CN109520840B - A calculation method for on-line detection of yield strength of pipes - Google Patents

Abstract

The invention provides a calculation method for on-line detection of the yield strength of pipes, comprising the following steps: pressing down a press equipped with a pressure sensing device to flatten the ends of the pipes, and when the flattening force reaches the maximum elastic deformation, The press stops pressing down, and the maximum elastic flattening force is read from the experience curve; the actual yield strength of the pipe is calculated by the following formula: σ _t =F _max R ₀ /(yπW _z ), where σ _t is the actual yield that needs to be calculated Strength, y is the fitting ratio, F _max is the crushing force when the actual maximum elastic deformation is read, R ₀ is the average radius, and W _z is the elastic section modulus of the ring wall of the annular tube. The invention provides a calculation method for the on-line detection of the yield strength of the pipe. The calculated actual yield strength of the pipe is more accurate than the theoretical yield strength. When the pipe is used for straightening, it helps to reduce the error in the calculation process of the flattening force and reduce the straightening. Errors in process parameters.

Description

A calculation method for on-line detection of yield strength of pipes

technical field

The invention relates to the technical field of pipe rolling, in particular to a calculation method for on-line detection of yield strength of pipes.

Background technique

As one of the important products in the rolling industry, the production quality of pipes directly reflects the economic development level of a country. In the face of the technical background of gradually improving quality and improving rolling process, domestic and foreign enterprises have paid attention to the development and innovation of straightening machines. Take the pipe and bar straightening machine as an example, especially when straightening the pipe, 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. , directly read the flattening force from experience and adjust the straightening parameters.

Another method is to obtain the flattening force by calculation, and adjust the process parameters of the straightening machine by calculating the flattening force. However, in the process of calculating the flattening force, there is an important parameter, the yield strength σ _t . The actual yield strength of the same grade of steel is a range value. In the production process, the more accurate the yield strength is, the more accurate the calculated flattening force will be. The adjustment of the process parameters of the straightening machine is more effective, and the straightening effect of the pipe is better.

When calculating the flattening force in the prior art, the theoretical value of the yield strength _σt is used to calculate the flattening force. However, the theoretical value and the actual value of the yield strength _σt have different degrees of deviation, which increases the accuracy of the calculation result of the flattening force. Bringing errors, resulting in deviations in the adjustment of the process parameters of the leveler.

Therefore, in order to solve the problems in the prior art, a calculation method for on-line detection of the yield strength of the pipe is required to reduce the error of the pipe straightening process parameters.

SUMMARY OF THE INVENTION

One aspect of the present invention is to provide a calculation method for on-line detection of yield strength of pipes, the method comprising the following steps:

Press down the press equipped with the pressure sensing device to flatten the end of the pipe. When the flattening force reaches the maximum elastic deformation, the press stops pressing down, and the maximum elastic flattening force is read through the experience curve;

Calculate the actual yield strength of the pipe by: σ _t =F _max R ₀ /(yπW _z ), where,

σ _t is the actual yield strength that needs to be calculated, y is the fitting ratio, F _max is the flattening force when reading the actual maximum elastic deformation, R ₀ is the average radius of the pipe, W _z is the elastic section modulus of the pipe wall of the annular pipe Quantity, W _z =bδ ² /6, where b is the width of the annular pipe, and δ is the thickness of the pipe wall.

In one embodiment, the fitting ratio is fitted by the following multiple fitting curves:

y=Ax+Bx ² +Cx ³ +Dx ⁴ , wherein A, B, C, and D are undetermined coefficients, 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 the following bivariate cubic fitting curve:

y=aD+bx ³ +c, where 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 is to provide a method for calculating the maximum elastic crushing force, comprising:

A section of annular tube is cut at the flattening point as a separation body, the width of the cut annular tube is b, the thickness of the tube wall is δ, and the diameter of the annular tube is the direct average value R ₀ of the tube material,

当

时，通过如下方法计算最大压扁力：FD_max＝πσ_tW_z/R₀，Taking the center of the annular tube separation body as the vertex, select any angle

when

, the maximum crushing force is calculated by the following method: FD _max =πσ _t W _z /R ₀ ,

Among them, FD _max is the calculated maximum elastic flattening force, R ₀ is the direct average value of the pipe material, W _z is the elastic section modulus of the ring wall of the annular pipe separation body, and σ _t is the calculated actual yield strength.

The invention provides a calculation method for the on-line detection of the yield strength of the pipe. By reading the maximum elastic flattening force of the empirical curve, the fitting ratio is obtained by using the curve fitting method, and the actual yield strength of the pipe is calculated by back-calculation, so that the calculated yield Compared with the theoretical yield strength, the strength is more accurate, so that the calculated flattening force is more accurate, and the process parameters of the leveler can be effectively adjusted.

The invention provides a calculation method for the on-line detection of the yield strength of the pipe. The calculated actual yield strength of the pipe is more accurate than the theoretical yield strength. When the pipe is used for straightening, it helps to reduce the error in the calculation process of the flattening force and reduce the straightening. Errors in process parameters.

It is to be understood that both the foregoing general description and the following detailed description are exemplary illustrations and explanations, and should not be used as limitations on what is claimed in the present invention.

Description of drawings

Further objects, functions and advantages of the present invention will be elucidated by the following description of embodiments of the present invention with reference to the accompanying drawings, wherein:

Fig. 1 is a schematic view of the annular elastic cross-sectional structure of the annular pipe at the end of the pipe material of the present invention.

Fig. 2 is the empirical curve of the crushing force and the crushing amount obtained by the crushing experiment.

Fig. 3 is a schematic diagram of the calculation process of the flattening force of the pipe of the present invention.

Detailed ways

Objects and functions of the present invention and methods for achieving these objects and functions will be elucidated by referring to the exemplary embodiments. However, the present invention is not limited to the exemplary embodiments disclosed below; it may be implemented in various forms. The essence of the description is merely to assist those skilled in the relevant art to comprehensively understand the specific details of the present invention. Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the same reference numbers represent the same or similar parts, or the same or similar steps. The content of the present invention will be described below through specific embodiments. According to the present invention, in order to solve the error in calculating the flattening force during the straightening process of the pipe material in the prior art, a calculation method for on-line detection of the yield strength of the pipe material is provided. The actual yield strength used in the flat force calculation process is calculated to reduce the error between the theoretical value and the actual value of the yield strength σ _t .

According to the embodiment of the present invention, for the pipe to be straightened, a section of the annular pipe at the end of the pipe is cut for the calculation of the actual yield strength. The annular tube is placed under a press equipped with a pressure sensor, and the annular tube is pressed down. Figure 1 shows a schematic view of the annular elastic cross-sectional structure of the annular tube _at the end of the pipe of the present invention.

According to an embodiment of the present invention, a calculation method for on-line detection yield strength of a pipe includes the following steps:

Press down the press equipped with the pressure sensing device (extrude the annular tube in the direction of the arrow in Figure 1), and flatten the annular tube cut at the end of the pipe. When the flattening force reaches the maximum elastic deformation, the press stops. Press down and read the maximum elastic crushing force through the empirical curve. Figure 2 shows the empirical curve of the flattening force and the flattening amount obtained from the flattening experiment. At the beginning of the flattening stage (section AB), due to the unstable contact between the roll shape of the roll and the steel pipe and the existence of local gaps, the law is slightly disordered. After that, the flattening force is proportional to the flattening amount. When the flattening amount is about 1mm, the curve enters the inflection point (BC segment). The force then has a non-linear relationship with the amount of squash (CD segment). Read the maximum elastic crushing force according to the experience curve in Figure 2, that is, when the reading of the pressure sensor is 52KN (point C in Figure 2), stop pressing down.

In the present invention, after reading the maximum elastic flattening force from the empirical curve, the following method is used to calculate the actual yield strength of the pipe: σ _t =F _max R ₀ /(yπW _z ), wherein,

σ _t is the actual yield strength that needs to be calculated, y is the fitting ratio, F _max is the flattening force when reading the actual maximum elastic deformation, R ₀ is the average radius of the pipe, W _z is the ring wall elastic section modulus of the annular pipe Quantity, W _z =bδ ² /6, where b is the width of the annular pipe, and δ is the thickness of the pipe wall.

For the fitting ratio, according to an implementation of the present invention, the fitting ratio is fitted by the following multiple fitting curves:

y=Ax+Bx ² +Cx ³ +Dx ⁴ , wherein A, B, C, and D are undetermined coefficients, and x is the ratio of the diameter of the pipe to the wall thickness of the pipe. In the embodiment, the obtained fitting proportional curve is y=1.90531x ^- 0.27877x2 ^{+ 0.2647x3-0.00099x4}

According to another implementation of the present invention, the fitting ratio is fitted by the following binary cubic fitting curve:

y=aD+bx ³ +c, where 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 embodiment, the obtained fitting proportional curve is y=0.00457D+8.2026x ³ +0.06525

The actual yield strength σ _t is obtained through the above calculation process, and the calculated actual yield strength σ _t is used to calculate the flattening force of the pipe to be straightened when the pipe is straightened, and the process parameters of the straightening machine are adjusted by the calculated flattening force. The calculation process of the crushing force will be described below.

According to an embodiment of the present invention, the crushing force calculation process is as follows:

A section of the same annular tube as described above is cut from the flattening action as a separation body. The width of the cut annular tube is b, the thickness of the tube wall is δ, and the diameter of the annular tube is the direct average value R ₀ of the tube.

According to the symmetry, the shear force on the cross-sections on both sides is zero, and the separated body is in a state of plane strain stress. Since the upper and lower parts of the pipe are symmetrical, in order to simplify the calculation, according to the embodiment of the present invention, only the upper half of the separation body is intercepted for calculation.

角处截面弯矩为

其中，FD为压扁力。The separation body is cut along the horizontal diameter plane, and the semi-circular ring of the upper half is taken, as shown in Figure 3, the schematic diagram of the calculation process of the flattening force of the pipe of the present invention, from the symmetry and balance equation, the The shear force is zero, the axial force is N ₀ =FD/2, and the bending moment is M ₀ . Taking the center of the annular tube separation body as the vertex, select any angle

The bending moment of the section at the corner is

Among them, FD is the crushing force.

角处截面弯矩为

满足：

The bending moment of the section at the corner is

Satisfy:

Let the elastic bending deformation energy of the semicircle be U, then

Among them, E ₁ =E/(1-μ ² ) is the converted value of the plane strain elastic modulus; E is the material elastic modulus; μ is the Poisson’s ratio; I is the moment of inertia of the cross section to the neutral axis, I=bδ ^3/12 , b is the width of the annular pipe intercepted, and δ is the thickness of the pipe wall.

Angular deformation of section A:

Due to the symmetry requirements of the annular tube deformation on the diameter of the horizontal plane, the A section should not be rotated, i.e.

所以From the formula (1), we know,

so

Substitute (1) into (3) to get:

时，最大弯矩M_max＝FD·R₀/π，when

, the maximum bending moment M _max =FD·R ₀ /π,

From the bending elastic stress σ=M _max /W _z ≤σ _t can be obtained:

FD≤πσ _t W _z /R ₀ ,

FD _max =πσ _t W _z /R ₀ ,

Among them, FD is the flattening force, FD _max is the calculated maximum elastic flattening force, R ₀ is the direct average value of the pipe, W _z is the elastic section modulus of the ring wall of the annular pipe, and σ _t is the calculated actual yield strength.

The invention provides a calculation method for the on-line detection of the yield strength of the pipe. By reading the maximum elastic flattening force of the empirical curve, the fitting ratio is obtained by using the curve fitting method, and the actual yield strength of the pipe is calculated by back-calculation, so that the calculated yield Compared with the theoretical yield strength, the strength is more accurate, so that the calculated flattening force is more accurate, and the process parameters of the leveler can be effectively adjusted.

The invention provides a calculation method for the on-line detection of the yield strength of the pipe. The calculated actual yield strength of the pipe is more accurate than the theoretical yield strength. When the pipe is used for straightening, it helps to reduce the error in the calculation process of the flattening force and reduce the straightening. Errors in process parameters.

Other embodiments of the present invention will be readily apparent to and understood by those skilled in the art in conjunction with the specification and practice of the present invention disclosed herein. The description and examples are to be regarded as exemplary only, with the true scope and spirit of the invention being defined by the 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: sigma_t＝F_maxR₀/(yπW_z) Wherein σ is_tFor the actual yield strength to be calculated, y is the fitting ratio, F_maxFor maximum elastic deformation of the read, R₀Is the mean radius of the annular tube, W_zModulus of elasticity of annular wall of annular tube, W_z＝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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