Terminal fire resistance

One effective approach in increasing the fire resistance of polyurethane (PU) is to incorporate PDMS into its structure.28 Microphase-segregated PU block copolymers containing hydroxyl-terminated silicone as the soft segment have been synthesized. The enhanced siliconated surface of the block copolymer has been confirmed by ESCA and x-ray analyses. 

Nylons are often used in electrical products, such as electrical connectors, terminal blocks, smah electrical housings, switch components, wire ties, and other industrial parts, where thermal stability and fire resistance are priorities. Because of this practical interest, the thermal stability and flame retardancy of nylons have been studied extensively. Halogen compounds are effective flame retardants for polyamides [14-17], but they have limited utility because their combustion products are toxic. Alternative flame retardants are used with polyamides, such as phosphorus- and nitrogen-containing substances. The most important organic nitrogen-containing flame retardants are melamine and its derivates [14, 18-20]. However, these traditional flame retardants are outside the scope of this chapter. 

Connell and co-workers [87] investigated silicate siloxane fire retardant composites derived from vermiculite by reaction with hydroxyl-terminated polydimethylsiloxanes. Cone calorimetry was used to obtain HRR measurements. The results show that even at the highest irradiance levels the samples have very long ignition times. Ignition resistance deceases as the hydrocarbon content of the composite increases. The results from the cone calorimeter were obtained by Py-GC-MS, which show that small, volatile, silicone-containing molecules are formed during pyrolysis. 

There is a wide range of suitable means of connecting conductors and we shaii look at these in a moment. Whatever method is used to connect iive conductors, the connection must be contained in an enciosed compartment such as an accessory for example, a switch or socket box or a junction box. Aitemativeiy, an equipment enclosure may be used for example, a motor enclosure or an enclosure partly formed by non-combustible building material (lET Regulation 526.5). This is because faulty joints and terminations in live conductors can attain very high temperatures due to the effects of resistive heating. They might also emit arcs, sparks or hot particles with the consequent risk of fire or other harmful thermal effects to adjacent materials. 

The chip resistor is constructed of a piece of alumina ceramic on top of which is deposited a thin film that serves as the resistive element. Attached to the resistive element at the top, on the ends, and partially at the bottom are the termination structures to which the solder joint is made. The termination structures are comprised of a fired, Ag-based thick film a Ni or Cu barrier layer and lastly an electroplated finish of Sn, Sn-Pb, or Au. 

---