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...