Large size optical glass has attracted much attention due to its applications in large optical devices. Due to stringent requirement in applications, extra thermal treatment should be investigated to increase the quality of product. During fine annealing, glass temperature is crucial for final quality of optical glass as a result of its influence on thermal stress and optical homogeneity. To ensure a high performance, temperature distribution in the glass should be homogeneous and symmetric, and maximum temperature difference is expected to be small. This paper proposed two approaches to improve the glass temperature uniformity during fine annealing. Firstly, the glass blocks are packaged with heat exchange blocks on the top and bottom surfaces and insulation layer on the side. Thickness of layers and materials usage are investigated. Simulation results show that the homogeneity and symmetry of glass temperature distribution can be improved. Temperature difference in the horizontal direction can be further reduced in the case of 10mm copper heat exchange block together with 50mm insulation layer. Secondly, a muffle apparatus is utilized and symmetry of temperature distribution can be improved. Furthermore, above two approaches can be combined. Knowledge learned in this work can be used to guide industrial fine annealing process to reduce the stress level and improve the symmetric of residual stress.
