[0001] The present invention relates to a metal wire. cord to be used for reinforcing articles
made of rubber, elastomers, plastics and similar materials, such as conveyor belts,
driving belts, high pressure pipes and mainly vehicle tires.
[0002] The known metal wire cords generally consist of strands with a predetermined length
of lay or pitch, which are then laid up or twisted together to obtain the finished
cord, which is generally comprised of a central core and an outer crown of filaments
or strands.
[0003] Although these metal wire cords, when used for the above mentioned purposes, reached
rather high performances, more particularly as to the mechanical properties, they
are still undergoing several drawbacks as to corrosion strength and fatigue resistance.
As the strand filaments are indeed twisted one another, this prevents a perfect penetration
of the rubber, plastics and like materials inbe- tween the various filaments of the
strands, so that microcavities are formed, from which oxygen and moisture start the
corrosive attack to the cord filaments, and moreover at the points of mutual contact
between said filaments, fretting friction is generated, leading to wear which aggravated
by corrosion, causes fatigue failure of the various filaments.
[0004] A metal wire cord was recently developed for the above mentioned purposes, consisting
of several strands of filaments grouped together without torsion, which are then subjected
all together to a torsional winding operation, so that the average length of lay of
all the filaments in the strands is equal to the average length of lay of the strands
in the cord, and the core is not formed always by the same filaments, but on the contrary
at any cross-section of the cord the core is represented by the filaments which at
that point are at the centre of the bundle of filaments (DE 29 09 832 Al); in this
way one obtains a cord with a rather open structure, thus suitable for penetration
of rubber or plastics, but lacking of a well defined core, which is the necessary
basis to obtain high properties of mechanical strength.
[0005] In order to overcome these drawbacks, the present invention relates to a metal wire
cord combining the advantages of the conventional cords having a core strand and a
peripheral crown of strands or filaments as well as of the cords with parallel filaments
wound together with a single pitch to from the cord but not wound around a core, at
the same time eliminating the drawbacks of either prior type.
[0006] The metal wire cord according to the present invention consists in winding one or
more outer strands around a core strand, with a normal length of lay comprised between
15 and 100 times the diameter of the strands forming the cord, and is characterized
by the fact that the core strand is always in the central position, thus being always
formed by the same filaments, and at least the outer strands are laid without twist,
thus with a substantially infinite pitch or length of lay.
[0007] The term "substantially infinite pitch or length of lay" means a pitch or length
of lay which is by far higher than any pitch or length of lay used in the technique
of laying up ropes, cables and cords, and in any way of a length higher than 200 times
the diameter of the single filaments forming the strand.
[0008] Preferably, but not necessarily, also the core strand is without torsion, namely
with a substantially infinite pitch, but it could also be a twisted strand, and moreover
said core strand could comprise two or more filaments having the same or a different
diameter with respect to those forming the outer strands, the latter being generally
comprised of two or more filaments generally having the same diameter. The diameter
of the filaments normally but not necessarily used is 0.15 + 0.35 mm.
[0009] The metal wire cord according to the present invention may be produced with a conventional
laying up machine, where the cord forming strands may come from more parallel filaments
wound on the same reel and a certain number of these spools may be loaded on the laying
up machine.
[0010] The method of making the cord according to the present invention is characterized
by the fact that the cord forming strands are prepared in a preliminary stranding
stage with a pitch equal to the pitch of the final cord, and for its manufacture a
double torsion cord making machine is used, where the cord length of lay is of identical
value but in the opposite direction of the strand lay, e.g. the cord lay is in the
Z direction and the strand lay in the S direction, so that the final cord has parallel
filaments in the strands and a core strand which is always the same.
[0011] The metal wire cord according to the present invention is shown in the single figure
of the accompanying drawing, in one embodiment which is being given as a non limiting
example only.
[0012] The figure shows diagrammatically a 7 x 4 cord construction, in which all the strands
have an infinite pitch or length of lay. The metal wire cord 1 consists of a core
strand 2 around which six outer strands 3 (to make understanding easier only two outer
strands are shown) are wound with a predetermined pitch. The core strand 2 consists
of four filaments which in the illustrative embodiment are not twisted one another,
said filaments always taking the central position in the cord so as to form the cord
core.
[0013] The outer strands 3 also consist of four filaments which in the illustrative embodiment
have the same diameter of the core filaments, they are not twisted one another, but
all the four filaments of a strand together are wound around the core with the same
pitch of all the other outer strands, all being formed by four filaments not twisted
to one another. As the outer strands consist of filaments parallel to one another
and not twisted, this allows during use to have an easier penetration of rubber and
the like around and between the filaments up to the cord inner core.
[0014] The higher penetration of rubber between the filaments causes their protection from
the corrosive phenomena and moreover increases the fatigue resistance of the cord
as the wear effects arising from fretting between filaments at the direct contact
points are reduced.
[0015] The resulting cord is uniform and with a regular geometric shape, with a well defined
core having the function of support for the outer strands. When the cord is under
strain, this gives rise to a greater uniformity in the stress distribution, thus obtaining
high properties of mechanical strength.
[0016] For the production of the metal cord according to the present invention, it is clear
that metal wires and generally steel wires may be used, having suitable features for
the indicated purposes, which were subjected to any treatment known in the technique
of manufacturing metal wire cords used for reinforcing articles made of rubber, elastomers,
plastics and similar materials, such as conveyor belts, driving belts, high pressure
pipes, and more particularly vehicle tires.
[0017] As an example only, it is to be mentioned the particular spiral wrapping process,
consisting in winding a small diameter thread around a metal cord to increase its
properties of compressive strength.
[0018] It is also to be understood that many variations, modifications, additions and/or
substitutions may be made to the details of the invention, without departing however
from its spirit and scope as defined in the appended claims.
1) A metal wire cord having strands with parallel filaments, consisting of one or
more outer strands wound around a core strand, characterized by the fact that the
core strand is always kept in the central position and is always comprised of the
same filaments, and at least the outer strands are laid without torsion, namely their
filaments are not twisted to one another or are twisted with a substantially infinite
pitch or length of lay, practically higher than 200 times the diameter of the single
filaments forming the strand.
2) A metal wire cord according .to Claim 1, characterized by the fact that also the
core strand is laid without torsion, i.e. with a substantially infinite pitch or length
of lay.
3) A metal wire cord according to Claims 1 and/or 2, characterized by the fact that
the core strand consists of filaments having the same diameter of the filaments of
the outer strands.
4) A metal wire cord according to Claims 1 and/or 2, characterized by the fact that
the core strand consists of filaments having a different diameter from that of the
filaments of the outer strands.
5) A metal wire cord according to the preceding Claims, characterized by the fact
that each strand of the cord consists of two or more filaments of the same diameter,
substantially not twisted to one another, or wound with a pitch or length of lay higher
than 200 times the diameter of the filaments.