This is an insert for my vacuum impregnating rig. It basically just holds two guide posts for a lowering basket, and a sealed shaft for cranking/lowering the basket while the chamber is at high vacuum. The vacuum impregnation rig build is here: http://forums.thehomefoundry.org/index.php?threads/pressure-vacuum-casting-impregnation-rig.69/ My go-to machine for machining foam is my overarm router. It does circular features very easily. In 20 minutes I had the two halves and then it took a couple hours to make the piece parts, detail it up, and coat it in mud. I taped up the gate with HVAC tape before I glued it to the pattern. I made it to the shop mid-morning put some metal in the pot and made a wooden flask to fit the part and screwed my turbine vibrator to it. I poured at 1540F as I had in my other castings. It was a fail and poured short. Rats!! As I was walking to my overarm router to make another pattern, I’m pretty sure I could hear Bonz screamin’ HOTTER!. So a few hours later after re-making pattern, letting the mud power dry in the sun and breeze, I had the second go…..and poured hotter……a lot hotter at 1825F! ……..Success! Wow, I would never have dreamed of pouring that hot but I can’t see any ill effects from it. This was about a 6 lb part but nearly 9lb pour with a large cup and sprue. The outside diameter of the part is 13” so it’s nearly 20” of metal travel through the foam on each side. At 1540F I was only getting about 12” in the metal propagation tests I ran on coupons. I may be starting to bump into the limits of gravity fed lost foam aluminum casting unless I get creative with gating or further develop the vacuum assisted approach. The latter would have been a little more involved considering the quicky flask made for the project. Best, Kelly
I have started using a router for making wood patterns, and I like what I can do with it. I would not have expected to get such quality from a foam casting. Cool piece. And I did not know you could pour that hot without adverse effects either.
Im shaking my head thinking "no way" with a big smile on my face. Then reality kicks in and I ponder how much a casting like that would cost to purchase. Then back to "no way!!" That is some really impressive foam work... I need to get some free time cleared out so I can have some fun too....
Thanks David. I'm still on quite the learning curve but I'm very encouraged by this part. It's 3x the mass and 2x the travel length than what I have done to date, but I have my sites set on even bigger parts and even though this took two attempts, it's a lot fewer than my first attempted part . I don't know the limits but at least in this instance it appears that gravity fed aluminum at 1570F pour temp wont travel 20"+ through 1.3lb/ft3 XPS foam but 1825F will. This is also one of the reasons I was putting bobs at the end of the flow paths to try to gauge how much if any leeway I might have in pour temperature.....and I'd like to be able to get it right the first time because re-making patterns is a drag. 1825F aluminum pour temp....no shrinks, tears, or defects? -Crazy. I do think I'm going to need to perform some additional metal propagation speed tests similar to what I previously did with the glass window videos and also work with vacuum assist method a bit more....because it definitely increases propagation speed extends travel distance. There's a classic foundry fluidity test method I've seen that I may try to replicate. The other variable: I used a cylinder head casting and I cant be sure of the alloy or how this might have affected fluidity. Best, Kelly
That last one looks great! Another approach to filling a ring is radially. I used all white foam sprues and runners both inside and outside an oval shape. The later was much easier to clean up. Yours could feed into the smooth side and keep your pour temps down.
Would have been my first choice except for the flask size and amount of sand required. That thing is over 13" OD!. Best, Kelly
Maybe down the road. Wouldn't need to be too deep and sand is dirt cheap. When I think I might be short on sand I fill in empty space in the flask with wood blocks like 2x4 cutoffs and such.
Just briefly touched on in my tubular foam thread. If you search "Turbine Vibrator" or "Turbine Vibrators" on eBay you'll get a bunch of hits. Some sellers will list the data sheet with dimensions, air consumption, and pricing for each size. I bought one and after receiving and testing it invested in three more of the GT25 size. I can't remember which seller but straight from the People's Republic of China and about $35 each with free shipping. Arrived in about 3 weeks after order. The US made equivalents were between 5x & 10x that $. Here's a couple examples of sellers. http://www.ebay.com/itm/GT-8-10-13-...hash=item3aee961a80:m:mdJVXUzBktmXjXrxZPIn2Zw http://www.ebay.com/itm/Industrial-...hash=item2a861366f5:m:mTJ0HEi4yYXv1MmAnC-UA-A I use one GT-25 and just sit my 5-gallon bucket on the dolly in the picture and video below. Best, Kelly
Yes But would probably require one of the larger vibrators is desiring a large scale cleaner. Kelly, I half arsh looked up the comparison of Mpa vs PSI but how many psi are your having to feed your vibrator to keep it continuously going? I was more interested in the CFM requirements but guess you have to do a formulation computation to figure that out.
If you go to those eBay links above they list air consumption. I believe the numbers they give are in liters/min. There are 28.3 l in a ft3. So divide those figures by 28.3 to get cfm. At .6Mpa (87psi) it indicates the air consumption of the GT-25 is 16 cfm. I can tell you mine is no where near that because although I'm feeding it 80 psi+ it's through a 1/4" OD nylon line. I have a 5HP air compressor that delivers about 16 scfm at 150 psi on an 80 gallon tank and althhough it does cycle when using the vibrator, the vibrator only runs for 5-10 minutes at a time and I have air tools that create much higher air demand. I'd guestimate I'm getting good vibe for a 5 gal bucket of sand at about 8 cfm. But my experience also suggests you could feed it more cfm with better plumbing and pressure and get more vibe amplitude and frequency out of them for short duration without a big compressor if you have a good surge tank. As is I think I get 90%+ of my sand settling and compaction in the first minute. .....food for thought. Best, Kelly
COOL! Thanks Kelly, I don't care what David says about you. I briefly looked yesterday but the only thing I saw was some long drawn out version of conversion. P + Sq + the 4 element of Blah, blah, blah. Hence, my reason for asking.
That is seriously hot for an aluminum pour. Looks like with lost foam it doesn't hurt the surface. Robert
I can't say I completely understand it. You do have one and maybe two phase changes in the foam occurring that require energy from the metal but very low foam mass. Several references including equipment manufactures indicate lost foam casting requires +50c higher pour temps for iron. I compared specific heats and thought that could translate to as much as 100c required for aluminum. I've been pouring most my lost foam parts in the low 1500F metal temp range so 1300F equivalency conventional sand casting doesn't seem too far out there but 300F up from that? Remember too for the most part these are fairly thin walled castings (1/4") with high surface area to metal volume ratios so they also loos a lot heat to the mold. Perhaps the mud coating helps a bit too since you're not getting as much interaction with mold media......I don't know. On this part, cosmetically I can't tell the side near the sprue from the farthest point away. But I have not sectioned a part poured at that temp. The parts poured at 1540F look good sectioned and under magnification. I'm going to do some additional reading and also more metal propagation speed tests to see what I can learn. At 1540F I can only get a lineal foot or so of travel through from before freeze. Right now I'm content to do what works and conduct science experiments later. This partly why I was putting bobs on the end of my parts for a while, to see how much heat was still left in the pour. Best, Kelly
