Rammed up two and poured. I charged with the worst lost foam failure and some miscellaneous pig and my usual oyster shell and a touch of the Desulco. I pushed the temp close to 2600 and when I poured there was no volatile off gassing from the core which is one of the advantages of NaSi cores. The chill wedge shows white iron up to about .070" and where I touched it with with the file it was nice and soft. This shot of the drag shows the screen cloth I put in the sprue to catch any slag the might get drawn in. If I chocked the sprue properly any slag will rise in the cup.
That's an interesting mix in the iron. I notice apparently no venting holes in the core, so I guess you are right about no off-gassing. I have not used enough NaSi cores to know how they act with iron, but I have been venting them with a 1/4" hole through the middle and then vented out the top of the cope, just in case. I have also started lightly flaming my cores with a propane torch. I have some round ceramic foam filters, but when I tried them a few years ago, they blocked the flow completely. I am guessing my melts years ago were not very hot. I think I have some calcium carbonate, and tossed a bit of that into a melt last year, but I am not sure if I should have added it early on in the melt, or added it with the ferro. At any rate, it did not seem to do anything. I have not tried the Desulco, but that sounds interesting. So I assume the parts turned out ok? We need photos of that stuff. .
It was still too hot when I posted above. Just shook them out and this is what they are supposed to look like. I had a vent in the center of the core and a vent from each end of the core print. Like I mentioned I charge with pulverized charcoal and oyster shell (chicken scratch ) . Ammen mentions Soda Ash, which is Sodium Carbonate, but I have never used it. The charcoal promotes the melting and the CaCO3 absorbs sulfur and maybe other impurities. When I pull I add Borax to clump the slag and then slide it off the surface with a carbon rod or wooden dowel. I buried the iron crucible in my pot of ash to cool, and loaded another crucible with what I think is Zamak from tilt mechanism of an old table saw. I poured the handwheel and machined it up, but no photos, camera died. Maybe tomorrow. C
It looks like it came out clean. I have heard of some using vermiculite to assist with the slag, but I have not tried it (I did buy some from the garden section of the hardware store). As I understand it, Lodge (cookwear people) use vermiculite to clean/solidify the slag. I am going to try your mix and see how it works with iron. .
That should be good soft iron to start with. When you make up your molds form some chill wedge molds and pour them with your castings. It will give you an indication of what to expect when you shake out or machine. When I was casting the Indian heads I pre poured wedges and then adjusted the melt prior to pouring and also cast a post pour wedge and compared the two. The wedge can be dunked as soon as it has solidified because the white iron has already formed. It only takes a minute and meanwhile the melt continues to heat.
I machined the guide this morning. It had the skin represented partially by what showed on the chill wedge because that face cooled on contact with the mold. Underneath nice machining grey iron. Faced and then bored to accept the bearings. And the handwheel mounted on the cross shaft with the eccentric and connecting rod.
Turned out nicely. I have seen one book reference that mentions that the first cut on cast iron should go completely under the surface and should cut into the base metal, since as you mention the surface can be a bit hard. .
I mean to take nothing away form the nice appearing and nicely machined casting. But, I'd be dissatisfied with a surface-chilled casting. Right or wrong that would suggest to me that the iron was right on the brink of generally chilling and could have used some ferro-silicon. Was ferro-silicon added to the melt. How much? When? Why did it chill at all? Denis
Denis, point taken. I might have mis diagnosed the surface as chill. The draft gave me intermittent cut at the start of the machining and that combined with a worn carbide insert gave a shined surface. I went to a single point HSS cutter and it machined nicely which wouldn't have happened with chill. As mentioned this charge was old iron plus misc. pig from prior melts, so I know the TC changed and that showed in the chill wedge as the difference between the two. Since the casting was all 1/2" thickness I chose not to use any FeSi. I usually just use it when I am pouring thin castings. I'm curious now so I'll do a test on the other guide. I'm also just learning to use my Brinnell tester and I think I had a 38 on the machined guide if I did the pre load correctly. I might try the same test on an unmachined surface.
So, your casting was very soft by your Brinell testing---less than zero on the Rc scale if you are using the 500kg 10mm steel ball method. You can not get a lot softer than that and I too have seen CI test slightly less than zero Rc on occasion. I have also found on Rockwell testing that hardness testing the unaltered casting surface (not recommended) and comparing to a ground or machined surface rarely resulted in a significant difference. So, the surface hardness experienced when machining cast iron (real I think) is just due to thin oxide crust laying on top of soft iron. That layer must be so thin that the Rc tester just cracks right though it and really is not much affected by it. But it is thick enough and slick or hard enough to inhibit skim cutting with a mill or lathe which is unavoidable if the surface undulates enough to cause interrupted cuts. (Speculation based on grossly observed cutter action) I made my "dissatisfied" comment as the above discussion seemed to be moving toward accepting surface chill as OK or common. It might be interesting to break a runner if you have one laying around to see if it has any evidence of chill when examined with a loupe. I agree that, in view of your comments, chill sounds very unlikely. I have found that cast iron is very unforgiving of unsharp cutters much as you did and bet that is really what was causing trouble. Denis
Yep. I think the initial deep cut with cast iron also comes from the repair of rusty pieces with outer oxide layer of rust being so abrasive. I'll break one of the gates today, and post up.
This is the gate on the other guide. Just a scant 1/16" of chill at the very edge. None showing in the body, so probably dull cutters and the skin oxide layer.
Yes, agreed. But, my takeaway is the iron, by showing any chill at all, is telling us that this particular melt was a bit “twitchy” and could have chilled significantly had it been just slightly more provoked. A little FeSi would have served as a calming agent. ;-). Calm is good! Thanks for checking it out and posting. Nice to see your wedge test precisely matched your gate break test. Denis
I made another foam. This is the lower guide that mounts on the lower arm. I fed the sprue into the base and oriented the mounting flange vertically. Two coats of mud and then set in the sand on the jolt squeeze. I packed the hollow as I filled and then jolted at each layer. When I poured, the soup can kush head failed so it had the effect of a bobble. This will call for a completely submerged pouring basin on the next attempt. The runout was contained, but the casting shows multiple folds and did not fill to the top of the flange. My phone died so pictures later. The loose sand core formed and held up against the metal. The jolting worked great because I had to use the flotation ring to extract the casting. I also seem to be losing Total Carbon. I added some of the piano harp iron to the fourth melting of the old iron and even though I added the Desulco and inoculated with FeSi the chill edge showed white slightly higher.
ESC, I saw the casting picture over at Allmetalshaping. Might want to post that up here too. Too bad, would have been nice to see the result of an uninterrupted poor. I'd be interested to hear your thinking on how you chose to gate too. Best, Kelly
I gated there because that was the solid bottom where I would drill and tap for the height adjustment screw. It was as close as I could get to bottom feed without sideways pressure on the loose sand core. I think I also poured cold to get that many folds. I thought I had posted that, but here it is. The saw cut shows nice clean CI so I will save it as bar stock. The rest back in the crucible for the part I need. Made this pattern yesterday. Loving the wax fillet Kelly. I keep coming back to this. The first CI lost foam I poured and it came out perfect, so I didn't learn anything from it except that I know it can be done.
It does look like it was poured very cold. Do you have a system/way that you like to judge the temperature of the melt? Denis
