SS Rod milling media

[DaMounty]

Hi,

 

Wondering what length to cut a 1/2" ss rod into for use as milling media? 2" lengths

 

Thanks in advance,

...DaM

[Nessalco]

I use brass, not stainless, but my rod sections are slightly off 'square' - for 1/2" rod, the sections are 1/2" to 3/4" long.

 

Be very sure your rod is non-sparking. I'm not sure I'd use any steel alloys in a mill for BP. Single chems, sure.

 

Kevin

[CaverCork]

Stainless or any ferrous metal would not even be my fourth choice for milling media, but 1/2 to 3/4".

[DaMounty]

The material and mill jar will be used exclusively for MgAl

 

...DaM

[MadMat]

I won't condone using stainless for milling Mg/Al either, but if you are intent on using it, at the very least try passivating it. The most common way of passivating stainless steel is to soak it in dilute nitric acid with a small amount (2-3 grams/liter) potassium or sodium dichromate. Warm up the solution to around 70 C and allow the media to soak for approximately 30-45 minutes. Rinse, dry and you are at least a little safer.

Edited April 11, 2016 by MadMat

[DaMounty]

What would be an ideal media for MgAl. I'm not stuck on SS.

 

DaM

[lloyd]

DaM,

Any of the 300-series stainless steels should be fine for grinding a non-explosive material.

 

Cut them 'square', so the length equals the diameter. Longer rods are useful when milling fibrous material, but not quite as efficient as 'square rods', which are actually slightly more-efficient than spherical media.

 

However... to prevent contamination from bits of steel that might break off the sharp edges (after cutting), the media should be "broken in" by milling a throw-away material like grain meal or 'grits-o-cob' for about 48 hours before use. Then discard the material, thoroughly wash and clean the media, and it should be ready to use.

 

Gently radiusing the sharp edges on a power-stone before you mill will speed that process. The edges should be gently rounded in order to be safe.

 

LLoyd

Edited April 11, 2016 by lloyd

[DaMounty]

It's 304 Stainless, i'm having them sheared into 1/2" pieces.

 

DaM

[Rkteer]

Can SS media be used for milling black powder?

SS 304 and 316?

[lloyd]

Some have done it, but I wouldn't. Even 300-series SS will spark, and its hardness invites very small impact zones that could cause impact ignition.

 

Lloyd

[Fulmen]

its hardness invites very small impact zones that could cause impact ignition.

I couldn't agree more. The focus on "sparking materials" is in my opinion somewhat misguided. Just try to get two mild steel objects to throw a spark from the type of impact seen in a ball mill, I doubt you'll be able to do so. Sparks from steel are caused from shearing/cutting action where the heat produced is enough to ignite the chip, and such conditions should be fairly rare in a mill. But even completely non-sparking materials can be too hard.

If one focuses on hardness first I doubt if there is a single sparking material left to choose from.