"surface rust" - what is that, really - definition proposed
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  1. #1
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    Default "surface rust" - what is that, really - definition proposed

    I suggest that we all consider oxidation to be "surface rust" if and only if it can be cleaned off to reveal no pitting.

    Thus if I buy something advertised as having surface rust and I clean it off and find pitting, I would feel like the advertiser didn't fully disclose the condition.

    Do you agree?

    metalmagpie

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    I dunno - to me, rust is automatically a "subtraction" from the original, undisturbed surface. Any rust, therefore, has to leave some pitting behind. It's just a case of how severe it is.

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    No detectable pitting depends on magnification

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    Quote Originally Posted by metalmagpie View Post
    I suggest that we all consider oxidation to be "surface rust" if and only if it can be cleaned off to reveal no pitting.
    metalmagpie
    Never seen this.
    Bob

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    I cleaned up 2 lightly rusted dead centers yesterday, both appeared to just be light surface rust. After cleaning 1 showed a fair amount of etching to the metal, the other had no etching and looks pristine. So you don't know how bad the rust is until you clean it up.

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    Realistically, yes I'd agree that "surface rust" leaves no visible pitting. I don't know that I would complain about something I bought used unless the level of rust has effected the thing dimensionally to the point it isn't really usable. It would then depend on how much I paid for the thing, as in if the investment is little enough that I don't mind the poor cosmetics of it.

    An example being the lathe in my garage at home, which spent part of it's life face down in the mud. Most of the bed ways are pitted, but so much of the original surface is still there around the individual pits that it doesn't effect their flatness, so it's just a lubrication aid. Conversely, I've had rusted wrenches end up in the scrap barrel because the pitted jaws were no longer the nominal size.

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    “Surface rust” is when you can’t see it but a rag comes up slightly red tinge when you wipe some oil on.

    Anything more than that is just rust..

    Shoot change that - even the stuff you can’t see is rust.
    The whole world is going to crap- no sense dressing it up with fancy explaining.

    Shoot- even our sun is dying.
    We are all doomed and the damn rusty machine table ain’t the half of it.

    I need a beer..

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    Quote Originally Posted by Trboatworks View Post
    I need a beer..
    As long as it's just a beer, and not a bier, it's all good...

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    I much prefer to have all my machinery with sub-surface rust only, so it does not detract from the patina, which they mostly are equipped with.

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    To me, its the stuff that can be removed easily - like on this cast iron. If this lathe bed was steel, it would be a much more issue

    dcp_1289.jpgdcp_1317.jpg

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    Quote Originally Posted by Trboatworks View Post
    “Surface rust” is when you can’t see it but a rag comes up slightly red tinge when you wipe some oil on.

    Anything more than that is just rust..

    Shoot change that - even the stuff you can’t see is rust.
    The whole world is going to crap- no sense dressing it up with fancy explaining.

    Shoot- even our sun is dying.
    We are all doomed and the damn rusty machine table ain’t the half of it.

    I need a beer..
    Wow! Someone's having a bad day. Hope things cheer up for you soon.

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    This might shake Milacron out of the trees, some good threads back in the day on this. His take was always all rust is surface rust (duh), so it's either light rust or heavy rust.

    Should start a thread on divining rods and Stabilant, that'll do it.

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    Is there a thought that "surface rust' is a entirely additive process and none of the parent material is involved?
    So this seen as a PVD/CVD coat or paint over the top type thing?
    Confused.
    Bob

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    "Surface rust" usually means "It's shagged, but I still want you to pay new price for it"

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    Quote Originally Posted by CarbideBob View Post
    Is there a thought that "surface rust' is a entirely additive process and none of the parent material is involved?
    So this seen as a PVD/CVD coat or paint over the top type thing?
    Confused.
    Bob
    The problem is that any tool or machine with rust on it is ALWAYS described as having "surface rust" no matter how eaten away it is. I'm certainly not arguing down at the chemical level. I'd just like to get agreement on what surface rust is.

    metalmagpie

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    Quote Originally Posted by metalmagpie View Post
    The problem is that any tool or machine with rust on it is ALWAYS described as having "surface rust" no matter how eaten away it is. I'm certainly not arguing down at the chemical level. I'd just like to get agreement on what surface rust is.

    metalmagpie
    I think it would be best to get a universal consensus of what "good condition" means first.

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    Without going too deep or technical,

    Red "rust" fast rate of corrosion - friable - is usually hematite (based corrosion products) - these are usually thought to be unstable - pitting will result and the ferrous base metal is being actively dissociated (in solution) through active corrosion processes - (ferric chloride and other acidic solutions nucleate inside the bottom of corrosion pits to further accelerate the corrosion of the individual pit but also destabilize the metallic surface creating new corrosion pits. ).

    Black / blackish brown corrosion products are usually thought to be magnetite based corrosion products and these are slower in action and actually have a slightly passivating effect - i.e. slows down the rate of corrosion esp. compared to RED corrosion products / hematite based.

    As far as machinery tables goes that's super tricky. And I agree you can only tell how bad or how deep or how chronic the corrosion is when you start to remove the stuff either mechanically or chemically. Inspection under a microscope (higher power dissecting binocular microscope is sufficient or shop microscope) - would be handy to document the how the pits start to disappear once a surface has been cleaned or abraded/ lapped or even ground. - The pits should get smaller in their radii. If you know you are taking off about 5 micron / two tenths in repeated successive passes [or more] (by whatever method) then you can map out the severity of the pitting.

    Not sure you can get someone looking to get rid of their old machine to do that for yah ?

    _______________

    For more ancient ironwork it's a given that the position of the original surfaces are lost and something that approximates to the original shape of the surface (called a pseudo-morph) occurs somewhere between the magnetite layer (dark yet stable) and the more voluminous and friable hematite layers + other intermediate corrosion products that are more brown and yellow such as Goethite.

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    Quote Originally Posted by CarbideBob View Post
    Is there a thought that "surface rust' is a entirely additive process and none of the parent material is involved?
    So this seen as a PVD/CVD coat or paint over the top type thing?
    Confused.
    Bob
    Yup, the American lathe in my friends potato barn is getting "tighter" every day, or so he says...but it's also adding a nice lapping grit to the cross slide.

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    Saying 'surface rust' is like saying a building has an 'exterior roof.'

    ALL roofs are on the outside. ALL rust is on the surface. Items rust from the *outside*.

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    If you wire brush it ....what happens ?

    if it comes off, then classify it maybe as light.

    if a wire wheel takes off flakes and leave deep pitting, there's another classification

    Look to the sandblasting association, for pix and definitions of rust/corrosion.


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