US2878709A - Mine roof bolts having segmented shell biased outwardly by resilient washer - Google Patents

Description

March 24, 1959 J. HORVATH 2,878,709 MINE ROOF BOLTS HAVING SEGMENTED SHELL BIASED OUTWARDLY BY RESILIENT WASHER Filed May 14, 1956 INVENTOR. Joseph Hon/0M Aria/nay MIN-E ROOF BOLTS HAVHNG SEGMENTED SHELL BIASED OUTWARDLY BY RESILIENT WASHER Joseph Horvath, Rillton, Pa., assignor toRepublic: Steel Corporation, Cleveland, Ohio, a corporation-of New Jersey Application May 14, 1956, Serial No. 584,496

2 Claims. (Cl.85'-2.4)

This invention relates to stay bolts, and particularly tostay bolts of the type known as mine roof bolts.

There is disclosed in the copending" application of Charles P. McCabe, Serial No. 358,414, filed May 29, 1953, entitled Mine Roof Bolts With Multiple Piece Shell, now U.SL Patent No. 2,787,931, issued April 9; 1957, a bolt having a wedge-shaped head adapted'for insertion head end first into a hole in the roof: of amine. The wedge head of each such bolt serves as a support for an anchor shell structure which moves with thebolt into the hole. After the boltand shell have been inserted tothe desired depth, e.g. substantially to the end of the hole, the bolt is then pulled downward a short distance; The anchor shell, which frictionally'grips the sides of the hole, does not follow this downward movement, but remains fixed in the hole. Wed'ging surfaces on the wedge head and the shell cooperate during that downward movement to anchor the shell and bolt firmly in the hole.

Said copending application discloses an anchor shell structure composed of two or more longitudinally separate sections, each attached at one end, as by riveting or welding, to a strap or tang which extends along the wedge head and is bent over to engage the end of the wedge head. Each strap or tang is made of resilient; yield'able spring steel stock and has an unstressed position in which its associated shell segment is spacedoutwardly from the bolt head. When the. bolt is inserted in the hole, the sections are deflected inwardlyfrom their unstressed positions, so that they press against the walls of the hole with an outwardly directed force, creating frictional contact between the shell sectionsand the sides of its hole.

Each shell section is provided on its outer surface with teeth adapted to engage the sides of the hole, and on its inner face with a wedging surface adapted to engage the wedge head on the end ofv the bolt; When. the bolt starts to move outwardly of the hole, each shell section is' held against movement by frictional engagement of its outer toothed surface with the shell hole so that the shell sections stand still while the bolt is drawn down to bring the wedge head on the bolt into engagement with the wedging surfaces of the shell, thereby driving the toothed surfaces into firm biting engagement with the walls of the hole.

The unstressed position of each tang or strap and: its associated shell section or segment is selected, inzthe mineroof bolt structures described in said copending applica tion, by a compromise between two different objectives. One objective is to have the shell segments. spread widely enough, when the straps or tangs areunstressed, so that the toothed outer. surfaces of the segments will engage with substantial force the walls of. the largest diameter hole in which the bolt is. likely to be. used- The other objective is to have the shell segments'located close to the wedge head, so that during shipment and handling. prior to insertion of the bolt in the hole,. the assembled bolt and shell will form a neat, easily handled unit,

States Patent 2,878,709 Patented Mar. 24, 1959 without having the shell. segments spread widely sothat they are likely to snagadjacent' objects;

In the use of this device, however, it has beenfound that a strap or tang constructed from spring steel often formed a weak and insecure weld" with forged steel shell segments. This was particularly'true wherever the initial welding operation was imperfect; Anchor shell structures formed withsuch insecure welds had' to be discarded during the manufacturing process, with consequent loss.

of material, labor and time. To remedy this" welding problem, it was proposed to construct the strap or tang from mild steel rather than spring steel. Such a steel readily forms a strong, secure weld with forged steel. Furthermore, such a strap may be riveted instead of welded, sincea hole adapted to receive a rivet is more easily provided in straps constructed ofmild steel than in spring steel straps. 'Mild steel, however, possesses a considerably lower spring rate than spring steel and straps constructed therefrom do not possess sufficient' resiliency to exert, when in a stressed position, the out"- wardl'y' directed'force necessary topermit secure engagement of the shell segmentsnandi' the walls of a hole in which the bolt st'ructureis likely to be used. This'characteristic of mild steel creates a particular difiiculty where thedeviceis'desiredto beused" in oversized holes; There the additional spread'of the shell'segments necessary' to firmly contacttlie walls=ofi the hole hasthe etfe'cti because of the lower" resiliency of the mild steel straps; of further reducing the force with. which the shell seg' ments engage such walls.

An object of the invention is to means for anchoring a mineroofbolt.

A further object of the present invention is to provide amine roof bolf'havinganimproved gripping and anchoring action.

A further object is to provide atmineroofbolthaving an improved gripping and anchoring action in oversized holes.

further object of the invention is to'provideimproved means for maintaining'an anchor shell and b'oltstructure as one unit during packing; handling andshipment.

It is afurth'er object of my presentinvention topro vide animproved means for retaining an anchonshell upona. bolt structure; which retaining means is inex; pensive, and easily attached and-removed The foregoing. and other objects of the invention" are attained by providing a compressiv'ely' resilient washer encircling th e wedge :head near itsthick: end, and between the wedge head and the: shell segments. The: shell segments are" forced resiliently" outwardly by the:wash'e'r,. and are spread thereby to positions where they engage the walls of a hole into which the bolt is inserted.

There is further provided a hollovv' retainer, of cardboard or the like; which" isadaptedito encircle the shell and hold the shell segments closely adjacent the bolt shank, against the forceo f the re'silie'nt wash'er; This retai'n'er: is used during shipment and handling, and is.: re movedpribr to insertion of the bolt in a hole.

The invention together with its objects and advantages will be' best understood from a study of. the following. description and claims taken in connection Withrther ac.- companying drawings;.in-which Figl is aview. partially sectional and: partially' ele vati'onal, of a bolt and anchor shellassembly embody;- ingthe invention;

Fig. 2 is a plan view of a retainer which forms past of the a ssembly of Fig. 1';

Fig. 3. isan-elevational view.- oil the retainer of: Fig.2;

Fig. 4 is. a. planview of a washer which formspartotl the assembly of Fig. l; n

Fig- 5. is an. elevational: view of. thewasheu of Figa; 4;

Fig. 6 is a view, partially sectional and partially eleprovide improved asvsnos 1 and an anchor shell generally indicated by the refer-' enee numeral 2. The bolt 1 is threaded at its upper end and carries an internally threaded wedge head 3 having plane wedging surfaces 312. The lower end of the bolt is provided with an integral head by which the bolt may be rotated. Alternatively, the wedge head 3 might be made integral with the upper end of the bolt and cooperating threads provided on the head 10 and the lower end of the bolt.

The wedge head 3 is assembled on the bolt 1 with the. end of the bolt somewhat below the end of the head, as shown at 1a. The upper end of the threaded hole in the head then provides a recess 3b in the center of the end of the bolt head.

The shell 2 is made up of two diametrically opposed longitudinal shell sections 2a. Each shell section 2a has an outer toothed surface 2b and an inner fiat wedging surface 2c, and in the preferred form of the invention constructed of forged steel. The shell sections 201 also have recesses 2d of arcuate cross-section formed on their inner faces to receive the shank of the bolt when the shell sections are squeezed together.

The respective shell sections 2a are connected at their upper ends, as by riveting or welding, to the opposite ends of a strap 4. The strap 4 has a wide U-shaped por-' tion 4a at the center thereof which extends into the wedge head recess 3b. The strap 4 may be formed of any rigid material capable of forming a strong weld or being securely riveted to forged steel shell segments 2a. In the preferred embodiment of the invention, however, the strap is constructed from mild steel, a material having low elasticity and resiliency as compared to other steels. The strap is so shaped and dimensioned that when the U-shaped portion 4a is received in the recess 3b, the wedging surfaces 20 of the shell section 2a are spaced from thewedging surfaces 311 of the wedge head 3, as shown in the drawing.

A ring or washer 8, illustrated in detail in Figs. 4 and 5, encircles the head '3 near its upper end. The washer is of material which is compressively resilient and preferably is also stretchable so that it frictionally grips the nut and holds itself in place. When in place, it assumes a conical contour, shown in Fig. 1, conforming to the periphery of the head 3. Alternatively, the washer 8 may have a conical shape when unstressed. This washer band may be constructed of any substantially elastic material as for example rubber or plastic compositions possessing a low spring rate. Its thickness and contour may be varied from that shown, depending upon the distance the shell sections are desired to be spread away from the bolt and the shape of the wedge nut or head which it will engage.

The washer 8 produces a wider spread of the shell segments than is obtained when no washer is used, and a resiliency sufficient to allow straps constructed of mild steel'to exert upon the walls of a hole into which it may be inserted an outwardly directed force sufiicient to permit secure engagement of shell segments and hole walls. It is extremely useful for mine roof bolts employed in oversize holes, whether or not the retainer described below is also used.

During packing, shipping and handling, the anchor shell 2 is provided with a retainer 9 illustrated in detail in Figs. 2 and 3 of the accompanying drawings. This retainer is preferably positioned about the lower portion of the shell structure and is of a diameter substantially less than the outside diameter of said anchor shell when the retainer is removed. Retainer 9 may be made of inexpensive material, as for example cardboard, strong paper, cloth, etc.

- When assembling the unit illustrated, the wedge head 3 is threaded part way on to the end of bolt 1, and the Washer 8 is then placed around the wedge head. The strap 4 and shell segments 2a are assembled as a separate operation, and the assembled shell is then placed over the wedge head. The upper ends of the segments 2 engage the washer 8, and resiliently compress it, the segments thereby being stressed and spread more widely than they are shown in the drawing. The retainer 9 is then placed over the shell, forcing the segments 2 inwardly against the resilience of the washer 8, so that all the parts then assume the positions shown.

The retainer 9 holds the segments 2 inwardly against the resilience of washer 8. Since the washer 8 is formed of easily compressed, low spring rate material, the retainer 9 may be formed of weak, inexpensive material such as cardboard, which may be discarded without substantial loss. It is intended in the use of the invention that the retainer be applied prior to packing and shipping and removed by the inserting operator immediately prior to use. It may be immediately disposed of or retained for further use, whichever is more desirable.

When the retainer is removed, the shell segments are spread outwardly by the washer 8. The dimensions of washer 8 and the shell must be such that the lower ends of the wedging surfaces 20 on the shell, in their most widely spread position, are separated by a substantially smaller distance than the upper ends of the wedging surfaces 3a. The U-shaped portion 4a of the strap 4 is then effective, by its engagement with the sides of the recess 3b, to center the shell loosely on the head 3.

A plate 11, adapted to engage the roof of the mine, may be placed over the bolt, either before or after removing the retainer 9, by threading the bolt out of the wedge head 3, inserting the shank of the bolt through a hole in the plate 11, and then threading the wedge head back on the bolt again.

After the retainer 9 is removed, and the plate 11 is in place, the bolt and shell are then pushed upwardly into a drilled hole in a mine roof or the like. The shell moves with the bolt by virtue of the engagement of the strap 4 with the end of the wedge head 3. The shell segments engage the walls of the hole frictionally as the shell is pushed into the hole with the bolt.

When file bolt has been inserted as far as desired, the operator simply pulls downwardly on it in order to lock it in place. The toothed surfaces 4a continue to engage the walls of the hole yieldably and frictionally and prevent downward movement of the shell. The bolt moves downward only a short distance until the wedging surfaces 3a engage the wedging surfaces 2c on the stationary shell, whereupon the teeth 2b of the shell sections are driven into a firm biting engagement with the walls of the hole by the wedging action and the bolt 1 is locked against further downward movement.

Thereafter, the head 10 may be rotated to tighten the bolt and move it farther into the hole. When the head 10 has engaged the plate 11, further rotation of head 10 will tighten the wedging surfaces together.

Washer 8 does not interfere with the engagement of the wedging surfaces during the anchoring operation. It is believed that either the wedging surfaces of the shell segments cut through the washer during the engagement of such surfaces, 01' the engagement process causes the washer to be forced upwardly upon and over the top of the wedge head.

By the use of washer 8, the resilience and spread of the anchor shell necessary for positive engagement with the walls of oversized holes has been attained, while allowing the straps of such anchor shell to he formed of mild steel having relatively low elasticity, and the shell to be retained in a compact shipping position by the use of an inexpensive, disposable retainer 9.

While the preferred embodiment of the invention dis closes the use of washer 8 with mild steel straps, it is of course apparent that such a washer may be employed with spring steel straps wherever an unusual degree of resiliency is required.

Other modifications of my invention will readily occur to those skilled in the art and it is therefore intended that the invention be limited only by the appended claims.

The invention claimed is:

1. A stay bolt comprising a shank having at one end a wedge head and adapted for insertion head end first into a hole, said wedge head increasing in thickness toward said one end of the shank, said wedge head having a recess in its end; an anchor shell structure comprising a wedge portion and a strap attached to one end of said wedge portion, said strap being insertable into said recess and effective ,to hold the shell structure in a normal position in which said wedge portion extends along the bolt from said one end facing but spaced outwardly from the wedge head; and washer means of radially yieldable resilient material engaging the outer surface of the wedge head and positioned between the wedge head and the anchor shell means and resiliently biasing the end of said" wedge portion opposite said one end to a position where its outer surfaces are outwardly spaced from said shank a distance greater than the distance from which said one end of said wedge portion is spaced from said wedge head.

2. A stay bolt comprising a shank with a wedge head at one end thereof and adapted for insertionhead end first into a hole, said wedge head increasing in thickness toward said one end of the shank and having a central recess in its end; an anchor shell structure comprising two shell sections, each comprising a wedge adapted to cooperate with said wedge head, and a strap of mild steel integrally attached to the ends of the shell sections nearest said one end of the shank, said strap spanning the end of the wedge head and having a central U- shaped bend extending toward the wedge head and receivable in said central recess to center the shell structure on the shank and eflective to hold said shell structure in a normal position in which said wedges extend along the bolt from said one end and facing but spaced outwardly from the wedge head; and a rubber washer yieldably and frictionally engaging said wedge head and interposed between the wedge head and the shell sections, said washer resiliently biasing the opposite ends of said shell sections outwardly to positions where their outer surfaces are spaced from the shank a distance greater than the distance from which said one ends are spaced from said wedge head.

References Cited in the file of this patent UNITED STATES PATENTS 1,223,051 Horton Apr. 17, 1917 2,667,099 Lewis Jan. 26, 1954 2,696,138 Olschwang Dec. 7, 1954 2,753,750 Dempsey July 10, 1956 OTHER REFERENCES Republic Mine Roof Bolt Brochure, Publ. Republic Steel Bolt and Nut Div., 1970 Carter R., Clevelend, Ohio.

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