Pulping and slushing

Question 1

What are the 4 main goals of pulping and how can they be supported either mechanically or chemically?

Answer 1

1) Defibering – mechanical support = sheer forces. Chemical support = additives and heat increase swelling
2) Ink detachment – mechanical support = friction. Chemical support = additives + heat. Swelling
3) Removal of contaminants – mechanical = coarse screen, junk trap, ragger
4) Mixing – stirring action

Question 2

Draw a basic schematic of a LC pulping unit and name the important parts!

Answer 2

Rotor at bottom, accept going out, junkomat used to remove heavy contaminants – course screen. Ragger and tail cutter inserted from above.

Question 3

How is the development of the flake content over time during LC pulping?

Answer 3

Flake content decreases as pulping time increases. Subjected to more of the mechanical forces, may be recirculated. The flake decreases at a slower rate than it does in a High consistency pulper, due to the forces being greater in HC.

Question 4

With what kind of equipment can you treat the flakes after pulping?

Answer 4

Deflaker – breaks down flakes with mechanical forces, wrapping, viscosity, and acceleration. The forces are much higher here than in a pulper. Can also use chemical treatments by increasing temperatures or adding chemicals to help break down wet strength but these materials may need processing through a disperser instead.
Shear forces are created as the flakes pass through filling slots.