MAKE Flickr photo pool member Vrogy is doing some metal casting, but somehow I think there’s more than meets the eye here… Link.
32 thoughts on “Metal casting”
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Wow.. is that the kind of finish lost foam gives you? I cast aluminum and have to work really hard to get a finish that bad using traditional pattern casting techniques with green sand. If the guy would have just made a permanent pattern using MDF or the like and gone the green sand route, this casting would look MUCH better.
The finish isn’t a reflection on the Lost-Foam method… It looks more like the molten metal needs to be degassed before pouring.
Pitting on the surface is called a porosity defect caused by hydrogen that becomes suspended in the molten Alum…
I use a chlorine lance to scavenge the hydrogen from a melt…
Also the use of some Flux agent wouldn’t hurt to aid in floating impurities to the surface to be skimmed prior to pouring… Rock salts used for melting sidewalk ice work good…
FrankG
http://www.theworkshop.ca
The finish isn’t a reflection on the Lost-Foam method… It looks more like the molten metal needs to be degassed before pouring.
Pitting on the surface is called a porosity defect caused by hydrogen that becomes suspended in the molten Alum…
I use a chlorine lance to scavenge the hydrogen from a melt…
Also the use of some Flux agent wouldn’t hurt to aid in floating impurities to the surface to be skimmed prior to pouring… Rock salts used for melting sidewalk ice work good…
FrankG
http://www.theworkshop.ca
Instead of just tearing down the post, how about posting some links to good info for beginners or writing your own and submitting it to Make:?
I’m Vrogy. I’ve looked up the problem already- it’s gases in the melt, as Frank G. mentioned. I even know the solution already- I just have yet to implement it.
Next time, please be positive in your criticism. Your karma will thank you.
Oh I see. So you’re all saying the porosity defect has nothing to do with the lost foam technique? I think it does. As I’ve stated previously, this level of porosity is difficult to achieve using pattern/cope/drag/green sand. Even when I was a noob, it wasn’t this bad because the scrap aluminum still contained enough flux to degas to a point of usefulness for my amateur attempts. My statement isn’t meant to “tear down” the OP rather as a statement of shock as to how badly the finish turned out. Sorry if your feelings were hurt. As your images didn’t state a lot of details, I saw some pictures of a cope and drag, some foam cutouts (one of them was invested), and some castings. My assumption from these images is that the OP cast the lost foam pattern in a packed green sand type of mold whereas most lost foam techniques I’ve seen involve immersing the pattern in dry, loose silica sand to allow the lost foam to gas away from the casting. Packing a pattern in green sand would likely cause the types of defects I see on the resulting castings as the gas from the foam has nowhere to escape to. I’ve spoken to professional industrial supply guys about what the pros use to form engine blocks and the like and he said, “it’s a trade secret.. but between you and me it’s regular investment mixed with nylon fibers that melt away and allow the foam to gas off”. I haven’t tried it yet but it’s on the top of my list of casting experiments. Again, sorry if my first post came off trollish.
Heres some criticism: you guys lack basic safety knowledge. Regardless of how “hardcore” or “experienced” you are, your photos lack basic precautions that need to be heeded when dealing with molten metals.
I have been casting bronze, aluminum, and iron for 5 years, and I wear full on leathers, helmet w/ face shield, and steel toed boots. You guys are wearing a t-shirts and shorts with only eye protection? Thats horrible.
I hope no one follows your bad example because they can be seriously hurt casting with no safety gear like you guys.
You are learning and having fun, and that is great stuff. The object, transformers I believe is well suited to your materials.
I am a sculptor and work in clay, resin and silicon. No cast metals but was a machinist for a few years and worked in a casting plant for a while.
Even though the resins I work in are very friendly it is very important to use an EXCESS of safety equipment. Here is an example scenerio; you get a tiny burn and instinctively you pull back drawing with your hand a pot of molten material, that splashes on your ankle. Or at the very least you waste some material.
I DIG it that it can be very hot working in leathers and a face shield and boots. But if you enjoy the work at all you will be doing a lot of it over time and accidents WILL happen. I know as my left index finger is one digit shorter than the right. Plus I knew not to jerk back from the hydrolic press as that can cause serious nerve damage to the whole hand. But instinct is not rational. So that hand is a bit wonky.
Have fun and remember we are all setting an example for each other whether we know it or not.
p.s. Looks like those tools might of been purchased at Harbor Freight. I was there today picking up another pair of stainless steel 6″ calipers for $15.00.
I likewise, did not intend my comment as a disparagement on the original Blog Post, but just offered my thoughts on how the finish could be improved…
My hat is off to anyone that engages in Hobby-Casting, as it’s just not that common a skill and just far enough outside the norm that the “Nanny-State” hasn’t cracked down on it (Yet)…
Certainly Home Foundry work is near the top of the “Make Ethic”.
As to safety, I certainly employ all the equipment that a previous post mentioned, including commercial foundry leggings that cover my boots and a full length coat of the same material…
Here is a quick and dirty link to a “Make” related project…
http://www.theworkshop.ca/casting/make/make.htm
FrankG
http://www.theworkshop.ca
Hm. I’ll definitely take the safety concerns to heart- we have some ancient chaps that can be repurposed, as well as some welding jackets. Know, though, that we’ve been doing less than one casting per day for maybe a week.. so it hasn’t really been a concern to us at this quantity.
Also, as there is balance in all things, we went ahead and did the Autobots logo last night:
http://www.flickr.com/photos/vrogy/1326487160/
I can pretty much prove that you can get clean castings from lost foam. Get a rag, wet it down with kerosene and go wipe off the bell housing of your car’s transmission. On both my V70 and my F-250 the grain of the styrofoam is clearly visible. Bubbles? Not so much.
In addition to flux, it might help to tweaking the gate and sprue design. To me the sprue seems kind of long and I’m not sure what I think about the way it hits the mold square on but aluminum and foam casting are both only tangentally related to what I usually play with. YMMV.
As for safty, at least you aren’t working over concrete.
Honestly, while the quality of the casting is relatively bad, in this case it lends a nice artifact feel to the whole thing.
But for safety- you can never be too safe- full suits everytime: one splatter to the face and you’ll regret it for the rest of your life.
But nice job on going out and just doing it. You got the initial cast down, now its just time to perfect the technique.
Austringer: Pardon my ignorance, but what exactly is wrong with doing this sort of work over concrete? And do the same concerns also apply to other forms of high temperature work (e.g. welding, acetylene torch, smithing)?
Concrete is porous and holds moisture. It will explode if molten metal drips on it because the moisture in it is superheated and cannot escape quickly enough.
When I worked at a foundry they told us never ever to throw aluminum cans in the recycle bins because just a few drops immersed in the master crucible would cause an explosion that could lead to death.
Pretty much what Shbazjinkens said. Even dry concrete is hydrated lime. When you add enough heat to it all those little waters of hydration decide to be steam again. For most hot work you don’t have enough heat there all at once to do much other than chip your floor.
If you dump a couple pounds of high-melting alloy onto a concrete floor a bunch of heat leaves the metal (which will obviously start to solidify) and going into the concrete (part of which will become a vapor). When the pressure of the steam overcomes the weight/hardness of the metal.
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