Gypsum board molding process of building gypsum quality requirements is strict, not only requires high wet strength, and coagulation time to stability. If residues of building gypsum dihydrate gypsum is more volatility, calcination temperature instability gypsum particles surface tightness, these factors will lead to an unstable slurry solidification time, continuous molding process is difficult. In addition, anhydrite A Ⅲ and A Ⅱ there is too much, the hydration incomplete, can lead to low strength of gypsum board. Therefore, gypsum processing to make the following further study on rotary kiln calcining process needs. Gypsum dehydration reaction in the calcination process, can use gesso differential thermal curve said.
From three different grade gesso of differential thermal curve, the gypsum powder mill seems to be as long as the calcination temperature controlled at 171 ℃, 158 ℃, 137 ℃, can obtain the single half water gypsum. But with rotary kiln calcining, the situation has become more complex. Front row, gypsum particle size is not uniform; Second, the impurity content in the gypsum is not uniform; Third, it does not agree the dehydration temperature. In order to improve the dehydration reaction speed, tend to improve furnace temperature, and high temperature air is easy to make some rapid dehydration gypsum particles, therefore, in the actual production could not get the ideal single half water gypsum, but a mixture of phase composition.
The curves of building gypsum phase composition, illustrates the problem. For example, low calcination temperature and calcination time short, the clinker containing more dihydrate gypsum, we call this kind of gypsum clinker D just a little water gypsum; H half water gypsum; A anhydrite llI (A Ⅲ) owes plaster, its solidification time is not very stable, and the intensity is extremely low.
Instead, control the water of crystallization in small range, which burnt A few, almost all of clinker is half water soluble anhydrous gypsum and gypsum (A Ⅲ), residual dihydrate gypsum is rarely so slurry solidification time is stable, the intensity is high.
Thus, the quality of the plaster and stability is much better than owe plaster, but burnt degree must be strictly controlled, otherwise too many soluble anhydrite (A 11 I) and calcined temperature formation of difficult soluble anhydrite (A II), will adversely affect the performance of condensation sclerosis, in forming production line may appear phenomenon of knife cutting intensity and low viscosity. So, need stability calcining process system, stable phase composition, and through the appropriate "aging" to improve the initial hydration performance. In addition, adding coagulant coagulation time adjustment measures, in order to meet the gypsum board production process requirement.
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