Explosives . orm of the pro-. When sufficiently pressed the pressure is released and the trolley is wheeledaway, and the press-cake removed from it by hand or with wooden tools. Theouter portion of each slab is rejected as it is not sufficiently compressed : it isadded to a later pressing. Blasting powder is sometimes compressed between rollers. The broken-up press-cake is put in barrels and taken to the granulating Granulatingor corning house. Here there is a machine having three or four pairs of gun-metal rolls, through which the press-cake is passed, and a number of automaticsieves, which s
Explosives . orm of the pro-. When sufficiently pressed the pressure is released and the trolley is wheeledaway, and the press-cake removed from it by hand or with wooden tools. Theouter portion of each slab is rejected as it is not sufficiently compressed : it isadded to a later pressing. Blasting powder is sometimes compressed between rollers. The broken-up press-cake is put in barrels and taken to the granulating Granulatingor corning house. Here there is a machine having three or four pairs of gun-metal rolls, through which the press-cake is passed, and a number of automaticsieves, which sort out the grains of the required si/.e i > Fig. 10). The toppair of rollers usually has pyramidal teeth : from this the material passes 1 Special Report No. 138. VOL. I. 6 32 EXPLOSIVES over a sieve to the next pair of rolls, which has smaller teeth. The lowestpaii are plain. The pieces that are not tine enough are passed through themachine again ; the dust and tine powder are milled for a short time and. In. Corning Machine, made by Mascninenhau Golzern-Grimma m. The bearings of one <?! both rolls f each pair ait- provided with »piiiiLr- or weights t keep them in position, and are not rigidly fixed. Consequently if an extra hard piece of cake passes through tin- rolls it i- not subjected to great violence : the rolls give way and the piece passes through. This type f granulating machine was invented in IS19 by < olonel < bngreve, MANUFACTURE OF GUNPOWDER 83 and is the one in most general use. Various other types have been tried, butnone produces such a good angular grain. In France the granulation is carried out in a horizontal drum covered withmetal sheet perforated with fine holes of a size suited to the sort of powder thatis to be produced. The broken down mill-cake is placed inside this drum to-gether with pieces of hard wood, which are caused by longitudinal strips to fallcontinually on to the powder and break it up. A charge of 20 kg. is granulatedin
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