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FIRING CURVE

 

In light of the above-described transformations the characteristics of a firing curve may be described as follows:

Up to 1O0 C the w ater absorbed during glazing is evaporated;

Between 100 C and 150 C the residual water contained in the Ixxly is removed; to prevent the pressure generated by the steam damaging the article, heating is gradual, alxwt 300 C/h;

Between 150 C and 800 C the firing gradient can be raised to 350 C/h;at j this stage combustion of organic substances takes place. The usable therri gradient is inversely pro{x>rtional to article thickness;

Between stK) C and the maximum temperature, the thermal gradient is reduced to about 65 C/h to allow gentle decarbonation; before 1000 C the gradienti low to delay the start of glaze melting;

 

The holding time at maximum temperature is a function of body and glaze composition and the particle size distribution of their components. Reductio of the holding time necessitates an increase in peak temperature in order to reach the correct level of vitrification;

 

Between maximum temperature and 800 C comes the maximum cooling ral at 800 C/h; this gives beneficial effects such as brilliance of glazes;

 

Between 800 and 600 C the cooling gradient is about I5<> C/h. Thisfl when the glassy phase of the body switches from molten to liquid; it is also necessary to ensure that temperature is homogeneous inside every chamber of the manufactured article to ensure ideal conditions for the Quartz B - Quartza transformation;

 

Between 6O0 and 500 C the thermal gradient is reduced to 60 C/h to prevent tensions during the Quartz B - Quartz a transformation.

 

Betw een 500 C and 50 C the cooling rate may be as high as 300 - 450 C/h; i particular precautions are required in this regard in that sanitaryvvare bodies do] not form Cristobalite, so there is no polymorphic transition between Cristobalite B and Cristobalite a and its pre-existent presence in the body should not be of

consequence.


FIRING CURVE - PILOT PLANT


400 Time (min.)


 


 


/■'/#. tttS - Intermittent kiln firing curve.

 

 


Date: 2015-04-20; view: 865


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Chapter 13 FIRING | RE-FIRING
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