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clearly_not_atara
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[*] posted on 8-2-2020 at 20:20
machine for grinding cement?


I’ve been trying to make a Sorel-type cement using reactive magnesia with potassium tetraoxalate. I have the chemicals but generally cement needs to be ground to a fine powder. The magnesia is ground already; it’s a bit old so I hope it hasn’t gone bad, but it is dry and sealed at least.

I have a budget in the low three figures, hopefully. Potassium tetraoxalate has a pH of about 1.6 in contact with water, solubility 2.5% w/v. What kind of milling machine could I use?




[Edited on 04-20-1969 by clearly_not_atara]
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Sulaiman
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[*] posted on 8-2-2020 at 22:52


before parting with lots of cash maybe a few small scale tests first ?
. as-is usage of materials
. a quick or long pulverisation in either an electric spice mill or coffee mill/grinder
. grinding to various degrees of fineness using a mortar and pestle

... no point getting a top-of-the-budget mill if not necessary.

P.S. what scale are you intending to work at ? (g, kg, tonnes etc.)





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[*] posted on 9-2-2020 at 05:10


Quote: Originally posted by clearly_not_atara  
I’ve been trying to make a Sorel-type cement using reactive magnesia with potassium tetraoxalate. I have the chemicals but generally cement needs to be ground to a fine powder. The magnesia is ground already; it’s a bit old so I hope it hasn’t gone bad, but it is dry and sealed at least.

I have a budget in the low three figures, hopefully. Potassium tetraoxalate has a pH of about 1.6 in contact with water, solubility 2.5% w/v. What kind of milling machine could I use?


Apparently potassium tetraoxalate does exist. Its a potassium hydrogen oxalate with a molecular of oxcalic acid and two of water, KHC204)(HC204).2H20

I could not find anything on a K Mg oxalate cement. Do you have a link to it?




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Deathunter88
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[*] posted on 9-2-2020 at 12:56


Ball mill (like the ones for black powder production).
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clearly_not_atara
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[*] posted on 9-2-2020 at 19:56


Quote: Originally posted by Sulaiman  
before parting with lots of cash maybe a few small scale tests first ?
. as-is usage of materials
. a quick or long pulverisation in either an electric spice mill or coffee mill/grinder
. grinding to various degrees of fineness using a mortar and pestle

... no point getting a top-of-the-budget mill if not necessary.


This is certainly an attractive idea, but even Portland cement, which I would think is the gold standard, requires an average grain size of about ten microns to form a strong bond. I don't think I could get there with a coffee grinder and a mortar/pestle is a weak maybe, although I guess I should probably try it.

Quote:
P.S. what scale are you intending to work at ? (g, kg, tonnes etc.)


I'm at gram scale right now, if early experiments are promising maybe low kg scale. One interesting thing about magnesia cement is the ability to make fiberglass composites without using alkali-resistant glass, or so I understand.

Quote:
Ball mill (like the ones for black powder production).


I was of course considering a ball mill, but there are so many different kinds! I'm not sure what kind to get, although I imagine potassium tetraoxalate isn't hard to grind, apart from it being mildly corrosive (acidic).

I was really hoping someone could recommend a product :D




[Edited on 04-20-1969 by clearly_not_atara]
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Herr Haber
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[*] posted on 10-2-2020 at 04:21


The Lortone ball mill works great for me. These can be found almost everywhere.
I have yet to grind really hard things though.

It's not inexpensive but I suppose that dépends on how much you are willing to invest.
I've found a few more uses to it that I first had in mind.




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clearly_not_atara
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[*] posted on 10-2-2020 at 06:51


HH: I looked around and Lortone describes its mill as a "rock tumbler". There are many reports of it being used as a ball mill, but some people mention that most grinding media are too heavy and it won't run when it's full of steel balls.

What kind of grinding media do you use in it? Have you had any issues with power -- and have you replaced the motor, as some pyrotechnics people do?




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 10-2-2020 at 13:20


If you are moderately handy and have the space, build a ball mill. The pyrotechnics community is full of amateurs building them. These are simple and reliable mills that can run optimally with any media, just ignore all the extra precautions they take due to the explosive nature of black powder.

Ball mills are extremely flexible, Lloyd Sponenburgh popularized the modern design using standard industry formulas that was known to all in the industry.

And those mills are a f*cking horror to behold. They're downright huge, EXTREMELY LOUD and spinning at a very uncomfortable rate for their size. And the fastener bolts for the wear plates makes it look like a meat tenderizer from hell.




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Sulaiman
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[*] posted on 11-2-2020 at 03:31


Quote: Originally posted by clearly_not_atara  
... but even Portland cement, which I would think is the gold standard, requires an average grain size of about ten microns to form a strong bond. I don't think I could get there with a coffee grinder and a mortar/pestle ...


A quick google search indicates that <=10um particle size should be achieved with 15 to 120 minutes of grinding in a mortar and pestle,
dependant upon the material,
I did not notice a specifically applicable time for your materials..




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[*] posted on 11-2-2020 at 04:21


Quote: Originally posted by clearly_not_atara  
HH: I looked around and Lortone describes its mill as a "rock tumbler". There are many reports of it being used as a ball mill, but some people mention that most grinding media are too heavy and it won't run when it's full of steel balls.

What kind of grinding media do you use in it? Have you had any issues with power -- and have you replaced the motor, as some pyrotechnics people do?


Indeed, it is a rock tumbler but seing a lot of people used it as a ball mill I got myself the smaller model.
So far I've used only alumina media. It works fully loaded but I dont doubt that the reports you saw about steel media are accurate.
I've had it running for 8 hours continuously and though it heats up in the first 30mn-hour it doesnt get any hotter.
I might have to change the motor if steel media are too heavy but at the moment I'll just stick with grinding a little bit longer with my Al2O3 media.

The quality of the drum is remarkable (got a second one for oxidizers).
If I hadnt been so convinced by the drums I would maybe have made one.
One thing to think about if you build one is that you wont want to be near it while in operation. It is noisy ! I suspect a homemade one with an HDPE drum will be even noisier.




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[*] posted on 22-2-2020 at 01:58


i just wanted to chime in and say if youre after protecting steel, which sorel cement appears to do, its a lot easier to just throw a bunch of sodium silicate on the steel

as for achieving specific particle sizes i would highly recommend you to sift the materials, even just through a 150 mesh screen will do wonders, a vibrator may be attached to the sieving container so you dont have to manually squeeze it all through, ive have produced black metal powders using 150 mesh screen just to discard the larger particles (black metal powder is somewhere around 1000 mesh)




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[*] posted on 22-2-2020 at 02:26


Actually sorel cements are considered incompatible with steel due to the moderate pH and high chloride concentration.



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clearly_not_atara
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[*] posted on 22-2-2020 at 06:38


Chloride is indeed bad for steel. But Mg-oxalate cement contains no chloride except impurities; oxalate is protective. So I think it would be okay. But protecting steel is definitely not the point. Concrete already does that!

High pH is good for steel. Low pH is bad. But MgO cements have a lower pH than CaO, which follows the trend of the oxides.

I'm more interested in protecting fiberglass. Portland cement's high pH will dissolve fiberglass. That's why alkali-resistant glass exists:

http://en.wikipedia.org/wiki/Alkali-resistant_glass
http://en.wikipedia.org/wiki/Fibercement

ARG contains lots of Zr which makes it too expensive for most applications. If you could make a cement that doesn't attack fiberglass, glass-cement composites become much cheaper.




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 23-2-2020 at 05:39


couldnt you coat the fiberglass with .. maybe glass, like sodium silicate? how would sodium silicate work with fiberglass? maybe just regular paint would do? maybe the fiberglass (unless its already made) could be made with different materials, different type of epoxy?
i think if you want to strenghten the material you can just get some plastic nets and add that, supposing youre after the fiberglass because its lightweight, only plastic that isnt really happy with high pH afaik is PET and PVC




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clearly_not_atara
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[*] posted on 23-2-2020 at 07:20


Antiswat: Stabilizing fiberglass in concrete has been the subject of intense research for decades. I'm not going to pretend to compete with that. All I know is that it isn't easy. Coatings don't work. Silicates don't help, cement is already full of them. See:

https://www.concretenetwork.com/glass-fiber-reinforced-concr...

Polymers generally aren't stiff enough. In order to provide tensile reinforcement, it's not enough to be stronger. The fiber must have a higher Young's modulus than the matrix, or the matrix will stretch first. But polymers are generally soft and extensible. The only really stiff polymer is UHMWPE and it sucks in composites due to low adhesion.

Fiberglass is better than say carbon fiber because it's cheap. The only real alternative here would be basalt fiber, but I don't know if that's actually alkali-resistant, and it's already new tech.

[Edited on 23-2-2020 by clearly_not_atara]




[Edited on 04-20-1969 by clearly_not_atara]
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[*] posted on 23-2-2020 at 17:17


Ball mill is good if you are going for small particle size; however, a rod mill will deliver a more consistant productinterms of size distribution. However, since your budget is low, you will probably need to live with a ball mill. I wouldn't worry too much about corrosion since it will not take long to grind. Also if you dry grind then you are really in good shape.
I would also really consider using a motor if all you are doing is some initial screening- I am always suppressed how consistent manual labor can be if one tries.




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[*] posted on 26-3-2020 at 15:56


I asked a seller and say ball mill machine can break upto level 4 as in the Mohs scale. I need to break 6 and up... so not enough. What hardess have your cement?
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