I certainly chose a difficult enough part for my first cast, no? OH! That makes a lot more sense. Sorry. No wonder. It did work quite well for the parting line. Thank you sir. I've been looking for a rule of thumb but what you said will work.
I use baby powder between the cope and drag. Not clumps...just a slight dusting. Probably not the ideal composition but it works.
Baby powders are either talc or corn starch with an added fragrance. I think talc is the most commonly used parting compound. I use talc that I buy super cheap from a local pottery shop. It is a very common ingredient used in quantity to make pottery. So, almost all shops will have it. They buy it in bulk containers and are happy to scoop out ten pounds and charge me 5 bucks. Before discovering that source, I was buying it in boutique amounts as a body powder costing twenty times as much per pound. Denis
I skipped the old socks and various talcs and went right to calcium carbonate (super cheap at ceramic / art supply store) in a homemade flannel bag ala HT1's cloth gift bags off Amazon or graphite right out of the container (cheaper as a seed lubricant at the farm store than from auto supply stores, I look for ones without talc). My other trick is small patterns get shook in a Ziplock-style bag with graphite before use. Any extra graphite just stays in the bag for the next pattern or is used in ramming the mold when I misplace the Ziplock with the calcium carbonate bag....
Thank you fellas! I used a bunch more propane, made a lot more mistakes and redesigned the pattern with draft. After burning myself I've been replacing my tools with longer versions as I can modify or build them. Blah, blah. The point: I'm starting to get a feel for the mold building. The gate is 2X wider (1in [25mm]) and the riser gate? 2X wider (1.2in [30mm]). I actually made a fan gate off the sprue..... trap under the sprue and tried to radius for flow. I think sand inclusions are near zero. I have some porosity on the top (as poured) of the part which I'm supposing means I need to turn my temp down (1600F) or add venting but I may not change anything just yet because the sprue went dry (sucked air) just after I started pouring. I just wasn't pouring fast enough. The part is good, strong and consistent. I did have damage to the sand that caused flash in general. Notes: I found it interesting that the riser shrank near the parting line more than at the top. Me thinks my sand is too fine for what I'm trying to do. May order the next course size, I think 90 as opposed to the 130 mesh. It's another $100 but I need more as I use all 30# every mold. Maybe I'll set aside 15# of the fine and add the remaining 15# fine to 30# of 90 mesh.
Thank you, thank you. Y'all certainly shortened my learning time considerably. Yessir Mark is correct. This is all pretty exciting. I'm itching to try some antique auto parts now. I ALMOST used the dry sand parting idea today but decided I didn't want the added variable when the talc has been doing a marginal job. My new Chinese crucible changed to a brown-gray color after several 2000F brass melts over the weekend. With the aluminum it stayed looking new. I have a Salamander new in the box, but figured I'd burn up the cheap one learning.
Groves on the inside walls of your flasks would let the sand key into the flask. I notice the walls are not thick, so they don't have to be deep.
Thank you sir. I will do this. I need to make a better alignment system too. In this case, the core enters the cavity long before the flask can be aligned..... which caused most of the flash you see on the part.
Way hotter than desired for aluminum. Depending upon alloy, I'd say you should be shooting for <1350F. As an aside, reducing the pour temp can greatly reduce porosity and related defects but may not eliminate the shrink. Porosity and shrink are often found in the same location because H2 comes out of soluton in the last location to freeze which will be the thickest features farthest from the feed system/hottest metal. You mention shrink at the riser parting line. I dont see a riser, just a sprue, but if the shrink is occurring outside of the casting, it's not much of concern because the casting has already frozen first. A cooler pour temp may require further mods to your gating and the feed system but should yield better metal quality in the casting. Still, hard to argue with success if it's giving you satisfactory results. Best, Kelly
Nice work. It looks like you hit on a set of variables that worked but perhaps need some dialing in. I'd try a few sets of castings under the same set of variables before changing anything though. Probably the most significant variable in this instance was the break in your pouring. Your sand has to hold together in the mold but outside of that at this point, it is not the most important variable. Your pouring temp, gating, and pouring technique are, so if you make any changes I would focus on those (but methodically, conservatively, and one at a time). Keep up the good work. Pete
Hadda' meeting with a prospective customer yesterday.... cast aluminum parts (which is admittedly optimistic for me at this point). I'm double the cost of China... I figured $2 per hour for propane, $2 per hour for crucible wear, $1.50 per lb aluminum (scrap). Ah, that's all a topic for another post. I guess I need to start thinking about efficiency. The next logical step is machining match plates I reckon. Maybe natural gas is less expensive but it's a large one time investment in SC. All that talk and I've made one successful part
Making castings for others is marginal at best, what they didn't mention is they have to buy thousands of that casting to get that price and the months of shipping time not to mention the slow times to make changes to the casting. You'd be better off selling one-off pre-production prototypes for ten times the price. Let them buy from China and find out the hard way about the quality control, price and finding their product copied. The place where I help out, had a gentleman turn up who had bought one of our products and took it to Taiwan where it was copied using all parts CNC'ed from plate, sheet and bar stock: He readily admitted they couldn't beat our price with parts cast in house. In other words, casting gives you a direct competitive edge to products made in house and is a barrier to those trying to copy your product and undercut you.
Thank you Mark. I still hope to get some work from them but you are exactly right. I did prod him about freight which closes the cost gap a little. I let it slip that I would go home and scan these parts. What!? you have a 3D scanner?! uuuuuh, yep. So he handed me a box of crap to scan...... most of which I'd be better and faster and just modeling but whatever. I'll play ball. Just made a pattern for a tiny part with a lot of potential, a big part with huge potential (If I am successful) and another part I probably won't be able to do anything with but we'll try.
