Minimum cure temperature determination

Suppose now that the designer has developed a tentative design for the vessel, which includes the number of layers, material specifications for each layer, and the thickness of each layer, as well as the determination of the installation temperature, cure and operating conditions, and the maximum and minimum ambient temperatures that will be encountered both during operation and when idle. These operating and cure conditions to be specified are inside temperature and pressure, ambient temperature, and inside and outside heat transfer coefficient. 

The maximum cure temperature was limited to 140°C to ensure minimum homopolymerization of the epoxldlzed oils. Gel times were determined In separate experiments at 120°C by noting the time required for gelation to prevent stirring. 

Polymer applications of DSC are numerous and concern the determination of Tm (ASTM E 794), Tg (ASTM E 1326-03, ISO/FDIS 11357-2), specific heat capacity of a material (ASTM E 1269, ASTM D 4816), crystallisation temperature upon cooling (ASTM E 794), transition temperatures (ASTM D 3418, ASTM D 4419, ASTM D 4591), purity of a material [79,80], contamination outgassing (ASTM E 1559), reaction rates, sample composition, reaction kinetic constants (ASTM E 698), reaction mechanisms, thermal stability (ASTM E 537), minimum processing temperatures, heat of fusion and crystallisation (ASTM D 3417), heat of crystallisation (ASTM E 793), additive effects on a material, quality control of raw materials [25], discrimination between materials, detection of polymorphism [81], characterisation of thermally and UV cured materials (cure state, degree of cure) (ASTM D 2471, ASTM D 5028), oxidative stability testing, QIT (ASTM D 3895, ASTM D 3012, ASTM E 1858-03), etc. 

In order to answer these questions, the kinetic and network structure models were used in conjunction with a nonlinear least squares optimization program (SIMPLEX) to determine cure response in "optimized ovens ". Ovens were optimized in two different ways. In the first the bake time was fixed and oven air temperatures were adjusted so that the crosslink densities were as close as possible to the optimum value. In the second, oven air temperatures were varied to minimize the bake time subject to the constraint that all parts of the car be acceptably cured. Air temperatures were optimized for each of the different paints as a function of different sets of minimum and maximum heating rate constants. 

To determine the wet bond strength coated panels were immersed in distilled water for 1500 h, removed and discs 25.4 mm in diameter stamped from them. The surfaces were wiped with a dry tissue and bonded between two cylindrical test pieces using a polyamide cured epoxide adhesive and immediately placed in a sealed container at 100% RH for the adhesive to cure. After 16 h the specimens were broken on an Instron Universal Test Machine with minimum delay. Recovered values were measured after the panels had dried out at room temperature and humidity for 7 days. Clearly, it is unlikely that the values reported represent the minimum bond strengths, as some drying out is almost inevitable, but the values are directly comparable. 

A one dimensional solution, as mentioned, is often sufficient to predict the temperatures achieved during cure and the time required to demold. Demold time is found by determining the point at which the entire cross section has achelved a minimum eject-able conversion. 

However, as shown in Figure 6.1, tracing the torque as a function of time obtained with the isothermal oscillating disc rheometer (ODR), the temperature of the sample varying with time according to an unknown law, it is not easy to determine the conditions of time and temperature for the scorch of cure, which are associated with the minimum torque value. Moreover, the moving die rheometer (MDR), gives a shorter... 

The determination of set in tensile strain is much less commonly specified than that in compression, although in principle it is a particularly straightforward procedure a strip, dumbbell or ring lest piece of known reference length is. stretched to a given extension, exposed in this condition to a combination of temperature and time, and then released for a specified period before measurement of the reference length. One clear advantage for the test, as say a measure of the state of cure, is that test pieces can be cut from even the thinnest of latex films, whereas the minimum ply thickness of a laminated compression set test piece is 2 mm. 

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