A liquidus furnace is useful for determining the maximum temperature at which crystallization will form in a glass, and a minimum temperature at which a glass can be held for extended periods of time without crystal formation and growth.

Samples of glass, frit, or cullet are loaded into a platinum tray then placed into the hot Orton Liquidus Furnace for 1 or 24 hours. The Orton Liquidus Furnace is a specially designed horizontal tube furnace with a controlled, reproducible, linear thermal gradient of approximately 120°C across a 12” long monitored zone, so the temperature of the glass in the tray corresponds to its position along that 12” zone. The tray is removed hot and allowed to quench cool, freezing the glass in the state it developed inside the furnace. Upon visual, or microscopic inspection, the crystal boundary plane (the Liquidus Point) is located and the temperature of that plane is interpolated from the temperature / position relationship of the known gradient.

Glass Batch Studies

The Orton Liquidus Furnace

The Orton Liquidus Furnace is a specially designed horizontal tube furnace with a controlled, reproducible, approximately linear thermal gradient across a 12” or 16” long monitored zone, and is composed of four main components: furnace, controller, power transformer, and temperature display system. The furnace is a rectangular, metal shell structure that houses the refractory fiber insulation and four molybdenum disilicide heating elements that surround one end of the 2-3/4” ID ceramic heating chamber tube.

This sectioned concept drawing of the furnace shows the sample tray, D-tube hearth, and monitoring thermocouples. The sample tray is placed on the top of the 2.5” wide high alumina D-tube hearth, which rests on the bottom of the ceramic heating chamber tube. Type “S” thermocouples are spaced on 2” centers along the monitored zone and extend vertically through the top of the heating chamber tube.