Coupling with hard metallic ductile conductive coating

A coupling for preventing the buildup of static electricity between adjacent conduits includes first and second threadably engageable coupling members in electrical contact with the adjacent conduits. The threads are coated with a hard metallic ductile conductive coating which is preferably a boron-nickel coating, to provide electrical conductivity between the coupling members. The coating has a relatively low co-efficient of friction so as to prevent binding of the threads during threading. In one embodiment, a detent spring, which includes one or more resilient detents, is rotatable with one coupling member and engages with a notch or notches on the other coupling member to provide a frictional force against relative rotation between the coupling members as the coupling members threadably engage. The coupling members may be entirely coated with the boron-nickel coating, or selectively coated to provide the required electrical conductivity between the coupling members. A bonding wire in electrical contact with each coupling member makes redundant electrical contact with the conduits.

BACKGROUND OF THE INVENTION 
1. Field of the Invention. 
The present invention relates generally to a coupling assembly for fuel 
lines and the like, and more particularly to a coupling assembly for 
interconnecting adjacent conduits in which the coupling assembly includes 
threadably interconnected male and female coupling members are coated with 
a hard metallic ductile conductive coating for preventing the buildup of 
an electrostatic charge between the conduits. 
2. Description of the Related Art. 
When conveying fluid, such as jet fuel, between interconnected fuel lines, 
it is necessary to provide electrical conductivity between the fuel lines 
to prevent the buildup of an electrostatic charge between the fuel lines. 
If an electrostatic charge were to build up, an electric spark could 
occur, thereby causing the fuel to ignite. The build up of static 
electricity poses a problem in other applications which use conduits for 
material transfer. For example, in sandblasters, if the hose used to 
discharge the sand is not grounded, static electricity may build up 
sufficiently in the hose so that an electric shock and/or arcing may occur 
at the coupling between hose lengths, causing personal injury or property 
damage. This situation is discussed in more detail in U.S. Pat. No. 
4,658,326. 
In order to overcome the problem of static buildup in fuel lines, U.S. Pat. 
No. 4,487,462, the contents of which are incorporated herein by reference, 
discloses a coupling that provides electrical contact between adjacent 
fuel lines. A pair of bonding jumpers is provided each of which includes 
i) an annular ring having a plurality of bonding jumper contact flanges 
that engage a surface of the threaded coupling, and ii) a plurality of 
spaced retaining tangs which snap into a retaining groove in the coupler 
and the nut. The nut also includes a plurality of circumferentially spaced 
contact tangs which are interspersed with the retaining tangs and which 
contact the outer end of the coupling beyond the threads. 
Another requirement for aircraft fuel lines, which is not necessarily a 
requirement for couplings used in other applications, is that the coupling 
be self-retained after installation in such a manner that the coupling 
will not loosen despite vibrations or other forces to which the coupling 
may be subjected. U.S. Pat. No. 3,669,472, the contents of which are 
incorporated herein by reference, discloses one of many patented devices 
that have been developed to prevent relative rotation of coupling members. 
This device relates to a coupling having an annular ring with spring 
fingers which releasably engage notches on the edge of a male connector to 
minimize the chance of the coupling becoming unthreaded due to vibrations 
or other forces on the coupling. A separate releasable bonding ring is 
provided between the two coupling elements. 
A related aspect of the coupling of fuel lines to reduce the buildup of 
static electricity is the contact between the coupling members and the 
fuel lines. This point of contact is preferably redundant so as to reduce 
the likelihood that the contact will fail, and must be capable of being 
rotated with the coupling members as they are threaded together. One 
method for providing such contact was developed by the Assignee of the 
present invention and sold as the 15J02 coupling. The 15J02 coupling is 
constructed of male and female threaded coupling members and a detent ring 
with a single resilient detent mounted to one of the coupling members. The 
other coupling member includes a surface facing the detent ring with 
spaced notches for engaging with the detent as the coupling members are 
rotated relative to each other. In order to provide electrical contact 
between the coupling members and the fuel lines, a split ring with a 
multi-sided bonding wire mounted therein is mounted in each coupling 
member. The bonding wires provide multiple electrical contact points 
between the fuel lines and coupling members. 
As shown in FIG. 1, U.S. Pat. Nos. 4,808,117 and 4,928,202, the contents of 
which are incorporated herein by reference, relate to a threaded coupling 
that is essentially a combination of the teachings of the aforementioned 
U.S. Pat. Nos. 3,669,472 and 4,487,462, and the 15J02 coupling. A pair of 
assembly sealing flanges 14 and 16 are connected to the ends of fuel lines 
(not shown). The flanges each have a cylindrical skirt 18 and 20 which is 
sealingly attached to the fuel lines by any suitable means. Each flange is 
provided with a peripheral recess 22 and 24 for receiving 0-rings 26 and 
28. Recess 22 is formed between a pair of peripheral ribs 30 and 32 and 
recess 24 is formed between a pair of similar ribs 34 and 36. The 
confronting ends of the fuel lines are interconnected by means of a 
threaded coupler 38 and nut 40 which cooperate to draw the coupler and nut 
axially toward each other to secure them together and to form a 
fluid-tight seal. Within coupler 38 is a circumferential retaining groove 
48 receiving a split ring 50. 
The nut or female member 40 has an inwardly projecting peripheral flange 52 
on its end and internal threads 54 which receive threads 44 of coupler 38. 
The peripheral flange 52 serves as a stop for split ring 56, which is 
mounted in female coupling member 40. Split rings 50 and 56 have internal 
grooves 58 and 88 within which bonding rings 60 and 76 are received 
respectively. Bonding rings 60 and 76 have a generally non-circular 
configuration and have upturned spaced ears 62, 64, 80 and 82 which are 
squeezed together to insert the bonding rings into grooves 58 and 88, and 
which project upwardly through apertures 66, 68, 84 and 86. Split rings 50 
and 56 serve to retain the coupling members 38 and 40 on sealing flanges 
14 and 16. The flat sides 70 and 78 of bonding rings 60 and 76 engage the 
cylindrical skirts 18 and 20 of sealing flange 12 and 14 to provide 
multiple electrical contact points between the coupling members 38 and 40 
and the sealing flanges. Flange 48 has a plurality of spaced notches 72 
which are utilized with a bonding jumper 74. 
Nut 40 is provided with a recess 90 within which bonding jumper 74 is 
received. The bonding jumper has a plurality of equally spaced spring 
detents 92, each of which has a curved end 94. The bonding jumper is also 
provided with spaced notches 96 into which the edge 91 is bent to form a 
crimp to prevent relative rotation of bonding jumper 74 with respect to 
nut 40. As nut 40 is tightened, the curved ends of spring detents 92 come 
into engagement with flange 46 of coupler 38 and engage notches 72. As the 
nut is drawn tight, the force of each spring detent against flange 46 and 
notches 72 increases. This arrangement provides a redundant electrical 
contact between nut 40 and coupling 38. Bonding jumper 74 also serves to 
minimize the possibility that the nut will turn in a reverse direction 
accidentally due to vibrations or other forces. 
In commercial versions of couplings of the type disclosed in U.S. Pat. Nos. 
4,808,117 and 4,928,202, the threads of the coupling members are coated 
with a non-electrically-conducting dry-lube coating in order to enable the 
members to be threadably engaged without binding. Thus, the redundant 
electrical contact provided by bonding jumper 74 is necessary because no 
electrical contact is provided between the coupling members through the 
threads. 
Accordingly, it would be desirable to have a coupling for preventing 
electrostatic build up between adjacent conduits in which the electrical 
contact is provided through the threads so that a bonding jumper is not 
required for preventing such electrostatic buildup. It would also be 
desirable to have such a coupling in which there is a low coefficient of 
friction between the threaded surfaces so as to avoid binding of the 
threads during threading. 
SUMMARY OF THE INVENTION 
The present invention is a coupling for preventing the buildup of static 
electricity between first and second conduits. The coupling comprises 
first and second coupling members in electrical contact with the first and 
second conduits respectively. The first and second coupling members each 
comprise threads and are threadably engageable. The threads are coated 
with a hard metallic ductile conductive coating, which is corrosion 
resistant, has a low coefficient of friction and provides electrical 
conductivity between the coupling members. A preferred hard metallic 
ductile conductive coating is boron-nickel. The boron-nickel coating has a 
satisfactory low coefficient of friction so as to prevent binding of the 
threads during threading. 
In a preferred embodiment, the first coupling member has a first surface, 
which includes at least one detent notch, facing the second coupling 
member. A detent spring is rotatable with the second coupling member and 
faces the first surface. The detent spring includes a detent which engages 
with the notch to provide a resistance force against relative rotation 
between the first and second coupling members as the coupling members 
threadably engage. The detent spring may be metallic or non-metallic, or 
coated with a dry-lube or other lubricant. If desired, the first and 
second coupling members may be entirely coated with the boron-nickel 
coating, or selectively coated to provide the required electrical 
conductivity between the coupling members. 
In order to provide electrical contact between the coupling members and the 
conduits, the coupling members are provided with inwardly facing 
circumferential retaining grooves. In one embodiment of the invention, 
split rings are mounted in the retaining grooves, with each split ring 
being in electrical contact with its respective coupling member. Each 
split ring has an internal groove, with bonding wires mounted within the 
internal grooves. Each bonding wire is in electrical contact with its 
respective coupling member and with its respective conduit. The bonding 
wires are preferably multi-sided and make multiple electrical contacts 
with the conduits. 
In an alternative embodiment, the bonding wires are mounted directly in the 
coupling members, with each bonding wire in electrical contact with its 
respective coupling member and with its respective conduit. Similarly, the 
bonding wires are preferably multi-sided and make multiple electrical 
contacts with the conduits. 
In a more general embodiment, the invention relates to a coupling in which 
the first and second coupling members are attachable in physical contact 
for establishing a passage conduit between the conduits. At least a 
portion of the areas of the coupling members that are in physical contact 
are coated with a boron-nickel coating for establishing electrical contact 
between the coupling members.

DETAILED DESCRIPTION OF THE INVENTION 
As shown in FIGS. 2-5, the present invention is an improved threaded 
coupling 100 for interconnecting the ends of adjacent conduits (not 
shown). The conduits may be any appropriate pipes, tubes or other conduits 
for carrying a fluid, such as fuel, or for carrying any other material, 
such as sand for a sandblaster. It will be appreciated that a function of 
coupling 100 is to provide electrical conductivity between the adjacent 
conduits. This is important for preventing electrical arcing or sparks 
caused by static electricity, lightning strikes or fault currents. The 
conduits may be constructed entirely of an electrically conducting 
material, or may include only a shielding or grounding layer constructed 
of an electrically conducting material. In general, the conduits must be 
at least partially constructed of an electrically conducting material that 
is in electrical communication with coupling 100. 
An assembly sealing flange 114 is sealingly attached to the end of each 
conduit by any method known to those skilled in the art provided that each 
flange 114 is in electrical communication with the electrically conductive 
portion of its associated conduit. Each flange 114 is provided with a 
peripheral recess 122 formed between a pair of peripheral ribs 130. An 
0-ring 126 is seated in each peripheral recess 122 for forming a fluid 
tight seal between flange 114 and coupling 100 as shown in detail in FIG. 
5. 
Coupler 100 consists of male and female coupling members 138 and 140 
respectively which are threadably interconnected by means of external 
threads 112 on male coupler 138 and internal threads 113 on female coupler 
140. Coupling members 138 and 140 are preferably constructed of aluminum, 
stainless steel, or titanium, but may be constructed of any other 
appropriate material, if desired. Grips 115 are machined on the outer 
surface of the male and female coupling members to facilitate rotation of 
the coupling members. As male coupling member 138 is rotated with respect 
to female coupling member 140 with threads 112 and 113 in engagement, the 
coupling members are drawn axially toward each other until a fully 
threaded position is achieved (FIGS. 4 and 5). Each of the coupling 
members 138 and 140 is generally cylindrical in shape and is slidable over 
its respective sealing flange 114. 
FIGS. 3-5 and FIG. 2 show first and second embodiments of the invention 
respectively with respect to the structure for securing coupling 100 to 
flanges 114 with the required electrical contact therebetween. Beginning 
with the first embodiment, a shown in FIGS. 3 and 5, male coupler 138 is 
provided with inwardly projecting flanges 142 which define a 
circumferential retaining groove 148. Seated within retaining groove 148 
is a split ring 150 which includes a circumferential groove 151. As shown 
in FIG. 5, female coupling member 140 has an inwardly projecting 
peripheral flange 152 which serves as a stop for split ring 156. Split 
ring 156 is seated against the face of flange 152 and includes a 
circumferential groove 157. Each split ring is preferably constructed of 
aluminum or any other appropriate electrically conducting material. 
Mounted within each circumferential groove 151 and 157 of split rings 150 
and 156 is a metallic bonding ring 160. Each bonding ring 160 preferably 
has a multi-sided octagonal shape and serves to retain the coupling 
members 138 and 140 on flanges 114. The straight sides of bonding rings 
160 engage the outer surfaces of sealing flanges 114 to provide multiple 
electrical contacts between the coupling 100 and flanges 114. It is 
foreseen that bonding rings with other shapes, e.g., with fewer or more 
sides, would provide the requisite electrical contact between coupling 100 
and flanges 114. Bonding rings 160 are preferably constructed of 
tin-coated beryllium copper or any other appropriate electrically 
conducting material. 
As shown in FIG. 2, the second embodiment for securing coupling 100 to 
flanges 114 is similar to the first embodiment except that split rings 150 
and 156 are not used to secure the bonding rings. Instead, female coupling 
140 is provided with inwardly projecting flanges 172 which define a 
circumferential groove 174. Seated within groove 174 is a metallic bonding 
ring 170 which has an octagonal shape that serves to retain the coupling 
member 140 on and in electrical communication with flange 114. As in the 
first embodiment, male coupler 138 is provided with inwardly projecting 
flanges 176 which define a circumferential groove 178 in which a metallic 
bonding ring 170 is mounted. Thus, with respect to male coupler 138, the 
principal difference between the first and second embodiments of the 
invention is that the inwardly projecting flange has a smaller inside 
diameter such that it performs a similar retaining function as the split 
ring. In the first embodiment, retaining groove 148 is sized to receive 
split ring 150, whereas in the second embodiment, groove 178 is sized to 
receive only the narrower bonding wire 170. 
Female coupler 140 has a plurality of spaced detent notches 180 formed in a 
circumferential lip 182. An annular groove 184 is formed on male coupler 
138 by outwardly extending flange 186 and circumferential lip 188. Mounted 
within groove 184 is a detent spring 190. Detent spring 190 has a detent 
192 which is formed on a curved end thereof and inwardly extending ears 
194. Annular groove 184 is preferably sized such that detent spring 190 
must be force pressed therein. When detent spring 190 is pressed into 
groove 184, ears 194 frictionally engage with male coupling 138 to prevent 
relative rotation of detent spring 190 with respect to male coupling 138. 
Those skilled in the art will appreciate that other techniques exist to 
prevent relative rotation of detent spring 190 with respect to male 
coupling 138. 
As male coupling 138 is tightened, i.e., rotated with respect to female 
coupling 140, detent 192 will come into engagement with circumferential 
lip 182 in female coupling 140 and with detent notches 180. As the male 
and female couplings are drawn tighter, the force of spring detent 192 
against detent notches 180 will increase. This arrangement provides a 
locking mechanism which minimizes the likelihood that the male coupling 
will accidentally turn in a reverse direction due to vibrations or other 
forces. The coupling may be disassembled by turning male coupling 138 
counterclockwise with sufficient force to overcome the engagement of 
detent 192 with detent notches 180. 
Detent ring 190 is preferably constructed of a metal, such as stainless 
steel or beryllium copper, or of any other appropriate material with 
sufficient resiliency and strength to perform the functions described 
herein. As discussed in detail below, unlike in prior art devices, the 
detent spring is not required to provide an electrical path between the 
male and female coupling members. Accordingly, a non-metallic detent 
spring may be used, if desired. In a preferred embodiment, detent spring 
190 is coated with a dry-lube coating of the type defined in Military 
Specification MIL-L-46010 Type 1. It will be appreciated that the 
lubricant or anti-wear coating is optional and that other types of 
lubricants or anti-wear coatings may be used in lieu of the dry-lube. 
Also, the detent spring may be eliminated if the prevention of unthreading 
of the coupling members is not critical or if an alternative approach is 
used to prevent such unthreading. 
In order to ensure electrical continuity between male and female coupling 
members 138 and 140, threads 112 and 113 are coated with a boron 
electroless nickel ("boron nickel") coating. The boron nickel coating also 
provides a relatively low co-efficient of friction between the male and 
female coupling members, thereby preventing binding of threads 112 and 113 
during mating of the coupling members and also obviating the need for a 
dry-lube coating on the threads. Without the dry-lube coating, strong 
electrical contact is provided between the threads of the male and female 
coupling members. Thus, with the coupling of the invention (in the 
embodiment shown in FIG. 2), an electrical path is provided from flange 
114, through bonding wire 170 to female coupling member 140, from threads 
113 to threads 112 and male coupling member 138, and through bonding wire 
170 to flange 114. A similar electrical path is provided in the embodiment 
shown in FIGS. 3-5, with the additional path through the split rings. No 
electrical path is required through detent spring 190, thereby enabling 
detent spring 190 to be dry-lube coated or constructed of a non-metallic 
material. In a preferred embodiment, the boron nickel is coated to a 
thickness of 0.0003"+/-0.0001". It is foreseen that the thickness of the 
boron nickel coating may vary as desired, provided that the dimensions of 
the coupling are such to allow the male and female coupling members to be 
threadably engaged. Furthermore, it will be appreciated that while it is 
only necessary that the threads of the coupling members be coated with the 
boron nickel coating, it is foreseen that any other portion of the 
coupling members, or the entirety of the coupling members may be coated 
with the boron nickel coating. 
Boron nickel coating is known to those skilled in the coating field and is 
defined in AMS 2433-A. Such coating is commercially available by 
Anodyne.TM., Inc., 2230 S. Susan Street, Santa Ana, Calif. 92704. The 
characteristics of boron nickel coatings are described in "Engineering 
Bulletin--Boron Electroless Nickel vs. Hard Chrome", Anodyne.TM., Inc., 
May 1992, the content of which is incorporated herein by reference. In 
general, boron nickel is a metallic coating consisting of uniformly 
deposited hard nodules interlaced in a soft matrix. Both the nodules and 
matrix are metallic, although the composition of each is different. The 
nodules lend hardness to the coating and provide low friction and 
ductility to the surface of the coating. The matrix "fills in" between the 
nodules and is ductile. 
The boron nickel coating is applied through an electroless immersion 
process in which the parts to be coated are submerged in an alkaline bath 
that operates at approximately 195.degree. F. at about 12 pH. A chemical 
reaction causes a continuous uniform coating to be deposited on all 
unmasked areas of the parts. The parts can be masked so that the coating 
will only be deposited where necessary. Immersion time determines the 
amount of coating deposited on the parts. The thickness of the coating can 
typically vary from 0.0002" to 0.010", although the invention is not 
limited to a particular coating thickness. 
Boron nickel forms an extremely hard coating, with a Knoop hardness of 800 
to 900. After heat treating, this hardness may be increased to 1235 to 
1245 on the Knoop scale, which converts to approximately 70 to 72 on the 
Rockwell C Scale. The nodules of the coating have a very strong bond to 
the substrate, passing ASTM C633. The nodules are bonded to each other 
through the soft matrix so that when the substrate flexes, the matrix 
flexes between the nodules. The flexing of the matrix allows the nodules 
to stay bonded to the coated part and allows the boron nickel coating to 
be extremely ductile. 
The boron nickel coating passes the ASTM B117 accelerated salt spray test 
for corrosion resistance and also has a very low co-efficient of friction. 
A part rising against a boron nickel surface will ride on the top of the 
nodules of the coating. The actual area of contact between two surfaces is 
less than one half of that for non-coated parts. Boron nickel also has 
excellent adhesion characteristics and can continually operate at 
temperatures up to 900.degree. F. and more. 
From the foregoing, the advantages of the invention are readily apparent. 
Through the use of a boron nickel coating on the threads, an electrical 
path is provided between the coupling members without the necessity of a 
metallic detent spring with multiple detents. It will be appreciated that 
although the present invention has been described in detail with respect 
to a particular type of coupling that is useful for airplane fuel 
couplings in which the avoidance of static electricity is critical, it is 
applicable to any type of coupling in which the portions of the coupling 
that are in contact may be coated with a boron nickel coating to provide 
electrical conductivity therebetween. For example, many different types of 
couplings are known, e.g., threaded couplings, quick disconnect couplings, 
etc., that are constructed of low-friction plastics but that could be 
constructed of boron nickel coated parts so as to provide electrical 
conductivity. More generally, although the present invention has been 
described in detail with respect to certain embodiments and examples, 
variations and modifications exist that are within the scope of the 
present invention as defined in the following claims.