Straight, less knotty and free from rot.

_ Wood moisture: The moisture of the wood should be as high as

possible. It should be over 35% in order to exceed the fiber saturation

Point.

_ Wood diameter: Useful wood diameters in grinding are 10–20 cm.

In refining, the thinnings (diameter 7–10cm) can also be processed.

_ Debarking state: Three different debarking states can be distinguished

for the wood:

– Bark is completely removed from wood (tanned, white peeled).

– Bark is removed from wood with some retention of phloem

(spotted, barked).

– Wood is completely or partly surrounded by bark (not debarked).

_ Resin content: A high resin content in wood is disadvantageous

In mechanical pulping as it causes foam; the situation is especially

Poor with pine.

_ Wood species: Spruce uniquely serves the purpose for mechanical

Pulping, especially in grinding. In refining procedures, both softwood

And hardwood species can be processed. Poplar and aspen

Are also suitable for grinding.

In mechanical pulping, those fibers that are responsible for strength properties

Are of major importance. In softwood, these are tracheids, and in hardwood they

are the libriform fibers. Tracheids cover about 90% of cell material in softwood

Handbook of Pulp. Edited by Herbert Sixta

Copyright © 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

ISBN: 3-527-30999-3

©2006 WILEY-VCHVerlag GmbH&Co.

Handbook of Pulp

Edited by Herbert Sixta

Species, whilst in hardwoods the amount of libriform fibers differs, depending

upon the wood species. As a mean value, they cover only 50% of the cell material,

And this is the reason why different wood species show different suitabilities in

Mechanical pulping.

3.2

Processing of Wood

3.2.1

Wood Log Storage

In mechanical pulping, the wood should have a high moisture content, and the

Processing of forest-fresh wood is the best way to achieve this. The storage period

Of wood should be of short duration, and the wood should be processed in as fresh

A state as possible. Nevertheless, most mills have high-capacity wood storage units

With capacities of between 10 000 and 500 000 m3.

The storage of wood can be performed using four basic approaches:

_ as irregular round log stacks (piles)

_ as round log water storage

_ as chip storage for refiner pulps

_ as regular round log stacks

Today, irregular piles are the preferred storage form, with the cone-shaped piles

Reaching heights of up to 30 m and being fed by so-called stackers. In summer,

And in order to keep the moisture content high enough, water sprayers are used.

Water storage – or even better, under-water storage – is the best way to maintain a

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