Mechanical fuse

In mechanical fuses, where percussion primers are required, it seems fairly obvious that space requirements impose limits on the size of spring mechanisms or other physical modes of causing firing pins to move. The result is that, for fuses and other applications of this type, it becomes necessary to use primers of greatly increased sensitivity (Refs 6 8). This condition is illustrated with the M29A1 primer which is required to fire with an applied energy of 16 inch-ounces. This increased sensitivity is achieved by the use of thinner primer cup metal of softer alloy. Sensitivity can be further enhanced by the use of more sensitive priming mixt (Refs 2,6 20)... 

The easiest way to light safety fuse is with a mechanical fuse lighter, widely used in military services, or with special hot-burning fuse lighting matches. If ordinary matches must be used, here s the surest way to do it ... 

This device employs a modified mechanical fuse lighter to construct a booby trap or a firing device which can be controlled by the operator. 

Stab initiators are used in military systems such as small mechanical fuses where very little mechanical energy is available because of weight limitations and the small dimensions of the springs. Stab detonators use the same ignition mix, or priming composition, as many percussion primers do. Some of these are listed Table 23.2. 

The boron-doped pyrocarbon sublayer of C(B) is used as the mechanical fuse which ensures crack deflection and fibre pull-out. A hydrocarbon (CxHy) and BXn(X=F or Cl) are used as reactant precursors to deposit the C(B) layer. Both Bi3C2 and SiC are employed as the glass former to improve the oxidation resistance of the composite. B13C2 is deposited with the same precursors as for C(B) but in different conditions. CH3SiCl3 and H2 are used as the precursor gases for the SiC deposition. 

Boilers with mechanical fuses that melt when water levels drop excessively and allow steam to escape, thus preventing a rupture... 

Fused silica has a mass density of 2200 kg.m while vitreous silica is slightly denser with a density of 2210 kg.m Mechanically, fused silica is a relatively strong but brittle material with a tensile strength of 28 MPa, a compressive strength of 1450 MPa, and a Mohs hardness of 5. Both grades exhibit an extremely low coefficient of thermal expansion (e.g., 0.6 x 10 K from 20 to 1000°C) and a remarkable thermal shock resistance together with a low thermal conductivity. Fused silica, with a dielectric field strength of 16 MV.m , exhibits also excellent electrical insulation capabilities up to 1000 C. When heated above 1150 C, fused silica converts irreversibly into a-cristoballite as follows ... 

It is, of course, important that the mechanical fuse is replaced after use, but this may be taken care of by periodic vehicle inspection and by having the bumper rattle after an impact. The problem of enforcement appears to be no more difficult than in the case of the electrical fuse. If we are to continue to improve the quality of life, it is important to eliminate waste associated with unnecessary design requirements and over restrictive construction codes. 

Capillary Tubes Figure 12.42 shows a cross section of a typical capillary tube. Most capillary tubes are made from fused silica coated with a 20-35-)J,m layer of poly-imide to give it mechanical strength. The inner diameter is typically 25-75 )J,m, which is smaller than that for a capillary GC column, with an outer diameter of 200-375 )J,m. 

Cera.micA.bla.tors, Several types of subliming or melting ceramic ablators have been used or considered for use in dielectric appHcations particularly with quartz or boron nitride [10043-11 -5] fiber reinforcements to form a nonconductive char. Fused siHca is available in both nonporous (optically transparent) and porous (sHp cast) forms. Ford Aerospace manufactures a 3D siHca-fiber-reinforced composite densified with coUoidal siHca (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see COMPOSITE MATERIALS, CERAMIC MATRIX). 

The Vanderbilt process involves the mechanical frothing of air into a plastisol containing proprietary surfactants by means of an Oakes foamer or a Hobart-type batch whip. The resulting stable froth is spread or molded in its final form, then gelled and fused under controlled heat. The fused product is open-ceUed with fine cell size and density as low as 160 kg/m (10 lbs/fT). 

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