U.S. patent application number 16/201919 was filed with the patent office on 2019-05-30 for blind fastener with frangible nut.
This patent application is currently assigned to SPS Technologies, LLC. The applicant listed for this patent is SPS Technologies, LLC. Invention is credited to Brian HOFFARTH, Su HUYNH, Florentin POPESCU, Terry VOVAN.
Application Number | 20190162222 16/201919 |
Document ID | / |
Family ID | 64734135 |
Filed Date | 2019-05-30 |
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United States Patent
Application |
20190162222 |
Kind Code |
A1 |
VOVAN; Terry ; et
al. |
May 30, 2019 |
BLIND FASTENER WITH FRANGIBLE NUT
Abstract
A blind fastener for connecting a plurality of panels includes a
core bolt and a core nut. The core nut surrounds the core bolt. The
core nut includes a main body, a nut head, and a tool engagement
section. The nut head has a larger outside diameter than the main
body. The core nut defines a frangible portion between the nut head
and the tool engagement section. The frangible portion is
configured to allow the tool engagement section to break off from
the nut head when a torque applied to the tool engagement section
is greater than a threshold torque after the blind fastener is
installed in the plurality of panels.
Inventors: |
VOVAN; Terry; (Upland,
CA) ; HOFFARTH; Brian; (Penfield, NY) ; HUYNH;
Su; (Jenkintown, PA) ; POPESCU; Florentin;
(Jenkintown, PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SPS Technologies, LLC |
Jenkintown |
PA |
US |
|
|
Assignee: |
SPS Technologies, LLC
Jenkintown
PA
|
Family ID: |
64734135 |
Appl. No.: |
16/201919 |
Filed: |
November 27, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62590915 |
Nov 27, 2017 |
|
|
|
62631560 |
Feb 16, 2018 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23P 19/062 20130101;
F16B 19/1063 20130101; F16B 37/145 20130101; F16B 31/021 20130101;
F16B 5/02 20130101; F16B 13/061 20130101; F16B 19/1072
20130101 |
International
Class: |
F16B 31/02 20060101
F16B031/02 |
Claims
1. A blind fastener for connecting a plurality of panels,
comprising: a core bolt; and a core nut surrounding the core bolt,
the core nut including a main body, a nut head, and a tool
engagement section, the nut head having a larger outside diameter
than the main body, wherein the core nut defines a frangible
portion between the nut head and the tool engagement section, the
frangible portion configured to allow the tool engagement section
to break off from the nut head when a torque applied to the tool
engagement section is greater than a threshold torque after the
blind fastener is installed in the plurality of panels.
2. The blind fastener according to claim 1, wherein the frangible
portion is configured to break off from the nut head such that an
end surface of the nut head is flush with or recessed from a front
one of the plurality of panels.
3. The blind fastener according to claim 1, wherein a radially
outward facing surface of the main body of the core nut includes a
plurality of dimples.
4. The blind fastener according to claim 1, wherein the blind
fastener consists of two pieces when in a pre-installed condition,
the core bolt being a first one of the two pieces and the core nut
being a second one of the two pieces.
5. The blind fastener according to claim 1, wherein the frangible
portion includes a break-off groove that extends along an entire
periphery of the core nut.
6. The blind fastener according to claim 5, wherein the nut head
defines a first cylindrical surface and the tool engagement portion
defines a second cylindrical surface, wherein the break-off groove
is recessed radially inward from the first and second cylindrical
surfaces.
7. The blind fastener according to claim 1, wherein the core nut
defines a counter bore having an enlarged part and a threaded part,
the enlarged part being formed in the tool engagement portion and
having a larger inside diameter than the threaded part, wherein the
threaded part is disposed in at least one of the nut head and an
end of the main body proximal to the nut head.
8. The blind fastener according to claim 1, wherein the main body
defines a counter bore having a smooth part and a threaded part,
the smooth part having an inside diameter larger than the threaded
part such that a nut stop shoulder is defined between the smooth
part and the threaded part, wherein the core bolt defines a bolt
stop shoulder that is configured to abut the nut stop shoulder when
a frangible portion of the core bolt is aligned with or recessed
from an outer surface of a front one of the plurality of
panels.
9. The blind fastener according to claim 1, wherein the core nut
further includes a sleeve coupled to an end of the main body that
is distal to the nut head, wherein the core bolt includes a bolt
head engaged with an end of the sleeve that is distal to the main
body, and wherein the main body includes a ramp surface configured
to slidingly engage an inner surface of the sleeve.
10. The blind fastener according to claim 9, wherein the bolt head
includes a central recess facing axially outward from the core
bolt.
11. The blind fastener according to claim 9, wherein the sleeve is
coupled to the end of the main body by a second frangible section
of the core nut.
12. The blind fastener according to claim 9, wherein the ramp
surface includes a plurality of grooves.
13. The blind fastener according to claim 1, wherein the nut head
defines a conical surface and an end surface, the conical surface
being configured to abut a countersunk surface of a front panel of
the plurality of panels, the end surface configured to be flush
with or recessed from a forward surface of the front panel when the
conical surface abuts the countersunk surface.
14. A blind fastener for connecting a plurality of panels,
comprising: a core bolt including a first tool engagement section,
a threaded section and a bolt head, the threaded section including
a first frangible portion configured to break the threaded section
when a torque applied to the first handling section exceeds a first
threshold torque, the threaded section being axially between the
first tool engagement section and the bolt head; and a core nut
including a main body, a nut head, a second frangible portion, and
a second tool engagement section, the second frangible portion
frangibly coupling the second tool engagement section to the nut
head and configured to break the second tool engagement section off
from the nut head when a torque applied to the second tool
engagement section exceeds a second threshold torque, the nut head
being axially between the second frangible section and the main
body, wherein at least one of the main body and the nut head
defines internal threads configured to engage the threaded section
of the core bolt, and the bolt head is configured to engage an end
of the core nut that is opposite the nut head.
15. The blind fastener according to claim 14, wherein the main body
includes a ramp section, a sleeve section, and a third frangible
section that frangibly couples the sleeve section to the ramp
section.
16. The blind fastener according to claim 14, wherein the core nut
further includes a sleeve section and the main body includes a ramp
surface configured to slidably engage an inner surface of the
sleeve section.
17. The blind fastener according to claim 14, wherein the nut head
defines a conical surface and an end surface, the conical surface
being configured to abut a countersunk surface of a front panel of
the plurality of panels, the end surface configured to be flush
with or recessed from a forward surface of the front panel when the
conical surface abuts the countersunk surface.
18. The blind fastener according to claim 16, wherein the main body
defines a counter bore having a smooth part and a threaded part,
the threaded part defining the internal threads, the smooth part
having an inside diameter larger than a major diameter of the
internal threads of the threaded part such that a nut stop shoulder
is defined between the smooth part and the threaded part, wherein
the core bolt defines a bolt stop shoulder that is configured to
abut the nut stop shoulder when a frangible portion of the core
bolt is aligned with or recessed from an outer surface of a front
one of the plurality of panels.
19. An assembly comprising: a front panel defining a front surface;
a rear panel defining a rear surface; a blind fastener inserted
into holes of the front and rear panels for connecting the front
and rear panels together, the blind fastener comprising: a core
bolt received in the holes of the front and rear panels and
defining a break-off notch and a bolt head; and a core nut
surrounding the core bolt, the core nut including a main body, a
nut head, a sleeve, and a tool engagement section, the main body
extending within the holes of the front and rear panels, the nut
head disposed in a counterbore or countersink of the hole of the
front panel, the tool engagement section disposed outside the front
and rear panels and adjacent to the front panel, the sleeve being
coupled to an end of the main body that is opposite the nut head
and disposed outside and adjacent to the rear panel, the sleeve
being configured to be deformed by axial force imparted by the bolt
head moving toward the panels, the core nut further defining a
break-off groove that frangibly couples the tool engagement section
to the nut head, wherein the break-off groove of the core nut and
the break-off notch of the core bolt are flush with or recessed
from the front surface of the front panel when the blind fastener
is fully installed.
20. The assembly according to claim 19, wherein the nut head of the
core nut includes an end surface that is flush with the front
surface of the front panel.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to and the benefit of U.S.
Provisional Application 62/590,915 filed on Nov. 27, 2017. This
application also claims priority to and the benefit of U.S.
Provisional Application 62/631,560 filed on Feb. 16, 2018. This
application is also related to co-pending application titled
"Two-Piece Blind Fastener," concurrently filed herewith and
commonly assigned with the present application. The disclosures of
the above applications are incorporated herein by reference.
FIELD
[0002] The present disclosure relates generally to fasteners, and
more particularly to blind fasteners having a core bolt and a
sleeve around the core bolt for connecting panels from one side of
the panels.
BACKGROUND
[0003] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0004] A blind fastener is typically used to secure multiple panels
together and to be installed from one side (i.e., a front side) of
the panels. The blind fastener may include a core bolt and a sleeve
surrounding the core bolt, which are inserted into a hole of the
panels. A portion of the sleeve adjacent to a rear side of the
panel may be deformed during installation of the fastener. The
deformed portion of the sleeve provides a bearing surface to induce
preload in the fastener such that the panels can be clamped
together.
[0005] After the deformed portion of the sleeve is formed, the core
bolt may be rotated to provide a preload to the fastener. When the
fastener is completely installed, a front portion of the core bolt
may break off. The break-off point of the typical core bolt cannot
be controlled and rotation of the nut relative to the bolt
typically needs to be controlled. In some circumstances it is
advantageous to have the fully installed fastener be flush with
panels for aesthetics and aerodynamic purposes. Typical fasteners
need to be prepared for painting by post-installation grinding to
be made flush with the panels when the break-off point is located
outside the countersunk head of the sleeve.
[0006] It can be difficult to control rotation of both the bolt and
the nut, while also ensuring a flush finished product, maximizing
the speed of installation, and reducing cost per fastener.
Furthermore, variations in grip length (i.e., the combined
thickness of the panels at the fastener) can occur based on
tolerances or design criteria. Accordingly, it is advantageous for
the blind fastener to be able to adapt to variations in grip length
without sacrificing strength of the joint. Moreover, the typical
fastener does not include a torque control feature. When excessive
torque is applied to the fastener, the sleeve of the fastener may
flare out to form a tulip configuration, resulting in a defective
installation.
[0007] These issues with the installation of blind fasteners are
addressed by the present disclosure.
SUMMARY
[0008] In one form, a blind fastener for connecting a plurality of
panels includes a core bolt and a core nut. The core nut surrounds
the core bolt. The core nut includes a main body, a nut head, and a
tool engagement section. The nut head has a larger outside diameter
than the main body. The core nut defines a frangible portion
between the nut head and the tool engagement section. The frangible
portion is configured to allow the tool engagement section to break
off from the nut head when a torque applied to the tool engagement
section is greater than a threshold torque after the blind fastener
is installed in the plurality of panels. In a variety of alternate
forms of the present disclosure: the frangible portion is
configured to break off from the nut head such that an end surface
of the nut head is flush with or recessed from a front one of the
plurality of panels; a radially outward facing surface of the main
body of the core nut includes a plurality of dimples; the blind
fastener consists of two pieces when in a pre-installed condition,
the core bolt being a first one of the two pieces and the core nut
being a second one of the two pieces; the frangible portion
includes a break-off groove that extends along an entire periphery
of the core nut; the nut head defines a first cylindrical surface
and the tool engagement portion defines a second cylindrical
surface, the break-off groove is recessed radially inward from the
first and second cylindrical surfaces; the core nut defines a
counter bore having an enlarged part and a threaded part, the
enlarged part being formed in the tool engagement portion and
having a larger inside diameter than the threaded part, wherein the
threaded part is disposed in at least one of the nut head and an
end of the main body proximal to the nut head; the main body
defines a counter bore having a smooth part and a threaded part,
the smooth part having an inside diameter larger than the threaded
part such that a nut stop shoulder is defined between the smooth
part and the threaded part, wherein the core bolt defines a bolt
stop shoulder that is configured to abut the nut stop shoulder when
a frangible portion of the core bolt is aligned with or recessed
from an outer surface of a front one of the plurality of panels;
the core nut further includes a sleeve coupled to an end of the
main body that is distal to the nut head, wherein the core bolt
includes a bolt head engaged with an end of the sleeve that is
distal to the main body, and wherein the main body includes a ramp
surface configured to slidingly engage an inner surface of the
sleeve; the bolt head includes a central recess facing axially
outward from the core bolt; the sleeve is coupled to the end of the
main body by a second frangible section of the core nut; the ramp
surface includes a plurality of grooves; the nut head defines a
conical surface and an end surface, the conical surface being
configured to abut a countersunk surface of a front panel of the
plurality of panels, the end surface configured to be flush with or
recessed from a forward surface of the front panel when the conical
surface abuts the countersunk surface.
[0009] In another form, a blind fastener for connecting a plurality
of panels includes a core bolt and a core nut. The core bolt
includes a first tool engagement section, a threaded section and a
bolt head. The threaded section includes a first frangible portion
configured to break the threaded section when a torque applied to
the first handling section exceeds a first threshold torque. The
threaded section is axially between the first tool engagement
section and the bolt head. The core nut includes a main body, a nut
head, a second frangible portion, and a second tool engagement
section. The second frangible portion frangibly couples the second
tool engagement section to the nut head and is configured to break
the second tool engagement section off from the nut head when a
torque applied to the second tool engagement section exceeds a
second threshold torque. The nut head is axially between the second
frangible section and the main body. At least one of the main body
and the nut head defines internal threads configured to engage the
threaded section of the core bolt. The bolt head is configured to
engage an end of the core nut that is opposite the nut head. In a
variety of alternate forms of the present disclosure: the main body
includes a ramp section, a sleeve section, and a third frangible
section that frangibly couples the sleeve section to the ramp
section; the core nut further includes a sleeve section and the
main body includes a ramp surface configured to slidably engage an
inner surface of the sleeve section; the nut head defines a conical
surface and an end surface, the conical surface being configured to
abut a countersunk surface of a front panel of the plurality of
panels, the end surface configured to be flush with or recessed
from a forward surface of the front panel when the conical surface
abuts the countersunk surface; the main body defines a counter bore
having a smooth part and a threaded part, the threaded part
defining the internal threads, the smooth part having an inside
diameter larger than a major diameter of the internal threads of
the threaded part such that a nut stop shoulder is defined between
the smooth part and the threaded part, wherein the core bolt
defines a bolt stop shoulder that is configured to abut the nut
stop shoulder when a frangible portion of the core bolt is aligned
with or recessed from an outer surface of a front one of the
plurality of panels.
[0010] In still another form, an assembly includes a front panel, a
rear panel, and a blind fastener. The front panel defines a front
surface. The rear panel defines a rear surface. The blind fastener
is inserted into holes of the front and rear panels for connecting
the front and rear panels together. The blind fastener includes a
core bolt and a core nut. The core bolt is received in the holes of
the front and rear panels and defines a break-off notch and a bolt
head. The core nut surrounds the core bolt. The core nut includes a
main body, a nut head, a sleeve, and a tool engagement section. The
main body extends within the holes of the front and rear panels.
The nut head is disposed in a counterbore or countersink of the
hole of the front panel. The tool engagement section is disposed
outside the front and rear panels and adjacent to the front panel.
The sleeve is coupled to an end of the main body that is opposite
the nut head and is disposed outside and adjacent to the rear
panel. The sleeve is configured to be deformed by axial force
imparted by the bolt head moving toward the panels. The core nut
further defines a break-off groove that frangibly couples the tool
engagement section to the nut head. The break-off groove of the
core nut and the break-off notch of the core bolt are flush with or
recessed from the front surface of the front panel when the blind
fastener is fully installed. In one form of a variety of alternate
forms of the present disclosure, the nut head of the core nut
includes an end surface that is flush with the front surface of the
front panel.
[0011] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the
description and specific examples are intended for purposes of
illustration only and are not intended to limit the scope of the
present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The present disclosure will become more fully understood
from the detailed description and the accompanying drawings,
wherein:
[0013] FIG. 1 is a cross-sectional view of a blind fastener
inserted through a countersunk hole of panels to be connected and
constructed in accordance with the teachings of the present
disclosure;
[0014] FIG. 2 is a perspective view of a blind fastener constructed
in accordance with the teachings of the present disclosure;
[0015] FIG. 3 is a cutaway view of the blind fastener of FIG.
2;
[0016] FIG. 4 is a perspective view of a core nut of a blind
fastener constructed in accordance with the teachings of the
present disclosure;
[0017] FIG. 5 is another perspective view of the core nut of FIG.
4;
[0018] FIG. 6 is a side view of the core nut of FIG. 4;
[0019] FIG. 7 is a cross-sectional view of the core nut, taken
along line A-A of FIG. 6;
[0020] FIG. 8 is a partial perspective view of the core nut of FIG.
4;
[0021] FIG. 9 is another partial perspective view of the core nut
of FIG. 4;
[0022] FIG. 10 is a cross-sectional view of a blind fastener in an
installed state before portions of a core bolt and a core nut break
off;
[0023] FIG. 11 is an end view of the blind fastener of FIG. 10;
[0024] FIG. 12 is an enlarged view of portion B of FIG. 10;
[0025] FIG. 13 is a cutaway view of a blind fastener in a final
installed state after portions of a core bolt and a core nut break
off;
[0026] FIG. 14 is a perspective view of a blind fastener after
portions of a core nut and core bolt break off to form flush
surfaces;
[0027] FIG. 15 is a cutaway view of the blinder fastener of FIG.
14;
[0028] FIG. 16 is a partial perspective view of the blinder
fastener of FIG. 14, wherein a core bolt is removed to show a
threaded part of the core nut;
[0029] FIG. 17 is a perspective view of a plurality blind fasteners
installed in a panel;
[0030] FIG. 18 is a perspective view of a blind fastener
constructed in accordance with a second form of the present
disclosure;
[0031] FIG. 19 is another perspective view of a blind fastener of
FIG. 18;
[0032] FIG. 20 is a perspective view of a blind fastener installed
in panels and constructed in accordance with a second form of the
present disclosure;
[0033] FIG. 21A is a cross-sectional view of a blind fastener
constructed in accordance with a second form of the present
disclosure;
[0034] FIG. 21B is an enlarged view of portion C of FIG. 21A;
[0035] FIG. 21C is a stress diagram of a portion of the fastener
under a load/force;
[0036] FIG. 22A to 22E depict a series of breakage and deformation
action of the blind fastener; and
[0037] FIG. 23 is a perspective view of a fastener in its initial
installation stage and a fastener in its final installation
stage.
[0038] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0039] The following description is merely exemplary in nature and
is not intended to limit the present disclosure, application, or
uses.
[0040] Referring to the FIGS. 1 to 3, a blind fastener 30 according
to a first form of the present disclosure is configured to connect
a plurality of panels including a front panel 1 and a rear panel 2,
and is configured to be inserted into a countersunk hole 31 of the
front and rear panels 1 and 2. The fastener 30 includes a core bolt
3, a core nut 5 surrounding a middle portion of the core bolt 3,
and a sleeve 4 surrounding a rear portion of the core bolt 3. The
rear portion of the core bolt 3 defines a smooth section 32, and
the front portion and the middle portion of the core bolt 3 define
a threaded section 34. A core bolt stop shoulder 10 is defined
between the smooth section 32 and the threaded section 34 of the
core bolt 3. An end of the front portion defines a tool engagement
section configured to be gripped by a tool (not shown) so that the
tool can impart torque on the core bolt 3 to rotate the core bolt
3. In the example provided, the tool engagement section of the core
bolt 3 includes a plurality of flat surfaces 23.
[0041] The smooth section 32 of the core bolt 3 has an outer
peripheral surface constituting a smooth rotational surface 12. The
threaded section 34 of the core bolt 3 includes outer threads and a
break-off notch 14 adjacent to the core bolt stop shoulder 10. The
break-off notch 14 constitutes a weaker point at the core bolt 3 so
that the core bolt 3 can be broken at the break-off notch 14 by
applying a torsional force (for a thread type fastener) or a
pulling force (for a pull type fastener) to the core bolt 3 after
the fastener 30 is completely installed in the panels 1 and 2. In
other words, the break-off notch 14 forms a frangible portion of
the core bolt 3. In the example provided, the break-off notch 14 is
disposed within the threaded section 34 such that the threads
extend in both axial directions relative to the break-off notch 14
and the break-off notch 14 is configured so that it does not
interfere with the threads of the threaded section 34 turning
through mating threads even when the area with the break-off notch
14 is threaded through the mating threads.
[0042] The core bolt 3 further includes a core bolt head 9 at a
rear end of the core bolt 3. The core bolt head 9 is disposed
outside the sleeve 4 and defines a recess 8 that facilitates a
removal process of the fastener 30 at the end of the product
lifecycle by drilling out the fastener 30. The core bolt head 9
extends radially outward of the rear end of the sleeve 4 to overlap
the rear end of the sleeve 4.
[0043] The sleeve 4 has a tubular configuration and includes an
inner peripheral surface 11 constituting a smooth rotational
surface 11 in contact with the smooth rotational surface 12 of the
core bolt 3. The smooth rotational surface 12 of the core bolt 3
and the smooth rotational surface 11 of the sleeve 4 function as
rotating bearing surfaces, which may be lubricated, when a front
end 13 of the core bolt 3 is tightened or loosened to move the core
bolt 3 relative to the core nut 5.
[0044] Referring to FIGS. 4 to 6, the core nut 5 has a tubular
configuration and includes a main body 40, a nut head 46 and a
second tool engagement section 42 having a larger outside diameter
than the main body 40. The main body 40 includes a cylindrical
portion 44 and a ramped portion 45. The second tool engagement
section 42 includes a cylindrical portion 48 and a flange 50. A
peripheral groove 52 is disposed between the nut head 46 and the
second tool engagement section 42 to form a frangible portion of
the core nut 5. The cylindrical portion 44 of the main body 40
further includes a plurality of dimples 58 at the front end. The
ramped portion 45 includes an outward facing ramp surface 22 and a
plurality of recess grooves 60 are formed on the ramp surface 22.
The ramp surface 22 and the plurality of recess grooves 60
facilitate a slide-over action of the sleeve 4 during installation
of the fastener 30, which will be described in more detail below.
The second tool engagement section 42 is configured to be gripped
by a tool during installation of the fastener 30 to prevent the
core nut 5 from rotating when the core bolt 3 is screwed into or
out of the core nut 5.
[0045] As clearly shown in FIG. 1, during installation of the
fastener 30, the cylindrical portion 44 of the main body 40 and the
nut head 46 are disposed in the countersunk hole 13 of the front
and rear panels 1 and 3, with the nut head 46 in the countersunk
portion of the hole 13 that is within the front panel 1. The second
tool engagement section 42 including the cylindrical portion 48 and
the flange 50 is disposed outside the front and rear panels 1 and
3. The peripheral groove 52 between the nut head 46 and the second
tool engagement section 42 functions as a break-off groove to allow
the second tool engagement section 42 to break off after the
fastener 30 is completely installed, which will be described in
more detail below.
[0046] Referring to FIGS. 7 to 9, the core nut 5 defines a counter
bore 20 including a smooth part 72, a threaded part 74, and an
enlarged part 76. The enlarged part 76 is formed in the tool
engagement section 42 of the core nut 5 and has a larger inside
diameter than the threaded part 74 and the smooth part 72. In the
example provided, the threaded part 74 is positioned such that the
internal threads extend axially through a portion of the nut head
46 and the cylindrical portion 44. The smooth part 72 has a larger
inside diameter than the threaded part 74 such that a core nut stop
shoulder 15 is defined between the smooth part 72 and the threaded
part 74. The nut head 46 includes a conical surface 80 and an end
surface 82 and is configured to be disposed in the countersunk hole
31 to retain the core nut 5 in one axial direction after the second
tool engagement section 42 breaks off. In the example provided, the
nut head 46 includes an outer cylindrical surface 83 (labeled in
FIG. 12) adjacent to the conical surface 80. The groove 52 is
recessed radially inward from the outer cylindrical surface 83 and
the outer surface of the cylindrical portion 48 of the second tool
engagement section 42.
[0047] Referring back to FIG. 1, during initial installation, the
threaded part 74 of the core nut 5 is threadedly engaged to the
threaded section 34 of the core bolt 3. The break-off notch 14 of
the core bolt 3 is disposed away from the front surface 16 of the
front panel 1, and the core bolt stop shoulder 10 is disposed away
from the core nut stop shoulder 15 of the core nut 5. The end
surface 82 of the nut head 46 of the core nut 5 and the break-off
groove 52 of the core nut 5 are flush with the front surface 16 of
the front panel 1.
[0048] Referring to FIGS. 1 and 10 to 12, by tightening the core
bolt front end 13, the core bolt head 9 is moved towards the core
nut 5 until the core bolt stop shoulder 10 comes to a positive stop
and abuts against the core nut stop shoulder 15. Concurrently, the
break-off notch 14 is moved to be flush with the front surface 16
of the front panel 1 and the end surface 82 of the nut head 46. The
break-off groove 52 is also flush with the front surface 16 of the
front panel 1. It is understood that the core bolt stop shoulder 10
and the core nut stop shoulder 15 are optional and do not have to
be present in the blind fastener 30 to create flush surfaces in the
blind fastener 30 after the blind faster is completely
installed.
[0049] As the core bolt 3 is tightened and the core bolt head 9 is
moved toward the core nut 5, the sleeve 4 is compressed and
deformed by the core bolt head 9. The sleeve 4 expands and covers
the ramp surface 22 of the core nut 5 and slides toward the rear
surface of the rear panel 2. Radial core nut serrations 19 may be
formed on the core nut 5 to prevent the sleeve 4 from freely
rotating during the initial installation. Before complete
installation of the fastener 30, the break-off notch 14 and the
external threads of the core bolt 3 are disposed inside the counter
bore 20 of the core nut 5 and are prevented against damage by any
external force. The break-off notch 14 and the external threads of
the core bolt 3 may be lubricated or sealants may be applied.
[0050] When the sleeve 4 is slid over the ramp surface 22 of the
core nut 5, the sleeve 4 is deformed, forming a bulb portion 21.
The bulb portion 21 may have a convex configuration depending on
the total grip length of the panels 1 and 2. The size of the bulb
portion 21 may be varied depending on the grip length, which is
equal to the thickness of the panels to be connected. The recess
grooves 60 formed on the ramp surface 22 of the core bolt 3 may
facilitate the sleeve front to cave into the recess grooves 60 to
avoid a defective tulip condition, i.e., the sleeve front flaring
out. As shown in FIG. 1, the sleeve 4 may have a counter bore 17
having an enlarged hole adjacent to the core nut 5. The enlarged
hole of the counter bore 17 also facilitates the slide-over action
of the sleeve 4 over the ramp surface 22 of the core nut 5.
[0051] As clearly shown in FIG. 10 and with continued reference to
FIGS. 1 and 7, an internal positive stop is provided between the
core bolt stop shoulder 10 and the core nut stop shoulder 15.
Therefore, the bulb portion 21, in a tensile linear stage, is not
in a fully compressed position. The bulb portion 21 can provide a
higher tensile preload in keeping the panels 1, 2 together in a
high frequency of vibration. Moreover, the internal positive stop
by the core bolt stop shoulder 10 and the core nut stop shoulder 15
allows the fastener 30 to reach a desired panel thickness,
preferably an average distance between maximum and minimum panel
thicknesses. This positive stop can also precisely regulate the
break-off position of the core bolt 3 and the core nut 5 of the
fastener 10, to ensure it would not exceed the tolerances of
protrusion or recess of the mounting panel 1 or the countersunk
head.
[0052] Referring to FIGS. 1, 7, and 13, after the fastener 30 is
installed in the panels 1 and 3, by continuing to apply a torsional
force on the core bolt 3, the threaded front portion of the core
bolt 3 is broken at the break-off notch 14. An end surface of the
core bolt 3 is formed and becomes flush with the front surface 16
of the panel 1. Also, by applying torsional force on the core nut
5, the second tool engagement section 42 breaks off at the
break-off groove 52. The end surface 82 of the main body 40 is
exposed and is flush with the front surface 16 of the front panel
1.
[0053] Referring to FIGS. 14 to 16, the fastener 30 is shown to be
in a completely installed state with the second tool engagement
section 42 of the core nut 5 and the front portion of the core bolt
3 broken off. The panels 1 and 3 being connected are not shown for
clarity. As shown, the end surface 82 of the main body 40 becomes
the outermost end of the fastener 30 in its completely installed
state, and the end surface 82 is flush with a surface of the core
bolt 3 that is formed after the front portion of core bolt 3 breaks
off at the break-off notch 14. In FIG. 16, the core bolt 3 is
removed to show the threaded part 74 of the core nut 5.
[0054] Referring to FIG. 17, a plurality of countersunk holes 31
are shown to be formed through a front panel 1. Fasteners are
installed in some of the countersunk holes 31. After the front
portions of the core bolts 3 and the second tool engagement section
42 of the core nuts 5 break off, flat end surfaces are formed on
the core bolts 3 to be flush with the front surface 16 of the front
panel 1. Also, the end surfaces 82 of the core nuts 5, which are
preformed and configured to be flush with the front surface 16 of
the front panel 1 during installation, are exposed. In one
countersunk hole 31 of FIG. 17, the front portion of the core bolt
3 breaks off but the second tool engagement section 42 of the core
nut 5 remains on the fastener 30, resulting in an uneven
appearance.
[0055] Referring to FIGS. 18 to 20, a blind fastener 90 according
to a second form of the present disclosure has a structure similar
to the blind fastener 30 of the first form except that the sleeve
and the core nut are integrally formed as a one-piece component. In
the following, like elements are indicated by like reference
numerals and the detailed description thereof is omitted herein for
clarity.
[0056] More specifically, the blind fastener 90 includes a core
bolt 3 and an outer member 92 surrounding the core bolt 3. The core
bolt 3 includes a core bolt head 9 at a rear end. The core bolt 3
is inserted into the outer member 92 with the core bolt head 9
disposed outside the outer member 92 and abutting against a rear
end of the outer member 92.
[0057] Referring to FIG. 21A, the outer member 92 includes a sleeve
96 and a nut 98 connected to the sleeve 96 at a breakable interface
100. The sleeve 96 and the nut 98 are integrally formed. The sleeve
96 is structurally similar to the sleeve 4 of the first form. The
nut 98 is structurally similar to the core nut 5 of the first form.
Therefore, the detailed description of the sleeve 96 and the nut 98
is omitted herein for clarity.
[0058] Referring to FIGS. 21A and 21B, when the core bolt 3 is
rotated relative to the one-piece outer member 92 to screw the core
bolt 3 out of the outer member 92 in a forward direction Y, a force
is applied on the outer member 92 and causes the breakable
interface 100 between the sleeve 96 and the nut 98 to break,
thereby separating the sleeve 96 from the nut 98. The breakable
interface 100 may be configured to break at a stress level of 20-30
in-lbs, though other configurations can be used. After the
breakable interface 100 breaks, the blind fastener 90 is
structurally similar to the blind fastener 30 of the first form. As
the force continues to be applied on the core bolt 3, the sleeve 96
that is disposed between the nut 98 and the core bolt head 9 slides
over the nut 98 and is compressed and deformed to form a bulb
portion. After the breakable interface 100 breaks, the blind
fastener 90 has the same operation as that of the blind fastener 30
and thus the detailed description thereof is omitted herein.
[0059] Referring to FIGS. 21A and 21C, a stress diagram of a part
of the blind fastener 90 and the panels 1 and 2 is shown. Under the
same load/force, the panels 1 and 2 and the nut 98 of the outer
member 92 have the lowest stress, whereas the sleeve 96 of the
outer member 92 has the highest stress. The core bolt 2 has a
stress level between the nut 98 and the sleeve 96 of the outer
member 92 under the same load/force. Therefore, using the blind
fastener 90 of the present disclosure, the panels 1 and 2 will not
be undesirably deformed by excessive force because the core bolt 3
will break before the panels 1 and 2 are deformed. On the other
hand, the sleeve 96 of the outer member 92 has the highest stress
under the same load/force and is first to be deformed, making the
blind fastener 90 relatively easily installed in the panels 1 and
2.
[0060] Referring to FIGS. 22A to 22E, a series of breakage and
deformation actions of the blind fastener 90 caused by a torsional
force applied to the core bolt 3 are described. FIG. 22A shows the
position of the outer member 92 relative to the core bolt 3 during
initial installation, where the sleeve 96 remains connected to the
nut 98 of the outer member 92. The sleeve 96 includes a front end
102 and a rear end 104. The panels 1 and 2 may be made of aluminum.
The core bolt 3 may be made of A286 stainless steel and can
withstand a stress of 177-196 ksi. The different portions of the
outer member 92, due to its varied thickness, can withstand
different stress. The front end 102 of the sleeve 96 of the outer
member 92 can withstand a stress of 75-78 ksi. The rear end 104 of
the sleeve 96 of the outer member 92 can withstand a stress of
130-140 ksi. The nut 98 of the outer member 92 can withstand a
stress of 177-196 ksi.
[0061] FIG. 22B shows the breakable interface 100 between the
sleeve 96 and the nut 98 is the first break point to break during
installation of the blind fastener 90, causing the sleeve 96 to be
separated from the nut 98. The breakable interface 100 can
withstand a stress of 20-30 in-lbs.
[0062] Referring to FIG. 22C, after the sleeve 96 is separated from
the nut 98, the sleeve 96, which is disposed between the core bolt
head 9 and the nut 98, is compressed therebetween as the core bolt
3 (and consequently the core bolt head 9) continues to move in the
forward direction Y. As a result, a bulb portion is created in the
sleeve 96.
[0063] Referring to FIG. 22D, as the core bolt 3 continues to be
moved in the forward direction Y, the sleeve 96 slides over the nut
98 and the core bolt stop shoulder 10 is moved toward the stop
shoulder 15 of the nut 98 until the two stop shoulders 10 and 15
contact each other. After the stop shoulder 10 of the core bolt 3
abuts against the stop shoulder 15 of the nut 98, continuing
application of force will cause the core bolt 3 to break at the
break-off notch 14, which is configured to break at a stress level
of 40-45 in-lbs. It is understood that the stop shoulders 10 and 15
do not have to be present to make the core bolt 3 breaks at the
break-off notch 14.
[0064] Referring to FIG. 22E, after the front portion of the core
bolt 3 breaks off at the break-off notch 14, a second tool
engagement section 42 of the nut 98 may break off at the break-off
groove 52, which is configured to break at a stress level of 75-95
in-lbs.
[0065] Therefore, the blind fastener 90 of the second form may
initially be a two-piece blind fastener that breaks at three
different break points at different stages of installation and
results in three separate pieces holding the panels 1 and 2
together. During initial installation, the sleeve 96 is separated
from the nut 98 of the outer member 92 at the breakable interface
100 at a stress level of 20-30 in-lbs. After the sleeve 96 is
deformed to have a bulb portion and the first panel 1 and the
second panel 2 are clamped between the second tool engagement
section 42 of the nut 98 and the bulb portion of the sleeve 96, the
front portion of the core bolt 3 can break off at a stress level of
40-45 in-lbs, creating a flush surface 108 at the core bolt 3.
Thereafter, the second tool engagement section 42 of the nut 98 can
break at the break-off groove at a stress level of 75-90 in-lbs,
thereby exposing the end surface 82 of the nut 98, which is another
flush surface created by blind fastener 90.
[0066] Referring to FIG. 23, the blind fastener 90 on the right
hand side is shown to be in its initial installation position where
the sleeve 96 has yet to be deformed to form a bulb portion,
whereas the blind fastener 90 on the left hand side is shown to be
in its final installation position where the front portion of the
core bolt 3 breaks off at the break-off notch 14 to form a flush
surface 108 on the core bolt 3 and the second tool engagement
section 42 of the nut 98 breaks off at the break-off groove 52 to
form a flush surface 82 on the nut 98 of the outer member 92.
[0067] A typical fastener (not shown) may result in a break-off end
being disposed inside the countersunk end of the core nut 5 or
protruding outside the countersunk end of the core nut 5.
Therefore, the secondary work to grind, shave, sand and fill in the
front side of the fastener is typically required. This process
requires a lot of labor time and costs, thereby increasing
manufacturing costs, which is particularly significant in the
aerospace industry where approximately 8,000 to 10,000 fasteners
are used in each commercial aircraft.
[0068] In contrast, the fastener of the present disclosure is
configured to create a flush surface with the front surface of the
front panel after the blind fastener is completely installed.
Therefore, the fasteners 30, 90 of the present disclosure can
shorten the manufacturing time and reduce the manufacturing costs
since no secondary work is required to treat the front surface of
the fastener.
[0069] The fastener of the present disclosure also provides an
aesthetic flush mounting and optimizes aerodynamic appearance. The
fastener of the present disclosure provides a higher preload
(compression pressure of the sandwiched mounting panels) with a
minimum 50% of the tensile strength. Current blind fasteners on the
market are fully compressed/deformed, which offers less preload
value. Higher preload values are significantly beneficial in
handling the high frequency vibrations of aircraft, in both
threaded-type blind fasteners and pull-type blind rivets. The
fastener of the present disclosure prevents over torque/pulling
that creates a lower preload value, and defective installation due
to a tulip configuration.
[0070] It should be noted that the disclosure is not limited to the
form described and illustrated as examples. A large variety of
modifications have been described and more are part of the
knowledge of the person skilled in the art. These and further
modifications as well as any replacement by technical equivalents
may be added to the description and figures, without leaving the
scope of the protection of the disclosure and of the present
patent.
[0071] As used herein, the phrase at least one of A, B, and C
should be construed to mean a logical (A OR B OR C), using a
non-exclusive logical OR, and should not be construed to mean "at
least one of A, at least one of B, and at least one of C.
[0072] Unless otherwise expressly indicated, all numerical values
indicating mechanical/thermal properties, compositional
percentages, dimensions and/or tolerances, or other characteristics
are to be understood as modified by the word "about" or
"approximately" in describing the scope of the present disclosure.
This modification is desired for various reasons including
industrial practice, manufacturing technology, and testing
capability.
[0073] The terminology used herein is for the purpose of describing
particular example forms only and is not intended to be limiting.
The singular forms "a," "an," and "the" may be intended to include
the plural forms as well, unless the context clearly indicates
otherwise. The terms "including," and "having," are inclusive and
therefore specify the presence of stated features, integers, steps,
operations, elements, and/or components, but do not preclude the
presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof. The
method steps, processes, and operations described herein are not to
be construed as necessarily requiring their performance in the
particular order discussed or illustrated, unless specifically
identified as an order of performance. It is also to be understood
that additional or alternative steps may be employed.
[0074] The description of the disclosure is merely exemplary in
nature and, thus, examples that do not depart from the substance of
the disclosure are intended to be within the scope of the
disclosure. Such examples are not to be regarded as a departure
from the spirit and scope of the disclosure. The broad teachings of
the disclosure can be implemented in a variety of forms. Therefore,
while this disclosure includes particular examples, the true scope
of the disclosure should not be so limited since other
modifications will become apparent upon a study of the drawings,
the specification, and the following claims.
* * * * *