Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION:
TERMINATION INSTALLATION METHOD FOR LONG CABLES
CROSS-REFERENCES TO RELATED APPLICATIONS
This non-provisional patent application claims the benefit of an earlier-filed
non-
provisional application. The parent application was assigned serial number
15/784,267 (to be
issued as U.S. Pat. No. 10,054,505). It listed the same inventor.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR
DEVELOPMENT
Not Applicable.
MICROFICHE APPENDIX
Not Applicable member
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DESCRIPTION
Title of the Invention: Termination Installation Method for Long Cables
1. Technical Field.
This invention relates to the field of tensile strength members. More
specifically, the
invention comprises a method for creating a long tensile strength member with
a high-
performance termination or terminations that can be pre-tested using equipment
that is limited to
testing shorter tensile strength members.
2. Background Art.
Tensile strength members must generally be connected to other components in
order to
be useful. A flexible cable provides a good example. The cable must generally
include some
type of end-fitting so that it can be transmit a load. For example, a cable
used in a hoist
generally includes a lifting hook on its free end. This lifting hook may be
rigged to a load. The
assembly of an end-fitting and the portion of the cable to which it is
attached is generally, called a
"termination."
A tough steel lifting hook is commonly attached to a wire rope to create a
termination. A
"spelter socket" is often used to create the termination. The "spelter socket"
involves an
expanding cavity within the end-fitting. A length of the wire rope is slipped
into this cavity and
the individual wires are splayed apart. A liquid potting compound is then
introduced into the
expanding cavity with the wires in place. The liquid potting compound
transitions to a solid over
time and thereby locks the wire rope into the cavity.
The potting compound used in a spelter socket is traditionally molten lead and
¨ more
recently ¨ is more likely a high-strength epoxy. However, the term "potting
compound" as used
in this description means any substance which transitions from a liquid to a
solid over time.
Examples include molten lead, thermoplastics, UV-cure or thermoset resins
(such as two-part
polyesters or epoxies). Other examples include plasters, ceramics, and
cements. The term
"solid" is by no means limited to an ordered crystalline structure such as
found in most metals.
In the context of this invention, the term "solid" means a state in which the
material does not
flow significantly under the influence of gravity.
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Terminations on wire rope are quite common in hoists and cranes. These
terminations
30 are well understood and their performance and reliability have been
established over many
decades. In recent years the opportunity to replace wire ropes with modern,
high-strength
synthetic cables has arisen. Many different materials are used for the
filaments in these synthetic
cables. These include KEVLAR, VECTRAN, PBO, DYNEEMA, SPECTRA, TECHNORA,
ZYLON, glass fiber, and carbon fiber (among many others). In general the
individual filaments
35 have a thickness that is less than that of human hair. They also tend to
have low surface friction.
They are quite different from steel wires.
Terminations are used for synthetic filament cables, but they assume a
different form than
those used for wire rope. Synthetic filament cables tend to be made by
braiding multiple strands
together. While the individual filaments are made using various modern
processes, the
40 construction of the cable itself tends to follow the patterns
established for natural-fiber ropes
many years ago. Perhaps not surprisingly, the methods used to create a
termination tend to
follow the old patterns for ropes as well.
FIGS. 1-2 shows a traditional method for adding a termination to one end of a
synthetic
cable. Cable 10 is made from advanced high-strength synthetic filaments. It is
known to join
45 multi-stranded cables using weaving or splicing methods. In these
methods, connections are
made by interweaving strands of one section of cable with strands of another
section of cable
(sometimes the sections lie in the same cable and sometimes they do not).
FIG. 1 shows an exemplary prior art operation. Cable 10 includes eight
individual strands
of synthetic filaments. Each strand may contain thousands or even millions of
individual
50 filaments, but the prior art weaving operations do not typically break
the cable down beyond the
strand level. The depiction of cable 10 is representative rather than entirely
accurate. The
example shown has 8 separate strands. The strands would typically be
interwoven with 2 pairs of
strands in a left-hand helix and two pairs in a right-hand helix.
The objective of the example shown in FIGS. 1 and 2 is to weave a length of
the cable
55 back on itself to form an "eye" on the cable's end. Considerable
mechanical skill and dexterity is
required to form an eye on the end of a cable and in other instances to join
lengths of cable
together. However, persons having these skills are commonly found in
industries where large
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cables are used. Further, the strength and reliability of cable splices made
by such persons are
well understood and accepted. As a result, it is readily accepted that these
proven methods of
60 connection do not require pretesting and can even be done in the
field, in a non-controlled
environment, by trained personnel. This is even true for critical
applications. This has been the
standard method of termination since inception, and it makes up over 99% of
the entire industry
of long synthetic fiber cables. Thus, there is considerable standardization,
knowledge, and field
support for such a method of termination.
65 In FIG. 1, a length of strands proximate the cable's end is unwoven
to create separated
strands 14. The end of the cable is bent into a loop or bight, sometimes
around a reinforcing
element such as thimble 12. FIG. 2 shows the continuation of the operation.
The weave of the
strands within the cable is loosened so that separated strands can be threaded
back into the cable
in a prescribed pattern. Interwoven section 24 is thereby created. The loose
ends of separated
70 strands 14 are typically cut off (after a sufficiently long
interwoven section 24 has been created)
and taped or otherwise secured.
The result is eye splice 16 on one end of cable 10. When produced by trained
personnel,
the eye splice does work and it is considered an efficient and reliable means
of termination. In
this context the term efficiency means the ratio of the breaking stress of the
complete cable with
75 the termination attached versus the breaking stress of the cable
without a stressed area such as in
the middle of the cable. A perfectly efficient cable would have an efficiency
of 100%, including
the termination. On synthetic fiber cables, achieving this or nearly this
efficiency is commonly
possible with many forms of prior art splices.
Although the eye splice is strong, it is ill-suited to many applications. For
example, while
80 one could use an eye splice to attach a lifting hook to the end of a
hoist line, the eye splice is
unable to withstand battering forces very well. In addition, the diameter of
the eye splice will be
too large in many instances. It would be advantageous to instead connect a
hook or other device
directly to the synthetic cable, analogous to the way a spelter socket is
connected to a wire rope.
Fortunately, the technology to create such terminations exists.
85 The prior art approaches to adding a termination to a synthetic
cable are explained in
detail in commonly-owned U.S. Pat. No. 7,237,336, which is hereby incorporated
by reference.
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The terminations can be added to the cable as a whole or some sub-component of
the cable such
as a strand. Commonly-owned U.S. Pat. No. 8,371,015 explains how multiple
terminations may
be attached to multiple strands of a larger cable. This too is incorporated by
reference.
90
In order to gain a strong and repeatable result, the addition of a termination
directly to a
synthetic cable must generally be done under highly controlled conditions such
as found in a
factory. This is particularly true of medium to large end fittings configured
for a cable having an
overall diameter of greater than 20 mm and sometimes being considerably
larger. In fact, those
skilled in the art recognize that terminating larger synthetic cables is
exceptionally difficult to
95
master in even a highly controlled environment. Unlike most metal strength
members, achieving
an efficient and repeatable result requires very stringent control of the
process, highly skilled
personnel and precise processing.
An end-fitting is commonly attached to a larger synthetic filament cable by
use of a
potting compound. Liquid potting compound (such as an epoxy or a polyester) is
added to a
100
cavity in the fitting after a length of filaments has been placed within the
fitting. It is preferable
to hold the components in a stable configuration while the potting compound
cures __ which may
take 12 hours or more. Temperature and other variables are preferably
controlled during this
process, as are the properties of the potting compound itself. The potting
compound may be
added to the cavity in a variety of ways, including pre-wetting, infusing,
etc.
105
The process of attaching an end fitting to a synthetic cable produces a wider
performance
variation than is typical for steel cables or for spliced techniques on
synthetic cables. In fact, the
creation of an advanced termination on an end of a synthetic cable will often
represent the
weakest link in the whole system. As such, in many instances it will be
necessary to test the
strength of the completed termination before it is used.
110
Exemplary applications include hoisting cables and mooring cables where a
known and
predictable strength is very important. This requirement creates challenges in
the field of
synthetic-filament cables since conventional tensile testing equipment used in
the industry is (1)
limited in strength and (2) limited in length. A typical large test frame can
pull loads of about
1,000 tons. The length of such a test frame is only about 20 meters though.
Longer test frames do
115
exist (some over 100 meters) but they are very rare. When tensile members are
made longer than
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the length of the readily available test frame, they are rarely able to be
tested properly given the
practical constraints that exist in industry. This creates limitations on what
can be tested and
impacts logistics on any large or remotely used tensile members requiring
specialty terminations.
It is desirable to use synthetic filament cables to replace steel and other
conventional
120 cables, but in order to do so the synthetic filament cables must have
an equivalent useful length.
Many large diameter applications are well beyond the typical test bed length,
such as 500 or even
1,000 meters as an example. In fact, most large and/or long cables will not
fit in any test bed in
the world. This complication does not present a serious issue for existing
steel or synthetic cables
using conventional technology because highly standardized methods and devices
have been
125 developed and proven to be reliable over the last century.
By comparison, it is not commonly possible to achieve the same level of
efficiency,
reliability, and repeatability with many of the more compact, mechanical,
versatile synthetic
cable methods of termination such as porting sockets, resin terminations,
composite terminations,
or spike-and-cone type frictional arrangements, etc. These types of
terminations tend to put far
130 greater stresses in a smaller area, meaning there is much less room for
operator error and the
efficiency can often be reduced if not handled properly. Further, these types
of terminations on
synthetic cables have by comparison a limited history, limited use, limited
standardization and
training, and introduce a significantly greater need for control over the
process in order to
achieve a repeatable result.
135 On a synthetic cable, known splicing techniques may not be suitable
for long lines and
are often not ideal from a termination perspective. For example, there is
often a need for a
termination analogous to those used for wire rope. Examples include
termination with a hard end
such as a hook, a threaded stud, a small eye, or a clevis on the end of a
spelter or resin socket,
etc. Such hard, versatile, and generally compact ends are well known and thus
a desirable option
140 in most industries where large and/or long cables are used. As an
example, an offshore steel
crane wire would typically have a very compact, potted socket made from steel
and including a
clevis or eye connection. As with splices used for synthetic fiber cables,
these versatile forms of
terminations are well established, standardized, trusted, and produced in the
field with
technicians that are trained in the process. Therefore high load testing in a
proofing bed is not
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145 generally necessary. However, when considering a high performance
synthetic cable, spliced
eyes do not provide the same level of functionality or versatility as those
from less proven
methods.
The proposed method creates a safe and reliable means to apply and validate
the
performance (pre-test) of a more desirable termination on such long synthetic
cable applications.
150 FIG. 3 __ a sectional view
________________________________________________ shows an example of an
advanced termination. Anchor 18 includes
an internal cavity 20. A length of strands from cable 10 is placed within this
cavity. Preferably
the strands are splayed apart in some form of expanding cavity (though other
techniques may be
used). A liquid potting compound is placed within the cavity (either before,
during, or after the
strands are added).
155 The liquid potting compound transitions to a solid over time to
create potted region 22.
Once solidified as shown, the strands within potted region 22 are locked in
place and anchor 18
is secured to the end of the cable. Some feature for transmitting a load to
the cable is typically
included. In this example loading feature 21 assumes the form of a loop.
Other classes of advanced terminations can be made without using a potting
compound to
160 secure the cable strands to the anchor. FIG. 10 shows an assembly that
is commonly referred to
as a "spike and cone" termination. A length of strands is splayed apart in
cavity 20 as for the
potting example. However, rather than using potting compound, they are
mechanically secured.
Cone 62 is introduced into the center of the strands. Compression plug 64 is
then screwed into
the open end of anchor 18 via threaded engagement 66. The strands are then
mechanically
165 clamped in place.
It is possible to combine the prior art approaches
_______________________________ such as by using potting compound in
the spike-and-cone configuration of FIG. 10. In addition, anchor 18 can be
made quite tough. As
an example, the anchor may be made of stainless steel so that it can endure an
abusive
environment. Such a termination is advantageous in many instances where a
synthetic cable is
170 used.
Countless forms of synthetic fiber cable terminations can be conceived,
including those
made entirely of composites for example. Any such versatile termination that
is not a splice, and
especially those which are more compact in nature, have many potential
limitations as covered
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previously. These limitations create the absolute need for production in a
controlled setting
175 (which is not in the field).
Given the above, the present industry issue exists: Large ropes are utilized
in the field,
often in remote areas, and they often need to be re-terminated. Going back to
the offshore crane
example, if a crane line is damaged in the ocean, there must be an immediate
remedy to get back
to work. Removing the line and shipping the cable to its original factory for
re-termination is not
180 a feasible option. Reliable field termination of many forms exist for
steel wire today, but they do
not exist for synthetic cable. If using a synthetic cable and the termination
is anything other than
a splice, it requires both a controlled setting and most often proof testing
to ensure safe and
reliable use. This very fact has prevented synthetic cables from being
utilized where a more
versatile or compact termination is needed. The present invention presents a
solution to this
185 problem, among other problems.
SUMMARY OF INVENTION
The present invention comprises a method for creating a composite cable having
at least
one advanced termination on at least one end. An advanced termination is added
to an end of a
190 short synthetic tensile strength member. The strength of the tensile
strength member and
termination is then tested. Once tested satisfactorily, the short cable is
spliced onto a long tensile
member of a comparable type using prior art splicing techniques. The union of
the short tensile
member and the long tensile member creates a "composite" cable having an
advanced
termination on at least one end. In most applications it is preferable to set
the length of the short
195 cable so that the interwoven splice will exist at a desired location.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a perspective view, showing the creation of a prior art eye splice.
FIG. 2 is a perspective view, showing the continuation of the operation of
FIG. 1.
200 FIG. 3 is a sectional elevation view, showing the addition of a
high-performance
termination to one end of a synthetic cable.
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FIG. 4 is a perspective view, showing a terminated short cable made according
to the
present inventive process.
FIG. 5 is a perspective view, showing a composite cable made according to the
present
205 invention.
FIG. 6 is an elevation view, showing an exemplary test rig used to test a
short cable made
according to the present invention.
FIG. 7 is an elevation view, showing an inventive cable in use on an oil
platform.
FIG. 8 is an elevation view, showing an inventive cable being used to hoist a
load out of
210 the water.
FIG. 9 is an elevation view, showing an inventive cable being used on a
dragline crane.
FIG. 10 is a sectional elevation view, showing another type of high-
performance
termination.
215 REFERENCE NUMERALS IN THE DRAWINGS
cable
12 thimble
14 separated strands
16 eye splice
220 18 anchor
cavity
21 loading feature
22 potted region
24 interwoven section
225 26 short cable
28 drum
test loading device
32 oil platform
34 crane
230 35 boom
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36 composite cable
38 sea surface
40 sea floor
42 payload
235 44 max hook height
46 lower splash boundary
48 drum
50 top sheave
52 dragline crane
240 54 boom
56 lifting crane
58 dragging cable
60 bucket
62 cone
245 64 compression plug
66 threaded engagement
DESCRIPTION OF EMBODIMENTS
The present invention applies to virtually any type of tensile strength member
using
250 synthetic filaments as the core load bearing elements. This would
include common device terms
such as ropes, cables, cords, etc. Cables are used as examples of elastic
strength members in the
embodiments described. While the present invention is not applicable to steel
wire cables, it is
highly applicable to synthetic fiber cables that are used principally for load-
bearing purposes,
and the like.
255 The main concept of the invention is to create a "short" tensile
strength member with one
or more advanced terminations attached. The term "advanced termination" is
defined to mean
any component that can be attached directly to a synthetic cable without using
interweaving
techniques. The term includes anchors attached by potting a length of
filaments into an internal
cavity and spike-and-cone type anchors, among others. The "short" assembly is
tested so that its
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260 useful working load is known for certain. The "short" assembly is then
joined to a "long" tensile
strength member using prior art interweaving techniques. The result is a
composite cable whose
overall performance is known by (1) the results of the testing done on the
"short" assembly, and
(2) years of accumulated practical understanding of the performance of
interwoven splices. The
terms "short" and "long" are of course vague and they will be defined in the
context of the
265 invention.
FIG. 4 shows two components of a composite cable before they are joined
together. Short
cable 26 includes an advanced termination that has been attached to one end as
described
previously. Cable 10 in this example is a "long cable" with no attached
hardware. In this
example both cables are made of braided strands. The drawing does not depict
the braided
270 construction completely accurately, since it is quite complex, but the
lines show that some of the
braid components are twisted in one direction and some are twisted in the
opposite direction.
It is possible using prior art techniques to create an interwoven,
interlocking, or otherwise
gripping splice between these two pieces of cable. FIG. 5 shows the two cable
segments joined
together by an interwoven splice. Short cable 26 and long cable 10 are joined
together by
275 interwoven section 24. The result is a much longer "composite" cable.
The terms "short" and "long" are relative to each other. A typical "short"
cable might
range from as short as 5 meters to as long as 100 meters. In some rare cases
this may be even
longer. A "long" cable might range from 50 meters up to several km in length.
When the terms
"short" and "long" are used in this description, the reader should understand
that the "long" cable
280 is typically 4 or more times longer than the short cable. The
determination of the length of each
component is often dictated by the availability of testing equipment for
evaluating the
performance of the short cable, and the actual application, as will be
explained subsequently.
A detailed explanation of the prior art interweaving techniques used in cable
splices is
beyond the scope of this disclosure, but the reader may benefit from some
general explanation.
285 An interwoven splice is applicable to any synthetic tensile strength
member made of multiple
strands, so long as the strands are arranged in some ordered fashion. Cable
strands are generally
braided, twisted, or laid in a helical fashion. Generally, however braids such
as a twelve strand
are most common due their ease of splice-ability. A permanent joint can be
created between two
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cables (or two parts of a single cable) by partly untwisting the strands and
then interweaving
290 them. Interwoven splices can be used to form a loop or eye on an end of
a cable. They may also
be used for joining the ends of two cables together (either directly or by
forming an eye on one
cable end that is interlocked with an eye on the other cable end).
In general, a section of completely unwoven strands are created on the end of
one cable
and a section of loosened (yet not unwoven) strands are created on the end of
a second cable.
295 The completely unwoven strands on the first cable are then woven into
the voids between the
loosened strands on the second cable in a prescribed and repetitive fashion. A
specified number
of weaves are created. Any excess material from the unwoven strands of the
first cable is then
removed and the free ends are secured by any suitable method, such as taping
or whipping.
The creation of a proper interwoven splice is a skilled job that is
customarily carried out
300 by a trained rigging specialist. Fortunately, such specialists are
common within the industries
needing high-strength synthetic fiber cabling. When properly done, an
interwoven splice can be
capable of maintaining the cable's full breaking strength.
The interweaving techniques are very old, as most were developed in the age of
sailing
ships. The performance of such interwoven splices is well understood and
perhaps as
305 importantly very well trusted within the industries where they are
used. Readers wishing to
know more of the details of accepted interwoven splicing techniques are
referred to The Splicing
Handbook, 2nd Edition, published by International Marine (ISBN 0-07-135438-7).
Terminations such as shown in FIGS. 3 and 10 are preferably created under
controlled
conditions. This will typically be a factory production facility, though a
smaller scale facility
310 could be set up to handle it as well. In the case of a potted
termination, cable and anchor
alignment is preferably maintained over the cure time of the potting compound.
This may take a
day or even longer. In addition, the strand alignment within the cable also
dictates the creation of
a constrained length of cable extending out of the anchor.
Potting compound mix ratios are important, as are other factors such as the
ambient
315 temperature. Preferably many conditions are controlled in order to
create a strong and repeatable
result. Even with the best process controls, however, these less conventional,
compact forms of
terminations are inherently less proven and much more susceptible to breaking
efficiency loss
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and general breaking scatter due to processing inconsistencies or errors. Thus
a critical element
of quality control for such terminations is the proof testing process, and
this is especially needed
320 on critical applications such as lifting, securing, towing, mooring,
etc.
FIG. 6 schematically depicts one of many possible testing rigs for a short
cable 26 with
an attached anchor 18. Cables made of synthetic filaments tend to have low
surface friction and
are not easy to grip. It is often important to apply very high tensile loads
in the test. In many
cases this will be a significant fraction of the calculated breaking strength
of the cable. Thus, it is
325 often not possible to apply this amount of tension through a
fixture that simply grips the cable's
exterior. Likewise, it is not desirable to knot a portion of the cable around
a loading fixture since
the knot will drastically reduce the cable's strength.
FIG. 6 shows one end of short cable 26 being wrapped around drum 28. It is
possible to
wrap several turns of the cable around a drum of suitable diameter and thereby
secure the cable's
330 free end without over-stressing it. Test loading device 30 is
attached to anchor 18 using a hook or
similar feature. Tension may then be applied through test loading device 30
while drum 28 is
held in position. In another version, test loading device 30 could be held in
a fixed position while
torque is applied to the drum. Other testing fixtures are obviously possible
and the example
provided is by no means limiting.
335 Alternately as could be imagined by those skilled in the art, if
the short cable is able to be
tested within the load frame, a dummy or sacrificial end such as a spliced eye
or potted
termination could be applied to the opposing end. In such a case a
conventional fixed point cable
could be used in place of the drum, and this dummy or sacrificial end could
then be removed if
desired.
340 However loaded, the result of the test is that the cable can be
certified as having been
loaded to a specified amount with no problem resulting. Any defect in the
manufacturing of the
components or the assembly process may thereby be reliably detected.
Returning now to FIG. 5, the reader will recall that short cable 26 is joined
to long cable
using known interweaving ("splicing") techniques. When properly executed,
interwoven
345 section 24 will have a break strength equal to or greater than the
break strength of the cable
itself. As explained previously, the break strength of the advanced
termination (created by
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attaching anchor 18), depending on the design and method of manufacture, will
commonly be
somewhat less than the break strength of the cable (though possibly quite
close).
Thus, in the assembly of FIG. 5 the "weak link" is the termination point.
However, the
350 termination has been tested (such as by the rig of FIG. 6) and
certified to exceed a specified
break strength. Thus, the assembly as a whole in FIG. 5 (a "composite cable")
may be certified
as having a break strength in excess of the tested amount.
At this point it may be natural to wonder why a composite cable is needed and
ask
instead why one would not simply attach the anchor to one end of long cable 10
and dispense
355 with the need for the interweaving process. There are several reasons why
such an approach
would be undesirable. First, long cable 10 is often extraordinarily long. It
is not unusual for such
a cable to be 15,000 meters or more in length. Such a cable is often rolled
onto a large and heavy
drum. It is not a simple matter to move such a large cable and bring it into a
controlled facility
for the addition of an anchor.
360 Second, it is generally true that a test such as shown in FIG. 6
must be carried out by a
device on one end of the cable that engages the anchor and a device on the
other end that
engages the free end of the cable. Thus, the length of the cable being tested
determines the length
of the apparatus required to test it. For example, it is not preferable to
engage a synthetic cable at
some mid-point and then apply considerable tension. The test of FIG. 6 shows
the free end of the
365 cable being wrapped around a drum and secured. Five or ten turns
may be needed to adequately
secure the cable to the drum. Applying the drum-wrap at the mid-point of the
cable would likely
produce slippage between the cable strands and a degradation of the cable's
performance. Thus,
the cable is preferably tested by holding it at its ends and applying tension.
Therefore, the distance between the drum and the test loading device 30 will
determine
370 the length of the cable that can be tested. A large facility might
have a test fixture that is 50
meters in length, but a longer fixture is rare. It is also not generally
feasible to have a "mobile"
end point such as a moving vehicle. Static testing of such cables often
requires huge tensile
forces
____________________________________________________________________________
such as 250,000 pounds. No vehicle remains stationary during the application
of such a
force. Even static structures must be carefully designed to withstand such
forces.
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375 Since one of the significant features of the present invention is
the actual testing of the
advanced termination, it is important for short cable 26 to have only a
moderate length.
Preferably it is less than 100 meters in length and may in fact be much
shorter. The length
selected for short cable 26 will of course determine the location of the
interwoven section.
Returning now to FIG. 5, the reader will note that interwoven section 24 is
thicker than
380 the other portions of the composite cable. This added thickness can cause
problems when
running the interwoven section over pulleys or other devices. Thus, the
location of the
interwoven section is preferably considered when creating a composite cable.
The pulleys and
other feeding devices can be designed to accommodate the added thickness of
interwoven
section 24. However, it is generally undesirable to have interwoven section 24
pass around a
385 pulley or other bend while it is heavily loaded.
FIG. 7 shows one representative application for a composite cable made
according to the
present invention. Crane 34 is mounted on offshore oil platform 32, well above
sea surface 38.
Composite cable 36 extends down into the water where it is connected to pay
load 42 resting on
sea floor 40. In this simple example, sea floor 40 might lie at a depth of
3,000 meters below sea
390 surface 38. It is apparent from this diagram that the interwoven
section of composite cable 36
lies well underwater at this point and in fact will be quite close to sea
floor 40.
However, when the crane reels in composite cable 36 the interwoven section
will be
pulled up toward the surface. FIG. 8 shows a closer view of crane 34. Crane 34
includes tension-
carrying drum 48 which is used to pay off and reel in composite cable 36. In
the version shown
395 the tension-carrying drum is also used to store the cable. As those
skilled in the art will know, in
other examples a tension-carrying drum is supplemented by a second drum that
is used to store
the cable. Boom 35 mounts tip sheave 50, over which the cable passes. Max hook
height 44
represents the maximum height to which the crane can lift the payload.
As those skilled in the art will know, the load imposed on the cable by
payload 42 varies
400 substantially depending upon whether the payload is immersed in the sea
or lifted clear into the
air. The weight of an object immersed in water is reduced by the weight of the
volume of water
displaced by the object. This concept is generally referred to as Archimedes'
Principle. For a
typical solid structure, its weight in water is less than 1/2 its weight in
air.
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Crane designers working in offshore applications carefully consider
Archimedes'
405 Principle. The water's surface is not stationary in offshore
applications but rather moves with
each passing swell. Thus, there is often not a clearly defined surface level.
Instead, the engineers
refer to a "splash zone" having a lower boundary and an upper boundary. They
consider that the
payload could be lifted free of the water anywhere within this "splash zone."
It is the lower extreme of the splash, zone that is often most important.
Lower splash
410 boundary 46 is shown in FIG. 8. At any time that payload 42 is lifted
above this height it might
in fact be free of the water and the composite cable would then be subjected
to the full weight of
the payload in air.
Designers in this off-shore application might decide that the interwoven
section of the
composite cable needs to be on drum 48 before payload 42 is lifted above lower
splash boundary
415 46. They may further conclude that the interwoven section needs to have
five turns on the drum
between itself and the paid off portion of the cable when payload 42 is lifted
above lower splash
boundary 46. These criteria represent examples of design constrains that
determine the length of
short cable 26 in a particular application.
Other designers working in a similar environment might prefer that the
interwoven
420 section never pass through top sheave 50. In that case the short cable
length would be determined
as the length necessary to provide adequate lifting height for the payload
while keeping the
interwoven section below top sheave 50.
FIG. 9 shows a different application with different selection criteria. Mining
dragline
crane 52 has a large boom 54 with an attached top sheave 50. Lifting cable 56
passes through top
425 sheave 50 and down to bucket 60. Dragging cable 58 pulls bucket 60
toward the crane's cab
during the digging cycle.
In this example interwoven section 24 is located far enough above anchor 18 to
prevent
its failing into the very hostile environment existing around the bucket and
its associated rigging.
However, interwoven section 24 is also located low enough so that it is never
pulled over top
430 sheave 50 during the normal operation of the dragline crane.
Alternatively, the interwoven
section might be located so that it always remains between top sheave 50 and
the drum located in
the body of the dragline crane.
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The reader will thereby perceive the advantages offered by a composite cable
constructed
of a short cable with an attached advanced termination that is connected to a
long cable.
435 Additional optional features and combinations include:
1. Attaching a short cable with an advanced termination to both ends of a
long cable;
2. Attaching a short cable to a long cable using interlocking eye splices
as shown in
FIG. 2; and
3. Attaching a short cable to a long cable using other known and trusted
techniques.
440 Although the preceding description contains significant detail, it
should not be construed
as limiting the scope of the invention but rather as providing illustrations
of the preferred
embodiments of the invention. Those skilled in the art will be able to devise
many other
embodiments that carry out the present invention. Thus, the language used in
the claims shall
define the invention rather than the specific embodiments provided.
445
450
455
460
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