Time/temperature loading

Reinforced Thermoplastic Sheet. This process uses precombined sheets of thermoplastic resin and glass fiber reinforcement, cut into blanks to fit the weight and size requirements of the part to be molded. The blanks, preheated to a specified temperature, are loaded into the metal mold and the material flows under mol ding pressure to fiU the mold. The mold is kept closed under pressure until the temperature of the part has been reduced, the resin solidified, and demolding is possible. Cycle time, as with thermosetting resins, depends on the thickness of the part and the heat distortion temperature of the resin. Mol ding pressures are similar to SMC, 10—21 MPa (1500—3000 psi), depending on the size and complexity of the part. 

The critical parameters of steam sterilization are temperature, time, air elimination, steam quaUty, and the absence of superheating. Temperature and time are interrelated, as shown in equation 8. The success of steam sterilization is dependent on direct steam contact which can be prevented by the presence of air in the chamber. The abiUty of steam to heat a surface to a given temperature is considerably reduced by the presence of air. Air elimination, therefore, is regarded as an absolute parameter. If the required amount of air has not been eliminated from the chamber and the load, no combination of time and temperature results in complete sterilization. 

The basic information involved in designing with plastics concerns the load, temperature, time, and environment. As reviewed throughout this book there are other performance requirements that may exit such as aesthetics. 

The tests are performed under carefully controlled stress (load), temperature, time, and creep (elongation) conditions. To save time, tests for different constant loads are performed simultaneously on different specimens of the same material. Creep tests may be rather extensively conducted, as for example when developing creep data prior to the design and fabrication of the first all-plastic airplane (41). The usual procedure is to plot the creep versus time curve, but other combinations are possible. 

This book provides a simplified and practical approach to designing with plastics that fundamentally relates to the load, temperature, time, and environment subjected to a product. It will provide the basic behaviors in what to consider when designing plastic products to meet performance and cost requirements. Important aspects are presented such as understanding the advantages of different shapes and how they influence designs. 

The behavior of plastic structures under compression plays a critical role in numerous applications. It has been recognized that the buckling of metals under elevated temperatures presents important distinctions from the classical Eulerian case, [11]. During an experimental study, [12], buckling times were registered for a range of compressive loads applied to the top of compression molded and annealed thermoplastic samples (see Fig. 2). A typical time - load dependence is shown in Fig. 3. 

C. H. Chen, Y. Xuan, and S. Otani, Temperature and Loading Time Dependence of LaB6, YB6 and TiC Single Crystals, Jour. Alloys and Compds., 350, L4... 

The allowable stress for occasional loads of short duration, such as surge, extreme wind, or earthquake, may be taken as the strength reduction factor times 90% of the yield strength at temperature times Mj for materials with ductile behavior. This yield strength shall be as listed in ASME BPV Code Section II, Part D, Table Y-l (ensure materials are suitable for hydrogen service see API 941), or determined in accordance with para. 

Neat thermoplastic polyethylenes have low moduli that involve high strains for moderate loading. Consequently, creep moduli are also low, the more so as the temperature rises, as we can see in Figures 4.3 ((a) and (b)) where creep moduli are displayed as a function of time, load and temperature. 

Figure 4.23(a) displays an example of creep modulus versus time at room temperature. The load is unfortunately unknown here but we can note the fair behaviour of COC. 

From this figure, safe wall stresses at various temperatures and loading times can be determined by extrapolation. We extrapolate the curves found at higher T to lower Ts. Here a ten years life (87,660 hours) at 80 °C is required. Extrapolation of the curve for 80 °C results in an estimated stress to break of 28 MPa. To remain at the safe side, we stay somewhat below this value, so that 20 MPa looks a reasonably safe wall stress for this purpose. 

Thus from a cold start at atmospheric pressure and without intervention by the operator distillation is in full swing in less than 45 minutes. The space heater is now in intermittent use, merely to float the still at the chosen operating temperature. Both load and capacity increase considerably with the temperature, so that the setting of the thermostat controls the output of the still. The constant electrical load of the still is now of the order of (1200 + 200 + 600) 100 ta 1500 100 watts. Factor rj is the proportion of time, less than unity, that the heater is energized and the factor 100 allows for the selected still temperature and the nature of the feed water, brackish or strongly saline. A breakdown of the energy requirements is shown in Table V. 

Five variables are critical to the EtO process. They are EtO concentration, relative humidity, temperature, time, and pressure/vacuum. Temperature is the easiest variable to measure and monitor, therefore temperature is used as the indicator of the worst-case location within the loaded EtO sterilizer. Once the worst-case location is identified the validation studies are conducted with the goal of inactivating a known concentration of indicator micro-organisms in the worst-case location using a specific loading pattern with a specific EtO cycle with all variables defined and controlled. 

XANES spectroscopy has been used to study the composition and mechanism of antiwear tribofilm formation. The absorption XANES spectra were recorded in total electron yield (TEY) versus fluorescence yield (FY) detection to investigate the chemical nature of P, S, Ca, O and Fe on the surface and in the bulk, respectively. The application of XANES surface TEY mode which analyzes the top 5 nm layer, and the FY technique which analyzes the 50 nm layer of the bulk, taken together, give a marvelous opportunity to study nondestructively the antiwear tribofilms. Both techniques can be used under a wide variety of conditions e.g., the formation of tribofilms at different rubbing times, load, concentrations, temperatures and surface roughness (Kasrai et al., 1993 and 1996 Koningsberger and Prins, 1988 Martin et al., 2001 Yin et al., 1997a). 

Physical parameters By using Table 4.3. The effect of physical parameters such as adsorption, rubbing, temperature, concentration, load, surface roughness on antiwear performance of ZDDPs , which term is described by the physical parameter (a) the tribofilm accumulated on the surface becomes thicker with adsorption time (b) long-chain phosphates are formed on the topmost surface, but short-chain phosphates were present in the bulk (c) sulfur and phosphorus ratio changes with rubbing time and (d) when load increased the concentration of (S) and decreased that of (P) ... 

To achieve adequate binder burn-out is a matter of experience, and size of component, green particle packing, manner of oven loading, temperature/time schedule and atmosphere are all determining parameters. Removal of the final traces of binder residues may be essential especially in the case of some electroceramics, for example superconductors (see Section 4.7.4) where residual carbon could be detrimental to properties. 

From previous experimental studies of sintering [2,9 11 12] it is evident that sintering and redispersion are strong functions of temperature time atmosphere and support. Sintering/redispersion rates are also significantly affected by choice of metal and/or promoter metal loading, and catalyst preparation. The discussion below of previous work will focus on how sintering rates are affected by these variables. 

Melt flow The flow rate obtained from extrusion of a molten resin through a die of specified length and diameter under prescribed conditions of time, temperature and load as set forth in ASTM D1238. 

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