Drop balls

Most limestone quarries use either 100% ammonium nitrate [6484-52-2] (fertilizer grade) and fuel oil (ANFO), or a combination of ANFO and ammonium or gelatin dynamite, for blasting (see Explosives and propellants, explosives). After blasting, oversized boulders usually are reduced to manageable sizes by drop ball cranes. 

Hard rock mining of these ore bodies requkes drilling and blasting with ammonium nitrate and dynamite. After blasting, the ore is reduced in size with a drop ball and then loaded on tmcks for transportation to the processing plant. Mica, quartz, and feldspar concentrates are separated, recovered, and sold from the hard rock ore. 

Impact sensitivities of mixtures of red phosphorus with various oxidants were determined in a direct drop-ball method, which indicated higher sensitivities than those determined with an indirect striker mechanism. Mixtures with silver chlorate were most sensitive, those with bromates, chlorates and chlorites were extremely sensitive, and mixtures with sodium peroxide and potassium superoxide were more sensitive than those with barium, calcium, magnesium, strontium or zinc peroxides. Mixtures with perchlorates or iodates had sensitivities comparable to those of unmixed explosives, such as lead azide, 3,5-dinitrobenzenediazonium-2-oxide etc. 

The principal input and output tests used by the US at the time of publishing NOLTR 1111(1952) included Drop Ball Testers (two types) Sand Bomb Apparatuses 100, 200, 360 500 gram Condenser Discharge Apparatus Torsional Ballistic Pendulums (two types) Drop Ball Test Set Mk 135 with Chronograph Thermocouple Drop Ball Test Set Mk 136 with Chronograph Gas Explosion Chambers (two types) Gas Volume and Impulse Apparatus Pressure Bomb Apparatus and Hopkinson Bar Apparatus (Ref 11, pp 9-2 9-3, Table 9-D... 

Sensitiveness (Sensitivity) Tests. In the so-called drop-ball test, described in NOLR 1111 (Ref 14, pp 9-4 to 9-7), using apparatus shown in this Section, Fig 1, the detonator (or primer) is inserted in an assembly shown in Fig 4. Each detonator is resting on a lead disc either 0.065 inch or 0.134 inch thick [PA-PD-124(1953), p 3l, while each primer is resting on an aluminum disc of thicknesses 0.012, 0.032 or 0.040 inches [MIL-P-14100 (Ord) (1955), 3l... 

The depth of the dent is a measure of the output. The test applies only to components producing dents greater than 0.005 and smaller than 0.100 inch in depth. A drop-ball apparatus similar to the one employed in lead-disc test, is used here. A new block is used for each test. A complete description of the procedure is given as Test No 303 in MIL-STD-331 d ) Explosive Component Output Measurement by Steel Dent. The test is similar to the A1 dent test. It applies only to components producing dents greater than 0.005 and smaller than 0.100 inch in depth. A complete description of the procedure is given as Test No 301.1 in MIL-STD-331... 

A pendulum may be used (Charpy, Izod, tensile impact) to determine the work of fracture (Brown, 1999). Instrumented devices provided with piezoelectric transducers are also available load-time or load-displacement curves can be recorded (Merle et al., 1985), giving as much information as static tests. Servohydraulic or pneumatic setups and falling weight devices are also used. The drop ball test from the US Food and Drug Administration, is especially useful for optical lenses (acrylate networks). 

Substances which explode by a weak impact (called highly sensitive substances) can be identified by a screening test like the drop ball test Whether deflagration occurs easily can be checked by an ignitability test Another screening test to examine the ease of occurrence of a reaction relies on the determination of the temperature at which decomposition is initiated by thermal analysis on micro-samples. This quantifies the ease of initiating a thermal explosion. 

Impact sensitivity varies widely from one chemical to another. Since it is not possible to test many chemicals with wide sensitivity ranges by a conventional drop hammer test, we have begun the trial use of a drop ball tester which allows us to change the weight of falling objects over a wide range 101. ... 

Table 1.7 Hazards of Reactive Chemicals which are predictable by SC-DSC (QDSC and TDSC), Drop Ball Test and Ignitability Test...

The ease of occurrence of explosion for a self-reactive chemical may be judged by its shock sensitivity and its ability to propagate the explosion. The shock sensitivity of highly sensitive chemicals can be measured by the drop ball test described above. However, those chemicals whose hazard can be measured by the drop ball test are too sensitive for daily use. Different methods are needed for those chemicals which are not likely to explode in daily use to determine whether a substance can cause explosion under extraordinary conditions. 

Evaluation of Oxidizing Materials (IV), A Drop Ball Test of... 

Evaluation of Reactivity and Hazards of Oxidizing Agents and Their Components (X), Mechanical Sensitivity of Oxidizing Agent Red-Phosphorus by Direct Impact Method of the Drop Ball Tester", Nihon Kasai Gakkai Ronbun-Shi (Bulletin of Japan Fire Control Association), 36, 9 (1987)... 

Detonation SC-DSC 50/60 Steel tube 50/60(under sand) Ignitability Friction Drop ball Ballistic mortar Explosion underwater Electronic spark... 

Deflagr- ation Ignitability SC-DSC 50/60(underwater) Ballistic mortar Ballistic pendulum time/pressure Flash point Drop ball Ballistic mortar Ballistic pendulum Explosion underwater Ignitability Time/pressure... 

Detonation SC-DSC Explosion underwater Ballistic mortar ballistic pendulum Explosion under sand Drop ball Explosion underwater... 

General drop ball type impact sensitivity test (B)... 

Bl. The name of the test Drop ball impact sensitivity test B2. The properties to be tested... 

Figure 3.7 The small sized drop ball test equipment...

The steel roller with the sample powder is placed in the center of the anvil on the drop ball test equipment... 

Table 3.6 Example of test results of drop ball test...

Properties of the drop ball impact sensitivity test... 

Some errors are unavoidable in impact sensitivity tests like the drop hammer test and drop ball test Important questions involve the precision and accuracy of acquired results. During the World War II in U.S.A., statistical investigations on drop hammer tests were carried out mainly by Professor Dixon 211 at the Bruceton Laboratory to achieve greater accuracy in determining impact sensitivity with the fewest trials. 

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