Moisture content is an important parameter to determine the quality of plywood. If the plywood is too dry (if the moisture content is low), the strength of the plywood will be affected and weaken. On the other hand, if the plywood is too wet, it will rot.
Therefore the moisture of
the plywood must be within acceptable limits, the Indian Standard Specification
IS:303 (Administered by BIS) The optimum moisture content in plywood
should be 5% to 15%. For
marine grade plywood, the humidity specification will be the same. At any time
of the year, the humidity of the plywood (depending on any part of the country)
should be between 5 and 15 per cent.
Also Read: Types Of Wood Used For Making Plywood | Lceted
So how is the moisture in plywood reduced?
Plywood is a very strong engineered
wood that is made by pressing several layers (thin pieces of wood) on top of
each other. During the production of plywood, the wood is dried using
mechanical dryers after rotary cutting to reduce the moisture content in the
wood. This is necessary because if the moisture is more than 10%, pressing
using glueing the layers is not possible.
For the purpose of drying
the veneers, they are passed through hot ovens on belts moved by cylinders,
while the fans spread the hot air generated by the heating coils of the oven
across the veneer faces. Let them dry completely. Once the veneers are
sufficiently dry, they are stacked on top of each other and bonded together
using hot press machines (glueing veneers under high pressure and temperature)
to form plywood sheets.
How is the moisture content determined?
The instruments like
moisture meters are used to check moisture content in the plywood. These meters are available in both analogue and digital versions and work in the same way that
a resistance meter works.
The moisture meter consists
of two probes (pins) that are inserted into the plywood at a certain distance,
and the battery-powered meter passes voltage through the wood.
Since water (which is in
the form of moisture on the plywood) is a good conductor of electricity, an
electric current is installed and the meter calculates the resistance of the
current and shows it based on the percentage of moisture.
However, it is important to
note that this content does not remain the same. For example, moving plywood to
an area with a very humid climate after manufacturing is very likely to
increase the moisture content. Ambient heat and humidity affect the plywood
and try to balance it with its new environment.
Also read: Plywood Strength Comparison with Other Wood Products
Also Read: Flush Door Vs Wooden Door Vs Plywood Door - Homeslibro
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