Petrobond Overhydrated or Worn Out?

Discussion in 'Sand Casting' started by Swiftsure 33, Jun 26, 2024.

  1. Swiftsure 33

    Swiftsure 33 Silver

    My batch of petrobond seems to be losing some green strength, and I'm wondering if it's time to get a fresh load, or if I've possibly just been adding too much oil when mulling. My sand has seen a lot of bronze castings, and I have to imagine that the binders would break down over time from that kind of abuse. But given that I am in the habit of going by feel when re-hydrating the sand, I'm thinking perhaps I've simply been overdoing it.

    I add a spritz of IPA to every load in the muller, and a small amount of non-detergent mineral oil whenever it seems necessary. I use calcium carbonate as a parting powder if that has any impact on the lifespan. Really just looking for some guidance on the subject from those who've been doing this longer than me. I started with 50lbs ~a year ago and added another fresh 50lbs to the batch ~6 months ago. Have probably 200 castings into the sand at this point, so if anybody has a guess as to whether this sounds like the sand is hitting the end of its usability or if I just need to burn off some of the oil I'd love to know.
    Tobho Mott likes this.
  2. FishbonzWV

    FishbonzWV Silver Banner Member

    This is what Melterskelter advised. What I found locally was vegetable glycerin.
    Initially I added 2 ounces per mixer load and it perked up. Last time I cast, put 1 ounce in the load.
    Seems to be gaining strength but haven't cast lately. I plan on adding 1 oz/load until it acts like it's old self.

    I would not be afraid to add to your sand. Not doing so more or less ensures decreased performance. I routinely add glycerin (glycerol) to mine to rejuvenate it as the alcohols in Petro do evaporate. Just pull out a couple cups of sand and try adding some glycerin 1 tsp at a time until it is nice and soft and packs well. Occasionally some oil may be needed as well since it gets burnt off a bit with each pour.
    Last edited: Jun 26, 2024
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  3. HT1

    HT1 Gold Banner Member

    i need some clarification: you have cast Bronze 200 time in 100 Lbs of sand ??? if so unless you are doing tiny jewelry pieces, Buy some new sand thats an insane amount of use and you will start to have gas issues from the fines building up in your sand ,

    im going to assume you have a good muller , if so mull a batch of sand for 11 minutes and check it, 11 minutes is where the bell curve of green strength goes almost flat, basically green strength has all but maxed, if its not what you are lookin g for now is time to make additions, the only addition you should need is oil 1 oz / 100 lbs to start, you can add whatever alcohol you use, but it is literally a mist , adding alcohol will make the sand fluffy, this can be good or bad , fluffy flows and fills the flask well, but too fluffy and you have to ram very carefully , if you have already gotten too much oil you either burn it out or add a little clay, its easiest to just use it and mull , adding clay can get you into trouble

    just a general rule if petrobond starts acting really wonky add new!!! it waters down the problem, eventually you will have to toss the sand , normally i would say a hobbiest would never need to do that, but 200 bronze pours, that gets you there, but it will not be green strength that you notice it will be gass issues
    I much prefer Petrobondforsale on ebay he was a member on AA not sure if he migrated , he adds a little extra oil for the hobbiests, and ive never gotten old sand from him( new petrobond that has sat to long especially in cold weather will need to be mulled when you first get it or the green strength will be lousy)

    V/r HT1
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  4. Tobho Mott

    Tobho Mott Administrator Staff Member Banner Member

    I'm having a similar issue after pouring a few hundred castings in my 300# of petrobond. And particularly after using petrobond for ingot molds for a couple years which I now think was a pretty bad idea. It's definitely hitting my green strength; if I have gas issues I haven't discovered them yet.

    I've got a 25kg bag of new OBB sand (the imported petrobond sold by the supplier here in Ontario) that I've been using for facing, and 4 new ~33# boxes of petrobondforsale's sand to add (IIRC yes he is a member here, goes by @Chasft I believe), since adding more clay can cause issues with I guess permeability, not to mention I've been looking for years and can't find any petrobond powder or other organoclay anyway. :rolleyes:

    Would you suggest mixing it all together right away, or just using the new sand for facing until it all gets mixed in? I want good strength at the parting, but I don't want to burn up too much of the new sand before it can get mixed in with the rest. Maybe I should use the new sand as facing but also add some to the backing sand as I ram up?

    Haven't opened my boxes of petrobondforsale sand yet, but have worked with some that @MichelHandJello ordered with me, so I can vouch for it, it's awesome. I think he uses finer sand (140gfn) than the OBB sand (130). And yes very oily! So much so that we had an 18"x18" cope stick to what we thought was a sufficiently well dusted drag and peel the facing sand right off it when we separated the mold halves... :mad: A little extra parting has kept that from happening again though.

  5. HT1

    HT1 Gold Banner Member

    I dont like using new petrobond for facing unless it gets mulled or aeriated first, coming out of the packaging its too Plastic( It has settled itself in shipping) and I dont really like working with it so, I just open it into my heap chop it up a bit with a shovel and go to work, and of course as mentioned above if its old or has gotten too cold it will lack green strength, so it's not great facing.

    this brings up an issue hobbiest may not know if their sand is "good" ever since the new sand they bought may not be the best sand

    V/r HT1
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  6. Swiftsure 33

    Swiftsure 33 Silver

    I feel confident that underhydration is not the issue for me. Whenever the sand starts to feel a bit 'crumbly' during mulling I toss in a bit of oil and that's kept my sand serviceable, I'm just starting to run into issues of my molds becoming more fragile. I am curious though, are you using vegetable glycerin as a substitute for both alcohol and oil? I've been using a combination of mineral oil and isopropyl alcohol, but if I end up ordering a new batch of sand I may try some glycerol on the old stuff to see if there's any appreciable difference.
  7. Swiftsure 33

    Swiftsure 33 Silver

    Something like that yes, I haven't kept track of the failures and personal projectss, but I've got over 150 castings sold since switching to PB. The vast majority are bronze castings between 1 - 2 lbs with generous venting, and I'm not seeing any major gas issues, but then again I haven't done anything big in a while. I also tend to leave whatever crusted burnt sand remains on the castings after the shakeout and scrape it right into the trash to try and slow the buildup of fines, so I guess that's been helping. I am using petrobondforsale's stuff from ebay, after my first order I never looked back at my old homemade green sand, it's amazing stuff. I just did a batch of castings yesterday and everything turned out great, surface quality was excellent, and flashing was at a minimum. But my reason for posting the question is that I'm starting to get more fragile molds, ie sand falling out when lifting the cope, or shifting in the flask if I'm not careful when moving them around. The last time this happened is when I doubled my sand with the fresh batch and that solved the problem until now. Based on your reaction though I'm assuming its more likely that I'm simply reaching the end of the service life for the sand rather than messing up with the oil ratios. I'll try mulling with no oil for the next few batches just to see but going to plan on ordering a fresh 100lbs soon. Any thoughts on mixing in the old sand with the new? I don't really need more than the 100lbs as I'm limited by the size of my crucible, but it would be nice to be able to do 2 batches worth when I'm set up for a ramming session.
  8. HT1

    HT1 Gold Banner Member

    ok simple question if you are scraping out the burnt sand , is your sand in any way still orange??? and that would eliminate your build up of fine sand and thus gas issues, if your sand is not completely black you dont have fine issues,

    im going to point out, just FYI the two issues you are having maybe at least exasperated, by equipment (flasks) and or Technique (ramming hard enough)
    do your flasks have some sort of interlock for the sand
    sand is not slipping out of that.
    are you ramming hard enough? this one is hard to quantify . but i suggest trying a smaller peen

    Here is a very common 3.5 inch rammer with about a 1 inch wide peen , i would not use that on any mold smaller then 12X12 ( I have no Idea what you are ramming) you cannot get sand rammed well with a large rammer without getting angry with it, (sort of advice) put about 3 inches of (facing)sand over your pattern and ram, and yes if your pattern has high areas you have to avoid them , Unless you are using a Pneumatic rammer you cannot ram more then about 3 inches of petrobond well, that should pack down 1/2 -1/3 so 3 inch becomes 1-1.5 inches , you do not have to pack the entire surface flat on your first ram, so only use the peel (on smaller molds) if you are doing something larger say 18X18+ get out the Butt and ram flat , then scrap the surface so the next layer of sand adheres to the facing, on your next layer of sand you can fill the mold and heap it high if your running 4 inch flask and finish it off, this does not need to be packed as tight as the facing , but does need to be finished off with the Butt to get a roughly flat surface, you will probably need to add a little sand to the corners before striking off .

    IM getting wordy for no reason
    go watch this

    i explain and show what your looking for , if you are doing small molds just shrink things down

    I will add one thing for everyone Facing sand has twoish definitions, any sand that you use directly against the face of the pattern is facing sand, often professionally is is a special or at least virgin sand riddled into the flask to assure it is free of foreign material, if it is a special sand you may use as little as possible then back it up with Heap

    V/r HT1
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  9. FishbonzWV

    FishbonzWV Silver Banner Member

    My normal routine is to open up the mould in a wheel barrow. I have a tub of oil with a rag in it and I'll use the rag to coat the mixer drum and then scrape the burnt sand into the mixer and tumble. In my mind, I'm adding a little bit of oil to the burnt stuff. Then I'll fill the drum to capacity with the remaining sand. Now adding the glycerin and tumbling for a few more minutes.
    The sand was feeling dried out and not performing like it did. Heating the sand would perk it up.
    When Denis suggested the glycerin, I ran my whole heap through the mixer adding the 2oz/load. Definitely saw a change in the performance. I've never added alcohol.
    Last edited: Jun 28, 2024
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  10. Swiftsure 33

    Swiftsure 33 Silver

    No I'd say my sand looks just about like yours in that video. I'm not making any major effort to separate burnt from fresh sand, but anything that is so charred it doesn't fall off the casting from a few taps of a hammer doesn't seem worth putting back into the load. I'm always working on improving my technique and appreciate seeing how others get it done. Great video! I want to be clear, though, that the issues I'm describing are coming up when ramming the same patterns in the same flasks that I've been using for a while, leading me to believe that there's some problem with the sand itself. Of course, if I can improve my own skills in order to keep the sand going longer then that's something I'm going to focus on as well. I haven't ever felt a need for a separate facing sand. I riddle the first layer straight from my main heap through a fine mesh sieve to remove foreign material and fluff the sand, and have no complaints about the surface quality of my castings.
  11. Swiftsure 33

    Swiftsure 33 Silver

    I see, so the glycerin is exclusively a substitute for alcohol. I'll definitely give it a shot at some point and see if it has a better effect than the IPA.
  12. FishbonzWV

    FishbonzWV Silver Banner Member

    Packed three moulds yesterday. The sand was well behaved. But the sand was in the 80*F range so that could also attribute to the performance.
    Poured this morning after running the vac system for about 2 hours to suck up the Yellow Jackets that built a nest under my shop. Right at the front door and I was in and out 3 times yesterday before I noticed them. The vac is still running and I'm stirring them up occasionally to get the guards. Little bastards, I was stung twice yesterday at the cemetery mowing. They usually don't split their nests until August around here. They're a month early this year.
    Had two mixer loads of breakout and added about an ounce of glycerin to each one and I figure that will do for a while.
    Edit: So for about 220 pounds of sand, I've added 15 oz's of Glycerin. There's still an ounce left in the bottle.
    Last edited: Jul 3, 2024
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