Graphite Spray Technique to Improve Cast Iron Surface Finish? How to?

Discussion in 'Sand Casting' started by Melterskelter, Mar 21, 2020.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I have seen several recommendations by members of use of graphite spray, often using alcohol as a suspending fluid, applied to sand castings to improve cast iron surface finish. But, I have not seen any details like what brand or fineness of powder is used. What mix of graphite to alcohol? What alcohol—-denatured ethanol, 95%, 70% isopropyl, wood alcohol? What gunning technique is used? Are there issues with decreasing detail rendition if the alcohol wets the mold surface? How heavy is the application of graphite? One coat or several?

    I ask because I tried graphite a time or two and evidently did not do it right as the results were poor. I ask in a dedicated thread to make it easier for “the next guy” to search for and find information that may be forthcoming on the subject.

    Denis
     
  2. HT1

    HT1 Gold Banner Member

  3. In my limited experience it works well but won't counteract any underlying issues with roughness of the sand mould. The resulting castings machined well with no hard spots and no noticeable skin, I was brushing a thin layer on dry (to avoid venting problems) to resin bound sand and using ferrosilicon inoculated iron. I was told to use a thin layer to avoid blocking the sand pores and cause venting problems.

    This is my very first iron casting, the mould had a thin brushed on dry coat of graphite and the runner had no graphite and some sand was washed into the mould and affected the casting surface. I should have hit the resin sand with compressed air to knock the loose sand off and graphite coated the runner too. In this photo the only cleaning was to hose off the casting with water and you can see it's a bit damp in places.

    So the runner has no graphite and "burnt in" sand in places while the casting is relatively smooth and almost shiny silver. You can see the tips of the feet of the casting had no graphite either and is a bit rougher as I could not brush graphite in there with the paintbrush. For scale the casting is about 6" or 15cm long approx.

    first iron spindle close.jpg

    first iron spindle.jpg
     
    Last edited: Mar 22, 2020
  4. Melterskelter

    Melterskelter Gold Banner Member

    Looks like it worked very well for you. I can see where the bound sand would tolerate brushing. so, your coat of graphite turned the sand a dark grey, but not black as a way to describe the amount applied?

    Denis
     

  5. That's about right, I took a frame grab from a video to make sure:

    graphite.jpg
     
  6. Melterskelter

    Melterskelter Gold Banner Member

    It is interesting that so little graphite was effective. That photo provides a pretty good data point for figuring out how much to use.

    In my case I am not using bound sand most of the time. There is one exception. So, I have to figure out application methods for green sand that will not blur letters and other fine details.

    Thanks for the info.

    Denis
     
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  7. What about having graphite mixed with your facing sand?.
     
  8. Melterskelter

    Melterskelter Gold Banner Member

    I do mix coal with the facing sand 5 or 6 per cent. Works well. But I can not always be sure of a supply of coal. And it is good for me not to be a “one trick” pony. Mixing in graphite powder would be many times more expensive than mixing in coal as I would guess it would need to be in similar proportions to the coal.

    I am wondering if I will get a description or a “recipe” for surface application of graphite to green sand.

    Denis
     
  9. What about spraying the green sand with a relatively dilute graphite alcohol mix, like ten percent graphite to ninety percent alcohol maybe with some dye to get a visual indication of missed areas.

    Also sugar chars to carbon, the bulk sugar shipping terminals round here have seawater flood systems in case the pile of sugar catches fire.

    Edit: Charring sugar also foams up and outgasses a bit so it may not be ideal
     
    Last edited: Mar 21, 2020
  10. Melterskelter

    Melterskelter Gold Banner Member

    Sure, there are plenty of possible ways to do it. And I am willing to try ideas. But, I’d rather start with a proven method if possible. My greatest concern is that I will wash off letters and other fine details. That is why I am hoping someone chimes in along those lines.

    Denis
     
  11. HT1

    HT1 Gold Banner Member

    you need to add western Bentonite to the Alcohol and Grapite mixture. it's outlined in one of the references I posted above. and I thought we had this conversation with some mold wash formulas once before???


    V/r HT1
     
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  12. HT1

    HT1 Gold Banner Member

  13. Melterskelter

    Melterskelter Gold Banner Member

  14. Patrick-C

    Patrick-C Silver

    I like to use pure powderd graphite on my brass and aluminum molds and I get some nice surface finishes. But brass and aluminum are not cast iron.
    Though it still should work because graphite has a softening temperature of ~ 3600 deg F, wher cast iron melt at ~ 2500 deg F correct? So as for applying it I use a small lock lubricant dispenser like the one below.
    [​IMG]
    I fill it with powderd graphite and kind of puff it out (like you would baby powder). I then use Q-tips or similar to smooth it out. Then I blow the mold out close it up and pour (I use greensand).
    You can get powdered graphite for a reasonable price on ebay - https://www.ebay.com/itm/GRAPHITE-P...450542?hash=item421349e1ae:g:rX4AAOSwyP5aLWx- and this will last awile depending on the size of your molds of course.
    Patrick
     
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  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    MS, just a thought, but given the seemingly small amount of graphite required, wouldn't applying a coating to the pattern that would release with the green sand mold be worth a go? Release agent on pattern, graphite coating applied over prepped pattern, facing sand and ram as usual? Seems like it would have a fighting chance of producing similar detail to what you presently are able to achieve and be repeatable. Perhaps the same type of washes described in HT1s links sprayed/gunned onto the pattern would work with a silicone mold release applied to pattern. -Easy to test.

    Best,
    Kelly
     
  16. Melterskelter

    Melterskelter Gold Banner Member

    Interesting thought, Kelly.

    At present I do brush graphite onto the pattern as a release agent. But, by itself, it only wants to make the thinnest coating---barely even visible. Getting a coat to apply itself to the pattern and then preferentially adhere not to the pattern, but to the sand sounds challenging to me.

    At the present I also tried using an airbrush to mist on the slightest amount of Sodium Silicate on the letters to keep the sand crisply in place---it makes a difference. But, if I use too much the moisture allows the sand grains to move just a bit and that softens the outline of the letters. (I am using 1/4" letters so they are only a few grains wide at their tops) I would like to be able to atomize graphite and dust it on using a dry spray technique. I do not know of a procedure like that to copy however. As I am writing this it occurs to me that maybe using a technique similar to applying parting compound only substituting graphite for the powder might allow dusting on the graphite. Then, to get heavy build up out of the nooks and crannies maybe I could use a gentle air blast. I think I will try that soon.

    Denis
     
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    No hill for a climber.....

    Without a carrier and binder of some sort, you probably wont be able to get a thick or consistent enough coating. Then, you need to get it to dry and preferentially adhere. Most washes use some sort of clay as a binder like the bentonite in HT1s links but probably not that simple because you want to use water as the carrier. The carrier needs to have high vapor pressure and be compatible with your pattern coating.......alcohol (if your patterns are not finished with shellac) or maybe Naphtha and then ram while coating is still wet.

    Washes are great for bound sand molds and cores but never seen them applied to green sand.

    Best,
    Kelly
     
  18. Melterskelter

    Melterskelter Gold Banner Member

    I am currently mixing coal dust into the green sand. But I am trying to broaden my knowledge/options.
     
  19. I had earlier been thinking of using used photocopier toner, it's mostly carbon black and some styrene although some older 1990's canon toners were magnetic so maybe magnetite. By mixing it with a suitable solvent it'll form a hot melt carbon rich "Paint". In fact a matte black paint aerosol paint should have a high carbon content too. Imagine if it was nothing more complex than spray painting a light coat of black paint on your green sand mould o_O.


    That reminds me, I'd been told some iron foundries used to use an oil can to give a very small squirt of mineral oil into the pouring spout of assembled moulds shortly before pouring iron. The oil flashes off to soot as the iron gets poured. I haven't tried that one yet.
     
    Last edited: Mar 23, 2020
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