Autoclaving temperatures

Perhaps a more severe comparison of model response is the time history of the centerline temperature. These values reflect the interaction of several phenomena the reaction itself, the heat liberated by the reaction, the heat storage capacity of the material, and the rate at which heat can be carried away from the centerline region by conduction. Figure 8 shows the temperatures predicted by the Chiao and finite element models, as well as the imposed autoclave temperature history. It also includes five thermocouple readings which were reported in Chiao s manuscript (8). 

Fq values may be calculated either from the area under the curve of a plot of autoclave temperature against time constructed using special chart paper on which the temperature scale is modified to take into account the progressively greater lethality of higher temperatures, or by use of the equation below ... 

It is quite rare that the composition or the packaging of an ophthalmic pharmaceutical will lend itself to terminal sterilization, the simplest form of manufacture of sterile products. Only a few ophthalmic drugs formulated in simple aqueous vehicles are stable to normal autoclaving temperatures and times (121°C for 20-30 min). Such heat-resistant drugs may be packaged in glass or other heat-de-formation-resistant packaging and thus can be sterilized in this manner. The convenience of plastic... 

Figure 4.15 shows the results from such a sensor controlled run in an autoclave. FDEMS sensor-measured viscosities from two sensors at the center ply and one sensor at the surface ply are shown in Figure 4.15. Air autoclave temperatures and the temperatures at the surface and center ply are also shown. The starting time for the FDEMS sensor-controlled autoclave run and the manufacturer s cure cycle run are defined as file time at which the tool surface temperature starts to increase.

As the thickness of the laminate increases, the strength of this thermal spike and the degree of thermal lag during heat-up increases. Figure 8.8 shows the results for a 62.5-mm (500 ply) laminate of the same material. Now the center-line temperature never reaches the autoclave temperature during the first dwell, and the thermal spike during the second dwell is nearly 135°C. The thermal spike is directly related to the release of internal heat during cure. The thermal lag is a manifestation of the low thermal diffusivity of polymer matrix composites. 

Figure 8.7 Centerline and autoclave temperature histories during cure of a 25-mm (200 plypthick AS4/3501-6 laminate...

The objective of the Springer KBES is twofold To ensure a high-quality part in the shortest autoclave curing cycle duration. This KBES is similar to QPA in that sensor outputs are combined with heuristics not with an analytical curing model. The rules for compaction dictate that dielectrically measured resin viscosity be held Constant during the First temperature hold in the autoclave curing run. The autoclave temperature is made to oscillate about the target hold temperature in an attempt to attain constant viscosity. Full pressure is applied from the cure cycle start. 

Perry and Lee [28,29] offer an enhancement of QPA, based upon use of dual heat flux sensors and additional thermocouples in autoclave curing. This enhancement entails determining heat transfer properties during the cure, then using these properties in conjunction with PID regulatory control of autoclave temperature. Using the additional sensors, Perry and Lee employ an on-line Damkohler number in lieu of the second time-derivative of temperature to avoid exothermic thermal runaway within the prepreg stack thermoset resin. The Damkohler number is defined as ... 

This section describes some of the tools available for intelligent development of process cycles, such as the time-temperature cycles used in curing composites. Current industrial practice is typically limited to the use of cure cycles. The cycles are based on a series of autoclave temperature and pressure states so that traditional linear, regulatory process control methods can be used. These recipes may not be the ideal method for process control of batch processes because they do not ... 

Figure 15.3 The temperature lag between autoclave (AIRTC) and composite part (PARTTC) is large, so a supervisory controller is used to drive the autoclave setpoint up and achieve the desired cure cycle in the composite. Because this cure cycle was developed for the autoclave temperature, however, the resin gels before compaction is complete...

Figure 15.4 The large thermal lag between the part (PARTTC) and autoclave (AIRTC) is not linear or a constant. This cure cycle, however, was written for the autoclave temperature. Pressure is applied at minimum viscosity and compaction is good with few voids...

IF the past autoclave temperature is less than the current autoclave temperature THEN the autoclave temperature is rising... 

It is also possible to use a single thermocouple at different positions in multiple mns. This requires careful control of autoclave temperature to reduce error caused by run-to-mn variation. Repeat studies are required to establish reproducible cold points and temperature profiles of the liquid in the container. The profile point having the lowest temperature or lowest Fq is designated as the cold spot. 

It is worthwhile to outline the behavior of the fluid in a hydrothermal autoclave. Consider a case where the autoclave is filled to 80% full. As the autoclave is warmed the pressure is that indicated by the co-existence curve (g+J, A-B, in Fig. 4). The liquid level rises as the autoclave temperature increases until the autoclave... 

With respect to thermosetting, it has been well documented that crude Ca-based SSL can be used as a particleboard adhesive (46). This application has been evaluated on a mill-scale basis in Denmark, Finland, and Switzerland, but has not been adopted on a commercial scale. This is because resin curing required both high press and autoclave temperatures as well as long heating times. While this development was a technical success, it was - according to Nimz (36) - never commercialized due to the frequency of fires experienced during mill-scale trials. 

Equipment. The liquefaction of coal was studied In a 1 liter magnetically stirred stainless steel autoclave. The autoclave was equipped with a thermowell a gas Inlet port connected to a synthesis gas (Hg C0 ratio of 1 1), or to a hydrogen cylinder and to a pressure gauge a port for connection to a rupture disk assembly and a port for gas discharge. The vertical magentlc rod with dashers stirred the coal, solvent and ash or catalyst particles. The autoclave temperature was measured by a thermocouple placed Into the thermowell. 

Wang, Y.J. Dahl, T.C. Leesman, G.D. Monkhouse, D.C. Optimization of autoclave cycles and selection of formulation for parenteral product. Part II effect of counterion on ph and stability of diatrizoic acid at autoclave temperatures. J. Parenter. Sci. Technol. 1984, 38 (2), 72. 

Capillary principle (Thermalog S) Consists of a blue dye in a waxy pellet, the melting-point of which is depressed in the presence of saturated steam. At autoclaving temperatures, and in the continued presence of steam, the pellet melts and travels along a paper wick forming a blue band the length of which is dependent upon both exposure time and temperature Temperature, saturated steam, time... 

Reaction conditions 0.21 autoclave, temperature 250 and 500°C, time 6 h, 15 ml water for 5 g adsorbent. Reprinted from R.Leboda, A.Gierak, B.Charmas, A.Lodyga, React.Kinet. Catal.Lett. 50(1993)63. 

---