TECHNICAL FIELD OF INVENTION
[0001] The present invention refers to a method for obtaining a laminated and/or drawn metallic
product of wire or tape type, in coils or reels, which is plated by electroplating
with layers of nickel and chromium. The product obtained through the method hereof
is, moreover, characterized by a low release of nickel.
[0002] With particular reference to the paper-transformation industry, the invention finds
its application in the industrial production of objects having a high aesthetic quality,
obtained from the processing of wire or metallic tape.
STATE OF THE ART
[0003] The main industrial processes used to plate metallic materials, so as to provide
specific characteristics of hardness, resistance to wear and/or to corrosion, are
known as processes of galvanic type.
[0004] These processes rely on electrochemical principles to obtain an electroplating that
can vary according to the material to deposit and the type of object to be plated.
The most widely used galvanic processes are nickel-plating, zinc-coating and chromium-plating.
[0005] In particular, the nickel-plating process is used both as coating and as primer base
for subsequent treatments, as it is enduring, ductile, fast clinging and also of attractive
appearance, a characteristic that makes nickel-plating preferable over zinc-coating,
being the latter less appealing in appearance.
[0006] The chromium-plating process makes it possible to obtain an especially hard surface
layer of bright glossy white color, which is thus greatly appreciated in products
or accessories requiring such characteristics of aesthetic finish.
[0007] The prior art chromium-plating process is however at the same time more complex and
costly compared to nickel coating.
[0008] The prior art galvanic treatments require the use of a tank, usually containing an
aqueous solution of the metal salt to be deposited, in which are immersed two electrodes,
a cathode and an anode respectively, both connected to an electrical circuit.
[0009] The cathode consists of the object to be plated, while the anode can consist of the
metal that must be deposited, or it can be another inert metal or graphite.
[0010] If a difference of potential is applied to the two electrodes, by means of the electrical
circuit to which they are connected, the cations of the metal to be deposited move
toward the negatively charged cathode, while the anions move toward the positively
charged anode.
[0011] The known treatments differ principally on the basis of the type and form of the
pieces being processed, as they can be pieces that can be processed entirely in a
bath in which they remain for a certain time or pieces that are processed only partially
or at different times.
[0012] The conventional treatments, for pieces that are processed entire and simultaneously,
include processing the whole piece through a static permanence of the same pieces
in the different stations or tanks of the production process. In other words, there
is a subdivision of the process and of its progressive phases in different stations,
in which the product is held while it is being plated, until the desired result is
obtained.
[0013] The phases that follow the cleaning and preparation of the piece and that make it
possible to achieve the plating consist, therefore, of immersing the piece in the
respective bath, so that an electric current can be applied that is functional to
the type of plating metal, which progressively builds up on the piece being plated.
[0014] An example of such galvanic processes is disclosed in the US patent application
US2010/0167085 (BYD Co. Ltd.), which suggests a method of plating articles made of aluminum alloy
with a multilayer, being free of nickel and with the last layer, in contact with the
skin, being a chromium layer.
[0015] In the scope of methods carried out in the continuous mode, to obtain a galvanic
plating of wires or tapes with nickel, processes are known that employ a plurality
of tanks or passage stations and act on the portion of wire or tape that is dipped
or submerged in each of them.
[0016] The galvanic treatment of wires or tapes in the continuous cycle presents specific
problematic and critical aspects unlike those found in treatments involving single
pieces.
[0017] The single pieces, such as for example car or motorcycle items, in fact remain substantially
motionless inside the same tank until the completion of the galvanic process, while
in the case of wires or tapes the treatment is applied in a continuous mode, depending
on the tanks being crossed and on the time during which each portion remains immersed
in the respective tank while moving through it.
[0018] An example of a known method to obtain the continuous-cycle nickel-plating of a wire
or bar is disclosed in
GB 938192 (Manson and others), in which is described a galvanic multilayer plating for metallic
wire, bars or tape, achieved in continuous cycle, in which the product being processed
is given a helical shape and placed in rotation, so that it can pass through a bath
of a first plating metal, and subsequently undergoes cold processing and is finally
subjected to a further bath, in a second plating metal, to obtain a desired thickness.
[0019] According to said document, an improved surface that is resistant and free of pores
or flaws is achieved, in which the metals used in the two plating cycles can be the
same or different, for example nickel, tin, copper, aluminum, steel or alloys.
[0020] In the paper-transformation field and in related fields, such processes can be used
to obtain steel wires or strips, to which is applied a nickel-plating treatment to
improve the aesthetic quality.
[0021] The nickel-plating treatment itself has recently received particular attention from
doctors, manufacturers and lawmakers, due to the proven high allergenic and irritating
properties of nickel, which is thus classified as a harmful, polluting and also carcinogenic
substance.
[0022] In particular, it is well known that the absorption of nickel in allergy sufferers,
even through the skin, generates a pathological condition called "allergic contact
dermatitis".
[0023] Companies operating in the galvanic field, particularly companies manufacturing metallic
objects intended for continuous contact with the skin, like costume jewelry, or even
for occasional contact, such as for example in the paper transformation field, have
been engaged in finding innovative solutions and safer galvanic coatings with low
or no nickel release, while trying to maintain the know characteristics of resistance
and aesthetic appeal.
[0024] European Directive 94/27/CE has also introduced the ban on the sale of products designed
to come in direct and prolonged contact with the skin of the wearer if they release
a quantity of nickel (Ni) higher than a minimum established value, measured according
to a specific measuring protocol.
[0025] This characteristic is conventionally referred to as "nickel-free", even though it
does not necessarily imply the total absence of nickel in the component but only in
the external coating, as is specifically the case foreseen in the present invention.
Alternatively, it is possible to define such products as being "low nickel release
products".
[0026] The metallic articles used in the paper-transformation field, even if their contact
with the skin is brief and not continuing, may be prudentially likened to the products
of the related field of costume jewelry, for the purposes of verifying the release
of nickel according to norms.
[0027] A possible improvement may essentially result, at the technological level, from two
solutions: the elimination and the substitution of the nickel or, alternatively, from
a further protective coating applied on the nickel.
[0028] The first solution, that is, the elimination and replacement of the nickel with other
processes, used in the clothing field, for example in belt buckles, or also in costume
jewelry, involves resorting to treatments that deposit substitute materials having
an overall higher cost or being more intricate to make, which prevents their use in
the paper-transformation field, where moderate costs and high volumes of production
are required.
[0029] Therefore, if a further protective coating is to be implemented in the production
of wires or tapes in the paper-transformation field, the process of research and development
that led up to the present invention considered the application of a layer of chromium
plating on top of the one or more nickel-plating layers, and at the same time many
problems were observed, as exemplified below.
[0030] In the first place, chromium plating is a more complex galvanic process to manage
compared to nickel-plating, due to the process parameters and conditions required
to achieve a satisfactory result, which makes it very problematic in the case of continuous
processing of wires or tapes, so that it is not yet applied in known methods. In fact,
methods are known in which, after having performed nickel-plating in a continuous
process and at a substantially constant speed, chromium plating is performed in a
so-called "batch" or discontinuous process.
[0031] A problem found at the experimental level and not solved in the prior art is due
to the quality of the surface finish, which proved to be strongly influenced by the
vibrations, although very slight, suffered by one or more wires inside the relative
electrolytic chromium-plating tank, tested with a bath of hexavalent chromium.
[0032] In other words, the portion of wire or tape that is temporarily immersed in the electrolytic
chromium-plating tank, with a bath of hexavalent chromium, if subjected to vibrations
or false contacts, incurs process complications that lead to undesirable surface defects,
called "scorchings", as they appear more opaque than the typical finish of the chromium-plating
operation.
SUMMARY OF THE INVENTION
[0033] The main objective of the present invention is to overcome the shortcomings of the
prior art by providing a method for metallic wire or tape that makes it possible to
obtain in a continuous cycle a product coated with a nickel-plating layer and with
a chromium-plating layer, with a finish that at least minimizes the so-called "scorchings".
[0034] In the scope of the above objective, one purpose of the present invention is to devise
a method of galvanic treatment that is suitable for plating wires or metallic tapes
in a continuous mode while avoiding finishing flaws.
[0035] A further objective of the present invention consists of providing a method of galvanic
treatment, used in a continuous mode at a constant speed, that makes it possible to
obtain a wire or a tape coated with nickel and chromium, by treating in a continuous
mode a whole wire or tape wound in coils or reels.
[0036] A not secondary purpose is to realize a product for the paper transformation field
that makes it possible to obtain a wire or tape coated with nickel and chromium and
having a low nickel release.
[0037] The above objective and purposes, and others that will become more evident in the
ensuing description, are achieved by a method as defined in claim 1 or with a product
as defined in claim 9.
BRIEF DESCRIPTION OF THE FIGURES
[0038] Further characteristics and the advantages of the present invention will become more
evident from the following description of a particular, but not exclusive, embodiment
illustrated purely by way of a non-limiting example with reference to the enclosed
drawings, wherein:
- Figure 1 is a schematic view of a processing cycle according to the present invention;
- Figure 2 is a graph showing the trend in the voltage applied to the wire or tape being
processed in relation to the length of the chromium-plating tank, according to a first
configuration;
- Figure 3 is a graph showing the trend in the voltage applied to the wire or tape being
processed in relation to the length of the chromium-plating tank, according to a second
configuration;
- Figure 4 is a schematic view of an element realized according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0039] With reference to figure 1, hereunder is described a process according to a first
experimental configuration of the present invention. A decoiler 20 holds a coil 12,
from which is unwound a wire 10 that, in a continuous treatment line, runs through
the following stations at a substantially constant speed and in series:
- A) Electrolytic degreasing, at a temperature between 30 and 80°C and a permanence
time of 1 to 60 seconds;
- B) Washing, preferably in countercurrent;
- C) Electrolytic pickling, at a temperature between 20 and 60°C and a permanence time
of 1 to 60 seconds;
- D) Washing, preferably in countercurrent;
- E) Electrolytic nickel-plating, at a temperature between 30 and 70°C and a permanence
time between 10 and 500 seconds, so as to achieve a continuous deposition of nickel
(Ni) with a thickness between 1 and 5 micron;
- F) Washing, preferably in countercurrent;
- G)Chromium electroplating, with a permanence time of between 1 and 30 seconds, so
as to achieve a continuous deposition of chromium (Cr) of a thickness of 0,01 to 1
micron;
- H) Washing, preferably in countercurrent;
- I) Neutralization;
- J) Drying, at a temperature between 60 and 90°C and a permanence time of 3 to 30 seconds.
[0040] The wire 10, after having undergone the above treatments, is a treated wire 30 that
is wound in a second coil 32 housed in a coiler 40 that also turns at a substantially
constant speed.
[0041] The set of phases preceding the electrolytic nickel-plating E is referred to as the
preparation phase, for example comprising phases A, B, C and D.
[0042] The intervals relating to the permanence times are, as described, obtained by adjusting
the substantially constant wire feeding speed comprised between 10 and 100 meters
a minute.
[0043] Naturally, if a tape is being processed, the tape is unwound from a reel housed in
a relative decoiler, in order to be treated and turned into a treated tape that is
rewound in a second reel housed in a relative rewinder, in a continuous-cycle mode
and at a substantially constant speed.
[0044] The treated wire 30 or the treated tape is thus obtained from a drawn and/or rolled
metallic product in reels and coils, obtained from a base material of ferrous type,
that is nickel-plated and also coated in a continuous cycle, at a substantially constant
speed, with a superficial metallic layer without nickel so as to substantially limit
the release of nickel from the substrate.
[0045] In particular, according to such first configuration, the portion of wire or tape
that is temporarily immersed in the electrolytic plating tank, if subjected to vibration
or false contacts, as previously described, incurs process shortcomings that lead
to undesirable surface flaws, called "scorchings", as they appear more opaque than
the typical finish of the chromium-plating operation.
[0046] Subsequent to painstaking and costly experimental tests, the inventors were able
to understand the problems at the basis of the formation of "scorchings", identified,
as shown in figure 2, in the trend of the voltage, indicated with V, applied to the
wire or tape being processed in relation to the length of the chromium-plating tank.
Within the station G, the chromium-plating tank is schematically illustrated in figure
2, with a length included between a first length L1 and a second length L2.
[0047] The voltage was in fact seen as being substantially decreasing, starting from an
optimal value V1, representative of the difference of potential between the wire or
tape to be treated and the anode, at the entrance of the chromium-plating tank, decreasing
to a low value V2, representative of the difference of potential at the exit from
the same chromium-plating tank according to the first configuration.
[0048] The voltage difference given by the passage from the optimal value V1 to the low
value V2 proved to be excessive and harmful, so as to determine, in case of even slight
vibrations or false contacts, the undesirable "scorchings".
[0049] Advantageously, through a second preferable configuration of the invention shown
schematically in figure 3, a trend of the difference of potential that remains around
the optimal value V1 is maintained, therefore without descending to the low value
V2.
[0050] Thus were determined some points of actuation within the chromium-plating tank, respectively
at a third length L3 and at a fourth length L4 within the chromium-plating station
G, in which to operate with stabilizing means or restoring elements that are capable
of restoring, or at least approximate, the difference of potential at the optimal
value V1, to the length of the portion of the immersed wire that is close to reaching
a voltage threshold value V3.
[0051] Preferably, such restoring elements are placed in contact with the wire or tape in
motion, when the latter is outside the chromium-plating bath, thus avoiding depositing
chromium on the same restoring element.
[0052] Advantageously, two or more chromium-plating tanks are used, so that the total sum
of the lengths of the two or more chromium-plating tanks is equal to the length of
one chromium-plating tank according to the first configuration.
[0053] As can be seen in figure 3, according to the invention the schematic length from
the first length L1 to the second length L2 of the chromium-plating station G is preferably
subdivided into three operating lengths: of a first tank G1, a second tank G2 and
a third tank G3, respectively.
[0054] According to a manner of embodiment of the invention, visible in figure 4, at each
point of actuation singled out, for example at the third length L3 and at the fourth
length L4, is placed, in contact with one portion of processed product 110 on which
to operate, a sliding contact 120, to which is applied a predetermined voltage, so
as to restore the difference of potential toward the value V1.
[0055] The sliding contact 120, according to one embodiment of the same, includes a sliding
element 122 that comes into direct contact with a portion of the processed product
110. The sliding element 122 is coupled to the free end of a boom 124 that is connected,
at the opposite end, to an arm 126, itself connected to the frame of the machine or
to another suitable support.
[0056] Advantageously, the chromium-plating bath is provided with trivalent chromium, which
experimentally has made it possible to obtain better and less polluting results compared
to a bath of hexavalent chromium.
[0057] Preferably, the trivalent chromium bath is based on chlorides or sulfates.
[0058] Thanks to the presence of actuation points to restore the difference of potential
between the wire or tape being processed and the anode in the chromium-plating bath,
it is possible to limit, and even to eliminate, the results of undesirable "scorchings".
[0059] This innovative application has demonstrated experimentally the possibility of performing
a chromium-plating treatment in a continuous mode with wires or tapes, that can be
carried out at a substantially constant speed, avoiding undesirable effects that were
previously unresolved in the field of galvanic treatments for the production of metallic
elements, for example for applications in the paper-transformation field.
[0060] The valuable and innovative result achieved thanks to the present invention has therefore
allowed the mass-produced nickel-plating and chromium-plating treatment of wires or
tapes, in a continuous cycle and at a substantially constant speed. It is thus possible
to achieve the continuous processing, without interruptions, of a whole coil 12 of
wire 10 or respective reel of tape, guaranteeing an optimal surface finish and avoiding
"scorchings".
[0061] This solution is applicable, in particular, to the metallic wire or tapes that are
subsequently processed by plastic deformation in order to obtain the finished product
such as finds application, by way of example but without limits, in the paper-transformation
field for the ring and lever mechanisms used in loose-leaf binders.
[0062] In general, the prior-art continuous-cycle industrial processes of galvanic type
to obtain superficially plated metallic wires and tapes are conventional and known
for some time, being diversified on the basis of the specific industrial field, with
different materials and thicknesses; the paper-transformation industry, in particular,
generally uses conventional nickel-plated wires and tapes.
[0063] The invention therefore provides an innovative multilayer plating that consists of
a first coating of nickel-plating type, as a substrate, to which is added an extremely
thin second surface coating of the chromium-plating type; said surface coating has
both protective purposes, being in contact with the skin of the final user, and aesthetic
purposes, being superficial and visible. In particular, the proposed innovative treatment
is one with a low release of nickel responding to European Directive 94/27/CE and
can be implemented at the industrial level starting from a conventional continuous-treatment
line of the mono-wire or mono-tape type, or also of the multi-wire or multi-tape type;
the invention also makes it possible to subsequently implement, without defectiveness,
the ensuing processes that are typical of the conventional articles found in the paper-transformation
field, and still more.
[0064] Generally, in metallic articles designed for industry, the coatings are considered
to be of technical and functional type when the thickness exceeds an average value
of about 6 or 8 micron, as for example in conventional nickel-platings and in chrome
platings intended to increase the hardness and resistance to wear, while they are
considered as being of decorative type when the thickness is smaller than this value.
[0065] In the specific case considered in the invention, the limitation in the release of
nickel and the other purposes are achieved with a layer of nickel of 1 to 5 micron
in thickness, additionally coated with an extremely thin layer of chromium, with a
thickness of 0.01 to 1 micron.
[0066] This productive approach makes it possible to meet the requirements of technical,
functional and aesthetic quality expected, for example, in the industrial paper-transformation
field.
[0067] In fact, a proper ductility of the nickel-plating is maintained, allowing the conventional
folding and bending achieved afterward in the cold processing step on automatic machines,
thus avoiding surface defects.
[0068] The chromium layer, although it is extremely thin, achieves the purpose of substantially
limiting the transfer of nickel, increasing at the same time the resistance to corrosion
of the processed wire or tape.
[0069] Naturally, the present invention is amenable to many applications, modifications
or variants without thereby departing from the scope of patent protection as defined
by the independent claims 1 or 9.
[0070] Furthermore, the materials and equipment used to implement the present invention,
as well as the shapes and dimensions of the individual components, may be the most
suitable in accordance with the specific requirements.
1. Method for plating a metallic product (10) with a prevailing dimension, the type wire
or tape, comprising a treatment cycle of the electrolytic type in continuous cycle
so as to progressively obtain a metallic product (30) with a multilayer plating with
low release of nickel, said method comprising the following phases:
- Preparatory phase (A, B, C, D);
- Phase of electrolytic nickel-plating (E);
characterized in that it also comprises a stage of electrolytic chromium plating (G) that follows the phase
of electrolytic nickel-plating (E),
and
in that the metallic product (10) passes through all the stages in a continuous manner and
at substantially constant speed.
2. Method for plating in accordance with claim 1, wherein the crossing speed of the phases
is between 10 and 100 meters per minute.
3. Method for plating in accordance with one of the preceding claims, wherein the step
of electrolytic chromium plating (G) comprises passing the metallic product through
at least one bath of trivalent chromium.
4. Method for plating in accordance with claim 3, wherein said at least one bath of trivalent
chromium is based on chlorides or sulfates, or both.
5. Method for plating in accordance with one of the preceding claims, wherein the step
of electrolytic chromium plating (G) comprises at least two galvanic baths (G1, G2,
G3) which allow to separate the passage of the metallic product for a total length
(L1, L2, L3, L4) that is equal to a length (L1, L2) which allows the permanence of
each portion of metallic product (10) for a time comprised between 1 and 30 seconds
or which allows to obtain a chromium plating having a thickness comprised between
0,01 and 1 microns.
6. Method for plating in accordance with claim 5, in which is included an anode and wherein
the step of electrolytic chromium plating (G) comprises stabilizing means (120, 122,
124, 126) interposed between the at least two galvanic baths (G1, G2, G3), said stabilizing
means (120) being adapted to maintain the electric potential difference between the
metallic product and the anode between an optimum value (V1) and a threshold value
(V3) in the stage of electrolytic chromium plating (G).
7. Method for plating in accordance with claim 6, wherein the stabilizing means (120)
comprise a sliding element (122) adapted to go into direct contact with the metallic
product being processed.
8. Method for plating in accordance with one of the preceding claims, comprises the following
steps:
A) Electrolytic degreasing, with temperature between 30 and 80 °C and a permanence
time of between 1 and 60 seconds;
B) Countercurrent washing;
C) Electrolytic pickling, with temperatures between 20 and 60 °C and a permanence
time of between 1 and 60 seconds;
D) Countercurrent washing;
E) Electrolytic nickel-plating, with temperature between 30 and 70 °C and a permanence
time of between 10 and 500 seconds, so as to provide a continuous deposit of nickel
(Ni) with a thickness between 1 and 5 microns;
F) Countercurrent washing;
G) Chromium electroplating, with a permanence time of between 1 and 30 seconds, so
as to provide a continuous deposit of chromium (Cr) of a thickness comprised between
0.01 and 1 micron;
H) Countercurrent washing;
I) Neutralization;
J) Drying, at a temperature between 60 and 90 °C and a permanence time of between
3 and 30 seconds.
9. Metallic product (30) with a prevailing dimension, the type wire or tape, obtained
starting from a metallic product (10) by a method for plating according to one of
the preceding claims.
10. Metallic product (30) with a prevailing dimension, the type wire or tape for use in
the paper industry, obtained starting from a metallic product (10) by a method for
plating according to one of the claims from 1 to 8.