Hi guys, I haven't hung out here lately, as I was working on my lathe project. It has been about a year since I last did any casting and it shows... - didn't weight down the cope - didn't melt enough iron - didn't skim often enough or thoroughly... Cheers, Mark
Sorry that the work was not successful; however, the video surely is! Love the 'caped crusaders' transitions.
I guess you don't have access to a pottery kiln that goes to 1750F. If you did, you could wrap that part in SS foil and annneal it and it would have been buttery soft. Heat to 1750, hold for 45 mins, turn off kiln and open it the next morning. Hopefully you will not be machining edge-chilled iron in the future. But, if you have to, rather than attacking it from the outside, turn your cutter speed down a lot and plunge into the casting inside the area of chill. Then work out to the hard edge rotating the cutter so that it lifts off the chill rather than beating down and into the casting. It will not be easy even so. But your cutter will have a chance and may successfully peel off a thin layer of white iron like what you showed. Denis And, BTW, glad you are back!
Mark, unless you cleaned the voids, they look more like gas than slag. At the circular depression it looks like a cold shut with the smooth edges. I have had good results annealing CI by packing in stainless foil and returning to the furnace and bringing to some critical temperature. I think most of the success is based on total carbon available. It looks like a good pour in that regard based on the drill chips. We don't think of pouring or molding as a depreciable skill, but I find that it bites me after a time away from the foundry. It's just the little things like remembering cope weights or slagging properly but it happens.
Hi Guys, thanks for the feedback. The circular depression is not a cold shut. It is part of the pattern. I definitely saw some pretty large blobs of slag flow out of the crucible. Getting cleaner metal is the first goal. I did the final slag scrape out of the furnace, as you always spill some, so I dont what a lot more sticking to the furnace liner. My little home made heat treat electric oven can heat to over 2000°F so I could anneal if the next one is chilled. I did pull this out of the sand way too early though. It was still red hot. Stupid. Mark
Using a small handful of unexpanded perlite tossed on top of the melt will make essentially all the slag coalesce into a big glob that can be lifted out en- masse. Cheap stuff. I really like using it. I think common garden-store expanded perlite would work as well, but being less dense might tend to blow a bit due to exhaust gas flow. I always do a final quick skim out of the furnace too. Denis
Comments: 1) You made a lot of progress over your prior attempt! Way to go. 2) The sand breakout is likely due to inadequate draft or poor surface finish. Make life easy where you can. Go ahead and use 5 degrees of draft or more on the center hole. It's machined anyway. For my own use, pigmented paint makes surface defects easier to see. I use white spray lacquer. Usually I have to spray at least 3 or 4 coats with light sanding, a bit of Bondo touch-up to dents and divots and then wax before molding. 3) Plaque-like patterns usually fill better if slightly inclined with the pouring basin low. 4) You likely had a lot of slag because your stock was made up of so much thin material. The more surface area on the feed metal the more slag. 5) Your gating is needlessly complex. A simple sprue ending in a hand-cut runner that then enters the cavity at a single hand-cut point should be adequate. You might need a blind hot riser at the gate. This part is on the border of having a thickness to width ratio that might need a riser. 6) The hot tear you had would be eliminated by the above. Generous radiuses also counteract tears. 7) When you made your skimming spoon you made it like a woodworker. ;-) No need to make a slot for the blade and use weld bead like glue. Just put the two parts abutting. Hit it with a bead or two and call it good. (That was a very picky criticism. But it is a time saver.) 8) I have a feeling you have spent a lot of time watching "Clickspring" on YouTube as your very well-done video has a similar very pleasant quality. Denis
Thanks for your feedback Dennis. Confirms pretty much what I was thinking. Your critique of the skimmer was a good one. I started skimming too cold, and now have a big slaggy lolli pop Wasn't worth the effort. I'll rough machine the X mount plate, and see how bad the inclusions are. If not too horrible, I'll probably just fill them with metal colored epoxy, and then fine machine. Mark
One way to reduce iron and slag build-up on skimmers is to soot them well prior to skimming. I do this by momentarily turning down the air which causes a sooty yellow flame. 5 seconds in the flame makes a good coat. You may be able to break off the accumulation on your lollipop by hitting it with a hammer. Using a small handful unexpanded perlite makes all the slag coalesce. Using tongs to then grab the glob is convenient. Since the linked post I added a couple flat fins to the tong arms so it can hold more slag. http://forums.thehomefoundry.org/index.php?threads/“skimming”-with-tongs.1588/ Denis
I bashed it with a hammer, but it laughed at me- I'll just chop it off, and weld on another skimmer. Thanks for the tip on sooting up the skimmer.
Sooting does work. One other suggestion is to consider a crook in the handle so that the handle is straight for perhaps a meter and then makes a 75 degree or so bend downward and then travels 8 to 12 inches to the skimmer blade. That allows the skimming hand to be out of the direct line of radiant heat coming from the flask. You can sort of "hide" your hand out of sight of the blistering heat coming out of the furnace. I also use a small straight-shaft skimmer for final skimming as it is a bit more dextrous than the crooked skimmer. Denis
