Suppliers quote capacity in TPD — tonnes per day of finished, reeled paper. Buyers then discover the machine never reaches that number. The gap is almost always the same two things: a catalogue capacity quoted at ideal conditions, and a stock preparation line sized below the machine. Here is how to check before you buy.
The formula
TPD = trim width (m) × speed (m/min) × grammage (g/m²) × 60 × 24 ÷ 1,000,000 × efficiency
Worked example: a 3.2 m trim machine running 350 m/min at 120 g/m²:
- 3.2 × 350 × 120 × 60 × 24 ÷ 1,000,000 = 193.5 tonnes per day at 100%
- At a realistic 85% efficiency: ≈ 165 TPD of saleable paper
That 15% is not a rounding error — it is the difference between a project that pays back and one that does not.
What the efficiency factor really contains
- Uptime — planned and unplanned stops, wash-ups, fabric changes.
- Broke — paper that is made and re-pulped; higher on start-up and after grade changes.
- Trim losses — the edge trim you cut and return to the pulper.
- Moisture and reel handling — saleable tonnage is measured at the reel, not at the wet end.
For a well-run containerboard machine, 85–90% is a fair assumption. For a dismantled and re-erected machine in its first year, assume less.
Check the other side of the machine
A machine rated 200 TPD cannot deliver 200 TPD if the pulper, screens and refiners behind it were sized for 150. Always size the stock preparation line above the machine, because OCC yield losses mean the pulper has to handle more than the finished output.
Questions to put to any supplier
- At what grammage is the quoted capacity measured?
- Is that a mechanical maximum or a demonstrated average?
- What efficiency factor was used, and can I see the calculation?
- Is the stock preparation line sized for the same number?