At the end of this module, you will be able to:
- Define sheet "formation"
- Explain why wet end edge trimming is important on a paper or board machine
- Identify and describe the functions of deckle boards, trim squirts, and wire cleaning showers
- Identify the trim squirt system parameters that are important to monitor during production
- Identify and describe the equipment (showers) used to remove the trimmed edges from the wire
The following key questions are answered in this module:
Why are the edges of the sheet removed at the end of the forming section?
The sheet edges are removed because they tend to have issues with formation, which can cause sheet breaks to originate at the edges
Why is the shower water supplied to the trim squirts filtered?
Trim squirt nozzles have very small orifices which are prone to plugging, so it is critical that the water supply be clean and free of debris
On machines with mutiple trim squirts or multi-orifice nozzles on both sides, why is the alignment of the nozzles or orifices so critical?
If they are not aligned properly, the edge cuts can be too thin or too wide, which can lead to issues with edge separation and even sheet breaks
Why do edge showers often follow the trim squirts?
If the edge stock is not removed from the wire, stock would tend to stick to it, which could lead to problems with buildup, deposits, and sheet transfer
Which wet end components of a paper or board machine are actively involved in establishing the sheet edges?
The deckles, curling boards, and trim squirts all help establish the sheet width and sheet edges
Below is a transcript of the video sample provided for this module:
A sheet with poor formation, even if it has the same number of fibers, has some areas with fewer fibers and fewer bonds. These areas with fewer bonds are weaker and they tend to fail quickly under load which negatively affects the overall strength of the sheet. If the formation is bad enough, it can lead to sheet breaks on the paper machine. The edges of the sheet tend to have issues with formation because the stock flow abruptly cuts off at the edges. This is why sheet breaks often originate at the edges. This is also why the edges of the sheet are trimmed at the end of the former to ensure clean, well-defined edges in the press section.
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