Field ammunition anti-static packaging design

Abstract : This paper expounds the causes and forms of electrostatic discharge under field conditions, analyzes the basic principles of electrostatic protection, introduces several protective materials that can be used in ammunition packaging under field conditions, and provides assistance for long-term storage of ammunition anti-static packaging technology.

Keywords: Field ammunition; Electrostatic discharge: Anti-static packaging design

With the increase in the application of electronic components and electric pyrotechnics in ammunition, the static sensitivity of ammunition is getting higher and higher, and its antistatic performance is getting weaker and weaker. In the past, foreign military and our armed forces often suffered from spontaneous combustion due to electrostatic discharge. Especially in field conditions, there are more accidental factors that cause electrostatic discharge in ammunition, and many anti-static measures are difficult to implement. The improvement of packaging structure and performance, and the enhancement of anti-static capability of ammunition have become an inevitable choice for field ammunition anti-static, which can effectively eliminate the occurrence of electrostatic hazards and is also of great significance for the long-term storage of anti-static ammunition.

1 The generation of static electricity and the forms of damage under field conditions

Static power generation under field conditions mainly has the following three aspects: 1) Contact-separation and electrification. In the transportation and transportation of ammunition, static electricity is generated when the packaging materials are separated from other objects and rubbed. When a person undresses or stands up from a leather chair, it generates a voltage of several kilovolts or even tens of thousands of volts; 2) Elimination of electrification. When the ammunition is sealed and packaged, the human body and the packaging material will generate a higher voltage. In addition, a high voltage is also generated when the plastic awning fabric on the surface of the ammunition is uncovered; 3) Inductive charging. When lightning occurs near the ammunition heap, the high potential of the lightning electrode can induce a very high voltage on the surface of the ammunition. Although the probability of direct mine strikes in ammunition piles is very small, there are many induced mines, especially in the southern thunderstorm season. The charge voltage of the ammunition surface is enough to penetrate the ammunition internal circuit and ignite electric explosives. This accident happened before our army. The rocket artillery shells piled up on a certain position were spontaneously ejected due to the thunder and lightning. When these high-voltage dangerous static power sources and ammunition circuits and electric pyrotechnic products form an energy coupling, electrostatic discharge occurs. The discharge voltage can be as high as tens of thousands of volts, the discharge current can reach hundreds of amps, and the frequency spectrum can be up to megahertz. The rise time of the current waveform can be less than 1 ns. Electrostatic discharge can cause accidental ignition and explosion of electrical firework, and can also cause serious interference and hard damage to electronic equipment. The electromagnetic pulse generated by electrostatic discharge may also cause malfunction of the microelectronic circuit and potential operational reliability reduction.

2 Principle of electrostatic protection

Although there are many dangerous static power sources in the field and the means of electrostatic protection are limited, electrostatic hazards can still be controlled and eliminated. The formation of electrostatic discharge must have three conditions at the same time: 1) dangerous static power with sufficient high voltage; 2) presence of sensitive electrostatic hazards; 3) formation of electrostatic energy coupling. From the electrostatic discharge conditions, it can be seen that at least one of the conditions must be eliminated to eliminate the electrostatic discharge. Without changing the design of the ammunition, the discharge phenomenon can only be eliminated by reducing the danger of static electricity and cutting off the electrostatic energy coupling channel. Although increasing the humidity can significantly change the surface resistance of the object and enhance the conductivity, the humidity of the field ammunition storage site is difficult to control. Therefore, the static electricity dissipating speed cannot be increased by adjusting the humidity of the local space, and the voltage of the dangerous static power source can be reduced.

The use of anti-static materials to improve packaging is a simple and effective method of protection. It can not only rapidly leak out the electrostatic charge on the ammunition packaging, but also can play an electromagnetic shielding role to prevent some powerful radars and electromagnetic pulse weapons from generating radio frequency intrusion. Ammunition forms an energy coupling, causing damage to electronic circuits or failure of electric firework or even explosion. For example, the minimum safety current of the thermal bridge type electric explosion device is only 50mA.

3 Methods to be taken

Under high-tech conditions, anti-static packaging has become a base for ammunition packaging. Anti-static packaging materials and products from the United States, Japan, Germany and other countries have taken the lead in the world. The United States also specifically revised the ammunition packaging specification to optimize and improve ammunition packaging. In view of our military's actual experience and drawing on the packaging experience of the foreign armed forces, the necessary anti-static packaging for ammunition can greatly improve the living space for ammunition. There are mainly the following methods:

3.1 Use of antistatic agents

According to different ways of adding, antistatic agents are divided into two types: outer coating type and inner additive type. External coating type antistatic agents are applied to the surface by brushing, spraying or dipping, and they are effective and widely applicable. In particular, it is better to use this method when improving the packaging of ammunition that was previously produced without ESD protection or with poor protection. It can use the original packaging, saves money, and is easy to operate. Some shielding coatings generally use gold, silver, copper, nickel or other metal powders or graphite powders to spray on the inner and outer surfaces of the package, which can also play a better anti-static and shielding effect, but its price is relatively high, not suitable for larger Ammunition on the packing box.

The internal antistatic agent is added to the resin at the time of compounding to uniformly disperse it into the polymer. These substances are all soluble in water and can migrate from the inside to the surface of the polymer material to form a uniform resistance on the surface. Electrostatic layer. It is resistant to friction, has good stability, has long-lasting efficacy, and is inexpensive, and is suitable for use in packaging materials for ammunition, since the average ammunition storage period required is more than 15 years.

3.2 Use of Structural Conductive Polymer Materials

Structure type conductive polymer material is a kind of new conductive unsaturated polymer. Through their own chemical structure, they have the molecular structure of the φ-electron that acts the same as metal free electrons. The electrons move through the π-conjugated system and become electrically conductive. They are then synthesized by electrolytic polymerization and then doped. Now their highest conductivity level is comparable to that of copper, silver and other metals.

Polyacetylene is currently the most cost-effective conductive material, its conductivity can be as high as 105 Ω-1.cm-1 after doping, and the conductivity of copper and silver is only 106 Ω-1.cm-1. It can be seen that the conductivity of polyacetylene after doping is close to that of a good conductor. However, due to the presence of a highly oxidizable double bond in polyacetylene, its stability is not very high. In addition, polyacetylene is insoluble or infusible, and processing and molding are difficult.

Compared with polyacetylene, polyaniline (PAn) has greater advantages. It is stable in nature, easy to process, and easy to form into films. The film is soft and flexible. More important is the low price. PAn has excellent electrical properties, and its electrical conductivity varies from 10-12 to 10 Ω-1.cm-1 with different doping degrees.

3.3 Using Filler Materials

The so-called conductive filler is a class of substances that impart electrical conductivity. According to its performance, there are mainly five series, namely metal systems, carbon systems, metal oxide systems, metallized fiber systems, and organic polymer systems. Among them, carbon is the most commonly used conductive filler. Carbon black is a natural semiconductor material with a bulk resistivity of approximately 0.1 to 10 Ω.cm. The raw materials are readily available and the conductive properties are persistent and stable. The resistivity of the material can be greatly adjusted (1 to 108 Ω). .cm). Therefore, the composite conductive polymer material made of carbon black is the most widely used and most used conductive material in antistatic and electromagnetic shielding.

Carbon fiber is a new type of paint with good conductivity. It is characterized by uniform and firm coating and good adhesion with resin. The metalized carbon fiber has a 50 to 100 times more conductive performance than a typical carbon fiber. However, its high price is only suitable for the protection of internal electronic circuits and electric pyrotechnics of parts with high electrostatic susceptibility.
The base polymer filled with metal powders and metal oxides can obtain excellent conductivity, and can obtain higher conductivity when filled with less. However, metal fibers are easily broken during processing, are easily oxidized, and are expensive.

4 Conclusion <br> Ammunition anti-static packaging should be combined with the actual situation of our military, design packaging, packaging and electrostatic protection should be combined together, select different protective packaging for different ammunition, select the appropriate packaging materials, so as to avoid excessive packaging increases Cost, or packaging is not enough to achieve results. It is also necessary to combine the internal and external packaging for comprehensive consideration and to determine the best protection scheme. It cannot be satisfied to improve only one type of packaging. The design of electrostatic protection should be practically used in the design of sub-ammunition packaging, and strive to achieve the best performance-cost ratio. In short, the promotion and application of anti-static packaging will effectively improve the anti-static capability of our military ammunition, and further strengthen the field survivability of ammunition.




Author: Ma Hui, high thread Yong, Yang Shiliang Source: Packaging Engineering

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