III. Heat is emitted by three types of materials: Transparent, Translucent, and Opaque

The material is transparent when the electromagnetic wave of thermal radiation travels directly through it without being absorbed.  If the electromagnetic wave of the thermal radiation travels through a material with part of it being abosorbed and part of it being reflected, the material is known as translucent to the light. When the electromagnetic wave of the thermal radiation is totally abosorbed by the material, then it is opaque to the electromagnetic wave.  In order to shorten heating time and improve efficiency, it is important to set a heating range in which the transition wavelength emitted by the heating elements can be completely absorbed by glass. 

IV. The heat conduction for glass in the heating chamber includes the heat transmitting process from glass surface to the center and heat transfer from the surface of ceramic rolls to the surface of glass.  

V.  General Rules of Glass Heating 

The heating chamber in the tempering furnace must reach the appropriate temperature; Heating process has to be rapid; Temperature distribution in the heating chamber must be balanced and symmetrical with glass surface heat temperature difference maintained under 5℃.

VI. Ideal Heating Temperature for Glass  

The ideal temperature for glass tempering is a special temperature range in which the glass is changing from solidified brittle state to a plasticity state while approaching glass softening temperature. Within this range, the residual stress in the glass is completely released and eliminated to allow the glass to get maximum temperature profile, the best level of tempering, and the most homogeneous distribution of tempering stress.

VII. Heating Process

As soon as the glass enters the heating chamber, it’s heated rapidly. The temperature of glass rises very fast due to the great temperature difference between the glass and heating oven. As this gap is narrowed, the heating speed will slow down as well.  When the temperature difference between the interior and outer surface approaches zero, the heat transfer will become very slow and the heating should be stopped.