Explosive Technology for Metal Processing
Optimization of the Conditions for Dynamic Effects in the Explosive Metal Processing Technology
Tech Area / Field
- MAN-MPS/Manufacturing, Planning, Processing and Control/Manufacturing Technology
3 Approved without Funding
VNIIEF, Russia, N. Novgorod reg., Sarov
- Siberian Branch of RAS / Lavrent'ev Institute of Hydrodynamics, Russia, Novosibirsk reg., Novosibirsk
- Karlsruhe University, Germany, Karlsruhe\nDynamit Nobel AG, Germany, Burbach\nNaval Surface Warfare Center, USA, MD, Indian Head
Project summaryEngineering processes of metal processing with pulsed dynamic effects have been actively developed and applied in the industry starting in the second half of the 20-th century. Using dynamic effects, it is possible to perform the processes of stamping of large-sized items, strengthening of metal structures, welding of mixed metals, compacting of powders, their application to metal surfaces, etc.
Explosive welding is the most popular technology. In many cases this technology has no alternative. This process has been theoretically described in detail. In most cases explosion of the high explosive (HE) charge is used as the pressure pulse source. For explosive welding this is the only possible pulse source.
For explosive welding the wave front propagation velocity must be much lower than the sound velocity in the processed materials, that is range within 1,500–3,000 m/s. For this purpose high-porosity ammonium nitrate HEs (mixtures of ammonium nitrate with TNT having ~ 1g/cm3 bulk density) are generally used.
Explosive welding requires stability of pressure pulses. In case of instability incompletely welded portions may be produced, the welding quality decreases drastically.
In this case there is a contradiction: as the charge density decreases, critical and limiting charge dimensions increase. A critical dimension, a diameter or a thickness is the charge diameter (thickness) below which detonation is impossible; a limiting dimension is the diameter (thickness) above which the detonation velocity is independent of the charge dimensions. If the charge dimensions are between critical and limiting, the detonation velocity is a function of the dimension (diameter or thickness).
To stabilize the pressure pulse, the charge density and the dimensions should be fixed rigidly. Distribution uniformity of mixed HE components should be also taken into account.
The main project objective is to determine the mechanism of forming a strong hermetically sealed layer of mixed metals depending on the conditions of dynamic effects that are governed mainly by stability of the detonation front in a high-porosity heterogeneous HE charge.
Scientific and Practical Importance.
Experimental studies of the detonation wave formation and propagation in high-porosity active environments presented, for example, by a combination of spherical surfaces confining gas-filled explosive surrounded spaces are of exceptional interest for understanding and simulation of steady detonation initiation and propagation. Experimental relations between the detonation rate, the critical diameter (thickness) and the components ratio, the dimensions of spherical hollow particles, the thickness of their walls, the properties of the surrounding HE are proposed to be derived. In this case there will be a unique combination of academic and practical interest for the problem. The studies to be carried out to the full extent will make it possible to master new precision processes in the field of explosive processing of materials and will promote further commercialization of this area in VNIIEF.
Technical Approach and Methodology.
The basic requirement specified to HEs in their application for explosive processing of materials is the explosive loading pulse stability over a wide range of pressures from units to tens of GPa (the detonation rate ranging within 1–8 km/s). The pressure stability is provided by stability of the detonation rate and the charge density. The detonation rate depends on the density and also on the dimensions if the charge has dimensions smaller than the limiting ones. Therefore, to stabilize the explosive pulse under dynamic effects, the density should be fixed and the critical charge dimensions should be minimized to operate over a stable range exceeding the limiting dimensions.
For the given pure HE the critical dimensions (the critical diameter, in particular) depend on the charge microstructure that is determined by the relationship between the porosity and the specific surface area of pores. For the given porosity the critical charge diameter is inversely proportional to the specific surface area, that is depends on the level of size reduction of solid HE particles: the smaller the average size of particles, the smaller the critical diameter. According to this approach, these regularities will be studied during the project implementation with respect to mixed explosive compositions based on ammonium nitrate. One of the methods for reducing the HE critical diameter is insertion of man-made pores such as glass or polymer microspheres into the HE volume. During the project activities this approach is proposed to be used both for ammonium nitrate HEs and for mixed high-strength HEs.
VNIIEF has developed the methods for producing 20–800 mm microspheres from various materials. Using this as the basis, the possibility of producing microspheres from such explosives as ammonium nitrate HEs should be studied. Based on the powders of microspheres, it is possible to shape charges (bulk or after vibration compacting) with the relative density of ~ 0.1 and a sufficient shock-wave sensitivity (a small critical diameter). The microstructure of detonation fronts of HE charges having an extremely high porosity is proposed to be studied using an electron-optical high-resolution recorder provided with micron light guides.
Addition of ultradispersed active metals, (nanopowders) may also result in HE shock-wave sensitivity increase (the critical diameter decrease). Formulations of ammonium nitrate HEs with active metal additives should be studied in the course of the project as applied to the processes of explosive processing of materials.
Using the above approaches, compounding and technological studies in the field of pasty explosives having a wide range of detonation rates and minimum critical diameters are proposed to be carried out.
In developing HE, explosive welding production of a high-grade bimetallic compound on check samples will be the main test parameter.
Metallographic analysis and physicomechanical tests will be made to examine the boundary between the explosive welded metals, its geometric parameters and their influence upon mechanical characteristics and hermetic nature of the weld including studies into temperature relations. Interrelation between the strength, the hermetic nature and the phase composition of weld materials should be specified.
Studies of welding and explosive strengthening of metals will use the technological basis of RFNC-VNIIEF that provides performing of explosion operations both in the open and in special-purpose explosive chambers.
Production and formulation HE development efforts will be made using the chemical and technological basis of VNIIEF that allows operations of grinding, dissolving, mixing, filtration and vacuum drying of HEs as well as chemical and analytical activities to be performed.
Control over explosive characteristics of HEs, that is determination of the detonation rate, critical dimensions and safety parameters will be based on the available techniques after their complete development. Experiments will be conducted in protection facilities of VNIIEF.
Experiments on optimization of parameters of dynamic effects will be planned together with the specialists from the Institute of Hydrodynamics, Siberian Department of the Russian Academy of Sciences.
The software developed at the Lavrentiev Institute of Hydrodynamics, Siberian Department of the Russian Academy of Sciences (IHD SD RAS)will be used for processing of the generated results.
Potential Role of Foreign Collaborators.
The project orientation towards solution of topical problems may contribute into development of business relations with foreign partners. Cooperation in exchange of information related to the project issues is of interest. Discussions, participation in seminars, joint studies of material samples may be arranged. Cooperation of this kind may promote improvement of the project ideas and practical implementation of its results.
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