Note: Descriptions are shown in the official language in which they were submitted.
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1 The present invention relates to inserts and studs for
use in materials which cannot be successfully fastened by
conventional screw threads due to the material' 5 hardness or
softness.
With the increasing use of materials such as composites
and plastics, the need for a fastener which will not delaminate,
split or otherwise damage the material has become apparent.
However, the known prior art has been developed Eor and directed
almost exclusively to fasteners for use in metal or non-composite
materials, e.g., aluminum. Thus prior art fastener technology
exists, but such technology is not directly applicable for
universal use in all types of materials. Hence the need for a
new fastener able to meet the particular needs of any industry
regardless of the type of material the fastener is to be secured
in.
The present invention is for use in materials that
cannot be successfully tapped with conventional screw threads.
The invention assembly includes fastener and insert components.
When installed the assembly of the invention exerts an external
pressure upon the parent material which secures the assembly
therein, and provides the user a pre-determined pullout strength.
The assembly is designed such that the fastener outer
thread mates with the insert inner thread to expand the insert
outwardly into the parent material as a seating torque is applied
to the fastener. The outer thread of the insert expands
uniformly into the opening in the parent material and e~erts a
compressive force upon the material in contact with the insert's
outer thread form. The installed assembly is locked in the
parent material against rotation by use of pins, serrations, or
the like.
A more thorough understanding oE the present invention
will be gained by reading the following description of the
preferred embodiments with reference to the accompanying drawings
in which:
Figure 1 is a view in perspective of a preferred
embodiment of a coil insert of the present invention.
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1 Figure 2 is an exploded view in elevation and partial
cross-section of a preferred embodiment of a fastener and an
insert of the present invention and the prepared opening in a
material for same.
Figure 3 is an enlarged view of a portion of the insert
shown in Fig. 2.
Figure 4 is a top plan view of the fastener shown in
Fig. 2.
Figure 5 is an enlarged view of a cross-section of the
outer thread of the fastener shown in Fig. 2.
Figure 6 is a view in cross-section of the present
invention prior to expansion of the insert into the material.
Figure 7 is a view in cross-section of the present
invention as installed in the material.
Figure 8 is a schematic view in elevation of the
installed invention illustrating the directional forces acting
when installation is completed.
Figure 9 is a view in elevation of a second embodiment
of an insert of the present invention.
Figure 10 is a view in elevation and partial cross-
section of a second embodiment of a fastener and of the insert of
the present invention shown in Fig. 9 prior to installation
within a prepared opening in a material.
Figure 11 is an enlarged view in cross-section of a
portion of the insert shown in Fig. 10.
Figure 12 is a view in elevation and partial cross-
section of the second embodiment shown installed in a parent
material.
Figure 13 is an enlarged view in cross-section of the
insert of the second embodiment shown in Fig. 13 as expanded into
the material.
Referring now to the drawings, Fig. 1 illustrates the
general appearance of the insert of a preferred embodiment for
the present invention. Fig. 2 shows this insert along with a
fastener and a prepared opening in a parent material. From Figs.
1 and 2 it can be seen that the insert 20 is formed as a
continuous, helical coil having a first or upper Eree end 21, a
second or lower free end 22, and a plurality of thread
convulutions 23 extending between the two ends 21, 22.
The insert 20 has an outer thread form defining an
outer diameter and an inner thread form defining an inner
diameter. The outer thread form 23a for each convolution is
arcuate in that the surface is radiused relative to an imaginary
longitudinal axis or the coil insert. The inner thread form 23b
is a substantially flat, planar surface sloping downwardly and
outwardly at approximately ten degrees with respect to a vertical
line. See Fig. 3. The insert is constructed a pre-determined
height dependent either upon the length of its mating fastener or
the depth of the prepared opening. The outer diameter is
preferably constant along the height H of the insert as is the
inner diameter. The insert may be wire formed or machined from
solid stock.
The coil insert 20 is constructed so as to be
threadable onto a fastener. Thus the outer diameter of a portion
of the fastener is preferably slightly smaller than the inner
; diameter of the coil insert to allow friction free, manual
assembly of the two items. In ~ig. 2 a -fastener 30 compatible
with the insert 20 illustrated. While a fastener of the insert
type with internal threads is shown in the preferred embodiment,
a stud-type fastener may also be used. The fastener 30 has an
uppermost end 31, a lowermost end 32, a shank portion 33 having a
plurality of outer thread convolutions extending between the two
ends, and a centrally located, internally threaded bore 34. The
uppermost end 31 is constructed so as to provide the fastener
with a shoulder portion 35 having a flat top surface 36 and an
inclined bottom surface 37 extending from the periphery of the
shoulder to the uppermost threaded convolution of the fastener.
In this embodiment the diameter of the shoulder portion 35 is
greater than the outer diameter of ~he threaded shank portion
33. At a location on the shoulder 35 intermediate the peripheral
edge 38 and the outer diameter of the threaded shank 33, at least
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1 one aperture 39 is provided which extends through the shoulder
portion from the top surface 36 to the bottom surface 37. In the
preferred embodiment a pair of apertures are provided opposite
each other. See Fig. 4.
With reference to Fig. 5, it can be appreciated that
the outer thread form of the fastener shank 33 is designed so as
to mate with the inner thread form of the coil insert 20. The
fastener outer thread form includes a substantially flat, planar
surface 40 inclined inwardly and upwardly at approximately ten
degrees with respect to a vertical line. Connecting the flat
planar surfaces 40 to each other are connecting portions 41 which
are relatively short compared to the planar surfaces 40. It will
be appreciated from a comparison of Figs. 3 and 5 that the outer
thread form of the fastener is thus compatible with the inner
thread form of the insert in that the surfaces of the two thread
forms will mate in view of the selected angle of inclination,
i.e., ten degrees. Depending upon the relative hardness of the
parent material, this angle of inclination in the illustrated
embodiments may vary.
The parent material 50 for the preferred embodiment is
prepared as shown in Fig. 2 by tapping a hole of pre-determined
depth with a thread form 52 compatible with the outer thread of
the insert 20. The uppermost portion 54 of the tapped hole is
countersunk to receive the shoulder portion 35 of the fastener so
that the top surface 36 of the installed fastener will lie flush
with the adjacent surface 56 of the parent material 50. The type
of parent material used will dictate the materials which are
suitable for constructing the insert and the fastener, thus no
particular materials are preferred for the present invention.
Turning now to Figs. 6, 7, and 8, the installation and operation
of the present invention may be explained.
Prior to installation the parent material is prepared
by tapping a hole therein of a si~e and shape to receive the
fastener with the coil insert threaded thereon. The tapped
thread is such as to mate with the outer t.hread of the installed
insert 20. The coil insert 20 is threaded on to the fastener 30
and together the assembly is loosely threaded into the prepared
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l opening or tapped hole to a position as shown in Fig. 6. At this
point in the installation procedure the fastener shoulder portion
35 preferably has not yet contacted the parent material, nor has
the coil insert 20 expanded outwardly relative to its initial
arrangement upon the fastener. Further rotational force applied
to the fastener causes the shoulder portion of the fastener to
settle into and contact the countersunk opening 54 of the
material 50. Once this has occurred a tightening or seating
torque T is applied as further rotation of the insert and
fastener assembly is attempted. As the seating torque T is
applied, the coil insert expands outward with the insert inner
thread moving along the mating outer thread of the fastener as
the fastener thread helix is caused to rotate in relationship
with the fastener shoulder 35. Simultaneously with the upward
movement of the insert inner thread, the insert outer thread
moves outwardly into contact with the tapped hole of the parent
material. The seating torque thus causes the coil insert to
exert an ou-tward Eorce which essentially compresses the parent
material it contacts. See Fig. 8. When the desired torque has
been applied, a pin 58 may be driven through each aperture 39 of
the fastener and into an underlying prepared opening 59 in the
parent material to prevent the installed assembly from
rotating. The insert and fastener assembly of the present
invention is thus locked into the parent material.
~5 From the foregoing a number of the unique features of
the present invention can be appreciated. The full thread form
of the coil insert is uniformly expanded as a result of the ramp
effect between the mating insert inner thread and the fastener
outer thread. The angle at which these threads are formed is
relatively shallow, e.g., ten degrees. As a result a better
outward thrust for expanding the insert outwardly into the parent
material is provided. The expansion of the coil insert is
constant and uniform as the seating torque is applied to the
fastener because of the unique thread forms provided by the
invention. The insert expands outwardly. It does not rotate as
the fastener is rotated during installation. The invention
provides to the user an insert and fastener assembly which may be
reliably secured in whatever material is selected.
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1 Figs. 9-13 illustrate a second embodiment for the
present invention. Briefly, this embodiment differs from the
preferred embodiment in that the outer thread form 60 for the
coil insert is not arcuate in shape but rather parallel with
respect to an imaginary longitudinal a~is for the insert.
Further, this outer thread form 60 is provided with a number of
serrations 61 spaced along the length of the coil convolutions.
The opening in the parent material for receiving the fastener is
not tapped but is instead a bored or molded hole of a diameter
which is slightly larger than the outer diameter of the coil
insert, such that the insert may be loosely received therein
apart from the fastener without binding.
To install the second embodiment, the coil insert 20'
is first placed into the prepared hole. The insert would appear
relative to the side wall of the bored hole as shown in Fig. 11,
i.e., flush but not secured. A thread compatible fastener 30' is
then threaded into the coil insert with the outer thread of the
Eastener mating with the inner thread of the coil insert in the
same manner as shown for the preferred embodiment. See Fig.
13. As the bottom surface of the bolt fastener head 62 contacts
the surface 71 of the structure 70 being secured to the
underlying parent material 50', further rotation of the bolt head
62 will exert a tightening torque upon the insert and fastener
assembly. Accordingly, this torque yields the above-discussed
ramp effect hetween the fastener and insert, with the insert
expanding outward into the parent material 50' as the inner
threads of the insert move along the fastener outer threads. As
can be seen in Fig. 13, when the pre-determined torque has been
achieved, the insert will have expanded sufficiently relative to
the fastener to embed at least a portion of its outer threads
into the parent material. The serrations 61 contained on the
outer threads provide an anti-rotation feature for this
embodiment.
Of course, further embodiments may be possible to one
skilled in the art in view of the above description, thus, the
invention is believed to be limited in scope not by the two
described embodiments but rather limited only by the claims which
; follow.
