McTeeth
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Excellent, Thank you
So what happened? Just a spruing issue?
Yup. Everything was done wrong here. Reservoir is too small; the button is so big that its mass was drawing the alloy that should have gone to the crown. Vent should be attached to the side of the crown opposite of the sprue and kept close to the side of the ring so it cools first, and your main sprue should attach at an angle , not flat to a side.Old school broken arm caster here.
Sprue to the thickest part of the pattern.
Sprue reservoir needs to be in the heat center of the ring. Pattern needs to be outside the heat center of the ring.
Sprue reservoir needs to be the same mass as the pattern.
Get this book: Metal Ceramic Technology, by Patrick Naylor. ISBN 0-86715-237-0
Chapter 5 has just about everything you need to know about the fundamentals of casting.
Agree. 100% and #1 reason for porosity.Sprue reservoir needs to be the same mass as the pattern..