Lost Foam Dip Coating Rig – The Big Dipper

Discussion in 'Lost foam casting' started by Al2O3, Jun 9, 2019.

  1. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Brushing coating on bigger pieces gets to be a bit time consuming. I had done some work with dip coating foam and sampled some commercial coating. A couple years ago when I started to build my foundry equipment, I came across a fellow with a bunch of these airtight 30-gallon clamp-lid drums that were very economical, so I bought a handful of them. They looked to be about prefect to store slurry and dip coating parts. So, I decided to build a dedicated dip coating rig.

    1 Barrel and Hoop.JPG

    Since the drum will have about 300lbs of slurry, I built a stout dolly to make it mobile. I have a bunch scrap 2 ½” x 1” x ¼” channel with those formed ends. Good clean metal and sturdy.

    2 Dipper Dolley.jpg

    I had a portion of the barrel in the scrap pile left over from my furnace build several years ago. I used it to make a barrel clamp to attach the adjustable arms and hardware to hang foam patterns after dipping.

    3 Clamp.jpg

    Tacked together the various clamps and mounting hardware.

    4 Bits and Pieces.JPG
    5 Hangers.JPG

    Arms, clamps, hangers.

    6 Hanging Parts.JPG

    Capped and folded up for storage

    7 Storage.JPG

    The barrel is unmodified so I could conceivably swap out barrels to change dipping materials in the future….shell slurry for example. At the moment I don’t see that happening, but these barrels are absolutely airtight. In fact, you typically need to vent the lid in order to remove it.

    I call it The Big Dipper.

  2. Jason

    Jason Gold Banner Member

    What is this SLURRY you speak of? Did you finally decide to use suspendaslurry instead of drywall mud?
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Either my own home brew or possibly the purpose formulated commercial lost foam coating I've been experimenting with if I can get an acceptable price and minimum buy.

    For lost foam casting?.....No that would be absolutely stupid. My comment was merely that the barrels could be swapped and hardware could be applied to different coatings.

  4. PatJ

    PatJ Silver Banner Member

    So clean and professionally done.
    You are the fab king for sure.
    My stuff has that broken crayon look, but is functional.
    Your stuff is functional, and something that could be mass-produced and sold for good money.
    You should be in the fab business (that is a joke, I know you are already in the fab business, and it shows in your work). :)
    Petee716 likes this.
  5. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Pat. Simple project and probably could have stopped at a barrel on the dolly but....well, you know. Now to fill it up and put it into service.

  6. garyhlucas

    garyhlucas Silver

    Nicely done! One comment, I never use Round tubing to make frame clamps like that. Too much work. Use a square tube with a setscrew on a corner that drives the round tube into the of the square and nothing wobbles. If you want no marks on the round tube use coupling nut welded on and put a brass slug in it for the set screw to press against.
  7. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Not sure I understand all of what you are describing there, and to each his own, but if you had a business that manufactures mandrel bent tubing like I do, and you had an unlimited supply of free drop/scrap of round tube of all sizes and material, you'd probably have a different opinion. It took me about 5 minutes to run that tube through the wire groves on my slip roll in my home shop and make those hoops. They added a convenient bit of mass to attach the arm upright clamps and weld the end plates for the pinch bolts. That chunk of barrel was only ~24ga so was a bit thin to weld but since it had the ridge rolled into it, it fit nicely over the same feature on the dip barrel.....and I had it, so I used it. -Works for me.



    I would like to know more about what your company offers.

  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I finished up the rig with a coat of primer on the piece parts. I have been experimenting with dip coatings……..and decided to fill it up with commercial refractory coating.

    8 Slurry Charged.JPG

    The slurry seems to stay in suspension well but I invested in a mixing paddle to re-suspended the slurry.

    9 Mixer.JPG

    Doing so only takes a few minutes. I spin it in a bucket of water to clean it after each use. The rig significantly reduces the labor required for the coating process to just a few seconds, but it does take up some shop space.

    I put it to work with one of my larger parts. A few seconds to dip, then let it hang for a few minutes.

    10 Dipped.JPG

    I’ve taken to adding legs to the patterns to use for drying stands.

    11 On legs.JPG 12 On Legs.JPG

    Tony and Tobho Mott like this.
  10. Petee716

    Petee716 Silver Banner Member

    Simple and functional. Very nice.
    I like Pat's broken crayon reference. I've got a whole box full of broken crayons. It's 20x30' and looks like a barn! Lol.

  11. garyhlucas

    garyhlucas Silver

    In reading your drying legs comment it reminds me of my thinking about leaving legs when I cut a part from foam to make easier to fixture for machining. The pump part I posted is a perfect example. Years ago I was tasked with CNC machining some castings that were being made from drawings that were 53 years old at the time. It involved fixturing the part many times and very close tolerances. I really had to study the raw castings and the drawings to come up with a machining sequence. It was then that I gained a great appreciation for the engineer that designed that part. What appeared to be somewhat random bumps on the castings in a location that didn't have any bumps in the drawing turned out to be there for the 1st machining operation on the other side. It was brilliant as holding this part without them was extremely difficult, as I found out.

    Management had a guy on a manual machine do some initial machining and he removed those bumps as step 1 instead of leaving them until step 4! A different machinist also worked on them. He chose a completely different starting point. I was supposed to do all the machining on a CNC with raw castings, and two different premachined parts that wouldn't fit the fixtures for raw castings. Yep we lost our shirt on that job and the customer rejected half the parts too.
  12. Tony

    Tony Copper

    I know this is an older thread, but I would like to say I admire your work. Very well done. If you dont mind me asking what is the comercial refractory coating you're using? Just wondering because it appears to be a different color than the stuff I've seen. Thanks and keep up the great work I really enjoy your threads.
  13. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Thanks Tony. I consider that high praise coming from a professional foundry man. Do you ever use the lost foam process at Waupaca?

    It's REFCOTEC Poly Cap 600.

    Poly Cap 600 sized.jpg DPOLY600 (002).jpg

    REFCOTEC is a sister company of my local refractory materials supplier. Select Refractory Coatings at the link below.


    IIRC, this this the non-ferrous formula and they may have a different product for ferrous use. The compositions are similar to their mold and core washes. They have a 600lb minimum. I like it but as far as completeness and useful info for this thread, for the two previous years I used the typical non-hardening drywall joint compounds available at retail outlets with great success and experimented with dip coating with them too.


    I'm still gaining experience with the Poly Cap 600 but I can also say I believe I could get similar results with thinned and dipped drywall compound.....at least in aluminum duty service. I was going to start trying to characterize permeability of my home brew and then I got sampled a pale of the Poly Cap 600. Comparing the two, the commercial materials seem to modestly wet the pattern, self level, and perhaps dry a bit faster. In regards to permeability I cant say for certain but in my experience the coating thickness is strongly correlated to that so I just try to control that with slurry viscosity.

    For anyone reading this thread, you don't have to by commercial coatings to get good results. If you read my dip coating link, just diluting the drywall mud and adding a little Dawn dishwashing soap as a surfactant will get you there.

    One other thread you may want to check out is my molding rig.



    Attached Files:

    Tony likes this.
  14. rocco

    rocco Silver

    Ignoring for the moment ease of use, how does the performance of this stuff compare to a drywall compound slurry?
  15. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    rocco, not sure I can add much more than what I said in the last two paragraphs of the post above but one of those links is to a thread where I was experimenting with thinned drywall slurry.......which worked well but the addition of Dawn soap as surfactant was important.

    IMO, the ease of use is more matter of dip coating vs brushing rather than the composition of the slurry but dipping also gives a more uniform coating thickness and thus consistent and repeatable permeability across the surface of the pattern. As I said above the commercial slurry is better in some respects but definitely not in economy.....$81/5gal vs $15/5gal for non-setting joint compound. There are better places for hobbyists getting into lost foam casting to invest their money before commercial coatings.

    Tony likes this.
  16. garyhlucas

    garyhlucas Silver

    How do you keep air bubbles from getting entrained in the slurry. Seems to be the toughest issue to control. I have added Dawn, but maybe not enough. I am also careful when mixing with a drill powered mixer to not mix so vigorously that I suck air in but still there seems to be lots of bubbles in the coating.
  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    You're brushing not dipping correct Gary?

    If you had a vacuum source you could take your slurry to high vacuum.....but if you are getting sizable bubbles in brushed on coating, I'd say it's too viscous and being applied too thick. Try thinning it just a bit. In my experience, if the drywall turns white when dry and you can't see through it to the pink foam it's thick enough.......and thinner is more permeable.

    When I started dip coating, I started getting very tiny bubbles in the coating at the pattern surface which became tiny balls on the surface of the casting. The solution to that was spritzing the pattern with Dawn soapy water, blow off the excess, and then dip. The surfactant would break the surface tension and the slurry would wet better.

  18. garyhlucas

    garyhlucas Silver

    Dipping everything now. I have it way thinned down now and it still isn't as good as I'd like. Yes the bubbles make tiny balls on the surface. Your coatings look much thicker than mine so maybe I have thinned too much. I have a high vacuum pump but the tricky part is finding a dipping container that won't collapse under vacuum but is easy to seal up. probably needs to be a low pressure tank with the end cut off. I have added Dawn to the mix but I haven't tried spraying it on and blowing the excess off yet.
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Did you have a look at the dip coating thread I linked in post 13? The dipped sample part had bubbles (lots on the surface of the slurry in the cup) when wet but looked ok when dry. I was experimenting with small pieces and small amounts of slurry I mixed and weighed on a triple beam scale. The bubbles were probably caused by too much soap which I didn't measure in the small samples. The drywall mud had to be diluted with a lot of water. That wasn't helpful to getting it to wet the hydrophobic foam pattern. It would probably would be aided by additional suspending and flow agents but when used close to mixing I thought the thermostat housings I dip coated with the mud slurry at the end of that link looked and cast great.

    I had a 3 gal paint pressure pot that I used for a long time but then bought this 8 gal unit for a little more capacity. I was amazed at how tight it was. I use it for a lot of things. If you already have the vacuum pump you can buy 5 gal versions of these all day on eBay and Amazon for around $80 (search "vacuum chamber"). Best if you have a pail you can just lift in and out of something like this.....sorry, a 5 gal bucket wont fit inside

    1 Impreg Rig.JPG

  20. garyhlucas

    garyhlucas Silver

    I think I am going to dump the slurry and start over with a fresh batch, no soap. Then I'll try the spray bottle approach with the Dawn.

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