MINE ROOF REINFORCING SYSTEM AS LOAD INDICATOR

Abstract

A component and method for evaluating load at a mine roof. An embossed bearing plate and a reinforcing washer are combined to thereby form a bearing system, wherein the bearing plate is a grade 2 plate (“x−1”), the bearing plate including a back surface which is adapted to contact a mine roof, an opposite surface and an aperture through which a shaft portion of a bolt can extend, the reinforcing washer including a rigid member having a first surface shaped to contact and complement the opposite surface of the bearing plate, a second opposing surface and a washer hole for alignment with the aperture through which the shaft can extend; driving a bolt with the shaft through the bearing system into a location of the mine roof, and, inspecting a curl of the grade 2 plate, wherein the curl and uniformity thereof is indicative of a load of around 20,000 pounds at the location.

Description

FIELD OF THE INVENTION

The invention relates to components and methods of indicating load within mine roofs, walls or ribs. More particularly, a combination bearing plate and reinforcing washer is used to contact and support a mine roof and is adapted to be used as a load indicator, revealing load upon the application of a particular tensile stress.

BACKGROUND OF THE INVENTION

Systems exist to support mine roofs, ribs and walls during work within mine tunnels. Of course, under excess loads one or more of the anchors may break off or naturally deform, or the supports themselves have load-indicating characteristics revealed prior to failure. For example, U.S. Pat. No. 3,161,174 to Harrison teaches a visual indicator including a metal tab that bends in response to tensile strength. In other words, in the preparation of a mine tunnel for mining operations it is a common practice to reinforce the formation of rock above the mine roof. Conventional practice calls for drilling holes in the mine roof and inserting bolts in the order of six feet or more in length into these holes. The bolts have an expansible anchor means on the end thereof inserted into the drilled hole and are provided with a mounting plate which abuts against the mine roof. The bolt head is rotated, causing expansion of the anchor means against the interior of the drilled hole. Tension is imparted to the bolt by drawing up the bolt head in tight abutment with the lower surface of the mounting plate.

So specialized components of the anchor can reveal excess load. The systems themselves, while still intact under the stresses, can show excess load. As another example, U.S. Pat. No. 11,105,199 to Locotos describes the use of rods traveling across the face of a mine wall which would bend in response to load, while also still concurrently supporting the load.

U.S. Pat. No. 4,708,559 to Locotos teaches a combination bearing plate and reinforcing washer, which together form a Grade 3 dome that can support a mine roof load of approximately 30,000 pounds. In contrast, a plate with a spherical washer typically underperforms, as would a grade 2 plate.

It has been discovered through experimentation that the device of U.S. Pat. No. 4,708,559, while traditionally used as a reinforced anchoring system, also includes load-indicating characteristics when used with a lower grade plate, such as a Grade 2 plate, as follows.

SUMMARY OF THE INVENTION

Described is a component and process for indicating load using a mine roof reinforcing washer and bearing plate. Comprehended is a component for a mine roof bolt system, comprising: an embossed bearing plate, wherein the bearing plate is a lower grade plate “x−1” such as grade 2 plate, as compared to a grade 3 plate “x”, the bearing plate including a back surface which is adapted to contact a mine roof, an opposite surface and an aperture through which a shaft of a bolt can extend; a reinforcing washer including a rigid member having a first surface shaped to contact and complement the opposite surface of the bearing plate, a second opposing surface and a washer hole for alignment with the aperture through which the shaft can extend; and, wherein the reinforcing washer is combined with the bearing plate, wherein, instead of the grade 2 plate failing in response to a load of around 20,000 pounds, the grade 2 plate curls uniformly in response to the load, thereby forming a load indicator for the mine roof.

In a method for evaluating load at a mine roof, the steps are comprised of: combining an embossed bearing plate and a reinforcing washer to thereby form a bearing system, wherein the bearing plate is a grade 2 plate (“x−1”), the bearing plate including aback surface which is adapted to contact a mine roof, an opposite surface and an aperture through which a shaft portion of a bolt can extend, the reinforcing washer including a rigid member having a first surface shaped to contact and complement the opposite surface of the bearing plate, a second opposing surface and a washer hole for alignment with the aperture through which the shaft can extend; driving a bolt with the shaft through the bearing system into a location of the mine roof, and, inspecting a curl of the grade 2 plate, wherein the curl and uniformity thereof is indicative of a load of around 20,000 pounds at the location.

Other features and advantages of the present invention will be apparent from the following more detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of the reinforcing washer itself.

FIG. 1a shows a perspective view of the reinforcing washer upon a grade 2 bearing plate.

FIG. 2 is a table showing bearing plate test results.

FIG. 3 shows a perspective view of the combination reinforcing washer and grade 2 bearing plate with a uniform corner curl resulting from load.

FIG. 3a shows a perspective view of a spherical washer upon a grade 3 bearing plate.

FIG. 4 is a table of wedge system test results.

FIG. 5 is a line graph of a grade 2 bearing plate with reinforcing washer and a grade 3 plate with spherical washer.

FIG. 6 shows perspective exploded view of the spherical washer and the grade 3 plate with a non-uniform corner bend.

Wherever possible, the same reference numbers will be used throughout the drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION

U.S. Pat. No. 4,708,559 ('559) is incorporated herein by reference in its entirety.

The subject washer as disclosed and claimed by '559, termed herein reinforcing washer, was used within an evaluation conducted on Mar. 8, 2022 by the Roof Control Division (RCD) at the Pittsburgh Safety and Health Technology Center's (PSHTC) Roof Support Laboratory in which the mechanical properties reinforcer washer were tested.

With reference to FIGS. 1-6, shown is a component for a mine roof bolt system, namely a reinforcer washer 6 combined with a bearing plate 1. “Component” means part of the system for stabilizing roofs, walls or ribs of mines. “System” typically would comprise the instant component, i.e. washer and plate, along with mine roof bolts having shafts (not shown) driven into the roofs of the mines. “Roof” as used herein is not meant to be limiting to only the roofs of the mines and is meant to encompass the roof, walls, ribs or any surrounding surface tunnel wall. Thus, the instant component is namely the bearing plate 1 along with the reinforcing washer 6.

The bearing plate 1 is an embossed bearing plate 1 (having a centrally raised embossment 2 as shown). Critically here, the bearing plate 1 is a grade “x−1” plate, meaning a plate with a grading of one less than a stronger plate, “x”, such as grade 2 plate (“x−1”) versus a grade 3 plate (“x”). A grade 2 bearing plate 1 (“x−1”) is the type having a strength and material thickness that passes a 20,000-pound load test over a 4-inch hole and not deflect more than about ¼″. It should be understood that this invention can apply to any “x−1” bearing plate, such a 3 or 4, wherein plate “x” would be the next higher-grade plate.

Bearing plate 1 includes a back surface 3. Back surface 3 is the surface adapted to contact the mine roof. The opposite surface 4 of bearing plate 1 therefore is the outward-facing surface which integrally transitions into embossment 2. An aperture 5 (FIG. 6, but inherently present for all plates) is defined through the bearing plate 1 (and through both surfaces 3, 4). This aperture 5 allows for the insertion of the bolts, and as such the bolts with bolt heads abut the bearing plate 1 and forces the bearing plate 1 against the mine roof, providing a supporting load thereto.

Combined for use with the bearing plate is the reinforcer washer 6, also referred to as the Donut Plate Insert (DPI) washer, which was originally designed to be used between a roof bolt and donut bearing plate to strengthen the plate's hole location where high loading and deformation occurs. Here, reinforcer washer 6 is a rigid body having a first surface shaped to contact and complement the opposite surface 4 of the bearing plate 1, a back surface 3 and a washer hole 10 for alignment with the aperture 5 through which the shaft would extend. The reinforcing washer 6 is contoured to sit flush within the bearing/donut plate's embossment 2. This unique combination provides increased strength to the plate 1 and reduces bolt pull-through in heavy ground conditions. The subject evaluation is in response to an inquiry from applicant herein about the use of the reinforcer washer as an angle-compensator.

Thus, the reinforcing washer 6 is to be combined with the bearing plate 1. “Combined” means placed over top of bearing plate (i.e., over opposite surface 4) and held flush there-against to thereby abut bearing plate 1, particularly embossment 2. It was determined, through experimentation, that, instead of the grade 2 (“x−1”) plate 1 failing in response to a load of around 20,000 pounds, the corners of the grade 2 plate curl uniformly in response to the load, thereby forming a load indicator for the mine roof. “Uniformly” as used herein means the curling occurs at all four corners of the bearing plate with generally the same curl angle. See FIG. 3 for example. Each curl angle may vary slightly of course due to conditions, but the curling does occur and appear to be visibly uniform at each corner, and as such the load appears to be dispersed across the entirety of the plate with generally symmetrical indicators numbering in four (4). In this manner, and as the tests show, the instant combination would not just break and fail at around a load of 20,000 pounds being the uniform curl happens first and is quite visible. In contrast, if the curl was not uniform, indeed not present or slightly present at only one corner, the plate 1 and washer 6 could abruptly fail. “Non-uniformity” means there is either no deformation of the plate, or there are fewer than four corners curling, which would inevitably result in a short-duration load failure, likely without sustained, visual indication. See FIG. 6 for example.

More specifically, the reinforcing washer 6 will be installed between a roof bolt and a lower grade (“x−1”), Grade 2 dome bearing plate 1, to be comparable to a Grade 3 dome plate (“x”) with a spherical washer. Again, “lower grade” means the bearing plate is one grade lower than the next higher grade, i.e. grade 2 versus grade 3, the “higher grade”, or grade 3 versus grade 4. The RCD evaluation showed that the reinforcer washer with a Grade 2 dome plate met the ASTM F432-19: Standard Specification for Roof and Rock Bolts and Accessories criteria for a higher grade, Grade 3 bearing plate, as well as outperformed a Grade 3 dome plate with a spherical washer. Therefore, the RCD would accept the underground use of the reinforcer washer with a Grade 2 dome plate in place of a spherical washer with a Grade 3 dome plate.

Again, as termed herein, a grade 2 (“x−1”) bearing plate is the type having a strength and material thickness that passes a 20,000-pound load test over a 4-inch hole and not deflect more than about ¼″. A grade 3 bearing plate (“x”) must pass a 30,000-pound load test (and same results and conditions). As also termed herein, a spherical washer is a typical, round washer being flat on one side with a slightly rounded surface on the opposite side, whereas a reinforcing washer is the type described by '559.

The reinforcing washer of '559 more specifically preferably has a 3-inch-outer diameter, 1-inch-inner diameter, and is 0.12 inches thick. The reinforcing washer 6 comprises a rigid member 7 in the form of an annular skirt portion transitioning to a substantially planar portion 34 by way of tapered annulus 38. In other words, unlike the spherical washer 12, which is dome-like, the planar portion 34 here extends downward into a slightly tapered annulus 38 which terminates in the rigid member 7. The washers 6 are marked with a depressed “D” symbol in accordance with ASTM F432-19 Section 15.9, which states “Each hardened washer shall be marked with a symbol identifying the manufacturer. Random washers may contain multiple markings. Markings shall be depressed on one face of the washer.” In accordance with ASTM F432-19 Section 10.4, the hardness of the washers should be evaluated per Test Methods F606/F606M. However, the RCD does not currently have the appropriate test apparatus needed to perform hardness testing. The reinforcer washers have been stored so they may be evaluated at a later date once the RCD has acquired the hardness test apparatus.

The reinforcer washer was proposed by applicant to be used with a Grade 2 dome plate to perform as a Grade 3 bearing plate. Therefore, the 4-inch-diameter hole test procedure was used to evaluate the washer and bearing plate combination in accordance with ASTM F432-19 Section 10.3.1.

Additionally, Frazer & Jones FSW-1 Spherical Seat Washers with Grade 3 dome plates were evaluated for comparison purposes. Ten tests were performed on the reinforcer washer 6 with Minova Grade 2 dome plates. Five tests were performed on the spherical washers with Minova Grade 3 dome plates. The test procedure consists of installing the bearing plate 1 centrally over a 4-inch-diameter hole in a uniaxial testing machine. A compressive load of 6,000 pounds was applied to the plate and washer combination via a load applicator, and displacement was then zeroed. A displacement reading was recorded at 15,000 pounds and 30,000 pounds, and the load was recorded at 0.25 inches of deflection. The components for the test setup can be seen in FIG. 2. All test results can be seen in FIG. 2, table 1.

Critically, after the above experimentation, all ten Grade 2 dome plates with a reinforcer washer met the ASTM F432-19 Section 10.3.1 criteria for a Grade 3 bearing plate. The reinforcer washer widened the loading profile onto the plate, effectively strengthening the system. Contrarily, the five Grade 3 dome plates with a spherical washer failed the criteria. It was observed that the profile of the spherical washer acted as a punch that prematurely and non-uniformly deformed the dome plate and ultimately weakened the system. A comparison of the two tested combinations can be seen in the figures.

The purpose of an angle-compensating washer is to permit bolts to be installed at a slight angle to the rock face while still maintaining the face of the bolt head perpendicular to the bolt axis. Therefore, the reinforcer washer 1 was also evaluated via the 100 wedge system test to determine if it would induce premature bolt failure in accordance with ASTM F432-19 Section 10.2, per FIG. 4. The bolts used during the evaluation were Minova's No. 6 Special Rolled Dimensions bolts. To meet the requirements of the specification, the bolt must support a load greater than the minimum yield and ultimate strength based on its grade and diameter. For the subject bolts, these loads are 26,800 and 36,125 pounds, respectively. In addition, the failure must not occur at the junction of the head and shank. The test procedure consists of installing the bolt into a uniaxial testing machine by gripping the body of the bolt and resting the bolt head, washer, and bearing plate against a 100 wedge plate. A tensile load was applied to the bolt until failure was achieved. The resulting tensile strengths are recorded at FIG. 4, Table 2. The break location for all the tests were away from the junction of the head and shank.

All 10° wedge system tests met the ASTM F432-19 requirements. However, it was observed that all tests done with a Grade 3 dome plate with spherical washer lost load around 34,000 pounds due to the plate deforming. The system would regain load once the dome compressed enough to make contact with the 100 wedge underneath. This can be observed in FIG. 5.

Additionally, the Grade 2 plate 1 with reinforcer washer 6 was observed to start to “curl” around 20,000 pounds. This can be interpreted as beneficial since it acts as a load indicator during underground applications when the system encounters excessive loading. A comparison of the two tested combinations can be seen from the figures, and FIG. 3 shows an example uniform curl.

Accordingly, the combination of the '559 Reinforcer Washer and a Grade 2 dome plate were evaluated as a Grade 3 bearing plate in accordance with ASTM F432-19 “Standard Specification for Roof and Rock Bolts and Accessories” by means of the 4-inch-hole test and 10° wedge system test. The RCD evaluation showed that the reinforcer washer-plate combination met the ASTM criteria for a Grade 3 bearing plate, as well as outperformed a Grade 3 dome plate with a spherical washer. Critically and additionally, the Grade 2 plate with reinforcer washer was observed to “curl” around 20,000 pounds. This can be beneficial during an underground application, as now discovered, since it acts as a load indicator warning of excessive system loading. Therefore, the RCD would accept the underground use of the reinforcer washer with a Grade 2 dome plate in place of a spherical washer with a Grade 3 dome plate, and the grade 2 plate uniformly curling in response to a load around 20,000 pounds thereby beneficially acting as a load indicator.

The below example shows further test results performed May 2023 for additional grades of plates, through Grade 5. More particularly, the subject washer as disclosed and claimed by '559 was used within an evaluation conducted at Pittsburgh Safety and Health Technology Center's (PSHTC) in which the mechanical properties reinforcer washer were tested in accordance with the standards of the Mine Safety and Health Administration (MSHA) (of the U.S. Department of Labor). Results show any “lower grade” plate with the reinforcing washer will act comparably to a “higher grade” and also uniformly visibly indicate load. For example, a grade 3 plate with the reinforcing washer will acts as a grade 4 plate and have uniform deformity at its corners, as would a grade 4 plate with the reinforcer washer thus acting as a grade 5 plate and having uniform deformity at its corners. Thus, “lower grade” and “higher grade” should be interpreted accordingly on this consecutive numbering scale.

Example

May 2023

• • Plate and reinforcer washer testing at MSHA
  • Tests 6×6 Donut plates Grades 3, 4, and 5 with FM Locotos Co. Reinforcer washer
  • For comparison, tests were run on all 3 grades with NO washer, FML reinforcer washer, flat hardened washer, and spherical washer. This was to establish a baseline and then side by side comparison to show FML reinforcer washer superiority.

A. Grade 3-6×6 Donut Plate

• • Baseline test showed 33,500 lbs. (30,000 lbs. minimum for Grade 3).
  • 3 tests with FML Reinforcer washer 39,500, 39,300, 39,400 all at 0.25″ depth penetration/deflection, no observable bend, curl, cupping, tuliping.
  • 5 tests to increase deflection to 0.50″ depth to induce observable curl all demonstrated significant observable, meaningful curl, from 42,000 lbs. to 50,000 lbs.
  • A test using a single flat washer resulted in less curl with 35,700 lbs.
  • Commented was that the FML Reinforcer washer out-performed all other tests.

B. Grade 4-6×6 Donut Plate Tests

• • No washer, baseline at 0.25″ depth 44,000 lbs, 0.30″ 48,000 lbs. (min req for Grade 4, 40,000 lbs.)
  • 3 tests Grade 4 with FML Reinforcer washer—at 0.25″ depth—36,300, 34,800, 36,500. The reason for the lower numbers here is the washer is being seated or conforming to the donut plate. After it is seated the data/graph goes rapidly upward again.
  • 3 tests with Grade 4 and FML Reinforcer washer—at 0.65″ depth 64,400 lbs., 66,000 lbs., 66,200 lbs.
  • 1 test Grade 4 with flat washer at 0.65″ depth 54,200 lbs.
  • 1 test Grade 4 with spherical washer at 0.65″ depth 42,700 lbs. (spherical washers tend to pull through the plate)
  • 1 test with Grade 4 and 4×4 cable bolt square plate adapter—55,600 lbs.
  • 1 test with Grade 4, Reinforcer washer, and square plate adapter—0.65″ good curl, 67,000 lbs.
  • 1 test Grade 4 and DOUBLE reinforcer washer—Big curl at 62,800 lbs. at 1″ deflection

C. Grade 5 Plate

Grade 5 no washer-	.25″ 73,000 lbs.	.65″ 74,000 lbs.
		(Grade 5 minimum
		50,000 lbs.)
Grade 5 1 FML Reinforcer	.25″ 37,000 lbs.	.65″ 85,400 lbs.
washer-
Grade 5 2 FML Reinforcer	.25″ 66,000 lbs.	.65″ 98,300 lbs.
washers-
Grade 5 3 FML Reinforcer	.25″ 74,000 lbs.	.65″ 110,000 lbs.
washers-
Grade 5 with flat washer-	.25″ 77,000 lbs.	.65″ 78,100 lbs.
Grade 5 with spherical	.25″ 51,700 lbs.	.65″ 59,800 lbs.
washer-

While the invention has been described with reference to one or more embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. In addition, all numerical values identified in the detailed description shall be interpreted as though the precise and approximate values are both expressly identified.

Claims

1. A component for mine roof bolt system, comprising: an embossed bearing plate, wherein said bearing plate is a grade x−1 plate, said bearing plate including: a back surface which is adapted to contact a mine roof, an opposite surface; and, an aperture through which a shaft portion of a bolt can extend;a non-spherical, reinforcing washer including a rigid member having: a first surface shaped to contact and complement said opposite surface of said bearing plate; a second opposing surface; and a washer hole for alignment with said aperture through which said shaft can extend; and,wherein said reinforcing washer is combined with said bearing plate, wherein, instead of said grade x−1 plate failing in response to a load, said grade x−1 plate uniformly curls in response to said load, thereby forming a load indicator for said mine roof.

2. The component of claim 1, wherein said rigid member transitions to a slightly tapered annulus, and said annulus extends to a substantially planar portion.

3. The component of claim 1, wherein said grade x−1 plate is a grade 2 plate, and wherein a grade x plate is a grade 3 plate.

4. The component of claim 1, wherein said grade x−1 plate is a grade 3 plate, and wherein a grade x plate is a grade 4 plate.

5. The component of claim 1, wherein said grade x−1 plate is a grade 4 plate, and wherein a grade x plate is a grade 5 plate.

6. A method for evaluating load at a mine roof, comprising the steps of: combining an embossed bearing plate and a reinforcing washer to thereby form a bearing system, wherein said bearing plate is a grade x−1 plate, said bearing plate including: a back surface which is adapted to contact a mine roof, an opposite surface; and, an aperture through which a shaft portion of a bolt can extend, said reinforcing washer including a rigid member having a first surface shaped to contact and complement said opposite surface of said bearing plate, a second opposing surface and a washer hole for alignment with said aperture through which said shaft can extend;driving said bolt with said shaft through said bearing system into a location of said mine roof; and,inspecting, visually, a curl of said grade x−1 plate at its corners, wherein said curl is indicative of a load at said location.

7. The method of claim 1, wherein said grade x−1 plate is a grade 2 plate, and wherein a grade x plate is a grade 3 plate.

8. The method of claim 1, wherein said grade x−1 plate is a grade 3 plate, and wherein a grade x plate is a grade 4 plate.

9. The method of claim 1, wherein said grade x−1 plate is a grade 4 plate, and wherein a grade x plate is a grade 5 plate.