Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE I~ TIO,`~
This invention relates to a substantially tubular insert which
is capable of collapsing in an axial direction in response to a com-
pressive force exerted by a fastening elemont, and to an assembly
incorporating said insert as an integral com?onent thereof. Upon
compression of the insert, a considerable`portion of the net com-
pressive load exerted by the fastener is absorbed by the insert
without excessive loading on the article.
As is well-known in the fastener ar~, the problem of maintaining
adequate compression or torque when assembling metal or non-metal
parts to other assemblies having dissimilar coefficients of thermal
expansion has persisted in industry for many years and has pre-
viously denied the acceptance of materials in fields of application
in which they would otherwise find great utility. A part which is
subjected to a compressive load due to the clamping action of a
fastener will tend to de~orm over a perio~ of time, as a result of a
condition kno~:~n as "cold flow", i.e. pemanent deformation resulting
from prolonged application of a stress belo~-~ the elastic limit of a
material. This condition is further aggraYated ~hen an assembly is
thermally cycled and the part tends to undergo a greater expansion
than the metal fastener will permit due to the dissimilarities in
thermal expansion coefficients. This is especially true, for in-
stance, in the automotive industry where assemblies are frequently
exposed to severe temperature cycles during ~hich the materials are
alternately subjected to thermal expansion and contraction.
In the past, various types of inserts have been employed in
plastic articles either by press-fitting ~he insert into a finished
molding or by placing the insert in the cavity so that it becomes
an integral part of the molding. Typical inserts of this type
30 include a ~ide variety of internally threaded bushings used for
attaching a molded plastic article to another object. By way of
example, U. S. Patent 2,591,575 to McCollum, describes an internally-
threaded, expandable fastener insert for use in molded plastic
articles adapted to be anchored to the plastic article by means of
35 which other parts may be fastened thereto.
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This and other similar prior art inserts are
distinguished from the insert of the present invention
which is not internally threaded to engage a fastener and
is not adapted to anchor the part by expanding outwardly
in a radial direction in response to compressive loading
by a fastener. Rather, the insert of this invention is
designed to collapse uniformly in an axial direction with-
out exerting lateral forces on the part due to lateral
motion of the external surface. In this manner, the
insert described herein will prevent substantial defor-
mation of the part while maintaining the specified com-
pressive loading on the assembly.
Accordingly, it is a principal object of the
instant invention to provide a means for mounting parts
onto a workpiece by employing a collapsible tubular
insert in the part which is adapted to absorb a sub-
stantial amount of the total compressive load exerted
upon tightening a fastener.
In accordance with one aspect of the invention
there is provided a tubular insert adapted for use in
mounting a part onto a base member, said insert having
a hollow inner core for receiving a fastener and further
having at least one annular groove formed around the
external surface thereof to permit said insert to
collapse uniformly in an axial direction responsive to
a compressive force exerted in an axial direction against
the end of said insert, whereby a substantial portion
of said compressive force is absorbed by said insert.
In another aspect of the invention there is
provided an assembly for mounting parts onto a base
member, said assembly comprising (1) a part having a
lower surface for attachment to a base member and a
mounting hole for receiving a fastener, and (2) a tubu-
lar insert of the invention engaged in said mounting
hole, the lower end surface of said insert being in
substantial alignment with the lower surface of the part,
and the upper end surface of said insert projecting out-
ward from the upper surface of the part. The insert
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collapses uniformly in the axial direction responsive to
the compressive force exerted by the fastener to absorb
a substantial portion of the compressive force upon
tightening the fastener.
In particular the assembly of the invention
comprises a part which may be formed from plastic, wood,
or a metal having a higher coefficient of expansion than
steel, and a hollow cylindrical insert. The part is
provided with a mounting hole which is sized to accomo-
date the insert. The insert is sized so that it is
securely engaged in the mounting hole, the engagement
being provided by fitting the insert in the mounting
hole after molding or machining the part. It is also
essential that the length of the insert exceed the thick-
ness of the part so that the upper end surface of the
insert can extend beyond the upper surface of the part
to provide the initial engagement with the fastener.
In order to permit the insert to collapse uni-
formly in an axial direction, relative to the axis of
symmetry of the insert, the insert may be provided with
an annular groove formed along its external surface.
There may be a single groove or a plurality of grooves or,
in an alternate embodiment, the cylinder walls may be
formed into evenly-spaced corrugations. They may have a
rounded, triangular, rectangular or squared cross-section,
although a
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rounded cross-section is preFerred. In an especially preferred
embodiment, the groove is designed with a centrally disposed annular
bulge or ridge, as shown in Fig. 1 and Fig. 2.
While the groove may have a variety of configurations, the
5 depth of the groove is significant since the thickness of the cylin-
der wall at the grooved section determines the compressive load
necessary to cause the insert to collapse. This collapsed load is
somewhat less than the total rated compressive load for the assembly.
Thus, the insert is caused to collapse until its upper end surface
10 is in substantial alignment with the upper surface nF the part. In
this configuration, the washer, if one is employed, makes physical
contact with both the insert and the part. As the fastener is
tightened further until the total rated compressive load for the
assembly is reached, the insert absorbs a substantial amount of
15 total load applied by the fastener.
In addition, the insert is adapted to collapse uniformly in an
axial direction without outward lateral motion of the cylinder walls
into the part. Thus, the insert does not exert forces on the part
which could result in excessive stress and deformation.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a sectional view of the assembly prior to the
application of compressive loading.
Fig. 2 is a sectional view of the assembly of Fig. 1 after
applying compressive force.
Fig. 3 is a sectional view analogous to Fig. 1 but illus-
trating an alternate groove design for the insert.
Fig. 4 is a sectional view analogous to Fig. 1 but illus-
trating an alternate insert configuration.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 1 shows the hollow cylindrical insert 2 engaged in a
mounting hole in part 14. The insert 2 is provided with an
annular groove 4 formed along external wall surface 6, and an in-
ternal wall surface 8 of uniform diameter. In this particular
embodiment, the groove design incorporates an annular ridge 5 formed
within the groove. The insert 2 is also provided with a lower end
surface 10, which is substantially aligne(l with the lower surface 18
of part 14, and an upper end surface 12 extending beyond the upper
surface 16 of said part. Fas-tener element 20, with washer 22, is
shown aligned through the insert 2, engaging the upper end surface
12 of the insert and base member 24.
Figure 2 shows the fastener assembly embodied in Figure 1
with the insert 2 depicted in a collapsed condition, wherein the
upper end surface 12 thereof is in substantial alignment with the
upper surface 16 of part 14, and the washer 22 is in contact with
both the upper end sur-face 12 of the insert and the upper surface
16 of the part.
Annular ridge 5 is shown with an outward fold or crease
relative to the axis of symmetry of the insert. It should, how-
ever, be noted that while Figure 2 is intended to illustrate a
typical compressed or collapsed configuration, this invention is
not limited to any particular collapsed configuration. Thus, the
ridge 5 may, in a particular instance, be caused to fold inward
if desired.
Figure 3 illustrates another embodiment of the assembly of
Figure 1 with insert 32 having lower end surface 40, upper end
surface 39, internal wall surface 38 of substantially uniform
diameter, and a substantially rounded annular groove 34 formed
along the external wall surface 36.
Figure 4 shows a further embodiment of the assembly of
Figure 1 wherein insert 42, having a lower end surface 50, an
upper end surface 49, internal wall surface 48, and external wall
surface 46, said insert being provided with a multiplicity of
evenly-spaced annular corrugations on both the internal and ex-
ternal wall surfaces.
The insert may be fabricated of any suitable materials which
satisfy the performance criteria. Suitable materials include,
but are not limited to, metallic materials, including steel, brass,
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and aluminum, and the like, as well as plastic materials, such as
nylon. The ternn "plastic", as employed in the instant specification
and claims, is intended to denote a molded synthetic polymer,
including both the thermoplastic and thermosetting varieties, which
may be cured to a hardened state. A typical example of such a
molded plastic material is a phenolic resin.
It is also contemplated that the base member may be formed of
any solid, i.e. physically rigid, material such as, for example,
plastic, metal, concrete, wood, glass, and the like.
The types of fasteners which may be employed in this invention
are conventional and include bolts, machine screws, wood screws and
the like, with the only limitation being that the particular fastener
be compatible with the base member and be capable of collapsing the
insert. The fastener is preferably fabricated from metal, especially
steel, and may or may not include a washer.
The article or part to be attached to the base member may be
formed from any physically rigid material having a higher coefficient
of thermal expansion than the fastener material, and would therefore
include materials such as plastic, wood, metals such as aluminum,
and the like. In a preferred embodiment, the part is fabricated from
a plastic material derived from a phenolic resin and various filler
materials.
Although the insert has been described in terms of the various
groove configurations embodied in the drawings, it is not intended
thereby to limit the types of inserts which may be employed herein.
Of those particular embodiments shown, however, the configuration
provided in Figures 1 and 2 is most preferred since it is less
likely to crack or fracture at the grooved section.
The novel assembly of this invention is useful in a number of
30 applications, particularly in those environments where the assembly
is subjected to repeated fluctuations in temperature. As a specific
example, an article such as a plastic component for an internal
combustion engine, such as a plastic water pump, could be mounted
directly to the engine block by employing the insert device as
35 provided herein.
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While this inven-tion has been illustrated and described in
terms of particular embodiments thereof, it is not intended to be
limited to the details shown, since various modifications and
changes may be made without departing in any way from the spirit
of the present invention.
