Tried a different riser sleeve on a small bronze pour and got a weird shrink cavity

I was pouring a set of small gear blanks last Thursday, maybe 4 inches across. Instead of my usual fiber sleeve, I grabbed a ceramic one from the back of the shop that was a slightly bigger diameter. The metal filled fine, but when we broke it out of the sand, there was a perfect little sinkhole right under the riser. The ceramic must have cooled the metal too fast up top, so it couldn't feed properly. Anyone have a good rule of thumb for when to switch sleeve types on smaller jobs?

4 comments

4 Comments

wendym821mo ago

Saw a video where a guy said the sleeve diameter should match the hot spot of the casting. Your bigger ceramic one probably pulled heat from the wrong spot. Might need to stick with fiber unless the shape really needs the extra chill.

jamiehayes1mo ago

I mean, that video guy's rule sounds a bit too strict. Sometimes a bigger ceramic sleeve can help control the whole thermal profile, not just one spot. Maybe @wendym82 just needs to try it on a test pour.

alice8171mo ago

Oh man, I feel this. I tried using a huge sleeve once thinking I was being smart, and my casting came out looking like a sad pancake. Totally messed up the whole solidification. Jamie's got a point about testing it, but I learned my lesson the hard way lol. Sometimes the simple rule is there because people like me will overcomplicate it and ruin good metal.

kai8396d ago

Ugh, classic move. I've definitely been the genius who grabs the fancy ceramic sleeve thinking it'll solve everything, only to make a perfect metal donut. @wendym82 is onto something with the hot spot idea, but my luck, I'd probably measure the wrong spot anyway. That shrink cavity is just the metal's way of telling you it wanted a cozy fiber blanket, not a cold ceramic bath.