Temperature-time zones

Plastics can be grouped into eight temperature-time zones, depending on the temperature at which they retain 50% mechanical or physical properties when heated for different periods in air. These temperature-time zones are shown in Figure 1.34, and the materials falling in the different zones are listed in Table 1.13. The materials in zone 6 and above can compete with metals in high-performance applications because they perform in the same temperature range. Most polymers in zone 6 and above do not burn, but they may char and may be consumed very slowly in direct flames. 

Figure 4.35 illustrates the different temperature—time zones of age-hardening of the Pb—0.11 wt% Ca—0.57 wt% Sn alloy. Zone A covers the discontinuous transformations zone B is the zone of continuous precipitation of (Pbi xSnx)3Ca and zone C is the zone of discontinuous precipitation of lamellar (Pbi xSnx)3Ca phase [75]. 

Industrial chemical processes are determined by recipe and production route. The recipe is the specification of a sequence of processing steps for the transformation of raw materials into the desired product(s). Specifications include quantity and quality of raw materials, composition of feeds, sequence of additions to the reaction zone, rate of dosing, temperature-time dependencies, pressures, etc. The production route also includes the specification of equipment in which processing steps are performed. 

The HIPS resin was extruded at screw speeds of 30, 60, and 90 rpm at barrel temperatures of 200, 220, and 240 °C for Zones 1, 2, and 3, respectively. The screw temperatures in Zone 3 as a function of time at the screw speeds are shown in Fig. 10.20. Because the RTDs were positioned within 1 mm of the screw root surface, they were influenced by the temperature of the material flowing in the channels. Prior to the experiment, the screw was allowed to come to a steady-state temperature without rotation. Next, the screw speed was slowly increased to a speed of 30 rpm. The time for the screw to reach a steady state after changing the screw speed to 30 rpm was found to be about 10 minutes. The temperature of the T12 and T13 locations decreased with the introduction of the resin. This was caused by the flow of cooler solid resin that conducted energy out from the screw and into the solids. At sensor positions downstream from T13, the screw temperature increased at a screw speed of 30 rpm, indicating that the resin was mostly molten in these locations. These data suggest that the solid bed extended to somewhere between 15.3 and 16.5 diameters, that is, between T13 and T14. When the screw speed was increased to 60 rpm, the T12 and T13 sensors decreased in temperature, the T14 sensor was essentially constant, and the T15, T16, and T17 sensor temperatures increased. These data are consistent with solids moving further downstream with the increase in screw speed. For this case, the end of the solids bed was likely just upstream of the T14 sensor. If the solid bed were beyond this location, the T14 temperature would have decreased. Likewise, if the solid bed ended further upstream of the T14 sensor, the temperature would have increased. When the screw speed was increased to 90 rpm, the T12, T13, and T14 temperatures decreased while the T15, T16, and T17 temperatures increased. As before, the solids bed was conveyed further downstream with the increase in screw speed. At a screw speed of 90 rpm, the solid bed likely ended between the T14 and T15 sensor positions, that is, between 16.5 and 17.8 diameters. These RTDs were influenced by the cooler solid material because they were positioned within 1 mm of the screw root surface. 

Fig. 12. Typical plot of weight loss vs. time for reaction of spectroscopic carbon rod with carbon dioxide at temperatures below Zone II.

At temperatures below Zone II, equilibrium burning (as illustrated in Fig. 10) obviously is not obtained. It is found, however, that after some bumoff (usually less than 5 %) the reaction rate is essentially constant over a wide burnoff range. A typical reactivity plot is shown in Fig. 12. If it is assumed that the porosity measured at the close of the run is derived from uniform burning over time Af, then... 

Passage of S02 containing gas was ceased and replaced by. Temperature was reduced to 650°C. This is a 10 min. time zone. 

For practical estimates and deductions of approximate relationships for determining the temperature-time conditions for reactoplast treatment, we may use a simplified model of the thermal field, namely by assuming that that the temperature of the material in each of the zones, the mold included, is constant for the entire period of the presence of a portion of the material in a specific zone. 

The relationships obtained (7-9) linking up the temperatures and the time that the material is present in the various zones of the plastification and molding systems constitute a basis for a further optimization of the temperature-time regimes of pressure casting of reactoplasts, including granulated cast aminoplasts. 

Kohn M. J., Catlos E. J., Ryerson F. J., and Harrison T. M. (2001) Pressure-temperature-time path discontinuity in the Main Central thrust zone, central Nepal. Geology 29, 571-574. 

Special features/comments on-line evaporation cleavage from support on the instrument, collection of products in custom block ( waste cube ) 4 zones with individually adjustable temperature and individually programmable temperature gradients temperature/time programs possible automated version available... 

Campanelli et al (2004) discuss a model of rubber mixing in an internal mixer based on kinetic, thermodynamic and rheological equations that is used to determine the extent of dispersion, batch temperature and relative batch viscosity over time. The chemoviscosity model is complex in that a model must be developed for the compaction zone, the incorporation zone and the size-reduction zone, as defined by the mixing-time zones in Figure 6.21. 

This method was used for the first time by Ray [6] to determine non-olefinic impurities in ethylene. The sample (10-25 ml) was first fed into a reactor (19 x 1.1 cm) filled with activated charcoal saturated with bromine (40%). The resulting liquid bromina-tion products of ethylene were securely retained on charcoal at room temperature. The zone of non-olefinic impurities (permanent and saturated hydrocarbon gases) moved in a flow of carbon dioxide (carrier gas) from the reactor into a chromatographic column (40 X 0.2 cm I.D.) packed with activated charcoal. A nitrometer was used as the detector [39, 40]. The method permitted the determination of trace concentrations of 10" -10" % in ethylene. The use of a more sensitive detector should substantially lower the detection limit. 

Mean Kinetic Temperature The single test temperature for a drug product corresponding to the effects on chemical reaction kinetics of a given temperature-time distribution. A mean kinetic temperature is calculated for each of the four world climatic zones according to the formula developed by Haynes (2). It is normally higher than the arithmetic mean temperature. 

Gander, PH., Myhre, G., Graeber, C. R., Andersen, H. T, Lauber, J. K. (1989). Adjustment of sleep and the circadian temperature rhythm after flights across nine time zones. Nvra/row, Space, and Environmental Medicine, 60, 733-743. 

Adventitious mineral matter is transformed directly to ash in the combustion zone. Depending on the temperature-time history, the ash particles will be spherical or semirounded. The size distribution of this ash depends on the size distribution of the adventitious mineral matter. Intrinsic mineral matter forms ash nodules in the pores of the char, and as char burnout proceeds, the ash nodules coalesce on the surface of the char. 

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