An excavation tunnel is commonly made in the side of a mountain or hill for the purpose of mining coal or removing other ore therefrom. To prevent the tunnel's roof from collapsing, mine roof bolt assemblies are typically installed throughout the mine. Such an assembly can include a bolt, a bearing plate, and a washer.
A mine roof bolt assembly is adapted to insure the integrity of a bolt flange, to compensate for tilted bore installations, to increase bearing-plate yields, to boost overall system play, to guard against cut-edge contact, to accommodate loose (but customary) bolt-manufacturing tolerances, and/or to protect against bolt bending.
Referring now to the drawings, and initially to
Each bolt assembly 10 is installed in the tunnel 11 by first drilling a bore 13 upwardly through the roof 12. An elongated member of the bolt assembly 10 (namely a shaft 21, introduced below) is then inserted into the bore 13 and anchored thereto. The relevant rock formation will commonly comprise a series of strata and the bolt assemblies 10 bind adjacent strata together.
Referring to
The bolt 20 also includes a head 22 connected to the lower end of the shaft 21, a flange 23 extending radially outward from the head 22, and a ledge 24 formed by the upper side of the flange 23. The bearing plate 30 has an upper roof-contacting face 32 and a lower washer-contacting face 33. The washer 40 is situated between the flange 23 and the plate 30.
The washer 40 comprises an elbow 42, a radially inner portion 43 extending upward from the elbow 42, and a radially outer portion 44 sloping upward from the elbow 42. The elbow 42 engages the bolt's ledge 24, the inner portion 43 surrounds the axial opening 41, and the outer portion 44 contacts the lower face 33 of the bearing plate 30. As is explained in more detail below, the arrangement helps to insure the integrity of the bolt's flange 23.
Referring to
The bolt ledge 24 has a podium section 25 and a plank section 26 extending radially outward therefrom. The podium section 25 corresponds to an area extending from a diameter axially aligned with the shaft diameter Dshaft to a diameter axially aligned with the head diameter Dhead. The plank section 26 corresponds to an area extending from a diameter axially aligned with the bolt diameter Dhead to a diameter axially aligned with the ledge diameter Dledge. As can be seen by referring briefly back to
While the illustrated bolt 20 is formed in one piece, this need not be the case. The shaft 21, the head 22, and/or the flange 23 could be separate parts. Additionally or alternatively, one or more of the individual parts 21-23 parts could itself comprise plural pieces. And the assembly of these parts/pieces could occur before, during, or after installation of the bolt assembly 10.
Although the drawings may seem to imply that the bolts 20 have clean and sharp silhouettes, this probably does not accurately reflect reality. Economic roof bolt manufacture is almost synonymous with generous tolerances, whereby bolts 20 are much more likely to have patchy profiles similar to those represented by the dashed lines shown in
Referring now to
The illustrated plate 30 has a square perimeter but other shapes (e.g., circular, rectangular, etc.) are possible and contemplated. In any event, the plate 30 can have a width Wplate that is at least three/five/ten times greater than the shaft diameter Dshaft. The plate width Wplate can be, for example, between about 100 mm and about 200 mm.
The bearing plate 30 comprises a central region 34 surrounding the aperture 31 and a peripheral region 35 surrounding the central region 34. In the plate 30 shown in
The plate's aperture 31 can be viewed as being formed by a rim 36 including a shaft-surrounding wall 37. The illustrated flat bearing plate 30 can be made by stamping the aperture 31 in the central region 34. If so, the edge 38 of the rim 36 will also be its shaft-surrounding wall 37. And the thickness Trim of the plate's rim 36 will be the same as the thickness Tplate of its peripheral region 35.
Referring now to
The washer 40 can have a width Wwasher that is less than the plate width Wplate and/or greater than the ledge diameter Dledge. For example, the washer width Wwasher can be between 50 mm and 100 mm. The washer's radially outer portion 44 can be at least 1.2/1.5/2.0 times wider than the washer's radially inner portion 43. The inner portion 42 extends upward from the elbow 42 at a generally acute angle ex and the radially outer portion slopes upward from the elbow at a generally acute angle.
The radially inner portion 44 comprises a lip 46 having a shaft-surrounding wall 47 and a cut edge 48 that is skewed relative to the shaft 21 (i.e., it does face the shaft 21). The washer 40 is preferably produced so that the wall 47 is an extruded cylindrical surface. Specifically, for example, a hole (with a diameter less than the intended opening diameter Dopening of the washer 40) is stamped in a metal sheet. Thereafter an extruding post (having a diameter corresponding to the intended opening diameter Dopening of the washer 40) is protruded axially through the hole whereby the material encircling the hole forms the lip 46. With such an extrusion step, the lip 46 will have a thickness Tlip that is less than the thickness Twasher of the washer's outer portion 44.
As is shown schematically in
Turning now to
Also, the upward angle of the inner radially portion 43 results in a clearance corner being created around the shaft 21. Such clearance allows the washer 40 to be suitable with a spectrum of shaft-to-ledge transition tapers. (As was explained, rough rather than sharp corners are typical in economically manufactured bolts). For this same reason, the angled arrangement of both the inner washer portion 43 and the outer washer portion is conducive to the accommodation of rough ledge landscapes.
Additionally, the washer design affords devised deformation that contributes to overall system movement. As is best seen by comparing
Furthermore, the cut edge 48 of the washer 40, both before and after deformation, remains skew relative to the shaft 21. If the lip 46 were to contact the shaft 21, the extruded surface 27 would play the touching role and acts as a bearing during shaft rotation. In contrast, a cut edge (such as edge 48) in the same position would be act as a scoring mechanism during rotation of the shaft 21, thereby essentially creating a weakened seam in this very vulnerable district of the bolt 20.
In
When the bolt assembly 10 is used in a tilted-bore situation, the elbow 42 can still engage the ledge 24 inboard thereby reducing strain on the flange 23. Also, it is the extruded surface 27 of the washer 40 that contacts the shaft 21 thereby greatly reducing stress riser. And, as shown in
Another possible version of the plate 30 is shown in
With the plate 30 shown in
As seen in
Turning now to
The domed bearing plate 30 shown in
As shown in
One may now appreciate that the mine roof bolt assembly 10 is adapted to insure bolt-flange integrity, to compensate for tilted bore installations, to fortify bearing-plate yields, to enhance overall movement capacity, to guard against shaft-scoring caused by cut-edge contact, to accommodate loose (but customary) bolt-manufacturing tolerances, and/or to protect against bolt bending.
This application claims priority under 35 U.S.C. 119 to U.S. Provisional Patent Application No. 61/453,700 filed on Mar. 17, 2011. The entire disclosure of this provisional patent application is hereby incorporated by reference.
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Number | Date | Country | |
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20140099167 A1 | Apr 2014 | US |
Number | Date | Country | |
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61453700 | Mar 2011 | US |