Glass fibres thermal effects

Acoustic insulation on the valve body and at least the first five pipe diameters downstream is an effective method of noise treatment to half the loss given in point 1. Note here, however, that the quality of insulation is very important. Although having no particular preference, the author has had reasonably satisfactory results with Refrasil insulation, a high temperature thermal and acoustic insulation made from basalt, glass fibre and silica which reduced... 

Fig. 23.8 Effect of PALF and glass fibre-volume fraction on experimental and theoretical thermal conductivity of PALF/glass hybrid fibre composites [51]...

Nowadays, these polymers (and others) are often reinforced with short-staple glass fibre or in some cases carbon fibre. The principle effects of such reinforcement are (a) to stiffen the material - increased modulus, (b) to increase its tensile strength, (c) to lower its coefficient of linear thermal expansion, (d) to increase its ceiling service temperature, (e) to reduce its impact strength - usually relatively unimportant for gears. Table 4.1 shows these effects (ref. 2). 

It is usually the case that af a then predict widely differing linear thermal expansion parallel and perpendicular to the fibres. As an example, a and aj (from eqns (6.25))are plotted versus (pf in Fig. 6.14 for epoxy reinforced by glass fibres. It is immediately clear that the fibres are highly effective at reducing thermal expansion in the direction in which they are aligned (axis 1). Meanwhile, at right angles (axis 2)... 

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