U.S. patent application number 16/932724 was filed with the patent office on 2020-11-05 for light weight seal cap.
The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Susan E. DeMoss, Larry S. Hebert, Michael D. Swan, Robin E. Wright, Sheng Ye, Jonathan D. Zook.
Application Number | 20200347874 16/932724 |
Document ID | / |
Family ID | 1000004961332 |
Filed Date | 2020-11-05 |
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United States Patent
Application |
20200347874 |
Kind Code |
A1 |
Zook; Jonathan D. ; et
al. |
November 5, 2020 |
LIGHT WEIGHT SEAL CAP
Abstract
The present disclosure provides methods and articles useful in
sealing fasteners, including seal caps and methods of their use,
and in particular light weight seal caps having higher dielectric
breakdown strength, lower weight, and/or lower wall thickness. In
some embodiments, the seal caps according to the present invention
are made of a material having a dielectric breakdown strength of
greater than 1.0 kV/mm, in some embodiments greater than 15.0
kV/mm, and in some embodiments greater than 50.0 kV/mm. In some
embodiments, the seal caps according to the present invention are
thin-walled, having an average wall thickness of less than 1.5 mm
and in some embodiments less than less than 0.5 mm. In some
embodiments, the seal cap comprises a polyurethane polymer, a
polythioether polymer, a polysulfide polymer, a fluorinated
thermoplastic polymer, a THV polymer, a fluorinated thermoset
polymer, an engineering thermoplastic, and/or a PEEK polymer.
Inventors: |
Zook; Jonathan D.; (Baytown
Township, MN) ; Hebert; Larry S.; (Hudson, WI)
; Swan; Michael D.; (Lake Elmo, MN) ; Ye;
Sheng; (Woodbury, MN) ; DeMoss; Susan E.;
(Stillwater, MN) ; Wright; Robin E.; (Hudson,
WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Family ID: |
1000004961332 |
Appl. No.: |
16/932724 |
Filed: |
July 18, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16217197 |
Dec 12, 2018 |
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16932724 |
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14783916 |
Oct 12, 2015 |
10174781 |
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PCT/US2014/034073 |
Apr 15, 2014 |
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16217197 |
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61811988 |
Apr 15, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64D 45/02 20130101;
F16B 37/14 20130101 |
International
Class: |
F16B 37/14 20060101
F16B037/14; B64D 45/02 20060101 B64D045/02 |
Claims
1. A method of protecting a fastener from lightning strikes, said
method comprising: a) providing a fastener; b) providing a seal cap
which defines an interior, wherein the seal cap comprises a THV
polymer; c) providing an uncured sealant to the interior of the
seal cap or to the fastener or to both; and d) positioning the seal
cap over the fastener such that at least a portion of the fastener
resides in the interior of the seal cap. e) curing the sealant.
2. The method according to claim 1 wherein the seal cap is
translucent or transparent, and curing the sealant comprises
application of actinic radiation to the sealant through the seal
cap.
3. The method according to claim 1 wherein the fluorinated
thermoplastic polymer has a dielectric breakdown strength of
greater than 30.0 kV/mm.
4. The method according to claim 1 wherein the fluorinated
thermoplastic polymer has a dielectric breakdown strength of
greater than 50.0 kV/mm.
5. The method according to claim 1 wherein the seal cap has an
average wall thickness of less than 1.5 mm.
6. The method according to claim 1 wherein the interior of the seal
cap is provided with a quantity of an uncured sealant.
7. A lightning strike protected fastener construction comprising:
a) a fastener; b) a seal cap defining an interior; and c) a cured
sealant in the interior of the seal cap; wherein the seal cap
comprises a THV polymer, the seal cap is positioned over the
fastener such that at least a portion of the fastener resides in
the interior of the seal cap, and the cured sealant binds the seal
cap to the fastener.
8. The fastener construction according to claim 7 wherein the seal
cap is translucent or transparent, and the sealant comprises an
actinic radiation curable composition.
9. The fastener construction according to claim 7 wherein the
fluorinated thermoplastic polymer has a dielectric breakdown
strength of greater than 30.0 kV/mm.
10. The fastener construction according to claim 7 wherein the seal
cap has an average wall thickness of less than 1.5 mm.
11. A lightning strike protection application-ready seal cap
comprising: a) a seal cap which defines an interior; and b) a
quantity of an uncured sealant in the interior of the seal cap,
wherein the seal cap comprises a THV polymer.
12. The application-ready seal cap according to claim 11 wherein
the seal cap is translucent or transparent, and the uncured sealant
is curable by the application of actinic radiation.
13. The application-ready seal cap according to claim 11 wherein
the fluorinated thermoplastic polymer has a dielectric breakdown
strength of greater than 30.0 kV/mm.
14. The application-ready seal cap according to claim 11 wherein
the fluorinated thermoplastic polymer has a dielectric breakdown
strength of greater than 50.0 kV/mm.
15. The application-ready seal cap according to claim 11 wherein
the seal cap has an average wall thickness of less than 1.5 mm.
16. A seal cap for lightning strike protection of a fastener, with
the seal cap comprising a THV polymer.
17. The seal cap according to claim 16 which is translucent or
transparent to actinic radiation.
18. The seal cap according to claim 16 wherein the fluorinated
thermoplastic polymer has a dielectric breakdown strength of
greater than 30.0 kV/mm.
19. The seal cap according to claim 16 wherein the fluorinated
thermoplastic polymer has a dielectric breakdown strength of
greater than 50.0 kV/mm.
20. The seal cap according to claim 16 having an average wall
thickness of less than 1.5 mm.
Description
FIELD OF THE DISCLOSURE
[0001] This disclosure relates to methods and articles useful in
sealing fasteners, including seal caps and methods of their use,
and in particular light weight seal caps having higher dielectric
breakdown strength, lower weight, and/or lower wall thickness.
SUMMARY OF THE DISCLOSURE
[0002] Briefly, the present disclosure provides a method of
protecting a fastener comprising the steps of: a) providing a
fastener; b) providing a seal cap which defines an interior,
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 1.0 kV/mm, and wherein the seal
cap has an average wall thickness of less than 1.5 mm; c) applying
an uncured sealant to the interior of the seal cap or to the
fastener or to both; and d) positioning the seal cap over the
fastener such that at least a portion of the fastener resides in
the interior of the seal cap. The method may additionally comprise
the step of curing the sealant. In some embodiments, the seal cap
is optically translucent and the step of curing the sealant
comprises application of actinic radiation to the sealant through
the seal cap.
[0003] In another aspect, the present disclosure provides a method
of protecting a fastener comprising the steps of: f) providing a
fastener; g) providing a seal cap which defines an interior,
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 1.0 kV/mm, wherein the seal cap
has an average wall thickness of less than 1.5 mm, and wherein the
interior of the seal cap contains a quantity of an uncured sealant;
and h) positioning the seal cap over the fastener such that at
least a portion of the fastener resides in the interior of the seal
cap. The method may additionally comprise the step of curing the
sealant. In some embodiments, the seal cap is optically translucent
and the step of curing the sealant comprises application of actinic
radiation to the sealant through the seal cap.
[0004] In another aspect, the present disclosure provides a
protected fastener construction comprising: q) a fastener; r) a
seal cap which defines an interior; and s) a cured sealant; wherein
the seal cap comprises a material having a dielectric breakdown
strength of greater than 1.0 kV/mm, and wherein the seal cap has an
average wall thickness of less than 1.5 mm; wherein the seal cap is
positioned over the fastener such that at least a portion of the
fastener resides in the interior of the seal cap; and wherein the
interior of the seal cap additionally contains the cured sealant
which binds the seal cap to the fastener.
[0005] In another aspect, the present disclosure provides an
application-ready seal cap comprising: v) a seal cap which defines
an interior; and w) a quantity of an uncured sealant; wherein the
seal cap comprises a material having a dielectric breakdown
strength of greater than 1.0 kV/mm, and wherein the seal cap has an
average wall thickness of less than 1.5 mm; and wherein the
interior of the seal cap contains the quantity of uncured
sealant.
[0006] In another aspect, the present disclosure provides a seal
cap for protection of a fastener comprising a material having a
dielectric breakdown strength of greater than 1.0 kV/mm having an
average wall thickness of less than 1.5 mm.
BRIEF DESCRIPTION OF THE DRAWING
[0007] FIG. 1 is an embodiment of a seal cap according to the
present invention.
[0008] FIGS. 2a-2c are schematic representations of certain
embodiments of seal caps according to the present invention.
[0009] FIG. 3a is a schematic representation of an embodiment of a
step in a process for making a sealed fastener according to the
present invention.
[0010] FIG. 3b is a schematic representation of one embodiment of a
sealed fastener according to the present invention.
DETAILED DESCRIPTION
[0011] The present disclosure provides seal caps, methods of their
use, and constructions comprising seal caps. In machine
construction using rivets, bolts, and other types of fasteners, it
may be beneficial to apply a sealant to the exposed portion of the
fasteners to protect them from corrosion and to provide electrical
insulation. The sealant may also function as a barrier to the
passage of fluids, particularly where the fastener protrudes into a
fluid containment tank, particularly where that fluid is fuel, and
most particularly where that tank is on board an aircraft. In such
cases, the fastener may also function to prevent or reduce passage
of electrical discharge, such as from a lightning strike, into the
interior of a fuel tank. The seal caps according to the present
disclosure may be useful in sealing fasteners in many such
applications. FIGS. 1 and 2a each represent an embodiment of a seal
cap 10 according to the present invention.
[0012] In some embodiments, the seal caps according to the present
invention are translucent. As used herein, the term "translucent"
means able to transmit some portion of visible light, typically
greater than 20% of light in the 360-750 nm wavelength range, in
some embodiments greater than 30%, in some embodiments greater than
40%, and in some embodiments greater than 50%. In some embodiments,
the seal caps according to the present invention are optically
transparent, meaning transparent to the extent that the article
does not prevent a viewer from resolving an image, e.g., reading
text. In some embodiments, seal caps according to the present
invention permit visual inspection for flaws in construction or
installation or both.
[0013] In some embodiments, the seal caps according to the present
invention are made of a material having a dielectric breakdown
strength of greater than 1.0 kV/mm, in some embodiments greater
than 5.0 kV/mm, in some embodiments greater than 10.0 kV/mm, in
some embodiments greater than 15.0 kV/mm, in some embodiments
greater than 30.0 kV/mm, in some embodiments greater than 40.0
kV/mm, and in some embodiments greater than 50.0 kV/mm. In some
embodiments, the use of a material having a higher dielectric
breakdown strength permits the manufacture of a lighter seal
cap.
[0014] In some embodiments, the seal caps according to the present
invention are thin-walled. In some embodiments, the seal caps have
an average wall thickness of less than 1.5 mm, in some embodiments
less than 1.2 mm, in some embodiments less than 1.0 mm, in some
embodiments less than 0.5 mm, in some embodiments less than 0.2 mm,
in some embodiments less than 0.1 mm, and in some embodiments less
than 0.08 mm.
[0015] The seal caps may be made of any suitable material. In some
embodiments, the material is jet fuel resistant. In some
embodiments, the material has a TB (brittle temperature) below
-20.degree. C. In some embodiments, the seal cap comprises a
polyurethane polymer. In some embodiments, the seal cap comprises a
polythioether polymer. In some embodiments, the seal cap comprises
a polysulfide polymer. In some embodiments, the seal cap comprises
a fluorinated thermoplastic polymer. In some embodiments, the seal
cap comprises a THV polymer. In some embodiments, the seal cap
comprises a fluorinated thermoset polymer. In some embodiments, the
seal cap comprises an engineering thermoplastic. In some
embodiments, the seal cap comprises a PEEK polymer. In some
embodiments, the seal cap comprises a mixture of a polymer and a
nanoparticulate filler. In some embodiments, the seal cap comprises
a mixture of a polymer and a nanoparticulate curative. In some
embodiments, the seal cap comprises no fillers or other
particulates having an average particle size greater than 10 nm, in
some embodiments not greater than 5 nm, and in some embodiments not
greater than 1 nm.
[0016] In some embodiments, the seal cap and sealant comprise
different materials. In some embodiments, the seal cap and sealant
do not comprise different materials.
[0017] In some embodiments, the seal cap is at least partially
filled with sealant. With reference to FIG. 2b, seal cap 10 may be
filled with sealant 20. In some embodiments, the seal cap is at
least partially filled with sealant shortly before use. In some
embodiments, the seal cap is at least partially filled with sealant
and stored in ready-to-use form. In some such embodiments, a filled
or partially filled cap is stored at low temperature. In some such
embodiments, the filled or partially filled cap must be thawed
before use. In some embodiments, the seal cap is at least partially
filled with sealant prior to application to a fastener. In some
embodiments, the seal cap is at least partially filled with sealant
after application to a fastener, e.g., by syringe, by a sealant
port, or the like. In some embodiments, the seal cap is applied to
a fastener after application of sealant to the fastener. In some
embodiments, the fastener penetrates a substrate article. In some
embodiments, the fastener protrudes from a surface of a substrate
article. In some embodiments the substrate article is a composite
material. In some embodiments, the substrate article is an epoxy
matrix and glass or carbon fiber composite material. In some
embodiments, every portion of the fastener which protrudes from the
substrate article is covered by cured sealant or seal cap or both.
In some embodiments, every portion of the fastener which protrudes
from the substrate article is covered by cured sealant.
[0018] With reference to FIG. 2c, in one embodiment, seal cap 10
filled with sealant 20 covers fastener 30 which protrudes from
substrate article 40. Some excess amount of sealant 22 may be
pressed out of seal cap 10 during application.
[0019] The sealant may be any suitable material. In some
embodiments, the material is jet fuel resistant. In some
embodiments, the material has a TB (brittle temperature) below
-20.degree. C. In some embodiments, the sealant comprises a
polyurethane polymer. In some embodiments, the sealant comprises a
polythioether polymer. In some embodiments, the sealant comprises a
polysulfide polymer. In some embodiments, the sealant comprises a
mixture of a polymer and a nanoparticulate filler. In some
embodiments, the sealant comprises a mixture of a polymer and a
nanoparticulate curative. In some embodiments, the seal cap
comprises no fillers or other particulates having an average
particle size greater than 10 nm, in some embodiments not greater
than 5 nm, and in some embodiments not greater than 1 nm.
[0020] The seal cap material and sealant material may be chosen
such that strong bonds are formed between the sealant and the seal
cap. The sealant material may be chosen such that strong bonds are
formed between the sealant and the substrate. Optionally, the
sealant material may be chosen such that strong bonds are formed
between the sealant and the fastener.
[0021] After application of seal cap and sealant to a fastener the
sealant is typically cured. In some embodiments, the sealant is a
radiation cured sealant. In some embodiments, the sealant is cured
by application of actinic radiation to the sealant. In some
embodiments, the sealant is cured by application of green light to
the sealant. In some embodiments, the sealant is cured by
application of blue light to the sealant. In some embodiments, the
sealant is cured by application of violet light to the sealant. In
some embodiments, the sealant is cured by application of UV light
to the sealant. In some embodiments, the sealant is cured by
application of radiation to the sealant through a translucent seal
cap. In some embodiments, the sealant is substantially fully cured
in less than 60 seconds, in some embodiments less than 30 seconds,
and in some embodiments less than 10 seconds. In some embodiments,
cure is accomplished by addition of a curing agent shortly prior to
use. In some embodiments, cure is accomplished by heat cure at
ambient conditions. In some embodiments, cure is accomplished by
heat cure by application of heat from a heat source.
[0022] In some embodiments, a combination seal and seal cap is
molded in place over a fastener using a seal cap mold. In some
embodiments, the seal cap mold is translucent or transparent to
allow inspection and radiation cure of the form-in place seal and
seal cap.
[0023] FIG. 5a depicts one embodiment of such a process, wherein
seal cap mold 50 containing sealant 60 is located over fastener 30
which protrudes from substrate article 40. In this embodiment,
sealant 60 is cured by application of radiation 70. FIG. 5b depicts
the completed seal 62 after removal of seal cap mold 50.
[0024] Objects and advantages of this disclosure are further
illustrated by the following examples, but the particular materials
and amounts thereof recited in these examples, as well as other
conditions and details, should not be construed to unduly limit
this disclosure.
EXAMPLES
[0025] Unless otherwise noted, all reagents were obtained or are
available from Sigma-Aldrich Company, St. Louis, Mo., or may be
synthesized by known methods. Unless otherwise reported, all ratios
are by weight percent.
[0026] Abbreviations for the materials used in the examples are as
follows: [0027] AC-240: A gray two-part polysulfide-based sealant,
having a cured specific gravity of 1.61, obtained under the trade
designation "AEROSPACE SEALANT AC-240 CLASS B" from 3M Company, St.
Paul, Minn. [0028] AC-360: A brown two-part polysulfide-based
sealant, having a cured specific gravity of 1.40, obtained under
the trade designation "AEROSPACE SEALANT AC-360 CLASS B" from 3M
Company. [0029] AC-380: A gray two-part polysulfide-based sealant,
having a cured specific gravity of 1.10, obtained under the trade
designation "AEROSPACE SEALANT AC-380 CLASS B" from 3M Company.
[0030] APTIV: A 2-mil (50.8 .quadrature.m) unfilled
semi-crystalline polyetheretherketone film, obtained under the
trade designation "APTIV 1000-050G" from Victrex USA, Inc., West
Conshohocken, Pa. [0031] DABCO-33LV: A solution of 33%
triethylenediamine and 67% dipropylene glycol, obtained under the
trade designation "DABCO-33LV" from Air Products & Chemicals,
Inc., Allentown, Pa. [0032] DMDO: 1,8-Dimercapto-3,6-dioxaoctane,
obtained from Arkena, Inc., King of Prussia, Pa. [0033] DVE-2:
Diethyleneglycol divinylether, obtained from BASF Corp., Florham
Park, N.J. [0034] DVE-3: Triethyleneglycol divinylether, obtained
under the trade designation "RAPI-CURE DVE-3" from Ashland
Specialty Ingredients, Wilmington, Del. [0035] E-8220: A
diglycidylether of bisphenol F, obtained under the trade
designation "EPALLOY 8220" from Emerald Performance Materials, LLC,
Cuyahoga Falls, Ohio. [0036] GE-30: Trimethylolpropane
triglycidylether, obtained under the trade designation "ERISYS
GE-30" from Emerald Performance Materials Company. [0037] I-819:
Phenylbis(2,4,6-trimethylbenzoyl)phosphine Oxide, obtained under
the trade designation "IRGACURE 819" from BASF Corp. [0038] IPA:
Isopropyl alcohol. [0039] MEK: Methyl ethyl ketone. [0040] PR-1776:
A brown two-part polysulfide-based sealant, having a cured specific
gravity of 1.29, obtained under the trade designation "PR-1776M
CLASS B LOW WEIGHT FUEL TANK SEALANT" from PPG Aerospace/PRC-Desoto
International, Inc., Sylmar, Calif. [0041] PTE-1: A liquid
polythioether polymer prepared as follows. Into a 5 liter round
bottom flask equipped with an air driven stirrer, thermometer, and
a condenser, was added 167.1 grams (0.51 mol) E-8220 and 1641 grams
(9.0 mol) DMDO. After several minutes of stirring the mixture
exothermed to 45.degree. C. After another 30 minutes, the
temperature of the flask was increased 75.degree. C. and a mixture
of 1428.1 grams (7.1 mol) DVE-3, 50.7 grams (0.2 mol) TAC and 13.1
grams (0.07 mol) VAZO-67 was added drop wise. The reaction
proceeded substantially to completion affording 3,300 grams of
polythioether polymer. [0042] PTE-2 Into a 1000-ml round bottom
flask equipped with an air-driven stirrer, thermometer, and a
dropping funnel, was added 392.14 grams (2.15 moles) DMDO and 82.23
gram (0.25 mole) Epalloy 8220; 0.15 g DABCO (0.03 weight percent)
was mixed in as a catalyst. The system was flushed with nitrogen,
then mixed and heated for four hours at 60-70.degree. C. 12.5 g
(0.05 mole) of triallylcyanurate was added along with approximate
0.15 g Vazo 67. The material is mixed and heated at approximately
60.degree. C. for 30-45 minutes. 313.13 g (1.55 moles) DVE-3 was
then added drop-wise to the flask over 45 minutes, keeping the
temperature between 68-80.degree. C. Vazo 67 is added in
approximately 0.15 g units over approximately 6 hours for a total
of 0.4-0.6 g. The temperature is raised to 100.degree. C. and the
material degassed for approximately 10 minutes. The resultant
polythioether is approximately 3200 MW with 2.2 functionality.
[0043] TAC: Triallylcyanurate, obtained from Sartomer, Inc., Exton,
Pa. [0044] THV-200: A colorless, transparent fluoroelastomer,
obtained under the trade designation "THV 200" from 3M Company.
[0045] THV-200W: White pigmented THV 200, meeting the
specifications for Federal Standard 595B, Color #17529, obtained
from 3M Company. [0046] THV-500: A colorless, transparent
fluoroelastomer, obtained under the trade designation "THV 500"
from 3M Company. [0047] VAZO-67:
2,2'-azobis(2-methylbutyronitrile), obtained under the trade
designation "VAZO-67" from E.I. du Dupont de Nemours and Company,
Wilmington, Del.
Test Methods
Composite Test Panels.
[0048] Composite panels for lighting strike testing and seal cap
installation were made using the follow materials and methods. Ten
layers of unidirectional pre-preg, type "P2353W-19-30S", obtained
from Toray Composites (America), Inc., Tacoma, Wash., were oriented
45,135,0,90,0,0,90,0,135,45 to give a balanced structure. A layer
of woven graphite fabric, type "CYCOM 970/PWC T300 3K NT" from
Cytec Industries, Inc., Woodland Park, N.J. was placed on each side
of the 10-ply stack of pre-preg. The panel's size was nominally 12
by 12 inches (30.48 by 30.48 cm). The lay-up was then bagged using
standard autoclave bagging practices and cured in an autoclave at
90 psi (620.5 kPa) under full vacuum at 350.degree. F.
(176.7.degree. C.) for 2 hours. The panels were then cut in half
and match drilled with ten holes to take Hi-Shear fastener shanks,
Part No. "HL10VAZ6-3", obtained from Peerless Aerospace Fastener
Co., Farmington, N.Y. The panels were drilled such that there was
an overlap of 1 inch (2.54 cm) with the fasteners uniformly spaced
along the center of the overlap joint. The two panels halves were
joined together using the above mentioned shank and collar
assembly, Part No. "HL94W6", also from Peerless Aerospace Fastener
Co. The joint was wetted with AC-240 placed between the two panels
and into the holes before tightening the fasteners. The final test
panel had 10 fasteners centrally located in the overlap joint
spaced uniformly across its 10 inch (25.4 cm) width.
Lightning Strike Test.
[0049] Composite panels having test fasteners covered with seal
caps of the present invention was electrically grounded at the ends
opposite the overlap joint. The cap side of the panel was placed
inside a dark box, with a high speed camera positioned to record
the event, and the electrode positioned 1.0 inches (2.54 cm)
distant from the panel and directly opposite the target fastener.
An igniter wire was used to direct the arc to attach to the target
fastener. 21 kA to 103 kA peak amplitude was imposed as the "D"
bank component as described in SAE ARP1512. The "B" and "C"
components were not used for this test. Various voltages were
applied for each test and recorded. The pass fail for the tests was
based on observed light in the dark box around the fastener.
Seal Caps.
Comparative A
[0050] AC-360 sealant mixture was prepared in a 10:1
base:accelerator weight ratio at 70.degree. F. (21.1.degree. C.)
and injected into the female tooling of an 8 by 8 inch (20.32 by
20.32 cm) 9-cavity aluminum seal cap mold the cavities were
designed to give a frusto-conical shaped cap with a base diameter
of 15 mm a height of 15 mm and a wall thickness of 2.5 mm. The male
tooling closed the mold and the sealant cured for approximately 12
hours at 75.degree. F. (23.9.degree. C.), followed by 1 hour at
130.degree. F. (54.4.degree. C.). The resulting seal cap was then
removed from the tool.
Comparative B
[0051] The general procedure described in Comparative A was
repeated, wherein AC-360 was substituted with PR-1776.
Comparative C
[0052] A curable polythioether composition was prepared as follows.
A 40 ml. amber glass vial was charged with 10 grams PTE-1 and 0.604
grams TAC at 21.degree. C. To this was added 0.106 grams I-819. The
vial was then sealed and placed on a laboratory roller mill for 30
minutes at 50.degree. C. until the I-819 had dissolved. Part of
this mixture was then injected into the female tool of the 8 by 8
inch (20.32 by 20.32 cm) 9-cavity aluminum seal cap mold. A clear
epoxy male tool was then used to close the mold and the composition
cured by exposure, through the male tool, to a 455 nm LED, model
"CF 2000" from Clearstone Technologies, Inc., Minneapolis, Minn.,
for 1 minute at a distance of 0.2 inches (0.51 cm). The resulting
seal cap was then removed from the tool.
Example 1
[0053] A 50:50 by weight mixture of THV-200 and MEK was brushed
onto a single impression male tool dimensioned to give a
frusto-conical shaped cap with a base diameter of 10 mm and a
height of 10 mm and allowed to dry at 70.degree. F. (21.1.degree.
C.) for approximately 60 minutes. A second application of the
fluoroelastomer solution was applied to the male tool and again
allowed to dry giving a wall thickness of about 0.25 mm. The
finished cap was removed from the tool and trimmed, resulting in a
light weight clear seal cap.
Example 2
[0054] A white fluorinated polymer backing was prepared by feeding
a uniform mixture of pellets having 97 weight percent THV 500 and 3
weight percent THV 200W into an extruder. The uniform mixture was
extruded to a uniform thickness of 43 .quadrature.m onto a smooth
127 .quadrature.m thick polyethylene carrier web using a Haake
extruder. The unsupported film was then positioned and clamped over
the single impression male tool, located over a vacuum table. The
film was then heated to 400.degree. F. (204.4.degree. C.) using
radiant heat. After the film started to sag the tool was driven up
into the film and a vacuum applied to pull the film over the tool.
The film was then cooled to approximately 21.degree. C., removed
from the male tool and trimmed, resulting in a light weight seal
cap.
Example 3
[0055] A sheet of APTIV brand PEEK film was positioned over the
single impression male tool that had been pre-heated to 200.degree.
C. The film was then softened and deformed over the male tool by
means of a hot air gun. A pre-formed cap was then pressed over the
softened film and male tool, after which the assembly was cooled to
approximately 21.degree. C. The pre-formed cap was then removed,
revealing a light weight, translucent PEEK film cap, which was then
removed from the male tool and trimmed.
Example 4
[0056] A cross-linkable fluoroelastomer solution was prepared as
follows. 3.75 grams of a 20:80 by weight mixture of THV-200 and MEK
was mixed with 1.5 grams of a 5% by weight solution of
gamma-aminopropyltrimethoxysilane in IPA at 21.degree. C. The
solution was brushed onto a conical shaped, single impression, male
tool having a conical shaped cap with a base diameter of 10 mm and
a height of 10 mm, and dried at 21.degree. C. for approximately 60
minutes. A second application of the cross-linkable fluoroelastomer
solution was applied over the first coating, and dried at
21.degree. C. for approximately 60 minutes, resulting in a total
wall thickness of about 0.25 mm. The coated tool was then placed in
an oven set at 60.degree. C. for 30 minutes in order to crosslink
the polymer, after which the tool removed from the oven, cooled to
21.degree. C., and the resulting light weight translucent seal cap
removed from the tool and trimmed.
Seal Caps With Sealant Cores.
Example 5
[0057] A clear polythioether resin composition was prepared as
follows. 100 grams PTE-2 was homogeneously mixed with 6.78 grams
GE-30, 4.52 grams E-8220 and 1.00 grams DABCO-33LV at 21.degree. C.
Part of this mixture was then poured into a seal cap made according
to Example 1.
[0058] This produced a light weight filled cap assembly. The filled
seal cap assembly was then placed onto a fastener on the composite
panel and cured at 21.degree. C. for 24 hours. This resulted in a
fastener protected by a light weight clear cured seal cap.
Example 6
[0059] A seal cap made according to Example 2 was filled with
AC-240, which was prepared by mixing in a 10:1 by weight
base:accelerator ratio at 21.degree. C. This produced a light
weight filled cap assembly. The cap assembly was then placed onto a
fastener on a composite panel and cured at 21.degree. C. for 24
hours. This resulted in a fastener protected by a light weight
cured seal cap.
Example 7
[0060] A clear polythioether resin composition was prepared as
follows. A 40 ml. amber glass vial was charged with 7.000 grams
DMDO, 4.439 grams DVE-2 and 1.812 grams TAC at 21.degree. C. To
this was added 0.132 grams I-819. The vial was then sealed and
placed on a laboratory roller mill for 10 minutes until the I-819
had dissolved. Part of this mixture was then poured into a seal cap
made according to Example 1. This produced a light weight filled
cap assembly. The filled seal cap assembly was then placed onto a
fastener on the composite panel and cured by exposure to the 455
nm, model "CF 2000" LED for 30 seconds at a distance of 1 inch to
the composite panel. This resulted in a fastener protected by a
light weight clear cured seal cap.
Example 8
[0061] A filled translucent seal cap was prepared as generally
described in Example 5, wherein the polythioether seal cap was
replaced by a PEEK seal cap made according to Example 3.
Example 9
[0062] A filled translucent seal cap was prepared as generally
described in Example 8, wherein the PEEK seal cap was replaced by a
cross-linkable fluoroelastomer seal cap made according to Example
4.
Comparative D
[0063] A seal cap made according to Comparative B was filled with
PRC-1776, which was prepared by mixing in a 10:1 by weight
base:accelerator ratio at 21.degree. C. The cap assembly was then
placed onto a fastener on a composite panel and cured at 21.degree.
C. for 24 hours. This resulted in a fastener protected by a
standard weight cured seal cap.
Comparative E
[0064] A seal cap made according to Comparative A was filled with
AC-360, which was prepared by mixing in a 10:1 by weight
base:accelerator ratio at 21.degree. C. The cap assembly was then
placed onto a fastener on a composite panel and cured at 21.degree.
C. for 24 hours. This resulted in a fastener protected by a
standard weight cured seal cap.
Comparative F
[0065] A fastener protected by a standard weight cured seal cap
having a light weight cured sealant core was made according to the
general procedure described in Comparative E, wherein the AC-360
sealant core was substituted with AC-380.
[0066] Lightning strike tests of selected Examples and Comparatives
D-F are reported in Table 1. Cap weights and cap densities of
selected Examples and Comparative are A-C listed in Tables 2 and 3.
Dielectric breakdown strength for cap materials is reported in
Table 4.
TABLE-US-00001 TABLE 1 Peak Example Test # Current kA Pass/Fail
Example 6 1 21 Pass 2 24 Pass 3 27 Pass 4 28 Pass Comparative D 1
21 Pass 2 21 Pass 3 27 Pass Comparative E 1 21 Pass 2 27 Pass 3 28
Pass Comparative F 1 28 Pass 2 28 Pass 3 33 Pass
TABLE-US-00002 TABLE 2 Cap Weight Cap Example Composition (grams)
Example 1 THY 0.05 Example 2 THV 0.05 Comparative A Polysulfide
1.81 Comparative B Polysulfide 2.01
TABLE-US-00003 TABLE 3 Cap Weight Cap Example Composition (grams)
Comparative C Polythioether 1.75
TABLE-US-00004 TABLE 4 Dielectric Breakdown Cap of Example Cap
Material Strength kV/mm Comparatives Polysulfide 0.35 A, B, D, E, F
Examples THV 62 1, 2, 5, 6, 7 Examples PEEK 20 3, 9
[0067] The present disclosure includes following numbered list of
illustrative embodiments:
[0068] 1. A method of protecting a fastener comprising the steps
of: [0069] a) providing a fastener; [0070] b) providing a seal cap
which defines an interior, wherein the seal cap comprises a
material having a dielectric breakdown strength of greater than 1.0
kV/mm, and wherein the seal cap has an average wall thickness of
less than 1.5 mm; [0071] c) applying an uncured sealant to the
interior of the seal cap or to the fastener or to both; and [0072]
d) positioning the seal cap over the fastener such that at least a
portion of the fastener resides in the interior of the seal
cap.
[0073] 2. The method according to embodiment 1 wherein step c) is
performed before step d).
[0074] 3. The method according to embodiment 1 wherein step d) is
performed before step c).
[0075] 4. The method according to any of embodiments 1-3 wherein
the seal cap is optically translucent.
[0076] 5. The method according to any of embodiments 1-4 wherein
the seal cap is visibly transparent.
[0077] 6. The method according to any of the preceding embodiments
additionally comprising the step of: [0078] e) curing the
sealant.
[0079] 7. The method according to embodiment 6 wherein the seal cap
is optically translucent and wherein said step of curing the
sealant comprises application of actinic radiation to the sealant
through the seal cap.
[0080] 8. The method according to any of embodiments 6-7 wherein
the fastener protrudes from a first surface of a substrate article
and wherein, following steps c), d) and e), every portion of the
fastener which protrudes from the first surface of the substrate
article is covered by cured sealant or seal cap or both.
[0081] 9. A method of protecting a fastener comprising the steps
of: [0082] f) providing a fastener; [0083] g) providing a seal cap
which defines an interior, wherein the seal cap comprises a
material having a dielectric breakdown strength of greater than 1.0
kV/mm, wherein the seal cap has an average wall thickness of less
than 1.5 mm, and wherein the interior of the seal cap contains a
quantity of an uncured sealant; and [0084] h) positioning the seal
cap over the fastener such that at least a portion of the fastener
resides in the interior of the seal cap.
[0085] 10. The method according to embodiment 9 wherein the seal
cap and uncured sealant recited in step g) are at a temperature of
less than 5.degree. C., and wherein the method additionally
comprises the step of: [0086] i) warming the seal cap and uncured
sealant to a temperature of at least 20.degree. C.
[0087] 11. The method according to embodiment 9 or 10 wherein the
seal cap is optically translucent.
[0088] 12. The protected fastener construction according to any of
embodiments 9-11 wherein the seal cap is visibly transparent.
[0089] 13. The method according to any of embodiments 9-12
additionally comprising the step of: [0090] j) curing the
sealant.
[0091] 14. The method according to embodiment 13 wherein the seal
cap is optically translucent and wherein said step of curing the
sealant comprises application of actinic radiation to the sealant
through the seal cap.
[0092] 15. The method according to any of embodiments 13-14 wherein
the fastener protrudes from a first surface of a substrate article
and wherein, following step j), every portion of the fastener which
protrudes from the first surface of the substrate article is
covered by cured sealant or seal cap or both.
[0093] 16. The method according to embodiment 8 or embodiment 15
wherein said first surface is an interior surface of a fuel
container.
[0094] 17. The method according to embodiment 16 wherein said first
surface is an interior surface of a fuel container of an
aircraft.
[0095] 18. The method according to any of embodiments 6-8 and 13-17
wherein the seal cap and cured sealant substantially prevent
electrical arcing around the fastener.
[0096] 19. The method according to any of the preceding embodiments
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 5.0 kV/mm.
[0097] 20. The method according to any of the preceding embodiments
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 10.0 kV/mm.
[0098] 21. The method according to any of the preceding embodiments
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 15.0 kV/mm.
[0099] 22. The method according to any of the preceding embodiments
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 30.0 kV/mm.
[0100] 23. The method according to any of the preceding embodiments
wherein the seal cap comprises a material having a dielectric
breakdown strength of greater than 50.0 kV/mm.
[0101] 24. The method according to any of the preceding embodiments
wherein the seal cap has an average wall thickness of less than 1.0
mm.
[0102] 25. The method according to any of the preceding embodiments
wherein the seal cap has an average wall thickness of less than 0.5
mm.
[0103] 26. The method according to any of the preceding embodiments
wherein the seal cap has an average wall thickness of less than 0.1
mm.
[0104] 27. The method according to any of embodiments 1-26 wherein
the seal cap comprises a fluorinated thermoplastic polymer.
[0105] 28. The method according to any of embodiments 1-26 wherein
the seal cap comprises a THV polymer.
[0106] 29. The method according to any of embodiments 1-26 wherein
the seal cap comprises a fluorinated thermoset polymer.
[0107] 30. The method according to any of embodiments 1-26 wherein
the seal cap comprises an engineering thermoplastic.
[0108] 31. The method according to any of embodiments 1-26 wherein
the seal cap comprises a PEEK polymer.
[0109] 32. The method according to any of the preceding embodiments
wherein the uncured sealant is translucent.
[0110] 33. The method according to any of the preceding embodiments
wherein the uncured sealant is visibly transparent.
[0111] 34. The method according to any of the preceding embodiments
wherein the uncured sealant cures to form a material that is
translucent.
[0112] 35. The method according to any of the preceding embodiments
wherein the uncured sealant cures to form a material that is
visibly transparent.
[0113] 36. The method according to any of embodiments 1-35 wherein
the sealant comprises a polyurethane polymer.
[0114] 37. The method according to any of embodiments 1-35 wherein
the sealant comprises a polythioether polymer.
[0115] 38. The method according to any of embodiments 1-35 wherein
the sealant comprises a polysulfide polymer.
[0116] 39. The method according to any of the preceding embodiments
wherein the sealant comprises a mixture of a polymer and a
nanoparticulate filler.
[0117] 40. The method according to any of the preceding embodiments
wherein the sealant comprises a mixture of a polymer and a
nanoparticulate curative.
[0118] 41. A protected fastener construction comprising: [0119] q)
a fastener; [0120] r) a seal cap which defines an interior; and
[0121] s) a cured sealant; [0122] wherein the seal cap comprises a
material having a dielectric breakdown strength of greater than 1.0
kV/mm, and wherein the seal cap has an average wall thickness of
less than 1.5 mm; [0123] wherein the seal cap is positioned over
the fastener such that at least a portion of the fastener resides
in the interior of the seal cap; and [0124] wherein the interior of
the seal cap additionally contains the cured sealant which binds
the seal cap to the fastener.
[0125] 42. The protected fastener construction according to
embodiment 41 wherein the fastener protrudes from a first surface
of a substrate article and wherein every portion of the fastener
which protrudes from the first surface of the substrate article is
covered by cured sealant or seal cap or both.
[0126] 43. The protected fastener construction according to
embodiment 42 wherein said first surface is an interior surface of
a fuel container.
[0127] 44. The protected fastener construction according to
embodiment 42 wherein said first surface is an interior surface of
a fuel container of an aircraft.
[0128] 45. The protected fastener construction according to any of
embodiments 41-44 wherein the seal cap and cured sealant
substantially prevent electrical arcing around the fastener.
[0129] 46. The protected fastener construction according to any of
embodiments 41-45 wherein the seal cap is translucent.
[0130] 47. The protected fastener construction according to any of
embodiments 41-46 wherein the seal cap is visibly transparent.
[0131] 48. The protected fastener construction according to any of
embodiments 41-47 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 5.0 kV/mm.
[0132] 49. The protected fastener construction according to any of
embodiments 41-47 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 10.0 kV/mm.
[0133] 50. The protected fastener construction according to any of
embodiments 41-47 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 15.0 kV/mm.
[0134] 51. The protected fastener construction according to any of
embodiments 41-47 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 30.0 kV/mm.
[0135] 52. The protected fastener construction according to any of
embodiments 41-47 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 50.0 kV/mm.
[0136] 53. The protected fastener construction according to any of
embodiments 41-52 wherein the seal cap has an average wall
thickness of less than 1.0 mm.
[0137] 54. The protected fastener construction according to any of
embodiments 41-52 wherein the seal cap has an average wall
thickness of less than 0.5 mm.
[0138] 55. The protected fastener construction according to any of
embodiments 41-52 wherein the seal cap has an average wall
thickness of less than 0.1 mm.
[0139] 56. The protected fastener construction according to any of
embodiments 41-55 wherein the seal cap comprises a fluorinated
thermoplastic polymer.
[0140] 57. The protected fastener construction according to any of
embodiments 41-55 wherein the seal cap comprises a THV polymer.
[0141] 58. The protected fastener construction according to any of
embodiments 41-55 wherein the seal cap comprises a fluorinated
thermoset polymer.
[0142] 59. The protected fastener construction according to any of
embodiments 41-55 wherein the seal cap comprises an engineering
thermoplastic.
[0143] 60. The protected fastener construction according to any of
embodiments 41-55 wherein the seal cap comprises a PEEK
polymer.
[0144] 61. The protected fastener construction according to any of
embodiments 41-60 wherein the cured sealant is translucent.
[0145] 62. The protected fastener construction according to any of
embodiments 41-61 wherein the cured sealant is visibly
transparent.
[0146] 63. The protected fastener construction according to any of
embodiments 41-62 wherein the cured sealant comprises a
polyurethane polymer.
[0147] 64. The protected fastener construction according to any of
embodiments 41-62 wherein the cured sealant comprises a
polythioether polymer.
[0148] 65. The protected fastener construction according to any of
embodiments 41-62 wherein the cured sealant comprises a polysulfide
polymer.
[0149] 66. The protected fastener construction according to any of
embodiments 41-62 wherein the cured sealant comprises a mixture of
a polymer and a nanoparticulate filler.
[0150] 67. The protected fastener construction according to any of
embodiments 41-62 wherein the cured sealant comprises a mixture of
a polymer and a nanoparticulate curative.
[0151] 68. An application-ready seal cap comprising: [0152] v) a
seal cap which defines an interior; and [0153] w) a quantity of an
uncured sealant; wherein the seal cap comprises a material having a
dielectric breakdown strength of greater than 1.0 kV/mm, and
wherein the seal cap has an average wall thickness of less than 1.5
mm; and wherein the interior of the seal cap contains the quantity
of uncured sealant.
[0154] 69. The application-ready seal cap according to embodiment
68 wherein the seal cap is translucent.
[0155] 70. The application-ready seal cap according to embodiment
68 wherein the seal cap is optically transparent.
[0156] 71. The application-ready seal cap according to any of
embodiments 68-70 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 5.0 kV/mm.
[0157] 72. The application-ready seal cap according to any of
embodiments 68-70 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 10.0 kV/mm.
[0158] 73. The application-ready seal cap according to any of
embodiments 68-70 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 15.0 kV/mm.
[0159] 74. The application-ready seal cap according to any of
embodiments 68-70 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 30.0 kV/mm.
[0160] 75. The application-ready seal cap according to any of
embodiments 68-70 wherein the seal cap comprises a material having
a dielectric breakdown strength of greater than 50.0 kV/mm.
[0161] 76. The application-ready seal cap according to any of
embodiments 68-75 wherein the seal cap has an average wall
thickness of less than 1.0 mm.
[0162] 77. The application-ready seal cap according to any of
embodiments 68-75 wherein the seal cap has an average wall
thickness of less than 0.5 mm.
[0163] 78. The application-ready seal cap according to any of
embodiments 68-75 wherein the seal cap has an average wall
thickness of less than 0.1 mm.
[0164] 79. The application-ready seal cap according to any of
embodiments 68-78 wherein the seal cap comprises a fluorinated
thermoplastic polymer.
[0165] 80. The application-ready seal cap according to any of
embodiments 68-78 wherein the seal cap comprises a THV polymer.
[0166] 81. The application-ready seal cap according to any of
embodiments 68-78 wherein the seal cap comprises a fluorinated
thermoset polymer.
[0167] 82. The application-ready seal cap according to any of
embodiments 68-78 wherein the seal cap comprises an engineering
thermoplastic.
[0168] 83. The application-ready seal cap according to any of
embodiments 68-78 wherein the seal cap comprises a PEEK
polymer.
[0169] 84. The application-ready seal cap according to any of
embodiments 68-83 wherein the uncured sealant is translucent.
[0170] 85. The application-ready seal cap according to any of
embodiments 68-84 wherein the uncured sealant is visibly
transparent.
[0171] 86. The application-ready seal cap according to any of
embodiments 68-85 wherein the uncured sealant cures to form a
material that is translucent.
[0172] 87. The application-ready seal cap according to any of
embodiments 68-86 wherein the uncured sealant cures to form a
material that is visibly transparent.
[0173] 88. The application-ready seal cap according to any of
embodiments 68-87 wherein the sealant comprises a polyurethane
polymer.
[0174] 89. The application-ready seal cap according to any of
embodiments 68-87 wherein the sealant comprises a polythioether
polymer.
[0175] 90. The application-ready seal cap according to any of
embodiments 68-87 wherein the sealant comprises a polysulfide
polymer.
[0176] 91. The application-ready seal cap according to any of
embodiments 68-90 wherein the sealant comprises a mixture of a
polymer and a nanoparticulate filler.
[0177] 92. The application-ready seal cap according to any of
embodiments 68-91 wherein the sealant comprises a mixture of a
polymer and a nanoparticulate curative.
[0178] 93. The application-ready seal cap according to any of
embodiments 68-92 maintained at a temperature of less than
5.degree. C.
[0179] 94. A seal cap for protection of a fastener comprising a
material having a dielectric breakdown strength of greater than 1.0
kV/mm having an average wall thickness of less than 1.5 mm.
[0180] 95. The seal cap according to embodiment 94 which is
translucent.
[0181] 96. The seal cap according to embodiment 94 which is
optically transparent.
[0182] 97. The seal cap according to any of embodiments 94-96 which
comprises a material having a dielectric breakdown strength of
greater than 5.0 kV/mm.
[0183] 98. The seal cap according to any of embodiments 94-96 which
comprises a material having a dielectric breakdown strength of
greater than 10.0 kV/mm.
[0184] 99. The seal cap according to any of embodiments 94-96 which
comprises a material having a dielectric breakdown strength of
greater than 15.0 kV/mm.
[0185] 100. The seal cap according to any of embodiments 94-96
which comprises a material having a dielectric breakdown strength
of greater than 30.0 kV/mm.
[0186] 101. The seal cap according to any of embodiments 94-96
which comprises a material having a dielectric breakdown strength
of greater than 50.0 kV/mm.
[0187] 102. The seal cap according to any of embodiments 94-101
having an average wall thickness of less than 1.0 mm.
[0188] 103. The seal cap according to any of embodiments 94-101
having an average wall thickness of less than 0.5 mm.
[0189] 104. The seal cap according to any of embodiments 94-101
having an average wall thickness of less than 0.1 mm.
[0190] 105. The seal cap according to any of embodiments 94-104
comprising a fluorinated thermoplastic polymer.
[0191] 106. The seal cap according to any of embodiments 94-104
comprising a THV polymer.
[0192] 107. The seal cap according to any of embodiments 94-104
comprising a fluorinated thermoset polymer.
[0193] 108. The seal cap according to any of embodiments 94-104
comprising an engineering thermoplastic.
[0194] 109. The seal cap according to any of embodiments 94-104
comprising a PEEK polymer.
[0195] Various modifications and alterations of this disclosure
will become apparent to those skilled in the art without departing
from the scope and principles of this disclosure, and it should be
understood that this disclosure is not to be unduly limited to the
illustrative embodiments set forth hereinabove.
* * * * *