DEFORMATION TEMPERATURE

Fabrication. After the preheat or homogenization step, the ingots may be fabricated directly. Often, however, the preheated ingots are reheated in a separate operation before the first metal working operation. Bulk deformation temperatures usually range from about 350 to 450°C. 

Commercial polystyrenes are normally rather pure polymers. The amount of styrene, ethylbenzene, styrene dimers and trimers, and other hydrocarbons is minimized by effective devolatilization or by the use of chemical initiators (33). Polystyrenes with low overall volatiles content have relatively high heat-deformation temperatures. The very low content of monomer and other solvents, eg, ethylbenzene, in PS is desirable in the packaging of food. The negligible level of extraction of organic materials from PS is of cmcial importance in this appHcation. 

When additional lubricants, eg, mineral oil and butyl stearate, are added to PS, easy-flow materials are produced. Improved flow is usually achieved at the cost of lowering the heat-deformation temperature. Stiff-flow PS has a high molecular weight and a low volatile level and is useful for extmsion apphcations. Typical levels of residuals in PS grades are Hsted in Table 2. Differences in molecular weight distribution are illustrated in Figure 4. 

Ash Fusibility. A molded cone of ash is heated in a mildly reducing atmosphere and observed using an optical pyrometer during heating. The initial deformation temperature is reached when the cone tip becomes rounded the softening temperature is evidenced when the height of the cone is equal to twice its width the hemispherical temperature occurs when the cone becomes a hemispherical lump and the fluid temperature is reached when no lump remains (D1857) (18). 

Ash fusion temperatures, including the spread between initial deformation temperature and fluid temperature... 

The common feature of the p-phenylene group stiffens the polymer backbone so that the polymers have higher TgS than similar polymers which lack the aromatic group. As a consequence the aromatic polymers tend to have high heat deformation temperatures, are rigid at room temperature and frequently require high processing temperatures. 

The main differences between the commercial types of PAEK arise largely from the differences in the T. Whilst the higher may lead to a higher heat deformation temperature, there is also a corresponding higher processing temperature required and this can have an adverse effect on the thermal stability. Some typical properties are given in Table 21.6 but it should be pointed out that the data have been acquired from different sources and are therefore not closely comparable. 

As for the compression test, the lowest stress amounted to 0.314 kp/mm at the lower deformation rate at 503K and to 0.535 kp/mm for the higher rate at the same temperature. For the lower deformation temperatures the values of the flow stress increased sharply and at 373K reached 2.3 and 4.5 kp/mm" for the lower and higher deformation rates, respectively At room temperature they were 9.0 kp/mm and 11.28 kp/mm . 

Fig.4. The dependence of flow stress on deformation temperature in tension test (left) and in compression test (right) of the A12n78 alloy after heat treatment.

Before discussing the relation of plastic deformation temperature dependence with the p transition motions, it is useful to recall the main results achieved through investigations into the motions involved in this transition (as described in [1], Sect. 5). 

Initial deformation temperature (IT) temperature at which the first rounding of the apex of the cone occurs... 

When determining the initial deformation temperature, shrinkage or warping of a cone is ignored if the tip remains sharp (Figure 7.5). 

Ash initial deformation temperature temperature at which coal begins to fuse and become soft. 

With a few exceptions one can say that a flowing polymer melt does not follow the model presented in eqn. (5.20). To properly model the flow of a polymer we must take into account the effects of rate of deformation, temperature and often time, making the partial differential equations that govern a system non-linear. 

The three different type of boilers used in this study were found to exhibit different temperature profiles. The flame and boiler temperatures monitored in Boiler A, when measured, were observed to be well below the initial deformation temperature of the ash (see Table II). On the other hand, the flame temperatures encountered in the B and D boilers were above the initial deformation point of the ash, and in some cases above the temperature at which the ash becomes fluid. In addition, the temperatures monitored in... 

It can be seen from Table II that the fly ashes produced in the A boiler essentially form acidic leachates even though the major element composition of these fly ashes were comparable to the amounts found in the boiler C and boiler D fly ashes (see Table III). The Militant, Deep Hollow, Upshur and Badger fly ashes produced in this boiler encountered flame and boiler temperatures that are below even the initial deformation temperatures of the fly ash. Hence, the fusion reactions probably did not occur that might have led to formation of products that generate an alkaline leachate. 

The yielding process is influenced by several parameters, e.g. rate of deformation, temperature and pressure. 

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