Drawing die and drawing method for improving surface quality of high-temperature alloy pipe

Abstract

The invention discloses a drawing die and a drawing method for improving the surface quality of a high-temperature alloy pipe, the drawing die is simple in structure and reasonable in design, rolling friction on the surface of the high-temperature alloy pipe in cold rolling deformation is changed into sliding friction on the surface of the high-temperature alloy pipe in the drawing process, and the surface quality of the high-temperature alloy pipe is improved in the drawing process. The outer die gradually extrudes through the first outer extrusion section and the second outer extrusion section and finally determines the outer diameter of the high-temperature alloy pipe through the outer sizing section; the floating core block gradually extrudes through the first inner extrusion section and the second inner extrusion section and finally determines the inner diameter of the high-temperature alloy pipe through the inner sizing section; the moving core block is matched with the outer die to realize stepped drawing deformation, and compared with rolling, the defects such as surface pits, wrinkles and microcracks can be effectively reduced, so that the purpose of improving the quality of the inner surface and the outer surface of the high-temperature alloy pipe is achieved; the problem that the surface quality of the existing small-caliber high-temperature alloy pipe is poor can be effectively solved, and the surface quality and the yield of the small-caliber high-temperature alloy pipe can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature alloy pipe processing, and particularly relates to a drawing die and a drawing method for improving the surface quality of a high-temperature alloy pipe. Background Art

[0002] High-temperature alloy pipes are widely used in the lubrication and fuel pipeline systems of aircraft engines due to their advantages such as high strength, good corrosion resistance, good oxidation resistance and the ability to maintain good mechanical properties for a long time under high temperature and high pressure environments. However, the high-temperature alloy pipes used in the lubrication and fuel pipeline systems of aircraft engines not only have a small diameter, but also have a relatively harsh working environment, so the quality requirements for the high-temperature alloy pipes used are relatively high.

[0003] At present, small-diameter high-temperature alloy pipes are generally rolled by multiple rollers. During processing, the inner and outer surfaces of the pipe are subjected to rolling friction along the rolling direction. During the rolling process, not only will repeated biting aggravate the degree of mold sticking between the pipe and the mold, but repeated rolling can easily lead to defects such as pits, orange peel, wrinkles, and microcracks on the surface of the pipe. In addition, due to the small diameter of the pipe, it is more difficult to deal with the defects on the inner surface and difficult to effectively remove them. The pits, orange peel, wrinkles, microcracks and other defects on the inner and outer surfaces of the pipe will not only cause the process performance of the pipe to be expanded, flattened, bent and other processing to drop sharply, but also have a huge impact on the subsequent performance of the pipe, which leads to a low yield of high-temperature alloy pipes that meet the quality requirements. The floating drawing technology is a common method for producing easily deformable metal pipes. During drawing, the surface of the pipe is subjected to the action of sliding friction, which causes the surface layer of the pipe to produce compressive stress deformation, which can effectively reduce and reduce the original surface defects, improve the surface defects caused by sticking to the mold and repeated rolling, thereby improving the surface quality of the pipe; but due to the high strength and hardness of high-temperature alloys and their high brittleness, cracks are prone to occur during processing, and high-temperature alloys have a close-packed structure at room temperature, with fewer slip systems that can participate in deformation. During plastic deformation, the orientation of each grain will also undergo a directional rotation to form a texture. Therefore, high requirements are placed on the mechanical balance system of the pipe wall reduction process, which makes the thinning and drawing of small-diameter high-temperature alloy pipes a technical bottleneck that has not been overcome in China for many years. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a drawing die and a drawing method for improving the surface quality of a high-temperature alloy tube, so as to solve the current technical problem that the surface quality of small-diameter high-temperature alloy tubes is poor, and to achieve the effect of improving the surface quality and yield rate of small-diameter high-temperature alloy tubes.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: A drawing die for improving the surface quality of a high-temperature alloy pipe comprises an outer die and a floating core block used in conjunction with each other; a drawing extrusion hole is penetrated through the outer die, and the hole wall of the drawing extrusion hole is axially divided into a first outer extrusion section, a second outer extrusion section and an outer sizing section, the first outer extrusion section and the second outer extrusion section have a taper, an end of the first outer extrusion section with a small diameter is smoothly connected to an end of the second outer extrusion section with a large diameter, and an end of the second outer extrusion section with a small diameter is smoothly connected to the outer sizing section; the floating core block is a rotating body and axially divided into a matching section, a first inner extrusion section, a second inner extrusion section and an inner sizing section, the first inner extrusion section and the second inner extrusion section have a taper, an end of the first inner extrusion section with a large diameter is smoothly connected to the matching section, an end of the first inner extrusion section with a small diameter is smoothly connected to an end of the second inner extrusion section with a large diameter, and an end of the second inner extrusion section with a small diameter is smoothly connected to the inner sizing section.

[0006] Furthermore, the semi-cone angle of the first outer extrusion section is 12° to 22°, the semi-cone angle of the second outer extrusion section is 6° to 13°, and the length of the outer sizing section is 1 mm to 6 mm.

[0007] Furthermore, the semi-cone angle of the first outer extrusion section is greater than the semi-cone angle of the second outer extrusion section, and the difference between the semi-cone angle of the first outer extrusion section and the semi-cone angle of the second outer extrusion section is 3° to 9°.

[0008] Furthermore, the length of the second outer extrusion section is 1.2 to 3 times the length of the first outer extrusion section.

[0009] Furthermore, the length of the fitting section is 0.5 mm to 3 mm, the semi-cone angle of the first inner extrusion section is 10° to 20°, the semi-cone angle of the second inner extrusion section is 5° to 12°, and the length of the inner sizing section is 2 mm to 7 mm.

[0010] Furthermore, the semi-cone angle of the first inner extrusion section is greater than the semi-cone angle of the second inner extrusion section, and the difference between the semi-cone angle of the first inner extrusion section and the semi-cone angle of the second inner extrusion section is 3° to 9°.

[0011] Furthermore, the length of the first inner extrusion section is 1.2 to 3 times the length of the second inner extrusion section.

[0012] Furthermore, the semi-cone angle of the first outer extrusion section is greater than the semi-cone angle of the first inner extrusion section, and the difference between the semi-cone angle of the first outer extrusion section and the semi-cone angle of the first inner extrusion section is 1° to 3°.

[0013] Furthermore, the first outer extrusion section and the second outer extrusion section are smoothly connected via an arc surface with a radius of 3 mm to 8 mm, and the first inner extrusion section and the second inner extrusion section are smoothly connected via an arc surface with a radius of 3 mm to 8 mm.

[0014] The present invention also includes a drawing method for improving the surface quality of a high-temperature alloy tube, the drawing method uses the drawing die as described above, and the drawing method is: a high-temperature alloy material is rolled to obtain a drawn tube blank, an oxide film is formed on the surface of the drawn tube blank by heat treatment and a lubricant is applied, one end of the drawn tube blank is rolled to form a drawing tip, a floating core block is placed from the other end of the drawn tube blank, and the inner sizing section is directed toward and close to the drawing tip; the outer die is installed on the die base of the drawing machine, and in the direction from the first outer extrusion section to the outer sizing section, the drawing tip is placed in the drawing extrusion hole and the drawn tube blank is drawn to obtain a drawn tube; the drawn tube is sequentially deoiled, pickled, annealed and straightened to obtain a high-temperature alloy tube with inner and outer surface roughness less than or equal to 1.6 μm.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The drawing die of the present invention has a simple structure and a reasonable design. The rolling friction on the surface of the high-temperature alloy tube during cold rolling deformation is changed to sliding friction during the drawing process. During the drawing process, the outer die is gradually extruded through the first outer extrusion section and the second outer extrusion section and finally determines the outer diameter of the high-temperature alloy tube through the outer sizing section. The floating core block is gradually extruded through the first inner extrusion section and the second inner extrusion section and finally determines the inner diameter of the high-temperature alloy tube through the inner sizing section. The floating core block cooperates with the outer die to realize step drawing deformation. Compared with rolling, surface defects such as surface pits, wrinkles, and microcracks can be effectively reduced, thereby achieving the purpose of improving the quality of the inner and outer surfaces of the high-temperature alloy tube.

[0016] 2. The drawing die of the present invention realizes step-by-step wall reduction drawing by cooperating with the floating core block and the outer die, which not only makes the inner and outer surfaces of the high-temperature alloy pipe smoother, but also improves the distribution state of residual stress inside the high-temperature alloy pipe, which is beneficial to prolonging the service life of the high-temperature alloy pipe.

[0017] 3. The drawing method of the present invention adopts the drawing die, which can not only realize single-pass large diameter reduction deformation, which is beneficial to improving production efficiency, but also improve the surface quality of high-temperature alloy pipes and increase product qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the drawing die described in the embodiment; Figure 2 It is a structural schematic diagram of the outer mold described in the embodiment; Figure 3 It is a structural schematic diagram of the floating core block described in the embodiment; Figure 4 It is a schematic diagram of the use of the drawing die described in the embodiment; Among them, the outer die 1, the first outer extrusion section 11, the second outer extrusion section 12, the outer sizing section 13; the floating core block 2, the matching section 21, the first inner extrusion section 22, the second inner extrusion section 23, the inner sizing section 24, the connecting section 25, the transition section 26, the guide section 27; the drawn tube 3, the drawing rolling tip 31; the drawing machine 4, the die base 41. DETAILED DESCRIPTION

[0019] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0020] Embodiment 1: See also Figure 1 , Figure 2 and Figure 3 A drawing die for improving the surface quality of a high-temperature alloy tube comprises an outer die 1 and a movable core block 2 used in conjunction with each other; a drawing and extrusion hole is provided through the outer die 1, and the hole wall of the drawing and extrusion hole is axially divided into a first outer extrusion section 11, a second outer extrusion section 12 and an outer sizing section 13, the first outer extrusion section 11 and the second outer extrusion section 12 are tapered, the end with a small diameter of the first outer extrusion section 11 is smoothly connected to the end with a large diameter of the second outer extrusion section 12, and the end with a small diameter of the second outer extrusion section 12 is connected to the outer sizing section 13. The sizing section 13 is smoothly connected; the movable core block 2 is a rotating body and is divided into a matching section 21, a first inner extrusion section 22, a second inner extrusion section 23 and an inner sizing section 24 along the axial direction. The first inner extrusion section 22 and the second inner extrusion section 23 are tapered. The end with a larger diameter of the first inner extrusion section 22 is smoothly connected to the matching section 21, the end with a smaller diameter of the first inner extrusion section 22 is smoothly connected to the end with a larger diameter of the second inner extrusion section 23, and the end with a smaller diameter of the second inner extrusion section 23 is smoothly connected to the inner sizing section 24.

[0021] See also Figure 4 The process of drawing a high-temperature alloy tube by using the drawing die of the present invention is roughly as follows: a high-temperature alloy material is rolled to obtain a drawn tube blank 3, an oxide film is formed on the surface of the drawn tube blank 3 by heat treatment and a lubricant is applied; one end of the drawn tube blank 3 is rolled to form a drawing tip 31, a floating core block 2 is placed from the other end of the drawn tube blank 3, and the inner sizing section 24 is directed toward and close to the drawing tip 31; the outer die 1 is installed on the die base 41 of the drawing machine 4, and the drawing tip 31 is placed in the drawing extrusion hole in the direction from the first outer extrusion section 11 to the outer sizing section 13, and the drawn tube blank 3 is drawn to obtain a drawn tube; the drawn tube is deoiled, pickled, annealed and straightened in sequence to obtain a high-temperature alloy tube.

[0022] The drawing die of the present invention has a simple structure and a reasonable design. The rolling friction on the surface of the high-temperature alloy tube during cold rolling deformation is changed to sliding friction during the drawing process. During the drawing process, the outer die 1 is gradually extruded through the first outer extrusion section 11 and the second outer extrusion section 12 and finally determines the outer diameter of the high-temperature alloy tube through the outer sizing section 13. The floating core block 2 is gradually extruded through the first inner extrusion section 22 and the second inner extrusion section 23 and finally determines the inner diameter of the high-temperature alloy tube through the inner sizing section 24. The floating core block 2 cooperates with the outer die 1 to achieve step drawing deformation. Compared with rolling, surface defects such as surface pits, wrinkles, and microcracks can be effectively reduced, thereby achieving the purpose of improving the inner and outer surface quality of the high-temperature alloy tube. It can effectively solve the problem of poor surface quality of small-diameter high-temperature alloy tubes at present, which is beneficial to improving the surface quality and yield rate of small-diameter high-temperature alloy tubes.

[0023] The drawing die of the present invention realizes step-by-step wall reduction drawing by cooperating with the floating core block 2 and the outer die 1, which not only makes the inner and outer surfaces of the high-temperature alloy pipe smoother, but also improves the distribution state of residual stress inside the high-temperature alloy pipe, which is beneficial to improving the service life of the high-temperature alloy pipe; the drawing method of the present invention adopts the drawing die, which can not only realize single-pass large diameter reduction deformation, which is beneficial to improving production efficiency, but also can improve the surface quality of the high-temperature alloy pipe and increase the product qualification rate.

[0024] See also Figure 2 and Figure 3 On the outer mold 1, the first outer extrusion section 11 is smoothly connected with the adjacent end surface through an arc surface, and the second outer extrusion section 12 is smoothly connected with the adjacent end surface through an arc surface. The outer mold 1 is integrally processed; on the floating core block 2, the end of the matching section 21 away from the first inner extrusion section 22 also has a connecting section 25, the diameter of the connecting section 25 is smaller than the matching section 21, and the matching section 21 and the connecting section 25 are connected through a tapered transition section 26, the maximum diameter of the transition section 26 is equal to the diameter of the matching section 21, and the end of the transition section 26 with a larger diameter is connected to the matching section 21, The minimum diameter of the transition section 26 is equal to the diameter of the connecting section 25, and the end of the transition section 26 with a smaller diameter is connected to the connecting section 25. The connecting section 25 is used to clamp the floating core block 2 when in use. The end of the inner sizing section 24 away from the second inner extrusion section 23 also has a guide section 27. The guide section 27 has a taper. The maximum diameter of the guide section 27 is equal to the diameter of the inner sizing section 24, and the end of the guide section 27 with a larger diameter is connected to the inner sizing section 24. The guide section 27 is used to reduce the end diameter of the floating core block 2 so as to place it into the drawn tube blank 3. The floating core block 2 is formed as an integral part.

[0025] During implementation, for the size of the outer die: the semi-cone angle of the first outer extrusion section is denoted as α1, the semi-cone angle of the second outer extrusion section is denoted as α2, the length of the outer sizing section is denoted as L1, the length of the second outer extrusion section is denoted as L2, and the length of the first outer extrusion section is denoted as L3; the value range of α1 should be 12° to 22°, the value range of α2 should be 6° to 13°, α1 should be greater than α2, and the difference between α1 and α2 should be within the range of 3° to 9°. During drawing, the deformation and stress of the outer surface of the pipe are greater, so α1 should be greater than β1, and the difference between α1 and β1 should be within the range of 1° to 3°. The value range of L1 should be 1mm to 6mm, and L2 should be 1.2 to 3 times of L3; the first outer extrusion section and the second outer extrusion section should be smoothly connected by an arc surface with a radius of 3mm to 8mm; For the size of the floating core block: the semi-cone angle of the first inner extrusion section is denoted as β1, the semi-cone angle of the second inner extrusion section is denoted as β2, the length of the fitting section is denoted as L4, the length of the first inner extrusion section is denoted as L5, the length of the second inner extrusion section is denoted as L6, and the length of the inner sizing section is denoted as L7; the value range of β1 should be 10°~20°, the value range of β2 should be 5°~12°, β1 should be greater than β2, and the difference between β1 and β2 should be in the range of 3°~9°, the value range of L4 should be 0.5mm~3mm, L5 should be 1.2 times to 3 times of L6, and the value range of L7 should be 2mm~7mm; the first inner extrusion section and the second inner extrusion section should be smoothly connected by an arc surface with a radius of 3mm~8mm.

[0026] In this embodiment, the dimensions of the outer die and the floating core block are as follows: α1 is 18°, α2 is 13°, L1 is 3 mm, L2 is 1.5 times of L3, L2 is 2.625 mm, and L3 is 1.75 mm; the first outer extrusion section and the second outer extrusion section are smoothly connected by an arc surface with a radius of 4 mm, β1 is 15°, β2 is 12°, L4 is 1 mm, L7 is 2.5 mm, L5 is 1.8 times of L6, L5 is 5.04 mm, and L6 is 2.8 mm; the drawing die based on the selected dimensions is used to draw the pipe as follows: A drawn tube blank with a specification of Φ20mm×1.5mm, a material of a high-temperature alloy and a chemical composition meeting the standard requirements is selected, a dense oxide film is formed on the surface of the drawn tube blank by heat treatment, a conventional lubricant is poured into the inner surface of the drawn tube blank, and a conventional lubricant is applied to the outer surface of the drawn tube blank, one end of the drawn tube blank is rolled to form a drawing tip, a floating core block is placed from the other end of the drawn tube blank, and the inner sizing section is directed toward and close to the drawing tip; the outer die is installed on the die base of the drawing machine, and the drawing tip is placed in the drawing extrusion hole in the direction from the first outer extrusion section to the outer sizing section, and the drawn tube blank is drawn, and a drawn tube of Φ18mm×1.0mm is drawn in one pass, and the drawn tube is subjected to conventional degreasing treatment, conventional pickling treatment and vacuum annealing treatment in sequence, and then straightened and cut to obtain a high-quality high-temperature alloy tube. The inner and outer surface roughness Ra of the high-temperature alloy tube manufactured in this embodiment are both 1.0μm.

[0027] Embodiment 2: The difference from Example 1 is that the dimensions of the outer die and the floating core block are respectively taken as follows in this embodiment: α1 is 16°, α2 is 10°, L1 is 2.5 mm, L2 is 1.4 times of L3, L2 is 2.24 mm, and L3 is 1.6 mm; the first outer extrusion section and the second outer extrusion section are smoothly connected by an arc surface with a radius of 5 mm, β1 is 15°, β2 is 12°, L4 is 0.5 mm, L7 is 2 mm, L5 is 1.6 times of L6, L5 is 3.52 mm, and L6 is 2.2 mm; the drawing die based on the selected dimensions is used to draw the pipe as follows: A drawing tube blank with a specification of Φ19mm ×1.8mm, a material of high-temperature alloy and a chemical composition that meets the standard requirements is selected, and a dense oxide film is formed on the surface of the drawing tube blank through pickling, drying and heat treatment, and a conventional lubricant is poured into the inner surface of the drawing tube blank, and a conventional lubricant is applied to the outer surface of the drawing tube blank, and one end of the drawing tube blank is rolled to form a drawing tip, and a floating core block is placed from the other end of the drawing tube blank, and the inner sizing section is directed toward and close to the drawing tip; the outer die is installed on the die base of the drawing machine, and the drawing tip is placed in the drawing extrusion hole in the direction from the first outer extrusion section to the outer sizing section, and the drawing tube blank is drawn, and one pass is drawn to Φ16mm ×1.2mm drawn tube, the drawn tube is sequentially subjected to conventional annealing treatment, and then subjected to conventional finish rolling and straightening to obtain high-quality high-temperature alloy tube. The inner and outer surface roughness Ra of the high-temperature alloy tube manufactured in this embodiment are both 0.8μm, and the flaw detection qualified rate is 80%. At the same time, compared with the high-temperature alloy tube of the same specification manufactured by the conventional rolling process, the metal flow on the inner surface of the rolled tube has significant directionality, and obvious wrinkles, pits and other defects can be observed. The density and flatness of the inner surface are worse than those of the tube drawn by the drawing die described in this embodiment. It can be seen that the present invention can effectively improve the inner and outer surface quality of the high-temperature alloy tube and improve the finished product qualified rate of the high-temperature alloy tube.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the technical solution. Those skilled in the art should understand that those modifications or equivalent substitutions of the technical solution of the present invention that do not depart from the purpose and scope of the technical solution should be included in the scope of the claims of the present invention.

Claims

1. A drawing die for improving the surface quality of a high-temperature alloy tube, characterized in that: It comprises an outer die and a movable core block for use in conjunction with each other; a drawing and extrusion hole is penetrated through the outer die, and the hole wall of the drawing and extrusion hole is axially divided into a first outer extrusion section, a second outer extrusion section and an outer sizing section, the first outer extrusion section and the second outer extrusion section have a taper, the end of the first outer extrusion section with a smaller diameter is smoothly connected to the end of the second outer extrusion section with a larger diameter, and the end of the second outer extrusion section with a smaller diameter is smoothly connected to the outer sizing section; the movable core block is a rotating body and is axially divided into a matching section, a first inner extrusion section, a second inner extrusion section and an inner sizing section, the first inner extrusion section and the second inner extrusion section have a taper, the end of the first inner extrusion section with a larger diameter is smoothly connected to the matching section, the end of the first inner extrusion section with a smaller diameter is smoothly connected to the end of the second inner extrusion section with a larger diameter, and the end of the second inner extrusion section with a smaller diameter is smoothly connected to the inner sizing section.

2. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 1, characterized in that: The semi-cone angle of the first outer extrusion section is 12° to 22°, the semi-cone angle of the second outer extrusion section is 6° to 13°, and the length of the outer sizing section is 1mm to 6mm.

3. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 2, characterized in that: The semi-cone angle of the first outer extrusion section is greater than the semi-cone angle of the second outer extrusion section, and the difference between the semi-cone angle of the first outer extrusion section and the semi-cone angle of the second outer extrusion section is 3° to 9°.

4. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 2, characterized in that: The length of the second outer extrusion section is 1.2 to 3 times the length of the first outer extrusion section.

5. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 1, characterized in that: The length of the fitting section is 0.5 mm to 3 mm, the semi-cone angle of the first inner extrusion section is 10° to 20°, the semi-cone angle of the second inner extrusion section is 5° to 12°, and the length of the inner sizing section is 2 mm to 7 mm.

6. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 5, characterized in that: The semi-cone angle of the first inner extrusion section is greater than the semi-cone angle of the second inner extrusion section, and the difference between the semi-cone angle of the first inner extrusion section and the semi-cone angle of the second inner extrusion section is 3° to 9°.

7. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 5, characterized in that: The length of the first inner extrusion section is 1.2 to 3 times the length of the second inner extrusion section.

8. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 1, characterized in that: The semi-cone angle of the first outer extrusion section is greater than the semi-cone angle of the first inner extrusion section, and the difference between the semi-cone angle of the first outer extrusion section and the semi-cone angle of the first inner extrusion section is 1° to 3°.

9. A drawing die for improving the surface quality of a high-temperature alloy tube according to claim 1, characterized in that: The first outer extrusion section and the second outer extrusion section are smoothly connected via an arc surface with a radius of 3mm to 8mm, and the first inner extrusion section and the second inner extrusion section are smoothly connected via an arc surface with a radius of 3mm to 8mm.

10. A drawing method for improving the surface quality of a high-temperature alloy tube, characterized in that: The drawing method uses the drawing die as described in any one of claims 1 to 9, and the drawing method is: a high-temperature alloy material is rolled to obtain a drawn tube blank, an oxide film is formed on the surface of the drawn tube blank by heat treatment and a lubricant is applied, one end of the drawn tube blank is rolled to form a drawing tip, a floating core block is placed from the other end of the drawn tube blank, and the inner sizing section is directed toward and close to the drawing tip; the outer die is installed on the die base of the drawing machine, and in the direction from the first outer extrusion section to the outer sizing section, the drawing tip is placed in the drawing extrusion hole and the drawn tube blank is drawn to obtain a drawn tube; the drawn tube is deoiled, pickled, annealed and straightened in sequence to obtain a high-temperature alloy tube with inner and outer surface roughness less than or equal to 1.6 μm.

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