The Influence of Batch Segregation and Bulk Flow on Glass Quality

Glass batch is typically a blend of various dry ingredients of widely varying particle size, often including extremely coarse cullet in addition to finer materials. Such blends are often prone to segregation, or the separation of material into regions of similar properties, as they are handled through bins and chutes, and conveyed to a furnace. Batch segregation can result in variations in chemical composition or physical properties (such as density) of the material entering a furnace. Such variations can be primary contributors to quality problems such as color variations, cord, seeds and blisters. This paper will discuss the various mechanisms by which glass batch can segregate, as well as methods for addressing or preventing common batch segregation problems. The basic flow patterns that occur during gravity discharge from silos and bins will be covered, differences of which can have a strong influence on segregation in the resulting stream of material. Examples of segregation behavior in industrial settings will be included, as well as methods for characterizing materials with respect to segregation tendencies and flow properties, the results of which are applied in a solution method.