Civil Engineering Reference
In-Depth Information
In the completed building fibreboards are not a problem, and because they are
porous they have good moisture-regulating properties. The glued products,
however, emit gases, e.g. from formaldehyde. This has caused a great number of
problems in the indoor climate. Much work has been done recently in the chip-
board industry to reduce these emissions, for example with so-called 'E1' boards,
which do not damage the indoor climate as much as the earlier boards. Urea
formaldehyde glue is only partly resistant to damp, so if it gets damp during
transport, on site or while being painted with a water-based paint, even the E1
board will give off much higher emissions than a factory dry board. Phenol glued
cork sheeting has also been known to cause problematic emissions. Other types
of surface treatment and glued finishes can also cause problems and need to be
evaluated individually. Cork coated with polyvinyl chloride can become quite
heavily electrostatically charged.
There is little chance of these products being re-used, with the exception of
those made of hard fibreboard and plywood. In theory, old chipboard can be
ground for new production but the centralization of manufacturing plants makes
it less practicable. Pure fibreboard can be burnt for energy in normal furnaces,
while other products need special filter systems for the fumes. With the excep-
tion of products containing phenol, all others can be composted. Formaldehyde
glue is quickly broken down by natural processes. Unused building and demoli-
tion waste must be deposited at certified waste tips, as these products can
increase the nutrients in the water seeping from the tip. Products containing phe-
nol have to be deposited at special dumps.
Production of fibreboard
The raw material used is relatively fresh waste timber from sawmills and the building
industry. The most common timbers are pine, spruce and birch. Low quality timber that
still has its bark is ideal. The machines at sawmills that strip the bark have caused this
particular resource to become quite rare. Leftovers from sawing planks and boarding
are not often used in fibreboard production, but can be used if they are cleaned of any
cement and all the nails are removed. Waste paper is used for the surface layer for
both porous and pressed sheeting, but can also be used in the main pulp used for the
porous boards.
Porous boards are usually made in thicknesses of 12-20 mm, though thicknesses up
to 40 mm are common. The thicker board needs more time to dry and is most commonly
used for insulation. As a raw material spruce is best, but pine or a hardwood can be mixed
in, up to a maximum of 10-15 per cent.
Semi-hard boards do not need such a high standard of raw materials, and can contain
a larger proportion of pine. They are usually produced in thicknesses of 6-12 mm, and the
hardboard in thicknesses of 3-6 mm.
The manufacturing process consists of the following stages:
1.
The raw material is collected and shredded by a shredding machine.
2.
The shredded wood is washed of any polluting substances.
