This case is made of material which will give strength as well as lightness to the body. As the case has to hold gases exerting a reasonably high pressure and as the walls of the case have to withstand a loading pressure when the powder is driven home, special care is taken to provide proper material for the manufacture. A case having a weight of about 8 ounces, being approximately 12 inches long by 1 1/4 inches inside diameter, should be so constructed that it will withstand a direct bursting pressure operating at right angles to the long axis of the tube of upward of 1,300 pounds to the square inch and an indirect pressure due to the loading of the powder charge which is driven home in the rocket body at a pressure upward of 2 tons per square inch. The manufacturers do not adhere strictly to any one method of forming the rocket body, but seem to favor the hand-rolled carton. The method of rolling is essentially the same, with slight modifications, among the different manufacturers, and is as follows:
Sheets of Bird's rocket hardware paper are purchased by the manufacturers, cut in sheets 25 by 36 inches. These sheets are manufactured especially for the building of rocket cartons, and consist of two sheets firmly attached together, forming a two-ply sheet 0.022 inch thick. In forming the two-ply sheet, one of the sheets is cut 22 by 36 inches, the small sheet being centered oil the larger one with the sides trued up. This allows for a strip of 1 1/2 inches, at both ends of the larger sheet, being single ply. These sheets are now cut lengthwise 12 by 25 inches, one of the large sheets making three of the smaller with the single-ply feathered edge at each end. In order to facilitate satisfactory rolling of the carton, a score of Bird's rocket-hardware-paper sheets are staggered so that only the one-ply edge protrudes. This protruding edge is now brushed with water to soften it. The brushing is violent in order to insure the proper softening of this edge. One of the sheets is now laid upon a fiat surface with the smaller sheet constituting the second ply facing upward, and the entire surface is giveth a coating of paste. On top of this sheet is now placed a second sheet of the two-ply paper, with the smaller sheet also facing upward and pressed down upon the pasted surface of the under sheet in such a manner that the single-ply strip of the under sheet protrudes the distance of its width beyond the upper sheet. The surface is now given a generous coat of paste. A brass mandrel with outside diameter 1 1/4 inches is now laid across these sheets, the ends of the sheets turned around the mandrel and held firmly. After the sheets have been rolled into a cylindrical form one of the laps is detached for a distance of 2 inches from the cylinder and a sheet of Paddock straw-board 12 by 26 inches, with the grain the 12-inch way, having been previously given a coat of paste, is slipped into the opening and then wrapped around the carton. Paddock strawboard is previously prepared by stacking a number of sheets and feathering the edges by rough rubbing. When complete these cases are 3/8 inch thick and are placed on racks in a drying room for 3 or 4 days at a temperature of 120° F.
The case-rolling machine is a special machine and described in detail, because it is not a standard machine that can be purchased in the open market, but one that the manufacturers have had to build for themselves at their plants.
It is a simple machine similar to a lathe in its design, as shown in figure 3. It consists principally of a driving pulley, and a shaft or spindle capable of both rotation and translation, carried in suitable bearings.
Fig. 3. - Case-rolling machine.
The shaft is moved longitudinally through the pulley and through its bearings by means of a counterweighted lever and is rotated by the engagement of a lug on the pulley with a pin on the shaft. The pulley rotates continuously and is carried in the center bearing of the machine, as shown in detail in figure 4.
Fig. 4. - Case-rolling machine showing pasting notch.
The above figure shows the shaft emerging through the pulley and the edge of the paper engaged in a longitudinal slot in the shaft. This slot extends for a length that will permit the paper to be inserted. The function of the slot is to hold the paper tight while rolling and the function of the pasting notch as shown in the figure is to automatically press the paper that is held in the slot against the inner wall of the case when the finished case is removed from the shaft. The large roller located under the shaft is a "pressure shoe" which is required in order to roll a tight and compact paper carton. The pressure to be applied by this shoe is regulated by the leverage of the counterweight shown in figure 5 The operation of the machine is as follows: The paper is given a coating of paste and arranged in the same maimer as that for hand operation, the bottom sheet extending over the edge of the table so as to engage in the slot on the shaft.
Fig. 5. - Case-rolling machine showing counterweighted pressure shoe.