Formulations delay

The purpose of incorporating a delay device in ammunition is (i) to cover the time of flight (ii) to provide safety of persons using the ammunition (iii) to ensure safety of carrier aircraft (iv) to ensure self-destruction and (v) to enhance post 

Delays ranging from a few milliseconds to one minute duration are common in military use and are widely used in different types of ammunition [23]. Accordingly, a variety of delay formulations have been reported in the literature in order to achieve delays ranging from a few milliseconds to a few seconds. 

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The historical developments in delay formulations have been traced by G. Weingarten (Ref 133, p 254), who also tabulated a wealth of performance data... 

Some of the most important requirements of an ideal delay formulation with reproducible results are ... 

The formulations falling in the zone AA only are selected for actual Service use as these formulations satisfy one of the most important requirements of an ideal delay formulation that is, any minor change in the proportion of ingredients should not affect the burning rate adversely . The delay formulations are categorized in terms of IBR as shown in Table 5.8. 

Table 5.8 Classification of delay formulations and their applications.

In order to achieve the goals of pyrotechnic delay formulation, ingredients are chosen and formulated in an elegant way. The ingredients of a pyrotechnic delay formulation are (i) fuel (carbonaceous materials or inorganic substances) (ii) oxidizer (iii) binder and (iv) retardant, if required. 

The fuel and oxidizer are the principal constituents of a delay formulation. In certain mixtures of oxidizers and fuels, exothermic reaction after ignition is very fast which is not always desirable. Therefore, it becomes mandatory to control the reaction by the addition of a third ingredient called a retardant which is an inert material and does not take part in the exothermic reaction. 

Gas-producing (Slagless) Delay Formulations These formulations are used in a system where a vent is provided for the generated gases to escape. The types of fuels used for these formulations can be classified into the following groups ... 

Casless Delay Formulations Gasless delay formulations were introduced around 1929 to replace the old fuse formulation based on gunpowder which used to give erratic results under conditions of low ambient pressure at higher altitudes. 

The basic reaction underlying the combustion of many gasless delay formulations is the Goldschmidt or thermite reaction where a metal powder and a metallic oxide interact in an oxidation-reduction reaction manner with the evolution of a large amount of heat but very little or no gas. Consequently, these formulations are used where no vent or very little vent is provided in the ammunition. Gasless delay formulations tend to burn faster under higher consolidation as the points of contact of fuel and oxidizer increase. This is because the reaction in this case is a solid state reaction by diffusion. 

The most important characteristic of a delay formulation is its IBR. In addition, other important characteristics are sensitivity to impact, friction and electric spark, ignition temperature, heat output and gas output. Therefore, before static evaluation of delays, the delay formulation must be characterized thoroughly for these properties. 

A formulation based on antimony trisulfide (Sb2S3)-20%, potassium perchlorate (KC104)-8% and barium chromate(BaCr04)-72% (with NC as binder) is a well-known slow-burning delay formulation with a burning rate of 0.43 cm s 1. The burning rate decreases to 0.23 cms 1 on substitution of barium chromate by bismuth chromate. These formulations are safe to handle as revealed by the sensitivity data [26]. 

Burning rate is of great significance in the case of pyrotechnic formulations as it is indicative of their functional performance. For example, characteristics such as luminosity, IR output etc. are closely related to the burning rate. Similarly, in a pyrotechnic delay formulation, the length of the delay column is decided in the light of the burning rate of the formulation. 

Their primary use has been as fuels in pyrot delay formulations (see under Delays and Fuzes in Vol 8, P512-R to P515-L Table 9), where they replaced the earlier use of. separate powders of Zr and Ni. Because of changes in burning rate on storage and at varying operational temps exhibited by delay compns contg individual Zr and Ni powders, and because treatment to resist corrosion of both the Zr and Ni did not alleviate the difficulties, their use was discontinued, and attention was focused on the alloys of Zr and Ni as a potential fuel. The alloys were less flammable and hazardous to use than fme Zr pdr, and eliminated the need for catalytic Ni pdr which must be manufd under very carefully controlled conditions (Ref 3)... 

Janssen Pharmaceuticals. Effect of cisapride on the plasma concentrations of a delayed formulation of propranolol and on its clinical effects on blood pressure in mildly hypertensive patients. Data on file (Study R 51619/23-NL), 1986. 

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