U.S. patent application number 09/779572 was filed with the patent office on 2001-08-30 for wire rope with reverse jacketed iwrc.
Invention is credited to Misrachi, Joseph.
Application Number | 20010017027 09/779572 |
Document ID | / |
Family ID | 4165347 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017027 |
Kind Code |
A1 |
Misrachi, Joseph |
August 30, 2001 |
Wire rope with reverse jacketed IWRC
Abstract
The wire rope of this invention has at most 18 outer strands and
an independent wire rope core, with the strands of the core being
laid in the opposite direction to the outer strands of the rope,
and a nylon jacket is provided between the core and the outer
strands of the wire rope.
Inventors: |
Misrachi, Joseph; (Cote
St-Luc, CA) |
Correspondence
Address: |
GEORGE J. PRIMAK
13480 HUNTINGTON
PIERREFONDS
QC
H8Z 1G2
CA
|
Family ID: |
4165347 |
Appl. No.: |
09/779572 |
Filed: |
February 9, 2001 |
Current U.S.
Class: |
57/215 ; 57/213;
57/218 |
Current CPC
Class: |
D07B 2201/2049 20130101;
D07B 2201/2076 20130101; D07B 2201/2062 20130101; D07B 2205/50
20130101; D07B 2801/14 20130101; D07B 2801/18 20130101; D07B
2801/24 20130101; D07B 2801/24 20130101; D07B 2801/24 20130101;
D07B 2801/24 20130101; D07B 2801/24 20130101; D07B 2801/20
20130101; D07B 1/0673 20130101; D07B 2801/14 20130101; D07B
2201/2019 20130101; D07B 2201/2061 20130101; D07B 2201/2065
20130101; D07B 2201/2061 20130101; D07B 2201/2065 20130101; D07B
2201/2073 20130101; D07B 2205/2046 20130101; D07B 5/007 20130101;
D07B 1/165 20130101; D07B 2201/2037 20130101; D07B 2201/2057
20130101; D07B 2201/2057 20130101; D07B 2201/2062 20130101; D07B
1/144 20130101; D07B 2201/108 20130101; D07B 2205/50 20130101; D07B
2201/2049 20130101; D07B 2205/2046 20130101 |
Class at
Publication: |
57/215 ; 57/213;
57/218 |
International
Class: |
D02G 003/36; D02G
001/00; D07B 001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 28, 2000 |
CA |
2,298,945 |
Claims
1. A wire rope having at most 18 outer strands and an independent
wire rope core, with strands of the core being laid in opposite
direction to the outer strands of the wire rope making such wire
rope essentially non-rotating during application of a load,
characterized in that a nylon jacket is provided between the outer
strands and the core of said wire rope.
2. A wire rope according to claim 1, in which the nylon jacket has
a thickness such as to substantially prevent perforations to occur
in said jacket before occurrence of degradation of the outer stands
of the wire rope.
3. A wire rope according to claim 1, in which the core is
lubricated.
4. A wire rope according to claim 1, in which the outer strands of
the rope crosscut the strands of the core at approximately
90.degree. angle.
5. A wire rope according to claim 1, which is a rope with eight
outer strands.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a wire rope construction with
reverse jacketed IWRC (independent wire rope core). More
specifically it relates to such construction where the wire rope
has no more than 18 outer strands and where the jacket consists of
nylon.
[0003] 2. Description of the Prior Art
[0004] Most wire ropes in the wire rope industry are designed so
that outer rope strands are laid in the same direction as the
strands of the core. For example, if the outer rope strands are
laid to the left the same is done with the strands of the core.
This is done so as to minimize contact loads between the two. In
this manner the core strands do not deteriorate very quickly
allowing the rope to fail first primarily from the outside. This
allows users to count outer rope strands broken wires and use these
as a retirement criteria for the rope. This method of making and
inspecting ropes is standard in the industry and is a recognized
method to use ropes in a safe manner.
[0005] Most of the ropes manufactured as described above will have
a tendency to have their ends rotate under load. This is because
all the strands of the rope want to straighten under load.
Non-rotating ropes are a special category of ropes designed in such
a way as to minimize or even prevent completely this rotation.
These ropes are usually utilized in crane applications where it is
not desirable to have the load rotate during lifting. The lifting
end of the rope is always used unrestrained and free to rotate. If
a conventional rope is used the rope will unlay, which is also
undesirable.
[0006] Common designs used for these applications consist of multi
strand ropes having the interior core strands laid in a direction
which is opposite to the one of the outer rope strands. In these
situations both the outer rope strands and the core strands want to
unlay under load but they do it in opposite directions. It is a
known fact in the industry that the larger the core diameter
relative to the individual diameter of the outer rope strands, the
better the antirotation properties of the rope. This is because the
torque developed by the core can better counteract the torque
developed by the outer strands of the rope.
[0007] There are three main categories of non-rotating ropes on the
market: the 34-35 strand ropes with round and compacted strands;
the 18 strand also with round and compacted strands; and finally
there is also an eight strand, low cost and lower performance
variety consisting of what is commonly known as 8 strand reverse
IWRC rope.
[0008] The following list identifies these ropes from worst to
better in relation to their anti-rotating properties.
[0009] Worst performance: 8 strand reverse IWRC rope
[0010] Intermediary performance: 18 strand non-rotating rope
[0011] Best performance: 34-35 strands non-rotating ropes.
[0012] The reason for this behaviour is quite simple: the core in
the eight strand rope is the smallest of the three types described
above so it does not counteract the torques of the outer strands as
well as the larger cores of 18 strand, and particularly 34-35
strands. It should be noted that non-rotating wire ropes with 18
outer strands or less have generally unsatisfactory performance,
with the worst cases being ropes of 8 strands or less.
[0013] Since the outer strands of these ropes cross-cut at
approximately 90.degree. angle, the outer strands of their
respective cores, they usually exhibit a rapid, invisible core
deterioration that cannot be detected from the outside. In other
words the detection of outer broken wires cannot be used to assess
the inner rope condition. This is particularly the case of 8
strands reverse IWRC ropes and also of 18 strands ropes, while this
condition is less severe with the 34-35 strands ropes.
[0014] It is hence normal to retire ropes having 18 strands or less
from operation after a fixed number of hours or cycles to avoid the
"surprise" of a sudden internal failure. Another alternative is to
jacket the core with plastic materials to prevent the abrasion
taking place at the rope strand-core strand interface.
[0015] It is already known to provide a jacket of a thermoplastic
material, such as polypropylene, around a lubricated core, as
disclosed for example in U.S. Pat. No. 4,120,145.
[0016] Applicant's own U.S. Pat. No. 5,386,683 also discloses a
jacketed core in which the plastic material of the jacket is
identified as polyethylene, polypropylene, nylon or another
suitable thermoplastic material.
[0017] However, none of the above prior art patents deal
specifically with wire ropes of 18 outer strands or less that have
reverse jacketed IWRC lay, since the applicant found that with such
wire rope construction the commonly employed jacket of
polypropylene produces essentially no improvement over the
non-jacketed construction and is therefore unsatisfactory.
[0018] When reviewing the situation it became obvious that a
conventional cushioned core solution and approach did not work in
this case. The examination of the polypropylene jacket showed that
it had perforated at all the contact points between the outer
stands and the core. A conclusion was reached that when dealing,
for example, with an 8 strand rope or an 18 strand rope of reverse
IWRC lay, the compression load applied by the outer strands on the
core would be higher than the compression load applied by the outer
strands of a 34-35 strand rope. The same would apply to all such
wire ropes of 18 outer strands or less, which must therefore be
considered as a special category of non-rotating ropes to which the
present invention applies.
SUMMARY OF THE INVENTION
[0019] The present invention resides in providing a nylon jacket in
lieu of polypropylene jacket in wire ropes having at most 18 outer
strands and a reverse IWRC lay. Despite the fact that nylon has
been mentioned as a suitable jacket material in the past, it was
always mentioned as a substitute or alternative material to
polypropylene, performing essentially the same function. It is,
therefore, surprising and unexpected that in the special category
of wire ropes which are under consideration herein, nylon jacketing
of the core acts very differently than that of polypropylene,
providing essentially double the protection as will be shown
later.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will now be described with reference to the
appended drawings in which:
[0021] FIG. 1 shows a schematic cross-sectional view of a wire rope
construction with a nylon jacket in accordance with the present
invention; and
[0022] FIG. 2 is a graph showing fatigue test results comparing the
wire rope of the present invention with similar ropes having no
jacket or a polypropylene jacket.
DETAILED DESCRIPTION OF THE INVENTION
[0023] The figures illustrate a preferred but non-limitative
embodiment of the invention.
[0024] FIG. 1 shows a 3/4" (1.875 cm) 8.times.31 reverse core rope
construction with eight outer strands 10, each having 31 wires. The
IWRC core of the wire rope is formed of six strands 12 wound around
a central strand 14. The core strands 12 are wound in the apposite
direction to the outer strands 10 as shown by arrows 11 and 13.
Arrow 11 indicates that the outer strands 10 of the rope are wound
in the clockwise direction, while the outer strands 12 of the core
are wound in the counter-clockwise direction. The core is also
filled with an appropriate lubricant 15. Between the core strands
12 and the outer strands 10 there is provided an nylon jacket 16,
which cushions the core against the pressure exerted by the outer
stands 10 during application of the load.
[0025] The wire rope described above is produced as follows:
[0026] 1. a core is produced by winding strands 12 over the central
strand 14 in a predetermined direction (in this specific case with
a left lay as shown by arrow 13);
[0027] 2. the core is then filled with a suitable lubricant 15;
[0028] 3. a nylon jacket 16 having in this case a thickness of
0.20" (0.5 cm) is then extruded onto the core; and finally
[0029] 4. outer strands 10 (which are also normally lubricated) are
wound onto the nylon jacket in the opposite direction to the core
strands 12 (in this specific case with a right lay as shown by
arrow 11), and compressed thereon so that the nylon from the jacket
16 penetrates between the interstices of the outer strands 10.
[0030] The above specific construction is used as a specific
example and the various modifications can be made therein and in
the method of its manufacture. For example, various sizes mentioned
herein may be modified and adopted to the requirements of the user.
Also, steps 2 and 3 of the method of manufacture mentioned above
could be combined so that the core is impregnated and jacketed at
the same time.
[0031] FIG. 2 gives comparative results for the wire rope described
above with reference to similar ropes produced without any jacket
and with a polypropylene jacket of the same thickness.
[0032] Thus, the applicant first prepared a 3/4" 8 strand reverse
IWRC wire rope such as shown in FIG. 1, but without any jacket
between the outer stands and the core. Two samples of such rope
were subjected to a reverse bend fatigue test using a load of 1000
lbs (450 kg). As shown in FIG. 2, such non-jacketed rope failed
after just over 100,000 cycles.
[0033] Then, to improve this result, a polypropylene jacket of
0.20" (0.5 cm) was used between the core and the outer strands.
Surprisingly, this construction produced essentially no
improvement, also as illustrated in FIG. 2.
[0034] Since polypropylene did not produce improved results one
would normally have expected that nylon, which is often mentioned
as an alternative to polypropylene in such cases, would also be
inadequate. Applicant had used nylon in other circumstances where
it was found to act in a manner similar to polypropylene. Applicant
has, however, decided to try to use nylon in this particular case
to see if it would enhance the performance. Two samples of the wire
rope with a nylon jacket of 0.20" (0.5 cm), such as shown in FIG.
1, where thus subjected to the same fatigue tests as the previous
samples. To applicant's surprise the number of cycles to failure
essentially doubled with the nylon jacketed construction as
compared to polypropylene jacketed or un-jacketed constructions.
This unexpected result shows that nylon is a selected material of
choice for such reverse core rope constructions.
[0035] The nylon jacket did not get perforated before the
occurrence of outer rope strand degradation and failure of the wire
rope due to such degradation. This was contrary to what happened
with the polypropylene jacket which perforated very rapidly under
load.
* * * * *