The Mechanical Fuse

Safety, in particular auto safety, has been receiving wide attention. Concern is not only with the welfare of the driver, but with the reduction in property damage associated with front and rear end collisions. The latter aspect was brought into sharp focus by the offer of an insurance company to reduce insurance rates 20% on cars capable of withstanding a front or rear end crash at a speed of 5 mph without damage. 

Equaling the kinetic energy ofthe vehicle ofweight (W) and velocity (V) to the work done by force (P) acting through a distance (f)  

If acceleration (a) is limited to 3g (the highest safe acceleration for a passenger without a seat belt), then for E= 5 mph  

for a 4,000 lb car, the force on the frame and bumper would be 12,000 lb and a minimum of 3.33 in. of travel would be required between bumper and car frame. These values appear to be reasonable and may be taken as the design requirements. 

For the 4,000 lb car considered, the required force is 12,000 lb. When cutting mild steel in this way, u will be about 0.3x10 in.lb/in.. Thus, for a tool of 1 in. diameter and for two points of attachment on the bumper, the wall thickness (t) required is  

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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. 

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. 

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). 

Oxidation of fused isoxazolidine (173) with one equivalent of m-chloroperbenzoic acid produced an oxazine. The mechanism of transformation involves formation of an A/-oxide... 

The mechanism by which analytes are transported in a non-discriminate manner (i.e. via bulk flow) in an electrophoresis capillary is termed electroosmosis. Eigure 9.1 depicts the inside of a fused silica capillary and illustrates the source that supports electroosmotic flow. Adjacent to the negatively charged capillary wall are specifically adsorbed counterions, which make up the fairly immobile Stern layer. The excess ions just outside the Stern layer form the diffuse layer, which is mobile under the influence of an electric field. The substantial frictional forces between molecules in solution allow for the movement of the diffuse layer to pull the bulk... 

Selective removal of the less noble constituent has been demonstrated by chemical analysis in the case of nickel-rich alloys in fused caustic soda or fused fluorides ", and by etching effects and X-ray microanalysis for Fe-18Cr-8Ni steels in fused alkali chlorides. This type of excessive damage can occur with quite small total amounts of corrosion, and in this sense its effect on the mechanical properties of the alloy is comparable with the notorious effect of intercrystalline disintegration in the stainless steels. 

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 mechanism of boride formation is not always well known. However, many studies have sought to understand the chemical processes involved in fused-salt electrolysis. 

One of the most important problems that has to be solved in the thiepin chemistry is the mechanism of the sulfur extrusion reaction. Ready loss of sulfur of the simplest thiepins presumably occurs by valence isomerization to the corresponding thianorcaradiene, which requires a [4n -I- 2] disrotatory electrocyclic process leading to a c/s-fused three-membered ring, followed by cheletropic loss of sulfur. A lot of evidence supporting the above mechanism, though inconclusive, is available to date. 

Because of the extreme importance of regularity and freedom from failure which must characterise safety fuse, detailed and exhaustive tests must be carried out on the product. Certain controls are obvious, namely, measurement of powder charge and of burning speed, both before and after immersion in water. Other tests usually carried out include resistance to cracking on flexing at low temperatures round a mandrel, coil tests in which the fuse is bunched into flat or complex coils and freedom from failure after immersion in water is determined. New types of fuse are usually tested to indicate the amount of smoke produced and also to determine the adequacy of the end spit. The end spit is the projection of particles of burning powder from a cut end and is of importance because it provides the mechanism which enables the fuse to ignite a detonator. 

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. 

Subsequent, investigation showed that with prolonged reaction times the initially formed cycloadduct 22a then underwent [2+4+]-polar cycloaddition followed by a sequence of rearrangements to afford a novel benzo-fused tricyclic compound 42 (see Equation 11) <1996CC2185>. Various experiments were conducted in order to elucidate the mechanism of the formation of 42. 

The synthesis of the benzoimidazo[l,2- ][l,2,3]thiadiazole 61 can be explained using the same mechanistic model to that used for the Hurd-Mori reaction. The amino benzimidazole 58 when treated with thionyl chloride at reflux affords the benzoimidazo[l,2-r ][l,2,3]thiadiazole 61. If, however, the reactant 58 is treated with thionyl chloride at room temperature, the chloromethyl derivative 59 is formed. This derivative was then transformed into product 61 on reflux with thionyl chloride. The proposed mechanism for the formation of product 61 is for the initial formation of the sulfoxide 60, which then undergoes a Pummerer-like rearrangement, followed by loss of SO2 and HC1 to give the c-fused 1,2,3-thiadiazole 61 (Scheme 7) <2003TL6635>. 

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