Cavity temperature

Close control of curing temperature can be accomplished by the use of individual heating and control units for each cavity. By this means it has been possible to obtain very consistent results from sample to sample and batch-to-batch. At the time of writing the author is not aware that this technique has been applied on a production basis. 

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The characteristics of a pressed compact are influenced by the characteristics of the powder rate and manner of pressure appHcation, maximum pressure appHed and for what period of time, shape of die cavity, temperature during compaction, additives such as lubricants and alloy agents, and die material and surface condition. The effect of various compaction variables on the pressed compact are shown in Figure 6. 

Blackbody cavity Temperature-induced mechanical displacement Temperature-induced... 

Because of the massive amount of insulation around the charge tube and susceptor, the oven cavity temperature becomes warm (about 50°C), but does not follow the temperature of the charge tube. 

The electron gun is located at the outer wall of the accelerating cavity, and the electrons are injected into the cavity at a voltage of abouf 35-40 kV. The cavify is cooled by a water jacket on the inner coaxial conductor and at the end flanges and by discrefe water channels along the outer diameter. The system is designed to operate with a 2 MW cooling tower up to an outside temperature of 35°C (95°F). Therefore, no water chiller is required. The RF amplifier defects and follows changes in fhe resonant frequency of the cavity so that accurate control of the cavity temperature is not required. 

Repeat Prob. 8-81, assuming a cavity temperature of I20°C and a surrounding temperature of 93°C. 

The cryostat is operated under computer control and easily maintains the cavity temperature within a 0.002K band. 

Figure 2. Cavity temperature versus control power at several shunt conductivities.

The samples placed in the DSC were taken from a larger sample of that particular catalyst, which had been previously pretreated and characterized in the chemisorption system then stored in a desiccator. Each sample was then given another pretreatment in the DSC in pure H2 or a 20 H2/80 Ar mixture, flowing at 40 cm3 min-1 and was heated at 40K min-1 to the desired temperature. Because of the greater thermal conductivity of H2, significant deviations occurred between the actual cavity temperature and the temperature indicated on the DSC when pure H2 was used. For example, with a flow of pure H2, a maximum temperature of 713K was achieved rather than the indicated 773K. A calibration between AT and the H2 mole fraction allowed the actual temperature to be obtained. 

Time, temperature, and pressure are the primary factors influencing the surface flnish of the molded part. Time factors include rate of injection, duration of ram pressure, time of cooling, cross-linking time, and rotation of the screw (RPM). Pressure factors are applied pressure (high or low), back pressure on the extruder screw, and pressure loss before the charge enters the cavity, which can be caused by a variety of restrictions in the mold cavity. Temperature factors are mold (cavity and core), barrel, and nozzle temperatures, as well as the melt temperature because of back pressure, screw speed, and frictional heat. 

Selection of the fluoropolymer depends on the end use requirements, part design, and process conditions. Viscosity of the molten pol5nner has a great influence on the transfer rate into the cavity. Temperature changes can alter polymer viscosity as long as it has sufficient thermal stability in the given temperature range. Cleanliness of the melt can affect the quality of the part and thermal stability of the molten resin. 

Detector (AED) Cavity temperature Transfer Line Temperature Helium Make-up flow Reagent Gases... 

After introduction into the flame, the cavity temperature increases from ambient to a maximum value, which depends on material and conditions. During the heat-up period of the cavity in the flame, a series of physical and chemical changes occur which are accompanied by generation of the characteristic molecular emission. A typical example of recorded response from thiourea, which generates the 2 emission, is shown in Figure 5. The cavity remains in the flame as long as required for recording the emission profile (emission intensity as a function of time). It is then removed and cooled before repetition of the process. 

There is a newer type of cure meter (e.g.. Fig. 4.18). The cavity is much smaller, and there is no rotor. In this type of cure meter, one-half of the cavity (e.g., the upper half) is stationary, and the other half oscillates. These instruments are called moving-die rheometers. The sample is much smaller and heat transfer is faster. Also, the cavity temperature can be changed more rapidly. 

Establish an action plan for the trial. This should take the form of a simple factorial experiment varying stock temperature, cavity temperature and cure time, similar to that shown in Table 6.1. 

Experiment number Cavity temperature ( C) Cure time (s) Stock temperature i°C)... 

Preheat the mould and platens to about 15 "C higher than that expected for the cavity operating temperature. Start to monitor the cavity temperature. 

When the cavity temperature is stable at the desired value, start to dry cycle the tool, mimicking the expected cycle. After several such operations, and whilst the tool is open, feed the rubber strip into the injection machine pre-plasticiser. This rubber will be used initially to purge the system of the previous rubber used (see Section 6.3 on purging). 

Back-rinding Cavity temperature too high Evaluate... 

Fourthly, avoid the use of very high cavity temperatures. These are not generally necessary to obtain short cure times, and certainly speed the rates at which residues are deposited. For natural rubber aim at a cavity temperature of 165 °C. For synthetic rubbers with low levels of unsaturation such as ethylene-propylene diene terpolymer this will need to be increased to 180 °C. The cavity temperature is usually 10 °C to 15 °C below the set point of the platens. 

In the case of measurements at a cavity temperature of 2K [15], a reduction of the signal could be clearly seen for atomic fluxes as small as 800 atoms/s. An increase in flux caused power broadening and finally an asymmetry and a small shift (Fig. A). This shift is attributed to the ac Stark effect, caused predominantly by virtual transitions to the 6ld level, which is only 50MHz away from the maser transition (Fig. 3). the fact that the field ionization signal at resonance is independent of the particle flux (between 800 and 22 x 10 atoms/s) indicates that the transition is saturated. This, and the observed power broadening show that there is a multiple exchange of photons between Rydberg atoms and the cavity field. 

Fig. 4. Maser resonance at a cavity temperature of 2 K (see also Reference [15]).

The crosses on the T = 3 K curve are obtained in the experiment. For these measurements the cavity temperature was raised to 3 K in order to have more thermal photons (2.5) in the cavity. The agreement between theory and experiment is excellent. 

The following parameters were used for the atomic emission detector spectrometer purge flow, nitrogen 21/min. There was solvent back flush. Transfer line temperature was 250°C cavity temperature was 250°C water temperature was 65°C. Element wavelengths for sulfur, carbon and nitrogen were 181.4, 193.0 and 174.3 nm, respectively. 

Moulding is too hot Reduce melt temperature. Reduce cavity temperature. Extend cooling time. 

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