Research On Non-contact Detection Method Of Flatness Stress In Steel Strip

The "latent" flatness existing in high/ultra-high strength hot/cold rolled steel strip products is also called flatness stress problem. It is a current prominent technical issue which restricts specification development and flatness quality improvement of this kind of products. Realizing the on-line continues detection of "latent" flatness for tension-free and tensioned un-straight steel strips is not only the basic condition to solve the flatness problem but also a technical difficulty failed to solve all the time. This dissertation proposed new magnetic detection methods for internal stress in ferromagnetic material for reference in recent years, put forward the new magnetic detection methods and technical solutions for "latent" flatness--flatness stress problem in steel strip, designed and built the prototype experimental system, validated and studied the feasibility of this technology. We also developed the industrially applicable five points measured flatness stress detection system, and verified the feasibility of the new methods.The main achievements of this dissertation are as follows.(1) Aimed at "latent" flatness detection problem in high/ultra-high steel strip, we put forward the corresponding magnetic penetration internal stress detection methods and designed the prototype experimental system. The comparative study on single-sided way and magnetic penetration way detection plan was carried out. Finally, we verified the technical feasibility of new methods in magnetic penetration and determined the magnetic flatness stress detection technical solutions.(2) Aimed at magnetic penetration stress detection methods for steel strip which is based on magneto-elastic effect, the mathematical model for magnetic force considering the influence of magnetic air gap was built by using the theory of magnetic circuit and magnetic anisotropy. We got the relation between the output voltage system and unidirectional stress loaded on the steel strip in the process of magnetic penetration flatness stress detection. We built the simulation calculation model of magnetic penetration stress sensor on the basis of mechanism analysis and theoretical analytical, analyzed the distribution and evolution of magnetic field for steel strip in the process of magnetic penetration internal stress detection, revealed the detection principle and action rules, and verified the calculation results by experiments.(3) We put forward the stress characterization methods through phase shifted signals based on the magneto-elastic effect, improved the stress induced measurement method of voltage amplitude based on the magnetic anisotropy of the material, developed the double-parameter magnetic penetration flatness stress detector for steel strip which can be practically used based on the embedded ARM +FPGA, and realized the representation of flatness stress for steel strip based on two different kinds of signals which are stress induced voltage amplitude and phase difference. By using the detector and magneto-elastic sensor developed and designed by ourselves, we did the testing experiments on sample took from Q235 and non-oriented silicon steel strip, and got the basic stable quantitative relationship and influence law between magnetic flux and the principal stress. We also verified the sensitive correlation between two signals and sample flatness stress, and made a further study of the sensor parameters’influence law on the stress measurement result.(4) We carried out several key technology researches on the magnetic principle flatness stress detection. The study showed that by using the sine wave low frequency resonance technology to power the circuit, the magneto-elastic stress sensor can achieve low power consumption. Aimed at the electromagnetic interference on the spot, the anti-jamming design can ensure stable detection signal transmission. The lift-off effect of the sensor in the non-contact detection process is discussed, and put forward the method to solve the fluctuation of the system stability caused by the lift-off value changes.(5) In order to realize the high speed dynamic test of the large size steel strip under tension and in the high speed running condition, we designed and manufactured the steel strip fast high precision scanning flatness stress simulation experimental platform, applied the self-designed sensor and magnetic penetration detection system on this experimental platform, and realized the internal stress detection for steel strip approximate to the production conditions. It laid a solid foundation to further put the magneto-elastic effect penetration flatness stress detection system of cold rolling process into field application.