tailieunhanh - Systematic Drilling and Blasting for Surface Excavations Part 3

Tham khảo tài liệu 'systematic drilling and blasting for surface excavations part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | EM 1110-2-3800 1 Mar 72 Fig. 3-1. Common sizes of dynamite cartridges 3 The term strength was first applied when dynamite was a mixture of nitroglycerin and inert filler such as kieselguhr diatomite . Then 60 percent dynamite contained 60 percent nitroglycerin by weight and was three times as strong as a 20 percent dynamite. Straight dynamites today contain such active ingredients as sodium nitrate and carbonaceous material in place of inert filler. Consequently a 60 percent straight dynamite which contains 60 percent nitroglycerin by weight is only about times as strong because of the energy supplied by the additional active ingredients in the 20 percent grade. Furthermore 60 percent weight strength straight dynamite and 60 percent weight strength extra dynamite will produce different results due to a difference in detonation velocity. 4 Normally the cartridge count . the number of cartridges in a 50-lb box and one of the strength ratings can be obtained for an explosive. A nomograph relating the two strength ratings is given in Fig. 3-2. The cartridge count is roughly 140 divided by the specific gravity. If a line is drawn through the cartridge count and the given strength rating the unknown strength can be read where this line intersects the scale of the unknown strength. 3-2 EM 1110-2-3800 1 Mar 72 _ 80 1 100 I 170 EXAMPLE _ __ 180 20 KNOWN CARTRIDGE COUNT 130 KNOWN CARTRIDGE STRENGTH 40 FIND WEIGHT STRENGTH 60 190 200 210 10 1 Fig. 3-2. Nomograph for comparing weight strength and cartridge strength 3-3 EM 1110-2-3800 1 Mar 72 5 Usually dynamites are rated on weight strength and gelatins on cartridge strength. Commonly only a trade name ÒT a coded designation is given and the strength as well as the explosive type usually must be obtained from the manufacturer. 6 These examples show that strength is not a good basis for rating explosives. Detonation pressure is a better indicator of an explosive s ability to perform work see d .