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- Reduced cooling costs
- Smaller plant "Footprint"
- Increase of tonnage pulls for the same size of equipment
- Can be retrofitted
- Substantial Cooling rates
- Can be utilised with forced cooling
Introduction
All forehearths comprise one or more Cooling Zones,
one Equalising Zone and sometimes a feed channel or Alcove.
The limiting performance capabilities of any forehearth design is related
to the type of glass, the operating temperature range and
the required quality of the thermal homogeneity at the exit.
If a zoned Working End is utilised such as the BH-F 400 series
The Mass Heat Extractor may be used allowing for a smaller plant "Footprint"
When the design is operating at its performance limit and
a higher Production capability is required,
the obvious solution is to install a wider forehearth or working end.
If however, the forehearth/working end can be re-zoned, by altering the
superstructure design, then a costly rebuild could be avoided.
Or, where the casing is too narrow and would be too expensive
to replace, then a narrower channel with a higher
performance capability would be commercially viable.
By installing a Mass Heat Extractor, either of the above options could be satisfied
Mass Heat Extractor
rate at which the cooling wind can absorb heat from the chamber.
This rate of heat removal will depend on the residence time of the cooling wind
in the zone: a short zone will have a lower capability than a long zone.
Increasing the cooling wind flow will not have a Proportional increase in cooling
as the exhaust temperature will go down, and a limit will be reached where
the exhaust severely restricts the air flow.
Additional heat can be removed, using lower grade
substructure insulation or bottom cooling,
but the main heat removal route is through the glass surface.
The mass heat extractor is a short zone or partial zone in the working end
or at the start of the forehearth which enables considerably more heat
to escape from the glass than with a forced cooling zone.
This is done by opening up the roof of the forehearth or working end
and allowing the glass to radiate direct to the atmosphere,
but in a way which can be adjusted.
Manual Operation of Mass Heat Extractor
The MHE zone is operated manually with regard to both the combustion control
and adjustment of the MHE doors (for cooling).
At low to moderate pull rates, when cooling assistance from the MHE zone
is Probably not required, the MHE doors should be fully closed.
The MHE zone combustion system firing is manually adjusted
to maintain the glass exit temperature at a level
which will allow the adjacent down stream cooling zone to maintain its required
set point whilst operating at sensible heat/cool output levels.
At increased pull rates with higher glass inlet temperatures to the MHE zone
and forehearth, it will be necessary to adjust (decrease) the glass exit
temperature from the MHE zone. This is achieved by opening
(in measured stages) of the MHE doors.
The doors are opened manually in pairs. Stable and sensible
control in the adjacent down stream cooling zone can be established and maintained
by considered setting of the MHE doors.
note. - It is advisable to maintain a reasonable level of firing pressure
in the MHE zone when the doors are open in order to
hold glass temperatures at the channel sides.
Once the desired MHE zone system settings are established,
automatic control of the down stream zones and forehearth exit temperatures
will be ascertained by the existing control system.
It will not be necessary to make further adjustments
to the MHE zone for the same pull rate.
Glass Conditioning
The quality of glass conditioning is usually related to the rate
at which the glass is cooled along the forehearth A low rate of cooling will
give better homogeneity than a high rate.
The cooling rate has more effect close to the spout than further away.
If the highest rate of cooling can be restricted to the back of the forehearth
and the cooling rate kept low near the spout,
then the performance of the system can be imProved.
A traditional, centre cooling zone combines the need to cool the fast moving
centre glass and keep the slow moving side glass hot.
A Mass Heat Extractor cannot readily achieve these two effects,
instead it can be used to remove a large quantity of heat from the glass
near the back of the forehearth and then rely on the cooling zones,
operating at much lower cooling rates, to re-instate the thermal homogeneity.
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