Thread inspection and polishing device

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.

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 '789 patent. The '789 patent discloses a bolt thread inspection and thread polishing device. The '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 '789 device did not provide inspection or repair capabilities for threaded holes. Another drawback of the '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.

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. 1shows thread details of a prior art concave polishing stone102, similar to that shown in FIG. 2B of the '789 patent. Polishing stone102has a plurality of threads104A-104D that engage corresponding threads108A-108D of bolt106. Each thread has a peak (shown generally as110). As the polishing stone102is moved over the threads of the bolt106, small metal fragments114from the bolt may form in the void (generally referred to as112) between the thread peaks110and the polishing stone102. These metal fragments can wear the bolt threads, causing damage to threads of bolt106. Polishing stone102has a spacing factor of 1, meaning that there is a polishing stone thread for every bolt thread. In one embodiment, the polishing stone102is formed from a mixture of epoxy and aluminum oxide. In one embodiment, polishing stone102has 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 stone102.

FIG. 2shows thread details of a polishing stone202in accordance with an embodiment of the present invention. Polishing stone202has a plurality of threads204A,204C, and204E that engage threads of bolt106. Polishing stone202has threads spaced at wider intervals than the prior art polishing stone102. InFIG. 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, thread108A and108B are bounded by thread204A and204C of polishing stone202. By using a spacing factor of 2 or more, a large void212is formed between the threads of the bolt106, and the polishing stone202. Large void212provides an escape path for metal fragments, so that they do not wear the peaks (see110ofFIG. 1) of the threads of bolt106. Note that while a spacing factor of 2 is illustrated inFIG. 2, larger spacing factors are contemplated, and within the scope of the present invention.

FIG. 2Bshows a perspective view of a concave polishing stone202, andFIG. 2Cshows a perspective view of a convex polishing stone302. In general, polishing stones202and302are arc-shaped, having threads on at least one side, either the inner side209or the outer side309. In one embodiment, both sides209and309of 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 3Bshow perspective views of a convex polishing stone302. Convex polishing stone302is intended for threads inside a nut or stud hole.FIG. 3Ashows a front perspective view of convex polishing stone302, having threads (shown generally as304). The convex polishing stone302has a spacing factor of 2 or greater.

FIG. 4shows an improved polishing stone holder400. U-shaped metal frame405has polishing stones202attached at the distal ends of each frame leg407. Wing nut402engages threaded bolt403to provide for adjusting the pressure that polishing stones202exert on bolt106. Strap404is used to provide additional security by being wrapped around the polishing stones202snug against bolt106. Strap404is intended to wrap around the outside of frame legs407to keep the polishing stones202centered. In one embodiment, strap404comprises a fastener such as a hook-and-loop fastener or snaps to secure the strap404around the polishing stones202. One end of the strap404may be permanently secured to a frame leg407via adhesive or another fastening means, such as a grommet. Drive nut408engages a ratchet (not shown) or drill (not shown) to turn the stone holder400. If a drill is used, a slow speed setting is preferable, to avoid damage to the bolt106.

FIG. 5shows a flowchart500indicating process steps to inspect and repair threads. In process step502, 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 step504, 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 step506. In step508, the polishing stones are lubricated with rubbing alcohol to facilitate smooth motion when the polishing stones are applied to the workpiece. In process step510, 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 as400ofFIG. 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 step512the 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 step514, damaged areas are repaired by chiseling at an approximate 90 degree angle to the X axis of the bolt (seeFIG. 8Aand corresponding description). In step516, the threads are tested again, similar to step504, 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 steps506-514may be repeated until the workpiece is repaired, and the nut turns smoothly on the bolt.

FIG. 6shows the method step of pre-cleaning. Absorbent pads618are soaked in a fast-evaporating solvent, such as rubbing alcohol, and then inserted in front of polishing stones202. Strap404is then wrapped around workpiece106, and the polishing stone holder is rotated around the workpiece (bolt)106to clean it in preparation for inspection and repair.

FIG. 7shows an indication of thread damage on bolt106. A damaged thread is indicated generally by reference721. Since the thread721was out of alignment, the polishing stone removed the dye from that area, making the defect immediately visible to a maintenance worker.

FIG. 8Ashows an instance of repairing threads in a bolt106. Chisel point822is oriented at angle C with respect to axis X of the bolt106. 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. 8Bshows an instance of repairing bolt threads with limited working space. In this case, bolt806A is undergoing repair. However, since bolt806A is in close proximity to bolt806B, using a conventional chisel is not feasible. Therefore, a special bar chisel852has been designed for this purpose. Chisel852has a blade that is applied to bolt806A and then struck with mallet864to make the repairs. In this way, bolt threads can be repaired, even in tight spaces.

FIG. 8Cshows a side view of chisel852. Chisel852is comprised of bar877, and chisel point879. During use to repair a bolt thread, chisel point879is applied to a bolt, and then a mallet is used to strike bar877on the opposite side, (e.g. at point881) to repair the bolt threads.

FIG. 9shows a polishing stone holder900as used with convex polishing stones302. Polishing stone holder900is similar to polishing stone holder400ofFIG. 4, with the exception of the polishing stones302which are fastened to the outer surface of U-shaped metal frame405, so they can contact the inner diameter of a threaded hole (indicated as909). The polishing stone holder is then turned back and forth along path D, so that the polishing stones302engage the threads of a threaded hole such as a nut or bolt hole within a piece of machinery.

FIG. 10Ashows an alternate embodiment of the present invention, a flexible polishing stone holder1000. Flexible polishing stone holder1000comprises a strap1001. Strap1001is elongated, preferably having a length at least four times its width. Depending on the application, the width W of strap1001is 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, strap1001is comprised of a urethane that us flexible after curing. The strap1001may also be comprised of rubber, canvas, or other sturdy textile. Strap1001comprises two end portions1002and1006, and middle portion1004. Affixed to the middle portion is polishing stone1010. In one embodiment, polishing stone1010is square or rectangular, and may be comprised of an epoxy casting with aluminum oxide mixed into the epoxy. In one embodiment, polishing stone1010is cast as part of strap1010, with the thread pattern as part of a mold (not shown) used to form the strap1001. In this case, the polishing stone1010and polishing stone holder (strap1001) are comprised of a single piece of cast urethane material.

In an alternative embodiment, polishing stone1010is a thin piece of urethane mixed with a metal oxide that is affixed to strap1001via an adhesive (e.g. epoxy or glue). In one embodiment, polishing stone1010has a spacing index of 2. As shown inFIG. 10B, end portions1002and1006may further comprise cutout areas1008disposed within end portions1002and1006. Note, for illustrative clarity, not all of the cutouts shown inFIG. 10Bare 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 strap1001allows polishing of threads in confined areas where other tools may not fit.FIG. 10Cshows an alternative embodiment of the flexible stone holder, comprising closed cutouts1011disposed within the end portions1002and1006. During use, a user can securely grip the strap1001by placing his fingers through closed cutouts1011.

FIGS. 11A and 11Bshow the use of flexible polishing stone holder1000.FIG. 11Ais a front view of a bolt1102being polished by flexible polishing stone holder1000. To polish the bolt1102, the flexible polishing stone holder1000is moved back and forth in the direction indicated by arrow D.FIG. 11Bis a side view, showing flexible polishing stone holder1000placed around threaded portion1103of bolt1102. The flexible polishing stone holder1000is moved back and forth in direction D by pulling on each end of the flexible polishing stone holder1000in an alternating manner.

FIGS. 12-14show additional alternative embodiments of the present invention.FIG. 12Ashows a top view (outer surface) of a polishing stone holder1200. Polishing stone holder1200comprises urethane strap1202, and a plurality of lugs, indicated as1205A,1205B, and1205C.FIG. 12Bis a side view of polishing stone holder1200, showing the lugs1205A-1205C, and corresponding holes for each lug1207A-1207C.FIG. 12Cshows a bottom view (inner surface) of polishing stone holder1200. The holes1207traverse the lugs1205such that additional apparatuses may be attached to the lugs1205, as will be described in upcoming figures.

Polishing stone1210is preferably cast as part of strap1202, with the thread pattern as part of a mold (not shown) used to form the strap1202. Preferably, polishing stone1210is larger than that of the embodiment shown inFIG. 10A, and occupies most of the available space on strap1202.

FIG. 13shows an example usage of a plurality of polishing stone holders similar to polishing stone holder1200. InFIG. 13, a plurality of polishing stone holders1200A-1200D are used to inspect a large-diameter threaded shaft1302. 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 holders1200A-1200D are linked together via connector bands1310. Connector bands1310are preferably elastic and engage hole (e.g.1207A ofFIG. 12B) of lugs (e.g.1205A ofFIG. 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 shaft1302, an up-and-down “shoeshine” motion is used by pulling on the opposite end polishing stone holders1200A and1200D in a reciprocal manner.

FIG. 14shows an example usage of a plurality of polishing stone holders similar to polishing stone holder1200. InFIG. 14, a plurality of polishing stone holders1200A-1200D are formed in a closed loop via connector bands1310. A plurality of handles1408are attached to the center lugs (e.g.1205B ofFIG. 12B) of one or more polishing stone holders1200A-1200D. The handles are then moved by the user to pass the polishing stone holders1200A-1200D over the threads of shaft1302.

FIG. 14Bshows detail of an exemplary embodiment of handle1408mounted to a lug1205. The lug1205is integral to strap1202, and a fastener1412traverses the handle1408and lug1205to secure the handle1408to the lug1205, and hence to a polishing stone holder. Fastener1412may comprises a threaded fastener, a friction-fit fastener, or any other suitable fastening mechanism to secure handle1408to lug1205. The use of the handles1408as shown inFIG. 14may be convenient in situations where there is not sufficient clearance to use the “open loop” configuration depicted inFIG. 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.