Note: Descriptions are shown in the official language in which they were submitted.
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SUSPENSION BRIDGE CABLE WRAP
AND APPLICATION METHOD
1. Field of the Invention
This invention relates to a wrap for a large,
lengthy outdoor tubular article, such as a cable of a
suspension bridge or cable-stayed bridge, and to a method
for applying such a wrap to such an article.
2. Description of the Prior Art
Cables for suspension bridges and cable-stayed
bridges are exposed to severe outdoor climatic conditions
and must be painted or otherwise coated to avoid rusting
and other forms of deterioration that can result from
such exposure. Traditionally, such cables were painted
with weather-resistant paint, but periodic repainting of
painted cables is still required, at substantial expense
due to the relative inaccessibility of such cables,
because of the severity of the climatic conditions to
which such painted cables are often exposed. Removal of
paint prior to repainting, which is often necessary for
proper repainting, also raises environmental concerns.
More recently, it has become known that bridge
cables can be more permanently protected from exposure by
spirally wrapping them with a strand of indefinite length
of a Neoprene or similar polychloroprene material.
However, a material of this type usually cannot be
properly precolored to match or blend in appearance with
the other elements of a bridge or other structure where
it is to be used. Thus, it is customary, after spirally
wrapping a bridge cable with a Neoprene covering, to
paint the outer surface of the wrapping to thereby ensure
a suitable color match between the cable and other bridge
elements. This after painting step, of course, is quite
labor intensive and therefore very expensive.
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Further, in spirally wrapping a suspension bridge
cable with a Neoprene covering, it is important that each
turn of the covering be securely bonded to the preceding
turn, to properly seal the seam therebetween and thereby
prevent the ingress of moisture and dust into the
interface between the covering and cable. In the use of
Neoprene coverings of the type described, it was known
that the seam could be sealed by providing a significant
overlap between the successive turns of the covering and
by bonding the overlapped layers to one another by the
use of a solvent. However, the application of the
solvent is also labor intensive, and therefore expensive,
and many solvents are objectionable on environmental and
health and safety grounds, therefore requiring great care
in the handling and disposal of such materials. Further,
the solvent sealing step tends to disturb a previously
painted surface.
SUMMARY OF THE INVENTION
According to the present invention a cable for a
suspension bridge or a cable-stayed bridge or other
large, lengthy outdoor tubular article may be
advantageously protected from exposure to severe climatic
conditions by spirally wrapping it with a flexible strand
of indefinite length of a suitable synthetic rubber
material, such as a material being sold for various uses,
such as a roof covering material, under the brand name
"Hypalon." Such material can be prepigmented in a wide
variety of colors, thus eliminating the need for after
painting that was characteristic of Neoprene coverings to
obtain a proper color match between the exterior of the
cover and the other elements of the bridge or adjacent
structure. Further, overlapping portions of successive
turns of such a synthetic rubber can be properly sealed
to one another to seal the seam therebetween by a heat
sealing operation, for example, by passing an annular
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radiant heater or an internally heated annular blanket
therealong, to thereby eliminate the need for a solvent
sealing step and ite attendant solvent handling problems
that was characteristic of Neoprene coverings.
A further advantage of a heat sealing step, as
described above, is that a synthetic rubber covering
material such as Hypalon brand synthetic rubber covering
material can be provided with a significant degree of
heat shrinkability in its longitudinal or machine
1o direction. Thus, the temperature level that is required
to seal superimposed layers or turns of such material to
one another will cause such layers to contract or shrink,
and thereby ensure that the bridge cable or other article
is very snugly engaged by its spirally extending
covering.
A Hypalon synthetic rubber strand used in the
practice of the present invention preferably is a
laminate of two layers of such material to provide a
suitable covering thickness. When such a laminate is
used, it is preferred that it is used with a reinforcing
scrim or screen, such as a scrim formed from a polyester
or other high tensile strength organic material, imbedded
between the layers to improve the overall tensile
strength of the strand. The use of such a scrim will
reduce the degree of heat shrinkability of the strand,
but if the strand is maintained under tension as it is
applied to the cable, a scrim reinforced synthetic rubber
strand will still have sufficient heat shrinkability to
ensure that the cable covering will snugly engage the
underlying cable.
In the practice of the present invention with
respect to a suspension bridge cable, it is important to
be able to properly seal the joint which is formed
between the cable and each cable supporting stanchion or
member, as several such stanchions or members are usually
used at spaced apart locations along the length of a
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typical suspension bridge cable. According to a
preferred embodiment of the present invention, such a
seal is provided by the use of a generally wedge-shaped
extrusion of a Neoprene or similar elastomeric material
which is joined end to end to form an annular member
snugly surrounding a portion of the cable which is
immediately adjacent to the stanchion or other supporting
member, with a thicker end of the annular member in snug,
sealing engagement with a surface of the cable supporting
stanchion. Preferably, the ends of the extrusion are
adhesively joined to one another and the annular member
is then preferably mechanically restrained in such
configuration by circumscribing it by a high tensile
strength plastic strap or band.
A relatively short sleeve of a Hypalon synthetic
rubber, which is long enough to cover the entire axial
length of the elastomeric annular member and a short
portion of the cable extending there beyond, is formed
around the cable at a location near the elastomeric
annular member and in snug engagement with the cable.
The synthetic rubber sleeve is then slid up the cable
toward the supporting member to surround the elastomeric
member which is adjacent thereto. This step inherently
stretches the sleeve, thereby increasing its tension
level, and it also inherently compresses the elastomeric
annular member, thereby improving the seal between it and
the joint formed between the annular member and the
cable. The sleeve is then preferably mechanically
restrained in place by circumscribing it by a high
tensile strength plastic band or strap, and the spiral
wrapping of the cable, as previously described, is begun,
with the spiral wrapping preferably extending from the
surface of the cable supporting stanchion and thereby
overlying the synthetic rubber sleeve and the elastomeric
member that is surrounded thereby.
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Accordingly, it is an object of the present
invention to provide an improved weather-resistant wrap
for a large, lengthy outdoor tubular article, such as a
suspension bridge cable, and to provide a method for
applying such a wrap to such an article. More
specifically, it is an object of the present invention to
provide a properly precolored wrap of the foregoing
character to such an article to eliminate the need to
paint such wrap after it is in place on the article. It
is also an object of the present invention to provide a
multiple layer wrap of the foregoing character whose
superimposed layers can be bonded to one another by heat
sealing, without the use of a solvent and the material
handling and disposal problems which are attendant
thereto. It is also an object of the present invention
to provide a multiple layer wrap of the foregoing
character from a heat shrinkable, heat sealable material
whose superimposed layers are heat sealed to one another
and are thereby shrunk into very tight engagement with
the tubular article. It is also an object of the present
invention to provide a suitable seal between a tubular
article supporting member and a wrapped tubular article
of the foregoing character. It is also an object of the
present invention to provide a method of wrapping a
previously painted tubular article which does not require
the prior removal of the paint, but which nonetheless
does not disturb the existing paint.
For a further understanding of the present invention
and the objects thereof, attention is directed to the
drawing and to the following brief description thereof,
to the detailed description of the preferred embodiment,
and to the appended claims.
BRIEF DESQZIPTTON OF 't'HR DRp~~3T'hTr
FIG. 1 is a fragmentary view, in cross-section, of a
tubular article, and a tubular article supporting member,
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which is wrapped and sealed with respect to its
supporting member in accordance with a preferred
embodiment of the present invention;
FIG. 2 is a fragmentary cross-sectional view, at an
enlarged scale, of a layer of a preferred embodiment of a
wrapping material used in the practice of the present
invention;
FIG. 3 is a fragmentary perspective view, at an
enlarged scale, of an article which is used in the
wrapped tubular article of Fig. 1; and
FIG. 4 is a fragmentary perspective view
illustrating certain of the steps used in the forming of
a wrap on an article in accordance with Fig. 1.
DETAILED D RrpT7pN QF TH PRERF RFn Fa~runnTOrFaTm
FIG. 1 illustrates a section of an elongate tubular
member 10, illustratively a cable of a suspension bridge
or a cable-stayed bridge, which is normally used in a
relatively inaccessible outdoor location and is subject
to corrosion and other forms of deterioration that are
likely to result from its exposure to outdoor climatic
conditions. In a suspension bridge, such tubular member
10 is used to enclose and restrain the radial movement of
a longitudinally extending tensile load bearing member
12, which is typically made up of an array of individual
steel cables. The tubular member 10 typically is
supported at various locations along its length by
vertical support members, such as an annular member 14,
which is fragmentarily illustrated in Fig. 1, a member
which is usually referred to as a saddle or a stanchion
in a suspension bridge.
While the tubular member l0 is illustrated as a
unitary element, typically in a suspension bridge it will
be formed by spirally wrapping a galvanized outer steel
cable around the load bearing member 12, with adjacent
winds of the spirally wrapped member in surface to
surface contact with one another. In many older
suspension bridges, the exterior of the tubular member
has previously been painted, usually with a lead-based
paint. Nevertheless, the wrap 16 can be applied over a
painted tubular member 10, whatever the condition of its
painted surface, and this can be done without disturbing
the condition of the painted surface. In any case, the
outer surface of the tubular member 10, whatever its
construction and condition, is protected from exposure to
climatic conditions by encapsulating it along its length
extending from the support member 14 to the next support
member, not shown, by an outer wrap 16 and by providing a
seal, indicated generally by reference 18, to seal the
joint formed between the support member and 14 and the
tubular member 10.
The outer wrap 16 is formed by spirally wrapping a
strand S of indefinite length from a roll or coil R
thereof around the tubular member 10, as is generally
indicated in Fig. 3. The strand S is a flexible organic
material which is of a suitable weather resistent
composition, and is preferably applied under tension to
ensure that it will snugly engage the exterior of the
tubular member 10. As illustrated in Figs. 1 and 3, the
strand S is applied with a substantial overlap between
adjacent winds, preferably an overlap equal to one-half
of the width of the strand S, to permit proper sealing of
the seam formed by adjacent winds of the strand S and to
provide a substantially uniform, double thickness wrap
along the tubular member 10. Further, the wrap 16 serves
to effectively encapsulate any lead-based paint that is
already applied to the tubular member l0, thereby
eliminating a potential environmental contamination
problem.
The strand S is illustrated in cross-section in Fig.
3, and preferably is made up of a laminate of inner and
outer layers Sl and S2 with a scrim or screen S3 of a
_$_
relatively high tensile strength material imbedded
therebetween. Preferably, each of the layers S1 and S2
is formed in a uniform thickness by calendaring or
otherwise from a synthetic rubber material, such as that
being sold by DuPOnt for roof covering and other uses
under the brand name Hypalon. Such a material may be
precolored in a wide variety of colors and shades of
colors by blending a suitable amount of a proper colorant
in the resin that is to be calendared. By this
technique, a suitable color match can be obtained between
the as calendared outermost of the layers S1 and S2 and
the surrounding elements of the bridge or other adjacent
structure to eliminate the need for painting the outer
wrap 16 after it is in place on the tubular member 10.
In an illustrated embodiment of the present invention, in
which the invention is utilized to wrap a 18 inch outside
diameter tubular member 10 in the form of a suspension
bridge cable, the strand S is 6 inches wide, each Hypalon
synthetic rubber strand Sl and S2 is 0.015 (15 mil) inch
thickness, and the scrim S3 is a 250 denier 8 by 8
polyester scrim. Each wind of such material as nearly as
exactly as possible overlaps one-half of the width of the
preceding wind.
After the outer wrap 16 is in place on the exterior
of the tubular member 10, it is heated to seal the
overlapped portions of its winds to one another, to
thereby seal the spirally extending seam defined by such
winds. As shown in Fig. 3, this heating step may be done
conductively by an internally heated electric blanket B
and by progressively advancing the blanket B along the
wrap 16 after it is in place on the tubular member 10.
Alternatively, the heat sealing step can be performed by
advancing an annular radiant heater along the wrap 16 on
the tubular member 10.
The seal 18 may be formed in an appropriate manner,
but in the preferred embodiment of the present invention
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it is formed by joining opposed ends of a generally
wedge-shaped Neoprene material or other elastic material
extrusion E, Fig. 4, into an annular member 20. The
annular member 20 snugly engages an annular portion of
the outside surface of the tubular member 10, and the
thicker end of the annular member 20 snugly engages an
end surface of the support member 14 in an annular
pattern. The opposed ends of the extrusion E are
preferably adhesively joined to one another to form the
annular member 20. In any case, after the annular member
is in place with respect to the tubular member 10 and
the support member 14, it is preferably secured in such
place by tightly circumscribing it with a high tensile
strength plastic band or strap 22, such as a ~~Delrim'~
15 brand polyoxymethylene (POM) band or strap, an annular
notch 24 being formed in the exterior of the annular
member 20 to receive the band or strap 22.
After the annular member 20 and the band or strap 22
are in place on the tubular member 10, as heretofore
20 described, an annular sleeve 26 is formed snugly around a
portion of the tubular member 10 which is immediately
beyond the annular member 20. The sleeve 26 is formed
from a stretchable organic material, preferably Hypalon
brand synthetic rubber, and after it is formed it is
advanced toward the support member 14 to surround the
annular member 20. As shown, the sleeve 26 has
sufficient axial length to cover the entire axial length
of the annular member 20 as well as a portion of the
support member 10 which extends there beyond. In any
case, the advancing of the sleeve 26 toward the support
member 14 will stretch and increase the tension in the
portion of the sleeve 26 which overlies the annular
member 20, thereby compressing the annular member 20 into
tight sealing engagement with the support member 14 and
the portion of the tubular member 10 which the annular
member 20 surrounds. After the sleeve 26 is in place, as
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described, it is preferably secured in such place by
circumscribing it with a second high tensile strength
plastic band or strap 28, such as a "Delrim" brand POM
band or strap, an outwardly projecting annular bead 30
being formed in the exterior of the annular member 2o to
axially position the band or strap 28 relative to the
support member 14. Thereupon, the outer wrap 16 is
formed on the tubular member 10, preferably beginning at
the support member 14 and thereby serving to wrap the
exterior of the sleeve 26 and cover the band or strap 28.
Although the best mode contemplated by the inventors
for carrying out the present invention as of the filing
date hereof has been shown and described herein, it will
be apparent to those skilled in the art that suitable
modifications, variations, and equivalents may be made
without departing from the scope of the invention, such
scope being limited solely by the terms of the following
claims.
