Anchor bolt assembly

An expansion anchor assembly having a segmented expansion shell containing two or more sections that are joined in assembly at the base of the shell. The base sections are interlocked along abutting radially extended side walls. An end cap is passed over the bottom of the base and securely locked to each section to close the assembly and hold the base immobile as the leaves of the shell are expanded outwardly.

BACKGROUND OF THE INVENTION 
This invention relates to an improved expansion anchor bolt assembly and, 
in particular, to an expansion anchor bolt assembly utilizing a segmented 
expansion shell that generally exhibits the holding characteristics of a 
more costly single piece unit. 
Anchor bolt assemblies of this type are used in a wide range of 
applications. The most important application, however, is the area of mine 
safety where the expansion device is employed to help support the roof of 
the mine. Typically, a hole is drilled or bored upwardly through the 
ceiling of the mine shaft into the overhead stratum. An elongated bolt, 
containing a plate at the head end and an expansion anchor assembly at the 
thread end, is passed upwardly into the opening. A wedge, contained in the 
expansion anchor assembly, is drawn down into the anchor assembly by 
turning the bolt. This, in turn, forces a number of finger-like elements 
to be expanded outwardly into holding contact against the wall of the 
opening and also draws the plate against the mine shaft roof. Further 
torquing of the bolt stresses the overhead formation of earth and rock to 
prevent it from moving and thus creating a potentially dangerous 
situation. 
Heretofore, it had been preferred to construct the expansion shell of the 
anchor from a single piece of generally malleable metal. In form, the 
shell conventionally includes an annular base section having a plurality 
of finger-like elements axially extended from the top surface thereof. The 
single piece base provides a foundation of considerable strength about 
which the relatively weaker fingrs deform as the wedge is drawn into the 
anchor assembly. As a result, the fingers move uniformly in an outward 
direction to provide for a parallel expansion of the shell members. It is 
well known in the art that this type of expansion delivers the greatest 
possible holding power and anything less will reduce the stressing ability 
of the assembly. The main disadvantage of the single piece shell relates 
to the high cost of producing this relatively intricate structure and the 
excessive scrap rate associated therewith. 
Attempts have been made, with varying degrees of success, to fabricate 
expansion shells in two or more parts which can be more conveniently and 
economically formed by well known casting, stamping and/or forging 
techniques. Bringing the parts together in assembly and properly 
supporting the parts during the expansion process has long been a problem 
in the art. 
A two or four leaf bail assembly is probably the most common type of 
segmented expansion shell device that is used in industry today. In this 
arrangement, two shell segments are generally joined together by a bail or 
strap by staking or welding the strap to the top section of each segment. 
In operation, a draw bolt acts between the strap and a wedge to force the 
wedge downwardly against the shell fingers. The shell is permitted to open 
at the bottom with each segment being deformed outwardly about the 
relatively thin strap. Any small resistance to the movement of one or both 
segments is immediately translated to the weaker strap, causing it to 
twist and/or bend in an unpredictable manner. As a result, parallel 
expansion of the shell segments cannot be maintained and less than optimum 
anchoring is delivered. 
Another common anchor arrangement involves joining two or more shell 
segments at the base of the shell by means of a clip-on "pal nut" that is 
formed from a thin sheet metal stamping. A threaded opening is provided in 
the stamping through which the draw bolt is turned into threaded 
engagement with the wedge. In practice, the bolt acts between the two 
threaded members to pull the wedge down into deforming contact against the 
shell fingers. Here again, the clip-on nut represents the weak element in 
the system and, as the wedge descends, the clip will usually release 
prematurely thereby allowing the shell components to be forced out of 
their original optimum operational position. As a consequence less than 
maximum performance is produced by the assembly. A clip-on device of the 
type noted is described in further detail in U.S. Pat. No. 3,941,028. 
Both the bail and clip-on nut mechanisms perform quite well in holding the 
expansion device together in assembly. They also provide a convenient 
means for allowing the wedge to move into operation against the fingers. 
However, in both arrangements, the retaining element forms a weak section 
in the assembly which usually deforms prematurely under stress thereby 
causing the anchor to fail or deliver less than the desired holding power. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to improve expandable 
anchor bolt assemblies. 
A further object of the present invention is to secure a segmented 
expansion shell in assembly in such a manner that the base of the shell is 
prevented from moving as the fingers of the shell are expanded outwardly. 
A still further object of the present invention is to provide a segmented 
expansion shell, suitable for use in a mine bolt assembly, that is able to 
deliver the performance characteristics of a single piece shell. 
Another object of the present invention is to reduce the cost of an 
expansion anchor assembly without sacrificing the strength of the device. 
These and other objects of the present invention are attained by means of 
an expansion anchor bolt assembly including a segmented expansion shell 
containing a cylindrical base made up of arcuate shaped sections that are 
interlocked along their abutting sidewalls and an end cap that is passed 
over the bottom of the base in close sliding relationship therewith, the 
cap having means associated therewith for securing each base section in 
locking engagement in assembly so that the base of the shell is held 
immobile as the leaves of the shell are driven outwardly by a wedge during 
the expansion process.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIGS. 1 and 3, there is shown an expansion bolt 
assembly, generally referenced 10, containing an expansion shell 12 that 
includes four quarter segments 14-17. The segments are brought together in 
assembly to provide a cylindrical base 20 having a plurality of 
finger-like elements depending outwardly from the top surface thereof in 
an axial direction. Each segment further includes an arcuate shaped base 
section 20a-20d having one or more fingers 19 depending therefrom. As is 
typical, the finger sections have a stem 21 affixed to the base section 
and a leaf 22 at the terminal end comprised of a number of teeth 25 that 
are for gripping earth and rock when the shell is expanded within a hole 
bored or drilled into a mine shaft roof. Although the present shell is 
herein depicted as being formed of four independent quarter sections, it 
is well within the scope of the present invention to utilize more or less 
shell segments provided that the segments can be simply formed by any 
well-known forming process and are brought together in a manner which will 
be explained in greater detail below. 
As best illustrated in FIG. 3, each of the arcuate base sections carried by 
the individual segments contains a radially extended sidewall 27 that has 
a sawtooth configuration 28. The sidewall of each base section compliments 
that of the next adjacent section so that when assembled, the base 
sections interlock to prevent the segments from moving inwardly in a 
radial direction or slipping over each other in an axial direction. 
Each base section also contains a locking groove, generally referenced 30. 
As illustrated in greater detail in FIG. 4, each groove has an entrance 
passage 31 beginning at the bottom surface 32 of the base and extending 
upwardly in an axial direction for a short distance. The entrance passage 
is then joined by a second circumferentially extending passage 35 that 
describes a portion of an upwardly directed spiral or helix. 
In assembly, an end cap 40 (FIG. 5) is passed over the bottom of the shell 
base 20. The end cap includes an annular side wall 41 and a cylindrical 
end wall 42. The cap typically is cast or machined from 0.060 inch thick 
steel with its inner diameter providing a close running fit with the 
outside diameter of the shell base. A plurality of dimple-like, inwardly 
directed, protrusions 44 are formed on the inner side wall of the cap, the 
number of protrusions being equal to the number of locking grooves formed 
in the base 20. The protrusions are circumferentially spaced about the 
side wall of the cap so that they are slidably receivable within the 
entrance grooves contained in the base. The cap can thus be conveniently 
slipped over the base. Upon reaching the bottom of the entrance grooves, 
the protrusions are directed laterally into spiral passages 35. As the 
protrusions on the cap move up the spiral passages, the inside end wall 48 
of the cap is drawn into seating contact against the bottom surface of the 
base 20 so that the cap and the base are locked together to create a high 
strength unitized pedestal for the fingers. 
The depth of spiral passage 35 decreases from its entrance region towards 
its terminal region. The depth at the terminal end of the passage is 
shallow enough to interfere with the extended end of a protrusion moving 
therealong. This, in turn, causes the side walls of the cap to be stressed 
further strengthening and securing the base section in assembly. An 
indentation 38 is formed in the bottom wall 39 at the end of passage 35 
for receiving in seated contact therein a coacting protrusion when the cap 
is turned to a fully locked position. The depth of the indentation, 
however, is insufficient to permit the cap from being totally unstressed 
when in the locked position. Equally spaced openings 45 are provided in 
the outer side wall of the cap to enable a spanner wrench or the like to 
engage the cap and thus facilitate locking and unlocking of the cap. 
Referring once again to FIG. 1, a draw bolt 50 is arranged to pass through 
the end cap into the expansion shell so that it can threadably engage a 
tapered wedge 51, which is of well-known conventional construction. A 
centrally located threaded opening 46 (FIG. 5) passes through the cap and 
engages the threaded end of the draw bolt. A plate 53 is located at the 
head end of the bolt which, although not shown, seats against the mine 
roof and exerts a compressive force thereagainst as the bolt head 54 is 
torqued. 
As can be seen, in this particular bolt assembly, the cap and wedge are 
drawn toward each other as the draw bolt is torqued down. This forces the 
wedge downwardly into deforming contact against the fingers of the 
expansion shell. The stem section 21 of each shell segment forms the 
weakest section in the assembly and, as a consequence, only the fingers 
are caused to expand outwardly in a uniform manner under the influence of 
the descending wedge to establish a true uniform expansion of the shell. 
As noted above, the cap 40 functions to lock the thicker base into a 
single acting unit incapable of shifting axially or radially as the 
fingers are undergoing expansion. 
Referring now to FIG. 2, there is shown another embodiment of the present 
invention in which like numbers depict like elements as described above in 
reference to the first embodiment. In this particular arrangement the 
threaded opening in the end wall 42 of cap 40 is replaced with a more 
generous clearance hole 58 through which the draw bolt 50 freely passes. 
An inverted, generally U-shaped, bail 60, of typical construction, is 
inserted into the shell assembly with the bottom leg 61 of the bail 
engaging the end of the bolt and horizontally turned arms 62 passing out 
of the hole 58 in the cap and being seated against the top surface of the 
cap. As is conventional in this type of assembly, the draw bolt acts 
between the wedge and the bail to permit the wedge to move down into 
deforming contact with the shell and thus engage the fingers to be 
expanded outwardly. Here again, the cap and base section of the segmented 
shell act in concert to hold the base of the shell unitized during the 
expansion process. 
While this invention has been described with reference to the structure 
disclosed herein, it is not confined to the details set forth, and this 
application is intended to cover such modifications or changes as may come 
within the scope of the following claims.