Single SH guided wave mode generation method for PPM EMATs

Using periodic permanent magnet(PPM)electromagnetic acoustic transducers(EMATs),different shear horizontal(SH)guided wave modes can form simultaneously in some situations,which can interfere with the inspection.The main cause of this phenomenon(typically named multiple modes)is related to the frequency bandwidth of excitation signals and the transducer spatial bandwidth.Simply narrowing the frequency bandwidth cannot effectively limit the number of different SH modes.Previous researches showed that unnecessary SH wave modes can be eliminated by using dual EMATs.However,in practical applications,it is more convenient to change the excitation frequency than to use dual EMATs.In this paper,the stress boundary conditions of the PPM-EMAT are analyzed,the analytical expression of SH guided wave is established,and the magnitude of SH guided wave mode under continuous tone and tone-burst input is obtained.A method to generate a single SH mode by re-selecting an operating point is proposed.Furthermore,the influence of the frequency bandwidth of the tone-burst signal is analyzed.Finally,a single SH mode excitation is achieved with tone-burst input.

Comparison study on hot state modification of converter slag by adding Al_(2)O_(3) or SiO_(2)

The value-added utilization of converter steel slag is crucial, with China’s annual production having reached 100 million tons. The utilization of converter slag in the construction materials sector is limited as it undergoes volume expansion during the aging process, mainly caused by the hydration reaction of free calcium oxide present in the slag. The influence of alumina addition on the mineral transformation of typical industrial converter slag was investigated. Different quantities of alumina were introduced into the slag, and the original and modified slags were remelted under argon atmosphere, followed by quenching. The experimental results were compared with thermodynamic simulation calculations for further analysis. As the alumina content increases, it reacts with the free calcium oxide in slag, leading to the formation of low-melting-point calcium aluminoferrite. Additionally, alumina addition effectively reduces slag viscosity. Finally, an assessment of the energy consumption for alumina-modified and silica-modified converter slags was presented.

Numerical investigation of basic oxygen furnace slag modification with gas bottom-blowing and SiO_(2) modifier

To avoid the volume expansion of basic oxygen furnace (BOF) slag for use in building materials, a hot slag modification process was proposed to reduce free CaO (f-CaO) in the molten slag. A transient 3D numerical model of BOF molten slag modification by SiO_(2) particles was established. The flow and heat transfer of molten slag, movement and dissolution of the modifier, and concentration distribution of f-CaO in slag during the modification of BOF were studied. The distribution of f-CaO concentration is inhomogeneous all over the molten slag. The mixing effect at the slag surface is weaker than that at the half-height plane of the slag. To consume the f-CaO below 2.0 wt.% in the slag, the optimum quantity of the SiO_(2) modifier is 10.0% of the mass of the slag. The fine SiO_(2) particles help attain a lower final mass fraction of f-CaO and a higher SiO_(2) utilization ratio.