Note: Descriptions are shown in the official language in which they were submitted.
CA 02254302 1998-11-23
FIELD OF THE INVENTION
This invention relates to friction washers, and more particularly to an
improved push-on
friction washer, also known as gripper plates, for securing a wire mesh
screening onto the
protruding end of rock bolts employed to stabilize rock structures in mining
and civil
engineering applications.
BACKGROUND OF THE INVENTION
To stabilize openings and improve safety in excavations, threaded end rock
bolts have
been in general use for some time in supporting rock surfaces and securing
wire mesh screening.
Rock bolts are typically installed by insertion into a drilled hole in the
rock structure. The rock
bolt is retained in these drilled holes by conventional means. In many
circumstances a wire
mesh screening is secured on the rock surface at the same time as a rock bolt
is being installed
into drill holes in the same rock surface.
Where wire mesh screening is not secured at the time that rock bolts are
installed, it may
become necessary to install the wire mesh at time in the future. This can be
accomplished by
drilling additional holes to anchor the wire mesh through the installation of
additional rock
bolts. Another obvious method is to secure the wire mesh onto the protruding
threaded end of
the rock bolt using a second bearing plate and nut. However both of these
operations have been
2o found to be inefficient.
The retention of this wire mesh screening using a secondary fastening system
has been
in use at least since 1982. The method generally employed is that of a bearing
plate, commonly
referred to as a washer, which secures the wire mesh in position by means of a
centrally located
opening comprising of a series of teeth, or legs, set into the inside diameter
that engage in the
threaded section of the protruding rock bolt. Devices which fit the above
description have been
variously known as friction washers and gripper plates. Examples of these
conventional forms
of friction washers can be found in Canadian Patent Nos. 1,244.,270 (Gagnon),
known as the
friction washer, and in Canadian Patent Nos. 2,086,705 (Saab), known as the
gripper plate.
As the securement of wire mesh screening has become more widespread in
underground
mining environments, several characteristics of the above mentioned prior art
friction washers
have been found to be sufficiently problematic to prevent their universal
acceptance and
utilization. The present invention is concerned with the provision of an
improved friction
washer which overcomes the present concerns of the currently available models.
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CA 02254302 1998-11-23
SUMMARY OF THE INVENTION
The present invention relates to a push-on friction washer used for securing
wire mesh
screening onto the protruding end of a threaded end rock bolt. The friction
washer, in
accordance with the present invention, comprises of a central opening having a
downwardly
deformed section which is slotted and formed to engage the threads of the rock
bolt, and a
plurality of downwardly formed loops spaced from the center of the washer and
placed so as to
secure the washer on the installation tube during the process of installation
onto the rock bolt.
l0 The hollow tube used for holding the friction washer during installation is
commonly known
as a rock bolt dollie wrench. The tool required for installation is not a part
of this embodiment,
it should be noted that the tool required is a standard non-modified piece of
equipment generally
located in mining environments. The friction washer described corrects the
many weaknesses
of prior art units which will now be described in some detail. The applicant,
having first hand
1 S experience in the design and use of this type of device, has overcome the
principal problems
associated with prior art friction washers in this original design of an
improved friction washer.
Previously referred to embodiments Canadian Patent Nos. 1,244,270 (Gagnon),
Canadian Patent Nos. 2,086,705 (Saab) are fabricated from approximately 0.06
inch thick
tempered mild or spring steel. The improved friction washer is manufactured
from readily
20 available and less costly commercial grade mild steel of 0.125 inches thick
with no further heat
treating or tempering required. The process of eliminating heat treating or
tempering eliminates
a major cause of variability in the performance of this device, as well a
resulting saving in
manufacturing is accomplished.
At the present time the device known as the gripper plate requires a specially
modified
25 tool to permit installation, the improved friction washer is installed
utilizing a standard readily
available tool. As a result of replacing the so called tabs with the deformed
loop design which
said loops are located to secure the washer onto a rock bolt wrench, handling
and shipping
concerns are also addressed as this unit will easily nest and thus be
stackable. Furthermore, said
loops may be employed for to suspend hoses and cables and other light hanging
applications
30 which may be required in mining situations.
All prior art friction washers exhibit a reduced resistance to corrosion this
is a result of
the heat treatment or tempering process. This weakness has resulted in this
device having
limited appeal in mining environments with high sulphide contents. As the
improved friction
washer is manufactured using untreated mild steel it naturally exhibits an
increased resistance
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CA 02254302 1998-11-23
to corrosion. Furthermore, the increased thickness of the material compared to
other washers
for this function, contributes greatly to a longer life expectancy and an
increased lateral strength
without requiring the need of embossments as on the aforementioned prior arts.
As has often been the case, the aforementioned previously available devices
have evolved
from the original design embodiments to respond to market demands and as a
result of worker
experience and due to general concerns and complaints of end users. The
designs in current use
incorporate design components, invariably pointed or sharp edges, also know as
tabs, which
have been known to cause injury during the installation process. In a
preferred embodiment of
the improved friction washer according to the invention, for securing the
washer onto the
installation tool the aforementioned protruding tabs are replaced by formed
loops. This is a
significant improvement in response to a safety concern as well as an
improvement in the
simplification of the manufacturing process. Additional improvement to prevent
possible injury
to users while taking full advantage of a generally square plan is the
inclusion of rounded
corners to the improved design.
These and other advantages as listed herein will become more apparent as the
invention
will now be disclosed, by way of example, with reference to the detailed
description of a
preferred embodiment illustrated in the accompanying drawings.
DETAILED DESCRIPTION OF A PREFERRED EMBODIIVVIENT
Figure 1 is a top view of the improved friction washer in accordance with the
present
invention ;
Figure 2 is a side view of the improved friction washer shown in figure 1;
Figure 3 is a detailed view of the central deformed section of the improved
friction
washer shown in figure 1;
Figure 4 is a detailed view of an individual loop section of the improved
friction washer
shown in figure 1; and
Figure 5 is a schematic view illustrating the process of installation of the
wire mesh
screening onto the threaded section of an installed rock bolt.
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CA 02254302 1998-11-23
Referring to the drawings, there is shown an improved friction washer 10
manufactured
from mild steel which includes a central section 14 with eight formed sections
12 positioned
around the perimeter of said opening and adapted to engage the threads of the
installed rock
bolt. Other prior art friction washers rely on teeth or on so called legs
which have been proven
to be weakened when subjected to underground blasting and which do not
effectively fully
contact the circumference of the rock bolt thread as is the situation with the
improved design.
The friction washer has a plurality of formed loops 15 which all face in the
same
direction off plane as the central section and are positioned at an equal
distance from the central
section and thus foam a secure attachment for the installation tool. As an
added benefit of this
design, said loops may be used multiply or singly for light hanging
applications.
The improved friction washer has a generally square plan of which the four
corners are
rounded to a radius of one half of an inch, this feature is included to
eliminate sharp edges and
thus reduce the possibility of injury resulting from inadvertent contact
during the installation
process. Dimensioning of the improved friction washer is such as to provide
adequate support
for the wire mesh screening considering that the dimensions of the openings of
said mesh that
is in common use for this function.
Referring to figure 5, there is shown a threaded end rock bolt 22 installed
into a rock
structure. A standard rock bolt bearing plate 24 is held securely against the
rock surface and
tightened by a nut 26. The wire mesh screening 30 is installed onto the
protruding thread of the
rock bolt using the above disclosed improved friction washer 10. Installation
is then completed
by setting the improved friction washer onto a standard rock bolt installation
tool 20 by fitting
the loops 15 around the perimeter of the said installation tool. In practice
the operation is
simple and can be accomplished using a pneumatic rock drill to push the washer
into place, as
well this installation process may be done by hand.
Preliminary bench testing, employing industry standard methodology, of the
improved
friction washer as illustrated, manufactured in mild steel strap of 1/8 inch
thickness, resulted
in a measured failure load of 2.5 tons. Using this same type of apparatus in
actual testing in the
past, the applicant consistently recorded lower values for all samples of
prior art friction
washers. It should be noted that ultimately the wire mesh in common use has a
load bearing
capacity of much less than this recorded value of 2.5 tons. This increased
load capacity would
be significant in the future as more mining is carried out in deeper zones and
higher stress areas,
and where the strand diameter, and therefore the strength of the wire mesh
screening may have
to be increased.
In reference to the diameter of the installed rock bolt, it should be noted
that the two
CA 02254302 1998-11-23
common diameters are the 5/8 inch and the 3/4 inch sizes. Previously available
friction washers,
Canada 1,244,270 (Gagnon) also, Canada 2,086,705 (Saab), or otherwise known as
gripper
plates, must be manufactured according to the diameter of the rock bolt onto
which the washer
will be installed. This results in double stocking for the users, and creates
manufacturing
problems in scheduling. The improved friction washer as herein disclosed will
perform equally
well on both size diameters of installed rock bolts resulting in a definite
advantage over the prior
art examples.
To the list of aforementioned advantages, this improved friction washer is
readily
treated to greatly improve resistance to corrosion by the common process of
galvanization, or
zinc coating. As resistance to corrosion has been recognized as a major
deterrent in the
application and utilization of these devices, this would greatly increase the
marketability of
friction washers. As an alternative to galvanizing the finished product, epoxy
coating would
constitute a lower cost protection although this coating would also be
somewhat less robust.
Although this invention has been disclosed with reference to a preferred
embodiment as
shown and described, it is to be understood that it is not limited to such
embodiment and that
other alternatives are envisaged within the scope of the following claims.
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