Tobho's HT1-Inspired Cement Mixer Muller Build

I did do some casting, or tried to... I most definitely melted close to 30# of bronze and poured it into a series of holes in some boxes of dirt...

First pours into my new sand, as well as my first time pouring silicon bronze.

I thought to myself, what would be a good test of my sand and would look cool in bronze?

I concluded that my most difficult pattern to mold would be a great test of the new sand. Took me several tries and eventually going back to old pictures and video to figure out how I molded it before to cast this:



...This is the closest I got to molding it successfully... Too bad I molded it upside down, I might have kept this mold otherwise!



All that coping down took a while and my sand dried out just enough, then maybe a little too much. A few failed molding attempts later, I opted to choose another pattern instead. I had not had nearly so much trouble with this antlers pattern before... I wonder if maybe my 75 mesh sand needs a bit more clay than 4.5% Bentonite, as it does not quite seem to have as much green strength as my old sand. Or possibly some other additive?

Tried molding a copy of my sand scoop too, thinking once I was done my bronze pour it should be really quick to melt a pot of aluminum afterwards while the furnace was till hot... Never expected it to actually fill as it's very thin, but was thinking a failed casting would still tell me something about my new sand. Once it was all rammed up, I did a test close to see if any loose grains of sand would fall into the drag... Opened it up to see the whole greensand core had broken off! I'm convinced this would not have happened with my Smelko sand, I was very surprised. The good news is, my new sand on its own is enough to ram up my 12X12 flask, and my 12X16, and a sand mold for ingots, with a little left over.

Went with the skull ashtray pattern instead of the antlers in the end, and no aluminum pour to follow up. Here's a pic of how it came out the first time I tried molding it in my old sand with no vents:



And again as my first silicon bronze pour and first pour in the new sand... also without any vents, since I was more worried about testing the sand than getting a successful casting. Now I would learn something about the permeability of my new sand, I thought...

I should probably mention that this mold was made on Friday night, but stuff came up and I had to cover it up and wait for Saturday night to pour it, and no doubt it had dried out quite a bit by then. I'm guessing it could have come out much better if I had poured it a lot sooner... Still, some parts of it don't look too bad. Not quite as good as the successful aluminum version from my old sand though...





This is after I hit it really quickly with a wire brush drill bit - it came out with a fair bit of sand stuck to it, which was quite unexpected! Never happened when I was pouring aluminum bronze axes in sand molds, so I didn't expect it here either... So I just used the wire brush bit to knock the sand off so I could see it. I also did not expect it to come out looking like it already had some kind of patina on it! I kind of like that dark brown look of the raw casting.

Not sure how or when, but my sprue got messed up somehow and lost all its taper during molding. The very bottom end should have been about this thick, but the rest should have been fatter. Not sure how I did this, but I am sure the casting would have came out better if I hadn't.



The ingots were poured into greensand molds I made with the new sand also. Also had to wire brush those because they were coated in stuck on sand (is this normal? For me it is not). The tops and the top of the sprue on the skull mold turned black when they froze, but the wire brush bit cleaned that off easily enough.



...and here's a look at the bottom of one of the ingots too, where all 3 I poured got weirdly scabby looking. I wonder what that says about my sand? Unlike the skull mold, the ingot mold was rammed up not too long before the pour and the bottom of the ingot cavities looked nice and smooth, so this was another surprise.



Other things of note that happened during this casting session:

- Attempted to cast 2 of my lost foam skull belt buckles in bronze as well. One for me and one for a (rare) customer who wants one in bronze and one in aluminum for her boyfriend. One must not wear an aluminum buckle with a brown belt after all, nor a bronze buckle with a black belt! One was a success; the other, mine I suppose, floated the sand and was a total failure. My bad, should have realized bronze would have more weight behind it than aluminum and been more careful with vibrating the sand in tightly, and maybe laid a brick or two on top of the sand in the bucket to weigh it down some as well. I don't have pix of those on me right now, but they have nothing to do with the sand made by the new muller in any case. I'll post them up somewhere later.

- had to refill my oil tank mid melt, a first for me. Easy enough, I just turned the propane back on while I brought the oil tank down off its raised hook to refill, then hung it back up, waited for the oil to flow back into the burner, and shut off the propane when the telltale fireball came out the vent to announce that the oil drip had resumed.

- I melted my furnace! These turnbuckle tighteners are NOT steel.



Both of them melted off during this bronze melt, which was a full crucible of bronze unlike any of my aluminum bronze pours, and surprisingly heavy and HOT. I wasn't sure what to expect without those turnbuckles when it came time to open the furnace, so I let the edge of the lid rest on the rim of the furnace instead of swinging it all the way open, just to be safe, when the time came. Sadly I have no pix of the melted furnace lid parts here either, but I'll get something posted about that soon whether it's pix or video.

Quite an adventure! Then I came in to have a beer while the molds cooled off and got to see the aftermath of Zap's eagle pour misadventure... At that point I only knew that one of the belt buckle molds had failed (when you see the sand lift up in the buclet, it doesn't take shaking out the mold to figure out what went wrong), so Zap's live video made me feel much less annoyed about that, since I had spent only maybe 15 minutes tops making that pattern and mold, and I know a lot more hard work and expensive materials than what I'd used up had gone into that bird mold!

One other thing, the bronze melt was one full ingot plus 3 out of 4 pieces of the one I chopped up on video back during the winter. I was surprised my crucible held so much, but I wanted a full crucible so there would be plenty of ingots to pour in my test ingot mold made of the new sand. I was very surprised how heavy my #12 crucible was when full of bronze! Maybe I could handle a little more, but I was pretty glad I didn't have to...

So, a few firsts and a few failures, one out of 3 castings successful and a partly melted furnace lid. That was my weekend of casting. At least I had fun, and hopefully the failed ashtray casting and the weird scabs on my ingots will help me figure out what I need to do to get the new sand working better.

Just glad there was really no bronze lost on this pour. There's no zinc or anything to burn off in everdur, and while I did a skim before pouring, one quick dip with my skim tool, this seemed more like a formality than anything else; the melt was clean like a liquid mirror even before that. I've never seen anything melt so clean!

Jeff

Edit - fixed missing pic of furnace lid t-buckles

 

Guess I'm ahead of the game then, my pyrometer is a hot steel rod dip test!

Dunno about a swirl, but the surface of the melt was getting waves going round and round it from the blower action once it was close to full and once all the thick lumps in it were gone fully molten. I don't think that is what you mean though, as I have seen the same happen in a crucible of aluminum. I did remember you mentioning this before; I'll continue to keep an eye out for that. Thanks.

Anyone able to suggest changes to my new sand based on any of this? I'm gonna add another percent clay if nobody talks me down soon.

... And was reading earlier today in Ammen's handbook about adding some corn flour, seems like another possible option. I know Smelko sand contains ''carbonaceous additives" for improved surface finish, just not sure what those would actually be... Don't really want to start adding new ingredients without a pretty good idea they are actually needed though...

Jeff

 

Rainbow pigeon-neck oilslick swirl, gotcha. I'll watch for it.

I usually end up waiting until the kids are pretty much settled, so that going out back to cast something doesn't become associated with extra bedtime parenting duties for the wife. That way I never get "that look" when I say I'm going out to melt something. This way I have enough light left to set up the molds and furnace, but it's just getting dark by the time I light it up. Neighbours tend to be inside by then too... that or sometimes they are sitting around one of their 20 foot wide raging bonfires that I never call the FD or cops about. They haven't noticed me casting metal yet...

Jeff

 

Might try wood flour (sanding fines) instead. You may find corn flour promotes mold growth during storage.

Best,
Kelly

 

That was mentioned as well. I've also read a few stories about cereal additives causing mold...

Sometimes my Smelko sand does smell a little funky when I open my bench after it's been closed up for a while, but that has always dissipated quickly and has never gotten any worse or been particularly offensive to begin with.

Jeff

 

Thanks Melterskelter. I did use western/sodium bentonite. After 5 years of keeping my eyes and ears open for bentonite, short of doing the kitty litter thing (who knows whats in there?!), or flying out to the Alberta badlands to mine my own (guessing that might be western b. anyhow), it was this or going to the wine making store to get four little 4oz. packets of unspecified bentonite for the same amount I ended up paying for this 50# bag.

Kelly was suggesting wood flour instead of corn flour due to concerns about mold... But I was reading how you're supposed to get wood flour with low ash and low sappy stuff levels, so of course it's not as simple and easy as throwing in a few handfuls of ordinary sawdust...

Can anyone confirm or give a 2nd opinion on me having used the wrong bentonite, or on wood flour vs corn flour's effectiveness as an aditive for improving green strength? As more of a weekend foundry, I feel like my sand dries out too often to support much mold growth so if corn flour improves green strength that might be worth the risk, but if the wood flour thing works just as well maybe it's worth tracking down the fancy low ash stuff instead... Not sure. If I am going to start monkeying around with additives, I think it would be best to sort out all the possibilities on the table and eliminate areas of confusion so that I am sure...

Petee - yeah that is more or less what happened to mine too, some bending and breaking and melting of the tighteners leading to total turnbuckle failure. We've been here before, you and I - remember our matching photos of crucible spill tuyere sword 'castings' displayed on radial arm saw tables from a few years back? Lol... I tried to get a pic of mine last night but by the time I got out there my phone battery was too low to run the flash. Maybe I'll weld some 1/4" rod in there to replace the t-buckles or something.

Jeff

 

I found that excerpt to be much clearer than the info on different bentonites in Ammen's sandcasting handbook or the navy manual, thanks!

I've seen several recommendations to use 50/50 sodium/calcium bentonite, and a bunch of farm pond videos where people are complaining about only being able to find the calcium bentonite. Figures...

Jeff

 

Been reading more about sand additives and casting defects in Ammen's sand casting handbook, which is much more convenient to check when I am away from wifi than the navy manual. Maybe this post isn't that well suited to the muller section, but the pictures of the test castings I'm going to refer to are all here...

- The scabby looking ingot bottoms seem like metal penetration into the sand, as opposed to what Ammen calls "scabs" (though they do look kinda scabby)

- The sand stuck to the castings seems to be what is called poor "peel".

- The handbook mentions that organic and carbonaceous additives improve peel (rather than surface finish, as the book says many believe to be the case).

- Sea coal is mentioned as improving peel, but where the cereal additives (which sound organic to me) are described, peel is not mentioned.

- Other than the potential for encouraging mold growth, the corn flour is sounding like a better and better idea... Anyone know if this is the type of organic additive he meant when he mentioned they improve peel?

My guess is that corn flour will be easier to find here than sea coal. The book says or implies that sea coal is more used for ferrous foundry work anyhow.

Where wood flour is mentioned, it does agree with Kelly's post suggesting it duplicates some of the benefits of corn flour, but it also says that each of these two has its own place and use.

Oh BTW melterskelter, I was looking into it and corn flour may not be the same thing as corn starch, unless you are in the UK or Australia.

From geniuskitchen.com (which has to do more with food than foundry, but I still thought it worth mentioning):

I can definitely find corn starch... any chance can I get a second educated opinion as to whether or not it's the same thing or has the same effect as corn flour when added to molding sand?

My Smelko sand designed for aluminum has great peel ("smooth as the belly of a she-mouse"), I have never had a single grain stick to a casting when using it (I've done mostly aluminum and a couple aluminum bronze castings), and I know it contains 'carbonaceous additives to improve surface finish (actually "peel"?)'.

Anyone have any guesses what they're putting in there? Or how much of it? The new sand is a little lighter in colour than the Smelko sand ever was FWIW, and the new sand stuck to every surface of the bronze casting and had to be wire-brushed off, though underneath the sand the casting looked ok other than some pinholes you can see on the raised ridges that were molded in the bottom of the drag, in the pic above, and a slightly less smooth finish than the Smelko sand which probably used finer silica at 115-130 AFS GFN than my 75 mesh stuff.

Thanks for all the continuing advice guys!

Jeff

 

I haven't done much with green sand composition but here are a couple thoughts from the now and past experience. I've used corn starch to bind granular media with water. When dried and lightly baked it was a reasonable glue. I've also seen it mentioned as a core binder. I do expect it would add substantial green strength. It's benefit will probably rapidly degrade with use. I didn't mean to concern you too much with the potential for mold growth unless you have a mold sensitivity. If mold became an issue I suspect a little bit of bleach in the water you use to freshen the green sand would take care of that.

Though more permeable, I think coarse sand will have lower strength than fine sand. For a given grain shape, packing density is the same irrespective of grain size as long as the grains are much smaller than the container. However, surface area increases with decreasing grain size so you have a lot more area to coat with binder and water so finer sand should require more of both and have higher strength at the cost of less permeability.

I was given a couple 5 gal buckets of clean dry sand from a local foundry that was supposed to be 80 mesh (I haven't sieved it to confirm). I was also given a bucket of "Dixie" binder....which sounds suspiciously like Southern bentonite but may be a blend. What the hey...it was a gift. I was playing with mixtures in 1/2 filled 12oz plastic cups, experimenting with binder, water content. When I first mixed a batch, I noticed improvement after I let it rest for a day and thereafter it was easy to revive when it dried out (which happened quickly). When I found a happy mix, I added some wood flower and I would say there was a very noticeable improvement in green strength and molding detail. I have a triple beam scale so could measure those small quantities accurately. I don't know if I kept my notes but I do still have the cup of sand.

Do you have a small scale? If so you could experiment with small amounts that mix and mull very quickly by hand until you find the composition that feels right.

Sand/mold media management, molten metal management, pattern making, heat treatment, casting finish machining,.....etc...there's a lot to manage and master in this casting game.

Best,
Kelly

 

That's what I did. Have a dedicated dust collector on my belt and spindle sander.

K

 

Could be. Or maybe aluminum. One thing is for sure, they're junk now!

How did I miss the link to alloy foundry above?! Thanks, your google-fu is more powerful than mine obvously, I've searched for local foundries several times and never ran across their site before...

Haven't replied directly to every post above but know that I am reading them all and considering all suggestions.

Got a pic of how the sand wants to stick to the bronze, finally...



Fixing that is my main concern right now. Would corn or wood flour eliminate this bad 'peel' (if I'm using that term right)? My old sand never did anything like this, I'm guessing the unspecified 'carbonaceous additives' Smelko uses are the ticket, if I can deduce what they might have been...
Powdered sea coal? No clue where to get that, even amazon seems not to be much help there. Ammen said organics improve peel too as I mentioned above, which is why I've been asking about those flours. If they would work, any added green strength they'd add would just be icing!

I'd be very interested to hear about anyone's experiences in successfully correcting this annoying stuck-on sand thing which I've not seen happening to anyone else before on any of the forums that I can recall. If you've had this problem and fixed it... How?

Thanks,

Jeff