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Measuring point of pit temperature and pit consistency;
VH, feeding speed = grinding pressure; VU, pulp stone rotational
Speed.
A high shower water pressure [at least 350 kPa (3.5 bar)] and the position of the
Shower water pipes at front of the grinding zone cleans the pulp stone surface,
And complete stone sharpening can occur. If pit-less grinding is carried out, these
Influences and interactions disappear, while high shower water pressures are
Applied.
The moisture of the wood is the most important parameter in grinding, as
High-quality pulp can be produced from moist wood, at a lower specific grinding
Energy consumption. Neither technical nor technological developments can
Replace the effect of moisture in wood. The highest possible quality values are not
found in the range of fiber saturation (moisture of wood ≥23%), but rather at a
wood saturation of 50–60% moisture content. The request by grinding mills to
receive pulpwood with at least 30% moisture content represents an objective need
For the optimal use of a wood source.
Groundwood made from logs with a higher moisture content has a higher
Brightness, higher strength properties (see Fig. 4.7), and a higher long fiber content
With high-quality fines.
The pulp stone requires a certain surface structure (stone surface profile) to produce
A certain pulp quality, and distinction must be made between the macrostructure
And microstructure of that profile. The macrostructure is gained by sharpening
Of the stone (see also Section II-4.1.4). A typical sharpness profile is shown
In Fig. 4.8, while the grit material of the pulp stone estimates the microstructure
(Fig. 4.9).
Mechanical Pulping Processes
Fines
Short fibers
Long fibers
Shives
0 20 40 60 80 100
Rel. moisture content of wood [%]
Fractional composition
0 20 40 60 80 100
Rel. moisture content of wood [%]
Strength values
Breaking length [km]
In-plane tear
strength [N]
Tear strength [N]
16.5 28 37.5 44.5 50
Abs. moisture content of wood [%]
16.5 28 37.5 44.5 50
Abs. moisture content of wood [%]
Fig. 4.7 Influence of wood moisture content on groundwood
properties. Left: Effect on tensile strength and tear strength.
Right: Effect on fractional composition.
Land
Groove
Grit
Fig. 4.8 Cross-section of a pulpstone pattern.
Fig. 4.9 Ideal grit positioning (according to Atack).
The mechanical defibration of wood to groundwood is a highly energy-intensive
Process. The specific grinding energy consumption can be used to characterize
The energy used, and with this the groundwood quality. In grinding, values between
0.6 MWh t–1 and 2.0 MWh t–1 o.d. pulp are typical for the production of
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Influence of Parameters on the Properties of Groundwood | | | Grinding Processes |