Important factors affecting change
There is a number of factors affecting this particular product change that must be considered in order to make it successful. The most important are:
Board weight changes dramatically from 8.1 kg/m2 for 1312RE board to 10.5 kg/m2 for 1312FR board. This represents change of approximately 40 kg/min to the Stucco set point. It is important to know that heavier board is harder to dry. Increase in board weight during this product change is achieved through slowing down Board-line and adding Fly-ash and Vermiculite to the mix. Reduction to Stucco set point during this change must FOLLOW reduction in Board-line speed to make sure that board weight is as required or HIGHER.
Balance between drying time and drying temperature
Drying temperature for both products is almost identical under standard operating conditions. Difference in drying time between these two products is 14.7 minutes. This is the main cause of problems resulting in board calcination manifested as paper delamination and soft edges. Extended drying time (for 1312RE) can be compensated by reduction in drying temperature. Timing of Dryer Chain speed adjustment will directly affect drying time. If Dryer Chain speed is changed too early then there is high probability that 1312RE board will suffer from calcination and if change is too late then there is high probability that 1312FR board will be wet.
Understanding of drying process – How Dryer operates under different conditions
The most important part of this understanding is regarding gap in the Dryer created by: Operating with Dryer Chain speed not being synchronised with Board-line speed and by rejecting board on the Wet End Transfer (change of board length, splice, defect product). It is fair to say, based on previous experience, that excessive gap in the dryer created by rejecting board on the Wet End Transfer is probably deciding factor between success and failure of this product change.
Starch consumption for 1312RE board is 35 g/m2 and for 1312FR board is 50 g/m2. Higher Starch consumption means harder drying of the board.