Abstract:
A method for making a self locking internally threaded fastener and an apparatus for making such fasteners, in which the self locking characteristic is derived from a patch of thermoplastic material having a circumferential extent of less than 360° adhered selectively to at least a portion of the thread defining surface of the fastener.

Description:
This application is a continuation of application Ser. No. 08/810,243 filed on Mar. 3, 1997, now U.S. Pat. No. 6,063,437, which was a divisional of application Ser. No. 08/285,547 filed on Aug. 3, 1994; now U.S. Pat. No. 5,607,720. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to fasteners and is more specifically related to internally threaded fasteners having self locking patches of thermoplastic material adhered to at least a portion of the threads thereof. 
     Self-locking fasteners of the type in which the self-locking characteristic is derived from a coating such as a patch material adhered to all or a portion of the thread defining surface of the fasteners have proven to be very popular for a wide variety of applications, in order to prevent loosening of the fastener due to vibration and the like in various applications. The prior art discloses various methods and apparatus for applying locking patches of resilient resin or thermoplastic type material to threaded articles. Many of these teachings, however, have proven to be effective only for coating externally threaded fasteners with patches of resilient material and do not find application when it comes to applying such patches on internally threaded fasteners to make them self-locking. To attempt to utilize many of these continuous powder feed type systems with internally threaded fasteners would result in the unwanted coating of surfaces other than the threaded portion of such fasteners. 
     The problem of providing a coating that will act as a self-locking element to the threads of an internally threaded article such as a nut has presented many difficulties. Such an article may be a friction nut capable of producing a fluid tight seal or the like. A suitable coating for this purpose may be any of numerous resins, such as nylon or other thermoplastic resins. Prior art references that have addressed the problem of forming self locking patches on internally threaded fasteners, have frequently required heating of the fastener to at least about 450° F., prior to directing the thermoplastic material towards the threads to form the self-locking patch. 
     To insure proper adhesion of the thermoplastic material to the threads with these types of processes, it was also necessary to include an epoxy resin component in the material. Since the entire fastener was preheated to a temperature significantly above the melting point of the thermoplastic resin, great care was required to be used in order to insure that the thermoplastic resin came into contact only with the precise portion of the internal threads of the fastener that was desired to be covered and nowhere else. Otherwise, upon application the resin would tend to adhere to other surfaces of the fastener, causing cosmetic problems, overspray and also improper and inconsistent torque values for the finished self-locking product. 
     To overcome this problem, various, rather complicated devices were developed. Some devices interrupted the stream of thermoplastic material at regular intervals or indexed the flow of material to coincide with a succession of fasteners passing by the powder supply station. Other systems have utilized special nozzles that were at least partially inserted into the openings of the internally threaded fasteners on a reciprocating basis, to attempt to more precisely control the deposition of powder onto only the desired number of threads and about a desired circumference. Many of these prior art devices also required a large number of powder supply tubes or nozzles in order to provide a separate nozzle for each internally threaded fastener to be coated, such as taught in U.S. Pat. No. 4,366,190. This became particularly troublesome, considering that these systems traditionally required the powder to be entrained in an airstream in order to be directed towards the fasteners. 
     An additional drawback to such methods and apparatus was presented as a result of the use by these systems of a recirculating powder feed system. Whatever excess thermoplastic powder was directed towards the internal threads of the fastener that did not adhere thereto was frequently, entirely or partially melted as it passed by the highly heated fastener. This resulted in particles fusing together and being recirculated into a powder feed system and then potentially agglomerating even further with other particles. This caused an uneven powder flow of particles of different size, diameter and character to be directed towards subsequent heated fasteners. This resultant variation, combined with pulsing of the airstream entrained powder flow, due to agglomeration of the powder from moisture or the presence of other contaminants, lead to significant variations in torque values of the self locking fasteners and also a shortened useful life of the powder that was recirculated. 
     Certain disadvantages have also been experienced with other known methods and apparatus to form resilient thermoplastic patches on internally threaded fasteners that do not require the fasteners to be heated prior to application of the patch material. For example, U.S. Pat. No. 4,262,038 discloses a method of producing coated internal threads of a fastener that is only capable of producing a 360° coating and necessitates completely filling the internally threaded opening of the article throughout the complete 360° circumferential extent thereof between the ends, with the thermoplastic resin prior to heating the fastener. This method is slow since it requires the entire cavity of the internally threaded fastener to be filled with powder, even though the vast majority of the powder is not utilized in the coating. Also, this method does not provide for formation of a patch that would either be less than 360° in circumference, or cover fewer than all of the threads of the fastener. 
     Other prior art systems that do not heat internally threaded fasteners prior to the deposition of the resilient powder present other shortcomings. The system taught in U.S. Pat. No. 3,830,902, requires each fastener to be coated to be placed upon a pin which masks a greater portion of the thread defining surface and establishes a cavity which permits the deposit of plastic powder upon a limited portion of the threads, resulting in the establishment of a plastic patch of limited axial and circumferential extent. These pins require a certain amount of spacing between each successive pin in order to properly position and remove the nuts. It was found that the use of pins upon which fasteners are seated during establishment of plastic patches on the fasteners in such systems was problematic. The pins would wear allowing uncontrolled distribution of powder upon the thread defining surface, even to the extent that the desired clear lead-on thread had not been preserved. 
     In addition, the limited circumferential extent of a plastic patch produced by such systems provides only a concomitant limited area of adherence between the patch and the threads of the fastener. Thus, where the presence of foreign matter such as water or oil at the interface between the patch and thread defining surface tends to come between the patch and the area of the surface to which the patch adhered, total adherence is diminished sometimes to an unacceptable level. These systems also required use of a powder distribution means that had a continuous flow that had to be indexed with the fasteners travelling thereunder to provide for powder flow only when the threaded surface of the fastener passes below the powder distribution means. 
     While the prior art systems, referred to above, have proven to be at least somewhat successful in achieving the objects for which they were intended, it has become desirable to have an improved method and apparatus which offers equal or superior speed and quality over existing systems for applying resilient self locking patches to internally threaded fasteners that does not require preheating of the fasteners prior to application of self locking materials, indexing of the fasteners, indexing or interruption of the powder stream to the fasteners, multiple, intricate or reciprocating nozzles for powder deposition, an airstream to be combined with the powder delivery system or the use of powders that have a resin included therein. 
     While the present invention will be described particularly with respect to applying heat softenable thermoplastic particles to the threads of internally threaded articles, it is to be understood that apparatus and process of the present invention can be used to apply a variety of materials, including resins and resin compounds and pure nylon. 
     It is therefore an object of the present invention to provide an improved method and apparatus for the manufacture of self locking internally threaded elements wherein the self locking feature is obtained through a thermoplastic deposited onto a selected portion of the internal threaded surface of the element. 
     Another object of the present invention is to provide an improved method and apparatus for the manufacture of self locking internally threaded elements wherein improved control of the application of the locking body of thermoplastic and thermoplastic application is obtained over a desired arcuate and vertical area of the internal threads of the element and preheating of the fastener is not required. 
     Yet another object of the present invention is to provide an improved method and apparatus for the manufacture of self locking internally threaded elements wherein the powder flow through the output of the powder delivery system to the elements is continuous and uninterrupted. 
     Still another object of the present invention is to provide an improved method and apparatus for the manufacture of self locking internally threaded elements that achieves substantially equal results in terms of locking ability regardless of whether the powder used is a resin or has an epoxy constituent. 
     A further object of the present invention is to provide a method and apparatus for the manufacture of self locking fasteners that allows for greater reusability and more economical use of coating powder. 
     A still further object of the present invention is to provide a method and apparatus for the manufacture of internally threaded self locking fasteners that utilizes a continuously moving conveyor belt with the internally threaded fasteners delivered onto the belt such that one of the external faces of the nut is in substantially complete contact with the upper surface of the conveyor belt and a portion of one of the sides of the nut is also supported. 
     SUMMARY OF THE INVENTION 
     The above objects and other objects which will become apparent after a reading of the detailed description of this invention are achieved by a method for applying a locking element of thermpolastic type material to a succession of internally threaded articles having open ends to the threaded portion thereof that includes the steps of conveying the threaded articles on a support in a path for treatment with the axes of their threaded portions in a substantially horizontal position and with their openings at the threaded portions uncovered, directing a continuous uninterrupted stream of thermoplastic type material onto and around an area of each of the threaded portions in an amount in excess of the amount needed to form the locking elements, removing the amount of thermoplastic type material in excess of the amount required to form the locking element from around the area of each of the threaded portions and from the threaded portions of each of the articles, and thereafter heating the threaded portions of the threaded articles to a temperature above the softening point of the thermoplastic type material to be applied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an embodiment of an apparatus for the manufacture of self locking internally threaded fasteners in accordance with the present invention. 
     FIG. 2 is a fragmentary perspective view of a portion of the path that fasteners travel in accordance with one embodiment of the present invention. 
     FIG. 3 is a fragmentary top view of a portion of the path that fasteners travel in accordance with one embodiment of the present invention. 
     FIG. 4 is a partial cross sectional view of a single fastener as it passes through the powder applicator of the present invention. 
     FIG. 5 is a partial cross sectional view of a single fastener as it passes through a powder removing airstream of the present invention. 
     FIG. 6 is a partial cross sectional view of a single fastener as it passes through a powder removing suction device of the present invention. 
     FIG. 7 is a plan view of a threaded fastener shown in the form of a nut constructed in accordance with the teachings of the present invention. 
     FIG. 8 is a cross sectional view taken along the line  8 — 8  of FIG.  7 . 
     FIG. 9 is a cross sectional view taken along the line of  9 — 9  of FIG.  7 . 
     FIG. 10 is a diagrammatic view of the path of the recirculating powder feed system in accordance with an embodiment of the present invention. 
     FIG. 11 is a top view of the powder feeder and powder sensor of the present invention. 
     FIG. 12 is a partial cross sectional view of the powder feeder of the present invention taken along the line  11 — 11  of FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and in particular FIGS. 7-9, a typical internally threaded fastener is illustrated that has been processed in accordance with the apparatus and methods of the present invention. This fastener  12 , is illustrated as exemplary of only one of the many different types of internally threaded fasteners that could be processed in accordance with the present invention and has six external sides  15  and two opposing faces  17 . The fastener  12  also has internal threads  13  and a self-locking patch  14  of applied resilient material  38 . In accordance with the present invention, this patch  14  can be accurately positioned and deposited on a selected number of threads  13  of a fastener  12  along a selected arc and at a selected thickness more economically, quickly and accurately than existing methods and apparatus for forming such patches on internally threaded fasteners. It should be noted that, as illustrated in FIG. 8, patch  14  when adhered to a selected number of threads  13 , is thicker in the region of the thread valleys  29  than in the area of thread crests  21  and tends to loosely follow the contour of the threads  13 . 
     Referring now to FIG. 1, the apparatus  10  of the present invention is generally disclosed. The apparatus  10  includes a continuous conveyor belt  20  that is preferably constructed of a material that is capable of withstanding significant repeated exposure to heating, such as fiberglass. The belt  20  is wider than the width of one of the external sides  15  of the fasteners such as fastener  12  that can be processed in accordance with the present invention. The belt  20  is driven by a belt drive system that features conveyor systems  24  and  26  that continuously circle the belt  20  at an adjustable pre-selected speed preferably on the order of 10-20 feet per minute, in accordance with the self-locking processing to be completed by the apparatus  10 . 
     As illustrated in more detail in FIGS. 1-6, during all times that fasteners  12  are present on the belt  20 , at least a portion of one of the external sides  15  of each fastener  12  is in contact with the surface of the belt  20 . Also, during the entire time that fasteners  12  are in contact with the belt  20 , at least a portion of the outer face  17  of each of the fasteners  12  is in contact with the guide bar  64 . The guide bar  64  provides a slick heat resistant surface to support and orient the fasteners  12  that are to be processed. The guide bar  64  is preferably of a height equal to or greater than the height of fasteners  12  to be processed, measured from one outer face  15  to a 180° opposing outer face  15 . The guide bar  64 , as previously mentioned, must provide a non-stick heat resistant support surface for the fasteners  12 . Although a variety of materials are suitable for construction of the guide bar  64 , it has been found particularly preferable to utilize a fiberglass or fiberglass reinforced material with a Teflon coating to achieve superior results. 
     As particularly illustrated in FIGS. 3-6, guide bar  64  is spaced horizontally a distance from the conveyor belt  20 . The space  54  between the guide bar  64  and the conveyor belt  20  is at its minimum, as indicated at W 1  in FIG. 3, at a point where fasteners  12  are first introduced onto the conveyor belt  20 . The space  54  between the guide bar  64  and conveyor belt  20  then continuously increases to a maximum spacing or width as represented at W 2  in FIG. 3, which is in the region where fasteners  12  processed with self-locking patches  14  in accordance with the present invention are exited from the conveyor belt  20  for the purpose of collection. 
     Device  10  is also provided with a belt rail  86  which runs substantially the entire length of the conveyor belt from the region where resilient thermoplastic material  38  is applied to the fasteners  12  to the region where the fasteners  12  are exited off of the conveyor belt  20 . The belt rail  86  serves to shield the drive means of conveyor belt  20  from resilient thermoplastic material  38  and further serves to shield the belt  20  from the operator. 
     The improvements of the present invention are more readily appreciated by tracing the path of fasteners through the apparatus  10 . Fasteners  12  are required to be presented to the conveyor belt  20  in a uniform closely spaced manner. Any of a number of different known types of parts feeding mechanisms, such as vibratory parts feeder  16 , can be used to accomplish this purpose. The feeder  16  arranges and moves fasteners in a manner to deposit them continuously and uniformly onto the orienting track  18 . Fasteners  12  are first deposited onto the orienting track  18  in a closely spaced continuous fashion with one of the fastener surfaces  17  resting against the bottom  33  of the orienting track  18 . As the fasteners  12  move down the orienting track  18  towards the conveyor belt  20 , the fasteners  12  are rotated to a different orientation such that they are substantially resting on one of the fastener outer faces  15 . The fasteners  12  then pass under guide roller  22  and are thereby urged onto the conveyor belt  20  such that a portion of one of the outer faces  15  of each fastener  12  is in contact with the top surface  19  of the conveyor belt  20  and a portion of one of the surfaces  17  of each fastener  12  is in contact with the guide bar  64 . 
     When the fasteners  12  are first introduced onto the conveyor belt  20  and are moved into the region of the powder delivery chute  62 , they continue to be in a substantially upright orientation wherein all of one of the outer faces  15  of each fastener  12  is either in contact with or very close to the top surface  19  of the conveyor belt  20  and the fastener opening  25  is substantially parallel to the top surface of the conveyor belt  20 . This orientation can be readily seen with reference to FIGS. 3 and 4, wherein the angle a 1  is very small. The preferred range of values for the angle a 1  is between about 1° to 20°. 
     The increase in the size of the gap  54  as the fasteners  12  traverse the length of the belt  20  causes a slight rotation of the fasteners  12  due to an increase in the value of angle a 1  first to a 2  and then ultimately to a 3  as indicated in FIGS. 4-6. The preferred range of values for the angle a 3  is between about 10° and 30°. As best illustrated in FIGS. 2 and 4, as fasteners  12  move along the conveyor belt  20  and pass in front of the powder delivery chute  62  each fastener  12  encounters a continuous flow of powdered resilient thermoplastic material  38  that is deposited around, on and in a circumferential portion of the threads  13  of each fastener  12  in an amount greater than that required to form the desired patch  14  of resilient thermoplastic material  38 . 
     As previously mentioned and as will be discussed hereafter in much greater detail, the powdered resilient thermoplastic material  38  is deposited onto a portion of the threads  13  of each fastener  12  from the powder delivery chute  62 , without the necessity of the material  38  being combined with or entrained in an airstream. Rather, the powder material  38  is delivered down the powder delivery feeder pipe  60  from the powder feeder exit area  58  under the force of gravity alone. It is preferred that the exit end of the delivery chute  62  be positioned such that the delivery of powder material  38  onto the threads  13  of the fasteners  12  is angled. It has been found that powder delivery has been best when angles of the chute  62  and delivery of the powder material  38  are close to 45° to the outer face  15  of the fastener  12  that is in contact with the top of the conveyor belt  20 . The chute  62  is constructed so that its angle of delivery of powdered material in relation to the outer face  15  of the fastener  12  passing by it can be adjusted depending upon the processing that is desired. 
     As the fasteners continue their traverse down the conveyor belt  20 , they next encounter one or more airstreams designed to shape and position the powdered resilient thermoplastic material  38  in an amount and in a way to produce the desired resilient thermoplastic patch  14  on the threads  13  of the fasteners  12  and remove. These airstreams also serve to recirculate all excess powdered resilient thermoplastic material  38  that was initially deposited to allow it to be ultimately delivered to other fasteners  12 . 
     It should be understood that the embodiments illustrated of various airstream configurations to be used in positioning and shaping the material  38  and removing the excess material  38  are only exemplary and that more or fewer airstreams could be used and their orientations could be changed. The airstreams used could also be either all air blowing or all air vacuum streams or a combination thereof and still be within the scope of the present invention. Additionally, the present invention also contemplates locating one or more airstreams in front of or behind the belt  20 , on top of or below the belt  20  and/or at any angle to the belt  20 . Given this, the particular embodiment illustrated in FIGS. 1-6 will now be described in detail. 
     As illustrated in detail in FIGS. 2 and 5, an airstream issuing from a device such as a nozzle  68  is used for removing all powder from the lead thread as is required in many specifications for applying the patches  14  to fasteners  12 . In addition, when angled properly, the airstream issuing from the nozzle  68  can be quite effective in removing the powdered material  38  from unwanted areas such as the fastener surfaces  17  and the conveyor belt  20 . By acting in conjunction with a vacuum system stray material  38  and material  38  moved by the airstream is drawn into the vacuum nozzle  78  and then the powder return tube  84 . In this manner, the excess material  38  can then be recirculated for ultimate deposition onto additional fasteners  12 . 
     As illustrated in FIGS. 3 and 5, as a result of this slight rotation of the fastener  12  on the conveyor belt  20  to the angle a 2 , it becomes easier to direct an airstream, such as that supplied by nozzle  68 , to clear the lead thread of the fastener  12 . This rotation also assists in clearing the areas of the conveyor belt  20  that are not in contact with the fastener  12 . The clearing of the belt  20  is further accomplished by an additional airstream issuing from tube  79  in which thermoplastic material  38  dislodged by the airstream issuing from the tube  79  is collected for recirculation by vaccum nozzle  78  located on the opposite side of fastener  12  from tube  79 . Both nozzle  68  and tube  79  can be of any standard design and could be either rigid or flexible. Preferred constructions include ⅛″ copper tubing, nozzles having a single slotted opening, nozzles having a face perforated with a plurality of small openings and open ended flexible plastic tubes. Nozzle  68  and tube  79  are movably attached to apparatus  10  to allow for easy removal or adjustment depending upon the type of fasteners to be processed. 
     Once the fastener  12  has passed the airstream issuing from tube  79 , it then encounters another airstream, such as that supplied from air vacuum  70 . As the fasteners travel along conveyor belt  20  and encounter the air vacuum  70 , they are rotated further on the conveyor belt  20 , to the increased angle designated as a 3  in FIG.  6 . The rotation of the fastener  12  to the angle a 3  allows for a relatively easy removal of excess powdered material  38  from the conveyor belt  20  and fastener surfaces  17  and outer faces  15 . Alternatively this angle of rotation of fastener  12  also allows for removal and shaping of the material  38  in the area of threads  13  without disturbing the powder material  38 , at the desired location of the threads where the patch  14  is to be located. Air vacuum  70  is utilized to remove powder from a region parallel to the nozzle, as illustrated in FIG.  6 . The force of flow through air vacuum  70  is controlled by air vacuum control  52 . Although a variety of different air pressures can be used to create a vacuum, the most preferred ranges of air pressure have been found to be on the order of approximately two inches of mercury. 
     As illustrated, air vacuum  70  can be used in conjunction with another vacuum system that directs stray powder material  38  into vacuum nozzle  88  and recirculating tube  90 , for ultimate redeposition onto additional fasteners  12 . Likewise, the powder material  38  that is removed with by air vacuum  70  is recirculated for ultimate redeposition onto additional fasteners  12 . 
     Once the fasteners  12  leave the area of air vacuum  70 , they continue along the conveyor belt  20  and pass through a heater  72 . By the time of entry into the heater  72 , only the powdered material  38  that is necessary and desirable to form the desired patch  14  remains in the area of the threads  13  of each fastener  12 , and substantially all of the excess powdered material  38  that was initially deposited and, either on or around the fastener  12 , has been removed and recirculated. 
     As the fasteners  12  traverse along the conveyor belt  20 , through the heater  72 , the fasteners are raised to a temperature sufficient to cause the powdered material  38  to adhere to the threads  13  of the fasteners  12  and to be fused by heat from the threaded surface  13  to form a continuous plastic body thereon. In order to cause sufficient adherence of the material  38 , it is preferable to use the heater  72  to raise the temperature of the fasteners  12  above the melting point of the material  38 . A preferred way of accomplishing this is by use of a high frequency 200 kilohertz induction heater. Although this heater is most preferred, those of a 30 kilohertz frequency or higher are sufficient in most instances to produce a suitable amount of heat. Once the fasteners  12  exit the heater  72 , they begin to cool and are exited off of the conveyor belt  20  using any of a number of known parts removal systems, such as the one illustrated at  76 . 
     The present invention necessitates a lesser degree of heating than prior art processing systems that directed powdered thermoplastic material against fasteners that had been preheated to a temperature sufficient to cause the material to adhere to the threaded surface of the fasteners. This is because in the present invention all of the thermoplastic powdered material that will ultimately form the patch is already deposited and resting in the threaded area of the fastener prior to heating of the fastener. The heat applied thereafter need only be great enough to cause the thermoplastic powder to adhere to threads of the fastener and coalesce and fuse the material to form a continuous plastic body. 
     In contrast, prior art systems required increased heating of the fasteners to enable not only adherence and fusing of the material into a continuous plastic body, but also the initial catching and softening of individual particles from a stream of the particulate material that was directed toward the threads of the fasteners. Since the present invention does not have to catch particles from a stream directed toward the threaded surfaces of fasteners it also either substantially lessens or in some cases eliminates the need for a primer or tying agent such as a thermosetting epoxy resin powder to be combined with the thermoplastic particles of the locking element. This results in a significant potential cost savings without sacrificing adherence and torque values of the finished patch. 
     The unique powder feed system of the present invention will now be described in more detail. Referring to FIGS. 1,  2 ,  10  and  11 , powdered material  38  is contained in the powder supply bin  42  and is exited from the powder block  36  by auger  40  that urges powder material  38  out through an opening in the block  36 . The auger  40  is rotated in response to the optical sensor assembly  30 , which is connected to the powder block  36  and is positioned partly within the vibratory powder feeder  28 . 
     The optical sensor arm  34  holds and connects the optical sensor  32 , which extends into the vibratory powder feeder  28 . The optical sensor  32  is directed toward the bottom  56  of the powder feeder  28 . If the optical sensor  32  senses that an insufficient amount of powdered material  38  is present in the bottom  56  of the feeder  28 , then it causes the auger  40  to move in the powder block  36  and force more powdered material  38  to drop into the bottom  56  of the feeder  28 . The sensor  32  provides very precise control over the amount of powdered material  38  in the bottom  56  of the feeder  28  in order to keep the level virtually constant. Although many different photoelectric sensors can be used, a particularly preferred sensor, for the purposes of this invention, was found to be an OMRON photoelectric switch (Model E3A2-XCM4T). 
     The vibratory powder feeder  28  is of a stepped construction, in the nature of an inside track cascading vibratory bowl. The feeder  28  is vibrated and controlled by a variable speed DC motor such as an FMC Centron controller. As illustrated in FIGS. 11 and 12, the vibratory action of the motor upon the feeder  28  causes powder material  38  deposited initially at the bottom  56  of the feeder  28  to move upwardly along the entire length of a track  47  having a bottom  46  and an inner wall  48 . The track  47  begins at the bottom  46  and extends in a spiralling manner to the top of the feeder  28  into the powder feeder exit area  58 . As best illustrated in FIG. 12, the track  47  is angled slightly toward the inner wall  48  so as to keep the powder material  38  on the track  47  moving toward the powder feeder exit area  58 . 
     The flow of powder material  38  from the feeder  28  can be regulated by varying the rate of vibration of the feeder  28  alone or in combination with an optional flow rate control device. An example of such a device consits of a deflector  97  adjustably attached to a boss  93  in the exit area  58  of the feeder  28  by a screw  99 . Both the height and the angle of deflector  97  in relation to the track  47  are adjustable. Deflector  97  serves to limit the flow of material  38  vibrated along the track  47  to the exit area  58 . Deflector  97  accomplishes this by directing substantially all of the material that extends above the bottom of the deflector  97  onto the slide  95 . Slide  95  is secured to the inside of the feeder. The slide  95  then guides material  38  deposited thereon to the bottom  56  of the feeder  28  in order to again be vibrated along the track  47  to the exit area  58 . The remaining material  38  that passes by the deflector  97  then drops down the powder feeder delivery tube  60  and down the powder delivery chute  62  under the force of gravity alone, to be deposited onto fasteners  12  as previously described in detail. 
     The powder feeder delivery tube  60  can be a standard pipe that allows a narrow path of delivery to the powder chute  62  and is wide enough so as to be connected to and accept and direct all of the powder material  38  leaving the powder exit area  58 , down the tube  60  without impediment. A ⅛″ thick copper tube has seen found particularly useful for this purpose. The adjustable powder chute  62  is connected to the end of the tube  60  furthest away from the powder exit area and can be made of any rigid material and preferably has a smooth surface or has been treated with a non stick material in order to allow free fall of the powder material  38  onto fasteners  12 . The width of the chute  62  may vary with the most preferable chutes being on the order of one to three inches wide. 
     This unique powder feed system affords several advantages to the present invention. It has been found that, for example, if the powdered material that is used is Nylon 11, that the vibratory action of the feeder  28  that the material  38  encounters along the entire spiralling track  47  from the bottom  56  to the top of the feeder  28  tends to substantially keep the material  38  from agglomerating. In addition, this action also tends to separate substantially all of the particles that may have joined together as a result of the presence of foreign materials on the surface of the particles or other reasons by the time the material  38  exits the feeder  28 . 
     As a result, the powder exited from the feeder  28  through the chute  62  onto the fasteners does not require a combination with an airstream, as do most prior art systems of this type. In addition, a particularly uniform flow of powder is maintained, virtually eliminating the pulsing action found in many prior art recirculating powder systems that require an airstream to be combined with the powdered material. A more uniform and consistent application of powdered material  38  to the fasteners  12  is thereby accomplished leading to more economical efficient patch application and powder utilization. 
     Powder flows in accordance with the present invention are in the range of 80-400 grams/minute with the most preferred range being around 350 grams/minute. The powder feed system of the present invention affords yet another advantage over the prior art systems. The powder application and the ability to locate material  38  on the threads  13  of fasteners  12  prior to heating has been found to be so consistent so as to allow a cost savings through elimination of some or all of the epoxy minor constituent used in most nylon powder coating systems without a substantial reduction in terms of adherence and torque values of the patch  14  formed on fasteners  12 . Additionally, it should be understood that the thermoplastic material  38  used in conjunction with the present invention could be any type of thermoplastic including nylon, nylon epoxy resins and Teflon compounds. 
     As illustrated in FIG. 10, the powder feeder  28  and powder supply bin  42  form two important parts of the recirculating powder system  96  of the present invention. As previously described, the powdered material  38  is applied to fasteners  12  through chute  62  in an amount in excess of that required to form the desired patch  14 . At each point along the conveyor belt  20 , where excess powder material  38  is removed, such as through nozzle  78  and tube  82 , nozzle  80  and tube  84  and tube  73 , the powdered material  38  is directed into the powder recirculation conduit  92 . The powdered material  38  is then directed from the conduit  92  into a recirculating powder supply  44  where it is combined with powder material  38  that has not previously been recirculated and is supplied through a recirculating powder connector  94  to the powder supply bin  42  for ultimate deposit into the bottom  56  of the feeder  28 . This recirculating powder system  96  allows for efficient and economical usage of powder. 
     In addition, since in accordance with the present invention, all material  38  is applied and excess material is removed prior to any application of heat to the fasteners  12 , none of the material  38  that is recirculated or ultimately applied is ever in a previously melted state or fused by heat to other powder particles prior to formation of the patch  14 . Likewise, when heated plated fasteners commonly exude smoke that contains moisture and oil. Since the vacuum nozzles of the recirculating powder system of the present invention remove powder from unheated fasteners, the nozzle and powder system do not ingest any moisture and oil filled smoke into the powder system. This leads to an improvement in both resuability and the consistency in quality of the powder flow of the present invention to the fasteners  12 . Although the recirculating powder system described above is particularly preferred it should be understood that other recirculating systems such as using the conduit  92  to direct material into a separate bin that is then manually deposited into the powder supply bin  42  at regular intervals could also be used. 
     The following examples are given to aid in understanding the invention and it is to be understood that the invention is not limited to the particular procedures or other details given in the examples. 
     EXAMPLE 1 
     Zinc plated flange nuts, ⅜″—16 were deposited with at least a portion of one of the faces of the nut resting on the conveyor belt as shown in FIG. 3 with the bottom of the threaded surface being substantially parallel to the belt. The belt speed was 13.25 feet/minute resulting in the nuts being fed at approximately 160 pieces/minutes. The nuts were introduced onto the belt at an initial angle between 10° to 12° from vertical with the spacing between the belt and the guide bar being 0.210 inches. The powder supply was adjusted to 100 grams/minute of a mixture of approximately 90% nylon powder and 10% of thermosetting epoxy resin having the following particle size distribution: 
     10% less than 78 microns 
     50% less than 165 microns 
     90% less than 287 microns 
     mean=174 microns 
     The powder used was nylon 11 sold under the tradename of Duralon JM by Thermoclad, Inc. As the nuts moved along the belt the spacing between the belt and guide bar increased to 0.260 inches and the angle of the nut to the belt was approximately 15° to 20° from vertical. The powder was delivered to the nuts from the powder chute at approximately a 45° angle. As the nuts continued down the conveyor belt, they encountered eight nozzles, four of which were vacuum nozzles utilizing two inches of mercury and four of which were blow-off or affirmative air flow nozzles utilizing approximately 40 psi of air pressure. The location of the nozzles was as set forth below in order of their upstream to downstream location, along with an indication of whether they were in front of or behind the fastener traveling down the conveyor: 
     1. lower belt vacuum slotted nozzle (front underneath) 
     2. upper belt blow-off—nozzle with rows of 132 inch holes (front) 
     3. parts blow-off—⅛″ copper tube (front). 
     4. upper belt blow-off underside of belt—⅛″ copper tube (front) 
     5. last thread vacuum—⅛″ copper tube (front) 
     6. nut face vacuum—⅛″ copper tube (front) 
     7. lead thread vacuum—⅛″ copper tube (rear) 
     8. lower belt blow-off—⅛″ copper tube (front) 
     Once the excess nylon material was removed and remaining material was shaped, the nuts were passed through a 15 kilowatt induction heater set at 200 kilohertz (88% setting) and the nuts were raised to a temperature of approximately 620° F. it was observed that the nylon material was fully softened and melted resulting in adherence and coalescing of a plastic body in the form of a patch on the bottom of the threaded hole with approximately 60° to 75° of circumferential coverage of three threads. After cooling the applied coating was found to be uniform and to follow the contours of the threads effectively. Torque tests then were carried out with ⅜″—16 bolts. The “First on”, “First off”and “Fifth removal” torque values expressed in inch pounds are set forth below: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 First on 
                 First off 
                 Fifth removal 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1. 
                 79 
                 58 
                 19 
               
               
                   
                 2. 
                 95 
                 62 
                 22 
               
               
                   
                 3. 
                 94 
                 64 
                 29 
               
               
                   
                 4. 
                 98 
                 79 
                 30 
               
               
                   
                 5. 
                 94 
                 81 
                 21 
               
               
                   
                   
               
             
          
         
       
     
     EXAMPLE II 
     A second group of zinc plated flange nuts ⅜″—16 were deposited with at least a portion of one of the faces of the nut resting on the conveyor belt as shown in FIG. 3 with the bottom of the threaded surface being substantially parallel to the belt. All of the parameters set forth in Example I were identically reproduced except that the powder coating material used was a substantially pure nylon powder that contained a small amount of titanium dioxide pigment. The powder mixture contained no epoxy resin. The powder had the following properties: 
     POWDER PROPERTIES 
     at least 99% less than 90 microns 
     100% less than 250 microns 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 COATING PROPERTIES 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Specific gravity 
                 1.04 
               
               
                   
                 Melting point, DSC Peak 
                 186-188° C., 
               
               
                   
                 Abrasion Resistance, 
                 5-8 Mg. 
               
               
                   
                 Tabor 1000 Cycles, 
               
               
                   
                 1 Kg. load, 
               
               
                   
                 CS17 wheels 
               
               
                   
                 Impact resistance, Gardner 
                 No failures 
               
               
                   
                 160 in.-lbs 
               
               
                   
                 Salt spray, ASTM B117 
                 &gt;1000 hours 
               
               
                   
                   
               
             
          
         
       
     
     The powder used was French Natural ES Nylon 11 coating powder sold by Elf Atochem North America, Inc. Similar results in terms of appearance, melting, adherence and coalescing of a plastic body in the form of a patch on the bottom of the threaded hole of approximately 60-75° of circumferential coverage of three threads in comparison to Example I were observed. Similarly, after cooling, the applied coating was found to be uniform and to follow the contour of the threads effectively. Torque tests were then carried out with ⅜″—16 bolts. The resulting “First on”, “First off” and “Fifth removal” torque values expressed in inch pounds are set forth below: 
     
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 First on 
                 First off 
                 Fifth removal 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1. 
                 76 
                 57 
                 25 
               
               
                   
                 2. 
                 92 
                 70 
                 20 
               
               
                   
                 3. 
                 78 
                 52 
                 21 
               
               
                   
                 4. 
                 84 
                 66 
                 25 
               
               
                   
                 5. 
                 71 
                 64 
                 22 
               
               
                   
                   
               
             
          
         
       
     
     The resulting torque test values on nuts that utilized the substantially pure nylon coating powder compared quite favorably to the torque tests values on nuts from Example I that utilized the nylon powder that contained a 10% epoxy resin constituent. 
     From these examples, the use of different types of coating powders in connection with the powder feed system, conveyor, heating and air nozzle configurations of the present invention was demonstrated to produce very effective results.