Note: Descriptions are shown in the official language in which they were submitted.
CA 02480689 2004-09-27
Arrangement and methods for the manufacture of composite layer structures
The invention relates to arrangements and methods for the manufacture of (core-
)
composite layer workpieces or composite layer structures (sandwich-structures)
from at least one first and at least one second cover sheet between which a
core
sheet is provided which comprises a composition of fibers like especially
short cut
fibers (flock fibers, flock material) and an adhesive.
The cover sheets and the fibers each can be made of steel, aluminium or any
other
metallic materials, even alloys, or can be made of non-metallic materials like
synthetic materials (for example nylon), ceramics, textiles or paperboard or
any
substances or mixtures comprising these materials, wherein neither the cover
sheets
nor the fibers must be made from the same material. Depending on the purpose
of
application almost any combinations of materials can be chosen.
Exemplary materials for the cover sheets and the core sheet are disclosed in
the EP
1 059 160 which shall be made by reference to a part of this disclosure.
With these composite layer workpieces numerous advantages can be achieved in
comparison to solid workpieces having the same dimensions. Depending on the
type, the shape, the density, the thickness, the length and orientation of the
fibers,
for example a particularly low weight and a high flexural strengths or a
superior
mouldability and flexibility, respectively, as well as a very high mechanical
and
acoustic energy absorption can be obtained, wherein the structures furthermore
can
be provided with an insensitive and corrosion resistant surface. All these
properties
can be optimized according to the proposed machining (like bending, deep-
drawing,
welding, cutting and so on), as well as according to the application of the
composite
layer workpieces.
WO 98/01295 for example discloses sandwich structures which comprise between
at least two plates metallic fibers. By this, substantially a higher
temperature
resistance shall be obtained in comparison to those structures which comprise
fibers
of organic materials. The manufacture which is as well disclosed in the EP 0
333
685 is conducted such that the plates are covered with an adhesive and then
the
metallic fibers are deposited onto at least one of the adhesive layers by
acceleration
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2
by means of an electrostatic field (electrostatic flocking process) so that
there are substantially perpendicularly fixed relative to the plate. Then the
plates are
pressed onto each other and the adhesive is hardened.
Furthermore, DE 41 31 394 discloses a sound insulation material which is
formed
by two outer sheets between which a core sheet containing a filling material
and a
binder is provided wherein the three sheets are continuously pressed against
each
other during the manufacture of the sound insulation material.
DE 36 21 599 discloses a method and a device for distributing of short fiber
materials onto a horizontally moved sheet-breadth wherein a funnel with a
chamber
is provided which has a dispensing opening for delivering fiber material
through a
screen sieve onto the moving sheet and wherein the screen sieve is laterally
oscillating. By this, a uniform distribution of the fiber materials over the
whole
width of the breadth shall be obtained.
Furthermore, EP 0 014 973 discloses a method for the manufacture of a machined
part. According to this method, a foil-breadth is coated with a liquid
adhesive in a
first station and in a second station flock fibers are applied onto the
adhesive
coating by means of an electrostatic field. Afterwards the adhesive is pre-
hardened
by means of a heating device so that the flock fibers adhere to the adhesive
in the
form of a coating and the foil breadth can be pressed and pre-formed together
with a
supporting part.
Finally, DE 38 24 842 discloses a heat insulating plate and a method for its
manufacture in which during a continuous process an inner coating comprising
lamella of a heat insulating filling material, mixed with a binder, is fed in
between
two shaped metal sheets and in which these three sheets are glued together by
means of an adhesive which is injected in between these sheets to achieve a
sandwich structure.
However, all these methods and a arrangements have the disadvantage that
either
they are provided only for the manufacture of specific elements and
consequently
are not generally applicable, or they are not suited for a continuous
production
process with which a high output of pieces of sandwich structures per time
unit can
be manufactured.
CA 02480689 2012-02-16
- 3 -
It is an object of the invention to provide an arrangement
with which composite layer workpieces and composite layer or
laminate structures of the above mentioned kind can be
manufactured with almost any shape at reasonable costs and
with a high-quality in a continuously running production
process.
It is another object of the invention to provide a method,
especially for applying such an arrangement, with which
composite layer workpieces and composite layer laminate
structures of the above mentioned kind can be manufactured at
reasonable costs and with a high quality in a continuously
running production process.
A particular advantage of the solutions according to the
invention is the fact that by the arrangement and the method,
respectively, composite layer workpieces and composite layer
structures can be manufactured with different properties and
dimensions without having to change the arrangement or the
method substantially. The manufactured composite layer
workpieces and composite layer structures can be used as a
starting material for the manufacture of almost any objects,
so that a high flexibility and considerable cost advantages in
comparison to the application of arrangements and methods
according to the prior art can be obtained.
Furthermore composite layer workpieces and composite layer
structures with new properties and for new applications can be
manufactured with an arrangement according to the invention
and a method according to the invention.
Such applications especially relates to the field of the
vehicle technology and construction (cars and motorcycles),
airplane and shipbuilding each as well for protection purposes
(for example for armouring or encapsulating of machines with
fast rotating parts), as well as for the manufacture of
housings, boxes, containers, wrappings and even furniture
wherein the composite layer workpieces and composite layer
structures can be plain or arched, for example in the form of
three- dimensional form elements.
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4
The subclaims disclose advantageous embodiments of single components of
the arrangement and of single method steps, respectively, by which a specific
variation of single manufacturing parameters can be obtained so that in a
relatively
simple manner composite layer workpieces and composite layer structures with
desired physical properties for example with respect to their weight, their
flexural
strengths, their mouldability and flexibility, respectively, their mechanical
and
acoustic energy absorption, their electric and thermal conductivity and so on
as,
well as with respect to their processability can be obtained.
Further details, features and advantages of the invention result from the
following
description of preferred and exemplary embodiments in connection with the
drawings, in which schematically shows:
Fig. 1 a schematic view in principle of a first embodiment of an arrangement
for
the manufacture of composite layer structures according to the invention;
Fig. 2 a cross section through a first composite layer structure manufactured
by
an arrangement according to Figure 1;
Fig. 3a a cross section through an advantageous first device for applying
adhesive
onto a cover sheet, as a part of an arrangement according to the invention;
Fig. 3b a three-dimensional view of the first device according to Figure 3a;
Fig. 3c a three dimensional view of an advantageous second device for applying
adhesive onto a cover sheet, as a part of an arrangement according to the
invention;
Fig. 3d a three-dimensional view of an advantageous third device for applying
adhesive onto a cover sheet, as a part of an arrangement according to the
invention; and
Fig. 4 a cross section through a second composite layer structure manufactured
by a method according to a preferred embodiment of the invention.
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The arrangement according to the invention shall be described in the
following with reference to an embodiment for the continuous manufacture of
composite layer (laminated or sandwich) panels from two cover sheets in the
form
of metal foils between which a core sheet with flock fibers is put in. If
instead of
one or both metal foils one or more such composite layer panels are used, a
multiple
composite layer structure can be manufactured as well.
Figure 1 shows schematically a first such arrangement. A first and a second
metal
foil 1, 2 which each have a thickness of for example about 0.2 mm are
introduced
into the arrangement each in the form of a coil. Alternatively it is as well
possible to
introduce one metal foil with a substantially double breadth, dividing the
same in
the longitudinal direction (conveying direction) and then feeding these parts
as the
first and second metal foils according to the following description.
As another alternative, instead of the two wind-up metal foils 1, 2, sheets
la, 2a
which have been pre-cut to size can be conveyed through the arrangement (if
necessary by means of or on a separate conveying belt). It is as well likely
to
combine a feeding of wind-up metal foils and single sheets of pre-cut metal
foil. For
example, the metal foil 2 shown in figure 1 could be replaced by pre-cut
sheets 2a
or the metal foil 1 could be replaced by pre-cut sheets la. The following
explanations are valid for all these alternatives wherein in the following the
term
"metal foil" shall be used acting for all these alternatives. This is true as
well if
instead of one metal foil a foil or cover sheet from another material like the
ones
mentioned above exemplarily is used.
At first, the first metal foil 1 is fed by means of a first roll 3 past a
first device 4 by
which an adhesive 5 is applied on to the first metal foil. In a similar manner
the
second metal foil 2 is fed over a second roll 6 and passes a second device 7
by
which an adhesive 5 is applied on to the second metal foil 2. If necessary,
before
applying the adhesive 5, the metal foils 1, 2 have to be pre-treated in a
usual manner
for example by etching and/or roughen or for activation of their surface they
have to
be subjected to a corona treatment and cleaned (not indicated).
Afterwards, the first metal foil 1 which has been coated by an adhesive 5 is
conveyed through a flocking device 8 which is preferably encapsulated and
conditioned (encapsulation and conditioning are not indicated) and by means of
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6
which the flock material which comprises single fibers 9 with a
thickness of for example between about 5 and about 40 gm, especially about 22
gm,
and a length of between about 0.1 and about 20 gm, especially between about 1
and
about 5 gm, is applied onto the surface of the first metal foil 1 which-is
coated with
adhesive 5 and especially in such a way that the fibers 9 are fixed in the
adhesive
coating as far as possible individually and with a desired orientation
relative to the
first metal foil 1 which in general is perpendicular to the same. This process
is
usually called flocking process.
Both metal foils 1, 2 are then joined together at a third roll 10 and conveyed
into a
dryer 12. According to the embodiment shown in figure 1 the dryer 12 comprises
at
its input a first upper conveying belt 121' and a second lower conveying belt
121"
and at its output a third upper conveying belt 122' and a fourth lower
conveying belt
122. The conveying belts 121', 121", 122', 122" are driven by means of a
driving
unit (not shown) wherein the first and third conveying belt 121', 122' is
acting upon
the composite layer structure from above and the second and fourth conveying
belt
121", 122" is acting upon the composite layer structure in a conveying manner
from
below.
In the region of the action of the conveying belts 121', 121", 122', 122" and
opposite
to the first and second metal foil 1, 2 there is provided each one heating or
cooling
unit 123 comprising a continuous pressing tool. Both metal foils 1, 2 are
conveyed
by means of the conveying belts 121', 121", 122', 122" through both of these
pressing tools 123. By means of the pressing tools 123 the metal foils 1, 2
are
pressed against each other and, in dependency of the type of adhesive,
simultaneously heated so that the adhesive 5 is hardened and a safe connection
between both metal foils 1, 2 and the fibers 9 is obtained. Afterwards, the
metal
foils 1, 2 and are cooled down in a definite way to ambient temperature to
avoid any
warping.
Between both pairs of conveying belts 121', 121" and 122', 122" a sizing
insulation
124 is provided by which the metal foils 1,2 are joined together and pressed
against
each other with a desired distance by means of two rolls which can be driven
as
well. Such an (additional) sizing installation can additionally or
alternatively be
provided as well between the first roll 10 and the first pair of conveying
belts 121',
121".
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7
Finally, at the output of the dryer 12 a cutting device 13 is provided by
which the
pressed metal foils 1, 2 are cut up in a desired manner.
For conveying the first and second metal foil 1, 2 through the arrangement,
another
driving unit (not shown) can be provided by which the first and the, second
roll 3, 6
are drivingly rotated.
Figure 2 shows a cross section through a first composite or laminated or
sandwich
panel manufactured by the arrangement in which the first and the second metal
foil
1, 2, as well as the core sheet 30 lying therebetvveen and comprising
substantially
perpendicularly oriented fibers 9, and both layers of adhesive 5 can be
recognized.
In the following specification, single components of the arrangement according
to
figure 1 shall be explained in more details.
Both devices 4, 7 for applying the adhesive 5 onto the metal foils 1, 2 can be
provided in different manner and can work according to different methods. The
selection of the method is dependent especially on the kind and consistency of
the
adhesive 5, on the surface of the metal foils 1, 2, and on the fact whether
the whole
surface or only specific regions have to be coated with the adhesive 5. In
dependency on the kind of the adhesive and if applicable, the first and the
second
roll 3, 6, their surroundings and/or the metal foils 1, 2 can be heated in
this region
and in the region of the flocking device 8 (for example by means of an air
stream,
by infrared or ultraviolett radiation or by inductive means) to prevent a
premature
cooling down of the adhesive 5 and to improve its application and to keep it
liquid
such that the fibers 9 can reliably penetrate into it during the subsequent
flocking
process. If the adhesive 5 is too liquid it could be hardened partly by an
appropriate
heating so that the fibers can reliably fixed in it.
According to a method which is similar to the well-known screen printing, the
adhesive 5 which is stored in a tank 51 is distributed on a sieve 47, 77 which
is
positioned on the metal foils 1, 2 which are to be coated. Afterwards the
adhesive 5
is pressed by means of a doctor blade (squeegee) 48, 78 through the sieve 47,
77
onto the metal foil 1, 2 as known from a screen printing process wherein the
position, the material, the pressure and the shape of the doctor blade
influences the
CA 02480689 2004-09-27
8
amount of the applied adhesive 5. By this method, a
particularly uniform
distribution even in the case of a non level surface of the metal foils 1, 2
can be
obtained.
Especially for achieving a uniform thickness of the adhesive layer it might be
advantageous to provide a heating device above the sieve 47, 77, and to heat
the
adhesive 5 and/or the sieve 47, 77 to decrease the viscosity of the adhesive 5
by a
related temperature increase and to improve its flowability.
For improving the separation of the adhesive 5 from the sieve 47, 77 it can be
provided with an appropriate anti-bond coating and/or a surface structure
which
makes easier the separation.
The adhesive 5 can be applied in several layers above each other. On the one
hand
this might serve to obtain a certain thickness of the total layer especially
if the
second layer is applied on to the first layer with a reduced pressure. On the
other
hand a second coating process may serve to complete and close the first layer
especially if during the first screen printing process adhesive has not been
applied
(in a sufficient amount) on to all regions. These coating processes can be
repeated
several times with different pressures.
Furthermore it can be advantageous to direct a stream of warm air over the
applied
adhesive layer. Surprisingly it revealed that by this small bubbles which are
present
in the adhesive layer can be removed and the surface of the adhesive layer is
becoming particularly plain.
Another alternative in which the principle of screen printing is used as well
is
shown schematically in figures 3a to 3c. In these representations it is
started
exemplarily from the fact that the adhesive 5 is applied onto the first metal
foil 1.
However, with such an arrangement the second metal foil 2 or an additional or
another cover sheet can be coated with adhesive 5 as well.
According to figure 3a and 3b a flexible and for the adhesive 5 semipermeable
tape
for example a fabric tape 41 is guided by means of three rolls 42, 43, 44 and
pressed
onto the metal foil 1 to be coated. Thereby the fabric tape 41 is usually
pulled with
the conveyed metal foil 1 so that a separate activation is usually not
necessary. On
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9
the side of the fabric tape 41 opposite to the metal foil 1 a stationary
doctor blade
(squeegee) 45 is positioned which presses a supply 46 of an adhesive which has
been fed from a funnel 461, through the fabric tape 41 onto the metal foil 1.
Again,
the application of the adhesive can be influenced substantially by the
position, the
material, the pressure and the shape of the doctor blade.
The adhesive 5 carried with by the fabric tape 41 is preferably removed in the
region of the roll 44 by means of an appropriate stripping element (not
shown).
Preferably at least one of the rolls 41, 43, 44 is shiftingly supported so
that the
tension of the fabric tape 41 can be adjusted.
Figure 3c shows an embodiment in which the fabric tape 41 is stretched over a
drum 411 within which the funnel 461 for the adhesive and the doctor blade 45
are
positioned. Alternatively, a sieve can be formed as a drum which is permeable
for
the adhesive 5 (rotational screen printing) and within which the doctor blade
is
positioned and into which the adhesive 5 is fed so that the adhesive is
provided
through the wall of the drum onto the metal foil 1, 2 if the drum is unrolling
on the
metal foil 1, 2. Additionally to the above mentioned measures the separation
of
adhesive can be improved by increasing the diameter of the drum.
By means of these arrangements and methods, respectively, it is as well
possible to
apply the adhesive 5 only on specific areas or in the form of a particular
pattern
onto the metal foil 1, 2 if a sieve and fabric tape 41, respectively, is
permeable for
the adhesive 5 only in specific areas. The generation of such patterns on a
sieve and
a fabric tape 41, respectively ,is known from usual screen printing processes.
Such patterns can for example have a honeycomb structure which is composed of
a
number of polygons (triangle, pentagon, hexagon, octagon). Furthermore,
patterns
of adhesive can be provided in the form of spirals, serpentines, rectangles,
circles,
dots, circular curves, ellipses, stars, crosses, as well as other geometrical
patterns
and any combinations of those patterns.
The choice of such a pattern can be made not only for saving adhesive 5 and
fiber
material but also in dependency on the future application of the laminated
panel. If
for example the laminated panel is proposed to be welded or cut, the metal
foils 1, 2
are not coated at the later weld points or weld seam or cutting edge to obtain
a
CA 02480689 2004-09-27
particularly clean weld seam and cutting edge, respectively, which is free
from
adhesive 5 and consequently free from fibers 9 as well. Furthermore, during
the
later welding no vapour of burning adhesive 5 is released. If along buckling
or
folding edges no adhesive 5 is applied the related later processing is easier
as well.
An only local coating with adhesive 5 furthermore is appropriate if specific
locally
differing (direction-dependent) mechanical, acoustical, thermal, absorption,
oscillation or other physical properties of the composite structure workpiece
(workpiece with gradient properties) shall be obtained.
In case of a large-surface coating of a metal foil 1, 2 with adhesive,
internal stresses
may arise because of differing thermal coefficients of expansion of both
materials.
These stresses can at least substantially be avoided if the adhesive is
applied in the
form of a non continuous layer which is formed for example from single islands
of
adhesive (dots pattern). Such an adhesive pattern can be applied preferably as
well
by means of a method known from screen printing.
This simultaneously serves to solve another problem. It has revealed that upon
using most of the presently known adhesives a temperature increase of the
composite layer structure has the consequence of a considerable decrease in
the
delamination resistance. If, however, the adhesive is not applied in a
continuous
layer but in the form of a plurality of adhesive islands this delamination
resistance
remains considerably higher even at higher temperatures.
Finally, it possible to keep certain areas between the metal foils 1, 2 free
of
adhesive, wherein these areas can have the form of cavities or channels
through
which later on for example a liquid or a gaseous medium is guided or into
which
before joining both metal foils 1, 2 objects are inserted or into which after
joining
the metal foils and object is pushed in from the rim of the structure.
As an alternative to the application by a screen printing, such a selective
application
of adhesive can be obtained as well by a spray system if it comprises a
plurality of
spray nozzles which can individually be controlled and which preferably can be
heated to achieve or maintain a sufficient low viscosity of the adhesive. Such
a
spray system is preferably controlled by a computer so that in a relatively
simple
manner almost any patterns of adhesive can be generated on the metal foils 1,
2.
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The use of a sheet die (slid die) which can possibly be heated can be
advantageous
as well for applying a first adhesive layer (pre-application) or the whole
adhesive
layer (pre- and final application).
Another possibility according to figure 3d is to apply the adhesive 5. from
the funnel
461 directly onto the metal foils 1, 2 by using a doctor blade (squeegee). For
achieving an adhesive layer which is as uniform as possible the related metal
foil 1,
2 is usually fed past the doctor blade by means of a drum 50 or, in the case
of a non-
continuous method, the metal foil is fixed on a vacuum table. In a similar
manner
the adhesive 5 can as well be rolled on and then calibrated by means of a
knife
blade or similar devices, wherein in both cases a certain adhesive pattern can
be
obtained after application by means of a comb like doctor blade which is drawn
over the metal foils 1,2 which are coated with adhesive.
The kind of the adhesive 5 used is substantially determined by the kind of
application, the later use of the composite layer structure and especially by
the
desired properties like for example the stiffness or flexibility, strength and
so on, as
well as the kind and distribution of the flock fibers. Substantially three
different
kinds of adhesive have to be considered. These are the so-called reactive
adhesives
which are adhesives which harden at normal or increased temperatures,
furthermore
the two-component adhesives and the well-known thermoplastics.
If for example a particularly high stiffness of the material is desired,
adhesives 5
which are similar to a foam and which expand can be used to enclose the fibers
9 to
the greatest possible extent during the hardening (curing) of the adhesive 5
if the
distance of the metal foils 1, 2 is held constant so that an especially firm
and
compact connection between the metal foils 1, 2 and the fibers 9 is obtained.
If however a good mechanical and acoustic energy absorption and ductility of
the
composite layer structure is desired, adhesives 5 can be used which keep a
certain
flexibility in their hardened (cured) condition. In these cases certain hot
melting
adhesives or epoxy adhesives can be used.
If the composite layer structure is to be machined by forming operations for
example deep-drawing, it is preferred to use adhesives with a strength which
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12
decreases in hardened condition by increasing temperatures. In this case the
sandwich structure as a whole becomes more flexible and elastic and can be
formed
to a greater extent without any damage wherein the necessary forces are
smaller as
well. Possibly even a manual forming can be conducted if the adhesive is
appropriately chosen and sufficiently heated.
Furthermore the adhesive 5 can be applied onto the metal foils 1, 2 in the
form of an
adhesive foil or in the form of several sections of an adhesive foil wherein a
certain
pattern having any shape can for example be punched into the adhesive foil.
The
adherence of the metal foils 1, 2 can for example be obtained by means of an
electrostatic charging. The thickness of the foil either corresponds with the
thickness of the desired adhesive coating or an adhesive foil with a greater
thickness
is accordingly stretched and rolled out. By this air inclusions can be avoided
or
removed simultaneously. By heating the adhesive layer and/or the metal foils
1, 2
during the following flocking process the fibers can penetrate to a sufficient
extent
into the adhesive coating and can be fixed therein.
In certain cases it may be advisable not to coat one or both metal foils 1,2,
partly or
as a whole, by means of the device but instead feed at least one metal foil
which has
been already coated with an adhesive layer. In this case the adhesive layer is
preferably covered with a non adhesive protection foil so that the related
metal foil
can be wind up to a roll. Before or at the beginning of supplying into the
arrangement, the protection foil is manually or automatically (not shown)
drawn
off.
Finally, it is as well possible to coat the first metal foil 1 according to
the
description above with a viscous adhesive 5, to apply an adhesive foil onto
the
fibers 9 after the flocking process and then, possibly after heating, to press
the
second metal foil 2 therewith.
The above mentioned measures can be combined with each other for optimizing
the
coating of the adhesive.
After having coated the metal foils 1, 2 with an adhesive 5, the flocking
process is
conducted by means of the flocking device 8. The flocking device 8 as well can
work according to different methods which are selected in dependence on the
kind
=
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of the materials from which the fibers 9 are made and the thickness, the
length
and the desired density and distribution, respectively, of the fibers 9 on the
first
metal foil 1.
Another criterion for the selection of the methods are the desired properties
of the
composite layer structure. If a flexibility and ductility as high as possible
is desired
the fibers 9 should be fixed as far as possible perpendicularly to the surface
of the
metal foils 1, 2 If. however, a stiffness as high as possible is desired the
fibers 9
should be positioned to a greater extent inordinate and especially angular and
diagonal, respectively, and crossing each other.
By means of the heating device (stream of warm air, infrared or ultraviolett
radiation, inductive heating and so on) the viscosity of the adhesives 5 can
be
decreased during the flocking process to ensure that the fibers 9 can
penetrate to a
sufficient extent into the adhesive layer.
The starting material for the flocking process is usually a bundle of metallic
wires
or a bundle of fibers made from another one of the above mentioned materials
which are at first cut to a desired length.
The embodiment of the flocking device 8 shown in figure 1 comprises one (or
more) vessels 81 into which the cut fibers 9 are and which is provided with a
bottom which is permeable for the fibers 9 through which the fibers 9 can be
applied onto the first metal foil 1. The vessels 81 on the one hand and the
metal foil
1 on the other hand are subjected to different electric and/or magnetic
potentials so
that between both an electric and/or magnetic field 82 is generated. For this
purpose
a related voltage source and devices for generating the electric and/or
magnetic field
(not shown) are provided. The field strengths and the permeability of the
bottom of
the vessel 81 are matched to each other such that the fibers 9 penetrate
through the
bottom, are accelerated by the electric and/or magnetic field in the direction
of the
metal foil 1, and then penetrate with one and into the adhesive layer so that
they are
fixed for example substantially perpendicularly to the metal foil 1.
In order to obtain a desired density of the fibers in the adhesive layer 5,
especially
the strength of the fields 82, the distance between the vessel 81 and the
metal foil 1
and the velocity with which the metal foil 1 is moved can be adjusted.
Furthermore
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14
at least one vibration device (not shown) can be provided with which the
vessel
81 is subjected to a vibrating motion in a horizontal and/or vertical
direction which
preferably can be adjusted, for increasing and modulating the amount of fibers
9
penetrating through the bottom and for loosen up the fibers 9.
Another parameter with which the density and distribution and homogeneity of
the
fibers 9 can be influenced is the kind of the bottom of the vessel 81. This
especially
concerns the number, the dimension, the shape and the density of the openings
in
the related bottom, wherein in order to obtain different delivery amounts of
fibers 9
a related screen device can be provided with which at least some of the
openings
can be closed partly or totally.
Especially in a case in which the bottom of the vessel 81 is provided in the
form of
a sieve the delivery properties can be influenced as well by shaping,
imprinting
and/or structuring the same. Such a sieve is preferably used in combination
with a
vibration device ("shaking screen") in order to loosen up, to separate from
each
other and to unmatch the fibers loaded into the vessel 81 and to prevent that
the
sieve is clogged more or less at single locations by fibers. In this
connection it can
be advantageous to vibrate the sieve with different frequencies and/or
different
amplitudes wherein alternatively or additionally acoustic pressure waves
and/or
compressed air can be used for example to separate fiber clusters or to
optimally
sieve fibers 9 with different lengths.
In order to inhibit or avoid the formation of clusters of fibers 9 it is
possible to
provide the fibers with an appropriate coating. Such a coating can be one
component of a two component adhesive wherein the second component is applied
according to the above description by means of the first and second device 4,7
onto
the metal foil 1, 2, respectively, to be coated.
Furthermore an electrode (not shown) can be positioned between the vessel 81
and
the metal foil 1 for example in the form of a ring which is subjected relative
to the
metal foil 1 and the vessel 81, respectively, to such a voltage potential that
the
fibers 9 are additionally accelerated or decelerated according to the
principle of the
well-known triode (three-electrode) valve.
CA 02480689 2004-09-27
The amount of the delivered fibers and the direction under which the fiber
stream is directed onto the metal foil 1 can be controlled as well by using
the well-
known principle of the Braun tube. In this case a device formed like a
modulating
Wehnelt electrode, and several cylindrical electrodes can be used for focusing
and
accelerating a related fibers stream, which moreover is directed by means of
electric
and/or magnetic fields and by a corresponding control of the devices for
generating
these fields, with different directions onto the metal foil 1.
By a variation of all these parameters during operation of the flocking device
8
sections with varying densities of fibers and sections with an inhomogeneous
distribution of the fibers or sections without fibers can be obtained on the
adhesive
layer.
Examinations of the delamination properties have shown that after hardening
(curing) of the adhesive 5 the fibers 9 are stronger fixed within the flock
adhesive
layer of the first cover sheet (which in the described method is the first
metal foil 1)
than in the adhesive layer of the second cover sheet (second metal foil 2)
which has
been applied onto the first cover sheet. In order to achieve an as uniform as
possible
delamination resistance and a uniform distribution of other physical
properties on
both cover sheets, both these cover sheets can be flocked with a
positive/negative
pattern in such a way that after joining the sheets the flocked areas within
the core
sheet are lying side-by-side and mesh with each other like tooths.
In this case it is particularly advantageous to use a method according to
which as
explained in the introductory part, a metal foil having substantially twice
the
breadth is supplied which is divided into two halves in the longitudinal
direction
after coating of the adhesive and flocking the fibers and possibly pre-curing
of the
adhesive wherein afterwards both halves are folded together, pressed and
subjected
to a final curing.
In order to achieve a positive/negative pattern, templates (not shown) can be
used
for flocking, with which on one of the cover sheets a pattern in the form of
flocked
areas is generated which represents the negative pattern (non flocked areas)
of the
pattern on the other cover sheet so that these mutually complete each other
upon
joining the cover sheets together.
CA 02480689 2004-09-27
16
The templates are preferably provided in the form of a belt made for example
from a fabric or foil material and are guided like a conveyor belt by means of
three
guiding rolls with the same velocity as the cover sheet to be flocked. This
has the
advantage that excess fibers 9 which have not reached the related cover sheet
through the openings within the template can be removed in the area of one of
the
guiding rolls by means of stripping or sucking devices.
Alternatively the fibers 9 can be applied through tubes having a desired cross
section and being positioned according to the related pattern wherein the
tubes (not
shown) each end shot above the adhesive layer of the related metal foil 1, 2,
and
possibly each end is provided with a sieve so that they fulfill substantially
the
function of the vessel 81. In this case as well the fibers 9 can be
accelerated or
influenced according to the above explanations by means of electric and/or
magnetic fields.
Another possibility for obtaining a certain distribution of the density of the
fibers 9
is to apply a foaming adhesive 5 in the form of dots on different places of
the first
metal foil 1, than placing a fiber bundle onto each dot and pre-curing the
adhesive
5. As a consequence of the foaming adhesive the single fibers 9 are separated
from
each other and/or fan out in their direction similar to a bunch of flowers, so
that
local regions with a relatively uniform density of fibers are obtained wherein
the
number and the distance of these regions is determined in dependence on the
proposed use of the composite layer structure. The joining of the metal foils
1, 2
and the final curing of the adhesive is then conducted according to the
explanations
below.
According to another embodiment of the flocking device 8 instead of the vessel
81 a
cutting device can be provided with which the supplied fiber bundles are cut
over
the metal foil 1 by means of a laser beam or a mechanical device and then
directly
guided to the metal foil 1 for example under the influence of a constant or
variable
electric and/or magnetic field according to the above explanations.
Another possibility is to fix the fibers 9 in a substantially non-cut
condition first on
the adhesive layer and a then cutting them for example by means of a knife or
a
laser beam in a desired height over the metal foil 1.
CA 02480689 2004-09-27
17
In order to achieve in a considerable dimension a non-perpendicular and
inordinate orientation of the fibers 9 relative the metal surface, during or
immediately after the application of the fibers 9 a continuous or swirled
stream of
air can be directed onto the fibers 9 and or the metal foil 1. For this
purpose
preferably in the region of the flocking device 8 a related fan device (not
shown) is
provided. If the fibers 9 are to be oriented with a common preferred direction
angular to the surface of the metal foil 1, a blade can be used which is
grazed after
application of the fibers 9 over the flocked surface.
In case of a suitable fiber material the fibers 9 can be oriented as well by
means of
an appropriate electric and/or magnetic field. The parameters with which the
orientation can be influenced are substantially the strength and the direction
of the
field, the distance of the field generating devices from the flocked surface,
and the
motion velocity of the flocked surface. By means of a plurality of relatively
small
field generating devices which are individually controlled, an orientation of
the
fibers 9 can be obtained which can be specifically controlled in the kind of a
pattern
extending over the whole flocked surface.
Another possibility is to guide the flocked surface under and past a metal rod
wherein the metal rod and the fibers 9 are connected to such potentials that
the
fibers 9 are attracted or repeled from the metal rod so that they are inclined
in this
way.
Finally, preferably and especially in such a case in which only certain areas
of the
metal surface are coated with adhesive 5, a third device (not shown) is
provided
with which fibers 9 which are lying between these areas are removed before the
metal foils 1, 2 are joined together. This third device can be a blow off or
suck off
device, or the fibers are removed for example by means of an electric and/or
magnetic field.
Especially in case of a relatively thin liquid adhesive 5 it can be
advantageous to
harden the same immediately before or after application of the fibers 9 a
little bit to
thereby obtained a pre-fixing of the fibers 9 before both metal foils 1, 2 are
joined
together. This pre-harden can for example be achieved by means of a stream of
hot
air, an inductive heating or by a radiation with infrared or ultraviolett
light
immediately before the first metal foil 1 enters the flocking device 8. If
there is a
CA 02480689 2004-09-27
a-
18
risk that the metal foil 1 warps, this can be prevented by either coating it
only
partly with adhesive 5 and/or using a metal foil 1 with a higher strength.
If on the other hand an adhesive 5 is selected with a very high viscosity it
might be
useful to melt it somewhat by heating before flocking so that the fibers 9 can
better
penetrate into the adhesive layer. This is valid as well for the adhesive 5
applied
onto the second metal foil 2 before joining it together with the first metal
foil 1.
Again, such a heating can be obtained by means of a steam of hot air, a
radiation of
infrared or ultraviolet light, by an inductive heating of the adhesive 5 which
is
possibly mixed with metal particles, and/or of the metal foils 1, 2 and/or the
fibers
9, or as mentioned above by means of rolls 3, 6 which are heated.
An alternative for the flocking of the metal foil 1 with fibers 9 is to apply
instead of
the adhesive 5 a mixture of adhesive 5 and fibers 9 which has been prepared by
a
mixer onto the first and/or the second metal foil 1, 2. By this, on the one
hand a
particularly arbitrary and inordinate orientation of the fibers relative to
the surface
of the metal foils 1, 2 can be obtained. On the other hand, however, it is
possible as
well to align the fibers 9 after the mixture has been applied as explained
above by
feeding an electric and/or magnetic field. In both cases it might be
sufficient to only
coat one of both metal foils 1, 2.
In this case it might be advantageous to feed at least one of the metal foils
to the
arrangement which is pre-coated with such a mixture which is covered by a
protection foil as explained above with regard to the metal foil which is
coated with
an adhesive and covered with a protection foil.
Summarizing, in order to obtain different or varying (i.e. direction-
dependent)
physical and/or electric properties along a width and/or a length of the
composite
layer structure, the fibers 9 can be applied with different kinds, density,
thickness,
length, material and/or different orientation relative to the cover sheet onto
at least
one of the cover sheets wherein the above mentioned measures, if desired, can
as
well be combined with each other. In this connection, the mutual displacement-
capability of the cover sheets can have a substantial influence on these
direction-
dependent properties.
CA 02480689 2004-09-27
19
The arrangement of the dryer 12 by means of which both metal foils 1, 2 are
firmly connected with each other by pressing against each other and hardening
the
adhesive 5 and especially the distance of the metal foils 1, 2, the value of
the
temperature and of the pressure, as well as the duration of their influence
onto the
metal foils 1,2 is substantially dependent on the kind of the used adhesive 5
and the
thickness and quality of the metal foils 1, 2.
With regard to this it has especially to be distinguished between the hot
melting
adhesives which are liquid in a warm or hot condition and which harden by
cooling
down, and the other adhesives for example epoxy-adhesives which harden upon
the
influence of heat. In dependence on this the pressing tool 123 possibly
comprises an
additional heating device.
In a case in which the composite layer structure is to be machined by forming
processes as for example a deep-drawing process in which the structure is
usually
heated, especially such an adhesive is advantageous whose strength decreases
with
increasing temperature so that the core sheet can adapt flowingly according to
the
forming of the metal foils 1,2.
In order to avoid that the metal foils 1, 2 warp during hardening (curing), it
is
essential that both metal foils 1, 2 are as homogeneous and uniform as
possible
heated within the pressing tool 123 and afterwards are as uniform as possible
cooled
down, and in both cases both metal foils 1,2 as simultaneously as possible.
This can be achieved on the one hand if both metal foils 1, 2 after reaching
the
pressing tool 123 are first heated up to a starting temperature before heating
is
continued until reaching the curing temperature of the adhesive, together with
simultaneously pressing the metal foils 1, 2 together. Depending on the curing
temperature of the adhesive and the thickness of the metal foils 1, 2 the
starting
temperature can for example be about 100 C.
Another possibility is to not directly contact the metal foils 1, 2 with the
pressing
tool 123 but to insert between the pressing tool 123 and the metal foils 1, 2
each one
plane element as for example a sheet steel, a metal plate, a foil, a fabric
material and
so on which has a higher thermal capacity and/or a lower thermal conductivity
than
the metal foils 1, 2. This prevents that the metal foils 1, 2 are abruptly
heated at the
CA 02480689 2004-09-27
first contact areas with the pressing tool 123, but a temperature gradient is
generated between the pressing tool and the metal foils 1, 2 along which the
metal
foils 1,2 are continuously and slowly heated. This heating process can be
optimized
by an appropriate selection of the materials and thickness of the plane
elements.
After compressing and curing the adhesive 5, the plane elements car; serve to
ensure
a uniform cooling down of the metal foils 1, 2 and to prevent a warping. If
necessary the cooling down can be controlled by means of a cooling device
which is
guided along or over the free sides of the plane elements. For this purpose
the plane
elements can comprise appropriate channels for feeding a coolant.
Especially in case of particularly thin metal foils 1, 2 and/or those with a
relatively
poor quality the risk of forming dents can considerably be reduced if the
temperature within the pressing tool 123 is decreased and the duration of the
compressing is increased correspondingly.
Inclusions of air can generate dents as well if the air cannot escape fast
enough
when the pressing tool 123 is closed. This can be prevented by inserting
between
the metal foils 1,2 on the one hand and the pressing tool 123 on the other
hand, a
heat resistance tissue through which the air can escape laterally from the
pressing
tool 123.
Both metal foils 1,2 can particularly uniform and fast be heated by means of a
well-
known inductive heating device (not shown). This is true especially if the
fibers 9
are metallic and the adhesive 5 as well contains metallic particles because in
this
case the heat is also generated between the metal foils 1, 2 and enables a
particularly fast and uniform heating of the adhesive 5 and prevents as well a
warping of the metal foils 1, 2.
Furthermore, the curing of the adhesive between both metal foils 1, 2 can be
conducted in two or more steps. For example, after joining together the metal
foils
1, 2 within the dryer 12 according to figure 1, a pre-curing can be conducted
in a
first step to such an extent that the metal foils 1, 2 do not expand any more
during
the later final curing. The metal foils 1, 2 can then first be cut by the
cutting device
13 in a desired manner and then the single parts can be final-cured in a
second step
(not shown) with the same or at a higher temperature with which the final
strength
CA 02480689 2004-09-27
21
is achieved, wherein for this purpose the parts can be introduced into an
appropriate oven having any orientation or position because of the pre-curing.
When using a well-known pressing tool 123 the distance to which the metal
foils 1,
2 are compressed together within the dryer 12 can usually be adjusted.
Modulating
the amount of adhesive 5 applied onto the metal foils 1, 2 and the thickness
of the
adhesive coating, two alternatives can be distinguished with respect to the
compactness of the generated core sheet which lead to different properties of
the
material.
Regarding the first alternative, the distance is so great and/or the amount of
the
adhesive 5 and the thickness of the adhesive layer, respectively, is so small
that the
fibers 9 present on the first metal foil 1 penetrate with their free ends only
so far
into the adhesives layer of the second metal foil 2 that after curing the
adhesive a
safe connection between both metal foils 1,2 is ensured.
Regarding the second alternative, the metal foils 1, 2 are compressed together
to
such a small distance and/or the amount of adhesive 5 and the thickness of the
adhesive layer, respectively, is so far increased that between the metal foils
1, 2 a
substantially homogeneous and porous and compact, respectively, core sheet is
generated in which the fibers are completely surrounded by foam and enclosed,
respectively.
In this case, however, it has to be ensured that air bubbles which are
possibly
present within the adhesive layer can substantially escape, or that the
adhesive layer
is substantially free from such bubbles before joining the metal foils 1, 2
together.
This can for example be achieved if between applying the adhesive 5 and
joining
the metal foils 1, 2 together, a certain time duration expires, or if a stream
of (hot)
air is guided over the adhesive layer so that the bubbles underneath its
surface burst.
For specific applications and for reasons of recycling of materials it can be
desired
not to use adhesive 5 at least as far as possible. In this case the fibers 9
at first can
be inserted according to figure 4 into a carrier 91 in the form of a sheet of
paper or a
similar material so that their free ends bear out on both sides of the carrier
91. If
necessary, the fibers 9 are then brought to a desired length by shortening the
free
ends (for example by means of a laser beam) before an electrically conductive
CA 02480689 2004-09-27
22
adhesive 5 is applied onto the fibers tips and the carrier 91 is then laid
upon the
first metal foil 1.
After this the fibers 9 are adhered to the first metal foil 1 by an inductive
heating of
the adhesive 5. The carrier 91 ensures that the fibers 9 keep their
substantially
perpendicularly orientation relative to the metal foil 1 or, if they haye been
inserted
into the carrier 91 with a certain angle, keep this angel during the adhering
process.
After the adhesive is cooled down the carrier 91 can be removed and the second
metal foil 2 can be applied for example by means of another such adhering
process.
Furthermore, it is possible as well to fix the metallic fibers 9 by an
inductive stitch
welding directly onto the metal foil 1. For this purpose, at first a substrate
is applied
onto the first metal foil 1 into which the fibers 9 can easily penetrate
during the
flocking process so that they are fastened. At next, the first metal foil 1 is
inductively heated. By an appropriate selection of the conductivity of the
substrate a
specific heating of the transition between the first metal foil 1 and the
fibers 9 is
achieved so that both are welded to each other. In the same manner or in a
manner
as explained above, finally the second metal foil 2 is applied.
The above disclosed methods for manufacture are applicable as well, with only
a
few exceptions which are obvious for persons skilled in the art, if instead of
one or
both metal foils 1, 2 and metal plates, respectively, a non-metallic material
(for
example synthetic materials like kevlar or similar) is used for a cover sheet
or if the
fibers 9 are manufactured from a non-metallic material. Especially it is
possible to
use sheets of paper or paperboard instead of one or both metal foils 1, 2
whereby a
considerable weight reduction can be achieved.
In this regard a plurality of different combinations of materials for the
cover sheets
and the at least one core sheet can be realized. For example a combination of
metal
and non-metal can be selected for both cover sheets with a core sheet
comprising
metal fibers there between. In case of a multiple composite layer structure it
can be
advantageous to manufacture the outer cover sheets from a non-metallic
material
like especially a synthetic material to achieve a corrosion resisting
structure,
whereas the inner cover sheets are made from a metallic material to achieve
certain
physical properties of the structure wherein the core sheets may contain as
well
metallic and/or non metallic fibers.
CA 02480689 2004-09-27
23
Especially in case of using a mixture of metallic and non-metallic fibers 9,
as well
with differing mixture ratios along a flocked surface, certain parameters like
for
example the electric conductivity between the cover sheets or the mechanical
damping properties can specifically be influenced and adjusted, respectively.
This is
true as well for example in case of use of a mixture of fibers 9
with,differing length
and/or thickness and/or differing materials and possibly differing mixture
ratios
along the flocked surface.
By using a certain fraction of shorter or formed fibers which are fixed in an
adhesive layer with only one end, the other end of which is standing free, a
considerable improvement of the acoustic- and oscillation-dampening properties
of
the composite structure can be obtained. These properties further improve with
an
increasing fraction of such shorter or formed fibers within the flock
material. A
possible small loss of strength which could possibly occur could substantially
be
compensated, if necessary, for example by an increase of the whole fiber
density.
Instead of the fibers 9 (or additionally to those) spherical bodies,
parallelepiped
bodies or other similarly formed bodies of metallic and/or non-metallic
materials
and/or with differing dimensions can be used.
The method according to the invention is as well applicable for the
manufacture of
multiple composite layer structures in which several layers of the above
disclosed
kind are joined together by means of fiber material or in which an additional
layer
of a same or another material is applied onto the composite layer structure to
achieve certain mechanical or other properties. Especially it is possible to
guide a
composite structure, comprising three sheets which has been manufactured as
disclosed above, together with a cover sheet or another composite structure
again
through the arrangement in order to join together both by generating a core
sheet
according to the explanations above.
Furthermore by means of the method according to the invention not only plane
composite structures can be manufactured. For example a pipe with a double
wall
can be manufactured by first coating an inner pipe with an adhesive, then
applying
flock fibers onto the adhesive and finally laying a sheet steel there around
or
CA 02480689 2004-09-27
24
winding like a helix a strip of metal or another material as an outer pipe
there
around and curing the adhesive.
The strength of the composite layer structures manufactured as disclosed above
can
be increased further if necessary by a final malleablizing.
The mechanical properties of the composite layer structures according to the
invention can be evaluated by means of the numerical method of the finite
elements
quite well. By this especially the influences of the density, the diameter,
the
orientation, the fixing, as well as of the materials of the used fibers, the
influences
of the materials and the thickness of the adhesive layers, as well as of the
materials
and the thickness of the cover sheets can be evaluated. Furthermore the
influences
of different patterns of the adhesive and of the fibers at the cover sheets
(shape,
covering ration, pattern) on the mechanical and thermodynamic properties can
be
evaluated.
The thermal warping of the composite layer structure especially in combination
with different materials can be investigated by means of the numerical method
of
the finite elements as well. For this purpose the inherent tension condition
which
arises due to the different heat expansion within the adhesive and within the
cover
sheets is calculated.
Finally, the method according to the invention is suitable as well for the
manufacture of workpieces from pre-formed cover sheets which are coated with
adhesive, flocked and joined together in the disclosed manner if the related
devices
for holding and guiding the cover sheets are provided in an appropriate way.
