My modified ball mill using brass balls

[MinamotoKobayashi]

Hello forum.

Sometimes ago I ordered this ballmill from Pyrocreations:

 

http://www.pyrocreations.com/image/cache/catalog/products/3_LB_MILL-500x500.gif

It has an internal barrell diameter of 103mm and a capacity of 0.8l.

The working voltage is 120V, but since I live in Italy, I was forced to buy a transformer 120 -> 220V

The first issue of this very cheap ballmill was the rotation: only 45 RPM!

Reading some infos on this site:

 

http://pyrodata.com/definitions/Ball-mill

 

and on this other site:

 

https://www.911metallurgist.com/blog/ball-mill-critical-speed

 

I have understood that the rotation was really too low, so following the hints of this link:

 

http://www.skylighter.com/fireworks/how-to/ball-mill.asp

 

I have modified my ballmill adding two thick and soft washers around the rotating axis:

 

 

Now the rotation is about 72 RPM .. not an optimal speed (the ideal rotation should be 93 RPM),

but surely better than before

 

As milling media I did a madness: I bought a very very expensive set of 100x15mm brass balls and

20x10mm brass balls: heavy, totally spark free, and without the chance of powder contamination

as happens with lead balls.

 

 

Again, the balls diameter was not the optimal one (optimal: 12,5mm),

and also the ball numbers was not perfect (optimal :125 balls).

 

The medias occupy about the 40% of the barrell, while the optimal charge is 50% of the whole barrell,

but since the total weight of the balls is about 2KG, I preferred not to overload further the engine.

 

 

I filled the barrel until the KNO3 had totally covered the balls:

 

 

and I actioned the ballmill:

 

https://youtu.be/tItkA30KNHw

 

Since my modify has increased the engine effort, I putted a powerful fan near the cooling fins to improve

the air circulation.

The first try was a real disaster: the KNO3 probably was slightly wet (and I do not use KNO3 with anti-caking),

so after 30 minutes all the powder was totally compacted against the end of the barrell.

So I have dried the KNO3 with my ventilated oven at 100° for 1 hours, then I have milled the powder for 1 hour:

the results was fantastic, the powder was extremely fluffy, very similar to the talcum powder!

 

---

 

Since I do not have often access to open spaces, and I need to make good BP indoor,

I have developed a strange solution to create a good BP indoor safetly:

 

 

Formula for 200 gr. of BP

---------------------------------

 

1. 75% potassium nitrate

30% airfloat charcoal

Mix for 4 hours in the ballmill with brass media;

2. 75% potassium nitrate

20% sulfur

Mix for 4 hours in the ballmill with brass media;

3. Mix the two compounds in the ballmill WITHOUT the brass media for an hour.

Of course between the first and the second step the barrell and the medias must be carefully cleaned!

So now I wish to hear some impressions and advices from the expert pyro users about

the two above mentioned solutions. Every extra hint will be really appreciated!

Thanks from Richard.

Edited July 4, 2017 by MinamotoKobayashi

[OldMarine]

DavidF will be your guru on this subject since he has the book but hasn't put it between covers yet.

[Mumbles]

First of all, the modifications and media both look good.

 

However, both of those mixtures are probably flammable, so you really aren't doing anything any more safely. The nitrate and charcoal one likely is at least. This general method you mention, with milling two separate mixtures can be done though. Typically it's done with the following ratios.

 

Mix 1:

75 parts KNO3

5 parts Charcoal

 

Mix 2:

 

10 parts Charcoal

10 parts Sulfur.

 

The charcoal helps to keep the nitrate from caking, and is a non-flammable mixture. The second mix is just everything that's left over. Milling with too small of a load is also relatively dangerous as it increases ball on ball impacts. Even if it the mixture isn't sensitive or flammable, it's still going to be hard on the media. Typically you can mill a few batches of mix #1 for every batch of mix #2. After you have both sets milled, you screen them together. You can tumble them like you have been, but you'll get just as good of mixing if not better by screening and it takes significantly less time.

 

Here are a few other links that may be of interest to you. You don't mention what sort of charcoal you're using, but the "hotter" the charcoal the better. Woods that are lightweight and fast growing tend to be best. In the US things like willow, paulownia, alder, cotton wood, etc. tend to be popular. I don't know what is local to you, but I do know that Alder Buckthorn is popular in Europe. Some vine charcoal is also pretty good, though uses a slightly different ratio.

 

http://www.amateurpyro.com/forums/topic/12403-3-component-vs-individual-milling/

http://wpag.us/learn/How%20To%20Make%20Black%20Powder.pdf

[MinamotoKobayashi]

Hi Mumbles, thanks a lot for the hints and for the links!

So, since the 10 parts of sulfur and 10 parts of charcoal occupies too few space in my ball mill, it is useful to prepare

much more compound and store it in a vacuum container with silical gel ready to be used later?

 

I have a 20mesh sieve .. it is enough to screen well the two compounds?

 

I use the airfloat pine charcohal from Pyrogarage. It is a good quality charcoal, very fast.

[insutama]

I have the duel drum ball mill but same brand as yours

I have never done any modifications to it so it still spins slow but when i mill my BP for 4 hrs shaking it real good halfway i get very fast bp and thats turning at original ball mill speed.

 

Would my bp be any faster with the correct 90rpm or would the mill time just be less?

[lloyd]

Both, Insutama. The steeper incidence angle mills faster because of more impacts per fall, and since the fall distance is greater, the impacts are more-forceful, resulting in smaller particles.

 

I read that you had 'mixed sizes' of media. A ball mill is most efficient when all the balls are of the same size. Otherwise, the larger media spends some of its energy milling the smaller media.

 

Lloyd

Edited July 10, 2017 by lloyd

[insutama]

What about if i speed up my ballmill with the same drum will that increase powder speed or just milling time ?

[lloyd]

Both. For a given size of jar, the optimum RPM will give you both faster AND better milling. The 'fall distance' is based upon the 'break angle' of the pile of balls, not the diameter of the jar.

 

Lloyd

[insutama]

well i think its about time i do the modifications to my ballmill

[DavidF]

Since you guys are using rock tumblers, you might want to check out the last page of Ball milling FAQ in the Newbie section. There I provide details on what I do to produce black powder with such an item.