Project topics and materials
Get Complete Project Material File(s) Now! »
Lead delay elements
A fixed amount of mixed composition (4 g, 11 g and 11 g for Si/Pb3O4, Mn/Sb2O3 and Mn/MnO2 mixtures respectively) was poured into a 166 mm long lead tube with initial inner and outer diameters of 7.0 mm and 11.5 mm respectively. The ends were crimp sealed to prevent any powders from escaping from the tubes during extrusion. The tubes were then subjected to a ten-step proprietary rolling machine in order to compress and consolidate the powders. The final outer diameter was 6.4 mm and the core diameter and overall length depended on the packing density of the filled composition. The lead tube was then cut into 100 mm and 44 mm sections to form long and short-delay elements. The length of the delay elements was determined by the burn rate measurement technique. The lead delay elements were assembled for testing by fixing an aluminium tube to one end of the lead tube and adding an aluminium cap, a rubber grommet, a rubber seal and a shock tube. The aluminium tube was then crimped onto the lead tube to ensure a secure fit. The other end of the tube was crimp sealed and a small hole drilled at the end to ensure that any gas produced could vent and did not build up in the element. The Mn/Sb2O3 and Mn/MnO2 compositions required a starter composition. The starter composition was added by scraping out a small amount of composition from the element and replacing it with the starter composition. Figure 3-11 shows the assembly of the entire lead-drawn delay element.
Aluminium delay elements
The aluminium delay elements were prepared by pressing the mixed delay composition into the aluminium tubes using a hydraulic press. Only the Si/Pb3O4 composition was tested using aluminium tube elements. The filling process was performed at 100 kg load, with ±0.2 g increments being filled and pressed until the tube was completely filled to the top (±11 increments). The aluminium tubes were manufactured to contain an extension that could accommodate all the ignition components. The ignition components used for the aluminium tubes were the same as for the lead tubes. The assembly of the aluminium delay elements is shown in Figure 3-12.
Thermocouple technique
The delay elements were also tested using the common laboratory technique of utilising thermocouples as triggers. The delay elements were assembled as shown in Figure 3-11.
Two ‘Type S’ thermocouples (one 2 mm (TC1) and one 3 mm (TC2)) were placed 70 mm apart in the lead elements. In order to ensure that the thermocouples could make proper contact, small holes were drilled into the element and the thermocouples were inserted into the holes. The burn rate was calculated from the time difference between a specific threshold temperature rise detected by the thermocouples. Figure 3-13 shows the typical temperature profiles measured using the two thermocouples. The effect of the depth of the thermocouples and also the distance between the thermocouples were investigated.
Mn + Sb2O3/MnO2 PACKING
The packing of the Mn + Sb2O3 and Mn + MnO2 compositions was investigated to determine the effect of the particle sizes of both materials on the packing arrangements of the composition, along with their impact on the burn rate. The different sized Mn, MnO2 and Sb2O3 materials used for this study are listed in Table 3-1, along with all related characteristics described in Section 3.1.
Particle packing in compacts were imaged with a JEOL JSM-IT300LV scanning electron microscope (SEM). The lead-drawn delay elements containing all combinations of fuel (Mn) and oxidants (Sb2O3 and MnO2) were sectioned and imaged to obtain a visual representation of the packed compositions. The images for a few of these compositions are shown in Figure 5-1. For the Mn + Sb2O3 compositions it was found that in all cases the Mn particles were significantly larger than the Sb2O3 particles. No discernible packing arrangement was found, and each of the Mn particles was encased in a ‘sea’ of Sb2O3 particles. There was almost no contact between the fuel particles themselves, but there was a large amount of contact between the oxidant particles and a single fuel particle. The largest number of contact points existed between the oxidant particles themselves. It was further found that the Sb2O3 had an attraction to the Mn particles and a layer of Sb2O3 particles stuck to the surface of any Mn particle. This can be seen in Figure 5–1 (b). This is likely due to the static nature of Sb2O3. Sb2O3 has been found to be naturally electrostatically charged, which likely leads to this ‘sticking’ of small oxidant particles to the Mn particles. This greatly assisted in facilitating proper mixing and prevented particle segregation afterwards.
The Mn + MnO2 packing was found to differ slightly from that of Mn + Sb2O3 since the MnO2 particle size distributions were much wider. It was therefore found that the Mn and large agglomerates of MnO2 were both encased in the sea of small MnO2 oxidant particles. It can further be seen in Figure 5–1 (d) that there was no ‘sticking’ of small oxidant particles to the large fuel particles, and therefore not the same attraction between the two materials.
1 INTRODUCTION
1.1 Background
1.2 Aims and objectives
1.3 Outline of the thesis
2 LITERATURE REVIEW
2.1 Pyrotechnic delay elements
2.2 Burn rate measurements
2.3 Pyrotechnic reaction mechanisms and kinetics
2.4 Modeling of delay elements
3 EXPERIMENTAL
3.1 Raw material characterisation
3.2 Delay element preparation
3.3 Burn rate measurements
4 NUMERICAL MODELING OF DELAY ELEMENTS
4.1 Governing equations
4.2 Geometry and meshing
4.3 Numerical solutions
5 RESULTS AND DISCUSSION
5.1 Mn + Sb2O3/MnO2 packing
5.2 Burn rate measurement technique
5.3 Numerical simulations
6 CONCLUSIONS AND RECOMMENDATIONS
REFERENCES
