WORKING END AND FOREHEARTHS
The Working End and Forehearth concept developed by BDF is based on the assumption, well proved and generally accepted, that the conditioning of the glass begins just at the furnace exit.
The forming process requires to be fed with glass on a viscosity range that is normally much different from the one we find at the furnace exit.
In the container plants the Working End and the Forehearths must cool the glass, being the exit furnace temperature much higher than what required to grant the necessary glass viscosity for the forming process.
The glass is a material that can not be strongly cooled, therefore the cooling process to be applied must be designed taking into account a number of variables such as the thermal balance, the glass colour, the path, the “head loss”.
We also cannot forget the chemical aspect, as sometimes the glass quality may be affected by the characteristic of the atmosphere which it is in contact with.
The process of glass cooling down taking place after the furnace throat through distributor and forehearths is commonly known as “conditioning”. The conditioning process involves not only the forehearth, but the whole path from the throat to the spout entry.
The molten glass exiting the throat must reach the spout with precise characteristics in terms of temperature, thermal & chemical homogeneity. Forehearths designed by the multi-skilled BDF Group are complete with automation and combustion systems specifically developed to achieve such targets with maximum flexibility.
Very often the energy to be removed from the glass to deliver the required gob temperature is much higher than what is possible to achieve by the dispersion from the refractory and it is necessary, in this case, to implement some additional cooling.
The forced convection cooling system is based on introducing cooling air through the forehearth superstructure.
Longitudinal centre line cooling, efficiently removes heat from the hot centre glass without adversely affecting side glass temperatures, and using relatively small volumes of cooling air.
The cover roof design has been developed in order to maximize the refractory surface exposed to the glass in the forehearth centre.
This shape allows increasing the heat exchange between the glass and the cover roof since the glass is exposed to a colder large refractory surface.
The application of this system basically involves the application of openings in the superstructure roof blocks, also used for the combustion waste gases exhaust.