Pressing is a mold forming process; heating glass in a molding furnace (Casting furnace), placing the glass to a metal mold, and molding it with a pressing machine.

In pressing processing, to shorten the time required for the next process (Grinding/Polishing), it is necessary for glass material to be pressed close to the shape of final product.

To obtain the consistent shape and characteristics of optical glass in molding, the adjustment of viscosity and temperature of the glass is very important.
NITTO OPTICAL controls temperature of the molding furnace and the metal mold precisely.

Annealing is to homogenize the optical performance by heat treatment as much as possible.

It is important that optical glass has high homogeneity in any part of the glass.

The refractive index and dispersion (change in the material refractive index according to wavelengths) of glass are determined when raw materials are refined. However the thermal history of glass is lost when pressing is carried out, it is necessary to align the molecules within the glass by subsequent annealing.
The internal refractive index and dispersion value (Abbe number) is very important for lenses. The homogeneity of the internal refractive index of high-quality prisms and filters is very important.

When annealing is insufficient, final products can not satisfy customers requirement, no matter how advanced the processing technology is. Establishment of precision annealing enables NITTO OPTICAL to hand over the high quality glass to the next production procedure.