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The film is a piece of good paper impregnated resins (usually phenolic resins).
The impregnated resin content in the paper is one of important factors which determine
the quality of film.
Usually, here are two types of films-Imported film and Chinese films. The black
film is very popular and economical in market. The brown film of Chinese brands
can be classified into 3 quality grades: economical grade, ordinary grade and high
grade. The economical brown film is cheap and the quality is acceptable. But usually
our factory prefers to use brown film of ordinary grade.
As for shuttering purpose, the quality of ordinary brown film is good enough. Furthermore,
ordinary brown film is about 15% cheaper than the Chinese brown film of high grade.
The Chinese brown film of high grade is as good as some imported brown film. Now,
the Chinese brown film of high grade is a little cheaper than or almost as expensive
as some imported brown film.
Usually, as for shuttering plywood, the imported brown film is 120g/m2; the brown
film of Chinese brand is usually 140g/m2 or more. If the film is heavier, the film
is impregnated more resins which can improve the quality of film. Panels can be
supplied with 120 g/m2 film or heavier, depending on the end use.
Melamine films also are available, such as white, yellow, grey, green, blue, and
red, black etc.
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2.Core |
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Usually, the material of core in our factory is available poplar, birch, hardwood
and combo etc..
1. The process of assembly: Different thicknesses of plywood have different assembly
orders;
A. The Principles
(1) Symmetry Principle: most middle layer of plywood for the center, two sides symmetry
(2) Odd Number Layers Principle: plywood is singular layer, 7,9,11,13 ... ... Symmetry
principle for arrive stable characteristics.
(3) Section Principle: in order to prevent rupture of plywood, the crack can moved
to other places. Enhance the plywood in compression.
(4) Fiber Direction of Adjacent Veneer Perpendicular to Each Other Principle: to enhance
the strength of plywood.
B. Assembling Principle:
(1) Lap Joint (2) Scarf Joint (3) Finger Joint
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3.Glue
Glues used to bond veneers together are an element that influences the application
of the plywood.
Common glues are as follows:
'A Bond' (WBP) - a waterproof glue line produced from phenolic resins (WBP -Water
Boil Proof adhesive) that will not deteriorate under extreme conditions. It is readily
recognizable by its black color.
What is WBP? The letter stands for weather and boils proof and relate solely to
the type and performance of the adhesive used to bond the layers of veneer. Boards
manufactured to meet this definition are commonly described and marked as WBP.
What plywoods are referred to as WBP? The term is applied to imported boards manufactured
in Europe, Africa, South East Asia and South America.
What plywoods are equivalent to WBP? For North American softwood plywood manufactured
to national standards the term equivalent to WBP is "Exterior" and the marks customarily
state such rather than WBP.
Does WBP have any legal status? The term WBP when applied to imported boards has
been demonstrated in the UK courts to mean the bonding quality should comply with
British Standards definition of WBP.
Is the glue bonding strong and resistant? WBP bonds are required to be highly resistant
to weather, micro-organisms, cold and boiling water and wet and dry heat. These
requirements are met through the use of adhesives of PF (Phenol Formaldehyde) type
which yield an appropriate minimum level of wood failure in relation to the shear
strength. Prior to the sheer test half the test samples are subjected to immersion
in cold water for about 24 hours and the other half are submerged in boiling water
for about 72 hours before being cooled in cold water. Alternative pressure vessel
tests are also set out in BS: 6566.
Why is wood failure important in the glue test? If the specified wood failure is
not reached then it is clear that the bond was not sufficiently strong. The rigorous
test is in essence a simulation of the high resistance of the glue bond in prolonged
exposure to weather.
Is the glue type identifiable from visual inspection? The glue lines are black or
dark in appearance. In other glue types the glue line is generally light or clear.
However, inclusion of additives by a manufacturer in the adhesive, which does not
meet the criteria for WBP, could result in a dark glue line. There are also some
boards manufactured with phenol based adhesives that do not meet the criteria for
WBP but may have a dark glue line.
'B Bond' - produced from melamine fortified urea formaldehyde resin and suitable
for limited exposure.
'C & D Bond' â€" is produced from urea formaldehyde resin and suitable for interior
use only. It relation to Concrete Formwork plywood is possible to have a C or D
type bond to AS 2754.1 where a single use is envisaged.
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