It is necessary after sifting the material that an accurate weighing should be made. Each can of the mixed barium nitrate and oil should contain 78 pounds in order that the final composition shall run uniform. In another building the powder and flake aluminum and sulphur are mixed by rubbing them through a 30-mesh screen by hand into a wooden or fiber tub where the mixture is again mixed by hand and is then passed through the screen a second time. These two mixtures, one of barium nitrate and oil and the other of aluminum and sulphur, are mixed in a wooden or fiber tub and passed twice through a 12-mesh screen. It is essential that the mixing be as intimate as possible, as the even burning quality and high candlepower are dependent almost entirely upon an extremely intimate mixture. Various attempts have been made to substitute machinery for the slow and antiquated method of mixing shown in figure 95, which illustrates the manner in which the powder is mixed by hand, but have not met with the approval of the manufacturers.
Fig. 94. - Mixing machine.
Fig. 95. - Mixing composition by band.
Powder mixing by hand is an operation where the danger from sparks and electric discharges have been minimized.
Up to the present time the substitution of machine mixers has not been adopted by the manufacturers.
In all operations where there is any compression of the burning compositions, such as the loading of cases with combustible materials, the work should be performed in buildings especially designed for this work and separated from the main part of the plant. There would appear to be little or no danger from explosion occasioned by the mere pressure in forming the compositions into their cases. Manufacturers who have had experience in this art for many years advise that the only source of danger which they seek to provide against is in the igniting of the fine dust that almost invariably occurs with the withdrawal of the plunger as the latter is drawn back from the case after having pressed the composition into form. Any sparking will very readily ignite this fine combustible dust and occasion serious trouble. It is usual to provide for work of this character press buildings separated from the main plant, each building having not more than two presses installed. The other equipment usually provided is a bench 3 feet square and a box 2 by 3 feet to contain the composition. A small scoop, a hardware scale, and a measure that will hold approximately 7 pounds of composition are all the equipment necessary as an adjunct to each press. The press itself consists of top and base sections connected by rods and a movable platform operated by a hydraulic ram controlled by valves at the side and operated by a lever. On the moving platform is a base plate with recess to accommodate the staple of the assembled light case, located at its top, which is called a pilot. Jacket and pilot rest on a metal plate 1/2 inch thick, which is so arranged that it may be shifted forward and backward on the moving platform of the press so that the case may be carried clear of the rammer.
Fig. 96 shows the loading machine with the jacket moved forward and clear of the rammer. The operator is shown pouring from a scoop a charge of the composition into the case held by the jacket. This charge weighs 7 pounds, the charging being done by successive compressions.
Figure 97 show the jacket, pilot and supporting plate slid back into a position which will permit the rammer to enter and move freely within the jacket.
Figure 98 shows the operation of removing the jacket after these successive charges of composition have been rammed into the case. The operator loosens the six nuts on the jacket, which are shown in the cut, permitting the jacket' to be moved freely away from the case which it has been holding during the process of charging. The lugs on the upper part of the jacket engage hangers which lift the jacket away from the case by sliding it over the rammer. It must be noted that the rammer is always in a fixed position, the operation being accomplished by the upward movement of the platform holding the jacket and case, thus pressing against the fixed rammer. An extension piece is provided for use in ramming the first loading charge. This extension piece is a solid cylinder approximately 8 inches long and of the same diameter as the rammer. It is provided with a hook socket in the head to permit lifting it from the case after the first charge has been rammed home. A tool with a long eye and a hook for lifting out the extension piece is used for removing the solid cylinder from the case after compression. A tin funnel is used as a convenience in loading. The jacket is lowered into position and clamped about the case, the halves making complete contact. The first charge of 7 pounds of composition is then poured in and the extension piece for ramming is placed in position. This assembly of the case jacket, extension piece, etc., is effected when the base plate is in its forward position. By manipulating the lever shown in the foreground of the cut the plate is thrown to the rear of the machine directly under the plunger. Hydraulic pressure is then turned on until 2,500 pounds pressure to the square inch is attained, but for an instant only. After releasing the pressure the plate is brought back to the loading point, the extension piece is removed, and a second charge of seven pounds is loaded in the case. This receives a pressure of 2,200 pounds to the square inch. The remainder of the charge is loaded by filling the case full to the top with composition and ramming down each successive filling until a total of 28 pounds is loaded. The third ramming should be compressed with 1,700 pounds pressure, the fourth with 1,400 pounds, and the remainder with only 1,000 pounds. The jacket is then loosened and by means of an air hoist is lifted clear of the case, so that the latter can be conveniently removed from the machine.
Fig. 96. - Hydraulic press; filling case.
Fig. 97. - Hydraulic press; ramming composition.
Fig. 98. - Hydraulic press; removing jacket.