Technology Guide Principles – Applications – Trends - hhimawan

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Wood processing
Related topics
5 Topic Renewable resources
5 Laser
5 Measuring techniques
5 Bioenergy
5 Sustainable building
Principles
Forest and timber products are an excellent example of
an economic cycle in which a renewable natural resource
(in this case wood) is used to make high-tech
and innovative products and is ultimately employed as
a CO 2-neutral energy source at the end of its life cycle.
Processing the raw material of wood into high-tech
products poses a variety of challenges. Its extraction
from the forest has to be sustainable, i. e. the number
of trees felled must not exceed the annual growth rate
of the forest. Forests need to serve as recreational, natural
landscapes for people and as climate regulators
producing oxygen and consuming CO 2, while at the
same time being an economic basis and resource for a
very large and competitive industry.
Applications
7 Harvesting.
Forestry supplies industry with the
renewable resource of wood in various forms. Highquality
hardwoods such as beech are used as solid
wood or veneer for furniture, while softwoods such as
pine are used on an industrial scale as solid construction
timber, for engineered wood products such as
glue-lam beams, or for wood-based panels such as
fibre boards. Moreover, softwood forms the basis for
pulp and paper.
sawmill
production and processing
of wood-based products
forest
consumer
biomass power plant
CO 2
recycling
� Eco­lifecycle of wood: Wood absorbs CO2 while growing. Sustainable forestry practices involve harvesting
only the annual increment of wood, which is then processed into lumber and further refined
to make wood­based products such as panels for construction. At the end of their life time, the panels
can be recycled, e. g. chipped and refined to be re­used as a resource for more wood­based products,
or burned in biomass power plants to produce energy. The bound CO2 in the wood is then released into
the carbon cycle again in the same quantities as originally absorbed, which makes wood a CO2­neutral
resource. Wood acts as a “carbon sink” while being used, as the CO2 is withdrawn from the carbon cycle
for the duration of its use. Source: Egger GmbH
In large and relatively homogeneously grown pine
stands, where profit margins for the raw material are
relatively low, tree extraction has to be highly cost-effective
while at the same time employing methods that
avoid causing harm to younger trees and compacting
the forest floor. Under these conditions, the generally
labour-intensive felling and extraction of the trees is
performed today by just one person operating what is
known as a harvester.
A harvester is a tractor with a harvester head
mounted on a crane arm. The harvester head embraces
the stem with grippers and rollers and cuts the retained
tree with an integrated chain saw. The cut tree is
lifted up and turned without touching younger trees
that must not be harmed. The rollers push the turned
tree through the grippers to remove the branches
(limbing) and immediately cut the stem into appropriate
log assortments. During embracing and limbing,
the harvested volume of the various log assortments is
automatically calculated by measuring the length and
diameter of each log segment.
7 Sawmills. The logs are stored in the lumber yard
to balance out times of intensive and less intensive logging
so that a continuous supply of raw material can be
provided in the quantities and quality required. In
many cases, the stored logs are kept wet by sprinklers
to prevent insect attack. Before being cut, the logs are
scanned using a 3D laser to determine the best board
dimensions and combinations to cut out in accordance
with the order list so as to achieve the highest possible
output. Each log is cut into log-specific beams, planks
or slats. Cutting by circular saws or band saws produces
a cutting gap and residual sawdust. In profile chipping,
the wood is chipped off by a rotating knife, resulting
in residual wood chips or strands of relatively
homogeneous size. Both residual materials are used to
produce wood-based panels such as particle boards or
“oriented strand boards” (OSBs).
After cutting, the individual planks are subjected
to a quality inspection. This can be done automatically
or manually by a person, who marks faults with luminescent
chalk. In the next step, a scanner identifies the
marks and activates a compound saw which cuts out
the fault. Automated quality inspections are carried
out using laser scanners to identify faults such as knotholes,
imaging cameras for detecting unwanted col-