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8/7/2019 Manufacturing of Plywood
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BU-CAS
Manufacturing of Plywood
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BU-CAS
Introduction
Plywood is a building material made from layers of thinly sliced wood, which is
glued together. Each layer called a ply is arranged so that the direction of the
wood fibers or grain is placed at right angles to the layer next to it
This placement of the layers equalizes a panels strength and prevents
splitting. Plywood is usually made of three plies, but five, seven, nine, or even
more plies may be used in some situations.
Plywood can be classified into 2 types - interior and exterior. Interior plywood
is made with adhesives that are moisture-resistant. This means that the
adhesive in the interior of the plywood has a limited resistance to water. On the
other hand exterior plywood is designed to better withstand conditions resultingfrom moisture and humidity. This means that the adhesive of exterior plywood
is capable of withstanding a certain amount of moisture before it starts to
decay. Exterior plywood is also made with waterproof adhesives.
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Manufacturing Process
The manufacturing process of making plywood consists of several steps. These stepsinclude
1. Selecting the log
2. Stripping the bark
3. Peeling the log
4. Making a continuous ribbon of wood
5. Cutting and stacking
6. Gluing the wood using adhesives
7. Pressing
8. Trimming, Sanding, and Finishing the wood.
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SELECTING THE LOG
Plywood is made from several different species of trees. Most softwood
plywood is made of Douglas-fir or southern pine. Hardwood plywood is
actually made from over eighty different species of woods. Some of the
most popular woods are oak, red gum, poplar, birch, cherry, and
walnut. Plywood and oriented strand board have many of the similarprocesses. These trees could be used for plywood or oriented strand
board.
The first step in the manufacturing process of plywood is the selecting
of the logs. The logs that are selected are chosen for their straightness
and roundness. They also must be relatively free from knots and decay
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STRIPPING THE BARK
The selected logs are then stripped of their bark. The logs are fed in
from the right by chain conveyors. The logs are going to be stripped so
therefore, they are rotated by ridged wheels as the cutting head on the
track reverses the log from end to end. This is also known as
debarking.
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PEELING THE LOG
The next step of the manufacturing process is peeling the log. The log
sections, which show the marks of the debarking knives, are fed into
the lathe loader where the log revolves around on a huge lathe against
a long cutter blade which is reduced to a 6-inch core or sawed into
lumber or chipped.
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MAKING A CONTINUOUS RIBBON OF WOOD
Following the peeler process, the next step in the manufacturing
process of plywood is taking the logs and making them into a
continuous ribbon of wood. The cutting edge of the lathe is forced
against the spinning log. The wood is unwound in a continuous ribbon
varying in thickness depending on how its used.
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CUTTING AND STACKING
The next step of the process is the cutting and the stacking of the
ribbons of wood. The standard size for the pieces of wood to be cut is
4 X 8. The thickness of the plywood will be determined later when the
sheets are adhesived and pressed together to a varying thickness of
which to is the most common.
As the sheet emerges from the peeler it is scanned automatically and
then it is stacked green and is prepared for the transferring to the
drying ovens. This next picture shows the wood after it is cut to rough
size and stacked green and ready to be sent to the drying ovens. The
moisture content of commercial plywood should not be lower than 6
percent nor greater than 14 percent at the time it leaves the factory.
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Wood ribbons Stacked for Drying Ovens
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GLUING THE WOOD using ADHESIVES
The next step in making plywood is the gluing of the plies together in
order to determine the desirable thickness of the plywood
sheet. Modern methods of manufacturing use synthetic plastics such
as urea resins or phenol-formaldehyde for bonding the plies
together. These adhesives are mixed mechanically and then spread onalternate layers of lumber by passing between pairs of grooved metal
or hard rubber rollers. The following picture shows the plywood sheets
moving through the rollers as the adhesive is being applied.
For Interior Urea Resins
For Exterior( Marine ) Phenol Formaldehyde
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Gluing Procedure
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PRESSING THE WOOD
The following step in manufacturing process is the procedure of
pressing the glued sheets together to a desired thickness. Hydraulic or
pneumatic presses squeeze the plies together with heat and pressure
or with just pressure only. When heat is used the adhesive hardens
within a few minutes. The adhesive solidifies as the plies are pressedtogether; and once the pressure is released, the boards are considered
dry. The hydraulic presses are equipped with a series of steam-heated
platens with a temperature from 120 degree C to 150 degree C. Each
pair of platens has a sheet of plywood between them that is pressed to
the desired thickness.
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TRIMMING, SANDING, AND FINISHING
Lastly the sheets have to go through a process that gets them ready to
be shipped out for market. This processes involves trimming, sanding
and finishing the sheets. This process also takes the sheets down to
the proper size that is desirable to the consumer. This is what makes
the final smooth edges that are seen in the modern lumberyard. Thefinished panels of plywood are then divided into two groups indicating
whether they are for interior or exterior use.
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Thank You for Your Attention
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