Metal Deposition Process Using Electroplasma
A process for treating a surface of an electrically conductive workpiece is provided, comprising placing a movable workpiece within a reaction chamber, wherein the reaction chamber includes an anode, and wherein the workpiece is a cathode; creating a gap between the anode and the cathode, wherein the anode includes a plurality of orifices; applying an aqueous electrolyte into the reaction chamber through the orifices in the anode and onto the workpiece, and applying the aqueous electrolyte from below the workpiece, to establish an electrically conductive medium around the workpiece, applying a DC voltage to the electrically conductive medium in excess of 30 VDC, such that a foam is formed within the reaction chamber, wherein the foam comprises a gas/vapor phase and a liquid phase which fills the entire reaction chamber; adjusting the voltage to establish an electro-plasma discharge between the anode and workpiece, sufficient to cause positive ions in the electrically conductive medium to become concentrated near the surface of the workpiece and cause micro-zonal melting of the surface in the area of discreet plasma bubbles; and moving the workpiece through the reaction chamber and away from the electrically conductive medium to allow re-freezing of the molten surface of the workpiece. The process applies to both cleaning and coating of the workpiece, wherein coating is achieved via sacrificial anodes.
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This application claims the benefit under 35 U.S.C. §119(e) to provisional application Ser. No. 61/787,269, filed Mar. 15, 2013.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENTNot applicable.
THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENTNot applicable.
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON COMPACT DISCNot applicable.
BACKGROUND OF THE INVENTION1. Field of the Invention
The present invention relates to metal deposition processes which can serve as replacements for hot dip galvanizing, tin plating, and electroplating, and more particularly to such processes which use electroplasma.
2. Description of Related Art
Galvanizing steel articles is typically done by dipping the article into a bath of molten zinc (or other molten metals) and is generally known in the art. For Zinc, the bath conventionally contains as much as 1.5 wt % lead to lessen the surface tension of zinc and to lessen the formation of floating dross.
Conventional hot dip coating methods operate through a bath of molten metal, in which the zinc or tin is maintained within the bath at a temperature which causes the metal to be molten. The temperature required to maintain the molten state for zinc is, +/−4200 C and for tin is, +/−2320 C and it is this temperature and time condition which causes the loss (to substrate) of tensile strength, loss of mechanical properties and the formation of the intermetallic zone between the substrate and coating. With the aqueous plasma process, due to substantially lower temperatures there is no loss of tensile strength, no loss of any mechanical properties and no intermetallic is formed between the substrate and coating, which is a major and substantial difference between hot dip coatings.
Conventional electroplating processes operate in a low-voltage regime in which the electrical current increases monotonically with the applied voltage. In this conventional process the generation or liberation of gas bubbles at the cathode do not in any circumstance experience arc discharge plasma. Typically, the deposition rate of electroplated coatings is relatively slow and slows greatly as thickness increases due to the creation of the phase diffusion boundary layer. It is this phase diffusion boundary which quickly moves electroplating to a normally un-economic condition as more current is required to move metal ions through the boundary layer as it increases in thickness. This layer also causes the loss of ductility and thereby causes thicker electroplated coatings to crack and become brittle, similar to and consistent with the intermetallic zone created in hot dip coatings.
UK-a-1399710, U.S. Pat. No. 5,958,604, U.S. Pat. No. 5,981,084, U.S. Pat. No. 5,700,366 & U.S. Pat. No. 6,585,875B1. Electrical plasma processing [high voltage] operates in an electrical regime in which the current decreases or remains essentially the same as voltage is increased and are characterized by the formation of plasma at the onset of the unstable region and further characterized; “it should be clearly understood that the required bubble regime cannot be obtained with any arbitrary combination of variables, such as, gap, flow rate, electrolyte concentration, temperature and so forth”.
UK-A-1399710 teaches that the gas film must be continuous and the electrical regime which describes the current as decreasing or remaining constant as voltage is increased described the “unstable regime” characterized as the descending half of the first current curve.
WO-A-97/35051 describes an electrolytic process for cleaning and coating electrically conducting surfaces in which the anode comprises a metal for metal coating of the surface of the workpiece. In WO-A-97/35051 and 35052 an arc discharge or electro-plasma is formed on the surface of the workpiece and is established within the bubble layer. If the anode is constructed from a non-inert material, such as a non-refractory metal, then metal atoms are transferred from the anode to the cathode. Coatings achieved by this regime [WO-A-99/15714] are a special form of electroplating because they occur at high voltage in the presence of an arc discharge and the plating is faster than normal electroplating.
U.S. Pat. No. 4,360,410 Fletcher, et al, describes the use of foam for an improved electroplating process. This is a typical electroplating process where low voltage is utilized for ion transfer, without are discharge or plasma generation. Fletcher et al operates in a different electrical regime with is typical conventional electrolytic processing. The importance of Fletcher et al is the verification that foam improves the uniformity.
WO-A-98-32892 describes a process which operates essentially in the manner described in WO-A-99/15714 but uses a conductive gas/vapor mixture as the conductive medium. This gas/vapor mixture is generated within a multi-chambered area by passing electrolyte through holes in the anode. The gas/vapor mixture is generated by heating an aqueous electrolyte within the chamber to the boiling point and the anode chamber may be heated either by primary electrical current or by independent electrical heaters.
WO-01/09410 A1-U.S. Pat. No. 6,585,875 describes a process similar to WO-A-98/32892 & WO-A-99/15714 and claims an improved process in which an electro plasma (arc-discharge) is utilized to clean and/or apply a metal coating to an electrically conductive substrate.
U.S. Pat. No. 6,585,875 teaches an improved process in which arc-discharge electro-plasma is employed to clean and/or apply a metal coating to an electrically conductive surface, in which the electrically conductive pathway is provided by a foaming electrolyte which fills the space between the anode and cathode and provides advantages with respect to lower power consumption, more uniform surface treatment and greater latitude in the size of the gap between the anode and cathode, thereby allowing for more diverse workpieces. Importantly, while the present invention employs the electro-plasma process generally described in U.S. Pat. No. 6,585,875, the present invention provides for substantial advances in the coating application processes which can replace the conventional hot dip and electroplating processes due to changes to the workpiece metal itself, e.g. phase, crystal orientation, grain size, corrosion properties, and the like.
SUMMARY OF THE INVENTIONA process for treating a surface of an electrically conductive workpiece is provided, comprising placing a movable workpiece within a reaction chamber, wherein the reaction chamber includes an anode, and wherein the workpiece is a cathode; creating a gap between the anode and the cathode, wherein the anode includes a plurality of orifices; applying an aqueous electrolyte into the reaction chamber through the orifices in the anode and onto the workpiece, and applying the aqueous electrolyte from below the workpiece, to establish an electrically conductive medium around the workpiece, applying a DC voltage to the electrically conductive medium in excess of 30 VDC, such that a foam is formed within the reaction chamber, wherein the foam comprises a gas/vapor phase and a liquid phase which fills the entire reaction chamber; adjusting the voltage to establish an electro-plasma discharge between the anode and workpiece, sufficient to cause positive ions in the electrically conductive medium to become concentrated near the surface of the workpiece and cause micro-zonal melting of the surface in the area of discreet plasma bubbles; and moving the workpiece through the reaction chamber and away from the electrically conductive medium to allow re-freezing of the molten surface of the workpiece.
The workpiece is exposed to the electro-plasma for a duration sufficient to clean the workpiece from oxide scales, lubricants, coatings, dirt and organic substances.
The workpiece is exposed to the electro-plasma for a duration sufficient to modify a surface profile of the workpiece to form a morphology which reduces wetting, serves as a carrier for drawing lubricants, and is passivated against corrosion.
The positive ions include one or more metals to form one or more coatings of the metals on the workpiece.
The coating includes a conductive metal coating comprised of independent layers of different metals on the workpiece.
The coating includes two or more conductive metals forming an alloy on the workpiece.
The positive ions are derived from one or more sacrificial anodes.
The aqueous electrolyte is heated to a select temperature to increase the effectiveness of the process.
The heated aqueous electrolyte is introduced into the reaction chamber and becomes a foam as electrical current is applied between the anode and the workpiece, sufficient to cause ebullition at the surface of the workpiece.
The effectiveness of the electrically conductive medium is increased by the addition of foaming agents and surfactants.
The cleaned surface of the workpiece exhibits a surface morphology comprising craters and spheroids sufficient to carry lubricant for drawing of the workpiece.
An iron oxide (FeO) layer on the surface is reconstituted into alpha (amorphous) iron, and wherein surface grain size is substantially reduced to nano-sized grains that are tightly packed against one another sufficient to reduce corrosive penetration.
Deposition of the metals is achieved without an initiation or growth of an intermetallic layer between the workpiece and the coating metals.
Deposition of the metals is achieved without creation of a phase diffusion boundary layer on the coating metal.
Deposition of the metals is achieved without causing hydrogen embrittlement to the coating metals.
The workpiece defines a core, and wherein the temperature of the core of the workpiece is maintained at or below a predetermined temperature sufficient to control the dissociation of oxygen and hydrogen, and to suppress the formation of oxygen bubbles at the surface of the workpiece.
The predetermined temperature is about 950 C.
Downward pressure is maintained within the electro-plasma against the workpiece sufficient to cause deposition of the coating metals to form in a plane parallel to the surface of the workpiece.
The workpiece is subjected to the electro-plasma across a plurality of isolated reaction chambers.
The reaction chamber includes exhaust ports above the workpiece adapted to permit expanding gas to vent from the reaction chamber.
For a further understanding of the nature, objects, and advantages of the present invention, reference should be had to the following detailed description, read in conjunction with the following drawings, wherein like reference numerals denote like elements.
Before the subject invention is further described, it is to be understood that the invention is not limited to the particular embodiments of the invention described below, as variations of the particular embodiments may be made and still fall within the scope of the appended claims. It is also to be understood that the terminology employed is for the purpose of describing particular embodiments, and is not intended to be limiting. Instead, the scope of the present invention will be established by the appended claims.
In this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs.
The present invention uses an anode and cathode in which the cathode is the workpiece and with the introduction of an electrically conductive medium [electrolyte] which contains ions of the metal to be deposited, deposits the metal in rapid succession onto the workpiece.
The electrical contact between the anode and cathode is maintained by the electrically conductive electrolyte which forms a foam inside the reaction chamber when a DC voltage is applied. Arc discharge plasma is formed at the workpiece and this plasma formation causes the workpiece to become enshrouded by a continuous gaseous vapor plasma envelope of low electrical conductivity. The electric field strength within this gaseous envelop [near cathode region] reaches a value between 106 and 108 V/m, which causes ionization of the gas within the foaming bubbles over the vapor envelop which shrouds the workpiece.
The ionization phenomena appear initially as a rapid sparking in scattered gaseous bubbles and then quickly transforms into a uniform glow distributed throughout the vapor plasma envelope. Due to the hydrodynamic stabilization of the vapor envelope, the current drops. The plasma formation is characterized as “arc-discharge plasma”. The entrance of electrolyte into the reaction chamber causes turbulence within the chamber which enhances the vapor/gas envelop enshrouding the workpiece. This action causes the chamber to contain less liquid and more vapor/gas, which causes the density of the foam to impact and encase the workpiece which in turn accelerates ion transfer within the gas envelope shrouding the workpiece.
Any metal which is conductive and is soluble in water can be coated with aqueous electro-plasma with deposition rates exceeding 1 μm per second. The coatings applied are characterized by the lack of the formation of an intermetallic zone between the substrate metal and the applied metal. In addition, the applied metal coating exhibits smaller grain size and at the near surface the grain size is tightly packed, nano-sized grains, which enhance corrosion inhibiting properties. Without the intermetallic zone the adhesion of the coating is increased, ductility is increased and unlike hot dip galvanize and tin, the coatings can be drawn to as much as a 97% reduction without the spalling or shredding (loss) of the coating. The new aqueous plasma process does not conform to Faraday's Law.
Conventional hot dip coating methods operate through a bath of molten metal, in which the zinc or tin is maintained within the bath at a temperature which causes the metal to be molten. The temperature required to maintain the molten state for zinc is, +/−4200 C and for tin is, +/−2320 C and it is this temperature and time condition which causes the loss (to substrate) of tensile strength, loss of mechanical properties and the formation of the intermetallic zone between the substrate and coating.
The aqueous plasma process, due to utilizing substantially lower temperatures there is no loss of tensile strength, no loss of any mechanical properties and no intermetallic is formed between the substrate and coating. These changes provide a major and substantive change to the process of hot dip coating by essentially changing the metallurgy of the applied metal (coating).
This improvement substantially changes the functional ability of the process itself by administering a change in the temperature of the workpiece which in turn changes the evolution of hydrogen at the workpiece surface which increases the plasma action and reaction. In the prior art the temperature of the electrolyte is controlled within a range of temperatures [550 C to 900 C] without regard or control of the workpiece temperature. Plasma [ionized gas bubble formation/micro-arc discharges] are controlled by voltage, current, flow rate of the electrolyte and the conductivity of the electrolyte. Previous studies found that in aqueous electrolyte with various applied voltages and various electrolyte compositions found that the main products, H2 and O2 are from the dissociation of the water molecules which result in plasma around the cathode when the glow discharge is maintained constant. The formation of H2 and O2 function in different regimes. The H2 bubbles, within the gaseous envelope around the workpiece move toward the anode but are blocked by the positive ions moving toward the cathode. As the resistance builds the gas within the bubble is ionized, causing the glow discharge to take place. The embodiment of the improvement is the temperature of the workpiece. In the conventional hot dip processes, no regard or control of the temperature of the workpiece is contemplated, the only necessity is to keep the bath of metal molten. In the electro-plasma process it is well to note that all references to workpiece heating regard the micro-surface region of the workpiece, with reference to cooling by the electrolyte, which cannot exceed 900 C, otherwise the process itself (plasma) will not work.
In the improved process the temperature of the workpiece is critical to newly achieved results which results are caused by the elimination of O2 formation from boiling of the electrolyte caused by excessive heating of the workpiece. This heating/boiling reaction, which causes the excessive production of O2, blocks the evolution of H2 and thereby substantially reduces the amount of plasma existing at any one time on the surface of the workpiece. By cooling the workpiece the evolution of H2 is unrestricted and substantially changes the process results by allowing more plasma to form at any one time. The electrolyte itself serves as the cooling agent keeping the workpiece well below the temperature required for phase transformation (eutectoid point) which occurs with hot dip processes.
In the existing process, the electrolyte is used to cool and quickly freeze the micro-surface with no regard to the core temperature of the workpiece. In electro-plasma processing, should the temperature of the workpiece increase past the boiling point of the electrolyte, the liberation of oxygen from boiling overcomes hydrogen evolution and results in the ability to form plasma, and the plasma is extinguished thereby decreasing the ability to feasibly clean, modify and/or apply a coating to the workpiece.
Conventional electroplating processes operate in a low-voltage regime in which the electrical current increases monotonically with the applied voltage. In this conventional process the generation or liberation of gas bubbles at the cathode do not in any circumstance experience arc discharge plasma. Typically, the deposition rate of electroplated coatings is relatively slow and slows greatly as thickness increases due to the creation of the phase diffusion boundary layer. It is this phase diffusion boundary which quickly moves electroplating to a normally un-economic condition as more current is required to move metal ions through the boundary layer as it increases in thickness. This layer also causes the loss of ductility and thereby causes thicker electroplated coatings to crack and become brittle, similar to and consistent with the intermetallic zone created in hot dip coatings. Electroplating follows precisely Faraday's Law.
The aqueous plasma process, uses high voltage, does not experience the phase diffusion boundary layer and does not follow Faraday's Law. With aqueous plasma the intermetallic zone created with electroplating or hot dip coatings does not exist and thickness of the coating layer does not influence ductility, and aqueous plasma coatings are always very ductile. The aqueous plasma process causes surface melting in a micro-zone (100-150 nanometers), the melting occurs only under discrete bubbles with a diameter of approximately 0.5/1.0 mm in diameter. These bubbles cover approximately 35% to 40% of the surface at any one time and the life of the bubble is 10-35/second and re-freezing of the molten metal occurs instantaneously, without influencing the core temperature of the workpiece. The core temperature is controlled by the electrolyte and cannot exceed 1000 C, otherwise the process ceases to exist. The aqueous plasma process is atmospheric which differs completely from vacuum gas plasma processing.
A further embodiment of the electro-plasma process is the reclaiming of waste materials. For example; as copper is cleaned by the electro-plasma process the concentration of metal ions in the electrolyte solution increases until it reaches a level in which the waste electrolyte can then be used as the coating electrolyte. The copper enhanced solution can be mixed with zinc enhanced solution to form brass.
Rinse water need not be discarded and can be used as make up water for the electrolyte solution modestly loss to vaporization. In addition and unlike conventional hot dip or electroplating processes the electro-plasma process is mobile and easily allows for portable or field units for large or small areas to be processed.
A further embodiment of the electro-plasma process is the ability that is created due to the surface morphology of a treated surface to act as a lubricant carrier during the drawing process for wire. This ability to draw a cleaned material without the addition of a lubricant carrier, such as zinc phosphate, is not possible with conventional cleaning processes.
Example 1A continuous high-carbon steel wire, 1.72 mm in diameter, with a tenacious “patenting” oxide scale covering the base metal surface as a tight, bright black oxide material [scale] which in turn is covered by a loose layer of carbon, created in the patenting furnace as the drawing lubricants and carrier chemicals are burned as the wire passes through the furnace for annealing was moved through the reactor [FIG. X] and a DC voltage applied. As electrolyte entered the reactor through conductive tubes, at 90 VDC, plasma formed on the surface of the cathode and with a dwell time of approximately 1 second in the reactor, the carbon layer and the oxide scale were removed, exposing the base cleaned metal.
Electrolyte Temperature 780 C
Electrolyte Concentration 10% NaHCO3 pH: 8.5
Electrolyte Flow Rate 1.25 L/min nominal flow rate
Travel Speed 9.15 m/min
Reactor Length 66 cm
Plasma Zone [active length] 52 cm
Voltage DC Range 135/90VDC
Amperage Range 34/18 A
Example 2A continuous high-carbon steel wire, 1.72 mm in diameter, with all contaminants as described in Exp. 1 removed, exposing a base metal surface free from oxide scale and other contaminants was moved through the reactor [FIG. X] and a DC voltage, of 150VDC was applied. As electrolyte entered the reactor through conductive tubes, plasma formed on the surface of the steel wire and a continuous, homogeneous nickel coating was applied.
Electrolyte Temperature 700 C
Electrolyte Concentration 16% NiSO4 (3.8% Ni) pH: 3.5
Electrolyte Flow Rate 1.5 L/min nominal flow rate
Travel Speed 6.7 m/min
Reactor Length 66 cm
Plasma Zone [active length] 52 cm
Voltage DC Range 165/145VDC
Amperage Range 42
Deposition Rate: 1 μm/4 seconds dwell
Example 3A continuous high-carbon steel wire, 1.72 mm in diameter, with all contaminants as described in Exp. 1 removed, exposing a base metal surface free from oxide scale and other contaminants was moved through the reactor [FIG. X].
The electrical polarity was changed from cathodic to anodic, that is the anode became earth and the cathode became positive. [workpiece is now positive +] The cleaned steel wire was moved through the reactor and DC voltage applied. The visible plasma, within the reactor changed from a violet/orange to a dark brownish/green color. A nickel oxide was applied to the surface of the cleaned steel wire. The oxide deposited on the wire surface was dark brown in color while the material deposited on the anodes was comprised of two layers, and outer layer of brown material and an inner layer of green material.
Electrolyte Temperature 800 C
Electrolyte Concentration 16% NiSO4 (3.8% Ni) pH: 6.0
Electrolyte Flow Rate 1.5 L/min nominal flow rate
Travel Speed 6.7 m/min
Reactor Length 66 cm
Voltage DC Range 200 VDC
Amperage Range: 15 A
Polarity: Anodic
Example 4A reinforcing steel rod with a diameter of 0.625″ with a heavy mill scale oxide, approximately 35 m thick was passed through a reactor with a length of 12″ in which plasma removed the oxide scale exposing the base metal including the ridges and lettering on the rod. The clean surface exhibited the typical plasma profile.
Electrolyte Temperature 800 C
Electrolyte Concentration 10% NaHCO3
Electrolyte Flow Rate 2.5 L/min nominal flow rate
Travel Speed 1 fpm
Reactor Length 30 cm
Plasma Zone [active length] 26 cm
Voltage DC Range 180 VDC
Amperage Range: 35 A
Polarity: Cathodic
Example 5A reinforcing steel rod, as in Example 4, with a diameter of 0.625″ which was cleaned in Exp. 4, all mill scale removed was passed through a reactor with a length of 12″ in which plasma formed and a coating of zinc was applied to the clean base metal. The coating was dense and ductile and very well adhered to the base metal. Iron was alloyed into the zinc coating, with iron being found very near the surface of the zinc coating.
Electrolyte Temperature 750 C
Electrolyte Concentration 16% ZnSO4
Electrolyte Flow Rate 2.5 L/min nominal flow rate
Travel Speed: 3 fpm
Reactor Length: 30 cm
Voltage DC Range: 200 VDC
Amperage Range: 40 A
Deposition Rate: 1 μm/second
Example 6A wire rod, 5.5 mm in diameter, having been previously cleaned with the electro plasma process is passed through a reactor with a length of 12″ in which plasma formed and a coating of nickel was applied to the clean base metal. The coating was dense and ductile and showed little or no porosity.
Electrolyte Temperature 750 C
Electrolyte Concentration 16% NiSO4 (3.8% Ni) pH: 3.5
Electrolyte Flow Rate 2.5 L/min nominal flow rate
Travel Speed 0.5 fpm
Reactor Length: 30 cm
Plasma Zone [active length] 26 cm
Voltage DC Range 200 VDC
Amperage Range 45 A
Deposition Rate: 0.5 μm/second
Example 7A fine wire having a diameter of 150 μm and having a brass coating was passed through a reactor with a length of two (2) inches with plasma forming on the wire surface. The surface of the wire was modified from the original state, without removing the existing coating.
Electrolyte Temperature 750 C
Electrolyte Concentration 8% NaHCO3
Electrolyte Flow Rate 0.25 L/min nominal flow rate
Travel Speed 15 fpm up 150 fpm
Reactor Length: 5 cm
Plasma Zone [active length] 3.8 cm
Voltage DC Range: 90 VDC [stable condition]
Amperage Range: 0.75 A-1.5 A
Example 8A wire rod with a diameter of 5.5 mm, having been cleaned with the electro plasma process, seventeen (17) days prior was drawn to a finish diameter of 1.72 mm without the use of a chemical lubricant carrier. The rod was passed through a open lubricant box, containing a dry powder lubricant. Approximately 2,500 meters of rod was drawn without a break and SEM analysis revealed a clean surface with only longitudinal lines.
Lubricant Carrier: None
Lubricant Dry powder
Entry Speed: 32 m/min
Exit Speed: 800 m/min
Number of Dies: 12
Example 9A wire rod with a diameter of 5.5 mm, having a coating of melted zinc-phosphate, borax and covered with a sterate was passed through a reactor with a length of 2.5 meters and plasma formed on the surface. SEM and EDAX analysis showed that all (99%) of the contaminants were removed from the surface of the wire rod.
Electrolyte Temperature 780 C
Electrolyte Concentration 12% NaHCO3
Electrolyte Flow Rate 8.5 L/min nominal flow rate
Travel Speed 30 fpm up 225 fpm
Reactor Length: 2.5 meters
Plasma Zone [active length] 2.35 meters
Voltage DC Range: 140 VDC [stable condition]
Amperage Range: 90 A
Example 10The exposed head of a stainless steel bolt which had a matte gray dull finish was placed inside the reactor during the cleaning of 5.5 mm wire rod. After processing for approximately five (5) minutes the stainless steel bolt was removed and examined. The exposed bolt head exhibited a very smooth, highly polished surface.
Electrolyte Temperature 800 C
Electrolyte Concentration 10% NaHCO3
Electrolyte Flow Rate 1.75 L/min
Voltage: 180 VDC
Example 11A plate [block] of Inconel 718 [anode] [0.750″×1″×4″] material was installed within the reactor chamber and electrolyte was flowed over the block of Inconel 718 for approximately 11 minutes in total time [not constant flowing] causing the Inconel 718 block to exhibit a reduced and/or modified surface. By directing the flow pattern the erosion area can be controlled, as exhibited in this example; the flow was directed across the center of the Inconel 718 block, and upon completion a smooth, even channel had been reduced from the center of the Inconel 718 block of material. Processed material, square rod, carbon steel 95 mm edge length was coated during the test.
Electrolyte Temperature: 700 C
Electrolyte Concentration: 15% ZnSO4
Electrolyte Flow Rate: 11 L/min nominal flow rate
Voltage: 170 VDC
Amperage: 100 A
Weight Loss of Inconel 718: 4 grams at top anode/10 grams at bottom anode [+/−18 seconds]
Deposition Rate: 0.8 μm/second
Coating: Ni, Cr, Fe & Zn
Example 12A tensile test sample of 4340 steel having notch in the center (length, 1.317 mm) was treated in a reactor with plasma forming of the surface. The surface of the sample was modified along with the notched region.
Electrolyte Temperature 700 C
Electrolyte Concentration 12% NaHCO3, pH 9.4,
Electrolyte Flow Rate 1 L/min nominal flow rate
Travel Speed: rotation, no linear speed
Voltage DC Range: 135 VDC [stable condition]
Amperage Range: 18-20 A
Example 13A square rod, 95 mm edge length, having been previously cleaned with the electro-plasma process, is passed through a reactor with length 12″ in which plasma formed and a coating of Zn was applied to the clean base metal. Reactor consisted of consumable anode assembly of IN 718 plates and Ni tubes. A significant loss in weight of anodes was observed. Dense coating consisted of Ni, Cr, and Fe along with Zn.
Electrolyte Temperature 700 C
Electrolyte Concentration: 15% ZnSO4 Monohydrate, pH 4
Electrolyte Flow Rate: 11 L/min nominal flow rate
Travel Speed: 2.25 fpm
Reactor Length: 30 cm
Plasma Zone [active length]: 10 cm
Voltage DC Range: 170 VDC [stable condition]
Amperage Range: 100 A
Deposition Rate: 0.8 μm/second
Loss in weight of plate anode: 4 g (Top) and 10 g (Bottom) for a run of ˜18 sec
Example 14A square tube, 2.54 cm edge length, having been previously cleaned with the electro-plasma process, is passed through a reactor with length 5.5″ in which plasma formed and a coating of Mo was applied to the clean base metal. Surface of the steel tube was alloyed with Mo. Concentration of Mo on the surface could be varied depending upon processing time and electrolyte make up. One of the examples is shown below
Electrolyte Temperature: 700 C
Electrolyte Concentration: 15% Na2MoO4
Electrolyte Flow Rate: 2 L/min nominal flow rate
Reactor Length: 14 cm
Voltage DC Range: 120 VDC [stable condition]
Amperage Range: 30 A
Treatment Time: 5 min
Mo concentration on surface: 35%
Example 15A square tube, 2.54 cm edge length, having been previously cleaned with the electro-plasma process, is passed through a reactor with length 5.5″ in which plasma formed and a coating of Zn—Mo alloy was applied to the clean base metal. Concentration of Mo in Zn coating could be varied depending upon processing time and electrolyte make up. One of the examples is shown below
Electrolyte Temperature: 700 C
Electrolyte Concentration: 10% ZnSO4 Monohydrate, pH: 5.0
Additions in electrolyte: Either Na2MoO4 or Mo powder
Electrolyte Flow Rate: 2 L/min nominal flow rate
Reactor Length: 14 cm
Voltage DC Range: 120 VDC [stable condition]
Amperage Range: 30 A
Treatment Time: 1 min
Mo concentration in coating: 20%
Example 16A wire strand, diameter 0.96 mm, consisting 18 fine Cu wires coated with Ni, is passed through a reactor with length 12″ in which plasma formed to remove oxide from Ni coating. Oxide was removed from the Ni surface of wire.
Electrolyte Temperature: 700 C
Electrolyte Concentration: 12% NaHCO3 pH: 8.3.
Electrolyte Flow Rate: 5 L/min nominal flow rate
Travel Speed: 40-60 fpm
Reactor Length: 30 cm
Plasma Zone [active length]: 26 cm
Voltage DC Range: 125 VDC [stable condition]
Amperage Range: 14 A-17 A
Example 17A fine brass coated steel wire, diameter 350 μm, is passed through a reactor with a length of 2″ of plasma forming on wire surface. Zn—Ni alloy coating was applied to the base metal.
Electrolyte Temperature: 700 C
Electrolyte Concentration: 15% ZnSO4 Monohydrate, pH: 5.0
Additions in electrolyte: 15% NiSO4 hexahydrate, pH: 4.8
Electrolyte Flow Rate: 150 ml/min nominal flow rate
Travel Speed: 7 fpm
Reactor Length: 5 cm
Plasma Zone [active length]: 3.8 cm
Voltage DC Range: 116 VDC [stable condition]
Amperage Range: 1.7 A-2 A
Treatment Time: 0.4 sec
Deposition Rate 0.65 μm/second
Example 18A square tube, 2.54 cm edge length, having been previously cleaned with the electro-plasma process, is passed through a reactor with a length of 5.5″ in which plasma formed and a coating of molybdenum was applied. Upon examination the molybdenum was also alloyed into the surface of the metal tube.
Electrolyte Temperature: 700 C
Electrolyte Concentration: 15% Na2MoO4
Voltage: 120 VDC
Amperage: 30 A
Treatment Time: 5 minutes continuous
Example 19A square rod 6.5 mm×95 mm in length, having been previously cleaned by the electro-plasma process is passed through a reactor with a length of 12″ in which plasma formed. The consumable anode consisted of an Inconel 718 plate and the electrolyte was ZnSO4.
Electrolyte Temperature: 700 C
Electrolyte Concentration: 15% ZnSO4 monohydrate
Voltage: 170 VDC
Amperage: 100 A
Deposition Rate: 0.8 μm/second
Coating: Zn/Ni/Cr & Fe
Example 20A copper wire with a diameter of 0.96 mm, coated with nickel is passed through a reactor with a length of 12″ in which plasma formed over the wire and removed the nickel coating.
Electrolyte Temperature: 700 C
Electrolyte Concentration: 12% NaHCO3
Travel Speed: 50 feet per minute
Voltage: 125 VDC
Amperage: 16 A
Example 21A threaded carbon steel rod with a diameter of 16 mm, length of 91 cm (36″) was passed through a reactor with 13% NaHCO3 at 700 C to remove any contaminants then the cleaned threaded rod was passed through a second reactor 12″ in length and zinc coated the threads and grooves between the individual threads, a nut was screwed on without the need to chase the threads.
Electrolyte Temperature: 700 C
Cleaning Electrolyte: 13% NaHCO3
Coating Electrolyte: 14% ZnSO4
Dwell Time: 10 seconds
Voltage: 135 VDC
Amperage: 24 A
Example 22A copper refrigeration tube with a diameter of 4.5 mm and a continuous length was passed through a reactor with 14% NaHCO3 with a dwell time in plasma of five (5) seconds to remove the copper oxide and any other contaminants and in succession pulled through a second reactor, 12″ in length, and coated with Sn (Tin).
Electrolyte Temperature: 750 C
Cleaning Electrolyte: Sodium Bi-carbonate 14%
Coating Electrolyte: SnSO4 @ 15%
Dwell Time: Six (6) seconds
Voltage: 120 VDC
Amperage: 14 A
All references cited in this specification are herein incorporated by reference as though each reference was specifically and individually indicated to be incorporated by reference. The citation of any reference is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such reference by virtue of prior invention.
It will be understood that each of the elements described above, or two or more together may also find a useful application in other types of methods differing from the type described above. Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention set forth in the appended claims. The foregoing embodiments are presented by way of example only; the scope of the present invention is to be limited only by the following claims.
Claims
1. A process for treating a surface of an electrically conductive workpiece, comprising:
- (a) placing a movable workpiece within a reaction chamber, wherein the reaction chamber includes an anode, and wherein the workpiece is a cathode;
- (b) creating a gap between the anode and the cathode, wherein the anode includes a plurality of orifices;
- (c) applying an aqueous electrolyte into the reaction chamber through the orifices in the anode and onto the workpiece, and applying the aqueous electrolyte from below the workpiece, to establish an electrically conductive medium around the workpiece,
- (d) applying a DC voltage to the electrically conductive medium in excess of 30 VDC, such that a foam is formed within the reaction chamber, wherein the foam comprises a gas/vapor phase and a liquid phase which fills the entire reaction chamber;
- (e) adjusting the voltage to establish an electro-plasma discharge between the anode and workpiece, sufficient to cause positive ions in the electrically conductive medium to become concentrated near the surface of the workpiece and cause micro-zonal melting of the surface in the area of discreet plasma bubbles; and
- (f) moving the workpiece through the reaction chamber and away from the electrically conductive medium to allow re-freezing of the molten surface of the workpiece.
2. The process of claim 1, wherein the workpiece is exposed to the electro-plasma for a duration sufficient to clean the workpiece from oxide scales, lubricants, coatings, dirt and organic substances.
3. The process of claim 1, wherein the workpiece is exposed to the electro-plasma for a duration sufficient to modify a surface profile of the workpiece to form a morphology which reduces wetting, serves as a carrier for drawing lubricants, and is passivated against corrosion.
4. The process of claim 1, wherein the positive ions include one or more metals to form one or more coatings of the metals on the workpiece.
5. The process of claim 4, wherein the coating includes a conductive metal coating comprised of independent layers of different metals on the workpiece.
6. The process of claim 4, wherein the coating includes two or more conductive metals forming an alloy on the workpiece.
7. The process of claim 1, wherein the positive ions are derived from one or more sacrificial anodes.
8. The process of claim 1, wherein the aqueous electrolyte is heated to a select temperature to increase the effectiveness of the process.
9. The process of claim 8, wherein the heated aqueous electrolyte is introduced into the reaction chamber and becomes a foam as electrical current is applied between the anode and the workpiece, sufficient to cause ebullition at the surface of the workpiece.
10. The process of claim 1, wherein the effectiveness of the electrically conductive medium is increased by the addition of foaming agents and surfactants.
11. The process of claim 2, wherein the cleaned surface of the workpiece exhibits a surface morphology comprising craters and spheroids sufficient to carry lubricant for drawing of the workpiece.
12. The process of claim 3, wherein an iron oxide (FeO) layer on the surface is reconstituted into alpha (amorphous) iron, and wherein surface grain size is substantially reduced to nano-sized grains that are tightly packed against one another sufficient to reduce corrosive penetration.
13. The process of claim 4, wherein deposition of the metals is achieved without an initiation or growth of an intermetallic layer between the workpiece and the coating metals.
14. The process of claim 4, wherein deposition of the metals is achieved without creation of a phase diffusion boundary layer on the coating metal.
15. The process of claim 4, wherein deposition of the metals is achieved without causing hydrogen embrittlement to the coating metals.
16. The process of claim 1, wherein the workpiece defines a core, and wherein the temperature of the core of the workpiece is maintained at or below a predetermined temperature sufficient to control the dissociation of oxygen and hydrogen, and to suppress the formation of oxygen bubbles at the surface of the workpiece.
17. The process of claim 16, wherein the predetermined temperature is about 950 C.
18. The process of claim 4, wherein downward pressure is maintained within the electro-plasma against the workpiece sufficient to cause deposition of the coating metals to form in a plane parallel to the surface of the workpiece.
19. The process of claim 1, wherein the workpiece is subjected to the electro-plasma across a plurality of isolated reaction chambers.
20. The process of claim 1, wherein the reaction chamber includes exhaust ports above the workpiece adapted to permit expanding gas to vent from the reaction chamber.
Type: Application
Filed: Mar 17, 2014
Publication Date: Sep 18, 2014
Applicant: CAP TECHNOLOGIES, LLC (Denham Springs, LA)
Inventors: Edward O. Daigle (Denham Springs, LA), Pratheesh George (Denham Springs, LA)
Application Number: 14/216,154
International Classification: C25D 5/04 (20060101); C25D 5/00 (20060101);
