At the end of this module, you will be able to:
- Define "formation" and "floc"
- Identify three mechanisms available to minimize flocculation
- Describe the differences between mechanical and chemical fibers related to fiber length, refining response and sheet strength
- Describe how the stock delivery system affects sheet formation
- List the three directions of fiber orientation in a sheet of paper or board
- The three directions of fiber orientation in a sheet of paper or board
- Define "jet-to-wire ratio" and "rush/drag"
- Describe the terms "rushing" and "dragging"
- Describe how common chemical additives can affect sheet formation
- Describe how forming section components can affect sheet formation
The following key questions are answered in this module:
How does a paper or board machine's stock delivery system affect sheet formation?
The shear forces created by agitators, pumps, valves, cleaners, and screens in the stock system help keep the fibers dispersed in the dilute stock suspension and prevent flocs from forming before the stock reaches the headbox, which ultimately improves formation.
How does headbox design influence sheet formation?
Rectifier rolls, tube banks, converging channels, and other internal headbox elements are designed to create turbulence and shear. This helps keep the fibers dispersed until they reach the forming zone.
Why aren't all headboxes run at lower consistencies, since this helps keep the fibers separate and improves formation?
The headbox consistency can only be lowered until the drainage capacity of the former has been reached. If it is lowered further, the sheet will be too wet going into the press section.
Does the addition of starch affect sheet formation?
Starch is sometimes added to stock to increase sheet strength properties and improve drainage and retention. This can improve formation to a point, but over-use can lead to foam in the stock, which hurts formation and drainage.
How can the forming section influence sheet formation?
Breast roll shake mechanisms, formation showers, dandy rolls, foil box angles, and vacuum levels on the former can all affect sheet formation.
Below is a transcript of the video sample provided for this module:
To better understand formation and how it is established, it is useful to understand fiber flocs. A floc is a bundle of fibers that forms due to physical entanglement and attractive forces between fibers. A floc can be as small as four fibers, a microfloc, or can consist of a network of fibers and fiber bundles, a macrofloc. To optimize sheet formation, it is important to keep the fibers in the papermaking stock from flocing together excessively. Dilution, turbulence, and shear forces can be used to prevent flocculation. Because dilution is limited by the dewatering capability of the former and economics of handling large volumes of water, the stock delivery system and some forming section elements must create shear and turbulence to keep the fibers dispersed until the sheet forms.
Use the additional resources and links below to learn more about this topic: