U.S. patent application number 15/836898 was filed with the patent office on 2018-04-12 for method for fabricating steel wire cable comprising zinc- aluminium alloy plating.
The applicant listed for this patent is JIANGSU FASTEN STEEL CABLE CO., LTD.. Invention is credited to Kebin HUANG, Zhongmei LIANG, Shiwei NING, Qiang QIANG, Weihong SHU, Jin WANG, Qiong WU, Huajuan XUE, Pengcheng ZHAI, Jun ZHAO, Zhubing ZHOU, Xiaoxiong ZHU.
Application Number | 20180100269 15/836898 |
Document ID | / |
Family ID | 56636912 |
Filed Date | 2018-04-12 |
United States Patent
Application |
20180100269 |
Kind Code |
A1 |
ZHAO; Jun ; et al. |
April 12, 2018 |
METHOD FOR FABRICATING STEEL WIRE CABLE COMPRISING ZINC- ALUMINIUM
ALLOY PLATING
Abstract
A method for fabricating a steel wire cable having a Zn--Al
alloy plating, the method including: arranging steel wires
according to an arrangement rule at a cross section of the steel
wire cable; controlling a length of the overall cable by a length
of a central standard wire; twisting a bunch of the steel wires
comprising a zinc-aluminum alloy plating with a torsion angle of
between 2.degree. and 4.degree.; wrapping the steel wire bunch with
a polyester wrapping bandage and covering a resulting product with
a double-layered protective polyethylene sheath; anchoring the two
ends of the steel wire cable by anchors using fillers; and coiling
the finished-product of the steel wire cables.
Inventors: |
ZHAO; Jun; (Jiangyin,
CN) ; NING; Shiwei; (Jiangyin, CN) ; XUE;
Huajuan; (Jiangyin, CN) ; ZHOU; Zhubing;
(Jiangyin, CN) ; WU; Qiong; (Jiangyin, CN)
; QIANG; Qiang; (Jiangyin, CN) ; HUANG; Kebin;
(Jiangyin, CN) ; ZHU; Xiaoxiong; (Jiangyin,
CN) ; SHU; Weihong; (Jiangyin, CN) ; WANG;
Jin; (Jiangyin, CN) ; LIANG; Zhongmei;
(Jiangyin, CN) ; ZHAI; Pengcheng; (Jiangyin,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
JIANGSU FASTEN STEEL CABLE CO., LTD. |
Jiangyin |
|
CN |
|
|
Family ID: |
56636912 |
Appl. No.: |
15/836898 |
Filed: |
December 10, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CN2016/083894 |
May 30, 2016 |
|
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15836898 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
D07B 9/00 20130101; D07B
7/145 20130101; D07B 2201/2044 20130101; D07B 2501/203 20130101;
D07B 1/162 20130101; D07B 3/00 20130101; D07B 2201/2045 20130101;
D07B 1/10 20130101; D07B 2201/2011 20130101; D07B 7/10 20130101;
D07B 2201/2087 20130101; D07B 2207/4031 20130101; D07B 2201/2088
20130101; D07B 2205/3092 20130101; D07B 5/006 20150701; D07B 7/14
20130101; D07B 5/00 20130101; D07B 5/002 20130101; D07B 2201/2089
20130101; D07B 2205/201 20130101; E01D 19/16 20130101; E01D 11/04
20130101; D07B 1/148 20130101; D07B 2205/3092 20130101; D07B
2801/18 20130101; D07B 2205/201 20130101; D07B 2801/18 20130101;
D07B 2801/22 20130101; D07B 2201/2089 20130101; D07B 2801/12
20130101 |
International
Class: |
D07B 1/16 20060101
D07B001/16; D07B 1/10 20060101 D07B001/10; D07B 7/14 20060101
D07B007/14; D07B 9/00 20060101 D07B009/00; D07B 5/00 20060101
D07B005/00; E01D 19/16 20060101 E01D019/16 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2016 |
CN |
201610229109.1 |
Claims
1. A method for fabricating a steel wire cable, comprising: 1)
preparing steel wires comprising a zinc-aluminum alloy plating,
wherein the zinc-aluminum alloy plating has an aluminum content of
between 4.2 and 7.2 wt. % or of between 9.2 and 12.2 wt. %, and a
weight of the zinc-aluminum alloy plating is equal to or larger
than 300 g/m.sup.2; 2) selecting a steel wire, which is to be
positioned at a center position of a cross section of the steel
wire cable, as a standard wire, applying a certain tension force to
two ends of the steel wire to straighten the steel wire and
performing stress correction and temperature correction to prepare
a steel wire having a standard length; making certain markers at
two ends of the steel wire; taking the steel wire having the
standard length as a reference, and controlling an overall length
of the steel wire cable; 3) relaxing the steel wires, positioning
the standard wire at the center position of the cross section of
the steel wire cable comprising a plurality of layers of steel
wires; twisting the steel wires to the left with a torsion angle of
between 2.degree. and 4.degree. to yield a steel wire bunch;
wrapping the steel wire bunch to the right by a wrapping bandage to
yield a naked steel wire cable as a semi-product; and calculating a
relaxed length L.sup./ of other layers of steel wires surrounding
the standard wire considering the length of the standard wire and a
torsion rate according to the following equation:
L.sub.0=L.sup./.times.cos .alpha.+K in which, .alpha. represents
the torsion angle ranging from 2.degree. to 4.degree.; K represents
a fabrication allowance, m, which is selected according to
specifications and operations; L.sub./ represents the relaxed
length, m, of other layers of the steel wires surrounding the
standard wire; and L.sub.0 represents the length, m, of the
standard wire at the center position; 4) preparing a double-layered
protective polyethylene outside the naked steel wire cable, wherein
the double-layered protective polyethylene has a density of between
0.942 and 0.978 g/cm.sup.3, environmental stress crack resistance
property of .gtoreq.5000 F.sub.0/h, and a melt index of
.ltoreq.0.45 g/10 min; before extruding, presetting a die aperture
of an extruder and an extrusion velocity according to an outer
diameter of the naked steel wire cable and thicknesses of two
layers of polyethylene; wherein the die aperture of the extruder is
provided with two layers of discharge channel, and the two layers
of polyethylene simultaneously cover the naked steel wire cable
during the extrusion; 5) determining original cutting positions of
the steel wire cable, locally stripping the double-layered
protective polyethylene, finding the markers for cutting at two
ends of the standard wire at the center position of the steel wire
cable; cutting the steel wire cable by using a non-liquid cutting
machine and ensuring end faces of the steel wire cable
perpendicular to an axis of the steel wire cable; stripping the
double-layered protective polyethylene according to a preset length
to expose the steel wires; 6) providing an anchor functioning as a
main connecting structure to transmit a tension of the steel wire
cable to a tower and a girder; performing hot galvanizing or paint
coating on the anchor for corrosion resistance, wherein a thickness
of the hot galvanizing is equal to or larger than 90 .mu.m, and a
thickness of the paint coating is determined according to
specifications and design requirements of a steel structure; and
casting the anchor by chill casting of heading anchor or by hot
casting of anchor, operations of which are as follows: A. chill
casting of the heading anchor comprising: a. fixing ends of the
steel wires in anchor cups on a casting platform, removing oil
stains and rusts from portions of the steel wires inside the anchor
cups, and synchronously washing inner walls of the anchor cups; b.
uniformly dispersing the ends of the steel wires corresponding to
holes of anchor plates, and heading each steel wire by using a
heading machine, wherein heading dimensions are as follows: heading
diameter .gtoreq.1.4 D, heading height .gtoreq.1.0 D, and D
represents a diameter of the steel wires; and c. providing and
uniformly mixing a chilled filler comprising steel balls, a stone
dust, an epoxy resin, a curing agent, di-n-butyl, and a diluent;
pouring a mixture of the chilled filler into the anchor cups while
vibrating by using a vibration pump to fully fill gaps among the
anchor cup and steel wires with the mixture of the chilled filler;
B. hot casting of anchor comprising: providing a zinc-copper alloy
comprising 98.+-.0.2 wt. % of zinc and 2.+-.0.2 wt. % of copper, or
a zinc-copper-aluminum alloy comprising 4-7 wt. % of aluminum, 1-2
wt. % of copper, and 91-95 wt. % of zinc; and performing casting as
follows: a. perpendicularly fixing ends of the steel wires in
anchor cups on the casting platform, dispersing steel wires
comprising a zinc-aluminum alloy plating inside the anchor cups in
the form of concentric circles, removing oil stains and rusts from
surfaces of the steel wires, and simultaneously washing the inner
walls of the anchor cups; b. keeping the center of the steel wire
cable coincide with centers of the anchor cups and preventing steel
wires from contacting the anchor cups; c. sealing bottom openings
of the anchor cups to prevent the alloy from leaking via the bottom
openings; and preheating the anchor cups; and d. pouring the
zinc-copper alloy or the zinc-copper-aluminum alloy into the anchor
cups for one-step casting while avoiding any vibration or
disruption; 7) according to fillers for the casting of the anchor,
performing tension detection on the steel wire cable with
chilled-casted anchor or performing top pressure detection on the
steel wire cable with hot-casted anchor before leaving a plant,
which comprises: for the steel wire cable with the chilled-casted
anchor, stretching the steel wire cable by an overstretching force
which is set to be between 1.1 and 1.5 folds of a designed tension
of the steel wire cable and satisfies that a retraction value of a
casting body inside the anchor cup after stretching is equal to or
less than 6 mm; unloading the overstretching force to be 20% of the
original overstretching force or to be the designed tension of the
steel wire cable after the stretching; measuring a length of the
steel wire cable at a constant temperature in the dark, and
calculating a stressless length of the steel wire cable at a
reference temperature according to the following equation: L CO = L
CP 1 + P 20 EA + .alpha. ( t - t 0 ) ##EQU00003## in which,
L.sub.C0 represents the stressless length, m, of the steel wire
cable at the reference temperature; L.sub.CP represents a length,
m, of the steel wire cable loaded with a tension force of P.sub.20;
P.sub.20 represents 20% of the overstretching force, N; A
represents a nominal area, mm.sup.2, of the steel wire bunch of the
steel wire cable; E represents an elastic modulus, MPa; .alpha.
represents a coefficient of linear expansion of a stay cable which
is equal to 0.000012/.degree. C.; t represents the constant
temperature, .degree. C., when measuring a length of the stay
cable; and to represents a designed reference temperature, .degree.
C., of the stay cable; and for the steel wire cable with hot-casted
anchor, applying, to the steel wire cable, a top pressure which is
1.25 folds of the designed tension of the steel wire cable and
satisfies that a retraction value of the casting body inside the
anchor cup after the top pressure detection is equal to or less
than 6 mm; and 8) packing an outer surface of the steel wire cable,
coiling layers of the steel wire cables successively by using a
coil frame, wherein an inner diameter of a resulting coil is equal
to or larger than 20 folds of an outer diameter of the steel wire
cable and is equal to or larger than 1.6 m.
2. The method of claim 1, wherein when determining the length of
the standard wire in 2), stress correction and temperature
correction are carried out according to the following equation:
L=L.sub.0.times.[(1+F/EA)+.alpha.(T-20)] in which, L represents a
length (m) of the steel wire in a stressed state, L.sub.0
represents a designed length, m, of the steel wire in an unstressed
state, F represents a tensioning force, N, E represents an elastic
module, MPa, of the steel wire, and fabrication of the standard
wire adopts a measured value, A represents an area of a cross
section, m.sup.2, of the steel wire, and fabrication of the
standard wire adopts the measured value, a represents an expansion
coefficient of the steel wire, and T represents a temperature of
the environment.
3. The method of claim 1, wherein in extrusion process in 4), a
magnetic field is arranged above the steel wire cable to make the
steel wire cable in a suspension state; after the extrusion
process, the double-layered protective polyethylene and the naked
steel wire cable are concentrically arranged.
4. The method of claim 1, wherein an outer surface of the
double-layered protective polyethylene is provided with helical
lines or embossments, and a drag coefficient is equal to or smaller
than 0.8.
5. The method of claim 1, wherein structures of the anchors in 6)
adopt a nut-screwing type anchor, an anchor plate gap adjusting
type anchor, or a fork-ear pin joint type anchor at two ends of the
steel wire cable.
6. The method of claim 1, wherein in 7), an error of the stressless
length of the steel wire cable at the reference temperature
satisfies the following requirements: when L.sub.C0.ltoreq.100 m,
the error is less than or equal to 10 mm; and when L.sub.C0>100
m, the error is less than or equal to L.sub.C0/20000+5 mm.
7. The method of claim 1, wherein the wrapping bandage is a bandage
made from a polyester fiber; the wrapping bandage has a width of
between 40 and 60 mm and a tensile strength of equal to or high
than 500 N/25 mm.sup.2.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of International
Patent Application No. PCT/CN2016/083894 with an international
filing date of May 30, 2016, designating the United States, now
pending, and further claims foreign priority benefits to Chinese
Patent Application No. 201610229109.1 filed Apr. 13, 2016. The
contents of all of the aforementioned applications, including any
intervening amendments thereto, are incorporated herein by
reference. Inquiries from the public to applicants or assignees
concerning this document or the related applications should be
directed to: Matthias Scholl P. C., Attn.: Dr. Matthias Scholl
Esq., 245 First Street, 18th Floor, Cambridge, Mass. 02142.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The invention relates to a method for fabricating a steel
wire cable comprising a Zinc-Aluminum (Zn--Al) alloy plating.
Description of the Related Art
[0003] A cable-stayed bridge includes one or more towers, from
which cables provide support for the bridge deck. In recent years,
to accelerate the development of coastal economy, the construction
of large-span cable-stayed bridges has become increasingly urgent.
However, conventional galvanized steel wire cables are not weather
resistant, and especially, are not durable under marine
climates.
SUMMARY OF THE INVENTION
[0004] In view of the above-described problems, it is one objective
of the invention to provide a method for fabricating a steel wire
cable comprising a Zn--Al alloy plating. The length of the overall
cable is controlled by the length of a central standard wire; a
bunch of the steel wires comprising a zinc-aluminum alloy plating
are twisted with a torsion angle of between 2.degree. and
4.degree.; the steel wire bunch is then wrapped with a polyester
wrapping bandage and covered with a double-layered protective
polyethylene sheath by using double-cavity co-extrusion process for
one-step formation, and the outer surface of the polyethylene
sheath is provided with embossments for rain-wind induced vibration
resistance; the two ends of the steel wire cable are fixed by
anchors using fillers, coiled, and stored. And the coils of the
steel wire cables are then transported to and respectively laid on
a construction field.
[0005] To achieve the above objective, in accordance with one
embodiment of the invention, there is provided a method for
fabricating a steel wire cable comprising a Zn--Al alloy plating.
The method comprises the following steps:
[0006] 1) Fabricating a Steel Wire Comprising a Zinc-Aluminum Alloy
Plating
[0007] The steel wire comprising the zinc-aluminum alloy plating is
adopted because the zinc-aluminum alloy plating possesses much
stronger anti-corrosive property, principle of which is as follows:
a) as aluminum has very active chemical property, a dense layer of
alumina is formed on a surface of the steel wire after hot dip of
aluminum, and therefore the surface of the steel wire is easily
inactivated to form a protective layer in corrosive environment. In
a corrosive medium, a zinc-enriched surface layer, functioning as a
positive electrode, is firstly eroded, the aluminum content
continuously increases to make the alumina content increase, thus
making the plating layer possessing stronger capability of
preventing external toxic substances. In the meanwhile, the
addition of the aluminum also inhibits the formation of a
zinc-aluminum transitional layer which has weaker anti-corrosion
performance and loosen tissue, thus being helpful for improving the
overall anti-corrosion performance of the plating layer. b) When
the zinc-aluminum alloy plating is destructed and the steel is
exposed, the plating functions as a positive electrode of an
iron-zinc aluminum battery and is dissolved, and a steel substrate
is therefore protected. A corrosion potential of the zinc-aluminum
alloy is slightly lower than a pure zinc layer and is approximately
-0.87, but the corrosion current of the zinc-aluminum alloy is only
1/5 of the hot dipped pure zinc. Under the protection of
sacrificing the positive electrode, the consumption time of the
zinc-aluminum alloy plating of the same amount is five folds of
that of the hot dipped zinc layer. Thus, the zinc-aluminum alloy
plating is able to provide much longer sacrificial protection time
and possesses better endurance. The zinc-aluminum alloy plating
includes two types, Zn95Al5 5 having an aluminum content of between
4.2 and 7.2 wt. %, and Zn90Al10 having the aluminum content of
between 9.2 and 12.2 wt. %. A plating weight is equal to or larger
than 300 g/m.sup.2. A homogeneity indicator of the plating
satisfies a time of copper sulfate of equal to or larger than 4
with each time lasting 60 s.
[0008] 2) Fabricating a Steel Wire having a Standard Length
[0009] As each layer of steel wires in the stay cable exists with a
certain torsion angle, it is unable to directly control the length
of the steel wire cable by using the outer layers of steel wires.
Only the central wire of the stay cable always remains straight
without being twisted during the whole fabrication process,
therefore, the central wire is utilized as the standard wire to
control the overall length of the steel wire cable.
[0010] The length of the standard wire is determined by baseline
measurement, and specific operation includes: applying a certain
tension force to two ends of a steel wire to straighten the steel
wire a performing stress correction and temperature correction
using the following equation:
L=L.sub.0.times.[(1+F/EA)+.alpha.(T-20)]
in which, L represents a length (m) of the steel wire in a stressed
state, L.sub.0 represents a designed length, m, of the steel wire
in an unstressed state, F represents a tensioning force, N, E
represents an elastic module, MPa, of the steel wire, and
fabrication of the standard wire adopts a measured value, A
represents an area of a cross section, m.sup.2, of the steel wire,
and fabrication of the standard wire adopts the measured value, a
represents an expansion coefficient of the steel wire, and T
represents a temperature, .degree. C., of the environment.
[0011] A steel wire having a standard length is prepared. Certain
markers for cutting are made at two ends of the steel wire.
Thereafter, the steel wire having the standard length is utilized
as a reference, and the overall length of the steel wire cable is
controlled by a transfer method. By using the above measurements,
the length error of the stay cable can be greatly reduced. The
fabrication precision of the standard wire exceeds 1/30000, and the
fabrication precision of the finished product of the steel wire
cable is improved from the China's national standard of 1/5000 to
1/20000.
[0012] 3) Twisting a Steel Wire Bunch
[0013] The steel wire cable is formed by multiple layers of steel
wires. When relaxing the steel wires, the standard wire is
positioned at a center position of a cross section of the steel
wire cable.
[0014] A steel wire bunch is twisted to the left with a torsion
angle of between 2.degree. and 4.degree.. The twisted steel wire
bunch is wrapped to the right by a wrapping bandage to yield a
naked steel wire cable as a semi-product. As lengths of the
multiple layers of the steel wires exist with differences, a
relaxed length L.sup./ of other layers of steel wires surrounding
the standard wire considering the length of the standard wire is
calculated according to the following equation:
L.sub.0=L.sup./.times.cos .alpha.+K
in which, .alpha. represents the torsion angle ranging from
2.degree. to 4.degree.; K represents a fabrication allowance, m,
which is selected according to specifications and operations;
L.sup./ represents the relaxed length, m, of other layers of the
steel wires surrounding the standard wire; and Lo represents the
length, m, of the standard wire at the center position;
[0015] An outer dimeter of the steel wire bunch, i.e., the naked
steel wire cable, after being twisted is measured. Because the
cross section of the steel wire bunch is in a shape of hexagon or
hexagon with missing angles, a circumscribed circle of the selected
cross section of the steel wire bunch is directly the diameter of
the naked steel wire cable.
[0016] The wrapping bandage is preferably a bandage made from a
polyester fiber. The wrapping bandage has a width of between 40 and
60 mm and a tensile strength of equal to or high than 500 N/25
mm.sup.2.
[0017] 4) Extruding
[0018] A double-layered protective polyethylene is prepared outside
the naked steel wire cable, in which, the double-layered protective
polyethylene has a density of between 0.942 and 0.978 g/cm.sup.3,
environmental stress crack resistance property of .gtoreq.5000
F.sub.0/h, and a melt index of .ltoreq.0.45 g/10 min. Specific
operation is as follows:
[0019] Before extruding, a die aperture of an extruder and an
extrusion velocity are preset according to an outer diameter of the
naked steel wire cable and thicknesses of two layers of
polyethylene. The double-cavity co-extrusion for one-step formation
is adopted. The two layers of the polyethylene plastics
simultaneously cover the naked steel wire cable during the
requirements of anti-corrosion. According to the requirement of
resistance of the rain-wind induced vibration, after the extrusion,
an outer surface of the double-layered protective polyethylene is
provided with helical lines or embossments. When reaching the
effect of the steel wire cable in effectively inhibiting the
rain-wind induced vibration, a drag coefficient is equal to or
smaller than 0.8.
[0020] 5) Accurate Cutting
[0021] Original cutting positions of the steel wire cable are
determined, the double-layered protective polyethylene is locally
stripped, and the markers for cutting at two ends of the standard
wire at the center position of the steel wire cable are found.
Then, the steel wire cable is cut by using a non-liquid cutting
machine and end faces of the steel wire cable are ensured
perpendicular to an axis of the steel wire cable. The
double-layered protective polyethylene is stripped according to a
preset length to expose the steel wires, during which, the plating
of the steel wires is prevented from being destructed.
[0022] 6) Casting Anchor
[0023] The anchor is a main connecting structure to transmit a
tension of the steel wire cable to a tower and a girder. The steel
wire cable adopts anchor structures including a nut-screwing type
anchor, an anchor plate gap adjusting type anchor, or a fork-ear
pin joint type anchor at two ends. The anchor is performed with hot
galvanizing or paint coating for corrosion resistance. A thickness
of the hot galvanizing is equal to or larger than 90 .mu.m, and a
thickness of the paint coating is determined according to
specifications and design requirements of a steel structure. The
types of the structures of the anchor is as follows:
[0024] a) Nut-Screwing Type Anchor
[0025] The nut screwing type anchor comprises: an anchor cup, a
screw nut, an anchor plate, and a sealing assembly of a connecting
cylinder. Such steel wire cable utilizes the end face of the nut to
support the pressure and to transmit the load. The nut and the
anchor cup are in rotary joint via a trapezoidal thread having high
strength to realize the continuous adjustment of the length of the
steel wire cable. The anchor cup is provided with tensional inner
threads. In installation of the steel wire cable on the
construction site, an installation force is applied on the steel
wire cable by drawing the anchor. The anchor plate primarily
functions in dispersing the steel wires, steel wire holes are
distributed on the anchor plate, and the steel wires pass through
corresponding steel wire holes and are headed. An external cone
boss can be tightly attached to an internal conical cavity.
[0026] b) End Face-Supporting Type Anchor
[0027] The end face-supporting type anchor comprises: an anchor
cup, an anchor plate, and a sealing assembly of a connecting
cylinder. End faces of such steel wire cable are directly supported
on anchor plate, and different gap adjusting plates are utilized to
regulate the length of the steel wire cable. The gas adjusting
plates have different thicknesses to satisfy the requirement of the
construction site. The anchor cup is provided with tensional inner
threads. In installation of the steel wire cable on the
construction site, an installation force is applied on the steel
wire cable by drawing the anchor. Such kind of anchor does not
necessitate nuts, and the anchor cup is not provided with external
threads. The anchor plate functions in dispersing the steel wires,
the steel wire holes are distributed on the anchor plate, and the
steel wires pass through corresponding steel wire holes and are
headed. An external cone boss can be tightly attached to an
internal conical cavity.
[0028] c) Fork-Ear Pin Joint Type Anchor at One End and
Nut-Screwing Type Anchor at the Other End
[0029] The fork-ear pin joint type anchor comprises: a fork ear, a
pin shaft, an anchor cup, a nut, and a sealing assembly of a
connecting cylinder. One end of such steel wire cable is connected
to the steel structure of the tower or the girder via the fork ear
and the pin shaft, and the other end of the steel wire cable adopts
an end face of a nut to bear pressure and to transmit the load,
thus realizing the continuous adjustment of the length of the steel
wire cable. the anchor cup is provided with tensional inner
threads. In installation of the steel wire cable on the
construction site, an installation force is applied on the steel
wire cable by drawing the anchor. The anchor plate functions in
dispersing the steel wires, the steel wire holes are distributed on
the anchor plate, and the steel wires pass through corresponding
steel wire holes and are headed. An external cone boss can be
tightly attached to an internal conical cavity.
[0030] The sealing assembly of the connecting cylinder in the above
three structures all adopts the new type of cable end sealing
technology, in which, an outer part of the connecting cylinder is
firstly sealed by a sealing cover, and an inner wall of the
connecting cylinder in the vicinity of a port is sealed again by an
elastic sealing ring and a sealing press ring. The two sealing
measurements finally realizes the sealing of the two ends of the
steel wire cable, that is, the sealing between the anchors and the
interfaces of the polyethylene steel wire cable. The sealing
assembly has stronger strength, thus being difficult to be
destructed, much longer service life, and much endurable sealing
structure.
[0031] The sealing structure at the ends of the steel wire cable is
a reliable mechanical sealing structure, configured to prevent the
corrosion resulting from the water penetration into the PE cable.
In the meanwhile, the sealing structure, as a substitute of a heat
shrink sleeve, is utilized for sealing, thus overcoming the problem
of damage of the heat shrink sleeve.
[0032] The technical solution to solve the above described
technical problem is as follows: an endurable sealing structure at
an end of the steel wire cable. The sealing structure fits together
with the connecting cylinder of the anchor and comprises: the
elastic sealing ring, a sealing press ring, and a sealing cover.
The sealing press ring is disposed in the port of the connecting
cylinder and an outer end of the sealing press ring is exposed
outside the connecting cylinder. A press surface is formed on the
inner wall of the connecting cylinder relative to the inner end
face of the sealing press ring. The elastic sealing ring is
disposed between the inner end face of the sealing press ring and
the press surface. Under the press of the press surface, the
elastic sealing ring is deformed and attached to the outer wall of
the steel wire cable. The sealing cover is disposed on a front end
of the connecting cylinder and possesses a Harvard structure. A
front part of the sealing cover contacts and fits with the outer
wall of the steel wire cable and a corresponding contact surface is
provided with a sealing ring. A rear part of the sealing cover
contacts and fits with the sealing press ring or the connecting
cylinder and a corresponding contact surface is provided with a
sealing strip.
[0033] The casting of the anchor is carried out by chill casting of
heading anchor or by hot casting of anchor, operations of which are
as follows:
[0034] A. Chill Casting of Heading Anchor
[0035] a. Ends of the steel wires are fixed in anchor cups on a
casting platform, oil stains and rusts are removed from portions of
the steel wires inside the anchor cups, and inner walls of the
anchor cups are synchronously washed.
[0036] b. The ends of the steel wires are uniformly dispersed
corresponding to holes of anchor plates, and each steel wire is
headed by using a heading machine. Heading dimensions are as
follows: heading diameter .gtoreq.1.4 D, heading height .gtoreq.1.0
D, and D represents a diameter of the steel wires.
[0037] c. A chilled filler comprising steel balls, a stone dust, an
epoxy resin, a curing agent, di-n-butyl, and a diluent is provided
and uniformly mixed. A mixture of the chilled filler is poured into
the anchor cups while vibrating by using a vibration pump to fully
fill gaps among the anchor cup and steel wires with the mixture of
the chilled filler.
[0038] d. A compression strength of the casting body of the chilled
filler is .gtoreq.147 MPa.
[0039] B. Hot Casting of Anchor
[0040] The hot casting anchor adopts a zinc alloy for casting, and
a zinc-copper alloy and a zinc-copper-aluminum alloy are the common
two alloys.
[0041] The zinc-copper alloy comprises 98.+-.0.2 wt. % of zinc and
2.+-.0.2 wt. % of copper, and the zinc-copper-aluminum alloy
comprises 4-7 wt. % of aluminum, 1-2 wt. % of copper, and 91-95 wt.
% of zinc. The casting is performed as follows:
[0042] a. Ends of the steel wires are perpendicularly fixed in
anchor cups on the casting platform, steel wires comprising a
zinc-aluminum alloy plating are dispersed inside the anchor cups in
the form of concentric circles. Oil stains and rusts are then
removed from surfaces of the steel wires, and the inner walls of
the anchor cups are simultaneously washed.
[0043] b. The center of the steel wire cable is kept coincide with
centers of the anchor cups, and steel wires are prevented from
contacting the anchor cups.
[0044] c. Bottom openings of the anchor cups are sealed to prevent
the alloy from leaking via the bottom openings. The anchor cups are
preheated.
[0045] d. The zinc-copper alloy or the zinc-copper-aluminum alloy
is poured into the anchor cups for one-step casting while avoiding
any vibration or disruption.
[0046] 7) Performing Tension Detection or Top Pressure
Detection
[0047] The tension detection or the top pressure detection are
important means to detect the quality of the steel wire cable.
According to fillers for the casting of the anchor, the tension
detection is performed on the steel wire cable with chilled-casted
anchor or the top pressure detection is performed on the steel wire
cable with hot-casted anchor before leaving a plant, which is
specifically as follows:
[0048] For the steel wire cable with the chilled-casted anchor, the
steel wire cable is stretched by an overstretching force which is
set to be between 1.1 and 1.5 folds of a designed tension of the
steel wire cable and satisfies that a retraction value of a casting
body inside the anchor cup after stretching is equal to or less
than 6 mm.
[0049] The overstretching force is then unloaded to be 20% of the
original overstretching force or to be the designed tension of the
steel wire cable after the stretching. A length of the steel wire
cable is measured at a constant temperature in the dark, and a
stressless length of the steel wire cable is calculated at a
reference temperature according to the following equation:
L CO = L CP 1 + P 20 EA + .alpha. ( t - t 0 ) ##EQU00001##
in which, L.sub.C0 represents the stressless length, m, of the
steel wire cable at the reference temperature; L.sub.CP represents
a length, m, of the steel wire cable loaded with a tension force of
P.sub.20; P.sub.20 represents 20% of the overstretching force, N; A
represents a nominal area, mm.sup.2, of the steel wire bunch of the
steel wire cable; E represents an elastic modulus, MPa; .alpha.
represents a coefficient of linear expansion of a stay cable which
is equal to 0.000012/.degree. C.; t represents the constant
temperature, .degree. C., when measuring a length of the stay
cable; and t.sub.0 represents a designed reference temperature,
.degree. C., of the stay cable.
[0050] For the steel wire cable with hot-casted anchor, a top
pressure is applied to the steel wire cable. The top pressure is
1.25 folds of the designed tension of the steel wire cable and
satisfies that a retraction value of the casting body inside the
anchor cup after the top pressure detection is equal to or less
than 6 mm.
[0051] 8) Coiling
[0052] The steel wire cable is coiled by a coil frame. Before the
coiling, an outer surface of the steel wire cable is packed, and
layers of the steel wire cables are successively coiled by using
the coil frame. An inner diameter of a resulting coil is equal to
or larger than 20 folds of an outer diameter of the steel wire
cable and is equal to or larger than 1.6 m.
[0053] 9) Storing
[0054] Finished product of the steel wire cable adopts indoor
storage or outdoor storage. When the indoor storage is adopted, an
oilcloth is used to cover the steel wire cable. A storage site is
equipped with ventilation and fire-proof facilities to ensure the
quality and the safety of the stored steel wire cables.
[0055] Advantages of the method for fabricating the steel wire
cable according to embodiments of the invention are summarized as
follows: the steel wires are arranged according to the arrangement
rule at the cross section of the steel wire cable. The length of
the overall cable is controlled by the length of the central
standard wire. The bunch of the steel wires comprising the
zinc-aluminum alloy plating are twisted with the torsion angle of
between 2.degree. and 4.degree.. The steel wire bunch is then
wrapped with the polyester wrapping bandage and covered with the
double-layered protective polyethylene sheath by using
double-cavity co-extrusion process for one-step formation, and the
outer surface of the polyethylene sheath is provided with
embossments for rain-wind induced vibration resistance. The two
ends of the steel wire cable are fixed by anchors using fillers,
coiled, and stored. And the coils of the steel wire cables are then
transported to and respectively laid on the construction field. The
fabrication of the steel wire cable of the invention is not
restricted by the construction site, and hardly affected by the
climate factors. And the management of the industrialized
production is easily controllable. All these satisfy the use
requirements of long length, high accuracy, and endurance of the
stay cable for the large-span bridge used in the marine
environment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0056] The invention is described hereinbelow with reference to the
accompanying drawings, in which:
[0057] FIG. 1 is a structure diagram illustrating two nut-screwing
type anchors at two ends of a steel wire cable in accordance with
one embodiment of the invention;
[0058] FIG. 2 is a structure diagram illustrating two anchor plate
gap adjusting type anchors at two ends of a steel wire cable in
accordance with one embodiment of the invention;
[0059] FIG. 3 is a structure diagram illustrating a fork-ear pin
joint type anchor at one end of a steel wire cable and a
nut-screwing type anchor at the other end of the steel wire cable
in accordance with one embodiment of the invention; and
[0060] FIG. 4 is a side view of FIG. 3.
[0061] In the drawings, the following numbers are utilized: 1.
Anchor plate; 2. Anchor cup; 3. Sealing assembly of a connecting
cylinder; 4. Steel wire cable; 5. Sealing structure at an end of a
steel wire cable; 6. Nut; 7. Gap adjusting plate; 8. Pin shaft; and
9. Fork ear.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0062] For further illustrating the invention, experiments
detailing a method for fabricating a steel wire cable comprising a
Zn--Al alloy plating are described below. It should be noted that
the following examples are intended to describe and not to limit
the invention.
[0063] In the method of the invention, steel wires comprising a
zinc-aluminum alloy plating are twisted together to form a naked
steel wire cable, an outer layer of the naked steel wire cable is
covered by a double-layered protective polyethylene by extrusion.
Two ends of a resulting steel wire cable are then anchored by
casting, coiled, transported to the construction site and laid
respectively.
[0064] 1) fabricating a steel wire comprising a zinc-aluminum alloy
plating
[0065] The steel wire comprising the zinc-aluminum alloy plating is
adopted because the zinc-aluminum alloy plating possesses much
stronger anti-corrosive property. The zinc-aluminum alloy plating
includes two types, Zn95Al5 5 having an aluminum content of between
4.2 and 7.2 wt. %, and Zn90Al10 having the aluminum content of
between 9.2 and 12.2 wt. %. A plating weight is equal to or larger
than 300 g/m.sup.2.
[0066] 2) fabricating a Steel Wire having a Standard Length
[0067] As each layer of steel wires in the stay cable exists with a
certain torsion angle, it is unable to directly control the length
of the steel wire cable by using the outer layers of steel wires.
Only the central wire of the stay cable always remains straight
without being twisted during the whole fabrication process,
therefore, the central wire is utilized as the standard wire to
control the overall length of the steel wire cable.
[0068] The length of the standard wire is determined by baseline
measurement, and specific operation includes: applying a certain
tension force to two ends of a steel wire to straighten the steel
wire a performing stress correction and temperature correction
using the following equation:
L=L.sub.0.times.[(1+F/EA)+.alpha.(T-20)]
in which, L represents a length (m) of the steel wire in a stressed
state, L.sub.0 represents a designed length, m, of the steel wire
in an unstressed state, F represents a tensioning force, N, E
represents an elastic module, MPa, of the steel wire, and
fabrication of the standard wire adopts a measured value, A
represents an area of a cross section, m.sup.2, of the steel wire,
and fabrication of the standard wire adopts the measured value, a
represents an expansion coefficient of the steel wire, and T
represents a temperature, .degree. C., of the environment.
[0069] A steel wire having a standard length is prepared. Certain
markers for cutting are made at two ends of the steel wire.
Thereafter, the steel wire having the standard length is utilized
as a reference, and the overall length of the steel wire cable is
controlled by a transfer method.
[0070] 3) Twisting a Steel Wire Bunch
[0071] The steel wire cable is formed by multiple layers of steel
wires. When relaxing the steel wires, the standard wire is
positioned at a center position of a cross section of the steel
wire cable.
[0072] A steel wire bunch is twisted to the left with a torsion
angle of between 2.degree. and 4.degree.. The twisted steel wire
bunch is wrapped to the right by a wrapping bandage to yield a
naked steel wire cable as a semi-product. As lengths of the
multiple layers of the steel wires exist with differences, a
relaxed length L.sup./ of other layers of steel wires surrounding
the standard wire considering the length of the standard wire is
calculated according to the following equation:
L.sub.0=L.sup./.times.cos .alpha.+K
in which, .alpha. represents the torsion angle ranging from
2.degree. to 4.degree.; K represents a fabrication allowance, m,
which is selected according to specifications and operations;
L.sup./ represents the relaxed length, m, of other layers of the
steel wires surrounding the standard wire; and L.sub.0 represents
the length, m, of the standard wire at the center position;
[0073] An outer dimeter of the steel wire bunch, i.e., the naked
steel wire cable, after being twisted is measured. Because the
cross section of the steel wire bunch is in a shape of hexagon, a
circumscribed circle of the selected cross section of the steel
wire bunch is directly the diameter of the naked steel wire
cable.
[0074] 4) Extruding
[0075] A double-layered protective polyethylene is prepared outside
the naked steel wire cable. before extruding, a die aperture of an
extruder and an extrusion velocity are preset according to an outer
diameter of the naked steel wire cable and thicknesses of two
layers of polyethylene. The double-cavity co-extrusion for one-step
formation is adopted. The two layers of the polyethylene plastics
simultaneously cover the naked steel wire cable during the
requirements of anti-corrosion.
[0076] According to the requirement of resistance of the rain-wind
induced vibration, after the extrusion, an outer surface of the
double-layered protective polyethylene is provided with helical
lines or embossments. When reaching the effect of the steel wire
cable in effectively inhibiting the rain-wind induced vibration, a
drag coefficient is equal to or smaller than 0.8.
[0077] 5) Accurate Cutting
[0078] Original cutting positions of the steel wire cable are
determined, the double-layered protective polyethylene is locally
stripped, and the markers for cutting at two ends of the standard
wire at the center position of the steel wire cable are found.
Then, the steel wire cable is cut by using a non-liquid cutting
machine and end faces of the steel wire cable are ensured
perpendicular to an axis of the steel wire cable. The
double-layered protective polyethylene is stripped according to a
preset length to expose the steel wires, during which, the plating
of the steel wires is prevented from being destructed.
[0079] 6) Casting Anchor
[0080] The anchor is a main connecting structure to transmit a
tension of the steel wire cable to a tower and a girder. Anchor
structures of the steel wire cable are as follows: two nut-screwing
type anchors disposed at two ends of the steel wire cable, as shown
in FIG. 1, two anchor plate gap adjusting type anchors at two ends
of the steel wire cable, as shown in FIG. 2, and a fork-ear pin
joint type anchor at one end of the steel wire cable and a
nut-screwing type anchor at the other end of the steel wire cable,
as shown in FIGS. 3-4.
[0081] a) Nut-Screwing Type Anchor
[0082] The nut screwing type anchor comprises: an anchor cup, a
screw nut, an anchor plate, and a sealing assembly of a connecting
cylinder. Such steel wire cable utilizes the end face of the nut to
support the pressure and to transmit the load. The nut and the
anchor cup are in rotary joint via a trapezoidal thread having high
strength to realize the continuous adjustment of the length of the
steel wire cable. The anchor cup is provided with tensional inner
threads. In installation of the steel wire cable on the
construction site, an installation force is applied on the steel
wire cable by drawing the anchor. The anchor plate primarily
functions in dispersing the steel wires, steel wire holes are
distributed on the anchor plate, and the steel wires pass through
corresponding steel wire holes and are headed. An external cone
boss can be tightly attached to an internal conical cavity.
[0083] b) End Face-Supporting Type Anchor
[0084] The end face-supporting type anchor comprises: an anchor
cup, an anchor plate, and a sealing assembly of a connecting
cylinder. End faces of such steel wire cable are directly supported
on anchor plate, and different gap adjusting plates are utilized to
regulate the length of the steel wire cable. The gas adjusting
plates have different thicknesses to satisfy the requirement of the
construction site. The anchor cup is provided with tensional inner
threads. In installation of the steel wire cable on the
construction site, an installation force is applied on the steel
wire cable by drawing the anchor. Such kind of anchor does not
necessitate nuts, and the anchor cup is not provided with external
threads. The anchor plate functions in dispersing the steel wires,
the steel wire holes are distributed on the anchor plate, and the
steel wires pass through corresponding steel wire holes and are
headed. An external cone boss can be tightly attached to an
internal conical cavity.
[0085] c) Fork-Ear Pin Joint Type Anchor at One End and
Nut-Screwing Type Anchor at the Other End
[0086] The fork-ear pin joint type anchor comprises: a fork ear, a
pin shaft, an anchor cup, a nut, and a sealing assembly of a
connecting cylinder. One end of such steel wire cable is connected
to the steel structure of the tower or the girder via the fork ear
and the pin shaft, and the other end of the steel wire cable adopts
an end face of a nut to bear pressure and to transmit the load,
thus realizing the continuous adjustment of the length of the steel
wire cable. the anchor cup is provided with tensional inner
threads. In installation of the steel wire cable on the
construction site, an installation force is applied on the steel
wire cable by drawing the anchor. The anchor plate functions in
dispersing the steel wires, the steel wire holes are distributed on
the anchor plate, and the steel wires pass through corresponding
steel wire holes and are headed. An external cone boss can be
tightly attached to an internal conical cavity.
[0087] The sealing assembly of the connecting cylinder in the above
three structures all adopts the new type of cable end sealing
technology, in which, an outer part of the connecting cylinder is
firstly sealed by a sealing cover, and an inner wall of the
connecting cylinder in the vicinity of a port is sealed again by an
elastic sealing ring and a sealing press ring. The two sealing
measurements finally realizes the sealing of the two ends of the
steel wire cable, that is, the sealing between the anchors and the
interfaces of the polyethylene steel wire cable. The sealing
assembly has stronger strength, thus being difficult to be
destructed, much longer service life, and much endurable sealing
structure.
[0088] The sealing structure at the ends of the steel wire cable is
a reliable mechanical sealing structure, configured to prevent the
corrosion resulting from the water penetration into the PE cable.
In the meanwhile, the sealing structure, as a substitute of a heat
shrink sleeve, is utilized for sealing, thus overcoming the problem
of damage of the heat shrink sleeve.
[0089] The technical solution to solve the above described
technical problem is as follows: an endurable sealing structure at
an end of the steel wire cable. The sealing structure fits together
with the connecting cylinder of the anchor and comprises: the
elastic sealing ring, a sealing press ring, and a sealing cover.
The sealing press ring is disposed in the port of the connecting
cylinder and an outer end of the sealing press ring is exposed
outside the connecting cylinder. A press surface is formed on the
inner wall of the connecting cylinder relative to the inner end
face of the sealing press ring. The elastic sealing ring is
disposed between the inner end face of the sealing press ring and
the press surface. Under the press of the press surface, the
elastic sealing ring is deformed and attached to the outer wall of
the steel wire cable. The sealing cover is disposed on a front end
of the connecting cylinder and possesses a Harvard structure. A
front part of the sealing cover contacts and fits with the outer
wall of the steel wire cable and a corresponding contact surface is
provided with a sealing ring. A rear part of the sealing cover
contacts and fits with the sealing press ring or the connecting
cylinder and a corresponding contact surface is provided with a
sealing strip.
[0090] The anchor is performed with hot galvanizing or paint
coating for corrosion resistance. A thickness of the hot
galvanizing is equal to or larger than 90 um, and a thickness of
the paint coating is determined according to specifications and
design requirements of a steel structure.
[0091] The casting of the anchor is carried out by chill casting of
heading anchor or by hot casting of anchor, operations of which are
as follows:
[0092] A. Chill Casting of Heading Anchor
[0093] a. Ends of the steel wires are fixed in anchor cups on a
casting platform, oil stains and rusts are removed from portions of
the steel wires inside the anchor cups, and inner walls of the
anchor cups are synchronously washed.
[0094] b. The ends of the steel wires are uniformly dispersed
corresponding to holes of anchor plates, and each steel wire is
headed by using a heading machine. Heading dimensions are as
follows: heading diameter .gtoreq.1.4 D, heading height .gtoreq.1.0
D, and D represents a diameter of the steel wires.
[0095] c. A chilled filler comprising steel balls, a stone dust, an
epoxy resin, a curing agent, di-n-butyl, and a diluent is provided
and uniformly mixed. A mixture of the chilled filler is poured into
the anchor cups while vibrating by using a vibration pump to fully
fill gaps among the anchor cup and steel wires with the mixture of
the chilled filler.
[0096] B. Hot Casting of Anchor
[0097] The hot casting anchor adopts a zinc alloy for casting, and
a zinc-copper alloy and a zinc-copper-aluminum alloy are the common
two alloys.
[0098] The zinc-copper alloy comprises 98.+-.0.2 wt. % of zinc and
2.+-.0.2 wt. % of copper, and the zinc-copper-aluminum alloy
comprises 4-7 wt. % of aluminum, 1-2 wt. % of copper, and 91-95 wt.
% of zinc. The casting is performed as follows:
[0099] a. Ends of the steel wires are perpendicularly fixed in
anchor cups on the casting platform, steel wires comprising a
zinc-aluminum alloy plating are dispersed inside the anchor cups in
the form of concentric circles. Oil stains and rusts are then
removed from surfaces of the steel wires, and the inner walls of
the anchor cups are simultaneously washed.
[0100] b. The center of the steel wire cable is kept coincide with
centers of the anchor cups, and steel wires are prevented from
contacting the anchor cups.
[0101] c. Bottom openings of the anchor cups are sealed to prevent
the alloy from leaking via the bottom openings. The anchor cups are
preheated.
[0102] d. The zinc-copper alloy or the zinc-copper-aluminum alloy
is poured into the anchor cups for one-step casting while avoiding
any vibration or disruption.
[0103] 7) Performing Tension Detection or Top Pressure
Detection
[0104] The tension detection or the top pressure detection are
important means to detect the quality of the steel wire cable.
According to fillers for the casting of the anchor, the tension
detection is performed on the steel wire cable with chilled-casted
anchor or the top pressure detection is performed on the steel wire
cable with hot-casted anchor before leaving a plant, which is
specifically as follows:
[0105] For the steel wire cable with the chilled-casted anchor, the
steel wire cable is stretched by an overstretching force which is
set to be between 1.1 and 1.5 folds of a designed tension of the
steel wire cable and satisfies that a retraction value of a casting
body inside the anchor cup after stretching is equal to or less
than 6 mm.
[0106] The overstretching force is then unloaded to be 20% of the
original overstretching force or to be the designed tension of the
steel wire cable after the stretching. A length of the steel wire
cable is measured at a constant temperature in the dark, and a
stressless length of the steel wire cable is calculated at a
reference temperature according to the following equation:
L CO = L CP 1 + P 20 EA + .alpha. ( t - t 0 ) ##EQU00002##
in which, L.sub.C0 represents the stressless length, m, of the
steel wire cable at the reference temperature; L.sub.CP represents
a length, m, of the steel wire cable loaded with a tension force of
P.sub.20; P.sub.20 represents 20% of the overstretching force, N; A
represents a nominal area, mm.sup.2, of the steel wire bunch of the
steel wire cable; E represents an elastic modulus, MPa; .alpha.
represents a coefficient of linear expansion of a stay cable which
is equal to 0.000012/.degree. C.; t represents the constant
temperature, .degree. C., when measuring a length of the stay
cable; and to represents a designed reference temperature, .degree.
C., of the stay cable.
[0107] An error of the stressless length of the steel wire cable at
the reference temperature satisfies the following requirements:
[0108] when L.sub.C0<100 m, the error is less than or equal to
10 mm; and
[0109] when L.sub.C0>100 m, the error is less than or equal to
L.sub.C0/20000+5 mm.
[0110] For the steel wire cable with hot-casted anchor, a top
pressure is applied to the steel wire cable. The top pressure is
1.25 folds of the designed tension of the steel wire cable and
satisfies that a retraction value of the casting body inside the
anchor cup after the top pressure detection is equal to or less
than 6 mm.
[0111] 8) Coiling
[0112] The steel wire cable is coiled by a coil frame. Before the
coiling, an outer surface of the steel wire cable is packed, and
layers of the steel wire cables are successively coiled by using
the coil frame. An inner diameter of a resulting coil is equal to
or larger than 20 folds of an outer diameter of the steel wire
cable and is equal to or larger than 1.6 m.
[0113] 9) Storing
[0114] Finished product of the steel wire cable adopts indoor
storage or outdoor storage. When the indoor storage is adopted, an
oilcloth is used to cover the steel wire cable. A storage site is
equipped with ventilation and fire-proof facilities to ensure the
quality and the safety of the stored steel wire cables.
[0115] Unless otherwise indicated, the numerical ranges involved in
the invention include the end values. While particular embodiments
of the invention have been shown and described, it will be obvious
to those skilled in the art that changes and modifications may be
made without departing from the invention in its broader aspects,
and therefore, the aim in the appended claims is to cover all such
changes and modifications as fall within the true spirit and scope
of the invention.
* * * * *