Powder mill

“ The charcoal is ground in a mill, either to a fine powder and sifted; or into a coarse granular state, like gunpowder, for the preparation of which two sieves are required, one with moderately fine meshes, to allow the small dust to pass through, and one with large meshes, to separate the proper sized grains from the coarser lumps. Either a corn-mill, an edgestone mill, or a steel cylinder mill, may be employed for grinding bone-black, and it is generally damped in the operation to keep down the fine dust. ”

“ On the small scale, pulverisation is usually performed by means of a pestle and mortar; on the large scale, by stamping, grinding or cutting the substance in a mill. A few soft substances, as carbonate of magnesia, carbonate of lead, &c., may be pulverised by simply rubbing them through a fine sieve, placed over a sheet of paper; whilst many hard, gritty substances can only be reduced to fine powder by porphyrisation or levigation. Elutriation, or ‘washing over,’ is adopted for several substances, as chalk, antimony, &c., which are required to be reduced to fine powder on the large scale. ”

“ After this, the powder is again passed through a second sieve, commonly called a grainer, the holes of which are of the same diameter as the powder we wish to obtain. It is then put into another sieve, which permits only the dust to pass, whilst the grain-powder remains. As the powder, however, contains some grains too large, as well as others too small, we may separate the former by a fourth sieve, of a suitable size. The dust and fine grain are carried to the mill, and worked over. The powder for war, and for mining, is dried immediately after the graining. ”

“ One man runs each of these mills. He cannot start the machinery in motion and go away, like the man who has charge of a rolling-mill, but he must stay in the place all the time, and feed the stones to the machinery that crushes them into grains of various sizes. He shovels the powder into a large hopper, big wooden wheels go around and around, and the powder passes between zinc rolls and through sieves of various sizes. ”

“ The excellent preservative qualities of English and American powders are largely due to their high densities,—the standard being about 1.75. A certain degree of density is absolutely essential to grain powder to prevent the inflamed gases from penetrating the pores of the powder and flashing off the whole mass to the destruction of the gun. In the manufacture of powder the density depends, first, upon the amount of trituration to which the ingredients are subjected in the incorporating mill ”

“ But one man—Wright—could be found in the Southern States who had seen gunpowder made by the incorporating mill—the only kind that can make it of the first quality; he had been a workman at the Waltham Abbey Government Gunpowder Works, in England. ”

“ Gunpowder-mills are mills, in which powder is prepared, by pounding and beating together the ingredients of which it is composed. They are always worked by water-power, and as there are generally many of them belonging to the same manufactory, one dam of water will furnish a sufficient supply. In the construction of powder-mills, the frame of the house is made very stout, and the roof put on lightly, so that in case of explosion, it may be carried off easily, and thus give vent to the powder, without much injury to the works. ”

“ Rarely is more than 150 pounds of powder rolled at one time, and it takes from three to eight hours to do the rolling, according to the grade of powder that is being made. The workman in charge will go to the door of the mill from time to time to look in, but he never steps inside until he has stopped the machinery and the rolling is done. ”

“ Usually the frit, a material similar to glass, is crushed to powder beneath stone rollers called chasers. Water is then added and the compound turned into the grinding-mill where it is ground for an entire day. Sometimes, however, a different process is preferred and the material is put into a kiln and melted instead. In either case it must finally be worked into a smooth liquid which can be strained through fine lawn. It is then sent to the agitators and constantly stirred until it can be pumped into the storage tanks in the dipping-room."
"That is just what I wanted to know," said Theo. ”

“ These precautions were rendered the more necessary by the carelessness of the powder-makers, who might not remove the broke up powder cake from the mill enclosure before placing a new charge under the rollers, thus having one hundred and twenty pounds of material to take fire at the same time—as once happened—producing a powerful explosion. ”

“ A wing wall, nearly as high as the main walls, and three feet thick, extended outwards from the centre of the exterior back wall of each mill twenty feet, to guard still further against the effects of an explosion. Behind these the powder-makers stood, for safety, while starting or stopping the motion of the ponderous rollers. ”

“ At the powder mills they generally allow for wasting, in making up, one pound and a half in a hundred. And their mixture for a hundred weight of good powder is thus: To seventy-six pound and a half of saltpetre, well refined and dry’d, twelve pound and a half of coal, and as much sulphur, all which added together makes one hundred one pound and a half, which when worked up will nearly weigh one hundred. ”

“ To carry the refining process to the extent of nearly absolute purity, required several successive crystallizations and washings, involving a large amount of manual labor in the manipulation, and consuming much time. This was particularly the case in the very large amount of saltpetre, eight to ten thousand pounds per day, used by the Works, the refining of which would demand extended buildings and apparatus, as well as requiring a large number of operatives. Hence, it became desirable to devise methods by which hand labor could be superseded by motive power and machinery ”

“ A fifth of the tenth already indicated is put through heavy rollers, and one half of this finely crushed ore is subjected to the Bucking hammer and powdered to an eighty-sieve grade. One sample of this powder, consisting of a fourth, is given to the miner, two samples are kept for reference, and the other is sent to the assayer, who takes his "assay ton," upon which the company buys and sells. The capacity of the works are all the way from 80 to 150 tons per day. For samples, $7.50 is charged for silver and lead per ton, and $10 per ton for gold; but in large quantities a less charge is made. ”

“ In mining, let us observe, the whole round of work consists in separations which bring masses from bigness to smallness, again and again. First of all the solid walls and floors are broken up by pick, or drill, or powder, or all together. Iron ores as hoisted to the surface of the earth are taken to breakers which crush them into pieces suitable for the blast furnace. When the ores carry gold, copper, lead, or tin, this crushing is followed by stamping to facilitate the final process by which metal is separated from worthless rock. ”

“ The ores when dug from the mine are generally stamped into powder, then “roasted,”—that is, made hot, and kept so for some time to drive off water, sulphur, or arsenic, which would prevent the “fluxes” acting properly. The fluxes are substances which will mix with, melt, and separate the matters to be got rid of, the chief being charcoal, coke, and limestone. The ore is then mixed with the flux, and the whole raised to a great heat; as the metal is separated it melts, runs to the bottom of the “smelting furnace,” and is drawn off into moulds made of sand ”

“ Notwithstanding the rapid construction of new stampers, and other parts, it was only in the latter part of September that five hundred pounds of powder daily were produced.
It was soon perceived that to increase the supply, a special refinery for saltpetre would have to be erected; works accordingly were projected, commenced, and mainly completed, at Nashville, by the 9th October, on which day 1,500 lbs. were refined, and this amount was gradually increased to 3,000 lbs. daily. ”

“ The powder-making facilities created during the war by the DuPont Powder Company near Wilmington, for instance, almost at once after the armistice turned to the manufacture of dyestuffs. Another war powder plant, with practically the same machinery, is to-day producing artificial silk, a cellulose commodity similar in chemical composition to smokeless powder. A third is making celluloid and artificial ivory ”

“ The change of the proportion of the materials composing it was not the only improvement it received. The invention of graining it is doubtless a considerable advantage to it; for powder, at first, was always in the form of fine meal, such as it was reduced to by grinding the materials together. It is doubtful whether the first graining of powder was intended to increase its strength, or only to render it more convenient for the filling into small charges, and the charging of small arms, to which alone it was applied for many years, whilst meal-powder was still made use of in cannon. ”

“ I cannot lay too much stress on the necessity for legislative action on this point, in order to give assurance to the workmen.
Powder—The mechanical means of the Bureau for the production of powder are ample for a war conducted on any scale, and are so arranged as to be almost beyond casualty. The supply depends alone on that of saltpetre and sulphur, and for the present on the former. While we must still depend on importation as our chief supply of nitre, it will be indispensable that the efforts of the Nitre and Mining Bureau be sustained, in order that the home production may be assured. ”

“ Charcoal for gunpowder must be made by what is termed the distilling process; that is, the wood must be heated in iron retorts to the proper degree, to have it of the best quality and free from sand or grit. For this purpose cast iron cylinders, or retorts, six feet long and four feet in diameter were used, placed over furnaces, each having one end solid and the other with a movable cover; into these were run the slip cylinders, which contained the kiln dried cotton wood, split up into sticks about one and a half inches in diameter, and entirely filling it. ”

“ The blow-pipe is especially useful, though to the skilled assayer often unnecessary. The ore is first powdered, and any metallic flakes picked out and tested separately. A fair sample must be selected, otherwise all the work will be thrown away and the result be valueless.
The next step is weighing the ore and the reagents. Moisture is drawn off by heating in a crucible, a low heat being sufficient. Roasting will eliminate sulphur, antimony, arsenic, etc., and must take place in a flat dish, so that the air may have free access. The powder should be stirred frequently. ”

“ Adjoining this Refinery was the department in which charcoal was made and pulverized. Charcoal for gunpowder has to be made of a porous fine-grained wood, having very little ashes when burned; willow is generally preferred, and was used at first in the Powder Works, but the exigencies of the war taking away those who would ordinarily have supplied it, rendered it impracticable to procure a sufficient quantity. ”

“ That only accelerates the action of the yeast.
On the negative side, stone mills grind slowly and are very fussy about which grains they will grind. If the cereal is a bit moist or if the seed being ground is a little bit oily, the mill becomes instantly blocked.
Steel burr mills grind fast and coarsely and are inexpensive. Coarse flour makes heavy bread. The metal grinding faces tend to wear out and have to be replaced occasionally--if they can be replaced. ”

“ But, as in the case of casting, powder processing uses dies to form parts. Again, the study of containerless forming techniques may be fruitful, with powder processing alleviating some of the heat dissipation problem, since sintering temperatures are lower than those required for casting. The applicability of powder formation via liquefaction and spraying should be assessed. Grinding and milling must also be examined, since the cold welding phenomenon between similar pure metals may be turned to advantage if it can be used to facilitate coalescence of the metals without sintering or melting. ”

“ The mills have the air of being pit-head workings dealing with a cleaner material than coal. About them are lengthy conveyors, built up on high trestle timbers, that carry the logs from the water to the mill and from the mill to the dumps, that one instantly compares to the conveyors and winding gear of a coal mine. ”

“ The substance when reduced by grinding to the finest powder is agitated in water which is then drawn off: the coarsest portion of the suspended matter first subsides, and that which requires the longest time to fall down is the finest. In this manner even emery powder, a substance of great density, is separated into the various degrees of fineness which are required. Flints, after being burned and ground, are suspended in water, in order to mix them intimately with clay, which is also suspended in the same fluid for the formation of porcelain. ”

“ Since air flows through with the grain the flour is not heated very much. This type of mill is small, very fast, intermediate in price between steel mills and stone mill, lasts a long time, but when grinding, sounds like a Boeing 747 about to take off. ”