Operation of a Cooling Zone fitted with a MHE Exhaust

A MHE cooling zone has automatically controlled heating and forced air cooling,
but manually controlled MHE door positions.
This ensures that the MHE is only adjusted when a large temperature
change is required, normally at a job change.
At low pulls and/or high exit temperatures cooling will not be required
and the MHE doors must be closed.
As the pull increases and/or the exit temperature reduces, a point will
be reached when some cooling is required.
With the MHE doors closed and the cooling on, check the internal forehearth pressure.
If it is high open the MHE doors slowly until the overpressure is removed.
At higher pulls and/or lower exit temperatures the
forced air cooling capacity will be reached.
When this occurs the MHE doors should be opened slowly until the forced air cooling
is operating in the middle of its control range.
When the MHE doors are open and the pull is reduced and/or the exit temperature
is increased the forced air cooling level should be checked.
If it is now operating near its lower limit or has gone to zero cooling,
the MHE doors should be closed slowly to return the forced
air cooling to the middle of its control range.
The MHE opening should be recorded for each job and used
as a starting point when the job is next run.

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 Heater 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.