Venting a cylindrical core

From molding systems to gating, what goes on at the molding bench will make or break a casting.
geoff_p
Posts: 21
Joined: Wed Jan 04, 2012 9:14 am
Location: Aranyaprathet, Thailand

Re: Venting a cylindrical core

Post by geoff_p »

Phew! Only a gazillion years ago, I promised to try again at the weekend. Shouldn't have opened my mouth just before the monsoon-season.
Updates:
A company in Bangkok sold me a kilo of Silica-gel for 100 Baht (3 dollars US), so I set about trying to dissolve it in Caustic-soda solution. I should have bashed it about a bit because those little beads took forever to dissolve. However, the end result beat sh*t-on-a-blanket. I'm impressed.
A quarter-cup of beads eventually went into the liquid, and amounted to about 400mL. I've been playing with it making cores galore and still have a 1/2 bottle left (and enough silica-gel for another two lifetimes.)

Last week, I molded a core for this darned cylinder but the weather turned bad so I left the core in my CO2 box overnight. Next day it had crumbled away at both ends, and totally collapsed when I touched it. Mai pen rai (Thai for No Matter) try again another day.

2nd attempt turned out quite hard but wet. Poured the casting, got a huge steam-bubble and a somewhat useless casting.

3rd attempt, today. Made the core yesterday, including a vent right through from end-to-end, left it in CO2 for an hour-or-two, then gently warmed it in the oven - 100C for 1/2 hour. This morning I re-heated the core, to 150C, while I prepared the rest of the mould.
While the pot was melting, I heated the core yet again so it was hot when I closed the mould and poured.

Beautiful (though I say it myself.)

I'll get the pics off the camera and post them tomorrow.

Geoff
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Jammer
Posts: 1487
Joined: Thu Jun 02, 2011 4:04 pm
Location: Ohio

Re: Venting a cylindrical core

Post by Jammer »

Sounds great Geoff, I guess "Beat s on a blanket" Means it worked? I haven't tried a core for a while, but I plan on baking them when I do.
Waiting on Pics.
quando omni flunkus moritati 8-)
geoff_p
Posts: 21
Joined: Wed Jan 04, 2012 9:14 am
Location: Aranyaprathet, Thailand

Re: Venting a cylindrical core

Post by geoff_p »

Sorry for my expression. I meant it makes a glue like nothing I've ever seen - doesn't want to let go of anything it touches, especially when mixed into sand.

I have no idea what proportions I used - just a splash into some sand and mix it in a small plastic shopping-bag a.l.a. MyfordBoy.

Ordinary powder onto a well-varnished mould just doesn't release. So I give it a spray of cooking-oil before putting the sand/sodium-silicate mix in. I then put the whole shebang into the CO2-box for a short while to harden to exposed bits and make handling and release easier. Despite the ever-so-slightly oiled surfaces, the CO2 seems to penetrate the core quite well.

Forgive my exceedingly vague methodology - my kitchen scales wont indicate at 40-gram resolution, so, in common with most things in my foundry, I tend to take a flying guess at quantities.

Geoff
dallen
Posts: 2321
Joined: Sat Jun 04, 2011 9:06 am
Location: Oklahoma

Re: Venting a cylindrical core

Post by dallen »

geoff_p wrote: Forgive my exceedingly vague methodology - my kitchen scales wont indicate at 40-gram resolution, so, in common with most things in my foundry, I tend to take a flying guess at quantities.

Geoff
hey if it works why change, glad the cores and working out, also nice to hear that the recipe that Jammer posted worked for someone else, I have the advantage of being able to purchase the stuff from a foundry here in town pretty cheap.

DAllen
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