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Thread: K-bond versus Petrobond sand - one users experience

  1. #1
    Senior Member 4cylndrfury's Avatar
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    K-bond versus Petrobond sand - one users experience

    So most people here know the difference between "greensand" and "oil sand". Ive never used the former. But I have used a k-bond recipe for many years, and have had good successes with it, right from the start.

    The K-bond recipe I used comes from THE RAY VIN FOUNDRY PAGE. I used real Bentone 34 clay, play sand, Isopropyl rubbing alcohol, and fully synthetic 2 stroke oil in place of the additive free stuff mentioned specifically in the linked page - 2 stroke was mentioned some time ago in the old forums as having less additives than traditional motor oils, so thats what I went with. I mixed the clay and sand together in a 5 gallon bucket - about 20 lbs of mix at a time, using a concrete mixing paddle in an electric drill. I then added the oil slowly, mixing by hand with a wide paint scraper, and smearing the mix against the wall of the bucket, spraying rubbing alcohol from a little hand sprayer - about 20 min per 20lbs. A high level of green strength was achieved almost immediately, and without the use of a traditional muller. Subsequent use has not inhibited green strength, though regular maintenance has been required: several re-applications of alcohol every several months as it evaporates, and 2 separate additions of a few fluid ounces of oil to replace what little is burned away with aluminum casting.

    I recently had the opportunity to acquire real Petrobond II clay, and the specified base oil. PBII requires no catalyst, so oil, clay and sand are all that are required. I was anxious to mix up some, but I do not have any fine mesh silica sand. I decided to just make up 2 or 3 lbs of PB sand. I did the math, mixed the proper ratios (within reason - my analog scale and standard mixing cups offer questionable resolution, but Id imagine I achieved less than 5% deviation from published ratios). I again mixed the dry ingredients in a plain bucket for several minutes, then slowly added oil as I smeared the mix against the wall.

    The results were less positive than my experiences with K-bond. Green strength appears to be little more than wet beach sand. the hand-squeeze test yeilded a poor break line with crumbled sand falling off the clump with almost no effort. I tried adding more oil, which made little difference. I added more clay to offset the oil, and again almost no effect. I sprayed some alcohol into the mix as there is supposedly no ill effect to adding PBII to a heap of original Petrobond sand. Again, little effect. I let the pile sit for 2 days - with traditional water based greensand, often, some time left idle will allow the mix to temper - letting the water dispers through the mix naturally. This had little effect.

    I tried to think logically and rationally - working my way through the variables. The sand is the literally from the same bags. The naked eye properties of the Bentone vs PBII clay appear to be the same (same density, same texture and mesh size). My methods were the same. The main difference I can see is the oil. Synthetic 2 stroke oil is rather thin - like 2% milk - almost watery. The PBII oil is thick - like gear oil. Im guessing the difference is tied to the difference in viscosity.

    In the past, several users have asserted that the use of oil bound sand is not possible for any length of time without access to a decent muller - one with both fluffing and smearing action. BobS, W3, HT1, Dallen, as well as others have all vouched for this statement. I have always disagreed - my personal experience with K-bond oil bonded sand proved otherwise. I now think I know why we disagreed - its the oil, or specifically, what is needed to disperse the oil/clay mix evenly onto the sand grains.

    To the best of my knowledge, there hasnt been any definitive analysis done by a forum user having access to both types of oil sand - If Im mistaken, please post references.

    My initial analysis is that higher viscosity oils will require more (powerful or time) mixing methods than thinner oils: A=X/Y where A is the desired result (full dispersion of th eoil within the mix), X is the force available (more with a muller, less if done by hand), and Y is the time necessary (less time with a muller, more by hand). I plan to try to mix 1lb of sand with the available Bentone 34 I have left on hand and the heavier oil, and a 1 lb batch of sand with some PBII clay and synthetic 2 stroke. I will "mull" both batches the same way I have that yielded success in my initial mixes - by hand in a bucket. If the PBII clay/2 stroke sand is able to achieve high green strength as measured by the hand clump test, or better green strength than the Bentone 34 and heavy oil mix, I would say that my analysis will have answered the question: Is a muller REQUIRED for mixing/maintaining oil bonded sand? My hypothesis is: A muller is not required for mixing/maintaining ALL oil bonded sands, just those mixed with a heavy gear oil.

    more to come...

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    Senior Member Robert's Avatar
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    I think time is a big factor too. For example, my petrobond was great right out of the package and had good strength for a few weeks. After it sat for a few weeks more in a sealed bucket it was dry and crumbly. Mulling and heating was required to get it back to normal. I did not need to add oil or catalyst. I don't think you can really do the experiment without letting the sand sit idle for a few weeks.
    R
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    Senior Member Bob S's Avatar
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    Your study may be correct, however, if I could buy full synthetic 2 stroke oil at a decent price I would go with it too. Over my years casting I have used over 300 gallons of base oil mixed with my petrobond sands. My last purchase for a 110 gallons of base oil which has been over 4 years ago now cost me $3. a gallon or a $175 for each of the two 55 gallon drums with drums being thrown in. For the same money I could only have gotten 14 gallons of the synthetic oil compared to the 110 gallons of base oil. This were the muller pays off, no real labor or time wasted and with cheaper oil.

    Don't get wrong I know I have a larger backyard foundry then most and have to use a bigger picture on my material purchases then those with a small hobby setting were time is not as important. At some point, however, the person has to make the call, hand mix with expensive oil or mull with cheap oil with a decent muller. I have never questioned the quality of my sand mixes or the casting I get from using it. If I were in a situation where I only needed to mix a couple pounds of sand to complete casting I too would use the more expensive oil in place of the base oil without the muller, especially if the item cast was just for myself and not for retail sales. I would also like to find a location for the Bentone 34 you are using also since I'm sure it can be gotten at a lower price then the trademarked Petrobond II is now going for. Bob
    I used to spend my time to save money but now I'm willing to spend my money to save time.

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    Senior Member 4cylndrfury's Avatar
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    FWIW, Bentone 34 is going for more than $4/lb - and that was a few years ago when I was last in touch with a distributor. The person I got the PBII clay from mentioned a lower cost than that, though they picked it up, so with shipping mixed in I cant say which one wins out...Also, Tixogel EZ is another amine treated clay used in oil industry that is supposed to work for foundry sand as well, but I never heard back from Southern Clay Products about a distributor in my area that I could contact to get a quote.

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    Senior Member Essej's Avatar
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    I looked into getting some bentone not too long ago- $5.94/#, sold in 50# bags, shipping not included and the nearest distributor was 582 miles from me... that made my decision to go with petrobond instead an easy one I got 210 lbs ready to use -140 mesh petrobond from chasft123 shipped to my door for less than it would have cost me for one bag of bentone... I think too, if one's really going to get into casting, no matter what molding sand you use, a muller is a wise investment...
    Last edited by Essej; 01-23-2013 at 04:18 PM.

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    Senior Member 4cylndrfury's Avatar
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    lol...yeah, Im beggining to think the DIY approach to foundry sand is not the best when you really start to break it down.

    The flat rate boxes from chasft123 are looking better and better...its just that I actually have some of this clay already...

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    Senior Member Essej's Avatar
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    The flat rate boxes from chasft123 are looking better and better...its just that I actually have some of this clay already...
    Yeah, at first I was hesitant to spend that much money on molding sand... but after researching other options, and even looking at sourcing my own petrobond supplies, the flat rate boxes looked a lot better. While I may have been able to put my own petrobond supplies together for less money, it would have been a lot more of a hassle; a lot more running around and a lot more time... I definitely understand wanting to make use of what you've got though...

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    Senior Member SolarFreak's Avatar
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    Any moisture in the sand? That could affect it, possibly. What kind of sand are you using? Mesh estimate?
    I seem to have accumulated so many things that I need, that I have no space left to use them in...
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    Senior Member 4cylndrfury's Avatar
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    my guess is up in the 80-90 range. Its just regular clean play sand. Probably no or VERY minimal moisture in it - Ive had it forever now. But Im thinking a touch of moisture in it shouldnt hurt...alcohol catalyst in PBI and Kbond sand is part water, so Im not really factoring moisture into my theory too much.

    Im thinking though the extreme cold could be a factor too now that Im thinking of it - less than 40 in the garage the last couple of days, that could effectivly make the oil even thicker than it already is. I thought about heating the small batch Ive got made up with a propane torch as I mix and mull, see if that helps.

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    Senior Member Robert's Avatar
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    Heating it will make a big difference! Try it.
    R
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