Table 4. AFS-GFN Results Sample ID
Sintered Bauxite 40/50 Sintered Bauxite 40/100 Sintered Bauxite 40/70 Sintered Bauxite 70/140 Chromite 40/100
Round Grain Silica 50/140
results, sintered bauxite 40/100 has a thermal heat capacity between silica 50/140 and chromite 40/100.
Tensile Strength Results
Te significant contributor to higher tensile properties of silica sand for the furan binder system can be attributed to the higher surface area and broad screen distribution, provid- ing numerous binder bridge contact points. Te bauxite 40/50 was com- parable in strength, though slightly lower, than silica sand. When tested using the phenolic ester-cured binder system, no observable differences were detected between all three aggregates. For the phenolic urethane binder sys- tem, the bauxite 40/50 was observed to have the lowest tensile strength. Because bauxite 40/50 is a sintered aggregate, it has a tendency to absorb the phenolic urethane resin. However, the bauxite 40/50 tensile strength pro- file would be acceptable for metalcast- ing applications.
Step Cone Casting Analysis
Te casting analysis results for coated and uncoated cores produced using the phenolic ester-cured binder system poured with a class 35 iron are shown in Table 1. Te best perform- ing aggregate was the bauxite 40/50 with a graphite coating. Te signifi- cant contributing factor to the overall index was penetration resistance. When comparing the index values for uncoated cores, penetration resistance was comparable to chromite sand, which can be attributed to the grain fineness value for bauxite and chro- mite. Silica sand performed the worst for coated and uncoated aggregate cores based on the overall index value, mainly due to a propensity to form veining defects. Table 2 shows the casting analy-
sis results for coated and uncoated cores produced using the furan binder system. Bauxite 40/50 performed the
Fig. 1. This graph shows the specific heat capacity of the three synthetic sands. July 2015 MODERN CASTING | 31
GFN 35 56 40 78 45 63
Screen Classification 2-screen 4-screen 3-screen 3-screen 4-screen 4-screen
best in overall defect resistance with the coated and uncoated bauxite ranking in the top three best overall performing aggregate material. Te major attribute was its veining resistance because of the low thermal expansion properties of bauxite 40/50. However, the penetra- tion resistance was markedly reduced, attributable to low grain fineness and high permeability of bauxite. Table 3 shows the casting analysis
results for coated and uncoated cores produced using the phenolic urethane coldbox binder system. Te overall defect index value of the bauxite aggregate performed noticeably better than silica sand but was slightly worse that chromite sand. Similar to the furan binder system, lower penetration resistance was the contributing factor to the overall defect ranking. Additional step cone castings were poured to evaluate three bauxite prod-
ucts that were engineered to combat metal penetration. Te aggregates investigated were bauxite 40/70, baux- ite 40/100 and bauxite 70/140. Screen distribution and GFN values for these aggregates are presented in Tables 4 and 5. Te purpose of the testing was to broaden the screen distribution and increase the GFN to decrease the high susceptibility of metal penetra- tion observed with the bauxite 40/50 product. Since no veining defects were observed with the bauxite product, only metal penetration was evaluated upon sectioning the castings. Addi- tionally, only class 30 gray iron and low carbon, low alloy steel were poured into phenolic urethane cold box cores. Noticeable improvement in metal penetration resistance was observed for both ferrous alloys, demonstrating synthetic sands are viable alternative aggregate materials if engineered for specific applications.
Gertzman Casting Analysis Analysis of Gertzman cores was
performed to assess metal penetra- tion, sintering and veining defects of bauxite 40/50, silica sand and chromite
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