Projects 1st Alum Casting - What Went Wrong?

As mentioned before, this is a very good read. I had thoughts years back of doing some casting, was told to get the “metal casters bible” book, which I did, after reading it over a few times I knew I would be out of my league.
Hats off to you guys!

 

My guess is that moisture in the sand made those small craters.Try to do what 1971BB427 said, preheat the mold. or maybe the humidity in your garage is to hi.

 

This is a big oops! From what I’ve read, the pouring environment needs to be below 70% Relative Humidity. Looking back, all of my pours were in the morning (probably around 80%+ RH). I think for the next pour, I’ll do it in the afternoon when (hopefully!) the humidity is well below 70%. Pre-heating the mold would be relatively easy on a hot plate set on low. The flasks are small enough to fit in an old frying pan.

 

I’m using the “United States Navy Foundary Manual” as my main reference. In the preface, it describes the book as more of a “how to” guide and the “why” was kept to a minimum. “The Charcoal Foundary” by David Gingery is also a good starter reference.

 

I read about tilting the mold during the pour to help distribution. But, I see where it can help the flow and keep it from washing out the surface of the cavity. More beer, less foam!

 

I'm spoiled here in Reno, low humidity so I have not had to concern myself with it when pouring.
Once I painted the battery tray in the RV with POR15 and it wouldn't cure. I called cutomer support and she looked up the current weather in Reno and just told me to wet the floor in the shop that did the trick.

 

My brother and I made some flathead heads at a lokal foundery in late 90s and they cast alot off fun stuff, sometime the flask was to small so intake and risers was to small, they scatter something they call "täcksalt" in swedish. I dont know maybe"coversalt". That stuff did not allowed the intake and riser metall to freeze to fast. I talk to one of the guy that helpt us and he cant remember what it contain.

 

That too, but mainly to reduce the introduction of gas into the pour. Try it in a glass of water you will see all the bubbles.

 

A somewhat successful pour, today! I changed my approach for inlet and outlet sprues. Though, the risers on the bosses remained the same. I did puff some graphite into the mold cavity and upped the pour temp to 760 C. The humidity was low at 57%. The outcome was a really busy piece:



The surface finish is pretty nice. But, there was some pocking/bubbles (maybe?) on the bottom of the casting:



It’s hard to see, but there was some shrinking on the center boss. The two end bosses were pulled down a bit toward the center. Probably why the surface finish in the center is a lot rougher than the ends. Notice the risers didn’t fill to the surface of the flask, again.



So, here’s a picture of the fuel block with all of the gates and risers cut off. Now, it’s easier to see how the center boss sank and pulled the other two. The center surface finish is really rough, as if the shrinkage occurred under the “skin” of the casting.



I think I can solve the shrinkage by upsizing the input/output gates and the risers on the bosses. I’m making a set of sprues and gates that I can attach to the pattern. They should help make the fill smoother and more consistant. It should be way better than my “guesstimate” mess on this pour!

 

I think you are being pretty hard on yourself. That looks very good. You have learned a lot.

 

I agree. The finish is typical of sand cast parts. I think you will always have shrink to deal with on that design.
Hand file the tops of those bosses and call it good.

 

You and noboD are right. After relooking at it, the casting is pretty good. Once drilled and polished, it would look right with my three Strombergs.

 

I once worked in metal art (HMW). They did beautiful bronze foundry work. Lost wax/ceramic. I usually would take the cast parts and braze them together to make what ever it was I was building. As nice as the stuff was cast, I still spent hours filing the castings into shape. Just make the part big enough to be filed to perfection and keep it to yourself Mike

 

I think you got it dialled in...whatcha gonna make next?

 

I think I’m going to do a few more practice pours. It takes me forever to prep a mold and I’m still a little nervous pouring molten metal.

 

You are right to be nervous. There is good reason for it.

 

A final project update - I was able to get a pretty decent pour on a low humidity (38%) day. That’s rare for us!



Degassing was fairly successful using table salt. The problem I ran into was keeping it down on the bottom of the crucible with my dross spoon. I need to make a small plunger to hold the foil packet on the bottom before it starts to melt.

So, here’s a mock up of my Y-block 3x2 (Chinesium carbs on a rather beat up Edelbrock 354) using a fuel block I made from a chunk of aluminum. Functional, but not an especially good look:



Here’s my cast fuel block after drilling/taping and a little filing and sanding:



It definitely looks better than the chunky block! Considering I have never done any metal casting before, I think it was a successful project.

 

Looks great!!!!

 

Nice!

 

I think that You have found the right mix . Looks great

 

That's Definitely an improvement, Congratulations!!

 

Very nice!
So , whats next?

 

Thanks, Jethro! What’s next? More practice! I need to do a little better ramming my molds. That should help improve the surface of my castings. As far as a next project, I’ve always wanted to do my own license plate topper. But, I’m not much of an artist, so making the pattern will be a really big challenge!

 

If you need lettering for your topper consider a place like Michaels or a hobby place that sells self adhesive lettering in different fonts and sizes. I think they use them for scrapbooking. I have also used plastic menu board letters from Amazon . My artistic ability is limited so I can use all the help I can get.

 

Those same letters are available from McMaster Carr too.

 

Great job. Interesting that ur getting shrink at the center but no shrink in the gates. They could be freezing off tho. In that case you'd b right to add to the runner thickness. Have you cut any of the horizontal pours in half to look for shrinks, porosity, etc? In the past I have had to build a handful of tools askew in order to counter a casting that won't turn out flat, or whatever the problem may be that you're compensating for. In my experience it was very rare tho. Nice work!! Keep it up and keep posting.

 

Chris, you do gorgeous work!

 

Thanks, Bruce!