their batch into an annealer and raised the temperature to 500-700° F. The hotter charge will lower your heat differential and cut your melt time.
The amount and frequency of charging is another key element. Small charges minimize the degree of temperature drop and the duration of time the contact surface remains at the reduced level. The amount of the charge is dependent upon your operation, the length of time you allot for the filling sequence, and the size and configuration of the crucible. A shallow, wide crucible affords the best receptacle for charging; it affords the least amount of wall space for potential material contact. It is recommended that the amount of each charge be limited to about one fourth of the volume of the crucible.
The interval between fills should be of a duration that allows the interior wall of the crucible to return as near to temperature equilibrium as possible. The minimum point for this occurs when the pile of the charge softens and flattens out. The sequence is repeated until the crucible is filled. The increased time between charges ensures a greater equilibrium between the inner and outer walls.
The next area of concern is crucible corrosion resulting from the batch charge as well as the relative corrosiveness of the batch glass itself. Keep in mind that the lower the viscosity of the glass the faster it will attack the liner. The higher the alkali and lithia the more corrosive the glass. Lithia is very popular as a batch addition because, in small amounts, it decreases glass viscosity appreciably.
Temperature is an important contributor to influencing the effects of corrosion upon refractory surfaces of a crucible. Temperature is an accelerator; its excessive use in combination with the alkali and other aggressive components in glass will destroy or disrupt the contact surface of the crucible to a point whereby unsatisfactory properties such as stones, seeds, and cords are imparted into the glass. Melt at the lowest temperatures possible because excessive temperatures will ultimately compound your problems. The correct temperature has to be determined by each operator; it is dependent upon factors related specifically to your operation, such as batch composition, desired glass properties, furnace design, etc.
The use of batch, cullet, or combination is a factor
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