Metal Corrosion and its Impact on Glass Tempering Furnace Design

A reliable well‐designed tempering furnace is considered to be the cornerstone of any modern glass‐processing facility. This paper addresses a series of engineering anomalies encountered during the commissioning of such a glass‐processing furnace. Following the installation of a furnace in a European facility, small black deposits were noticed on both the silica‐fused rollers used to transport the glass through the hearth of the furnace and on the processed glass surface itself. EDAX and scanning electron microscopy investigations indicated conclusively that the deposits were primarily constituted of sodium sulfate and trace elements consistent with stainless steel (chromium, iron, and nickel). Traditionally, high‐density glass fiber was used to insulate the roof walls and side walls of tempering furnaces; however, it was noticed in this particular case that rolled stainless steel sheeting (SS316) was used. Chemical and X‐ray diffraction analyses were used to pinpoint the origin of the deposits. It was determined that poor material selection choices taken during the design stage of the furnace in question were at fault. The combination of stainless steel and sulfur dioxide (SO2 is used as a lubricant to prevent scuffing) at elevated temperatures (>650°C) generated droplets of sodium sulfate, which condensed due to the convectional flow of the heat currents within the oven. These droplets scorched the glass surface and destroyed the fused silica rollers. As a recommendation, the usage of stainless steel and other nonrefractory metals should be avoided in the design of any future glass tempering furnaces.