How is Plywood made : The Full Process Explained | Part-4
This article explains the post–hot press stages of plywood manufacturing, including trimming, putty filling etc. It highlights how these processes ensure dimensional accuracy, surface smoothness, and strong bonding for high-quality plywood production.
This is the fourth article of this blog series. To read the third article,
please refer this link.
In the previous article, we explored the key processes that give plywood its
fundamental strength and rigidity, and we understood what a Mat Ply is.
In this article, we will look at the subsequent processes that the Mat Ply
undergoes, such as -
Trimming
Putty Filling
Calibration
Face Veneer Overlaying
Cold Pressing (with Face Layer)
Hot Pressing (with Face Layer)
Plywood Manufacturing Stages Flow
Chart
Trimming
Once the veneer assembly has passed through the hot press and formed into Mat Ply,
the panel carries rough, uneven edges and surface.
The first step in achieving finishing is trimming, where the sheet is cut to
a clean, uniform shape using a Double Dimension Saw (DD Saw).
At this stage, the panel is trimmed to the 4×8 ft (2440×1220 mm) size with
an extra margin, typically around 8–10 mm on each side. This allowance is
crucial because the sheet will later undergo face veneer overlaying and another
pressing cycle, during which the panel may experience slight shifts or
misalignment.
Note :
Do checkout the tech specs of Edge Cutting Machine on
this link
Putty Filling
Although the hot-pressed veneers are firmly bonded, the surface may still contain
natural defects such as small gaps, splits, knots, overlaps, or minor depressions
created during pressing. These imperfections become more noticeable once the face
veneer is applied, so they must be corrected beforehand.
Putty filling involves applying a specially formulated wood putty into these
surface defects. The putty is pressed into the gaps and smoothed out to ensure
that the surface becomes even and stable.
Once filled, the panel is allowed to dry so the putty hardens and integrates
with the surface. This prepares the Mat Ply for the next critical stage,
calibration, where thickness uniformity is achieved.
Calibration
Calibration is a crucial mechanical process in plywood manufacturing that ensures
the panel achieves a perfectly uniform thickness across its entire surface. Even
after hot pressing and putty filling, a plywood sheet may have minor thickness
variations. These variations can affect both the performance and appearance of
the final product.
To eliminate these inconsistencies, the Mat Ply is passed through a calibrating
machine, which is equipped with Steel Roller, with an abrasive belt of 40 - 60
grit wrapped around it. These rotating heads carefully shave off excess material
from the surface, leveling high spots and creating a smooth, consistent base.
The process is highly controlled, ensuring the panel retains its structural
strength while achieving dimensional accuracy.
Once calibrated, the panel becomes dimensionally stable and ready for face veneer
overlaying, where the final decorative layer is applied.
Face Veneer Overlaying
In this stage, a thin, high-quality face veneer is applied to both sides of the
calibrated Mat Ply to complete the plywood’s surface structure. Before placing
the veneers, a fresh and uniform layer of adhesive is spread across each surface
using a glue spreader to ensure consistent bonding.
Once the adhesive is applied, the face veneers are positioned on the top and
bottom surfaces with their grain direction running perpendicular to the grain
of the outermost layer of the Mat Ply.
Note :
Veneer grains and the importance of its direction is explained in previous
article. Please check it
on this link
Cold Pressing (with Face Layer)
After the face veneers are overlaid, the panel is subjected to cold pressing to
create a temporary pre-bond between the Mat Ply and the face veneers.
This step ensures proper contact and stabilizes the assembly before final bonding.
Note :
Detailed information about the cold-pressing process has already been covered
in the previous article. Please check it
on this link
Hot Pressing (with Face Layer)
After the cold-pressed panel stabilizes, it is moved to the hot press, where
high temperature and controlled pressure permanently strengthen the bond
between the face veneers and the Mat Ply.
Note :
A detailed explanation of the hot-pressing process has been covered in the
previous article. Please check it
on this link
The plywood panel is then kept at normal room temperature for a few hours to
allow proper conditioning.
Conclusion
In this article, we covered the calibration process and the application of
face veneers.
In the next article, we will explore the final set of finishing steps,
including sanding, dipping, and quality checks.
