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.
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.
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.
Purpose of this Guide is to provide information and knowledge required for performing product change from 1312RE to 1312FR without stopping board-line in aim to improve machine efficiency, increase product output and improve profitability of the business.
Board-line downtime for this particular type of product change is approximately 15 minutes. This change is performed at least once a week (usually some 24 hours before weekly maintenance. Approximately fifty of these changes are performed during a year equaling 750 minutes. That equals 36,000 square meters of most commonly produced product in our plant at current board-line speed (1012RE). It is needless to say that dryer would be better utilized by 750 minutes (due to rapid temperature loss we do not shut drier down as it would be counterproductive in terms of energy consumption)
Every shut down and start up are associated with inevitable product loss – this varies but an average loss for this product change would be around 150 square meters.
Change from 1312RE to 1312FR is not particularly demanding at forming station (we don’t have to change product width nor edge thickness. Core mix changes are more significant but not outside crew’s abilities to handle them.
Previous trials have been performed without taking into account drying process. Feedback from our customers is pointing to problems associated with this change that is pointing to drying process – paper de-lamination and “soft edge”.
Gap in the dryer – Gap between boards going through the dryer created by rejecting boards on the Wet End Transfer for whatever reason (faulty product, splice, change of the length…)
Drying Process – The process of removing water (moisture) from plasterboard. In this process air stream applies the heat to the board causing evaporation and carries away the vapor.
Drying Time – The time board spends travelling through dryer. Drying time is different for every product manufactured in our plant. Drying time directly depends on the dryer chain speed, which depends on the board line speed.
Drying Temperature – Temperature set points for dryer zone 1 and zone 2. We have only two zones dryer in Matraville plant. Drying temperature is not constant throughout the length of the dryer. It depends on temperature set point, position of board in the dryer, level of heath exchange etc.