Introduction to papermaking - Sheet Formation Paper

Introduction to Paper Formation

Overview of Session Topics

• This session, led by Steve, will cover the sheet formation of paper and address several key questions regarding the process.

• Questions include:

• How is stock applied onto the forming fabric?

• What does e-lux ratio mean?

• Do all paper machines have similar configurations?

• What are drainage elements in paper machines?

Stock Application Process

Transition from Raw Materials to Forming Fabric

• The raw materials for paper are processed through various stages before reaching the floor box, which spreads stock onto the forming fabric.

• Floor boxes have evolved significantly over time to improve efficiency and speed in applying stock.

Evolution of Floor Boxes

• Open Floor Box: Early design that relied solely on gravity; limited speed due to air exposure. Rarely used today.

• Pressurized Floor Box: Introduced an air cushion for better pressure application but faced issues with fiber deposition leading to mold or blockages.

• Hydraulic Floor Box: Fully liquid-filled design eliminates air gaps, reducing risks of mold and improving consistency in stock application.

• Dilution Flow Box: Modern mills utilize this technology for enhanced performance in stock distribution.

Understanding E-Lux Ratio

Definition and Implications

• The e-lux ratio compares the speed of stock exiting the slice to the speed of the wire itself, influencing fiber orientation during formation.

Fiber Orientation Scenarios

• Drag Scenario: If stock exits slower than wire, fibers align straight along machine direction, enhancing tensile strength in that direction but weakening cross-direction strength.

• Tumble Scenario: If stock exits faster than wire, fibers tumble randomly upon contact with wire, resulting in more uniform tensile strengths across both directions (machine and cross). This leads to a "square sheet" where properties are balanced between directions.

Roles on a Paper Machine

Cost Implications and Types of Rolls

• Approximately 70% of a paper machine's cost is attributed to rolls including press rolls and drying cylinders due to their critical functions in production processes.

Key Rolls Explained

1. Breast Roll:

• Supports wire position and creates vacuum for dewatering as it turns against the wire surface at an outgoing nip point.

2. Table Roll (Historical):

• Previously used for supporting wires but fell out of favor due to damage caused at high speeds; replaced by foils for improved water management without harming sheets.

3. Foils:

• Angled devices designed to draw water from beneath the wire while creating additional vacuum support during operation; crucial for modern high-speed machines.

4. Dand Roll:

• Positioned above other rolls; primarily responsible for adding security features like watermarks by manipulating fiber density within sheets produced.

This structured approach provides clarity on each topic discussed throughout Steve's presentation on paper formation processes while ensuring easy navigation through timestamps linked directly back to specific content segments.

Paper Machine Operations and Configurations

Overview of Cooch Roll Functionality

• The cooch roll is integral in the paper-making process, facilitating better light transmission and aiding in dewatering the sheet.

• Excessive vacuum application on the cooch roll can lead to shadow marking by removing fibers and filler particles from the sheet.

Drive Roll Mechanics

• The drive roll grips the wire and turns it, providing necessary power for movement through the machine.

• Continuous monitoring of wire tension is crucial; if tension decreases due to stretching, it can hinder grip on the drive roll.

Wire Path Control

• Guide rolls are employed to correct any wandering of the wire as it travels down the machine, ensuring proper alignment.

Paper Machine Configurations

• Not all paper machines utilize horizontal flat wires; inclined wire configurations exist for improved water removal efficiency.

• Twin wire formers allow for simultaneous drainage from two sheets, resulting in lower grammage sheets with more even fiber distribution.

Drainage Elements in Paper Production

• Various drainage elements like breast rolls and table rolls can enhance water removal through their outgoing nip functionality.

• Foils create a vacuum effect that aids dewatering; they are angled devices that help manage water flow effectively.

Advanced Dewatering Techniques

• Vacuum foils consist of multiple angled devices designed to collect water efficiently while creating additional vacuum pressure.