Patent Publication Number: US-6220802-B1

Title: Apparatus for spreading a bolt load with improved holding capacity

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a Division of application Ser. No. 08/911,222 filed Aug. 15, 1997, now U.S. Pat. No. 6,048,150. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     NOT APPLICABLE 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to spreading the clamping load of a bolt which holds an inner liner to an outer shell used in ore milling operations, sealing the shell so that the wet ore slurry in the inner lining does not leak out of the shell through the mounting holes, and repairing enlarged mounting holes which go through the liner and shell to re-establish the ability of the bolt to maintain its designed and desired preload. 
     2. Description of the Related Art 
     a. Prior Mill Liner Bolting Techniques and Problems 
     Because of individual geometry, the head shape of a conventional tapered or spherical head, counter sunk mill liner bolt, presents a poor load bearing contact with the liner and its mating surface. This condition is due primarily to clearance and manufacturing tolerances between the liner, which is cast, and the radiused, tapered, load bearing area of the bolt, which is forged. This poor load area contact always causes early embedment with subsequent loss of bolt clamp load soon after assembly. It requires repeated, expensive mill shut downs, for bolt tightening, before an adequate surface contact can be formed to support the required bolt clamp load. In a majority of instances, bolts never establish enough surface area contact to stay tight and have to be periodically tightened through the life of the liners. Often, loose bolts fatigue and break with expensive consequences if the liners fall out. 
     While it is known to provide round headed bolts with a plurality of hard metal protrusions of various types, i.e., wings, keys, or fins, formed along the neck and shank of the bolt which embed themselves in the softer work piece to prevent the bolt from turning when a load is applied to the bolt, such structures are unnecessary when a non-round bolt head is supported in a non-round recess and, moreover, will not work in the environment of the present invention where the work piece, i.e., the mill liner, is made of harder steel than the bolt of the fastener. 
     Accordingly, it is an object of the present invention to provide improved bolt tightening features and processes which provide improved mating surfaces and preload holding ability which overcomes the problems of the prior art. 
     Moreover, running with loose bolts is also the cause of bolt holes in the mill shell becoming enlarged, which encourages further loosening and leaking problems eventually leading to expensive repair. Typically, the bolt holes in the liners are cast approximately ⅛″ larger, all around the bolt head, for a standard 1½″ liner bolt. FIG. 3 shows how inadequately the bolt load surface mates with the liner in a horizontal (radial) plane. FIGS. 1,  2  show loss of vertical (axial) contact face with small neck angle differences. 
     Accordingly, it is an object of the present invention to provide improved bolt tightening mechanisms which prevent loosening and enlargement of the holes through which the bolt passes thereby overcoming the problems of the prior art. 
     b. Prior Liner Bolt Sealing Problem 
     Prior sealing systems used with liner bolts are designed to give good sealing characteristics, but in doing so, sacrifice jointing efficiency. Typically rubber is introduced between the joint surfaces so that a hard joint, i.e., metal-to-metal, is never attained. This condition then becomes a gasketed joint and will never hold bolt preloads adequately. 
     While it is known to provide a repair washer with a metal-to-metal contact using a two- or three-piece metal and rubber washer combination atop a repair washer to effect an outboard seal at the outer circumference of the bolt of the fastener and the outboard end of the central bore of the repair washer, such structure ignores the further need for a simultaneous metal-to-metal contact with a resilient member beneath the repair washer to effect an inboard seal at the inborad end of the central bore of the repair washer. 
     Accordingly, it is an object of the present invention to provide an improved sealing system without sacrificing joint efficiency by providing metal-to-metal contact with simultaneous adequate sealing thereby overcoming the problems of the prior art. 
     BRIEF SUMMARY OF THE INVENTION 
     Set forth below is a brief summary of the invention in order to achieve the forgoing and other benefits and advantages in accordance with the purposes of the present invention as embodied and broadly described herein. 
     A first aspect of the invention is a bolt including a head of predetermined shape, a shank, a neck integral with the head and shank, and a plurality of raised contact surface portions uniformly positioned adjacent the neck and constructed and configured for spreading an applied bolt load. 
     Another feature of this aspect of the invention is the raised contact surface portions include a base portion contiguous the neck, and a ridge portion raised above the base portion and constructed and configured to contact a congruent wall portion of a bolt bore in a support structure. 
     Still other features of this aspect of the invention include the bolt is a forged bolt, the head shape may be round, elliptical, square, oblong, spherical, or rectangular, and has an axially extending portion of predetermined thickness having a constant circumference, and a tapered neck portion between the head and shank. 
     Still other features of this aspect of the invention include the neck having a circumference either intermediate the circumferences of the head and shank or greater than both said circumferences. 
     Another feature of this aspect of the invention is the raised contact surface portions are elongated V-shaped ridges raised above the base portion and are forged integrally with the neck. 
     Still other features of this aspect of the invention include the raised portions are symmetrically placed relative to the neck, extend substantially an entire length of the neck, may also extend substantially along an entire length of the head, extend axially and radially relative to the longitudinal axis of the bolt, and are deformable and fay to an adjacent bore wall portion whereby when a load is applied to the bolt the load is spread more uniformly over a surface of the neck. 
     A second aspect of the invention is an insert including a base portion having a width, a length and a thickness, and a plurality of surface contact portions raised above and extending along a length of the base portion. 
     In this aspect of the invention the plurality of surface contact portions are short relative to a width of the insert, are coterminous with a length of the base portion, and are formed as parallel, symmetrically placed, V-shaped ridges, the height and width of which vary relative to each other according to the amount of a clearance of an adjacent wall portion of a bore hole in a support structure. 
     A further feature of this aspect of the invention is the insert has a flat shape in one stage of its production and an arcuate shape in its final form which is self-aligning relative to the neck of the bolt when a load is applied to the bolt whereby the load is spread onto the raised contact surfaces. 
     A third aspect of the present invention is a repair washer for enlarged holes including a shaped body having a top major surface and a bottom major surface and a central bore therethrough, an annular groove in the top major surface constructed and configured to receive an o-ring seal, an annular groove in the bottom major surface constructed and configured to receive an o-ring seal, and a plurality of teeth integral with the bottom major surface constructed and configured for gripping a surface which is to be sealed. 
     In this aspect of the invention the annular groove in the top major surface is located near the central bore and is constructed and configured to cooperate with a bolt through the central bore and through an overlying fastener to seal the central bore at the top surface, while the annular groove in the bottom major surface is located near the periphery of the bottom major surface and is constructed and configured to cooperate with the bolt through the central bore and through the fastener overlying the top major surface to simultaneously seal the central bore at the bottom surface. 
     Other features of this aspect of the invention include the teeth are serrated and are constructed and configured to prevent movement and subsequent loosening of the washer while the top and bottom seals are effected when the washer is tightly secured to the sealed surface by an overlying fastener, the bottom major surface portion may be either flat or curved to cooperate with the curved surface which is to be sealed, and the bottom major surface is a load surface and the annular groove therein is constructed and configured to effect a bottom seal on the periphery of the load surface. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a front vertical elevation view in partial section of a prior art mill liner bolt through a liner and shell to hold the assembly together. This drawing shows radial contact with existing geometry. 
     FIG. 2 is a view similar to FIG. 1 showing different angles between the countersunk hole in the liner and the chamfered edge of the bolt head of the prior art. This drawing shows axial contact with mismatch of neck angles. 
     FIG. 3 is a top view in partial section taken along the lines  3 — 3  of FIGS. 1,  2  showing the point of contact between the oval shaped countersunk liner hole and chamfered oval shaped bolt head. 
     FIG. 4 is a view similar to FIG. 1 showing the forged spreader with ridges of the present invention which make good and complete contact with the countersunk hole of the liner when the bolt is preloaded to its desired amount. This drawing shows spreader correcting action both radial and axial. 
     FIG. 5 is a view similar to FIG. 2 again showing the forged ridged spreader of the present invention. 
     FIG. 6 is a top view in partial section taken along the lines  6 — 6  of FIGS. 4,  5 . 
     FIG. 7 is a elevational schematic view of the assembly of FIG.  4  and is identified as Liner 1.5 Shape/A. 
     FIG. 8 is a plan schematic view of FIG.  7 . 
     FIG. 9 is an oblique perspective of the mill bolt with forged ridged spreader of the present invention seen in FIGS. 4-8. This drawing shows a load spreader liner  20  having spreader areas  31  and a liner bolt hole  12 . 
     FIG. 10 is a perspective view similar to FIG.  9  and 
     FIG. 11 is a sectional view taken along the line  11 — 11  of FIG. 10 showing an alternative round head and neck shape of the bolt of the present invention. 
     FIG. 12 is a perspective view similar to FIG.  9  and 
     FIG. 13 is a sectional view taken along the line  13 — 13  of FIG. 12 showing an alternative elliptical head and neck shape of the bolt of the present invention. 
     FIG. 14 is a perspective view similar to FIG.  9  and 
     FIG. 15 is a sectional view taken along the line  15 — 15  of FIG. 14 while 
     FIG. 16 is an end view of FIG. 14 showing an alternative square head and round neck shape of the bolt of the present invention. 
     FIGS. 17 and 19 are full and partial perspective views, respectively, similar to FIG. 9 and 
     FIG. 18 is a sectional view taken along the lines  18 — 18  of FIGS. 17,  19  showing an alternative oblong head and convex (FIG. 17) or concave (FIG. 19) neck shape of the bolt of the present invention. 
     FIG. 20 is a perspective view similar to FIG.  9  and 
     FIG. 21 is a sectional view taken along the line  21 — 21  of FIG. 20 showing an alternative round head with one flat face and spherical neck shape of the bolt of the present invention. 
     FIG. 22 is a perspective view similar to FIG.  9  and 
     FIG. 23 is a sectional view taken along the line  23 — 23  of FIG. 22 showing an alternative rectangular head and neck shape of the bolt of the present invention. 
     FIG. 24 is an oblique perspective view of an alternate embodiment of the present invention in the form of forged spreader inserts having deformable ridges according to the present invention. This drawing shows a standard liner bolt  20  in a liner bolt hole  2  with load spreader inserts  40  having spreader areas  41 . 
     FIG. 25 is a form of the forged spreader of FIG. 10 during an early step in the manufacturing process of the present invention prior to being forged in its curved final form and is identified as Line 1.5 Shape/A. 
     FIG. 26 is a top plan view of the forged insert of FIG.  25 . 
     FIG. 27 is a top plan view of FIG. 26 following the forming step which forms the forged spreader into its final curved form. 
     FIG. 28 is an oblique perspective view of the underside of the special repair washer of the present invention. This drawing shows a special repair washer for enlarged mill liner holes. FIG. 28 shows a serrated load area  53  to prevent movement and subsequent loosening and a special o-ring sealing groove  51  to seal on outside of load area. 
     FIG. 29 is an oblique perspective top view of the special repair washer of the present invention. This drawing shows a liner bolt, nut  23 , washer  50 , and additional “o”-ring  54  (in phantom). 
     FIG. 30 is a perspective view of a special repair plate of the present invention also showing an additional embodiment of the improved repair washer of the present invention. This drawing shows a special repair washer (rectangular) having a concave bottom face to match shell  1  curvature, holes for socket screws to clamp plate to shell, and, in a top view, a Valley Forge™ two piece sealing system around liner bolt  20  and under nut  23 . 
     FIG. 31 is an oblique partial perspective view of the underside of the repair plate of FIG.  30 . This drawing shows a back view of the “o”-ring special sealing groove to seal plate to shell. 
     FIG. 32 is a plan view of the repair plate and repair washer assembly of the present invention, and is identified as a repair washer new S/A. This drawing also shows 2 dowell pin holes (unnumbered). 
     FIG. 33 is a front elevation view in partial section of the repair plate of FIG.  32 . The bottom face of this plate will be concave. 
     FIG. 34 is a front elevation view of a drill stopper bushing used in making the present invention. 
     FIG. 35 is a top plan view of FIG.  34 . 
     FIG. 36 is a top plan view of a center drill bushing used in making the present invention. 
     FIG. 37 is a front elevation view in partial section of the center drill bushing of FIG.  36 . 
     FIG. 38 is a top plan view of a tap drill bushing used in making the present invention. 
     FIG. 39 is a front elevation view in partial section of the tap drill bushing of FIG.  38 . 
     FIG. 40 is a top view in partial section of a drilling process step which is used in making the present invention. This drawing shows a tap bushing in one hole of plate  61 . 
     FIG. 41 is a front elevational view of a drilling process step used in making the present invention. This drawing shows the repair assembly having a certain drill  71  in a drill stopper  74  on a tap bushing  73 . The bottom face of the repair assembly will be concave with radius to order. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Load Spreading Bolt 
     As seen in FIGS. 4-9 the bolt  20  with forged head shape  30  is designed to increase contact by spreading the load area in the taper neck both radially and axially even with mismatched neck angles. This design introduces additional bolt head forged surfaces  30  with ridges  31 , which project into the vacant clearance zones and touch the liner hole surfaces  12  uniformly around the faying surface of the bolt head. These projecting areas or ridges  31  are dimensioned so that they deform under load when tightened against the harder steel liner surface  12 . As the bolt  20  is tightened, plastic deformation takes place resulting in additional radial and axial surface contact, until full clamp load is reached, at which time this load will be spread over a larger and more uniform surface at the neck. FIGS. 10-23 show the alternative round, elliptical, square, oblong, spherical, and rectangular neck and head shapes of the present invention. 
     Alternative Insert Mode 
     As best seen in FIGS. 24-27, using the same theory, spreader inserts  40  are used to fit between a regular standard head bolt  20  and the liner hole  12 . Two inserts  40  with ridges  41  are temporarily attached, one at each neck area on the bolt, and held in place with an elastic band. Once the bolt head is assembled into the liner hole, the inserts will align themselves to spread load surface contact. Spreader inserts may be added to existing standard liner bolts, to increase their load supporting capabilities. The choice of using a forged spreader bolt (FIGS. 4-9) or spreader inserts (FIGS. 24-27) would depend on the application and customer preference. 
     Solution With Metal-to-Metal 
     As best seen in FIGS. 28-30, the system of the present invention will allow the joint to be metal-to-metal and the seal to do its function independently. It will also apply the nut  23  load directly on the shell  1  through hardened serrated teeth  53  so that the assembly cannot move to loosen. The rubber or neoprene O-ring seal in O-ring groove  51  on the underside of repair washer  50  stays on the periphery of washer  50  away from the metal-to-metal contact area  53  where the actual load application is made. Another smaller O-ring (not shown) in annular groove  54  (FIG. 29) seals the inner hole and the threads. 
     Special Repair Plate and Washer to Repair Enlarged Holes in Liner Shell 
     As best seen in FIGS. 30-41 a further aspect of the invention includes the provision of a special repair plate and special repair washer  60  which allows repair of enlarged holes in the liner and shell caused by dynamic movement resulting from loosening of the bolt in place when prior art bolts were used. The improvement of the present invention includes a repair plate  61  having a central bore  62  (FIG. 30) and a plurality of socket holes  63 . The top surface  64  of the repair plate  61  is flat, the bottom surface may be curved to match the shell Those skilled in the art would readily understand that the improved bolt of the present invention would be inserted through the hole in the liner  10  and the hole in the shell  1  through the plate  61  which is held in place by bolts (not shown) through socket holes  63 , which bolts go through plate  61  and into shell  1  but not through shell  1  (to avoid causing a hole which only then would also have to be sealed). A repair washer  50  (FIG. 29) or in alternate form as shown by repair washer  60  (FIG. 30) is used to provide metal-to-metal contact and the improved sealing as described above. 
     The process for making repair plate  61  is demonstrated in FIGS. 32-41. After socket holes  63  are drilled, the holding bolt is removed and replaced by a bolt  20  of the present invention having forged areas  30  or alternatively using load spreader inserts  40  to which is then secured repair washer  50 , 60  and nut  23  as described above. A center drill  71  held in place by center drill bushing  72  allows socket holes  63  to be precisely drilled while tap drill bushing  73  coupled with drill stopper bushing  74  superimposed on top of tap drill bushing  73  as shown in FIG. 41 controls the depth to which the holes are drilled into the shell  1  but not through shell  1 . When all of holes  63  are drilled, plate  61  is held in place by bolts through socket holes  63  into shell  1 . First, repair plate  61  is superimposed over the central bore  11  which goes into the shell  1  and liner  10  and is held in place by a large bolt through bore  11  to prevent repair plate  61  from moving while socket holes  63  are being drilled. 
     The foregoing description of a preferred embodiment and best mode of the invention known to applicant at the time of filing the application has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in the light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.