Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
2000-05-24
2001-11-06
Falik, Andy (Department: 3765)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S902000, C428S592000
Reexamination Certificate
active
06311466
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a steel structure adapted for the reinforcement of elastomers such as rubber conveyor belts, rubber tyres, rubber hoses, rubber timing belts or timings in polyurethane. The steel reinforcement comprises one or more steel filaments.
The present invention also relates to a method of treating a steel filament so that the steel filament receives a spatial wave form.
BACKGROUND OF THE INVENTION
Such steel structures are widely known in the art. Recent prior art documents have disclosed a tendency towards steel structures where the steel filaments present one or another type of waviness, i.e. where, in addition to the plastic deformation as a consequence of the possible twisting of the steel filaments, the steel filaments have another plastic deformation. This additional and other plastic deformation is conveniently a consequence of a preforming operation, and results in a wavy pattern on the steel filament.
In this way U.S. Pat. No. 5,020,312 (Kokoku—priority 1989) and U.S. Pat. No. 5,111,649 (Kokoku) disclose steel cord structures consisting of three to five steel filaments. At least one steel filament is provided with a so-called ‘crimp’: this is a zigzagged form with relatively sharp angles, the sharpness depending upon the formation tools. The crimp is a planar wave form and is formed by means of two toothed wheels. The holes created at the level of the angles promote penetration of elastomer into the steel cord structure.
Another wave form has been disclosed in EP-A-0 462 716 (Tokusen—priority 1990). According to this document, the steel cords have three to twenty-seven steel filaments, 25% to 67% of which have a particular helix or helicoidal form. The plastical helix deformation is carried out by means of rotating preforming pins. The purpose is to promote penetration of the elastomer into the steel cord structure without increasing the so-called part load elongation (PLE, for definition see below). These steel cords are marketed under the name SPACY® cord. An important drawback of this cord is that its manufacture is energy-consuming or inefficient or both. Indeed, if the pitch of the helix is taken smaller than the twist pitch, then the rotation speed of the preforming pins must be more than twice as high as the rotation speed of a down-stream double-twister.
Still another wave form has been disclosed in WO-A-95/16816 (Bekaert—priority 1993). According to this document, the steel structure comprises steel filaments and at least one steel filament has been polygonally preformed. This is a spatial wave form and is the result of a preforming device with varying radii of curvature. The steel structures are marketed under the name BETRU®.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide still another wave form to steel filaments of steel structures. It is another object of the present invention to provide a wave form to steel filaments where the wave form combines advantages of existing wave forms. It is still another object of the present invention to provide a wave form which can take a lot of specific forms depending upon the choice of the parameters of the wave form.
It is yet another object of the present invention to provide a wave form, the manufacture of which does not necessitate energy-consuming tools.
It is also an object of the present invention to provide a steel structure with an oval transversal cross-section as a consequence of the wave form of some filaments, e.g. a core filament.
According to the invention, there is provided a steel structure adapted for the reinforcement of elastomers. The steel reinforcement comprises one or more steel elements. At least one of these steel elements is provided with a first crimp and a second crimp. The first crimp lies in a plane that is substantially different from the plane of the second crimp.
In this way a spatial wave form is obtained without using driven and energy-consuming preforming tools.
Another advantage of this steel structure is that a lot of wave forms become possible. Indeed, the first crimp has a first crimp pitch and a first crimp amplitude. The second crimp has a second crimp pitch and a second crimp amplitude. This means already four design parameters which each can be varied, independently of each other over a certain range.
The first crimp pitch may be equal to or different from the second crimp pitch. With equal crimp pitches circular or oval spatial helixes can be obtained. Different crimp pitches, however, lead to spatial forms different from helixes.
The first crimp amplitude may be equal to or different from the second crimp amplitude. A different crimp amplitude enables to obtain a spatial form with an oval transversal cross-section on condition that the filament which is provided with the first crimp and the second crimp is not rotated around its own axis in the final steel structure. Still another parameter which can be varied is the angle between the two planes. It is preferable, however, that the planes differ as much from each other as possible: so the best choice is a maximum difference of about 90°.
The steel element of the steel structure according to the invention can be a steel filament, a bundle of non-twisted steel filaments or a steel strand of twisted steel filaments. The steel structure according to the invention may also be constituted by any combination hereof.
The steel structure may be an untwisted structure consisting of one or more steel filaments lying parallel adjacent to each other and bound by each other by means of another wrapping filament or by means of an adhesive that is compatible with the elastomer to be reinforced. An alternative embodiment is that the steel filaments lie nearly parallel adjacent to each other, which can be obtained by twisting them with a very large twist pitch e.g. by passing them at a relatively high linear speed through a twisting apparatus rotating at a convenient or relatively low rotation speed.
The steel structure may also be a twisted structure with some or all of the composing filaments twisted in to a coherent structure.
At least one of the first crimp pitch and the second crimp pitch is preferably smaller than the twist pitch of the steel filament provided with the first and the second crimp.
Within the general group of twisted structures, a first application of the invention are nx1 steel cords, i.e. cords essentially consisting of two to five steel filaments. In a first embodiment, some but not all of these filaments are provided with the first and the second crimp in order to allow rubber penetration. An example is a 4×0.28 cord with one or two filaments provided with the first and the second crimp. Such a cord is used in the breaker plies of a tyre. In a second embodiment, all of the filaments are provided with the first and the second crimp in order to increase the elongation at break above 5% or more. An example is a 5×0.38 cord with the five filaments provided with the first and second crimp. An additional advantage is that the cord may be twisted with a relatively large twist pitch (14 mm to 20 mm) without decreasing substantially the elongation at break. Another example are 4×0.22 and 5×0.22 where all filaments are provided with the first and the second crimp. These high elongation cords are suitable for reinforcing tyres of a motor cycle (lying at nearly 0° with respect to the equatorial plane of a motor cycle tyre).
A second application of the invention are the so-called l+m (+n) steel cords comprising a core of l core steel filaments and a layer of m steel filaments twisted around the core. Additionally, a second layer of n steel filaments may be twisted around the first layer of m filaments.
One or more core steel filaments may be provided with the first and the second crimp in order to:
a) increase the penetration of the elastomer into the core; and/or to
b) obtain an oval transversal cross-section of the core, and as a consequence, an oval transversal cross-section of the whole cord; and/or to
c) prevent
De Vos Xavier
Lippens Yvan
Somers Albert R.
Van Giel Frans
Falik Andy
Foley & Lardner
N. V. Bekaert S.A.
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