Abstract:
A system and method providing improved capability for inspecting and repairing threads of bolts and threaded holes is disclosed. Polishing stones comprised of epoxy and metallic oxide are used in conjunction with dye to identify threads in need of repair and make them visible to a maintenance worker.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit to U.S. Provisional Patent Application No. 61/278,959, filed Oct. 14, 2009. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to maintenance and repair of threaded bolts and threaded holes. More particularly, the present invention relates to a method and apparatus for inspecting and repairing large-sized bolts and threaded holes. 
     BACKGROUND 
     U.S. Pat. No. 5,932,789, to Stein is incorporated herein by reference, and is hereinafter referred to as the &#39;789 patent. The &#39;789 patent discloses a bolt thread inspection and thread polishing device. The &#39;789 patent provides a variety of advantages, such as the ability to quickly identify damaged areas of bolts, and also provides a method of repairing the identified damage. However, there is an ongoing need to improve maintenance of bolts and threaded receptacles in large-size, critical situations, such as large power generators, boilers, and ship propulsion systems, to name a few. 
     SUMMARY OF THE INVENTION 
     While the device disclosed in U.S. Pat. No. 5,932,789 provided an efficient way to detect damage to large bolts, there were various shortcomings of that device. In particular, the &#39;789 device did not provide inspection or repair capabilities for threaded holes. Another drawback of the &#39;789 device is that in certain conditions, the use of the device may adversely affect the threads. These issues are addressed in embodiments of the present invention. These advantages, and others, are disclosed in the detail description that follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows thread details of a prior art concave polishing stone. 
         FIG. 2  shows thread details of a concave polishing stone in accordance with an embodiment of the present invention. 
         FIG. 2B  shows a perspective view of a concave polishing stone. 
         FIG. 2C  shows a perspective view of a convex polishing stone. 
         FIGS. 3A and 3B  show a convex polishing stone. 
         FIG. 4  shows an improved polishing stone holder. 
         FIG. 5  shows a flowchart indicating process steps to inspect and repair threads. 
         FIG. 6  shows the method step of pre-cleaning. 
         FIG. 7  shows an indication of thread damage. 
         FIGS. 8A and 8B  show instances of repairing threads. 
         FIG. 8C  shows a side view of a chisel. 
         FIG. 9  shows a polishing stone holder as used with convex polishing stones. 
         FIGS. 10A-10C  show alternative embodiments of the present invention. 
         FIG. 11A  and  FIG. 11B  show use of the embodiment of  FIG. 10B . 
         FIGS. 12-14  show additional alternative embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention provide improved capability for inspecting and repairing threads of bolts and threaded holes. More particularly, embodiments of the present invention are well suited for large bolts, typically found in heavy industry such as power plants, large ships, and the like. The threads on these bolts may be damaged during the course of periodic maintenance. In some cases, these bolts have a diameter of over 4 inches, and may cost over $10,000 per bolt, and therefore, repair is often preferable to replacement. In addition to bolt threads, repair and inspection is also needed for threaded holes, such as nuts or tapped bolt holes in machinery. 
       FIG. 1  shows thread details of a prior art concave polishing stone  102 , similar to that shown in FIG. 2B of the &#39;789 patent. Polishing stone  102  has a plurality of threads  104 A- 104 D that engage corresponding threads  108 A- 108 D of bolt  106 . Each thread has a peak (shown generally as  110 ). As the polishing stone  102  is moved over the threads of the bolt  106 , small metal fragments  114  from the bolt may form in the void (generally referred to as  112 ) between the thread peaks  110  and the polishing stone  102 . These metal fragments can wear the bolt threads, causing damage to threads of bolt  106 . Polishing stone  102  has a spacing factor of 1, meaning that there is a polishing stone thread for every bolt thread. In one embodiment, the polishing stone  102  is formed from a mixture of epoxy and aluminum oxide. In one embodiment, polishing stone  102  has a shape of a 120 degree arc, with internal threads to line up with the threads on a bolt of similar diameter to the inner surface of polishing stone  102 . 
       FIG. 2  shows thread details of a polishing stone  202  in accordance with an embodiment of the present invention. Polishing stone  202  has a plurality of threads  204 A,  204 C, and  204 E that engage threads of bolt  106 . Polishing stone  202  has threads spaced at wider intervals than the prior art polishing stone  102 . In  FIG. 2 , a polishing stone with a spacing factor of 2 is shown, meaning that there is a polishing stone thread for every two bolt threads. For example, thread  108 A and  108 B are bounded by thread  204 A and  204 C of polishing stone  202 . By using a spacing factor of 2 or more, a large void  212  is formed between the threads of the bolt  106 , and the polishing stone  202 . Large void  212  provides an escape path for metal fragments, so that they do not wear the peaks (see  110  of  FIG. 1 ) of the threads of bolt  106 . Note that while a spacing factor of 2 is illustrated in  FIG. 2 , larger spacing factors are contemplated, and within the scope of the present invention. 
       FIG. 2B  shows a perspective view of a concave polishing stone  202 , and  FIG. 2C  shows a perspective view of a convex polishing stone  302 . In general, polishing stones  202  and  302  are arc-shaped, having threads on at least one side, either the inner side  209  or the outer side  309 . In one embodiment, both sides  209  and  309  of the polishing stone may be threaded, providing a polishing stone capable of polishing both a bolt and a threaded hole, such as a nut. 
       FIGS. 3A and 3B  show perspective views of a convex polishing stone  302 . Convex polishing stone  302  is intended for threads inside a nut or stud hole.  FIG. 3A  shows a front perspective view of convex polishing stone  302 , having threads (shown generally as  304 ). The convex polishing stone  302  has a spacing factor of 2 or greater. 
       FIG. 4  shows an improved polishing stone holder  400 . U-shaped metal frame  405  has polishing stones  202  attached at the distal ends of each frame leg  407 . Wing nut  402  engages threaded bolt  403  to provide for adjusting the pressure that polishing stones  202  exert on bolt  106 . Strap  404  is used to provide additional security by being wrapped around the polishing stones  202  snug against bolt  106 . Strap  404  is intended to wrap around the outside of frame legs  407  to keep the polishing stones  202  centered. In one embodiment, strap  404  comprises a fastener such as a hook-and-loop fastener or snaps to secure the strap  404  around the polishing stones  202 . One end of the strap  404  may be permanently secured to a frame leg  407  via adhesive or another fastening means, such as a grommet. Drive nut  408  engages a ratchet (not shown) or drill (not shown) to turn the stone holder  400 . If a drill is used, a slow speed setting is preferable, to avoid damage to the bolt  106 . 
       FIG. 5  shows a flowchart  500  indicating process steps to inspect and repair threads. In process step  502 , the workpiece (“workpiece” refers to a bolt or threaded hole) is pre-cleaned prior to inspecting the threads. In one embodiment, the step of pre-cleaning is performed via absorbent pads soaked with rubbing alcohol. This step cleans the threads, and removes any major deposits of grime and grit that may be present on the workpiece. In process step  504 , the threads are given a first test. For a bolt, this comprises slowly putting a corresponding nut on the bolt and feeling for any areas where the nut does not turn freely, which may be indicative of an issue with the threads. If the workpiece is a threaded hole, then a bolt is used to test the threads. Next, a layout die is applied to the workpiece in step  506 . In step  508 , the polishing stones are lubricated with rubbing alcohol to facilitate smooth motion when the polishing stones are applied to the workpiece. In process step  510 , the polishing stones are applied to the workpiece. This step may be performed by hand initially, and then subsequently, performed via a stone holder such as  400  of  FIG. 4 . The stone holder allows the polishing stones to be applied to the workpiece via a ratchet or drill. When a drill is used, it is preferable to use a slow speed to avoid damage to the workpiece. In step  512  the workpiece is checked for damage. Any areas with notable thread damage are indicated by an absence of layout die. In the case of a threaded hole, an inspection mirror may be used to view the threads if direct viewing is not feasible. In step  514 , damaged areas are repaired by chiseling at an approximate 90 degree angle to the X axis of the bolt (see  FIG. 8A  and corresponding description). In step  516 , the threads are tested again, similar to step  504 , to confirm that the thread damage has been fixed. At this point, a nut should move smoothly when engaged with a repaired bolt. If there are still some places where the nut does not turn freely around the repaired bolt, process steps  506 - 514  may be repeated until the workpiece is repaired, and the nut turns smoothly on the bolt. 
       FIG. 6  shows the method step of pre-cleaning. Absorbent pads  618  are soaked in a fast-evaporating solvent, such as rubbing alcohol, and then inserted in front of polishing stones  202 . Strap  404  is then wrapped around workpiece  106 , and the polishing stone holder is rotated around the workpiece (bolt)  106  to clean it in preparation for inspection and repair. 
       FIG. 7  shows an indication of thread damage on bolt  106 . A damaged thread is indicated generally by reference  721 . Since the thread  721  was out of alignment, the polishing stone removed the dye from that area, making the defect immediately visible to a maintenance worker. 
       FIG. 8A  shows an instance of repairing threads in a bolt  106 . Chisel point  822  is oriented at angle C with respect to axis X of the bolt  106 . Angle C is preferably about 90 degrees, so that the chisel point is aligned with an imaginary Y axis that is perpendicular to the X axis of the bolt. The chisel is then struck with a mallet (not shown) to move the threads back to their proper position, without excess metal loss that occurs with sanding, or with taps and dies. 
       FIG. 8B  shows an instance of repairing bolt threads with limited working space. In this case, bolt  806 A is undergoing repair. However, since bolt  806 A is in close proximity to bolt  806 B, using a conventional chisel is not feasible. Therefore, a special bar chisel  852  has been designed for this purpose. Chisel  852  has a blade that is applied to bolt  806 A and then struck with mallet  864  to make the repairs. In this way, bolt threads can be repaired, even in tight spaces. 
       FIG. 8C  shows a side view of chisel  852 . Chisel  852  is comprised of bar  877 , and chisel point  879 . During use to repair a bolt thread, chisel point  879  is applied to a bolt, and then a mallet is used to strike bar  877  on the opposite side, (e.g. at point  881 ) to repair the bolt threads. 
       FIG. 9  shows a polishing stone holder  900  as used with convex polishing stones  302 . Polishing stone holder  900  is similar to polishing stone holder  400  of  FIG. 4 , with the exception of the polishing stones  302  which are fastened to the outer surface of U-shaped metal frame  405 , so they can contact the inner diameter of a threaded hole (indicated as  909 ). The polishing stone holder is then turned back and forth along path D, so that the polishing stones  302  engage the threads of a threaded hole such as a nut or bolt hole within a piece of machinery. 
       FIG. 10A  shows an alternate embodiment of the present invention, a flexible polishing stone holder  1000 . Flexible polishing stone holder  1000  comprises a strap  1001 . Strap  1001  is elongated, preferably having a length at least four times its width. Depending on the application, the width W of strap  1001  is preferably in the range of 2 inches to 4 inches, and the strap length L is in the range of 8 inches to 10 inches. In one embodiment, strap  1001  is comprised of a urethane that us flexible after curing. The strap  1001  may also be comprised of rubber, canvas, or other sturdy textile. Strap  1001  comprises two end portions  1002  and  1006 , and middle portion  1004 . Affixed to the middle portion is polishing stone  1010 . In one embodiment, polishing stone  1010  is square or rectangular, and may be comprised of an epoxy casting with aluminum oxide mixed into the epoxy. In one embodiment, polishing stone  1010  is cast as part of strap  1010 , with the thread pattern as part of a mold (not shown) used to form the strap  1001 . In this case, the polishing stone  1010  and polishing stone holder (strap  1001 ) are comprised of a single piece of cast urethane material. 
     In an alternative embodiment, polishing stone  1010  is a thin piece of urethane mixed with a metal oxide that is affixed to strap  1001  via an adhesive (e.g. epoxy or glue). In one embodiment, polishing stone  1010  has a spacing index of 2. As shown in  FIG. 10B , end portions  1002  and  1006  may further comprise cutout areas  1008  disposed within end portions  1002  and  1006 . Note, for illustrative clarity, not all of the cutouts shown in  FIG. 10B  are labeled with a reference number. The cutout areas facilitate a user gripping the end portions to polish threads of a bolt in a manner similar to that described previously. An advantage of the embodiment utilizing a flexible stone holder is that the flexible strap  1001  allows polishing of threads in confined areas where other tools may not fit.  FIG. 10C  shows an alternative embodiment of the flexible stone holder, comprising closed cutouts  1011  disposed within the end portions  1002  and  1006 . During use, a user can securely grip the strap  1001  by placing his fingers through closed cutouts  1011 . 
       FIGS. 11A and 11B  show the use of flexible polishing stone holder  1000 .  FIG. 11A  is a front view of a bolt  1102  being polished by flexible polishing stone holder  1000 . To polish the bolt  1102 , the flexible polishing stone holder  1000  is moved back and forth in the direction indicated by arrow D.  FIG. 11B  is a side view, showing flexible polishing stone holder  1000  placed around threaded portion  1103  of bolt  1102 . The flexible polishing stone holder  1000  is moved back and forth in direction D by pulling on each end of the flexible polishing stone holder  1000  in an alternating manner. 
       FIGS. 12-14  show additional alternative embodiments of the present invention.  FIG. 12A  shows a top view (outer surface) of a polishing stone holder  1200 . Polishing stone holder  1200  comprises urethane strap  1202 , and a plurality of lugs, indicated as  1205 A,  1205  B, and  1205 C.  FIG. 12B  is a side view of polishing stone holder  1200 , showing the lugs  1205 A- 1205 C, and corresponding holes for each lug  1207 A- 1207 C.  FIG. 12C  shows a bottom view (inner surface) of polishing stone holder  1200 . The holes  1207  traverse the lugs  1205  such that additional apparatuses may be attached to the lugs  1205 , as will be described in upcoming figures. 
     Polishing stone  1210  is preferably cast as part of strap  1202 , with the thread pattern as part of a mold (not shown) used to form the strap  1202 . Preferably, polishing stone  1210  is larger than that of the embodiment shown in  FIG. 10A , and occupies most of the available space on strap  1202 . 
       FIG. 13  shows an example usage of a plurality of polishing stone holders similar to polishing stone holder  1200 . In  FIG. 13 , a plurality of polishing stone holders  1200 A- 1200 D are used to inspect a large-diameter threaded shaft  1302 . In practice, such a shaft may exceed 18 inches in diameter. A propeller shaft of an ocean-going ship is one example where such large threaded shafts may be found. The polishing stone holders  1200 A- 1200 D are linked together via connector bands  1310 . Connector bands  1310  are preferably elastic and engage hole (e.g.  1207 A of  FIG. 12B ) of lugs (e.g.  1205 A of  FIG. 12B ) of neighboring polishing stone holders. In one embodiment, the connector bands are adjustable in length to accommodate various sizes of threaded shafts. To inspect the shaft  1302 , an up-and-down “shoeshine” motion is used by pulling on the opposite end polishing stone holders  1200 A and  1200 D in a reciprocal manner. 
       FIG. 14  shows an example usage of a plurality of polishing stone holders similar to polishing stone holder  1200 . In  FIG. 14 , a plurality of polishing stone holders  1200 A- 1200 D are formed in a closed loop via connector bands  1310 . A plurality of handles  1408  are attached to the center lugs (e.g.  1205 B of  FIG. 12B ) of one or more polishing stone holders  1200 A- 1200 D. The handles are then moved by the user to pass the polishing stone holders  1200 A- 1200 D over the threads of shaft  1302 . 
       FIG. 14B  shows detail of an exemplary embodiment of handle  1408  mounted to a lug  1205 . The lug  1205  is integral to strap  1202 , and a fastener  1412  traverses the handle  1408  and lug  1205  to secure the handle  1408  to the lug  1205 , and hence to a polishing stone holder. Fastener  1412  may comprises a threaded fastener, a friction-fit fastener, or any other suitable fastening mechanism to secure handle  1408  to lug  1205 . The use of the handles  1408  as shown in  FIG. 14  may be convenient in situations where there is not sufficient clearance to use the “open loop” configuration depicted in  FIG. 13 . 
     As can now be appreciated, embodiments of the present invention provide an improved method and apparatus for inspecting and repairing threads on large bolts and threaded holes. Although the description above contains many specific details, these should not be construed as limiting the scope of the invention, but merely as providing illustrations of some of the presently preferred embodiments of the present invention. The present invention may have various other embodiments. Furthermore, while the form of the invention herein shown and described constitutes a preferred embodiment of the invention, it is not intended to illustrate all possible forms thereof. It will also be understood that the words used are words of description rather than limitation, and that various changes may be made without departing from the spirit and scope of the invention disclosed. Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than solely by the examples given.