Reinforcing 12 Inch deep pattern for green sand?

Discussion in 'Sand Casting' started by Mark's castings, Oct 9, 2021.


  1. It's narrow side down when the sand is packed into the pattern, so I lifted it out with pattern stuck to it and flipped it to have narrow end up. The dark green steel lugs spin on the lifting snap rings fairly easily so long as you steady it against gravity.

    On a more positive note, the casting is complete!, texture is a bit rough, in places I was ramming too much at a time and you can see smooth and rough layers...nothing that can't be sanded off :D. I poured fast and the mould took it in as fast as I could pour it. Furnace is running better now with the precise needle valve and a final filter to stop metal particles from the fuel pump despite it's integral filter. Burned 8 litres in 36 minutes to get a full A25 of aluminium so it's running well now and also fixed a vapour leak in the stainless keg inner skin.


    IMG_20211126_095018.jpg

    PB260497.JPG


    PB260498.JPG
     
    Last edited: Nov 25, 2021
  2. Melterskelter

    Melterskelter Gold Banner Member

    I'm gonna try one more time: How did you change the cope mold orientation from narrow side up as shown in the 2nd to bottom photo in post 77 to narrow side down as shown in the last pic in post 77?

    The casting looks quite usable as is. Yes, you can now work on refining you sand packing etc to get a finish you like better. But you are over the biggest hurdles. Must feel good.

    Denis
     
  3. I seem to have a touch of heatstroke from the 90 degree ambient heat and sweating..... massive headache this afternoon. I used the hoist to lift the cope straight up into the air using one hand to steady it as it's top heavy in that orientation (post 77, 2nd last pic), you can see the chains attached, ready to lift. Then use both hands, one on each end to spin it around using the lifting lugs as the pivot. It's then stable facing down and ready to lower into the drag (post 77, last). The chains are deliberately long so the large flask can spin using the lugs as the pivot point and still clear the green lifting bar. So the flask spins on a horizontal axis line running through and between the center of both lugs.

    It does feel good to finally get a good result from months of effort, especially when you don't know it's going to work. The sand packing is a challenge, I hand pressed and then rammed, with only rammed finish being any good, maybe vibration would help too.
     
    Last edited: Nov 25, 2021
  4. Petee716

    Petee716 Gold Banner Member

    I’m pleasantly surprised you were able to manhandle the cope successfully without losing control of it, let alone have the core not come apart on the way around. The internal steel worked out well for that. Back in post 18 I posted some pictures of the cope with the goose egg in it. In a couple of them you can see 2 sticks of 3/4x1” slats extending from the top side edges of the cope. Those are for the purpose of controlling the flask during the flip. My application wasn’t nearly as imbalanced as yours so they didn’t need to be any stronger than that, but they gave me something to hang on to and worked well. You will also see some light gauge chain attached to the spreader frame. Those attach to either side of the cope to keep it stable while lifting and allowed me to attach one of them to hold it during mid flip in case I needed to reposition myself during the operation.
    Nice work.

    Pete
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    Pete and I were wondering the same thing. Controlling that super-unbalanced flip must have been really tough. So, to make it way easier, I would suggest welding maybe 3/8x1” flat bar arms onto your lugs. They should be long enough to allow mounting new lugs near the level of the center of gravity of the packed cope flask. The arms will give something to hold onto during the flip and will change the flip to a “rotation.” ;-)

    Denis
     
  6. It was one of those situations where you don't anticipate everything until you encounter it for the first time: I was really glad to have the steel reinforcement when flipping the mould. It was unbalanced, but not that bad really, the steel bar grips on the ends of the flask provided enough grip and the flip seemed fairly easy, trivial even. One thing I did encounter was the core/cope shifting slightly off center at the narrow end but still centered at the wide base of the casting, this could be assembly misalignment rather than the core distorting during the flip. I'm thinking of trying longer pins and nylon guide bushes as steel on steel has too much friction/galling to work and lubricating pins in a sandy environment is a bad idea.

    Edit: Cutting the sprue hole would cause enough distortion to cause the off centre effect I saw in the casting.
     
    Last edited: Nov 26, 2021
  7. Chazza

    Chazza Silver

    Nice work Mark and a great result.

    I use a piece of tapered timber when moulding, to make the sprue hole. It is the work of a few minutes to turn one on a wood lathe and it is easily removed from the sand, using a back-and-forth twisting motion. Much easier than cutting a hole for the sprue,

    Cheers Charlie
     
    Melterskelter likes this.
  8. It's definitely on the "to-do" list, I can see there will be a lot of refinement on future casting to get a good finish, fortunately any surface defects protrude above the surface so they can be sanded, filed or machined down....just very time consuming compared to a resin sand casting where everything is close to final shape when in an "as cast" state.
     
  9. Melterskelter

    Melterskelter Gold Banner Member

    I think it should be possible to get pretty good results in green sand. I cast in both oil-bound and green sand. the oil-bound gives just a little better finish but the green does pretty well.

    Here are some flask components cast in green sand shown in this a nearby posts.

    http://forums.thehomefoundry.org/index.php?threads/free-3d-flask-pattern.1300/page-4#post-30992

    Not going to win any awards with them, but plenty good for the intended purpose. I did not get very good results with the first few tries, but things got better with time.

    Denis
     
    Mark's castings likes this.
  10. That sort of finish (the flasks) would be great, perfectly usable.
     
  11. The casting is getting rough machined on top with a flycutter as that's all I can fit in the mill and clear the height of the casting. There's a shrink defect zone around and under where the runner was located (on the bottom during pouring) where the wall is thinnner, obviously it was the last place to fill and solidify. I'm thinking of adding a piece to the top of the pattern which should sit above the casting wall (easier to cut off) and hopefully move the shrink off the wall and into the runner.

    PB280500.JPG
     
  12. Made some more progress: the self centering bearings are fitted temporarily to get some idea of the wheel and shaft location. The wheels will have a sheet metal guard to catch the water flung off the wheels in operation.

    PB300507.JPG
    PB300506.JPG
     
  13. Managed to cast the lid for the cabbing machine today, I ran the furnace quite low, only burned 5 litres for a half full A25 of aluminium. This time I set the flame so it just went over the rim of the crucible and had it much leaner than I normally do, at first the aluminium scrap was getting soot, so I boosted the air until it was clean and then the crucible was dull red with metal molten in 20 minutes. This is way lower and leaner than I normally have things set at but the new fuel needle valve makes settings consistent now, just crack it 90 degrees open each time.

    The mould is 6mm/0.25" thick so I drilled five air vents and cast it upside down and was gratified to see metal appear in all five vent while pouring. I did some 3.5" aluminium cylinders for the pulley castings, one with an aluminium slug at the botton under 1/2" of sand and the other with a 4" slug of iron at the bottom of the mould in direct contact with the aluminium....only the iron slug casting had any shrink at the top so the other one may be rotten inside.


    PC220537.JPG


    PC220540.JPG



    PC220538.JPG



    PC220542.JPG



    PC220534.JPG



    PC220533.JPG
     
    Last edited: Dec 21, 2021
  14. Melterskelter

    Melterskelter Gold Banner Member

    Nice looking cap. I can see where the tray will be handy. And the green sand appears to be providing a nice finish.

    Is that flash surrounding the cap in the third photo above? If so, why so much flash? It appears uniform like maybe the cope floated or did not close tightly on the drag. The cavity has a lot of surface area to promote float. Or is that a very thin gate surrounding the mold cavity?

    Denis.
     
  15. Petee716

    Petee716 Gold Banner Member

    Looks like the flange.
     
  16. Melterskelter

    Melterskelter Gold Banner Member

    Duh! Now I see that. Ooopsies!

    Denis
     
  17. Phew! had me worried for second there, Denis. The pattern has extra material round the edge/rim so I can hand fit it to individual housings. The finish was good enough to clean it up without too much trouble: I gave it a general hit all over on the 2" belt grinder with a 36 grit zirconia belt to remove any high spots and even the texture of the underside. The inside of the tray had a few sand burns and got some filing and sanding with 80 grit paper to smooth the texture. With the casting sitting on the housing, I used a red feltpen to mark areas to remove round the flange to get a good match for the spindle housing. The lid will be hinged to give access to the stepped pulley to change speeds (with kill switch!). After all that a fine file broke all the sharp edges and corners and it got a heavy coat of Auto primer/surfacer that I used on the pattern.

    PC230547.JPG


    PC230546.JPG


    PC230545.JPG
     
  18. Melterskelter

    Melterskelter Gold Banner Member

    Looks great! Sorry for my goofy goof.

    Denis
     
  19. I'm very pleased with how the green sand casting turned out compared with resin sand (resin just doubled in price in one go :eek:). There's a lot to learn about using the stuff but I'm getting in the experience. I'm machining the pulley blanks now, I expect the casting with aluminium cylinder as a chill under sand to have voids while the one in direct contact with cast iron showed some contraction and also rings like a bell when tapped compared to a dull thunk for the first one.
     
  20. Have almost finished the next pattern for the cabbing machine's motor mount, this one is unusual in that it has a negative draft lean on the rear face to mate with the spindle housing casting. I'm hoping the overall taper will still let me withdraw it from the sand intact.
    P1230570.JPG

    P1230569.JPG

    P1230568.JPG

    P1230566.JPG
     
    Last edited: Jan 22, 2022

Share This Page