View single post by Keith Pashina
 Posted: Sat Apr 1st, 2017 09:17 pm
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Keith Pashina


Joined: Sun Nov 4th, 2012
Location: Minneapolis, Minnesota USA
Posts: 761

Rod mills inside the Frontenac/Iron City Mill. Not available as a kit anywhere, but it wouldn't be hard to scratch build models off one

Another illustration of a rod mill
To also get the ores to a uniform size, and smaller than what stamp batteries and jaw crushers would provide, other crushing and grinding equipment was used – this was not all that common in the Gilpin Tram era, and seems to be a “modern” technology that came in in the 1900s. The large Iron City/Frontenac Mill did have this equipment, and maybe others did, too. Three types used were:
·       Ball mills
·       Rod mills
·       Chilean or Huntingdon Mills
Ball mills are a horizontal rotating metal cylinder, filled with large metal balls. As ore slurry is fed into one end, the gradual grinding action crushes the ore to a fine sand or powder like consistency.  Rod mills were also horizontal metal cylinders, but filled with metal rods, similarly crushing the ore.  The type of mill, speed of rotation, etc. were generally customized to the ores being processed at the time – there didn’t appear to be one universal standard.

A small ball mill, Russell gulch area

Once ore was concentrated further, where it went next for processing depended on the ore’s chemistry and mill practices. The concentrates might be run through more bumping, Wilfley, Card or other tables, or vanners, or jigs, or… From my limited reading, it seems sometimes one bumping or Wilfley table would be set up to process one very limited size of concentrate, and paired with that would be another one for the next smaller size, and so one. So, there could be multiple lines of concentrating tables lined up in a mill. Some photos seem to show two levels of tables, one row above the other, to do this.
But, not all ore went back onto tables, some of it, again depending on the mill and its practices, went onto final grinding and amalgamating.

A ball mill, this one with a conical shaped end

The inside of a partially dismantled rod mill - protective plates lining the metal barrel have been partially removed, and so have the steel rods that rolled around and crushed the ores

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