Sunday, July 24, 2016

Black Powder - VIII

In our last post, we saw how people started to manufacture corned black powder starting in the early 15th century. In today's post, we will look at how it was done from then on until the end of the 19th century.

As we saw in our last post, by the early 15th century people had started doing the pulverizing, mixing and caking of the three ingredients of gunpowder (i.e.) saltpeter, charcoal and sulfur, in one operation in a stamp mill, in order to keep the grain sizes consistent. We will look at the development of automated machines that did this.

A stamp mill from 1686. Click on the image to enlarge
Image taken from "Teatrum Machinarum Novum" by George Andreas Bockler of Nuremberg. Public domain image.

Parts of a stamp mill.

A stamp mill has a heavy block made of oak or beech wood (b in the diagram above), about 2 feet in thickness, in which a number of mortar holes (a) are carved into the block, to a depth of about 20 inches, with diameter of about 15 inches. At one time, those holes were cylindrical, but they were later carved into spherical shapes with a funnel-shaped opening at the top. At the bottom of each hole, a piece of hardwood (c) is inserted to act as an anvil. The block of wood is tied down by means of straps and bolts and rests on a foundation (usually a wooden grating), so that the bottom is supported to withstand the blows from the  stamp head.

The stamp rod stems (d) are rectangular in cross-section, about 7 to 10 feet long and 4 inches thick and made of maple or beech wood. At the end of each rod is attached a pear-shaped head (e) made of bronze. At the other end of each stamp rod, a lifting pin is wedged on.

Stamp mill in Austria. Public domain image.

By the 19th century, each mill usually had only one stamp rod per mortar hole, but before that it was common to use multiple stamp rods per hole. For instance, in Sweden, they would use four stamp rods per mortar and in Austria, they would use three rods, as the image above shows. Also, some machines used metal mortars instead of wooden ones, but this was abandoned because of sparking risks.

To drive the stamp rods, a cam-shaft (AB) with cams (c) attached to it is used. As the shaft rotates, the cams engage the lifting pins on the stamp rods and lift the rods vertically up to a certain point, whereupon the cam disengages from the pin and the stamp falls back due to gravity. The cam-shaft is driven by the wheel L, which is either powered from a water-wheel or animal-power.

Each rod is dropped about 16-17 inches and the weight is anywhere from 40-90 lbs. Each mortar is filled with the three ingredients of gunpowder in their proper proportions and the contents of each mortar weigh about 15-25 lbs., depending on the size of the machine. The mixture was originally moistened with water in the early part of the 16th century, to reduce chances of spontaneous combustion. Later on, vinegar was used as well and in the middle of the 16th century, it was considered good practice to moisten the mixture with "man's urine who drinks wine"!

The time of stamping also changed during the centuries. In the 16th century, they would generally let the procedure run for 6 hours; by the beginning of the 17th century, it had increased to 10 hours for cannon powder and 12 hours for musket powder; by the year 1700, the time of stamping was about 24 hours at the rate of about 1 blow per second.

In the UK, stamp-mills were prohibited by the 19th century, because of the dangers associated with them. Instead, incorporating mills were used in the UK, as well as Germany and Italy. The technology of incorporating mills was known as early as 1540 and mentioned by Biringuccio. They were imitations of olive oil mills, but were not used early on because they were considered dangerous. Later on, the technology improved and these were used in the UK, France, Germany, Sweden, Italy etc.

An incorporating mill. Click on the image to enlarge.
Image taken from "Teatrum Machinarum Novum" by George Andreas Bockler of Nuremberg. Public domain image.

Sweden got its first incorporating mill in Cnutberg in 1684. In France, they were first introduced in 1754 by Pater Ferry at Essonne. These mills have a rotating millstone running over a bed. Each millstone is powered by a system of gears driven by a water wheel. Millstones were made of marble in the early days and the beds made of copper or wood.

In our next post, we will study improvements to the pulverizing process.

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