrasonic cleaning and drying of the outer surface.

[0019] Another aspect of the present invention discloses a capillary seamless steel pipe, which is prepared by the aforementioned method for preparing capillary seamless steel pipe. The capillary seamless steel pipe has an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm, a wall thickness accuracy of ±0.003mm, an inner wall smoothness of less than 0.6μm, and a hardness of not less than 280HV.

[0020] Beneficial effects

[0021] The capillary seamless steel pipe preparation method of this invention selects austenitic stainless steel seamless pipe as the pipe blank, which can effectively reduce the number of process steps, facilitate the smooth progress of cold working, and improve the yield. Based on this, the preparation method of this invention optimizes the size of the pipe blank, uses a preferred long mandrel for movable drawing to obtain a floating drawn blank of preferred size, and then uses a floating mandrel for drawing to obtain a capillary seamless steel pipe with a high degree of inner surface smoothness and very uniform wall thickness. Compared with the existing three-roll cold rolling + floating mandrel drawing scheme, the preparation method of this invention reduces the number of processing passes, shortens the processing cycle, and improves the dimensional accuracy of the pipe, making it very suitable for the production of small batches of capillary seamless steel pipes. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method for preparing the capillary seamless steel tube of the present invention in some embodiments. Detailed Implementation

[0023] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0024] See Figure 1 , Figure 1A schematic flowchart of a method for preparing a capillary seamless steel tube according to an embodiment of the present invention is shown. The method for preparing the capillary seamless steel tube comprises the following steps in sequence:

[0025] S100. Select austenitic stainless steel seamless steel pipe as the pipe blank, wherein the outer diameter of the pipe blank is 8mm-15mm, the wall thickness is 0.5mm-1.2mm, and the wall thickness accuracy is ±0.015mm;

[0026] S200. Using a drawing machine with a long mandrel, the tube blank of S100 is cold-drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated. The above cold drawing, cleaning and solution treatment are repeated until a floating drawn blank with an outer diameter of 3.8mm-4.2mm and a wall thickness of 0.125mm-0.3mm is obtained. The hardness of the long mandrel is 780HV-860HV, and the diameter accuracy of the long mandrel is ±0.005μm.

[0027] S300. Using a drawing machine with a moving mandrel, the moving drawing billet obtained in S200 is cold-drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated. The above cold drawing, cleaning and solution treatment are repeated to obtain capillary seamless steel pipes with an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm and a wall thickness accuracy of ±0.003mm.

[0028] S400. The capillary seamless steel pipe obtained from S300 is subjected to external grinding treatment to obtain the final product.

[0029] The capillary seamless steel pipe preparation method of the present invention, by selecting austenitic stainless steel seamless steel pipe as pipe blank in step S100, can effectively reduce process steps compared with the prior art, which is more conducive to the smooth progress of cold working and improves the yield.

[0030] Based on this, the preferred method for preparing capillary seamless steel pipes of the present invention uses a billet with an outer diameter of 8mm-15mm, a wall thickness of 0.5mm-1.2mm, and a wall thickness accuracy of ±0.015mm. In step S200, a floating drawn billet with an outer diameter of 3.8mm-4.2mm and a wall thickness of 0.125mm-0.3mm is obtained after dynamic drawing using a long mandrel. Then, in step S300, the floating drawn billet obtained in step S200 is subjected to dynamic mandrel drawing to finally obtain a capillary seamless steel pipe with an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm, and a wall thickness accuracy of ±0.003mm. The wall thickness accuracy mentioned here refers to the transverse wall thickness deviation of the pipe, that is, the difference between the maximum and minimum wall thickness values ​​on the same cross-section perpendicular to the pipe's extension direction. This invention replaces the traditional three-roll cold rolling + floating mandrel drawing or full-process floating mandrel drawing deformation method, fully considering the technical characteristics of medical metal capillary seamless steel tubes. Since medical metal capillary seamless steel tubes do not need to be very long, but rather need to be made into segments of moderate length, long mandrel cold drawing technology can be well applied to the production of such medical metal capillary seamless steel tubes. Furthermore, by optimizing the dimensions and wall thickness accuracy of the tube blank in step S100 and the dimensions of the floating drawing blank in step S200, combined with steps S200 and S300, capillary seamless steel tubes with outer diameter and wall thickness meeting actual requirements and extremely high wall thickness accuracy can be obtained.

[0031] In the method for preparing capillary seamless steel tubes of the present invention, by controlling the hardness of the long mandrel to 780HV-860HV, the overall wear resistance of the long mandrel is excellent. The inner surface of the floating drawn billet obtained by drawing with it has a high degree of smoothness, making it very suitable for further processing to obtain high-quality medical capillary seamless steel tubes. By controlling the diameter accuracy of the long mandrel to ±0.005μm, the wall thickness of the floating drawn billet obtained by drawing with this long mandrel is very uniform. The capillary seamless steel tubes processed on this basis can meet the requirements for their application in the medical field in terms of wall thickness, dimensions, and smoothness. Moreover, the production organization flexibility of the long mandrel drawing method is also better than the existing three-roll cold rolling scheme. Compared with the existing technology, the preparation time is shorter, the number of processing passes is reduced, the processing cycle is shortened, and the dimensional accuracy of the tubes can be improved, making it very suitable for the production of small batches of capillary seamless steel tubes.

[0032] The method for preparing capillary seamless steel tubes of the present invention involves drawing a floating mandrel after cold drawing with a high-precision long mandrel. This makes the entire preparation method of the present invention a pure drawing process, resulting in better uniformity of product wall thickness and smooth inner and outer surface roughness.

[0033] The method for preparing capillary seamless steel tubes of this invention particularly emphasizes that during the cold drawing process of the long mandrel and the cold drawing process of the moving mandrel, when the single cold drawing deformation compression rate is 30%-75%, the inner and outer surfaces of the tube blank and the moving drawn blank should be cleaned and solution treated. This is because if surface cleaning and solution treatment are not performed, the surface finish of the tube blank and the moving drawn blank will be problematic during processing. In particular, if there is dirt on the seamless steel tube and the long mandrel, the relative movement of the seamless steel tube and the long mandrel during the drawing process may cause scratches on the product, which will seriously affect the stability of product quality.

[0034] In summary, the capillary seamless steel pipes prepared using the method of the present invention meet the end customer requirements in terms of dimensional deviation, surface finish, surface quality, and process performance. Compared with existing technologies, the method requires less equipment investment, has simpler production steps, offers greater production flexibility, and is more suitable for small-batch production.

[0035] It is understandable that the method for preparing the capillary seamless steel tube of the present invention does not strictly limit the specific material selection for the long mandrel. Those skilled in the art can select a suitable material for the long mandrel based on the technical guidance provided by the present invention. As a specific and feasible embodiment, the long mandrel is made of SKD11 die steel. For ease of understanding, SKD11 die steel is described below: SKD11 is a Japanese JIS standard grade, which is a high wear-resistant and tough general-purpose cold work die steel, a high-carbon and high-chromium alloy tool steel, and a vacuum degassing refined steel. The steel is pure and has good hardenability with good hardenability and small quenching deformation. This steel is softened by spheroidizing annealing, has good machinability, and the carbide particles are fine and uniform. There is no need to worry about quenching cracking due to the special addition of strengthening elements molybdenum and vanadium. It has high hardness, high wear resistance, uniform eutectic carbides, high toughness, and is not easy to crack.

[0036] In some embodiments, step S100 of the method for preparing capillary seamless steel tubes of the present invention preferably uses seamless steel tubes with an elongation greater than 55%, an inner and outer surface finish of less than 0.8 μm, and made of 304L or 316 stainless steel as the tube blank. By optimizing the elongation, surface finish, and material of the tube blank, the capillary seamless steel tube prepared according to the aforementioned method can achieve an inner wall surface finish of less than 0.6 μm and a hardness of not less than 280 HV. This type of capillary seamless steel tube has a high inner surface finish and meets the hardness requirements, belonging to high-quality medical metal consumable capillary seamless steel tubes.

[0037] In a preferred embodiment, the drawing frequency of the long mandrel in step S200 is 3-6 Hz, and the cold drawing elongation coefficient of the tube blank in each pass is 1.2-1.5. By reasonably limiting the drawing process, the long mandrel drawing effect is better, and the wall thickness uniformity and inner wall smoothness of the floating mandrel drawing blank are both high, laying a good foundation for the next step of floating mandrel drawing.

[0038] Preferably, in step S300, the wall reduction elongation coefficient of the floating mandrel drawing is 1.3-1.5, and the floating drawing frequency is 20Hz-25Hz; the diameter reduction compression rate of the floating mandrel drawing is 5%-10%, and the floating drawing frequency is 25Hz-30Hz. The wall reduction refers to both reducing the wall thickness and the outer diameter; the wall reduction elongation coefficient refers to the change in cross-sectional area before and after cold drawing; the diameter reduction compression rate refers to the change in outer diameter before and after cold drawing. By controlling the floating mandrel drawing process parameters, and with the support of the floating drawn billet obtained from the aforementioned long mandrel drawing, excellent dimensional control of capillary seamless steel tubes can be achieved.

[0039] Specifically, in some embodiments, in step S300, the floating mandrel is made of cermet, and the drawing die is a polycrystalline die. By selecting a suitable die and a suitable floating mandrel, it is possible to ensure that the capillary seamless steel tubes that meet the requirements are produced.

[0040] It should be noted that in some embodiments, high-purity hydrogen is used as the medium for solution treatment in steps S200 and S300. This is because the entire cold working process employs bright solution treatment with a high-purity hydrogen atmosphere for protection, which improves the surface quality of the product's inner and outer surfaces and ensures smooth processing. The high-purity hydrogen, as a protective atmosphere, is introduced into the muffle belt bright annealing furnace, preventing oxidation of the steel pipe surface, maintaining the original surface finish of the pipe, and ensuring uniform microstructure and properties on the pipe surface and in the core, which is more conducive to subsequent processing.

[0041] Specifically, in steps S200 and S300, the solution treatment temperature is 1050℃-1080℃, the holding time is 15min-20min, the heating rate is 30-50℃ / min, and the cooling rate is 40-50℃ / min; the cooling rate after solution treatment is greater than 500℃ / min. These solution treatment conditions and process parameters can effectively eliminate work hardening and improve the plastic deformation capacity of metals.

[0042] It should be noted that, in some embodiments, the internal and external surface cleaning methods in steps S200 and S300 include the following steps: ultrasonic cleaning to remove oil from the internal and external surfaces; cleaning and blowing air onto the inner wall; and ultrasonic cleaning and drying of the outer surface. This cleaning process ensures the cleanliness of the inner and outer walls of the steel pipe during processing, while also ensuring the cleanliness of the inner wall and the smoothness of the outer surface of the capillary tube.

[0043] Specifically, the cold-drawn or ground pipes are first ultrasonically cleaned in a specialized cleaning agent solution at 70°C for 60 minutes. After ultrasonic cleaning, the pipes are then subjected to internal cleaning and air blowing on a specialized internal wall cleaning device for 60 minutes of rinsing and 30 minutes of air blowing. Following the internal cleaning process, the pipes are immersed in 80°C hot water for ultrasonic cleaning for 30 minutes, and then dried using a drying device. This cleaning method offers high cleaning efficiency and produces high cleanliness and smoothness for both floating drawn billets and capillary seamless steel pipes.

[0044] In some embodiments, the method for preparing capillary seamless steel tubes of the present invention further includes step S400 after completing step S300: subjecting the capillary seamless steel tubes obtained in S300 to external grinding to obtain the final product, so as to further improve the surface quality of the final product, including the surface finish.

[0045] Another aspect of the present invention discloses a capillary seamless steel tube, which is prepared using the aforementioned method for preparing capillary seamless steel tubes. After steps S100 to S400, the final product of the capillary seamless steel tube can achieve a hardness greater than 280HV, a wall thickness accuracy of ±0.003mm, an outer surface finish of less than 0.2μm, and an inner wall finish of less than 0.6μm, meeting the requirements for capillary seamless steel tubes for medical metal consumables.

[0046] The following specific embodiments and comparative examples are provided to further illustrate in detail the specific process of the preparation method of the capillary seamless steel pipe of the present invention and the beneficial effects of the preparation method of the capillary seamless steel pipe of the present invention.

[0047] Example 1

[0048] Step S100: Select 304L high-precision bright annealing seamless steel pipe raw material with a diameter of 8mm x 0.5mm (outer diameter 8mm, wall thickness 0.5mm, the same below) and a billet length of 1800mm.

[0049] Step S200: Using a hydraulic drawing device, the long mandrel is cold-drawn in 5 passes to deform the φ8mm x 0.5mm diameter to φ4mm x 0.175mm. The long mandrel cold deformation process is as follows: (1) After reducing the wall thickness of the φ8mm x 0.5mm long mandrel to φ7.2mm x 0.44mm, the long mandrel is continuously drawn to φ6.2mm x 0.345mm. The inner and outer surfaces of the φ6.2mm x 0.345mm tube are cleaned, and then solution annealed at 1050℃ for 20 minutes; (2) The wall thickness of the φ6.2mm x 0.345mm long mandrel is reduced to φ5.2mm x 0.275mm. mm, then the long core rod is pulled to φ4.5mmx0.225mm, the inner and outer surfaces of the φ4.5mmx0.225mm pipe are cleaned, and then solution annealed at 1050℃ for 20min; (3) the long core rod of size φ4.5mmx0.225mm is reduced in wall size and deformed to φ4.0mmx0.175mm, the inner and outer surfaces of φ4.0mmx0.175mm are cleaned, and then solution annealed at 1050℃ for 20min.

[0050] Step S300: Using a coil drawing machine, through 14 cold drawing passes, a capillary seamless steel pipe of φ0.79mm x 0.09mm is prepared by coil drawing with a moving mandrel. The cold deformation process of coil drawing with a moving mandrel is as follows: (1) The moving drawing billet of size φ4mm x 0.175 is deformed by moving mandrel reduction to φ3.45mm x 0.15mm, and then continuously drawn with a moving mandrel to φ2.95mm x 0.12mm. The inner and outer surfaces of the φ2.95mm x 0.12mm pipe are cleaned, and then solution annealed at 1050℃ for 20min; (2) The moving mandrel of size φ2.95mm x 0.12mm is deformed by moving mandrel reduction to φ2.45mm x 0.11mm. m, then move and pull to φ2.05mmx0.095mm, clean the inner and outer surfaces of φ2.05mmx0.095mm, then solution anneal at 1050℃ and keep warm for 20min; (3) reduce the wall of the moving core head with size φ2.05mmx0.095mm to φ1.55mmx0.085mm, and pull it in multiple passes to φ0.79mmx0.09mm. During the pull deformation process, the outer diameter size changes continuously to 1.45mm, 1.35mm, 1.25mm, 1.15mm, 1.05mm, 0.95mm, 0.90mm, 0.85mm, 0.79mm, then clean and straighten the inner and outer surfaces.

[0051] Step S400: The obtained capillary seamless steel pipe is subjected to external grinding treatment to obtain the final product.

[0052] The dimensions of the final product were measured. The product hardness is 330HV, the outer diameter is 0.790mm-0.795mm, the wall thickness is 0.088mm-0.093mm, the wall thickness accuracy is ±0.003mm, the outer surface finish (Ra) is 0.163μm, and the inner wall finish (Ra) is 0.320μm.

[0053] Example 2

[0054] Step S100: Select 304L, φ10mmx0.6mm high-precision bright annealed seamless steel pipe raw material, with a billet length of 1000mm.

[0055] Step S200: Using a hydraulic drawing device, the long mandrel is cold-drawn in 6 passes to reduce the size from φ10mm x 0.6mm to φ4mm x 0.125mm. The long mandrel cold deformation process is as follows: (1) After reducing the wall thickness of the φ10mm x 0.6mm long mandrel to φ8.3mm x 0.48mm, the long mandrel is then continuously drawn and deformed to φ7.2mm x 0.38mm. The inner and outer surfaces of the φ7.2mm x 0.38mm tube are cleaned, followed by solution annealing at 1080℃ for 15 minutes; (2) The wall thickness of the φ7.2mm x 0.38mm long mandrel is reduced and deformed to φ6.2mm x 0.29mm, followed by continuous drawing and deformation. (2) The inner and outer surfaces of the core rod with a diameter of φ5.3mm x 0.22mm are cleaned, and then the core rod is solution annealed at 1080℃ for 15 minutes. (3) The long core rod with a diameter of φ5.3mm x 0.22mm is reduced in wall size and deformed to φ4.5mm x 0.170mm. The long core rod is then pulled to φ4.0mm x 0.125mm. The inner and outer surfaces of the core rod with a diameter of φ4.0mm x 0.125mm are cleaned, and then the core rod is solution annealed at 1080℃ for 15 minutes.

[0056] Step S300: Using a coil drawing machine, through 17 cold drawing passes, a capillary seamless steel pipe φ0.59mmx0.05mm is prepared by coil drawing with a moving mandrel. The cold deformation process of coil drawing with a moving mandrel is as follows: (1) The moving mandrel with a size of φ4mmx0.125 is reduced to φ3.45mmx0.110mm, and then continuously drawn with a moving mandrel to φ2.95mmx0.090mm. The inner and outer surfaces of φ2.95mmx0.090mm are cleaned, and then solution annealed at 1080℃ for 15min; (2) The moving mandrel with a size of φ2.95mmx0.090mm is drawn and reduced to φ2.45mmx0.075mm, and then continuously drawn with a moving mandrel to φ2.05mmx0.060mm. The inner and outer surfaces of φ2.05mmx0.060mm are cleaned. (3) Draw the floating core head with dimensions φ2.05mmx0.060mm to reduce the wall to φ1.55mmx0.050mm, clean the inner and outer surfaces of φ1.55mmx0.050mm, then solution anneal at 1050℃ and keep warm for 15 minutes; (4) Draw the floating core head with dimensions φ1.55mmx0.050mm to φ1.25mmx0.045mm, then draw it in multiple passes to φ0.59mmx0.05mm, with the deformation process of 1.15mm, 1.05mm, 0.95mm, 0.90mm, 0.85mm, 0.79mm, 0.74mm, 0.69mm, 0.64mm, and 0.59mm, then clean and straighten the inner and outer surfaces.

[0057] Step 4: Perform external grinding on the obtained capillary seamless steel pipe.

[0058] Through this technical solution, the final product has a hardness of 330HV, an outer diameter of 0.589mm-0.595mm, a wall thickness of 0.048mm-0.052mm, a wall thickness accuracy of ±0.003mm, an outer surface finish (Ra) of 0.150μm, and an inner wall finish (Ra) of 0.361μm.

[0059] Comparative Example 1

[0060] Step 1: Select the same 304L, φ8mmx0.5mm high-precision bright annealing seamless steel pipe raw material as in Example 1, with a billet length of 1800mm.

[0061] Step two: Using a three-roll cold rolling mill, the φ8mm x 0.5mm material is rolled and deformed to a φ4mm x 0.175mm specification. Three-roll cold rolling process: (1) Cold roll the size φ8mmx0.5mm to φ7.2mmx0.44mm, then roll it to φ6.2mmx0.345mm. Clean the inner and outer surfaces of the φ6.2mmx0.345mm pipe, then solution anneal at 1050℃ and hold for 20min; (2) Cold roll the size φ6.2mmx0.345mm to φ5.2mmx0.275mm, then roll it to φ4.5mmx0.225mm. Clean the inner and outer surfaces of the φ4.5mmx0.225mm pipe, then solution anneal at 1050℃ and hold for 20min; (3) Cold roll the size φ4.5mmx0.225mm to φ4.0mmx0.175mm. Clean the inner and outer surfaces of the φ4.0mmx0.175mm pipe, then solution anneal at 1050℃ and hold for 20min.

[0062] Step 3: Using a coil drawing machine, through 14 cold drawing passes, the capillary seamless steel pipe φ0.79mmx0.09mm is processed by the coil drawing method of the floating mandrel. The cold deformation process of the floating mandrel coil drawing is as follows: (1) The floating drawing billet with a size of φ4mmx0.175 is deformed by the floating mandrel to φ3.45mmx0.15mm, and then continuously drawn by the floating mandrel to φ2.95mmx0.12mm. The inner and outer surfaces of the φ2.95mmx0.12mm pipe are cleaned, and then solution annealed at 1050℃ for 20min; (2) The floating mandrel with a size of φ2.95mmx0.12mm is deformed by the floating mandrel to φ2.45mmx0.11mm. Then, the moving core head is continuously drawn to φ2.05mmx0.095mm. The inner and outer surfaces of φ2.05mmx0.095mm are cleaned, and then it is annealed at 1050℃ and kept warm for 20min. (3) The moving core head of size φ2.05mmx0.095mm is reduced and deformed to φ1.55mmx0.085mm. It is drawn in multiple passes to φ0.79mmx0.09mm. During the drawing deformation process, the outer diameter changes continuously to 1.45mm, 1.35mm, 1.25mm, 1.15mm, 1.05mm, 0.95mm, 0.90mm, 0.85mm, and 0.79mm. Then the inner and outer surfaces are cleaned and straightened.

[0063] Step four: The obtained capillary seamless steel pipe is subjected to external grinding treatment to obtain the final product.

[0064] The product prepared according to the scheme of Comparative Example 1 has an outer diameter of 0.790mm-0.795mm, a wall thickness of 0.082mm-0.098mm, a wall thickness accuracy of ±0.008mm, and an inner wall surface finish (Ra) of 0.461μm.

[0065] Comparative Example 2

[0066] Step 1: Select the same 304L, φ10mmx0.6mm high-precision bright annealing seamless steel pipe raw material as in Example 2, with a billet length of 1000mm.

[0067] Step 2: Roll the φ10mm x 0.6mm material into φ4mm x 0.125mm material using a three-roll cold rolling mill. Cold rolling process: (1) Cold roll the size φ10mmx0.6mm to φ8.3mmx0.48mm, then roll and deform it to φ7.2mmx0.38mm. Clean the inner and outer surfaces of the φ7.2mmx0.38mm pipe, then solution anneal at 1080℃ and hold for 15min; (2) Cold roll the size φ7.2mmx0.38mm to φ6.2mmx0.29mm, then roll and deform it to φ5.3mmx0.22mm. Clean the inner and outer surfaces of the φ5.3mmx0.22mm pipe, then solution anneal at 1080℃ and hold for 15min; (3) Cold roll the size φ5.3mmx0.22mm to φ4.5mmx0.170mm, then roll it to φ4.0mmx0.125mm. Clean the inner and outer surfaces of the φ4.0mmx0.125mm pipe, then solution anneal at 1080℃ and hold for 15min.

[0068] Step 3: Using a coil drawing machine, through 17 cold drawing passes, the capillary seamless steel pipe φ0.59mmx0.05mm is processed by the coil drawing method of the moving mandrel. The cold deformation process of the moving mandrel coil drawing is as follows: (1) The moving mandrel with a size of φ4mmx0.125 is reduced to φ3.45mmx0.110mm, and then continuously drawn to φ2.95mmx0.090mm. The inner and outer surfaces of φ2.95mmx0.090mm are cleaned, and then solution annealed at 1080℃ for 15min; (2) The moving mandrel with a size of φ2.95mmx0.090mm is drawn and reduced to φ2.45mmx0.075mm, and then continuously drawn to φ2.05mmx0.060mm. The inner and outer surfaces of φ2.05mmx0.060mm are cleaned. , then solution anneal at 1050℃ and hold for 15 minutes; (3) draw the floating core head with dimensions φ2.05mmx0.060mm to reduce the wall to φ1.55mmx0.050mm, clean the inner and outer surfaces of φ1.55mmx0.050mm, then solution anneal at 1050℃ and hold for 15 minutes; (4) draw the floating core head with dimensions φ1.55mmx0.050mm to φ1.25mmx0.045mm, then draw it in multiple passes to φ0.59mmx0.05mm, the deformation process of the drawing process is 1.15mm, 1.05mm, 0.95mm, 0.90mm, 0.85mm, 0.79mm, 0.74mm, 0.69mm, 0.64mm, 0.59mm, then clean and straighten the inner and outer surfaces.

[0069] Step four: Perform external grinding on the obtained capillary seamless steel pipe.

[0070] The product prepared by the scheme of Comparative Example 2 has an outer diameter of 0.589mm-0.595mm, a wall thickness of 0.041mm-0.056mm, a wall thickness accuracy of ±0.008mm, and an inner wall surface finish (Ra) of 0.522μm.

[0071] As can be seen from the above embodiments and comparative examples, by using the capillary seamless steel pipe preparation method of the present invention, capillary seamless steel pipe products that meet the end customer's requirements in terms of dimensional deviation, inner and outer surface finish, inner and outer surface quality, and process performance can be obtained. Compared with the products obtained in the comparative examples, the wall thickness accuracy of the products obtained according to the capillary seamless steel pipe preparation method of the present invention is improved from ±0.008mm to ±0.003mm, and the inner surface is also smoother.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a capillary seamless steel tube, characterized in that, The preparation method consists of the following steps performed sequentially: S100. Select austenitic stainless steel seamless steel pipe as the pipe blank, wherein the outer diameter of the pipe blank is 8mm-15mm, the wall thickness is 0.5mm-1.2mm, and the wall thickness accuracy is ±0.015mm; S200. Using a drawing machine with a long mandrel, the tube blank of S100 is cold-drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated. The above cold drawing, cleaning and solution treatment are repeated until a floating drawn blank with an outer diameter of 3.8mm-4.2mm and a wall thickness of 0.125mm-0.3mm is obtained. The hardness of the long mandrel is 780HV-860HV, and the diameter accuracy of the long mandrel is ±0.005μm. S300. Using a drawing machine with a moving mandrel, the moving drawing billet obtained in S200 is cold-drawn. When the deformation compression rate of a single cold drawing is 30%-75%, the inner and outer surfaces are cleaned and solution treated. The above cold drawing, cleaning and solution treatment are repeated to obtain capillary seamless steel pipes with an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm and a wall thickness accuracy of ±0.003mm. S400. The capillary seamless steel pipe obtained by S300 is subjected to external grinding treatment to obtain the final product.

2. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In step S100, the pipe blank has an elongation of more than 55%, a surface finish of less than 0.8μm on both the inner and outer surfaces, and is made of 304L or 316 stainless steel seamless pipe. In step S300, the inner wall smoothness of the obtained capillary seamless steel tube is below 0.6μm and the hardness is not less than 280HV.

3. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In step S200, the material of the long core rod is SKD11 mold steel.

4. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In step S200, the drawing frequency is 3-6Hz, and the elongation coefficient of the tube blank in the cold drawing is 1.2-1.

5.

5. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In step S300, the wall elongation coefficient of the moving mandrel is 1.3-1.5, and the moving mandrel drawing frequency is 20Hz-25Hz; the diameter reduction compression rate of the moving mandrel drawing is 5%-10%, and the moving mandrel drawing frequency is 25Hz-30Hz.

6. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In step S300, the moving core is made of metal ceramic, and the drawing die is a polycrystalline die.

7. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In steps S200 and S300, hydrogen gas is used as the medium for the solution treatment.

8. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, In steps S200 and S300, the solution temperature is 1050℃-1080℃, the holding time is 15min-20min, the heating rate is 30-50℃ / min, the cooling rate is 40-50℃ / min, and the cooling rate after solution treatment is greater than 500℃ / min.

9. The method for preparing capillary seamless steel tubes according to claim 1, characterized in that, The internal and external surface cleaning methods in steps S200 and S300 include the following steps: degreasing and ultrasonic cleaning of internal and external surfaces; cleaning and blowing air into the inner wall; ultrasonic cleaning and drying of the outer surface.

10. A capillary seamless steel pipe, characterized in that, The capillary seamless steel tube is prepared by the preparation method according to any one of claims 1-9, wherein the capillary seamless steel tube has an outer diameter of 0.59mm-1mm, a wall thickness of 0.05mm-0.09mm, a wall thickness accuracy of ±0.003mm, an inner wall smoothness of less than 0.6μm, and a hardness of not less than 280HV.

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