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1.5 REFRACTORY CURING CYCLE <br />A properly executed refractory curing cycle is essential for satisfactory refractory service. <br />The refractory in this unit has been cured in our factory only sufficiently to permit shipping <br />final curing must be performed after assembly. <br />The recommended curing cycle is given in Table 1 (Section 1.5.1)and should be followed as <br />closely as possible. If modifications to the recommended cycle are found necessary in the <br />field, the following should be carefully considered: <br />1. Heat penetrates refractory slowly, thus the interior of the refractory reaches a stable <br />temperature significantly later (often many hours) after the surface temperature has <br />stabilized. This is the reason for holding times at various temperatures. <br />2. Large amounts of water are liberated at two points in the initial cure - firstly when <br />free water is vaporized at 100°C(2120F) and secondly when water of crystallization <br />is liberated at approximately 480°C (9000F). Most refractories are very dense and <br />resistant to the passage of steam. This water must be allowed to escape gradually <br />from the refractory or the steam pressure developed will cause explosions within the <br />refractory, with consequent massive failure. This is the reason for the slow rate of <br />heating during the initial cure. <br />3. The initial cure should be undertaken as one continuous operation if at all possible. <br />If it is found necessary to interrupt the cycle at some point (such as for a power <br />outage), complete the cycle by heating at 381C/hour (100°F/hour)up to the point at <br />which the cycle was interrupted, and then complete the curing process. <br />The refractory insulation consists of an outer layer of insulating board and an inner layer of <br />cast in place refractory. The refractory requires drying out and curing. The water vapour <br />will exit via the exhaust fan and associated ducting. <br />E