Surface finish help

Im not real sure on this one. What was the parts orientation during the pour?? And what was the pattern material, wax, foam, other ??

 

I have a few more questions, and some ideas on how to correct... but wife is making me mow the yard Ill be back later....

 

What was your shell temperature when poured??

Im thinking this is mostly caused by your pour temp being a bit low, but could have been caused during solidification with the thicker parts drawing metal from the thinner sections. I would try raising your pouring temp to 1550 with a shell temp of 600 F and do not bury them in sand...

I would also not mess with degassing, alot of times this can cause more problems than it cures (but I don't think that was the issue here)

Biggest improvement would come from gating into the bottom of the casting so that the part fills from the bottom up. You could run the sprue down the side in the same orientation as you previous casts and gate it into the bottom section, the round protrusion, and finally at the top flange as a vent point. Im assuming this part is for a auto intake??? Looks pretty trick!

 

Ok, I see what your doing..
Fire your shells, then let them cool and inspect them for cracks and blow them out in case any loose bits are in them. You can patch them up later with some slurry if you need to. You really dont want the shell temp too high for casting as it can cause all sorts of weird shrinkage issues with aluminum..
I actually cast aluminum into cold shells if the casting has any kind of thickness to it. But with your cross section I think you should shoot for 600f (or 550 in the wife's oven) while melting your aluminum in the kiln.

I've also found that doing a slow ramp up in temps for burn out of the pla has less cracking issues than if you flash fire.
Also the pla seems to have less issues with cracking the shell than regular pla.

Gating more like this.... excuse my horrible art work, but should give you an idea...

 

Pretty slick!! I'm dropping an LQ9 into my 56 buick when I find the time....

 

Try the solutech ultra pla, so far it seems to have made a big difference for me. Prints nice too.. and let me know what you think.
And be sure to post pictures of the finished product. We love pictures here

 

Yea, you won't need the cup for the riser...
And you can slim down that sprue. Might want to consider printing the gating system so it has a bit of strength to it...

 

Hey, how many shell layers have you been going with??
I've been using 10 but I use a graded play sand for all the layers. Makes the shell between 1/4" and 3/8" when done...

 

To me that looks like debris in the mold but as David notes, there can be some strange Ju-Ju from time to time with aluminum in shell. If it was on the bottom (sinking debris) or top (floating debris) I'd say more likely the latter but the burn out residue can sometimes adhere to the shell as well.

I'm a lost foam caster but used to use shellac occasionally as glue and to in attempts to improve surface finish. I stopped using it because as glue it didn't burn out very cleanly compared to other glues and didn't improve the finish because of how it burned and reacted with molten metal. Of course, this was unfired before metal contact, and with shell, you are able to burn out at much higher temp.

That's an enormous sprue for the size of the part. I realize with shell it can be as much about having enough strength to handle the shell weight. Styrofoam cups are convenient but conical pouring cups are notorious for aspirating air. Since you have a preheated mold, you can probably tolerate some air entrainment because it will buoyantly escape, but it is suboptimal and can create oxide defects.

To eliminate entrained/aspirated air, I think you'd see a big improvement if you used a rectangular offset pouring basin with a Weir, and a tapered sprue (rectangular is actually preferred). You could just carve it out of Styrofoam and glue it to the top of your sprue then shell as usual.



I don't know how big you're crucible is, but you could also hang 2-4 of those intake runners around a central sprue and shell and cast four at a time.

I cast a lot of automotive parts and have built many carbed and EFI independent runner induction systems.......we're kindred spirits.

Best,
Kelly

 

An intake has been on my to do list for some time now. Been working on a cylinder head for a v8-60 for now. It wont be investment cast, just sand cast using the print to cast a master pattern in aluminum. One day I'll get it finished up....
This one was printed to double check the bore and valve locations..