Laser Measurement Technology Used in Metallurgy Intelligent Manufacturing

The metallurgical manufacturing industry puts forward higher requirements for the monitoring of various process parameters in the production process: online dynamic real-time monitoring, non-contact (optimal), certain monitoring accuracy, and strong environmental adaptability (harsh environment).

It is well known that laser has the characteristics of good monochromaticity, good directionality, and good coherence. Therefore, precision measuring equipment using laser technology has the following advantages: non-contact measurement, which does not affect the movement of the measured object, high precision, and large measurement range. Large size, short detection time, and high spatial resolution. Because of this, laser measurement technology is more and more widely used in metallurgy, automobile production, equipment manufacturing, and other fields.

The iron and steel industry is accelerating the transformation and upgrading of the iron and steel industry on the basis of actively resolving excess capacity. The current focus is to accelerate the development of intelligent manufacturing, that is, to use intelligent manufacturing technology to transform the production management model, realize agile manufacturing and refined management, and then promote the development of the iron and steel industry.

Some large steel mills divide smart manufacturing into a “3+1” model, namely “smart equipment, smart factory, smart interconnection and infrastructure” for exploration and implementation. The online detection-monitoring technology of the whole process of iron and steel manufacturing is the basic problem to be solved first. The following takes the metallurgical industry as an example to introduce the application of laser measurement technology in the field of metallurgical intelligent manufacturing.


Laser Measurement Technology Used in Metallurgy


1. Laser high-precision plate thickness measurement, width measurement, and length measurement


The working principle of the laser thickness gauge is based on the principle of triangulation. The upper and lower sets of laser emitting systems project the light spots onto the upper and lower surfaces of the steel plate respectively. The optical receiving system images the diffuse reflected light of the spot on the target plate on the linear array CCD.

The CCD converts the light signal of the image point into an electrical signal to measure the position of the image point. When the measured object moves in the normal direction, the light spot on its surface will change with the position relative to the objective lens. Correspondingly, the position of the image point on the photosensitive device CCD will also change. Accurately measure the image point The displacement on the CCD can get the displacement of the measured object.

Since it is an absolute measurement, the laser upper and lower surface double triangulation method is used. The real-time position value of the upper and lower surfaces of the steel plate is preliminarily calculated through circuit processing, and the value is transmitted to the host computer through the communication interface, and then the position data of the upper and lower surfaces are subjected to relevant mathematical model calculations to calculate the instantaneous thickness measurement value H of the measured steel plate.

It can be seen from the measurement principle that the outstanding advantage of this method is that the measured steel plate thickness value has nothing to do with the material, temperature, and standard value of the measured object; the up-and-down symmetrical measurement can automatically eliminate the vibration caused by the measured object’s beating, bending and vibration. The introduced measurement error greatly improves the accuracy of dynamic measurement. The basic measuring principle of measuring the width and length of medium and thick plates is basically the same as that of the laser thickness gauge.


2. Laser Doppler Velocimeter LDV


Laser Doppler Velocimetry (LDV), which applies the Doppler effect, uses the high coherence and high energy of the laser to measure the flow rate of fluid or solid. It has the advantages of linear characteristics and non-contact measurement, and the accuracy of high, fast dynamic response.

Its basic working principle is that after two homologous laser beams intersect in the measurement area, they interfere to generate a fringe three-dimensional space, take the cross-section of the measured object, and form a light and dark fringe band in this area. The fringe interval is d, which is determined by the laser wavelength λ and the half angle k between the two laser beams, d = λ/(2*sin k).

When the measured steel plate passes through the stripes in this area, the surface of the steel plate will produce light and dark interlaced diffuse reflection light signals, which are converted into electrical signals of a certain frequency by the photodetector of the instrument. relevant.

The ZK-D-SC/H/L series laser speed and length measuring instruments produced by our company are widely used in the metallurgical industry. The equipment adopts high-precision high-speed AD sampling, high-speed FPGA calculation, high precision, low noise, and can measure accurately on almost any surface (can measure 1000°C high-temperature steel billet, adapt to lower speed measurement, and use light intensity automatic for the oxide scale surface Gain function, the measurement accuracy can reach ±0.1%.)

Direction automatic detection can measure “0” speed

Maximum measuring speed ( m / min ): 20000

Accuracy: better than 0.05%


Laser Measurement Technology Used in Metallurgy


3. Laser sheet three-dimensional dimension measurement


In traditional operations, the inspection of the three-dimensional dimensions of steel plates only relies on manual measurement. With the improvement of the production capacity of the medium and heavy plate production line, new challenges have been brought: the labor intensity of workers has increased significantly, and it is difficult to adapt to the requirements of the production rhythm; it is difficult to guarantee the accuracy and reliability of the measurement data; it is not conducive to the automatic management of production data.

Therefore, it is necessary to update the inspection methods of steel plates. First, it can improve inspection efficiency. Second, it can make the production data enter the production management network in time, and finally realize the automatic management and output of reports. The three-dimensional dimension detection of steel plate is the most basic detection of steel plate, and it needs to realize automatic measurement first.

The measurement system is mainly composed of comprehensive applications such as laser thickness gauge, laser width gauge, laser length gauge, and laser speedometer. The system can continuously, online, in real-time, and automatically measure the thickness, width, speed, and length of the steel plate; and through computer information processing, on the basis of fusing the above measurement data, analyze the three-dimensional contour shape of the steel plate to obtain various sizes of the steel plate, including thickness, width, length, camber, diagonal, slant, vertical and horizontal difference between the same plate, etc.

The system can automatically record the measurement date, shift, steel plate serial number, length, width, and thickness measurement values and curves, steel plate bevelled diagonals, sickle bends, etc., and provides a size measurement database that can store the length, width, and thickness of each steel plate The maximum value, minimum value and average value of, for network query and technical and quality analysis.


4. Laser plate flatness measurement


Steel plate shape is an important content of steel plate quality control, and flatness is an important index of plate shape detection.

During the rolling process of the steel plate, when the steel plate passes through the roll gap of the rolling mill, the reduction rate of each point along the width direction is uneven, resulting in differences in the extension of the fibers along the width direction inside the steel plate. When the uneven extension of the fiber accumulates to a certain extent, will produce apparent and visible waves on the surface of the steel plate, such as scooping, waves, and warping of the steel plate.


Most of the shapers widely used in cold rolling and hot rolling production lines are imported from abroad.

Most of the cold-rolling applications are contact detectors, including the segmented flatness detection device of ABB Company in Sweden and the air-bearing type detection roll shaper of DAVY Company in the United Kingdom.

The hot-rolling production line basically uses non-contact optical shape detectors, mainly including the optical hot-rolled shape detectors of the Belgian Metallurgical Research Center and the optical section method shape detectors of Sumitomo Corporation of Japan.


China proposed a linear laser plate shape inspection system.


Its design principle is to place multiple linear laser emitters in two directions parallel to and perpendicular to the moving direction of the sheet, emit multiple laser lines to the surface of the sheet, form a comprehensive interlaced multi-channel laser line on the surface of the sheet, and form multiple laser intersection spot.

Install multiple area array CCD cameras above these laser intersection points to image the laser lines and laser intersection points formed by the vertical and horizontal laser emitters on the surface of the plate and the image is collected and processed by the image processing system to extract the characteristic curve in the image The flatness information of the plate can be obtained by analyzing and solving the pixel position of the intersection point.

The laser plate shape detection device has great advantages over other plate shape detection devices in terms of principle and structure. It adopts a continuous measurement method and avoids measurement errors caused by strip vibration. It replaces the traditional method of manual measurement, reduces measurement time and labor intensity, and improves safety. In particular, the measurement accuracy of the linear laser plate shape detection device is obviously higher than that of other devices, and it is easy to maintain and use and has a good application prospect.


5. Laser scanning blast furnace lining wall thickness measurement


The converter lining is a high-temperature material brick laid inside the converter, which plays a role in thermal insulation protection for the converter. An accurate and timely grasp of converter lining thickness plays an important role in safe production and improvement of furnace life.

The measurement methods used in the early days include the thermocouple method, heat flow meter method, infrared temperature measurement method, etc., but all of them are affected by the change of thermal conductivity of the lining refractory material, and the test accuracy is not high.

With the wide application of laser technology, the laser scanning converter lining wall thickness measurement system combined with laser distance measurement and automatic measurement and control technology has been applied and achieved good results. The system can scan the inner surface of the furnace lining point by point, and measure the height fluctuation of the inner surface of the furnace lining, so as to grasp the erosion of the furnace lining.

The system is mainly composed of a laser measuring head, scanning motion mechanism, distance measuring unit, control, and computing computer.

1) The laser measuring head is installed on the scanning motion mechanism and can rotate accordingly. It includes laser emitting and receiving optical systems, aiming lasers and optical telescopes, etc.;

2) The scanning motion mechanism includes horizontal and vertical two-degree-of-freedom motion mechanisms, servo motors, drivers, and high-precision shaft encoders;

3) The distance measurement unit completes the laser work control and the distance measurement between the measuring head and the converter lining;

4) The control and calculation computer realizes the motion control of the scanning mechanism and the calculation of the furnace lining thickness.

When the system is measuring, the computer controls the laser measuring head to emit a point laser and controls the scanning movement mechanism to move according to the predetermined trajectory. The emitted laser falls through the converter mouth to the point to be measured on the furnace lining and is received by the optical receiving system after reflection. The unit calculates the distance between the measuring head and the measuring point, and the computer obtains the spatial polar coordinate data (distance, horizontal angle, vertical angle) of the measured point in real-time, and the converter’s internal temperature can be calculated through the measurement mathematical model and the calibrated lining data. The wall thickness or variation of the lining.

There are two types of laser ranging, pulse type, and phase type, among which pulse type is more commonly used.

However, the phase method has the highest ranging accuracy, and its ranging accuracy can generally reach ±1 to 2 centimetres, and some can reach millimetres or even a few tenths of a millimetre. The phase method of distance measurement requires the emission of modulated continuous light waves, so the instantaneous power emitted cannot be very large, and the measurement range is relatively short. In the furnace lining measurement, the distance between the measurement system and the blast furnace does not exceed 10m, and there is no need to determine the number of half-waves in the phase measurement, so it is very suitable for the application of furnace lining thickness measurement.

The furnace lining thickness measurement system used in the metallurgical industry has been promoted and applied in many iron and steel enterprises.

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