The mandrel by suitable mechanism is always stopped in a position permitting the sheet to be easily fed into the slot. This slot is cut parallel to the long axis of the mandrel, and has a slightly spiral twist at one end. Care must be exercised to see that the case is tightly rolled as the external diameter must be constant, in order that it may fit into the outer case or shell. The operator, using his hands as a band brake, exerts pressure to form properly the case while it is being wound about the mandrel. The case is now removed from the mandrel with the assistance of a collar. The spiral twist of the slot in the mandrel smoothes the edge of the paper against the inner surface of the carton as it is forced from the mandrel.
Fig. 89. - Rolling machine; removing case from mandrel.
Fig. 90. - Trimming machine.
Figure 89 shows the operation of removing the case from the mandrel. The man is forcing the case off the mandrel by means of a collar, the case being received by the woman operator.
The cases are stood on shelves in a drying room, where they are kept for a period of time sufficient to dry them very thoroughly. No special provision is made for circulation of air or maintaining a constant temperature, it being the practice of the manufacturer to dry these cases as slowly as is consistent with the demands for their output. Three days is the time usually required to accomplish this drying, which is carried on at room temperature. If the cases are dried too rapidly or if sunlight is allowed to play upon them, they are likely to bulge and thus become unfitted for use. The finished tubes are trimmed on a trimming machine so as to have smooth ends, the tube being cut to a measure of 28 1/2 inches long. The outside diameter should be 4 1/4 inches.
Fig. 91. - Case and case top.
The trimming machine is essentially a cut-off lathe which trims both ends of the case to the required length simultaneously. The case is placed on the revolving mandrel by swinging out the headstock and placing the case in position. The headstock is then set and the machine started, the steel cutting wheels revolving at a rate which insures a clean cut.
The case top is made of No. 18 gauge galvanized iron and has a staple riveted firmly in the center to which is attached the parachute cable. This cap is shown resting against the side of the light case in figure 91.
Figure 92 shows the case top inserted into the end of the case flush with the end. Eight 1/8-inch holes are punched through the case and flange of the top by a specially designed punching machine, as shown in the figure, which turns the case 7/8 of a revolution, punching at each 1/8 of a turn.
Fig. 92. - Punching machine.
Eight copper rivets 1/8 inch by 5/16 inch, with 3/8-inch heads and copper washers, are used to securely rivet the case top to the case. Riveting is done with a specially designed riveting machine as shown in figure 92.
This machine is a combination of a foot-operated punch press and drill press. The rivets are hand assembled in the holes in the case and case top from the inside by means of specially constructed pliers, and the washers are put on each rivet just before the rivet is upset on the riveting machine.
The upset rivets are smoothed off by a die fitted in the chuck of the drill press. This is necessary as otherwise a burr on the rivets would prevent the case from fitting into the shell.
Fig. 93. - Riveting machine.
Illuminating composition is one which when ignited by proper means, to be described later, burns slowly, emitting an intense white light. The burning of this composition produces the illumination of the aeroplane flare.
In practice the light composition is made up in batches of 100 pounds by mixing the following chemicals in their respective proportions:
Barium nitrate (Ba(NO2)2)....................
Sulphur (flour) .........................
Castor oil or vaseline....................
The proportions of the above formula are subject to slight changes because of variance in the purity of the various ingredients. In practice the barium nitrate, castor oil or vaseline, and sulphur remain practically constant in amount. The principle variation from the above formula is in the amount of aluminum used in the composition.
The barium nitrate is crushed and ground through a Coggswell mill, to reduce it to a very fine powder. The finer the grinding of the barium nitrate, the more intimate will be its mixture with the other ingredients of the formula and the loading of the charge in the light case will also be more even. The barium nitrate is now taken from the mill and for the purpose of safety is removed to another building where 76 pounds of it is carefully weighed out and placed in the mixing machine, to which 2 pounds of castor oil or heated vaseline is slowly added and mixed. This mixing operation should continue for a period of not less than 4 or 5 minutes. The mixing machine is a combination of a belt-driven shaft with open arms revolving in a horizontal cylindrical trough and a revolving metal screen. The arms of the shaft are designed to thoroughly mix the barium nitrate and binding material. When ready to be screened through the revolving sifter it is only necessary to open the gate at the bottom of the mixer over the sifter and allow the material to run into the hopper above the sifter. The function of the sifter is to eliminate any lumps passing through, and the operator at the completion of each batch forces any accumulation through the sifter with his hand. The sifted material falls into a bin, located above a bucket, shown at the right of the cut.