Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02258255 1998-12-21
Structural Member
The invention relates to a structural member according to the
preamble of claim 1, and to a process for the production of a structural
member, according to the preamble of claim 20.
s Such structural members are frequently, but not exclusively, used in
the building industry. A structural member is known from German T'atent
Dh-41 37 649 A1 which consists in general of plastic with a first low
modulus of elasticity and with a layer within the building element of a
material which has a second, substantially higher modulus of elasticity.
to This layer, which preferably consists of an aluminum alloy, has a system
plane along which the profiled layer extends. For a plate-shaped element,
for example, the system plane lies in a cross section of the plate-shaped
structural member and the layer is constructed in a trapezoidal shape, with
the layer running point-symmetrically to the system plane. The sections of
1 s the trapezoidal layer which run substantially parallel to the outer wall
are
connected together by sections which run diagonally, so that a section of
the layer is provided reciprocally to the system plane and running
substantially parallel to the outer layer. The stratification of such a layer
in
a shwctural member consisting of plastic with a low n lodulus of elasticity
2o can give an increase of 5-15% in the modulus of elasticity of the
structural
CA 02258255 1998-12-21
member, for example. The sections of the layer which run diagonally and
traverse the system plane then serve as shear bridges whereby the shear
forces acting on the structural member can be better taken up and the
modulus of elasticity of the structural member can be increased.
s An I-beam is furthermore known from DE 41 37 694 A1, and is
constructed analogously to the plate-shaped structural member. A layer
which has a head region and a foot region connected together by a zigzag-
shaped middle region is installed in the I-beam. 'this middle region forms
a shear or thrust bridge between the head and foot regions of the layer
to which is installed in the structural member. rI'hus forces acting on the
structural member can be better taken up, since an increase in the overall
modulus of elasticity is attained by means of this layer, in comparison with
a structural member without such a layer.
Such structural members are indeed superior to the heretofore
i5 known structural members of wood or plyboard in regard to waste
disposal and recycling capability. However, the construction and
development of the layers requires more processing steps for their
profiling, so that production is expensive because of the bonding of the
profiled layer into the structural member. The modulus of elasticity of the
Zo shuctural member of plastic with inlaid layers could be improved over
2
CA 02258255 1998-12-21
those made of wood or by a phenolic resin bonding; however, the field of
application is limited because of the relatively low modulus of elasticity of
the member.
The invention therefore has as its object to provide a structural
s member which is easily produced and which makes possible an increase of
the load-bearing ability because of a higher modulus of elasticity of the
member due to the construction. A further object of the invention is to
provide a process for the production of the structural member, making
possible a cost-effective production of the structural member accordi~ g to
1 o the invention with a high output of structural members.
The objects are attained according to the invention by the features of
claims 1 and 29.
The structural member designed according to the invention has the
advantage that at least a 1 1 /2 times increase of the modulus of elasticity
of
i5 the member can be attained, in comparison with the structural members
known from the state of the art, by means of a simple arrangement and
design of the layers constructed with a second, higher modulus of elasticity
and built into the plastic body. It is provided therefor that two layers,
which are separate from each other and which traverse the system plane,
2o with a second higher modulus of elasticity are inserted into the structural
3
CA 02258255 1998-12-21
member between an inner layer and an outer layer. 'T'hese layers have
respective points of intersection with the system plane which
advantageously are as far apart as possible and are arranged near the wall
region of the structural member. A so-called sandwich structure can
s thereby result, in which a core layer consisting of plastic is bounded by an
upper and a lower Layer with a second, higher modulus of elasticity, which
in their turn can be covered with at least one outer layer consisting of
plastic.
The layers with the second, higher modulus of elasticity are not
to connected together directly, i.e., the sections traversing the system plane
and forming a shear bridge were omitted. It would have been expected,
from calculations according to Steiner's theorem, that in such a
configuration a smaller load-bearing capacity or a smaller stiffness of the
member would be attained, since a combined action between an upper and
i5 a lower layer would not be given by the lacking middle region or shear
bridge. It was assumed that a structure with a shear bridge omitted would
not act as an overall structural member, but rather as two structural
members connected in parallel and only slightly affecting each other.
Furthermore, it was assumed that creep would not be prevented, due to the
a o lacking shear bridge.
9
CA 02258255 1998-12-21
Contrary to this interpretation, however, it has been found that
exactly by means of this configuration, in which an upper and a lower layer
are arranged separated from each other in an edge region of the outer
layers of a structural member, an increase of the stiffness of the member by
at least a factor of 1.5 can be made possible.
This increase of the stiffness of the member is based, according to
knowledge at the time of the application, firstly on the use substantially of
layers which go all through in the edge region of the structural member,
and which make it possible for forces to be better taken up. In contrast to
to this, it is known from tile plate-shaped member according to the state of
the art, that because of the trapezoidal construction of the layer, only
partial sections are provided which are not mutually connected in the edge
region, whereby a smaller load absorption is given when bending stresses
are applied. On the other hand, a combined action can nevertheless be
i5 attained, so that an increase of the modulus of elasticity of the member
can
be attained by the cooperation of the inner layer with the layers with
higher modulus of elasticity bounding the inner layer, and the outer layers
applied to these layers. It has furthermore been found that creep behavior
is directly dependent on the high tensile stresses in the outermost zone and
a o on the shear bridge formation.
s
CA 02258255 1998-12-21
An advantageous embodiment of the invention provides that the
layers have a adhesion primer. A full-surface bonding between the inner
layer and the outer layer to the layers with higher modulus of elasticity can
thereby be made possible.
s 'The adhesion primer, preferably applied to both sides, furthermore
has the advantage that the bonding of the plastic layers and the layers
which are preferably of alununum alloy is not loosened in the cooling
process during production. The thermal expansion of an aluminum alloy
is smaller than that of plastic. A good bonding of the cooling plastic to the
l o layer can nevertheless be maintained by means of the adhesion primer. A
foamed inner layer is preferably used, having a degree of foaming which
increases toward the middle axis, so that elastic displacements are possible
which in addition contribute to the bond's not becoming loosened.
The process according to the invention for the production of such
is structural members has the advantage that a continuous production of
structural members is made possible in a simple manner. In this process,
the materials required for the whole structural member for the formation of
the individual layers of the sandwich structure can be supplied and
processed simultaneously, or nearly simultaneously, through a coextrusion
2o nozzle. The layers are then fed as a composite to a gauging step. The
6
CA 02258255 2006-02-09
layers which are mutually spaced apart and are separated by an inner layer can
be
drawn from a coil of sheet metal and supplied to an upper side and a lower
side of the
inner layer. Furthermore, an outer layer can be simultaneously applied to the
layers by
means of the coextrusion nozzle. The coextrusion nozzle can be followed at a
short
distance by a gauging step. It is thereby possible for the inner layer, which
can have a
high foaming fraction of at least 30%, to be supplied directly to the gauging
step. The
foaming process thus takes place exclusively in the gauging step. The two
layers, seen
from a longitudinal middle axis, can be pressed into an upper and a lower edge
region
by the inner layer in the course of foaming, so that the intersection points
of the layers
with the system plane can be spaced mutually far apart.
In a broad aspect, then, the present invention relates to an elongate
structural
member with at least one system plane along which the structural member has
substantially homogenous properties and is substantially homogeneously
constructed,
comprising: at least one inner layer of plastic along the system plane, a
respective
outer layer of plastic along the system plane, and at least two respective
layers of a
material of a substantially higher modulus of elasticity than plastic
traversing the
system plane and located within the structural member between the inner layer
and the
outer layer and arranged separate from each other and not connected by a
middle
region of the same material as said at least respective layer.
In another broad aspect, then, the present invention relates to a process for
production of elongate structural member having at least one system plane
along
which the structural member has substantially homogeneous properties and is
substantially homogeneously constructed, with at least one inner layer of
plastic along
the system plane, a respective outer layer of plastic along the system plane,
and at least
two respective layers of a material of a substantially higher modulus of
elasticity than
plastic traversing the system plane and located within the structural member
between
the inner layer and the outer layer and arranged separate from each other and
not
connected by a middle region of the same material of said at least respective
layer,
comprising the following steps: a) supplying an unfoamed inner layer from an
extruder
to a coextrusion nozzle, b) supplying by means of the coextrusion nozzle a
respective
7
CA 02258255 2006-02-09
layer of substantially higher modulus of elasticity taken off from a
respective sheet
metal coil to an upper side and a lower side of the inner layer, c) applying a
respective
outer layer by means of the coextrusion nozzle to the layers of substantially
higher
modulus of elasticity, d) supplying a multilayer composite emerging from the
coextrusion nozzle to a gauging, e) withdrawing the multilayer composite from
the
gauging after the inner layer has foamed, and cutting the multilayer composite
into
structural members.
Further advantageous embodiments and developments are given in the further
claims of the description hereinafter and in the accompanying drawings.
The invention is now described with reference to preferred embodiments. In the
drawings:
Fig. 1 shows a schematic cross section through a plate-shaped structural
member,
Fig. 2 shows a schematic cross section through an I-beam,
7a
CA 02258255 1998-12-21
Fig. 3 shows a schematic cross section through an angle profile,
Fig. 4 shows a schematic cross section through a '1'-profile,
Fig. 5 shows the course of a curve over the cross section which
qualitatively indicates the ratio of plastic material to cavities, and
Fig. 6 shows a schematic diagram of a plant for carrying out the
process and for the production of a structural member according to the
invention.
A cross section through a plate-shaped structural member 11 is
shown in Fig. 1. These structural members 11 can have a thickness of 12-23
i o mm, for use in the building industry. The length and width can be
provided in dependence on the case of application; preferably, a width of
1-2 m and a length of 2.5-6 m is provided.
The structural member 11 has a system plane 12 which corresponds
to a principal axis of the plate-shaped structural member 11. An inner
layer 13 or a core layer of the plate-shaped structural member 11 consists of
a plastic, which can have a modulus of elasticity corresponding to the
application. A foamed plastic is advantageously provided, having a degree
of foaming between 20% and 60%. The inner layer 13 is preferably made of
a relatively inexpensive material, for example, polypropylene which has
ao been recycled. The inner layer 13 can additionally be filled with materials
8
CA 02258255 1998-12-21
which increase the strength. These can for example be talc and/or glass
fibers. Talc has the advantage over glass fibers that it reacts isotropically,
in contrast to which glass fibers have a preferential direction during
heating, which can be disadvantageous in some cases.
s The inner layer 13 of the structural member 11 is bounded by an
upper layer 14 and a lower layer 15. The layers 14, 7 5 extend substantially
completely over the whole width of the structural member 11 and traverse
the system plane 12 at an intersection point 16 and 17. The layers 14, 15 are
constructed of a light metal, in particular, aluminum or an aluminum alloy
io such as, for example, AIMgSio.S. Alternatively, other light metal materials
or metals, can be used. Furthermore, woven fabrics, mattings, or knitted
fabrics can be provided, which are worked in depending upon direction
corresponding to the principal direction of loading. 'the layers 14, 15 are
made planar and extend substantially completely over the whole width of
is the plate-shaped structural member 11. Alternatively, it can be provided
that a perforated and/or corrugated and/or trapezoidal and the like
shaped layer, or if necessary a layer constructed as a hollow profile, is
inserted.
The layers 14, 15 are constructed as foils or metal sheets, and have a
a o thickness of 0.25-3 mm, in dependence on the distance between them and
a
CA 02258255 1998-12-21
the forces to be taken up, and also in dependence on the material used for
the inner layer 13. In order to attain a composite action with the plastic
materials, it is required that the layers 14, 15 are relatively thin. This has
the advantage that the structural member 11 is easily nailed and/or sawn,
s in particular when a layer of light metal is used.
An outer layer 18, which likewise consists of plastic, is provided on
the layers 14, 15. The same plastic as for the inner layer 13 can be used for
this outer layer 18. An unfoamed plastic is preferably used for the outer
layer 19, and is, for example, a polyamide and/or polypropylene. The
io outer layer is filled with glass fibers; in a proportion of 20-40% of glass
fibers. An outer layer 18 can thereby be created which has a high modulus
of elasticity in comparison with the inner layer. In order to be suitable for
building sites, the outer layer 18 is constructed as a high strength layer.
Additives can be incorporated into this outer layer 18, in order to make the
15 outer layer 18 weather resistant and/or UV resistant and/or impact
resistant. The abrasion resistant outer layer 18 has a thickness of about 1-2
mm. It is basically provided that the thickness of the outer layer 18 makes
up about 10% of the total thickness of the structural member 11.
According to the embodiment shown in Fig. 1, a slip layer 19 is
ao applied to the outer layer 18. The object of this is substantially that
smaller
io
CA 02258255 1998-12-21
forces are required in order to forward the structural member out of a
gauging step during the continuous production of the plate-shaped
structural member 11. A thermoplastic material, for example,
polypropylene with additives, which has good sliding properties, is used
s for the slip layer 19. Furthermore, cement rejecting or UV resistant or
weather resistant additives can be included. A slip layer 19 having a layer
thickness of 0.1-0.2 mm is sufficiently thick.
The side faces 21., 22 of the structural member 11 can be constructed
as open, in contrast to wood. The layers 14, 15 can extend as far as the side
io faces 21, 22 or be arranged at a small distance from the side faces. The
plastics used take up substantially no water, and also no water can
penetrate between the individual layers 13, 14, 15, 18, 19. Thus a further
work step, and thus costs, to close the side faces can be saved.
By means of a sandwich construction for a plate-shaped structural
15 member 11 according to Fig. 1, an increase of the modulus of elasticity by
a
factor of at least 1.5 is made possible, in comparison with the plate-shaped
structural members known from the state of the art with a trapezoidal
layer. The known plate-shaped structural member with a trapezoidal
aluminum layer known from DE 41 37 649 A1 has, for example, a modulus
a 0 of elasticity of the member of about 2,200 N/ mm'-. Using the same
m
CA 02258255 1998-12-21
materials, a modulus of elasticity of the member of about 3,500 N/mmz can
be attained by means of the embodiment of the plate-shaped structural
member 11 with an aluminum sheet which has a hole proportion of about
40%, and a modulus of elasticity of the member of about 5,000 N/mm2 with
s an unperforatecl aluminum sheet. This rise of the modulus of elasticity is
substantially based on the layers 14, 15 having a adhesion primer layer on
both sides, so that in the ideal case the materials of the inner Layer 13 and
the outer layer 18 can become bonded together as one. An increase of the
stiffness of the plate-shaped element 11 under the action of a bending force
to or shearing stress can thereby be given. The layers 14, 15 then do not act,
as was at first assumed, as loose layers ~~hich are arranged one above the
other and would thus exclude a mutual effect. It has surprisingly been
found that the foamed plastic of the inner layer 13 and also the outer layer
18, in conjunction with the primer, have a high adhesion to the layers 14,
1 s 15, and higher bending stiffness than in the state of the art, given by
the
modulus of elasticity multiplied by the geometrical moment of inertia, can
be attained.
In the embodiment of a plate-shaped structural member 11, attention
has to be paid to the proportionality of the thicknesses of the individual
20 layers 13, 14, 15, 18, 19 and also the selection of materials for the
respective
12
CA 02258255 1998-12-21
layers 13, 14, 15, 18, 19. With an overstressing of the structural member 11,
two effects can arise: firstly, the outer layer can first tear, and this can
then
lead to breakage of the layers 14, 15, until there is a complete break of the
plate-shaped element. Secondly, the core layer can first fail because the
s shear stress was too great and the shear strength was not sufficiently
large,
so that a break of the plate element can likewise occur.
In the first case, this means that the outer layer 18 can no longer take
up the outer fiber extension, which thereby suggests that the outer layer 18
ought to be made more elastic or thicker. Furthermore, to prevent this
io case, the measure was taken that the layers 14, 15 become thicker and the
member stiff, so that the outer fiber extension becomes reduced.
In the second ease, the thickness of the inner layer 13 can be
increased, or another plastic with higher strength properties can be
selected. It can furthermore be provided that in order to increase the
15 stiffness of the inner layer 13, the foam fraction is reduced and the talc
and/or glass fiber fraction is increased.
The matching of the materials to each other is evident from the above-
mentioned cases. For example, the ratio between the first, higher modulus
of elasticity and the second, lower one can be 3-5:1, where the lower
2o modulus of elasticity can be in the region of 600-1,200 N/mm'-. Further
13
CA 02258255 1998-12-21
larger and smaller ratios can also be in dependence on the primer.
A preferred embodiment for a structural member with a plate
thickness of 20 mm has an inner layer of foamed polypropylene, 17 mm
thick, with a 20-40% fraction of talc. The layer 14, 15 consists of a foil,
0.3
s mm thick, of an aluminum alloy AIMgSin. ~ with adhesion primer on both
sides. The outer layer 18 is an unfoamed 1'T' with a 30-40% glass fiber
fraction, and is 1 mm thick, finished with a slip layer 19, 0.1 mm thick.
An I-beam 23 is shown in Fig. 2, and has a structure along the system
plane 12 analogous to that of the plate-shaped structural member 11. The
layers 14, 15, with their points of intersection 16, 17, are spaced apart as
far
as possible, so that the layers 14, 15 with a higher modulus of elasticity are
as near as possible to the edge region of a transverse web 24 and 26, in
order to make possible the greatest possible influence on the outer fiber
extension during bending. The layers 14, 15 measure about 1 mm in this
is embodiment. Specifically to the application, it can be possible for one of
the layers 14, 15 to be made thicker than the other. Such an I-beam would
then be arranged such that the transverse web 26 with the thicker layer 15
would have to take up the maximum outer fiber extension. In the side
surfaces of the transverse webs 24, 26 and in the middle web 27, the inner
2 0 layer 13 and the outer layer 18, and also the slip layer 19, are situated
14
CA 02258255 1998-12-21
immediately adjacent. The I-beam 23 can thereby have an all-around wear
resistant layer and can be made suitable for a building site.
For example, with an embodiment of an I-beam 23 with a layer 14, 15
of, for example, 1 mm and an inner layer 13 which can take up a shear
stress of about 2.5 N/mm2, according to the equation by which the shear
stress is equal to the quotient of the lateral force and the surface area of
the
middle region or web, the middle region would have to have a width of 50
mm, the height of the I-beam 23 being 160 mm, in order to be able to take
up a lateral force of 20 kN.
to As for the rest, the alternative embodiments or their optional
combinations set out for the structural member 11 also hold for the I-beam
23, and vice versa.
Fig. 3 shows an angle profile 31 which is constructed to be
substantially symmetrical to the system plane 12. The layers 14, 15 run
i 5 substantially parallel to the outer surfaces 32, 33 and are arranged near
to
the outer surfaces 32, 33.
Fig. 4 shows a T-beam, which has a structure analogous to that of the
structural member 11 along the system plane 12. It can advantageously be
provided for the T-beam 41 that the layer 15 is thicker than the layer 14, in
20 order to be able, because of the smaller width which the free end of the
CA 02258255 1998-12-21
vertical web has, to better take up the bending which arises. The layer 15
can, for example, be made twice as thick as the layer 14. This cn~ill
substantially be the case when the layer 14 and the layer 15 are made of the
same material. The layers 14, 15 can also be of ecfual thickness, and
s different materials can then be used, so that, for example, the layer 14 is
made of an aluminum alloy and the layer 15 of sheet steel or the like. The
thickness dimensions can thereby be matched in dependence on the elastic
moduli.
The use of different materials and substantially equal thicknesses, or
to of the same materials and different thicknesses, can also be provided in
all
the other embodiments.
A diagram along the system plane is shown in Fig. 5. The outer
surfaces 18, 19 have.a density of respectively 100%. The inner layer 13 is
foamed, that is, in the middle region with a 60% foam content, a 40%
15 content of material is present. The foam content continuously decreases
toward the layers 14, 7 5, and there is practically no foam content near the
layers 14, 15, so that there can be an optimum bonding to the layers 14, 15.
Such a structure or course of the density can basically be provided for
any shape of structural member and can have the advantageous properties
ao such as, for example, that a structural member of good flexural strength
16
CA 02258255 1998-12-21
can be provided by means of a small structural member volume and by the
use of inexpensive materials, and is constructed to be weather resistant, UV
resistant and impact resistant, and can furthermore be used for building
operations, in which it is distinguished by being easily nailed and sawn
s because of the relatively thin layers 14, 15.
A plant is shown in Fig. 6 for carrying out a process which is
provided for the production of the structural members 11, 23, 31, 41. The
production of the different structural members 11, 23, 31, 41 is described
using the plate-shaped structural member 11 as an example.
i o Various kinds of plastic granules, fillers and further additives which
are required for the production of the plate-shaped element 11 are made
available in bins 62. For example, polypropylene can be provided in a first
bin 62, polyamide in a second bin 62, and glass fibers in a third bin 62. For
the production of the inner layer 13, polypropylene and also an additive for
i s foaming are supplied via supply ducts 64 from the bins 62 to a double
screw extruder 63. The individual components are homogenized in the
double screw extruder 63 and are fed via a melt pump 65 to a coextrusion
nozzle 66. A coil 67 with a takeoff device 68 is arranged respectively above
and below the coextrusion nozzle 66. The layers 14, 15, which for example
a o are made from an aluminum foil, 0.3 mm thick, are taken off from the coils
17
CA 02258255 1998-12-21
67 and fed to the coextrusion nozzle 66. The aluminum foils 14, 15, stored
beforehand on respective coils 67, are provided on both sides with a
adhesion primer so that an optimum adhesion of the inner layer 13 and the
outer layer 18 to the aluminum foil 14, 15 is made possible. These layers
s 14, 15 can also be sprayed with primer, and if necessary dried, directly
after
takeoff from the coil 67.
An extruder 69 follows the supply of the aluminum foil 14, 15, and is
supplied with, for example, polyamide and/or polypropylene and glass
fiber from the bins 62. The homogenized mass for the outer layer 18 can be
io supplied by means of this extruder 69 to the coexhwsion nozzle 66.
Furthermore, a slip layer extruder 71 can be provided, following the supply
of the outer layer 18, in order to be able to apply the slip layer 19 to the
outer layer 18.
A 5-layer plate with a sandwich structure can be produced in one
is operation by means of the coextrusion nozzle 66, which is provided for a
plate thickness of 20 mm, for example. 'The coextrusion nozzle is followed
by a gauging step 72. 'The path between the outlet of the coextrusion
nozzle 66 and the beginning of the gauging step 72 is made short, since the
inner layer is provided with a blowing agent for foaming the
ao polypropylene. This blowing agent has the effect that the layers 14, 15
as
CA 02258255 1998-12-21
which bound the inner layer 13 are substantially uniformly pushed apart
during the passage through the gauging path. It can thereby be attained
that the layers 14, 15 run substantially parallel to each other. Furthermore
it can be attained by means of the increased pressure that the outer layers
s 18 have a nearly 100% density. The force acting on the outer layers 18, 19
furthermore has the advantage that a substantially closec.l outer layer can
be produced, which is known as a so-called "bacon layer".
Due to the application of the slip layer 19, the structural member 11
can pass through the gauging step 72 with little friction and can more
to easily be withdrawn from the gauging step 72 with a takeoff device 73. The
gauging step 72 is constructed such that the gauging path is sufficient for
the structural member 11 leaving the gauging step 72 to have a completely
foamed inner layer 13. The continuously produced structural member 11
can be cut into the desired plate sizes by means of a saw device 74 which
15 travels corresponding to the production or extrusion speed, and can be
made ready for transportation or storage, by a stacking device 76.
Such a plant 61 can have a production speed of 0.5-1 m/min. A
relatively simple bringing together of the individual components for a
composite structure of the structural member 11 can be given by the
ao embodiment according to the invention of the structural member 11 with
19
CA 02258255 1998-12-21
two layers 14, 15 running substantially parallel to the inner layer 13 and the
outer layers 18, 19, and furthermore the structural member 11 also has a
higher bending stiffness. This process can likewise be used for the
structural members 23, 31, 41 described in Figs. 2-4, and also for other
s shapes of structural members.
A sinter press process can also be provided for the production of
structural members 11, particularly plate-shaped structural members. In
this process, the individual layers are successively placed one on the other
and then caused to bond together by heat and pressure. High
i o temperatures and pressures are necessary for this, so that no
inhomogeneities arise which could act as fracture loci. Because of the
discontinuous production and the high pressures, this process is preferably
used for special shapes with low numbers of pieces.
The structural member 11 can advantageously have a prestress so
i 5 that there is an increased ability to take up forces or loads in a given
built-
in position. This prestress is advantageously applied during the extrusion
process. After the sandwich structure of the element has been completely
extruded, a gauging follows by means of a calendering technique or the
like, the gauging step being placed immediately following the extruder
2 o nozzle so that the still heated plastic can be processed. The extruded
plate
CA 02258255 1998-12-21
can also be taken off over a large radius in order to apply the prestress.
The prestress is advantageously provided such that the neutral fiber of the
structural member lies nearly in a flat plane in the case of controlled
loading.
s It can alternatively be provided that the structural members can be
produced by means of a pressing technique. In this technique, the layers of
higher elasticity, such as for example a layer of an aluminum or titanium
alloy, are preshaped, preferably plastically, are placed in, and then have
plastic extruded around them. Alternatively, the pre-shaping can take
io place by means of a corresponding tool construction and its control.
o.
