A Process for Manufacture of Plywood Through MAT
FIELD OF THE INVENTION
The present invention relates in general, to processes for
manufacturing plywood, and in particular, to a process for
manufacturing defect less plywood. It involves preparation of
a core layer called MAT, which is free from all defects and
then fixing the core layer to a face veneer.
BACKGROUND AND PRIOR ART
Plywood is a layered composite product made by surface
joining of wood veneer (thin layered slice of peeled wood) by
adhesive. Traditionally, plywood was made by laying veneer
one above another with alternate layer at right angle to each
other in which wood grain of surface layer runs along the
length of the plywood. The layer across the face grain is glued
(called the glue core). The assembly made in this way is
subjected to high pressure and usually high temperature in a
mechanical device called hot press which results in a flat
sheet called plywood.
In India this traditional process of manufacturing plywood has
been followed for years. The traditional process of making
plywood definitely produces a plywood sheet but very often
with a few or several defects which create problems for its

end users. Such defects are blisters, delamination, warpage,
core gap and many others.
Accordingly, there is a great need in the industry for a.process
of plywood manufacture which yields defect-less plywood as
the end product. The present invention seeks to fulfill this
requirement.
The present invention teaches an innovative and upgraded
process for manufacture of plywood. The basic process
involves making of an intermediate product called a core
layer, also known as MAT, by pre-composing of veneer and
prepressing. The salient features of the process are screening
of defect-less veneer, repair of minor defects in veneer (if
any), screening of veneer into glue and panel layer, laying of
core composite, pre pressing and hot pressing, thickness and
surface leveling and repairing of the core layer (MAT). The
MAT is finally overlaid with a surface layer (face veneer) in a
hot press provided with proper cushioning mechanism.
OBJECTS OF THE INVENTION
The primary object of the present invention is to provide a
process for manufacturing a defect-less plywood by first
making a defect-less core layer (MAT).
Another object of the invention is to provide a core layer
which is calibrated to obtain uniform thickness.

How the foregoing objects are achieved will be clear from the
following description. In this context, it is clarified that the
description provided is non-limiting and is only by way of
explanation.
SUMMARY OF THE INVENTION
A process for manufacturing defect- less plywood is disclosed.
It comprises of the following steps:
Preparation of defect free core layer:
- Preparation of logs;
- peeling of logs into veneer;
- screening of defect- less veneer;
- repair of minor defects, if any, in veneer;
- tenderizing by slit cutting into veneer
surface;
- drying of veneer;
- conditioning of veneer for 24 hours ;
- pre setting of small size veneer into actual
size of the plywood to be prepared;
- repair of natural defects found in veneer
during pre setting;
- gluing and. assembly for making the core
layer;
- preparation of the core layer by cold
pressing;
- repair of the cold pressed core layer;

- hot pressing of the repaired core layer;
- stabilizing of the core layer for 12 hours;
- trimming of four sides of core layer with
margin;
- calibration for uniform thickness ;
Preparation of Plywood :
- glue application on the core layer;
- overlaying the core layer with face veneer;
- hot pressing of the combination of core layer
and face veneer;
- trimming to final size;
- conditioning of plywood;
- sanding;
- marking and dispatch.
The step of conditioning of veneer for 24 hours comprises of
conditioning for moisture content of 6-8% and veneer
temperature equal to room temperature.
The step of pre setting of small size veneer comprises of
cutting small pieces of veneers to square end, scarf joining or
finger joining and spicing the veneers to actual size of the
plywood to be prepared.

The steps of calibrating comprises of thickness and surface
leveling and repairing of the core layer by sanding on either
size so as to get a panel of uniform thickness.
The process does not require any new machinery hitherto not
known to the plywood-making industry.
The step of overlaying the core layer with face veneer is
conducted in a hot press provided with proper cushioning
mechanism.
DETAILED DESCRIPTION OF THE INVENTION
Having described the main features of the invention above, a
more detailed and non-limiting description of a preferred
embodiment will be given in the following paragraphs.
All through the specification including the claims, the technical
terms and abbreviations are to be interpreted in the broadest
sense of the respective terms, and include all similar items in
the field known by other terms, as may be clear to persons
skilled in art. Restriction or limitation if any referred to in the
specification, is solely by way of example and understanding
the present invention.
As mentioned below, the heart of the process according to the
present invention lies in making a defect-less core layer or
MAT. This process is a part of the total process for
manufacturing defect less plywood, which is described below.

The process for making the defect-less plywood comprises of
the following steps:
Preparation of defect free core layer:
- Preparation of logs;
- peeling of logs into veneer;
- screening of defect-less veneer;
- repajr of minor defects, if any, in veneer;
- tenderizing by slit cutting into veneer
surface;
- drying of veneer;
- conditioning of veneer for 24 hours ;
- pre setting of small size veneer into actual
size of the plywood to be prepared;
- repair of natural defects found in veneer
during pre setting;
- gluing and assembly for making the core
layer;
- preparation of the core layer by cold
pressing;
- repair of the cold pressed core layer;
- hot pressing of the repaired core layer;
- stabilizing of the core layer for 12 hours;
- trimming of four sides of core layer with
margin;
- calibration for uniform thickness ;

Preparation of Plywood:
- glue application on the core layer;
- overlaying the core layer with face veneer;
- hot pressing of the combination of core layer
and face veneer;
- conditioning of plywood.
- trimming to final size;
- sanding of surface;
- marking and dispatch
The process outlined above has several new and inventive
steps. The salient steps are described below.
Veneer Conditioning:
In the prior art, dry veneers are directly taken for the plywood
manufacture. According to the present process, all veneers
are first conditioned for moisture content of 6-8% and veneer
temperature equal to room temperature.
Pre setting of Veneer: This is an important step, wherein
small pieces of veneers are cut to square end. Veneers are
scarf jointed or finger jointed and spliced to the actual size of
the plywood to be prepared.
Upgradation of Veneer: Any natural defect found in veneer are
either repaired or eliminated by cutting during pre-setting.

Preparation of core layer or MAT: Plywood is usually made by
first assembling the veneer and then hot pressing the
assembly. In the present process, the inner core veneers are
first assembled without the face veneer and the core
assembly is pre-pressed (cold pressing). Then the pre-pressed
assembly of core layer is repaired for any defect. The repaired
core layer assembly is then hot pressed, edges trimmed and
stabilized for about 12 hours. The MAT (as it is called now) is
sanded (calibrated) on either side so as to get a panel of
uniform thickness. The MAT is repaired for any defect before
hot pressing.
The process according to the present invention does not call
for any machinery that is not known to the plywood
manufacturing industry. Therefore, no new machinery has
been used. However, some machines which are commonly not
used by a plywood manufacturer in India have been used.
Some of them are:
1. Scarf joint machine: The machine taper-cuts a veneer at
one end along length and two taper-cut ends of two
veneer pieces are joined by adhesive. This process helps
to increase the length of the veneer.
2. Finger joint machine: This is another machine which
helps to lengthen the veneer. This machine cuts the
veneer end into finger. Two pieces of veneer with finger
cuts are glued and joined to form a longer piece.

3. Pre-press: This machine is used to compress the
assembly of veneer into a compact mass without
heating.
4. Calibrator: This is a sanding machine which sands the
flat panel on both its sides simultaneously. This machine
helps to obtain a uniformly thick flat sheet.
Other machines used in the process like veneer peeling/slicing
machine, dryer, glue applicator, resin kettle, hot press,
trimming and sanding, machine, preservative treatment plant,
boiler etc. are common to all plywood manufacturing
factories.
Advantages: The mother board or core layer (MAT) forms the
central or core portion of the finished plywood. While making
plywood by conventional methods by direct pressing of all
veneer layers, defects present in the core layer cannot be
eliminated. Moreover in direct pressing accurate thickness of
the plywood cannot be maintained. In the present "MAT"
process, after making the MAT, all the defects in the MAT like
core gap, voids cracks on the face layer etc. are filled up. If
any separations of individual plies are noticed, the concerned
ply is coated with an adhesive so that during the final hot
pressing the layers are bonded. Finally the MAT is calibrated
to obtain uniform thickness. Calibration means sanding off the
flat MAT on either side in a sanding machine. The uniformly

thick core layer, which is fully repaired, is finally overlaid with
the face layer and they are hot pressed together to form
finished plywood. Thus, the final plywood is free from any
defect.
The advantage of the process is that it produces 100% defect
free plywood because all defects are eliminated in making the
MAT. Comparison of the traditional process and the present
process (MAT process) is given below, which reveals the facts.



The present invention has been described with reference to a
preferred embodiment purely for the sake of understanding
and not by way of any limitation and the present invention
includes all legitimate developments within the scope of what
has been described herein before and claimed in the
appended claims
We claim:
A process for manufacturing defect- less
plywood comprises of the following steps:
- Preparation of logs;
- peeling of logs into veneer;

- screening of defect less veneer;
- repair of minor defects, if any, in veneer;
- tenderizing by slit cutting into veneer
surface;
- drying of veneer;
- conditioning of veneer for 24 hours ;
- pre setting of small size veneer into actual
size of the plywood to be prepared;
- repair of natural defects found in veneer
during pre setting;
- gluing and assembly for making the core
layer;
- preparation of the core layer by cold
pressing;
- repair of the cold pressed core layer;
- hot pressing of the repaired core layer;
- stabilizing of the core layer for 12 hours;
- trimming of four sides of core layer with
margin;
- calibration for uniform thickness ;
- preparation of defect free surface of core
layer;
- glue application on the core layer;
- overlaying the core layer with face veneer;
- hot pressing of the combination of core layer
and face veneer;
- conditioning of plywood;
- Trimming to final size;

- Sanding of surface;
- Marking and dispatch

1. The process for manufacturing defect less
plywood as claimed in claim 1, wherein the step
of conditioning of veneer for 24 hours comprises
of conditioning for moisture content of 6-8%
and veneer temperature equal . to room
temperature.
2. The process for manufacturing defect- less
plywood as claimed in claim 1, wherein the step
of pre setting of small size veneer comprises of
cutting small pieces of veneers to square end,
scarf joining or finger joining and spicing the
veneers to actual size of the plywood to be
prepared.
3. The step of upgrading of veneer by repair /
elimination of defective parts in veneer.
4. The process for manufacturing defect less
plywood as claimed in claim 1, wherein the step
of preparation of MAT as an intermediate
product is adopted. The MAT is made defect
free by repeated process after prepressing and
hot pressing of the MAT. The MAT is calibrated
to uniformly thick smooth surface, all layers of
veneer uniformly bonded, no holes, gaps, splits
on surface and inner layer. The MAT is stabilized
for 12 hours for uniform moisture distribution so
that final plywood is warp free.