Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
1999-08-25
2001-08-21
Calvert, John J. (Department: 3741)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S211000, C057S212000, C057S213000, C074S502500
Reexamination Certificate
active
06276120
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a push-pull steel cable comprising a core and an outer layer of filaments twisted around the core, and possibly an intermediate layer of filaments between the core and the outer layer.
The present invention particularly relates to a push-pull steel cable for use as a brake cable or as a derailleur or shift lever cable in vehicles or for use as a window elevator cable or cable for directing mirrors in vehicles.
Typically for such a push-pull steel cable is that it exercises a to and fro movement inside a casing. So the cable must meet high requirements such as good corrosion resistance, high flexibility, low friction resistance, high tensile strength and high fatigue resistance.
Within the context of the present invention, it is irrelevant whether or not the to and fro movement inside the casing is exercised by means of spring.
BACKGROUND OF THE INVENTION
Push-pull steel cables are known as such in the art.
For example, such a steel cable comprises a core and an intermediate layer with zinc coated filaments and an outer layer of filaments coated with a tin-lead alloy. Although having a low friction resistance due to the tin-lead alloy coating on the filaments of the outer layer, such a cable has a number of drawbacks. Apart from the drawback of using two different types of coatings, zinc for the filaments of the core and the intermediate layer and tin-lead for the filaments of the outer layer, there is the major drawback of using lead in one of the coatings, which may cause environmental problems.
Another example is a steel cable consisting only of stainless steel filaments. Such a cable has the advantage of a good resistance against corrosion but has the drawback inherent to stainless steels that the tensile strength is rather limited, which means that thicker and heavier filaments must be used in order to obtain the same breaking load.
Japanese patent application JP-A-02/093113 discloses a push-pull cable with a coating of polybutylene terephtalate (PBT) resin. Also the liner of the casing of the push-pull cable, i.e. the inner coating of the casing, comprises PBT.
Japanese patent application JP-A-52/033944 discloses a control cable with a coating of a PBT graphite wax. The liner of the casing also comprises PBT graphite wax.
SUMMARY OF THE INVENTION
The present invention aims at avoiding the problems of the prior art.
It is an object of the present invention to provide a cable which can be manufactured in an environment friendly way.
It is another object of the present invention to allow for applying different colors on the coating of a cable.
It is still another object of the present invention to provide for a coating which is resistant against corrosion, which gives sufficient adhesion and adhesion retention in humid conditions, which gives a low friction resistance to the cable and which gives the cable a good weatherability.
Yet another object of the present invention is to obtain a good corrosion resistance in combination with a high tensile strength.
According to a first aspect of the present invention, there is provided a steel cable which comprises a core and an outer layer of filaments twisted around the core. The steel cable is provided with an external coating of polyethylene terephtalate. There is possibly also an intermediate layer of filaments between the core and the outer layer.
Within the context of the present invention, the terms “polyethylene terephtalate” or “PET” denote not only homopolymers of ethylene therephtalate but also copolymers of ethylene terephtalate containing not more than 20% of other copolymerized units, e.g. derived from other acids than terephtalic acid, such as isophtalic acid or from other glycols than ethylene glycol. The polymer may also contain mixtures of polymers in order to modify certain of the properties thereof.
In comparison with coatings of polyamides such as nylon-6 (PA6), a polyethylene terephtalate coating gives the cable a friction resistance which is equally low. In addition thereto, the polyethylene teraphtalate coating has a better adhesion and adhesion retention, has a higher corrosion resistance, has a better resistance against ultra-violet light (=) better weatherability) and has a lower absorption of water or moisture. A polyethylene teraphtalate coating absorbs only one tenth of the amount of moisture absorbed by a nylon-6 coating in the same circumstances. This means that a steel cable with a polyethylene teraphtalate coating does not swell up to the same degree as a steel cable with a nylon-6 coating. Moreover, application of a polyethylene teraphtalate coating can be done in an environment-friendly way, i.e. with a much more simpler pre-treatment and without the use of primers.
Due to the higher corrosion resistance given by the coating to the cable, plain carbon steels or high-carbon micro-alloyed steels (from 0.70% to 1.10% C with additions of Cr, V, Cu, Ni, B or Nb . . . up to maximum 0.50%) can be used instead of stainless steels so that much higher tensile strengths (up to 3000 MPa and higher) can be obtained. This results in cables which are lighter and more flexible.
The coating of the extruded material preferably has a thickness ranging from 20 micrometer to 120 micrometer, most preferably from 0.20 micrometer to 60 micrometer. Such thin coatings are difficult to achieve with polyvinylchloride due to the substantially different viscosity values. Preferably the coating on the cable is so thin that it still shows the cable structure, i.e. the irregularities of the surface of the outer layer. This thin coating is favorable to the flexibility of the cable.
The extruded material preferably has a melt viscosity measured at about 280° C. ranging from 100 Pa.s to 2500 Pa.s for a corresponding shear rate going down from 10000 1/s to 1 1/s. A still more preferable value is a melt viscosity ranging from 200 Pa.s to 1000 Pa.s for a corresponding shear rate going down from 5000 1/s to 20 1/s.
The PET coating is preferably more than 50% amorphous. This may be achieved by rapid cooling after the extrusion process. In comparison with a crystalline structure of the coating, an amorphous polyethylene teraphtalate coating, for example, has a more pronounced luster and is more flexible. Recrystallisation, however, may occur in course of time. In comparison with a PBT coating, recrystallisation happens much slower with a PET coating. This is an advantage for a PET coating.
The steel cable may be provided with a lubricant oil, such as a silicon oil, on top of the polyethylene teraphtalate coating in order to further reduce the friction resistance.
In order to further increase the corrosion resistance, the cable further comprises a synthetic product, a super absorbent powder or a lubricant between the core and the outer layer. The synthetic product may be in the form of another extruded layer of polyethylene teraphtalate around the core filament or core filaments.
Another measure to increase the corrosion resistance is that the filaments of the cable have an individual metal coating of zinc or of a zinc alloy such as a BEZINAL® alloy comprising 95% zinc and 5% aluminium.
According to a second aspect of the present invention, a push-pull steel cable according to the first aspect of the present invention can advantageously be used as:
a brake cable for vehicles such as bicycles, jetscooters and snowscooters;
derailleur or shift lever cable for vehicles such as bicycles, jetskis, waterskis and scooters;
an elevator cable for windows in vehicles or a cable for directing mirrors in vehicles.
Conveniently, the diameter of the steel filaments ranges from 0.10 mm to 0.50 mm, e.g. from 0.25 mm to 0.35 mm. The filaments may have been flattened or rolled. The non-circular transversal cross-section of the filaments can also be the consequence of the compacting of the cable as a result of pulling the cable through a compacting die. In the case of a non-circular transversal cross-section, the term ‘diameter’ refers to the diameter of a circular cross-section with the same su
Adriaensen Ludo
Vandewalle Gerard
Calvert John J.
Foley & Lardner
Muromoto Jr. Robert H.
N.V. Bekaert S.A.
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