Sand casting session

Discussion in 'Sand Casting' started by Mark's castings, May 4, 2019.

  1. My foundry friend has a hand injury, so I offered to run his furnace and pour some 356 aluminium for him. He runs a propane gas fired furnace with a 25 sized silicon carbide crucible and uses a one man pouring shank. The crucible takes a full ingot to fill, the stack beside the furnace are ingots sawn into three pieces to give some indication of size.

    I poured four crucibles over 5 hours, there was a lot of initial setup of the sand moulds and then waiting for the aluminium to cool before setting up the next batch for pouring. The furnace once it's hot will melt a full A25 crucible in 12 minutes, I noticed that even with it hot but not running, it could melt 1/3rd of an ingot with residual heat alone. By the second pot, I could feel my upper back muscles starting to complain. Anyway it was a great way to help out a friend and get some aluminium casting experience, I had a 100% success rate with no bad castings even on the thin sections. My chrome leather welding apron had a 30cm/1' extension fitted on the bottom so that the leather reached the top of my boots and I wore welder's spats over my leather boots. Judging by the burn marks on the lower apron from aluminium splatter, the extension was well worth it and even protected the leather welder's spats from burns. The long apron didn't get in the way at all, you have to crouch and hunch over at the same time to be able to trip on it with your boots.

    Furnace session 3.jpg

    Furnace session 4.jpg

    Furnace session 5.jpg


    Furnace session 7.jpg


    Furnace session 10.jpg
     
    Last edited: May 8, 2019
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  2. oldironfarmer

    oldironfarmer Silver Banner Member

    Very cool!

    Post title said Sand Casting, I was expecting green sand. Nice looking castings.

    Why all the aluminum splatter?
     
  3. PatJ

    PatJ Silver Banner Member

    Its hard to go wrong with bound sand.
    Assuming your gating, risers and pour temperture are right, you can get high quality castings first time, every time, very predictably.

    Its fantastic stuff, and works well with iron too.

    Nice castings !

    Edit:
    I need to make some of those casting stands.

    .
     
  4. The first time round they were unfamiliar castings and the pouring cups and sprue are quite small, so I poured as fast as I could. Once I had a feel for how much each mould took, I spilled almost nothing.


    Resin sand makes casting so easy, even the design of gating and runners is simplified as the sand can't break loose (maybe molten brass on a sharp corner would). I just open the mould halves, blow them out with compressed air and assemble and clamp reasonably firmly with the F clamps, then you sit a loose pouring cup on top. Once the metal is poured and the aluminium has shrunk a bit and mostly solidified, the pouring cups get nudged and broken off to make de-gating easy. All of the moulds are placed at a height to eliminate bending over and I found I could take the weight of the crucible on one hip when tired (If you are really fatigued, you put the crucible back on top of the furnace).

    The only problem is the relatively short life of some products of say 6 months, I'm going halves with a guy to buy about 4 gallons of the 15 minute cure resin this winter to help extend the life (dry cool climate).
     
    Last edited: May 4, 2019
  5. PatJ

    PatJ Silver Banner Member

    I was told by a supplier to put the resin in a refrigerator, and he said it will last a year if kept cool.
    I am not really sure if I want to run a refrigerator for a year, but I may try it.

    I am transitioning to sodium silicate, and so far I have not noticed it having a shelf life, and none of the fumes either.

    .
     
    Last edited: May 4, 2019
  6. DavidF

    DavidF Administrator Staff Member Banner Member

    It does have a shelf life..Think its 7 years :rolleyes::rolleyes:
     
  7. This is what I'm planning to get: Fennotec 810, if anyone has used it before I'd love to hear about it. 6 months shelf life at 30 deg C/86 deg F for the resin and 24 months for the hardener. I guess the deal is to make as many sand moulds as possible then store them for later use.

    Edit: Just to get some numbers on Pat's idea of cooling the resin: I have a 150W fridge, electricity in my state is AUD$0.25 per KWHr. If I assume a 50% duty cycle that gives 75 Watt hours, so for a year we have 8760 hours x 75 Watt Hours = 657 KWHrs. 657 x 25 cents = $164.25 to run the fridge for a year. The resin is $157 for a 20 Kilo pail so for me at least it's cheaper not to cool it. I should make a 4" thick styrofoam insulated box and see what the average temperature is, it may be possible to average under 20 deg C and get a few extra months life.
     

    Attached Files:

    Last edited: May 4, 2019
  8. PatJ

    PatJ Silver Banner Member

    The molds also have a shelf life, and I think for the resin-bound sand, the rep said 3 months, but check me on that, since it could vary by product, etc.

    I have not used Fennotec 810.
    The resin I use requires a serious respirator, and thus the reason I want to change to sodium silicate with a catalyst to harden it.

    I made a core using sodium silicate and a 5 second gas with CO2, and it has been on the shelf in the shop for well over a year, and is showing no signs of deterioration.
    The cores I made using ss that I overgassed did not last more than an hour before they began to break down.

    You should try sodium silicate molds with catalyst on a small scale and see if that works, because no it has no fumes, the shelf life appears to be much longer, and I think ss is cheaper than resin binder.
    Sodium silicate bound sand is not as strong as resin bound sand, but I think ss sand is still plenty hard for most if not all uses.

    Edit:
    The cut sheet on Fennotec sounds good, especially the percentage of reusable sand, but again, if you can do the same with ss, then the price could be substantially lower if the shelf life is extended to a year or more.

    Don't forget that the sand used with resin binder has to be very dry, ie: a commercial sand that is baked and very dry. I suppose a non-commercial sand could be used if it were baked.

    I am considering using facing sand made from new sand and binder near the pattern, and recycled bound sand mixed with new binder for the balance of the flask material.
    I have heard that binders may not work with recycled sand, but it is worth a try, and I am not sure if "may not work" means that the surface finish is not good with recycled sand, or that the binder does not adhere the sand.
    I am going to do some testing.

    And with bound sand, if you can make an indentation in it with your finger, then you have not reached "set" time.
    And if you leave your patterns in the mold after "strip" time, you may not get the pattern out of the sand, since it tends to permanently glue itself into the mold.

    Edit02:
    Note that the Fennotec sheet mentions "bench life", but this is not to be confused with shelf life.
    "Bench life" = "Set time", ie: this is the period of time during which you can mix and mold the sand. At the end of the set time, you should not disturb the sand, else you will break the bond and crack the mold.
    And I found it best to keep the molds on a flat surface within the flask until strip time is reached, and perhaps a little after that too, since the sand can warp slightly if you move the mold before it fully cures.

    I generally like a 10 minute set time, and whatever strip times corresponds to that, with the understanding that mixing may take 2-4 minutes.

    And I use a commercial Hobart mixer, which works well with bound sand.
    A muller could also be used, but you would have to keep the buildup cleaned out of the muller, just as you do with a mixer, but it is easier to clean a mixer than a muller.

    .
     
    Last edited: May 4, 2019
  9. Sodium silicate is certainly an option: I have a few small samples of the microwave cured sodium silicate lying around the workshop and they have stayed hard and dry all throughout the wet season this year. Microwaving wood patterns is too hard on them though. We are drying the sand with a gas burner aimed at a cheap cement mixer with the sand in it.....I completely forgot about that little detail. There's a landscaping company selling fine graded silica sand from a nearby mine that produces it for overseas foundries and glass factories after washing and sizing the particles......just remains to see what the cost is. The only issue I've seen with recycled sand was the excess smoke and the smell of double and triple burnt resin, it's just less effort to buy fresh sand.
     
  10. oldironfarmer

    oldironfarmer Silver Banner Member

    Can you pull the pattern like green sand then bake the empty mold?
     
  11. I actually tried something like this today and it's got the appearance and consistency of brown sugar: very fragile. There might be some additive like starch to boost the uncured strength and allow it to be pulled.
     
  12. oldironfarmer

    oldironfarmer Silver Banner Member

    I've been able to pull simple patterns then cook the sand.
     
  13. Chazza

    Chazza Copper

    Just an observation on safety.

    I have noticed that many people on this forum pour metal on a concrete floor, or even outside on damp ground. Spilling molten metal on either, is inviting a steam explosion with the resulting spray of molten metal being too nasty to contemplate.

    The best practice is to set up whatever type of moulding you are using, over a dry-sand floor. Any spillage will not explode and it doesn't splatter much either, removing another hazard. The sand can be placed on top of the concrete or, as in my case, the floor is sand over gravel. Even a dropped crucible, or one knocked over, will not present a disastrous situation if the work-area has been carefully prepared.

    I set a piece of 50 x 50mm angle in the sand with loose sheetmetal ends on it, held in place with sand and pour any excess metal into it, which makes long thin easily breakable scrap.

    Be safe people! Who wants to end up in a burns-ward?

    Cheers Charlie
     
  14. PatJ

    PatJ Silver Banner Member

    There has been much discussion about pouring metal above a concrete floor.
    Sometimes it depends on the type of concrete.
    I can spill on mine with impunity, but it is rather low strength washed gravel type, and it does not explode.

    I think there are a number of veteran foundry folks here who routinely pour on concrete, and spill on it.
    Its not really a big deal.

    I do believe in safety first though, and I observe a lot of precautions.
    Pouring above concrete is something that I do routinely though, and I never use sand anywhere, and don't consider it necessary.

    I did get a nasty burn when pouring into an ingot mold that had been preheated, but not preheated enough, and it popped molten iron down my gloves. Ouch !

    .
     
  15. The smart thing to do would be to have a drip tray with tall sides to contain splatter, that said, this particular poor quality concrete slab seems to handle molten bronze spills without any spalling problems.
     
  16. HT1

    HT1 Silver Banner Member

    I suspect this will get to be like people wanting to put guards on Mullers because they cannot keep their hands out of them :-(

    a Proper Foundry Floor is Normally Fire brick with the 2 1/4 side facing up put down like pavers, but with little sand betwixt , sometimes that is covered with a 3/8 or 1/2 steel plate That is How my first shop was
    the Next way which is pure evil is deck grating above sand , this lets metal fall through and cool safely ... Think what a BITKH this is to clean up

    Now Both of these options are out of the hobbiests range

    The Navy s wizbang new foundry school 1990 had an all concrete pouring deck, and alot of spalling from spilt metal.

    wear appropriate PPE and I little flying molten metal and Concrete is no big deal.

    You Nuts doing Cast Fe, should really consider some Dry sand .

    I pour 9 molds at a time, so My sand tray would be about 2 X 15 Feet, that is alot of not portable sand and tray and, well just generally a bother I dont have the time for . I wear two layers of FR clothing one leather, and leather leggings , I have been hit with alot of Molten Metal and as a Hobbiest have only had minor burns (from that ) Ive had some pretty good ones from other metal working


    V/r HT1

    P.S. if you spill alot of metal stop the pour go back to the furnace, keep the metal at temp while you shovel up the Hot metal and Carry on, In a real foundry there is normally a member of the pouring team standing by with a shovel to throw sand on molten metal or shovel it up to stop the popping so the team can keep right on going
     
  17. oldironfarmer

    oldironfarmer Silver Banner Member

    A muller needs guards?:eek:
     
  18. Tobho Mott

    Tobho Mott Silver Banner Member

    Not if you follow the rules:


    :D

    Jeff
     
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  19. Rocketman

    Rocketman Silver

    The foundry I used to work in used PEP-Set binder. The issue that one seems to run into with recycled no-bake that is not thermally reclaimed is the presence of catalyst / hardener in the reclaimed sand, it messes with the hardening times so you get wildly fluctuating set times.

    The other issue is excessive binder build up that causes some gas issues.

    Thermal reclaimers burn out the old binders but I wouldn't want to pay the energy bill on even a hobby size version, hah.

    What are you guys doing with your no-bake molds once broken out?
     
  20. Pep-set would be the ideal resin to buy but I can't get small amounts of it anymore.

    The used sand goes into the skip bin in the last photo and gets taken to an approved landfill and dumped: I once read the data sheet for the product being used and the suggested disposal was to use it as clean dirt to cap off landfills. The resin is formulated to break down over time into CO2 and water. I think there's some law now that glues like urethane have to be formulated to degrade over time, that's why your nice shoes that you bought three pairs of, falls apart after a year or two in storage.

    Here's a photo of the apron extension: it's long enough that it covers the welder's spats and touches the toes of the boots, you'll notice there's almost no burns on the original, they're all down low with the biggest one where one my boots would be. After I poured the first few moulds the spills were almost eliminated. I've been told by a guy who started his foundry in 1947 that aluminium "Sticks like jam to skin"

    apron extension.jpg
     

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