Molding Methods & Materials (Div. 4) 1999 Best Paper Award


Porosity in Iron Castings from Mold-Metal Interface Reactions


Last year’s Molding Silver Anniversary presentation updates research on iron casting porosity with a focus on current urethane nobake technology and eliminating defects.

R.L. Naro,
ASI International Ltd., Cleveland
This article was adapted from an AFS Transaction paper .**

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Editors Note—Each year at the AFS Casting Congress, presenters from 25 years ago are asked to revisit their research, updating findings as prestigious Silver Anniversary speakers. In this case, 1999 presenter Rod Naro also was honored with the Molding Methods & Materials (Div. 4) Best Paper Award for his work to uncover causes of and remedies to iron porosity defects attributed to nobake binders.
Since the original presentation on nobake binder-related porosity was made in 1974, innovations in synthetic binder technology have resulted in the widespread use of nobake molding and coremaking systems, but casting defects continue to pose a problem.

The chemistry of phenolic urethane binders is essentially the same as in 1974, but the Part I resin (a poly-benzylic-ether-phenolic resin diluted 50% by solvents) has less free formaldehyde to reduce odor. In addition, the solvent system has a higher boiling point for improved environmental properties.

The phenolic urethane binder family contains four basic elements: 72% carbon (C), 8.5% hydrogen (H), 3.9% nitrogen (N) and 15.5% oxygen (O). The gases responsible for subsurface porosity in iron castings are N and H—because the high silicon (Si) content of gray iron suppresses carbon monoxide porosity. C and O from the binder usually present no problem.

The original research was aimed at determining how coremaking parameters and melting variables influence porosity and developing remedial techniques to alleviate these problems. This update examines the same questions in current formulations.

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]