U.S. patent application number 10/537173 was filed with the patent office on 2006-06-15 for metal wire coated with a layer of metal material intended to reinforce elastomeric materials and methods for producing the same.
Invention is credited to Simon Agresti, Pietro Luigi Cavallotti, Luca Nobili, Federico Pavan.
Application Number | 20060123862 10/537173 |
Document ID | / |
Family ID | 32676773 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060123862 |
Kind Code |
A1 |
Pavan; Federico ; et
al. |
June 15, 2006 |
Metal wire coated with a layer of metal material intended to
reinforce elastomeric materials and methods for producing the
same
Abstract
A metal wire for reinforcing an elastomeric material includes a
metal core and a metal coating layer. The core includes a
predetermined initial diameter. A method for producing the wire
includes submitting the core to at least one surface treatment,
thermally treating the core, depositing the coating layer on the
core, and drawing the metal-coated metal core. The at least one
surface treatment predisposes a surface of the core to being coated
with the coating layer. The coating layer is deposited on the core
to a predetermined initial thickness using a plasma deposition
technique. The metal-coated metal core is drawn until the core
includes a final diameter smaller than the predetermined initial
diameter and the coating layer includes a final thickness smaller
than the predetermined initial thickness. A metal cord for
reinforcing an elastomeric material and a method for producing the
metal cord are also disclosed.
Inventors: |
Pavan; Federico; (Firenze,
IT) ; Agresti; Simon; (Prato, IT) ;
Cavallotti; Pietro Luigi; (Milano, IT) ; Nobili;
Luca; (Milano, IT) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
32676773 |
Appl. No.: |
10/537173 |
Filed: |
December 22, 2003 |
PCT Filed: |
December 22, 2003 |
PCT NO: |
PCT/EP03/14810 |
371 Date: |
December 2, 2005 |
Current U.S.
Class: |
72/47 |
Current CPC
Class: |
C23C 16/545 20130101;
D07B 2205/3089 20130101; C23C 14/562 20130101; D07B 2205/3089
20130101; C23C 14/5886 20130101; C23C 14/165 20130101; C23C 14/021
20130101; D07B 1/0666 20130101; B21C 37/042 20130101; D07B 2801/18
20130101 |
Class at
Publication: |
072/047 |
International
Class: |
B21C 1/00 20060101
B21C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 23, 2002 |
WO |
PCT/IT02/00823 |
Claims
1-31. (canceled)
32. A method for producing a metal wire for reinforcing an
elastomeric material, wherein the metal wire comprises: a metal
core; and a metal coating layer; wherein the metal core comprises a
predetermined initial diameter, wherein the method comprises:
submitting the metal core to at least one surface treatment;
thermally treating the metal core; depositing the metal coating
layer on the metal core; and drawing the metal-coated metal core;
wherein the at least one surface treatment predisposes a surface of
the metal core to being coated with the metal coating layer,
wherein the metal coating layer is deposited on the metal core to a
predetermined initial thickness using a plasma deposition
technique, and wherein the metal-coated metal core is drawn until:
the metal core comprises a final diameter smaller than the
predetermined initial diameter; and the metal coating layer
comprises a final thickness smaller than the predetermined initial
thickness.
33. The method of claim 32, wherein submitting the metal core to at
least one surface treatment, thermally treating the metal core,
depositing the metal coating layer on the metal core, and drawing
the metal-coated metal core are carried out in a substantially
continuous manner.
34. The method of claim 32, wherein the metal core is conveyed
through a sequence of respective positions for submitting the metal
core to at least one surface treatment, thermally treating the
metal core, depositing the metal coating layer on the metal core,
and drawing the metal-coated metal core, at a speed in a range from
about 10 m/min to about 80 m/min.
35. The method of claim 32, wherein submitting the metal core to at
least one surface treatment comprises: pickling the metal core in a
pickling bath; and washing the pickled metal core in water.
36. The method of claim 35, further comprising: drying the washed
metal core.
37. The method of claim 36, wherein drying the washed metal core is
carried out using at least one blower.
38. The method of claim 32, further comprising: dry drawing the
metal core before thermally treating the metal core.
39. The method of claim 32, wherein the plasma deposition technique
is selected from the group comprising: sputtering, evaporation by
voltaic arc, plasma spray, and plasma-enhanced chemical vapor
deposition (PECVD).
40. The method of claim 32, wherein depositing the metal coating
layer on the metal core is carried out in at least one vacuum
deposition chamber at a first predetermined pressure.
41. The method of claim 40, wherein depositing the metal coating
layer on the metal core is carried out a plurality of times.
42. The method of claim 40, wherein the first predetermined
pressure is in a range from about 10.sup.-3 mbar to about 10.sup.-1
mbar.
43. The method of claim 40, further comprising: conveying the metal
core in at least one pre-chamber at a second predetermined pressure
higher than the first predetermined pressure; wherein the at least
one pre-chamber is arranged upstream of the at least one vacuum
deposition chamber.
44. The method of claim 43, wherein the second predetermined
pressure is in a range from about 0.2 mbar to about 10 mbar.
45. The method of claim 32, further comprising: descaling a wire
rod; and dry drawing the wire rod to obtain the metal core
comprising the predetermined initial diameter.
46. The method of claim 32, wherein the metal coating layer
comprises a first metal material different from a second metal
material of the metal core.
47. The method of claim 32, wherein the metal core comprises
steel.
48. The method of claim 32, wherein the metal coating layer
comprises a metal material selected from the group comprising:
copper, zinc, manganese, cobalt, tin, molybdenum, iron, and alloys
thereof.
49. The method of claim 32, wherein the metal coating layer
comprises brass.
50. The method of claim 49, wherein the brass comprises a copper
content of about 60%-by-weight to about 72%-by-weight.
51. The method of claim 46, wherein the first metal material
comprises a predetermined amount of a lubricating agent.
52. The method of claim 32, wherein the predetermined initial
thickness is at least about 0.5 .mu.m.
53. The method of claim 32, wherein the predetermined initial
thickness is between about 0.5 .mu.m and about 2 .mu.m.
54. The method of claim 32, wherein drawing the metal-coated metal
core causes the final diameter to be about 5-25% of the
predetermined initial diameter.
55. The method of claim 32, wherein the final diameter is in a
range from 0.10 mm to 0.50 mm.
56. The method of claim 32, wherein drawing the metal-coated metal
core causes the final thickness to be about 5-25% of the
predetermined initial thickness.
57. The method of claim 32, wherein the final thickness is in a
range from 80 nm to 350 nm.
58. The method of claim 32, wherein the predetermined initial
diameter is between about 0.85 mm and about 3 mm.
59. The method of claim 32, wherein the predetermined initial
thickness is between about 0.5 .mu.m and about 2 .mu.m.
60. A metal wire for reinforcing an elastomeric material produced
by the method of claim 32.
61. A method for producing a metal cord for reinforcing an
elastomeric material, the method comprising: producing a plurality
of wires by the method of claim 32; and stranding the plurality of
wires.
62. A metal cord for reinforcing an elastomeric material,
comprising: a plurality of wires produced by the method of claim 32
that are stranded together.
Description
FIELD OF THE INVENTION
[0001] The present invention refers to a method for producing a
metal wire intended to reinforce elastomeric materials, such as for
example semi-finished products intended for the manufacture of
tires, tubes, conveyor belts, transmission belts and cables.
[0002] In particular, the present invention refers to a metal wire
of the type comprising a metal core and a metal coating layer.
[0003] In the present description and in the following claims, the
term "metal" is used to indicate both a single metal and a metal
alloy.
[0004] The present invention also refers to a metal wire intended
to reinforce elastomeric materials, of the type comprising a metal
core and a metal coating layer, as well as to a metal cord
comprising a plurality of such metal wires and to a method for
producing the same.
PRIOR ART
[0005] Methods for producing metal wires comprising a metal core
and a metal coating layer and intended to reinforce elastomeric
materials, such as for example semi-finished products intended for
the manufacture of tires, are known. The latter are commonly
reinforced by embedding metal wires or metal cords (comprising a
plurality of metal wires stranded together) in an elastomeric
material to form, for example, the belt layers of a tire. The metal
core of such wires is provided with a metal coating layer to carry
out the dual function of providing a suitable corrosion resistance
to said wires and of ensuring a good adhesion thereof to the
vulcanized elastomeric material.
[0006] For example, methods for producing brassed steel wires
essentially involving the steps described hereafter are known:
[0007] an electrodeposition step in two distinct electrolytic
baths, in which a coppering and, respectively, a zinc plating of
the steel core are successively carried out;
[0008] a thermal treatment step of zinc diffusion into copper thus
deposited to form the brass alloy;
[0009] a pickling step in acid solution, typically phosphoric acid,
for removing the zinc oxides formed on the surface due to the
thermal diffusion treatment step; and
[0010] a drawing step aimed at obtaining a predetermined diameter
and a predetermined mechanical resistance of the brassed wire.
[0011] Conventional methods of such type, although substantially
suitable for the purpose, nevertheless have a series of drawbacks
which have not been overcome yet, such as the excessive number of
steps, the excessive duration of the above-mentioned diffusion step
and the reduction of mechanical resistance of the wire following
such a diffusion step. Furthermore, in the brass coating layer
there are undesired gradients of concentration of copper in the
radial direction and in the axial direction of the wire, as well as
a variability of the amount of brass both in the axial direction
and in the radial direction of the wire.
[0012] More specifically, the variations of the copper percentage
in the radial direction of the wire reach values equal to about
.+-.3% by weight, the radially outermost zone of the brass layer
generally being richer in zinc and the radially innermost zone of
the brass layer, i.e. the zone at the interface with the steel,
being richer in copper. The variations of the copper percentage in
the axial direction of the wire reach values equal to about .+-.2%
by weight. As to the variations of the brass amount, these reach
values of 0.5 of brass/kg of steel both in the axial direction and
in the radial direction of the wire, whereby the thickness of the
brass layer is not uniform.
[0013] In addition to the above-mentioned drawbacks, .beta. brass
with a body-centered cubic structure might form. The presence of
.beta. brass, particularly when in a concentration of more than 10%
by weight, makes the drawing step extremely difficult and results
in an excessive wear of the drawing dies, as well as the risk that
there are areas of wire not completely coated and/or containing
unacceptable amounts (in the order of about 50 mg/m.sup.2) of
impurities, such as oxides deriving not only from the acid used in
the above-mentioned picking step, but also from the oxides present
in the coppering bath and from those present in the lubricant used
in the drawing step.
[0014] Methods for coating metal wires are also known, such as for
example the method described in U.S. Pat. No. 4,517,066, which
provide, for the purpose of obtaining a suitable adhesion of the
coated wire to the elastomeric materials, to carry out a deposition
step by sputtering for applying an extremely thin metal film on the
core of the wire. However, the metal film is so thin (from some
.ANG. to 0.4 .mu.m) that there is the risk that more or less large
areas of the surface of the core are not perfectly coated or that
surface areas, although substantially coated, present surface
defects, thus not ensuring a suitable corrosion resistance of the
wire.
[0015] In the same way, in order to obtain a suitable adhesion of
the coated wire to elastomeric materials, in U.S. Pat. No.
5,403,419 a method for coating metal wires is described in which a
thin metal film is deposited by means of vacuum deposition, ion
plating, DC or RF magnetron sputtering, bipolar sputtering or RF
sputtering processes.
SUMMARY OF THE INVENTION
[0016] The Applicant has perceived the necessity of providing a
method for producing a metal wire intended to reinforce elastomeric
materials, of the type comprising a metal core and a metal coating
layer, which allows to obtain a wire having suitable mechanical
strength in view of the incorporation of the wire into elastomeric
materials to be reinforced and comprising a coating layer of high
quality, in particular with reference to the uniformity and
homogeneity thereof, and improved corrosion resistance, with a
positive effect upon the adhesion of the wire to elastomeric
materials.
[0017] In accordance with a first aspect thereof, the present
invention relates to a method for producing a metal wire for
reinforcing an elastomeric material, the metal wire comprising a
metal core and a metal coating layer, said core having a
predetermined initial diameter, said method comprising the steps
of:
[0018] a) submitting the metal core to at least one surface
treatment for predisposing the surface of the core to being coated
with said coating layer;
[0019] b) thermally treating said core;
[0020] c) depositing said metal coating layer to a predetermined
initial thickness on said thermally treated core by means of a
plasma deposition technique; and
[0021] d) drawing the coated core until the core has a final
diameter smaller than said predetermined initial diameter and the
metal coating layer has a final thickness smaller than said
predetermined initial thickness.
[0022] In the following description and in the subsequent claims,
the expressions "initial diameter of the core" and "initial
thickness of the coating layer" are used to indicate the diameter
of the core and, respectively, the thickness of the coating layer
before the drawing of the coated core.
[0023] In the following description and in the subsequent claims,
the expressions "final diameter of the core" and "final thickness
of the coating layer" are used to indicate the diameter of the core
and, respectively, the thickness of the coating layer after the
drawing of the coated core.
[0024] In the following description and in the subsequent claims,
the expression "plasma deposition technique" is used to indicate
any deposition technique which uses plasma as means for activating
the vaporization of the metal to be deposited (such as for example
in sputtering and in evaporation by voltaic arc), as carrier for
the metal to be deposited (such as for example in plasma spray) or
as means for dissociating the process gases (such as for example in
plasma enhanced chemical vapor deposition (PECVD)) in a vacuum
deposition chamber.
[0025] Firstly, thanks to the fact that the metal core is
superficially treated so as to predispose the surface of the core
to being coated, i.e. to obtain a core adapted to uniformly receive
the coating layer on the whole surface thereof, it is
advantageously possible to obtain a wire of improved quality. In
other words, any macrorugosity or unevenness of the core surface
deriving from the thermal treatment is advantageously substantially
eliminated, thus rendering the core surface suitable for the
deposition of the coating layer thereon. This advantageous effect
is particularly desirable if the core is made of a metal having a
very rough surface, such as for example steel.
[0026] Secondly, thanks to the fact that the metal core is
thermally treated, a structure suitable for a cold deformation,
such as the deformation involved in the drawing step, is
advantageously imparted to the metal core.
[0027] Furthermore, thanks to the fact that the metal coating layer
is deposited by means of a plasma deposition technique, it is
advantageously possible to obtain a wire coated in a uniform and
homogeneous manner.
[0028] In other words, it is advantageously possible to obtain a
wire coated in such a manner as to minimize both the variations of
the amount of metal deposited in the axial direction and in the
radial direction of the wire. Furthermore, in the case of
deposition of layers consisting of metal alloys, the formation of
concentration gradients of each component of said alloys in the
axial direction and in the radial direction of the wire is
advantageously reduced. Such characteristics of uniformity and
homogeneity of the coating layer are particularly important for the
purposes of obtaining the desired properties of corrosion
resistance.
[0029] A deposition based on a plasma technique advantageously
allows to form a finished coating layer in a faster manner with
respect to the formation of the finished coating layer in the
electrodeposition methods of the prior art since the method of the
present invention does not require a thermal diffusion treatment
step after the application of the metal coating layer--the thermal
diffusion treatment step being provided, in the methods of the
prior art, downstream of the electrodeposition--nor a subsequent
pickling step in phosphoric acid.
[0030] The elimination of the thermal diffusion treatment in turn
allows to eliminate the inevitable reduction of the mechanical
resistance--due to such thermal diffusion treatment--of the wires
produced with the methods of the prior art.
[0031] Furthermore, the plasma deposition technique allows to
obtain a coating layer having a crystalline structure conveniently
deformable in the subsequent drawing step. Thus, for example, if
the metal coating layer comprises brass, the plasma deposition
technique allows to obtain a layer of brass having a crystalline
structure consisting of .alpha. brass (face-centered cubic). The
deformability of .alpha. brass facilitates the subsequent drawing
step, while allowing at the same time a reduction of the wear of
the drawing dies with respect to the wear involved in the drawing
of wires coated with a layer of brass containing .beta. brass
(body-centered cubic).
[0032] Furthermore, the amount of impurities, such as for example
oxides, present in the coating layer is drastically reduced with
respect to the amount present in the wires produced by the
electrodeposition methods of the prior art.
[0033] Preferably, the above-mentioned surface treatment, thermal
treatment, deposition and drawing steps of the method according to
the invention are carried out in a substantially continuous
manner.
[0034] In the following description and in the subsequent claims,
the expression "in a substantially continuous manner" is used to
indicate the absence, between the various steps of the production
method, of intermediate storages of semi-finished products, so as
to continuously produce a coated wire having undefined length or,
following the stranding of a plurality of such coated wires, a
metal cord of undefined length in a single production line.
[0035] In accordance with a preferred embodiment of the method of
the invention, the core of the wire is conveyed through a sequence
of respective surface treatment, thermal treatment, deposition and
drawing positions at a speed comprised in the range from about 10
to about 80 m/min.
[0036] In such a way, it is advantageously possible to obtain a
metal wire coated with a metal coating layer having a desired
thickness by means of a single productive process carried out in a
substantially continuous manner from the step of producing the
metal core of the wire to the step of drawing the coated core,
optionally including additional conventional preliminary treatments
effected on the core or additional finishing treatments effected on
the coated core (e.g. a phosphating treatment of the core or of the
coated core in order to improve the drawing thereof).
[0037] It is also advantageously possible to carry out additional
manufacturing processes intended to produce a final product by
using the coated core as starting product. By way of illustrative
example, in order to produce a metal cord comprising a plurality of
coated metal wires, a stranding step of said plurality of coated
metal wires may be provided after the drawing step carried out on
the coated core.
[0038] The production method may optionally also include a series
of preliminary steps aimed at obtaining a metal core of a
predetermined diameter starting from a wire rod.
[0039] For example a mechanical removal of the oxides present on
the wire rod, known in the field with the term of descaling, may be
carried out. The descaling step is carried out to smooth the wire
rod, i.e. to substantially eliminate the roughness thereof. In such
way, any surface roughness, for example in the form of peaks and
valleys at the outer surface of the wire rod, which may have a
remarkable depth in the case of a rod made of steel, typically in
the range of from about 1.5 .mu.m to 2.0 .mu.m, is advantageously
eliminated, thus improving the adhesion of the coating to the core
in the successive depositing step and the effectiveness of the
deposition step. The descaling step is preferably followed by a dry
drawing of the wire rod, at the end of which a wire core having a
predetermined initial diameter is obtained.
[0040] Subsequently to these preliminary steps, according to the
method of the invention, the metal core undergoes a surface
treatment which aims to remove oxides possibly present on the metal
core surface. The surface treatment preferably comprises the steps
of pickling, washing and optionally drying the metal core. The
pickling step is carried out by introducing the metal core into a
pickling bath, such as for example a bath containing sulfuric acid.
Successively, the pickled core is washed by means of water and
optionally dried, preferably by means of hot air produced by a
blower (e.g. at a temperature comprised from about 70.degree. C. to
about 90.degree. C., more preferably at a temperature of about
80.degree. C.).
[0041] Alternatively to the pickling step, the core may undergo
alternative surface treatments, such as for example etching,
cleaning and activation by a plasma etching technique, for example
by conveying argon ions onto the core surface.
[0042] According to a preferred embodiment, the method of the
invention further comprises the step of dry drawing the core before
said thermal treatment, preferably in such a manner to obtain a
slight reduction of the core diameter, such as for example
comprised between about 1 and about 3%.
[0043] According to an alternative embodiment of the method of the
invention, the above-mentioned surface treatment, such as for
example the pickling or any other alternative treatment suitable
for the purpose, may be carried out on a wire rod, preferably
preliminarily descaled, and the surface treatment is followed by a
dry drawing aimed at obtaining a metal core having a predetermined
initial diameter.
[0044] Successively, according to the method of the invention, a
thermal treatment is carried out on the metal core. By way of
indication only, said thermal treatment of the metal core
preferably comprises the step of gradually heating the core to a
predetermined temperature, such as for example comprised between
about 900.degree. C. and about 1000.degree. C., and the subsequent
step of cooling the core to a predetermined temperature, such as
for example comprised between about 530.degree. C. and about
580.degree. C. Preferably, the cooling step is carried out by
introducing the metal core into a molten lead bath. Alternatively,
the cooling step is carried out by introducing the metal core into
a bath of molten salts (i.e. chlorates, bicarbonates), by passing
the metal core through zirconium oxide powders or by means of
air.
[0045] The method of the present invention preferably further
comprises a further thermal treatment, which is preferably carried
at the same working conditions mentioned above and which comprises
a further gradual heating step and a subsequent cooling step of the
metal core.
[0046] When a first and a second thermal treatment are provided, a
further dry drawing is preferably carried out after the first
thermal treatment. If additional thermal treatments are provided, a
dry drawing between each couple of thermal treatments is preferably
carried out.
[0047] When a single thermal treatment is provided, a further
slight dry drawing is preferably carried out by using a drawing die
which is preferably connected in an gas-tight manner with the
vacuum deposition chamber, at the inlet thereof. More preferably,
such slight drawing step may be carried out by means of a so-called
split drawing die, which essentially comprises a drawing die having
two symmetrical halves. Thanks to this feature, the drawing die may
be advantageously substituted in a simple manner, without
interrupting the production process.
[0048] Subsequently to said thermal treatment(s), the method of the
present invention further comprises the plasma deposition step
mentioned above, which is preferably carried out in at least one
vacuum deposition chamber at a first predetermined pressure.
[0049] In accordance with a preferred embodiment of the method of
the invention, the above-mentioned plasma deposition technique is
selected from the group comprising: sputtering, evaporation by
voltaic arc, plasma spray and plasma enhanced chemical vapor
deposition (PECVD).
[0050] Preferably, the deposition technique used by the method of
the invention is sputtering. In such a case, the control of the
composition of a coating layer consisting of an alloy is
advantageously improved and simplified since, in order to obtain an
alloy having a desired composition, it is sufficient to use a
cathode consisting of an alloy of such a composition.
[0051] In order to carry out a sputtering, it is possible to use at
least one conventional vacuum deposition chamber provided with a
vacuum pump suitable for creating a predetermined pressure and with
means for supplying a carrier gas. In the at least one vacuum
deposition chamber at least one cathode is provided consisting of
the metal to be deposited, for example in the form of a tube in
which the core of the wire to be coated, constituting the anode, is
made to pass through. Alternatively, the at least one cathode may
be provided in the form of a circular or rectangular plate in which
or, respectively, parallel to which, the anode is made to pass.
[0052] Sputtering essentially consists of a ionic bombardment of
the cathode, typically at an energy equal to about 200-500 eV, with
ions of the carrier gas obtained under the action of an electrical
field generated by applying a voltage between the cathode and the
anode. More specifically, ions of the carrier gas are accelerated
towards the cathode, essentially causing a series of collisions
with a consequent emission of cathode atoms directed towards the
anode, i.e. towards the core, towards which free electrons are also
accelerated. The free electrons ionize by collision further atoms
of carrier gas, whereby the process repeats itself and
self-sustains as long as sufficient energy is supplied.
[0053] Preferably, the deposition technique is magnetron sputtering
which, thanks to the effect exerted by the magnetic field on the
electrically charged particles, and in particular thanks to a
confinement action of the electrons in proximity of the cathode and
to an increase of the plasma density, allows to increase the
deposition rate.
[0054] Alternatively, a deposition by voltaic arc technique can be
used, the latter consisting of an ionic or electronic bombardment,
typically at an energy in the order of 100 eV, of the metal to be
deposited.
[0055] The plasma deposition technique may also consist of the
so-called plasma spray, essentially consisting of feeding a plasma
flow of fine powders of the metal to be deposited, preferably
having a size of about 0.1 .mu.m. The powders, accelerated and
heated by the plasma until the melting point of the metal is
reached, are directed onto the metal core to be coated, thus
creating a coating consisting of a plurality of overlaying layers
of metal particles.
[0056] The plasma deposition technique by means of which the
above-mentioned deposition step of the method of the invention is
carried out may also be plasma enhanced chemical vapor deposition
(PECVD). Such a technique essentially consists of the plasma
dissociation of precursor gases in a vacuum chamber (for example at
a pressure equal to about 0.1-10 Torr). Preferably, the precursor
gases comprise metallorganic compounds, such as for example
(hexafluoroacetylacetonate)copper(trimethylvinylsilane)
((hfac)Cu(VTMS)),
(hexafluoropentadionate)copper(vinyltrimethoxysilane)
((hfac)Cu(VTMOS)), diethylzinc and diphenylzinc, which
advantageously have low decomposition temperatures, in the order of
25-80.degree. C.
[0057] According to a further preferred embodiment, the method of
the invention comprises the steps of providing a first vacuum
deposition chamber and a second vacuum deposition chamber which are
arranged in series, each of said vacuum deposition chambers being
at a first predetermined pressure, and of depositing the metal
coating layer in at least one of said vacuum deposition chambers at
said first predetermined pressure by conveying the core to be
coated in succession through said vacuum deposition chambers.
[0058] The device intended to perform the plasma deposition
technique of the second vacuum deposition chamber may be put in
stand by mode. In such way, it is not necessary to interrupt the
production process to substitute the source of the metal to be
deposited onto the core, e.g. the metal cathode in a sputtering
process. Such substitution of the source of metal intended to form
the coating layer, which must be effected when the metal source is
totally consumed or a different metal has to be deposited, may be
advantageously made in the first of the two vacuum deposition
chambers while the second of the two vacuum deposition chambers is
switched to an operative mode, thus avoiding production stops and
resulting in an increase of the productivity of the method of the
invention.
[0059] Advantageously, in addition to the possibility of
substituting the metal source to be deposited on the core without
interrupting the production process as described above, such
preferred embodiment of the method of the invention allows to
obtain different wires in a substantially simultaneous manner by
switching to an operative mode both chambers and setting different
deposition conditions or by providing metal sources having
different compositions in the two vacuum deposition chambers both
set in an operative mode.
[0060] The core is preferably conveyed through said at least one
vacuum deposition chamber according to a path such as to be subject
to the above-mentioned deposition step a plurality of times. In
other words, the wire is passed back along a deposition zone of the
at least one vacuum deposition chamber for a predetermined number
of times.
[0061] In such a way, it is advantageously possible to deposit a
metal coating layer to a suitable initial thickness also on a core
maintained at a high conveying speed, in the order of 80 m/min. For
illustrating purposes, the core may be conveyed, for example by
means of suitable means for feeding back the core arranged in the
at least one vacuum deposition chamber, according to a forward and
backward path to be covered for a predetermined number of times
which increases the residence time of the core in such at least one
vacuum deposition chamber until a desired initial thickness of the
coating is achieved.
[0062] Furthermore, a preferred embodiment of the method of the
invention provides that the deposition step is carried out
simultaneously on a plurality of cores conveyed along a
predetermined conveying direction, so as to advantageously increase
the productivity of the method.
[0063] Preferably, the metal core is coated in at least one vacuum
deposition chamber subject to a first predetermined pressure, which
is preferably comprised between about 10.sup.-3 mbar and about
10.sup.-1 mbar when the plasma deposition technique is sputtering,
more preferably in the order of 10.sup.-2 mbar.
[0064] By way of illustrative example, the method of the invention
allows to deposit a coating layer, for example made of brass,
having a suitable thickness in the order of some microns,
preferably comprised from about 0.5 .mu.m to about 2 .mu.m, more
preferably of about 1.5 .mu.m, on a core for example made of steel,
at a pressure comprised in the above-mentioned preferred range of
values.
[0065] Preferably, the method of the invention further comprises
the step of conveying the core in at least one pre-chamber subject
to a second predetermined pressure higher than said first
predetermined pressure, said at least one pre-chamber being
arranged upstream of said at least one vacuum chamber.
[0066] In such way, the desired vacuum condition is advantageously
achieved in at least two subsequent steps, i.e. in a stepwise
manner, which is simpler and more convenient from an economical
point of view with respect to the achievement of a vacuum condition
in a single step.
[0067] Furthermore, the provision of at least one pre-chamber
advantageously allows to preserve the vacuum deposition chamber (in
which the depositing step is carried out) from the contamination of
dusts and external agents in general, such as oxygen, which are
detrimental to the effectiveness of the depositing step and to the
purity of the metal of the coating layer to be deposited. Such
advantageous effect can simply be achieved by introducing in the at
least one pre-chamber a flow of a chemically inert gas.
[0068] Preferably, for such a purpose the at least one pre-chamber
contains the same gas used as carrier gas in the at least one
vacuum deposition chamber, thus allowing to use a supply of gas of
the same type both for the at least one pre-chamber and for the at
least one vacuum deposition chamber.
[0069] More preferably, the above-mentioned chemically inert gas is
argon, which is convenient from an economical point of view,
resulting in a limitation of the production costs.
[0070] Preferably, a further pre-chamber subject to the
above-mentioned second predetermined pressure is provided
downstream of the at least one vacuum deposition chamber.
[0071] Preferably, said second predetermined pressure is comprised
between about 0.2 and about 10 mbar, more preferably in the order
of about 1 mbar.
[0072] According to a further preferred embodiment, the method of
the invention comprises the step of providing a first and a second
vacuum deposition chambers arranged in series as described above,
the first vacuum deposition chamber being arranged downstream of a
first pre-chamber as described above and the second vacuum
deposition chamber being arranged downstream of a second
pre-chamber separating the two vacuum deposition chambers, a third
pre-chamber being arranged downstream of the second vacuum
deposition chamber.
[0073] In such way, in addition to the above-mentioned advantageous
achievement of the desired vacuum condition in a stepwise manner,
it is advantageously possible both to substitute the metal source
in the first vacuum deposition chamber by switching the first
vacuum deposition chamber to a stand by mode and by switching the
second vacuum deposition chamber to an operative mode, and to set
different deposition conditions or provide different metal sources
in the two vacuum deposition chambers by putting both vacuum
deposition chambers into an operative mode.
[0074] Preferably, the core is made of a different metal with
respect to the metal of which the coating layer is made.
[0075] In such way, the metal of the core may be selected among the
metals more suitable for carrying out a mechanical supporting
function, while the metal of the coating layer may be selected
among the metals more suitable for obtaining a suitable adhesion
between the metal wire and an elastomeric material, and a suitable
corrosion resistance. Thanks to these features, it is
advantageously possible to produce metal wires or metal cords
(comprising a plurality of metal wires stranded together) intended
to reinforce an elastomeric material to form, for example, tires,
tubes, conveyor belts, transmission belts and cables having a good
quality.
[0076] Preferably, the metal core is made of steel, which is a
particularly suitable material for reinforcing elastomeric
materials such as for example semi-finished products intended for
the manufacture of belt layers of a tire.
[0077] The metal coating layer may comprise a metal or a binary or
ternary metal alloy.
[0078] Preferably, the coating metal is selected from the group
comprising: copper, zinc, manganese, cobalt, tin, molybdenum, iron
and their alloys.
[0079] Still more preferably, the coating metal is brass.
Advantageously, a wire comprising a core coated with a layer of
brass is provided with a high corrosion resistance.
[0080] In accordance with a preferred embodiment, the coating metal
is brass having a copper content of from about 60 to about 72% by
weight, more preferably of from about 64 to about 67% by
weight.
[0081] If copper is present in a percentage lower than 60% by
weight, in fact, there is the undesired formation of .beta. brass
while, if copper is present in a percentage greater than 72% by
weight, the wire is excessively reactive with the elastomeric
material which the wire is intended to reinforce. Such a reactivity
of the wire with the elastomeric material causes the formation on
the wire of a thick layer of sulfides which causes an undesired
worsening of the wire properties. As a consequence, in the
above-mentioned preferred range of values of copper composition,
the formation of .beta. brass is advantageously avoided, while
maintaining the reactiveness of the wire with elastomeric materials
at an acceptable level.
[0082] Preferably, the coating metal is an alloy selected from the
group consisting of: Zn--Co, Zn--Mn, Cu--Zn--Mn, Zn--Co--Mo,
Cu--Zn--Sn.
[0083] By coating the metal core with one of such alloys, the
corrosion resistance of the wire is further improved.
[0084] Preferably, the method of the invention comprises the step
of depositing a coating metal consisting of a ternary Cu--Zn--Mn
alloy having a composition 63% Cu, 34% Zn, 3% Mn.
[0085] The preferred composition of the Zn--Co alloy is 99% Zn, 1%
Co, the preferred composition of the Zn--Mn alloy is 98% Zn, 2% Mn,
the preferred composition of the Zn--Co--Mo alloy is 99% Zn, 0.5%
Co, 0.5% Mo, while the preferred composition of the Cu--Zn--Sn
alloy is 67% Cu, 30% Zn, 3% Sn.
[0086] Preferably, said coating metal further comprises a
predetermined amount of a lubricating agent intended to facilitate
the drawing of the metal wire.
[0087] In such way, the drawability of the wire is advantageously
improved.
[0088] Such embodiment is particularly preferred when the coating
layer comprises a material having poor drawability, such as for
example a Zn--Mn alloy.
[0089] More preferably, the lubricating agent is selected from the
group comprising: phosphorous containing compounds (e.g. organic
phosphates), sulfur containing compounds (e.g. thiols, thioesters,
thioethers), chlorine containing compounds (e.g. organic
chlorides). Preferably, said lubricants are the so-called "Extreme
Pressure Lubricants", i.e. lubricants which decompose at high
temperature and pressure (e.g. giving rise to the formation of
phosphides, sulphides and chlorides of iron, copper or zinc).
[0090] Still more preferably, the coating material comprises a
predetermined amount of phosphorous. Advantageously, the
drawability of a metal wire including a coating layer comprising a
predetermined amount of phosphorous is improved without affecting
the adhesion of the coating layer to the elastomeric material in
which the wire is intended to be embedded.
[0091] Preferably, the coating material comprises phosphorous in an
amount of about 1-3% by weight, more preferably in an amount of
about 2% by weight, with respect to the total weight of the coating
metal.
[0092] Advantageously, by including phosphorous in such preferred
amount in the metal to be deposited onto the metal core, e.g. by
providing a cathode containing phosphorous, the plasma deposition
step involved in the method of the invention allows to deposit a
metal coating layer comprising phosphorous exactly in the same
amount (i.e. 1-3%) in an uniform manner. Therefore, since
phosphorous is uniformly present in the whole thickness of the
coating layer, the subsequent drawing step is improved thanks to
the lubricating action of the phosphorous, independently of the
drawing degree which has been set.
[0093] Furthermore, thanks to the fact that the coating layer is
deposited by means of a plasma deposition technique, the percentage
variation of the amount of said lubricating agent in said coating
layer is lower than about 1% by weight, more preferably comprised
between about 0.01% and about 1% by weight, in the radial direction
of the wire with respect to the weight of the metal forming the
coating layer.
[0094] In an analogous manner, the percentage variation of the
amount of said lubricating agent in said coating layer is lower
than about 1% by weight, more preferably comprised between about
0.01% and about 1% by weight, in the axial direction of the wire
with respect to the weight of the metal forming the coating
layer.
[0095] Preferably, the initial thickness of the metal coating layer
is at least about 0.5 .mu.m.
[0096] Still more preferably, the initial thickness of the metal
coating layer is between about 0.5 and about 2 .mu.m.
[0097] In such a way, a suitable value of the initial thickness of
the metal coating layer in view of the drawing step of the coated
core is obtained, which allows to obtain the desired value of final
diameter of the core and an advantageous increase of the properties
of mechanical resistance of the wire. For illustrative purposes, a
wire having an initial breaking load--i.e. before the drawing step
of the coated core--equal to about 1200 MPa can reach--due to the
drawing step of the coated core--a final breaking load of about
3200 MPa.
[0098] Preferably, the drawing step is carried out in such a way as
to obtain a core having a final diameter which is reduced of about
75-95% with respect to the initial diameter of the core, more
preferably of about 80-90% and, still more preferably, of about 85%
with respect to the initial diameter.
[0099] In accordance with a preferred embodiment of the method of
the invention, the drawing step is carried out in such a way as to
obtain a coating layer having a final thickness which is reduced by
about 75-95% with respect to the initial thickness of the coating
layer, more preferably by about 78-88% and, still more preferably,
by about 83% of the initial thickness.
[0100] Preferably, the initial diameter of the core is comprised
between about 0.85 mm and about 3 mm and the drawing step is
carried out in such a way as to obtain a core having a final
diameter comprised in the range 0.10-0.50 mm.
[0101] Preferably, the initial thickness of the coating layer is
comprised between about 0.5 and about 2 .mu.m and the drawing step
is carried out in such a way as to obtain a metal coating layer
having a final thickness comprised in the range 80-350 nm.
[0102] In accordance with a second aspect thereof, the present
invention relates to a metal wire intended to reinforce elastomeric
materials, of the type comprising a metal core and a metal coating
layer, obtained by means of the above-mentioned production
method.
[0103] Advantageously, thanks to the features of the method of the
invention defined above, the wire of the invention comprises a
uniform and homogeneous metal coating layer and has an improved
mechanical resistance.
[0104] Furthermore, a wire comprising a layer of brass having a
crystalline structure consisting of a brass, which is easily
deformable in the subsequent drawing step, is advantageously
obtained.
[0105] Advantageously, a metal wire produced by the method of the
invention comprises a metal coating layer substantially free of
impurities.
[0106] Preferably, the coating metal is brass and the percentage
variation of the amount of copper in the coating layer is lower
than about 1% by weight in the radial direction of the wire.
[0107] Preferably, the metal core is made of a different metal with
respect to the metal of which the coating layer is made.
[0108] Preferably, the metal core is made of steel.
[0109] Preferably, the coating layer is made of brass having a
copper content of from about 60 to about 72% by weight, more
preferably of from about 64 to about 67% by weight.
[0110] Preferably, the percentage variation of the amount of copper
in the coating layer is lower than 0.5% by weight in the axial
direction of the core.
[0111] In accordance with a further preferred embodiment of the
invention, the variation by weight of the amount of brass in the
coating layer is lower than about 0.15 g of brass/kg of steel in
the axial direction of the wire.
[0112] Preferably, the variation by weight of the amount of brass
in the coating layer is lower than about 0.15 g of brass/kg of
steel in the radial direction of the wire.
[0113] Preferably, the coating metal of the wire of the invention
consists of a ternary Cu--Zn--Mn alloy having a composition 63% Cu,
34% Zn, 3% Mn.
[0114] The preferred composition of the Zn--Co alloy is 99% Zn, 1%
Co, the preferred composition of the Zn--Mn alloy is 98% Zn, 2% Mn,
the preferred composition of the Zn--Co--Mo alloy is 99% Zn, 0.5%
Co, 0.5% Mo, while the preferred composition of the Cu--Zn--Sn
alloy is 67% Cu, 30% Zn, 3% Sn.
[0115] Preferably, the wire of the invention comprises a core
having a diameter comprised in the range 0.10-0.50 mm. Preferably,
the wire of the invention comprises a metal coating layer having a
thickness comprised in the range 80-350 nm.
[0116] Finally, the present invention relates to a method for
producing a metal cord intended to reinforce elastomeric materials
as defined by attached claim 30 and to a metal cord as defined by
attached claim 31.
BRIEF DESCRIPTION OF THE DRAWINGS
[0117] Additional features and advantages of the invention will
become more readily apparent from the description of some preferred
embodiments of a method according to the invention for producing a
metal wire intended to reinforce elastomeric materials, of the type
comprising a metal core and a metal coating layer, made hereafter
with reference to the attached drawings in which, for illustrative
and not limiting purposes, two flow diagrams of said method are
represented.
[0118] In the drawings,
[0119] FIGS. 1 and 2 are two flow diagrams which illustrate
respective preferred embodiments of the method of the invention for
producing a metal wire intended to reinforce elastomeric materials,
of the type comprising a metal core and a metal coating layer.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0120] A preferred embodiment of the method of the invention for
producing a metal wire intended to reinforce elastomeric materials,
of the type comprising a metal core and a metal coating layer, is
illustrated in a flow diagram shown in FIG. 1.
[0121] With reference to such a figure, the method of the invention
comprises the descaling of a metal wire rod.
[0122] The descaling step is followed by a dry drawing of the wire
rod, at the end of which a wire core having a predetermined initial
diameter is obtained.
[0123] The metal core so obtained is submitted to at least one
surface treatment intended to predispose the core surface to being
coated by the coating layer.
[0124] Alternatively, as shown in FIG. 2, the surface treatment is
carried out on the metal wire rod descaled and the drawing aimed at
obtaining a wire core having a predetermined initial diameter is
carried out on the wire rod superficially treated.
[0125] The surface treatment step preferably comprises the step of
electrolytically pickling the core (FIG. 1)/the rod (FIG. 2) into a
bath containing for example sulfuric acid, and by subsequently
washing the pickled core in water. With reference to FIG. 1,
subsequently, in order to eliminate any residual water from the
washed core, the core is dried, for example by means of hot air at
about 80.degree. C. produced by a blower arranged downstream of the
washing step.
[0126] As shown in FIG. 1, the drying step is followed by a dry
drawing step and by a thermal treatment, for example by means of a
patenting thermal treatment carried out in a furnace.
[0127] All the steps of the method are preferably carried out in a
substantial continuous manner.
[0128] As shown in FIG. 2, the dry drawing and the thermal
treatment step may be carried out a plurality of times in case
substantial section reductions are desired or in case metals having
a high tensile breaking load are treated, such as for example in
the case of steels with a carbon content equal to about 0.8% by
weight.
[0129] In a step of the method of the invention subsequent to the
thermal treatment step, a metal coating layer is deposited to a
predetermined initial thickness on the metal core so treated by
means of a plasma deposition technique.
[0130] In accordance with a preferred embodiment of the method of
the invention, the plasma deposition technique may, for example, be
the sputtering technique.
[0131] Preferably, the metal core is coated in at least one vacuum
deposition chamber subject to a first predetermined pressure, which
is preferably comprised between about 10.sup.-3 mbar and about
10.sup.-1 mbar.
[0132] In order to avoid any interruption in the sputtering process
due to the consumption of the metal to be deposited or due to a
change of production, e.g. a change of the type of coating layer,
the deposition of the coating layer is carried out in a first
vacuum deposition chamber, a second vacuum deposition chamber being
arranged in series with the first one and being set in a stand by
mode. Both first and second vacuum deposition chambers contain a
carrier gas, such as for example argon, at a predetermined first
pressure, preferably comprised between about 10.sup.-3 mbar and
about 10.sup.-1 mbar.
[0133] In particular, before being conveyed in the first vacuum
deposition chamber, in order to preserve the first and, when used,
the second vacuum deposition chamber from dust and other
contaminants, a first pre-chamber and a second pre-chamber arranged
upstream of the first and, respectively, the second vacuum
deposition chamber, are provided.
[0134] A third pre-chamber is further provided downstream of the
second vacuum deposition chamber. In other words, the first
pre-chamber, the first vacuum deposition chamber, the second
pre-chamber, the second vacuum deposition chamber and the third
pre-chamber are successively arranged in series.
[0135] The first, the second and the third pre-chambers contain
argon subject to a second predetermined pressure higher than said
first predetermined pressure, for example in the order of 0.5
mbar.
[0136] In such way, the desired vacuum condition of 10.sup.-3
mbar-10.sup.-1 mbar is advantageously achieved in each vacuum
deposition chamber in a stepwise manner.
[0137] In the first and second vacuum deposition chamber two
respective cathodes are provided consisting of the metal to be
deposited, for example brass, preferably in tubular or plate-shaped
form. Furthermore, in each vacuum deposition chamber a respective
anode is provided, consisting of the core to be coated. In order to
carry out the above-mentioned deposition step, each anode is
introduced into the respective tubular cathode or, respectively, is
made to pass parallel to the respective plate-shaped cathode.
[0138] In the first and second vacuum deposition chamber a
plurality of means for feeding back the core is preferably provided
in order to increase the residency time of the core in each vacuum
deposition chamber, thus allowing the achievement of the desired
initial thickness of the coating also at high conveying speeds of
the core, preferably comprised between about 10 and about 80
m/min.
[0139] Preferably, the sputtering is carried out by setting a
pressure in the order of 10.sup.-3-510.sup.-2 mbar, a voltage
applied to the electrodes comprised between about 100 and about
1000 V and a current comprised between about 0.1 and about 10 A.
Due to the consequent discharge, ions of the carrier gas are
accelerated towards the cathode of the metal to be deposited and
atoms of such a metal are vaporized towards the core to be
coated.
[0140] By complying with the above-mentioned preferred voltage,
current and gas pressure values, a deposition rate of the brass
comprised in the range from about 100 to about 1000 nm/min,
depending on the distance between the cathode and the anode and on
the shape of the cathode, is advantageously achieved. A distance
between the cathode and the anode ranging from about a few cm to
some tens of cm as a function of the size and shape of the cathode
has been found particularly preferred in terms of effectiveness of
deposition.
[0141] In accordance with a subsequent step of the method of the
invention, the core thus coated is drawn until a core having a
final diameter lower than the predetermined initial diameter and a
metal coating layer having a final thickness lower than the
predetermined initial thickness are obtained.
[0142] Preferably, as illustrated by the corresponding block of the
diagram of FIG. 1, such a drawing step of the coated core is
carried out in an emulsion bath, for example containing a
lubricating oil conventional per se, and preferably by means of
drawing dies made of tungsten carbide, which are also conventional
per se.
[0143] The drawing of the coated core is facilitated by the
deformability characteristics of the brass, essentially comprising
.alpha. phase brass, obtained by means of the above-mentioned
plasma deposition technique.
[0144] At the end of such a drawing step of the method of the
invention, a metal wire uniformly and homogeneously coated with a
metal coating layer is obtained.
[0145] Finally, a further stranding step of a plurality of coated
wires obtained as described above allows to obtain a cord intended
to reinforce elastomeric materials, such as for example the belt
layers of a tire.
[0146] In accordance with an alternative embodiment of the method
of the invention, in order to carry out the deposition step of the
metal coating layer, two cathodes are provided in each vacuum
deposition chamber, which allows to double the deposition rates
with respect to the rates which can be achieved by the use of a
single cathode. In the case in which two plate-shaped cathodes are
provided, these are arranged parallel to each other and the wire to
be coated is conveyed in an intermediate position between the
cathodes at a predetermined distance therefrom, preferably
comprised between about 1 and 10 cm.
[0147] In accordance with a preferred embodiment of the metal wire
of the invention intended to reinforce elastomeric materials, of
the type comprising a metal core and a metal coating layer, the
coating layer may comprise a ternary metal alloy, such as for
example Cu--Zn--Mn, preferably having a composition 63% Cu, 34% Zn,
3% Mn.
[0148] In order to deposit a metal coating layer of such a type on
a metal core, for example made of steel, two alternative
embodiments of the method of the invention may, for example, be
provided.
[0149] In accordance with a first embodiment, the method provides a
deposition step of the coating layer on the core by means of the
sputtering technique in a way completely analogous to the way
described above with reference to the deposition of a brass layer,
the only difference being the composition of the cathode, which in
such a case consists of the above-mentioned ternary alloy of the
desired composition.
[0150] In accordance with a second embodiment, the method provides
two consecutive deposition steps by means of the sputtering
technique or by another plasma deposition technique. More
precisely, in a first step, a brass layer is deposited on the core
using a corresponding brass cathode whereas, in a second step, a
layer of manganese is deposited on the brassed core using a
corresponding manganese cathode.
[0151] As an alternative to manganese, other chemical elements,
analogously intended to increase the corrosion resistance of the
wire and the adhesion thereof to the elastomeric material, in
particular the adhesion after ageing, such as for example cobalt,
tin, molybdenum, iron, may be deposited.
[0152] Independently of the nature of the metal coating layer, when
the coating of the core is obtained by means of two consecutive
deposition steps, a first deposition step of a metal coating
consisting of a binary alloy and a second deposition step of a
single component coating, the initial thickness of the coating
layer made of binary alloy is preferably comprised between about
0.5 and about 2 .mu.m, whereas the initial thickness of the single
component coating layer is preferably comprised between about 0.01
and about 0.2 .mu.m.
[0153] Each of the above-mentioned steps of the method of the
invention may be carried out simultaneously on a plurality of
wires.
[0154] The invention is further described by way of the following
illustrative examples.
EXAMPLE 1
[0155] A steel wire rod, having a diameter of about 5.5 mm, was
subjected to a descaling step and to a dry drawing--at the end of
which the wire core having an initial diameter equal to about 1.4
mm was obtained--in a substantially continuous manner.
[0156] Subsequently, an electrolytically pickling of the core with
sulfuric acid was carried out. In particular, the core was pickled
by conveying the same in a sulfuric acid bath arranged downstream
of the descaling position in a substantially continuous manner. The
core was successively washed by conveying the core in water, said
washing step being provided downstream of the pickling bath.
[0157] Successively, a patenting thermal treatment of the core,
consisting of a heating step in a furnace at a temperature of about
950.degree. C. and of a subsequent cooling step in air at a
temperature of about 550.degree. C., was carried out in a
substantially continuous manner. The exit rate of the core from the
furnace was equal to about 36 m/min.
[0158] Subsequently, the steel core was fed, in a substantially
continuous manner, into a first pre-chamber containing argon at
about 0.5 mbar.
[0159] Subsequently, the core was conveyed, in a substantially
continuous manner, to a vacuum deposition chamber such as the
vacuum deposition chamber described above, in particular
containing, as carrier gas, argon at a pressure of about 10.sup.-3
mbar, and comprising a cathode of tubular shape having a diameter
equal to about 30 mm, consisting of brass having a copper content
of 64% by weight and 36% by weight of zinc. The steel core was fed
in a substantially continuous manner into such vacuum deposition
chamber at a speed of about 36 m/min. A brass coating layer having
an initial thickness equal to about 1.4 .mu.m was deposited on the
steel core in a substantially continuous manner.
[0160] For such a purpose, after a pressure of about 10.sup.-3 mbar
was set within the vacuum deposition chamber, the core (i.e. the
anode) was introduced into the tubular cathode of brass at a speed
of about 36 m/min and was slid more times by means of the feedback
means within the tubular cathode of brass until the above-mentioned
initial coating thickness was achieved. The distance between the
cathode and the anode was maintained equal to about 29 mm.
[0161] More specifically, a voltage equal to about 379 V and a
current equal to about 2.74 A were used. With such preferred
voltage and current values and with the above-mentioned preferred
value of gas pressure, a deposition rate of the brass equal to
about 800 nm/min was achieved.
[0162] Subsequently, the coated steel core was conveyed, in a
substantially continuous manner, in a second pre-chamber containing
argon at a pressure of about 0.5 mbar and arranged downstream of
the vacuum deposition chamber.
[0163] The steel core was then drawn in a substantially continuous
manner in a bath containing a lubricating oil (it is an emulsion in
water of 10% by weight of a lubricating agent mentioned above) by
means of drawing dies made of tungsten carbide, until a core having
a final diameter equal to about 0.25 mm and a metal coating layer
having a final thickness equal to about 0.2 .mu.m were
obtained.
[0164] The drawing of the core thus coated was facilitated thanks
to the deformability characteristics of the brass coating which, by
a X-ray diffraction analysis, appeared to consist only of a
phase.
[0165] At the end of the above-mentioned drawing step, a steel wire
uniformly and homogeneously coated with brass was obtained.
[0166] An atomic absorption spectroscopy (AAS) analysis carried out
on steel wires coated with a brass coating layer produced in
accordance with the embodiment of the method illustrated above has
shown that the copper content of the brass coating layer was
comprised in the range 63.5-64.5% by weight in the axial direction
of the wire.
[0167] A scanning electron microscope (SEM) analysis of the same
wires has shown that the copper content of the brass coating layer
was comprised between 63-65% by weight in the radial direction of
the wire.
[0168] Furthermore, an AAS analysis of the same wires has shown
that the variation by weight of the amount of brass in the coating
layer was equal to about .+-.+0.15 g of brass/kg of steel both in
the axial direction and in the radial direction of the wire.
[0169] Finally, the nature and the composition of the coating layer
being the same, mechanical tensile strength tests have shown an
increase of the mechanical resistance of the wires produced by the
method of the invention equal to 5-10% with respect to the
resistance shown by the wires produced by the methods of the prior
art comprising an electrodeposition step.
[0170] Furthermore, a further stranding step of a plurality of
steel wires coated with brass obtained as described above was
provided to obtain a cord reinforcing elastomeric materials, such
as for example the belt layers of a tire.
[0171] In a way known per se, cords produced in accordance with the
method of the invention were incorporated in articles of
elastomeric materials, such as semi-finished products intended for
the manufacture of tires, tubes, conveyor belts, transmission belts
and cables.
EXAMPLE 2
[0172] A steel wire rod, having a diameter of about 5.5 mm, was
subjected to a descaling step as in Example 1.
[0173] After the descaling step, an electrolytically pickling of
the wire rod with sulfuric acid and a subsequent washing in water
were carried out as described in Example 1.
[0174] The rod so pickled and washed was dried and submitted to a
dry drawing--at the end of which a wire core having an initial
diameter equal to about 1.4 mm was obtained--in a substantially
continuous manner.
[0175] Successively, a patenting thermal treatment, a deposition
and a wet drawing step were carried out as described in Example
1.
[0176] A further stranding step of a plurality of steel wires
coated with brass obtained as described above was provided to
obtain a cord reinforcing elastomeric materials, such as for
example the belt layers of a tire.
[0177] In a way known per se, cords produced in accordance with the
method of the invention were incorporated in articles of
elastomeric materials, such as semi-finished products intended for
the manufacture of tires, tubes, conveyor belts, transmission belts
and cables.
EXAMPLE 3
[0178] A core of steel wire having an initial diameter equal to
about 1.4 mm was obtained as described in Example 1.
[0179] Subsequently, the steel core was superficially treated and
patented as described in Example 1.
[0180] The exit rate of the core from the furnace was equal to
about 36 m/min.
[0181] The steel core was fed into a first pre-chamber and then
into a vacuum deposition chamber as described in Example 1, with
the exception that the vacuum deposition chamber comprised a
plurality of rectangular-shaped cathodes (45 cm.times.7 cm),
consisting of brass having a copper content of 63.5% by weight and
36.5% by weight of zinc. The steel core was fed in a substantially
continuous manner into such a vacuum deposition chamber at a speed
of about 36 m/min and a brass coating layer having an initial
thickness equal to about 1.5 .mu.m was then deposited on the steel
core in a substantially continuous manner by means of the magnetron
sputtering technique.
[0182] For such a purpose, after a pressure of about 310.sup.-3
mbar was set within the vacuum deposition chamber, the core (i.e.
the anode) was passed more times--by means of the feedback
means--parallel to the rectangular-shaped cathode at a speed of
about 36 m/min until the above-mentioned initial coating thickness
was achieved. The distance between the cathode and the anode was
maintained equal to about 29 mm.
[0183] More specifically, a voltage equal to about 369 V and a
current equal to about 2.64 A were used. With such preferred values
of voltage and current and with the above-mentioned preferred value
of gas pressure, a deposition rate of the brass equal to about 800
mm/min was achieved.
[0184] Subsequently, in accordance with a third step of the method
of the invention, the coated steel core was drawn in a
substantially continuous manner in a bath containing a lubricating
oil using drawing dies of tungsten carbide, until a final diameter
equal to about 0.25 mm and a metal coating layer having a final
thickness equal to about 0.2 .mu.m were obtained.
[0185] The drawing of the core thus coated was facilitated thanks
to the deformability characteristics of the brass coating which, by
an X-ray diffraction analysis, appeared to consist only of .alpha.
phase.
[0186] At the end of the above-mentioned drawing step, a steel wire
uniformly and homogeneously coated with brass was obtained.
EXAMPLE 4
[0187] Two cores of steel wire having an initial diameter equal to
about 1.4 mm were prepared as described with reference to Example
1.
[0188] Successively, the steel cores were superficially treated and
patented as described with reference to Example 1.
[0189] The exit rate of the core from the furnace was equal to
about 36 m/min.
[0190] The steel cores were fed in succession into a first
pre-chamber and into a first vacuum deposition chamber as described
in Example 1 with the exception that the first vacuum deposition
chamber comprised two cathodes of tubular shape comprising brass
having a copper content of 64% by weight and 35.5% by weight of
zinc and further comprising 0.5% by weight of phosphorous.
[0191] A second pre-chamber was arranged downstream of the first
vacuum deposition chamber and a second vacuum deposition chamber
was arranged downstream of the second pre-chamber. The magnetron of
the second vacuum deposition chamber was put in a stand by
mode.
[0192] Furthermore, a third pre-chamber was arranged downstream of
the second vacuum deposition chamber.
[0193] The first and the second vacuum deposition chambers were set
at a pressure of about 510.sup.-2 mbar. The first, second and third
pre-chambers contained argon at a pressure of about 0.5 mbar.
[0194] The steel cores were fed parallel in a substantially
continuous manner into the first pre-chamber and into the first
vacuum deposition chamber at a speed of about 36 m/min. In the
first vacuum deposition chamber a brass coating layer having an
initial thickness equal to about 1.5 .mu.m was deposited on each of
the steel cores in a substantially continuous manner by means of
the magnetron sputtering technique.
[0195] For such a purpose, after a pressure of about 510.sup.-2
mbar was set within the first vacuum deposition chamber, the cores
(i.e. the anodes) were respectively introduced in the tubular
cathodes of brass at a speed of about 36 m/min and were slid more
times by means of the feedback means within the respective tubular
cathode of brass until the above-mentioned initial coating
thickness was achieved. The distance between the cathode and the
anode was maintained equal to about 30 mm.
[0196] More specifically, a voltage equal to about 387 V and a
current equal to about 3.36 A were used. With such preferred
voltage and current values and with the above-mentioned preferred
value of gas pressure, a deposition rate of the brass equal to
about 800 nm/min was achieved.
[0197] The steel cores leaving the third pre-chamber were then
drawn in a substantially continuous manner in a bath containing a
lubricating oil using drawing dies made of tungsten carbide, until
cores having a final diameter equal to about 0.25 mm and metal
coating layers having a final thickness equal to about 0.2 .mu.m
were obtained.
[0198] At the end of the above-mentioned drawing step, two steel
wires uniformly and homogeneously coated with brass were
obtained.
[0199] The drawing of the cores thus coated was improved because,
in addition to the fact that the brass consisted only of a phase,
as detected by an X-ray diffraction analysis, the phosphorous
within the coating layer further facilitated the cold deformability
during drawing.
* * * * *