Abstract:
An apparatus and method for use with powdered resin feeders provides a continuous stream of powder to a plurality of threaded or non-threaded fasteners. In one preferred embodiment, the apparatus generates a gravity induced powder stream at the free end of a discharge conduit which is intersected by a series of fasteners carried on a conveyor. A vacuum nozzle is positioned adjacent to the powder stream and the conveyor. Both the vacuum nozzle and the free end of the discharge conduit are adjustably positionable relative to the path of the fasteners carried on the conveyor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to specially processed fasteners, and, more particularly, to apparatus and methods for the manufacture of fasteners having a resin material applied to achieve a self-locking or sealing function or for other purposes well known in the art. 
     There are a variety of ways to apply a resin coating to a fastener. Many devices and methods have been developed and directed toward this purpose. One common technique involves the deposition of powdered resin by passing the fastener through a gravity induced cascade of the resin as shown in prior art patents such as U.S. Pat. No. 3,830,902 (Barnes) and U.S. Pat. No. 3,286,964 (Burgess). Another technique employs entrainment of the powdered resin in an air stream and spraying the resulting air entrained powder through a nozzle toward a passing fastener as shown in U.S. Pat. No. 3,498,352 (Duffy). To prevent waste of the powdered resin that bypasses the fastener during the referenced processes, others have proposed the use of vacuum devices that collect and recirculate the excess powder such as U.S. Pat. No. 5,836,721 (Wallace). 
     Among the known disadvantages of the gravity feed process is the lack of precision in the deposition of the powdered resin. An excessive powder flow rate is commonly induced to insure that at least the minimum required quantity of powder is applied to the fastener, resulting in an undesirable level of waste or excessive recirculation of the resin which can diminish the quality of the resin materials. Entrained air spraying processes reduce waste and improve precision, but with a concomitant increase in cost. Use of the spraying process requires a higher energy demand to generate the pressurized air stream and to preheat the fasteners in advance of the powder application. Moreover, the compressed air typically used in such processes is preferably cleaned to remove moisture and oil to minimize powder contamination. The preheated fastener required by the spraying process creates a condition where the powder coating is instantly bonded to the fastener, thereby preventing removal of the resin inadvertentaly deposited onto areas of the fastener where the coating is not required or desired. 
     It would be advantageous, therefore, to have a powder application system for applying coatings on fasteners having the cost benefit of the gravity feed process while retaining a measure of the precision of the air spray process. It would further be advantageous to retain the ability to clean excess powder from the fastener prior to heat bonding. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an apparatus and a method for applying a powdered resin coating to a fastener that incorporates a combination of adjustably positionable gravity deposition and vacuum recirculation components so as to overcome the limitations of the prior art. 
     The present invention is, therefore, an apparatus and a method for applying a resin coating to a fastener. A reservoir for the powdered resin materials is provided with a discharge means that has an adjustably positionable free end. The discharge means or conduit forms a gravity induced cascade for feeding the resin material onto the fastener. Variation in the dimensions of the discharge conduit allows for a variety of configurations for the cascading powder stream leaving the free end. Fasteners are passed through the powder stream by conveyor means. Adjacent to the powder stream and the conveyor carried fasteners, an adjustably positionable vacuum nozzle is provided to collect excess resin. The ability to adjust the spatial and positional relationship of the discharge conduit and the vacuum nozzle allows more precise control over the location and amount of powdered resin material that is deposited on the fastener. Following the powder deposition and collection steps, the fasteners are passed through a heating means to permanently fuse the resin material to the fastener. 
     In a preferred embodiment, the conveyor means is a rotating carousel with a means for rotating individual fasteners as they pass through the powder stream. One potential means for rotating the fasteners involves the application of vertical posts to the rotating carousel. The posts can be adjustably spaced to accommodate a variety of fastener sizes. A fastener is placed in a fixed position at the top of each post, and the rotation is accomplished by means that make the posts themselves rotate. 
     Another preferred feature of the invention is the inclusion of a means for vibrating the reservoir to assist in control of the feed rate of the resin material into the discharge conduit. The discharge conduit may also include an adjustable input baffle at the head of the discharge conduit to provide for further control of the feed rate. Additionally, a means for adjusting the negative pressure on the vacuum nozzle provides still further control over the removal of excess deposited resin material on the fasteners. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features which are characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and attendant advantages thereof, will be best understood by reference to the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a preferred apparatus for practicing the present invention; 
     FIG. 2 is a partial plan view of the apparatus shown in FIG. 1 taken at line  2 — 2  of FIG. 1, showing the relationship between the discharge conduit and the vacuum nozzle with respect to fasteners positioned on an associated rotating carousel conveyor; 
     FIG. 3 is a partial side elevation of the apparatus shown in FIG. 1 indicating the adjustable relationship between the free end of the discharge conduit and the free end of the vacuum nozzle with respect to the fastener; and 
     FIG. 4 is a cross section view taken at section line  4 — 4  of FIG. 1, showing the adjustable port between the reservoir and the discharge conduit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a perspective drawing that depicts the general features of the invention. Powder hopper  10  supplies powdered resin material to reservoir  12 . When the apparatus is in operation, the resin material flows by vibrational actuation and gravity from the reservoir  12  through the port  18  and into the discharge conduit  14 . The discharge conduit  14  terminates at a free end  16 . When the resin material passes over the free end  16 , a free falling cascade or stream of the powdered resin is created that has a lateral length equivalent to the width of the discharge conduit  14 . It is acknowledged, therefore, that the feed rate of the resin material and the contact time between the fastener  20  and the resin material are both, in part, a function of the width of the discharge conduit  14 . 
     In one embodiment, illustrated in FIG.  1  and FIG. 2, fasteners  20  are passed along the length of the cascade by a conveyor means such as horizontally rotating carousel  32 . The fasteners  20  are held in place on carousel  32  by magnetic vertical posts  30 . Alternatively, a vacuum system may be disposed within the posts to hold non-magnetic parts in proper position throughout the process. The spacing of vertical posts  30  may be adjustable to accommodate a variety of fastener shapes and sizes. When a carousel  32  is used as the conveyor means, the cascade of the coating material is positioned tangential to the arc of the conveyor path as shown in FIG.  2 . As each fastener  20  passes through the cascade falling from free end  16 , resin material is deposited. The sequence of the contemplated coating method requires that the fasteners  20  pass between the discharge end portion  16  and the coincident vacuum nozzle  22  prior to entering a heating station  40 . Arrows A at each fastener  20  depict rotational movement which is desirable when a circumferential coating is required. In a preferred embodiment, the fastener  20  is rotated provided by rotating vertical post  30 . A variety of apparatus are well known to those skilled in the art to achieve rotation of individual parts  30 . Examples of such mechanisms are illustrated in U.S. Pat. No. 4,775,555 and U.S. patent application Ser. No. 08/779,684 filed Jan. 7, 1997, the disclosures of which are incorporated herein by reference. 
     A vacuum nozzle  22  is positioned adjacent to free end  16  such that, when the conveyor means moves fastener  20  into communication with the resin material stream, fastener  20  is positioned between the free end  16  of the discharge conduit  14  and the vacuum nozzle  22 . FIG. 3 shows the positional relationship between the free end  16 , the fastener  20  and the vacuum nozzle  22 . An important feature of the invention is that both the discharge conduit free end  16  and the vacuum nozzle  22  are adjustably positionable with respect to the fastener  20 . FIG. 3 shows the positional adjustment of the free end  16  and the nozzle  22  in both horizontal and vertical planes. Such adjustment can be achieved using manually adjustable mechanisms or motor driven assemblies well known to those of skill in the art. Typically, vertical and/or horizontal displacements ranging from a few thousandths of an inch up to about one to two inches will be sufficient to accommodate a full range of resin coating applications. The ability to control both horizontal and vertical positioning during coating application allows more precise location of the resin material on a specific portion of a fastener  20  and to more precisely control the thickness of the coating to be applied. The vacuum nozzle may also communicate with a variable speed fan  24  by means of a vacuum conduit  26 . Adjusting the speed of the fan  24  may be used in conjunction with adjustment of the nozzle  22  position to control the amount of resin material deposited and retained on a fastener  20 . 
     The resin material collected by the vacuum nozzle  22  is transported back to the reservoir  12  by means of a recirculation system. Fan  24  draws excess coating material from the nozzle  22  into the vacuum conduit  26  and through conduit  28  into the supply hopper  10 . Hopper  10  has a conical bottom with an open access to the reservoir  12 . A vent  34  at the top of tank  10  exhausts the air flow to atmosphere. 
     After fasteners  20  pass through the cascade of coating material between the free end  16  of the discharge conduit  14  and the vacuum nozzle  22 , they are transported via carousel  32  through a heating station such as induction coil  40  to permanently bond the coating to the fastener. Other conveyors well known in the art, as disclosed for example in U.S. Pat. Nos. 3,787,222; 4,060,868; and 4,842,890, may also be used. The disclosure of this patent is also incorporated herein by reference. 
     In one embodiment of the invention illustrated in FIG. 4, the interface between the reservoir  12  and the upstream end of the discharge conduit  14  is comprised of an adjustable input port  18 . The baffle plate  50  defines input port  18  and is sized to overlie the reservoir opening. Plate  50  is held in place laterally by slotted channels formed in the side walls of discharge conduit  14 . Plate  50  is vertically adjustable and may be maintained in position by retaining bolt  54  disposed within adjustment slot  52 . 
     An additional measure of flow rate control can be achieved by adjustment of a variable vibrating means. The vibration system, designated generally as  34 , benefits the operation of the resin feed mechanism not only by providing improved discharge rate control, but also by breaking up agglomerations of the resin materials. The vibration system  34  includes a control device  36  operable to regulate the amplitude and frequency of the vibration. The ability to adjust the speed of vibration allows more precise control of the resin material discharge rate from reservoir  12 . 
     The apparatus and method of the present invention are ideally suited for the application, as depicted, of powdered resin material at the junction of a fastener&#39;s head and shank. Typically, such powdered resins may comprise polyolefins which, after curing, form a resilient and pliable, integral seal, as more fully disclosed in U.S. Pat. No. 5,141,375, which is incorporated herein by reference. When applying such powdered polyolefin resins in the practice of the present invention, it has been found that the free end  16  of discharge conduit  14  should be positioned about ½ inch above and about ⅛ inch horizontally from the juncture of the shank and head of the fastener. The vacuum nozzle, on the other hand is preferably about ⅜ inches below and about {fraction (3/16)} inches horizontally from that same fastener juncture. Also, the following process parameters have been found suitable for this process: 
     powder discharge conduit width—2 inches 
     fastener rotation within discharge stream—about 3 revolutions 
     powder discharge flow rate—about 2 oz./min. 
     linear speed of fasteners through powder stream—about 1 in./sec. 
     temperature of fastener exiting heating station—about 500° F. 
     vacuum air flow at vacuum nozzle—about 1500 FPM 
     vacuum air flow at fastener—about 950 FPM 
     Increasing the vacuum generated at nozzle  22  or positioning nozzle  22  closer to the fastener (either vertically or horizontally) will result in deposition of less powdered resin on the fastener. 
     Of course, it should be understood that various changes and modifications to the preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the following claims: