Papermaking (1) Forming

Summary

The video explains the process of making paper, starting from a pulp suspension of fibers in water. It describes how the pulp is spread onto screens, drained, pressed, and dried to form paper, noting that the process can be done at home or on an industrial scale. It covers traditional Fourdrinier machines, their limitations, and the issue of uneven paper surfaces. The video then introduces twin wire formers, both horizontal and vertical, which improve dewatering efficiency and paper uniformity. The discussion highlights practical considerations for retrofitting older mills and modernizing production for better quality and consistency in paper manufacturing.

Takeaways

• 😀 Paper is made by creating a pulp suspension of fibers in water and forming it into sheets using a screen.
• 😀 At home, paper can be made by draining pulp on a screen, pressing it, and drying with heat and blotting paper.
• 😀 Industrial paper-making uses a headbox to supply a constant flow of pulp slurry to machines.
• 😀 The Fourdrinier machine uses a continuous wire screen with vacuum boxes underneath to remove water from the pulp.
• 😀 Limitations of the Fourdrinier machine include slower water removal due to vacuum limitations and atmospheric pressure variations.
• 😀 Paper produced on Fourdrinier machines has distinct sides: a wire side (rough) and a felt side (smooth), affecting print quality.
• 😀 Twin wire formers improve paper quality by squeezing pulp between two rotating wire screens, allowing higher pressure and better dewatering.
• 😀 Horizontal twin wire formers are easier to retrofit into existing paper mills and reduce the wire side vs. felt side difference.
• 😀 Vertical twin wire formers offer further improvements but require taller building structures and are typically part of new mill designs.
• 😀 Modern paper-making focuses on uniformity, efficiency, and control over water removal to enhance final paper quality.

Q & A

What is the basic process of making paper at home or in simple setups?

The basic process involves creating a pulp, which is a suspension of fibers in water, placing it on a screen to drain the water, pressing the pulp, removing it from the screen, and then drying it with heat.

What is a head box in industrial paper-making?

A head box is a component of a paper-making machine that holds the pulp suspension and ensures a consistent flow of pulp onto the wire screen for forming the paper sheet.

How does a Fourdrinier machine work?

A Fourdrinier machine uses a continuous rotating wire screen. Pulp is applied to the screen, and vacuum boxes underneath remove water from the pulp. The formed paper is then collected on a take-up roll for further processing.

What limits the speed of a Fourdrinier machine?

The speed is limited by how quickly water can be removed through vacuum boxes. The maximum pressure applied is limited to around one atmosphere, and environmental factors like weather can also affect the efficiency.

Why does paper made on a Fourdrinier machine have distinct sides?

Because water is pulled through the screen, one side of the paper, called the wire side, has a different texture than the other side, which can affect ink absorption and print quality.

What is a twin-wire former, and why was it introduced?

A twin-wire former has two rotating wire screens that squeeze the pulp slurry between them. It allows for more efficient dewatering, reduces the difference between sides of the paper, and improves overall paper quality.

What is the difference between horizontal and vertical twin-wire formers?

Horizontal twin-wire formers are easier to retrofit into existing mills and work similarly to Fourdrinier machines but with better dewatering. Vertical twin-wire formers require taller buildings and are generally designed from the outset of a mill, allowing pulp to be applied from top to bottom or vice versa.

What is the main disadvantage of using a vertical twin-wire former in an existing paper mill?

The main disadvantage is that the building must have sufficient height to accommodate the vertical design, which is often not possible in mills originally built for Fourdrinier machines.

How do vacuum boxes contribute to paper formation?

Vacuum boxes pull water out of the pulp on the wire screen, helping to form a continuous paper sheet. However, they are limited in efficiency by the pressure differential they can create.

How does the twin-wire former improve the uniformity of paper compared to a Fourdrinier machine?

By squeezing the pulp between two wires with applied pressure, the twin-wire former reduces the differences between the wire side and the smooth side, producing a more uniform paper structure.

Why is the wire side of paper important in printing?

The wire side affects ink absorption. On older papers, the wire side can produce fuzzier printing, which is undesirable for print quality, making uniformity between sides important for newspapers and high-quality printing.