Panels & Furniture March/April 2022

WOOD CLINIC
Hello Mr Shim,
I am working for a company supplying adhesives, and am
responsible for sales of woodworking adhesives. Recently, a wood
factory produced small round tables with 20mm-thick mediumdensity
fibreboard (MDF) with mahogany veneer facade and edged
with mahogany veneer, adopting our ethylene-vinyl acetate (EVA)
hot melt adhesive. However, we have received complaints that the
adhesive force is unstable, and poor local adhesive force is found
after painting, while the same problem was not found when other
customers use the same batch of hot melt adhesive. I hope you can
tell us some factors that affect the stability of veneer edgebanding
glue and some suggestions for improvement. Thank you!
Sincerely,
Mr Chen
Stability of adhesive force
for veneer edgebanding glue
Shim Yee Shin is a specialist consultant
in the woodworking and panel industry,
with more than four decades of experience
in the field. He graduated from Taiwan’s
National Chun-Hsing University with a
major in forestry in 1973, and has since
accumulated a wealth of experience
through his work in various countries
across South East Asia and Greater China.
Mr Shim now runs his own consultancy
firm providing ad-hoc consultancy services
and bespoke training workshops. Prior
to this, he was Henkel’s Woodworking
Adhesives technical service director for
the Asia-Pacific region.
Mr Chen, thank you for your letter. Factors
causing the unstable bonding force of the
veneer edgebanding glue are briefly described
as follows, according to the information you
provided:
UNSTABLE SUBSTRATE PROCESSING
QUALITY
If the precision of producing round tables with
20mm-thick MDF and the trimming of edges
with a single-axis planer is not well-controlled,
there will be the following defects. When
edging with the veneer, if the adhesive force
is not strong enough, it will risk foaming and
degumming in local areas.
Coarse mark: If the operator rotates and
trims the round table at an uneven speed,
it will cause coarse marks and lead to
unstable adhesive force (Figure 1). If there
are such orders for a long period of time, it is
recommended to use an automatic planer,
which can improve the quality and output of
the round table trimming.
Knife jumping marks: When trimming the
edge using a single-axis planer, the template
must be kept stable and close to the collar
of the planer. If there is a gap between
the template and the collar, there will be
jumping marks, which causes poor edging
adhesive force. A fixed and skilled operator
is recommended to operate the planer to
improve the quality of the trimming.
Hit-and-miss: If the setting of the band saw
or the single-axis planer is not in place, and
hit-and-miss occurs during edge trimming,
it will result in poor adhesion of partial edge
sealing. It is recommended to check the
template regularly to ensure that there is no
damage and to check the set accuracy.
Non-right angle: If there are residual wood
chips on the template, or the round table
board is not flat enough on the template,
these cause the edges to be trimmed at a
non-right angle, leading to poor adhesion of
the edgebanding glue.
UNSTABLE QUALITY OF THIN VENEER
If the veneer has the following quality
problems, it will cause poor adhesion force
when edging with the veneer, leading to
local foaming and degumming:
Moisture content: Excessively high moisture
content of the veneer edgeband will lead
to poor adhesion force of edgebanding.
It is recommended to check the moisture
content of the veneer edgeband before use,
and a scope of 8-10% is recommended.
Unstable thickness: When the thickness
of the veneer is uneven or the tolerance
of different batch numbers differs greatly,
if the edgebander uses the edgebanding
tape to apply glue, the amount of glue
applied will be uneven, causing partial poor
64 Panels & Furniture Asia | March / April 2022