Got It Wrong on an Aluminum Melt

Everybody shows how easy it is to pour aluminum... Check youtube, I will wait... Try the Anthill pours for example...

Too slow, too fast, wrong heat, wrong materials, sun goes behind a cloud, who knows, it just didn't work even after all the prep...

The fail here is both a void which looks like a crack and a slump near the vent edge of the pour.

OK so the crack looks real cool, almost like an ancient mistake. I like it and am having a hard time destroying the piece by remelting...

Step 1: Make the Mould

Dry sand casting is perhaps the simplest of casting. when it works, it works well, when it doesn't, well you will just have to remelt and start again.

I spent several minutes getting this form in foam just right. I made precision cuts with the lathe and made sure that there was ample vents for the foam gas to escape during the pour.

The final shape was an envisioned perfection of form and function...

Step 2: Bury It in Sand

Lost foam casting means that you will take a foam structure, bury it in sand pour hot metal over it and pray for the metal to take the form left by the foam as it melts under tremendous heat.

I took the foam structure then buried it in dry sand with the foam sprue in a metal receiving cup and vent showing on the top of the sand

Step 3: MELT...

I used scrap aluminum from many sources and added borax and washing soda for flux. all is great and I am happy so far.

Step 4: Pour

The molten metal is then poured into the receiving cup at a steady rate until it flows freely from the vent foam section.

Keep water nearby to quench any overflow.

They don't tell you but the burned foam stinks! really bad!! I'm serious, it's awful!!! The sand will stink for many months afterward as well.

Despite the rank nature of the foam, so far it looks great.

Step 5: AND... FAIL!!!

Form secure... Check!

Molten metal... Check!

Flux added... Check!

Dross removed... Check!

Safety equipment worn... Check!

Steady pour... Check!

Wait for cooling... Check!

Remove from Sand... Check!

Flawless form... FAIL!!!

Now we start again! But I like the nature of the fail and will definitely keep this one as a conversation piece. Stop by my garage and I will show it to you...

Comments

[MartijnD]

Hello all, nice project, shame it failed the first attempt... Maybe a crazy idea, would it not be possible to use lava particles? at some more expensive gardening stores that sell lava rocks, compress those with hydraulic presses, filter to get small particles sand size, compress again until all is size one needs. Since it broken and sharp it would seem a good casting medium...

[rbetel]

I'm wondering if you are just making the aluminum travel too far? Maybe have the sprue connect to two points, and/or more vents?

[Random_Canadian]

Great points but I'm thinking I may have to go beyond lost foam for this one.

[rbetel]

if you do, I'm gonna make suggestions: 1) I would love to read an 'ible about experiments in slip casting! You could machine the foam, then dip it a few times in watered down clay. Let dry and harden then fire it, burning out the foam in the process, then use it a a mold. I'm dying to know if it's half as easy as it sounds. 2) green sand casting. If you haven't yet, check out myfordboy.blogspot.co.uk and his youtube channel...

[Random_Canadian]

Believe it or not your suggestion 1 is something that I'm currently working on, I've had a little preliminary success with it and am working to post as part of a future project. Part 2, no success here, proper green sand is either not available or prohibitively expensive here in Calgary, don't even get me started on trying to obtain Sodium Silicate. Further, after numerous attempts, I could not get cat litter and play sand to work at all.

And yes the quality of myfordboy's work is impeccable, both in precision and detail, on par and in most cases better than the work from the turn of the century, he is definitely a master.

[MarkF30]

Hi Random_Canadian, I am making my greensand using myfordboy's method of powdered cat litter and play sand, so fingers crossed I get it to work.

On the subject of Sodium Silicate, I can if required order it through the science lab tech at the school I work at, so check out lab supply companies and it gets cheaper the more you purchase.

I also found I could purchase 500 ml jars from a pottery supply store. Potters use Sodium Silicate as a glaze for their work.

I found many of the "suppliers" on E-Bay to be way over priced.

Depends upon how much you reckon you will require, plus add some allowance for casting failures.

Hope this helps.

[Random_Canadian]

I wish you the best in your casting attempts. please let me know how they turn out.

Thanks for the additional information. I have tried locally but several suppliers said that they could get it but there is a surcharge for hazardous materials transport ranging from $150 to $675 depending upon size.I have yet to find a supplier that has pure in Calgary. Got to love Canada, we cant even buy hydrogen peroxide 3% from a chemical supplier but it is still available from a drug store.

[rbetel]

OK, I spent a little time with wikipedia, and I think you can synthesize sodium silicate. Basically, you need washing soda (sodium carbonate) and silica sand. You get the soda up to about 850 Celsius, which is its melting point, and the silica will dissolve into it and then react, producing sodium silicate and co2. Fortunately, you have the apparatus to generate such temps.

Note: in no way am I kinda sorta a chemist. I just got good marks in it in high school, a quarter century ago.

[johnip4]

I got some lane mountain 120 grit from Target Products. It was quite a while ago but IIRC it was about $10/ hundred pounds. I got bentonite from a driller. I wouldn't say it's perfect but it works ok.

[MarkF30]

With the cat litter, make sure it is bentonite clay and then crush it down to a fine powder.

You will want to mix it with the dry sand in a ratio of 10 to 12%, ie 100 to 120 grams of dry kitty litter to 1000 grams [1 kilo] of play sand.

Explanation for those of us who have forgotten how to work percentages from school days.

Try going to a pottery supplier for the Sodium Silicate or failing that you may have to check out YT for how to make your own water glass.

It would appear to me that your lost foam attempt worked well, it reproduced the pattern with very high detail, which makes me suspect that the crack was a thermal contraction issue, possibly at the meeting point of the molten aluminium. I think that the crack would have started at the apex of the bevel on the inside of the ring.

Try repeating the casting without the same level of pre-machining, cast as a coarser ring with more material to machine away to avoid stress points in the finished product.

[thormj]

Not sure I can make an entire 'ible out of it, but one thing not to do is try to sand cast a HIPS print. Parts made of HIPS are just too dense and you end up with a gooey, stinky mess...

[Random_Canadian]

That just sounds like a bad idea. Kind of like trying to work with UHMW? I hate sticky. that is probably the only root hate that I have in the world...

[thormj]

I was being hopeful and myopic. My reasoning - hey, lost foam is Styrofoam, which is polystyrene -- maybe I can make an aluminum cast of a 3d print without having to have a burnout -- because burnouts make Plaster of Paris brittle.

But when I poured it, it didn't "fall down the hole" in the mould; it slowly melted through the HIPS, releasing noxious fumes.

I threw the result in the trashcan in disgust because I didn't want to mess with sawing and remelting it (with the accompanying noxious fumes)...

[Random_Canadian]

Have you perhaps thought of trying a full burnout then put the form in the sand . I am under the belief that brittle is no necessary a bad thing. The problems arise during thermal shock. A lot of cast forms for pulleys are made like this.

Try burning the plastic to ash, keep the form hot add sand then pour. Use high heat for the burnout like an incinerator. surprising low fume.

[johnip4]

I once needed a large lathe dog so I made a lost foam casting. I cut the shape with a hot wire cutter. I cut in from one side to cut out the interior. That left a slit that I intended to cover with scotch tape but forgot. The casting came out perfectly including the slit.

[Random_Canadian]

It is funny how the mistakes seem to work out better than planned. I am kind of pleased to see that others have noticed effect this as well... did you need machining or did it work out of the sand?

[graydog111]

All that work...........can't you just pick it up and smack a coconut with it? LOL

You have my vote in the Epic Fail Contest.

[Random_Canadian]

Smacking something you love with hard metal is not the way to go... you have to treat it with respect then gradually crush it until weakness prevails and it reveals its inner beauty to you... OK that's a little disturbing, I may need therapy...

Seriously though thanks for the vote. That hidden failure may not have been apparent in my write up.

I kind of wish I had a video to add of the aluminum detonation I mentioned in another reply because there is no way I would ever create another situation like that. In Canada we call that a hat-trick

On another note Sometimes "I think this is innovative" ideas are not born out of common sense, I once worked with a guy who was trying to figure out, for 2 months, a way for an individual with no right arm to shift the manual transmission in his Datsun until I randomly suggested he get an automatic.

[jo'neil2]

I just did my first aluminum sand cast using discarded foam packing material. It came out quite rough, of course but basically it was a proof of concept attempt. It looks like you're using pink insulation foam, how did you turn it on the lathe, what tools were you using to make your cuts (I'm wondering if you used files and/or sand paper instead of chisels)? I amazed at how smooth your finished foam piece is.

[Random_Canadian]

I find that pink foam machines nicely with the proper speeds and feed rates. You can use standard tools but treat the material as delicate, wear a dust mask and prepare for the backlash of pink static bits everywhere... I'm not kidding, I opened an can of coconut milk a couple of days ago and I swear that the pink foam was already inside of the can.