quent investigation using an improved sintered bauxite product showed improvement in metal penetration resistance. Based on the laboratory results and industrial trial, the sin- tered bauxite aggregate meets casting requirements for ferrous applications without veining defects.
Specific Surface Area, pH, Acid De- mand Value and Base Permeability
According to the test results, the Bauxite 40/50 aggregate exhibited a surface area half of silica, indicat- ing sintered bauxite could require less binder, though not in the same percentage reduction, based on the baseline surface area of silica sand. Te binder demand for sintered bauxite would be comparable to chromite sand. However, chromite exhibited lower surface area, which is unex- pected because of the sand distribution and acicular nature of chromite. Based on this observation, bauxite might have surface porosity that increases the surface area and could influence
Aggregate Silica 50/140 Bauxite 40/50
Chromite 40/100 Silica 50/140 Bauxite 40/50
Chromite 40/100 Coating
Graphite Graphite Graphite None None None
P Index 35
34.3 43.8 27.8 37.0 37.3
binder demand. Te most notable feature of the bauxite product was the exceptional permeability. Tough the advantage of lower permeability would be related to a decrease in gas-related defects, the increase in permeability would lead to a higher propensity of metal penetration defects.
Bulk & Tapped Density Te sintered bauxite has a density
between chromite and silica sand, indicating molds and cores using sintered bauxite would be lighter than chromite sand and heavier than silica sand. Additionally, sintered bauxite would require less binder than chro- mite based solely on the density.
Linear Expansion As seen in Fig. 1, silica, as expected,
goes through the alpha-beta phase transition at 1,045F (580C) and starts undergoing a cristobalite transition at 2,410F (1,300C). Bauxite 40/50, bauxite 40/100, and chromite display lower linear expansion than round
V Index 38.5 4.3 0.0
61.5 1.3 0.0
Overall Index P Index Rank 73.5 35.5 43.8 89.3 40.3 37.3
3 2 6 1 4 5
grain silica. Te bauxite 40/100 exhib- ited a lower linear expansion rate up to 1,475F (800C) than the bauxite 40/50 product but then the expansion rate increases up to the identified sintering point. Chromite starts sintering near 2450F (1350C) while bauxite 40/50 and bauxite 40/100 start sintering at 2,100F (1,150C).
Specific Heat Capacity Te bauxite 40/100 showed a rise in
thermal heat capacity to approximately 800C, starting at 0.75 J/g C and increasing to roughly 1.4 J/g C (Fig, 2). Chromite 40/100 showed a thermal capacity range of 0.65 to 1.4 J/g C for the temperature range investigated. In the case of silica 50/140, the specific heat capacity increased from 0.8 to 1.1 J/g C to approximately 575C followed by a decrease to 1.0 J/g C at 650C with a subsequent increase to 1.1 J/g C at 800C. Tis change in thermal heat capacity between the range of 575C and 650C can be attributed to the phase change of silica. Based on the
Table 1. Class 30 Gray Iron Step-Cone Castings Analysis – Phenolic Ester-Cured Binder System. In the table, P represents penetration and V represents veining.
V Index Rank 5 3 1 6 4 1
Overall Index Rank 5 1 4 6 3 2
Table 2. Class 30 Gray Iron Step-cone Castings Analysis – Furan Binder System. In the table, P represents penetration and V represents veining.
Aggregate Silica 50/140 Bauxite 40/50
Chromite 40/100 Silica 50/140 Bauxite 40/50
Chromite 40/100 Coating
Graphite Graphite Graphite None None None
P Index 34
46.9 28
30.3 53.9 38.3
V Index 59.5 4.3 47 66 0
13.5
Overall Index P Index Rank 93.5 51.2 75
96.3 53.9 51.8
3 5 1 2 6 4
V Index Rank 5 2 4 6 1 3
Overall Index Rank 5 1 4 6 3 2
Table 3. Class 30 Gray Iron Step-cone Castings Analysis – Phenolic Urethane Cold-Box Binder System. In the table, P represents penetration and V represents veining.
Aggregate Silica 50/140 Bauxite 40/50
Chromite 40/100 Silica 50/140 Bauxite 40/50
Chromite 40/100 Coating
Graphite Graphite Graphite None None None
P Index 46.5 58.8 38
41.8 51.3 44.5
30 | MODERN CASTING July 2015
V Index 58
0.8 8
20.5 0 0
Overall Index P Index Rank 104.5 59.5 46
62.3 51.3 44.5
4 6 1 2 5 3
V Index Rank 6 3 4 5 1 1
Overall Index Rank 6 4 2 5 3 1
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