Nylons Thermal expansion coefficient

Fig. 3.14. Relative linear thermal expansion coefficient of (1) Invar, (2) Pyrex, (3) W, (4) Ni, (5) Cuo.7Ni03, (6) stainless steel, (7) Cu, (8) brass, (9) Al, (10) Torlon, (11) soft solder, (12) Vespel SP-22, (13) Hg, (14) In, (15) Araldite, (16) Stycast 1266, (17) PMMA, (18) Nylon, (19) Teflon [60]. Some additional data are Ag between (8) and (9) Stycast 2850 GT slightly larger than (9). The integral contraction between 300 and 4K is 103AL/L = 11.5, 4.2, 6.3 and 5.7 for Stycast 1266, Stycast 2850 GT, Vespel SP-22 and solders...

Example 2.7 A nylon ring with a nominal inside diameter of 30 mm, an outer diameter of SO mm and a width of S mm is to be made an interference fit on a metal shaft of 30 mm diameter as shown in Fig. 2.17. The design condition is that the initial separation force is to be 1 kN. Calculate (a) the interference on radius needed between the ring and the shaft and (b) the temperature to which the nylon must be heated to facilitate easy assembly. What will be the maximum stress in the nylon when it is in position on the shaft The coefficient of friction between nylon and steel is 0.2S. The short-term modulus of the nylon is 1 GN/m, its Poisson s ratio is 0.4 and its coefficient of thermal expansion is 100 X 10- °C- . 

Thermal expansion-contraction of plastics will be considered in detail in Chapter 10, Temperature-driven expansion-contraction of wood-plastic composites. Linear coefficient of thermal expansion-contraction. Here it can be briefly mentioned that this property is about the same with HDPE, polypropylene, PVC, ABS, and Nylons 6 and 6/6, and the respective coefficients of thermal expansion are all overlapping in the range of 2-7 X 10 1/°F (4-13 X 10 1/°C). Only with LDPE the coefficient is noticeably higher and equal to 6-12 X 10 1/°F (10-22 1/°C) [12]. 

Figure 6.187 Coefficient of thermal expansion vs. temperature according to ISO 11359 for Evonik Industries Vestamid DX9300—low viscosity, heat stabilized, with improved release properties Nylon 612 resin [9].

For composites consisting of axisymmetric particles (e.g., spheres, fibers, and disks) and epoxy resin, they predicted that (i) the coefficients of thermal expansion for spherical inclusions are the same in all directions and decrease modestly as the volume fraction of particles increases and (ii) with the increase in aspect ratio, the thermal expansion becomes anisotropic. For composites consisting of three-dimensional nonaxisymmetric ellipsoidal particles (i.e., day platelets) and nylon 6, they predicted that (i) the coefficient of thermal expansion in the longitudinal direction decreases as the primary and secondary aspect ratios increase and (ii) the value in the transverse direction decreases as the primary aspect ratio increases but decrease with the secondary aspect ratio. 

Nylon family These are polyamides resulting fi-om the condensation reaction of an amine funetion and an acid function. As a family, they are tough and hard. They are resistant to many liquids and have low coefficients of thermal expansion. They ean be reinforced with glass fibers, carbon, and minerals. Applications include molded parts for electrieal power transmission, molded parts for a wide range of automotive functions, pulleys, bearings and items which need good abrasion resistance and toughness. 

One of the major brakes on the expansion of the MCLCP market has been the relatively high cost of the polymers resulting from expensive feedstocks, and considerable research activity in industry has centred on attempting to lower monomer costs. In addition to this there has also been considerable effort blending MCLCPs with other thermoplastics with the objective of combining the optimum properties of both components while producing the most cost-effective material for a given application. An example of this is a MCLCP/nylon blend which exhibits a very low coefficient of thermal expansion. The blends area is likely to be an area of major market activity for MCLCPs in the future. 

Like other thermoplastic materials, nylon has a high coefficient of expansion and low thermal conductivity. It also readily absorbs moisture. The inclusion of additives such as glass fibre, graphite and molybdenum disulphide reduces these disadvantages and increases the wear-resistance and operating temperature. 

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