Foam insulation void content

These results suggest that sulfur-bonded composites may have uses in civil enginering where thermal insulation is required. General principles indicate that increased voids content or a stable retention of a noncrystalline form by the sulfur would reduce the thermal conductivities of the composites. A composite incorporating potters flint did have a fine void structure, but nonetheless its thermal conductivity was higher than that of sulfur (24) presumably a still larger void content is required. Use of moist fillers such as damp soil produced foaming, but a stable, well distributed system of voids was not produced the bubbles which formed collapsed under the conditions used. 

The main driver for fluoroplastic foams has been the insulation for data transmission cables. An example is coaxial cables that have relatively thick insulation. Its low dielectric constant and dissipation factor are desirable electrical properties. Air has the ideal dielectric constant (1.0). The ideal dissipation factor for data-cable insulation is zero. Perfluoropolymers have low dielectric constant and dissipation factor values (Table 11.2, see Ch. 6 for additional data). Foaming perfluorinated fluoropolymers further reduces the dielectric constants toward 1.0 and moves the dissipation factors closer to zero because the resin is replaced with air-filled cells in the insulation. The decrease in the dielectric constant is proportional for example, FEP insulation with 60% void content had a dielectric constant of More uniform foam cell size and smaller cells yield foams with the best electrical properties. 

The thickness of the foam insulation on the wire was 1.12 mm. The foam cells had a diameter ranging from 25 to 75 pm and the total void content was 53%. The density of the foam was 1.02 g/cm and it had a dielectric constant of 1.47. Table 11.3 shows the effect of foaming agents, exposure time, and pressure on the properties of the foam. All of the tested FEPs contained 1% by weight boron nitride except for one composition that contained 1 % by weight aluminum oxide. 

Wires have been insulatedl and jacketed with ETFE and ECTFE resulting in excellent electrical and mechanical properties. A 24-gauge wire was insulated with an ETFE jacket and core. The jacket was solid (25 pm thick) and covered a foam insulation core (0.127 pm). This insulation had 45% void content and a dielectric breakdown voltage of 20 kV/mm. 

A fixed center or an adjustable crosshead could be used for the extrusion of foam onto the conductor (Fig. 11.5). More information about wire extrusion and crosshead die design can be found in Sec. 8.3. Operating conditions for FEP and PFA foaming have been given in Fig. 11.6(a). A boron nitride concentrate was blended at a 1 9 ratio with virgin resin. The concentration of boron nitride depends on the desired void content and foam cell size. For example, when the concentrate contained 2% boron nitride, FEP wire insulation had a void content of 60% and a dielectric constant of 1.3. 

In temperate and cold regions structures of nearly all kinds require good thermal insulation to reduce heating costs. In the construction industry, thermal insulators made from materials such as fiberglass and foamed plastics have been used widely because they are noncrystalline and incorporate a large void space with high entrapped air content. 

Figure 1.34. Aerated concrete is a foamed concrete with large content of air. It is among others available as building blocks and precast elements. The large content of air voids gives the concrete particularly good beat-insulating properties. The density of aerated concrete is typically 500-800 kg/m. ...

Figure 4.47. Cross-section of aerated concrete with density 500 kg/m the porous structure is produced by foaming the fresh concrete by a gasifying substance, e.g. aluminium powder. The beat insulating properties of the concrete are good due to the high content of air voids.

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