Hi guys This post serves as kind of an update to my sword casting trials and tribulations. Following on from the previous problems I was having (https://forums.thehomefoundry.org/index.php?threads/help-needed-bronze-sword-blade-casting.2698/), I thought I had these problems ironed out somewhat by keeping metal hotter as well as a fast pour, as recommended to me by someone who has experience doing this. For people who aren't familiar- I am basically sand casting the sword vertically with a sprue at the top which also apparently serves as the vent. It's difficult to cast long blades like this horizontally, and this is the manner in which the ancients did it. It's also the most common method of casting bronze swords- pretty much every youtube video uses the same method. However, just when I thought I was doing well, a new problem has raised it's head in the form of big ugly blow- holes within the castings. The annoying thing is that the castings seem fine on the outside, and the holes only show themselves upon filing. Never really had this problem previously. Maybe its due to the fast vertical pour, which causes splashing as the mould fills up? Even though others have success using the exact same method. I may try tilting the moulds a bit which may cause the metal to more evenly fill up the mould but this will also cause some heat loss due to filling it more slowly, bringing me back to my previous woes. I'd appreciate if anyone could help. No complex foundry talk please: this is a process which should be relatively simple and i'm sure just requires a tweak or two. Not being rude, but no point recommending some really complex, out-there technique or product when I see multiple people having results using the same simple setup and method as me! It's frustrating! On the brighter side- here's the ONE in about half a dozen swords that has turned out OK. Hilted with pommel and ready for final polishing.
To be fair Conor, you're showing us the result but very little else. Consequently, absent additional clues, all people can do is guess. You indicate you pour vertical but haven't shown us a mold. I saw multiple comments in the other thread about cold metal but no indication you know the temperature of your melt. There can be multiple causes of such things and just because you see a YouTube video and result doesn't necessarily mean you're getting the whole story. A couple examples: Is the tip the only place you have the flaws you show? The tip is the farthest from your pouring point. The metal is tumbling down your vertical mold in a disorganized fashion. It is undoubtedly bouncing off the sides and losing heat all the weigh to the tip. Along with this, it's knife edge thin so the tip will freeze very fast and conduct heat away from above. Could be entrained air and it's just freezing off before buoyancy can do it's job with the entrained air. Have you carved any sort of pouring cup in the top of the mold or just pouring down a hole? I'd be inclined to put a bunch of scratch vents on each side of the blade near the tip/end. Could be trash washing down your mold. Could be gas in your melt. What is you mold media? Green sand (how wet? could be caused by gas evolved from mold binder)? Petrobond? .....or it could be you just don't have enough heat. If we knew more about your funrace and fuel, there might be clues there but nothing as reliable as actually measuring you melt temp. Best, Kelly
Hey Kelly, I get what you mean completely. Aside from a step by step video which i will do if the problem persists, i can only try to clarify through words! So its petrobond that im using. Yes i carve a pouring cup at the top of the mould. I do agree with your hypothesis about the metal cooling as it goes up the mould but i cant see any way in vertical casting to eliminate this. Have tried scratch vents with little success. Im using coins (pre decimal scrap bronze UK pennies) so im confident my metal is good quality. Fluxed and skimmed in furnace and lid closed again to allow heat back in as per advice from last post. I shared a video by Will Lord in my last post which i have followed step by step, so i am confident this will show you exactly how i set up my molds. I dont hace a thermometer or any means of gauging temperature, though. I wait till the bronze is almost watery in its consistency then pour. Here is the vid. Hope this helps some bit. C
That video is pretty much all mold making, and mostly mold packing, which I mostly skimmed over but two comments: That's not a pouring cup or at best a thimble sized one. He seems to hit the hole ok though. Wow, I have never seen anyone use that much parting compound. Usually just dusting from a burlap bag. Johnson's baby powder is mostly talcum (or at least was), but excessive amounts can cause defects like you show. Is that what you are using and applying that liberal of an amount? Have you posed the problem to any of the YouTubers? One other thought, after having either observed or particpated in 100+ threads that go like, "I did it just like they/you said and it didnt work", with no other info, nine times out 10 it wasn't done just like it, and the majority of times it was being caused by missing information, and more often than not, it was poor melt/molten metal management. Bad metal = bad casting.....but as I said, just guessing......but that's how it usually goes. You should video what you are doing including the melt or if you cant do that, post more detailed pictures of your own work. It's the one big advantage of technical forums that the twitter/instagram/YT users dont fully appreciate.....you can actually have an interactive multimedia dialogue with pictures and video versus an excahnge of a few sentances. Best, Kelly
Hi, Sorry i've been ages replying. Hoped to do a few more casting experiments today but realised my crucible was a bit worse for wear so no point risking anything- a new one's in the post. I did get a mould made, though- and here are two pics. (The lines along the length of the impression are just where I applied a length of tape around the wooden pattern to thicken it up slightly). This is how I make my moulds usually. Yes I noticed in the vid he uses a lot of talcum powder- I too have been guilty of this but would it cause internal defects like I've shown? Bear in mind that the photo in my original post shows the sword after grinding down. On the surface the sword looked fine. These holes were internal. Have been looking through camera roll and came across this vid from a while back. https://photos.app.goo.gl/ih5mXxC7NRtmYKxFA Now, before anyone says it- I realise now the crucible was out of the furnace waay too long while I clumsily skimmed it LOL- I am careful now to keep the metal as hot as possible and skim etc while it's still in the furnace. But maybe there's something in the pour that I might be doing wrong or something? I have also invested in a much better tongs which grips around the crucible since making this video. For anyone wondering, this sword came out OK but the edge didn't cast 100%. As you can see, I have angled the mould here which I didn't do with the swords these new defects are presenting on. At the moment this seems to be the front runner for what's causing the issues.
That's good to know. Hopefully you've also invested in some decent protective gear. A full face shield, cuffed leather welding gloves, some spats for your shoes, and cover that bare skin, preferbaly with leather or high heat gear....-be safe my friend. It would also be wise to buy a firebrick or two to set the crucible on. The paver bricks looked moist. Water becomes steam in an instant. Even if the surface of the pavers is not wet, that hot crucible can super heat the area under the crucible and cause a spall/steam explosion of water suspended in the brick......potentially explosively sending molten bronze everywhere. Have you polished and worked it? Have a picture as cast and after? It does look like you have pretty good heat and liquidity of the melt. Talc has a reltively high melting temp, so probably not the talc itself, but baby/cosmetic powders often contain other things like corn starch, and even pure talc can absorb moisture and has chemically bound H2O that can be released as heated and decomposed. Most of the casting flaws I recall here on the forum related to parting compound were surface flaws. Best, Kelly
Looks to me like air inclusions caused by the metal tumbling turbulently for such a long distance. It could be something about the shape of your pouring basin or your pouring technique, etc., that is making your attempts not work out the same as Will Lord's. Many factors could be involved, and it's hard to guess without more info. Lord has also had a fair bit of practice molding and pouring bronze swords, and experience makes a difference... This youtuber does not have a lot of sword casting experience, and IMO his approach of bottom-gating into the sword tip with a really long skinny sprue might help prevent those air bubbles (if they are) from ever entering the flow of molten metal. I'm sure there are lots of things people might critique about his molding technique, but in the end the result was a nice looking surface and I'd bet it wasn't swiss cheese inside either. Always many ways to skin a cat though... Make sure you keep the sprue full and don't interrupt the pour until the mold is full. That is actually good to keep in mind for making any casting, but IMO a sprue as long and skinny as is used in the video below could freeze off prematurely in an extra big hurry and cause a misrun almost the very instant the metal stopped moving, should you fail to keep pouring hard enough to keep the sprue full. It's not historically accurate, but hey, neither is using Petrobond! Jeff
Tapered sprue that extends past the casting with a trap at the end and a very thin ingate that runs from the bottom to the top of the casting. Not the best method but very simple and will stop some of the turbulence in your casting. The thin ingate will help clean any sand or other impurities that might get picked up along the way down.
