Graining Mill and Tram. Hagley Museum.
by Chris Kusik
Title
Graining Mill and Tram. Hagley Museum.
Artist
Chris Kusik
Medium
Photograph - Digital
Description
This structure built between 1822-1824 is called a "graining mill". The Dupont Company, manufacturing gunpowder installed roll mills in which 8-ton vertical rolls mixed saltpeter, sulpher, and charcoal grinding and shearing them as the heavy rolls turned. The powder was then pressed to increase its density. Hydraulically powered horizontal presses, developed by Lammot du Pont, a grandson of the founder, replaced early vertical screw presses driven by hand. Sorting and classifying the resultant powder cake by size took place in the graining mill, again with mechanical methods, originally with leather sieves and later using rotating classifiers called bolters. The moisture added to powder in the incorporating process was reduced to 1⁄2 of 1%. Originally this was done on dry tables or in dry houses. Later improvements combined drying with glazing. The rough edges of the powder grains were smoothed off in the glazing mill. In the pack house, workers gave the powder a final screening, and then packed it into wooden barrels for shipment. Extensive granite outcroppings in the valley provided the stone to build the dams, raceways, and mill buildings. On three sides the mills had heavy stonewalls up to three-feet thick, well buttressed, while the riverside and the roof were of light wood. This design vented the force of explosions toward the river and sky and away from other structures.Raw materials were transported on a narrow gauge railway network that laced back and forth up in the bluffs. Horses and men pulled the small freight cars on rails that were made of wood near the buildings,
to prevent sparks. In later expansions, steam engines drove cable
drums that pulled cars to the processing buildings higher on the bluffs.
Uploaded
July 29th, 2013
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