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Thread: Petrobond Questions

  1. #11
    Senior Member cactusdreams's Avatar
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    Many opinions about using PB and many good results. You can mull with the "stomping" method but I think machine mulling is best and far less work, after you build a muller that is. Surprised how well DavidF's bucket & stirrer works but it does seem to work. If you shake out your mold too soon and there's lots of smoke that's oil you're loosing which will eventually need to be replaced. Patience is a virtue on that one. I scrape off the burnt stuff that I can easily, especially when casting higher temp metals. But the best thing I do is always face the mold with freshly mulled and sifted virgin PB then back it with the used mulled sand. Doesn't take much and gives pristine results.
    People who say it cannot be done should not interrupt those who are doing it.

  2. #12
    Moderator DavidF's Avatar
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    That mixer on a drill will wear you out!! You can only put about 6" in the bucket at a time.
    Thats a gear reduction drill, I think it runs at 450 rpms and has enough torque to twist you into a pretzel. But it does do an excellent job on small batches
    A calm sea does not make a skilled sailor....

  3. #13
    Quote Originally Posted by scottyk View Post
    I bought 35lbs of PB about 6 or 7 months ago and used that to cast a few smaller aluminum parts, then I ran ALL the sand thru a screen and into a 5 gallon bucket to store it. I opened it up to use it a couple weeks ago and it has lost ALOT of green strength. I have it on a tarp right now and I have been mixing it up with a hand shovel and constantly stepping on it to smash it together, I have added a very small amount of 40 weight non detergent oil "1/4oz ish" and a quick spray of isopropyl alcohol as I have read on this forum. I had to order another 35 lbs last week for my large flask and I have to say my old sand is still no where near the green strength as the new stuff. My old sand looks basically new as it is bright red still and I have separated the black burned sand from the rest so I dont think it would take much oil/binder to replace what has been burned off.

    So Im not totally sure if my "mulling" method is to blame, or if my oil/binder mixture is off, but either way its not easy to get this sand back the way it was, maybe a muller is key to success, maybe I need to try the paint mixer in a bucket.. Either way I thought I would share my experience and hopefully it helps you.


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    What is the proper way to store petrobond? Does it need a lid and how long would it last without one?

  4. #14
    Quote Originally Posted by JumpinJulius View Post
    - - - Updated - - -

    What is the proper way to store petrobond? Does it need a lid and how long would it last without one?
    I couldnt tell ya, I just know mine has been in a bucket with a lid "that was NOT completely snapped one I noticed" and I had this sitting in my shop over the course of a long winter and it is very weak compared to how it went into the bucket. Has not been below 45 degree's but has been subject to fairly dry winter air. I have heard grumblings on the forum about this sand not liking the cold weather, I have no real world successful experience to compare.

  5. #15
    Before I got my mini muller I used a plate tamper and one of the plastic concrete mixing troughs from the big box store. Tamp it down hard and break it up with a garden hoe. Much faster than molding practice :-) Never scraped the burnt stuff off then either and the green strength was fine although noticeably better with the muller. It does work a lot better when it is warm. Mine is stored in plastic bins with lids, not air tight by any means.

    Where are you located JumpinJulius? Perhaps a helpful member could give you petrobond a little massage?

    Ward

  6. #16
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    Quote Originally Posted by wshelley View Post
    Before I got my mini muller I used a plate tamper and one of the plastic concrete mixing troughs from the big box store. Tamp it down hard and break it up with a garden hoe. Much faster than molding practice :-) Never scraped the burnt stuff off then either and the green strength was fine although noticeably better with the muller. It does work a lot better when it is warm. Mine is stored in plastic bins with lids, not air tight by any means.

    Where are you located JumpinJulius? Perhaps a helpful member could give you petrobond a little massage?

    Ward
    Sounds like it just needs a little use. I assure you he doesn't live anywhere near me! It's been colder than a bastard here for months, but in the few brief warm spells my petrobond has been fine. I keep mine in those yellow plastic kitty litter pails with the blue lids. Not airtight. I do use a muller, but I doubt just sitting over the winter would have depleted any of the active ingredients, even subfreezing.


    Pete

  7. #17
    After spending countless hours over the last few weeks stomping and mixing I got the old PB sand to have decent green strength. I admit I did have to ram up a mold about 4 times, and it was a large mold, but the last time it finally held together and produced a great casting! BUT the very next day I went to use the PB again, I think its either the temperature is too cold or the mold was so large it burned alot of the oil out of the sand because it has lost its green strength again. I'm done with the hand/foot mulling and mixing of this stuff, with the amount of time it takes to go thru the whole process I just cannot justify it. Im going to bite the bullet and start building a muller. Now I am casting things with 70lbs of sand per flask and trying to mull this by hand is just not cutting it. I tried the drill/paint mixer for a couple nights and that had me sweating, not to mention it bent the mixer and I had to weld extra steel on to take the abuse and the poor drill let out a little smoke a couple times.

    So theres my take on hand mulling PB sand, the stuff is amazing when it first arrives, very strong and easy to work with, can ram it hard and it still vents great, but it is not a easy road to keep it that way, at least not for us cheap backyard guys.

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