This depicts Vingas’ RHR vs. AFS-GFN results.
This depicts Vingas’ RHR vs. AFS-GFN results.
PRESENTATION Critical Characteristics Affecting the
Surface Finish of Castings, 17-094
AUTHORS Nathaniel Bryant and Jerry Tiel,
University of Northern Iowa (Cedar Falls, Iowa)
BACKGROUND Surface finish is an integral part of
casting quality specifications. Rough internal surface finishes on castings can cause the loss of efficiency for both fluids and high velocity gasses. Such is the case for turbocharger and intake manifold components. Te University of Northern Iowa has been investigat- ing mold material characteristics that affect surface smoothness for cast- ings. Te research was conducted on aluminum castings but has applica- tions and relevance in ferrous alloys that don’t exhibit defects such as pen-
etration or fused sand defects. Te study investigates the influence of molding media characteristics such as sand fineness, material type and refractory coating selection. Te goal of the project was to accomplish investment casting surface finishes in sand cast parts. Te dimensional accuracy at
which sand castings now can be produced has approached that of investment castings. 3-D sand printing technologies have greatly improved the dimensional accuracy of molds and cores but have failed to match the surface smoothness of conventional sand castings let alone investment castings. Investment casting provides
very smooth parts with excellent feature resolution and dimensional accuracy. 3-D printed sand molds and cores may provide a cost ef- fective alternative to investment
44 | METAL CASTING DESIGN & PURCHASING | May/Jun 2017
casting if the process can meet both dimensional and surface requirements. Although many changes and
improvements have been made in the area of foundry consumables, sand is the one material that has stayed somewhat constant. After mining and washing, if
required, foundry sands are clas- sified into individual or two mesh groupings and stored. Tey are combined into normal distribu- tions for shipping to the foundry customer. Although there are many different mine distributions, sand of similar AFS-GFN is supplied in similar distributions. Te industry has completed minimal study on the optimization of the sand’s screen distribution. In 1962, Swing and Vingas published their research on surface finish in castings. Tey de- termined that there was a maximum
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