Note: Descriptions are shown in the official language in which they were submitted.
~L~S~ 3
1 ~lind-Riveting Assembly
Background of the Invention
Field of the Invention
This invention relates to a metal blind-riveting assernbly
comprising a rivet having a tubular body portion with a head flange
at one end and a mandrel having a stem with a neck of reduced cross
section at which the stem will break at a predetermined tension, the
mandrel being upset at both ends, one of which forms a rivet-setting
head while the other is a pulling head for engagement by pulling
means of a rivet-setting tool.
Statement Of The Prior Art
, ~
A blind-riveting assembly of this general type, and its
production method, are shown in U.S. Patent No. 2,317,360. In this
latter assembly there are two upset ends of the mandrel which are
cylindrical, or substantially so, which with their greater
diameters, are shouldered in relation to the part of the stem lying
between them. The terminal end of each of the two heads remote from
the mandrel stem is defined by a flat radial surface normal to the
axis of the mandrel. The head used as the pulling head of the
mandrel also meets the mandrel stem at an annular Face normal to the
mandrel axis, while the head forming the rivet-setting head is
conical at its underside where it joins the mandrel stem and forms
an angle of about ~5 w~th the mandrel axis. The cone is intended
to widen the body portion of the rivet when the rivet is being set.
The pulling head of the mandrel is thus rectangular, or
substantially so, in axial section, while at the opposite end of the
mandrel, there is a corresponding profile but with the exception
that here the transition into the mandrel stem is conically formed.
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1 U.S. Patent Nos. 2~183,543 and 2,538,623 also illustrate other types
of rivet assemblies.
With the method described in those specifications for produciny
the pulling head of the mandrelS with its substantially rectangular
profile, a considerable amount of pressure is necessary in order to
make the material blank yield to form this profile shape, and the
reaction to this pressure is taken at least in part by an abutment
engaging the other end of the mandrel. Thus, in the course of this
heading operation the predetermined breaking point or neck of the
mandrel, where the cross section of the mandrel stem is reduced~ as
shown in Figures 8 and 9 of U.S. Patent No. 2,183,543 and in Figures
1 and 3 of U.S. Patent No. 2,538,623, is subject to a conslderable
load. If the neck is one in which there is a reduction of about
30% in the cross section, as known and commonly used in the art,
then there is a risk that the parts of the mandrel meeting at the
neck will shift against each other in such a way, in the event of a
particularly high pressure in the upsetting process, that they will
no longer lie axially aligned if the mandrel is not tightly enclosed
at either side of the neck by a tool which prevents any lateral
yielding of the parts of the mandrel at these localities. Over and
above this, high axial pressures exerted on the neck may lead to
such a compressive strain on it that its predetermined breaking
force changes, which would deprive the blind-riveting asse~bly in
question of its required properties and under certain circumstances
would even prevent proper execution o~ the rivet-setting process.
The properties described above, on the part of the known
blind-riveting assembly with a mandrel upset at both ends
essentially like flat-topped cylinders, no doubt contributed to the
situation whereby such a blind-riveting assembly has not become
widely established in practice. The blind-riveting assembly
~L~5~3~3~
1 predominantly used in practice consists of a smooth continuous
nail-like mandrel with a predetermined breaking point or neck inside
the rivet sleeve and a rivet-setting head which is generally conical
or hemispherical in axial section terminatiny at a flat annular
base, and no pulling head.
In other blind-riveting assemblies known in the art, the
mandrel projects beyond the rivet flange in the usual way over a
length which represents a multiple of the length of the rivet, and
runs to a slender point. Behind this there is a bead formed on the
mandrel, behind which the setting tool grips the stem and which
partially absorbs the tensile forces exerted on the mandrel by the
setting tool. In front of the bead, in the direction of the rivet
head flange, the mandrel is roughened so as to increase the friction
between its surface and the jaws of the setting tool, with the
result that the tensile force exerted by the setting tool is
absorbed firctly by the mandrel stem via its friction-increasing
surface and secondly via the bead. According to this type of rivet
assembly, the bead fullfils only the function of an additional
safeguard, and does not absorb the full tensile force of the setting
tool all on its own. The bead formed adjacent the pointed end of
the mandrel makes it impossible to push the mandrel with the bead
through the rivet when producing the blind-riveting assembly. The
bead must therefore be initially shaped subsequent to the insertion
of the mandrel in the rivet, which is technically difficult,
particularly in view of the mandrel's pointed tip extending beyond
the bead. In practice, therefore, the metal blind-riveting
assemblies have been used with a smooth nail-like mandrel, upset at
only one end to provide the rivet setting head, in which the length
of the part projecting out of the rivet head flange represents a
multiple of the length of the rivet, in order to provide the pulling
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1 jaws of the setting tool with a sufficiently long application
surface for transmitting the tensile force.
In addition to the above, there are also known solutions to the
problem of applying the tensile force, which amount to providing
ring grooves on -the mandrel in the area of the part projecting from
the rivet head flange, in such a manner that on this part of the
mandrel there are no parts going beyond its stem diameter. When
producing the blind-riveting assembly in question, a mandrel of this
type can still be pushed into the rivet sleeve after forming the
ring grooves.
The above~described developments show that the specialist field
has long had the idea of improving the blind-riveting assembly from
the point of view of its gripping surface for the setting tool.
~low it should be borne in mind with regard to the technique of ring
grooves on the mandrel that ring grooves of this type may under
certain circumstances degenerate into an unwanted breaking point
below the predetermined tensile strength of the neck. The same risk
also applies, moreover, to the above mentioned blind-riveting
assembly commonly used today, which possesses a smooth-surfaced
nail-like mandrel and which, precisely because of this smooth
surface, has to be gripped with a high contact pressure by the
setting tool on the part projecting from the rivet head flange.
Setting tools are usually equipped with serrated jaws, and the
serrations are frequently sharp edged, and, because of the high
2~ pressure they exert, occasionally produce notch marks on the mandrel
which create breaking points where the tensile strength is below
that of the neck, thus causing the mandrel to break in the wrong
place, as a result of which the setting process is not reliably
carried out.
~.25~ i3
1 The patents hereinbefore referred to all describe
blind-riveting assemblies of what are called the "open type", that
is to say where the mandrel stem passes right through the rivet, its
pulling stem projecting from the head flange of the rivet and its
rivet-setting head exposed at the other end where its base engages
the tail end of the rivet. The problem of providing for the pulling
of the mandrel as hereinbefore discussed involves the same
considerations, however, in the case where the rivet is closed at
its tail end, and the setting head of the mandrel is wholly
enveloped in the body portion of the rivet.
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1 Brief Summary Of The Invention
It is the object of the present invention to provide an
improved blind-riveting assembly of the kind with an upset head on
both ends of a break stem mandrel, which can be made in the known
way involving subjecting a necked portion of the mandrel stem to
axial pressure when upsetting the pulling head, but with minimal
risk of interference with the configuration of the mandrel at the
locality of its predetermined breaking point.
The invention provides a metal blind-riveting assembly
comprising a rivet having a tubular body portion with a head flange
at one end and a Mandrel having a stem with a neck of reduced cross
section at which the stem will break at a predetermined tension,
which neck lies within the body portion oF the rivet, the mandrel
being upset at both ends, one of which forms a rivet-setting head
while the other is a pulling head for engagement by pulling means oF
a rivet-setting tool, and both the pulling head and rivet-setting
head oF the mandrel having an end face which is arch-shaped in axial
section and terminates at a flat annular base facing the mandrel
stem.
The foregoing design of the pulling and setting hPads of the
Mandrel of an assembly in accordance with the invention results in a
lower degree of deformation being required on the part of the
material of the Mandrel when upsetting the pulling head. If the
rnandrel end face is arch-shaped in axial section, (i.e. the face is
hemispheriçal, conical, pyramidal, frust-conical or
frusto-pyramidal, for example) and ter~inates at a flat annular base
where it joins the mandrel steM, or in other words is reduced in
transverse cross sectional area progressively froM its annular base.
This special shape of the two upset heads of the Mandrel of an
assembly in accordance with the invention requires a correspondingly
~2563~3
1 lower pressure in the course of shapiny, especially since the
specified contour, preferably rounded and most conveniently
hemispherical, facilitates this shaping. It -is thus possible to
avoid adversely affecting the predetermined breaking point of the
neck of the mandrel in terms of its position and properties, and it
can therefore lie within the rivet where the adjacent parts uf the
mandrel itself are not given any particularly stable lateral
support, such a support being precluded by the relative flexibility
of the material of the rivet. Nor is the predetermined breaking
point so loaded, by the pressure in the course of upsetting the
pulling head, that its properties are thereby changed.
Furthermore, because the rivet-setting head, whether or not of
the same size or shape as the pulling head, by having a flat annular
base, it is ensured that this annular base, during setting5
initially clinches the rivet sleeve in the desired manner, in order
to fill satisfactorily the respective openings of the parts being
joined. When, however, the rivet-setting head, is initially outside
the rivet, the respective tail end of the body portion of the rivet
bulges, and the head is partially drawn into the latter. This means
that because of the flat annular base of the rivet-setting head, the
adjacent part of the rivet sleeve partially closes again behind the
setting head and thus holds the latter after the mandrel has broken.
Furthermore, the specified configuration of the pulling head of
the mandrel of an assembly in accordance with the invention, namely
its arch shaped outline in axial section, produces the ef-Fect of
improving the sliding properties of the blind-riveting assembly when
it is automatically fed into and through tubes or pipes, pulling
head foremost. Moreover, if heads of the specified shape are at
both ends of the mandrel of an open type blind- riveting assembly,
both can serve as guide heads so that whichever is leading, the
~5 Ei~3
1 assembly has little tendency to catch anywhere in the guide duct.
The shape of the pulling head of the mandrel of an assembly in
accordance with the invention thus has a combined ef-Fect in both
improving the reliability of manufacturing a product with
predictable performance and improving the readiness with which it
can be fed automatically. Such shape also facilitates inserting,
automatically or by hand, the mandrel axially into a nose-piece and
pulling device of a rivet-setting tool.
Because a mandrel with a pulling head can be pulled positively
by a pulling device of a rivet-setting tool in engagement with the
pulling head, rather than by engagement of clamping jaws of the tool
which require a comparatively long area of contact to create
sufficient friction to withstand the setting load, the mandrel of an
assembly in accordance with the invention can be significantly
shorter than the smooth nail-like mandrels of conventional blind
rivets. In particular, the pulling head is separated from the rivet
head flange by a distance corresponding at most to roughly the
length of the rivet, that is to say of both the body portion and the
head flange. This shortening of the mandrel entails firstly a
considerable saving of material and secondly simplification of the
removal of the broken-off part of the mandrel stem. This broken-off
part of the mandrel stem has to be led away from the tool, and where
this involves it passing through a passage in the tool through which
there is a flow of air to assist such removal, the pulling head both
counteracts jamming and offers the current of air a suitable surface
(its annular base) for propelling it along the passage. In addition
the relatively short blind rivet can be fed through guide ducts
which change direction through correspondingly small radii.
There now follows a detailed description, to be read with
reference to the accompanying drawings, of a blind riveting assembly
63~3
in accordance with the invention and illustrative thereof.
It will be realized that this illustrative assembly has been
selected for description by way of example and not of
limitation of the invention.
According to a still further broad aspect of the
present invention there is provided a metal blind-riveting
assembly which comprises a rivet having a tubular body
portion with a head flange at one end and an opposite end
adpated to be deformed when the rivet is set and a mandrel
having a stem of uniform cross-section with a neck of reduced
cross-section at which the stem will break at a predetermined
tension, which neck lies within the body portion of the rivet.
The mandrel is upset at both ends, one of which forms a
rivet-setting head while the other is a pulling head for
engagement by pulling means of a rivet-setting tool. The
pulling head is spaced from the rivet flange a distance
substantially equal to the length of the rivet. Both -the
pulling head and rivet-setting head of the mandrel are of
larger diameter than the diameter of the mandrel therebetween
and each have an end face which is hemispherical and which
terminates at a flat annular base facing the mandrel stem.
The annular base joins -the mandrel stem at a sharp corner.
The rivet-setting head has a diameter the same as that of
the pulling head and is adap-ted to be partially enclosed in
the opposite rivet end when the rivet is set to be locked
therein. The reduced neck is located adjacent the rivet-
set-ting head so as to lie within the confines of -the rivet
body when broken upon setting -the rivet. The hemispherical
pulling and rivet-setting heads have improved sliding
properties when the blind riveting assembly is automatically
fed into and through tubes or pipes.
~S~i303
1 Brief Description Of The Drawi~
Figure la represents the illustrative blind- riveting assembly
in side view and partly in section;
Figure lb represents a modification of a pulling head of the
illustrative blind-riveting assembly;
Figure 2 shows the illustrative blind-riveting assembly of
Figure 1 in perspective;
Figure 3 shows the illustrative blind-riveting assembly of
Figure 1 after setting of the rivet sleeve, and
Figure 4 represents a closed-ended variant of the illustrative
blind-riveting assembly.
;3~3
1 Description Of The Preferred Embodiment
._ ___
The metal blind-riveting assembly shown in Figure la consists
of a tube-shaped rivet body portion or sleeve 1 with a rivet head
flange 2 and a mandrel 3 with a rivet-setting head 4 upset at one
end and a pulling head 5 upset at the other; the pulling head 5 has
roughly the same diameter as the setting head. The pulling head 5
is arch-shaped in axial section, or more particularly, exhibits a
semi-circular profile 5a. The mandrel 3 is provided with a
predetermined breaking point or neck 6 where its stem is reduced in
cross-section. The neck 6 lies within the rivet sleeve 1. The
rivet 1, 2 and mandrel 3, 4, 5 are both made of metal, the material
of the mandrel exhibiting a higher strength than the material of the
rivet. The pulling head 5 serves for engaging pulling means of a
setting tool (see for example U.S. Patent No. 2,183,543).
As can be seen, the mandrel 3 is upset at both ends to form the
rivet-setting head likewise 4 having a semi-cylindrical profile 4a
and the end 5 serving as a pulling head. Both upset ends 4 and 5
undergo transition into the mandrel 3 with a flat annular base 11 or
7 normal to the axis of the mandrel and meeting the mandrel stem at
a sharp corner. The base 7 thus forms a particularly favorable
contact surface for the application of a setting tool, from which it
cannot slip even if considerable tensile force is applied. The
distance between the rivet flange 2 and the pulling head 5 is here
roughly equal to the length of the rivet l; thus the blind-riveting
assembly shown in Figure 1 is overall considerably shorter than the
usual commercial blind-riveting assemblies with smooth nail-like
mandrels, insofar as the rnandrel 3 does not project so far out of
the rivet flange 2 as is customary.
The pulling head of the mandrel of the illustrative assembly
has been shown in Figure la as hemispherical at its end face 5a with
3l~5 E;3~3
12
1 a flat annular base 7. The mandrel of an assembly in accordance
with the invention may have a pulling head with other arched shapes
as viewed in longitudinal section, and in particular may be conical
or frusto-conical as depicted in Figure lb, or may be at least part
pyramidal; in either case, it is preferably rounded, at least at its
tip, and it is preferred to retain the flat annular base. It is not
essential that the rivet-setting head 4 is of the same size or
configuration as the head 5, the head 4 serving a different function
and being designed with its intended purpose in mind. If the rivet
1 is open-ended with the setting head 4 of the mandrel exposed and
engaging the tail end of the rivet as shown in Figure la, a similar
shape to the head 5 may be preferred, with a flat annular base 11
and an end face correspondingly arch shaped (e.g. curved or
tapering~ in longitudinal cross section. The head 4 may, in the
case of a blind-riveting assembly of the closed ended variety, be
wholly enveloped in the metal of the rivet at its tail end, as
depicted in Figure 4; in this case also, the setting head, while
also arch-shaped in axial section, may be of smaller diameter than
the pulling head.
In the two cases shown in Figures la and lb, therefore, the
upset ends 4 and 5 of the mandrel have a profile reducing in cross
section from a Flat base in a plane normal to the mandrel axis.
Figure 2 represents the metal blind-riveting assembly according
to Figure la in a perspective view. This clearly shows the base 7
which runs radially to the mandrel 3, and forrns the flat engagement
surface for a setting tool.
Figure 3 shows the blind-riveting assembly oF Figure 2 in
longitudinal section after setting of the rivet. ~lere the rivet
sleeve 1 connects two plate-like components 9 and 10, by means of
the rivet flange 2 and the counter head 8, which is formed by
31 ~5~3~3
1 widening the rivet sleeve by means of the setting head 4 in the
known way. In this method the setting head 4, by virtue of its flat
base, is partially surrounded by the counter head 8, so that it
cannot fall out of the latter. Inside the rivet sleeve 1, the
mandrel 3 ends where it has broken at the neck 6.
