AN EXPLOSIVE DEVICE

Abstract: Castable, solid explosive device intended primarily for deep water welding purposes. The explosive device has the form of a structure comprising granular explosive material, hollow glass spheres, and metal powder embodied in a plastics matrix.

Description: An explosive device. The present invention relates to an explosive device, and more particularly to an explosive device for deto¬ nations at high pressures. The explosive device according to the invention is particularly suited for explosive welding of pipes or tubes at elevated pressures, such as the explosive welding of pipe-lines on the sea bed, although the de¬ vice can also be used advantageously in other contexts, where elevated or high pressures prevail. At a water depth of 500 meters, the pressure is about 50 atmospheres: The properties of the majority of known explosive materials suitable for explosive weld¬ ing purposes, i.e. have a detonation rate of between 2000 m/s and 5000 m/s, undergo a charge when subjected to pressure. Because such materials are normally in powder form or plastically deformable, they become compressed, which results in a change in density and also in compression of the air bubbles which normally facilitate initiation of the detonation or explosion. Consequently, the detonation rate will increase at low positive or guage pressures. Initiation of the detonating process, or explosion, can no longer occur at high pressures, this condition being referred to as "total compaction". The present invention overcomes this disadvantage and relates to an explosive device or material that has a high mechanical strength and that will function at pressures as high as 50 to 60 atmospheres above at os- pheric. Accordingly, the present invention relates to an ex¬ plosive device having a detonation rate of approximate¬ ly 2000 m/s to 5000 m/s and comprising an explosive material and a matrix, and is characterized in that the matrix comprises a castable or moldable material having embodied therein explosive granules, hollow spherical bodies, and a metal powder. The invention will now be described in more detail with reference to the accompanying drawing, in which Figure 1 illustrates in cross-section an exemplifying embodi¬ ment of an explosive device according to the invention. The cross-sectional view of Figure 1 is highly schemat¬ ic. Thus, the explosive device according to the invention comprises a diluted explosive in which explosive gran¬ ules are dispersed in an homogeneous, inert matrix of moldable or castable material. In Figure 1 the reference 1 identifies the matrix, and the reference 2 the explosive granules. Assuming that all granules 2 are of mutually the same size and are uniformly dispersed in the matrix 1 , the detonation rate of the thus diluted explosive can be calculated from the expression: where p is the diameter of the explosive granules d is the distance between the granules D, is the detonation rate within each granule D is the average detonation rate of the diluted explosive, and c is the speed of sound in the matrix material. Example 1 Assume the following values: p - 1 mm D = 8000 m/s The density of the explosive material = p = 1-76 g/cm 3 c = 1500 m/s The density of the matrix material = p = 1*5 g/cirr The explosive material is present in an amount corres¬ ponding to 30% by weight, The following relationship then applies: d p spr . m m (2) where m is the weight of the p p m . mspr matrix material m is the weight of the explosive material When the numerical values are inserted in (2) above there is obtained: d 1 -76 • 0-7 _ 7Δ p 1 -5 - 0-3 Z' 4 When p equals 1 mm, d will equal 2-lk mm When the numerical values are inserted in ( 1 ) above there is obtained: 1 + 2-74 + 2-74 which results in D 8 1-5 D = 1 916 m/s The following table sets forth the detonation rate (D) of the diluted explosive device at differing sounds of speed (c) in the matrix material c (m/s) D (m/s) 1500 1916 2000 2504 2740 3324 3000 3603 4000 4617 5000 5558 Other factors influence detonation of the device however. When a shock-wave, such as that illustrated at 3 in Fig¬ ure 1 , is transmitted towards and passes through the explosive material 1, 2, the shock-wave, provided that it contains sufficient energy, will initiate detonation of the first granules it strikes. This results in a supply of energy, and the shock-wave propagates to further ex¬ plosive granules. During passage of the shock-wave through the matrix material, the pressure amplitude of the wave declines. In order to initiate detonation of further granules, the shock-wave must still contain suffi¬ cient energy herefor. Consequently, the explosive gran¬ ules 2 must not be spaced too widely apart. Other factors which influence detonation are the density of the matrix material and the prevailing porosity of the device. A given quantity of air will favourably affect the deto- nation properties of the device, since when the pores collapse, as the shock wave passes, they provide a local increase in pressure and also an increase in temperature. Consequently, when manufacturing the explosive device according to the invention, there is added thereto a controlled quantity of air, enclosed in minute, spherical, hollow bodies. In order to pre¬ vent additional air from entering the explosive device, the components are mixed together under a vacuum, when manufacturing the device. According to one preferred embodiment of the invention, the aforesaid spherical bodies are made of glass or a plastic material. Glass is preferred in this repect, because the explosive device is intended for high am- bient pressures and because glass spheres can withstand greater ambient pressures than plastic spheres. The air-filled glass spheres used have a very small diame¬ ter, e.g. 0-01 mm, and are known per se. In accordance with the invention, the density of the matrix material is increased by admixing a heavier material therewith, in order to maintain thereby de¬ compression of the shock-wave within acceptable values. According to the invention this heavier material may be a metal powder. According to one preferred embodiment of the invention, the metal powder comprises powdered zinc or iron. In Figure 1 , the dots 4 and 5 indicate uniformly dis¬ persed glass bodies and uniformly dispersed metal pow¬ der-grains respectively. i the case of the explosives having detonation rates a s low as between 2000 m/s and 5000 m/s, the rate of detonation is dependent on the dimensions of the charge body. The smaller the dimensions, the higher the per¬ centage of pure explosive that must be incorporated in order to achieve a given rate of detonation. When the explosive devices are to be inserted into pipes, such as pipe-lines, the devices must exhibit a certain degree of elasticity, since the pipes are often slightly oval in cross-section. The matrix material used may be selected from a large number of castable or moldable materials. In the case of underwater devices however, the matrix material chosen should have suffi¬ cient stability and water resistance to withstand pressure and wetness. Above all, the material used must not be capable of influencing the explosive mate¬ rial incorporated in the device, or generate high temperatures during the mixing and curing processes. Consequently, according to one preferred embodiment of the invention, the matrix material consists of a plas- tics material, and preferably a two-component poly- urethane cast plastic. According to the invention, the explosive granules may comprise any one of a number of explosive substances. A preferred explosive, however, is pentaerythritol- tetranitrate (PETN) , due to its high initiation sensi¬ tivity, thereby enabling a high degree of dilution to be achieved. In this case, the explosive material constitutes 20-50 % by weight of the explosive device, preferably 25-45 % by weight. However, it may be ad- vantageous to use cyclotetramethylene-tetranitramine (Octogen) , cyclo - 1, 3, 5 - trimethylene - 2, 4, 6 - trinitramine (Hexogen) or Trinitrotolvene (Trotyl) . According to one embodiment of the invention, the explo¬ sive material comprises two or more of the explosives Octogen, Hexogen, Trotyl, PETN. Mention has been made in the aforegoing of admixing spherical bodies with the components of the explosive device. According to one preferred embodiment of the invention, the quantity of spherical bodies used is such that the explosive material constitutes from 4 to 10 % by weight of the spherical bodies, preferably 7% by weight. According to a further preferred embodiment of the in¬ vention, the quantity of metal powder used is such that the explosive material constitutes from 10 to 30 % by weight of the metal powder, preferably 20 % by weight. Example 2 The following explosive material was manufactured. The ingredients used were: 1400 g PETN 800 g Zn 288 g glass spheres 1008 g polyol 504 g isocyanate Zinc, glass spheres, and PETN were mixed in polyol and isocyanate was added. The mixing vessel was then evacu¬ ated to about 11 mm Hg and the mixture stirred or agi¬ tated for 65 minutes, prior to casting the mixture into a 50 mm-thick plate-like explosive device. The device was stored for two days, to allow the mixture to harden, and was then detonated. The rate of detonation was measured as 3650 m/s. A large number of explosive devices were cast with vary- ing explosive compositions, and then tested experimen¬ tally. The devices were found to be particularly stable chemically, and the manufacturing method used affords good reproduceability. Underwater tests showed that the devices function independent of ambient pressure. In certain applications, an advantage is gained when part of the matrix material is formed as a dam or bar¬ rier against the remaining matrix material. Accordingly, in accordance with a further embodiment of the invention, a first part of the matrix has solely metal powder embodied therein, this first part being located along at least one side of a second part of the matrix, this second part also incorporating granular explosive and air-filled spherical bodies, said first part constituting a damming mass or barrier. It will be evident from the aforegoing that the present invention circumvents the aforesaid problems associated with explosives. Although the invention has been described with reference to a number of embodiments thereof, it will be under- stood that modifications and variations can be made within the framework of the expertise of those skilled in this art and that the invention is solely limited by the scope of the following claims.

Claims: CLAIMS 1. An explosive device having a rate of detonation of approximately 2000 m/s - 5000 m/s, and comprising an explosive material and a matrix, characterized in that the matrix (1) comprises a castable or moldable materi¬ al which incorporates a granular explosive material (2) , hollow spherical bodies (4) and a metal powder (5) . 2. An explosive device according to Claim 1, charac¬ terized in that the matrix (1) comprises a plastics material. 3. An explosive device according to Claim 1 or 2, characterized in that the spherical bodies (4) are made of glass or a plastic material. 4. An explosive device according to Claim 1 , 2 or 3, characterized in that said metal powder (5) is powder- ized zinc or iron. 5. An explosive device according to Claim 1, 2, 3 or 4, characterized in that the explosive material (2) incorporated in said device is pentaerylthritol-tetra- nitrate, and in that the explosive material (2) consti¬ tutes 20-50 % by weight of the explosive device, preferably 25-45 % by weight. 6. An explosive device according to Claim 1 or 5, characterized in that the explosive material (2) in- corporated in the device comprises at least one of the explosives cyclotetramethylene-tetranitramine, cyclo - 1, 3, 5 - tri ethylene - 2, 4, 6 - trinitramine or trinitrotoluene. 7. An explosive device according to Claim 1 , 2, 3, 4, 5 or 6, characterized in that the number of spherical bodies used is such that the explosive material consti¬ tutes from 4 to 10 % by weight of the spherical bodies (3) , preferably 7 % by weight. 8. An explosive device according to Claims 1, 2, 3, 4, 5, 6 or 7, characterized in that the quantity of metal powder (5) used is such that the explosive material constitutes from 10 to 30 % by weight of the metal powder, preferably 20 % by weight. 9. An explosive device according to Claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that the matrix includes a first part in which solely metal powder Is incorpor¬ ated and which is located along at least one side of a second part of the matrix which incorporates granular explosive material and air-filled spherical bodies, said first matrix part forming a dam or barrier mass.

Inventors: DELERSJOE JAN CHRISTER, PERSSON PER INGEMAR, DELERSJOE, JAN, CHRISTER, PERSSON, PER, INGEMAR
Applicants: EXPLOWELD AB
Application year: 1986
Main classification: C06B45
IPC codes: C06B25, C06B45