I have seen mention of sea coal various times over the last year or so as an aid to cast iron casting in green sand. I recently purchased some sea coal (a persistent but archaic term for mineral coal as opposed to charcoal) and due to the vagaries of ramming up a mold and collapse of a cope after packing the drag in 3% sea-coal-augmented sand, ended up with a drag with 3% sea coal and a cope without---the ideal controlled setup to test the benefit of sea coal. The results were convincing. The sea coal resulted in a surface that the sand simply fell cleanly away from and was nearly lustrous. The cope, while very acceptable, had much more adherent but not burned in sand. There is no doubt in my mind that sea coal will be included in my future. Just passing this along. I am sure the experienced people here have drawn their own conclusions about sea coal and may disagree with my observations or know of even better options. But the pulverized coal I used was a big help to me. See photos. In the last photo the sea coal side is on the right and the non-coal side is on the left. Just for reference, the casting and runner weigh 41 pounds and is 36" long and 6" high.
How much difference is likely? Can you provide some background for the suggestion? I do have a Wilson hardness tester, though the piece would be a bit awkward to position.
Try drilling the runner on both sides and just see if you can feel the difference in the skin from the side with the sea coal and without. You should be able to tell the difference ??
I know of one other individual who is trying the sea coal. Its a funny story about how he got some. He saw some in a video somewhere in the world, got in touch with the person in the video, said "I know this sounds crazy, but can you send me some of that sea coal you are standing on in that video?", and they did package up some sea coal and send it to him, I think from a different country if I remember correctly. People will do a lot for you if you are nice (he is a nice guy and I admire him for that). Another thing I have noticed is a difference between the finish on the top and bottom of an iron casting. One side is good, and the other side not so good; and as I recall this was with petrobond and iron, but may have been with resin-bound sand also. I will check my photos and see if I can post an example. It was discussed once why this occurs, and I forget the reason, but I am guessing the bottom of the mold gets hotter and stays hotter longer than the top, and thus has more time to penetrate the sand grains at a hotter temperature before it hardens. Ironman's castings seem to be pretty consistent top-to-bottom, and I think he uses water-based green sand.
Isn't the surface hardness because the sand forms silicon carbide with the carbon in the iron?. I know with the resin bonded sand they spray a layer of graphite and alcohol over the mould before assembly. The thin layer of graphite keeps the hot iron from directly touching the sand.
OK, you got me curious. I tried a 1/4" hole from both sides. I hate to say it but I could detect no difference! Maybe I am too insensitive to detect what might be a difference. The bit I used is pretty sharp and that might reduce its sensitivity to surface hardness variation. I was happy the material drilled nicely as it should. My sand is new Olivine 100 mesh mixed with southern bentonite 5%.
Ammen mentions that sea coal is used to improve the surface finish by reducing burning in and creating a reducing atmosphere. He calls for a mix between 4 and 6 % in molding sand used for cast iron. It would seem that carbon on the surface of the mold will give the same results. When I did the Indian heads I sprayed the baked sand molds with a graphite spray and noticed an improvement in the surface finish. With cores I have mixed locksmith graphite with denatured alcohol and brushed it on then lit it to burn off the carrier. Another method for cores is graphite and molasses painted on and then baked to set. I wouldn't expect any change in surface hardness since that is a function of Total Carbon and the speed of solidification. I dust aluminum gates and runners with graphite and it seems improve the finish there also, but talc does the same thing too.
When I gave specific planned usage (iron) to Smelko (industrial casting supplier) back I purchased greensand from them, it included "sea coal". Now I haven't attempted iron yet, so that means I have no real experiences to pass on. Just thought I'd add that "sea coal" is something the big boys use.
On that note, when I was asking Tim (Smelko) about their sand blend for aluminum, the end of the description he gave me was "...then a couple other carbonaceous additives to make casting surface finish as good as possible!" I wondered if that might include sea coal, but then again this is just for aluminum, so I'm not sure if this helps or not. Jeff
Just an added observation on sea coal used in green sand for cast iron. The other day I had just completed pouring 20 pounds of iron into a green sand mold with 2% sea coal added. I had previously notice charring of my wood flasks along the seam between the cope and drag and simply attributed the charring to super-heated gases venting there and thus heating the wood to charring temps. The amount of burning was relatively small with each pour into those flasks, but clearly is going to limit the lifespan of those flasks constructed from 2X fir to ten or less pours. The interesting (to me at least) observation was that I saw a broad thin horizontal ribbon of faint blue flame emanating from the seam. This was clearly different than the typical flame one sees when wood burns as that flame is more yellow orange, is closely applied to the wood, and sort of curls along the surface of the wood. This flame was barely visible in direct sunlight and persisted only for maybe 5 to ten seconds. It did leave the wood smoldering but not in flames. My conclusion, maybe incorrect conclusion, is that I was gasifying the sea coal and that gas was venting along the seam in enough concentration to actually burn briefly. (I am wondering of others have seen the same thing.) This probably explains to some extent the charring I have been noting at that seam and also around the central vent holes in my 3/4" plywood bottom board. Today I am just finishing welding up some steel flasks to replace the charring wood flasks. These flasks will be dedicated to a casting I expect to pour 20 times or more over the next year and hopefully for a few years after this. I hate to spend the time on the metal flasks but hate even more spending time making decent wood flasks only to have them slowly burn away. Denis
I have seen foundry videos where a press and jolt machine is used (correct term?), and they use a snap flask, and remove it, and then slip a thin metal jacket over the mold before they pour it. Solves the problem of damaging the permanent flask. I use custom wooden snap flasks, but use bound sand, so I can remove the flask and cement the cope to the drag, thus I never damage the original flasks. I have found that pretty much anything flammable in the vicinity of the furnace and the pour area will catch fire and burn sooner or later, so I have tried to remove flammable materials in general when I can, such as rubber pouring cart tires, rubber or plastic furnace casters, wood flasks, etc. .
I have used resin-bound sand (and not reused it), and have been transitioning to sodium-silicate-bound sand (about 3% sodium silicate), which I intend to try and reuse after washing, mulling/mixing, and drying it. I will add a post with some mold examples. Edit: An example of a bound-sand mold is here (post #64): http://forums.thehomefoundry.org/index.php?threads/jumbo-coin-casting.111/page-4
I did an after-dark pour last night into a steel flask set. It was very revealing concerning off-gassing caused by cast iron in contact with 3% sea coal in my sand. I thought I had previously seen a few light blue flames when casting in sunlight. But just how extensive they were was evident in the dark. (Also, the crucible looked gorgeous glowing sun-like in the darkness!!). This was the reward for a melt that took longer than expected and challenged my patience.
I actually prefer night pours just because it is so hot here in the summer, but it can be tricky to see what you are doing. There is no doubt a lot of strange stuff happening during a melt and pour. I tried a mold coat one time, which consisted of graphite and alcohol sprayed onto (of all things) petrobond (in my totally-clueless days). It was an unmitigated disaster, and I have not tried mold coatings again. I have heard that brushing graphite onto the inside of the mold helps with surface finish and I will try that again some day with sand that is not petrobond. I used some sodium silicate cores on some small engine cylinders with iron, and had a lot of out-gassing, which ruined the parts. I have since learned that ss cores can be lightly flamed (or even baked) to drive off any moisture, and so I am going to try that. Another advantage of night pours as you mention above is that you can see things/flames, ie: coming out of the top of the furnace, around the furnace lid, and sometimes leaking around the burner tube/tuyere joint, that you would not otherwise notice. And lifting an iron-temperature crucible up out of the furnace at night is like a phoenix-rising phenomena, and a site to behold if you are impressed by the eye candy stuff like I am. Edit: It looks like you are having (have had) some significant success with melting/casting iron parts. From someone who is still "in the curve" and definitely not there yet, that is some impressive work.
Here are a few pics mostly just for fun, but one shows a whisp of coal gas rising out of the sprue as I poured iron tonight just after sunset. The others just sort of set the scene. the closeup of the pour might look odd as there is aluminum foil covering much of the mold with it just torn back in the area of the sprue. It is November in the PNW and if I wait for a dry day to cast, I would have to wait til May! So, I cover the mold with aluminum foil and rip it back a minute or two prior to pouring. the second image shows my hoist rig depositing the crucible on my sand box plinth. This was a 50 pound pour done a 2600 degrees.
Great photos. That lid/chimney combination is quite an affair, but seems to work well for you. I wondered how you were swinging that lid open. Did you box your blower also for sound? And you can get an arm workout with the crane, without having to pay for a Club membership. That is a nice setup. What does the aluminum foil do? .
I use an upright bar with a sleeve that is cammed to lift the lid and swing it. You can just see the lever and cam to the left of the base of the chimney in the second pic. the chimney is not by choice but by necessity as a neighbor complained of noise. But it does what is needed as it reduces sound by almost 20dB. But it is a pain in some respects as it prevents glancing into the vent to see the color of the metal and condition of the flame. But I am gradually adjusting to it. Having cut my teeth with an open chimney/vent, I have to relearn how to read the operational clues of the furnace. Not a simple task. The blower was boxed for sound, but is actually somewhat more convenient to use boxed. Foil?:this is November and rain is a nearly continuous condition in the PNW. I cover the entire mold with it and rip back the foil at the sprue just before pouring. I actually cover my mold with foil year around as it prevents general crap, dirt, and critters entering the sprue since I usually pack my mold the day before pouring. And it prevents drying of the sand. The arm workout is not so big a deal since the crucible and metal weigh only 60 pounds and I have a 3:1 mechanical advantage. I really like not being close to the molten metal when pouring and I like being able to work safely alone. Denis Edit: I also clamp the cope to the drag with plywood boards 1/2" by about 6" wide by a few inches greater than the mold width. 1/4-20 all-thread connects to the drag and the board lays over the top of the cope and is pulled down by the all-thread firmly clamping cope to drag. (I haven't had a leak or fin between cope and drag since starting this) I wrap the board in foil to act as a heat shield from the crucible. There is so much radiant heat from the crucible that the board, unprotected, lights up as I am pouring due to the radiant heat. Wrapped in foil, the board survive unscathed. That is the wrapped clamping board seen at the right of the closeup.
