Fail Of The Week: Sand Casting Copper

There’s trouble in the Kingdom of Random – the smithies of the realm are having trouble sand-casting copper. And while [King Grant] might not be directly asking for help, we think the Hackaday community might have plenty to say about his efforts.

We’ve all seen plenty of sand casting efforts before, including attempts to make otherwise unobtainable engine parts. And “lost foam” casting, where a model of the part is constructed of polystyrene foam that flashes off when the molten metal is poured, is a relatively new twist on the technique that’s been used to good effect on a recent Gingery lathe build. But most backyard foundries work in aluminum, which is apparently much easier to work with than the copper that [Grant Thompson] is working with. Ironically, his first pour worked the best — not perfect, but at least the islands defining the spokes of his decorative piece didn’t break off and float away as they did in every pour shown in the video below. That leads us to think that the greensand is too dry by the second video. Or perhaps the density of copper just makes it more likely for the sand to float. Maybe a cope and drag mold is in order to keep the islands in place and direct the flow of the copper better.

We know there’s a lot of expertise out there, so sound off in the comments about what you think is going on with these pours.

[via r/Metalworking]

90 thoughts on “Fail Of The Week: Sand Casting Copper

    1. This is a good tip. A little more involved then most people get when sand casting but a good tip regardless.

      One of the things I have found that has helped me is mixing Elmers Glue (just the white stuff you used in school) in with warm water, and then using that to wet the sand when creating the mold. I dont have ratios, Ive always just kind of eyeballed it.
      Ive found it to make my molds much more likely to stay together.
      (Maybe hes doing this, I havent read the source)

      1. High copper casting requires better temperature control than most backyard foundries, oxygen free crucible conditions, graphite flux floating on top of the melt, moisture free molds ( think castable not green sand, much like casting jewelry) and lots of patience and observed practice. This is not something th begin casting study. Start with art bronzes and grow ever more copper rich until you find the best compromise alloy. Even 3%aluminum can make a huge difference in the casting quality.

          1. That is awesome! Not the getting cut, not the betadine in the wound- I’m surprised the butterfly held. Id have thought that needed stitches no matter what.

  1. Form your mold in two parts with a cope and drag .even if the top is just smooth and flat . That will help hold the bottom of the mold in place. good luck.

    1. I cast iron and steel in green sand all the time, and it’s close to the same weight as copper. I’m thinking he is simply screwing up the green sand by adding too much reclaimed into it and not packing it down well. a vibrating table is a MUST.

  2. Pure copper does not flow well in anything but a very low humidity environment and even then it is tricky. Your copper pipe may be an alloy and that may cause trouble. Ideally you should buy an ingot of pure copper. I don’t see any flux being used. I’m guessing a bit, but some anhydrous borax may help. You should skim off the slag floating on top in the crucible before pouring. A two part sand mould may help prevent the pieces popping off.

    1. According to ASTM B88 all types (K, L, M) of domestic copper water tube are better than 99.9% copper + silver. So the problem may be the opposite, they’re too pure.

        1. It’s domain-specific.

          Hackaday commenters are some of the most capable communities on the Internet when it comes to actual Real Engineering™. You’re not going to find a better community anywhere, with possible ties with the EEVBlog forums and some other very very niche forums.

          Anything outside of this domain… let’s just say I’ve seen better, more intelligent, and less hostile communities on forums that rhyme with ‘tour bran’. Case in point: someone define ‘clickbait’ for me. No one here can. We’ve got a bunch of media illiterates here, and the worst part about it is they think their experience in engineering translates into other domains. That’s really the crux of it, right there.

          1. Stackexchange EE isn’t bad, and you can use LaTex for equations. Plus there are schematic drawing tools for comments. It makes for really useful info. But you must pose your question in the form of an answer.

          2. Some of those, say, candlepower flashlight forum people have an impressive amount of depth of knowledge and free time to spend on evaluating LEDs and flashlights. But it’s like any hobby, I guess? At least when you combine it with obsession to detail and free time. Bodybuilding, car repairs, baking, you name it. They all have their niches and communities, many of which have been together for a decade or more. Even sex machines have their own books and communities and designs and opinions and factions. Not everybody actively participates in these various communities (only a few percent of people do) and for most people, they have other interests or just don’t put the time in to do more than read but it’s still neat to see a community come together and share knowledge and techniques and new ideas and concepts around whatever topic is at hand.

            Asking an engineer type to define a tangible yet somewhat new word but that most people agree on? Really? Clickbait. Noun. Clickbait is a pejorative term for web content that is aimed at generating online advertising revenue, especially at the expense of quality or accuracy, relying on sensationalist headlines or eye-catching thumbnail pictures to attract click-throughs and to encourage forwarding of the material over online social networks. Clickbait headlines typically aim to exploit the “curiosity gap”, providing just enough information to make readers curious, but not enough to satisfy their curiosity without clicking through to the linked content.

            If HaD was truly clickbait, I and many others would probably stop coming and stop contributing. But you have to admit, there is a certain level of sensationalism involved that isn’t truly necessary to help gain clicks. It’s not historically absurd or over the top here though but it has felt like it has moved a tad in that direction over the last few years / since the acquisition. One has to know their audience, I guess.

          3. To make the assumption that no one here can define “clickbait” is a bit of a stretch. The thing I like most about this community is the diversity within it. Yes quite a few of us are engineers by trade, however I imagine many of us are also hobbyist who do work in soft sciences as well. I’m fortunate to have done both, as an embedded systems engineer and a managing editor for a small lit journal.

            You may be right, we likely do have several media illiterate folks among our ranks. However, argument is a valid form of discourse. Complacency is the enemy of knowledge and progress, complacency is hardly something you’ll find here.

            So once again, to assume us all to be knuckle draggin’ wrench monkeys with no understanding of the world outside our ‘domain’ makes an unfair assessment of this community. I can’t even fathom this community being shackled by any sort of ‘domain’, if it were it wouldn’t really be hacking would it?

            P.S. I rather like your articles, they tend to create a lot of conversation. I assume your trolling is by design to aid in that, if so bravo.

    1. Well, that’s the Internet for you, isn’t it? You could get a response from Dr. Expert McActualGenius, who happened to do his PhD on the subject; or you could instead hear from Derp Knuckledrag, who never finished 2nd grade but claims he built a perpetual motion machine that the government is trying to steal.

      1. Yep, those are different points of reference.
        I recall Larry Lippman from the early ’90’s USENET, he had Ph.D.s in Electronics and Chemistry. He also had real life experience in those areas. But, he was know by many as Larry the Lid.

  3. I would assume that the copper doesn’t do so well in sand due to the silica content. Isn’t copper attracted to silica, which can cause crystallization to occur? He may have better luck with casting in actual greensand instead of the playsand he’s using.

  4. No actual experience here, all the videos I have seen usually would fully enclose the foam insert, and have sprue channels to let the metal in and air out. This would prevent the sand islands from floating up over the metal.

    1. There are other examples online (read “free on YouTube”) that do exactly that. For example, there is a guy who cast a copper apple, stem and all, and it worked very well.

      I noted too that another poster mentioned Borax. This could also help.

      1. I believe it made clay less brittle. I’m not sure – I was 13 at that time. But they used straw both as a filler inside the bell and to reduce the humidity of clay-manure mixture. And smell wasn’t as bad as one might expect…

      2. My father used horse manure that he got from a neighbors stables in his garden. In my experience hauling and spreading it, it was always dry and relatively odorless.

        He once used a load of cow manure from a nearby farm and that was impressively smelly.

    1. Strangely enough the same materials used for building huts and houses in medieval times, and to this day in less developed areas., the poop has some structural qualities, they explained it on time team or something once but I forget now.

  5. He would have better results using both a cope (top) and drag (bottom) in his casting flask. He should also put some draft angle on the foam part and pull it out manually before casting.

    A lot of this information is already out there and pretty easy to find.

  6. Never done sand casting for copper but I’ve cast other things in sand. Others have suggested he ensure the mold is properly formed like a mold by rounding the corners and giving a slight outward slant to the sides, both necessary here. Also, try putting some elmers or wood glue into a spray bottle with alcohol and spray the mold down. Also, he could just do his mold out of plaster like a sane person trying to do metal casting with intricate parts.

    1. Copper is too hot for plaster. Aluminum is about at the edge of what plaster can handle (in my experience.) Casting refractory as used by jewelers would work well, though. It has plaster, perlite, sand, and other stuff that make it stand up to much higher temps, even up to platinum.

  7. when i first watched the video, all i could think was.. why is he pouring into the open face like that, won’t the spoke holes break of… oh, yup, they will. I could have sworn he had used sprues when he was casting aluminum, but could be wrong.

  8. I’m amused at some of the hate for this information being out there and easy to find, as if Grant had actually asked for help – He hasn’t, or didn’t as far as I recall when I viewed the video a few days ago. Which makes me wonder which of y’all actually watched it all and who just watched 10 seconds, went ‘newb!’ and came to comment…

  9. Petrobond greensand will keep it from flaking out. I suspect steam is causing issues with his casting. Simultaneously stealing heat from the melt. The finer sand in commercial petrobond in addition to the different binder should help keep the mold together. He should try alloying a few percent of tin or zinc. Pure copper is notoriously hard to cast.
    Why mess around burning out the foam on an open top mold? Just stick a screw in it and pull it out. If your mold can’t hold up to that, it won’t survive a cast.

    Unrelated to his copper problems, his technique could use some correcting.
    Loading your crucible cold, at best you’re shortening it’s life at worst it’ll crack full of molten metal
    And DON’T POUR ON CONCRETE. Those pavers are all stamped concrete, not actual fired brick. Not that standard facing brick will fare much better to molten metal but it shouldn’t spall.

    Wanting perfection is not OCD.

    1. My don’t-pour-on-concrete moment came when I floated the cope and a bunch of aluminum on the concrete caused it to spall, and suddenly I had molten aluminum running down my face shield. That was pretty inspirational.

  10. This guy doesn’t seem to know at all what he’s doing, least of which is how to make a sand mold properly for casting. He’s going to end up with a face full of molten metal one day.

  11. The amusing part about some (many) of these comments is that Grant Thompson has done cope and drag casting, even making a tutorial video on how to build a simple set of boxes for it.

    He also has said in at least one of the casting videos that he’s working in new territory for him, learning some of this as he goes.

    A year or more ago he was doing lost foam casting with aluminum.
    More recently he did some home brew arc furnace stuff melting other metals in said furnace.

    As his YouTube channel name suggests, his content is random.
    Sometimes it’s chemistry, sometimes physics. Sometimes it’s construction or tool testing.

    And this time, it was open mold casting, after a prior video testing if the new furnace could get the crucible hot enough to melt copper.

  12. More pressure! Use a hydraulic jack or something! Two piece mold and a wooden form that is removed maybe? Come on!

    The kinds of postings are real comment collectors.

  13. He needs to use a proper 2 part mold. If the Spur and runners were anywhere near proper the sand washing out would be less. Also Green sand needs some help a few nails with the heads removed to help keep the sand from floating…..ETC. I commend the man for just going for it, but a little more research my have increased the success rate.

  14. If he really was going to do this as open casting, he should have taken simple note that every time he pours in the center, the molten metal would push outwards anything that is not supported. If he had poured in a circle then worked his way inward, then repeat, he may have actually had no problems. However, the main problem here is that he’s trying to rush it by just pouring at one point. This is why closed casting does the one point as close to the edge of the mold as possible. You know? Because of Newton’s Third Law.

  15. Like others have said, you need a proper rammed two part mold with petrochem sand, whatever the heck he is using is incredibly coarse.

    And use a pattern, lost foam is crap for quality and you are just adding more impurities to what looks like a heavily oxidized melt.

  16. Oh, you can also use a sodium silicate type mold. It uses sodium silicate to hold the mold together for detail. Though the sand is generally only used once with this method.

    1. If you riddle it (shake if through some hardware cloth or a proper sieve) you should be able to reuse a healthy portion of it. Only the sand in immediate contact with the pour will irreversibly set up.

    1. Lost *wax* requires melting and burning the wax out in an oven or kiln. Lost foam is new, quick and dirty technique where the foam is burnt out in-situ during the pour. It works quite well with fully enclosed molds with sprues etc.

  17. Why on earth did he go and buy formed copper tubing for this…..
    Is it not commen knowlige you can genrilly buy scrap copper back froom a recycler?
    yes it’s more than thay paid for it but sttill most prepared scrap is more than sefishent for this.

    yes i know bad spelling on a touch device right now.

    1. looks better on camera, and he doesnt care about money he has more then 20 thousand dollars from every video from viewers only, if he adds some product he get paid even more(did not saw him do that yet tho.)

  18. The problem is a combination of the oxidation due to the lack of flux…The source of the O2 is the atmosphere and how copper combines with it while in a molten state. To minimize the oxidation, set a good amount of charcoal on top of the melt, (ACTUAL charcoal, not the junk for BBQ grills. Purity counts here!).
    Since carbon and oxygen attraction is much stronger than that between O2 & Cu, the purity of the copper stays in tact.
    Also, the initial purity of the copper is super important. If you’re using melted scrap, the pour will never give a good result. You will have to start with 100% refined copper.

  19. I’m pretty sure this is an example of Cunningham’s Law. We should be thanking Grant for helping educate his audience by showing them the wrong way to cast copper!

  20. Bad form on this one. As mentioned before petrobond sand is an option, however at the high temp of copper it would not last many pours. Green sand has to have an amount of bentonite in it to hold form and not steam too much. This looks like strait sand. Not a good idea. Additionally with no flux its a total loose loose. As mentioned before as well you need a cope and drag. Copper has never lent itself very well to the lost foam method. It likes proper casting methods and a gas purged mold to give any sort of proper results. It’s why they came up with bronze. Copper could only really be wrought in the old days with any success.

  21. His ‘green sand’ seemed to be a lot less compactable and clumping in the newer video. My thoughts on the original video, when the copper most definitely seemed to be cooling before he completed the pour, was that maybe it’d help if he did a two part mold JUST so it’d be enclosed and better trap the heat of the molten metal.

  22. the sand in the holes between the spokes isn’t actually rammed propperly. Notice he only starts ramming after there is a lot of sand covering the gear. That means the sand above the hole “bridges” over the hole and spreads the force around, so the sand in the hole doesn’t get compacted properly. That means the sand there is simply too fragile. Just the slightest touch was enough to damage the mold on his first pour.

  23. This problem isn’t unique – Thomas Edison punked the copper industry (that was wildly grateful for his electrical developments making copper permanently valuable) by asking for a “solid cubic foot of copper”. They were unable to do it – the cube it got had voids that had been filled.

    Picture here:

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