BLOWHOLES


Causes: • Gas volume and pressure; insufficient venting. Remedies:


• Improve core venting. • Reduce gas. • Dress cores; dry cores.


PINHOLES


Causes: • More common in areas away from the gate, they begin with a surface reaction between water vapor and other elements.


SCABBING


Causes: • Poor quality, insufficiently conditioned or too little bentonite; fine quartz or salt proportion too high.


• Molding sand too fine. • Excessive or irregular compaction. • Sand heated too much by inflowing metal and long exposure to radiated heat.


Remedies:


• Improve and/or increase bentonite and use coarser sand. • Improve water quality. • Reduce compaction and ensure even distribution of sand. • Improve gates and/or aim for shorter pouring times.


PITTED SURFACE


Causes: • On ductile iron, it can indicate too much moisture or fluoride in clay-bonded sand.


Remedies:


• Replenish sand. • Use insulating materials.


Remedies:


• Reduce impurities and deoxidize melts as much as possible.


• Reduce additives. • Increase pouring temperature, reduce flow rate and avoid turbulence.


PENETRATION


Causes: • Coarse sand. • Excessive compactiblity. • Nonuniform core or mold compaction.


• Hot spots near a gate. Remedies


• Add finer sand, additives or fines to improve sand texture and flowability, and reduce compactibility.


March 2014 MODERN CASTING | 57


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