Shaft (the lower part of the log magazine) and control of the grinding zone temperature.

Pulp Stones

The pulp stone is the most important part of the groundwood process. During the

Early days of industrial grinding natural stones were used, but for more than 100

Years these have been replaced by artificial pulp stones. In Europe, the pulp stones

Were made from cement-based concrete, whilst in North America the modern-day

Grinding Processes

Ceramic-based stones were developed. The use of artificial stones has enabled tailor-

Made surface structures of the pulp stones to be developed. After an exact

Adjustment of the pulp stone, it is fixed on the grinder shaft with flanges (see

Fig. 4.18), and the free distance between the stone and flange is sealed with either

Concrete or sulfur.

M.

Production efficiency during

Operating time (based on

Stacked wood)

Operating time 3.5 – 5.0 years

T

Specific grinding efficiency

(produced o.d. pulp per mm

Grinding layer)

Sharpening interval 350 – 500 hours

Mm

Initial thickness of the

Abrasive layer

Operation parameters

Fig. 4.18 Structure of an artificial pulp stone.

The structure of a ceramic stone that is most commonly used today is shown in

Fig. 4.18 (left). The stone consists of a steel-reinforced core to which the honeycombed

Ceramic segments are fixed with anchor screws. The spaces between the

segments have elastic joint material filling. Although the abrasive layer, at 60–

Mm thickness, is much thinner than that of a concrete pulp stone, much

Longer operating times are attained. The abrasive layer material estimates the

Quality of the ceramic pulp stone, and differs in basic mineral, grit size, and grit

Size distribution. The basic abrasive minerals used are aluminum oxide (Alundum)

Or silicon carbide (Crystolon), and these are manufactured in several grades

Of hardness and density. The ceramic bonding is achieved with the use of a sintered

Silicon-based bonding agent.

Fig. 4.19 Scheme of a macrostructure before and after sharpening

(according to Suttinger). 1, Material removed by abrasion

During a sharpening interval; 2, material removed by the

Subsequent sharpening.

Pulp Stone Sharpening

The pulp stone requires a certain surface structure to produce a certain groundwood

quality, the so-called “macrostructure” (Fig. 4.19). This is achieved by sharpening

The pulp stone with a special device, although the abrasive layer becomes

Worn-out during grinding. The top area of the structure profile becomes wider,

Mechanical Pulping Processes

And the pulp stone becomes dull so that the quality and quantity of the groundwood

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