Note: Descriptions are shown in the official language in which they were submitted.
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Washer and fastening element
The present invention relates to a washer for a
fastening element, having a circumferential flange,
having an annular washer body provided with an opening,
and having at least one holding web: The invention
further relates to a fastening element having a washer
of this type.
A washer of the generic type is known from
EP 1 091 135 A2. This washer has a washer body having
at least two formed-on holding lugs, which can be
placed around a circumferential flange provided on the
fastening element. The washer is thereby held captively
against the fastening element.
When a nut with washer is tightened on a fixed screw
bolt, the washer is meant not to twist relative to the
clamped structural part. To this effect, the
coefficient of frict~.on between the washer and a
structural part is enhanced by the fact that notches
are provided on the washer body of the washer. These
cause the washer to remain on the surface of the
structural part as tightening takes place on a screw
bolt, even if the coefficient of friction between
washer body and structural part is low per se.
German utility model DE 94 00 671 U1 describes a washer
which, instead of holding lugs, has an annular web
running round the washer body. Measures to enhance the
coefficient of friction between washer body anal
structural part are not disclosed. In this embodiment,
there is additionally the risk of nut and washer
sticking together when surface coatings are applied.
US 2,151,919 A likewise relates to a nut having a
washer, the washer body of which has on the top and
bottom side notches which interact both with the
surface of the structural part and with the bottom side
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of the nut. The notches serve merely to protect against
loosening of the joint.
In the use of fastening elements having washers of the
generic type, there is always the risk of damage to the
surface of the structural part as a result of the
notches being canted or pressed in in the structural
part. Moreover, the manufacture of the previously known
washers, with the modifications of their washer bodies,
is complex, since the notches or other surface
alterations have to be added subsequent to the washer
having been made.
The object of the present invention consists in
providing a washer of the generic type, which, whilst
offering comparable performance, is of simpler
configuration and easier to make and can be used
without damage to the surface of the structural part,
and in which the risk of fastening element and washer
sticking together is at least reduced.
The solution consists in a washer having the features
of claim 1. According to the invention, it is thus
envisaged that on the inner face of the opening there
are disposed at least two claws, which jut radially
into the opening.
The advantage of the inventive design of the washer
consists in the fact that, in each phase of the
fastening operation, i.e. as the fastening element is
screwed in and tightened on a screw bolt, it always
remains stationary on the surface of the adjoining
structural part to be fastened, regardless of the
magnitude of the acting forces. This effect is based
essentially upon two mechanisms.
At the beginning of the fastening operation, it is
possible to distinguish between two differently sized
friction radii. The first, smaller friction radius rl
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is defined by the diameter of the bearing region of the
fastening element on the claws. The second, larger
friction radius r2 is defined by the diameter of the
effective friction surface of the washer on the
structural part. Since the effective friction torque is
proportional to the friction radius, the friction
torque between washer body and structural part is
greater than the friction torque between fastening
element and claws.
The result is that the washer, even at the beginning of
the fastening operation and also in the further course
thereof , remains stationary and does not turn with the
fastening element. This effect can be further
reinforced, where necessary, if the bearing surface is
arched slightly inwards so that it bears upon the
structural part only with its outer rim. The washer can
therefore be configured in the style of a cup spring.
In a later phase of the fastening operation, a
sufficiently large pressure is exerted upon the claws
by the bottom side of the fastening element that they
move downwards in the direction of the structural part
and, at the same time; inwards into the opening in the
washer body. This means that the claws are pressed into
the thread of the screw bolt and are wedged therein.
This has the effect, on the one hand, that the washer
remains stationary also in a later phase of the
fastening operation and, on the other hand, that the
strength of the joint between fastening element and
screw bolt is enhanced.
The pressing of the claws into the thread of the screw
bolt causes the free end of the claws to deform in such
a way that a screw thread is formed. This means that,
when the fastening element is loosened, the washer
turns along with it.
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This design further has the effect that a fastening
element connected to the washer according to the
invention bears in the unlined state upon the claws . A
gap consequently remains between the bottom side of the
fastening element and the washer body. If the fastening
element is coated, for example, with paint, oil or wax,
the excess material is better able to drain away when
the coating material is then spun off. The risk of
fastening element and washer sticking together is hence
at least diminished.
The washer according to the invention is suitable for
all types of fastening elements, especially for various
nut types, for example standard hexagon nuts. It can be
easily made by punching-out and forming of the holding
web and the claws, holding web and claws being able to
be formed in a single operation.
The subject of the present invention is additionally a
fastening element having a washer of this type.
Advantageous refinements are derived from the sub-
claims.
A particularly preferred embodiment of the washer has
three or four claws, which are preferably disposed such
that they are mutually offset. The aforementioned
effects are particularly effective in this embodiment.
Another advantageous refinement envisages that the free
ends of the claws, in the direction of the fastening
element, lie above the washer body, so that, in the
fastening operation, they are pressed particularly far
downwards and inwards and hence particularly firmly
into the thread of the screw bolt.
Advantageously, the claws, on their side facing the
fastening element, are respectively provided with a
bearing surface for the bottom side of the fastening
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element, so that the relevant friction radius r1 can be
more exactly defined. This bearing surface can be
formed, for example, by the craws having an approximate
S-shape or Z-shape in cross section.. The claws can
also, however, be of rectilinear configuration. The
height of the claws above the washer body is preferably
just as large to twice as large as the material
thickness.
The claws can further, at their free end, have an
indentation in the shape of a circular segment, which
makes it easier for the claws to be pressed into the
thread of the screw bolt. The shape and size of the
indentation can herein be matched to the circumference
of the screw bolt. Alternatively, however, the claws
can also have a straight edge at their free end, with
the result that they are pressed particularly far into
the thread of the screw bolt, are even more heavily
deformed and are even more effectively wedged.
Depending on the design of the washer and of the
fastening element, the claws can be about 1 to 3 mm
long. Preferably, their length corresponds to about
twice the thickness of the material used for the
manufacture of the washer (e.g. sheet metal). It is
important that the length of the claws is dimensioned
such that, following the screw connection, the diameter
dl which they define is less than the core diameter of
the screw bolt which is used. That is to say,
therefore, that they have an oversize relative to the
core diameter of the screw bolt. Finally, it is
advantageous to tailor the diameter d2 of the opening
in the washer body to the nominal diameter of the
thread of the fastening element, thereby producing an
optimal, force-absorbing supporting surface.
The at least one holding web of the washer can be
configured as a closed circumferential annular web, ox
in the form of an annular web having single or multiple
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radial slots, or in the form of at least two holding
lugs. A closed annular web simplifies the punching tool
for the manufacture of the washer, whilst divided
holding webs facilitate the forming.
The invention is described in greater detail below with
reference to an illustrative embodiment represented in
the appended figures, in which:
Figure 1 shows a top view of an embodiment of a
washer according to the invention in
diagrammatic non-scale representation;
Figure 2 shows a sectional representation of the
washer along the line II-II in figure 1;
Figure 3 shows a partially cut representation of a
fastening element with the washer according
to figure 1, after structural parts have
been bolted together.
Figures 1 and 2 show an illustrative embodiment of a
washer 10 according to the invention, the fastening
element 30, in the example a standard hexagon nut,
being indicated in figure 2 in dash-dot representation.
The nut 30 has a nut body 31 having a circumferential
outer flange 32. The flange 32 is formed onto the nut
body 31 in one piece.
The washer 10 has a washer body 11 having a
circumferential annular web 12. The washer body 11 is
provided with an opening 13, which in the illustrative
embodiment has a diameter d2 which is tailored to the
diameter of the fastening element used. The annular web
12 juts in the axial direction over the flange 32 of
the nut body 31 and, at its upper end 14, is bent
radially inwards over the flange 32. Of course, instead
of a circumferential annular web, a single-slotted or
multi-slotted annular web can also be configured.
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Finally; individual (at least two) holding lugs can
also be provided.
The washer 10 is held on the fastening element 30 in a
loosely rotatabie manner. To this effect, an at least
minor play is provided both axially and radially
between the flange 32 of the nut body 31 and the
annular web 12 of the washer lo.
From the inner face 15 of the opening 13, claws 16, in
the illustrative embodiment four, offset by the same
angle, jut radially into the opening 13. More than four
or Less than four claws 16 may also be provided. Nor do
the claws 16 necessarily have to be mutually offset by
the same angle.
In the illustrative embodiment, the ends 17 of the
claws 16 are disposed, in the direction of the
fastening element 30, above the washer body 11. The
distance to the washer body 11 amounts, in the
illustrative embodiment, to twice the thickness of the
sheet metal used for the washer, i.e. about 2 mm. The
distance can also, however, be larger or smaller, as
desired. The claws are additionally bent in an
approximate S-shape in cross section. The upper part of
the S herein forms a bearing surface 18 for the bottom
side of the fastening element 30.
In the illustrative embodiment, the length of the claws
16 corresponds to about twice the thickness of the
sheet metal used for the manufacture of the washer 10
and amounts to about 2 mm in the case of a 1 mm sheet
thickness. With their free ends 17, the claws 16 define
a diameter dl within the opening 13 in the washer body
11. The diameter dl is therefore smaller than the
diameter d2 of the opening l3 itself. The length of the
claws 16 is dimensioned in the individual case such
that the diameter dl, following the screw connection,
is less than the core diameter of the screw bolt
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respectively used. The claws 16 therefore have an
oversize relative to the core diameter of the screw
bolt.
In the illustrative embodiment, the ends 17 of the
claws 16 are of linear configuration. In figure 1, a
further variant is indicated in dash-dot
representation, in which the ends 17 have indentations
19 in the shape of a circular segment. The curvature of
the indentations 19 can additionally be matched to the
diameter of a screw bolt to be subsequently screwed in.
The washer 10 according to the invention is
manufactured, in a manner which is known per se, by
punching out a blank and then forming the annular web
12 and the claws 1&. The annular web 12 and the claws
16 can herein be formed in one operation.
Figure 3 shows the fastening element 30 with the washer
10 from figure 1 after two structural parts 21, 22 have
been fitted together by means of a screw bolt 33. It
can be seen from figure 3 that the forces generated by
the screw bolt 33, as the fastening element 30 has been
pulled down in the direction of the washer body 11,
have forced the claws l6 downwards and inwards, and, in
so doing, have pressed them into the thread 34 of the
screw bolt and wedged them therein.
The washer according to the invention thus manages
without subsequent modifications of the washer body 11
and yet reliably prevents the washer from turning
during the fastening operation.
