Textiles: spinning – twisting – and twining – Apparatus and processes – Unitary multiple twist devices
Reexamination Certificate
2001-06-22
2002-09-10
Worrell, Danny (Department: 3765)
Textiles: spinning, twisting, and twining
Apparatus and processes
Unitary multiple twist devices
C057S311000
Reexamination Certificate
active
06446423
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device for preforming one or more elementary wires forming a metal reinforcing cord. This cord is especially suitable for reinforcing composite elastomeric matrix products, such as tire.
2. Description of the Related Art
In particular, the preforming device according to the present invention is suitable for operating on highcradlebon content metal wires, which are preferred for manufacturing high elongation cords. The expression “high elongation” is used to indicate the capacity of the reinforcing elements to be stretched under stress, at least initially, to a considerable extent, thanks to the employment of specific materials and/or certain specifically selected geometrical shapes so as to fulfil particular manufacturing phases of tire and/or conditions of use of tire.
In particular, these cords, defined as “HE” (High Elongation), present an ultimate elongation between 4% and 10%.
The wires led out of this preforming device according to the invention are subsequently fed to a traditional stranding station known from the art where the wires thus preformed are twisted around the longitudinal axis of the cord thus obtained.
A further object of the present invention is a procedure for manufacturing said cord, comprising the following phases: preforming one or more elementary wires forming said cord by subjecting them to a permanent deformation along their longitudinal development; stranding the elementary wires by means of a helicoidal twisting around the longitudinal axis of the cord.
Furthermore, the present invention relates to a metal cord, preferably a reinforcing cord, obtained by means of a preforming process and of a subsequent stranding of the aforesaid type.
The cord hereof is specifically designed to be used in manufacturing tire components for motor vehicles but can be easily employed to manufacture other items, such as for example pipes for high pressure fluids, belts, belt conveyors or any other product made of elastomer-based composite material.
As is known, the metal cords usually employed to reinforce elastomeric products are generally made of several elementary wires helicoidally twisted around an axis which coincides with the longitudinal development of the cords themselves.
Preferably said cords are produced by means of stranding machines comprising: a supporting structure; a rotor coupled to said supporting structure which is rotatable according to a predefined axis; a cradle fastened to the supporting structure according to an oscillation axis which coincides with the axis of rotation of the rotor; feeding devices operatively assembled on said cradle and/or on its outside, suitable for feeding one or more elementary wires coming from respective feeding spools, said one or more elementary wires being driven along suitable stranding paths; and preferably at least one preforming device operating on one or more elementary wires in a section of the wires which preceeds the subsequent stranding phase.
This preforming device imposes to said one or more elementary wires a permanent flexure deformation suitable for supporting and improving the subsequent arrangement of the wires according to a helicoidal development which ensures the necessary keeping of the structural compactness of the cord.
Furthermore, it is important to note that these cords, especially when employed in the manufacturing of tire, are generally required to be provided with high mechanical resistance and to allow a good physico-chemical adhesion with the elastomeric material in which they are embedded, as well as an efficient penetration of said material in the space surrounding each wire of said cord.
In fact it is known that in order to eliminate the risk of the cords undergoing undesired corrosion phenomena once introduced in a tire, or inside any product made of elastomeric material, it is very important that the elementary wires forming the cords are entirely coated, for their entire superficial extension, by the elastomeric material in which the cord is embedded.
This result, which is more difficult to be achieved when more complex cords are considered, is not easily achieved even when dealing with cords formed by a low number of elementary wires.
In fact, in order to confer the required geometric and structural stability to the cord, the elementary wires forming the cord are compacted, i.e. positioned intimately in contact with one another, leading to the formation of one or more closed cavities inside said cord which extend along the longitudinal development of the cord.
These cavities are closed and, consequently, cannot be reached by the elastomeric material during the normal rubberizing phases of the cord and, as a consequence, corrosion may develop inside said closed cavities and propagate along the elementary wires forming the cord.
As a consequence, this means, for example, that owing to cuts or punctures in the tire structure, or to any other reason, humidity and/or external agents can penetrate into said closed cavities inevitably starting a rapid process of corrosion of the elementary wires, thus severely compromising the structural resistance of the cord and of the tire.
Furthermore, the presence of said closed cavities which cannot be reached by the elastomeric material involves a reduced adhesion of the wires to the elastomer, which—above all if said cords are used for manufacturing tire—in use can cause an undesired tendency of the wires to separate from the elastomer.
An additional disadvantage due to insufficient rubberizing of the wires, caused by the presence of said closed cavities, is the development of fretting of the wires in contact with one another. This generates an inevitable degeneration of resistance to fatigue of the wires and, consequently, of the cord. An attempt to overcome this type of problem known in the art consists of using so-called “open” cords, where the wires (generally from three to five) are kept distant from one another during the entire rubberizing phase, carried out according to known procedures consisting of keeping a traction load not exceeding five kilograms applied to the cord.
Said cords are, for example, described in U.S. Pat. No. 4,258,543 in the name of the Applicant. These cords allow a greater penetration of the rubber between the wires forming the cords.
However, the cords thus obtained present several problems, especially in use, since the wires forming the cords tend to be distanced also when they are subjected to considerable traction stress during tire manufacturing and in tire use. This fact causes undesired geometric and structural instability of the cords which damages the performance of the tire.
According to a further embodiment of the prior art, so-called double-diameter cords are used, i.e. cords with two pairs of wires where the diameter of the wires of the first pair is suitably differentiated from that of the second pair.
It is also known (see EP Patent 168,857) to make a metal cord having a first pair of elementary wires of equal diameter and a second pair of elementary wires with a diameter smaller than that of the first pair. Said first and second pairs are fed into a conventional internal collection stranding machine after crossing a circular preforming head where the wires of the first and second pair follow paths which ensure differentiated preforming actions with respect to each other.
The cord thus obtained, consequently, presents the pair of wires with a larger diameter helicoidally twisted together and in reciprocal contact, while each wire of the second pair is interposed between the two wires of the first pair and extends in parallel to the latter, being suitably distanced from them.
In this way, the aforesaid closed cavities are eliminated from the cross section of the cord, ensuring total coverage of elementary wires by the elastomeric material used during the rubberizing phase.
However, the suggested technical solution involves that the wires with the smallest diameter are distanced from those with the largest diameter also
Finnegan Henderson Farabow Garrett & Dunner LLP
Hurley Shaun R
Pirelli Pneumatici S.P.A.
Worrell Danny
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