Gob weight fluctuations due to a stirrer and to glass melting firing reversals

Abstract

It was difficult to adjust gob weights from a stirred, molten glass delivery System. The difficulty decreased when rotation of the gobbing stirrer was stopped. However, this was not a satisfactory Solution as it left objectional striations in the glass items being produced. The weight changes were due to the superposition of several effects, each of which by itself would have been acceptable. Small temperature fluctuations and spontaneous changes in the stirrer's position and stroke were found but they were not the major causes of the weight fluctuations. Cyclic variations in weight with an amplitude of about 1% and a period of about 11 min were due to the stirrer's rotation. It became clear that close but approximate matching of the gobbing and rotational rates was inadequate and that synchronization of these two rates had to be perfect to eliminate this cyclic weight Variation. The inevitable conclusion was that run-out associated with stirring was the cause of this problem. A second cyclic Variation with a period of 20 min and an amphtude of about 0.4% was associated with tank reversals of the cross-fired melter with its regenerative checkers. This was the first time that weight changes due to tank reversals were noted. A composite weight Variation curve was synthesized, with one component representing an 11 min cycle and a second component representing a 20 min cycle formed by a ramp with a linear decay A comparison of the synthesized and actual weight curves revealed many similarities and strengthened the conclusion that most of the actual weight run changes resulted from the stirrer and from tank reversals.