Model selection method for improving surface roughness of cold-drawn refined pipe

Abstract

The invention discloses a model selection method for improving the surface roughness of a cold-drawn refined pipe, and relates to the technical field of cold-drawn steel pipe model selection, and the method comprises the following steps: measuring parameters of steel pipe blank pipes of different specifications before and after drawing deformation; calculating the medium-diameter wall thickness ratio growth rate lambda of the steel tube blanks with different specifications, and implementing the model selection of the steel tube blanks according to the calculated medium-diameter wall thickness ratio growth rate lambda; and after the model selection of the steel pipe blank, cold drawing is performed through a cold-drawing fine pipe process. According to the method, production waste can be avoided in a theoretical calculation mode before production, so that the effective purpose of reasonably formulating a process to implement production is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of cold-drawn steel tube selection, in particular to a selection method for improving the surface roughness of a cold-drawn precision tube. Background Art

[0002] In the production of cold-drawn precision steel tubes, with the development of precision manufacturing, higher and higher product quality requirements are an inevitable trend. Many manufacturers have adopted the method of adding rolling process to specifically improve the surface roughness of products. However, with the continuous development of new technologies and the increasing demand for surface roughness, the advantages of cold-drawn steel tubes have been gradually reduced.

[0003] In view of the above situation, it is particularly important to improve the processing technology of cold-drawn steel tubes. After years of practical summary, the roughness of cold-drawn steel tubes can also be achieved through process control. This application focuses on introducing a new selection method for improving the surface roughness of drawn precision tubes. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art, provide a selection method for improving the surface roughness of cold-drawn precision tubes, change the traditional concept of improving the surface quality of precision tubes, and adopt a theoretical calculation method before production to avoid production waste, thereby achieving the effective purpose of rationally formulating processes and implementing production.

[0005] The object of the present invention is achieved through the following technical scheme: a selection method for improving the surface roughness of a cold-drawn precision tube, the selection method comprising the following steps:

[0006] The outer diameter D1 before drawing deformation, the inner diameter d1 before drawing deformation, the wall thickness T1 before drawing deformation, the outer diameter D2 after drawing deformation, the inner diameter d2 after drawing deformation, and the wall thickness T2 after drawing deformation of steel tube blanks of different specifications are measured.

[0007] The growth rate of the mid-diameter to wall thickness ratio of steel tube blanks of different specifications is calculated. The formula of the growth rate of the mid-diameter to wall thickness ratio is as follows: The steel tube blank is selected by calculating the size of the growth rate Λ of the mid-diameter-to-wall thickness ratio.

[0008] After the steel tube blank is selected, it is cold drawn through the cold drawing precision tube process.

[0009] The cold-drawn precision tube process comprises the following steps: longitudinal shearing, production of steel tube blanks, annealing of steel tube blanks, pickling, phosphating, tipping, drawing, straightening, bundling, oiling, and packaging for storage.

[0010] The steel tube blank can be made of St12 material, the annealing temperature is 760-920℃, and the rotation speed is 950rpm. The steel tube blank can also be made of St37-2G material, the annealing temperature is 830-920℃, and the rotation speed is 900rpm, so as to reduce the strength of the blank tube, improve the plastic deformation ability of the metal, and make the deformation of the metal material consistent during drawing.

[0011] The pickling comprises the following steps: using sulfuric acid with a content of 30% and a temperature of 60-80° C. to corrode the oxide scale produced during annealing on the surface of the steel tube blank, and then washing it with clean water.

[0012] The phosphating process comprises the following steps: at room temperature, the pickled steel tube billet is immersed in a mixed solution of Zn(NO3)2 and Zn(H2PO4)2 for 15 seconds, and a phosphating film is plated on the surface of the steel tube billet to play a lubricating role in drawing.

[0013] The tipping process comprises the following steps: reducing the diameter of one end of the steel tube blank to a size that is convenient for the drawing clamp to clamp.

[0014] The beneficial effects of the present invention are:

[0015] The selection method of the present invention changes the traditional concept of improving the surface quality of precision tubes, and adopts a method of theoretical calculation before production to avoid production waste, thereby achieving the effective purpose of rationally formulating processes and implementing production. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of the drawing structure of the present invention. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0019] The surface roughness of cold-drawn precision tubes is improved by drawing, because the cold-drawn precision tube process is the key process directly facing the blank tube to the finished product. Its principle is to implement plastic deformation of the blank tube to reduce the diameter and wall. The performance and surface quality of the cold-drawn precision tube are directly reflected after drawing. In production, it is found that the blank tubes of the same batch and the same specifications have different surface roughness after going through all the same processes, just because the finished drawing products are different.

[0020] The cold drawn precision tube process is a process of metal plastic deformation. During drawing, the metal flow produces the phenomenon of reducing the wall and diameter of the steel tube, and recombines to form the finished precision tube. The effect of metal flow is directly reflected in the roughness of the surface quality of the precision tube, and the driving force of metal flow comes from the deformation during the drawing process, such as Figure 1 (The blank tube is the steel tube blank tube, the inner mold is the core rod inner mold, the outer mold is the drawing outer mold, and the finished precision tube is the finished precision tube). Therefore, different metal plastic deformations can be used to analyze and summarize the influence of the surface roughness of the cold-drawn precision tube.

[0021] The cold drawn precision tube process includes the following steps: longitudinal shearing → billet tube production → billet tube annealing → pickling → phosphating → pointing → drawing → straightening → bundling and oiling → packaging and warehousing.

[0022] In one embodiment of the present application, different finished tubes are drawn from the same specification steel tube blank to compare the surface roughness:

[0023] Test ① Steel tube blanks are selected with φ38mm×1.8mm (φ38mm refers to the diameter, 1.8mm refers to the wall thickness), and the material is St12 (08 steel), and then annealed to reduce the strength of the blank tube, improve the plastic deformation ability of the metal, and make the deformation of the metal material consistent during drawing. The annealing temperature is 760-920℃, the speed is 950rpm, and then the oxide scale produced during annealing on the surface of the steel tube blank is corroded with sulfuric acid with a content of 30% and a temperature of 60-80℃, and then washed with clean water. At room temperature, the washed steel tube blank is immersed in Zn(N O3)2 and Zn(H2PO4)2 mixed solution for 15 seconds, the surface of the steel tube is coated with a phosphate film to play a lubricating role in drawing. After the phosphate film is coated, the diameter of one end of the steel tube is reduced to 140mm so that it can pass through the drawing outer die during drawing, and the front end is pre-treated for drawing, which is convenient for the drawing clamp to clamp and deform for drawing. The drawing outer die is φ33mm, and the core rod inner die is φ30mm. The steel tube is drawn from φ38mm×1.8mm to φ33mm×1.5mm precision tube. The roughness of the φ33mm×1.5mm cold-drawn precision tube is measured as follows:

[0024]

[0025] Table 1. Roughness sampling statistics of cold drawn precision tube φ33mm×1.5mm

[0026] Test ② uses the same batch of φ38mm×1.8mm steel tube blanks prepared in Test ①, made of St12 (08 steel), and is subjected to the same process of annealing → pickling → phosphating → sharpening → drawing as in Test ①, but the outer drawing die is φ35mm, and the inner core die is φ32mm. The steel tube blank is drawn from φ38mm×1.8mm to φ35mm×1.5mm finished tube. The roughness of the φ35mm×1.5mm cold-drawn tube is measured as follows:

[0027]

[0028]

[0029] Table 2. Roughness sampling statistics of cold drawn precision tube φ35mm×1.5mm

[0030] In another embodiment of the present application, the surface roughness is compared by drawing finished products of the same specification of steel tube blanks with different specifications:

[0031] Test ① Steel tube blanks were selected with a diameter of φ38mm×1.5mm and a material of St37-2G (15 steel), and then annealed to reduce the strength of the blanks and improve the plastic deformation capacity of the metal so that the deformation of the metal material is consistent during drawing. The annealing temperature was 830-920°C and the rotation speed was 900rpm. The oxide scale produced during annealing on the surface of the steel tube blank was corroded with sulfuric acid with a content of 30% and a temperature of 60-80°C, and then washed with clean water. At room temperature, the washed steel tube blanks were immersed in Zn(NO3)2 and Zn(H2PO4 )2 mixed solution for 15 seconds, the surface of the steel tube billet is coated with a phosphate film to play a lubricating role in drawing. After the phosphate film is coated, the diameter of one end of the steel tube billet is reduced to 140mm so that it can pass through the drawing outer die during drawing, and the front end of the drawing is pre-treated to facilitate the clamping of the drawing claw for drawing deformation. The drawing outer die is φ32.4mm, and the core rod inner die is φ30mm. The steel tube billet is drawn from φ38mm×1.5mm to φ32.4mm×1.2mm finished precision tube. The roughness of the φ32.4mm×1.2mm cold-drawn precision tube is measured as follows:

[0032]

[0033]

[0034] Table 3. Roughness sampling statistics of cold drawn precision tube φ32.4mm×1.2mm

[0035] In test ②, the steel tube blank was selected as φ35mm×1.5mm, and the material was St37-2G (15 steel). After the same process of annealing → pickling → phosphating → sharpening → drawing in test ①, the drawing outer die was selected as φ32.4mm, and the mandrel inner die was selected as φ30mm. The steel tube blank was drawn from φ35mm×1.5mm to φ32.4mm×1.2mm finished tube. The roughness of the φ32.4mm×1.2mm cold-drawn tube was measured as follows:

[0036]

[0037] Table 4. Roughness sampling statistics of cold drawn precision tube φ32.4mm×1.2mm

[0038] Through the four tests of the two embodiments, it can be found that under the same process and the same material conditions, when the specifications of the steel tube blanks used before drawing deformation are different or the specifications of the finished drawn tubes are different, the surface roughness of the finished tubes is completely different. This is the inevitable result of metal flow and plastic deformation during metal processing. As for how to quantify the influence of metal flow and deformation on the surface roughness of the finished product during drawing, the present application adopts the growth rate of the middle diameter to wall thickness ratio Λ to quantitatively describe it. The middle diameter is the middle value of the inner and outer diameters of the steel tube, and the middle diameter to wall thickness ratio is the ratio of the middle diameter value of the steel tube to its corresponding wall thickness. Then the growth rate of the middle diameter to wall thickness ratio refers to the percentage increase of the middle diameter to wall thickness ratio of the steel tube after deformation relative to the middle diameter to wall thickness ratio before deformation. The formula of the growth rate of the middle diameter to wall thickness ratio Λ is as follows: The steel tube blank selection is implemented by calculating the size of the growth rate Λ of the mid-diameter-to-wall thickness ratio; wherein D1 is the outer diameter before drawing deformation, d1 is the inner diameter before drawing deformation, T1 is the wall thickness before drawing deformation, D2 is the outer diameter after drawing deformation, d2 is the inner diameter after drawing deformation, and T2 is the wall thickness after drawing deformation.

[0039] According to the above formula for the growth rate of the median diameter to wall thickness ratio Λ, we can obtain the calculation results of different schemes under the above test scheme as follows:

[0040]

[0041] Table 5. Growth rate of the mid-diameter-to-wall thickness ratio and its roughness of steel pipes of different specifications drawn

[0042] From the above statistics, it can be seen that when the growth rate of the middle diameter wall thickness ratio before and after the steel tube deformation increases, the roughness of the finished fine tube will decrease. For example, the steel tube blank is selected The finished fine tube can be pulled out The finished fine tube can also be pulled out The growth rates of the mid-diameter to wall thickness ratio Λ were -1.22% and 1.22% respectively. It was found that the growth rate of the mid-diameter to wall thickness ratio Λ was small or even negative. The growth rate of the mid-diameter to wall thickness ratio Λ was calculated to recalculate the finished precision tube. and The steel tube blank is selected, and optional The steel tube blanks were used to produce the above two specifications of precision tubes, and the roughness was immediately significantly improved. The results are as follows:

[0043]

[0044] Table 6. Growth rate and roughness of the middle diameter to wall thickness ratio of steel tube blank after drawing

[0045] In this way, the steel tube blank selection can be completed according to the size of the growth rate of the mid-diameter-to-wall thickness ratio Λ, so as to achieve the purpose of improving the surface roughness of the refined tube.

[0046] The above is only an embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A selection method for improving the surface roughness of a cold-drawn precision tube, characterized in that: The following steps are involved: Measure the outer diameter D1 before drawing deformation, the inner diameter d1 before drawing deformation, the wall thickness T1 before drawing deformation, the outer diameter D2 after drawing deformation, the inner diameter d2 after drawing deformation, and the wall thickness T2 after drawing deformation of steel tube blanks of different specifications; Calculate the growth rate Λ of the center diameter to wall thickness ratio of steel tube blanks of different specifications. The formula for the growth rate Λ of the center diameter to wall thickness ratio is as follows: The steel tube blank is selected by calculating the growth rate Λ of the median diameter to wall thickness ratio; After the steel tube blank is selected, it is cold drawn through the cold drawing precision tube process.

2. A method for improving the surface roughness of a cold-drawn precision tube according to claim 1, characterized in that: The cold-drawn precision tube process comprises the following steps: longitudinal shearing, production of steel tube blanks, annealing of steel tube blanks, pickling, phosphating, tipping, drawing, straightening, bundling, oiling, and packaging for storage.

3. A method for improving the surface roughness of a cold-drawn precision tube according to claim 2, characterized in that: The steel tube blank is made of St12 material, the annealing temperature is 760-920℃, and the rotation speed is 950rpm.

4. A method for improving the surface roughness of a cold-drawn precision tube according to claim 2, characterized in that: The steel tube blank is made of St37-2G material, the annealing temperature is 830-920℃, and the rotation speed is 900rpm.

5. A method for improving the surface roughness of a cold-drawn precision tube according to any one of claims 2 to 4, characterized in that: The pickling comprises the following steps: using sulfuric acid with a content of 30% and a temperature of 60-80° C. to corrode the oxide scale produced during annealing on the surface of the steel tube blank, and then washing it with clean water.

6. A method for improving the surface roughness of a cold-drawn precision tube according to any one of claims 2 to 4, characterized in that: The phosphating process comprises the following steps: at room temperature, the pickled steel tube billet is immersed in a mixed solution of Zn(NO3)2 and Zn(H2PO4)2 for 15 seconds, and a phosphating film is plated on the surface of the steel tube billet.

7. A method for improving the surface roughness of a cold-drawn precision tube according to any one of claims 2 to 4, characterized in that: The tipping process comprises the following steps: reducing the diameter of one end of the steel tube blank to a size that is convenient for the drawing clamp to clamp.

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