Note: Descriptions are shown in the official language in which they were submitted.
CA 02882967 2015-02-23
SERRATED SHAFT-ENGAGING SURFACE FOR SHRINK DISC
FIELD OF THE INVENTION
[0001] The present invention pertains in general to the field of shrink discs
for mounting
to an element such as a cylindrical shaft, and in particular to a serrated
shaft-engaging
surface for use with or integrated into a shrink disc.
BACKGROUND
[0002] Shrink discs are well-known devices in the art that may be employed for
radially
engaging a radially symmetric element, such as a cylindrical shaft, in
furtherance of various
purposes. For example, International Patent Application Publication No. WO
2013/049885
discloses a shrink disc type coupler assembly for transmitting torque between
two
concentric rotating shafts. As another example, shrink discs may be used to
apply inward
radial compression to a hollow shaft into which another component is inserted,
thereby
causing the hollow shaft to grip the component.
[0003] A first style of shrink disc includes a compression ring with a
cylindrical bore and
a conical outer surface, and a pressure ring with a conical inner surface
which is fitted
overtop of the compression ring. A second style of shrink disc includes a
compression ring
with a cylindrical bore and a bi-conical outer surface which tapers outward in
both
directions from its axial center, and a two-part pressure ring, each part
defining a
corresponding portion of a mating bi-conical inner surface which is fitted
overtop of the
compression ring. In either case, as the pressure ring is moved axially, it
engages the
compression ring and causes a radial compression due to a wedge effect induced
by
engagement of the two conical surfaces. The axial movement can be induced for
example
by operation of a set of screws, bolts, or other means which function to move
the pressure
ring axially overtop of the compression ring. In the first style, the screws
may engage bores
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formed within a flange of the compression ring and within the pressure ring.
In the second
style, the screws may engage bores formed within the two parts of the pressure
ring. Other
means of applying radial pressure may be used which potentially do not rely on
the wedge
effect. For example, a heated pressure ring and/or compression ring may be
applied to the
shaft, with radial pressure applied due to thermal contraction of the pressure
ring/compression ring material upon cooling thereof.
[0004] However, in various instances, if a sufficient amount of torque is
applied to a
shrink disc, it may undesirably rotationally slip relative to the shaft.
Therefore there is a
need for a method and apparatus for facilitating engagement between a shrink
disc
apparatus and a shaft that is not subject to one or more limitations of the
prior art.
[0005] This background information is provided to reveal information believed
by the
applicant to be of possible relevance to the present invention. No admission
is necessarily
intended, nor should be construed, that any of the preceding information
constitutes prior art
against the present invention.
SUMMARY
[0006] An object of the present invention is to provide a serrated shaft-
engaging surface
for use with or integrated into a shrink disc and an associated method. In
accordance with
an aspect of the present invention, there is provided an apparatus for
interposing between a
shaft and a portion of a shrink disc assembly, the shrink disc assembly
configured to receive
the shaft within an aperture thereof and to selectably apply a radially inward
pressure to the
shaft, the apparatus comprising a serrated inner surface configured to
grippingly engage the
shaft.
[0007] In accordance with another aspect of the present invention, there is
provided a
shrink disc assembly comprising: a ring mechanism defining an internal
aperture configured
to receive a shaft therein, the ring mechanism operable to selectably apply a
radially inward
pressure to the shaft, the internal aperture comprising an inner surface
having one or more
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protrusions configured to grippingly engage the shaft upon application of said
radially
inward pressure.
[0008] In accordance with another aspect of the present invention, there is
provided a
method of coupling a shrink disc assembly to a shaft, the method comprising:
locating the
shaft within an internal aperture defined by the shrink disc assembly, the
internal aperture
comprising an inner surface having one or more protrusions; and operating the
ring
mechanism to apply a radially inward pressure to the shaft via the inner
surface, the radially
inward pressure causing the one or more protrusions to grippingly engage the
shaft.
[0009] In accordance with another aspect of the present invention, there is
provided a
method of coupling a shrink disc assembly to a shaft, the method comprising:
providing an
insert apparatus defining an internal aperture, the internal aperture
comprising an inner
surface having one or more protrusions; locating the shaft within the internal
aperture of the
insert apparatus; locating the insert apparatus within a further internal
aperture defined by
the shrink disc assembly; and operating the ring mechanism to apply a radially
inward
pressure to the insert apparatus and to the shaft via the insert apparatus,
the radially inward
pressure causing the one or more protrusions of the insert apparatus to
grippingly engage
the shaft.
BRIEF DESCRIPTION OF THE FIGURES
[0010] FIGs. 1 A to 1C illustrate cross-sectional partial views of a serrated
shaft-engaging
surface and a corresponding shaft, in accordance with an embodiment of the
present
invention.
[0011] FIG. 2 illustrates an insert apparatus provided in accordance with an
embodiment
of the present invention.
[0012] FIG. 3 illustrates an insert apparatus provided in accordance with
another
embodiment of the present invention.
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[0013] FIG. 4 illustrates a compression ring portion of a shrink disc, in
accordance with
embodiments of the present invention.
[0014] FIGs. 5A to 5C respectively illustrate plan, cross-sectional and
perspective views
of a shrink disc comprising the compression ring portion of FIG. 4 as well as
a pressure ring
portion disposed radially outward of the compression ring, in accordance with
embodiments
of the present invention.
[0015] FIG. 6 illustrates a single-conical style of shrink disc assembly
provided in
accordance with another embodiment of the present invention.
[0016] FIG. 7 illustrates a thermal expansion style compression ring for
disposal on a
shaft, in accordance with embodiments of the present invention.
[0017] FIGs. 8A to 8D illustrate configurations of protrusions of a serrated
surface, in
accordance with various embodiments of the present invention.
[0018] FIGs. 9A to 9C illustrate a pair of shafts coupled together using a
shrink disc
assembly, in accordance with embodiments of the present invention.
DETAILED DESCRIPTION
Definitions
[0019] As used herein, the term "axial" refers to a substantially straight-
line direction
which is parallel to a relevant axis of symmetry, such as the axis of a
cylindrical shaft to
which a shrink disc is to be fitted, or the axis of a central bore of the
shrink disc.
[0020] As used herein, the term "radial" refers to a substantially straight-
line direction
which extends perpendicularly from or to the axial direction.
[0021] As used herein, the term "circumferential" refers to a substantially
circularly
curved direction which follows the circumference of a circle of appropriate
radius and
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centered on a relevant axis of symmetry, such as the axis of a cylindrical
shaft to which a
shrink disc is to be fitted, or the axis of a central bore of the shrink disc.
[0022] As used herein, the term "serrated" refers to a surface, such as a
cylindrical
surface, having one or more protrusions extending from the surface. A
protrusion may
extend perpendicularly from the surface or at an angle. Different protrusions
may be shaped
and oriented similarly or differently. The protrusions may be sparsely placed
or may be
arranged in a regular pattern over the surface, such as in a two-dimensional
array. A
protrusion may terminate substantially at a point, such as in a spike, or at a
ridge, or the like.
[0023] As used herein, the term "about" refers to a +/-10% variation from the
nominal
value. It is to be understood that such a variation is always included in a
given value
provided herein, whether or not it is specifically referred to.
[0024] Unless defined otherwise, all technical and scientific terms used
herein have the
same meaning as commonly understood by one of ordinary skill in the art to
which this
invention belongs.
[0025] In accordance with an embodiment of the present invention, there is
provided an
apparatus comprising a serrated shaft-engaging surface for use with or
integrated into a
shrink disc. The serrated shaft-engaging surface is disposed on one or more
members
which generally define an aperture, such as a cylindrical aperture having two
open ends.
The aperture is sized and shaped for receiving a shaft of appropriate shape
and diameter,
and various embodiments of the invention may be configured for receiving
various shapes
and diameters of shaft. The shaft is typically cylindrical in shape, although
it is
contemplated that other shapes, such as conical shafts, may be accommodated.
[0026] The apparatus is configured to apply a radially inward pressure, via
the shaft-
engaging surface, which is generally adjustable within a predetermined range.
In some
embodiments, adjustment of the radially inward pressure may be associated with
an
adjustable diameter of the aperture. For example, the aperture diameter may be
adjustable
between a larger diameter and a smaller diameter. The larger diameter is
associated with
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reduced radially inward pressure and is such that the shaft is movable within
the aperture
for insertion or removal. The smaller diameter is associated with increased
radially inward
pressure and is such that the serrated shaft-engaging surface grippingly
engages the shaft,
thereby inhibiting relative axial and/or rotational movement of the shaft with
respect to the
shaft-engaging surface and associated apparatus. As the shaft-engaging surface
is serrated
and hence comprises teeth or similar structures, the aperture diameter as
mentioned above
may correspond to the diameter as measured from the tips of the teeth.
[0027] Further, when the shaft is engaged within the aperture, the shaft may
interfere with
the serrated aperture surface and hence substantially inhibit reduction in the
aperture
diameter. As such, operation of the apparatus which would otherwise tend to
reduce the
aperture diameter may instead apply a radially inward pressure to the shaft,
which may
potentially increase in magnitude. In some embodiments, the radially inward
pressure may
cause the protrusions of the serrated surface to "bite" or intrude into the
surface of the shaft,
thus marking the surface of the shaft, and the aperture diameter may
correspondingly
reduce. Such biting action may correspond to the gripping engagement of the
shaft. In
various embodiments, the amount of intrusion of protrusions into the shaft may
be
significantly less than the total length of the protrusion. That is, the
intrusion may
correspond to a relatively shallow marking on the surface of the shaft rather
than a deep
intrusion into the shaft. This may aid in preserving structural integrity of
the shaft as well
as reducing the required range of diametric adjustability of the shrink disc.
[0028] In some embodiments, the protrusions on the serrated surface function
to localize
the radially inward pressure to a set of points or sub-regions which initially
engage the shaft
over less than an entirety of the shaft surface area. For example, the
protrusions may
correspond to an array of sharpened spikes or ridges. This localization of
pressure may
facilitate the intrusion of the protrusions into the shaft surface. Once the
intrusion is
established, the tortuous profile of the interface between the protrusions and
the marked
shaft surface may function to inhibit relative motion of the apparatus and the
shaft, such as
axial or rotational motion.
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[0029] In some embodiments, the nature of the motion inhibition may depend on
the
shapes and orientations of the protrusions used. For example, if a protrusion
is asymmetric,
having at least one steeper side, that protrusion may operate to brace more
effectively
against forces which approach the protrusion from opposite the steeper side.
In some
embodiments, a plurality of protrusion shapes and orientations may be used in
combination.
[0030] FIGs. 1A to 1C illustrate cross-sectional partial views of the
apparatus of the
present invention with a serrated shaft-engaging surface 100 and a
corresponding shaft 120,
in accordance with an embodiment of the present invention. In the
configuration depicted
in FIG. 1A, the shaft 120 is movable within the aperture defined by the shaft-
engaging
surface 100. A gap 107 may be present between the shaft 120 and shaft-engaging
surface
100 in this configuration. In FIG. 1B, the aperture is reduced in size by an
increase in the
radially inward pressure 105 until protrusions 110 of the serrated shaft-
engaging surface
100 engage the shaft 120 but impart substantially little or no pressure
thereto. Thus, in FIG.
1B, the shaft is still at least somewhat movable within the aperture. In some
embodiments,
the arrangement of FIG. 1B may correspond to the largest diameter of the
aperture, in which
case FIG. 1A may be omitted. In FIG. 1C, the radially inward pressure 105 is
increased so
that the protrusions 110 intrude into the shaft-engaging surface 100, thereby
forming marks
125 in the surface of the shaft 120.
Insert
[0031] In some embodiments, the apparatus may be an insert apparatus for
interposing
between a shaft and a compression ring of a shrink disc assembly. The insert
apparatus,
which may be separate from the compression ring, includes an outer surface and
a serrated
inner surface configured for grippingly engaging the shaft. The insert
apparatus may be
ring-shaped, for example. In some embodiments, the outer surface of the insert
apparatus
may also be serrated and configured for grippingly engaging an inner surface
of the
compression ring. In other embodiments, the outer surface is unserrated, and
may be
smooth or roughened. Radial inward force is applied by the shrink disc to
the insert,
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thereby gripping the insert within the shrink disc. The insert further
transmits part of the
applied radial inward force therethrough, so that the insert in turn grips the
shaft.
[0032] FIG. 2 illustrates an insert apparatus provided in accordance with an
embodiment
of the present invention. The insert apparatus comprises two arcuate,
semicircular bodies
212, 214 separated by gaps 216, 218 extending in the axial direction. The
bodies 212, 214
collectively provide a serrated inner surface 220 of the insert, which is
configured for
surrounding and grippingly engaging a cylindrical shaft when the bodies are
arranged
circumferentially around the shaft. The insert further includes an outer
cylindrical surface
230 which is configured for engagement within and compression by a separate
shrink disc
apparatus. The outer cylindrical surface 230 is also collectively provided by
the bodies 212,
214. The serrated inner surface 220 may be configured in a variety of ways,
for example
similarly to the serrated inner surface 420 as illustrated in FIG. 4, or as
described elsewhere
herein.
[0033] FIG. 3 illustrates an insert apparatus provided in accordance with
another
embodiment of the present invention. The insert apparatus is similar to that
of FIG. 2,
except that the outer cylindrical surface 330 is also serrated, in order to
provide for gripping
engagement with the shrink disc apparatus.
[0034] In some embodiments, the outer diameter of the insert is configured to
provide an
adequate amount of surface area such that a shrink disc assembly may
adequately grip the
insert substantially without slippage. As the outer diameter is increased by
increasing radial
thickness of the insert, a larger surface area of the outer surface is present
for engagement
with the shrink disc of appropriate size. In some embodiments, such an outer
surface is
unserrated. As such, the insert may be used as an adapter for facilitating
mounting of a
shrink disc onto a shaft which would otherwise have too small a diameter for
adequate
coupling with a conventional shrink disc, for a given application. The
protrusions facilitate
enhanced gripping of the shaft, while the serrated or unserrated outer surface
of the insert
provides a bearing surface for gripping by the shrink disc.
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[0035] While a serrated outer surface of the insert may provide for enhanced
gripping of
the insert by the shrink disc, an unserrated outer surface may be desirable in
some cases.
For example, use of an unserrated surface allows for use of a shrink disc
having an inner
aperture diameter which more closely matches the insert outer diameter. As
such, a shrink
disc with a limited amount of diametric adjustability may be used. Further,
the shrink disc
itself remains substantially unmarked by an unserrated outer surface.
Compression Ring
[0036] In other embodiments, the apparatus may be a compression ring portion
of a
shrink disc assembly. In such embodiments, the serrated inner surface is
integral with the
shrink disc rather than being provided as a separate insert component. For
example, the
compression ring portion may comprise an outer surface and a serrated inner
surface
configured for grippingly engaging the shaft as above. The outer surface may
comprise an
outer surface having at least one outer conical surface. The at least one
outer conical
surface may be used to cooperate with at least one mating inner conical
surfaces of a
pressure ring portion which is disposed radially outward of the compression
ring portion.
These inner conical surfaces cooperate with the outer conical surfaces of the
compression
ring portion to radially compress the compression ring portion when the
pressure ring
portion is axially moved against the compression ring portion, in accordance
with a wedge
effect.
[0037] FIG. 4 illustrates a compression ring portion 410 of a shrink disc, in
accordance
with embodiments of the present invention. The compression ring portion
comprises two
arcuate, semicircular bodies 412, 414 separated by gaps 416, 418 extending in
the axial
direction. The bodies 412, 414 collectively provide a serrated inner surface
420 of the
compression ring portion, which is configured for surrounding and grippingly
engaging a
cylindrical shaft when the bodies are arranged circumferentially around the
shaft. The
compression ring portion further includes a pair of oppositely oriented outer
conical
surfaces 432, 434 and a ridge 436 extending in the circumferential direction
and separating
the pair of conical surfaces. The conical surfaces correspond to parts of
oppositely facing
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cones which are centered on the axial center of the shaft. The conical
surfaces 432, 434 and
the ridge 436 are also collectively provided by the bodies 412, 414.
[0038] The serrated inner surface 420 comprises a plurality of teeth arranged
in a
rectangular grid. As illustrated, the interior teeth are shaped substantially
as a regular
square pyramid, while the teeth formed around the perimeters of the bodies
412, 414 are
halves of rectangular pyramids. As also illustrated, the grid can comprise
about 11 teeth in
the axial direction and about 50 teeth per body 412, 414 in the
circumferential direction. It
will be appreciated that the serrated inner surface 420 may alternatively
comprise a different
arrangement of teeth.
[0039] FIGs. 5A to 5C illustrate plan, cross-sectional and perspective
views, respectively,
of a shrink disc comprising the compression ring portion 410 of FIG. 4 as well
as a pressure
ring portion 560 disposed radially outward of the compression ring, in
accordance with
embodiments of the present invention.
Example dimensions are also illustrated, which
may be absolute or relative dimensions. The illustrated shrink disc is of the
bi-conical style,
and hence the pressure ring portion 560 comprises two halves 565, 570. Each
half defines
an inner surface 567, 572 (see FIG. 5B) which has an inward conical portion
configured to
contact a mating one of the pair of outer conical surfaces 432, 434. As the
pressure ring
halves 565, 570 are moved axially overtop of the compression ring portion, the
pressure
ring halves can be moved into or out of alignment with the pressure ring
portion. The axial
movement is induced by turning of the screws 575 to move the pressure ring
halves 565,
570 toward or away from each other, thereby bringing the pressure ring into or
out of
alignment with the compression ring portion 410, respectively. The screws
engage bores
576, 577 (see FIG. 5B) formed within the two halves of the pressure ring to
impart the
relative motion therebetween. The bores 576 of the pressure ring half 565 may
be threaded
while the bores 577 of the pressure ring half 570 may be drilled. The heads of
the screws
may impinge, for example directly or via washers 578 (see FIG. 5B), onto a
surface of the
pressure ring half 570 to assist in imparting the relative motion of the two
halves. As the
pressure ring moves into alignment with the compression ring portion in the
axial direction,
a wedge effect due to the mating conical surfaces imparts a radially inward
pressure on the
CA 02882967 2015-02-23
compression ring and toward the shaft. Thus, the screws allow for selectable
application of
the radially inward pressure. The pressure ring halves 565, 570 are separated
by a gap 580
which generally aligns with the ridge 436 of the compression ring. This gap
580 facilitates
the relative motion of the two pressure ring halves.
Number of Gripping Bodies
[0040] In some embodiments, the apparatus, either the insert or the
compression ring,
may be formed of a single unitary body. In some embodiments, the unitary body
may
include a gap formed in the axial direction. Thus, for example, the insert
apparatus may be
"0" shaped or "C" shaped. The gap facilitates adjustment of the aperture size
as the gap is
narrowed or widened. Whether or not a gap is not present, the apparatus may
transmit a
radially inward pressure from its radially outer surface to its radial inner
surface, potentially
with limited or no change in the aperture diameter.
[0041] In other embodiments, the apparatus may be formed of a plurality of
bodies which
are cooperatively arranged to define an aperture therebetween. For example,
the apparatus
may comprise a pair of half-ring shaped bodies each defining part of the shaft-
engaging
surface, or three or more bodies each defining a corresponding fraction of the
shaft-
engaging surface. The bodies are sized such that, when arranged around the
shaft, gaps are
present between adjacent bodies. These gaps may cooperatively facilitate
adjustment of the
aperture size as the gaps are narrowed or widened.
[0042] In some embodiments of the present invention, use of a plurality of
bodies rather
than a single body may be advantageous for one or more reasons. First, the
aperture
diameter may be adjusted with reduced distortion in the aperture shape
compared to a single
"C"-shaped body. For example, this may be due to avoidance of exaggerated
bending of the
"C"-shaped body at a location opposite to the gap thereof. As such, the
effective range of
diameter adjustment of the aperture may be increased. This may in turn
facilitate an
adequate amount of diameter adjustment required in order to allow the
protrusions to
sufficiently intrude into the shaft surface. Second, the bodies may be
arranged about the
shaft directly, rather than sliding a single body onto the end of the shaft.
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[0043] In some embodiments, the insert or compression ring is formed of a
resilient
material which returns to an initial shape as radially inward pressure
thereupon is released.
The material may be steel, such as spring steel, or another suitable metallic
or non-metallic
material. The material may have sufficient hardness that the protrusions
thereof bite into or
mark the shaft when sufficient radially inward pressure is applied.
Shrink Disc Assembly
[0044] Yet other embodiments of the present invention provide a shrink disc
assembly
comprising a ring mechanism defining an internal aperture, which is configured
to receive a
shaft therein. The ring mechanism is operable to selectably apply a radially
inward pressure
to the shaft. Thus, in one configuration or mode, the ring mechanism may not
apply the
radially inward pressure, while in another configuration or more, the ring
mechanism may
apply the radially inward pressure. This allows the ring mechanism to be
disposed on the
shaft prior to tightening. The amount of radial inward pressure may be
adjustable for
example by turning of screws. As described elsewhere herein, the internal
aperture includes
an inner surface having one or more protrusions configured to grippingly
engage the shaft
upon application of the radially inward pressure.
[0045] In various embodiments, the radial pressure of the shrink disc is
provided based on
an application of the wedge effect. The shrink disc may therefore further
include a radially
inner compression ring portion having an outer surface and an inner surface.
The outer
surface includes at least one outward conical portion while the inner surface
is the serrated
surface. Such a shrink disc further includes a radially outer pressure ring
portion having a
second inner surface comprising at least one inward conical portion configured
to cooperate
with the at least one outward conical portion to apply the radially inward
pressure by
compression of the compression ring portion in response to alignment of the
pressure ring
portion with the compression ring portion in an axial direction.
[0046] A bi-conical style shrink disc employing the wedge effect and a
compression ring
thereof has been described above with respect to FIGs. 4 to 5. Alternative
styles of shrink
disc may also be provided. For example, FIG. 6 illustrates a cross-sectional
view of a
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single-conical style of shrink disc assembly provided in accordance with
another
embodiment of the present invention. As illustrated, the shrink disc includes
a compression
ring 600 having a serrated inner surface 605 and an outer surface comprising a
single
outward conical portion 610. The compression ring 600 further includes a
flange 620
having apertures 625 for receiving a plurality of screws 627 therein, the
apertures being
arranged circumferentially around the shrink disc. The flange may be
unthreaded. The
shrink disc further includes a pressure ring 630 having a plurality of
threaded apertures 635
for receiving the screws 627. The pressure ring 630 includes an inner surface
comprising a
single inward conical portion 640 configured to cooperate with the outward
conical portion
610. As the pressure ring 630 is aligned with the compression ring 600 by
turning action of
the screws 627, radially inward pressure is applied to the compression ring
600, thereby
causing gripping engagement of the shaft and/or intrusion of protrusions of
the serrated
inner surface 605 into the shaft. The compression ring 600 may be formed of a
single "C"-
shaped body rather than plural separate bodies. This arrangement may simplify
operation
by reducing the potential for different parts of the compression ring to come
out of
alignment during tightening. However, it is contemplated that the compression
ring 600
may alternatively comprise a plurality of arcuate portions arranged
circumferentially around
a shaft and separated by gaps.
[0047] In some embodiments, a mechanism other than screws or bolts may be used
to
align the pressure ring with the compression ring. For example, an axial force
applied by an
external tool such as a hydraulic driver may be used to induce such alignment.
Frictional
forces or other means may then be used to retain the axial alignment until an
opposite axial
force is applied by the same or a different external tool.
[0048] As another example, FIG. 7 illustrates a thermal expansion style
compression ring
700 for disposal on a shaft 730. The compression ring 700 is formed of a
material, such as
metal, which expands upon heating and contracts upon cooling. As such, the
compression
ring 700 may be heated prior to disposal on the shaft, and radially inward
pressure may be
applied as the compression ring cools. Although in some embodiments a surface
of the
compression ring's interior aperture may be serrated, the present embodiment
illustrates an
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insert apparatus 710 which is interposed between the compression ring 700 and
the shaft, by
locating the shaft within a serrated aperture 715 of the insert apparatus and
locating the
insert apparatus within an aperture of the compression ring 700. An external
cylindrical
surface 720 of the insert apparatus may be serrated or unserrated. This
configuration may
be desirable in various instances, since the protrusions of the serrated
surface are not
directly heated (although they may be indirectly heated to a certain degree by
the
compression ring), and therefore may be more resilient to deformation.
Protrusion Configurations
[0049] Embodiments of the present invention may incorporate various sizes,
shapes,
orientations, arrangements, varieties and/or densities of protrusions
corresponding to the
serrated surface or surfaces of a compression ring or insert. The protrusion
configuration
may depend on one or more factors, such as desired performance
characteristics,
manufacturability, part tolerances, diametric adjustability of the shrink
disc, and the like.
Although several particular examples are set forth below, it should be
understood that other
protrusion configurations may also be possible.
[0050] In various embodiments, the protrusions may be arranged sparsely or
densely upon
the serrated surface, in a regular or irregular pattern. In one embodiment, a
small number of
protrusions are located in a spaced-apart configuration, for example as
illustrated in FIG.
8A. This may provide for adequate functionality in some applications while
limiting shaft
marking. In another embodiment, the protrusions are arranged in a grid
pattern, such as a
rectangular or hexagonal grid pattern, which covers some or substantially all
of the serrated
surface. The protrusions may in particular be substantially sharp, spiked
protrusions
terminating at a point.
[0051] In yet another embodiment, the protrusions are elongated to form
substantially
sharp ridges extending in the axial direction, such as illustrated in FIG. 8B,
a
circumferential direction, such as illustrated in FIG. 8C, or in a clockwise
or counter-
clockwise spiral direction, or the like, and may be arranged side by side with
or without
spacing. Axially extending ridges may be used for example when it is desired
to primarily
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inhibit slippage in the circumferential direction, while circumferentially
extending ridges
may be used for example when it is desired to primarily inhibit axial
slippage. Axially
extending protrusion ridges may also function substantially similarly to a key
block which is
self-tapping. Spiral protrusion ridges may inhibit slippage in plural
directions while
potentially being susceptible to slippage under a twisting motion commensurate
with the
spiral.
[0052] In some embodiments, the protrusion size may be configured based on
considerations such as durability, available amount of diametric adjustment of
the
associated shrink disc, desired angle of the protrusion faces, desired amount
of intrusion
into the shaft, or the like, or a combination thereof. In one embodiment, the
protrusions
have a base length equal to about 1% of the circumference of the serrated
surface base, and
a height about equal to the base length.
[0053] In some embodiments, the angle of the protrusion faces may be
configured based
on considerations such as manufacturability, a desired amount of force
required for
intrusion into and/or marking of the shaft, or the like.
[0054] In some embodiments, a protrusion may extend radially, that is
perpendicularly
from a base portion of the serrated surface, and may further be substantially
symmetric
about its axis of extension. Regular conical or pyramid-shaped protrusions are
examples of
this configuration.
[0055] In some embodiments, a protrusion may be asymmetric. For example, at
least one
face of the protrusion may extend from the base of the serrated surface at a
steeper angle
than at least one other face. In some embodiment, an asymmetric protrusion may
be
substantially sawtooth shaped, for example having a first portion extending
directly radially
inward, that is, perpendicularly from the base portion of the serrated
surface, and having a
second portion extending at an angle to form a peak with the first portion.
The first portion
may correspond to a single face or two adjacent faces of a protrusion. The
sawtooth
protrusion may have a square or triangular base, for example. In one
embodiment, a
double-sawtooth configuration, in which pairs of adjacent protrusions exhibit
an
CA 02882967 2015-02-23
shaped cross section, may be provided. Various examples of asymmetric
protrusion shapes
are illustrated in FIG. 8D.
[0056] In some embodiments, asymmetric protrusions, such as sawtooth
protrusions, may
be used to preferentially brace against slippage in a given direction. For
example, when it is
desired to preferentially brace against slippage due to a force (or component
of a force) that
is applied in a particular direction, such as an axial direction, clockwise or
counter-
clockwise circumferential direction, or a combination thereof, protrusions may
be provided
which include a steeper face on the side of the protrusion that is further
from the force
origin than on the side of the protrusion that is closer to the force origin,
as also illustrated
in FIG. 8D where the steeper face 820 is shown relative to the applied force
825. In other
words, the steeper face 820 faces away from an expected source of slippage-
inducing force
825. Such forces may include forces expected to be induced when tightening
screws, forces
resulting from shaft rotation or axial loading, or the like.
[0057] In some embodiments, a variety of different protrusion types may be
provided on
the same serrated surface. This may allow for a mixing of advantages of the
different
protrusion types.
Methods of Coupling Shrink Disc to Shaft
[0058] Embodiments of the present invention provide for methods of coupling a
shrink
disc to a shaft, wherein either the shrink disc or an insert includes a
serrated surface for
grippingly engaging the shaft.
[0059] In some embodiments, there is provided a method of coupling a shrink
disc
assembly to a shaft. The method includes locating the shaft within an internal
aperture
defined by the shrink disc assembly. The internal aperture includes an inner
surface having
one or more protrusions as described elsewhere herein. The method further
includes
operating the ring mechanism to apply a radially inward pressure to the shaft
via the inner
surface. The radially inward pressure causes the one or more protrusions to
grippingly
engage the shaft.
16
CA 02882967 2015-02-23
[0060] In other embodiments, there is provided a method of coupling a shrink
disc
assembly to a shaft. The method includes providing an insert apparatus
defining an internal
aperture. The internal aperture includes an inner surface having one or more
protrusions.
The method further includes locating the shaft within the internal aperture of
the insert
apparatus. The method further includes locating the insert apparatus within a
further
internal aperture defined by the shrink disc assembly. The method further
includes
operating the ring mechanism to apply a radially inward pressure to the insert
apparatus and
to the shaft via the insert apparatus. The radially inward pressure causes the
one or more
protrusions of the insert apparatus to grippingly engage the shaft.
100611 In some embodiments, and in association with the methods described
herein, the
shrink disc assembly includes a radially inner compression ring portion and a
radially outer
pressure ring portion. The compression ring portion includes an outer surface
comprising at
least one outward conical portion as well as the inner surface of the internal
aperture. The
pressure ring portion includes a second inner surface comprising at least one
inward conical
portion configured to cooperate with the at least one outward conical portion.
The method
in such embodiments further includes aligning the pressure ring portion with
the
compression ring portion in an axial direction, thereby applying the radially
inward pressure
to the shaft via compression of the compression ring portion.
Applications
100621 Embodiments of the present invention may be used in coupling together a
pair of
shafts, such as cylindrical rotating shafts, for example in association with a
tool joint. One
of the shafts may be driven by a motor while another is connected to a load or
tool, for
example. Further, a first shaft may comprise a tapered or non-tapered cavity,
while a
second shaft may comprise an extension which fits within the cavity to provide
a mating
connection between the shafts. The first shaft may include a slot which
facilitates inward
movement of the part of the first shaft surrounding the cavity, in order to
grip the second
shaft when inserted therein.
17
CA 02882967 2015-02-23
[0063] In some embodiments, a shrink disc may be coupled to an exterior of the
cavity-
containing first shaft so that an inner surface imparts a radially inward
force to the first shaft
in order to impart radially inward force for gripping of the second shaft
within the first shaft
cavity. The first shaft may include at least one slot in its surface, the slot
communicating
with the cavity, so that the first shaft can deform to grip the second when
subjected to
radially inward compressive force.
[0064] In some embodiments, the shrink disc may be located so that straddles
both of the
first shaft and the second shaft. That is, the shrink disc may grippingly
engage both an
exterior surface of the first shaft as well as an exterior surface of the
second shaft. As such,
the shrink disc itself may provide at least part of the coupling between the
two shafts. A
first circumferential portion of the shrink disc inner surface may surround
and engage an
exterior portion of the first shaft, while a second circumferential portion of
the shrink disc
inner surface, adjacent to the first circumferential portion, may surround and
engage an
exterior portion of the second shaft when mated with the first shaft.
[0065] FIGs. 9A to 9C illustrate cross-sectional views of a pair of shafts for
coupling
together using a shrink disc assembly, in accordance with embodiments of the
present
invention. FIG. 9A illustrates a first shaft 910 having a tapered, frustro-
conical aperture
920. The sidewall of the aperture may be threaded. FIG. 9A further illustrates
a second
shaft 930 having a tapered, frustro-conical extension 940. The face of the
extension may
also be threaded for mating with the aperture 920. The aperture 920 and the
extension 940
may be sized and shaped such that the extension fits or screws snugly into the
aperture.
[0066] FIGs. 9B and 9C illustrate the first shaft 910 coupled to the second
shaft 930,
including insertion of the extension 940 of the second shaft into the aperture
920 of the first
shaft. In FIG. 9B, a bi-conical shrink disc 950 is positioned straddling the
first shaft and the
second shaft, such that a first portion of a serrated inner surface 955 of the
shrink disc
contacts an outer surface of the first shaft, and a second portion of the
serrated inner surface
955 contacts an outer surface of the second shaft. Similarly, in FIG. 9C, a
single tapered
shrink disc 960 is positioned straddling the first shaft and the second shaft,
such that a first
18
CA 02882967 2015-02-23
portion of a serrated inner surface 965 of the shrink disc contacts an outer
surface of the
first shaft, and a second portion of the serrated inner surface 965 contacts
an outer surface
of the second shaft. In both cases, the shrink disc may then be tightened to
provide gripping
engagement of both the first shaft and the second shaft.
[0067] Embodiments of the present invention may facilitate gripping engagement
of both
of a pair of mated shafts when straddling same, even when the outer diameters
of the pair of
shafts are mismatched by up to a nominal amount. For example, as illustrated
in FIGs. 9B
and 9C, a shrink disc may be located such that a serrated inner surface of the
shrink disc (or
associated insert) straddles both of the pair of mated shafts as described
above. Notably, the
outer diameter of one of the mated shafts may differ by up to a nominal amount
from the
outer diameter of the other of the mated shafts. This difference in outer
diameters may be
due to manufacturing variation, for example. In some embodiments, the nominal
amount
by which two shaft diameters differ may be up to about one or two times the
length of the
protrusions of the serrated inner surface.
[0068] In
some embodiments, whereas a prior art shrink disc with a flat inner surface
may fail to grippingly engage both shafts when the shaft outer diameters are
mismatched,
the serrated inner surface provided in accordance with the present invention
may in fact
facilitate or enhance engagement of both shaft outer diameters. For example,
the serrations
may intrude further into the larger-diameter shaft while still contacting the
smaller-diameter
shaft and potentially intruding into the smaller-diameter shaft to a lesser
degree. As another
example, the serrations may deform under compressive contact with the larger-
diameter
shaft, thereby facilitating further travel of the shrink disc to engage the
serrated inner
surface with the smaller-diameter shaft. In effect, the serrated inner surface
presents a range
of aperture diameters for accommodating and grippingly engaging a range of
shaft
diameters therein. For
example, two shafts having different diameters can be
accommodated and grippingly engaged concurrently when the serrated inner
surface is
disposed to contact both shafts.
19
CA 02882967 2015-02-23
[0069] In various embodiments, the gripping engagement provided by the
serrated surface
or surfaces is configured to inhibit slippage during installation of the
shrink disc on the
shaft. For example, during tightening of the shrink disc to the shaft by
application of radial
inward pressure, but before full tightening of the shrink disc to the shaft,
mechanical forces
corresponding to the tightening may tend to cause slippage of the partially-
engaged shrink
disc. Such mechanical forces may result from turning of tightening screws or
bolts, for
example. To counter this, the protrusions of the serrated surface may be
configured to
grippingly engage the shaft to a greater degree earlier in the tightening
process, relative to a
comparable non-serrated shrink disc. In some embodiments, the protrusions may
be sized,
shaped and/or oriented particularly so as to brace against slippage, such as
rotational or
axial slippage, in directions that are anticipated to occur during tightening.
[0070] Various embodiments of the present invention may be applied in the
following
situation. For a shrink disc operating based on the wedge effect, a
compression ring portion
and a pressure ring portion thereof may interface along mating conical
surfaces. When the
angle between the conical surfaces and the axial direction is less than 45
degrees, a
mechanical advantage may be present in which an axial force, which is applied
to move the
compression ring portion axially relative to the pressure ring portion, is
amplified as it is
transformed into a radially compressive force. When a screw mechanism, such as
a set of
screws, is used to effect the axial movement, a further mechanical advantage
may be
applied due to the helical pitch of the screw mechanism. However, in practice,
the axial
force may not be perfectly transformed into the radially compressive force.
For example,
static friction or "stiction" between the mating conical surfaces may tend to
induce an axial
translation moment of the compression ring with respect to the shaft. As
another example,
when a pair of oppositely facing conical surfaces are present, static friction
present
simultaneously on both conical surfaces may tend to induce a radial buckling
moment in the
compression ring, which may potentially result in uneven distribution of the
compressive
force. Such an axial translation moment and/or radial buckling moment may be
countered
by use of a serrated surface engaging the shaft, as described elsewhere
herein. This in turn
may allow for a greater freedom in choosing the design parameters of the
shrink disc. For
CA 02882967 2015-02-23
example, a greater freedom in choosing the angle of the conical surfaces may
be provided as
constraints due to the above-described static friction problems are relaxed.
100711 As another example, when tightening screws located around the perimeter
of a
shrink disc in order to apply compressive force, the turning of a screw may
result in a force
applied to the shrink disc in the circumferential direction. This may tend to
cause slippage
of the shrink disc in the circumferential direction. The protrusions may be
configured to
brace against such slippage by appropriate angling of the protrusions. For
example, if the
potential slippage of the shrink disc due to a force oriented in the clockwise
direction, the
protrusions may include sawtooth shaped teeth each having a steeper face on
the clockwise
side of the protrusion, that, the side which is further from the force origin
than on the side of
the protrusion that is closer to the force origin.
[0072] In some embodiments, the gripping engagement provided by the serrated
surface
or surfaces is configured to inhibit slippage after installation of the shrink
disc on the shaft.
For example, a tool may be coupled to the shrink disc assembly which functions
to impart
rotation of the shaft for operation of the tool. As another example, the
shrink disc may be
part of an assembly which is configured to couple a driven rotating shaft to a
second
rotating shaft, so that torque is transmitted through the assembly to the
second rotating
shaft. The serrated surface may function to provide grip which braces at least
against
counter forces induced by the shaft rotation, when the shaft rotates in at
least one direction.
As yet another example, the shrink disc may carry an axial load, and the
protrusions may be
configured to brace against potential slippage due to such an axial load. Such
protrusions
may for example include appropriately oriented sawtooth shaped teeth which are
pointed or
ridged.
[0073] It is obvious that the foregoing embodiments of the invention are
examples and
can be varied in many ways. Such present or future variations are not to be
regarded as a
departure from the spirit and scope of the invention, and all such
modifications as would be
obvious to one skilled in the art are intended to be included within the scope
of the
following claims.
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