Note: Descriptions are shown in the official language in which they were submitted.
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STRUCTURAL SLIDING BEARING AND DIMENSIONING METHOD
The invention relates to a structural sliding bearing having at least one
first
bearing part to which at least one sliding element is attached and a second
bearing part displaceable arranged relative thereto and which in combination
with a contact surface of the sliding element forms a sliding surface that
allows sliding movements between the two bearing parts. The invention
further relates to a method for dimensioning a structural sliding bearing.
Structural sliding bearings are a special design of a structural bearing.
Structural bearings, also called bearings in the building industry, generally
are for the defined support of any structures such as bridges, girders,
buildings, towers, or parts thereof, if possible without constraints. That is,
they allow relative movements between two components of the concerned
structure. In accordance with the European rule EN 1337 various designs
and operations are known. Depending on the design and operation the
structural bearings have a different construction and a different number of
degrees of freedom.
Structural sliding bearings, in the following briefly also referred to as
sliding
bearings, have at least one first bearing part to which at least one sliding
element is attached and a second bearing part that is arranged displaceable
relative thereto. The second bearing part in combination with the contact
surface of the sliding element of the first bearing part forms a sliding
surface
allowing sliding movements between the two bearing parts.
Typically, the sliding element is made of a sliding material. As the sliding
material various plastics having low friction such as for example PTFE,
UHMWPE, or polyamide are used. Also, composite materials such as CM1
and CM2 given in EN 1337-2 are employed.
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In order that the desired properties regarding sliding behavior, durability
etc.
are achieved in the whole sliding surface the surface of the second bearing
part typically has a special surface coating, such as for example a hard-
chrome plating, if it directly interacts with the sliding element. However,
the
second bearing part may also indirectly interact with the sliding element in
that it additionally has a mating sliding element. This may be a so-called
sliding plate, e.g. made of an austenitic steel sheet, that has been applied
to
the second bearing part and that in its turn has a defined surface quality.
EN 1337 contains regulations how to realize the sliding element, the optional
mating sliding element as well as the associated mounting elements and
bearing parts. There is aimed a sliding resistance as low as possible upon a
relative displacement or twisting of the structure or parts of the structure
separated by the sliding bearing. However, for dimensioning the sliding
bearing as well as the structure generally an upper dimensioning value of
the coefficient of friction is used to be on the safe side. Here, the sliding
resistance is defined via the coefficient of friction. The coefficient of
friction
is the quotient from the force required for the movement toward the sliding
movement and the force acting in a right angle to the sliding surface.
In addition to the movable support of structures sliding bearings for some
time are also used to separate structures or parts thereof from further
surrounding structures and/or from the ground. The aim of such a separation
may be for example to prevent structural damages due to earthquakes. A
particular design of such a sliding bearing for separation is the so-called
sliding isolation pendulum bearing. In this, at least one sliding surface is
curved. The curvature of the sliding surface results in that at horizontal
deviation re-centering forces are generated. Regulations for such bearings
are given for example in the European rule EN 15129.
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If in such an application not only the movement of the structure should be
made possible, but also energy generated by the earthquake should be
dissipated, then a certain numerically defined friction behavior in the
sliding
surface is required. In sliding bearings dissipation of energy may take place
in the sliding surface by the friction between the bearing parts that occurs
upon movement. In addition to the desired effect of energy dissipation at the
same time the friction causes that reaction forces are applied to the
structure. With increasing friction, both reaction forces and dissipated
energy
increase. Since on the one hand high reaction forces are to be avoided, but
on the other hand it is desired to eliminate a large amount of energy, a
structure-related optimum has to be sought between the reverse effects.
A decisive parameter for the friction between two moving objects is, as
mentioned, the friction coefficient. According to the current state of the
art,
the friction coefficient is substantially controlled by the choice of the
sliding
and mating material, the type of lubrication of the sliding surface as well as
the contact pressure.
It is a problem with the prior art sliding bearings that depending on the
desired purpose and minimum or maximum friction desired or required
therefor the sliding bearing has to be individually designed for the
respective
purpose. Against the background of the partially reverse design objectives it
is not easy to dimension and adapt the bearings. So, for example there have
already been attempts with sliding isolation pendulum bearings in which a
first lubricated sliding material was used in a first sliding surface and an
unlubricated second sliding material in a second sliding surface. The first
sliding material is to ensure the movement of the bearing parts during
normal usage if possible without constraints, that is, to generate a low
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friction. The second sliding material is for providing a high energy
dissipation
in case of an earthquake, that is, should have a great friction.
However, coordination of the sliding properties and the use of different
sliding materials is not trivial. On the one hand, EN 1337-2 only provides
guidelines for the use of PTFE that has to be lubricated in certain manner. If
one wants to use another sliding material or modify the lubrication special
tests for suitability have to be performed that are very complex and
expensive. Also, the use of different sliding materials, lubrications, surface
qualities etc. in the manufacture is extremely complex.
Thus, it is the object of the present invention to provide a structural
sliding
bearing that is easily adaptable in view of its frictional properties and can
be
manufactured as simple and economical as possible.
The solution of said problem according to the invention is achieved with the
structural sliding bearing invention wherein the structural sliding bearing
has
at least one first bearing part to which at least one sliding element is
attached and a second bearing part that is arranged displaceable relative
thereto and which in combination with a contact surface (AK) of the sliding
element forms a sliding surface allowing sliding movements between the two
bearing parts, characterized in that the contact surface (AK) is subdivided
into several partial contact surfaces and that the shape of the contact
surface (AK) of the sliding element is designed such that a desired friction
coefficient (Y) is established in the sliding surface, wherein the friction
coefficient (Y) in the sliding surface is adjusted as function of a form
factor
(S) considering the ratio of contact surface (AK) to the free circumferential
surface (Am) of the sliding element .
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The solution of said problem according to the invention is further achieved
with a method for dimensioning a structural sliding bearing characterized in
that the friction coefficient (Y) in the sliding surface is adjusted by
considering a form factor (S), wherein the friction coefficient (Y) in the
sliding surface is adjusted as function of a form factor (S) considering the
ratio of contact surface (AK) to the free circumferential surface (AM) of the
sliding element .
That is, the structural sliding bearing according to the invention is
characterized in that the shape of the contact surface of the sliding element
is configured such that a desired friction coefficient is established in the
sliding surface. The invention is based on the finding that the friction
coefficient with the same sliding material changes with the shape of the
contact surface of the sliding element and this behavior can be used to
specifically adjust the friction coefficient and thus, also the friction of
the
structural sliding bearing. That is, the frictional behavior of the sliding
bearing not as previously common is adjusted by the choice of the sliding
and mating material, the way of lubricating the sliding surface as well as the
contact pressure. Rather, by specifically shaping the contact surface of the
sliding element the friction coefficient is influenced in the desired manner
and thus, by a further decisive parameter. Tests of the applicant have shown
that in structural sliding bearings different deformation behaviors of the
sliding material in the center of the contact surface and at the edge of the
contact surface adjust the sliding resistance and this effect can be
specifically used to adjust a desired frictional behavior in the sliding
surface.
In a suitable further development of the structural sliding bearing the
desired
friction coefficient in the sliding surface is adjusted depending on the
circumferential length and/or the ground plan type of the contact surface
and/or the sliding slit height and/or the orientation of the edges of the
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contact surface with respect to the sliding direction. So, it is conceivable
that
edges extending in parallel to the sliding direction have a minor influence on
the friction coefficient than edges that orthogonally extend to the friction
direction. Accordingly, a defined orientation of the free circumferential
surface toward the various degrees of freedom of the structural sliding
bearing causes that different friction coefficients and thus, friction
resistances are present toward the various degrees of freedom. Moreover, it
is conceivable to represent the influence of the individual shaping of the
sliding surface ground plan on the friction coefficient via a shape
coefficient.
Here, it may be relevant whether the sliding surface ground plan rather has
chubby outline edges or sharp corners as well as the respective number of
edges as well as their distance and orientation to the sliding surface center
of gravity. Also, the sliding slit height may be used to influence the
friction
coefficient in the sliding surface. So, for example it is conceivable that for
large sliding slits due to the flow of the sliding material at the edge of the
sliding surface the friction coefficient decreases, but also with very low
sliding slits the effect of an influence of the friction coefficient is only
partially established. Accordingly, depending on the desired effect on the
friction coefficient an optimum sliding slit height may exist.
Since sliding elements of structural sliding bearings cannot be of any desired
shape it is possible to adjust the friction coefficient by designing the shape
of the sliding element especially by adjusting the ratio of contact surface to
free circumferential surface. Here, free circumferential surface means the
surface that can freely deform in the sliding slit between the first bearing
part
and the second bearing part at the circumferential side of the sliding
element, that is exposed. In the case of an embedded support of a sliding
disc that fits completely flat to the opposite side this is the circumference
multiplied with the height of the sliding disc minus the depth of the
embedding. Contact surface means the proportion of the surface of the
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sliding element that totally contacts the second bearing part. If the free
circumferential surface is decreased at constant contact surface by
increasing the circumference of the contact surface at constant height of the
sliding slit, then the friction increases.
By specifically influence of the frictional behavior of the sliding bearing by
shaping the sliding element the sliding bearing can very easy be adapted to
different problems and application purposes. And this without complex tests
for suitability or having to request special approvals. Rather, this way
different problems can be solved with one and the same sliding material for
which for example an approval as sliding material has already been
achieved. So, on the one hand it is possible to construct normal sliding
bearings with the material or an earthquake isolator that in comparison
should have an increased friction in the concerned sliding surface by
increasing the proportion of the circumferential surface of the sliding
element. Moreover, the invention has the effect that in manufacture there
must no longer be stored different materials. This reduces the storage costs,
prevents confusion of bearings in manufacture, and brings advantages in
purchasing. That is, the bearing according to the invention can be prepared
considerably easier and more cost-effectively.
An advantageous further development of the invention provides that the
friction coefficient in the sliding surface is adjusted as function of a form
factor considering the ratio of contact surface to free circumferential
surface
of the sliding element. Here, the form factor is a quotient of the contact
surface to the free circumferential surface, wherein, as already mentioned,
the free circumferential surface is the length of the circumference of the
contact surface multiplied with the height of the sliding slit. Suitably, the
size
of the contact surface of the sliding element has been optimized depending
on the form factor, preferably minimized, such that the desired friction
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coefficient in the sliding surface is achieved without a change of the
pressure. In this way, the structural sliding bearings for the respective
application purpose may be made smaller and thus, more economical.
In particular, if the sliding bearing is intended for use in earthquake
isolation
it is suitable to shape the sliding element such that the amount of the
friction
coefficient in the sliding surface has been maximized depending on the form
factor. Thus, for practical application that means that by increasing the free
circumferential surface at the same contact surface for the structural sliding
bearing a greatest possible friction coefficient and thus, also a greatest
possible dissipation capacity can be achieved. For example, the increase of
the free circumferential surface can be done by changing the shape of the
contact surface. For example, the contact surface may have an oval or star-
shaped shape or any other conceivable shape that results in a larger free
circumferential surface.
Preferably, in such applications the structural sliding bearing is designed as
a spherical bearing, in particular as a sliding isolation pendulum bearing.
Typical of spherical bearings is that they have at least one curved sliding
surface, whereas sliding isolation pendulum bearings have several curved
sliding surfaces. So, it is conceivable that the friction coefficient in
different
sliding surfaces is specifically adjusted differently, but consisting of the
same sliding material as described above. So, one sliding surface may be
designed for normal use as a conventional sliding bearing with low friction,
whereas a second sliding surface especially in view of an earthquake is
designed with an increased friction coefficient, that is, an increased
dissipation capacity.
In a further development the contact surface of the sliding element is formed
of two, in particular more than four partial contact surfaces. Subdivision of
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the contact surface into partial contact surfaces causes an increase of the
free circumferential surface of the sliding element. Such a subdivision can
be effected by several sliding elements or by notching or the like. Here,
subdivision facilitates fabrication since it can be easily generated and needs
to be changed little on the basic geometry of the sliding element or its
initial
materials (often plates of a certain thickness made of a sliding material).
An advantageous further development of the structural sliding bearing
provides that the sliding element has at least one sliding disc with the
contact surface being formed of at least a part of the surface of the at least
one sliding disc. The sliding element also has a conventional sliding disc
known per se or may even completely consist thereof.
In this case it is suitable if at least a part of the surface of the at least
one
sliding disc by at least one recess is subdivided into partial contact
surfaces.
So, friction can be increased in comparison to a conventional sliding disc of
the same material. For example, such a recess may be one or more grooves
that are applied to a part of the surface of the at least one sliding disc.
Applying said one or more grooves can be effected for example by milling
into a part of the surface of the at least one sliding disc.
Applying recesses to the sliding material is a particularly economical method
to generate partial contact surfaces. Generally, the width of the recess is
between a few millimeters and twice the thickness of the first bearing part to
ensure on the one hand a sufficient support of the sliding material and on
the other hand uniformly distribute the pressure in the adjacent components.
Subdividing at least a part of the surface of the at least one sliding disc in
turn causes that the free circumferential surface of the sliding element
increases relative to the contact surface and thus, the form factor is
affected.
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Basically, the at least one recess may be of any desired shape to produce
arbitrary partial contact surfaces. However, preferably the recess is
designed such that it is oblong or has the shape of a circle, ring, or a
segment of any of them. For that, fabrication methods such as turning or
milling due to their high flexibility are suitable. However, alternatively the
recess may also already be prepared in the manufacture of the sliding
element, for example when casting or sinter-pressing into plate shape.
In particular, if the sliding bearing or the sliding material of the sliding
disc,
respectively, is exposed to high pressures it is suitable that at least one
spacer is inserted into at least one recess. Inserting a spacer into the
recess
ensures that the sliding material of the sliding disc at the edge of the
partial
contact surfaces cannot laterally swerve under the load. In analogy to the
embedded support of the sliding element in the first bearing part the sliding
disc is embedded to the inside. By the inner embedding at the same load the
sliding discs and the structural sliding bearing may be made smaller or with
the same size of the sliding disc higher loads can be taken up with the
structural sliding bearing.
In an advantageous further development of the structural sliding bearing the
sliding element has a number of sliding discs. In this way, on the one hand
the sliding element can be composed of equally and/or differently shaped
sliding discs and on the other side also the sliding element can be variably
constructed from different sliding materials by using sliding discs. Further,
it
also becomes possible to compose large and/or individually shaped sliding
elements from a number of standardized sliding discs, whereby the
production of the structural sliding bearing according to the invention
becomes particularly economical.
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Preferably, the contact surface and/or at least a partial contact surface have
the shape of a circle, ring, or a segment of any of them. Said shaping has
the advantage that only a few or no corners are formed that would result in a
selective increase of the friction. That is, said shaping helps to keep wear
low.
An advantageous further development of the structural sliding bearing
provides that the sliding element and/or at least one sliding disc of the
sliding element is held embedded in the first bearing part. By the embedded
holding of the sliding element or the at least one sliding disc flowing of the
sliding material due to the pressure generated from structural loads is
reduced. Moreover, the type of embedding has influence on the size of the
free circumferential surface, since this depends on the height of the sliding
slit, in other words the height of the projection of the sliding element above
the first bearing part.
If needed it may be suitable that at least one spacer is arranged between
two sliding discs. Generally, said spacer has a width between a few
millimeters and twice the thickness of the first bearing part. In this way, it
is
ensured that on the one hand a sufficient support or inner embedding of the
sliding material against flowing is guaranteed. On the other hand, it is
ensured that the pressure is uniformly distributed in the adjacent
components.
Preferably, the sliding element and/or at least one sliding disc at least
partially consists of a sliding material, in particular a thermoplastic
sliding
material. Thermoplastic materials can be readily poured into molds that may
already have webs to produce recesses for subdivision into partial contact
surfaces, for example.
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Particularly preferably, the sliding element and/or at least one sliding disc
at
least partially consists of PTFE, UHMWPE, polyamide, and/or a combination
of at least two of such materials. Here, both the sliding element and the at
least one sliding disc may consist of the mentioned materials in the pure
form or alternatively of a material mixture of two or more of such materials.
It
is also conceivable that several sliding discs of different of such materials
in
the pure form and/or different mixtures of such materials are composed to a
sliding element.
The method for dimensioning a structural sliding bearing according to the
invention provides that the friction coefficient in the sliding surface is
adjusted by considering a form factor. Unlike in the prior art, where the
friction coefficient and thus, also the friction of the structural sliding
bearing
are influenced by the choice of the sliding and mating material, the type of
lubrication of the sliding surface as well as the contact pressure, the
approach according to the invention is based on the fact that the friction is
specifically adjusted by affecting the shape of the contact surface, that is
not
by affecting material or unit stresses but by affecting geometrical
parameters. Accordingly, by shaping the contact surface of the sliding
element the friction coefficient can be affected in a surprisingly simple and
highly flexible manner.
Preferably, dimensioning of the structural sliding bearing is performed in
that
the desired friction coefficient in the sliding surface is adjusted depending
on
the circumferential length and/or the ground plan type of the contact surface
and/or the sliding slit height and/or the orientation of the edges of the
contact surface with respect to the sliding direction. For calculating the
friction coefficient it is conceivable that in the calculation methodology of
the
friction coefficient the influence from the circumferential length, ground
plan
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type of the contact surface, sliding slit height and orientation of the edges
to
the direction of displacement via individual coefficients is considered.
An advantageous further development of the method according to the
invention provides that the friction coefficient in the sliding surface is
adjusted as function of a form factor considering the ratio of contact surface
to free circumferential surface of the sliding element. As already mentioned
above, the form factor is a quotient of the contact surface to the free
circumferential surface.
In a further development, the size of the contact surface of the sliding
element is optimized, preferably minimized, depending on the form factor
such that the desired friction coefficient in the sliding surface is achieved.
In
this way, the structural sliding bearings for the respective application
purpose may be made smaller and simultaneously more economical.
Alternatively or additionally, the amount of the friction coefficient in the
sliding surface may be maximized depending on the form factor. This
especially makes sense if the bearing has to be designed for earthquake
isolation.
Preferably, dimensioning is performed such that the material combination in
the sliding surface is kept constant during optimization. This allows a
simplified dimensioning of the sliding bearing.
In the following the invention is explained in detail with the help of the
drawings. Here:
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Fig. 1 schematically shows a section through a first example of a
structural sliding bearing according to the invention with a flat
sliding surface;
Fig. 2 schematically shows a detail from a section through a second
example of a sliding bearing according to the invention with a
curved sliding surface;
Fig. 3 schematically shows a detail from a section through a third
example of a sliding bearing according to the invention;
Fig. 4 schematically shows a detail from a section through a fourth
example of a sliding bearing according to the invention;
Fig. 5 schematically shows a section through a fifth example
designed as
a sliding isolation pendulum bearing of a sliding bearing according
to the invention;
Fig. 6 schematically shows a section A-A of the sliding isolation
pendulum bearing shown in Fig. 5;
Fig. 7 schematically shows the top plan view of the contact surface
of a
sliding disc in a sixth embodiment;
Fig. 8 schematically shows the top plan view of the contact surface
of a
sliding disc in a seventh embodiment;
Fig. 9 schematically shows a measuring chart illustrating the friction
coefficient Y as a function of pressure X; and
Fig. 10 schematically shows a measuring chart illustrating the
friction
coefficient Y as a function of the product of form factor and
pressure.
In the figures same reference numbers are used for identical parts.
Fig. 1 shows a first example of a structural sliding bearing 10 according to
the invention. As to construction it basically corresponds to the structural
sliding bearings described in EN 1337. It has a first bearing part 15, a
sliding
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element 20 attached thereto and a second bearing part 25. The second
bearing part 25 in turn has a mating surface 55 that in the present case is
designed as a hard chromium coating, but may also consist of a sliding plate
of austenitic steel or the like. The first bearing part 15 and the second
bearing part 25 are designed displaceable relative to each other, so that a
sliding surface 30 is formed from the combination of the present flat surfaces
of the sliding element 20 and the mating surface 55. In the present case, the
sliding element 20 consists of a flat sliding disc made of a sliding material
and is held in the first bearing part 15 by means of embedding. However,
additionally according to the invention the geometry of the sliding plate 20
in
the ground plan here not illustrated is star-shaped, so that a relative large
circumferential surface with respect to the contact surface is established,
whereby an increased friction coefficient is established in the sliding
surface
30 in comparison to a circular sliding plate.
In Fig. 2 there is shown a schematic section through a second example of a
structural sliding bearing 10 according to the invention with a curved sliding
surface 30. Also, this example has a first bearing part 15, a plate-like
sliding
element 20 and a second bearing part 25 displaceable relative thereto. The
sliding element 20 contacts the second bearing part 25 via the contact
surface AK of the sliding element 20. Since here, the sliding element 20 is
also held embedded in the first bearing part 15 the free circumferential
surface Am results from the product of the circumferential length with the
height of the sliding slit h, that is, the thickness of the plate-like sliding
element 20 tp minus the depth of the embedding.
Fig. 3 is a detail from a section through a third structural sliding bearing
10
according to the invention. It can be seen the first bearing part 15 and the
second bearing part 25 with a mating surface 55. The sliding element 20 in
the illustrated first embodiment is composed of several sliding discs 35. The
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sliding discs 35 are held embedded in the first bearing part 15. For this to
work spacers 45 are located between the sliding discs 35 of the sliding
element 20 that keep the sliding discs at a constant distance to each other
and at the same time provide for an inner embedding between the sliding
discs 35. In this way, the contact surface AK is interrupted in the sliding
surface 30 and the proportion of the free circumferential surface Am is
increased over the contact surface AK of the sliding element. So, by
geometrically design of the surface of the sliding element 20 the form
factor S may be affected. As a result, with a sliding element having a number
of sliding discs 35 and spacers 45 the friction coefficient Y is increased in
comparison to a continuous sliding disc. As an alternative to the inserted
spacers 45 there can also be present a web on the first bearing part 15 in a
material-closed manner.
Fig. 4 is a top plan view of a section through a fourth example of a
structural
sliding bearing 10 with a sliding element consisting of a single curved
sliding
disc 35 the surface of which is subdivided into several partial contact
surfaces by recesses 40. Recesses 40 are applied to the surface of the
sliding disc 35 such that they interrupt the surface of the sliding disc 35.
In
this way, the contact surface AK in the sliding surface 30 is subdivided and
the size of the free circumferential surface Am of the sliding disc 35 or
sliding
element 20, respectively, is increased. In this way, by geometrically design
of the surface of the sliding disc 35 or sliding element 20, respectively, the
form factor S may be affected. As a result, the friction coefficient Y is
increased.
In fig. 5 a sliding isolation pendulum bearing is illustrated which has two
sliding surfaces 30 and two sliding elements 20 each having a contact
surface AK. Both contact surfaces of the sliding element 20 may be designed
such that a desired friction coefficient is established in the respective
sliding
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surfaces 30. One of the sliding elements 20 consists of several sliding discs
35. An intersection line A-A is passed through said sliding element 20 that
indicates the section through the sliding element 20 and the sliding discs 35.
Fig. 6 shows the section along the line A-A through the sliding element 20
indicated in fig. 5. In said section several sliding discs 35 can be seen of
which the two outer sliding discs 35 have an angular shape and the inner
sliding disc 35 has a circular shape. In fig. 6 there can also be seen the
first
bearing part 15 that includes and embeds the outer sliding disc 35.
Moreover, the individual sliding discs 35 are kept evenly spaced by spacers
45. Accordingly, the spacers 45 cause an inner embedding of the sliding
element 20 composed of sliding discs 35, so that it can completely be held in
the bearing part 15 in an conventional manner, that is embedded. The part of
the sliding discs 35 protruding over the spacers 45 acts as the free
circumferential surface Am and thus affects the form factor S. In addition to
the illustrated representation of a sliding element 20 it is also conceivable
that the sliding element 20 is not only composed of angular or circular
sliding
discs 35. Rather, it is conceivable that the sliding discs 35 may take any
shape and form an arbitrarily shaped sliding element 20.
In fig. 7 there is illustrated a further example of a sliding element 20
consisting of a single sliding disc 35. In addition to a variation of the
circumferential shape also the surface of the sliding disc which as contact
surface AK in the sliding surface 30 contacts the second bearing part 25 may
be varied. In figure 7 a sliding disc 35 is illustrated that has recesses 40
so
that the contact surface AK is composed of a number of partial contact
surfaces 50. In the illustrated example the partial contact surfaces 50 are
circular. Here, the sum of the partial contact surfaces 50 forms the contact
surface AK of the sliding disc. Further, application of a recess 40 to the
sliding disc 35 causes that the partial contact surfaces 50 protrude above
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the recess. In this way, the free circumferential surface Am of the sliding
disc
35 is increased and the form factor S is affected such that the friction of
such a sliding plate is increased in comparison to one with a continuous
contact surface.
Fig. 8 shows a further example of a sliding disc 35 according to the invention
in which the recesses 40 are applied to the sliding disc 35 in the form of
straight grooves or rings. In this way, the contact surface AK of the sliding
disc 35 can be subdivided into angular faces and/or circles as well as ring
segments and/or circle segments can be formed.
In fig. 9, the measuring results of a test series are represented during which
structural sliding bearings 10 with an unlubricated circular sliding element
20
made of the sliding material UHMWPE have been studied. During the test
series at a constant sliding slit height on the one hand the diameter of the
circular sliding element was varied and also the pressure of the sliding
element. It was proven on the one hand that a sliding element of a diameter
of 80 mm at the same pressure has a markedly higher friction coefficient
than a comparable circular sliding element of 120 mm in diameter. The
circular sliding element of 120 mm in diameter in turn has a markedly higher
friction coefficient than a comparable circular sliding element of 300 mm in
diameter. It can also be seen that the friction coefficient for a circular
sliding
element with a constant diameter at increasing pressure decreases.
Obviously, the different deformation behavior of the sliding material in the
center and at the edge of the contact surface AK affects the sliding
resistance. With an increasing diameter of the circular sliding element the
contact surface AK increases disproportionately to the free circumferential
surface Am. The friction coefficient decreases accordingly.
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In practice, this phenomenon for example can be used to increase the
friction coefficient Y for a sliding element 20 with the same contact surface
AK by subdividing the contact surface AK into several partial contact surfaces
50 that in sum of the same have the same contact surface AK. However,
because in this way the size of the free circumferential surface is increased
the friction coefficient of the structural sliding bearing is increased
accordingly.
Fig. 10 shows the connection between friction coefficient and form factor S
at constant pressure X determined in tests, wherein the abscissa shows the
product of form factor S to the power of 0.6 multiplied with pressure X. It
has
shown in the tests that with increasing form factor, that is a growing
proportion of the contact surface AK in relation to the free circumferential
surface Am, the friction coefficient Y decreases. The test results show that
the friction coefficient Y for the tested UHMWPE can be given with sufficient
accuracy as function of pressure and form factor S and pressure X for
example as follows.
y = 34 * 5-0.78 * x-1.3 + 0.02
In the shown formula the form factor S is non-dimensional. However,
pressure X due to the exponent has dimensions. Thus, the illustrated
connection requires input of pressure in [N/mm2]. Form factor S is calculated
as follows (U is the circumferential length of the contact surface AK):
S = AK ./. Am = AK ./. (U . h)
The effect of the form factor is shown when replacing a circular sliding
element of a diameter D1 by four discs of a diameter D2, wherein D2 = 1/2
Dl.
Date Recue/Received Date 2020-04-16
- 20 -
It turns out that with an identical contact surface AK the form factor is
halved
by the subdivision into four individual discs. In the present practical
example,
by such a subdivision the friction in the sliding surface can be increased by
up to 60% without a change of the material properties, or there can be
achieved the same friction coefficient at an almost double pressure as a
result of a reduction of the contact surface AK. This enables a higher energy
dissipation with structural sliding bearings. Alternatively, said effect may
be
used to significantly reduce the sliding contact surface AK at the same
friction coefficient and thus make the structural sliding bearing more
economical.
Date Re9ue/Received Date 2020-04-16
-21 -
List of Reference Numbers
= structural sliding bearing
= first bearing part
5 20 = sliding element
= second bearing part
= sliding surface
= sliding disc
= recess
10 45 = spacer
= partial contact surface
= mating surface
Y = friction coefficient
15 AK = contact surface
Am = free circumferential surface
S = form factor
h = height of the sliding slit
X = pressure
20 Tp = thickness of the sliding element 25 or sliding disc 35
Date Recue/Received Date 2020-04-16
