Manufacturing of Plywood

8/7/2019 Manufacturing of Plywood

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Manufacturing of Plywood


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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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Manufacturing of Plywood