Green sand casting updates

Discussion in 'Sand Casting' started by Mark's castings, Dec 2, 2022.

  1. This posting directly relates to some earlier threads and is an update of them kind of lumped together. I'm at the point where I'm successfully using green sand to make my aluminium castings. The results are quite usable but there's room for improvement and the sand handling is inefficient: I use the power riddle to sieve onto a plastic sheet and then drag it to the main pile on a tarp and mix it in with a rake and by foot while trying to keep leaves and the odd falling mango out.

    The power riddle has an extra steel mass attached with a couple of high tensile screws to get enough "out of balance" mass working and I cut some PVC pipe to cover the assembly and keep the dust out and hopefully act as a scatter shield if the mass breaks and tries to take out my kneecaps. The whipper snipper flex drive stuffed in a 5/8" hose works beautifully and keeps the DC motor out of the dirt and vibration, I'm only running it at 80 out of 240 Volts and the variable speed lets me tune it for maximum vibration. It can process a wheelbarrow brim full of sand in under half an hour but I have to stop every three shovelfuls and use a sheet steel spreader to break up the big lumps whack a mole style. If it was a rotating drum with a few blocks of wood tumbling it'd run unattended. It's still way better than hand sieving and if the green sand is completely dry I can lay some fly screen down and fine sieve any foreign material out to maintain the sand.

    riddle vibrator1.jpg

    power riddle 1.jpg



    The green sand is giving a satisfactory result but it's clay content is likely too high as it sticks to my hands and feet in a thick layer and when rammed it has a noticeable hard packed layer over the top of a less packed zone and no amount of hard ramming will penetrate to the lower strata. I've added a half bucket of sand and it's already made a difference and I have to be careful about getting one layer to stick to another and not breaking off, the sand might have been a bit too dry too, with the pile in direct sunlight.


    The box casting (top middle of photo) shows the rammed layers with alternating smooth and rough finishes. As it's cast upside down there's a fair bit of pressure on the metal which tend to hydraulic into the sand if not packed tight. The shrink defects in the box casting around the feeder/casting area has been cured with a larger diameter feeder up from 7/8" to 1 & 1/8" diameter. The rear motor mount casting had shrink defects in the flat base away from the two vertical fins and a third feeder on the horizontal runner cured this. I'm going to add runners to the patterns now that the shrink defects have been sorted out.

    green sand aluminium 3.jpg


    green sand aluminium 1.jpg


    green sand aluminium 2.jpg



    I have a selection of steel flasks to be able to make a full set of castings in one casting session and have no complaints with sand retention, the small lip is more than enough and they take a bit of work to shake out after casting. The pins still need work, I tried bronze sockets that are a bit less grabby than stainless pins in steel holes, I'll have to file one hole oval to help and fall back to nylon sleeves maybe. The pins could be thicker too, say 3/4" diameter.




    steel flask 1.jpg

    bronze flask guide 1.jpg
     

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    Last edited: Dec 2, 2022
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  2. Melterskelter

    Melterskelter Gold Banner Member

    Mark,

    Lots of progress made!

    I would suggest making sure that the bronze/steel/nylon pin lugs have holes that are NOT long straight-sided cylinders of about the same diameter their full length. Instead get out a die grinder or rat-tail file and make their walls have draft both to the top and bottom of the hole leaving just the mid portion (up and down mid) a loose fit on the pin. The tightest portion of the hole should still have few thou clearance. And at the top and bottom of the hole it out to have maybe 15 to 20 thou clearance. Having one hole generally a round hourglass coupled with the other hole being an oval hour glass will prevent the grab inherent in long straight-sided cylinders. Hourglassing the holes will allow you to tip a bit in the x-y plain without locking up the lugs on the pins. The long axis of the oval should be in line with the long axis of the flask.

    Draft exaggerated in this sketch intended to illustrate my intended point. On my flasks I use angle iron tabs rather than blocks as the tabs act like hourglassed cylinders.
    upload_2022-12-3_7-9-40.png

    Might be worth a try.

    Denis
     
    Last edited: Dec 3, 2022
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  3. I have some sheet metal tapered reamers that would be ideal for touching up the holes... first thing would be to re-jig the steel pin holders and try and weld a bit more accurately as there's some distortion there that doesn't help. I made the mistake of not having the whole flask built before welding and tried to align the bronze sockets after welding. If I'd had it all assembled I could shim any misalignments before tack welding the pin holders to the flask. My small black flask has angle iron pin sockets, one circular and one an elongated slot ( as discussed by others on this forum earlier) and it works great: both halves are aligned accurately and it goes together easily.
     
  4. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I can't see both sides but if they are both pins in holes, you might try a slot on one end instead. All the removable bushings I have are slotted on one end. One hole is sufficient to locate if have a decent size pin. The extra degree of freedom makes a big difference because even if you have perfect on center alignment of pins and bushings, a slight cocking will cause bind.....lesser so with a slot.

    Best,
    Kelly
     

  5. I knew I'd seen it somewhere before....so this morning I made two more castings and used a round file to ovalize (not to be mistaken for "ovulate") one hole in the manner suggested by Denis and by Kelly at the same time. So the hole is now a slot that looks like Denis' drawing on one axis only and it works much better, much less sensitive to cocking and subsequent binding but still able to accurately register both halves of the pattern.
     
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  6. Just a short update on the power riddle: after six hours use at most, the flex drive broke where it entered the out of balance unit shaft and gets secured with a grub screw. The cable was made with a kind of square cross section end that appears to be resistance welded. I just undid the grub screw and removed the broken off stub and put the cable end back in place and tightened the grub screw again. Took maybe five minutes to fix.... will see how long it lasts for.
     
  7. Just finished up on the first machine using the sand castings, seven all told. Took about 90 days to make two machines from making the green sand moulds to delivery.

    Cabbing 9.jpg

    Cabbing 4.jpg

    Cabbing 2.jpg

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    Cabbing 7.jpg
    Cabbing 6.jpg
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    Cabbing 3.jpg
     

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  8. Melterskelter

    Melterskelter Gold Banner Member

    Mark, you should be proud. That machine looks first rate!

    Denis
     
  9. Thanks Denis!, It's the Mk2 unit, I counted about 20 improvements over the first unit before I stopped counting.
     
  10. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Those are very nice. You must do a fair amount of lapidary work. I bet whoever purchases one will be very happy with it. It's so pretty, but just like a new lathe needs to become slathered in swarf and cutting fluid from use, so must your machine!

    Best,
    Kelly
     
  11. Thanks for the kind words Kelly, yes the machine's splash trays will be coated with a fair bit of stone dust, The trays are quick disconnect, so the user can lift them a quarter inch or so and they will detach from the main body. They can then be hosed off in the backyard for a deep clean. I was able to use a wide variety of similar machines at the local club to gain ideas on what to improve on these machines.
     
  12. BattyZ

    BattyZ Silver Banner Member

    I second Kelly's praise! Nicely done.

    What size crucible were you able to pour all these with? My A25 is becoming too little too fast.
     
  13. I can easily do a full set of castings with two A25 crucibles full, a full set of fettled castings weighs 19 kilograms from memory.
     

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