Technology Guide Principles – Applications – Trends - hhimawan

our differences, X-ray sensors for establishing density
profiles, and acoustic sensors for determining the stiffness
of the planks. All the data is transferred to the
compound saw, which cuts out the fault.
Planks that are cut because of faults can be automatically
transferred to a parallel process line where
the plank sections are automatically finger-jointed into
planks of standard and ordered dimensions.
Mass customisation (every board is cut to order),
quality and speed are the key factors in any competitive
sawmill. Logs are driven through the cutting line
and the cut boards inspected in-line at a speed of
150 m/min.
7 Wood-based panels.
Mass-produced wood-
based panels such as medium-density fibre (MDF)
board, particle board or oriented strand board (OSB) –
coated or uncoated – are utilised in many everyday
settings, e. g. as the substrate in laminate or wooden
flooring (MDF), as the core material of virtually all
home and office furniture (particle boards) or as the
sheeting of wood-frame constructions (OSBs). As an
alternative to solid wood, these wood-based products
offer the consistent quality and engineered properties
required in mass products, and serve as a raw material
that can be further processed on an industrial scale.
Moreover, wood-based panels fully utilise residual material
of the sawing process, for instance sawdust, particles
or chips/strands.
These boards are all manufactured in a continuous
process that allows them to be mass-produced. A mat
of particles, fibres or strands is formed and fed into a
sometimes over 70-m long pressing line where it is
slowly compressed at high temperatures to its final
thickness and density. The only difference in the production
technology to fabricate particle, MDF and OSB
boards lies in the preparation of the particles, fibres or
strands:
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Particle boards are manufactured from flakes,
chips, shavings, sawdust and/or other lignocellulosic
material in particle form (flax shives, hemp shives,
bagasse fragments and the like) with the addition
of an adhesive.
Medium-density fibre (MDF) boards are manufac-
tured from lignocellulosic fibers by a “dry process”,
i. e. with a fiber moisture content of less than 20%
at the forming stage, and are essentially produced
under heat and pressure with the addition of an
adhesive.
Oriented strand boards (OSBs) are engineered
structural wood panels. Rather long strands of
wood are bonded together with a synthetic resin
adhesive. Sometimes in all three layers, but usually
only in the outer layers of these panels, the
strands are orientated in a particular direction.
� Log scanning: Before entering the cutting line, the logs are measured by a laser scanner to determine
the optimal cutting programme for each one on the basis of the order list. The most suitable boards or
planks, e. g. in terms of surface area (a) and thickness (b), are then cut out of each scanned log according
to its dimensions and quality. In (a), the dark green area indicates unacceptable wood quality and
limits the possible surface area of the boards. In the illustrated example, it was decided to produce a
board measuring 25 x 125 x 3000 mm 3 from the outer right part of the log; (b) shows the cross section
of the log, again indicating the 25­mm thick board to be cut at the outer right edge. In a later step, the
board will be trimmed to the desired 25x125 mm 2 . Source: Heinola
7 Continuous hot press technology. Today, nearly
all mass-produced wood-based panels are produced
using continuous hot press technology. After the raw
material (i. e. the particles, fibres or strands) has been
prepared and mixed with the adhesive, it enters the
pressing process. This begins with the mat-forming
system. The formed mats can be homogeneous singlelayer
mats for MDF boards, or three-layer mats for
particle boards or OSBs, where the core and face layers
differ, e. g. in particle size, to create a sheeting effect,
or in orientation, to enhance the specific strength of
the board in a preferred direction. In the case of MDF
boards, the raw material (forest thinnings, sawmill
byproducts) is reduced to fibres by steam and between
grinding discs, which rotate at great speed. An adhesive,
usually urea formaldehyde, and wax emulsion
are applied to the fibres inside the inlet pipe (blow
line) leading to the drying tube. The fibre/adhesive
mix is dried in the drying tube. The dry fibres are then
formed into a fibre mat on caul plates. The dry mat is
pre-pressed to consolidate it and then cut and formed
to press sizes. Following this pre-compaction, it is possible
to pre-heat the resulting mat in order to raise its
temperature before it enters the actual hot press. The
� Typical cutting programme of a sawmill step by step: The log is
continuously transported through each step at speeds of up to
150 m/min. First, the log is reduced and de­barked by rotating
de­barking knifes (a). This is followed by log and cant positioning.
As the logs are not symmetrical columns but are naturally grown
with some twists and turns, they are rotated into the optimal
cutting position according to their laser­scanned volumes (b).
Then they are canted by rotating plates – this is known as profile
chipping – and cut into planks, for example, by band saws (c). Alternatively,
or in addition, they can be profiled and cut with circular
saws (d). Finally, the boards are sorted and, if necessary, edged
(e). Source: Soederhamn and Eriksson
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