Blending Towers

Someone recently asked if blending towers were used at all facilities where single base propellant  (smokeless powder) was manufactured.  The resident expert, D. Harting, says there were two different processes used.  The DuPont process used blending towers and the Hercules process did not.

Plants using the DuPont process:  Indiana, Alabama, Picatinny Arsenal

Plants using the Hercules process:  Radford, Sunflower, Badger, and probably Cornhusker

In the DuPont process, three blending towers were required for proper blending.  Propellant from three different lots, 50,000 lb each, were transported by cart to the top of each blending tower and manually dumped into a hopper.  The propellant grains were dropped in a controlled manner to the bottom of the tower, then returned to the top of the tower and dropped again.  This was repeated until all powder had been dropped three times. Each 150,000 load was then divided into thirds and distributed to one of the three blending towers where the process was repeated another three times.  This ensured a uniformity in each drum of powder shipped.  Each series of three drops was performed in approximately one shift, so one lot of $450,000 lbs could be dropped every two shifts, an average of 675,000 lbs per day with three shifts working.  The workers were removed from the area while the powder was dropped.  Indiana had 6 blending towers.

Rifle powder required a different group of blending towers with a total capacity of 150,000 lbs.  One rifle powder blending tower was struck by lightning at Indiana, causing a fire which injured two people.

The Hercules drum process was similar in theory but used rotating drums to mix the propellant grains.  Capacity in the Hercules process is approximately half that of the blending towers but could also be used for glazing powder.  In the DuPont process, the Sweetie Barrel was used for glazing and so required an extra step in processing.

The other major difference between the two processes was this:

The DuPont process used Jordan engines and the Hercules process used “beaters.”  More on this later.

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