found
The period of time when a furnace is at its hottest; the interval in which the furnace is meant to fully melt glass.
found: when the glass furnace reaches full melt
The found is the operational window when a glass melting furnace reaches and maintains its designed working temperature, typically between 1700 and 2100 degrees Celsius depending on the glass composition and furnace type. During this period, the raw materials (batch) have fully fused into a homogeneous molten mass ready for forming. The found is not instantaneous but extends over hours or even days, representing the stable high-temperature zone where the furnace can consistently feed forming equipment at the required rate and viscosity.
The term originates from glassmaking's long history, where found derives from the French fond, meaning bottom or foundation. Early furnace operators used this word to describe the settled, fully-melted glass at the base of the crucible or pot, which was the only usable material for gathering and shaping. The word retained its meaning even as furnace technology evolved from pot furnaces to continuous tanks and day tanks.
Reaching found requires careful control of heating. A new furnace being brought online, or one reheated after maintenance, must be brought up slowly to avoid thermal shock to the refractory brickwork. Once found is achieved, maintaining it depends on steady fuel input, proper batch addition rates, and chemical balance. If the furnace cools below found temperature, the melt becomes too viscous to gather or form reliably; if it exceeds safe limits, the refractory begins to degrade and unwanted chemical reactions occur.
Different furnace types have different found characteristics. A pot furnace found might last 8 to 12 hours per cycle, after which it must cool and be cleaned. A continuous tank furnace maintains a perpetual found, broken only by planned maintenance shutdowns every 5 to 15 years. Day tanks and small melters reach found more quickly, sometimes within 2 to 6 hours, but cannot sustain production as long without refurbishment.
Problems arising during found include refractory erosion from chemical attack by molten glass, segregation of components (heavier materials sinking, lighter ones floating unevenly), and gas inclusions that remain trapped in the final product. The homogeneity and clarity of glass depend on complete dissolution during found and proper retention time for bubbles to rise and escape. Operators monitor found stability through visual inspection of melt color and fluidity, and increasingly through thermocouple readings and infrared sensing.