Abstract
The addition of grain refiner particles in the aluminum melt is known to reduce the filtration efficiency of ceramic foam filter (CFF). In the present work, a systematic study on the influence of the addition level of Al-Ti-B master alloys and the inclusion level on the filtration performance of aluminum melt has been investigated by pilot-scale filtration tests using 50 PPi and 80 PPi filters. The inclusion level of the melt has been measured using both LiMCA and PoDFA. For 80 PPi CFF, the N20 inclusion (diameter larger than 20 μm) value in the post-filtrated melt does not increase when an ultra-high level of inclusions is introduced in the form of chips. For the melts with a low level of grain refiners (~ 0.5 kg/ton), the filtration performance of CFF is not affected by grain refiners, regardless of inclusion load. An addition of 2.0 kg/ton grain refiners reduces the filtration performance for melts with a high inclusion level, where post-filtration inclusions with the size of 15-20 µm were significantly increased. It is found, however, for the melts with an ultra-high inclusion load, the filtration performance of 80 PPi CFF is not affected by the grain refiner addition up to 2.0 kg/ton. The interactions between inclusions and grain refiner particles and the filtration mechanism have been studied by characterizing the spent filter and measuring the pressure drop during the filtration process. It is revealed that the strong adherence between oxide film with grain refiner particles dominates the grain refiner influence on the filtration performance of CFF. During the filtration process, oxide films have strong influences on the capturing of other inclusions such as oxide particles and TiB2 particles by the filter. A mechanism based on the interactions between oxide films and grain refiner particles is proposed to explain the CFF performance under the influence of grain refiner.
Highlights
AN aluminum melt of high cleanliness, namely a less content of contamination, is crucial for the metal quality of aluminum castings, the subsequent thermomechanical processes, and the mechanical properties of final products
Sampling at 68 minutes, which brings oxide skin at the melt surface into the bulk of melt, disturbing the Liquid Metal Cleanliness Analyzers (LiMCA) measurement. These results show that a low level of grain refiner addition (0.5 kg/ton) does not seem to affect the 80 PPi filter performance at any inclusion load
Test-7 (2.0 to 4.0 kg/ton grain refiner) shows a much lower total removal efficiency than test-6 (0.5 to 1.0 kg/ton grain refiner) with 50 PPi filter, which confirms the strong influence of a high addition level of grain refiner particles on reducing the filtration performance of 50 PPi filter
Summary
Manuscript submitted on April 22, 2021; accepted August 20, 2021. carbides, borides, nitrides, etc.[1]. The grain refiner particles were supposed to be the reason for filtration efficiency reduction They pointed out that the inclusions can form a ‘‘bridge’’ at the filter window, which increases the filtration efficiency by changing the filtration mode from a less efficient depth mode into a more efficient cake mode. They suggested that the grain refiner particles could destroy or prevent the formation of the inclusion bridge, which, caused the reduction of filtration efficiency. Different from the particle bridge theory, a new explanation for why grain refiner reduces filter performance is given
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