Numerical Simulation and Optimization Design for Magnetic Fluid Sealing Device
In this paper the principle of magnetic fluid seals is discussed. Based on the finite element software ANSYS, the magnetic field of magnetic fluid sealing device with three slots and four pole teeth is analyzed, and the size parameters of magnetic fluid sealing pole are optimized. The results show that the difference between the maximum and minimum intensity of magnetic field in the area near the shaft determine the sealing capacity of sealing device. The gap of seal should not be larger than 0.3mm. The optimized parameters which are provided for practical design can increase sealing capacity of sealing device as well as decrease the volume of sealing device.
Numerical Simulation and Experimental Validation of the Critical Pressure Value in Ferromagnetic Fluid Seals
Ferrofluids have various engineering applications, and one of them is magnetic fluid seals. Development for this design is a complex process, which requires knowledge about ferrofluid physical properties and magnetic field distribution inside the sealing gap. One of the most important parameters of ferromagnetic fluid seals is a critical pressure value. It is a pressure at which rapid leakage will occur. This publication presents the results of critical pressure value obtained from experimental studies and calculations based on numerical simulations. Shape of sealing stage, volume of ferrofluid, and volume of permanent magnet used in seal construction were taken into account. Experiments and calculations were performed for four ferrofluids differ in saturation magnetization, density, and zero magnetic field viscosity.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.