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  1. #1
    Join Date
    Jun 2012
    Location
    Germany, Outback of Munich
    Posts
    211

    Default Regenerating oil bound casting sand

    Hi!

    I don't know how many backyard casters we have here. I know two of them: RayG and me.

    This thread is intended to be only about oil bound sand, green sand is something completely different (try adding water to you PetroBond ...).
    The sand I do have is OBB. That's a German brand. I do not think it is completely different to PetroBond or other local brands.

    Well, I started quite naively. I just added some oil and binder and mixed the sand. That worked for some time, until the binding deteriorated over time ...
    Then I built a real muller (and not the crap I initially had). That helped a bit.

    Then I compared my regenerated sand to a fresh sample out of the bag. I acquired (to an unknown and doubtful extent) three skills:
    Detect wetness
    Detect ductility
    Detect binding ability

    "Judging" by the three "precise measurement" I add oil, binder and alcohol. But the results still are not as good as a new sand.

    If the sand feels try, I add oil. If there is too much oil, a lot of sand sticks to you hand.
    After adding oil, I sometimes add binder. That reduces the free oil in the sand and increases binding ability (breaking the sand).
    Sometimes, it is good to add alcohol. This increases binding, reduces wetness and a bit of ductility is lost (but not harmful). But I have the impression, that by adding alcohol, the positive effect evaporates (pun intended) over time.

    What I found is, that it sometimes is just enough to sieve the sand after a pour. Now, I stick to sieving always before doing anything else.


    As you can see from my descriptions above, my skills are limited, and the results leave room for improvements.

    Is there anybody who has better knowledge?

    Thanks,
    Nick

  2. #2
    Join Date
    Jun 2008
    Location
    Victoria, Australia
    Age
    74
    Posts
    5,080

    Default

    Hi Nick,

    You raise some good questions, I think some experiments will be required to get the answers.

    My big problem is the lack of a decent Muller, Hand mulling just doesn't work as well as a good machine.

    I haven't done any casting since I got back home, but a few projects are starting to pile up.. soon ...

    Regards
    Ray

  3. #3
    Join Date
    Jun 2012
    Location
    Germany, Outback of Munich
    Posts
    211

    Default

    I think some experiments will be required to get the answers.
    Ray, do you remember the core for the spindle mount? Made out of oil bound sand?
    Well, I let that rest for more than a week. Supported just at both ends. It didn't break or sag.
    I also tried that with my regenerated sand. It just took a few seconds ...


    Nick

  4. #4
    Join Date
    Jun 2008
    Location
    Victoria, Australia
    Age
    74
    Posts
    5,080

    Default

    Quote Originally Posted by MuellerNick View Post
    I also tried that with my regenerated sand. It just took a few seconds ...

    Nick
    Yes I remember that test, I'm surprised the regenerated sand failed so quickly, but, on the positive side, that means it's a good test to start with. If we can find out why it's lacking green strength.

    Regards
    Ray

  5. #5
    Join Date
    Nov 2006
    Location
    Darwin HowardSprings
    Age
    52
    Posts
    41

    Default

    im just starting out , and are still looking for "decent sand " , i got some (7kg) pertro bond 2 binder sent out from usa from http://shop.petrobondforsale.com/Mul...on=alloyavenue , it should make 150kg of sand(AU$180 delivered to my door )

    some of the sand ive looked at are" blunt " or after rubbing together ends up blunt quickly , im still looking for some freshly crunched decent sand , the local " sharp plasters sand" seams to blunten too quick ( too soft , the rock it was crushed from ),crushed quality quartz might be better ( silicon dioxide ) , smashed and graded "glass " would be better than the local sand

    im thinking that might be apart of the problem , the sand gets its sharp edges knocked off too easy in the muller

    ive looked at sandblasters grit , but that is made "Blunt" so it dosnt compact in the hopper ,
    i was thinking a nice hard "garnet " sand would ware out the mullers liner rather than loose its sharpness ( hardness of 7 on the diamond scale )
    there is a local " zircon " mine in the Northern Territory , i might see if they can supply freshly crushed and graded zircon ( high melting point ) sand ( hardness of 9 on the diamond scale , 4x harder than garnet )

    the tumbling action of a muller is probably what you dont want , the sand will knock the edges off its self , the longer it is tumbled ,
    from what i understand , a muller just evenly distributes the clay/oil over each partial of sand , there must be a " gentler " way of doing this ? add "metho" until its a slurry , then heat to 80c to boil off the "metho" leaving the clay /oil even on each sand grain, with out the blunting affect of rubbing it together ? ( a tiny cement mixer with a heater turning 1 revolution , every min , and stopping most of the time )??? im a newbie , just my thoughts

    i still have to make a muller so any photo's of working ones would be greatly appreciated

    cheers ken
    how come a 10mm peg dont fit in a 10mm hole

  6. #6
    Join Date
    Jun 2008
    Location
    Victoria, Australia
    Age
    74
    Posts
    5,080

    Default

    Hi Ken,

    I'm waiting on the Stephen Chastain book to arrive eBay Australia: Buy new & used fashion, electronics & home d

    There are some extracts of the book on google books Build a Muller - Stephen Chastain - Google Books

    I don't have a cupola, so I'm not looking for huge quantities, and looking at the horsepower required for various drum sizes, I'm thinking of a 24" diameter drum, with a 2" drive shaft and a 2 hp motor, running the drum at 30+ rpm. A 30" drum would require a 5hp motor ( according to Chastain).

    There's more to sand than sharp edges, grit size and grit size distribution is important as well, mulling by hand is ok, but it's just hard work and doesn't work as well as a proper muller.

    I keep reading that iso-propanol is supposed to increase green strength, that's the area I'd like to concentrate on for some more testing.

    Regards
    Ray

  7. #7
    Join Date
    Jun 2007
    Location
    vancouver island
    Posts
    30

    Default mixing the petro-bond

    When stirring up the already used petro-bond, I use non-detergent 30 weight oil. I mixed it using a 1/2 inch low speed drill and hand made blade in a triangle shape. I did this for about 36 years in a small school shop. I admit the petro-bond did get a "liitle" black and did order new petro-bond 3 times in those 36 years. The message being, the petro-bond still works. Wayne.

  8. #8
    Join Date
    Jun 2012
    Location
    Germany, Outback of Munich
    Posts
    211

    Default

    OK!

    So I'll say green strength from now on.
    Yes, alcohol seems to improve that. At least, my observation. Not every alcohol works (at least for my sand). Isopropanol does. After mulling and seeing that the sand feels good, but lacks strength, I add two shots of alcohol and mull for a few minutes more. Helps most of the times, but not always. At least, the sand feels sticky, before it felt oily.
    The problem here is, that "it feels" is very vague.

    Sidenote:
    Stefan (he's a member here too), told me, that they had one man doing the sand that made it always perfect. When they had to make expensive and complicated castings, they did them only when that man was on shift.

    Sand sharpness:
    I don't think that plays a role.
    The core sand I have is not crushed, it is a natural one. Must be zillion years old, former sea sand. At a foundry of a big automobile manufacturer in Stuttgart (name not told), they prefer used sand. Makes a better surface. But that sand is used for cores. They recycle it over and over again. They only remove the dust (won't work here). The sand is blown through pipes, so it certainly gets dull.

    In PetroBond's PDF, they say that you should add FeO when the sand gets grainy. Whatever grainy is!? My sand seems to contain FeO, judging from the color. The K-bound sand is white, no FeO.
    Stefan mixed his K-bound in my muller. And I can tell you, it has green strength like hell. You have to hammer it into the mold.

    For small moulds, I don't need much green strength, but for bigger (to my scale) molds, I need it. Or they keep falling apart while closing the two halves.


    Nick

  9. #9
    Join Date
    Jun 2012
    Location
    Germany, Outback of Munich
    Posts
    211

    Default

    A few more findings, but still some way left to get perfect …

    Regenerating in between:
    You don't always have to fully regenerate the sand (mulling etc.). It works for a few times to sieve the sand and then re-use it without further work. I use a sieve with a mesh width of about 3 mm. This breaks the burnt parts into small ones that don't hurt. Still, you should use a finer mesh for the first layer onto the pattern. Then proceed with the roughly sieved sand.

    Determining mulling time:
    I have two methods.
    First the crude one.
    Take a hand full of new sand, compress it in your fist and put it into the miller, together with the to-be-mulled-sand. If you can't see any remains (different color) you are done.
    A more elaborate method that will result in much longer mulling time:
    Take a sample (hand full) of sand, and slam it against a polished surface (mirror, shiny sheet metal etc.). If you look at the flat surface of the sand and you see spots (diameter will be something like 3 mm), the sand needs more mulling.

    Throw away the most badly burnt sand and fill up with fresh sand. The more often you regenerate, the more tar like residues you will have in your sand. I don't have the impression that these make a bad surface, but you simply have more work to regenerate and loose green strength.

    I'm still not really convinced that adding alcohol makes a difference in the long run. Maybe just fresh out of the muller?

    I haven't tried yet, but I'll do. Way-oil might be a candidate as regenerating oil. It has tackyfiers in it, and I do have about 10 l CPLG220 of a brand that doesn't work in my MAHO*)

    *)
    I had problems with the Z-axis for a long time now. It stick-slipped badly. This way has some plastic way liner. After changing the brand (from Fina to Shell, but with the same specs) the problem disappeared immediately.


    Nick

  10. #10
    Join Date
    Nov 2012
    Location
    australia
    Posts
    10

    Default

    Nick

    I've had similar problems with petrobond. I mull it and then one hour later it has a dry feel to it, adding oil to it helps a bit. The sand feels really good after a casting session and put in the muller. I think what happens is oil recondenses in the cooler parts or the sand mold sand and remixes into the sand. One day later the sand feels dry!

  11. #11
    Join Date
    Oct 2012
    Location
    Australia
    Posts
    621

    Default

    Quote Originally Posted by MuellerNick View Post
    A few more findings, but still some way left to get perfect …

    Regenerating in between:
    You don't always have to fully regenerate the sand (mulling etc.). It works for a few times to sieve the sand and then re-use it without further work. I use a sieve with a mesh width of about 3 mm. This breaks the burnt parts into small ones that don't hurt. Still, you should use a finer mesh for the first layer onto the pattern. Then proceed with the roughly sieved sand.

    Determining mulling time:
    I have two methods.
    First the crude one.
    Take a hand full of new sand, compress it in your fist and put it into the miller, together with the to-be-mulled-sand. If you can't see any remains (different color) you are done.
    A more elaborate method that will result in much longer mulling time:
    Take a sample (hand full) of sand, and slam it against a polished surface (mirror, shiny sheet metal etc.). If you look at the flat surface of the sand and you see spots (diameter will be something like 3 mm), the sand needs more mulling.

    Throw away the most badly burnt sand and fill up with fresh sand. The more often you regenerate, the more tar like residues you will have in your sand. I don't have the impression that these make a bad surface, but you simply have more work to regenerate and loose green strength.

    I'm still not really convinced that adding alcohol makes a difference in the long run. Maybe just fresh out of the muller?

    I haven't tried yet, but I'll do. Way-oil might be a candidate as regenerating oil. It has tackyfiers in it, and I do have about 10 l CPLG220 of a brand that doesn't work in my MAHO*)

    *)
    I had problems with the Z-axis for a long time now. It stick-slipped badly. This way has some plastic way liner. After changing the brand (from Fina to Shell, but with the same specs) the problem disappeared immediately.


    Nick
    Hi Nick,
    We keep out petrobond in 30L plastic buckets with lids. Our petrobond is the type 1 (version that needs the catalyst) After mulling with isopropanol I put it back into the buckets overnight. When I open them the next day, I get a very strong smell of the isopropanol and the green strength seems to be much better than the night before. My guess is that the reaction with the binder, oil and isopropanol needs a little time to happen. This is all subjective i have not tested the green strength properly, it is just by feel.

  12. #12
    Join Date
    Jun 2012
    Location
    Germany, Outback of Munich
    Posts
    211

    Default

    I put it back into the buckets overnight.
    Ahhh! That makes sense, thanks! I'll try that.


    Nick

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