Anchor member with electrical insulation jacket

An anchor member is formed of an axially extending core member enclosed from one end toward the other by an electrically non-conductive plastics material jacket. The anchor member can be secured in a borehole in a receiving material by a hardenable mass. The jacket at the one or leading end of the core member has a tip located on an extension of the core member axis, so that the tip abuts the center of the base of the borehole. With the centering action afforded by the tip, damage to the jacket is prevented as the anchor member is inserted into the borehole.

BACKGROUND OF THE INVENTION 
The present invention is directed to an anchor member securable within a 
borehole in a receiving material by a settable or hardenable mass. The 
anchor member includes an axially extending core member formed of metal 
with an axially extending connecting thread thereon. The portion of the 
core member inserted into the receiving material is enclosed in a jacket 
of a electrically non-conductive plastics material. 
Anchor members of the type described above are used mainly in railroad 
construction for securing rails, carrying an electrical current, to a 
substructure formed of concrete. Initially, a settable hardenable mass in 
a premixed state or in separate compartments of a destructable cartridge 
is injected into a borehole and subsequently the anchor member is placed 
into the borehole. During the insertion of the anchor member, usually with 
a rotational motion, a mixing of the hardenable mass components as well as 
a uniform distribution of the mass takes place within the borehole. The 
attachment member is inserted into the borehole until its leading end in 
the installation direction reaches the base of the borehole. 
In known anchor members of this type, for example as disclosed in DE-OS No. 
33 20 429, the leading end of the jacket is shaped in the manner of a 
wedge-like or roof-like cutter extending transversely of the core member 
axis. With this type of leading end of the jacket, initially the anchor 
member contacts the base of the borehole at its radially outermost points. 
The jacket can be damaged or destroyed at its leading end, particularly 
when the anchor member is being installed with a turning or rotational 
action, so that the insulating effect of the jacket around the core member 
may not be complete. 
SUMMARY OF THE INVENTION 
Therefore, the primary object of the present invention is to provide an 
anchor member securable by a hardenable mass and laterally enclosed at 
least in part in an electrical insulating jacket so that the jacket is not 
destroyed during the installation of the anchor member. 
In accordance with the present invention, the jacket is formed at the 
leading end of the anchor member with a stop arranged to abut against the 
receiving material at the center of the base of the borehole. 
With a centered stop located at the leading end of the anchor member, where 
the cross-sectional area of the stop represents only a small fraction of 
the surface of the leading end of the anchor member, it assures that the 
anchor member is centered in the borehole base and does not contact the 
circumferential surface of the borehole. The relative motion or contact 
between the jacket on the anchor member and the borehole surface is small. 
Accordingly, damage to the jacket is prevented at the leading end of the 
anchor member as it contacts the base of the borehole. 
Preferably, the stop is formed by a tip at the leading end of the jacket 
having a conically-shaped contour. The tip can be in the form of a 
circular cone or shaped as a four-sided pyramid. To obtain a uniform wall 
thickness of the jacket, it is preferable that the leading end of the core 
member also has a conically shape. 
It is advantageous if the cone angle of the tip of the jacket is smaller 
than the cone angle of the base of the borehole. With this angular 
relationship, it is assured that the tip of the jacket is located at the 
center of the borehole. This angular difference between the jacket tip and 
the borehole base can be small. As a result, the amount of the hardenable 
mass at the leading end of the anchor member is small. If a 
pyramidally-shaped tip is used, it must be assured that the angle between 
opposite sides of the surfaces forming the pyramidally-shaped tip is 
smaller than the corresponding angle of the surfaces forming the borehole 
base. 
In still another desirable embodiment, the stop is in the form of a 
lug-like projection. Such a lug-like projection can be molded as a part of 
the jacket or it can be attached to it subsequently. The lug-like 
projection can be attached to the jacket by a rated breaking point, so 
that the projection is broken off from the jacket as soon as it contacts 
the base of the borehole. 
The core member can be in the form of an axially extending anchor stud with 
an external thread section projecting outwardly from the jacket opposite 
to the installation direction. Threaded rods can be used for the anchor 
stud and can be cut to the desired length as required, whereby an 
economical fabrication of the anchor members is obtained. The thread on 
the anchor stud affords an effective positive locking engagement between 
the stud and the jacket. 
In accordance with the present invention, it is also possible to form the 
core member as a threaded sleeve with an internal thread so that the 
internal thread serves to receive an anchor stud. Such an anchor member 
has the advantage that, after the anchor stud is screwed out of the 
sleeve, the remainder of the anchor member does not project out of the 
receiving material. To prevent any damage to the thread in the sleeve 
during construction work, a detachable plug can be used to protect the 
internal thread. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the accompanying drawings and descriptive matter in which 
there are illustrated and described preferred embodiments of the invention 
.

DETAILED DESCRIPTION OF THE INVENTION 
In FIGS. 1 and 3, an anchor member is shown made up of a core member 1 in 
the form of a threaded sleeve and a jacket 2 of an electrically 
non-conducting plastics material enclosing the core member from its 
leading end, the left-hand end in FIGS. 1 and 3, towards its trailing end. 
The core member or threaded sleeve 1 has a closed leading end 1a and an 
open trailing end 1b. An internal thread 1c extends from adjacent the 
trailing end 1b toward the leading end 1a of the threaded sleeve. Note in 
FIG. 3 that the internal thread 1c stops at an axial distance spaced from 
the base of the blind bore in the sleeve. The jacket 2 has a leading end 
2a and a trailing end 2b with the trailing end forming an inwardly 
directed flange bearing against the trailing end 1b of the threaded sleeve 
1. The circumferential outer of the jacket 2 has arrow-shaped ridges or 
lands 2c. The ridges or lands 2c start at a location spaced axially from 
the leading end 2a of the jacket and end at a spaced location from the 
trailing end 2h of the jacket. At its leading end 2a, the jacket has a 
pyramidally-shaped tip 2d. In FIG. 3, the anchor member made up of the 
core member or threaded sleeve 1 and the jacket 2 is inserted into an 
axially extending borehole 3a in a receiving material 3. A hardenable mass 
4 is inserted into the borehole 3a prior to the insertion of the anchor 
member. The hardenable mass 4 secures the anchor member in the receiving 
material 3. The anchor member is inserted into the borehole 3a of the 
receiving material 3 until the tip 2d at its leading end contacts the base 
of the borehole 3b. Cone angle A of the pyramidally-shaped leading end 2a 
is smaller than the cone angle B of the base of the borehole 3b. As a 
result, the insertion of the anchor member is completed when it contacts 
the center of the base 3b of the borehole 3a. The centering action 
prevents contact of the circumferential region of the jacket 2 with the 
base 3b of the borehole 3a. Accordingly, damage to or destruction of the 
jacket 2 is prevented while the anchor member is driven into the borehole 
and is rotated about its axis. 
After the hardenable mass 4 has set, a axially elongated bolt 5 is threaded 
into the internal thread 1c of the threaded sleeve 1, passing through an 
opening formed in a structural member 6 to be attached to the surface of 
the receiving material 3. Bolt 5 has a hexagonal head 5a at its trailing 
end and a shank 5b threaded for a portion of its axial length from the 
leading end of the bolt. A washer 7 is located between the head 5a of the 
bolt 5 and the member 6 to be attached to the receiving material. By 
tightening the bolt 5, the structural member 6 can be pressed against the 
surface of the receiving material 3. The arrow-shaped ridges 2c on the 
circumferential surface of the jacket 2 provide a positive lock with the 
hardenable mass. Initially, an adhesive connection is provided between the 
hardenable mass 4 and the surface of the borehole 3a in the receiving 
material 3. 
Another anchor member is displayed in FIG. 4 made up of an axially 
elongated anchor stud 8b with an axially extending external thread 8a, and 
a jacket 9 enclosing an axially extending section of the anchor stud from 
its leading end toward its trailing end. Jacket 9 has spaced arrow-shaped 
ridges or projections 9a, extending around its circumferential surface. 
The ridges 9a afford a positive lock with a hardenable mass which secures 
the anchor member within a borehole, such as shown in FIG. 3. At its 
leading end, the jacket 9 has a conically-shaped tip 9b. The cone angle of 
the tip 9b is smaller than the usual cone angle of the base of the 
borehole in the receiving material into which the anchor member is 
inserted. 
Another anchor member embodying the present invention is illustrated in 
FIG. 5 and is made up of an anchor stud 8 and a jacket 10 formed of an 
electrically non-conductive plastics material with the jacket enclosing an 
axially extending section of the stud from its leading end toward its 
trailing end. Jacket 10 has ridges 10a extending around its circumference 
and a lug-like projection 10b at its leading end. Projection 10b serves as 
an axial stop when the anchor member is inserted into a borehole. The 
projection 10b can be formed so that it breaks off if the attachment 
member is driven with excessive force into a borehole without the jacket 
10 being damaged or destroyed. 
The jackets 9 and 10 in FIGS. 4 and 5 are inserted into a borehole in 
receiving material in the same manner as the jacket 2 in FIG. 3, so that 
the anchor member or stud is spaced from the receiving material by the 
jacket. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the inventive principles, it 
will be understood that the invention may be embodied otherwise without 
departing from such principles.