U.S. patent number 4,703,711 [Application Number 06/822,221] was granted by the patent office on 1987-11-03 for load-indicating devices.
This patent grant is currently assigned to The Clay Cross Company Limited. Invention is credited to John M. Haynes.
United States Patent |
4,703,711 |
Haynes |
November 3, 1987 |
Load-indicating devices
Abstract
The device consists of first and second load-receiving members,
a breakable member and a part-spherical washer received in a seat
in the second load-receiving member. In use, a load is applied by
way of a rod or bar passing centrally through the load-receiving
members and the breakable member positioned therebetween, the rod
or bar also passing through a central bore in the washer and being
angularly movable because of the support provided by the seat. When
a predetermined load is achieved, annular cutting surfaces on the
load-receiving member cut the breakable member with a predominantly
shear action to indicate that the load has been achieved. Fractured
parts of fingers of the bearing member are retained between
surfaces to be visible at the periphery of the device.
Inventors: |
Haynes; John M. (Derbyshire,
GB2) |
Assignee: |
The Clay Cross Company Limited
(Chesterfield, GB2)
|
Family
ID: |
10573393 |
Appl.
No.: |
06/822,221 |
Filed: |
January 24, 1986 |
Foreign Application Priority Data
|
|
|
|
|
Jan 25, 1985 [GB] |
|
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8501896 |
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Current U.S.
Class: |
116/212;
116/DIG.34; 73/761; 411/14; 441/8 |
Current CPC
Class: |
E21D
21/02 (20130101); F16B 31/028 (20130101); Y10S
116/34 (20130101) |
Current International
Class: |
E21D
21/02 (20060101); E21D 21/00 (20060101); F16B
31/00 (20060101); F16B 31/02 (20060101); G01L
005/00 () |
Field of
Search: |
;411/2,3,5,8-14,537,538
;116/212,DIG.34 ;73/761 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Frankfort; Charles
Assistant Examiner: Worth; W. Morris
Attorney, Agent or Firm: Young & Thompson
Claims
I claim:
1. A device for indicating attainment of a predetermined value of a
load applied to the device, said device comprising
a first member,
a second member and
a breakable member lying between said first and second members,
said first and second members having respective faces directed
towards each other and said faces of said first and second members
having
first co-operating formations which co-operate to guide said first
and second members for relative movement in a first direction
decreasing the separation between said first and second members and
a second, opposite direction increasing said separation and
second co-operating formations which co-operate when said load
tending to cause relative movement of said first and second members
in said first direction is applied to said device,
said second co-operating formations comprising respective surfaces
on the faces of said first and second members, said surfaces
co-operating to cause breakage of said breakable member with an
action which is at least partially shearing when said applied load
attains said predetermined value, and
said breakage of said breakable member providing an indication that
said applied load has attained said predetermined value.
2. The device of claim 1, further comprising means for locating
said breakable member on one of said first and second members
against movement relative thereto in directions transverse to said
first and second directions.
3. The device of claim 1, wherein said first co-operating
formations comprise a first cylindrical alignment surface formed in
said face of said first member and a seocnd cylindrical alignment
surface formed in said face of said second member, said first and
second cylindrical alignment surfaces having respective axes which
are aligned with said first and second directions.
4. The device of claim 1, wherein said second co-operating
formations comprise a fitst cylindrical breakage surface formed in
said face of said first member and a second cylindrical breakage
surface formed in said face of said second member, said first and
second cylindrical breakage surfaces having respective axes which
are aligned with said first and second directions.
5. The device of claim 1, wherein said first co-operating
formations comprise a first cylindrical alignment surface formed in
said face of said first member and a second cylindrical alignment
surface formed in said face of said second member, said first and
second cylindrical alignment surfaces having respective axes which
are aligned with said first and second directions, and
said second co-operating formations comprise a first cylindrical
breakage surface formed in said face of said first member and a
second cylindrical breakage surface formed in said face of said
second member, said first and second cylindrical breakage surfaces
having respective axes which are aligned with said first and second
directions,
said first and second cylindrical breakage surfaces being
concentric with said first and second cylindrical alignment
surfaces and located radially outwardly of said first and second
cylindrical alignment surfaces.
6. The device of claim 1, wherein said first co-operating
formations comprise a first cylindrical aligment surface formed in
said face of said first member and a second cylindrical alignment
surface formed in said face of said member, said first and second
cylindrical alignment surfaces having respective axes which are
aligned with said first and second directions, and
said second co-operating formations comprise a first cylindrical
breakage surface formed in said face of said first member and a
second cylindrical breakage surface formed in said face of said
second member, said first and second cylindrical breakage surfaces
having respective axes which are aligned with said first and second
directions,
said cylindrical alignment surface and said cylindrical breakage
surface of said first member being joined by a first annular
surface which is inclined to said first and second directions,
said cylindrical alignment surface and said cylindrical breakage
surface of said second member being joined by a second annular
surface which is inclined to said first and second directions,
and
said first and second annular surfaces defining therebetween an
annular cavity, for reception of a fragment of said breakable
member after said breakage thereof.
7. The device of claim 6, wherein said first and second annular
surfaces are planar and extend parallel to each other.
8. The device of claim 1, wherein said first co-operating
formations comprise a first cylindrical alignment surface formed in
said face of said first member and a second cylindrical alignment
surface formed in said face of said second member, said first and
second cylindrical alignment surfaces having respective axes which
are aligned with said first and second directions, and
said second co-operating formations comprise a first cylindrical
breakage surface formed in said face of said first member and a
second cylindrical breakage surface formed in said face of said
second member, said first and second cylindrical breakage surfaces
having respective axes which are aligned with said first and second
directions,
said first and second cylindrical alignment surfaces being located
radially inwardly of said first and second cylindrical breakage
surfaces, and
said first and second members being shaped outwardly of said first
and second cylindrical breakage surfaces to define between said
first and second members at least one recess which is open to
visual inspection from the exterior of the device,
said at least one recess receiving a portion of said breakable
member, and
said portion occupying respective first and second different
positions relative to said first and second members prior to and
after said breakage, whereby
said breakage of said breakable member having taken place can be
detected visually by inspection as to which of said positions is
occupied by said breakable member portion and a said
sensorily-perceptible indication thereby achieved.
9. The device of claim 1, wherein said first and second members and
said breakable member are each annular and have respective
apertures which overlap to form a passage extending through said
device.
10. The device of claim 1, wherein said breakable element comprises
an annular portion and a plurality of portions extending outwardly
therefrom, said second co-operating formations co-operating to
cause breakage of said breakable element at locations on said
outwardly-extending portions.
11. The device of claim 2, wherein said breakable element is
annular and receivable around one of said cylindrical alignment
surfaces in order to locate said breakable element against said
relative transverse movement.
12. An end plate or pattress having means for indicating attainment
of a predetermined load applied thereto, said end plate or pattress
comprising
a first annular member,
a second annular member, and
an annular breakable member lying between said first and second
annular members, said first annular member, said second annular
member and said annular breakable member having respective openings
which overlie to form a passage extending through said end plate or
pattress,
said first annular member being engageable by an elongate
load-application member extending through said passage to apply a
load to said end plate or pattress,
said first and second annular members having respective faces
directed towards each other and said faces of said first and second
annular members having
first co-operating formations which co-operate to guide said first
and second annular members for relative movement in a first
direction decreasing the separation between said first and second
members and a second, opposite direction increasing said separation
and
second co-operating formations which co-operate when said load
tending to cause relative movement of said first and second members
in said first direction is applied ot said end plate or pattress
through said elongate member,
said co-operation between said second formations causing breakage
of said breakable member when said applied load attains said
predetermined value, and
said breakage of said breakable member providing an indication that
said applied load has attained said predetermined value.
13. The end plate or pattress of claim 12, wherein said first
annular member comprises a first portion having said face thereon
and a second portion which is moveable relative to said first
portion, said passage through said first annular member extending
through said first and second portions thereof, and said first
portion of said first annular member being engageable by said
elongate member, whereby said elongate member can adopt any of a
plurality of possible orientations relative to said first portion
of said first annular member through movement of said second
portion of said first annular members relative to said first
portion.
14. The end plate or pattress of claim 13, wherein said first and
second portions have respective part-spherical surfaces which
co-operate to permit said relative movement of said portions.
15. The end plate or pattress of claim 13, wherein said second
portion is located at an end of said through passage of first
portion distant from said face of said first, said passage flaring
outwardly in cross-section in the direction away from said second
portion.
16. The device of claim 12, wherein said second co-operating
formations comprise respective surfaces on said first and second
annular members, said surfaces co-operating to cause breakage of
said breakable member with an action which is at least partially
shearing when said applied load attains said predetermined value.
Description
This invention relates to devices for indicating when an applied
load has achieved a desired value. A device provided by the
invention may be used when a load is applied to a rock bolt or a
tie bar used, for example, to stablise a rock face or strengthen a
brick or masonary structure, in a building, tunneling or mining
project.
In the past applied loads have been measured using various
hydraulic, electrical and optical load-indicating devices. These
devices tend to be delicate and expensive and are therefore not
completely satisfactory, particularly when used in building,
tunneling, mining or civil engineering projects. One aim of the
present invention is to overcome this disadvantage of the known
devices.
It is one object of the present invention to provide a sturdy and
inexpensive load-indicating device.
It is another object to provide a load-indicating device in which a
breakable member is broken at a predetermined load with a breaking
action which is at least in part shearing.
It is a further object of the invention to provide a
load-indicating device which can be incorporated into end plates
and pattresses such as are used in mining and civil engineering
projects.
Yet another object is to provide a load-indicating device in which
fractured portions of a breakable member are retained in the device
for visual inspection after fracture.
The present invention provides a load-indicating device and
load-indication method in which the load is applied to a breakable
member which breaks when the load is equal to or greater than a
predetermined value.
More specifically, the present invention provides a load-indicating
device comprising first and second loadreceiving members which tend
to move relative to each other when a load is applied to the
device, a breakable member and means for applying the applied load
to the breakable member in such a way that the breakable member
breaks when the applied load is equal to or greater than a
predetermined value and thus provides an indication that the
predetermined load value has been achieved or exceeded.
Usually, the applied load will be increased from a value less than
the predetermined value and the breakable member will then break
upon the predetermined load value being achieved.
Preferably, the breakable member is positionable between the
load-receiving members. In such a construction, the
load-application means may comprise formations on at least one of
the surfaces of the load-receiving members which contact the
breakable member, the formations acting upon the breakable member
to produce the desired breaking action when the predetermined load
value is reached. Advantageously, the breakable member is subjected
to a shearing and/or bending action which causes breakage of the
member, the spacing of the points of application of the load to the
breakable member determining the relative magnitudes of the
shearing and bending actions.
This shearing and/or bending action may be produced by a pair of
annular cutting surfaces, the surfaces of the pair each being on a
different one of the first and second load-receiving members and
being relatively movable towards each other along the line of
movement of the load-receiving members from an offset position
prior to breaking of the breakable member. The annular cutting
surfaces are preferably cylindrical and advantageously extend
parallel to the direction of relative movement of the
load-receiving members. For reception of the fractured parts of the
breakable member after breakage, the device parts preferably form
annular cavities lying radially inwardly and radially outwardly of
the cutting surfaces.
Conveniently, fractured portions of the breakable member are
retained after breakage in positions which are visible from the
exterior of the device and which are displaced from positions
adopted before breakage.
Preferably, the device has means for positioning of the
load-receiving members in their working positions. Advantageously,
the positioning means serve also to position the breakable member
relative to the load-receiving members.
The positioning means conveniently comprise respective annular
surfaces on the load-receiving members, the surfaces overlapping
and lying adjacent each other when the load-receiving members are
in their working positions. Advantageously, one of the annular
positioning surfaces is received snugly in an aperture in the
breakable member which it thus serves to position relative to the
load-receiving members.
In a preferred arrangement, the load-receiving members and the
breakable member have aligned apertures through which a rod or bar
can be passed and, in such a device, an annular alignment surface
on one load-receiving member may form at least a portion of the
aperture extending therethrough. If the rod or bar is provided with
a means for engaging one of the load-receiving members (for example
a nut screw-threaded onto the rod or bar) and movement of the other
load-receiving member is resisted, a load can be applied to the
device by tensioning of the rod or bar. In this way, the
load-indicating device of the invention can act as an end plate or
pattress and can be used for setting a pre-load in a rock bolt or
tie bar in a building or civil engineering application.
When the breakable member is apertured, it preferably comprises a
plate having an annular portion with inwardly- or
outwardly-protruding portions which are engaged by formations on
the load-receiving members and are fractured when the predetermined
load value is reached. By modification of the dimensions of the
protruding portions and/or the formations on the load-receiving
members, the predetermined load value can be altered. Preferably,
this is achieved by changes in the dimensions of the protruding
formations or the thickness or material of the plate so so that
alteration of the load value is achieved without modification of
the load-receiving members.
When apertured as mentioned above, one of the load-receiving
members advantageously has a portion through which a portion of the
aperture extends and which is movable relative to the remainder of
the loadreceiving member. In this way, the orientation of a rod or
bar received in the aperture of the movable portion relative to the
load-receiving member can be varied. Conveniently, the movable
portion has a part-spherical surface engaging a
complementarily-shaped surface on the remaining portion of the
load-receiving member, the aperture in which is preferably flared
to allow angular movement of the rod or bar.
An embodiment of the invention will now be described by way of
example with reference to the drawings, in which:
FIG. 1 is a vertical sectional view of a load-indicating device in
the form of a load-indicating end plate, a shear plate of the
device being omitted,
FIG. 2 is a plan view of the shear plate omitted from FIG. 1,
FIGS. 3a, 3b and 3c are scrap sectional views showing cutting teeth
of the device of FIG. 1 and, in FIGS. 3b and 3c, also the shear
plate of FIG. 2, and
FIG. 4 is a view similar to FIG. 1 showing the device and a nut
fitted to a lock bolt, a portion only of which is shown.
FIG. 1 of the drawings shows a first, annular loadreceiving member
10, having a central circular aperture 12, and a second,
load-receiving member 14 which has a central bore 16 and supports a
part-spherical washer 18. The load-indicating device is completed
by a breakable member in the form of an annular plate 20 which is
shown in FIG. 2. The load-receiving members 10, 14 and the washer
18 are of SG iron, whilst the shear plate 20 is of mild steel. In
other embodiments, other materials, such as stainless steel and
non-ferrous metals, may be used.
The first load-receiving member 10 is circular in plan and has a
base area to suit the load bearing properties of the substrate.
Typically, the diameter of the load-receiving member is seven times
the diameter of the bar or rod to be used with the device. The bar
or rod will usually have a diameter within the range of 16 mm to 39
mm, thus giving a range of load-receiving members diameters of 112
mm to 273 mm.
The annular surface of the member which is uppermost in FIG. 1 has
inner and outer ramped annular surfaces 22, 24 which, as shown, are
inclined upwardly in the radially-inward direction. A cylindrical
cutting surface 26 joins the ramped surfaces 22, 24 and, inwardly
of the inner ramped surface 22, a cylindrical alignment surface 28,
which provides annular alignment of the first and second load
members, joins the inner ramped surfaces to an annular shoulder 30
which is inclined in the opposite direction to the ramped surfaces
22,24.
The second, domed load-receiving member 14 is also circular in plan
and has in its upper surface a part-spherical seating 32 for
support of the part-spherical washer 18. The washer 18 has a
circular cylindrical bore 34 in which a screw-threaded rod or bar
is a somewhat slack fit. By virtue of movement between the washer
and its seating 32 and the frusto-conical shape of the bore 16, the
rod or bar can adopt positions in which its axis is inclined to the
axis of the frusto-conical bore 16.
The surface of the second load-receiving member 14. which confronts
the first load-receiving member 10 has inner and outer ramped
annular surfaces 36, 38 which are parallel to the ramped surfaces
22, 24 of the load-receiving member 10. The ramped surfaces 36, 38
are joined by a cylindrical cutting surface 40 which is parallel to
the cylindrical cutting surface 26 of the first load-receiving
member. A cylindrical alignment surface 42 extends parallel to the
cylindrical alignment surface 28 to provide alignment of the
load-receiving members. A further annular surface 44 extends
between the cylindrical surface 42 and the wider end of the bore 16
in the second loadreceiving member 14 to face the inclined shoulder
30 on the first load-receiving member. The alignment and cutting
portions of the load-receiving members are shown in more detail in
FIG. 3a.
The annular plate 20 of this embodiment is about 4mm in thickness
and, in other embodiments, will usually have a thickness in the
range of 1 to 10 mm. The plate has an annular portion 46, defining
a central circular aperture 48, and eight outwardly extending
protruding portions 50 defined by gaps 52. The diameter of the
aperture 48 is slightly greater than the diameter of the
cylindrical surface 42 on the second load-receiving member 14, on
which the plate 20 is positioned by reception of the aperture
central boss formed by the surfaces 42 and 44 in the aperture 48 of
the plate 20 The portions 50 of the plate 20 extend from the
annular portion 46 to a radial distance equal to the radius of the
outer edges of the outer ramped surfaces 38 on the second
load-receiving member 14. The material and thickness of the shear
plate 20 and the number and the sum of the circumferential widths
of the protruding portions 50 at the radius of the cutting surfaces
26, 40 can be varied in order to set the predetermined load to be
indicated by the device.
For use of the load-indicating device the parts shown in FIG. 1 are
first assembled with the plate 20 positioned between the
load-receiving members 10, 14 and the cylindrical surface 42 of the
second load-receiving member 14 received in the aperture 48 of the
shear plate. The members 10, 14 and plate 20 are shown in more
detail in FIG. 3b. The tie rod or rock bolt is then passed through
the aligned apertures 12, 48, 16, 34 and a nut fitted to a threaded
end portion of the rod or bolt extending beyond the washer 18. With
the first load-receiving member 10 supported by a fixed structure
and the rod or bolt possibly inclined to the axis of the
frusto-conical bore 16, the nut is tightened. When the tension in
the rod or bolt corresponding to the breaking stress of the annular
plate 20 is exceeded, the plate 20 is fractured by a shearing and
bending action between the leading edges of the pair of cutting
surfaces 26, 40, the radial spacing of the cutting surfaces
determining the relative contributions of shearing and bending to
the fracture.
The fractured plate is shown in more detail in FIG. 3c, it being
evident that the protruding portions 50 of the shear plate 20 are
fractured along a circular line corresponding to the radius of the
cylindrical cutting surfaces 26, 40. The resulting relative
movement of the load-receiving members 10, 14 when fracture takes
place produces a visual indication that the predetermined load has
been achieved and, moreover, a further visual indication is given
by the fact that the peripheral gaps between the ramped surface 24
on the first load-receiving member 10 and the lower surfaces of the
protruding portions 50 of plate 20 have become closed, the
fractured parts of the portions being retained between the two
device parts 10, 14.
One use of the load-indicating device described with reference to
FIGS. 1-3 of the drawings is in the tensioning of a rock bolt used
to stabilise a rock face in, for example, a mine. This is shown in
FIG. 4. A blind bore is first drilled in the rock face. The rock
bolt 53 is then inserted into the bore and secured by a suitable
cement or grout. To stabilise the rock face, the bolt must be
tensioned to a predetermined value by tightening of its nut 54.
This is achieved by use of the load-indicating device described.
Attainment of the predetermined load will serve to indicate that
the bolt is properly secured to the rock. After tensioning, the
device remains to serve as a load-distributing end plate. After
tensioning and fracture of the plate 20, the rock bolt 53 can be
re-tensioned to the same or a different predetermined value by
removal of the nut 54, the second load-receiving member 14 and the
fractured plate 20 and replacement of the plate before re-assembly
of the load-receiving member and nut.
The load-indicating device according to the present invention has
many other applications, for example as overload-indication devices
in weighbridges and cables.
It will be appreciated that the bending contribution to the
fracture will be zero when the clearance between the cutting
surfaces is zero and will increase with increasing spacing. Thus,
when the clearance is small as shown, the mode of fracture will be
predominantly shearing with a small bending component.
It is evident that those skilled in the art will make numerous
modifications of the specific embodiment dscribed above without
departing from the present inventive concepts. It is accordingly
intended that the invention shall be construed as embracing each
and every novel feature and novel combination of features present
in or possessed by the apparatus herein described and that the
foregoing disclosure shall be read as illustrative and not as
limiting except to the extent set forth in the claims appended
hereto.
* * * * *