CN109520840B - Calculation method for detecting yield strength of pipe on line - Google Patents

Calculation method for detecting yield strength of pipe on line Download PDF

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CN109520840B
CN109520840B CN201811596853.0A CN201811596853A CN109520840B CN 109520840 B CN109520840 B CN 109520840B CN 201811596853 A CN201811596853 A CN 201811596853A CN 109520840 B CN109520840 B CN 109520840B
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yield strength
flattening
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马立东
杜宇康
马立峰
刘佩钰
刘子健
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Taiyuan University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0014—Type of force applied
    • G01N2203/0016—Tensile or compressive
    • G01N2203/0019—Compressive
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
    • G01N2203/0075—Strain-stress relations or elastic constants
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/02—Details not specific for a particular testing method
    • G01N2203/026—Specifications of the specimen
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Abstract

The invention provides a calculation method for detecting yield strength of a pipe on line, which comprises the following steps: pressing down a press machine provided with a pressure sensing device to flatten the end part of the pipe, stopping pressing down the press machine when the flattening force reaches the maximum elastic deformation, and reading the maximum elastic flattening force through an empirical curve; the actual yield strength of the pipe is calculated by the following formula: sigmat＝FmaxR0/(yπWz) Wherein σ istFor the actual yield strength to be calculated, y is the fitting ratio, FmaxFor the actual maximum elastic deformation of the read-out flattening force, R0Is an average radius, WzIs the modulus of elasticity of the annular wall of the annular tube. According to the calculation method for the on-line detection of the yield strength of the pipe, the actual yield strength of the pipe obtained through calculation is more accurate than the theoretical yield strength, and when the calculation method is used for straightening the pipe, the calculation method is beneficial to reducing errors in the flattening force calculation process and reducing errors of straightening process parameters.

Description

Calculation method for detecting yield strength of pipe on line
Technical Field
The invention relates to the technical field of pipe rolling, in particular to a calculation method for detecting yield strength of a pipe on line.
Background
The production quality of the pipe serving as one of important products in the rolling industry directly reflects the economic development level of a country. Under the technical background of gradually improved required quality and increasingly perfect rolling process, domestic and foreign enterprises pay attention to development and innovation of the straightening machine. Taking a pipe and bar straightening machine as an example, particularly when a pipe is straightened, in the prior art, in the straightening process, one method is to draw the relationship between the flattening amount and the flattening force through experience, and when the pipe is straightened, the flattening force is directly read through experience, and the straightening parameters are adjusted.
The other method is to obtain the flattening force by a calculation method and adjust the technological parameters of the straightener by calculating the flattening force. However, there is an important parameter in calculating the yield strength σ in the process of flatteningtThe actual yield strength of the steel of the same grade is a range value, and the more accurate the yield strength is in the production process, the more accurate the calculated flattening force is, the more effective the adjustment of the technological parameters of the straightening machine is, and the better the straightening effect of the pipe is.
In the prior art, the yield strength sigma is adopted when the flattening force is calculatedtThe crushing force is calculated, whereas the yield strength σ istThe theoretical value and the actual value have different degrees of deviation, which brings errors to the accuracy of the calculated result of the flattening force and causes the deviation of the adjustment of the process parameters of the straightening machine.
Therefore, in order to solve the problems in the prior art, a calculation method for online detection of yield strength of a pipe is needed to reduce errors of pipe straightening process parameters.
Disclosure of Invention
One aspect of the present invention provides a method for calculating yield strength of a pipe by online detection, wherein the method comprises the following steps:
pressing down a press machine provided with a pressure sensing device to flatten the end part of the pipe, stopping pressing down the press machine when the flattening force reaches the maximum elastic deformation, and reading the maximum elastic flattening force through an empirical curve;
the actual yield strength of the pipe was calculated by the following method: sigmat＝FmaxR0/(yπWz) Wherein, in the step (A),
σtfor the actual yield strength to be calculated, y is the fitting ratio, FmaxFor the actual maximum elastic deformation of the read-out flattening force, R0Is the average radius of the pipe, WzModulus of elasticity of wall of annular tube, Wz＝b2And/6, wherein b is the width of the annular pipe and is the thickness of the pipe wall.
In one embodiment, the fitting ratio is fitted by fitting a curve a plurality of times as follows:
y＝Ax+Bx2+Cx3+Dx4wherein A, B, C, D is a undetermined coefficient, and x is the ratio of the diameter of the pipe to the wall thickness of the pipe.
In one embodiment, the fitting ratio is fitted by a binary cubic fit curve as follows:
y＝aD+bx3+ c, wherein a, b and c are undetermined coefficients, x is the ratio of the diameter of the pipe to the wall thickness of the pipe, and D is the diameter of the pipe.
Another aspect of the present invention provides a method of calculating a maximum elastic crushing force, comprising:
cutting a section of annular pipe at the flattening position as a separating body, wherein the width of the cut annular pipe is b, the thickness of the pipe wall is b, and the diameter of the annular pipe is the direct average value R of the pipe0，
Selecting any angle by taking the circle center of the annular tube separating body as a vertex
Figure BDA0001921519960000021
Figure BDA0001921519960000022
When in use
Figure BDA0001921519960000023
Then, the maximum flattening force was calculated by the following method: FDmax＝πσtWz/R0，
Wherein FDmaxFor the calculated maximum spring flattening force, R0Direct average of pipe material, WzModulus of elastic section of annular wall, sigma, of annular tube separatortIs the calculated actual yield strength.
According to the calculation method for the yield strength of the pipe in the online detection, the maximum elastic flattening force of the empirical curve is read, the fitting proportion is obtained by using the curve fitting method, the actual yield strength of the pipe is obtained by reversely pushing and calculating, and the calculated yield strength is more accurate than the theoretical yield strength, so that the calculated flattening force is more accurate, and the effective adjustment of the process parameters of the straightener is realized.
According to the calculation method for the on-line detection of the yield strength of the pipe, the actual yield strength of the pipe obtained through calculation is more accurate than the theoretical yield strength, and when the calculation method is used for straightening the pipe, the calculation method is beneficial to reducing errors in the flattening force calculation process and reducing errors of straightening process parameters.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
Drawings
Further objects, features and advantages of the present invention will become apparent from the following description of embodiments of the invention, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view showing an annular elastic cross-sectional structure of an annular tube at the end of a pipe material of the present invention.
Fig. 2 is an empirical plot of crush force versus crush volume obtained from a crush experiment.
FIG. 3 is a schematic diagram of the flattening calculation process for a tube according to the present invention.
Detailed Description
The objects and functions of the present invention and methods for accomplishing the same will be apparent by reference to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it can be implemented in different forms. The nature of the description is merely to assist those skilled in the relevant art in a comprehensive understanding of the specific details of the invention. Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numerals denote the same or similar parts, or the same or similar steps. The following description of the present invention is provided by way of specific embodiments, and according to the present invention, in order to solve the error occurring in the flattening calculation process in the prior art, a calculation method for online detecting yield strength of a pipe is provided, which calculates the actual yield strength used in the flattening calculation process, and reduces the yield strength σtThe error of the theoretical value and the actual value of (c).
According to the embodiment of the invention, a pipe needing straightening is cut out, and a section of annular pipe at the end of the pipe is used for calculating the actual yield strength. The annular pipe is arranged below a press machine provided with a pressure sensor, and the annular pipe is pressed downwards. As shown in FIG. 1, the annular elastic section of the annular tube at the end of the tube of the present invention is schematically shown, the width of the annular tube is b, the thickness of the tube wall is b, and the diameter of the annular tube is the direct average value R of the tube0。
According to the embodiment of the invention, the calculation method for the online detection of the yield strength of the pipe comprises the following steps:
and (3) pressing down a press machine provided with a pressure sensing device (pressing the annular pipe in the direction of an arrow in figure 1), flattening the annular pipe cut at the end part of the pipe, stopping pressing down the press machine when the flattening force reaches the maximum elastic deformation, and reading the maximum elastic flattening force through an empirical curve. The empirical curve of crush force versus crush volume obtained from the crush experiment is shown in fig. 2. In the beginning of the flattening step (AB segment), the roll profile of the roll is not stably in contact with the steel pipe, and the roll profile has a local gap, so that the roll profile is slightly irregular. Then the flattening force and the flattening amount are in a direct proportion relation, and when the flattening amount is about 1mm, the curve enters an inflection point (BC section). The force then has a non-linear relationship (CD segment) to the amount of flattening. The depression was stopped when the maximum spring flattening force was read according to the empirical curve of fig. 2, i.e. the pressure sensor read 52KN (position C in fig. 2).
According to the invention, after the maximum elastic flattening force is read from the empirical curve, the actual yield strength of the pipe is calculated by reverse deduction through the following method: sigmat＝FmaxR0/(yπWz) Wherein, in the step (A),
σtfor the actual yield strength to be calculated, y is the fitting ratio, FmaxFor the actual maximum elastic deformation of the read-out flattening force, R0Is the average radius of the pipe, WzModulus of elasticity of annular wall of annular tube, Wz＝b2And/6, wherein b is the width of the annular pipe and is the thickness of the pipe wall.
For the fit ratio, according to one implementation of the present invention, the fit ratio is fitted by fitting the curve multiple times as follows:
y＝Ax+Bx2+Cx3+Dx4wherein A, B, C, D is a undetermined coefficient, and x is the ratio of the diameter of the pipe to the wall thickness of the pipe. In the examples, the resulting fitted scale curve is y-1.90531 x-0.27877 x2+0.2647x3－0.00099x4
According to another implementation of the invention, the fitting ratio is fitted by a binary cubic fit curve as follows:
y＝aD+bx3+ c, wherein a, b and c are undetermined coefficients, x is the ratio of the diameter of the pipe to the wall thickness of the pipe, and D is the diameter of the pipe. In the examples, the resulting fitted scale curve is y-0.00457D +8.2026x3+0.06525
The actual yield strength sigma is obtained through the calculation processtUsing the actual yield strength sigma obtained by calculation during pipe straighteningtCalculating the flattening force of the pipe to be straightened, and adjusting the technological parameters of the straightening machine through the calculated flattening force. The calculation of the collapsing force will be explained below.
According to one embodiment of the invention, the flattening force calculation process is as follows:
a section of the same annular tube as set forth above is cut off as a separate body at the flattening, the width of the cut-off annular tube is b, the wall thickness of the tube is such that the diameter of the annular tube is the direct average value R of the tube0。
According to the symmetry, the shearing force on the cross sections of the two sides is zero, and the separating body is in a plane strain stressed state. Because the tube is symmetrical up and down, in order to simplify the calculation, according to the embodiment of the invention, only the upper half part of the separation body is intercepted for calculation.
Cutting the separating body along the horizontal diameter surface, taking the semicircular ring of the upper half part, and obtaining a schematic diagram of the calculation process of the tube flattening force shown in figure 3, wherein the shearing force on the sections A and B is zero and the axial force is N according to the symmetry and balance equation0FD/2, bending moment M0Selecting any angle by taking the center of the circle of the annular tube separating body as a vertex
Figure BDA0001921519960000051
Figure BDA0001921519960000052
Figure BDA0001921519960000053
The bending moment of the cross section at the corner is
Figure BDA0001921519960000054
In this case, FD is the flattening force.
Figure BDA0001921519960000055
The bending moment of the cross section at the corner is
Figure BDA0001921519960000056
Satisfies the following conditions:
Figure BDA0001921519960000057
the elastic bending deformation energy of the semicircular ring is U, then
Figure BDA0001921519960000058
Wherein E is1＝E/(1-μ2) Converting the plane strain elastic modulus into a value; e is the elastic modulus of the material; mu is Poisson's ratio; i is the moment of inertia of the cross section to the neutral axis, I ═ b3The width of the annular tube taken at/12, b is the tube wall thickness.
Angular deformation of section a:
Figure BDA0001921519960000059
due to the symmetry requirement of the deformation of the ring-shaped pipe on the diameter of the horizontal plane, the A section should not rotate, i.e. the A section is not rotated
Figure BDA00019215199600000510
According to the formula (1), the compound has the characteristics of,
Figure BDA00019215199600000511
therefore, it is not only easy to use
Figure BDA00019215199600000512
Substituting formula (1) into formula (3) can obtain:
Figure BDA00019215199600000513
Figure BDA00019215199600000514
when in use
Figure BDA00019215199600000515
Time, maximum bending moment Mmax＝FD·R0/π，
From bending elastic stress sigma-Mmax/Wz≤σtThe following can be obtained:
FD≤πσtWz/R0，
FDmax＝πσtWz/R0，
wherein FD is the flattening force, FDmaxFor the calculated maximum spring flattening force, R0Direct average of pipe material, WzModulus of elastic section of annular wall of annular tube, sigmatIs the calculated actual yield strength.
According to the calculation method for the yield strength of the pipe in the online detection, the maximum elastic flattening force of the empirical curve is read, the fitting proportion is obtained by using the curve fitting method, the actual yield strength of the pipe is obtained by reversely pushing and calculating, and the calculated yield strength is more accurate than the theoretical yield strength, so that the calculated flattening force is more accurate, and the effective adjustment of the process parameters of the straightener is realized.
According to the calculation method for the on-line detection of the yield strength of the pipe, the actual yield strength of the pipe obtained through calculation is more accurate than the theoretical yield strength, and when the calculation method is used for straightening the pipe, the calculation method is beneficial to reducing errors in the flattening force calculation process and reducing errors of straightening process parameters.
Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims (3)

1. A calculation method for detecting yield strength of a pipe on line is characterized by comprising the following steps:
pressing down a press machine provided with a pressure sensing device, flattening the annular pipe cut from the end part of the pipe, stopping pressing down the press machine when the flattening force reaches the maximum elastic deformation, and reading the maximum elastic flattening force through an empirical curve, wherein the empirical curve is a relationship curve of the flattening force and the flattening amount obtained by a flattening experiment;
the actual yield strength of the annular tube is calculated by the following formula: sigmat＝FmaxR0/(yπWz) Wherein σ istFor the actual yield strength to be calculated, y is the fitting ratio, FmaxFor maximum elastic deformation of the read, R0Is the mean radius of the annular tube, WzModulus of elasticity of annular wall of annular tube, Wz＝b2And/6, wherein b is the width of the annular pipe and is the thickness of the pipe wall.
2. The calculation method according to claim 1, wherein the fitting ratio is fitted by fitting a curve a plurality of times as follows:
y＝Ax+Bx2+Cx3+Dx4wherein A, B, C, D is undetermined coefficient, and x is a pipeIs proportional to the wall thickness of the pipe.
3. The calculation method according to claim 1, wherein the fitting ratio is fitted by a binary cubic fitting curve as follows:
y＝aD+bx3+ c, wherein a, b and c are undetermined coefficients, x is the ratio of the diameter of the pipe to the wall thickness of the pipe, and D is the diameter of the pipe.
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CN111014351B (en) * 2019-12-17 2021-07-30 江苏隆达超合金股份有限公司 Method for controlling yield strength of nickel tube by multi-inclined-roller straightening

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