JEC COMPOSITES MAGAZINE - Issue #113 - June 2017 - 47

From fibreboard to composite honeycomb cores for custom-built doors

The significant humidity and temperature differences
on each side of the door meant it had to be thicker
than normal to provide insulation. However, a door
that large using conventional fiberboard cores would
be very heavy and would bring many challenges.

Nylon and polyester fibres
The patented honeycomb core is made
from a tough, heavy-duty fabric woven

No changes in the production process
The RhinoKore product was tried on the
cooler door for a couple of reasons. The
team had some weight issues with the overly
large front door to this house, so they opted
to use the lighter core for the cooler door,
which was also oversize. The new core gave

them added dimensional stability and resistance to warpage and cracking, which
they felt was really important given the
significant temperature and humidity
differences on either side of the door.
The cold/dry side of the door wants to
shrink, while the warm/humid side is in
a different dynamic equilibrium. And the
fact that the core is insulated is a bonus,
as it helps make the cooler and its door
more energy efficient.
The Fenstür team built the door using
the composite core and found that it was
a drop-in replacement for the fibreboard
they had previously used. Nothing had
to be changed in the production process
- even the adhesive (polyvinyl acetate
(PVA, also known as white carpenter's
glue)) they had previously used to bond
fibreboard to wood faceskins could be
used with the honeycomb core. The final
door consisted of a 1.9 centimetre-thick
layer of hackwood panelling on the outside, a 2.5 centimetre-thick composite
core, and a 1.3 centimetre-thick layer
of birch panelling on the inside. Once
the new door was assembled, Fenstür's
carpenters and finishing specialists were
amazed to see that it was less than half
the weight it would have been with a
fibreboard core. It also was quieter and
took less effort to open and close. The
team knew that that would not only
make it less costly to ship to the work
site, but would make it easier for the
local builder's construction crew to hang
and true the door. They also felt that
door sag would not be an issue, since the
hinges were not stressed thanks to the
reduction in door weight.

Focus
Since 2007, RhinoKore Composite Solutions (Armstrong, B.C., Canada) has produced a unique
honeycomb core for sandwich-panel composites originally developed for the oil and gas exploration industry. The core is produced from a tough nylon/polyester fabric that is formed
(under heat and pressure) into a series of conjoined hexagonal cells, which after cooling are
filled with a two-part closed-cell polyurethane foam. The core can be bonded to a wide variety
of materials ranging from thermoset and thermoplastic composite skins to metal, wood, or
even concrete, forming a lightweight but stiff and strong sandwich structure that also provides
good thermal and acoustic insulation as well as impact strength (damage tolerance). The core
is impervious to water and will not trap moisture or rot like fibreboard cores can. While not as
stiff as paper/phenolic cores, it is far more durable (impact resistant). And unlike balsa wood
cores (a rainforest product with inconsistent properties and limited supplies), the honeycomb
core is tougher and stiffer. To date, the core has been used for crane pads, rig mats, insulated
water tanks, load floors on commercial buses and long-haul trucks, and now as door cores.

No113 June 2017

/ jec composites magazine

Feature Construction

then laid out across the door and marked.
Board offcuts were made and labelled so
they could be attached to the walls adjacent to matching boards on the exterior/
warm-room side of the door. This extra
effort allowed the team to "board match"
panelling on the exterior of the door so
that the grain lines up and continues onto
the walls, helping the door blend even
better into the exercise room.
Due to the significant differences in both
temperature and humidity anticipated
between the cold/dry cooler-facing
side of the door and the warm/humid
exercise-room-facing side, the Fenstür
team knew the door would need to be
thicker than normal (5.72 centimetres) to
provide insulation. However, a door that
thick and large (107 by 213 centimetres)
using a conventional fibreboard core was
also going to be very heavy, which would
bring numerous challenges. That's when
the local builder mentioned RhinoKore's
unique composite core as a possible solution to replace the heavy fibreboard.

with nylon (polyamide) and polyester
fibres. The fabric is fed into a custom-built
"honeycomb" machine where it is quickly
exposed to hot air (427°C), which heats
and softens the fibres and allows them to be
manipulated and formed easily. The fabric is
then pressed into sheets of conjoined hexagonal cells (13 mm in diameter with 1.1
mm walls) and cooled. Next, the solidified
honeycomb sheets (122 centimetres wide
by 244 centimetres long by 152 mm thick)
are removed and placed in a mould, where
a two-part, closed-cell polyurethane foam
is injected into all the cells and allowed to
cure in a heated press. The finished core is
then sliced to thicknesses ranging from 0.64
to 15.2 centimetres so that it can be bonded
to faceskins of thermoplastic or thermoset
composite, metal, wood, or even concrete.
The honeycomb core has a very good stiffness and strength-to-weight ratio and helps
improve the structural integrity - especially
torsional rigidity - of any structure it is
bonded to. It is dimensionally stable and
provides very good compression and shear
strength, as well as thermal and acoustic
insulation. At any thickness, the core offers
excellent impact strength (energy absorption/damage tolerance). And unlike fibreboard, it is impervious to water and will not
trap moisture or rot. It is also much lower in
density than fibreboard, which helps reduce
part mass significantly.

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #113 - June 2017