US3478523A - Mine roof bolt bearing plate - Google Patents

Description

Nov. 18, 1969 H. E. REUSSER ET AL 3,478,523

MINE ROOF BOLT BEARING PLATE Filed Feb. 16, 1968 INVENTORS HANS E. REUSSBR. MoRsE- HILL.

ATTORNEY United States Patent US. CI. 6145 7 Claims ABSTRACT OF THE DISCLOSURE A mine roof bearing member including, a plate having a substantially straight peripheral flange and a central conical frustum provided with an opening the circular wall of which comprises a spherical seat adjacent the plate bottom and an axially extending socket edge adjacent the plate top.

This invention relates generally to mine roof bolt bearing plates and more particularly to mine roof plates of relatively small size intended to be used to cover localized surfaces within subterranean areas such as a mine roof, as opposed to larger forms of plates as utilized to completely cover extensive portions of a mine roof.

The invention has particular application in mines, tunnels, rock cuts and other excavated locations to bind together the various rocks strata so as to stabilize the rock formation and to prevent collapse thereof. The plates are intended to be used together with a rock bolt having a conventional bolt anchoring device mounted on its inner end which is disposed within a hole bored in the rock, whereupon tightening of the bolt applies a tension thereto which is transmitted to the roof plate to retain the various rock strata in compression.

In accordance With the present invention a shallow dish bearing plate is provided having the desirable feature of a low silhouette, while at the same time providing for a high load capacity with a minimum of plate material thickness. The US. Bureau of Mines, in considering forthcoming specifications relating to mine roof plates, has intimated that one of the most important features of a mine roof plate is its ability to resist axial deflection when it is fully bolt loaded. Tests have been conducted in an effort to I establish a minimum plate rigidity, whereby rectangular mine roof plates have been positioned over a 4" diameter opening and bolt loaded from 6,000 to 15,000 pounds with the resultant deflection being noted. The 4" diameter figure has been selected as this area has been considered torepresent the crumbling loss in the bearing area with loads concentrated adjacent to a bolt hole drilled in a mine roof. Presently, to confirm that the roof plate is of suflicient rigidity, it has been determined that the aforementioned deflection of the plate as it is bolt loaded from 6,000 to 15,000 pounds should be no greater than 0.120 inch. The preceding objective is achieved by means of the present invention which includes a preferably rectangular mine roof plate, which when subjected to a bolt loading at a pressure of not greater than 6,000 pounds, includes an outer flange which is completely flattened out beyond a 4" diameter central dished portion.

Accordingly, one of the objects of the present invention is to provide an improved shallow dish mine roof bolt bearing plate having a low silhouette and a greater load capacity than prior known plate forms of no higher silhouette when plate material strength and thickness are equivalent.

Another object of present invention is to provide a mine roof plate including a flattened peripheral flange and a central conical portion, which latter portion when loaded from 6,000 to 15,000 pounds undergoes a minimum of axial deflection.

3,478,523 Patented Nov. 18, 1969 A further object of the present invention is to provide a mine roof plate having a central conical frustum portion provided with a spherical seat whereby axial bolt loading pressure is transformed into inclined radial compressive stress directed to the flange of the plate.

With these and other objects in view which will more readily appear as the nature of the invention is better understood, the invention consists in the novel construction, combination and arrangement of parts hereinafter more fully described, illustrated and claimed.

A preferred and practical embodiment of the invention is shown in the accompanying drawing, in which:

FIGURE 1 is a bottom plan view of a mine roof bolt bearing plate according to the present invention.

FIGURE 2 is an elevational view, partly in section, showing the roof plate and a bolt fastener after the installation and application of final bolt loading.

FIGURE 3 is an elevational view, partly in section, showing the mine roof plate and a bolt fastener after the initial installation and prior to the application of any bolt loading pressure.

FIGURE 4 is an enlarged fragmentary sectional view of the plate socket as shown in FIGURE 2.

Similar reference characters designate corresponding parts throughout the several figures ofthe drawing.

The mine roof support plate, generally designated P. is preferably of square construction and is provided with a centrally disposed circular bolt opening 1, as well be most clearly seen in FIGURE 1 of the drawing. Alternatively a circular or other shape of plate may be used in connection with the present invention.

Attempts have been made in the past to provide mine roof plates having a low silhouette form in relatively thin material and likewise there are many known examples of mine roof plates exhibiting high strength or rigidity under bolt loading by means of deep dishing or excessive material thickness; however the present invention is believed to be the first practical solution providing a shallow dish mine roof plate of relatively thin material having both a low silhouette and at the same time a high load capacity with a minimum axial deflection during loading thereof. Several features of construction in the instant roof plate cooperate to provide the novel results of the present inventon. The dish portion D of the plate P is formed within the inner face thereof as a result of a conical frustum 2 on the outer face of the plate surrounding the bolt opening 1 and having a height of preferably not more than twice the plate material thickness, the radial extent of which comprises a substantial portion of the overall area of the plate. Extending from the sharply defined outer circumference 2a of the conical frustum 2 is a peripheral flange portion 3, which terminates in the outer edge 4 of the plate. This flange 3 will be seen to comprise a relatively straight surface both prior to application of bolt pressure, at which time it is preferably slightly concave in bearing, and after bolt loading, whereupon it assumes a horizontal disposition.

Referring now more particularly to FIGURES 2 and 3, it will be seen that the area of the plate P which immediately surrounds and thereb forms the bolt opening 1, comprises two intersecting circular surfaces. An angularly disposed spherical seat or socket 5 is formed adjacent the bottom or outer face 6 of the plate and intersects an axially disposed inner socket edge 7 disposed adjacent the top or inner face 8 of the plate P at the bottom of the dish D. The axial extent of the peripheral surface 7 should be no greater than one-fourth the plate material thickness. The spherical seat 5 is formed with a concavity to mate with the juxtaposed spherical surface 9 of a bolt fastener 10 when the mine roof plate P is fully loaded as in FIG- URE 2. Prior to the application of any significant tension by means of the bolt fastener 10 to the mine roof plate, it

will be seen that a clearance 11 exists between the spherical seat of the plate and the spherical surface 9 of the bolt head 12, as shown in FIGURE 3.

A socket perimeter 13 extends radially from the bottom edge of the spherical seat 5 and comprises a flat horizontal surface, the radial dimension of which is preferably less than the plate thickness, for reasons which will be apparent hereinafter.

The present construction provides a plate-stiflening arrangement which heretofore has not been achieved in a low silhouette mine roof plate and, as a result of using the instant device, a noticeable improvement in mine safety will be apparent. In applying the present mine roof plate P against a roof strata 14, the top 8 of the plate is disposed adjacent the lower roof surface 15 with the bolt opening 1 aligned with a prepared mine roof hole 16, as shown in FIGURE 3. The bolt fastener has been inserted through plate opening 1 intothe mine roof hole 16 and includes at its inner end a suitable expandable bolt anchor device 10a which is actuated by rotation of the bolt fastener 10 by means of a tool which may be inserted within the polygonal recess 17 in the face of the bolt head 12. During the above assembly operation the inner end of the bolt may be passed through the bolt opening 1 with the unexpanded anchoring device mounted thereon.

The curvature of the spherical surface 9 of the bolt head 12 matches that of the spherical seat or socket 5 of the mine roof plate so that when the plate is fully assembled, as in FIGURE 2 of the drawing, a pivotal connection is achieved without loss in contact area between the bolt head and the mine roof plate, to accommodate with no bending stress on the bolt any angular disposition of the shank of the bolt fastener 10 and the horizontal plane of the mine roof plate, such as would occur whenever the plane of the roof surface and the center axis of the mine roof hole 16 were disposed at any angle other than 90 degrees with respect to one another.

Referring back to the initial placement of the plate and bolt fastener, as shown in FIGURE 3, only portions of the outer edge 4 of the plate engage the exposed roof surface 15. It will be seen that as the bolt fastener 10 is initially tightened a resultant axial movement of the shank of the bolt fastener upwardly into the mine roof hole 16 transmits a compressive force in an angular and radial direction from the spherical surface 9 of the bolt head through the spherical seat 5 of the mine roof plate. The aforedescribed initial tension applied by the bolt fastener 10 is transmitted practically in its entirely to the peripheral flange 3 of the roof plate, causing this flange 0 to be flattened to the position shown in FIGURE 2. During this flattening of the peripheral flange 3 of the plate, which is achieved prior to a loading of 6,000 pounds upon the bolt 10, it is important to appreciate that substantially no deflection takes place in the area of the conical frustum 2 of the mine roof plate and that this area 2 is merely axially displaced upwardly substantially an amount equal to the depth of initial concavity between extremities of flange 3 and intersecting conical circumference 2a.

In view of the above described condition, it will be understood that the axial depth as well as the radical width of the dished portion D of the plate top 8 has remained substantially unchanged. During the final tightening of the bolt fastener 10 as the loading is increased from 6,000 pounds to, say, 15,000 pounds, substantially all of this loading will be transmitted as a compressive force extending angularly and radially from the face of the spherical surface 9 of the bolt head through the material forming the conical frustum 2 and into the flattened peripheral flange portion 3, whereby the subsequent overall axial deflection of the mine roof plate will be less than 0.120" and will still appear as shown in FIGURE 2 of the drawing.

As previously mentioned, the flat horizontal socket perimeter 13 which intersects the outer edge of the spherical seat 5, on the one hand, and joins with the sloping wall of the conical frustum 2, on the other, includes a radial dimension which is no greater than the thickness of the plate P itself. This construction, together with another about-to-be described feature, insures a maximum rigidity being imparted to the plate with a minimum of axial deflection during bolt loading thereof. It has been found that the axial length of the inner socket edge 7 should be no greater than one-fourth the thickness of the plate P to allow for enough spherical area in seat 5 to properly contact bolt head surface 9. The foregoing arrangement permits the transformation of axial bolt loadings into conically inclined radial compressive stresses which are directed to and restrained by the peripheral flange portions 3 of the plate, and thus precludes the excessive deflection or callapse of the central conical frustum 2 of the plate during its installation.

We claim:

1. A mine roof bolt bearing member, comprising, a plate having top and bottom surfaces and including a pcripheral flange, a conical frustum portion in the center of said plate extending downwardly from said bottom surface and including a bolt opening therethrough, a dish area formed on the top surface of said conical frustum portion radially projecting to said flange and adapted to be placed in juxtaposed relationship to a roof surface provided with a roof hole, said conical frustum portion including a horizontal socket perimeter on said bottom surface adjacent said bolt opening, the periphery of said bolt opening through said conical frustum portion including a female spherical seat the outer edge of which intersects said horizontal socket perimeter, the periphery of said bolt opening also including an inner socket edge extending axially from said spherical seat to said top surface in said dish area, whereby, upward pressure exerted by means of a spherically headed bolt extending into said roof hole and engaging said plate at said spherical seat flattens said flange against the roof surface with negligible axial deflection of said frustum portion.

2. A mine roof bolt bearing member according to claim 1, wherein said plate comprises a constant thickness material throughout.

3. A mine roof bolt bearing member according to claim 1, wherein, said horizontal socket perimeter extelnds radially a distance less than the thickness of said p ate.

4. A mine roof bolt bearing member according to claim 1, wherein, the axial depth of said inner socket edge is no greater than one-fourth the thickness of said plate.

5. A mine roof bolt bearing member according to claim 1, wherein, the height of said conical frustum is no greater than twice the thickness of said plate.

6. In a mine roof bearing assembly including a plate, bolt and anchor, said plate having top and bottom surfaces and including a peripheral flange, a conical frustum portion in the center of said plate extending downwardly from said bottom surface and including a bolt opening therethrough, a dish area formed on the top surface of said conical frustum portion radially projecting to said flange and adapted to be placed in juxtaposed relationship to a roof surface provided with a roof hole, said conical frustum portion including a horizontal socket perimeter on said bottom surface adjacent said bolt opening, the periphery of said bolt opening through said conical frustum portion including a female spherical seat the outer edge of which intersects said horizontal socket perimeter, the periphery of said bolt opening also including an inner socket edge extending axially from said spherical seat to said top surface in said dish area, whereby, upward pressure exerted by means of said bolt extending into said roof hole and engaging said plate at said spherical seat flattens said flange against the roof surface with negligible axial deflection of said frustum portion.

7. In a mine roof bearing assembly including a plate and bolt, said plate having top and bottom surfaces and including a peripheral flange, a conical frustum portion in the center of said plate extending downwardly from said bottom surface and including a bolt opening therethrough, a dish area formed on the top surface 'of said conical frustum portion radially projecting to said flange and adapted to be placed in juxtaposed relationship to a roof surface provided with a roof hole, said conical frustum portion including a horizontal socket perimeter on said bottom surface adjacent said bolt opening, the periphery of said bolt opening through said conical frustum portion including a female spherical seat the outer edge of which intersects said horizontal socket perimeter, the periphery of said bolt opening also including an inner socket edge extending axially from said spherical seat to said top surface in said dish area, whereby, upward pressure exerted by means of said bolt extending into said roof hole and engaging said plate at said spherical seat flattens said flange against the roof surface with negligible axial deflection of said frustum portion.

References Cited UNITED STATES PATENTS 2,748,594 6/1956 Edwards 6145 X 3,385,155 5/1968 Michell 85-62 FOREIGN PATENTS 375,314 2/1964 Switzerland. 405,204 1/ 1966 Switzerland.

JACOB SHAPIRO, Primary Examiner US. Cl. X.R.

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