Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.


  1. Advanced Patent Search
Publication numberUS3469407 A
Publication typeGrant
Publication dateSep 30, 1969
Filing dateDec 22, 1967
Priority dateDec 22, 1967
Publication numberUS 3469407 A, US 3469407A, US-A-3469407, US3469407 A, US3469407A
InventorsLajos J Kovacs
Original AssigneeOhio Brass Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Mine roof support
US 3469407 A
Previous page
Next page
Description  (OCR text may contain errors)

p 0, 1969 1.. J. KOVACS 3,469,407

MINE ROOF SUPPORT Filed Dec. 22, 1967 2 Sheets-Sheet 1 INVENTOR.

LAJOS J. KOVACS' ATTORNEY Se t. 30, 1969 L. J. KOVACS MINE ROOF, SUPPORT Filed Dec. 22, 1967 2 Sheets-Shela; 2

FIG. 8

INVENTOR. LAM/0:; J. KOVACS v ATTORNEY United States Patent 3,469,407 MINE R001 SUPPORT Lajos J. Kovacs, Mansfield, Ohio, assignor to The Ohio Brass Company, Mansfield, Ohio, a corporation of New Jersey Filed Dec. 22, 1967, Ser. No. 692,847 Int. Cl. E21d 21/00; E0412 1/38; F16b 13/06 US. Cl. 61-45 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to mine roof support and particularly to expansion anchors for mine roof bolting.

The principal object of the invention is to provide a roof bolt and expansion anchor which is adapted for use in mine roofs having soft spots and soft strata.

Another object of the invention is to increase the holding power of multiple anchors and roof bolts.

In arrangements for mine roof support, it is known to drill an Opening vertically into the roof, install a bolt having a blind anchor for gripping the overburden or roof material, and a roof plate which bears against the surface of the roof on the interior of the mine opening. The bolt is then tightened to achieve a tension upon the bolt and a compression upon the roof material such that the overburden acts as a continuous body, the static characteristics, stabilityl, etc. of the overburden are increased, and shifting of the roof is prevented. Various types of roof bolts and accessories, such as expansion anchors, bails, plates, and the like, are well known in the mining art.

Although the art of roof bolting has been extensively developed as just described, no satisfactory arrangement has been devised for holding mine roofs which have layers or strata of soft material, also referred to as soft roof. Various designs of special anchors and multiple arrangements of anchors, including multiple anchors in tandem on a single bolt, have been tested but have not heretofore been satisfactory. The present invention relates to a tandem arrangement of expansion anchors on a single roof bolt which is useful for holding soft roofs and may be manufactured at a cost which permits economic utilization in mines.

It is an important feature of the invention that plastic creep or unloading may be substantially eliminated in weak roofs.

The invention will be more clearly understood from the following specification and claims, taken in connection with the appended drawing in which:

FIG. 1 is a side elevation view of an expansion shell assembly embodying the invention;

FIG. 2 is a side elevation view taken in the direction 22 of FIG. 1;

FIG. 3 is a top plan view taken in the direction 3-3 in FIG. 1;

FIG. 4 is a top plan view taken in the direction 4-4 in FIG. 2;

FIG. 5 is a sectional view of a mine roof installation incorporating a roof bolt and the expansion assembly of FIG. 1 and FIG. 2 in one species of weak roof;

FIG. 6 is a view of another roof bolt installation in another species of weak roof;

FIG. 7 is a view of an installation similar to that of FIG. 5 with an expansion assembly incorporating three expansion anchors; and

FIG. 8 illustrates an embodiment of the invention utilizing a multiple expansion plug assembly.

Referring now to FIG. 1, the expansion assembly 10 comprises a bolt 11, a first expansion anchor 12, a second expansion anchor 13, and a bail 14. A coupling 15 is provided at the lower extremity of the bolt 11 for connection to a headed bolt assembly in order that the bolt 11 may be turned to expand the expansion assembly 10.

The bolt 11 comprises a rod threaded along the length thereof for receiving the threaded coupling 15 at its lower extremity and for receiving the two expansion plugs 16 and 17 of the anchors 12 and 13. The anchors 12 and 13 are of identical construction, each comprising two laterally opposed complementary shells 18 and 19 of the anchor 12 and two laterally opposed and complementary shells 20 and 21 of the anchor 13. The shells 18 and 19 and 20 and 21 have complementary recess and pivot means 22 and 23 and 24 and 25 at the lower extremities thereof for mutual bearing engagement of the two shells at the lower extremities thereof. The upper extremities of the shells have inclined faces 26 and 27 and 28 and 29 comprising openings for receiving the guides 30 and 31 of the expansion plugs 16 and 17.

The bail 14 comprises an elongate U-shaped metal strap having the yoke 32 arranged over the end of the bolt 11 and the upper end plug 16, and the two arms 33 and 34 extending along the outer sides of the shells 18 and 19 and 2t and 21 at opposite sides of the bolt 11.

As illustrated, particularly in FIG. 2, the bail 14 has the arm 33 received in a slot 35 in the plug 16, a recess 36 in the shell 18, a slot 37 in the plug 17, and a recess 38 in the shell 20. The bail 14 is fixed to the Shell 18 by the cars 39 which overlap the arm 33 and are engaged therewith. The bail 14 is secured to the shell 20 by cars 40, and similar arrangements of ears are provided for securing the shells 19 and 21 to the arm 34. The construction of the shells, pivots, and clamping arrangements for the shell and bail is described in detail in US. Patents 2,647,431 and 2,667,099 to W. J. Lewis.

A cylindric sleeve or retainer 41 is provided about the shells 20 and 21 to insure contact of the shells with the expander plug 17, retention of the plug 17 against turning with the bolt, and expanding movement of the plugs 16 and 17 upon engagement of the shells with the roof at any point along the bolt opening. It will be recognized that the use of the retainer 41 is, to some extent, optional since the walls of the bolt opening will ordinarily position the shells relative to the expander plugs after the assembly is inserted into the bolt opening. Thus, in many cases, the retainer 41 will be removed from the assembly just prior to its insertion completely into the bolt opening in the roof.

FIG. 5 illustrates the expanded condition of the assembly 10 in a mine roof 43 constituted by a relatively uniform soft strata or so-called weak roof. As shown, the assembly 10 is attached to a roof bolt 44 having 'a head 45, and the entire assembly is received in an opening 46 in the roof. A roof plate 47 is arranged over the head 45 and engages the face of the roof 43 so that the bolt is tensioned and the roof plate is drawn against the outer surface of the roof by turning the bolthead.

Inasmuch as the shells 18 and 19 and 20 and 21 are connected together and the plugs 16 and 17 are held by the bail 14, engagement of any one of the shells with the face of the roof along the opening 46 serves to hold the anchors 12 and 13 against turning movement with the bolt 44. When the bolt 44 is turned, the plugs 16 and 17 are drawn between the shells 18 and 19 and 20 and 21, respectively, causing the shells to expand into engagement with the face of the opening 46 in the roof 43.

According to the invention, the uniform expansion of the shells 18 and 19 of the anchor 12 and the shells 20 and 21 of the anchor 13 causes the tensile load effected by the bolt 44 to be exerted relatively uniformly on the associated portions of the roof 43, so that the loading of the individual anchors for a given movement of the bolt, or movement of the shell assembly along the bolt, is limited only by the nature of the material. Accordingly, a maximum loading of the anchors is accomplished having regard for the material which constitutes the strata of the roof.

The functioning of the apparatus as illustrated in FIG. is of importance for a soft roof having a relatively uniform nature including soft shale, fossil-bearing shale, and the like, as is known in the art pertaining to roof bolting. With such overhead, the unit load exerted upon the wall of the opening 46 must be kept as low as possible so that the functioning of the anchor assembly to distribute the load over a large area has an important effect on the ultimate strength of the installation, that is, the maximum loading which can be achieved with a given assembly. It will be recognized that the distribution of load over all of the bearing portions of the shells 18 to with the associated facing portions of the roof effects a reduction in the load exerted at any elementary portion of the wall or hole face of the bolt opening and, thus, minimizes or avoids the limiting effect which would otherwise result from the excessive loading of the roof material at the face of the opening 46 in concentrated or specific areas, as in prior art devices.

The invention is useful also in a weak roof which is characterized by lamina of hard and soft material, such as layers of hard rock, limestone, sandstone, and the like, with intervening layers of soft material, such as Stratified mud, fossil-bearing shale, laminated soft shale, and the like. FIG. 6 illustrates the expanded condition of the assembly 10 in a roof 48 constituted by soft and hard strata, indicated by the symbols S and H. The assembly 10 is attached to a unitary bolt 49 which is received in an opening 50 with the head 51 of the bolt engaged with a roof plate 52. The anchor 12 is positioned adjacent a soft strata 53 and the anchor 13 is positioned adjacent a hard strata 54 so that the principal load-bearing function is accomplished by the engagement of the shells of the anchor 13 with the hard strata 54.

In installation, the head 51 of the bolt 49 is turned until the anchor 13 is expanded into engagement with the hard strata 54 after initial engagement of the shells of the anchor with the walls of the opening 50 at that point. Since the plug 16 and the shells 18 and 19 are also retained by the bail 14, the shells of the anchor 12 are expanded into engagement with the soft strata 53. Accordingly, the shells of the anchor 12 provide some contribution of holding power or load to the tension of the bolt 49, although limited by the character and quality of the strata.

In addition to the above, the anchor 12 provides a safety function, that is, in case of slipping of the anchor 13 due to movement of the roof or for some other reason. The anchor 12, being in an expanded condition, engages the hard strata 54 after initial engagement of the shells of bly 10 in the opening 50.

FIG. 7 illustrates an embodiment of the invention in which an expansion assembly 55, otherwise similar to the expansion assembly 10 of FIG. 1, is constituted by three anchors 56, 57, and 58 arranged in tandem on a roof bolt 59. The anchors 56, 57, and 58 are each identical with the anchors 12 and 13 of the assembly 10 and are provided with a common bail 60 and a retainer (not shown) for the anchor 58. The bolt 59 and assembly 55 are received in an opening 62 in the roof 63 with the head 64 of the bolt 59 bearing against the face of the roof 63 through a roof plate 65. The arrangement is adapted for use in laminated roofs, such as the alternate soft and hard strata 66, 67, and 68, or in weak roofs having uniform strata.

The assembly 55 functions in generally the same way as the two anchor assemblies described with respect to FIG. 5 and FIG. 6. However, because of the increased bearing area provided by the additional anchor and the resultant decrease in unit loading of the roof material at the face of the bolt opening 62, a greater total tension load can be obtained in a given roof. Multiple assemblies, such as the triple assembly 55 and assemblies of four or more anchors, are useful in weak roofs constituted by very soft shale or the like.

Another aspect of the invention is apparent from FIG. 7 wherein a wide-spaced double anchor unit may be constituted in a single assembly, such as an assembly comprising only the anchors 56 and 58 on the bolt 59 in the longitudinal spacing shown in FIG. 7. In this arrangement, the anchors 56 and 58 engage only the soft strata above and below the single hard strata. In such circumstances, the complete load is divided equally between the two anchors and may result in a greater total load than an arrangement in which a single assembly engages only the hard strata. It is to be understood that such arrangements are primarily illustrative of the advantage of the present invention and may or may not be useful in practical applications because of the difficulty in determining the nature of the roof strata and the actual bearing load which may be imposed.

In the arrangement of FIG. 7, the bolt 59 is constructed as a composite assembly, with the bolt for the expansion assembly 55 comprising a separate rod threaded throughout its length, similar to the bolt 11 of FIG. 1 and FIG. 2, and coupled to a headed roof bolt by means of a threaded coupling such as the coupling 15. This arrangement is advantageous because of the length of thread required for the multiple expansion assembly. In the arrangement shown, a standard threaded rod may be used for the bolt 11 and there is no extraordinary requirement for special bolts either in manufacture or in stocking or warehousing at the mine.

According to the embodiment of the invention illustrated in FIG. 8, a roof bolt assembly comprising two or more anchors, such as the assembly 10 of FIG. 1 with the anchors 12 and 13, is provided with a unitary expander assembly 70 comprising two plugs 71 and 72 threaded upon a bolt 73 with a connector 74 uniting or holding the two expander plugs for simultaneous movement upon the bolt. In the embodiment of the invention illustrated herein, the connector 74 comprises two rigid rods 75 and 76 which are received in openings drilled in adjacent portions of the plugs 71 and 72 and bonded or brazed in place to constitute a unitary assembly.

In operation, the expander assembly 70 insures simultaneous movement of both expander plugs along the roof bolt so that if, for example, the upper anchor is positioned in a hard strata with the shells pressed closely together and the lower anchor 13 is positioned in a soft strata in an enlarged or fallen portion of the opening, the lower expander plug is constrained to move into the separating position with the upper plug, and upon slipping movement of the bolt or shifting of the roof the lower anchor is effective to engage a hard strata below its former position.

During manufacture the plugs 16 and 17 are held in longitudinally spaced relation by a plastic tube which is held between the shells 18 and 19 in the assembly which includes the anchors 12 and 13 and the bail 14. With this arrangement, the correct longitudinal positioning of the plugs 16 and 17 is maintained when the bolt 11 is threaded into the expansion plugs.

It is to be understood that the foregoing description is not intended to restrict the scope of the invention and that various rearrangements of the parts and modifications of the design may be resorted to. The following claims are directed to combinations of elements which embody the invention or inventions of this application.

I claim:

1. A shield assembly for a mine roof comprising a threaded bolt, a plurality of expansion anchors each comprising complementary elongate generally semi-circular opposed shells, a longitudinal slot in the upper end of each of said shells the several anchors being spaced along the bolt, an expander for each anchor comprising an annular part having an interior thread engaged with the bolt and a tapered exterior for separating the expansion shells when drawn along the bolt, and a bail for the several expansion anchors comprising a U-shaped elongate metal loop extending longitudinally between the anchors and over the end expander, and means securing the bail to the lower ends of said opposed shells along opposite sides of each of the anchors, said bail being received in said slots, all for simultaneous movement of the expanders and separation of the shells of each anchor with turning movement of the bolt relative to at least one of the said expansion anchors.

2. A shield assembly in accordance with claim 1, in which the complementary shells are pivoted together at the lower extremities and the expanders have laterally opposed wings comprising guide means for the expander and shells, arranged between the shells at the upper extreniities thereof.

3. A shield assembly in accordance with claim 2, in which the bail is received in longitudinal slots in the expanders.

4. A shield assembly in accordance with claim 1, in which the bolt is threaded throughout the extremity thereof, a rod coupling at the lower extremity of the bolt end, in combination therewith, a headed bolt threaded into the coupling to constitute a composite bolt for the assembly.

5. A shield assembly in accordance with claim 1, with means connecting the expanders for simultaneous movement thereof on the bolt independent of the bail.

6. A shield assembly according to claim 1 wherein a removable sleeve surrounds the lowermost opposed shells for holding together the assembly during shipment.

References Cited UNITED STATES PATENTS FOREIGN PATENTS 2/1963 France. 6/1961 Norway.

JACOB SHAPIRO, Primary Examiner.

US. Cl. X.R.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1654346 *Dec 13, 1922Dec 27, 1927John Edward OgdenBolt anchor
US2783673 *Mar 30, 1953Mar 5, 1957Ohio Brass CoExpander nut having three surfaces of different inclination
FR80182E * Title not available
NO98206A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4523880 *May 4, 1983Jun 18, 1985H. Weidmann, AgTie rod assembly for rock borehole anchor
US5762451 *Feb 26, 1997Jun 9, 1998Jennmar CorporationMulti-piece, split bail expansion anchor
US7963725 *Oct 28, 2004Jun 21, 2011Aveng (Africa) Ltd.Rock bolt
EP0094908A2 *May 6, 1983Nov 23, 1983H. Weidmann AGAnchor bolt for ground strengthening
U.S. Classification411/61, 405/259.1, 52/704
International ClassificationE21D21/00
Cooperative ClassificationE21D21/008
European ClassificationE21D21/00N