Patent Number: 047117605
Section: description

DETAILED DESCRIPTION The present locking device prevents the loosening of a threaded bolt connection between two components, such that upon exertion of stresses that would tend to cause the threaded bolt to back out of a threaded bore or upon breakage of the threaded bolt, which could cause separation of the components, a lock nut prevents such a backing or separation of broken bolt sections. While the conventional securement of a bolt in a threaded bore is often suitable in maintaining two components connected to each other, problems sometimes arise where stresses or vibrations occur that cause the bolted connection to lose its initial secured position and loosen the connection. Also, at times, the bolt may be subjected to such severe stresses that a break in the bolt will occur that can cause loosening or separation of the two components, and disengagement of the head portion of the bolt from the bore. In accordance with the present invention, a means is provided that, when used with a threaded bolt connection will prevent loosening of the bolt connection under adverse conditions that would cause loosening or separation of a conventional bolted connection. The present invention uses a lock nut of particular design, engageable with the bolt head, which has a threaded outer wall having a thread of an opposite direction to that of the direction of the thread of the bolt, such that upon turning of the bolt in a direction that would tend to loosen the two components, the lock nut is turned in a direction that actually tightens its relationship to the bolt head and retains the two components in a secure manner. The bolt, as disclosed hereinafter may have a right-handed thread or a left-handed thread, provided that the lock nut, also hereinafter described, has an opposite thread. Thus, the thread of the bolt is in a first direction (right- or left-handed thread) and the thread of the lock nut is of a second or opposite direction (left- or right-handed thread) respectively. For the purpose of brevity, the device will be described wherein the bolt has a right-handed thread, and the lock nut a left-handed thread, although it is applicable also to bolts and lock nuts having oppositely directed threading. Referring now to FIGS. 1 through 5, the locking device 1 of the present invention is illustrated wherein a first component 3 is secured to a second component 5. The first component 3 has a bore 7 therein having right-handed threads 9. The second component 5 has a bore 11 therethrough coaxial with the bore 7, and a recess 13 also coaxial therewith, extending inwardly from the outer surface 15 of the second component. A bolt 17 also having right-handed threads, as is conventional, is threadedly engaged with the threads 9 in the wall of the bore 7 in first component 3 to pull flush the lower surface 19 of the second component 5 and the upper surface 21 of the first component 3. Threads 23 are provided in the wall 25 of the recess 13 of the second component 5, which threads are left-handed threads, opposite the threads of the bolt 17. The locking nut 27 comprises a base 29 and a downwardly depending skirt or cylindrical wall 31 (FIG. 4), with threads 33 in the outer surface of the wall engageable with the threads 23 of the wall 25 of the recess 13, which threads are also left-handed threads. The base 29 of this cup-shaped lock nut 27 has a central aperture 35 therethrough, and a plurality of radially outwardly extending slots 37 extending from the aperture 35 towards the downwardly depending cylindrical wall 31, but terminating spaced from said wall. The slots 37 form a plurality of deformable sections 39 therebetween in the base 29 of the lock nut 27. The head 41 of the bolt 17 has a cavity 43 in the end surface 45 thereof which has an unsymmetrical wall 47 thereabout, preferably of a polygonal shape, the cavity illustrated in FIG. 4 having a hexagonal or six-sided wall 47. The end surface 45 of the head of the bolt may be downwardly and inwardly directed, as indicated at 48 in FIG. 2, from the outer edge thereof to the cavity 43. The head 41 of the bolt is of a first diameter, while the recess 13 is of a second diameter greater than the first diameter of the head of the bolt. This enables the head 41 of the bolt 17, when securely engaged in the threaded bore to engage a shoulder 49 formed by the recessed portion 13, while a gap is provided between the head 41 of the bolt and the threaded wall 25 of the recess 13, for placement of the lock nut. The locking device is used by engaging the lock nut after the bolt has been inserted through the bore 11 of the second component and threadedly secured in the bore 7 of the first component. After the bolt 17 has been threadedly engaged in the right-handed threads 9 of the bore 7, with the head 41 of the bolt flush against shoulder 49 of the second component 5, the lock nut 27 is threadedly engaged with the threads 23 in wall 25 of the recess 13, with the undersurface 51 of the base 29 of lock nut 27 in contact, about at least its periphery, with the end surface 45 of the head 41 of the bolt 17 (FIG. 2). The deformable sections 39 of the base 29 are then deformed downwardly into the cavity 43 of the head of bolt 17 by impacting the inward ends of the deformable sections 39 adjacent the aperture 35, such as by a blunt punch or other suitable tool (FIG. 3). The position of the deformable sections, as deformed, is illustrated in FIG. 5. With the deformable sections 39 in contact with the unsymmetrical wall 47, about recess 43 in the head 41 of the bolt, any forces acting upon the bolt 47 to cause it to turn in a left-handed direction, which would tend to loosen the bolt from the right-handed threads of the bore will cause the lock nut to also attempt to rotate in a left-handed direction, and thus cause the lock nut to tighten within the left-handed threads of the wall of the recess. In an instance where the bolt experiences a break between portions of the bolt shaft, unless a prefectly clean, horizontal break occurs, a very unlikely possibility, the broken bolt section will still tend to cause rotation of the head of the bolt if loosening is to occur, such that tightening of the lock nut will again result. Other embodiments of the lock nut, usable in the present locking device, are illustrated in FIGS. 6 through 8, wherein the lock nut need not be threaded into securement with the threads of the recess but rather deformation of the deformable sections causes such securement. As illustrated therein, the lock nut 51 has a base 53 and a downwardly depending cylindrical wall 55, with left-handed threads 57 on the outer surface thereof. A central aperture 59 is provided through the base 53, with radially outwardly extending slots 61 extending from the central aperture 59 towards the cylindrical wall 55 to form deformable sections 63. The downwardly depending cylindrical wall 55 has a plurality of vertical slits 65 therein, spaced about the cylindrical wall 55, extending from the terminus 67 towards the base 53. The diameter of the lock nut 51 will be slightly less than the second diameter of the recess 13 in the second component 5, but larger than the first diameter of the head 41 of the bolt, such that the cup-shaped lock nut 51 is insertable into the recess over the head 41 of the bolt 17, without the need to threadedly engage the threads 56 with threads 25 of the wall 23 of recess 13, with the undersurface 69 of the base 53 in contact with the head 41, over the unsymmetrical cavity 43. Deformation downwardly of the deformable sections 63 about the aperture 59 will cause the portions of the cylindrical wall 55 between spaced slits 65 to bow outwardly and engage with the threads 25 of the wall 23, as illustrated in FIG. 8. In a further embodiment of the lock nut 71, illustrated in FIGS. 9 and 10, a lock nut, such as illustrated as 51, is provided with downwardly depending legs 73 on the ends 75 of the deformable sections 63 to provide even better contact and engagement with the unsymmetrical wall 47 of the cavity 43 in the head of the bolt. As described, the tendency of a bolt to loosen from a threaded securement will cause the lock nut to tighten and prevent such loosening. Also, upon breakage of a bolt, after threaded securement, any tendency of the bolt fragment to rotate, will be in the direction of loosening of the bolt and will also cause tightening of the lock nut and prevent such a fragment from separating or dislodgment from the bore in which the bolt is secured, and thus will retain the fragment within the bore. The locking device is especially useful in securing baffle plates to a baffle former and a baffle former to a core barrel, or in other bolted connections in a pressurized water nuclear reactor. As is well-known, and described in the aforementioned U.S. Pat. Nos. 4,069,102 and 4,080,257, a nuclear reactor comprises a substantially cylindrical, vertically disposed tubular pressure vessel, the bottom of which is in the form of a hollow, hemispherical shell. A core barrel is disposed within the pressure vessel. Reactor control rod guide tubes are located within the upper region of the core barrel, while the reactor core internals, including the fuel element assemblies, the fuel element assemblies support grid structure and framework, and the like, are housed in the lower region of the core barrel. The core barrel, or first element, has about its inner periphery, a baffle former structure that is covered with a plurality of baffle plates, or second element, that aid in channelling the flow of coolant through the core region and assembly thereof. The baffle former is secured to the inside surface of the core barrel and the baffle plates are then secured to the baffle former. Numerous connections, generally bolted connections are made to secure the baffle former to the core barrel and the baffle plates to the baffle former. The baffle bolts used for these connections are subject to loosening due to vibrations or other causes and means to prevent such loosening are highly desired. Referring now to FIGS. 11 and 12, an improved nuclear reactor 81 contains a core barrel 83, positioned within a nuclear reactor pressure vessel 85, which core barrel has a baffle former 87 secured by bolted connections to the inner surface 89 thereof. The inner surface 91 of the baffle former 87 has a plurality of baffle plates 93 covering said inner surface, and secured thereto by bolted connections. Each baffle plate 93 secured to the baffle former 87 by a plurality of bolts 95, while the baffle former 87 is secured to the core barrel 83 by a plurality of bolts 97. Only a portion of the bolts and bolted connections are illustrated. In the context of the fastening of two components together, the first component 3, as illustrated in FIGS. 1 through 4 and 10 would correspond to the first or second elements, the core barrel 83 or plurality of baffle plates 93, while the second component 5 would correspond to the baffle former 87. By use of the locking means, the bolted connections between the core barrel 83 and the baffle former 87, or the bolted connections between the baffle plates 93 and the baffle former 87 are prevented from loosening, and if fragmenting of a bolt were to occur, the bolt fragment would still be retained by the locking means.