Thickness and crown measurement technology of Baos

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Thickness and crown measurement technology of Baosteel Heavy Plate Mill

the thickness gauge and crown gauge of Baosteel Heavy Plate Mill are the measuring devices of the main product quality characteristics (thickness and crown) control system in the heavy plate rolling process. The designed product width range is 5 m and the thickness range is 5~125 mm. Due to the requirements of product accuracy, there are high functions and accuracy requirements for thickness and convexity control, and there are corresponding requirements for the real-time and accuracy of the thickness gauge and convexity gauge of the measurement system. Therefore, the use of appropriate measurement methods and compensation technology for the possible influence of the measurement process are the characteristics of the measurement system. At the same time, the technical characteristics of the measurement device itself also ensure its reliability

1 Composition of thickness and convexity measurement system

the thickness gauge and convexity gauge of Baosteel Heavy Plate Mill are radioisotope thickness measurement systems imported from German IMS company. Compared with thickness gauges previously used by other companies and Baosteel, IMS' new equipment adopts INTERBUS bus, measurement signal digitization, computer network and measurement channel redundancy technology. The structure of the whole system is clear, compact, simple and efficient, representing the latest development direction of thickness gauges and other special instruments

1.1 thickness and convexity measurement principle

produced by the nuclear decay of radioisotopes (137Cs) γ When the ray penetrates the tested object, the intensity attenuation occurs due to scattering and absorption. The degree of attenuation is related to the type, thickness and other factors of the tested object. The relationship is shown in formula 1:

. In the formula: I represents the intensity when the ray penetrates the tested object; I0 refers to the intensity when the ray does not pass through the tested object; μ Represents the mass absorption coefficient of the tested object; ρ Indicates the density of the tested object; DH refers to the thickness of the measured object

in the process of practical application, the difference of steel grade will lead to its density( ρ) Different, corresponding mass absorption coefficient( μ) It will also change. For a specific steel type, as long as the chemical composition content is known, the alloy compensation coefficient can be calculated by formula (4)

where: AI is the compensation coefficient of steel alloy; Ai( ρ) Is the compensation coefficient of steel grade density; AI (z) is the compensation coefficient of steel quality absorption coefficient; ρ Fe=7.853 8g/cm3, which is the standard density of iron; ρ X is the density of element X; μ X is the mass absorption coefficient of element X; μ Fe is the mass absorption coefficient of iron; G% (x) is the content of element X in strip steel

in the process of thick plate rolling, the measured thick plate is actually in a high temperature state, and the product thickness needs to be output by the thickness gauge in the cold state, so it is necessary to convert the hot state thickness into the cold state thickness according to equation (5)


where: DH is the thickness of thick plate (hot thickness) when the temperature is t; D0 is the temperature of thick plate when the temperature is t0 (usually normal temperature, cold thickness); α: Linear expansion coefficient of thick plate

the cold thickness of steel plate after compensation is:

1.2 composition of the system

the whole thickness and convexity measurement system is composed of two devices, namely, single point thickness gauge and convexity gauge. The main components of each equipment have a test sheet installed on site. The above data do not constitute a profit prediction element, including 50 Curie 137Cs radiation source, ionization chamber, driving device, etc., as well as the central control system. Thickness gauge and crown gauge share a set of central control system, including central processing unit, INTERBUS bus module, etc. In addition, there are some auxiliary equipment, such as cooling water control unit, blower, compressed air filtration device. The on-site detection unit of the single point thickness gauge is directly installed between the rolling mill roll and the vertical roll. Due to the limitation of installation space, the fixed installation method is adopted; The on-site detection unit of the convexity meter is concentrated in the driveable C-frame and installed at the exit of the rolling mill. It is about 10 m away from the rolling mill, considering the tensile range of the material to be tested. Three groups of radiation sources and detectors are used, as shown in Figure 1, which are respectively defined as CS side, CL side and DS side. The CL detector is fixed to measure the center of the thick plate, and the detectors on CS side and DS side can set the required thickness of the edges of the thick plate, The thickness from the edge of the thick plate to the center can also be measured by continuous scanning, and the convexity and wedge of the thick plate can be formed according to the measurement results of three groups of detectors

one group of detectors of single point thickness gauge has 8 measurement channels (ionization chamber), and each group of detectors of convexity gauge has 4 measurement channels, a total of 12 measurement channels. When the ray passes through the thick plate and enters the ionization chamber, the micro current signal generated is amplified in two levels inside the measuring head and converted into a digital voltage signal

each part of the thickness gauge and crown gauge system is connected by network. In order to ensure the independence and integrity of the system, the thickness gauge and convexity gauge build an internal independent network. The internal parts of the system communicate through internal switches, and only the server and user switches are connected with the external parts. The main functions of the server are to receive the setting data from L2 and route it to the client, collect and send the convexity data of thickness gauge and convexity gauge to L2, store various variables and parameters required by the client during operation, long-term storage and analysis of thick plate rolling thickness data, system diagnosis, and provide various data for the operation station and engineer station

Figure 2 network structure of thickness gauge and convexity gauge

the client is the core unit of processing and control in the whole measurement system. The control logic and mathematical processing of thickness gauge and convexity gauge are completed by the client. It adopts wiindow CE operating system, communicates with the server through tcp/ip, controls the bus module through the bus controller, receives the control command from L1 through UDP message, and sends the system status and real-time measurement data to L1 to participate in closed-loop control

Figure 3 INTERBUS module block diagram

the bus controller installed in the client is responsible for the control, status acquisition and diagnosis of the bus modules of each part of the thickness gauge and crown gauge. INTERBUS bus is a field bus researched and developed by Phoenix Contact company in Germany, which is suitable for its own experimental machine company. In 2000, it became the international standard of IEC61158. INTERBUS bus system is a data ring structure. This data ring is composed of a bus control board and i/o devices with INTERBUS bus interface. Bus controller is the central device controlled by data ring, which realizes the interaction between control data and peripherals

ims uses logicad software as the programming and control software of thickness gauge and crown gauge. Logicad software is a kind of graphical programming software, which can provide users with a friendly interface and can easily configure, monitor and diagnose the functional modules of the system (including INTERBUS module). Using this software, we can easily design the complete structure of a measurement system and configure all the equipment connected to it. During the operation of the system, the process data of the connected equipment can be displayed on the software or controller display screen, and the on-site process data can be read and interfered in real time. It can not only identify the faults of the system, but also locate the fault type, location and cause. Through the expansion of functions, it can provide corresponding solutions

2 system performance index

measurement range: mm

repeatability: ≤± 0.1% target thickness (thickness range: 5~80 mm)

≤± 0.2% target thickness (thickness range: 80~125 mm)

linearity: ≤± 0.1% target thickness (thickness range: 5~80 mm)

≤± 0.2% target thickness (thickness range: 80~125 mm)

drift: ≤± 0.1%/8 hours

statistical noise:

plate thickness: noise value:

5 mm ≤± 0.015 mm

10 mm ≤± 0.018 mm

20 mm ≤± 0.024 mm

30 mm ≤± 0.033 mm

50 mm ≤± 0.060 mm

60 mm ≤± 0.082 mm

80 mm ≤± 0.117 mm

100 mm ≤± 0.231 mm

125 mm ≤± 0.655 mm

3 conclusion

Baosteel 5 m wide and thick plate mill is a heavy plate collar in China The first set of ultra wide modern heavy plate mill in the region [1]. Thickness gauge and crown gauge play a very important role in the control of plate thickness and crown. Due to the special environment of rolling site, the measurement of thickness gauge and crown gauge still needs to be improved. For example, the impact of rolling mill vibration on measurement will produce random errors; Secondly, the thickness of the thick plate ranges from 5 to 150mm, and there is a temperature distribution in the thickness direction of the steel plate. Although the thickness gauge is equipped with a high-temperature radiometer, it measures the surface temperature of the steel plate, which cannot truly reflect the actual temperature distribution, which will affect the accuracy of thickness measurement; Other factors such as the influence of moisture, dust and high-temperature radiation on the measurement channel will also affect the measurement accuracy, which will be reduced through appropriate maintenance

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