Baking time

Dicalcium Phosphate Dihydrate (DPD). Dicalcium phosphate cHhydrate is completely nonreactive at room temperature. At 65—71°C and in the presence of water, it dehydrates and decomposes into hydroxyapatite and acidic monocalcium phosphate, or a free phosphoric acid (18). It is used to some extent in cake mixes in combination with faster acting acid. Its primary function is to provide acidity late in the baking cycle and thus produce a neutral and palatable product. DPD has an NV of 33. It provides sufficient acidity only in products requiring long baking times. 

Fig. 2. Baking time as a function of temperature for A, residual heat curing B, fast curing C, medium-fast curing D, slow curing powders where (--)...

The agreement between the experimental and calculated values of Ce, is excellent. The data shown in Figure 2 are for a constant bake time of 17 minutes. The upper and lower limits on define a cure window. The cure window for the low solids coating is 50 C. The model was further tested by measuring extents of reaction and temperature profiles for samples attached to different parts of a car body which passed through a pilot plant oven. This simulation tested the model under conditions where the substrate temperatures were far from constant. As shown in Table II, the agreement between the experimental and calculated values of Ce is again excellent. 

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. 

Values of ACe decrease with increasing Zm- since the car body temperature profiles become more uniform. Another way to increase car body temperature uniformity (and thus decrease ACe ) is to increase the bake time. For example, increasing the bake time from 17 minutes to 25 minutes essentially compensates for a decrease in cure window of 50 C to 35 C. 

Figure 6. Minimum bake time versus minimum heating rate constant for the low solids paint (O) high solids 1 ( ), high solids 2 ( ), and high solids 3 ( ). The open symbols are for a maximum air temperature of 149 C. The half filled circles are for a maximum air temperature of 157 C and the filled circles are for a maximum air temperature of 166 C.

A network structure model has been developed from which a parameter that correlates well with physical measures of paint cure can be calculated. This model together with a kinetic model of crosslinking as a function of time and temperature has been used to evaluate the cure response of enamels in automotive assembly bake ovens. It is found that cure quality (as measured by the number and severity of under and overbakes) is good for a conventional low solids enamel. These results are in agreement with physical test results. Use of paints with narrower cure windows is predicted to result in numerous, severe under and over bakes. Optimization studies using SIMPLEX revealed that narrow cure window paints can be acceptably cured only if the bake time is increased or if the minimum heating rate on the car body is increased. 

AX image on PMMA, Reducing either the baking time or temperature... 

Figure 6. Extent of hydroxy reaction versus bake time for reaction with isocyanate...

Example 1 What Is the Correlation Between the Baking Time... 

We can now easily answer the question concerning the correlation between the baking time and the weight of the Christmas turkey, without explicitly knowing the function f which connects both numbers [Eq. (4)]. To achieve the same temperature distribution T/T or Tq—T)/Tq in differently sized bodies, the dimensionless quantity aOlA = o must have the same (=idem) numerical value. Due to the fact that the thermal diffusivity a remains unaltered in the meat of same kind a = idem), this demand leads to... 

Figure 4. Infrared absorbance of epoxy and azide groups in EAP film containing triethlylamine, as a function of baking time (baking temperature ...

Example 1 What Is the Correlation Between the Baking Time and the Weight of a Christmas Turkey We first recall the physical situation. To facilitate this we draw a sketch (Sketch 1). At high oven temperatures the heat is transferred from the heating elements to the meat surface by both radiation and heat convection. From there it is transferred solely by the unsteady-state heat conduction that surely represents the rate-limiting step of the whole heating process. 

Shown in Figure 2 are the electron donor and acceptor concentrations as a function of baking time at 800 °C for the growth of GaAs by LPE (57). The level of unintentional impurity dramatically decreases with increasing baking time. The residual acceptor and donor were attributed to C and Si, respectively. 

Similar results are shown in Figure 3 for the growth of In Ga As layers on InP (55). The measured carrier concentration at room temperature decreases with increased baking time for baking times up to 50 h. 

Figure 2. Donor ( ), acceptor (O), and net carrier ( ) concentrations as a function of baking time at 800 °C for growth of GaAs. (Reproduced with permission from reference 57. Copyright 1984 American Institute of...

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