Requesting Advice on Drying/Warming Green Sand Molds Prior to Pouring Cast Iron

Discussion in 'Sand Casting' started by Melterskelter, Aug 12, 2018.

  1. Melterskelter

    Melterskelter Gold Banner Member

    I have read mention of drying mold surfaces prior to closing green sand molds but have not seen much written about it or videos showing the practice. I am interested in trying it. Can anyone provide a few pointers? In some ways the idea seems counter-intuitive as I would think there might be problems with loose sand and fragility of the mold. But, then, I read it is considered a good practice. So? I am interested in pros and cons and cautions from anyone with knowledge. This seems to be one area not mentioned in the Naval Foundry Manual.

    Any help appreciated.

    Denis
     
  2. HT1 has mentioned brushing it with a torch, I think. He'll be along by and by. I tried it and did just as you suggest, it powdered the sand. I didn't pursue it.
     
  3. HT1

    HT1 Gold Banner Member

    Navy foundry Manuel page 64 skin-dried molds

    V/r HT1

    P.S. Dont doubt the Navy we have the answers!
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    Ahhh, there was reference in the Manual, indeed. Shoulda known it;-) I excerpted it below plus a reference in the Navy Manual on special washes that I think the first quote is alluding to.

    From pg 64:
    "Skin-dried molds are green-sand molds which have been dried only on the mold surface by the use of a torch or some other source of heat. Skin-dried molds are used where a mold surface low in moisture content is necessary. The mold surface is usually sprayed with additional special binding materials and then dried by the use of a torch. This type of mold combines the firm sand face obtained from a dry-sand mold with the collapsibility of a green-sand mold in the backing sand. In general the sand used for skin-dried molds has a moisture content higher than for a green-sand mold and dry sand molds require a still higher original moisture content."

    And the bit about washes:
    "Core and mold washes may be needed in some cases to prevent erosion of the sand and metal penetration into the sand. The following mix contains the same bonding material as the molding sands, with silica flour replacing the sand, and with sodium benzoate added to prevent the mixture from becoming sour.

    Weight percent
    Silica flour 64.0
    Bentonite 1.5
    Dextrine 3.0
    Sodium benzoate 0.2
    Water 31.3
    The dry material should be mixed thoroughly in a closed container. The water is then added, and the mixture stirred thoroughly. The mixture is sprayed onto the green core like paint and then baked, or it may be brushed on the dried core or mold. It must be allowed to dry thoroughly in air or be baked in an oven, and should be used only when absolutely necessary. (bolding added by me)

    In most cases, the green or air-dried sand mixtures will produce excellent casting surfaces without use of the wash.
    In brass castings, where erosion and penetration are problems, a core wash made from a silica base is satisfactory. A plumbago wash is useful for bronze castings. A core wash for use with high-lead alloys and phosphor bronzes, may be made from a paste of plumbago and molasses water. Such a treatment should be followed by a thin coating of the regular core wash."

    HT1, have you any personal experience with dry sand molds and washes. Love em, hate em?

    How do you (or anyone else) think Stanley molded their beautiful Bedrock planes whose bodies are only about 1/8" thick in the soles and sides and yet are as buttery soft to machine as can be and are beautifully smooth on the cast surfaces? Do you think they used sand molds? Washes too?

    Bedrock605C.jpg
     
    Last edited: Aug 12, 2018
  5. PatJ

    PatJ Silver

    For a long time I made the (false) assumption that since old machines and equipment were old (say 1875-1900), then the casting and foundry techniques must be primitive, but the more I see of the old techniques, the more I realize just how well they had casting techniques mastered.
    And they generally used greensand for the molds, which is more impressive.

    There is a video out there of the process of making aircraft cylinders I think using green sand, and that was with aluminum (during the war years).

    Here is a video of cast iron cook plates:


    I have heard that cast iron flows very well, although my experience is that with pieces that are thin, they tend to be excessively hard without ferrosilicon additive.

    And toys use to be made from iron too, with some very small details and thin sections.
    Do an internet search for "cast iron toys". Antique cast iron toys sell for an impressive amount.
     
  6. HT1

    HT1 Gold Banner Member

    I have never used Dry sand Molds... Never really had an oven big enough to heat any real molds our shop oven has about a cubic yard. we always skin dried mold surfaces. we used a torch with a large rosebud, a propane weed burner would be better, but the Navy does not allow Propane on ships . we also used burnt off alcohol base mold washes. they where sprayed on , then lit, as soon at they went out you closed the mold. this trapped the heat in the mold cavity pushing moisture into the sand away from the casting. skin drying with a torch does the same thing, you want to get the surface of the sand up to like 180 VERY gently , you will see steam rising if your sand is wet... BTW if you see that you are screwed anyway. unless your venting is perfect, I have discussed venting at length elsewhere... most of you do it poorly, if your vents fill with metal they did not work

    V/r HT1
     
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  7. Melterskelter

    Melterskelter Gold Banner Member

    Concerning proper venting, I do it two ways on each mold and one of the ways must be wrong. The wrong way (since it always fills with metal) consists of skewering a hole through the cope from various high points in the molds and extending to the exterior cope surface. The second (also wrong?) set of vents are made from the exterior surface of both the cope and drag extending 2/3 of the way to the pattern.

    OK, my teeth are clenched and I'm gripping the chair arms waiting to get blasted...

    Denis

    erning
     
  8. HT1

    HT1 Gold Banner Member

    you almost have it right, Vents do not need to open into the mold cavity, but rather create a path of least resistance for the gas , the easiest way to do this is to use a very small brass rod, sharpen it with a long taper. now with the pattern in the mold, right after you ram and strike off the mold, push this rod gently down til it kisses the pattern. done well in good sand you wont even be able to see the vents from the mold cavity, they will not fill with metal, but will provide an easily accessible path for gas to escape... even better if you are really shit hot and your pattern is perhaps flat you can measure the depth you need to push the rod in, stop 1/4 inch short of the pattern, that is plenty good enough... ...

    Now on a related subject, you all know that if you use green sand, your bottom boards should have holes drilled in them, ESPECIALLY if you use metal bottom boards and BIG flasks ... water as steam will come out the drag, and if it has no place to go you can have problems, it's rare, but safe not sorry

    V/r HT1
     
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  9. Melterskelter

    Melterskelter Gold Banner Member

    I can attest to the venting through my wood bottom boards. Every hole is quite charred by the hot gases and flaming coal gas that vents out of them. The mold side of the board is slightly heat darkened, but the vent holes are charred and externally around each hole is charred.

    Denis
     
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  10. Melterskelter

    Melterskelter Gold Banner Member

    And to go back a few posts, if the Fleet Admiral (I know Nimitz is long gone) wanted a cast iron plane body like the one I pictured but with his name and and five stars on it, how would you go about casting it? To my mind, that is one fine piece of work. And for you a pay-grade promotion hangs in the balance;-)

    People talk about adding ferrosilicon to make cast iron soft, but how much do you add? I have seen quite a number of videos recommending the addition, but never a quantitative recommendation. Certainly, maintaining softness would be challenging in such a thin-section casting and is an issue I am presently dealing with in a considerably thicker sectioned casting.

    Denis
     
  11. HT1

    HT1 Gold Banner Member

    OK Mod needs to pull this out

    1) use alot of sand... in other words a really big mold to hold the heat longer
    2) there is also an important percentage of silicon 1.25 to 2.2 percent about .80 percent Manganese is also PRESENT... this is cast iron ingots
    3) Many cast irons are innoculated with ferrosilicon, ferromanganese, ferronickel or graphite. innoculation is a process in which an alloy addition is made to molten cast iron the porpose is to alter or change the size shape and amount of graphite particles in the iron using this process you can control the mechanical and physical properties to a degree not possible by simply melting and pouring
    4) in the Navy we actually bought a commercial inoculation that made Nodular iron https://en.wikipedia.org/wiki/Ductile_ironmelt cast Fe take it up to pouring temp plunge the measured amount.. take a temp Mag made temp rise, then pour

    Hope that helps

    V/r HT1
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    Thanks, HT1. I think I am asking the impossible question if one does not own or have access to a spectrometer so that you know the starting point of the iron you want to inoculate. If one does not know that bit of information, then adding ferrosilicon is just a wild guess, evidently. Same is true for carbon as both are burned off during melting to some degree. So remelted iron is likely lower in both than it was the first time melted. Much of the time small differences may not matter much, I suppose. But since I am running into harder iron than I want, I am trying to sort this. I was just looking for some reasonable rule of thumb that folks might use. Looks like I will just have to add a guessed measured amount and see what happens. That will be time and energy consuming.

    Here is some info I found on silicon that suggests that too much silicon can be as bad as too little:
    Metals 2015, 5, 150-161; doi:10.3390/met5010150
    "Silicon is like carbon in many respects. It has been long recognized as an important element, and, therefore, controls are typically adequate. While silicon control in a cupola can be difficult, in induction melting it is relatively easy.

    Also like carbon, the higher the silicon the more likely larger graphite will occur as well as more ferrite in the matrix. This, of course, will generally be a weaker iron but with less likelihood of having carbides to degrade machinability.

    When silicon becomes very high it hardens the ferrite and can increase the hardness of the iron."

    How high is "very high" is not stated (of course). So, just how much leeway there might be I don't know.

    The idea of using a large mold makes perfect sense and seems likely helpful to maintain softness.

    First, I will try adding more ferrosilicon.

    HT1, Thanks for your helpful post.

    Denis
     
  13. PatJ

    PatJ Silver

    From the cast iron steam engine parts I have made, a rough rule (just my experience) is 1" thick does not require ferrosilicon; it will machine well.
    Parts less than 1" thick, and especially as you get down to 1/4" and thinner do need ferrosilicon in order to be machinable.
    I found that parts 1/4" and thinner in cast iron are basically the hardness of tool steel, and according to the Navy Foundry Manual, for all practical purposes are tool steel (I call it "No-cutium", ie: it immediately ruins the teeth on a hack saw or Portaband); you can only grind it.

    I have the amount recorded somewhere.
    I will dig that out.
    It comes from scavenger, who cast a bunch of mufflers for old hit-and-miss engines.
    As I recall, he said too much is just as bad as too little.
    And it also reinforces what I discovered, that thin parts (mufflers tend to be about 1/4" thick) need ferrosilicon in order to be machinable.

    Be back in a minute.

    Edit:
    I think I recall ironsides saying he does not use ferrosilicon, but check me on that; I am not sure if that is a true statement or not.

    Porositymaster does use ferrosilicon on his cast iron parts.

    The local metal museum uses ferrosilicon on their cast iron art pieces, and the iron melt gets noticeably more fluid after the ferrosilicon has been stirred in, which I have also observed with my iron melts when I used ferrosilicon.
     
  14. While Pat's looking, I have wondered about Stanley (and other) planes. I assumed they are cast rather thick then the excess is machined down to size. Cast iron was used because it was cheap and durable. But I believe a lot of things would have been cast in brass or bronze except for the cost. A brass plane is a thing of beauty.

    I have only melted iron accidentally and have never cast any. But it is coming.
     
  15. PatJ

    PatJ Silver

    This is some info I found concerning a Morgan furnace used to melt iron:

    MORGAN FURNACE DATA: IRON

    A Morgan furnace has a range of iron melt capacities of 44/110/176/297 pounds (20/50/80/135 kg),
    with first melt times of 50/ 60/ 80/ 90 minutes,
    and repeat melt times of 45/55/65/75 minutes,
    and oil usage for the repeat melt of 3.7/5.5/6.6/11 gallons (14, 21, 25, 42 liters)
    (The fuel used for the first melt will be slightly higher than the repeat fuel usage).

    The Morgan will melt iron in the four ranges above using 4.9/6.0/6.09/8.8 gal/hr.
    I am not sure why the gallons per hour rate is about the same for the 110 and 176 pound melts, but the curve does not seem to be linear.

    The Morgan furnace would use 0.084/0.05/0.0346/0.037 gallons of oil per pound of iron.
     
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  16. PatJ

    PatJ Silver

    One person online said that when silicon (not sure if he meant "ferrosilicon" or just the general silicon content in the iron) gets above 3.5%, the iron is low in carbon and becomes brittle.

    Another thing I recall about adding ferrosilicon to an iron melt is that it needs to be the last thing that you do.
    It is generally added to the center of the melt (per one iron guy), and stirred into the melt with a graphite or steel rod.
    The iron should be poured as soon as practical after adding the ferrosilicon.
    Don't wait after adding the ferrosilicon, since its effects will only last perhaps 5 minutes.

    Some people use limestone as a flux with iron.
    I purchased some powdered limestone, but have not tried it.
    If I do try it, I will add it to the crucible before I begin the melt, but I an not sure if that is the correct way to do that.

    Some people also use borax to break up the slag, but borax will degrade the crucible, and the more borax you add, the faster your crucible will degrade.
    Porositymaster does not use borax; he does sort of a continuous skim once the melt gets going, and skims a little bit about every two or three minutes.
     
  17. I bet it's a typo and the 176# melt uses 8.6 gallons (7.9 gph) and 0.049 gallons per pound. Gallons per pound is the fuel required to heat the furnace plus fuel to heat and melt the iron. Fuel to heat and melt the iron does not change. Fuel to heat the furnace does not change, but that fuel per pound of iron results in less fuel to heat the furnace per pound of iron for a bigger charge. Then there's the fuel to keep the furnace hot but it is really not much if it's insulated.
     
  18. PatJ

    PatJ Silver

    FERROSILICON
    Add approximately 0.75 oz per pound of iron (check me on this value, but this is what I have been using).
     
  19. Melterskelter

    Melterskelter Gold Banner Member

    Wow! That seems like a lot of ferrosilicon. In other words, if I am reading this correctly, you add 1/2 pound to 10 pounds of iron? If the target silicon percentage is in the low single digits and, depending on the amount of silicon in your particular version (I have read the content can vary over a wide range)

    "Ferrosilicon - Frequently Asked Questions - DMS Powders
    What is Ferrosilicon?
    Basically, Ferrosilicon (FeSi) is a ferroalloy of silicon and iron. The ratio in which the silicon and iron substances are combined differs, with the weight percentage of silicon ranging between 15% and 90%. "

    you could end up with 1% silicon to 6% silicon in your iron assuming a 90% yield.

    I wonder why the ferrosilicon effect is so brief. That also seems surprising, though I was instructed to indeed add it at the end of my melt. I did find an article that indicated fs and carbon are burned out of a melt in a diesel furnace over time. http://lejpt.academicdirect.org/A26/059_064.pdf

    It could well be, as suggested by oldironfarmer, that the plane bodies in question were cast much thicker and then the excess milled away. (That thought went through my mind too.) Even so, the body I examined tests at close to zero on the Rockwell C scale. That is similar to the Durabar segment I tested. I have a feeling those guys back in the day had a trick or two up their sleeves. Man, I wish I knew how they did that.

    Thanks for the clues provided HT1, PatJ and oldironfarmer. I'll be trying out some fs in the next day or two. Any more ideas---I am all ears.

    Denis
     
  20. PatJ

    PatJ Silver

    For a 10 lb iron melt, 7.5 oz ferrosilicon.
    I bought a 60 lb bucket of it, not that I have done that much iron melting, but it is cheaper in quantity.

    Edit:

    I dredged out a bunch of old data that I have collected over the years from various places concerning iron melts, and I posted it on my keg furnace build for reference.
    You may or may not have all this info, but this is what I have for iron.

    http://forums.thehomefoundry.org/index.php?threads/a-thin-hotface-beer-keg-furnace.26/page-5
     
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