Plywood Manufacturing Process

Plywood Manufacturing Process
Mike Russell
Plywood Manager
mrussell@tpinspection.com
Raw Material:
A large variety of species can be used to make plywood to the
applicable standards. Forest types vary throughout North and
South America. Species have been grouped into classes, and this
information may be needed on the TP Stamp.
Log Yard Stock:
A certain volume of log yard stock is needed to keep
the veneer species and quality distribution consistent.
Log Storage:
Depending upon the area and the type of storage facilities available, logs are
either piled dry and kept wet by continuous or intermittent water spray, or are stored in
freshwater ponds. Dry land storage of logs under sprinkler systems must give complete coverage of the log piles, and must be kept in continuous operation during high temperatures
and humidity in order to minimize fungai growth, and to prevent drying out and degradation.
Log Conditioning:
The logs are conditioned using steam or hot water to improve peel quality.
Lathe:
A sharp blade peels the log now called a block into continuous sheets of veneer. All veneer
has a tight and loose side. The side against the pressure bar is the tight side, sometimes
referred to as the bark side. Since veneer is bent at the knife-edge, it has a tendency to split
or check. These are known as lathe checks and occur on the underside, or loose side, where
the knife separates the veneer from the block.
Dryers:
Green veneer is dried in steam or gas heated
dyers. The purpose of drying is to reduce
the moisture content of the stock to a predetermined percentage, and to produce flat
and pliable veneer.
Lay- Up:
Plywood is a flat panel built up of sheets of veneer called plies, united
under pressure by a bonding agent to create a panel with an adhesive
bond between plies as strong or stronger than
the wood. Plywood is constructed with an odd
number of layers with grain of adjacent layers
perpendicular. Layers consist of a single ply or
two or more plies laminated in the parallel grain
direction. The veneers are coated with waterproof glue and laid up in sandwiches.
Pre-Press:
Prior to hot pressing most mills pre-press loads when they are discharged from the gluing
operation. The pre-press flattens the veneers and transfers the adhesive to the uncoated
sheets. The load is held under pressure for several minutes to develop consolidation of the
veneers. The primary purpose for the pre-press is allow the wet adhesive to “tack” the veneer
together to permit easier shifting of veneers when loading.
Hot Pressing:
The veneer sandwiches are subjected to heat and pressure in the hot press until the glue is
cured. Hot pressing cures most synthetic resins adhesives. In hot pressing it is absolutely
necessary to load, close to the press and apply full pressure as quickly as possible. The goal of
hot pressing is for the center glue line to reach the needed curing temperatures, and for it to
remain at that temperature until the bond is strong enough to be handled.
Trimming Plywood:
Trimming Plywood: After pressing, the plywood panels are trimmed,
squared and selected for grades.
Sanding, Grading, and Repairing Plywood:
Before sanding any further patchwork should be done. Repaired panels
have to be given a final
grade once they are
finished. Many panel
grades must be sanded to
fulfill the requirements of
their ultimate end use.
TP Trademarking:
Once a panel has been graded it should receive its grade stamp.
Warehouse and Shipping:
Each load should be supported on at least three separators. The separators should be of a
length no longer than the load width. Care should be taken when loading the panel bundles
onto boxcars or trucks. Panels should arrive at the customer’s door in the same condition
that the grader last
saw them.
TP “Inspector in the Mill”:
Plywood samples are randomly selected
on a daily basis and tested in a TP
Laboratory located at the mill.
Additional periodic testing is completed
at the Conyer’s GA laboratory.
Test Reports are compiled and electronic reports are circulated. The “Audited by TP” mark
is an assurance to consumers that our plywood meets the high quality standards established
by the industry, and that it will perform in a satisfactory and predictable manner. Only
plywood manufactured by member companies of Timber Products Inspection are licensed to
use this stamp.