Note: Descriptions are shown in the official language in which they were submitted.
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Conaeoting Elem~at ~'or Ths 8riational
Conaeation Of Compoaenta
The invention relates to an element for the
frictional connection of components.
8_aokq~ouad of tho Iav~ation
Frictional connections are used in all sectors of
mechanical engineering, often to, transmit transverse forces
or torque. The magnitude of the force which can be
transmitted in each case depends, in addition to the design
features, primarily on the coefficient of static friction
(friction coefficient) of the component surfaces which are
joined to, one another. Steel/steel pairings typically have
friction coefficients of 0.15, which is frequently
insufficient to provide reliable frictional connection given
the increasingly rising demands placed on machine
components. Measures for increasing the friction
coefficient, e.g. in shrink joints, have been known from the
very early times of mechanical engineering: for example, as
early as 1860 it was recommended to introduce sand in the
joint gap, in order to improve the seating of gearwheels on
shafts. The grains of sand are pressed into the surfaces of
the components to be joined together under the effect of the
shrink forces and bring about a certain form fit, with sand
grain penetration depths of a few tenths of a millimeter. In
practice, however, it is difficult to incorporate loose
particles~or particles which have been mixed in a spreadable
carrier media evenly~into the joint gap.
Although this method is effective in principle, the
effect of relatively coarse particles in the joint gap
entails an increased risk of long-term fracture. 3f the
prevailing operating conditions indicate that such a risk
exists, the impressions which the particles, used for force
transmission make in the component surfaces must not be
significantly deeper than the peak-to-valley heights caused
by prior machining.
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Various methods are known for ;incorporating hard
particles uniformly and reproducibly in a joint gap. DOS
23 64 275 of 07.10.1975 (corresponds to GB 1,483,124)
describes the application of a layer containing hard-
y material bodies onto one of two interacting surfaces by
vapor deposition, spraying on, sintering on or diffusion of
a foreign material into the component surface.
In "ant-Antriebstechnik [Drive Engineering]" 20, No.
1-2, Jan.-Feb. 1981, Peeken et al. propose surface layers
for the frictional transmission of moments which are
produced using an electrodeposition method by jointly
depositing fine grains of hard material and a metallic
binding phase. By means of such layers, the static friction
of a shaft-hub shrink joint is more than doubled. These
layers even allow the friction coefficients under rotating
'flexural loading to be even better than under purely static
loading.
The measures which are described in the literature
for increasing the static friction coefficient are all based
on directly plating one of the two components to be
connected with friction-increasing layers. However, in
practice the desired coating often cannot be applied to
either of the two components for process engineering
reasons. If the surfaces which are to be joined together are
planar surfaces, intervening plates which are covered on
both sides with a friction-increasing layer can be used to
alleviate this problem. However, such plates are expensive
to produce, since they must be precisely plane-parallel and,_
in addition, must only have a low roughness. In practice,
only precision-ground plates are suitable. However, rigid
plates with a significant inherent weight are often
impractical during assembly, since they have to be fixed in
the desired position at additional cost until the two parts
to be joined together are connected to one another.
The present invention is' based on the object of
providing a friction-increasing connection between
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workpieCes to be joined together, which connection avoids
the drawbacks of the prior art.
Brief D_~acriptioa of the Invsatio:n
The object is achieved according to the invention by
means of a connecting element which comprises a thin,
flexible layer which bears particles of defined size at its
surface, these particles consisting of a material with a
compressive and shear strength which exceeds that of the
workpieces to be joined together.
The particles of a material with a compressive and
shear strength which exceeds that of the workpieces to be
joined together are referred to herein as hard particles.
Thin layers are preferably to be understood as meaning
layers with a thickness of 5 0.2 mm.
~,5 The connecting element of the invention has the
following advantages over known frictional connections:
a) the difficulties associated with partial coating of
relatively large or bulky components do not occur:
b) it is possible to connect components which are not
suitable for direct coating;
c) the friction coefficient of frictional connections
is increased by at least 50~r;
d) it is economical to produce;
e) it is easy to adapt even to joint surfaces of
complex shape or to nonplanar joint surfaces;
f) it does not require any significant additional
expenditure during assembly:
Brief Description of the Dra~~iaqa
Fig.~.1 is a~view in cross-section of a thin resin film
carrying hard particles.
' Fig. 2 is a view in cross-section of a thin metal film
carrying hard particles on two sides.
Detailed Description of tha Invention
The hard particles preferably consist of a material
which, under the particular conditions of use, does not
react chemically either with the materials of the components
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to be joined together or with environmental media. It is.
preferably. an inorganic material.
Preferably, the hard particles are selected~from the
group consisting of hard materials. Examples of hard
materials are carbides, such as SiC, WC and BBC, nitrides,
such as Si3N, and cubic BN, borides, SiOz. A1z03, and
diamond..
The size of the hard particles is selected in such a
way that the damage to the joint surfaces caused by the
particles being pressed into the surfaces does not reach an
impermissible level. Preferably this is ensured if the
particle diameter is not greater than about three times the
peak-to-valley height of the joint surfaces, which peak to
valley height results~from machining of the joint surfaces.
A particle size with a maximum diameter of about 0.1 mm
generally fulfils this requirement. Preferably, hard
particles with a maximum diameter of about 15 dun are used.
Ideally, the hard particles are of identical size.
However, this is technically impossible to achieve within .
the preferred grain size range. Several of the above-
mentioned preferred hard materials are commercially
available in very narrow grain size ranges, in which the.
scatter about a given nominal diameter amounts to no more
than about t 50%. This is th4 case in particular with
diamond and cubic BN, and to a limited extent also with
A1203, SiC, B4C. Such grains within the size ranges are
preferred as hard particles in the component according to
the invention. from the diameter range of up to about 15 ~m
which is suitable. it is preferred to select commercially
available grain size ranges of 6 ucn or 12 Eun average
'diameter.
The number of hard particles per unit surface area
of the contact surfaces of the components to be joined
together is preferably selected in such a way that the
normal force which is available for joining the components
together is sufficient to ensure that the particles are
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pressed into the opposite surface. This will generally be
the case if no more than about 30% of the surface of the
friction film/foil is covered with hard particles.
An insufficient covering leads to the hard particles
being pressed completely into the joint surfaces and direct
contact between the metal of the joint surfaces occurs, with
the risk of so-called fretting rust being formed, which can
reduce the force which can be transmitted. This is the case
if less than 3% of the friction film/foil is covered with
to particles.
Preferably, friction film/foils are designed~in such
a Way that the particles embedded therein cover about 5 to
about 15%~of the friction film/foil.
Depending on whether relatively coarse or relatively
fine particles are selected for the application envisaged,
the friction film/foil can be of a single-layer or
multilayer structure, as demonstrated by way of the
examples.
Embodit~at 1: Single-laytar friction film/fail:
A thin, flexible film of the friction film/foil
according to the invention may, for example, be a film,
preferably made of organic material, the thickness of which
is less than the diameter of the incorporated hard
particles. Such a single-Layer friction film is illustrated
in Fig. 1. In this embodiment, the force is transmitted
directly by the hard particles, which are in contact with
each of the two surfaces to be joined. In Fig. 1, 1 is the
film of the invention, with hard particle 3 embedded in an
organic material 2.
~mbodina~nt 2: ~dultilmyer frictioa f3.ha/foil:
The thin, flexible layer may be formed as a strip
with sufficient inherent strength, e.g. made of metallic
material, on which the hard particles are fixed by means of
a binding phase. In this case, the binding phase is
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preferably applied to the thin, flexible layer by means of
electroless deposition methods. Such a multilayer friction
foil is illustrated in Fig. 2. Where 1 is the friction foil
comprising a thin metal foil 4, having hard particles 3 by a
binding phase 3 which can be an electroless metal layer. In
this embodiment, the hard particles are only in contact in
each case with one of the surfaces to be joined and the
force is transmitted by means of an interlayer of sufficient
inherent strength.
l0 Organic carrier films are primarily suitable for the
production. of a carrier film which is thinner than the
particles of hard material in accordance with Embodiment 1,
since a metallic binding phase is extremely sensitive to
fracture in self-supporting form. In addition, organic films
have the advantage of being able to adapt to three-
dimensional, multiply curved surfaces largely without
cracks.
Suitable materials for organic carrier films of this
nature are, for example, paint resins, such as for example
polyvinyl butyral (trade name PIOLOFORMs"") or vinyl
acetate/vinyl chloride copolymers (VINNOLT"" paint resins),
but also dispersions, such as for example ACRYLATE LL 979T"'
(manufacturer: blacker-Chemie GmbH, Munich). As is known, the
composition of such films can be varied within wide limits,
in order to adjust various properties, such as elongation at
break, elasticity, tear strength, or self-adhesive
performance.
The production of such a film/foil containing
particles of hard material can be carried out analogously to
methods which are known and are used, for example, ~in the
production of abrasive agents on a substrate (abrasive
paper) or laminate layers. For example, during the
production of abrasive paper, a tightly packed layer of
grains of abrasive is applied to a carrier strip, which has
been coated with glue, by gravity spattering or by
electrostatic scattering. The particles, which initially
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only adhere lightly, are fixed.on the substrate by means of
a second layer of glue.
A substrate which is provided with a nonstick
coating or release coating is advantageously used to produce
a self-supporting film which is studded with particles. Such
nonstick coatings are known, for example, from the adhesive
label and transferant. Either an organic layer which is
studded with a single layer of particles, can be applied to~
the release coated substrate using the above-mentioned
processes which are conventional when producing abrasive
agents, or else a prepared mixture of binder and particles
of hard material can be applied in a uniform, single layer
using the.processes which are known for in the production of
laminates.
The quantity and composition of the organic binding
agent are set in such a way that the thickness of the film
which remains after drying or curing is less than the
average diameter of the embedded particles of hard material.
Preferably, the thickness of the film which remains
after drying or curing amounts to at most about 50~ of the
average diameter of the embedded particles of hard material.
It is unimportant here whether the particles protrude from
the film on both sides or only on one side, since the normal
forces which occur during subsequent use exceed the shear
strength of the particle/film composite. The quantity of .
particles introduced into the film is such that the
advantageous surface-coating proportions described above are
achieved.
The finished self-supporting film can be pulled off .
the substrate which is provided with the nonstick or release
coating in a simple manner. It represents an embodiment of
the component according to the invention which can easily be
applied to joint surfaces of components which are to be
connected.
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In a further embodiment, the friction film/foil can
be made self-adhesive by adjustment of the organic binder,
in order to facilitate application to joint surfaces.
If because of sensitive components only very small
particles, e.g. < 10 dun, are required for the transmission
of forces, as a rule it is not reliably possible to handle a
single-layer friction film/foil. It is therefore necessary
to select a carrier material on which the particles can be
anchored and which itself has sufficient strength to
'transmit the forces occurring. Such a friction film/foil is
illustrated in Fig. 2. In the case of highly stressed
frictional connections, these are generally metallic
components, preferable made of fexrous materials, so that
the demand for 'sufficient strength" of the carrier material
is essentially fulfilled by steel. The further demands
relating to coatability, planarity, plane parallelism,
flexibility and elasticity are fulfilled to a satisfactory
extent by a strip-metal preferably strip steel, in
particular spring steel strip. Therefore, for the preferred
embodiments of friction film/foil which is coated on.both
sides, commercially available, unalloyed spring steel strip
having a thickness of about 0.1 mm is preferred.
In principle, the force-transmitting particles can
be applied to the carrier material using the methods which
have been described for the production of a self-supporting,
particle-studded film, with the nonstick coating of the
carrier material being omitted, so that a firmly adhering,
particle-studded film is applied to both sides of the
carrier material.
3o However, in practice it is difficult to apply
particles with a diameter of only a few micrometers
uniformly to a carrier using an organic film whose thickness
is preferably only half the diameter of the particles. The
particles are therefore preferably fixed on both sides 'of
the carrier material by means of a deposited layer of metal.
In this case, the hard materiai/metal layer is preferably
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produced by means of electroless deposition processes, e.g.
an external current-free process (e. g. chemical nickel
plating). Such processes are known and are described, for
example, in the literature references which have already
been mentioned. Chemically plated nickel layers can be
hardened by means of heat treatment at up to about 400°C,
with the result that adhesion to the base metal is improved
and the inherent hardness of the layer is increased.
In principle, the components according to the
to invention are useful as friction films/foils in any type of
frictional connection throughout the field of mechanical
engineering, and in particular if the 'forces which can be
transmitted by the component surfaces which are imposed by
the design are insufficient. This may be the case in
particular with clamp or press joints in the presence of
lubricants, but may also be useful in dry pairings.
Steel/steel combinations typically have friction
coefficients of 0.15 in the unlubricated state. The trend
toward smaller, more lightweight structures is increasingly
leading to the normal forces which can be achieved being too
low to transmit the transverse forces required given
friction coefficients of 0.15. A higher friction coefficient
is required in order to keep the structure capable of
functioning.
~xa~lr 1: Broduction Of A Connecting El~w~st Bcaording To
Embodi.~nwnt 2
The connecting element is an annular plate of steel
foil which is 0.1 mm thick and is coated on both sides. The
friction-increasing coating consists of diamond particles
with an average diameter of 6 ~m in a binding phase of
electroless deposition nickel in a layer thickness of 4 ~tm.
The coating density of the diamond particles on the foil
surface is 7 area %.
To produce this connecting element, firstly an
annular plate of the required dimensions is punched from an
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uncoated spring steel sheet with a thickness of 0.1 rnm.
Although in principle it is possible to produce such plates'
from sheet metal which has already been provided with a
friction-increasing coating on both sides, this causes. a
very large amount of expensive waste owing to scrap.
Usually, a relatively large number of plates are treated
simultaneously.
The prepared plates are placed on suitable mounts
and are pre-treated in accordance with the general rules of
to electroless deposition by degreasing, pickling and
activating.
Then, the carrier bearing the plates is immersed in
a chemical nickel bath in which diamond powder with an
average particle diameter of 6 Eun is dispersed. The quantity
of dispersed diamond powder is selected in such a way that
under the parameters prevailing in the coating bath
(agitation, deposition rate), the desired proportion of
diamond' in the deposited layer of metal reaches the desired
thickness of slightly more than half the diameter of the
diamond particles. Under customary process conditions, the
immersion time amounts to approximately 15 minutes.
The carrier comprising the plates, which are now
coated, is then removed from the coating bath and cleaned in
an ultrasonic bath, to remove diamond particles which are
only loosely attached.
The cleaned plates are taken off the carrier and are
subjected to a heat treatment for 2 h at 350°C. The heat
treatment increases the adhesion of the chemically deposited
nickel layer to the steel foil and the seating of the
particles in the layer itself.
E~xm~ple 2: Production Of A Connaoting El~nant According To
Embodiment 1
The connecting element consists of a self-supporting
organic film which is 15 dun thick and in which silicon
carbide particles with an average diameter of 30 Eun are
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evenly distributed in a quantity which is such that they
cover a total of approximately 10% of the surface area.
The connecting element is produced in the following
way: using the principles of paint technology, a solvent
s containing paint comprising a VINNOLT"' paint resin is made
"soft", in order to obtain a film which is ductile after
drying. The solvent proportion amounts to fi0%. Silicon
carbide powder with an average particle size of 30 dun is
mixed into the paint in a quantity of 5% by volume. The
material prepared in this way is applied with the aid of a
doctor blade uniformly, in ~a thickness of approx. 40 ~,un, to
a carrier film/foil which has been release coated. Following
evaporation of the solvent, a film with a thickness of
approx. 15 dun remains on the carrier film/foil, from which
film the embedded silicon carbide grains project in
accordance with their diameter. When viewed from above, the
silicon carbide grains take up approx. 12% of the coated
surface area.
The fiim/foil produced in this way is ready for use
as and is cut to an appropriate size for the application. The
release carrier film/foil can easily be separated from the
particle-studded film, which far its part, as a result of
the ."soft" setting mentioned at the outset, can be handled
in a freely supporting manner and is easy to apply to the
assembly location.
F.~cample 3: Uae of s coanatstiag slsmant in accordaaca ~rith
Example 1~
A gyrating mass made of gray iron is to be attached
at the end side to a rotating shaft made of heat-treated
steel. It is not possible to achieve a form-fitting
connection by means of press fitting, since precise
positioning takes place only during assembly. Attachment is
carried out using a clamping screw Which provides a normal
force of 16,000 N. The presence of lubricants at the contact
surfaces is not to be .ruled out. The holding moment required
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amounts to 500 Nm, but only 350 Nm (dry) or 290 Nm
(lubricated) are achieved.
By inserting a connecting element in accordance with
Example 1, a holding moment of 540 Nm is achieved at the
available normal force of 16,000 N. In order, with the given
structure, to allow the foil to be inserted, the latter has
to be bent elastically.
~zamplo 4: Use of a aoanoating al~mant in :aaardanae ~rith
Ezampla 2
An auxiliary unit is to be attached in a
nondisplaceable manner to a motor casing made of cast light
metal, by means of 4 M 6 screws. The tightening torque of
the screws is limited, to prevent the threads in the light-
metal casing from being destroyed. In test operation, the
operation-induced vibrations lead to a change in the
position of the auxiliary unit after 60 hours. It is
required that the assembly position should be reliably
maintained after 1000 hours.
This requirement is fulfilled by means of a
connecting element in accordance with Example 2. This film
is cut to an appropriate size and is applied to the contact
surface before the components are screwed together. The
position of the auxiliary unit attached in this way did not
changed after a long-term test lasting 1000 hours.
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