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Thread: steel/iron/arn potatoe/potaato

  1. #1
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    steel/iron/arn potatoe/potaato

    The discussion I fired up re: Grizzly vs. Jet brought a question to (my) mind. First a qualifier. I've told y'all my knowledge of electricity is about a .1 on a 1 to 10 scale. When it comes to metallurgy, I'm probably a 2.5. I know steel is iron with carbon added and whole varieties of steels can be made by varying the amount of carbon and adding other stuff. I know that pure iron is the stuff dug out of the ground and smelted down. Y'all also know I hang around a lot with guys who live in the pre-1830 world. Some of them are blacksmiths who bemoan the fact that they cannot buy pure iron anymore. What they are able to acquire comes from junked antiques, like decorative fences from old, very old, houses. What they can buy is usually really a steel. I had a Vermont Castings woodburning stove that was advertised as 'cast iron' but the fine print in the literature said it was made from old engine blocks. Methinks those are really some kind of steel rather than pure iron. We are also all aware that much of the merchandise coming from China that is steel/iron was first sent to them as scrap iron/steel from the U.S. So, with regards to the lathes, and other tools, we talk about here, I'm wondering just what the 'iron' is that they are made from. Whether it is the Grizzly's I talk about or Bill Grumbines big Robust. Is that cast 'iron' really iron or sumptin' else? And, while we're at it....why does cast iron benefit from being aged? I hear old iron is better than new iron. This ain't wine. Wassup?
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    Frank you have asked a question with out one simple answer to it, most of the points you bring up, I could answer "Yes......no........depends....... ah.... sometimes......"

    Cast iron is just that, it is cast, poured in a liquid state into a form, which then cools, changing the iron into a solid stated. Most of it, like 95%, is iron Fe, and the other common components are Carbon, (C) and Silicon (Si). What you get for a end product depends on the amounts of these to components.

    The kind of cast iron most of us are familiar with would be the Gray Cast iron, it is what the old engine blocks were made from. I remember in my automotive classes we were taught that when a certain amount of silicon was present in the mix, then the result was that the carbide in the iron would change into graphite, which was a good thing, as it meant that the castings were better, sharper, could fill into smaller defined spaces, and that ability to machine gray cast iron was a lot better too, not only that, the graphite would offer some protection against rust.

    The other type of cast iron you commonly see is White Cast iron, it has less silicon in it, and it quite brittle, and you cannot make large castings out of it. The one area it does excel at is high wear properties, stuff like impellers come to mind.

    There is also malleable and ductile cast iron, which, IIRC is basically heat treated white cast iron.

    The other kinds of steel we are usually familiar with are Mild steels, these are fairly low carbon content, and they are usually forged to make thing into whatever we need, not cast.

    Well that is it off the top of my head, hope it helps!
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  3. #3
    Frank, you pose some good questions. The only thing I can add is that the iron coming out of the ore mines is iron oxide, or iron rust. There are at least three types of this rust as I recall. If you ever get up around Hibbing MN. make sure you see the worlds largest open-pit iron ore mine. Outside of the Grand Canyon, it is the biggest hole in the ground you will ever see.

    Maybe your blacksmith friends need to build their own Bessemer converter to refine the 'junk' they are getting.

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    OK, Frank, one question you asked that no one has yet addressed, is "Why does Cast Iron benefit from being Aged"?

    When the Iron is cast, it develops "Stresses" in it as it cools. These stresses can be caused by the shapes, thicknesses, etc. of the casting, which cause uneven cool down, thus causing uneven stresses inside the casting. When the castings are set out in the weather and endure the normal weather heating and cooling cycles over a long period of time, the stresses relieve themselves. As an example, one, (or maybe all) of the car manufacturers used to pile their engine castings out in the weather for four or more years, IIRC, before they would even consider machining them. The other methods of stress relieving that I am familiar with use large ovens to heat the castings and then do a controlled time/temp cool down, and the other is that Cryogenic method (that is fairly new and very expensive). The internal stresses are the main cause of warping in cast iron.

    Someone more metalurgically knowledgeable may have a better/more accurate explanation.

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    It's a very common story, accepted as truth, that many old line manufacturers wouldn't machine the castings unless they had set for a year in the yard. I assume that was mainly for the bigger castings and that smaller ones were relieved in an oven. Kind of hard to imagine a 36"-48" bandsaw casting going through and oven.
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  6. #6
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    Quote Originally Posted by Jeff Horton View Post
    It's a very common story, accepted as truth, that many old line manufacturers wouldn't machine the castings unless they had set for a year in the yard. I assume that was mainly for the bigger castings and that smaller ones were relieved in an oven. Kind of hard to imagine a 36"-48" bandsaw casting going through and oven.
    That wouldn't be hard to do at all, Jeff, if you could see some of the Autoclaves, and Heat treating ovens that some of the Oilfield equipment Mfr's around here have. Some Ovens are large enough for them to roll an 8' or 10' dia pressure vessle into, that is 30' or more in length and then they close the doors and fire them up. I'm sure there are some even larger that I haven't noticed. I have heard though, (but don't know if it is correct), that the BEST and most complete stress relief still comes with the old method of setting them out in the weather and leaving them for a long time, (the longer, the better). That method is by far the cheapest, except for the fact that the money is tied up in the castings for too long, AND, these days with so many advances in design so quickly, that by the time the castings were aged enough to mill, the design would probably be outdated.

  7. #7
    Are you sure your friends are using the correct terminology here?

    I think cast iron is VERY easy to obtain. Wrought iron is different and no maker in the world currently produces wrought Iron on a commercial bases. That would explain why your friends are going after "very old fences" and stuff. They are cleaning up the old wrought iron fences. Wrought iron and cast iron are two very similar metals, but not the same thing whatsoever.

    I may be wrong, but I think someone has got their metals mixed up.
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    To my knowledge, "Wrought Iron" is basically iron without any measurable carbon in it.
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  9. #9
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    Quote Originally Posted by Stuart Ablett View Post
    To my knowledge, "Wrought Iron" is basically iron without any measurable carbon in it.
    I dunno. That's why I asked. Still a puzzlement. What do y'all think we are getting back from China that is called "cast iron"?
    "Folks is funny critters."

    Think for yourselves and let others enjoy the privilege to do so, too. ~Voltaire

  10. #10
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    What we are getting from China is most certainly gray cast iron, that is by far the most common type. That being said,there is good gray cast iron and poor gray cast iron, the good stuff costs more, so if one buys a machine based only on price, you are more likely to get poor quality cast iron, if that price point is low.

    BTW, the Chinese where the ones who first developed casting of metals on any scale, as well as the first "blast furnaces".

    Castiron seems to be mainly Pig Iron with some scrap steel and such tossed in for good measure.........and Pig Iron is.........

    Pig iron is raw iron, the immediate product of smelting iron ore with coke and limestone in a blast furnace. Pig iron has a very high carbon content, typically 3.5%, which makes it very brittle and not useful directly as a material except for limited applications.
    BTW, I had to look it up, but this is why Pig Iron is called Pig Iron..........

    The traditional shape of the molds used for these ingots was a branching structure formed in sand, with many individual ingots at right angles to a central channel or runner. Such a configuration is similar in appearance to a litter of piglets suckling on a sow. When the metal had cooled and hardened, the smaller ingots (the pigs) were simply broken from the much thinner runner (the sow), hence the name pig iron. As pig iron is intended for remelting, the uneven size of the ingots and inclusion of small amounts of sand was insignificant compared to the ease of casting and of handling.
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