Wet Edge Control
Deckles run along the wire edges adjacent to the headbox to keep the stock on the wire until it has dewatered sufficiently. Curling boards and water jet deckles can help minimize the formation of deckle wakes. Edge showers are used to keep the deckles, curling boards and wire edges clean and lubricated. Trim squirts are used to trim off the edges at the end of the former and establish the sheet width into the press section. They must all be installed and positioned properly to minimize wear and prevent edge profile and edge transfer issues. This module will describe the function and operation of each of these device.
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Learning Objectives
• Identify where sheet formation is established on a paper or board machine • Describe the relationship between sheet formation and sheet properties • Describe why wet edge control is important and identify sheet properties affected by edge control issues • Identify and describe the functions of deckle boards, curling boards, edge showers, and trim squirts
Specs
| Course Level | Intermediate |
| Languages | English, Portuguese, French |
| Compatibility | Audio, Video |
| Based on: | Industry Standards and Best Practices |
Key Questions
Why do sheet breaks on a paper or board machine often originate at the sheet edges?
The edges of the sheet tend to have issues with formation because the stock flow abruptly cuts off at the edges, which can lead to poor formation at the edges and cause sheet breaks.
What is the purpose of deckle boards?
They keep the stock from flowing off the edges of the wire.
Why have water jet deckles replaced deckle boards on many paper and board machines?
Water jet deckles use a curtain of water to contain the stock. Because there are no longer boards for the stock to deflect off of, this minimizes the formation of deckle waves or wakes.
Why is the position of the end deckles on forming section suction boxes so critical?
If they are too far in, this can cause wet sheet edges. If they are too far out, air will be sucked in to the box at the edges, reducing the overall vacuum level. Also, they should be staggered to reduce wire edge wear.
What is the purpose of curling boards?
Curling boards help contain the stock on the wire at a low angle, which helps prevent the formation of deckle wakes.
Sample Video Transcript
Normally, showers are installed to keep the deckles clean and clear of stock buildup, and provide lubrication between the flexible strips and the wire. As machine speeds increased, it was observed that the stock tended to rise up on the vertical surfaces of the stationary deckle boards, and then flow back down at a reduced speed. This created diagonal waves or wakes in the stock, which led to problems with uniformity at the edges of the sheet.
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