Large casting fail

Discussion in 'Lost PLA casting' started by Frank Clark, Mar 7, 2018.

  1. Frank Clark

    Frank Clark Copper

    This is an intercooled supercharger intake for a Lotus Evora. My son’s project, but I casted it from his pla print.

    While I made sure the plaster/sand mold would fit in my kiln, I neglected to consider that I had no way to lift it in/out. I could maybe have managed to get it in, I was not going to be able to get it out w/o building something to lift it. In the end, I decided to burn it out, outside if the kiln. While I am sure that could work, I obviously failed to burn it out long enough.

    This was my first pour this large. I’ve ever had smoke during the pour so knew right away I had a problem and what it was.

    Learned enough that I think I can get it right on the next attempt. Need better sprues to runners, larger vents, longer burnout.

    Pics with plaster/sand show black from all the smoke. I only cleaned off a bit to verify it failed. Will let my son take the power washer to it for recycle.

    This casting is about 18” wide. Printed in 2 parts (runners and plenum) then hot glued together. B7403A1E-DBB5-4173-9F2F-84B73FE71DE8.jpeg 3F37D85A-590E-4BB3-B7C4-B0999E708D42.jpeg



  2. Frank Clark

    Frank Clark Copper

    Can someone suggest a wax for making filets where we glue PLA parts together?
  3. Jason

    Jason Gold

    Microcrystalline or jewelers sticky wax. The latter is easier to work with.
  4. garyhlucas

    garyhlucas Silver

    Was wondering about the issue of PLA expansion when burning out. Could a PLA part maybe be coated with wax so that when you burn out the wax melts first and leaves the PLA loose in the plaster? Haven't tried casting yet but got the grandson a 3D printer and he is anxious to try it.
  5. Frank Clark

    Frank Clark Copper

    I've had no issue with PLA expanding. I have had molds crack when the sand is too fine (325 mesh is useless, 200 works, but will crack a fair amount, 85 and larger does not seem crack prone). I usually use chicken wire around the perimeter so cracks are not a big issue.

    I do heat the mold a long time at about 220f, then quite a while at 350 or so. I expect on my 'normal' castings (fist sized or so), that a good bit of PLA flows out at in the 350f hold.

    I am going to try the sticky wax for 'glueing' PLA parts together where hot-glue is problematic. And for forming fillets on the glued areas.
  6. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Frank, just looking this over for the first time. We can see the outcome but not the starting point as far as the pattern, gating and venting. Can you post a picture of those features?

    You mentioned placement in your kiln but the picture shows what looks like some temporary wool and fire mat. Can you elaborate on that?

    On the fillet wax, I use the freeman preformed wax fillet, #1 through #4 depend on the radius, and their fillet tools to apply it. I actually use this wax in lost foam and it burns out very clean. I don't think hot melt glue is the source of your problem as I have found that to also burn out very cleanly in lost foam.....and that is just the hot metal doing that, not a burn out cycle.

    Ball and Scraper.jpg

  7. Frank Clark

    Frank Clark Copper

    It was marginally too heavy for me to get into the Kiln cold, there was no way (without building some kind of lift), for me to safely get it out of the kiln hot. So I wrapped it with heaters/insulation and fired it outside the kiln. I stuck a thermocouple between a heater and the plaster. Next time I will put insulation and a heater under it as well, and burn it out for an extended period of time.

    I did not take any pictures of the PLA/Sprue/Vents. But here are the models to give you an idea of the parts. I simply hot-glued these together - you can see the extra hot-glue where the runners meet the intercooler section.

    We are going to clean that casting up, machine the head side flat and make sure the shrinkage allowance was correct.

    The top section was printed on the end, the runners where printed flat. Both parts were printed with no supports.


  8. Melterskelter

    Melterskelter Gold Banner Member

    Kelly, where do you buy the wax fillets? Not much other than Freeman coming up on various searches.

  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    There may be others or possibly available from other pattern supply companies but I bought them from Freeman a long time ago. So long, I can't even remember when or the cost but I bought the boxes of 24" strips. You can see how many feet of each constitutes a box at that link above but likely a life time supply at least in smaller sizes. Store them in a cool place.

    The Freeman site requires you request a quote. That's a drag but they do respond within a day and they will open a credit card account for small users. I occasionally buy other pattern supplies from them as well.

  10. Melterskelter

    Melterskelter Gold Banner Member

    Thanks, Kelly. Yes, I usually interpret “Request a Quote” as “if you are a small-timer, don’t bother is, also we will be slow to respond, prices will be high and shipping outrageous.” Perhaps that is unfair. I will see what Freeman says.

    The quantities available are, indeed, several lifetime supplies. Maybe someone would be interested in splitting a box or boxes. Maybe I shouldd start a new thread on this.

    BTW, I make my own filet tools by simply silver soldering ball bearings of various sizes on 1/8” steel rod. Quick and works well.
  11. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I would tend to agree but haven't found Freeman to be that way. On price, I think they are fair. I don't think they are inexpensive but professional materials rarely are. On shipping, if it's heavy or hazmat, it can get pricey, but in those cases that's probably not a Freeman issue.

  12. Melterskelter

    Melterskelter Gold Banner Member

    Here is the quote from Freeman. This would constitute several lifetime supplies for me. I would be happy to split with two other people. The 24” pieces should fit diagonally in a large Game FRB for 18.90 anywhere in the US. Anyone interested? Cost would be 42 + 18.9 for 3 1/3voxes of filet. See Freeman’s site for descriptions.

    FOB Unit Price Sub Total
    1 085216
    FREEMAN FILLET WAX #4 2LB BOX A $31.32 $31.32
    1 085212
    FREEMAN FILLET WAX #3 2LB BOX H $34.55 $34.55
    1 085220
    FREEMAN FILLET WAX #5 2LB BOX A $31.32 $31.32
    Shipping Estimate » $28.00
    Total »

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