Cure time calculator

Modern IM processes offer the user numerous, almost confusing settings. Process windows are searched for different times, velocities, pressures, temperatures, forces and paths for the individual phases with respect to their dependencies for each product, the mold used, and the used elastomer mixture. The goal is to produce a product as economically and qualitatively robust as possible. The time required to find optimum process windows is, in spite of technical assistance (e.g., by so-called cure time calculators), still dependent on the experience of the particular user or process engineer and the quality of the resources used (mold, elastomer, machine). 

From these data an a [COz]saturated/[COz]100Z gas of 1.5 can be calculated. For the model calculations a has been kept constant for the entire concentration range and curing time. 

Several epoxy powders were formulated in a homologous series where the EEW of the base resin changed from 858 8/eq. to 1487 8/eq. All formulations contained 10% carboxyl-terminated rubber, were extruded two times, and were cured with calculated amounts of P-108. The standard cure schedule of 200OC for 15 minutes was used. MEK absorptions were measured in the usual manner. A definite dependence of MEK absorption on EEW was found. Table V summarizes the data. 

Method 2 A sample is cured for various times until no additional curing can be detected. The samples are then scanned (heating rate ranging from 2 to 20°C/min) in order to measure the residual enthalpy, AHres. The degree of cure is calculated directly by Equation 2.25,... 

Nevertheless, it was decided to make the measurements of density and of refractive index for specimens after different times of curing. Since the molecular weight of the polymerized silane was not known, the molecular refractivity could not be calculated but only the ratio of this to the molecular weight. Nevertheless, interesting results were obtained with a linear relationship between the cure time and refractive index up to 18 h. The relationship between the cure time and the ratio of molecular refractivity to molecular weight is shown in Fig. 3 and indicates a steady increase in molecular complexity up to 24 h, when it approaches a constant value suggesting a final state of crosslinking. 

Figure 9.18 gives a clear view on the stabilization of the coating by condensation with the surface hydroxyls during curing under vacuum conditions. The amount of hydrogen bonded aminosilane, as calculated from the absorbance data, is plotted as a function of curing time in vacuum. 

Figure 6. Cure curves calculated with roller model for four systems, under "normal" bake schedule. Nominal temperature 180 °C, beating time constant 30 sec.

When drying and curing are done separately in two steps, the curing time can be controlled easily. As speed is defined by distance divided by time, the curing time can be calculated by Equation 2.14 ... 

Figure 3. Plot of Ca/(5a l) versus cure time to calculate rate constant (k ) for epoxy-primary amine reaction. (Reproduced from Ref. 4. Copyright 1986 American Chemical Society.)...

In the case where two materials have different scorch times but the same 90% crosslink cure time, it is obvious that the cure reaction is proceeding faster in the latter stages for the material with the longer scorch time. A calculation based on a single point from the cure-time curve will give the same answer for both samples, although in practice they have different cure distributions. To make accurate calculations the whole of the cure-time curve must be used, and this is the basis of this new model. 

It is also of interest to evaluate the effect of the thickness of the rubber sheet when the heating system is on the external surface of the mold in contact with the surroundings, as shown in Figure 4.10 for the temperature-time history and in Figure 4.11 for the state of cure-time history. These curves are drawn as they are calculated at the mold temperature of 180°C with the rubber compound containing 2% sulfur responsible for an enthalpy of cure of 14.3 J/g. 

The effect of the kinetic parameters on the cure is evaluated in this subsection by using the values collected in Table 4.1, which are the basis values around which they are varied. The mold-rubber is considered with the heating system placed on the mold surface in contact with the rubber sheet. The results are expressed in terms of temperature-time histories and of state of cure-time histories calculated either at the rubber surface or at the mid-plane of this rubber sheet. The rubber thickness is 2 cm, and the mold temperature is 170°C. The cure enthalpy is 14.3 J/g associated with sulfur at 2%. 

Figure 4.25, where the state of cure-time history at the rubber surface and at the mid-plane are drawn as they are calculated with the three values of the order n, with n = 1.25 (curve 1) n = 1 (curve 2) n = 0.75 (curve 3). 

Thus, the temperature-time history and the state of cure-time history are calculated either at the mid-plane or on the surface of a rubber sheet of thickness (2L) 2 cm, during the cure at 170°C, by taking the three couples of values shown above. 

The result is expressed in terms of the state of cure-time history obtained at various values of the temperature of the reservoir T. The curves drawn in Figure 5.1 show the increase in the state of cure of the rubber with time, as they are calculated under isothermal condition by using the kinetic parameters of the cure reaction collected in Table 5.1. 

The rubber material is obtained by curing a scrap rubber powder at various times and temperatures, and the various values of the state of cure are calculated from the partial heat evolved from the cure reaction measured by calorimetry, as already shown in Chapter 4. The dynamic properties in compression are determined at room temperature by using several samples for which the state of cure is ranging from 36 to 90%. The apparatus used enables the measurement of the visco-elasticity of the rubber sample under various conditions such as compression, traction, shear (vis-coelasticimeter from Metravib, France). 

Other studies have been carried out by considering the heat transfer by conduction through the rubber, as well as the heat generated by the overall cure reaction. The state of cure at any time t is thus defined as the heat evolved up to time t as a fraction of the total heat evolved from the cure reaction. In a particular method, the state of cure was calculated from the temperature history at any place in the rubber by introducing a rate of reference at 149°C and a temperature coefficient of cure, assuming that the rate of cure increases by a factor of 1.85/10°C. In another study, the profiles of temperature developed through the rubber were calculated assuming that the rate... 

Exercise 3.7. The data below were obtained in a study of the influence of two factors on the initial curing time of plaster of Paris, that is, the time when the plaster of Paris starts to harden after the powder is mixed with water (M.F. Pimentel and B.B. Neto, Anais do XXXI Congresso Brasileiro de Quimica, Recife, 1991). The runs were carried out in duplicate and in random order. Calculate all effects and their standard errors. Interpret the results. 

For the high-resin-content formulation (Table 12), a partial addition of the PF resin can be made just after the initial mix and before sodium hydroxide addition if more fluidity is needed for propeller-type stirring. This formulation is more properly termed a blood-fortified exterior PF resin adhesive for hot-pressing plywood or laminated veneer lumber [52]. Even in quantities this small, the effect of the animal blood is to reduce the hot-press curing time by 2(%30% over that of phenolic resins used alone. For purposes of adhesive solid, calculation, the blood content can legitimately be included with the phenolic resin solids. 

When degree of cure is calculated from H, as measured by DSC, it is seen that addition of PSF decreases the degree of curing at any given time as has been found for other thermoplastics, and slower cure rates give larger phase separated PSF particles. 

---