Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVED POWDER FEEDING APPARATUS FOR THREADED ARTICLES
Backqround Of The lnvention
This invention is generally directed to a powder application system and, more
specifically, to an improved powder metering and feeding system for spraying powder
onto threaded articles such as nuts in the manufacture of prevailing torque fasteners.
Powder feeding systems for applying powder to threaded articles have long
been know. Powder feeding systems are inherently more accurate when they are
operated continuously, i e., in a steqdy-state condition, rather than operated in an
intermittent or go-and stop fashion. Intermittent operation is prone to powder surges on
start-up and powder dribble at the end of a spray cycle
There are useful devices which apply power in an iutc~ llel ll cycle, as
disclosed in U.S. Patent No. 5,362,327. Automatic systems employing continuous-flow
powder application devices are also known (see, e g., U.S. Patent Nos 4,054,688
4,100,882, and 5~025l750), in which threaded articles are sprayed in a continuous
fashion rather than, an intermittent fashion. The powder application device of U.S.
Patent No. 4,060,868 provides a continuous powder flow with intermittent spray air
flow, and is Sl l~cprtihle to powder surges and inconsistent powder application.Accordingly, it would be advantageous to provide a powder application system
for threaded articles which applies powder in an intermittent fashion, yet which takes
advantaoe of the more uniform flow rate and inherent accuracy of a continuous powder
feeding operation The present invention may be used with powder applicators, such
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as those disclosed inlJ.S. Patent No. 5,362,327, to provide more consistent torque
values in the resulting product.
Summary Of The Invention
These and other objects are realized by the present invention, which overcomes
disadvantages ~cso~i~tPd with prior art iulen~,lllenl-flow powder feeding d,u~ "~
for threaded articles, and also provides new advantages not found with such existing
systems or apparatus.
In one preferred embodiment, a continuous-flow powder feeding device is
provided for applying powder to a threaded article The device includes a powder
source; a powder spray tube for delivery of powder to the threaded article; a powder
by-pass tube for delivery of powder to a collector for receiving powder; and a powder
supply tube in communication with the powder source and in selective communication
with either the powder spray or powder by-pass tubes The powder supply tube
continuously moves powder through it with the aid of pressurized air. The device
automatically moves the powder supply tube into selective communication with the
powder spray tube in response to a signal that the threaded article is in a powder
application position.
Preferably, the device automatically moves the powder supply tube into selective
communication with the powder by-pass tube in response to a signal that powder has
been applied to the threaded fastener. As one example, the device may be used to
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form a patch on the tlireaded fastener, and the variation in installation torque of the
resulting threaded article is minimized, and relatively uniform. In one preferred
elllbu~ nl~ the device includes a shuttle valve carrying the powder spray and powder
by-pass tubes, and an actuator for autu" l~,lic~lly moving the shuttle valve in response
to the signal The actuator may take the form of a solenoid or air cylinder, as non-
limiting e~amples A powder metering apparatus, such as a helical auger, may be used
in conjunction with the device for delivering a relatively constant amount of powder from
the powder source to the powder supply tube.
In another preferred embodiment, the present invention involves a method for
applying powder to a threaded article employing a continuous-flow powder feeding
device. A powder source and a powder spray tube for delivering powder from the
powder source to the threaded article are provided, as well as a powder by-pass tube
for delivering powder to the powder source or to a second collector for receiving
powder A powder supply tube in selective communication with either the powder spray
or powder by-pass tubes i5 also provided Powder is continuously moved from the
powder source through the powder supply tube using pressuri~ed air The powder
supply tube is aulomdtiLally moved into selective re-i,u, u~il lu~ communication with the
powder spray tube or with the powder by-pass tube, d,:,uendin~ on whether the
threaded article is in a position for powder to be applied. Preferably, the powder supply
tube is moved in response to a signal indicative of the position of the threaded article.
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Brief Descrir~tion of Drawings
These and other features, objects and advantage5 of the present invention will
become apparent from the following des-,d,uliu u and drawings whereln llke reference
numerals represent like elements in the several v:ews, and in which:
FIGURE 1 is a schemabc of a preferred ~Illbodim~nl of the present invention
employing a flow-diverting valve for a single-nozle powder system;
FIGURE 2 is a front view of a second, preferred embodiment of the present
invention employing a flow-diverting valve for a double-nozzle pDwder feeding system;
FIGURE 3 is a partial sectional view taken along reference line 3-3 of FIGURE
2;
FIGURE 4 is a graph showing the variation in installation torque of nuts
processed on a single nozzle, inl~nllillt!ul powder feed system of the type described in
U.S. Patent No 5,362,327, incorporated herein by reference;
FIGURE 5 is a graph showing the variation in i" ' " ' ., torque of nuts
processed on a single-nozzle, contjnuous-flow powder feed system of the present
invention'
FIGURE 6 is a graph showing the variation in installation torque of nuts
processed on a continuous flow powder feed system similar to FIGURE 5, but using a
double-nozzle valve; and
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FIGURE 7 is a graph showing the torque variation of nuts pruu~:s:,~d on a
continuous-flow powder feed system of the type described in U.S. Patent No.
4,10û,882, io~ul,lGIqI~d herein by reference'.
Detailed Description of the Preferred C."l,od;~ t
The present invention employs a by-pass line for the powder stream, to provide
an inI~o~ilIe~ flow powder application operation, while also taking advantage of the
accuracy of a continuous-flow powder application operation The by-pass line diverts
the powder stream during the non-spray portion of the machine cycle A mechanism is
also provided to divert the powder stream from the by-pass line to the spray or
application line during the spray portion of the cycle.
Referring nowto FIGURE 1, a preferred ~",L:odi",~"l of the i"t~n~ "I-flow
powder feed apparatus of the present invention is generally referred to by reference
numeral 10. A shuttle valve 20 having a valve body 40 slides along rod 33, and is
shown in the by-pass position labeled "A~. In operation, a relatively constant flow of
metered powder, flowing in the direction of the arrows, is drawn from a feeder
discharge (not shown) by negative pressure developed downstream from shuttle valve
20. The powder passes into by-pass line 25 where it is directed to a suitable collector
or returned to a feeder supply hopper (neither enclosure is shown~.
In response to a signal, a threaded article to which powder is to be applied is
sensed to be in the proper position for spraying Now, actuator 30 shifts shuttle valve
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20 to the spray position labeled "B' The powder stream passes through aperture 2ûA
within shuttle valve 20, into spray line 35, and is deposited on the threads of the article.
When the spray cycle is completed, a second signal activates actuator 30 to shift
shuttle valve 20 back to by-pass position A at the same time that the sprayed article is
discharged Also at this same time, the next threaded article moves into the spray
position, causing another signal to be generated, and the process is repeated.
Negative pressure may be continuously developed in both the spray and by-
pass lines by qir jets, as those of ordinary skill in the art will d~ Cidlt~ from the
disclosures in U.S. Patent Nos. 5,620,520 and 5,620,741, each of which is incorporated
by reference herein. As one specific example, the samples shown in FIGURES 4-7 (all
airflow measurements are in SCFM) were M8 nuts 1,, uuu~d with an air vacuum at
about 45 SCFM and at a spray speed of about 9.5 SCFM. These figures will vary
depending upon the size and type of fastener, and the desired p~ U~ il 19 speeds and
other parameters.
Actuator 30 may take the form of either a single or double-acting air cylinder, or
a solenoid, or any other fast-acting, linear actuators, for example. As one specific, non-
limiting example, a Husky compact cylinder, Model SFM 118 v. 38 VC3 CB555, may be
used, and connected to air fitting 43. Signals for activating actuator 30 may be
electrical or fluidic in nature; if electrical, they may be generated using fiber optic
sensors or microswitches, for example.
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If desirable based on the particular threaded article size, type and shape to
which powder is applied, valve stem 47 may be shuttled between stops for more
precise positioning alignment within shuttle valve 20.
In one preferred embodiment, the powder metering device for supplying powder
to powder feed apparatus 10 consists of two stacked funnels and a vibrator (not
shown) Each funnel is initially filled with powder, and the larger funnel is located on
top of the smaller funnel, with the discharge opening of the larger funnel being flush
with the powder level of the smaller, lower funnel. Thus, as the power level of the lower
funnel increases, it eventually reaches a level such that the powder flow through the
upper funnel is au lullldliudlly shut off. Vibration of the funnels occurs continuously
This approach has been found to provide a desirable, relatively constant powder flow.
The present invention may be used to accommodate virtually any type of powder
feeder which possesses the capability of providing the required accurate metered flow
As examples, an AccuRate helical dry powder feeder available from Schenck
AccuRateO of White Water, Wisconsin, or a modified stacked funnel\ valve, vibration-
type feeder as described above or in U S Patent No 5,571,323, iu-,ugJr ~ dt~d herein by
reference, may be used
Referring to FIGUR~S 2-3, shuttle valve 20 may be modified as shown to
process two or more threaded articles, such as nuts, simultaneously In this
embodiment, spray tubes 35A, 358 receive powder. Tubes 25A, 25B are the by-pass
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tubes, while tubes 35A, 35B, are the spray tubes. Again, powder flow is shown by the
direction of the arrows.
Cylinder 30 is shown in FIGURE 3 in the extended position, with powder flowing
through spray tubes 35A, 35B. When cylinder 30 retracts, powder flows through by-
pass tubes 25A, 25B. Still referring to FIGURE 3, L-shaped bracket 46 and threaded
fastener 4B mount shuttle valve 20 and cylinder 30 to a suitable fixture A clevis
bracket, generally deaiu,ldled as 55, joins valve stem 47 to cylinder 30 using sleeve
55A, pin 55B, threaded mount 55C and rod 55D Valve stem 47 moves relative to plate
60, which is fixed by fastener 48 to L-shaped bracket 46 Fixed plate 60 includes
apertures 60A, which house the ends of tubes 25A, 25B, and 35A" 35B1.
Referring to FIGURES 4-5, uo" I,Udl jaUI I test results are shown in graph form
Referring to FIGURE 4, actual installation torque is shown for nuts processed on a
single-nozle il ,l~m~illun l powder feeding system as described in U.S. Patent No.
5,362,3Z7 Referring to FlGuRE 5, the variation in installation torque (i e.~ the
difference between the actual value and the mean value) is shown for nuts processed
on a single-nozle power feeding system according to the present invention. Sigma
(i.e., the measure of the degree of scatter) was 1.697 for the test results shown in
FlGURE 4, and O 198 for the test results shown in FlGURE 5 (0.202 and O 196 for the
first and second 20-lot Samples, respectively).
FIGURE 6 shows the variation in il laLdlldliun torque, similar to FIGURE 5, but for
the use of a double-nozzle powder feeding system according to the present invention
g
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(as shown in FIGURES 2-3). The Sigma values are as follows: 0 239 (for the entire
sample); 0.253 (front nozzle); 0.201 (rear nozzle), 0 223 (hrst 20-lot samples); and
0.252 (second 20-lot samples). These Sigma values dull~u~ dLu the torque uniformity
betvJeen the two nozles, and also the torque uniformity over time. In contrast,
FIGURE 7 shows the torque variation in a continuous system (such as that according to
U.S. Patent No. 4,100,882); the Sigma value is 0.511.
It will be Ul ,de, :,I,.od that the invention may be embodied in various specific
forms without departing from its spirit or central chdl d~lul i~tiu~. For example, the
powder feeding systems of the present invention may be used to form a patch on a self-
locking fastener, or to apply a masking or lubricating coating (of, e.g., Teflon) as taught
in U.S. Patent No. Re. 33,366. The present examples and ~",L,od;"~u"l~, therefore, are
to be considered in all respects as illustrative and not restrictivel and the invention
recited in the claims i5 not to be limited to the details gjven here.
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