Removal of Alumina Inclusions from Molten Steel by Ceramic Foam Filtration

Abstract

The efficiency of removal of solid alumina inclusions by filtration and the distribution of inclusions captured through the thickness of the filter was investigated for an aluminum killed 316 stainless steel casting. A mold design was developed using modeling software to produce two castings that fill simultaneously, one with a filter and the other without a filter. The design was optimized to produce the filtered casting and unfiltered casting from a single ladle pour, while also matching the fill rates and avoiding turbulence and reoxidation during pouring. Samples from the filters and the castings were analyzed using an SEM with EDS and automated feature analysis to measure the efficiency of inclusion removal for a 10 ppi zirconia foam filter. Results showed that inclusion removal efficiency depends strongly on the initial inclusion concentration and that the alumina inclusions are captured within the filter at the filter web-steel interface. This study also documented that inclusion floatation inside the mold cavity plays a role in reducing the inclusion concentration in the casting. The distribution of alumina inclusions captured through the filter thickness was quantified using elemental mapping and the inclusion distribution was found to decrease exponentially, following first-order capture kinetics.

A theoretical investigation into gallic acid pyrolysis

“…[1][2][3][4][5][6][7] Due to the enhanced durability of the steel castings after filtration, castings have to be fixed or discarded less often, leading to an economic advantage. 5 Although steel filtration can also be performed with the help of sintered oxidic filters, [8][9][10][11] carbon-bonded filters exhibit excellent hightemperature behavior, such as a marked resistance to thermal shock and corrosion, and they do not suffer as much from creep as other filter materials. 1,[3][4][5][6][7]12,13 These desirable features of carbon-bonded filters are rooted in the use of carbon-containing binders, which form a stabilizing carbonaceous matrix between the filter particles after heat treatment.…”

Filtration Efficiency in the Recycling Process of Particle-Reinforced Aluminum Alloys Using Different Filter Materials

“…26 The highest detected filtration efficiency of non-metallic inclusions was 41%. 25 Higher removal efficiency of 95% for large alumina inclusions from steel alloys was reported by Raiber et al 27 using 25 ppi CFFs.…”

“…Other studies recommended this critical velocity in dissimilar alloy systems such as FeM-nAl steels to minimize air entrapment and reoxidation defects. 24,25 Thereby, 10 ppi zirconia foam filters (Stelex, Foseco) were used with a predefined pouring time, providing that a longer filling time resulted in higher air entrainment and slower filling rate, which created premature solidification defects, such as cold shuts or misruns. 25 Contrarily, shorter filling time led to a higher absolute velocity and more turbulences.…”

“…5 Furthermore, the application of 10 ppi CFF made of zirconium oxide (Stelex, Feseco) similarly resulted in the effective removal of non-metallic inclusions from austenitic steel castings (FeMnAl steels). 24,25 Besides nonmetallic inclusions, liquid inclusions can be also removed by 10 ppi magnesia-stabilized zirconia foam filter from stainless steel 316 melt. 26 The highest detected filtration efficiency of non-metallic inclusions was 41%.…”

Testing Self‐Interaction Correction for Molecules in Solution

“…The Collaborative Research Center (CRC) 920 aims at developing filter materials and filtration techniques for metal melts to achieve a significantly higher purity of the resulting raw materials. For the specific purpose of removing nonmetallic impurities from molten steel, sintered oxidic filters [1][2][3][4] and carbon-bonded alumina foam filters [5][6][7][8] have been applied successfully. Currently, the standard manufacturing process of carbon-bonded filters includes the use of pitch binders such as CarboresP or closely related resins such as resoles and novolaks.…”