AU2013242795A1 - Improvements in Electro Chemical Metal Cleaning Apparatus - Google Patents

Abstract

An electro cleaning and electro polishing apparatus comprises with an inverter power source for the passivation, cleaning and polishing of metal surfaces by electrochemical action where the surface is contaminated from welding, other heat treatment or general fabrication and the contaminates .The invention improves the affect of the electrochemical action and accelerates the process. A device comprises pulse wave modulation enables the electrical frequency and wave form to be manipulated for selective removal of metal more easily and rapidly so that optimum polishing and corrosion resistance is accomplished. Furthermore to achieve this with the electrode that best suits the frequency and wave form ,the metal type, the finish of the parent, the finish of the fabricated piece, the amount of surface area, the shape of the surface and speed required. Further more a device for controlling the current is provided so unlimited electrodes and many permutations of voltage and current ratios are possible using the same inverter power source Drawings Fig. 1. Fig.2. Figure descriptions Fig.1. is perspective view of the inverter power supply apparatus. Fig.2. is a perspective view of an example of a hand piece operating a large carbon fibre brush style electrode.

Description

1 IMPROVEMENTS IN ELECTRO CHEMICAL METAL CLEANING APPARATUS FIELD OF THE INVENTION 5 This invention relates to an apparatus with an inverter power source for the passivation, cleaning and polishing of metal surfaces by electrochemical action where the surface is contaminated from welding, other heat treatment or general fabrication and the contaminates must be removed .The aim of the invention is to improve the affect of the electrochemical action and to 10 accelerate the process. The apparatus will improve the electrochemical action for electro polishing or electro cleaning of the metallic surface .A device for controlling the current is provided so unlimited electrodes and many permutations of voltage and current ratios is possible using the same inverter power source 15 BACKGROUND OF THE INVENTION Electropolishing is the controlled electrochemical removal of surface metal and contaminates resulting in improved properties of the metal. The process is sometimes called "reverse plating" or "super passivation" and has a leveling effect which produces a smooth surface with increased reflectivity. With 20 stainless steel welds the deformed amorphous outer layer of the metal is removed leaving a chromium rich passive surface free of embedded contaminants and work induced residual stresses. Electropolishing draws surface contaminants away from the work piece as well 25 as removing micro projections resulting in micro leveling of the surface greatly improving resistance to bacteria and corrosion. Most metals can be successfully electropolished but the best results are obtained with metals that have fine grained boundaries which are free of non metallic inclusions and seams. 30 Metals which have a high content of silicon, lead or sulphur are usually troublesome. Electropolishing is most commonly used on stainless steel but aluminium, brass and carbon steels may also be electropolished as well as 2 copper, beryllium copper, bronze, nickel, nickel silver, wrought aluminium alloys, titanium and gold. The final quality and consistency of the finish is determined by controlling the 5 voltage, current density and frequency of the inverter supplied power. The appropriate electrolyte for the particular metal must be used and is normally a liquid solution but a gel form may also be used. Conventional electropolishing has been achieved by immersing the work piece 10 connected to the positive terminal of a DC power supply thereby becoming an anode, in an electrolyte bath. Metal plates in the bath are connected to the negative terminal of the DC power supply thereby becoming the cathode for ionic conduction which removes unwanted particles from the anodic work piece. Fine burrs become high current density areas and are removed while smooth 15 sections become low current density areas and are polished. The result is an overall reduction of the micro surface profile with a simultaneous smoothing and brightening of the metal surface. In the case of stainless steel alloys, iron and nickel atoms are more readily 20 extracted from the crystal lattice than are chromium atoms. Accordingly the process removes iron and nickel preferentially leaving a surface rich in chromium and chromium oxides resulting in passivation of the surface. The oxide rich layer reduces the absorption of moisture which prevents corrosion and maintains a clean surface. 25 In the course of fabricating and welding stainless steel weld scale (oxide scale /heat tint) is formed which prevents the formation of the chromium oxide film. Surface contamination with iron particles, grease and dirt can also occur during fabrication such as cutting, grinding and general handling. 30 The high temperature of welding also results in severe chromium depletion not only at the weld surface but through out the heat affected area. Contaminates need to be cleaned away or otherwise removed and the chromium restored.

3 Any etching of the surface creates a surface roughness to which deposits and residue contaminates can bind so a smother surface as achieved with electro polishing reduces the risk of contamination. Electro cleaning is similar to Electro polishing but uses an alternating current 5 and is not effective at smoothing the surface. Electro cleaning will remove contaminates and allow passivation. Passivation is a process for maintaining clean stainless steel vessels and piping surfaces. Passivation can be thought of as a specialised cleaning procedure in which iron and other contaminants are removed from the surface 10 to provide a chromium rich surface layer. This process makes iron less available at the surface to form iron oxides (rust or rouge) during operations. Passivation is typically done with a chemical and no electrical current. Pickling is a chemical process for removal of heat tint and requires more aggressive and toxic chemicals than passivation. 15 Surface staining and contaminates on stainless steel can be removed using a pickling or passivation gel of toxic acids including hydrofluoric and nitric acids. This prior art method has an etching affect and requires a significant amount of time and occupational health and safety risks result. Nitric acid can release N02 which can be very dangerous 20 OBJECT OF THE INVENTION It is therefore an object of the present invention to provide an apparatus which overcomes the known disadvantages of electrochemical cleaning process which is that the duration to get an optimum finish is relatively slow and in 25 particular slows as material thickness increase and when MIG welding is done. The present invention has no limitations on electrode size or shape that can be used with the apparatus so electrodes can be used effectively on unlimited surface areas, unlimited metallic shapes and forms and internal and external pipes and tubes. 30 It is a further object to overcome the disadvantages' of chemical cleaning and -,,--.; - -frrr+-11;,- - ~ -4 ^1-n ,r.rin .,., rr~r ,rd rIn , -4 -id na 4 possible with current electrochemical processes due to their lack portability or limited electrode sizes. 5 STATEMENT OF THE INVENTION According to the present invention an electro cleaning and electro polishing apparatus comprises a an electrical power supply whereby the power supply is an electronic inverter with pulse wave modulation and has a lead that carries 10 current to an electrode Preferably the inverter has insulated gate bipolar transistor and is cooled with an non conductive coolant 15 Preferably the inverter has pulse wave modulation electronic circuitry that allows manipulation and control of current density, volts and frequency and the shape of the current wave. Preferably the frequency has ultrasonic current vibration 20 Preferably the cathode or electrode is made of brass, copper, stainless steel or carbon fibre Preferably the cathode or electrode is covered with an electrolyte absorbent 25 boot. Preferably the coolant that cools the electrode is a non conductive fluid Preferably the apparatus has a switch to switch the electrolyte supply from 30 automatic to manual. Preferably the apparatus has a controller to control the rate of flow of electrolyte to the cathode or electrode 5 Preferably the handle which is connected to the cathode or electrode has an on/off control for the supply of electrolyte to the cathode block. 5 VARIATIONS It will be realised that the foregoing has been given by way of illustrative example only and that all other modifications and variations as would be apparent to persons skilled in the art are deemed to fall within the broad scope 10 and ambit of the invention as herein set forth. Throughout the description and claims of this specification the word "comprise" and variations of that word such as "comprises" and "comprising" are not intended to exclude other additives, components, integers or steps. 15 20 25 30

Claims (10)

1. An electro polishing, electro cleaning and passivation apparatus comprising an electrical power supply from an inverter

2. An apparatus of claim 1 with reservoirs of electrolyte and coolant, a lead which carries current to the cathode or electrode. A pump which pumps the electrolyte from its reservoir to the cathode or electrode and a pump which pumps the coolant from its reservoir through tubes to cool the inverter and or the cathode or electrode

3. The apparatus of claim 1 in which the inverter has an insulated gate bipolar transistor

4. The apparatus of claim 1 in which the inverter has pulse wave modulation electronic circuitry

5. The apparatus of claim 1 in which the coolant is non conductive

6. The apparatus of claim 1 which has a switch to turn the power supply on.

7. The apparatus of claim 1 which has a switch to switch the electrolyte supply from automatic to manual.

8. The apparatus of claim 1 which has a controller to change and control the frequency of the high frequency of the secondary voltage.

9. The apparatus of claim 1 which has a controller to change and control the current flow as to control the level of particle removal.

10. The apparatus of claim 1 which has a controller to control the rate of flow of electrolyte to the electrode.