EP1378299A1 - Method and apparatus for determining the eccentricity of a hollow block - Google Patents

Abstract

Device for determining the eccentricity (e) of a hollow block (1) comprises a measuring unit (2) for measuring a number of wall thickness measurements as the block passes it. The measuring unit is connected to a computer (3) which is suitable for determining the functional progression of the wall thickness as a function of the longitudinal coordinates and the rotational angle of the block from the measured wall thickness data via Fourier transformation. An Independent claim is also included for a process for determining the eccentricity of a hollow block.

Description

The invention relates to a method for determining the eccentricity of a hollow block, preferably in the inlet of a rolling mill, that of a cross rolling mill succeeds, especially in the run-in of a continuous rolling mill or a push bench system, into which the hollow block enters in the direction of the longitudinal axis of the hollow block, by means of at least one measuring device which measures the wall thickness of the hollow block can determine a length and circumference position of the hollow block. Furthermore The invention relates to a device for determining the eccentricity of a Hollow block.

In many areas of technology, steel pipes are required, for example can be made by a method in which the cylindrically shaped Starting material in a cross rolling mill using an axial fixed hole dome is formed into a tubular hollow block. to Forming the cylindrically shaped starting material into a seamless one The raw material is rolled over the perforated dome. Such a process is known for example from EP 0 940 193 A2.

For stretch reduction rolling and for reducing and sizing rolling seamless steel tubes the pipe to be processed passes a rolling mill in the direction of conveyance a number of roll stands are arranged one behind the other of the tube. In each Roll stands are mounted on the rolls, which each move the tube by one during the rolling process contact defined circumferential section. Overall, everyone works Roll stand several, for example three rolls together so that the tube in the is contacted by the rollers essentially over its entire circumference. The Pipe is thus rolled to a reduced diameter and thereby to one brought exact shape.

The tube should have an ideal shape after rolling, i. H. the cylindrical Contour of the outer circumference and that of the inner circumference should be two concentric Form circles. In fact, there are always tolerances in the finished pipe, so that a certain eccentricity of the circular contour of the inner circumference relative to that the outer circumference.

A crucial quality parameter in pipe manufacturing is the pipe wall thickness, which is measured and monitored in the production process. For investigation the wall thickness of the tube, ultrasonic measuring methods are known. Ultrasonic thickness measurement method Determine using the pulse-echo method using the transit time measurement of an ultrasonic pulse the wall thickness.

Another very important parameter or another important quality criterion of hollow blocks and their precursors is the eccentricity of the hollow block. To obtain this parameter at the earliest possible stage of production the wall thickness measuring devices mentioned are used, for example Such a wall thickness measuring device is positioned in the outlet of a cross rolling mill becomes. This makes it possible with relatively little effort in the process To determine wall thickness. After the hollow block in the exit of the cross rolling mill rotates, a number of wall thickness measuring points can be used with such a wall thickness measuring device be determined over the circumference of the hollow block, the determination the eccentricity can be used.

The eccentricity in question is not just an eccentric one Offset of the outside diameter of the hollow block relative to the inside diameter of the hollow block, this offset along the length coordinate of the hollow block remains constant or stationary, but the eccentricity "wanders" towards the length coordinate of the hollow block in such a way that there is a helical course of the inner surface of the hollow block relative to outer surface of the hollow block results. This course of eccentricity is through the rolling process in the cross rolling mill, so that the circulation character similar to the course of a corkscrew. The course of this eccentricity is determined by the so-called main inner helix, the pitch or Lay length from the process in the cross rolling mill and there from the feed angle of the cross rolling mill. The course of eccentricity is repeated periodically with the lay length. Other eccentricities of a circulating character with a large pitch or low frequency are superimposed z. B. by non-uniform heating of the block in the rotary hearth furnace.

The measurement of the eccentricity curve over the length coordinate of the hollow block, that is, the detection of the inner surface of the hollow block relative to the outer Surface of the hollow block over the length coordinate of the hollow block, is problematic at the exit of a cross rolling mill for the following reasons:

First of all, there is only a very small space for the measuring device, so that there is insufficient space for the measuring device. To the others are unable to rotate the full length of the hollow block. The latter aspect is particularly important from a rolling technology perspective, because hollow blocks have particularly distinctive eccentrics at the ends.

This has led to other measurement concepts also being considered. Additional measuring roller tables or measuring manipulators were used, on which the hollow block rotates and the measuring head on the hollow block in the longitudinal direction is moved past. For the sake of the cycle time and the related However, these procedures have disadvantages in terms of costs. Farther it was also recognized as a disadvantage that such systems are difficult to access existing rolling lines can be retrofitted.

It is therefore very difficult with the previously known methods and devices or possible with great effort, especially in the inlet of a subsequent rolling mill, for example, a continuous rolling mill or a shaping bench system Eccentricity of a hollow block in its spatial extension along the hollow block length coordinate to capture and thus a usable for practical use Measure the eccentricity.

The invention is therefore based on the object of a method and an associated one To create device with which the disadvantages mentioned are overcome can be.

s₀

die mittlere Wanddicke des Hohlblockes,

s₁

die der mittleren Wanddicke S₀ überlagerte Wanddickenamplitude und

δ

der von der Längenkoordinate z abhängige Lagewinkel ist,

wobei ferner die Messvorrichtung beim Passieren des Hohlblocks eine Anzahl Wanddickenmessungen vornimmt und die gemessenen Werte einem Rechnermittel zuleitet, das diese einer Fourier-Transformation unterzieht, um für den funktionalen Verlauf der Wanddicke s als Funktion der Längenkoordinate z und des Drehwinkels  eine Näherung der Form s(, z)≅ s0* + ∑ si,1 cos( + 2 π/pi z + ξi,1) zu ermitteln, wobei

s₀*

und

s_i,1

die ermittelten Fourier-Koeffizienten für die Wanddicke des Hohlblocks bei Summation über die Anzahl der Fourier-Reihenelemente und

p_i

und

ξ_i,1

die Fourier-Koeffizienten für die Ganghöhen bzw. für die Anfangslagewinkel bei Summation über die Anzahl der Fourier-Reihenelemente sind.

The achievement of this object by the invention is characterized according to the method in that the course of the eccentricity of the hollow block is approximately mapped as the course of the wall thickness s as a function of the length coordinate extending in the direction of the longitudinal axis z of the hollow block and the angle of rotation  about the length coordinate according to the relationship s (, z) = s 0 (z) + s 1 (z) cos ( + δ (z)), in which

s ₀

the mean wall thickness of the hollow block,

s ₁

the wall thickness amplitude superimposed on the mean wall thickness S ₀ and

δ

is the position angle dependent on the length coordinate z,

the measuring device also takes a number of wall thickness measurements as it passes through the hollow block and feeds the measured values to a computer means which subjects them to a Fourier transformation in order to approximate the shape for the functional profile of the wall thickness s as a function of the length coordinate z and the angle of rotation  s (, z) ≅ s 0 * + ∑ s i, 1 cos ( + 2 π / p i z + ξ i, 1 ) to determine where

s ₀ *

and

s _{i, 1}

the determined Fourier coefficients for the wall thickness of the hollow block when summing over the number of Fourier row elements and

p _i

and

ξ _{i, 1}

are the Fourier coefficients for the pitches or for the initial position angles when summing over the number of Fourier row elements.

The hollow block preferably does not rotate about its longitudinal axis during the measurement. Furthermore, it can be provided that more than one measuring device is used. The laser ultrasound wall thickness measurement method has been used to determine the wall thickness of the pipe proven, provided for in the training is. In the latter method in particular, it is advantageously possible for the Measurement of the wall thickness of the hollow block with one arranged in the hollow block To carry out tools, in particular with a dome rod arranged in the hollow block, which gives the process great flexibility.

The device for determining the eccentricity of the hollow block has at least a measuring device that measures the wall thickness of the hollow block along a length and determine the circumferential position of the hollow block. According to the invention provided that the at least one measuring device for carrying out a Number of wall thickness measurements when passing the hollow block is suitable, whereby the at least one measuring device in connection with a computer means stands, which is suitable, from the measured wall thickness data via a Fourier transformation an approximate functional course of the wall thickness as Determine the function of the length coordinate and the angle of rotation of the hollow block.

According to a further development, at least one measuring device is in the area of the outlet a rolling mill, in particular an inclined rolling mill.

The ultrasound wall thickness measuring device used advantageously in accordance with the training has a means for introducing an ultrasonic signal into the surface of the hollow block. This agent can be a laser, in particular a flash lamp-pumped Nd: YAG laser. It can also Measuring device Means for measuring a time interval between two echo ultrasound signals have the hollow block due to the introduction of the ultrasonic signal emitted; these means can be a laser, in particular a laser diode-pumped Nd: YAG laser, and an optical analyzer, in particular a Fabry-Pérot interferometer.

With the proposal according to the invention, it is possible to reduce the eccentricity in one Hollow block to determine and represent in a simple manner and thus a to make a fast and practical statement about the quality of the hollow block It is therefore possible with the invention in a simple manner to form an image the spatial course of the eccentricity over the length coordinate of the Hohiblock to obtain and from this a practical statement about the size and location of eccentricity. The approximations used make it possible, in particular, to use them in a very simple manner Derive assessment criteria for the quality of the hollow block.

Fig. 1

schematisch in dreidimensionaler Ansicht einen Hohlblock mit Exzentrizität samt einer Messvorrichtung zu deren Erfassung; und

Fig. 2

schematisch das Prinzip der Messung der Wanddicke eines Hohlblocks.

In the drawing, an embodiment of the invention is shown. Show it:

Fig. 1

schematically in three-dimensional view a hollow block with eccentricity together with a measuring device for its detection; and

Fig. 2

schematically the principle of measuring the wall thickness of a hollow block.

Reference is first made to FIG. 2, where it can be seen how the measurement of the Wall thickness s of a hollow block 1 can take place.

The laser ultrasound wall thickness measurement method is used, which is based on eliminates the classic principle of ultrasonic transit time measurement. Out of time for the - twice - passing through an ultrasound pulse through the wall of the Hollow blocks 1 result from a known sound velocity in the material of the Hohlblocks the wall thickness s. The coupling of the ultrasound at the Hot wall thickness measurement with temperatures in the range of approx. 1,000 ° C is required Non-contact, optical on the excitation as well as on the detection side Methods in which the measuring head (2 'in Fig. 1) itself in a thermal safe distance to the hollow block 1 can remain.

High-energy light pulses in the infrared range are in the surface of the Hollow blocks 1 absorbed. They are directed towards the wall of the hollow block by a Flashlamp-pumped Nd: YAG laser 4 (excitation laser) generates which has a wavelength of 1,064 nm with a pulse duration of less than 10 ns may have. The laser 4 applied to the surface of the hollow block 1 Energy (ultrasonic signal), which is absorbed by the wall of the hollow block, leads partly for evaporation of a very thin surface layer (material ablation in the nm range). The evaporation pulse arises - because of the conservation of momentum - In the hollow block 1, an ultrasonic pulse that is perpendicular to the surface of the hollow block into which its wall runs. The ultrasonic pulse is on the inner surface reflected from the hollow block, runs back to the outer surface of the Hollow block, is reflected again, etc., so that a in the wall of the hollow block Ultrasonic echo sequence of decreasing amplitude arises.

The reflected ultrasound pulse generates on the outer surface of the hollow block 1 vibrations (in the sub-miniature range) that are generated by means of a second laser 5 (Illumination or detection laser) without contact using the Doppler effect be recorded. This laser 5 can be a CW laser (continuous wave Laser), namely a frequency-doubled, diode-pumped Nd: YAG laser, who works with a wavelength of 532 nm and on the point of excitation is aligned. The low-frequency ultrasonic vibration compared to the light frequency leads to a frequency modulation of the on the material surface reflected light.

The reflected cone of light, which is now the "carrier" of the ultrasound signal, is over a bright collecting optics 6 and an optical waveguide 9 an optical analyzer 7, d. H. a demodulator, in particular a confocal Fabry-Pérot interferometer is used; whose output signal contains already the ultrasound echo sequence.

The further amplification, filtering and signal evaluation of the ultrasound echo sequence can with a conventional electronic ultrasonic evaluation unit 8 (Evaluation computer). The output signal of the evaluation computer 8 is the Wall thickness s of the hollow block 1, which is the product of the speed of sound and measured time interval is determined.

In Fig. 1 it is shown how the eccentricity e of the hollow block 1 over the course the length coordinate z of the hollow block 1 is determined. Because of the rolling process The eccentricity runs in the cross rolling mill - as indicated in FIG. 1 e helical in the manner of a corkscrew in the direction of the longitudinal coordinate z of the hollow block 1. Three cuts are shown schematically, based on which It can be seen that the wall thickness s changes with the period of the pitch or Beat length H repeated periodically.

To detect the eccentricity e as a function of the length coordinate z and the A number of wall thickness measurements are made, for which purpose the measuring device 2 or its measuring head 2 'along the length coordinate z is moved relative to the hollow block 1. The wall thicknesses s are determined and in a computer means 3 stored.

s₀

die mittlere Wanddicke des Hohlblockes 1,

s₁

die der mittleren Wanddicke s₀ überlagerte Wanddickenamplitude und

δ

der von der Längenkoordinate z abhängige Lagewinkel ist.

To represent the eccentricity of the length coordinate z and the angle of rotation des, a functional approach is used, such as that given by the relationship s (, z) = s 0 (z) + s 1 (z) cos ( + δ (z)) is defined, where

s ₀

the average wall thickness of the hollow block 1,

s ₁

that superimposed on the mean wall thickness s ₀ and

δ

is the position angle dependent on the length coordinate z.

The approach is based on the assumption that the eccentricity changes with a Pitch or pitch length H repeated periodically.

s₀*

und

s_i,1

die ermittelten Fourier-Koeffizienten für die Wanddicke des Hohlblocks 1 bei Summation (i) über die Anzahl (n) der Fourier-Reihenelemente und

p_i

und

ξ_i,1

die Fourier-Koeffizienten für die Ganghöhen bzw. für die Anfangslagewinkel bei Summation (i) über die Anzahl (n) der Fourier-Reihenelemente.

As already mentioned, the measured wall thicknesses are stored in a computer means 3. This is followed by a Fourier transformation (marked with FFT in FIG. 1: Fast Fourier transformation) in order to approximate the shape for the functional profile of the wall thickness s as a function of the length coordinate z and the angle of rotation  s (, z) ≅ s 0 * + ∑s i, 1 cos ( + 2π / p i z + ξ i, 1 ) to investigate. Here are:

s ₀ *

and

s _{i, 1}

the determined Fourier coefficients for the wall thickness of the hollow block 1 at summation (i) over the number (n) of the Fourier series elements and

p _i

and

ξ _{i, 1}

the Fourier coefficients for the pitch or for the initial position angle at summation (i) over the number (n) of the Fourier row elements.

The Fourier coefficients are determined by means of the Fourier analysis Course of the eccentricity of the hollow block 1 approximately as a superposition harmonic Vibrations with different amplitudes and different Show initial position angles.

The "FFT" - "Fast Fourier Transformation" noted in the computer means 3 in FIG towards a preferred implementation of the Fourier transformation. details this can be found, for example, in "Hut - The Basics of Engineering", 29th edition, p. B 34 ff.

In the above approximation, the wall thickness s with "ideal eccentricity" is described by the eccentric amplitude s ₁ (z), which is dependent on the length coordinate z of the hollow block 1. The associated circumferential distribution is represented by the cosine function and the circulating character, including the circulating speed, is adequately formulated with the current eccentric position angle (δ). The wall thickness curve is used as a mathematical approximation with an overall mean wall value with superimposed "impact vibrations". For a fixed angle  you get a conventional Fourier series in "z". The initial position angles ξ _{i, 1 of} the longitudinal vibrations depend on the hollow block position during the measurement (initial angles). If the angle Längs is varied for each longitudinal coordinate of the approximation, the entire course of the eccentricity in the hollow block 1 is described.

The described evaluation of the measured values for the wall thickness is running in addition to the fact that methods of interpretation or evaluation known per se are used as they are used in telecommunications, like that of frequency shift and modulation.

It should also be mentioned that the measurement of the wall thickness by means of the explained Ultrasonic measuring method also with mandrel bar located in the hollow block can be done successfully.

It has already been mentioned that more than one wall thickness measuring device 2 for Use can come. Then the system will not only be single-channel, but multi-channel realized. In particular, several wall thickness measuring devices can be used be arranged equidistantly over the circumference of the hollow block.

For a sufficiently accurate representation of the spatially extending eccentricity as a function of the length coordinate z and the angle of rotation  it is also important that a sufficiently high sampling frequency is maintained. Here it goes by name therefore, minimum sampling frequencies according to Shannon's sampling theorem observed. Details can be found in "Hut - The basics of Engineering Sciences ", 29th edition, p. H 68 f. For example, at 50 Hz sampling rate the stroke frequency of a feed spiral in the hollow block with 40 mm Pitch height can still be determined if a hollow block with less than 1 m / s without Rotation past the measuring head.

The following should also be noted: In the above explanations, special attention was paid to this received that the "helix" to be measured and imaged in the hollow block is designed as a spiral course of the inner surface of the hollow block. The described method and the associated device can do the same are used when the "helix" is on the outer surface of the Hollow blocks located.

LIST OF REFERENCE NUMBERS

1

hollow block

2

measuring device

2 '

probe

3

computer means

4

Means for introducing an ultrasound signal (excitation laser)

5

laser lighting

6

collection optics

7

Fabry-Pérot interferometer

8th

evaluation computer

9

optical fiber

e

eccentricity

L

longitudinal axis

s

wall thickness

H

Pitch height, lay length

z

Longitude coordinate of the hollow block

()

Angle of rotation (circumferential direction of the hollow block)

s ₀

average wall thickness of the hollow block

s ₁

superimposed wall thickness amplitude

δ

position angle

n

Number of Fourier series elements

s ₀ *

Fourier coefficient for the wall thickness

s _{i, 1}

Fourier coefficient for the wall thickness (i = 1, ..., n)

p _i

Fourier coefficient for the pitch (i = 1, ..., n)

ξi, 1

Fourier coefficient for the initial position angle (i = 1, ..., n)

Claims (9)

Method for determining the eccentricity (e) of a hollow block (1), preferably in the inlet of a rolling mill that follows a cross-rolling mill, in particular in the inlet of a continuous rolling mill or a ram bench system, into which the hollow block (1) in the direction of the longitudinal axis (L) of the hollow block (1) occurs by means of at least one measuring device (2) which can determine the wall thickness (s) of the hollow block (1) at a length (z) and circumferential position or angle of rotation () of the hollow block (1),
characterized in that the course of the eccentricity (e) of the hollow block (1) is approximately mapped as the course of the wall thickness (s) as a function of the length coordinate (z) and the angle of rotation extending in the direction of the longitudinal axis (L) of the hollow block (1) () around the length coordinate (z) according to the relationship s (, z) = s 0 (z) + s 1 (z) COS ( + δ (z)), where s _{0 is} the mean wall thickness of the hollow block (1), where s _{1 is} the wall thickness amplitude superimposed on the mean wall thickness s ₀ and where δ is the position angle dependent on the length coordinate (z),
wherein the measuring device (2) takes a number of wall thickness measurements as it passes the hollow block (1) and feeds the measured values to a computer means (3) which subjects them to a Fourier transformation in order to determine the functional profile of the wall thickness (s) as a function of the length coordinate (z) and the angle of rotation () an approximation of the shape s (, z) ≅ s 0 * + ∑S i, 1 cos ( + 2π / p i z + ξ i, 1 ) to be determined, where s ₀ * and s _{i, 1 are} the determined Fourier coefficients for the wall thickness of the hollow block (1) at summation (i) over the number (n) of the Fourier series elements and where p _i and ξ _{i, 1} are the Fourier coefficients for the pitch or for the initial position angle at summation (i) over the number (n) of the Fourier row elements. Method according to claim 1,
characterized in that the hollow block (1) does not rotate about its longitudinal axis (L) during the measurement. Method according to claim 1 or 2,
characterized in that the wall thickness (s) of the hollow block (1) is measured by means of the laser ultrasound wall thickness measurement method. Method according to one of claims 1 to 3,
characterized in that the wall thickness (s) of the hollow block (1) is measured with a tool arranged in the hollow block (1), in particular with a dome rod arranged in the hollow block (1). Device for determining the eccentricity (e) of a hollow block (1), preferably in the inlet of a rolling mill that follows a cross-rolling mill, in particular in the inlet of a continuous rolling mill or a ram bench assembly, into which the hollow block (1) in the direction of the longitudinal axis (L) of the hollow block (1) occurs, in particular for carrying out the method according to one of claims 1 to 5,
the device having at least one measuring device (2) which can determine the wall thickness (s) of the hollow block (1) at a length (z) and circumferential position () of the hollow block (1),
characterized in that the measuring device (2) is suitable for carrying out a number of wall thickness measurements when passing through the hollow block (1), the measuring device (2) being connected to a computing means (3) which is suitable for using the measured wall thickness data (see ) to determine an approximate functional profile of the wall thickness (s) as a function of the length coordinate (z) and the angle of rotation () of the hollow block (1) using a Fourier transformation. Device according to claim 5,
characterized in that at least one measuring device (2) is arranged in the region of the outlet of a rolling mill, in particular an inclined rolling mill. Apparatus according to claim 5 or 6,
characterized in that the at least one measuring device (2) is designed as an ultrasonic wall thickness measuring device which has a means (4) for introducing an ultrasonic signal into the surface of the hollow block (1). Device according to claim 7,
characterized in that the measuring device (2) has means (5, 6, 7, 8) for measuring a time interval between two echo ultrasound signals which the hollow block (1) emits as a result of the introduction of the ultrasound signal. Device according to claim 8,
characterized in that the means (5, 6, 7, 8) have a laser (5), in particular a diode-pumped Nd: YAG laser, and an optical analyzer (7), in particular a Fabry-Perot interferometer.

Images