Papermaking — the water removal ladder

Every stage exists because removing water gets more expensive the less of it there is.

Consistency through the machine

Headbox stock runs around 0.5–1% fibre. The wire section takes it to roughly 20% by drainage, the press section to around 45% mechanically, and the dryers take the rest thermally. (Broadly true: The general process is documented; details vary by manufacturer.)

Why that order

Drainage is nearly free, pressing costs mechanical work, evaporation costs latent heat — about 2.3 MJ per kilogram of water. Every point of dryness won in the press section is energy the dryer section never spends.

Fibre orientation

The jet-to-wire speed ratio sets machine-direction alignment, which drives the tensile and tear anisotropy of the finished sheet and the way it curls with humidity. (Broadly true: The general process is documented; details vary by manufacturer.)

Bonding

Sheet strength is inter-fibre hydrogen bonding developed as the last water leaves. Refining raises bonded area and strength while lowering drainage rate and therefore machine speed — the central trade-off of the process.

Where this comes from

Smook, Handbook for Pulp & Paper Technologists; Britannica — papermaking. Every stage above is marked with how confident we are in it, and an uncertain one says so rather than reading like the rest.

• Difficulty: industrial.
• Time: continuous process.
• Written for: engineer — Tolerances, materials, formulae, and the failure modes.

Questions

How is paper made?

Wood becomes a suspension of fibres, the fibres are drained into a mat, and the mat is pressed and dried into a sheet. The stages above set it out at the engineer level.

Can I build this myself?

This is an industrial process rather than a home build, so it is described rather than instructed.