Identification of cord sources in glass using CFD

Abstract

Cord appearance in the glass industry is a serious problem in high glass quality tableware production. The increased frequency of sharp cords provoked a serious analysis on cord origin and their elimination at the production line. Optical microscopy and electron microprobe analysis (EMA) were applied as direct methods for cord identification. A computational flow dynamics calculation (CFD) and process data analysis were used to verify the hypothesised source of the inhomogeneity. The hypothesis on origin of ZrO2 free cords containing high amounts of Al2O3 was postulated in relation to the refractory material composition of the forehearth. Calculations showed that the suggested mechanism at temperatures between 1200 and 1300°C was relevant. The hypothesis was supported by a change of chemical character of the cords after partial removal of the poorly resistant material. Also the average cord frequency was reduced on a production line from 53 to 17%. CFD simulations indicated that there may exist an effective mixing strategy on cord dissolution. Increasing stirrer rotation speed in a tempering part of the forehearth had a positive effect on cord disruption. The proposed stirrer set up decreased the cord frequency to less than 2%.