Karolina NIKOLCZUK, Justyna HADZIK, Zenon WILK ? Institute of Industrial Organic Chemistry in Warsaw, Branch in Krupski Młyn

Abstract:
The objective of this paper was to describe a series of tests related to the application of silicone polymers which can be added and modified with explosive materials  under ambient conditions without using the complex technological processes, high temperatures or complex, multi-stage chemical reactions. Moreover, the selection of  silicone polymers was economically justified and conducted regarding their availability in Poland. The technology for obtaining flexible linear shaped charges (LSC) was  developed and field tests of obtained charges were carried out, that is, the detonation velocity and effectiveness were tested on the basis of punching a steel plate of a specified thickness.

Please cite as: CHEMIK 2013, 67, 13, 33-40

Introduction

For more than 50 years, polymers and their derivatives have been used as components of propelling charges in artillery and small arms ammunition, and in explosives of reduced sensitivity to mechanical stimuli, and they have been applied in rocket propellants since the 1940s [1, 2]. Regarding the widespread presence of natural polymers in the environment, it was obvious that they were the first to be used in plastic explosives as so called natural binding agents. The development of knowledge on synthetic polymers caused that the research on using them also in explosives began in the United States in the 1950s. This resulted in creating a group of plastic explosives defined under the general name of PBX (Plastic Bonded Explosives).

As opposed to the explosive mixtures containing natural polymers as binding agents, the explosive mixtures with synthetic polymers are characterised by:
? increased durability over time
? increased resistance to external factors
? higher detonation parameters
? high level of safety at the production and processing phases as well as during their application.

Depending on the purpose of their application, the technology of PBXs production (casting, pressing or injection moulding), their composition and plastic characteristics are different [1]. PBXs are used everywhere where high explosive force, high and narrowband impulse of pressure, low sensitivity to external stimuli and easy application are required. The explosives with plastic polymer additives can be applied not only in the armaments industry, but also in the civil engineering, e.g. in mining (to intensify the output of crude oil and gas in pressure generators supplied by fuel and perfogenetators), metallurgy, and the processes of reinforcing, plating or pressing metals. When the advantageous properties of the explosives with plastic polymer additives had been found, the demand on them significantly increased in comparison to so far applied explosives. The economic and ecological arguments also weigh in favour of the production and applications of such explosives. It is caused by relatively low costs of production, the possibility of using them nearly in all fields of military engineering and simple reprocessing or disposal due to the use of the binding agent subjected to thermal decomposition [3, 4].

The dynamic development of science related to polymers and new materials provides opportunities for conducting numerous tests with the use of new polymer materials as the binding agent for popular explosives to modify their characteristics. Thus, the objective of this paper was to present the results of the tests involving organosilicon polymers and the explosive ? hexogen (RDX). Organosilicon polymers are high molecular compounds with organic (carbon derivatives) side chain substituents and inorganic main chain containing silicon, aluminium, titanium, phosphorus and other chemical elements. Regarding the numerous high molecular compounds, polysilicones, commonly referred to as silicones, are the most important in the group of organosilicon polymers. Their significance in engineering is huge. As their inorganic characteristics predominate, the properties of silicones differ in comparison to conventional polymers [5]. Silicon atoms may form polymer chains by silicon-silicon bond, but they are also capable of forming polymers with carbon as well as, more often, with heteroatom in a chain. The list of unique properties of oxosilanes, resulting from the flexibility of the oxosilane chain related to the type of ?Si-Obond and a lack of substituents in every second atom in the chain, is long. This has influenced a wide range of applications of both polymers and numerous oxosilane copolymers in various branches of industry [6÷7].

Experimental part

From among silicone polymers, room temperature vulcanisable (RTV) and heat temperature vulcanisable silicone polymers can be distinguished [7]. In case of applying heat temperature vulcanisable polymers, the process should be verified at an increased temperature (120 ? 170 °C) which could carry some risk as the studies are conducted on explosives. Thus, it was decided to apply in the tests two-component versions of RTV silicones. In this case, silanolterminated polymer was the primary polymer because the vulcanising agent (multifunctional silane) with hydrolysis catalyst was found in the second component of the vulcanising system. Spontaneous hydrolysis and then vulcanisation occurred after mixing both components. Silicone polymers of Smooth ? Sil Company were selected for the purpose of our tests. KauPoSil company from Siemianowice Śląskie distributes them in Poland. Table 1 presents the fundamental physical properties of silicone polymers as specified by the manufacturer ? Smooth ? Sil [8].

The flexible compositions of silicone-based RDX were prepared in a mixer containing different percentage content of selected additive silicones. The total content of inert substances was within a range from 20 to 30%. During the preliminary test, the mixed composition was placed in a simple, flat matrix specifically designed for this purpose, from which charges of 60 mm x 200 mm dimensions were produced. Then, the pressure of 2-5 MPa was applied (depending on the mixture consistence) to achieve a homogeneous structure without pores. To accelerate the process of vulcanisation, the pressed composition was heated in the mould at a temperature of ca. 60?C for a few (4÷6) hours. Photo 1 illustrates exemplary specimens of obtained flexible explosive compositions using Smooth ? Sil silicones and the flat matrix of different percentage content of polymers.

 

As the new explosives contain a significant quantity (20-30%) of an inert component, the material density and their detonation parameters are reduced in comparison to a pure crystalline explosive. Such explosive materials also require adequately strong initiation and a proper thickness of the explosive layer. It necessitated conducting preliminary field tests to determine the minimum layer of explosive to detonate the charge. The density of obtained materials and the velocity of detonation were determined for experimental flat charges.

The measuring stand at the Branch Krupski Młyn of the Institute of Industrial Organic Chemistry was used to determine the velocity of explosive detonation

The test on determining the velocity of detonation consisted in measuring passing time of detonation wave over a specified distance. Photo 2 illustrates the measuring stand for the velocity of detonation for flexible flat charges and a way of placing ionisation probes.

The simple flat matrix was used in additional technological tests on simultaneously combined layers of flexible explosive compositions and flexible compositions of metal powders mention above, using the common binding agent. The flexible composition of metal powders with Smooth-Sil silicones acted as a cumulative liner for flexible linear shaped charges. As it is known from practice, an adequately selected material and shape of the liner influences the efficiency of punching or cutting of the shaped charge. Photo 3 illustrates an exemplary shaped piece combined of an explosive, a metal powder and silicones based on vulcanisation.

On the basis of positive results obtained for flat shaped pieces, the technological tests on flexible linear shaped charges prepared from a simple matrix of 200 mm length were conducted (Photo 4).

The experimental model charges in a form of flexible shaped pieces were based on hexogen and Cu powder with a silicone binding agent of Ecoflex 0030 trade name and the content of 15% and 22%. Such prepared charges were denoted as LSC (LŁK)-26/200 ? charge length of 200 mm and transverse dimension of 26 mm, basis weight of an explosive in the charge of ca. 1000 g/rm. Additionally, for the purpose of comparing the detonation parameters of new flexible LSCs, the experimental model charges LSC 26/200 were made from other materials: in a form of stable shaped piece (explosive: hexogen and a liner made from electrolytic copper powder with polytetrafluoropolymer additive ? PTFE, i.e. tarflen) and a flexible shaped piece (explosive: PBX and a liner made from electrolytic copper powder with epoxy resin additive) (Photo 5).

The preparation of matrices for other dimensions of elongated LSC (types LSC-18/500, LSC-32/350, LSC-50/350) was based on the positive results of application tests on obtaining flexible charges LSC 256/200. Finally, silicone of Ecoflex 0030 type was selected to produce the charges of the above types. Table 3 presents the fundamental parameters of obtained LSCs.

The photos below illustrate the examples of obtained LSCs (Photo 6).

The flexibility of charges shown in Photo 6 depends to a large degree on the dimensions, and specifically, on the dimension of transverse section. The lower the dimension is, the more flexible the charge is.

Field tests
The field tests on charges of LSC-26/200 type were performed as a result of applying the explosives of new properties. The detonation velocity was determined and the effectiveness was tested on the basis of punching a steel plate of a specified thickness. The testing system is presented in Figure 1, and the linear charge in the measurement stand is illustrated in Photo 7.

The measurement results were recorded through a data acquisition system (oscilloscope, data acquisition board, PC) and archived on storage media, and then analysed. The measurement results are presented in Table 4.

Photo 8 illustrates the effects of cutting the steel plate of 10 mm thickness.

The numbering seen in the Photo corresponds to a sequence of testing charges LSC-26/200 as specified in Table 4.

Also the second group of linear charges of other transverse dimensions and basis weight were subjected to field tests. Photo 9 illustrates the research testing for the charge LSC-32/350 and the observed cut effect in the steel plate (cut depth 18-22 mm, width 8-9 mm). During the test, the nominal distance from the obstacle was 0.5 D = 16 mm.

Photo 10 illustrates the research testing for the charge LSC-18/500 and the observed cut effect in the steel plate (width 10 mm). In this case, the distance from the obstacle was 0.5 D = 9 mm.

For the third type of charge LSC-50/350, the depth of cut in the steel was tested depending on a variable parameter, that is, the distance of a charge from the obstacle (Photo 11).

Photo 12 shows a cut (depth and width) in the steel plate after detonating the tested charge and the dimensions of the cut depending on the charge distance.\

The most spectacular cut effects were observed for the distance from the obstacle of 0.5 D. For such a distance, the adequate velocity of cumulative jet was obtained which was capable of directing the explosive energy into the obstacle material and consequently, the most desirable depth of the plate steel cut was achieved.

Summary and conclusions

The studies on applying silicone polymers as additives to the explosives resulted in working out a series of types of flexible linear shaped charges demonstrating high detonation parameters and consequently, the suitable capability of explosive cutting. Moreover, LSCs of a new type have the following advantages: a simple production process without complex technological processes and energy inputs, mainly based on raw material inputs. It should be emphasized that in case of the charges of a new type, the splinters do not have any impact on the surroundings (LSC without lining) and the charges are characterised by additional desirable utility parameters such as flexibility and possibility of giving them any shape. New flexible linear charges are intended for performing specialist blasting works for civil and specialised use.

Literature
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2. Urbański J., Chemia i technologia materiałów wybuchowych, WSI Radom, 1992.
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5. Rościszowski P., Zielecka M.: Silikony właściwości i zastosowanie, WNT Warszawa, 2002.
6. Szlezyngier W. Tworzywa sztuczne ? chemia, technologia wytwarzania, właściwości, przetwórstwo, zastosowanie ? tom I. Politechnika Rzeszowska, Rzeszów 1996.
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8. Karty charakterystyki polimerów silikonowych firmy Smooth ? Sil; www.kauposil.com

Karolina NIKOLCZUK ? M.Sc., graduated from the Faculty of Chemistry at the Silesian University of Technology in Gliwice in 2006 in the field of Chemical Technology. She is an assistant lecturer in the Institute of Industrial Organic Chemistry in Warsaw, Branch Krupski Młyn. She is involved in issues on testing and using explosives.
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Justyna HADZIK ? M.Sc., graduated from the Faculty of Chemistry at the Silesian University of Technology in Gliwice in 2005 in the field of Chemical Technology, specialisation: Organic Technology. She completed the post-graduate studies in the field of Technology of Explosives in 2007. She is an assistant lecturer in the Institute of Industrial Organic Chemistry, Branch Krupski Młyn. Her research interests are related to the development of and research on explosives and blasting agents.
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Zenon WILK? M.Sc., assistant professor, graduated from the Silesian University of Technology in Gliwice, specialisation: Conversion and Use of Energy. Postgraduate studies: Chemistry and Technology of Explosive materials. He got his Ph.D. degree at the Faculty of Mechatronics at the Military University of Technology in Warsaw. He is an expert in the field of technology of explosives, mechanics and modelling the explosion issues, particularly the cumulation phenomenon. He is the head of the Institute of Industrial Organic Chemistry Branch in Krupski Młyn. He was involved in many research and application projects on producing explosives and blasting equipment for borehole mining and specialist works.
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