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Thread: what did you do in your foundry today?

  1. #21
    Administrator Site Admin Anon's Avatar
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    Here's a quick project I did today:


    These are brackets for an exercise machine. It has a design flaw and a bolt keeps breaking (fatigue failure at about 1 million cycles, which is every couple months with the use it sees). The original brackets are thin webbed die castings, so I can't drill them out for bigger holes. Instead, I stuck some pieces of pipe through for core prints, used electrical tape to cover the webbing and fillet in the core prints, and I'm molding them up to cast some solid ones.


    Drag flipped and coped down, ready for the cope to be rammed. I am working with zero draft on these patterns, but it's easier to deal with bad patterns than to make a good one when I'm only casting two pieces.


    There's the mold, cores inserted (rammed up in a scrap of pipe, again zero draft), and ready to close and pour. I do have some crumbled edges from the lack of draft. I rammed a little lighter than normal, which will make a rougher surface finish, but it also allows me to rap those patterns side to side and get enough clearance to pull them without breaking the mold.


    And poured. This is generic Si casting alloy, melted in a steel crucible. No flux or degassing, though I did inoculate with Sr and Ti-bor (modifier/grain refiner), as I will be machining these without heat treatment.



    Not five minutes later, after shakeout and quench. That Si alloy is very fluid--I guess I'm getting too used to casting with 6061. Both castings came out fine, the surface finish is nothing exceptional, but it'll work for what I'm doing.


    Some judicious bandsaw and grinder work yields these semi-finished castings. I got a little over-happy with my gating and risering there--the Si casting alloy hardly shrinks at all compared to 6061, so I really didn't need all that. Probably two pounds of gating for half a pound of castings. Those little divots are not shrink defects, that's where the tape spans the hole in the casting.


    Machined. Unfortunately I didn't get any pictures of machining, but it was pretty basic, using a three-jaw to grab for one bore, then flipping it around and CA glue onto a fixture to hold for machining the second bore.


    And installed. Gone is the wimpy 6mm bolt, replaced with a 3/8" bolt. And if that messes with me, I'll drill it out again and put a grade 8 1/2" bolt in there, because now I have the meat in the casting to do that.
    The process of turning stumbling blocks into stepping stones can at times require the use of a large sledgehammer.

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  2. #22
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    Nice work! A couple of questions, you mentioned you rammed up the cores in a piece of pipe. Did you just use green sand for the core? Also you used SI alloy, where do you find this? Thanks in advance.

  3. #23
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    Nice work Anon. Let us know when this one breaks, we are counting the cycles for you.

  4. #24
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    We since it's still early. Nothing today. But this weekend. I did Ram up a mold for a lever arm.
    IMG_1449.jpg
    and a sign for a buddy of mines desk at work. Unfortuanately the sign did not fill the letters and so i endend up with a nice rectangular block of aluminum.

    Other than that i turned my scrap in to ingots.
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  5. #25
    Senior Member Bob S's Avatar
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    Just some advice on your molding. In your first picture this half should have ended up being your cope side not the drag. A shrink bob should not be inverted on the drag side since it now has to feed metal up hill to the pieces not down hill to them. You probably noticed a shrink bob always divots on its top from gravity when feeding the piece. I use this method which I call a "double flip". I mold up just as you have shown but then flip it once again so the bob is facing standing up and then cut the sprue and gating. Since you were using good casting aluminum and didn't have a problem my point is a little mute but if you had been using a higher shrink aluminum like 6061 you may have ended up the pieces feeding the bob by gravity's effect. Bob
    I used to spend my time to save money but now I'm willing to spend my money to save time.

  6. #26
    Administrator Site Admin Anon's Avatar
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    Yes, there was a lot that needed work with the gating in that mold. I kind of goofed on the riser--I meant to put it in after the flip so it was in the cope, but I put it in the drag so I could see how to space out my patterns, and then went ahead and molded it up without remembering to remove it. I also kind of missed when I punched down the sprue--it really didn't need to be so far away. I could have done a double roll instead of just going with it, but I figured it wasn't worth the bother.

    ---

    Yes, that's a greensand core. They're rammed a little loose, because a tightly rammed core is never coming out of a zero-draft pipe like that, but they're good enough.

    My generic casting aluminum comes from dead lawnmowers and other small engines, and I think there's the head off a car engine in there too. I have a lot more 6061 (a couple hundred pounds, actually) which isn't so nice to cast, but machines beautifully once it's heat treated. 6061 + 7% Si is better for casting, but still not as good as a real alloy. I have some Mn and Mg to whip up a batch of A535, which is supposed to have excellent castability and machinability without heat treatment (only moderate strength, though), but I need to source some pure Al (wire or something) for it.
    The process of turning stumbling blocks into stepping stones can at times require the use of a large sledgehammer.

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  7. #27
    Senior Member metalmelter2693's Avatar
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    Piepans are made of pure Al.
    What are you going to melt today?

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  8. #28
    How many pounds do you get from one lawnmower? I think rolled aluminum is near pure. Cans and sheet. And yesterday the rc car parts turned out well, but I need to refine the way I make the patterns. I made them just using the stock part as a template and cut some foam sheet. Will post pics tomorrow, I'm going to do a melt tomorrow as well. Also going to make a rest for my hand crank bench grinder. I wonder if that thing is like a vintage tool that's worth a lot... its very well made, just the wheel is out of balance. Anyone know how to shape the wheel with some sort of super hard grinding stone? Its alumina I think, kind of a pink color to it.
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  9. #29
    Administrator Site Admin Anon's Avatar
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    Cans are 3004 or similar, which is not particularly closer to pure than 6061. It is a Mg-Mn alloy, like A535 (instead of 6061, which has Cu, Si, and Cr in smallish amounts), but it has too much Mn in it, so I could still only use about 15% cans. And the yield is so crappy that I don't think it would be a productive use of my time.

    I don't know the alloy for foil, pie pans, and other thin rolled products offhand, but I suspect it's in the same vein as 3004: something fairly ductile for heavy processing, likely another Mg-Mn alloy, which seems to be common for heavily formed products. Pure aluminum (I mean like 99.9% pure or better) is so uselessly soft, it's basically only used for electrical wire, and various other things that don't rely on physical strength and need the purity for whatever reason.

    EDIT: I just looked it up, and apparently a couple of 1000 series alloys (I'd call them industrially pure Al, not quite electrical grade) are used for foil, but apparently the 3003 and 5052 et al. are more common, as I'd expect due to the considerably higher strength per thickness.

    ---

    Uh, more than 10 pounds, less than 20? Whatever the lawnmower weighs, minus the weight of all the steel parts. (Probably not a very helpful answer.)

    And you can dress grinding wheels. There are various styles of wheel dresser available: I have a single-point diamond dresser. They aren't all that expensive (I think I paid $7 or so for a 1/4 carat dresser) and they last a pretty long time. Mine is getting kind of blunt (still works though--I'm not sure how blunt they can be and still clean up the wheel effectively), but I've dressed probably an inch diameter off each of the two wheels I have, one of which is a SiC green wheel, which I'd expect to wear the dresser faster than a standard alumina wheel.
    The process of turning stumbling blocks into stepping stones can at times require the use of a large sledgehammer.

    Foundry Tutorial
    My Website <<Now at prometheus-foundry.com

  10. #30
    Senior Member HT1's Avatar
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    Quote Originally Posted by president of pyromania View Post
    How many pounds do you get from one lawnmower? I think rolled aluminum is near pure. Cans and sheet. And yesterday the rc car parts turned out well, but I need to refine the way I make the patterns. I made them just using the stock part as a template and cut some foam sheet. Will post pics tomorrow, I'm going to do a melt tomorrow as well. Also going to make a rest for my hand crank bench grinder. I wonder if that thing is like a vintage tool that's worth a lot... its very well made, just the wheel is out of balance. Anyone know how to shape the wheel with some sort of super hard grinding stone? Its alumina I think, kind of a pink color to it.
    http://www.wkfinetools.com/contrib/j...ingGrinder.asp
    good info in fixing up a stone


    HT1

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