Patent Application
20220186396
The present invention relates to an apparatus for the oxidation of planar metal surfaces, that is an apparatus for applying the desired oxidation onto metal surfaces in order to obtain a desired uniform coloring or decoration in limited areas of the surface being treated, so as to obtain graphic shapes and drawings or even lettering on the surface concerned. The method for applying the treatment of the planar, sheet metal, cloth or wire mesh surface is also described.
The state of the art comprises generally continuous metal surface oxidation apparatuses wherein the apparatus applies the chemical action, possibly enhanced and accelerated by electrolytic action, of a product acting on the metal of the surface to force the formation of an oxide on the surface itself.
The metals involved in the aforementioned treatment are those that, in oxidation, generate a stable oxide at the end of the treatment and do not further damage the metal itself over time, hence iron and carbon steel, which are subject to the formation of the unstable oxide constituting the ferrous or ferric oxide, are conveniently excluded, although nothing prevents the treatment of these metals with oxidation, though they can still subsequently rust.
On the other hand, surface anodizing methods are known which apply electrochemical actions to act on the metal constituting the surface and create an oxide layer, albeit of minimal thickness which, although capable of being formed naturally, is obtained in a controlled and very rapid manner by treatment. The application of this treatment takes place mainly using electrodes covered with a layer of insulating fabric, or a buffer impregnated with an electrolytic solution which, if it manages to create an electrolytic cell located between the electrode and the surface being treated, generates noteworthy wear of the electrode as well as the soiling and wear of the insulating fabric, as described in the earlier document US 2015/014173 A1.
With the setting of the electrolytic etching by means of a soaked buffer, devices are known that carry out general oxidations on the complete surface being treated, or even merely on defined parts thereof, by masking the surface in various ways, that is with a printing screen, or application of layers that protect from the action of electrolytic etching, said layers being fixed on the surface being treated and removed at the end of said treatment, leaving a drawing, figures, lettering or even only graphic halos, which decorate the treated surface in the desired way. With buffer oxidation, in addition to the wear and soiling of the insulating fabric, the oxidation action occurs on the metal surface treated unevenly. If the lack of uniformity with the drawings, figures or lettering is not evident, with continuous surface oxidation over the entire metal surface being treated, with the use of the electrolytic buffer oxidation cell it is, conversely, irregular, that is its surface is colored by dark and/or light spots due to the effect of the irregular oxidation of the electrode with the buffer soaked and dragged by its sliding action or by that of the surface being treated with respect to it.
Known in the art from prior document JP 2003211324 A is a method of surface action engraving on a metal surface in which an electrode conformed to the shape to be engraved on the workpiece is facing, though not in contact with the surface being worked upon. The electrode has a layer of high electrical conductivity in the electrolytic action parts and an insulating mask applied to define the contours of the electrolytic action surface that is to be reproduced on the surface being treated. The electrolytic solution, here a sodium hydroxide solution obtained by dissolving sodium nitrate in water, is forcibly circulated in the space between the electrode and the surface being treated, without any part of the electrode being in contact, but placed at a short distance of less than 1 millimeter from the surface being treated. The treatment takes place in a closed cell into/from which the electrolyte enters and exits and where the advantage for the electrode is that there is little or no wear of the electrode that is covered by the high electrical conductivity layer; hence the limitation of the surface extension of the treatment is given by the limitation of the cell, meaning that this method is not suitable for carrying out oxidations on large surfaces.
In addition, a method for decorating metal surfaces is also known by arranging a thin spacer screen between an electrode and the metal surface to be decorated in which figures, shapes or lettering are provided and highlighted for electrode attachment mediated by the electrolyte solution. The electrode is equipped with a buffer soaked in an electrolytic solution and is moved in a variable motion over the surface to be treated. A similar embodiment is described in US 2014/03600881 A1.
However, the procedures described above are unusable for the decoration of large metal surfaces, where it is necessary to oxidize the metal surface in order to give a particular shade to the oxide produced on it, while also managing to limit or reduce to a minimum the wear of the electrode that activates the electrolytic action, since it is necessary to work on large surfaces at the same time and in a short time.
It is known in the art that the decoration of metal surfaces takes place as mentioned with the electrolytic action mediated by an insulating fabric impregnated with electrolytic solution, which makes the action on discontinuous surfaces very complicated. Indeed, although the electrode and buffer oxidation treatment of discontinuous surfaces, such as wire mesh or wire cloth, is known, the effect of uniformity of oxide coloration on the discontinuous surface is uneven, identical to what occurs for a metal foil or continuous plate surface already described.
Finally, the presence of surface discontinuities prevents the long life of the buffer in oxidation by the means known in the art that operates by friction, such as the use of the buffer in insulating fabric or electrode in contact with the insulating fabric, or even if carried out with a bath in an electrolytic tank. The treatment is carried out on the entire surface of the grid or metallic cloth, with a limitation on the operation times, the treated surface being much greater than that in the external view of the cloth or grid/metallic mesh which, conversely, is to be decorated and/or colored with a special uniform oxide on the visible parts from only one side of the grid/mesh or metallic cloth surface.
This state of the art is subject to considerable improvements with regard to the possibility of making an oxidation apparatus for metal surfaces, which overcomes the aforementioned drawbacks and limitations found in the prior art and which achieves a cheaper and faster way of generating the specific oxidation for the metal being treated, achieving a saving in the costs of application and implementation of what is currently known and allowing high rates of treatment even of discontinuous planar surfaces such as metal meshes or cloths.
The technical problem, therefore, underlying the present invention is that of making an apparatus that allows application of the electrolytic oxidation of large planar metal surfaces by carrying out the treatment quickly and limiting the wear or damage of the active surfaces of the electrode that applies the treatment to the metal surface, also limiting or reducing to zero the wear of the device interposed between the electrode and the surface being treated.
An aim inherent in the above technical problem is to produce an apparatus that applies the aforementioned electrolytic action which in turn allows the rapid treatment of large metal surfaces such as metal sheets, cloths or wire meshes in the application of the treatment.
A corollary to the technical problem described above is the possibility of making the apparatus for applying the electrolytic oxidation treatment with zero electrode wear and that is indifferent to the size of the treated surface.
Finally, a further part of the above-mentioned technical problem concerns the realization of rapid electrolytic oxidation treatment of the planar surfaces, in a single operation, both for the complete coloring of the material treated and for achieving a specific decoration.
This technical problem is solved, according to the present invention, by an apparatus for oxidizing planar metal surfaces, comprising a tank within which the planar metal surface being treated is laid; a circuit electric power supply; the two electric power supply heads of the circuit are in contact with electrodes, with high electrical conductivity; a first planar electrode is placed below the metal surface being treated on the bottom of the aforementioned tank; an electrolyte is placed in the tank to close the electrolytic oxidation circuit; a second electrode is placed sliding and spaced on the planar metal surface being treated in an immersed position at the level of the electrolyte in the tank; characterized in that it has the second electrode consisting of a conductive roller placed so as to roll on the planar metal surface being treated, avoiding contact between the cylindrical surface of the roller electrode towards the planar metal surface being treated by the interposition of a permeable spacer element; the spacer is made of a material resistant to the electrolytic action of oxidation and is placed on at least one of the two surfaces, either the cylindrical surface of the roller electrode or the planar metal surface being treated, neither of which must not come into contact.
In addition, a specific form of the spacer element is applied to the cylindrical surface of the roller of the roller electrode and consists of absorbent and insulating material to form a coating sheath covering the cylindrical surface.
A further improved form of the spacer element is created by a passage printing screen placed, before treatment, on the planar metal surface to be treated, in contact with it, and creating a distance with the thickness of the screen itself between the cylindrical surface of the roller electrode and the planar metal surface being treated.
In addition, a specific form of application on the planar metal surface under treatment are masks, resistant to electrolytic action, to make decorations, images or lettering on the planar metal surface with the oxidation treatment.
In one embodiment variant, the passage printing screen features electrolytically resistant masks for creating decorations, images or lettering on the planar metal surface with the oxidation treatment.
Furthermore, in a preferred embodiment, the passage printing screen with masking, in order to create decorations, images or lettering on its planar metal surface with oxidation treatment, is laid against the planar metal surface under treatment with the masking facing above and in contact with said planar metal surface, while the electrolytic oxidation action of the roller electrode with its cylindrical surface is applied on the upper side of the passage printing screen.
In a preferred embodiment, the first planar electrode is constituted by a graphite planar plate or graphite mesh placed on the bottom of the tank on which the planar metal surface being treated is laid.
Furthermore, in a preferred and advantageous embodiment, the roller electrode is made from a cylindrical graphite tube in which an axial metal pin is connected at the ends with the second head of the electrical circuit: the rotational support between the central pin and the graphite tube roller is achieved by a conical turning pair, made of metallic material, close to each end of the roller.
Finally, a method of applying the electrolytic oxidation action on planar metal surfaces, made by an apparatus defined according to the aforementioned embodiments, is as follows:
the planar metal surface to be treated is placed in a tank in an electrolyte bath with a level sufficient to cover the planar surface being treated and part of the aforementioned roller electrode;
the two power supply heads of the circuit are placed one end in contact with the first planar electrode and the second end with the second electrically conductive roller electrode;
the electrolytic surface oxidation action is applied with unidirectional or bidirectional back-and-forth rotation, rolling the roller electrode on the planar metal surface being treated with a permeable spacer element in between;
the electrolytic action is activated with either a direct or alternating electric current, generated by the electric power supply circuit;
the electrolytic action is obtained by rolling the roller electrode on the metal surface being treated, so as to achieve a rapid and uniform distribution of the desired oxidation on the metal surface being treated.
Further features and advantages of the present invention, in the realization of an oxidation apparatus of planar metal surfaces, will result from the description, given below, of examples of realization of the constructive form and some variants, as illustrated above, given by way of example only, with reference to the six attached drawings.
The Figures show the oxidation apparatus 1 of a metal surface 2 of a planar plate 3, visible in
In the constitution of the roller electrode 12, the roller 13 is rotatably supported on the frame 15 by means of a pin 21 to the ends 22 of which the connection and union cables are connected to the second electrical head 14 of the circuit. The pin 21 crosses the entire roller within a hole 23 with diameter DI and, near the ends 24 of the roller 13, has conical turning pairs 25, each formed by an outer ring 26, keyed to the end housing 24 of the roller 13, and an inner ring 27 keyed and tightened against the taper of the outer ring, on said pin 21, with the thrust of a ring nut 28. To close the end housing 24 of the roller, so as to prevent the electrolyte from re-entering, sealing rings 29 are keyed to said end housing of the roller and in contact with the pin 21 for sealing. Finally, the roller 13 has an outer diameter DE which in operation is maintained below the level 11 of the electrolyte.
In
Finally,
Utilization of a metal surface oxidation apparatus as described above is as follows.
The metal surface being treated is placed in an electrolyte containment tank so as to keep the entire metal surface 2 being treated wetted by the electrolyte: the level of the electrolyte 11 in the tank 5 must be higher than the lower cylindrical surface 17 of the roller electrode 12, so as to maintain at all times an electrolyte head on the metal surface 2 being treated. The planar metal surface 2 is in contact with the lower planar electrode 6 and, therefore, is connected with the first head 8 of the electrical circuit for activating the oxidation electrolytic action. The roller 13 of the roller electrode 12 is in electrical contact with the second head 14 of the electrical circuit for activating the aforementioned electrolytic oxidation action. The applied current can be either direct or alternating, depending on the type of metallic surface 2 being treated and the metallic material that, to achieve the required oxidation, requires one or other type of electric current. The interposition of a passage printing screen 30 or of the coating layer in insulating and permeable material 18 allows the surface to avoid direct contact and the formation of high intensity short circuits that would prevent activation of the electrolytic oxidation action.
The motion of the treatment takes place by rotating the roller electrode 12 on the surface either in an alternating motion or in a one-way motion normal to the axis of rotation of the roller 13. The electrical current applied can be in direct or alternating current with a voltage of between 5 and 25 Volts and a current intensity on the affected surface of the electrode and the underlying metal surface with density commensurate with the size of the surface being treated. In fact, the electrolytic action takes place from the contact line of the cylindrical surface 17 near the metal surface 2 being treated; with a coated roller 18 it can therefore operate from 1.0 to 10.0 A/cm2, whereas with only the rigid surface 17 of the roller 13 it operates at a current density ranging from at least 4.0 to 20.0 A/cm2. The adjustment of the type of current, and its value in voltage and current, is made based on the metal being treated and the desired coloring or density of the final oxidized surface. In addition, in the experiment, processing times of 1 m2 produced in 6 minutes were obtained, with a voltage of 12 Volts, an alternating current of 300 Amperes and using a roller with B=1550 mm on a plate with a width of 1500 mm. Using a roller of smaller size, for example B=450 mm, machining times of 1 m2, produced in 3 minutes of work were obtained, with a voltage of 12 Volts and an alternating current of 100 Amperes operating on a plate with a width of 400 mm.
The material constituting the roller electrode 12 is graphite, which in the most convenient dimension has the roller with an outer diameter DE of 64 mm and an inner diameter of 42 mm, while the electric current passes through the pin 21; only in the turning conical pair 25 does it pass from the pin to the roller which is substantially a graphite tube with the inner and outer diameters in the more advantageous size already mentioned.
In the use of the graphite roller 13 in the oxidation with a passage printing screen 30, 37, it has been verified that the electrolytic action occurs without appreciable wear on the graphite of the roller, that is on the cylindrical surface 17 of the roller, and also, at the same time, does not occur on the surface of the mask of the aforementioned screen. Furthermore, the lower application of the masking 38 on the passage printing screen 37 allows, with said masking, the mask itself to be more resistant, allowing multiple application cycles in succession, even if the same masking 38 is made with a digital printing ink, possibly UV printing.
The material constituting the pin and the turning pair, such as nickel, titanium and the like, is metallic and corrosion resistant. Furthermore, the turning pair can be made more advantageously of graphite. The planar electrode, whether in a single plate or in a mesh, can be made either of metallic material, advantageously nickel, titanium and similar corrosion-resistant materials, or of graphite in the form of a continuous plate or even of a perforated plate, similar to a mesh, to allow the electrolyte to pass through the holes inside it. The graphite design is preferred as it is cheaper and equally functional.
The advantages of using the oxidation apparatus of planar metal surfaces, according to the invention, can be summarized as follows.
In the parts of the apparatus involved, that is the roller electrode and, mainly, the metal parts in contact with the metal sheet, metal cloth or metal mesh, which are the most exposed to the action of oxidation, it has been found that the planar electrode, whether it is made of a metal that is obviously different from the metal of the surface being treated, or even of graphite, is not at all subject to wear by the electrolytic action developed. Conversely, the oxidation action was concentrated on the metal surface undergoing treatment so as to achieve high oxidation rates even for large surfaces to be treated. Another very advantageous result over the known art lies in the uniformity of the treatment on the metal surface, be it sheet metal, wire cloth or wire mesh. In fact, the metal surfaces on which the treatment takes place without masking the effect of the uniformity of the current density on the electrode and the constant distance, determined either by the thickness of the coating 18 or by the thickness of the passage printing screen, between the electrode and the metal surface allows, as mentioned, quick achievement of a desired and uniform coloration with the oxidation of the metal surface.
In addition, a very large advantage, verified in the tests carried out, is the lack of wear of the roller electrode, even if the latter applies currents with high density during the treatment and the working range near the generator of the cylindrical surface of the roller 13 is only a few millimeters, at most 3 if the roller has the active surface 17 directly on it, or 4 mm if the coating 18 of insulating and permeable material is applied to the active surface. In other words, after the tests carried out, none of the electrodes showed signs of wear even after long hours of operation. In addition, the advantage of placing the mask 38 on the passage printing screen 37 in the lower face of the screen itself, in contact with the surface being treated, has been verified: in this arrangement, even a simple digital ink printing, possibly carried out with UV printing, allows the mask to perform its function even for dozens of subsequent treatments. The advantage obtained results from the practicality of the masking (very weak but effective), as it is not applied directly to a plate or surface being worked upon, thus avoiding the known operations of removing the masking applied to the surface being worked upon.
Moreover, a very useful advantage is obtained in the construction of the tank 5 which contains the electrolyte in non-conductive material, hence no longer subject to electrolytic interactions with the electrolyte itself; in other words, the form of construction of the electrolytic cell does not interact with the planar electrode either in plate or mesh form.
Finally, the advantage of using a band-coated roller electrode in absorbent and heat-resistant material makes it possible to carry out the treatment even with mechanized handling or robotic means, that is already present in devices and therefore not requiring direct human intervention. The simplest form, and of manual application, has allowed the functional and production tests described above, both with the various current densities indicated and with the treatment of the most varied metal surfaces as described. The method of applying the oxidation described with the tank apparatus in forming an electrolytic cell makes it possible to automate fully the execution of the oxidation process.
Obviously, with regard to an oxidation apparatus of planar metal surfaces described above, in order to satisfy specific and contingent needs a person skilled in the art may make numerous modifications, all however contained within the scope of protection of the present invention, as defined in the following claims. Thus, although the masking described above is more advantageously achieved by digital ink or UV printing, it can, albeit less conveniently, also be achieved by any medium and material that endures to the electrolytic action of oxidation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020000030569 | Dec 2020 | IT | national |
