Note: Descriptions are shown in the official language in which they were submitted.
j7~Q
ME~HOD FOR ELECTROSTATIC COATING THREADED FASTENERS
WITH A THERMOPLASTIC ~ESIN
TECHNICAL FIELD
The invention relates to self locking fasteners having a
coating of a thermoplastic resin material applied thereto and
particularly to a method of applying resin to the fastener.
More particularly, the invention relates to an improved method
o~ applying the resin coating electrostatically throu~hout a
predetermined circumferential portion of the fasteners
preferably between 180 degrees and 360 degrees. __
BACKGROUND ART
The use o~ self locking fasteners has increased
considerably in recent years for a variety of fastening
applications wherein the integrity of the fastened members is
~o critical. One common form of providing a sel~ locking fastener
i~ by the use o~ a thermoplastic resin coatin~ which i8 applied
to portions of the threaded bolt end or internal threads of a
nut. Various methods have been developed for applying the
thermopla~ic material to the threaded area oP the fastener.
One type of method use~ a patch of a soft pliable thermoplastic
material which i~ pressed or melted into the threaded area.
Some examples o~ this method and resulting fastener are shown
in Patent Nos. 3,0g3,17~; 3,263,726; 3,294,139; 3,313,01~;
3,416,492; 3,43~,541; 3,552,46~; 3,56~,~46; and 3,634,5~.
~o Another common method i8 to heat the bolt and then direct a
spray of powdered resin against the heated bolt whereby the
resin will melt and adhere to the threaded areas of the bolt.
Examples of such coating methods are shown in Paten~ Nos.
;6~
--2--
3,766,584; 3,~31,724; 3,579,684; 3,787,222 and 4,120,993. In
another method, the fastener has a wetting agent applied over a
predetermined area and the powdered thermoplastic resin applied
to the wetted area after which the fastener i5 heated to bond
the resin to the bolt.
Although many of these known methods provide a satisfactory
procedure ~or applying the thermoplastic resin material to the
bolt, one of the disadvantages is that it is difficult to
regulate the size of the circumferential area covered by the
resin in a simple and inexpensive manner, and in particular to
form a resin coated fastener wherein the coating i~ applied
over a circumferential area of bPtween 180 and 360 degrees
instead of the 180 degrees area provided by as most known
spraying operations. The application of the resin by spraying
of the powdered material i8 believed to be the most economical
and satisfactory but does not provide for the satisfactory
coating of a circumferential area of the bolt greater than 180
degrees.
Patent No. 4,428,981 shows a method for applying a resin
2~ coating covering approximately 360 degrees about a bolt by
spinning the bolt as it passe~ through the coating or spray
area. Although thi~ method provides a bolt having a resin
coating of more than 180 degrees, it requires a dual drive
mechanism for spinning the bolts. An alternative means of
coating the bolt throughout a full 360 degrees is by the use of
a pair of spray nozzles, one on each side of the moving bolt to
attempt to provide the 360 degree coatlng.
Another problem when applying a resin coating to a threaded
fastener is tha~ it is dif~icult to achieve a relatively thick
coating of the resin on the fastener without the use of multiple
spray nozzles since it is difficult to achieve a sufficient
buildup oP the resin part~cles with only a single nozzle.
Therefore, the need has existed for an improved method for
~ ~ S 6 ~ 5 ~
coating fasteners and in particular bolts, with a self locking
thermoplastic resin in which the coating can be applied
throughout a predetermined circumferential area of between 180
degrees and 360 degrees of the threaded area in an extremely
simple, efficient and economical procedure.
DISCLOSURE OF THE INVENTION
Objectives of the invention include providing an improved
method for coating fasteners with a self locking thermoplastic
resin by electrostatically applying the resin to the fas-teners by
spraying the fasteners as they move past a spray station with a
powdered resin electrically charged at an opposite polarity to
the charge placed on the fasteners whereby the particles are
attracted to the fasteners by the electric field surrounding the
fasteners. In a specific embodiment of the invention there is
provided an improved method in which the fasteners may be at
ambient temperature when the spray of powdered resin particles is
directed toward the fasteners whereby certain portions of the
electrostatically adhered resin particles may be removed by
subsequent air jet nozzles providing a predetermined pattern of
resin particles adhered to the fastener prior to the fasteners
passing through a heating zone to firmly bond the desired pattern
of resin particles to the threaded area.
In still another embodiment of the invention there is
provided an electrostatic coating procedure in which the fas-
teners upon entering the spray zone are contacted by a plurality
of rnetal wires or brushes which are connected to ground to form
an induced ground, and in which a positive polarity is applied to
the powdered resin particles by high voltage electrodes which
extend into the path of the particles as they are sprayed
i7~
-- 4
through a nozzle by pressurized air. In a further embodiment
there is provided an improved method in which the spray nozzle
assembly is formed of a dielectric material except for an outer
flared nozzle end, which end is subjected to a lower voltage of
the same polarity as the electrodes which are located upstream in
the path of the moving powdered material to maintain the polarity
on the powder without presenting a problem of flashover with the
adjacent metal fasteners which are at the opposite potential.
In a further embodiment of the invention there is provided
an improved method in which a vacuum duct is positioned on an
opposite side of the fasteners from the resin spray nozzle
assembly at the spray station to recover excess powder, and in
which air jet nozzles may be located downstream of the resin
spray station to remove portions of the adhered powdered resin
from certain portions of the fasteners to obtain the desired
circumferential coated distance and to dress and clean the ends
of the threaded area to provide an uncoated area enabling the
fasteners to be started easily with their mating elernent before
encountering the self locking resin coated area. In still
2~ another embodiment there is provided an improved method in which
a specially designed vacuum duct having an air defuser as a part
thereof confines the powered resin particles to a generally
specific area on the bolt shank instead of completely covering
the bolt due to the attraction of the particles to the bolt of
opposite polarity. In another embodiment there is provided an
improved method which provides an extremely simple, inexpensive
and highly eEfective procedufe for coating threaded fasteners and
in particular bolts, with a predetermined circumferential area of
resin material.
In yet another embodiment of the invention there is provided
an improved me-thod in which the fasteners may be heated before
entering the spray station whereby a relatively thick coating of
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resin material can be deposited on the heated fasteners without
requiring multiple spray nozzles and without reducing the linear
Qpeed of the fasteners as they move through the spray station.
These objectives and advantages are obtained by the
improved method of the invention, the general nature of which
may be stated as a method for electrostatically coating a
threaded fastener with a thermoplastic resin extending around a
predetermined circumferential threaded portion of fastener
including the steps of moving a threaded fastener along a
predetermined path having a spray zone and a heating zone;
polarizing the fastener at the spray zone; and polarizing a
stream of powdered resin to an oppos~te polarity than the
fastener and directing the resin towards a port~n~of the
threaded end of said fastener whereby the polarized resin is
attracted to and oling~ to said threaded portion forming a
coating of powdered resin about ~a~d threaded end.
BRIEF DESCRIPTION OF THE~ DRAWIN~S
A preferre~ embodimen~ of the invention, illustrative of
the best mode in which applicants' have contemplated applying
the princlple~, i8 set forth in the following description and
i8 ~hown in the drawings and i8 particularly and distinctly
pointed out and set forth i~ the appended claims.
FIG. 1 i~ a perspectlve view showin~ a type of fastener
with the thermopla~tic resin applied to a predetermined area
thereof by the ~teps of the improved method;
FIG. 2 is an enlarged view with portion~ broken away and ln
seGtion showing certain of the threads of the fastener FIG. 1
with the resin applied thereto;
FIG. 3 is a diagramatic top plan view showing a type of
~ZS~i7~;0
apparatus for carrying out the steps of the improved method;
FIG. 4 is a diagrammatic side elevational view of the
apparatu shown in FIG. 3;
FIG. 5 i8 an enlarged fragmentary sectional view taken on
line 5-S, FI~. 4;
FIG. 6 is an enlarged fragmentary sectional view taken on
line 6-6, FIG. 4;
FIG. ~ is a fragmentary diagrammatic top plan view showing
a type of spray nozzle for applying the resin to a fastener of
the type shown in FIG. 1;
FIG. 8 is a fragmentary diagrammatic side elevational view
of the spray nozzle of FI¢. 7;
FIG. 9 is an enlar~ed fragment~ry sèctional v~ew taken on
lin~ 9-9, FIG. 8; and
FIG. 10 is a perspective view w1th portions broken away and
in section showing the vacuum duct for recovering spent resin
particles.
Similar numerals refer to similar parts throughout the
drawings.
BEST MODE FOR CARRYING OUT THE INVENTION
The improved method i de-~cribed below in relationship to
applying a powdered thermoplastic resin coating on a bolt
although the improved method could be used for applyins similar
material~ onto other types of threaded fastener~ whether having
internal or external threads or other arrang~ents than a
threaded area at the end of a ~hank, and need not be limited to
the fastener bolts shown in the drawin~ and described below.
FIG. 1 shows a bolt indicated generally at 1, consisting o~
a shank 2 having a lower threaded area 3, a smooth upper area
4, and a head 5. The individual threads consi~t of vall~ys ~
and peaks 8 as shown in ~IG. 2. The resin coating is indicated
at 9 and is shown in FIG. 2 being bonded to the bolt and
providing a desired uniform coating of valleys 7 preferably not
extending above peaks 8.
The apparatus for carrying out the steps of the improved
method i5 shown particularly in FIG. 3 and includes a pair of
pulleys 11 and 12 which are power driven preferably by an
electric motor and a single shaft (not shown) connected to the
pulley shafts 13 whereby the pulleys will rotate at the same
speed. Other types of drive mechanisms can b~ used if desired.
Pulleys 11 and 12 are double grooved pulleys in which a pair of
endless flexible belts 14 and 15 are located which preferably
are formed of nylon or similar flexible inexpensive material.
Belts 14 and 15 could al~o be formed of other typ~s of pla6tlc
or dielectric materials.
A spray station, indicated generally at 1~, is located
generally ad~acent pulley 11 and consists principally of a
spray nozzle assembly indicated at 18, a vac~um recovery duct
19, and a grounding a~sembly indicated yenerally at 20.
Grounding assembly 20 consists of a plurality of metallic
strands 22 preferably formed of copper to provide good
conductivlty. Strands 22 extend downwardly from a supporting
bar 23 which is connected to ground 24 to form an induced
ground. The resiliency and thickness of metallic strands 22
may vary depending upon the particular size and weight of bolts
being ~oved past the spray station by belts 14 and 15 since the
larger more rigid strand3 22 could affect the movement of the
bolts in contrast to a thinner more flexible strand. Other
types o~ grounding strands or brush arrangement can be util~zed
from that chown in FIG. 3 to provide a grounding affect on the
bolts as they pass through the ~pray station without affecting
the concept of the invention.
Spray nozzle assembly 18 i8 shown particularly in FIGS.
and 8 and .~ncludes a mixing block 26 formed of a dielectric
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material such a~ nylon or other type of plastic. A passage 27
extends completely through the nozzle block, one end of which
is connected to the end of a hose 28 by a connector 29, with
hose 28 being connected to a source of compressed air. A
powder inlet opening 30 extends vertically into block 26 from
top surface 31 and terminates in passage 27. Preferably
passage 2~ and inlet opening 30 are of the same uniform
diameter size.
A feed ~unnel or hopper 33 i5 mounted on upper surface 31
and contains a supply of resin powder 34 which is fed by
gravity through opening 30 into passage 27 where the incoming
supply of compressed air carrie~ the resin powder through
passage 27 and through a nozzle supply sleeve 35 which iB
connected to block 26 and then to a flared defusing nozzle 3~.
Sleeve 35 and feed funnel 33 also are formed o~ a dielectric
material with flared nozzle 37 preferably being formed of
copper or other metallic material.
In accordance wlth the invention, high voltage electrodes
39 and 40 extend through supply sleeve 35 and across sleeve
bore 41. ~ore 41 preferably is tapered outwardly as shown in
FIG. 8 to reduce the velocity o~ the powdered resin being
carried by the pres~urized air stream along the ~leeve upon
approachlng nozzle 3~ for discharge onto bolt l. This enables
sufficient air pres~ure to be used for carrying the powdered
resin material discharged from funnel 33 through sleeve 35 and
out of nozzle end 37 w1thou~ too great a velocity being
imparted ~o the powdered material as it approaches bolt l.
Another electrode 42 preferably is connected to defusing nozzle
3~.
Electrodes 39 and 40 pre~erably are section~ of tungsten
wire and extend across sleeve bore 41 whereby the particles
moving past the electrodes will have a positive D.C. charge
applied thereto. In the preferred embod1ment, electrodes 39
3~25~7~
~nd 40 will be at a potential of approximately 20 kv positive
D.C. voltage with nozzle electrode 42 being at a considerable
reduced voltage such as 3 kv. Electrodes 39, 40 and 42 are
connected to a usual D.C. transformer (not shown) which i5 well
known in the art.
Vacuum recovery duct l9 preferably i8 mounted directly
opposite nozzle 3~ to recover any powdered re~in particles
which do not adhere to bolt 1. Recovery duct l9 ~FIG. 10~
includes an air defuser housing indicated generally at 55 which
is connected to a source of suction by a hose 56. Housing 55
includes a ~enerally rectangularly shapad front portion and a
conical shaped rear portion wi~h the front portion being formed
with an inlet end 57 which converges into a narrow elongated
opening 58. The air entering inlet opening 5~ indicated by
arrow3 A, flows through a hollow rectangular-shaped passageway
or chamber 59 and into a tapered area 60 where it flows out of
a round outlet 61 and into hose 56. An aiF defuser mechanism
indicated generally at 62 is formed a~ a part of housing 55 and
extends upwardly therefrom having a rectangularly shaped air
lnlet openin~ 63 which communicates with conical shaped passage
60. A baffle 65 1~ pivotally mounted within air defu~er 62 and
is ad~ustable by a nob 56 to regulate the amount of air flowing
into the air defussr indicated by arrow B.
The particular configuration and construction of vacuum
recovery duct 19 enables ~he exces~ powder resin particles not
attracted to the bolt to be collected and removed from the
~pray area. More lmportantly the air stream which it creates
moving across the bolt prevents the particles from completely
covering the bolt and provides for a general uniform pattern of
the resin particle~ in a specific area of the bolt shank. The
use of defuser 62 greatly aids and assists in maintaining the
powered resin particles in a defined area on the bolt instead
of completely covering the bolt in its entirety with resin
-10~ ;75(~
particles due to the natural tendency of the particles to
adhere to all surfaces of the metal bolt due to the opposite
polarities of the balt and particles and by eliminating
turbulence in the ~oving stream of pressurized air.
As shown in FIG. 5, the powdered resin particles 34 upon
being ~ischarg~d through nozzle 37 are directed toward a
predetermined area of threaded end 3 of bolt shank 2. The
electric field established by the opposite polarities of the
bolt and resin particles cause the particles to be attracted to
the bolt whereby these particle~ which normally flow past the
bolt are captured by the side and rear area~ of the bolt to
provide the 360 degree~ circumferential coverage of the
threaded end of the shanX. The axial height or length of the
powdered coated area 43 ia determ~ned by the height of
dl~charge opening 44 of nozzle 37 and vacuum duct 19. Thus in
accordance with the concept of the invention, the charging of
the res~n particles and ~olt at opposite polarities enables the
heretofore passing particle~ to adhere to the side and rear ,`_
portions of the bol~ with the front portions being covered by /i
the normally directed contacted particles being sprayed ~rom
the nozzle.
The powder particles impinge against the surface of the
bolt and ln the thread valleys and cling sufficiently to the
threads until the bolt passes through a heating zone lndlcated
generally at 4~ where th~ bolt i8 heated above the fusion point
of the resin material whereby the resin melts and bonds to the
sur~aces of the thread valleys to form the deslred
thermoplastic coating 3.
However, be~ore the powder coated bolts reach the heatlng
zone, they are passed throu~h a control zone indicated
generally at 4~, having one or more air ~et nozzles 48.
Nozzles 48 direct streams of pressurized air 49 against
predetermined areas of the threaded ~hank to remove certain of
the powdered resin particles as shown in FIG. 6 especially at
the extended end of the threaded shank. Removal of the
powdered resîn at the end of shank 2 provides a predetermined
uncoated length of lead thread3 which enables the threads to
have a start with a mating nut or threaded hole before the
mating thread~ encounter the resin coated threads.
If desired, other air nozzles 51, only one of which is
shown in FIG. 3, may be positioned at control zone 4~ or
further downstream therefrom and direet against a stream of
pressurized air against predetermined portions of the bolt, for
: example, the back surface thereof, in order to remove the -
powdered resin from certain areas thereof. Baffilo also may be
-- ~used to direct this pressurized air to the desired areas of the
powder coated threads. For example, the powdered resin can be
removed from the rear 180 degree surface or portion of the bolt
to provlde a circumferential powdered coating of between 180
degrees and 360 degrees. If a full 360 degree circumferential
coating is desired, air nozzles 51 will not be used. Nozzles
51 provide the means for varyin~ the size of the
circu~ferential resin coating which will be firmly bonded to
th~ threaded area of the bolt at heating zone 46. Since the
bolt i8 at aobient temperature and the resin particles are
still in the powdered form, they are removed easily by the ~ets
- of air fro~ noz~les 48 an~ 51 to provide the desired pattern of
the ultimate thermoplastic coated area 9.
Heating zo~e 46 preferably l~cludes an induction heater 53
which rai~e~ ~he te~perature of the metal bolt passlng
therethrough to a point above the fusion or melting point of
the thermopla~tic powdered material. After the bolt leaves
heating zone 46 it i9 cooled whereby the resln forms a firm
bond with the bolt threads. Other types of heaters can be used
~or heating either the bolt or resin particles for adhering the
particles to the bolt than the induction heater shown in the
-12- ~ Z 5 ~7 ~
drawing After the coated bolts,leave the heating zone, they
are cooled, either by the ambient air or preferably by
depositing the bolts into a bath of oil or water, from which
they are removed for subsequent stora~e and/or shipment. The
heat of fusion o~ a type of nylon resin found suitable for
coating the threaded bolts ends i~ approximately 450 to 500
degrees Farenheit.
Although the above described method indicates that the
powdered resin particles are sprayed onto the moving fastener
before it passes through the heating zone, it may be desirable
for certain applications ~o heat the fastener before it moves
through the spray zone. Thi~ enables a considerably larger
deposit o~ resin particles to be formed on the fastener and
provides a strong bond between the powdered resin and fastener
~ince the resin immediately melts upon contacting the heated
fastener with additional resin particles than being attracted to
the fastener to provide a thicker coating than believed
heretofore pnssible with known nonelectrostatic coating methods.
The improved method steps of the invention
consist broadly of moving one or a plurality of fasteners along
a predetermlned linear path pa~t a spray station, at w;~ich
station the fastener~ have a certain polarity applied thereto and
an OppO8~ te polarity i8 lmparted to particles of thermoplastic
resin which are sprayed toward the fasteners from a nozzle
whereby the resin particle~ which heretofore would pass by the
fa teners are attracted to and clin~ to the sides and rear
portions of the fastener shank to provide a powder coatlng
-' completely about the shank. Next the powder coated fasteners may
pa88 by a control zone in which one or more nozzles remove the
powdered particles from selected areas of the fasteners by
dlrecting a stream of compressed air toward the selected bolt
areas after which the fasteners pass through the heating zone
where the powder material i8 firmly bonded thereto. The
-~3~
~asteners after leaving the heating zone are cooled either by the
a~bient air or external means at which time the resin material is
firmly bonded to the threads to provide the self locking effect
desired thereof. If desired, the fasteners are moved through the
heating zone before movlng through the spray zone.
The above sequence of steps is carried out in a continuous
movement of the fasteners by equipment which i5 extremely simple
to operate and relatively inexpensive to manufacture, in contrast
to equipment heretofore used ~or coating fasteners with such a
thermoplastic material, and in which the improved method is able
to provide a re~in coatin~ between 180 degrees and 360 degrees
which i8 difficult to achieve economically by ~nown method~ and
`~~ a~paratus. Although the electrostatic coating of metal ob~ects
has been performed ~or years, it has never been applied nor used
with the ther~oplastic coating of fasteners, and in particular
bolts, which enables the powdered resin material to be applied to
the bolts when either ln a heated or unheated state whereby the
powder will adhere completely about the circumference of the bolt
enabling ~he final resin material to be bonded throughout this
2Q . 360 degree area, i~ d~sired, and whlch permits the easy removal
~ of the powderod resin partlcle~ from selected bolt areas by ~ets
- of air if app led before the bolt i8 heated and the resin
: material fused to the threaded area, thereby enabling a re~in
- coatlng to be applied to a circum~arential thread0d area between
180 degrees and 360 degrees in an sxtremely ~imple and economic
manner.
In production lot~ the heads of the bolts u~ually will be
closely ad~acent or in abutme~t with each other as they move
down the coating line by belts 14 and 15 with one or more bolt
~hank~ being sprayed with the resin powder upon passing spray
nozzle 37. Also the polarity applied to the bolts and powdered
resin could be reversed from that described above and -qhown in
the drawings. Likewise, other apparatus can be used for
-14- ~25~75~
.,
applying the opposite polarities to the bolt and resin
particles than that shown without affecting the concept of the
invention. Preferably, the powdered resin is applled uniformly
360 degrees about the bolt shank to provide a final uniform
coating of resin material 9 as shown in FIG. 2. Also, it is
readily understood that the bolts will be cleaned with a
solvent to remove all ~rease and oil therefrom be~ore being
placed on belts 14 and 15 as i9 customary in most resin coating
procedure~.
Accordingly, the improved method is simplified, provides an
e~fective, safe, inexpensive, and efficient procedure which
achieves all the enumerated ob~ectives, provide3 for
eliminating difficulties encountered wlth the prior .neth~ds,
and solves problems and obtain~ new re~ults in the art.
In the foregoin~ descriptlon, certain terms have been used
for brevity, clearness and understanding; but no unnecessary
limitations are to be implied therefrom beyond the requirements
o~ the prior art, because such terms are used for descriptive
purposes and are intended to be broadly construed.
~0 Moreover, the description and illustration of the invention
is by way o~ example, and`the ~co~e of the in~Q~tion i8 not
limited to the exact details qhown or described.
Havin~ now de~cribed the features, discoverle~ and
principles of the invention, the manner in which the improved
method ~or electrostatic coating threaded fasteners with a
thermoplastic re~in i~ carried out, the characterl~tics of the
improved method, and the advanta~eous, new and useful results
obtained; and the structures, device-~, elements, arrangementc,
part~, and combinations thereof for carrying out the stPp~ of
the invention are set ~orth in the appended claims.
