Friday, June 19, 2015

Trying a few new things.

Once I got the crucible cleaned up last night, I had just enough time to try and get a pour in. Actually, I didn't have time, but who needs sleep anyway.

There were a couple of existing problems with my casting process that I wanted to address so I grabbed my go-to test patterns: the OF keychains. 

The first issue I to look at was the separation I keep getting between the layer of fresh versus used Petrobond. If I didn't mention it before, I use new/fresh PB against the patterns with the belief it will help me get a better mold face. I then back that up with used PB just because I can't afford to use all fresh for a mold. One of these days I need to figure out how to reclaim and refresh this stuff.

To try and fix the separation between the new and old, first, I rammed the new layer of PB into the flask. Then, using a pointy wire, I scratched up the back surface of the PB to make a sub-layer of loose PB for the older stuff to mix with.

Yeah, that didn't work for shit. As soon as I flipped the drag, most of one corner flaked off and fell on the table.

Not a total loss so, I kept going.... I'd also been having problems with sections around the parting line in the cope falling off and becoming a part of the drag. I've since learned (thanks to the great info on the Kansas Brass Foundry website) that it is usually an indicator that the parting line isn't quite at the right spot. That is certainly the case most of the time with the bear, but these keychains are so thin, I think it's that I'm overdoing it.

For this round, I was very meticulous about getting them as close to halfway as possible and also very, very even and level. The result was a nice set of clean parting lines in the cope half of the mold.

One final issue I wanted to investigate was the little imperfections I keep getting in the faces of my castings. I'm reasonably sure that it's the result of loose sand (and not parting dust) in the mold faces. Previously, I only removed the major chunks that broke loose but tried to leave the rest of molded surface alone. This time, though, I tried to be very thorough cleaning any loose sand that was in the mold faces. I did this with a soda straw and gently blew the dust out.

In some cases, I wasn't quite so gentle and ended up blowing part of the pattern away. (Look at the Jar pattern in the bottom middle.) In other cases, I wasn't as thorough as I thought. (See the nugget near the bottom of the top left OF pattern? I didn't.)

With molds made and the furnace to temp, it was time to pour. I forgot to mention, this was the first attempt with my new, larger flasks I made during 1.2. What better way to break in a new flask? Over pour it and let metal squirt out to set it on fire! (Sorry, this was after I blew the flames out. I thought about getting a picture while it was ablaze but I decided I didn't want to destroy the thing during it's maiden voyage.)

Once things had cooled down, it was time to inspect the results of the changes.

First things first, I have no fucking clue where the third Jar pattern went. I think I didn't dig the gate to it well enough so no aluminum ever flowed in.

As for the patterns that did take, the surface finish was greatly improved but still not to the level I would like. So I'm on the right path, I think, just not there yet. Also, did you see the nugget in the top left pattern? I did, this time.

And one final thing, I didn't weigh down the flask... AGAIN. I didn't think I needed it since it was so large compared to the volume of the actual patterns. WRONG! I need to make that a mandatory step every time regardless of the pattern. The extra flashing isn't a huge deal, I can clean it up, but it would be nice to not have to. 

Anyway, still nothing I'm ready to show off to everyone as a finished product but... we're getting there, one mistake at a time.

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