Movement In Plywood
Due to the many variable factors associated with the moulding
of plywood, it is not possible to produce a product, which
will hold its dimensions exactly to the mould it was pressed
These variables include
• Moisture content in MDF (Medium density fibre
board) or veneer,
• Grain density and texture
• Ambient temperature and humidity
• Glue viscosity
• The number of laminations, cooking and dwell times
• Whether the veneer was peeled from the outside
of a log or closer to the heartwood
All of these variables and even the way the product is
stacked has an influence over the integrity of the shape.
Where tolerances are critical, we strongly advise to contact
us prior to ordering for an approximate estimation of
movement. If the moulded plywood component is to be fitted
in or over another item or structure, it is most important
to obtain the moulded plywood fist and make any design
modifications necessary. Movement is usually consistent
through a batch run and therefore only one design modification
should have to be made.
A common misconception is that moulded plywood is manufactured
by taking flat plywood and pressing it into a shape, then
steaming it, when in fact it is made up layer by layer
in veneer or MDF. Every second layer in most cases is
run through a double-sided gluing machine. Once the desired
thickness including face veneers is achieved, the entire
veneer mattress is placed into a male and female mould
and pressed under a predetermined amount of pressure.
Curing takes place by bombarding the electrons within
the moisture molecules of the glue lines using radio waves
at 13.75 MHz.
The more laminations in a moulded plywood product generally
results in less movement.
Plywood half cylinders for example tend to close in slightly
whereas MDF half cylinders will open out.
The glue used in the process of Radio Frequency curing
of moulded plywood is Urea Formaldehyde. It has a HMR
(Highly moisture resistant) rating and is not recommended
for outdoor use.
Nearly 100% of all veneers used at Plywood Engineering
come from Australian owned sustainable re-growth plantation
Plywood Engineering P/L does not make recommendations
for strength and durability of plywood for customer’s
applications. We strongly advise all customers to have
the appropriate testing carried out by the Australian
Furniture Research and Development Institute (Furntech)
or similar body.