What is the "right" amount of moisture for greensand?

Discussion in 'Sand Casting' started by Tobho Mott, Jan 15, 2018.

  1. Tobho Mott

    Tobho Mott Gold Banner Member

    I guess the amount and type of clay in your sand would probably also affect the amount of water that is needed to get the desired green strength.

    People above were talking about numbers more like 3-5% to 5%, now you're talking about 15 and up... Is that also a percentage you're referring to?! I'm still waiting to test the cheap moisture meter I ordered off Amazon on my sand once spring actually gets here, but it keeps being freezing cold out, so I haven't bothered yet. I'll make sure to try and remmber to post about that here when the time comes to get the molding bench opened up again... Chirpy AKA Cae2100 who gave me the idea to order that meter told me that for best results he uses his similar meter to aim for about 4% moisture in his sand.

    Jeff
     
  2. Melterskelter

    Melterskelter Gold Banner Member

    Yes, I'm talking about per cent water figured by dividing
    (Wet weight minus dry weight) by dry weight.

    So for example 16 oz wet minus 15 oz dry divided by 15 oz dry would give 1/15 or 6.6 per cent.

    I do realize there will be a lot of variability in sand formulations and so also in moisture content. But it could be interesting to see what folks are actually using.

    I think cooking method is more reliable than a moisture meter for comparisons from one person'a formulation to another as the meter reading would be influenced by that formulation. A meter MIGHT reduce the guess work providing a measurement on a given formulation from one batch to another.
     
  3. Tobho Mott

    Tobho Mott Gold Banner Member

    Still, that's quite a difference: 3-4% with a meter vs. 15-17% by cooking the water out... Took me by surprise is all.

    Jeff
     
  4. Melterskelter

    Melterskelter Gold Banner Member

    Me too! Which is one of the reasons I brought it up. I think it might be interesting to see the range of what people are using. This information may be helpful to folks ( like me) who are new to green sand. Is 6 % a commonly used content? Is it a real content or a moisture meter reading that may not be particularly accurate? It could reduce confusion to know the answer.
     
  5. Melterskelter

    Melterskelter Gold Banner Member

    Out of curiosity I bought a garden moisture meter to hopefully use as a quick and simple way to determine the moisture in my foundry sand. My conclusion is that the meter is positively worthless as the reading I get is totally dependent on how hard the sand is packed. As my sand came from the muller quite "fluffy" and with desirable moisture by the squeeze test, it tested 1% moisture unless I packed it down some then it was 5% and packing more resulted in a 9% reading.

    I know from prior baking out of the moisture that my sand runs considerably higher than 9% in fact. So, maybe I am doing something wrong, but I think the moisture meters aren't going to be of much use as a means of even roughly approximating moisture content let alone accurately determining sand moisture. Disappointed.
     
  6. HT1

    HT1 Gold Banner Member

    3 - 5.5 % moisture is the answer as far as moisture testing, https://www.ebay.com/i/382434218709?chn=ps&dispItem=1 here is the correct tool at a really nice price if it still works...

    but really the most likely issue is mulling, I played with green sand when I was first starting hobbyist work and quickly realized I would never be able to get consistent results without a muller... BTW professionally the only place I ever used a moisture tester was in school, in the shop we did the squeeze test... if it got too wet you mulled it longer and parked the muller under a vent .. if you torch off the mold face before closing and have good venting... and yes you need vents in the drag, and your bottom board especially if you use metal must have holes to let the moisture get away... wood will absorb enough water most of the time... dont risk it, drill holes in a nice bullseye pattern...

    V/r HT1
     
  7. crazybillybob

    crazybillybob Silver Banner Member

    The cheapy mosisture meters look at the electrical resistance of the soil. The theory is more moisture the lower resistance. This works well for plants as your looking at medium moisture (15% -20%) and semi-packed soil. But it gets a little squirrelly when you get into the lower moisture areas with variable soil/sand compaction. The style of meter that HT1 has linked is much more accurate, but much more expensive as well. The best procedure for the cheapy digital ones is figure out what good sand is for you and test it.... write down that number and shoot for it each time you mull or temper your sand. But make sure the sand is in the same state each time you test (relative temp, compression, etc).

    CBB
     
  8. Tobho Mott

    Tobho Mott Gold Banner Member

    That's about how I'm now planning on using my cheapy garden moisture meter, especially having read these recent posts about how the amount of compaction affects readings. Ie. I'll take a reading in the molding bench when I think it's a bit dry and one right after dumping out the muller. Or maybe I'll make a tiny flask and use it rammed up hard just for taking readings from. Mostly as a curiosity really - I'm getting more experience with each mold, so I'm sure I'll get better and better at just knowing it's right by feel alone.

    Jeff
     
  9. Melterskelter

    Melterskelter Gold Banner Member


    What you just described, a method to follow my own sand from batch to batch was exactly what I had in mind as I realized the absolute number was less important than just comparing the moisture content of one batch to another. The rub is that compaction of the test sample so strongly influences the reading. That dependence on compaction means you’d have to have a standardized compaction to measure with the garden moisture meter. As near as I can tell that makes the garden meter useless. I’ll play with it a bit more. But it does not look hopeful

    I have still been hoping someone(s) would actually take a pound or so of their sand and stick it in the oven and weigh it pre and post baking. Doing so caused no odor and no complaint from my long-suffering wife. It requires only the most basic equipment and provides data that can be trusted.
     
  10. Melterskelter

    Melterskelter Gold Banner Member

    I agree that it is common practice to go by the feel of the sand. And that obviously works pretty well. On the other hand, I also know that discriminating relatively small variations in sand moisture content from day to day has to be an inexact science since many factors like how tired or distracted you are has to influence your judgement.

    I suppose I am spending more time thinking about this than may be truly necessary. But to some extent I have noted as a practical matter that getting the moisture just right helps my pattern pull cleaner and has a definite influence on surface finish. With a lot of effort and some failures I have been able to get a fairly fussy pattern to make good molds. But I sure wish I could calibrate better (than by feel) an important variable in that process.
     
  11. Tobho Mott

    Tobho Mott Gold Banner Member

    That is much along my line of thought upon starting this thread. Personally, it costs me nothing to stop and overthink the minutiae, as I am strictly a fair weather hobbyist in this for fun and to learn (for now anyway). If I were casting parts for profit, that might not be true.

    However, if that were the case, I'd hopefully be pouring more often than just the one mold per non-rainy non-snowy weekend at most that I'm able to find time for now, so I'd already have mastered that feel for when the sand is just right and would not have had to ask... :D

    Jeff
     
  12. Melterskelter

    Melterskelter Gold Banner Member

    One more step in trying to figure out the true moisture contented of foundry sand:

    I went to a local foundry that is now in its more than 100th year of operation and grabbed a simple of their sand. I weighed out 455 gms and then baked it at 350 for 2 hrs spread out on a small cookie sheet. Dry weight was 385 gm. So his moisture content is 18 percent based on dry weight. This casts further doubt on the 6 per cent figure that is often quoted.

    Sure would be interesting to hear what other people measure using the bake-out method for their sand. Meters not allowed. ;-)
     
  13. DavidF

    DavidF Administrator Staff Member Banner Member

    Ive been reading this thread for a bit now but have been reluctant to comment. My thoughts are that you can not give a moisture percentage and have it be an accurate correct for all number.
    Green sand should have just enough moisture to be able to pack it and break cleanly, not crumbly.
     
  14. J.Vibert

    J.Vibert Silver

    Exactly... Attempting to derive a usable number for one "blend" of greensand would be great for the owner(s) of that blend, and no one else. ...and then you'd have to have a stringent test protocol that everyone would have to follow.
     
  15. HT1

    HT1 Gold Banner Member

    524242DE-54FF-4795-B27D-AB9EB14BFD5F.jpeg Here is the US Navy’s procedure ... enjoy.. keep in mind while you are doing this your sand is drying out

    V/r HT1
     
  16. HT1

    HT1 Gold Banner Member

    Oh everyone please let me know how your wife feels about you baking sand ... 4.4 lbs of sand in her oven
     
  17. Melterskelter

    Melterskelter Gold Banner Member

    I agree that there is no way to give a single "right" number, but, let's not be telling newbies that 6% is any sort of guideline if it is likely to be way off the mark or is not based on any first-hand measurements. My intent is not so much to say that any given number is the right number. I would have liked to establish some sort of range though. That could only be done if some folks actually measured what works for them. I suspect that it is likely that a ballpark figure is much higher than 6%. All I can report myself is that on the sand I am using and that that came from a well-established foundry around 18% is what I have observed. It would have been interesting to see what the range really is. But I will drop it since there seems to be zero interest in finding the range.

    And my observation is also that baking green sand causes no noticeable odor. No need for 4 pounds really, as it is more convenient on my gram scale to measure roughly 500gm quantities. My wife, was curious about the sand, but raised no objection as there was no odor and no mess.
     
  18. HT1

    HT1 Gold Banner Member

    A large sample is required for accuracy..
    You will get odors based on the contaminates and binders in the sand , if you have a cereal or wood flour in the sand, you will get an odor, I think it is pleasant, but my wife would find it overwelming.

    Lastly, and I think i went into this before. but Again, moisture REQUIREMENTS varies based on the binders in your sand, if you are using both Southern and western Bentonite, in their recommended ratios, , about 50/50, and your sand is properly dry mulled, (dry mulling distributes the binders evenly on the sand grains) 3-6 % moisture is pretty normal, if you are only using kitty litter clay, not particularly well ground up, and cannot properly dry mull, you will need more moisture to get the proper "feel" to your sand... But the sand will be too wet, and is likely to not have all the property's you desire, I believe hot strength will be lacking, if you used too much clay, which is likely as you try to get the sand drier feeling while still compacting properly, you will get gas issues, because the porosity of your sand will have went way down... with proper molding techniques... Venting, and face drying you can overcome those issues.

    There are a lot of issues at play... really more than a hobbiest wants to dig into... for instance, after you use your sand how much moisture remains???? you need to know that so you can add the proper amount of water to your muller... at the same time you have to know the exact weigh of the sand in your muller. In the Navy in a professional Foundry with all the test tools available this was over whelming... your process would be:
    1. weigh the sand into the muller (300 LBS)
    2. test for moisture ( for example 3% You would expect it to be dry after use)
    3. weigh and add water to the muller...( we want to add 3%... so just shy of a gallon... feel free to check my math. because that sounds like to much)
    4. test for moisture again... if the sand is good start making molds.


    Here in FL on a normal day my sand might get too moist to use, because the humidity is so high... Had that problem in Japan, literally had to dry the sand before use...

    Enough

    V/r HT1 out
     
  19. DavidF

    DavidF Administrator Staff Member Banner Member

    FWIW, we have a scale in the lab used for measuring moisture content in small samples. The scale is about the size of a silver dollar inside a glass case about the size of shoe box. You put your wet sample in and record the reading, then turn on the heater (located in the scale) to dive the moisture out and record the reading. It only measures the weight, and its in a glass case because any air movement effects the reading....
     
  20. Melterskelter

    Melterskelter Gold Banner Member

    Probably you have something like this:
    upload_2018-4-16_5-14-39.png

    Yes, nice to have a super-precise scale capable of measuring to thousandths of a gram.
    But, in my case I used a simple balance beam lab scale though a simple digital kitchen or postage scale provides more than adequate sensitivity and precision for measurement to +/- 1% moisture content.

    Care to share what sort of percentage moisture you have found in your particular sand mix?
     
    Last edited: Apr 16, 2018

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