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  1. #46
    BobL is offline Member: Blue and white apron brigade
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    I've blued a few more things since the previous posts using 3 passes trough the fume camber/tank.
    The pieces are all more or less variations of those already posted but I thought this one looked pretty good.
    It's the hand brake handle bar on the HP measuring rig.
    I made it in 2014 and 4 years later was just starting to rust.
    Brake-handle.jpg

    This morning I also upped the heating power on the fume chamber hotplate from 50 to 60W.

  2. #47
    BobL is offline Member: Blue and white apron brigade
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    In a couple of previous posts I referred to a supposedly faster method of cold rust bluing using Hydrogen peroxide (H2O2) and salt as the rusting agents.
    Well my H202 finally arrived and I had a crack at it this morning.

    The method I used closely follows the method posted here https://thecogwheel.net/2018/03/16/v...d-rust-bluing/

    CHEMICALS
    The H2O2 can be purchased on line and comes in various strengths (eg 3%, 4.5% 6% and 12%)
    Any of the strengths will work but the greater strengths will be faster.

    I purchased (~$30 in delivery) the 12% H2O2 which was mailed in well padded Al foil pouch.
    H2O2.jpg
    H202 solutions are temperature sensitive and there are instructions to keep it well stoppered and refrigerated.
    Also it pays to keep the working solution cool when the container is open or you will lose some of the active agent (ie the oxygen)

    The working stock solution is a mixture of H2O2 solution and salt (NaCl)
    I used 120 mL of H202 solution and 2 heaped Tabsp (40g of salt).
    The salt does not all dissolve in that much liquid but that doesn't matter.
    Don't warm it to try and dissolve the salt as this releases the oxygen from the peroxide.

    I transferred some (a few mL) of the working stock solution to another open container that I could dip a paint brush into as you don't want to contaminate your working stock solution.

    WORKPIECE PREP.
    The pieces must be grease free.
    Start by wearing latex or rubber gloves so no skin oils get onto the pieces
    There are lots of ways to clean the pieces - I use foot bath salts dissolved in water and boiling the workpieces in this for about 10 minutes.
    Then the pieces apparently benefit from some time in regular white spirit Vinegar - about 10 minutes.
    Then rinse the pieces in water and warm them with a hot air gun.

    APPLICATION OF THE WORKING STOCK.
    Place the pieces on a sheet of cling film and apply the working solution with a small paint brush. I found dabbing better than painting but it probably makes little difference. You can dunk the pieces in a large volume of working solution but at the end of the session you will have to discard the remaining dunking solution as the rust will neutralise the solution.

    The first application of the solution will look like this.
    Yep it starts rusting rapidly before your eyes
    InitApp.jpg
    Don't worry the reaction dies down rapidly and then you keep applying small amounts of teh working solution 3-4 times on each side.
    Eventually the reaction slows down and looks like this.
    SubsApp.jpg

    Now you blow try the pieces with a hot air gun and place the dry hot pieces in boiling distilled water for 10 minutes.

    Meanwhile clean up the mess - yes it is very messy and maybe lay out new cling film.
    S is the stock solution and W is the working container.
    Workmess.jpg

    When the come out of the boiling water first time they will look like this with the red oxide converted to black oxide
    1stpassa.jpg

    Then the loose black oxide "soot" is rubbed off with fine steel wool and they end up looking like this.
    This first layer looks like a faint medium grey coating - hardly looks like any coating at all.
    This is similar to the low temperature cold fume bluing using acids.
    1stpassb.jpg

    Then you repeat the H202/salt application, boiling water, rub off soot process and by the 3rd pass it looks like this
    This is after the loose black oxide soot has been removed. Its a bit patchy but not that dissimilar in depth compared to the cold fume bluing.
    Thridpass.jpg

    By the 5th pass its like this
    5thpass.jpg

    The website where I got this procedure from suggests that 4 or 5 passes would suffice but I decided to try one more and here they are also after being warmed in in oil for 15 minutes.
    The spanner is fine but I think the black oxide coating on the mild steel extension shank is a bit patchy and thin compared to where the cold acid fume bluing would be after this many passes.
    6tgpass.jpg

    So to summarise;

    Pros:
    It took me about 3 hours to do the above (Website said it would take 1 hour) but either way it is no question it's quicker than cold acid fume bluing
    Chemicals are easily obtained and not too complicated to setup.
    Chemicals are safe to use and dispose of.
    Uses very little chemicals if the above procedure is followed. To do the two pieces above cost about $1 worth of the original solution

    Cons
    It's messy.
    The finish does not seem quite as good as the cold acid fume bluing - I will need to try it again a few times and maybe I will also get faster.
    There's still some waiting around time eg waiting for water to boil etc when you can't really go off an do anything else.
    A batch process where by the H2O2 was being applied to one set of workpieces while the others were being boiled would speed things up when a lot of pieces needed to be done.

    I think the elevated temperature acid fume blued produces a nicer finish so I will keep using that as it only needs 3 passes and these can be done in a day in between other jobs. However if I need a quick bluing I will use the H2O2 method.

  3. #48
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    Looks pretty good Bob.

    The black looks blacker than any of the stuff I blackened with my Blackfast setup. Blackfast doesn't really blacken cast iron, it leaves a grey finish. How do you reckon the peroxide would work with cast?

    Bob.

  4. #49
    BobL is offline Member: Blue and white apron brigade
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    I suspect that CI will be tricky but it is next on my todo list. Still trying to think of Something made of CI that I can try

  5. #50
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    If you can't find something to experiment on Bob, I have plenty of smallish 4E offcuts. Being cast bar the results might differ from those on more commonplace cast iron.

  6. #51
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Anorak Bob View Post
    If you can't find something to experiment on Bob, I have plenty of smallish 4E offcuts. Being cast bar the results might differ from those on more commonplace cast iron.
    I found a clunky CI gear from a piece of farm machinery that I can use - It's pretty rust so I will need to clean it up first.

  7. #52
    BobL is offline Member: Blue and white apron brigade
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    This time it's some CI - at least I assume it's CI but maybe it's just rough cast steel.
    The pieces are from a piece of old farm machinery.
    Either way I'm using it to contrast another form of rust generation with the cold fume bluing.

    This method is to just hang the work pieces outside and spray them with a rusting agent.
    In the first pass the object was hung outside overnight. the object was sprayed with water plus it also rained (light showers) several times during the night.

    This is what the object (W) hanging up outside looked like in the morning compared to the other which spent the same time in the warm acid fume tank.
    1stPassa.jpg
    The rust layer is clearly thicker on the acid fume exposed gear than the other.

    After boiling in water and removing soot.
    The piece labelled W has a thinner layer of black oxide than the other but W's blackness is still respectable for a single pass and not that different to what one would see with an ambient temperature acid fume first pass.
    1stPass.jpg

    To speed things up I hung up the W piece outside and sprayed it with a 50:50 vinegar solution and this is what resulted after 4 hours.
    The gear on the LHS spent the same time in the warmed acid fume tank. This did not rust much, because it had already developed a pretty thick layer of black oxide in the first pass. As expected much more rust on the other piece now labelled V.
    It wont all be rust (iron oxide) - some will be ferrous acetate which is soluble and just dissolves away when the gear is placed in the boiling water.
    The clue that this is happening is the bright orange broth that results.
    Maybe a better procedure would be to spray the diluted vinegar on to activate the surface and leave it there for a bit and then wash off the vinegar and just spray it with water.
    2ndpassa.jpg

    After boiling and soot removed.
    Given the amount of rust on the V piece I was surprised to see not that much of an increase in black oxide. It's about where I'd expect to see a piece of steel after two ambient Temp acid fume exposures.

    2ndpass.jpg

    Will post a final result when I reckon its done.

    It seems like water/vinegar and outside exposure is working albeit slowly. Bt at least in involves nothing nasty or difficult to dispose of.

  8. #53
    BobL is offline Member: Blue and white apron brigade
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    This morning I realised I did have a nice big piece of CI that I could test bluing out on.
    This is my chunk of CI from the 2014 Scrapefest



    Below is the same piece after 3 passes through the acid fume chamber.
    It doesn't look like it's been blued at all but it is a lot darker darker than it looks.
    Getting a true colour representative photo is a bit like photographing the Monolith from 2001.

    IMG_3307.jpg

    If you look closely you can still see the scraping pattern
    I have deliberately rubbed the usual black soot layer down more than usual so that I can still see the pattern as this will tell me that the remaining layer is microns thin.
    In fact this would be a good activity for any novice bluer to undertake as this will provide a good indication as to how much soot should be removed for close fitting objects.

    IMG_3306.jpg

    IMG_3308.jpg

    I will get the better camera out after the next pass.

  9. #54
    BobL is offline Member: Blue and white apron brigade
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    After the next pass here is the CI block in comparison to a steel object that has had the same number of passes (4) through the warm acid fume tank.

    The CI does not appear as dark as the steel (which has been oiled)

    comparison.jpg

    Now with the CI block oiled they look a lot closer.
    Like I said, it's very tricky to take a decent photo of these shiny grey/black surfaces.
    oiledComp.jpg

    In this shot the CI block appears if anything darker
    Comp2oiled.jpg



    Below is a close up of the surface.
    The remains of the scraping pattern can be seen on the RHS but the LHS looks like it might have been slightly etched by spending too long in the warm fumed tank.
    Despite this the surface feels super smooth but I won't know what effect this has had on the flatness of the surface until I set up my surface plate and test it against that.
    detail1.jpg

  10. #55
    BobL is offline Member: Blue and white apron brigade
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    After all these experiments I think a Summary might be in order.
    Some of these are based on unreported experiments and may conflict in some ways with statements posted above.

    1) The warmed fume tank generates more acid fumes and water vapour than an ambient temp tank. The result is more red rust in a shorter time.

    2) The resulting red rust layer is thicker and more uneven that an ambient temperature tank. For protective only purposes this might not matter but for higher quality finish and precision fitting parts, shorter exposures and resulting thinner layers are advisable.

    3) If an ambient temp workpiece is placed into a warm tank the acid fumes may quickly condense out on the surface of the workpiece leading to large liquid droplet formation which can generate further uneven/spot rust formation. One way to avoid this problem is to preheat the object with a heat gun before placing it into the tank.

    4) The lid of the tank being cooler may also condense out vapours which may then drop onto the work pieces leading to problems. A possible way to get around this would be to warm the whole tank but this is not that easy. A Conical top may also allow drops to run down the inside of the cone and down the wall of the tank instead of dropping onto the object.

    5) The droplet formation issue may arise when objects are exposed outside to rain as suggested by the outside exposure instead of a fume tank method. It may be better not to expose the object direct to rain but allow it to rust under cover.

    6) A warmed fume tank will result is greater loss/usage of acid as more vapour is released and lost from the tank when opened. All of my fume tank bluing since 2014 has been done using the same ~100mL of HCl and HNO3 but since warming the tank a few weeks back I reckon the amount of fumes coming off have decreased.

    Still lots more experiments to do, and I will do these slowly over time, but now I want to get back to some MW.

  11. #56
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    Many thanks Bob for the typically thorough documentation of your processes and revelations.

    BT

  12. #57
    BobL is offline Member: Blue and white apron brigade
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    In this experiment I attempt to measure the thickness of cold fume metal bluing.

    Feeling confident I wouldn't stuff up I used a parallel as test piece and using a 0.001 mm mic, measured the thickness of the parallel in the vicinity of the same location. I measured it 10 times and the result was 2.9530 +/- 0.0017 mm

    Then I subjected it to a standard pass through the medium warm acid fume tank.

    Then I measured the thickness of the parallel plus sooty layer that covered the parallel.
    The thickness was difficult to measure because the soot immediately crumbled - this measurement is not that important anyway since most of the soot is removed. The most consistent reading I got was 2.980 mm (+/- ~0.005mm)

    Then I removed the soot as per usual and got a reading (again for 10 measurements) of 2.9542 +/- 0.0015 mm
    The difference is 0.0012 +/- 0.0022 ie so < 2.2 microns and as this is for two layers of bluing one layer of one pass is <1.1 microns thick.

    This is what it looks like with the soot is removed compared to the original - this is just one pass and no oil (which makes it look darker)
    PArallel.jpg

    Then I repeated the bluing process and got a difference from the original of 0.0017 +/- 0.0022 mm, again still < 1.1 microns thick.

    What I suspect happens is that when the workpiece is smooth the initial bluing pass generates most of the thickness of black oxide and the subsequent passes just fill in the gaps.

    I will repeat the bluing a few more times to see if I can get it to build up.

    [EDIT]
    I have done two more passes through the tank.
    To summarise, from above
    Pass 1: 2.9530 +/- 0.0017 mm
    Pass 2: 2.9542 +/- 0.0015 mm
    and the two extra passes measured at
    Pass 3: 2.9548 +/- 0.0017 mm
    Pass 4: 2.9545 +/- 0.0014 mm

    So even though it gets darker and darker with each pass it doesn't look like it's thickness is building significantly up after about the second pass so the overall thickness is still about a micron thick.

  13. #58
    BobL is offline Member: Blue and white apron brigade
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    Latest batch.
    Latestbatch.jpg

  14. #59
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    Looking impressively black Robert!

    I picked a kilo of Lectric washing soda for just under four dollars at Woolworths and a few two dollar hand spray bottles from Supercheap. I need to buy some cheap vinegar then I'll have a go on the freshly filed and too bright vice handlle.

    BT

  15. #60
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    Default Blueing in 1939

    Apropos of nothing attached I hope is an extract from 'Fortunes In Formulas For Home, Farm, and Workshop' printed around 1939
    I have a fragile paper book but it can be found as .PDF on the 'net for free download. Has some interesting cough mixture formulas as well.

    it is some 900 pages so would be a fair download.
    Attached Images Attached Images

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