For this study, a carbon-based
coating resilient in an aluminum diecasting environment, where cast- ing pressure is added, was tested. Te report includes durability tests of carbon nanofiber, carbon-graphite and carbon-fullerene coatings and their effects on solidification structure and casting quality.
parts and lead to galling defects. Fig. 2 shows a testing setup to evaluate metal flow by mold surface roughness and carbon materials. It consisted of an electric furnace and a 7.9 × 7.9 × 1.2 in. (200 × 200 × 30 mm) sample mold. The test piece mold was tilted 20 degrees to create a slope for metal flow. All coated surfaces of the molds were recorded with a thermo camera to study the heat transfer condition. The condition of metal flow was classified into four grades and each was indexed. The sum of indexes, obtained by pouring molten metal three times, was defined as the metal flow index. Te metal flow test results are shown in Fig. 3. For all types of
2 Procedure
When the uneven- ness of a mold’s surface is significant, aluminum can flow into concave
carbon coatings, metal flow was not smooth on a mirror surface, that is, Ra<1.0 µm. Any type of car- bon coating showed a good result at Ra=1.5 µm or above. Infrared images taken by a thermo camera indicated that immediately after metal was infused, the temperature of the test piece surface was within the range of 167F (75C) and 181F (83C) for the case of a metal flow index score of 3 or less; between 143F (63C) and 158F (70C) for a score between 5 to 7; and 122F (50C) or less for a score of 8 or over. In this way, a relationship between the heat transfer at metal flow and the metal flow property was confirmed. Te indicated tem- peratures were corrected using the infrared emissivity that had been measured in advance. Te emissivity of the carbon nanofiber, carbon- graphite and carbon-fullerene
coatings were 0.9 or higher, which proved the temperature measure- ments were accurate. Figure 4 shows the experimental
setup for a durability test. A given carbon material was coated on the mold surface and a ring-shaped die body was placed on it. No parting agent was used. A total of (44 lbs.; 20kg) aluminum was melted, and 1.1 lbs. (480g) was poured into the ring. A weight of 21.6 lb (9.8 kg) was placed above the casting. Te weight, the casting and the die body then were horizontally pulled at once. When they started moving, it was defined as the mold release force. If nothing moved, it was defined that they were stuck. Te test results in Fig. 5 show the CF15 coating, which is the combination of C15 and fullerene coatings, displayed significantly superior durability.
Fig. 1. The diagrams show the wettability models between molten metal and mold surface at (a) molten metal infusion, (b) pressurization and (c) solidification.
Fig. 2. The experimental setup of the molten metal flow test featured an inclined mold plate with different types of carbon coatings.
Fig. 3. The graph shows various carbon coatings on a test mold. The metal flow index of each surface coating is the total score of three experiments.
February 2014 MODERN CASTING | 57
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