THE PICK-UP OF MICRO BUBBLES DURING LiMCA II MEASUREMENTS POST AN INLINE GAS FLUXING UNIT

摘要

The most common and reliable method of documenting the removal efficiency of a particle filter is to use the LiMCA apparatus. This method measures the electrical resistance through a 300 mu m opening of an insulating aluminosilicate probe as melt is sucked into the probe. As particles are passing the orifice the resistance is continuously changing. The resistance versus time information is used to calculate the number and size of particle. All gas fluxing units produces various amounts of micro bubbles, which stays in the melt for a long time. These small bubbles are to some extent measured as particles in the LiMCA measurements. This work has focused on determine the pick-up of micro bubbles in the LiMCA apparatus after the 1-60 SIR melt refining unit. After this unit an probe with an extension tube were used to minimize the micro bubble pick-up. Only micro bubbles smaller than diameter 40-50 mu m were found to be picked up in the LiMCA measurements. The measurements in the 15-20 mu m range were largely influenced by the micro bubbles. Finally the removal efficiency of the SIR unit was calculated accounting for the micro bubble pick-up. The removal efficiency was estimated to be 50 percent for particles of diameter 2 mu m. 98 percent for particles of diameter 40 mu m and close to 100 percent for particles with diameter larger than 50 mu m.