BACKGROUND OF THE INVENTION
1) Field of the Invention
[0001] The present invention relates to an arrangement for closing out the edge of a honeycomb
panel, in particular honeycomb panels employing graphite skins.
2) State of the Prior Art
[0002] Panels, such as floor panels used in aircraft, have been made from panel skins which
have a honeycomb core material therebetween. Both graphite and glass panel skins have
been used for these types of honeycomb panels.
[0003] In the above-types of panels, the panel skins have peripheral edges with the periphery
of the honeycomb core located between the peripheral edges of the panel skins. n using
honeycomb panels, especially for aircraft flooring, one potential disadvantage has
been that the edges of the various layers may not be flush with each other. In addition,
the edges need to be protected, because it is likelier that the edges will be damaged
by an impact than other parts of the panels. Such damage can occur during installation,
handling and fitting. Panels can also be damaged when they are removed during aircraft
maintenance. After panels have been installed, the edges thereof can also have slight
gaps therebetween. This thus leaves a vulnerable area which is generally more subject
to impact.
[0004] To solve the above problems, it has been known to close-out the edge of a panel,
protecting the edges, raking the edges of the panel become flush with each other and
decreasing the vulnerability by reinforcing and supporting the edges.
[0005] Present methods of closing out the edges of a panel involve mechanically removing
the honeycomb core 1/2 to 1 cells deep about the entire periphery of the panel and
then hand fill the resulting open core area with a syntactic resin. After the syntactic
resin cures, the edge is either machined or hand sanded smooth and flush with the
edges of the panel. However, this type of closing out of panel edges is expensive
and time consuming, but yet is performed on almost all aircraft honeycomb core panels,
unless they are fitted with a channel or other edge covering.
[0006] In addition, when honeycomb panels employ graphite panel skins, their edges tend
to experience galvanic corrosion when in contact with metals. This can cause problems,
for example when the graphite skin edge of a honeycomb panel is employed as a floor
panel for a vehicle such as an airplane and is installed against aluminum seat tracks.
SUMMARY OF THE INVENTION
[0007] The object of the present invention are to provide an improved method of closing
out the edge of a honeycomb panel. More particularly, the object of the present invention
is to provide an arrangement and method of closing out the edge of a honeycomb panel
so as to provide a significant measure of mechanical impact protection against damage,
to reinforce the panel edge and to place a physical separation between the panel components
and any adjacent or joining component. More particularly, a specific object of the
present invention is to provide an arrangement and method of separating the edges
of graphite panel skins in a honeycomb panel from any adjacent metallic components
so as to avoid the generation of galvanic corrosion.
[0008] The above objects of the present invention are accomplished by the provision of a
panel edge closeout arrangement which comprises first and second panel skins having
respective peripheral edges, a honeycomb core between the first and second skins,
with a honeycomb core having a peripheral core slot, and a closeout having a web portion
extending between and covering the peripheral edges of the first and second panels
and a flange portion extending from the web portion into the peripheral core shot
of the honeycomb core. The flange portion has an engaging arrangement thereon engaging
the honeycomb core.
[0009] Furthermore, in particular when the panel skins are made of graphite, the closeout
is preferably made of an electrically non-conducting material. It is preferred that
the electrically non-conducting material is an extrudable resin. Furthermore, the
resin is preferably a material selected from the group consisting of acrylic, ABS,
polystyrene, polyethylene, PVC, polycarbonate, acetate, butyrate, propionate, polyurethane
and thermoset materials. Of the above materials, polyurethane is preferred.
[0010] According to a further preferred feature of the present invention, an adhesive may
be provided in the peripheral core slots so as to bond the closeout in the peripheral
core slot. The adhesive is preferably a syntactic resin, the syntactic resin comprising
glass or phenolic microballoons, epoxy resin and a hardener. This syntatic resin could
also comprise a polyester resin with glass or phenolic microballoons.
[0011] The first and second panel skins may also be resin imprenated fabric skins. In this
case the purpose of the closeout, as discussed above, is primarily for protecting
the edges and corners of the laminate skins from damage.
[0012] The peripheral core slot in the honeycomb core has opposite walls defining the peripheral
core slot therebetween. The opposite walls are spaced apart by a predetermined amount,
and the engaging arrangement engages at least one of the opposite walls with an interference
fit. That is, the flange, at the engaging arrangement, is provided so as to be wider
than the predetermined amount by which the opposite walls are spaced apart. The engaging
member is preferably a projection which protrudes from both sides of the flange equally.
Also, the flange preferably has a tapered front end which tapers outwardly and rearwardly
toward the web to a point on the flange defining the projection. Also, the flange
may have a projection from one side only with the opposite side flat and without projection.
[0013] The flange can have at least one projection on each opposite side thereof engaging
respective opposite walls with an interference fit. Further, the flange can also have
two such projections on each opposite side thereof engaging the opposite walls of
the core slot with an interference fit.
[0014] The web can also be provided with two separate flanges for two separate core slots
for use in a sandwich panel employing two separate honeycomb cores to be adhered together
as a double honeycomb core sandwich panel.
[0015] The above objects according to the present invention are further accomplished by
providing a method of closing out the edge of a panel which has two panel skins with
peripheral edges and a honeycomb core therebetween. This method comprises the steps
of first providing a closeout which has a web portion and a flange portion extending
from the web portion. The flange portion has an engaging arrangement thereon. A peripheral
core slot is then cut in the honeycomb core, and the flange portion is inserted into
the peripheral core slot, engaging the honeycomb core with the engaging member with
an interference fit and covering the peripheral edges of the panel skins with the
web portion. The method according to the present invention may further comprise the
step of providing an adhesive in the peripheral core slot prior to inserting the flange
portion so as to bond the flange position in the peripheral core slot.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Further objects, features and advantages of the present invention will become apparent
to those of ordinary skill in the art from the following detailed description of the
preferred embodiments of the invention when taken in conjunction with the accompanying
drawings, wherein:
Fig. 1 is a cross-sectional side view of a panel edge closeout according to a first
embodiment of the present invention;
Fig. 2 is a cross-sectional side view of a honeycomb panel employing a panel edge
closeout according to Fig. 1;
Fig. 3 is a cross-sectional side view of a panel edge closeout according to a second
embodiment of the present invention;
Fig. 4 is a cross-sectional side view of a honeycomb panel employing the panel edge
closeout of Fig. 4;
Fig. 5 is a cross-sectional side view of a third embodiment of the panel edge closeout
according to the present invention;
Fig. 6 is a cross-sectional side view of a honeycomb panel employing the panel edge
closeout according to Fig. 5;
Fig. 7 is a perspective view of a honeycomb panel with a peripheral core slot having
adhesive applied to a peripheral core slot;
Fig. 8 is a partial plan view of a panel edge closeout according to the present invention,
with the panel edge closeout making a 90° turn with closeout slot geometry to accomplish
the 90° turn with low residual stresses;
Fig. 9 is a partial cross-sectional top view of a honeycomb panel employing a panel
edge closeout according to the present invention for closing out the circular edges
of a hole in the panel;
Fig. 10 is a cross-sectional side view of a panel edge closeout according to a fourth
embodiment of the present invention; and
Fig. 11 is a cross-sectional side view of a double honeycomb panel employing the panel
edge closeout according to Fig. 10.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] A first embodiment according to the present invention is illustrated in Fig. 1 and
2. Figure 1 illustrates a panel edge closeout 10, and Figure 2 illustrates the panel
edge closeout 10 engaged with a honeycomb panel structure 50.
[0018] The panel edge closeout 10 includes a web 40 which acts as an edge shield for shielding
the edges of the panel skins of the honeycomb panel. A flange 30 is integral with
the web 40 and extends from one side thereof. The flange 30 has a distal end 33 which
is inserted into the honeycomb panel. The flange 30 also has an engaging arrangement
20 on one side thereof, the engaging arrangement comprising a projection 21 projecting
from one side of the flange 30.
[0019] The panel edge closeout 10 can be made of acrylic, ABS, polystyrene, polyethylene,
PVC, polycarbonate, acetate, butyrate, propionate, polyurethane or thermoset materials,
such as phenolics, melamines, epoxy and glass reinforced materials. However, polyurethane
is generally preferred, because polyurethane has good resistance to most fluids and
solvents and is formulated to be self-extinguishing. Furthermore, polyurethane passes
FAA requirements for deflammability of aircraft interiors.
[0020] However, a thermoset material, for example pultruded out of glass and phenolics,
may be particularly preferred in applications requiring materials that are not flammable.
Further possible extrusion materials include polyethermide, polysulfone, polyether
sulfone, polyphenyl sulfone and poly-carbonate.
[0021] Noting Fig. 2, a honeycomb panel 50 comprises a first panel skin 80, a second panel
skin 90 and a honeycomb core 60 sandwiched between the first and second panel skins
80 and 90. The first and second panel skins have first and second edges 83 and 93,
the edges being aligned with each other. The honeycomb core 60 may be Nomex or glass.
The first and second panel skins 80 and 90 may be a reinforced laminate such as glass
or graphite/phenolic or epoxy panel skins. The honeycomb panel 50 is generally similar
to the honeycomb panel described in commonly assigned U.S. Patent No. 4,956,217, which
patent is incorporated herein by reference.
[0022] According to the present invention, the periphery of the honeycomb core 60 is provided
with a core slot 62 extending along the periphery parallel to the panel skins 80 and
90 and opening on the peripheral edge of the honeycomb panel 50. The core slot 62
has lower and upper walls 63 and 64. The flange 30 of the panel edge closeout 10 is
inserted into the core slot 62, with the projection 21 engaging one of the upper and
lower walls 63 and 64 with an interference fit to hold the panel edge closeout 10
on the peripheral edge of the honeycomb panel 50.
[0023] The panel edge closeout 10 is dimensioned such that the web 40 covers and protects
the edges 83 and 93 of the panel skins 80 and 90 as illustrated in Fig. 2. Further,
the engaging arrangement 20 with the projection 21 on the flange 30 of the panel edge
closeout 10 is dimensioned, relative to the core slot 62, such that the interference
fit will be produced when the flange 30 is inserted into the core 62. That is, the
core slot 62 has a predetermined spacing between the lower and upper walls 63 and
64, and the width of the flange 30 at the projection 21 is chosen so as to be wider
than the predetermined spacing between the walls of the core slot 62.
[0024] According to an optional feature of the present invention, a syntactic foam adhesive
70 is provided in the core slot 62 prior to the insertion of the flange 30. When the
flange 30 is inserted into the core slot 62, the syntactic adhesive 70 is displaced
around the flange 30 and into adjacent core cells of the honeycomb core 60. After
the adhesive has cured, there is formed an interlocking mechanical bond with the projection
21 to help retain the projection 21 in the core slot 62. The syntactic adhesive 70
can also help to increase the mechanical strength of the first and second panel edges
83 and 93 during flexure and impact. A syntactic adhesive, it is noted, is thick and
non-draining, and thus has less of a tendency to drain and settle on the lower panel
skin 80 due to gravity than would a liquid adhesive. A preferred syntactic adhesive
comprises a syntactic resin comprising glass microballoons, epoxy resin and a hardener.
In the absence of non-flammability requirements, a polyester or epoxy resin with phenolic
microballoons may be used.
[0025] It should be stressed that syntactic adhesive 70 is optional. An interference fit
of the projection 21 may be sufficient to secure the panel edge closeout 10 in position.
[0026] The panel edge closeout arrangement according to the present invention is formed
as follows. First, the honeycomb panel 50 is formed with the Nomex or glass honeycomb
core 60 between the panel skins 80 and 90 of glass-graphite/epoxy or glass-graphite/phenolic
panel skins, an epoxy adhesive film for assembling the honeycomb panel 50 being employed.
The panel assembly is cured at 50 psi and 260°F for one hour. The peripheral edge
of the cured panel is then slotted with a tool having a centering guide and a saw
blade to the depth and width of the desired slot 62. After slotting to the correct
depth, and noting Fig. 7, a pneumatic sealing gun 91 is loaded with a syntactic foam
70. The sealing gun 91 is fitted with a tip 92 that can fit into the core slot 62.
The syntactic foam 70 is then injected into the core slot 62 so that the foam will
fill the slot 62. The panel edge closeout 10, formed as an extrusion, for example,
is then snapped into place in the slot 62, with the web 40 being pushed to be flush
with the edges 83 and 93. The engaging arrangement with the projection 21 is fully
inserted into the core slot 62 and the syntactic foam 70. By forcing the flange 30
into the core slot 62, the syntactic foam 70 is displaced into the adjacent core cells
above and below the core slot 62. The flange 30 is then encapsulated by the syntactic
foam 70 to integrate the syntactic foam, the honeycomb core 60 and the panel edge
closeout 10. The assembly is left to cure for 8 - 10 hours at ambient temperature,
after which is formed an interlocking mechanical bond which retains the engaging arrangement
20.
[0027] Noting Fig. 8, the corner of a honeycomb panel 50 can be turned by the panel edge
closeout 10 simply by cutting a notch, for example a notch with two 47-50° cuts, through
the flange 30, but not the web 40. The web 40 can then be bent around the corner as
illustrated in Fig. 8. The corner, after being bent, may be momentarily heated to
stress relieve the web.
[0028] Also, noting Fig. 9, other edges shapes can be conformed to by the panel edge closeout
10. In the example illustrated in Fig. 9, a circular hole is formed in the honeycomb
panel 50, and the panel edge closeout closes out the inner peripheral edges of the
honeycomb panel 50 by having the flange 30 cut at a number of locations to allow the
web 40 to be bent into a circle as illustrated.
[0029] As discussed above, adhesive 70 is employed to bond the panel edge closeout 10 to
the peripheral edge of the honeycomb panel 50 and the core slot 62. However, it is
not absolutely necessary to use an adhesive. The core slot 62 may be machined sufficiently
undersized so that the interference press fit of the projection 21 of the engaging
arrangement 20 will stay in place in the core slot 62 without an adhesive. For example,
the width of the flange 30 at the projection 21 might be 0.104", and the core slot
might then be approximately 0.060" wide. Generally, however, the core slot 62 is machined
to 0.010 to 0.030" narrower than the minimum width of the flange 30 at the engaging
arrangement 20. In one example, the core slot is machined to 0.090" wide +/- 0.005",
with the extrusion being 0.104" +/- 0.002" wide. This provides a minimum of 0.007"
and a maximum of 0.021" of interference fit. Generally, the core slot 62 should be
a minimum of 0.04" deeper than the length of the flange 30.
[0030] The critical dimension of the panel edge closeout 10 of the present invention is
thus the width of the flange 30 at the projection 21 relative to the width of the
core slot 62. There must be an interference fit sufficient to hold the panel edge
closeout 10 in position while the syntactic adhesive 70 cures. It is also preferred
that there be a minimum of 0.02" from the projection 21 to the adjacent wall of the
flange 30. Also, preferably the flange 30 has a minimum thickness of 0.050". These
preferred dimensions are primarily necessary only for the requirements for extruding
the panel edge closeout 10 and for adequate flow of the material during the manufacture
of the closeout, and do not relate to the performance of the panel edge closeout 10.
[0031] Figs. 3-6 illustrate further embodiments according to the present invention. Except
as otherwise indicated, these embodiments operate on the same principles as discussed
above. In addition, features similar to those illustrated in Figs. 1 and 2 have been
referenced with the same reference numerals in Figs. 3-6.
[0032] Figs. 3 and 4 illustrate a second embodiment according to the present invention.
The major difference with this embodiment is that a panel edge closeout 110 has the
engaging arrangement 20 with two projections 21 and 22 extending from opposite sides
thereof for engaging both the lower and upper walls 63 and 64 of the core slot 62.
The distal end 33 of the flange 30 is tapered outwardly and rearwardly therefrom to
the projections 21 and 22. Fig 4 illustrates the panel edge closeout 110 in place
in a honeycomb panel 50.
[0033] Figs. 5 and 6 illustrate a panel edge closeout 210 which employs four projections
21, 22, 23 and 24 in the engaging arrangement 20 for further engaging the lower and
upper walls 63 and 64 of the honeycomb panel 50.
[0034] It should be noted that, instead of a projection such as projection 21 for holding
the panel edge closeout in the core slot o2, a groove could be provided instead, the
groove engaging with the hardened syntactic adhesive 70 to hold the panel edge closeout
in the core slot 62.
[0035] Figs. 10 and 11 illustrate a panel edge closeout 310 that employs two flanges 30
extending from the single web 40 for use in a double honeycomb sandwich panel 50.
Each flange 30 has an engaging arrangement 20 thereon, the engaging arrangement comprising
a projection 21 that tapers toward distal end 33 as illustrated.
[0036] The primary difference between this fourth embodiment of the present invention and
the other above-described embodiments lies in the fact that this embodiment is used
for a double honeycomb sandwich panel 50 as illustrated in Fig. 11. In this honeycomb
panel 50, two separate honeycomb cores 60a and 60b are used in a layered formation,
being adhered together with a septum 61 therebetween. The edge closeout 310 is used
similarly to the edge closeouts in the above embodiments, but is used for two core
slots 62 in the respective honeycomb cores 60a and 60b. In addition to providing the
advantages as discussed above, the edge closeout 310 can also help to secure the two
honeycomb cores 60a and 60b together.
[0037] In one example of this fourth embodiment, the web 40 is 1" top to bottom as illustrated
in the figures, and is 0.060" thick. The flanges are similarly 0.60" thick and are
spaced 0.170" from the ends of the web 40. Engaging arrangements 20 project approximately
0.60" from the respective flanges 30, to a separation of approximately 0.420". Engaging
arrangements 20, further, can extend about 0.25" along the ends of the flanges 30,
from the projections 21 to the distal ends 33. The material may be ULTEM 9065 with
an opaque brown or natural color.
[0038] From the above, it can be seen that a panel edge closeout arrangement and method
of forming this arrangement can be provided which provides a simple and inexpensive
closeout system and can be easily and securely formed for a honeycomb panel in order
to both strengthen the edges of the panel, protect the edges of the panel and prevent
galvanic corrosion. Various modifications of the above panel edge closeout arrangement
and method will occur to those of ordinary skill in the art without departing from
the scope of the invention as defined by the appended claims, and as such, should
be considered a part of this invention.
Claim 1. A panel edge closeout arrangement, comprising:
first and second panel skins having respective peripheral edges;
a honeycomb core between said first and second skins, said honeycomb core having
a peripheral core slot; and
a closeout having a web portion extending between and covering said peripheral
edges of said first and second panel skins, a flange portion extending from said web
portion into said peripheral core slot of said honeycomb core, and an engaging means
for engaging said closeout with said honeycomb core.
Claim 2. The panel edge closeout arrangement of claim 1, wherein said panel skins are graphite
and said closeout is made of an electrically non-conducting material.
Claim 3. The panel edge closeout arrangement of claim 2, wherein said electrically non-conducting
material is an extrudable resin.
Claim 4. The panel edge closeout arrangement of claim 3, wherein said extrudable resin is
a material selected form the group consisting of acrylic, ABS, polystyrene, polyethylene,
PVC, polycarbonate, acetate, butyrate, propionate, polyurethane and thermoset materials.
Claim 5. The panel edge closeout arrangement of claim 3, wherein said extrudable resin is
polyurethane.
Claim 6. The panel edge closeout arrangement of claim1, wherein said engaging means further
comprises an adhesive in said peripheral core slot bonding said closeout in said peripheral
core slot.
Claim 7. The panel edge closeout arrangement of claim 6, wherein said adhesive comprises a
syntactic resin.
Claim 8. The panel edge closeout arrangement of claim 7, wherein said syntactic resin comprises
glass microballoons, epoxy resin and hardener.
Claim 9. The panel edge closeout arrangement of claim 7, wherein said syntactic resin comprises
an epoxy or polyester resin with phenolic microballoons.
Claim 10. The panel edge closeout arrangement of claim 1, wherein said first and second panel
skins are glass skins.
Claim 11. The panel edge closeout arrangement of claim 1, wherein:
said peripheral core slot in said honeycomb core has opposite walls defining said
peripheral core slot therebetween;
said opposite walls are spaced apart a predetermined amount; and
said engaging means engages said flange with at least one of said opposite walls
with an interference fit.
Claim 12. The panel edge closeout arrangement fo claim 11, wherein said flange, at said engaging
means, is wider than said predetermined amount by which said opposite walls are spaced
apart.
Claim 13. The panel edge closeout arrangement of claim 11, wherein said engaging means comprises
a projection protruding form one side of said flange.
Claim 14. The panel edge closeout arrangement of claim 13, wherein said flange has a tapered
front end tapering outwardly and rearwardly toward said web to a point on said flange
defining said projection.
Claim 15. The panel edge closeout arrangement of claim 13, wherein said flange has at least
one said projection on each opposite side thereof engaging respective said opposite
walls with an interference fit.
Claim 16. The panel edge closeout arrangement of claim 15, wherein said flange has two said
projections on each opposite side thereof engaging said opposite walls with an interference
fit.
Claim 17. A method of closing out the edge of a panel having two panel skins with peripheral
edges and a honeycomb core therebetween, said method comprising the steps of:
providing a closeout having a web portion and a flange portion extending from said
web portion, said flange portion having a projection thereon;
cutting a peripheral core slot in said honeycomb core; and
inserting said flange portion into said peripheral core slot, engaging said honeycomb
core with said projection with an interference fit and covering said peripheral edges
of said panel skins with said web portion.
Claim 18. The method of claim 17, and further comprising the step of providing an adhesive
in said peripheral core slot prior to inserting said flange portion.
Claim 19. The panel edge closeout arrangement of claim 1, and further comprising:
a second honeycomb core between said first and second skins having a second peripheral
core slot;
a septum between the first said honeycomb core and said second honeycomb core;
and
a second flange portion, extending from said web portion of said closeout into
said second peripheral core slot, having a second engaging means for engaging said
closeout with said second honeycomb core.
Claim 20. The panel edge closeout arrangement of claim 2, wherein said electrically non-conducting
material is a thermoset material selected from the group consisting of phenolics,
melamines, epoxy and glass reinforced materials.
Claim 21. The panel edge closeout arrangement of claim 20, wherein said thermoset material
is pultruded out of glass and phenolics.