Fuse wire

Abschmelzdraht, m. fuse wire, fusible wire. Vbschmelzeu, v.i. melt off, melt. fuse, separate by melting seal off, seal. — v.i. melt off. Abschmelz-konstante, /. fusion coeflScient. -achweissung, /, flash welding, -sicherung, /, (Elec.) safety fuse. 

FIGURE 6.12 A bomb calorimeter is used to measure heat transfers at constant volume. The sample in the central rigid container called the bomb is ignited electrically with a fuse wire. Once combustion has begun, energy released as heat spreads through the walls of the bomb into the water. The heat released is proportional to the temperature change of the entire assembly. 

Induction time. In firing electric detonators, the time between the breaking of the fuse wire and the detonation of the base charge (see p. 112). 

The igniter can be of several types, including a fuse wire, spark, or chemical ignition system. A typical energy for ignition is 10 J, although... 

In equations 7.27 and 7.28 m(BA), m(cot), m(crbl), and m(wr) are the masses of benzoic acid sample, cotton thread fuse, platinum crucible, and platinum fuse wire initially placed inside the bomb, respectively n(02) is the amount of substance of oxygen inside the bomb n(C02) is the amount of substance of carbon dioxide formed in the reaction Am(H20) is the difference between the mass of water initially present inside the calorimeter proper and that of the standard initial calorimetric system and cy (BA), cy(Pt),cy (cot), Cy(02), and Cy(C02)are the heat capacities at constant volume of benzoic acid, platinum, cotton, oxygen, and carbon dioxide, respectively. The terms e (H20) and f(sin) represent the effective heat capacities of the two-phase systems present inside the bomb in the initial state (liquid water+water vapor) and in the final state (final bomb solution + water vapor), respectively. In the case of the combustion of compounds containing the elements C, H, O, and N, at 298.15 K, these terms are given by [44]... 

In an attempt to understand the combustion mechanism of catalyzed double-base propellants, several investigators have conducted experiments to measure the burning rates of strands of liquid nitrate esters. The various measurement techniques were very similar to that employed in a conventional solid propellant strand burner. The liquid esters were placed in a tubular container, and the liquid surface regression speeds were measured by optical methods or by the fuse-wire method used in solid-propeUant strand burners. The only important difference between the solid and the liquid strand burning-rate measurements is that the liquid strand burning speed is very much dependent on the diameter of the container. 

HN03 to the bomb, place the crucible in the electrode support of the bomb, and attach the fuse wire. Assemble the bomb and add oxygen to a pressure of 24 atm (gage). Place the bomb in the calorimeter (a cold water bath in a large stainless steel beaker is also satisfactory) and ignite the sample using appropriate safety precautions ordinarily employed in bomb calorimetry work. 

Then the tap is closed and the strand ignited at the top. When flame reaches the upper "timing lead it breaks the fuse wire. This activates electrical relay causing a timing device to start. When the flame reaches the lower wire the relay would stop the timing device. Thus a measurement can be taken for the burning to travel betw the accurately known distance along the strand. This method... 

After firing, the contents of the bomb are washed into a beaker and titrated with standard sodium carbonate solution to determine the amount of acid (nitric acid, HN03 and sulfuric acid, H2S04) produced in the combustion. Corrections for the amount of acid, the amount of fuse wire used in firing, and the sulfur content of the sample are then made to the total heat produced in the calorimeter (energy equivalent times corrected temperature rise) to determine the gross calorific value of the solid fuel. 

Fuse Wire Correction. This correction is made by measuring the length (in cm.) of wire burned and multiplying it by the known heat of combustion per centimeter of the wire (2.8 cal./cm). 

Transformer ignition circuit for bomb calorimeter. The switch is a momentary-contact push switch that is only on when it is held down. Release the switch if ignition does not occur after about 5 s (the pilot light will indicate when the fuse wire bums through). The choice of resistor R will depend on the type of calorimeter and the length of fuse wire to be used (a current of 3 to 4 A is desired). 

Use Jewelry ( medium platinum is 95% platinum, 5% iridium and hard platinum is 90% platinum, 10% iridium), electrical contacts (10-25% iridium), fuse wire (10-20% iridium), hypodermic needles (20-30% iridium), and in general where high corrosion resistance is needed. 

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