With over 130 years of experience in optics and glass production, SCHOTT is the last remaining company in the Western Hemisphere that still melts optical glass. As early as 1911, SCHOTT became the first specialized glass manufacturer worldwide to start using a continuous glass melting tank.
Before melting can begin, raw materials – or “batches” – must be gathered together. The first step in this process involves weighing – so the ingredients of the so-called batch recipe are measured. The batch consists of the specified ingredients. Precision is especially important here, since even just 1 extra gram can completely change the result. In order to ensure the batch is uniform, all ingredients are thoroughly mixed in large mixing units. The subsequent glass melting phase is a central step in glass production. Ultimately, it is the raw material composition and quality of raw materials, the manner of heat applied, and the specific melting process that determine the type of melted glass and thus the end product.
Crucible ovens or pot furnaces were originally used for this melting process. Here the individual steps in the glass melting process are performed in sequential order. With tank melting, which is the most common method used today, the processes are completed continuously in sequential order as they move through the system. Both melting processes are still used today for glass melting.
Building upon this basic procedure, SCHOTT has continuously developed the processes, and derived special methods for making a variety of different glass types. Advanced Optics uses a wide variety of raw materials and compositions to achieve the diverse characteristics of its products.
SCHOTT Advanced Optics melts its glass using the following methods:
Most of the melting processes are performed in Mainz – from the melting of small batches in the lab to mass production of optical glasses and optical filters employing tank melting.
Each glass melt is conducted in four phases:
Fusing: The batch consisting of high-purity raw materials placed inside the furnace is heated, a molten mass forms due to a chemical reaction, and gaseous byproducts often result in the formation of bubbles.
Purification: Elimination of the gas bubbles in the molten mixture
Homogenization: Stirring of the bubble-free molten mixture.
Casting & hot forming: Liquid glass exits the feeder and is formed into bars, rods, or blocks.