Initiating Strength of Primary Explosives

The determination of the initiating strength or priming ability of primary explosives is very important for the correct solution of tasks related to the service application of the primary explosives in initial devices, explosive trains, etc. 

One gram of selected high explosive is press-loaded at 1000 kp/cm in a copper tube 45 mm high, 7 mm in external diameter, and 0.3 mm in wall thickness. Above it, the primary explosive is also press-loaded at 500 kp/cm. The mass of the primary explosive is varied. 

By means of a plastic or wooden holder, the copper tube is plac in a vertical position on a lead plate 35 mm in diameter and 5 mm thick. The initiation of the primary explosive is performed by means of a safety fuse. If a clear hole is cut in the witness lead plate, a complete detonation of the high explosive has occurred. By reducing or increasing the mass of the primary explosive, the minimum mass necessary to cause a complete detonation of the selected high explosive is determined. Six consecutive trials have to be performed for each applied mass. The data related to the minimum mass of the primary explosives that may cause a complete detonation of given high explosives are presented in Table 2.8. 

The test is conducted in the following manner 200 mg of hexogen are press-loaded at 1115 kp/cm in a polymethylmetacrylate (PMMA) holder. Above it, a primary explosive is filled in the state at which its initiating strength is to be tested freely poured or pressed to a desired density. The initiation of the primary explosive is performed by means of a safety fuse. If the depth of the dent produced after initiation in the steel witness plate of 70-90 Rockwell B hardness is greater than 0.76 mm, the complete detonation of hexogen is 

SAFETY FUSE COPPER TUBE TUBE HOLDER 

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The initiating strength of primary explosives can also be determined by the method illustrated in Figure 2.19. It differs from the previous method in a way that shock effects, caused by the complete or incomplete detonation of a high-explosive charge, are registered on the basis of the dent depth produced in the witness steel plate. 

Figure 2.18. Setup for the determination of the initiating strength of primary explosives...

It should be pointed out that the initiating strength of primary explosives depends on several factors, such as explosive purity, leading density, confinement conditions, etc. Thus, the results obtained by different testing methods are not directly comparable. 

Initiating Efficiency (or Strength) of Primary Explosives by Sand Test. See Vol 1, pp... 

A major difference between primary and secondary explosives arises from the fact that primary explosives are initiated to detonate by burning whereas secondary explosives are initiated to detonate by shock waves. Therefore, the most important property of a primary explosive is its ability to undergo a fast deflagration-to-detonation transition (DDT). Thus, fast DDT is the strength of primary explosives as well as their weakness. All other parameters being equal, the faster the DDT, the better the primary explosive. At the same time,... 

Initiating E((iciency(or Strength) of Primary Explosives by Sand Test. Using 0.400 g charges of tetryl and 0.400 g of the initiating explosive under test, det the wts of sand crushed by initiator alone and by initiator + tetryl. Subtract from the last value, the amt cruMied by 0.400 g of initiator and record this as the value crushed by tetryl. Repeat the test with initiator tetryl a total of 5 times and compare the.results. If the values for tetryl do not vary by more than 3.0 g and the av of these is within 2.0 g of the av value for tetryl obtained with 0.300 g of LA aa an initiator, consider it as the maximum. Repeat the test using smaller amts (0.350 g, 0.300 g etc) of initiator(and always 0.400 of tetryl) until the minimum is reached. (Compare with Sensitiveness to Initiation by Detonators, etc). Refs l)L.V.Clark, lEC 25, 666(1933) 2)PATR 1401,... 

One of the possible methods for testing the initiation strength of the primary explosives is illustrated in Figure 2.18. The test is conducted as follows. 

The comparative initiating strength of different types of primary explosives may be obtained in a similar way—on the basis of the dent depth produced in the steel witness plate after the detonation of the primary explosive alone. For this, 300 mg of primary explosive alone is press-loaded at 1115 kp/cm into a PMMA sample holder, wliich is then placed on the steel witness plate. The initiation of the primary explosive is performed by means of the safety fuse. The depth of the dent produced in the steel witness plate after the detonation of the primary explosive is connected with its initiating performance and serves for the comparative evaluation of the initiating strength of different types of primary explosives. 

Initiating efficiency, sometimes referred to as initiating power, strength, or priming force, is the ability of a primary explosive to initiate detonation in a secondary explosive adjacent to it. It is usually reported as a minimum amount of primary explosive necessary to cause detonation of the adjacent high explosive with 100%... 

Detonators) XXII (SENSITIVITY TO FLAME, SPARK, ELECTROSTATIC DISCHARGES, ETC) XXIII [Sensitivity to Initiation by Primary (Initiating) Explosives, Detonators and Boosters, Tests] XXIV (Small Lead Block Compression Test is described in Vol 3 of Encycl, p C493-L) XXIV (Small Lead Block Expansion Test is briefly described under Trauzl Test) XXIV (Sound Test for Detonators) XXIV (Strength of Detonators. See under INITIATING EFFICIENCY, p XVIII) XXIV (Surveillance Tests) XXIV (Taliani Test) XXV (Trauzl Test) XXVI (Vacuum Stability Test) p A2 (Abel s or Kl-Starch Test) p A573-L (Ball Drop Test for detg sensitivity of LA or other primary expls)... 

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