US3496754A - Mine roof bolts - Google Patents

Description

Feb. 24, 1970 w. E. WORLEY 3,496,754

MINE ROOF BOLTS 4 Sheets-Sheet 1 Filed Jan. 20, 1967 INVENTOR: WILLIAM E. WORLEY Feb. 24, 1970 w. E. WORLEY 3, ,7

MINE ROOF BCLTS Filed Jan. 20, 1967 4 Sheets-Sheet 2 INVENTOR. WILLIAM E. WORLEY ATTYS.

Feb. 24, 1970 w. E. WORLEY 3,496,754

MINE ROOF BOLTS Filed Jan. 20, 1967 4 Sheets-Sheet 4 25d; FIG. 25.

7' 1 1 4660 p i W I 5/ WE "Fl raeq: Fifi! R 1. L Far? M/L L INVEN O WILLIAM E WORLEY United States Patent US. Cl. 72339 Claims ABSTRACT OF THE DISCLOSURE A method and system of making a mine roof bolt comprising a pair of elongated bar members having a plurality of cooperating cam surfaces on their inner confronting faces so that upon longitudinal displacement of the bar members the bolt may be firmly seated in an opening in a mine roof. One of the bar members is made by shaping a flat strip of material having side edges of a stepped or undulating configuration into a hollow shape of generally U-shaped cross section, the opposed side edges defining the cam surface of said one. bar member. The other bar member may be made by forming an elongated piece of bar stock, for example, of semi-circular cross section into a serpentine shape by means of a die press or the like.

This is a continuation-in-part application of my prior application Ser. No. 538,807, filed Mar. 30, 1966 now Patent 3,301,123, and entitled Mine Roof Bolts.

Since the inception of underground mining, the need to support the overhead ceiling or roof in the underground passageways of a mine has been recognized as essential in order to prevent failure or collapse of the roof thereby jeopardizing the lives of men working in the underground mine. Thus, the problem of safe and adequate roof roof support is a very serious one. One of the oldest supports employed is used of timbers or other similar support means such as masonry walls and arches, steel timber sets, metal props, steel and masonry supports and others. These installations are comparatively expensive due to the cost of the support materials and mainly the high installation costs. Moreover, the beam supports are cumbersome and take up valuable space in the mines. Additionally, it has been found that in some instances activity in the strata or layers above the mine roof sets up forces which the timber supports cannot withstand and cave-ins result.

A more recent development in this area is the use of elongated roof bolts which are inserted into openings drilled in the strata above the roof of a mine passageway at predetermined spaced apart intervals. These bolts are usually three to four feet long and are mounted in vertical holes drilled into the ceiling. These bolts conventionally include some type of anchor-like fastening means at one end adjacent the uppermost part of the hole and means at the opposite end of the bolt to place the bolt under tension. By this arrangement it was thought that the strata above the roof would be compressed in a vertical direction whereby several thinly bedded bands or strata of rock or other material above the roof level would be bound together by means of the bolts to simulate a thicker strata which would be sufficiently strong to prevent flexure of the roof. In other words, the pattern of roof bolts in the roof was thought to secure weak roof material to strong massive overlying rocks or to reinforce the immediate roof strata to form a laminated beam. However, in certain situations, for example, where the roof strata does not have a solid rock layer for anchorage, this type of bolt has not provided adequate roof support. An important factor in this regard is that by compressing the strata vertically, only the tension component of shear is supported while the compression component is not supported.

3,496,754 Patented Feb. 24, 1970 "ice Further it has been found that if the anchor is located in soft areas of the strata above the roof, the anchor slips and the roof starts to sag or bulge in the areas between the bolts and in some cases the entire roof has ultimately failed.

In order to provide optimum support for the roof strata, it is important that the strata supported by the roof bolts be held firmly in place. It has been found that comparatively small initial movements of the strata has a compounding effect which ultimately leads to larger movements of the strata and movement of adjacent strata and eventually to complete failure of the roof. Further, it has been found that the presently used roof bolts do not support the strata in a manner to resist this initial movement. More specifically it has been observed that anchor slippage with these prior bolts and bolt elongation by reason of the great distance between the anchor and the other terminal end of the bolt permit small movement of the strata which, as noted above, can lead to complete failure of the roof.

One prior roof bolt of the type discussed above is known as the slot and wedge bolt. This bolt comprises an elongated rod which has a tapered opening in its upper end to receive a wedge block and is threaded at its lower end. This bolt is installed in a hole in the mine roof by driving the wedge block against the top of the hole so that it expands the upper end of the rod into engagement with the side wall of the hole to provide anchor means. A plate is placed over the threaded end of the rod and a nut is applied to the threads to tension the bolt. One of the shortcomings of this type of bolt is the fact that it has to be driven into the hole which could disrupt the mine roof and set up forces which weaken the roof. Additionally, the hole in the mine roof has to be a predetermined fixed depth and requires a firm top in order to provide a strong surface against which the wedge block engages. Moreover, since the anchor end in its expanded condition is of a larger diameter than the rod, a considerable amount of space exists between the hole and the rod throughout its length thereby permitting horizontal or lateral shifting of the strata and thus failing to resist the compression component of shear stress for a major portion of the bolt. Further, it is clear that this type of bolt is difficult to remove from the mine roof and is not suitable for reuse.

Another former type of expansion bolt discussed above is the bail-type expansion unit. This unit comprises an elongated bolt which is threaded at its inner end and has a head at its other end to accommodate a wrench for turning. An internally threaded wedging plug is adapted to be mounted on the threaded end of the bolt and upon downward movement, engages internally of a split sleeve to wedge it outwardly whereby an outer serrated surface of the sleeve grips the wall of the hole and serves as an anchor. In preparing this bolt for installation, a roof plate has to be assembled prior to application of the sleeve and this is usually done at the mine site. After the unit is inserted up into the hole, the head is turned, whereby the tapered plug is threaded downwardly along the top end of the bolt and spreads the wings or leaves of the sleeve outwardly to engage the wall of the upper portion of the hole. This anchors the bolts at the upper end and continued turning of the head places the bolt under tension. As noted above, the theory of this type of support is that a series of these bolts will compress the layers of the material above the roof vertically to compact the roof strata to form a laminated beam. One of the problems with this type of bolt, however, is that the expansion anchor provides a relatively small contact area with the wall of the hole, and if the material surrounding the anchor end is not firm, the sleeve tends to slip and slippage can eventually lead to failure of the roof. Furthermore, small strata movements produce elongation which also could result in failure of the roof. Moreover, this conventional type of bolt only supports the tension component of shear stress in the layers above the roof. Furthermore, the bolts are difiicult to remove and often are damaged upon removal and thus are not generally suitable for reuse.

Another prior type of expansion bolt is the type comprising an elongated rod having a hollow shell portion at its inner end within which is contained a small explosive charge. This bolt is inserted into a hole in the mine roof and the small explosive charge is set off to expand the shell into engagement with the wall of the hole at the inner end thereof and serve as an anchor. A bearing plate is then positioned over the lower threaded end of the bolt and a nut is applied to place the bolt under tension. The principle of support of a series of bolts of this type is the same as that outlined above. In other words, a series of spaced bolts are designed to compress the roof strata vertically thereby compressing the layers above the roof into the form of a beam. However, it is apparent that if slippage takes place or if the bolt is overstressed, there is the danger of roof failure. Moreover, it is readily apparent that this type of bolt is not reusable. Additionally if the upper portion of the hole is not a solid layer, the anchor will not grip firmly and slippage is inevitable. Further as noted above, this type of support only resists the tension component of shear stress and not the compression component by reason of the fact that there is only a comparatively small contact area between the anchor sleeve and the wall of the hole.

With the foregoing in mind, the principal object of the present invention is to provide a bolt for supporting the roof of mines which is characterized by novel features of construction and arrangement to provide a firm support for the roof and which is highly economical to manufacture and install. The bolt of the present invention supports the roof strata firmly and resists initial small movements of the strata much more effectively than prior bolts by reason of the fact that anchor slippage is practically eliminated and the effect of bolt elongation is localized. The bolt of the present invention engages the side wall of the hole at a plurality of contact zones throughout the length of the bolt thereby providing a plurality of anchor points as contrasted with the prior bolts discussed above which have only a small contact with the side wall of the hole at the upper end thereof. Additionally, whereas localized strata movement effected elongation of the entire rod in prior bolt constructions, localized strata movements effect small elongation of the bolt of the present invention by reason of the many longitudinally spaced contact zones. Thus, the effect of the bolt of the present invention is to strongly resist strata movement which is the major cause of roof failure.

The bolt of the present invention comprises broadly a pair of elongated bars of stepped configuration having confronting, longitudinally extending faces, each face having a plurality of planar angularly disposed longitudinally spaced cam surfaces which in the stacked position of the bolt are in overlying, confronting engagement. Each of the bars has a stepped outer face opposite the cam face provided by a plurality of cutout sections defining a plurality of projections forming contact points or zones.

One of the elongated bars has a threaded shank depending from one end thereof and the other bar has an axially extending depending stem portion which, when the engaging cam surfaces overlie one another, confronts a portion of the threaded shank. When installing this bolt, the bars which are in a stacked position are inserted up into a hole in the roof, the hole being of a slightly greater cross section than the opposed contact zones. The bars are now displaced longitudinally relative to one another, whereby the opposed contact zones are displaced radially relative to one another due to the cooperating cam surfaces to engage diametrically opposed areas of the side wall of the hole at a plurality of longitudinally spaced points the entire length of the hole. The bars may be displaced by placing a bearing plate over the threaded shank to engage the lower end of the stern and then applying and turning a nut on to the shank whereby one bar member is drawn downwardy and the contact points are moved laterally apart to engage the side wall of the hole at a plurality of longitudinally spaced points as shown in FIG. 5 of the drawings.

By this arrangement, there is a large contact area with the wall of the hole along the entire length thereof, thus eliminating the possibility of slippage of the bolt in the hole. Accordingly, when a series of spaced bolts is inserted into the roof, the various layers are compressed laterally whereby the bolts support the compression as well as the tension component of shear stress in the roof layers. Thus, by essentially filling the hole in the mine roof, lateral movement of the various layers of the roof is resisted and a safe roof is provided. Moreover, unlike the prior bolts discussed above, the roof top need not be solid to firmly anchor the bolt against slippage. Additionally if there are projections or irregularities along the side Wall of the hole into which the bolt is inserted, the localized contact areas of the bolt exert a great compressive force to crush the projection thereby insuring a good firm anchorage of the bolt in the hole.

The principle of operation of the bolt of the present invention is entirely different from the bolts discussed above and does not rely on tensioning of the bolt as the sole means of support. However, since the bolt of the present invention is vertically oriented and is anchored essentially throughout its length with the strata of the roof, it effectively supports the tension component of shear stress as well as the compression component.

The bolt of the present invention eliminates the need for a separate expansion device and hence is less costly to make and assemble than some of the prior 'bolts discussed above. Furthermore, since the bolt can be completely assembled prior to shipment, there is less handling at the mine site and hence it is less costly to install.

Even though it is preferred to make the bolt of the present invention of steel, it can be made of a lighter, less corrosive material by reason of its design.

The bolt of the present invention in addition to being easy and quick to install, may be easily removed after a period of time and reused an indefinite number of times.

With the foregoing in mind, an object of the present invention is to provide a roof bolt for use particularly as a support means for mine roofs which is characterized by novel features of construction and arrangement providing a firm support for the mine roof.

Anoher object of the present invention is to provide a roof bolt which firmly grips the strata of the roof essentially throughout its length, thus, substantially eliminating anchor slippage and minimizing the harmful effect of bolt elongation.

Another object of the present invention is to provide a roof bolt which pre-stresses the strata or layers of materials above the roof laterally so that a pattern of these bolts arranged in the mine supports the compression as Well as the tension component of shear stress in the roof layers.

A further object of the present invention is to provide a bolt which may be economically and easily manufactured, which is also easy to remove and which can be reused many times.

A further object of the present invention is to provide a new and improved means for making a mine roof bolt of the type described above in a highly economical manner.

Still another object of the present invention is to provide a system or method for making these bolts which lends itself to high production techniques.

Still a further object of the present invention is o provide a novel method for making these bolts which insures accurate and precise manufacture of the parts with a minimum amount of waste.

These and other objects of the present invention and the various features and details of the construction and use thereof are hereinafter more fully set forth with references to the accompanying drawings, wherein:

FIG. 1 shows a section of roof strata with a bolt in accordance with the present invention mounted therein;

FIG. 2 is a view taken on lines 22 of FIG. 1 showing a section of the roof with a plurality of bolts in accordance with the present invention installed therein;

FIGS. 3 and 4 are enlarged sectional views taken on lines 33 and 44 of FIG. 1;

FIG. 5 is an enlarged fragmentary view similar to FIG. 1 showing the bolt in the expanded operative position engaging the side wall in the hole in the roof;

FIG. 6 is an enlarged sectional view taken on lines 66 of FIG. 5;

FIGS. 7 and 8 are fragmentary perspective views of a bolt in accordance with the present invention in the stacked and expanded positions respectively;

FIG. 9 is a fragmentary perspective view of one of the elements of a bolt in accordance with the present invention;

FIG. 10 is a side elevational view of another embodiment of mine roof bolt constructed in accordance With the present invention;

FIGS. 11, 12 and 13 are sectional views of the mine roof bolt assembly of FIG. 10 taken on lines 1111, 1212 and 1313 respectively;

FIG. 14 is an enlarged section of a roof strata With the mine roof bolt in accordance with the present invention mounted therein;

FIG. 15 is a sectional view through the bolt taken on line 1515 of FIG. 14;

FIG. 16 is a fragmentary exploded perspective view of the bar members comprising the second embodiment of bolt;

FIG. 17 is a fragmentary layout of one of the bar members in a stage of manufacture;

FIG. 18 is a schematic illustration showing a method for making the bar members of the mine roof bolt shown in FIG. 10;

FIGS. 19 and 20 are fragmentary views of one of the bar members of the mine roof bolt at various stages of manufacture;

FIG. 21 is a view taken on line 2121 of FIG. 20;

FIG. 22 is a sectional view of stock material from which the other bar member of the bolt is made;

FIG. 23 is a fragmentary side elevational view of the other bar member at a stage of manufacture;

FIG. 24 is a view taken on lines 2424 of FIG. 23; and

FIG. 25 is a schematic illustration showing another method of making the bar members of the mine roof bolt shown in FIG. 10.

Referring now to the drawing and particularly to FIG. 1 thereof, there is shown a typical cross section of the roof of a mine passageway or tunnel which as illustrated is comprised of several strata or layers L. A mine roof bolt 10 in accordance with the present invention is mounted in a vertically extending hole 11 in the roof strata. These bolts are adapted to be inserted in the roof at predetermined spaced apart locations usually about three to four feet apart as illustrated in FIG. 2, and when in the expanded anchored position, the bolts serve to prestress the strata laterally thereby supporting the compression as well as the tension component of shear stress in the various layers comprising the roof, and thereby minimizing fiexture and thus, preventing roof failure.

Considering now the specific details of construction, the bolt 10 comprises a pair of elongated bar members 12 and 14 having confronting interengaging inner faces 13 and 14 respectively. The face 13 is of a stepped configuration comprising a plurality of angularly disposed, 1ongitudinally spaced flat cam surfaces 18 and a plurality of short radially directed shoulders 19, each shoulder 19 connecting adjacent cam surfaces 18. The face 15 of the bar 14 is also of a stepped configuration comprising a plurality of angularly disposed, longitudinally spaced, fiat planar cam surfaces 20 and a plurality of radially directed shoulders 21 connecting adjacent cam surfaces. The cam surfaces 18 and 20 are approximately of equal length so that the bar members nest snugly together when in the stacked position shown in FIG. 1. As best illustrated, the cam surfaces 18 and 20 are disposed at a slight angle to the longitudinal axis of the bar members and the shoulders 19 and 21 seat against one another in the stacked position to limit relative longitudinal movement of the bar members in one direction.

Each bar member as best illustrated in FIGS. 7-9 inclusive, has a rounded outer side wall opposite the cam face, the outer side wall 30 of the bar 12 having a plurality of longitudinally spaced cutouts 31 defining a plurality of longitudinally spaced projections which comprise contact zones Z adapted to engage the side wall of the opening 11. As best illustrated in FIG. 9, the cutout in the outer side wall is at an angle relative to a longitudinal axis of the bar member to form a series of triangularly shaped planar faces 33 approximately parallel to the cam surfaces 18. The bar 14 also has a rounded outer side wall 40 with a plurality of longitudinally spaced cutouts 41 defining longitudinally spaced projections which comprise contact zones Z adapted to engage the side wall of the hole or opening 11. These cutouts 41 are also angularly directed to form a series of triangularly shaped faces 43 approximately parallel to the cam surfaces 20. By this arrangement, as best illustrated in FIG. 1, the contact zones Z and Z are slightly staggered on either side of a plane transverse to the axis of the bar in the stacked position. In the present instance as illustrated in the drawings, the spacing between substantially all of the adjacent contact zones is at least equal to the largest cross sectional dimension measured in a plane perpendicular to the longitudinal axis of the bolt in the stacked position.

The bar members are adapted for longitudinal movement relative to one another between a stacked or closed position (see FIG. 1) and an expanded position (see FIG. 5 In the stacked position, the maximum cross sec tional dimension D of the bolt or the distance between contact zones Z and Z is the smallest to facilitate insertion into the hole 11 of a mine roof. In the expanded position (see FIG. 5) the contact zones Z and Z are displaced laterally due to interengagement of the cam surfaces to a distance apart greater than D. In order to facilitate longitudinal movement of the bars, the bar member 14 is provided with a threaded shank 50 depending from its lower terminal end which is of a cross section smaller than the greatest cross section of the bar to define an abutment shoulder 52 adjacent its lower end. The other bar member 12 has a depending stem 56 which in the stacked position of the bar members (FIG. 7) projects downwardly beyond the shoulder 52. The lower end of the stem 56 is spaced from the terminal end of the shank 50 to expose a portion of the threaded shank thereby to accommodate a plate 60 and nut 62.

In the installation of a bolt in accordance with the present invention, the bar members are initially in the stacked position shown in FIGS. 1, 3 and 7, wherein the cam surfaces 18 and 20 are in confronting relation for their entire length and the stem 56 projects downwardly beyond the shoulder 52 of the threaded shank 50. The bar members may be detachably held in this stacked position simply by wrapping tape around the bar members at selected locations along their length. The bolt in its stacked position is then inserted up into the opening 11 in the mine roof, the opening being of a slightly greater cross sectional dimension than the greatest cross section 7 D of the bolt in its stacked position to provide a very small clearance therebetween. For example, for an opening 11 having a diameter of about 1.375 inches, the distance D between the contact zones Z and Z of the bar members is approximately 1.250 in. Thereafter, the bearing plate 60 is positioned over the threaded shank S and the nut 62 is threaded on the shank 50. Now, as the nut 62 is tightened against the bearing plate 60, the bar member 14 is displaced longitudinally downwardly relative to the bar member 12. Relative longitudinal displacement of bar members causes relative lateral displacement of contact points or zones Z and Z due to the interaction of the cam surfaces 18 and 20 whereby the side wall of the opening 11 is engaged at a plurality of longitudinally spaced points along the length thereof as best illustrated in FIG. 5. By this arrangement, when a series of bolts is installed in the roof at predetermined spaced apart locations in the manner shown in FIG. 2, the layers L are prestressed in a lateral direction for a substantial height above the roof level whereby the compression and the tension components of shear stress in the layers or strata L are supported. In this manner a firm support is provided. Now, when it is desired to remove the bolts, the nut 62 is simply threaded off the shank 50, the plate 60 is removed and then merely by tapping the free terminal end of the shank 50 upwardly, the bar members are urged to a stacked position whereby they may be easily removed from the opening in the roof.

The roofs bolts of the present invention may be made relatively economically. For example, the bolt may be made by die stamping, forging or rolling.

There is shown in FIGS. -17 another embodiment of mine roof bolt 100 in accordance with the present invention. The specific details and construction of the bolt are best illustrated in FIGS. 10, 14 and 16, and as illustrated therein, the bolt 100 comprises a pair of elongated bar members 102 and 104 having confronting interengaging inner faces or surfaces 106 and 108 respectively of a predetermined configuration whereby upon relative axial displacement of the bar members, the members may be actuated from a stacked position (see FIG. 10) for insertion into a hole or opening 110 in the roof strata to an expanded position (see FIG. 14) wherein the opposing outer surfaces of the members are displaced laterally into pressure-applying relation with the side wall of the opening 110 in the roof strata.

To this end, the bar member 102 which may be halfmoon in cross section and of a serpentine shape, has an inner surface or face 106 of stepped configuration comprising a plurality of angularly disposed longitudinally spaced planar or fiat cam surfaces 112, each cam surface 112 terminating in a rounded edge and merging with a plurality of short angularly directed shoulders 114, each shoulder connecting adjacent cam surfaces 112. The outer surface or face 117 of the bar member 102 is also of a stepped configuration defining a plurality of longitudinally spaced projections defining contact zones Z adapted to engage the side wall of the opening 110 in the roof strata at a plurality of spaced locations. In

the present instance, as illustrated in the drawings, the

spacing between substantially all of the adjacent contact zones Z is at least equal to the largest cross sectional dimension measured in a plane perpendicular to the longitudinal axis of the bolt in the stacked position.

The bar member 104, in the present instance, is an elongated hollow member of generally U-shaped cross section having longitudinal spaced apart side edges 117a and 11717 of a stepped configuration to define a plurality of angularly disposed, longitudinally spaced fiat cam surfaces 120 and a plurality of short, angularly directed shoulders 122, each shoulder merging with adjacent cam surfaces 120 in a rounded edge and connecting adjacent cam surfaces 120. In the present instance, the outer face of the bar member 104 is a continuous surface defining one continuous contact Zone Z extending the length of the bar member 104. The cam surfaces 112 and of the bar members are approximately of equal length so that the bar members nest snugly together when in stacked position shown in FIG. 10. As illustrated, the cam surfaces 112 and 120 are disposed at a slight angle to the longitudinal axis of the bolt and the shoulders 114 and 122 seat against one another in the stacked position to limit relative longitudinal movement of the bar members in one direction.

The bar members are adapted for relative longitudinal movement between a stacked or closed position and an expanded position and in the stacked position the maximum cross sectional dimension D' of the bolt or the distance between the contact zones Z and Z at any point along the length of the bolt is smaller to facilitate insertion into the hole 110 of the roof strata. In the expanded position, the contact zones are displaced latera ly due to interengagement of the cam surfaces to a distance apart greater than D. This means for effecting longitudinal movement of the bars includes, in the present instance, a threaded shank 127 depending from the lower terminal end of the bar member 104 which is of a cross section smaller than the outer cross section of the bar member to define an abutment shoulder 129 adjacent its lower end. The bar member 102 has a depending stem 130 which in the stacked position of the bar members projects downwardly beyond the shoulder 129 so that its lower end is spaced from the terminal end of the shank to expose a portion of the threaded shank 127 to accommodate a plate 132 and nut 134.

In the installation of bolt of the type described above, the bar members 102 and 104 are initially in the stacked position shown in FIG. 10, being held in that position by means of strips of tape at longitudinally spaced points. It is noted that the bolt is delivered to the mine site in this condition thereby obviating the need for any time-consuming assembly operation. Furthermore, the assembly is comparatively light thereby facilitating handling in the mines. In its stacked position, the bolt is then inserted up into the opening 110 in the mine roof, the opening 110 being of a slightly greater cross sectional dimension than the greatest cross section D between the contact zones Z and Z With the bolt so positioned, the nut 134 is turned to effect relative longitudinal displacement of the bar members. This longitudinal displacement effects lateral displacement of the contact zones Z and Z due to the interaction of the cam surfaces 112 and 120 whereby the side wall of the opening is engaged at a plurality of longitudinally spaced points of the bar member 102 and the contact zone Z of the other bar member 104 engages the side wall of the other opening along its entire length. By this arrangement, when a series of bolts is installed in the roof at a plurality of predetermined spaced apart locations, the layers of the roof strata are pre-stressed in a lateral direction for a substantial height above the roof level whereby the compression and tension components of shear stress in the layers are supported It is noted that this bolt arrangement provides for a large gripping area. Furthermore, bolt elongation is minimized due to the continuous area of contact between the bolt and the wall of the hole. Thus, forces developing between adjacent layers of strata are supported by relatively short length of bolt and elastic elongation is therefore minimal. The bolts may be removed from the mine when desired simply by threading down the nut 134 and tapping the free terminal end of the shank 127 whereby the bars are urged to a stacked position. It is noted that if an elastic tape is used, the tape retains the bar members in the stacked position when removed from the roof to facilitate reuse. The specific configuration of the mine roof bolt shown in FIGS. 10-17 inclusive and more particularly the provision of the tubular bar member 104, minimize the possibility of flattening out of the confronting cam surfaces accordian-style which would tend to reduce the effective gripping force of the mine roof bolt when assembled in an opening in the roof of a mine. This construction also minimizes bolt elongation, which, as noted above, is an important factor contributing to failure of the roof.

Another feature of the present invention is the provision of a simple and economical means for manufacturing a mine roof bolt of the type illustrated in FIGS. l6. In accordance with the present invention, the bar member 104 may be formed by bending an elongated fiat strip having a predetermined, irregular side edge configuration to a generally U-shape or semi-circular cross section so that the side edge portiton defines the cam surface and shoulders. In the preferred method of the present invention the bar member 104 may be formed from flat sheet stock by cutting the sheet into a plurality of strips having the desired edge configuration to define the cam surfaces and shoulders. Thereafter, each individual fiat strip is formed, for example, by a rolling process to the U-shaped configuration as shown in FIG. 16, the continuous rolled strip then being cut to size by suitable means. The other bar member 102 may be formed from a continuous piece of bar stock having a half-moon cross section by a bending operation in a cold forge press or a joggle mill to define the configuration shown having the series of adjacent angularly disposed cam surfaces. Alternatively, the bar stock may be of a rectangular or square cross section and formed to the serpentine shape shown in FIG. 23 in a hot press operation. This zig-zag or serpentine piece of bar stock is then suitably cut to size and assembled to the other bar member and held thereto by means, for example by a series of adhesive strips. The bolt is now ready for use. -It is noted that, as mentioned above, the adhesive may be an elastic type so that when the bolt is used in a mine roof, the adhesive does not sever and remains in place when the bolt should be removed from the hole in the mine roof for reuse.

There is shown schematically in FIG. 18 a method for making and assembling a mine roof bolt in accordance with the present invention. As illustrated therein, there are two separate assembly lines A and B for making the respective bar members 104 and 102 of the roof bolt. 'In line A, flat sheet stock 150 is fed to a cutting device 152 such as a torch, plasma, or laser cutting apparatus or a plurality of cooperating disc-like cutting knives to cut the sheet 150 longitudinally into a plurality of side by side strips 154 having a serpentine or corrugated side edge configuration to define the cam surfaces 120 and connecting shoulders 122 when the strip is rolled. The strips 154 are then taken up on a plurality of take up rolls at a storage or recoiler station 156, the roll assembly being mounted on trackways so that a selected roll may be positioned in registry with the remainder of the stations in line A. It is noted that the direction of feed from the storage rolls for alternate strips has to be reversed for proper orientation at a later time at the assembly station with the other bar member.

As a strip 154 is wound from the storage roll, it passes through an uncoiling device 158 and a leveler 160 to a prenotch press 162, where, as illustrated in FIG. 19, the strip 154 is cut part way through transversely to its axis at predetermined spaced apart intervals which define the length of the bar. The strip 154 is then formed into a circular cross section of generally U-shaped configuration in a roll forming mill 164 and from there, the rolled up strip 154 passes through the cutoff press 166 where the rolled up strip is severed at the prenotched points to form the bar member 104. The threaded stud 127 is then assembled to each of the individual bar members 104 at an automatic welding station 170.

The bar member 102 of the bolt is formed on line B in FIG. 18 and as illustrated therein, a continuous piece of stock 172 of half-moon cross section is fed through an uncoiler 174 to a leveler 176 and then is fed into a joggle mill 178. In the joggle mill 178, the flat bar stock 172 is deformed by suitable means to the serpentine configuration illustrated in FIG. 18. The so deformed bar leaves the joggle mill and passes through a cutoff press 180 where the bar is cut into suitable lengths and one end of the bar is straightened out to define the stem. The completed bar is then transferred to the automatic assembling station 182 where it is mated with a bar 104 and the tape 135 is applied at preselected points so that the finished assembly is ready for use.

From the above, it is readily apparent that the present invention provides a comparatively simple and highly economical method for manufacturing mine roof bolts. By this method of the present invention there is comparatively little waste since no machining operations are required to produce the bolt. Further, substantially all of the manufacturing and assembly operations may be carried out on automatic equipment thereby reducing labor costs. Even though the preferred material for making the bolt is steel, other materials such as other metals or fiberglass reinforced plastic may be used.

While the bolt of the present invention is primarily used in mines for supporting the roof of the mine, it is to be understood that it may be used effectively in other underground passageways to support the overlying strata. Additionally, the bolt has other useful applications, for example, in certain road excavation operations the bolt may be used to prevent rock slides.

There is illustrated in FIG. 25 another method for making and assembling a mine roof bolt in accordance with the present invention. As illustrated therein there are two separate assembly lines, line A for making the bar member 104 and line B for making the bar member 102.

Considering first the line A for making the bar member 104, flat sheet stock 250 is fed by means of feed rolls 251 continuously to a cutting device 252. In the present instance, the width W of sheet material 250 is approximately equal to the finished length of the bar member 104 so that strips 254 are formed as the sheet stock is passed widthwise through the cutting device. The cutting device 252 which may, for example, be a die cutting press having an even number of spaced, side by side cutting edges 255 of such configuratiton to produce serpentine-like side edges 253 on each strip 254, one side edge being the mirror image of the other. The cutting device may also comprise a torch, plasma, or laser cutting means to cut strips 254 having a serpentine or corrugated side edge configuration defining the cam surfaces and connecting shoulders 122 of the finished bar member 104. It is noted that in the present instance, the cutting apparatus cuts the strip material so that the cut between adjacent ones of the strips 254 defines two side edges and adjacent strips are oriented in opposite directions. This provides for simplicity of operation, insures a high production technique or process and minimizes waste. Accordingly, as the strips 254 are discharged from the die cutting press, an orientor 256 is provided which orients the strips 254 so that they are all facing in the same direction before entry into a forming device 258 such as a roll form mill or forge press. -In the forming device 258, the strips 254 are bent to a semi-circular or U-shaped cross section and from there, the rolled bar member is fed to an automatic welder 270 where the stud 127 is applied. The finished bar member 104 then moves on to an automatic assembly, packaging and bundling station 282 where the other bar member 102 of each assembly is assembled and the tape 235 applied at preselected points so that the finished bolt assembly is ready for use.

The bar member 102 of the bolt is formed in line B. As illustrated therein, a continuous piece of bar stock 272 of half-moon cross section or of any other desirable cross section is fed to an uncoiler 274, then to a leveler 276 and then to a means for forming the bar into a serpentine or undulating configuration. At the forming station 278 there may be provided a forge press to hot or cold work the bar stock, or even if desired a joggle mill. The so deformed bar leaves the forming station 278 and passes through a cut off press 280 where the bar is cut into suitable lengths. At the same time the bar stock is cut to the desired length, one end of the bar is straightened out to define the stem of the bar member 102. The finished bar is then transferred to the automatic assembling station 282 where, as noted above, it is mated with a bar member 104 and tape 135 is applied.

While particular embodiments of the present invention have been illustrated and described herein, it is not intended to limit the invention and changes and modifications may be made therein within the scope of the following claims. For example, the coefiicient of friction between one or both the bar members and the Wall of the opening in the mine roof may be increased by roughening the surfaces of the bar members confronting and engaging the wall of the hole, for example, by knurling, ridging or other suitable roughening means. Additionally, the internal friction between the confronting cam surfaces of the bar members may be reduced by suitable permanently applied lubricant means to the cam surfaces.

Iclaim:

1. A method for making one of the bar members of a mine roof bolt comprising a pair of elongated bar members having inner confronting longitudinally extending surfaces with a plurality of cooperating cam surfaces thereon consisting of the steps of forming a plurality of elongated fiat strips from sheet material by simultaneously severing the sheet material along at least a pair of spaced serpentine lines whereby adjacent lines so formed are mirror images of one another and define the opposite side edges of at least one strip, the side edge of each strip consisting of a series of uniformly spaced apart first edge sections angularly disposed at a slight angle to the longitudinal axis of the strip and a plurality of shoulder edge sections connecting adjacent side edge sections extending at a greater angle to the longitudinal axis of the bolt, bending the strip to form it into an elongated hollow member of generally Ushaped configuration so that the first side edge sections are spaced apart and define the cam surfaces of one of said bar members, and assembling a stud member at one terminal end of each strip.

2. A method as claimed in claim 1 wherein the first edge sections of adjacent strips are facing in opposite directions and including the step of orienting the strips so that the first edge sections are facing in the same direction.

3. A method for making one of the bar members of a mine roof bolt comprising a pair of elongated bar members having inner confronting longitudinally extending surfaces with a plurality of cooperating cam surfaces thereon consisting of the steps of dividing a fiat sheet of material lengthwise into a plurality of strips by simultaneously severing the sheet material along at least a pair of spaced serpentine lines whereby adjacent lines so formed are mirror images of one another and define the opposite side edges of at least one strip, the side edge of each strip consisting of a series of uniformly spaced apart first edge sections angularly disposed at a slight angle to the longitudinal axis of the strip and a plurality of shoulder edge sections connecting adjacent side edge sections extending at a greater angle to the longitudinal axis of the strip, forming each strip into an elongated hollow member of generally U-shaped configuration so that the first side edge sections are spaced apart and define the cam surfaces of one of said bar members, separating the so-formed strip into a plurality of sections of the desired length of the finished bar member, and

assembling a stud member at one terminal end of each strip.

4. A method as claimed in claim 3 including the step of winding each cut strip into a coil after cutting thereof and thereafter uncoiling each of said strips so that they are oriented in the same direction or formation thereof to a U-shaped cross section.

5. A method as claimed in claim 4 including the step of leveling the strip after uncoiling thereof and prenotching the strip at a plurality of spaced locations prior to formation thereo to a U-shaped cross section.

6. A method as claimed in claim 4 including the steps of cutting the strip into section of predetermined length.

7. A method as claimed in claim 6 including the method for making the other bar member consisting of the steps of forming an elongated piece of bar stock into an undulating configuration to define a plurality of side-by-side angularly disposed cam surfaces, dividing the so formed bar stock at a plurality of spaced points to a desired length assembling the bar members in confronting overlying relation by applying a plurality of adhesive strips at selected locations.

8. A method for making one of the bar members of a mine roof bolt comprising a pair of elongated bar members having inner confronting longitudinally extending surfaces with a plurality of cooperating cam surfaces thereon consisting of the steps of dividing a fiat sheet of material widthwise into a plurality of strips by simultaneously severing the sheet material along at least a pair of spaced serpentine lines whereby adjacent lines so formed are mirror images of one another and define the opposite side edges of at least one strip, the opposite side edges of each strip consisting of a series of uniformly spaced apart first edge sections angularly disposed at a slight angle to the longitudinal axis of the strip and a plurality of shoulder edge sections connecting adjacent side edge sections extending at a greater angle to the longitudinal axis of the bolt, forming each strip into an elongated hollow member of generally} U-shaped configuration so that the first side edge sections thereof are spaced apart and define the cam surfaces of one of said bar members, and assembling a stud member at one terminal end of each strip.

9. A system for making one of the bar members of a mine roof bolt comprising a pair of elongated bar members having inner confronting longitudinally extending surfaces with a plurality of cooperating cam surfaces thereon from a flat sheet material comprising means for feeding the sheet material to a cutting device, a cutting device for dividing the sheet material into a plurality of elongated strips having cutting means for simultaneously severing the sheet material along at least a pair of spaced serpentine lines whereby adjacent lines so formed are mirror images of one another and define the opposite side edges of at least one strip, the opposite side edges of each strip consisting of a series of uniformly spaced apart first edge sections angularly disposed at a slight angle to the longitudinal axis of the strip and a plurality of shoulder edge sections connecting adjacent side edge sections extending at a greater angle to the longitudinal axis of the bolt, means for forming the strip into an elongated hollow member of generally U-shaped configuration so that the first side edge sections thereof are spaced apart and define the cam surfaces of one of the bar members, and means for assembling a stud member at one terminal end of the U-shaped elongated member.

10. A system as claimed in claim 9 wherein said cutting device includes a plurality of even-numbered serpentine cutting edges adjacent cutting edgesbeing mirror images of one another.

References Cited (Other references on following page) 13 UNITED STATES PATENTS Kenehan 72--379 Kennedy 8579 Bradley 164382 Rosner 72379 Morgan 83241 Goetze 113116 CHARLES W. LANHAM, Primary Examiner 5 E. M. COMBS, Assistant Examiner US. Cl. X.R.

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