Troubleshooting Tip: Sealed Sheet

I know it has been a while since my last post, but I'm still here.  I've just been busy.  Anyhow, without further ado, sealing the sheet can be a very big problem.  This is basically when the sheet is not draining properly.  It seals itself and does not allow the water to drain.  This problem can be quickly diagnosed by just looking at the sheet as it moves along the table. 

Once the situation has been assessed, what do you do?  There are several options.  The simplest thing to do is to remove some broke.  Broke contains lots of fines so reducing broke can alleviate the sealing.  Another thing you can do is refine less mainly with the hardwood refiners.  You can also adjust your furnish to increase softwood.

Those were the simple solutions.  If none of those options helped then you've got to dig deeper.  These are more machine specific options.  You can increase the amount of water going to the headbox.  This seems counter intuitive but in many cases this added water will create channels in the sheet to allow for improved drainage.  Another option is to adjust the jet to wire ratio.  This will change the fiber orientation which may help.  One more option is to adjust the slice position which will change the delivery angle.  This will effect other parameters such as the jet to wire ration, so be cautious when adjusting the slice.  This will change where the jet lands on the forming board as well.   Just be aware of the adjustments.  Remember these are machine specific and may not apply to all machines.

I hope that helps.  I know some of it is a little vague and general.  Consult your process engineer and wet end operators before making these changes.  They may have some insights that could prove useful in troubleshooting.