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Thread: Petrobond Questions

  1. #1

    Question Petrobond Questions

    So I'm fairly new to metal casting. I'm 16 and I got some stuff to make a foundry for Christmas and the extent of my knowledge is YouTube videos. I have done some minor lost foam castings but we ordered some petrobond II recently. I have made a casting flask, but I need to have some questions answered before I start. I noticed that when people make a casting that the petrobond appears to be burnt around the metal like in this photo. https://www.google.com/search?q=petr...&dpr=2#imgrc=_

    Questions:
    Does the black petrobond need to be scraped away and put in a separate pile?
    Can the black petrobond ever be recovered?
    Do I need vents for air to escape when I pour metal with petrobond?

  2. #2
    Moderator DavidF's Avatar
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    Its better if you scrape away the black and separate it. It can be recovered but I would advise against it, it takes some additions of the binder, catalyst and oil to do so. petrobond vents pretty well and typically you would not need to vent it like you would green sand...
    A calm sea does not make a skilled sailor....

  3. #3
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    I've been contemplating buying some PB. That sucks if you have to toss it out. Can't you throw the whole batch in a muller and get it back in shape?
    Bones

  4. #4
    So far most of my casting with J82 (petrobond equivalent) has been with aluminum and I don't remove the black sand. I typically only wait about 10-15 minutes for the aluminum to cool and then shake out. I remull and the sand is ready to go. The last casting session I added a bit of non detergent oil and then a bit of alcohol while mulling and the sand seems as good as new. YMMV

    Ward

  5. #5
    Quote Originally Posted by wshelley View Post
    So far most of my casting with J82 (petrobond equivalent) has been with aluminum and I don't remove the black sand. I typically only wait about 10-15 minutes for the aluminum to cool and then shake out. I remull and the sand is ready to go. The last casting session I added a bit of non detergent oil and then a bit of alcohol while mulling and the sand seems as good as new. YMMV

    Ward
    I don't have a muller (is that what its called?) Is there any other way i could mull it? Maybe i could use a drill attachment or something.

  6. #6
    Moderator DavidF's Avatar
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    A calm sea does not make a skilled sailor....

  7. #7
    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.

  8. #8
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    Ramming up molds also mulls the sand. If you spend a hour doing molding practice without actually pouring, you notice the sand gets a lot better.
    Mark

  9. #9
    Senior Member Tobho Mott's Avatar
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    Note, the reverse is not true - you could run your muller all day long and it will never spit out a completed mold. Don't bother trying, you'll only end up damaging your patterns and flasks...



    Sorry, dumb joke, but I could not help it.

    Great tip Rotary, that makes sense to me. "Molding practice" sounds way more fun than "hand mulling" to begin with anyhow!

    David - just to confirm, your video was of freshening up PB *with the burnt black stuff removed*, not left in... Right? That was my interpretation at least. I think you would need to mull to reclaim the burnt sand without losing some good molding qualities. But then I have only used the water bonded stuff, so what do I know? You recommended the former (setting it aside) above, but you also described the latter (reclaiming it, including mentioning the addition of oil as done in the video, plus other ingredients not seen), so I was a little concerned that someone might mistake this for the 'reclaiming burnt PB sand without a muller' video that I believe it is not...

    Jeff
    Tobho had learned to work Valyrian steel at the forges of Qohor as a boy. Only a man who knew the spells could take old weapons and forge them anew.

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  10. #10
    Moderator DavidF's Avatar
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    Technically you should remove the burnt sand.....not all that easy when it comes down to it and some gets back into the mix. You can mull the burnt sand back in, but over time and many casts you might start having problems with the mix. Now that i have stated the above, i just throw the burnt sand right back into the mix.
    The petrobond in the video had been sitting for a couple years and had seen very little use before sitting. Last week i tried ramming up a mold with it after mulling it the same way as the video shows but without oil addition and it had very little green strength. So i mulled it again, same way but added oil. Green strength back to normal
    I buy small amounts of petrobond at a time and mix new with the old to maintain it, and thats also how i have been slowly growing my supply of it. Eventually i will have all the sand i could ever need.
    A calm sea does not make a skilled sailor....

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