Yes sir...been my experience with it as well. If you want good peel it will definitely help but it does add quite a bit of gas and the perm is much lower. In our foundry because we have such thin wall castings we probably do not generate as much gas so and only have to worry about the gas in initial filling. Some of our thicker castings tend to generate more heat and gas and we have to vent those more thoroughly and with greater concern on location. We do not use risers. Our inclusion rate will go up and we will see streaks if we add too much. Probably lots of different variables as to why the inclusion rate would go up such as sand strength and gas all the way down to whether the sand was mixed or mulled properly. Nice job on finding information on it. I can probably ask and get some info from our sand and premix vendor and some AFS info on it but I think for the most part every foundry is unique and you just need to experiment with it and see what works best for your foundry and it may be more job specific depending on how diverse your foundry is.
The thing that I found interesting about it relates to the question I posed a few posts ago about using bit coal versus anthracite. It appears that the volatiles in the bituminous coal do play a role in the process, not just the carbon according to the linked study.
Pete, Could you point me to the page(s) that talk about bituminous vs anthracite? Interesting article. When you think of the work involved in researching, experimentation, and writing it, it is remarkable. Denis.
In the introduction portion of the linked study they mention the proximate analysis of what they believe to be the best sea coal for foundry use. Those figure best match the proximate analysis of typical bit coal as opposed to that of anthracite coal as shown in these two tables https://phyllis.nl/Biomass/View/1144 https://phyllis.nl/Biomass/View/958 All I know about proximate analysis is that it's one of several standards used to describe basic content. I don't know any more about it than that and other than my current research I've never even heard of the term before, but the similarities in the respective analysis figures lead me to believe that they are talking about bituminous coal as opposed to anthracite. There doesn't appear to be anything comparing the two in the study. The information presented on pages 5-10 in the context of permeability make mention of the action of the volatile components of the sea coal further suggesting that those components are desirable in the process. So I'm getting the idea that anthracite is not the right stuff. On a semi-related note I found the wiki article which may give some clue to the origins of what was once called sea coal and what it is now. Mainly that it was originally collected from the surface from exposed seams in the cliffs by the seashore or washed up from undersea exposure and also that it was delivered by sea. From the history section of the Wikipedia article "A grade between bituminous coal and anthracite was once known as "steam coal" as it was widely used as a fuel for steam locomotives. In this specialized use, it is sometimes known as "sea coal" in the United States.[41] Small "steam coal", also called dry small steam nuts (or DSSN), was used as a fuel for domestic water heating." So the term has likely gone through some evolution. Cliff Clavin signing out.
I know Anthracite is dryer and has less volatiles than bituminous. Honestly I think either one would show an improvement to surface finish and metallurgy. The biggest difference would probably be the amount used for the result you want to obtain. Each job could use a different mix depending on mainly geometric shape, weight and height and pour time and pour rate. Lots of different factors can come into play. That is why big companies buy premix. They have sand experts who can tell you the best blend for your specific needs. Doing it at home may require more of a touch and go in small increments. I know it will cause problems like streaks and misruns and gas if used in excess. I have to admit that I am mainly familiar in thinner castings. Thicker castings from what I have seen tend to be less sensitive to the addition.
It is surprising where this casting interest can take a person. I have to say I had never thought much about volatility of coal previously. The volatile content of coal evidently does vary by quite bit depending on its rank. Below is a link to an article that mentions this. https://www.netl.doe.gov/research/coal/energy-systems/gasification/gasifipedia/coal-rank "The volatile matter content of coal varies widely for the four main coal ranks and is low for high rank coals such as anthracite and higher for increasingly low rank coals. The higher the volatile matter content the more reactive a coal is which means it can be more readily converted to gas while producing less char. Thus for high rank coals, the utilization of char within the gasifier is much more of a concern. For low rank coals, char is not a major concern; however, the ease with which they are gasified leads to high levels of tar in the syngas which makes syngas cleanup more difficult." That would lead me to think that lower ranking bituminous coal may be preferable as far as gas production is concerned. It is possible though that for reused sand more residual tars etc may build up in the sand over time. I have tended to use 6% coal in newly mixed sand. I have then found replenishing the sand with about an ounce of coal per ten pounds of sand after each use seems to maintain a reasonable level of coal. But that is purely a guess and I could be way off on the "correct" replenishment rate. I know the replenishment rate I use can only be a gross approximation as the amount of sand in a mold vs weight of cast iron varies widely from one type of casting to another. So, the percentage burnout of coal on any given casting has to vary considerably as well. I do vary the replenishment rate if I think I may have gotten to a excessive level of coal in the sand---also a wildly inexact assessment I am sure. I came across another article that speaks to the volatile content of coal. https://www.uky.edu/KGS/coal/coal-analyses-volatile-matter.php "Volatile matter is directly related to coal rank; as rank increases, volatile matter content decreases (Stach and others, 1982). Volatile matter has the opposite trend of fixed carbon with rank. As volatile matter is driven from the coal matrix with increasing rank, the relative carbon percentage tends to increase. Both volatile matter and fixed carbon are used to define coal rank in high-volatile, medium-volatile bituminous, and higher-rank coals in the U.S. classification system (ASTM method D388-12; American Society for Testing and Materials, 2013, p. 390–396). Along with moisture and ash contents, the percentage of volatile matter in a coal sample is needed to calculate the fixed-carbon content of a coal." Denis l
Absolutely... will build up an excess of tar over time. We have had tar build up on our tooling during production that on the casting resembled burn in but was actually just tar stuck on the pattern. Our supervisor did not believe us when we told him what it was so we scraped it off and had it sent to lab for testing. Never heard the results of those test, but I have only seen it a couple of times since, so I am sure they reduced the additive or switched blends. We also started seeing lots of streaks about the same time which also went away with the tar build up. I had some pics on my old drive and if I can find them I will post them. I doubt many of you will be running 600 molds an hour and will probably never see that build up like we do but you may see an increase in stickers and streaks as the sand seems to stick much worse and does not permeate well.
Although I've never owned either I found there's a difference in the function of coal stoves that burn bit coal as opposed to those that burn anthracite. Specifically there is a "mouse hole" air intake separate from the primary combustion air intake that supplies secondary air to burn off the pyrolized volatiles in bit coal- a provision that is apparently not needed in an anthracite stove. I may not be 100% accurate with that info but I think that's right. Pete
Here is a vid about substituting sawdust for sea coal: It looks like he had good results. He also talks about a work-around chilled iron. Myself, I’d anneal rather than machine as is. But there may be times when that is impractical. Small castings are problematic as they cool quickly. It does help to make sure the mold fills fairly quickly. Smaller slowly filled molds are more likely to chill at the edges than those that quickly and completely fill. Makes sense, but it took me a while to actually observe that. Denis,
<iframe width="560" height="315" src="" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe> Thanks for the Youtube link Denis. I remember some time ago that you mentioned greensand strength testing. There is a test at 18 minutes on the movie, Cheers Charlie
Yes, I remember seeing that fairly impressive strength test. The only “problem” with it, in my mind, was its lack of potential member-to-member standardization as the amount and method of compression and the internal shape of the flask were uncontrolled/unspecified variables. Denis
From what I’ve read, annealing to cure white iron is a much slower process than merely normalizing steel.
