|
|
POROSITY STUDYA cylindrical test casting (Fig. 1) was developed to observe porosity formation under various conditions. This stepped-cone configuration was selected because core decomposition gases would be generated rapidly, while the casting was still molten. Also, this design was conducive to studying section size, re-entrant angle (hot spot) and other geometric effects. Fig. 1. This schematic shows the dimensions of the castings used to test core-making variables related to porosity.
Molds were made with a zero-N nobake furan binder. The base core sand used for the experiments consisted of the phenolic urethane nobake binder (PUNB) mixed with a high-purity, washed-and-dried, round-grained silica sand. Coremaking consisted of adding Part I and the catalyst to the sand and mixing for 2 min, followed by the addition of Part II (a polymeric di-isocyanate resin diluted with 25% solvents) and mixing for another 2 min. The mix was hand-rammed into the corebox, and the stepped-cone cores were stripped within 5 min. Gray and ductile irons were utilized, as well as a high-carbon equivalent iron (4.3 CE) inoculated with standard foundry grade [0.75% minimum Calcium (Ca)] FeSi in the ladle. Inoculant addition levels were 0.25% Si, based on the pouring weight. All heats were prepared with virgin charge materials to ensure low initial gas content. The extent of porosity was determined by sectioning castings at several locations. Scanning electron microscopy (SEM) was utilized to observe the internal surfaces of gas porosity. |
Table of contents |
| [Paper Header] |
[Porosity Study]
 [Binder Ratio] [Binder Level] [ Casting Temperature] [Section Size]
[Sand Effect] [Iron Oxide Additions] [ Binder Dispersion/Mixing]
[Metal Composition] [Core Age] |
|
[Eliminating Porosity]
[Ti and Zr Additions] [In-the-Mold Additions] [ Core Washes]
[Core Post-Baking] |
| [Discussion] |