Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR COATING THREADED FASTENERS
BACKGROUND OF THE INVENTION
The present invention generally relates to discrete
parts having a useful barrier coating applied to a
portion thereof and a method and apparatus for processing
parts such as threaded fasteners with such a coating
material. More particularly, the invention relates to
the deposition of liquid fluorocarbon or hydrocarbon type
coating materials in a precise, continuous and high speed
manner onto selected surfaces of metal fasteners to form
a barrier coating on the fasteners. A particular
application of the invention is the application of liquid
fluorocarbon coating material to the internal threads of
a nut.
In many industries, metal parts are being
increasingly exposed to electrodeposition paints, primers
and corrosion resistant materials. For example, recent
advances in improving the corrosion resistance of
automobile bodies have made the use of formulations such
as Uniprime~, made by PPG Corporation for the treatment
of steel structural members, a standard in the industry.
Many fastening elements are permanently attached to basic
vehicle structural components prior to processing of the
components with electrodeposited primers, paints and rust
inhibitors. Therefore, any exposed threads of fasteners
attached to such vehicle components may become
contaminated, making it difficult or impossible to thread
such exposed fasteners with a mating fastener for
subsequent assembly. The need therefore arose to develop
a way of preventing contamination of these exposed
fastener threads that would not substantially interfere
with the ultimate performance of such fasteners.
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The prior art has proposed a variety of coating
systems to attempt to solve the problem of resisting
corrosion inhibitor build up on the threads of fasteners.
Each of these known systems, however, has suffered from
some rather substantial drawbacks. Several alternative
methods have been proposed for the coating of the threads
of internally threaded fasteners including pierce nuts
and weld nuts that utilize liquid epoxy paints or other
fluorocarbon coating materials that include Tefionc~ and
an organic solvent.
In one of the earliest of these known methods, a
liquid Teflon~ coating material containing FEP and a
solvent was sprayed onto the threads of a nut using a
small high pressure nozzle. The fastener was then heated
to a temperature of about 450°F for twenty minutes
vaporizing the organic solvent and curing the remaining
fluorocarbon material. This method had several
disadvantages.
First, with the pressurized spraying techniques used
by this method, the coating material impacted the sprayed
area at relatively high speeds causing bounce back of
some of the material and non-uniform coating or coating
of undesired surfaces. Second, because the fluid
suspension had to be relatively dilute to avoid clogging
of the spray nozzle, the coating at times ran off prior
to curing. Third, substantial portions of the expensive
fluorocarbon were wasted as excess fluid suspension was
applied and dripped down or ran off the fastener prior to
curing.
Several liquid fluorocarbon coating systems have
been devised to address some of these problems, but these
solutions have introduced new problems and limitations.
U.S. Patent No. 4,652,468 to Gould et al. discloses a
process for high pressure impact coating of threaded
openings of fasteners that attempts to avoid the
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deposition of coating material on any other surfaces of
the fastener. This process requires a masking of the
surfaces of the nut in order to restrict the coating
material from contaminating the outer surfaces of the
nut. Additionally, this process required a choked. area
for drawing any excess coating material from the opening
of the nut. The mandrels and seals utilized to mask
fastener surfaces other than the threads have a tendency
to wear out quickly due to abrasion and solvent attack.
Also, the need to index, mask and remove excess material
during the coating process of Gould is complicated,
expensive and slows processing speeds.
U.S. Patent No. 4,701,348 to Neville discloses a
method of coating the threads of an internally threaded
fastener. Neville requires a metering device with a
nozzle to be selectively introduced and removed from a
succession of internally threaded fasteners. The
reciprocating movement of the nozzle necessitates an
indexing of the fasteners that stops the flow of
fasteners each time coating material is being applied to
any single fastener dramatically slowing processing
rates. Furthermore, the nozzle has an ultrasonic tip
which is vibrated after the metering of a drop of coating
material in order to explode the drop and cause a fine
mist of the fluid suspension to be sent toward the
threads of the nut. Due to the difficulty in metering
identically sized drops in succession and exploding them
in the exact same manner using an ultrasonic power
source, this system often exhibits uneven coating of the
fasteners.
Published PCT International Application No.
W08906757 of Prittinen et al. discloses a method and
apparatus for coating internally threaded fasteners with
materials such as Teflon~. This invention provides an
indexed flgw of fasteners before an application device
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that introduces a reciprocating rotary probe into each
fastener to be coated. The rotary probe has an opening
that deposits a layer of coating material on a
preselected portion of the threads of each fastener
utilizing a combination of pressurized spraying and
centrifugal force. The liquid Teflon~ coating material
emitted from this spray probe is difficult to control.
This system is incapable of operating at relatively high
production rates since it requires fasteners to be
indexed and stopped in place during the entire time of
application of the coating material.
Other known solutions, such as those taught by U.S.
Patent No. RE33,766 to Duffy et al. have utilized a
stream of powdered Teflon material sprayed onto preheated
fasteners. Such systems require_a great deal ofheat to
be applied to the fasteners prior to exposing them to a
stream of Teflon powder. The heat utilized in raising
the temperature of the fasteners to approximately 700°F
or greater can be both expensive to generate and
potentially detrimental to the finish or appearance of
the subsequently coated fastener. Due to the inherent
difficulties of attempting to adhere powdered Teflon~
type coating materials, this system generally requires
all parts to be cleaned, pickled or plated prior to
powder application in order to obtain minimal acceptable
adhesion. Production rates in such systems are further
limited since a reciprocating rotatable nozzle must be
introduced and removed into each internally threaded
fastener opening and powder pressure and flow through the
multiple nozzles of this system is difficult to maintain
in a consistent and uniform manner.
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Other liquid material delivery systems such as taught in
applicant's U.S. Patent No. 5,672,376 of September 30, 1997 are
also known. Such systems feature high speed accurate delivery
of liquid materials such as PVC liquids onto a continuously
moving succession of preheated parts. Such systems have not
contemplated the application of fluorocarbon or Teflon~ type
barrier coating materials onto the threads of fasteners to
prevent electrodeposition of paints or corrosion resistant
materials.
Subsequent use of vibratory feed mechanisms to feed
fasteners coated with fluorocarbon type material by these prior
art systems to assembly machines has sometimes caused loosening
of the coating material. Yet a further problem is created by
robotic assembly devices that are now frequently being used in
many industries. These robotic assembly devices attach
fasteners to structural components. There is an increasing
desire, however, to utilize fasteners in such devices in the
form of a roll of nuts connected by metal filaments, rather
than having the nuts individually presented in loose form to
the robotic device.
The individual nuts on these rolls often require
fluorocarbon barrier coatings on the threaded surfaces thereof.
The ability to teed the coated nuts in the form of an
interconnected roll can eliminate the aforementioned loosening
of the coatings caused by vibratory feed systems. A further
drawback of existing prior art devices is that most of the
known methods for the. application of fluorocarbon type
materials cannot accommodate nuts in the form of a roll of nuts
connected by metal filaments, other than by removing all of the
nuts from the filaments which is prohibited.
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It is therefore apparent that there exists an
overwhelming need in the art for an improved apparatus
and method of coating the threads and/or other portions
of a fastener or other discrete object that overcomes the
drawbacks of prior liquid and powdered fluorocarbon
deposition systems and features increased quality of
coating, increased production rates and the ability to
alternatively process fasteners presented individually or
in the form of a roll of fasteners connected by metal
filaments with equal ability.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention
to provide an improved method and apparatus for the
application of liquid masking, insulating or lubricating
substantially pin-hole free barrier coatings on discrete
objects that overcomes the problems posed by prior art
systems.
A further object of the present invention is to
provide an improved method and apparatus for providing a
barrier coating on the threaded surfaces of a succession
of fasteners that does not require intermittent stopping
of the feed of fasteners as they travel through the
coating apparatus.
A further object of the present invention is to
provide an improved method and apparatus for providing a
barrier coating on the threaded surfaces of a fastener
that features precise metering and location of a deposit
of the liquid material applied to the fastener.
Still another object of the present invention is to
provide an improved method and apparatus for the
application of a barrier coating onto the threaded
portion that requires little or no preheating of the
fasteners.
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It is still a further object of the present
invention to provide a method and apparatus for the
application of a barrier coating of liquid material onto
the threads of an internally threaded fastener that does
not require a nozzle to be introduced within the opening
of the threaded fastener.
It is also an object of the invention to provide a
method and apparatus for coating the threads of a
fastener with a barrier coating at production rates far
faster than those attainable in the prior art.
Yet another object of the present invention is to
provide a method and apparatus for coating the threads of
a fastener that provides a barrier coating on the
fastener protecting, lubricating, insulating and masking
the threads from unwanted contamination or deposition of
material thereon that does not require rotation of the
material applying element during the coating process.
It is yet another object of the present invention to
provide a method and apparatus for coating the threads of
a fastener with a barrier coating that can easily
accommodate fasteners fed loosely or in the form of a
continuous roll of nuts connected by metal filaments.
Still a further object of the present invention is
to provide a method and apparatus for coating the threads
of a fastener that can accommodate a succession of
irregularly spaced centered fasteners.
The above and other objects, which will become
apparent after reviewing the detailed description, are
achieved by utilizing the method and apparatus of coating
the threads of a fastener of the present invention.
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In one aspect of the invention, individual articles
such as nuts are deposited onto a continuously moving
conveyor in a uniform orientation with a belt that
travels over a magnetic rail that maintains the fasteners
in contact with the belt. The fasteners are contix~uously
fed in a uniform high speed manner past a liquid coating
material deposition area where optical sensors trigger
precisely metered discrete shots of material to be
deposited onto specific locations of the threads of the
fasteners in order to form a barrier coating thereon.
With the barrier coating material deposited on the
fasteners, they are then transferred to a second conveyor
system having a magnetic rail and a belt thereover in an
opposite orientation where coating material deposited on
the threaded surfaces of the fasteners is dried or heated
in order to stabilize the coating and vaporize the
organic solvent contained in the coating material.
In another preferred embodiment of the present
invention, a fastener cleaning station is included and
utilized prior to depositing any coating material onto
the fasteners and a station is provided to remove any
excess coating material that may have been deposited on
surfaces of the fasteners other than the threaded surface
prior to heating or drying off of the solvent from the
coating material.
In another embodiment of the present invention, the
fasteners are fed, processed with barrier coating
material and removed from the apparatus in the form of a
continuous roll of nuts connected by metal filaments.
The nuts presented in this form in this embodiment of the
invention continue to move through the entire apparatus
at a constant rate of speed and do not have to be stopped
for the deposition of coating material to occur.
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BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described further in
connection with the attached drawings wherein like
reference numbers refer to corresponding parts throughout
the several views of preferred embodiments of the .
invention and wherein:
FIGURE 1 is a side view of one embodiment of the
present invention.
FIGURE 2 is a perspective view of a nut having
coating material applied to all threads.
FIGURE 3 is a combination top and bottom view of a
plurality of nuts illustrated in the form of a strip of
nuts connected by metal filaments.
FIGURE 4 is a top view of a portion of the apparatus
illustrated in Fig. 1.
FIGURE 4A is a top view of the take-up spool system
of the embodiment of the invention illustrated in Fig. 1.
FIGURE 5 is a partial side view of the transitional
area between the first and second conveyor systems of the
present invention.
FIGURE 6 is a partial cross sectional view of the
first shot of coating material being applied to the
threads of a fastener in accordance with the present
invention.
FIGURE 7 is a top view of a fastener shortly after
deposition of a single discrete shot of coating material
having been applied to a portion of the threads of the
fastener.
FIGURE 8 is a partial cross sectional view of the
fastener illustrated in Figs. 6 and 7 having a second
discrete shot of coating material applied to its threads.
FIGURE 9 is a top view of the fastener illustrated
in Fig. 8 shortly after deposition of a second discrete
shot of coating material onto the threads.
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FIGURE 10 is a partial cross sectional view of the
fastener illustrated in Figs. 8 and 9 a short time after
the second discrete shot of coating material has been
applied to the threads.
FIGURE 11 is a partial cross sectional view o~ the
fastener illustrated Fig. 10 a short time after when the
coating material has covered substantially all of the
threads.
FIGURE 12 is a partial cross sectional view of the
apparatus of the present invention for removing coating
material from unwanted surfaces.
FIGURE 13 is a side view of another embodiment of
the present invention that presents a succession of loose
fasteners for coating by the present invention.
FIGURE 14 is a partial top view of a mesh belt that
can be utilized in connection with the present invention.
FIGURE 15 is a perspective view of a clinch nut that
can be coated utilizing the present invention.
FIGURE 16 is a perspective view of a stamped nut
that can be coated utilizing the present invention.
FIGURE 17 is a perspective view of a tapping plate
that can be coated in accordance with the present
invention.
FIGURE 18 is a perspective view of an additional
fastener that can be coated in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
While the present invention will be described
particularly with respect to applying fluorocarbon or
Teflon~ type material to form a continuous, substantially
pinhole free barrier coating on the threads of threaded
articles, it is to be understood that the present
invention can be utilized to apply to a variety of
fluorinated ethylene propylene copolymers or other
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similar type materials such as silicones, waxes and
petroleum greases. The present invention contemplates
supplying the coating material as a fine unpolymerized
powder material in an epoxy paint containing a fluid
solvent. Additionally, while the invention contemplates
providing coatings on a variety of discrete metal objects
and threaded articles and/or fasteners including, but not
limited to, nuts, bolts and similar articles, the present
invention will be described for exemplary purposes only
with reference to a nut. Also, although the invention
will be described in connection with providing a coating
on substantially all of the threads of a threaded
fastener, it is also to be understood that such coating
could be placed on a limited number of threads and/or be
provided on non-threaded surfaces if so desired.
Figure 1 generally illustrates one preferred
embodiment of the apparatus 10 for practicing the present
invention. The apparatus 10 functions to achieve the
process steps of the present invention. The apparatus 10
has a frame 12 that serves as a mounting base for a lower
conveyor system 24 and an upper conveyor system 36 that
has one end that partially overlaps one end of the lower
conveyor system 24. The lower conveyor system 24 has two
conveyor wheels 26 and 28 respectively that have a
continuous conveyor belt 32 running therebetween. The
belt 32 can be constructed of a number of different
materials provided that they exhibit good heat resistance
and provide a non-stick surface. A particularly
preferred belt has been found to be a Teflon coated _
fiberglass solid belt that is approximately 2 inches wide
and approximately .014 to .050 inches thick. The belt 32
may have a solid, perforated or mesh construction. A
variable speed motor operating the wheels 26 and 28
allows the speed of the belt to be selectively adjusted
to a desired consistent speed.
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The lower conveyor system 24 provides a magnetic
rail 30 that runs along substantially the entire length
of the belt 32 onto which the nuts 14 are introduced
between the wheels 26 and 28. The magnetic force from
the rail 30 beneath the belt 32 serves to attract and
hold ferrous nuts 14 against the top surface of the belt
32 so that the tractive force of the belt 32 will cause
the nuts 14 to move continuously with the belt 32 in a
stable fixed manner at a consistent speed. The magnetic
rail 30 further serves to hold the fasteners 14
substantially flat against the belt 32 so that no further
devices are needed to attach the nuts 14 to the belt 32
for processing.
The structure of the conveyor system 24 has proven
to be very effective in providing a continuous stream of
nuts 14 in a very consistent position thereby enabling
coating materials to be applied to the nuts 14 while
using very high belt speeds. The conveyor system 24 is
also provided with an accessory rail 34 which provides a
point of attachment to the base 12 for various cleaning,
heating or application devices which will be described
later in detail.
The upper conveyor system 36 is similar in
construction to the lower conveyor system 24 and is
mounted to the frame 12 using a subframe 44. Like the
lower conveyor system 24 previously described, the upper
conveyor system 44 utilizes a variable speed motor 88
that drives a continuous belt 50 between the conveyor
wheels 38, 40 and 42 respectively. The belt SO is of a
type and construction similar to the belt 32 previously
described. A magnetic rail 46 is provided above
substantially the entire length of the belt 50 and runs
between the wheels 42 and 38 that the fasteners 14 will
contact. This results in the fasteners 14 being
attracted to and retained on the belt 50 and being pulled
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along the length of the rail 46 by the tractive force of
the moving belt 50. An accessory rail 48 is provided to
mount additional devices such as blowers or heating
systems. The upper conveyor system
36 is mounted downstream from and above the lower ,
conveyor system 24 in a partially overlapping manner. As
the nuts 14 travel along the lower conveyor system 24,
their top surfaces are exposed and their bottom surfaces
rest against the belt 32. As the nuts 14 continue to
traverse along the device 10 and encounter the upper
conveyor system 44, the previously exposed top surfaces
of the nuts 14 then contact the belt 46 of the upper
conveyor system 44 and the bottom surfaces of the nuts 14
which had been in contact with the belt 32 are then
exposed.
The embodiment of the present invention illustrated
in Figure 1 will now be described in detail by tracing
the path of fasteners through the apparatus 10 with
reference to Figure 1 and Figures 4-12. This embodiment
of the present invention will be described, for exemplary
purposes only, in connection with nuts 14 such as pierce
nuts that have a threaded hole 16 and are joined together
by metal filaments 20 that pass through the slots 18 of
successive nuts 14 as illustrated in Figures 2 and 3.
A coiled strip 21 of nuts 14 is provided on a spool
52. The spool 52, on which the strip 21 is wound, has a
hub with a center hole. The spool 52 is suspended on a
shaft 98 mounted on the frame 12. The spool 52 is
allowed to spin freely on the shaft 98 and is further
preferably allowed some freedom of movement from side to
side. The shaft 98 is often connected to a semiautomatic
motorized decoiler that senses tension to thereby
maintain an adequate and consistent feed of the strip 21.
13
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As illustrated in Figures 1 and 4, the leading end
of the strip 21 of nuts 14 is set into the centering
guides 58 and under the rotating pressure wheel 56 which
urges the nuts 14 into contact with the upper surface of
the belt 32. The magnetic force of the rail 30 attracts
the ferrous nuts 14 to the conveyor 32 and results in the
strip 21 of nuts~l4 then being pulled off the spool 52 by
the tractive force of the moving conveyor belt 32. The
present invention is capable of pulling a strip 21 of
nuts 14 along the belt 32 at a variety of different
speeds with the most preferred speeds being on the order
of about 17 feet per minute for M6 pierce nuts. The
present invention contemplates belt speeds that enable
the processing of about 30,000 to as high as 80,000 nuts
per hour depending upon the type and size of the nuts.
As the strip 21 of nuts 14 is pulled further from
the spool 52, the nuts 14 next encounter an on-line
cleaning station referred to generally as 100. Prior to
coating the nuts 14, it is sometimes necessary to loosen
surface oil or dirt from the threaded areas 16 of the
fasteners 14 prior to coating. To accomplish this
purpose, one or more guns, such as gun 62, are provided.
A preferred gun for this purpose has been found to be a
Nordson zero cavity gun with a no. 27655 module
manufactured by the Nordson Corporation of Norcross
Georgia. The gun 62 is mounted on a stage 66 that is
capable of adjustment in at least three different axes.
This enables precise adjustment of the gun 62 to
accommodate a wide variety of different fasteners or
other parts. The stage 66 is mounted to the accessory
rail 34.
The gun 62 is supplied with solvent from the supply
container 64. An optical sensor 60 is mounted to the
rail 34 opposite the gun 62. When the sensor 60 senses a
threaded hole 16 of nuts 14, it triggers a discrete shot
14
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of an appropriate type of rapid evaporating solvent to be
precisely delivered onto the threads 25 of the detected
fastener 14. A particularly preferred sensor for this
purpose has been found to be a model no PZ-101
manufactured by Keyance Corporation. Although a variety
of different solvents can be used for this purpose, a
particularly preferred solvent has been found to be
methyl ethyl ketone (MEK). Once applied to the nuts 14,
the solvent is given sufficient time as the strip 21
continues to traverse through the device 10 on the belt
32 to loosen any surface oil and dirt that may be on the
threaded surface 16 of the nut 14.
The strip 21 of nuts 14 then enters an exhaust
enclosure 68 where two blow off ports are utilized to
blow air into the threaded hole 16 causing the solvent
and loosened dirt and oil to atomize and be sharply blown
out of the now clean threads 25 of the fasteners 14. The
atomized material that is blown off is carried away from
the device through a vacuum tube 69. After exiting the
exhaust system 68, the nuts 14 are allowed some
additional time for any solvent remaining on the threads
25 to dry prior to the application of any coating
material. If additional drying capacity is needed, an
air blower or heater could be added to the conveyor
system 24 in this area.
In the alternative, the gun 62 of the on-line
cleaning station 100 can be used to deliver discrete
shots of solvent such as N methyl pyrrolidone (NMP) onto
the threads 25 of each detected fastener 14. In this
situation, the blow off ports of the exhaust enclosure 68
are not used and the solvent remains on the fasteners 12
to act as a wetting agent and improve the wicking of the
subsequently applied liquid coating material 22. In
either case, once the strip 21 of nuts 14 leaves the area
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of the exhaust enclosure 68 it is then passed through a
centering guide 70 to insure proper positioning for
subsequent coating.
As the strip 21 of fasteners 14 is carried further
down the belt 32, it next encounters the liquid
application section designated generally as 101 of the
device 10. In this section, one or more liquid
applicator guns 72 are provided for applying liquid
coating material 22 such as a suspension of a
fluorocarbon in a liquid solvent to successive nuts14 on
the strip 21 that pass by the guns 72. Each of the guns
72 is attached to the device 10 by a stage 76. The
stages 76 allow the guns 72 to be selectively secured in
fixed locations for the application of liquid coating
material 22 to different size or shape nuts 14.
Preferred stages for use in connection with the present
invention allow adjustment of each gun 72 along two or
three different axes.
As a result, the stages enable the vertical distance
between the gun 72 and the conveyor belt 32, the
horizontal location of the gun 72 in relation to the
width of the belt 32 and the angle and direction of the
gun 72 with respect to the nuts 14 to be adjusted. This
permits the present invention to process many different
types and sizes of parts with a minimum of set up time
being required. A commercially available stage that
meets these requirements is the 4500 Series ballbearing
stage manufactured by Daedal Division of Parker
Corporation of Harrison City, Pennsylvania.
The guns 72 are capable of delivering accurate high
speed metered shots of a wide variety of liquid coating
materials. These materials include, but are not limited
to, fluorocarbons, hydrocarbon and fluorocarbon
copolymers, silicones, waxes, petroleum greases,Teflont~
and Teflon~ type materials. Two particularly preferred
16
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materials have been found for use in connection with the
present invention. The first is a mixture of about 70~
by volume Du Pont Teflon-S (#954-101) liquid and about
30~ DuPont T-8748 thinner. The second is a mixture of
about 70~ by volume Whitford XYLAN 1661 dry film y
lubricant manufactured by Whitford Corporation of Frazer,
Pennsylvania and about 30~ of a solvent mixture
containing about 60~ N methyl pyrrolidone (NMP) and about
30~ XYLENE~. The guns 72 have very high cycle speeds
with a particularly clean cut-off at the end of each
discrete shot. This is critical to maintaining the
present invention's desired combination of high
production speeds and precise and accurate delivery of
coating materials to a desired portion of a succession of
nuts 14.
It is preferred that the guns 72 used be fully
capable of applying at least 20,000 and preferably 50,000
to 80,000 discrete metered shots of coating material 22
per hour. Although a variety of different guns 72 can be
used in connection with the present invention, a
particularly preferred gun has been found to be the
Nordson Zero Cavity gun having a Nordson 276515 gun
module. The guns 72 preferably utilize a nozzle diameter
in the range of between .008" and .040" and are supplied
with coating material under a pressure of about 401bs/sq.
inch. As can be appreciated, it is also possible to use
only a single gun 72 and a single discrete shot of
material in connection with the present invention or more
than two guns that would deliver more than two discrete
shots of material 22 onto a series of nuts 14. In
addition, the present invention can also be utilized to
place discrete shots of material 22 on surfaces other
than the threads 25 of nuts 14. The guns 72 can also be
primed or cleaned without any parts present.
17
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As particularly illustrated in Figures 4, 6 and 7,
as the strip 21 of fasteners 14 moves into the
application section 101, the threaded hole 16 of each of
the respective nuts 14 is detected by photo-optic sensors
74. Although a variety of different photo-optic sensors
are capable of being utilized for this purpose, it has
been found that a particular preferred sensor for use in
the present is manufactured by Keyance Corporation under
the model no. PZ-101. Once the sensor 74 detects the
threaded hole 16 of each successive nut 14, it sends an
electrical signal to the gun 72 which fires a discrete
shot of liquid coating material 22 onto a portion of the
threads 25 of each nut 14. Once deposited, the first
shot of coating material 22 flows
down the threads 25 toward the bottom of the nut 14 and
also, as a result of capillary action, flows somewhat
upward along the threads 25 as well.
As this first deposit of material 22 is flowing
around the threads 25, the nut 14 passes a second optical
sensor 74 and gun 72 mounted on a stage 76 as previously
described. As the nut 14 passes the second gun 72, a
second discrete shot of coating material 22 is deposited
circumferentially apart from and preferably 180° apart
from the location of the first shot of coating material
22, as illustrated in Figures 8 and 9. As best
illustrated in Figures l, 10 and 11, once the appropriate
coating material 22 is deposited on the nut 14, it is
carried further by the belt 32 away from the application
section. During this period of time, the applied liquid
coating material 22 wicks around the threaded opening 16
and covers all of the threads 25 in a substantially even
manner.
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The location, amount, speed and pressure of material
22 that is deposited is controllable by the guns 72. The
minimum amount of liquid coating material 22 sufficient
to wick around and cover all of the threads 25 is in
totality shot into the threaded hole 16. By accurately
positioning and metering these shots of material 22 from
the guns 72, the material 22 is substantially entirely
confined within the threaded hole 16 and does not extend
onto either the belt 32 or any other surfaces of the nut
14 other than the threads 25.
Most specifications for the application of
fluorocarbon barrier coatings on fasteners require that
the entire threaded surface be covered with coating
material 22. Therefore, to form such a substantially
pinhole free coating, the metered shots of coating
material 22 in accordance with the present invention are
usually sufficient to insure that there is enough
material 22 deposited to wick around all of the threads
25. This can sometimes cause a small amount of excess
material 22 to build at the bottom threads 25 of the nuts
14 possibly wicking onto the belt 32.
The present invention provides two separate features
for dealing with this potential problem. First, the belt
32 can be provided with a meshed construction as
illustrated in Figure 14. This belt construction still
provides proper support for the nuts 14, but at the same
time minimizes the amount of surface area of the belt 32
that comes into contact with the bottom surface of the
nuts 14. In this manner, excess material 22 that may be
present at the bottom of the threads 25 makes little or
no contact with the belt 32 and is therefore usually
retained on the threads 25 due to surface tension
effects.
19
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A second feature for dealing with the potential of
excess material 22 building up at the bottom of the
threads 25 of the nuts 14 is best illustrated in Figures
1 and 5. The lower magnetic rail 36 is constructed so
that its magnetic effect on the nuts 14 fades out before
the end of the lower conveyor system 24 and simultaneous
to the nuts 14 passing under the beginning of the upper
conveyor system 36 and the upper magnetic rail 46. This
construction allows the upper magnetic rail 46 to attract
and lift the nuts 14 off of the lower conveyor system 24
and onto the belt 50 of the upper conveyor system 36 and
subsequently be carried further along the device 10 by
the tractive force of the belt 50.
As the nuts 14 travel along the upper belt 50 their
top surfaces are in contact with the belt and their
bottom surfaces are completely exposed. In order to
facilitate the nuts to start conveying along belt 50, the
speed of the belt 50 is synchronized with the speed of
the lower belt 32. A centering guide similar to the
centering guide 70 previously described may also be
utilized in this area to assist in accurate transfer of
the nuts 14 from the lower conveyor system 24 to the
upper conveyor system 36.
If there is concern that either excess coating
material 22 has been applied to the threaded hole 16 of
the nuts 14, or that some of the applied liquid coating
material 22 may migrate out of the threaded hole 16 onto
the outside surfaces of the nut 14, then the present
invention provides an additional system illustrated in
Figures 5 and 12 for solving such problems. As the strip
21 of nuts 14 traverses further along the upper belt 50
and encounters one or more blotters 78. The blotters 78
preferably take the form of soft foam wheels rotating
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under the nuts 14 and pressing lightly on the bottom
surface of each successive nut 14 to remove and carry
away any e~~cess coating material 22.
It is generally preferred that the rotational speed
of the blotters 78 be synchronized with the belt speed
carrying the nuts 14 so that there is no wiping action on
the surface of the nuts 14. However, in certain
applications it may be desirable to move the blotter
wheels 78 asynchronously to effect a wiping action on the
bottom of successive nuts 14. As the blotter 78 rotates
away from the belt 50, it becomes partially submerged in
a tank 80 containing a solvent such as methyl ethyl
ketone (MEK) or a mixture of NMP and XYLENE which
cleanses the blotters 78 of any excess coating material
22 between presentations of the same section of blotter
78 to successive nuts 14. If additional cleaning of the
blotter 78 is needed, then a knife-like scraper 82 can be
added to remove remaining excess, coating material 22 from
the surface of the blotter 78 prior to successive
contacts with additional nuts 14.
Once any coating material 22 that may have migrated
outside of the threaded hole 16 of the nuts 14 is
removed, the nuts 14 then travelling on the belt SO are
conveyed through a drying section 102, as illustrated in
Figure 1. This drying section can take the form of one
or more air blowers 84, heaters 86 or combinations
thereof. The heaters 86 can take the form of infrared,
radiant or induction heating elements. One or more
vacuum ducts can also be provided in the drying section
to draw solvent fumes away. The purpose of the drying
section 102 is to accomplish sufficient flashing off of
the solvent contained in the coating material 22 in the
nut 14 to stabilize the coating.
21
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Once the belt 50 moves the fasteners beyond the last
blower 84 or heater 86, the solvent from the coating
material 22 has been flashed off and the coating material
22 remains on the desired threads 25 of the nuts 14 to be
' subsequently cured. An optional inspection stations
utilizing mirrors and lights can be presented on the
upper conveyor system 36 at this point if so desired, in
order to have the opportunity to visually inspect the
nuts that have been coated to insure proper coverage.
The coating material 22 on the nuts 14 at this point is
no longer liquid and cannot flow or shift on the fastener
surface. The coating material 22 may still be sticky to
the touch and is uncured.
Once the parts leave the drying area 102, the upper
magnetic rail 46 thereafter terminates and the strip 21
of fasteners 14 falls away from the belt 50. The strip
21 is then directed to a curing spool 54 which semi-
automatically maintains a tension of the strip and
respools the strip 21 of nuts 14 that now contain a
barrier coating. The spool 54 is preferably constructed
of a nonmagnetized metal and is mounted for rotation on a
magnetized fixed hub 105. As the strip 21 of nuts 14 is
lead to the spool 52, the magnetic force from the hub 105
attracts the end of the strip 21 and efficiently starts
the winding process. The tensioning and respooling of
the strip 21 is accomplished using a motor 94 connected
to a slip clutch 96 that rotates the curing spool 54 as
illustrated in Figure 4A. The curing spool 54 winds the
nuts 14 in a single width coil so that air and heat can
reach all of the nuts evenly. The spool 54 is then
removed from the device 10.
Once the spool 54 is removed from the device 10, it
is placed alone or with other spools 54 on an oven
conveyor where they are first subjected to the first
stage of drying using fans blowing at room temperature.
22
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The spools 54 are subsequently heated in two stages, a
first stage usually utilizing fast blowing air at about
250°F and a second stage utilizing slow moving air at
about 450°F. Since the hub 105 is magnetized rather than
the spools 54, no degradation of the magnets occurs~from
exposing the spools to heat. The spool 54 is
subsequently allowed to cool and the strip is threaded
through an oiling station to apply a protective, but
light, coat of oil to the nuts. The spooled nuts 14 are
then ready for shipping.
Turning now to Figure 13, another embodiment of the
present invention is illustrated and generally referred
to at 11. This embodiment is substantially identical to
the previously described embodiment illustrated in Figure
1, but differs in several important respects. In this
embodiment, unconnected parts such as, for example, loose
nuts 19 are fed in a uniformly centered orientation onto
the belt 32 of the first conveyor system 24 by a known
parts delivery system such as a vibratory feed bowl 15
and.a track 17. Additionally, the present invention only
requires successive parts to be centered on its belts.
The amount or regularity of spacing between subsequent
parts is immaterial. In this embodiment, the feed wheel
56 is utilized to help meter the nuts 19 onto the belt 32
at a controlled rate. Similarly, in this embodiment,
once the individual nuts 19 are no longer exposed to the
magnetic force of the upper magnetic rail 46, they simply
drop off of the upper belt 50 and into a bin 90 for
further processing.
This embodiment demonstrates an important feature of
applicant's invention, namely, that it is capable of
achieving heretofore unattainable processing speeds for
application of barrier coating materials onto a variety
of different parts or fasteners with superior coating
results, regardless of whether the parts are fed to the
23
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WO 96/40444 PCT/US96/09571
machine individually or in an interconnected strip from a
spool. Changeover and set up time required for coating
parts of different types or sizes is likewise minimized
as a result of the ease of adjustment of the belt speeds,
guns and sensors. As illustrated, for example, in
Figures 15-18, unlike the prior art, the present
invention can efficiently process very small parts such
as clinch nuts, parts with off
center threaded openings such as stamped nuts, parts with
multiple threaded openings such as tapping plates, or
parts having extended vertical chimney-like structures.
The embodiment of the present invention illustrated
in Figure 13 also demonstrates other optionalfeatures of
the present invention. At times it may be desired to
sufficiently warm the fasteners 19 to influence the
rapidity with which the later applied liquid coating
material 22 will subsequently flow on the surfaces of the
fasteners 19 that it is supplied to. An optional
preheater 71 may be provided to raise the temperature of
the fasteners 19 from room temperature to between about
100-150°F upon exit from the preheater 71. Additionally,
the previously described inspection station can be
combined with a parts ejector to remove parts from the
belt that do not meet the inspection criteria. A belt
cleaning station 99 can also be provided that wipes any
excess coating material off the belt 32 after each time
the belt 32 passes through the liquid application section
101 and prior to the introduction of additional uncoated
nuts 14 onto the belt 32.
The following examples are given to aid in
understanding the invention. It is to be understood that
the invention is not limited to the particular procedures
or parameters set forth in those examples.
24
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Fxa~r~r.~ ,
M6-1 pierce nuts were deposited onto the moving belt
of a lower conveyor system of an apparatus as illustrated
in Figure 1. The parts were connected together by metal
filaments and were fed in a strip from a spool mounded on
a shaft. The length of the conveyor belt was
approximately 28 feet long, which presented an
approximately 14 foot track for the nuts to travel with
the nuts being retained~on the belt by the force of the
magnetic rail thereunder and removed continuously by a
conveyor belt driven by a two inch wide, ten inch
diameter pulley near the point of introduction of the
nuts in a 'two inch wide, ten inch diameter pulley located
at the opposite end of the conveyor belt. The belt was
constructed of a Teflon coated fiberglass reinforced
material having a .030 inch square open mesh construction
and was moving at a speed of about 17 feet per minute.
The nuts were cleaned by having a discrete shot of
MEK solvent deposited into each respective threaded
opening by a Nordson Zero Cavity gun having a Nordson
#276515 gun module, with each shot being triggered by a
Keyance PZ-101 optical sensor. The flow rate of the
cleaning material from the gun was approximately 30
ounces per hour and the pressure was approximately 2 psi.
Once the solvent was applied, the parts subsequently
entered an exhaust enclosure where two blow-off ports
blew into the threaded holes causing the MEK and loosened
dirt and oil to atomize and be blown out of the now clean
threads and vacuumed away.
The nuts then encountered two Nordson Zero Cavity
gun with a #276515 Nordson module located on opposite
sides of the belt. Each gun applied a single discrete
shot of du Pont Teflon-S (954-101 green) and du Pont T-
8748 thinner in a 70/30 mixture at.room temperature. The
discrete shot were triggered by a pair of Keyance PZ-I01
CA 02223463 1997-12-04
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optical sensors, one mounted opposite each of the guns.
The discrete shots were placed on opposite sides of the
internal threads of each nut.
The nuts with the coating material applied travelled
approximately another two feet along the lower conve~ror
belt allowing a sufficient time for the coating material
to wick and cover all of the threads. At that point, the
lower magnetic rail of the lower conveyor system
terminated and the nuts jumped onto the belt of an upper
conveyor system that partially overlapped the lower
conveyor system being attracted by the magnetic force of
the upper magnetic rail above the belt. Once travelling
on the upper belt, which was substantially the same as
the lower belt and travelling at the same speed, the
fasteners were passed through two foam blotting wheels
with MEK solvent thereon in order to remove any excess
coating material that may have been present on the
bottoms of the fasteners once the blotting wheels were
moving at the same speed as the nuts passing thereby.
The nuts then were carried by the upper conveyor
past a set of drying fans that blew room temperature over
the coated nuts to flash out the solvents and dry the
coating material. The strip of nuts was then rewound on
a take-up reel that was powered by a variable speed
Bodine motor and driven through a slip clutch to keep the
strip tension for a tight and neat wind around the reel.
The reel was then removed from the coating apparatus and
subjected to drying and curing as follows:
1. Five minutes drying in front of a fan blowing
room temperature air onto the parts.
2. Ten minutes in the first stage of an oven-fast
blowing air at about 250°F.
3. Ten minutes in second stage of oven-slow moving
air at about 450°F.
26
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4. The strip of fasteners was then led through an
oiling station to apply a protective, but light, coat of
oil to the fasteners. The parts were then reloaded back
onto the customers spool and secured for shipping. Each
of the~nuts on the spool exhibited a substantially
pinhole free coating
M6 pierce nuts processed in the above-example were
tested for conformance with General Motors Engineering
Standard No. GM6076M entitled "Fluorocarbon Coating for
Anti-Weld Splatter Electrodeposition Masking". Five
pierce nuts were removed from each spool of 5,000 pieces
for testing. The parts were electrostatically primed and
baked to cure the primer then the parts were tested in
the torque tension tester as instructed in the above-
listed GM specification. The coating present on the nuts
had a uniform appearance and was free of tears, runs and
flaked areas. In addition, the cured coating was
sufficiently damage resistant to prevent chipping or
other coating removal during normal handling and shipping
of the parts. The parts were then tested at 9 Newton
meters of torque. The bolt and test pierce nuts should
generate between 6 and 12 kilonewtons of clamp load in
accordance with the GM specification. The sampled pierce
nuts generated 7.9 kilonewtons of clamp force when 9
newton meters of torque was applied, thereby meeting
torque tension requirements of General Motors standard.
EXAMPLE 2
M8 weld nuts made of plain steel having a 1 1/4" _
diameter and a total thickness, including boss and weld
studs, of .375" were fed from a vibratory bowl through a
downtrack on a 30° incline onto the moving belt of a
27
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lower conveyor system of an apparatus as illustrated in
Figure 13. The details of the apparatus and process were
the same as those set forth in Example 1 above, except as
indicated hereafter.
The nuts were carried by the lower conveyor belt in
centered, end-to-end configuration through a station
where liquid coating material was delivered into the
threads of each nut, covering parts of all but the bottom
thread. Two dispensing guns were used and placed 180°
apart from one another, to each deliver a single metered
shot of liquid coating material to the opposite sides of
each threaded area. The discrete shots of liquid
material were fired by the guns having a shot duration of
30 milliseconds. The belt speed was approximately 19.5
feetlminute. The pot pressure of the liquid material
delivered to the fasteners was approximately 23.4 psi.
The material applied to the weld nuts was delivered at
room temperature and contained a mixture of about 70~
Whitford XYLAN~ 1661 high build purple dry film lubricant
and about 30~ of a solvent mixture containing N methyl
pyrrolidone (NMP) and XYLENE~.
The nuts were then transferred to the upper conveyor
system where they were suspended from and moved by a
conveyor belt, being held against the moving belt by the
force of a magnet located above the rail. The nuts then
passed through a blotter station where any excess
material was removed from the faces of the nuts. The
nuts were then carried by the upper conveyor past a set
of transflow blowers that blew room temperature air over
the coated nuts to assist in flashing out the solvents
and drying the coating material. The nuts were then
dropped onto an intermediate conveyor with blowers to
further dry the parts for approximately 30 seconds. The
nuts were placed in a curing oven with two heat zones.
The first zone exposed the nuts to a first stage of
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heating in an oven with fast moving air at a temperature
of about 180°F. The nuts were then exposed to a second
stage of heating in an oven with slow moving air at a
temperature of about 480°F for 10 minutes.
Each of the nuts processed exhibited a substantially
pinhole free fluorocarbon coating. Nuts processed in
this example were then tested for conformance with
General Motors Engineering Standard #GM6076M. The
coating present on the nuts had a uniform appearance and
was free of tears, runs and flaked areas. In addition,
the cured coating was efficiently damage resistant to
prevent chipping or other coating removal during normal
handling and shipping of the parts. The sampled test
nuts also met the torque tension and weld splatter
requirements of General Motors Standard #6076M.
From these examples, the benefits of the present
invention can be seen in the high speed application of
liquid barrier coating materials to a continuous stream
of parts such as fasteners in a very precise manner.
29
