Method for Cleaning Metal or Metal Alloy Surfaces

Abstract

A method for cleaning a surface of a metal or metal alloy body by immersing the surface in a basic aqueous electrolyte containing carbonate ions, and flowing DC current through the body to make the body anodic. After a time, the flow of DC current is stopped and the surface is removed from the electrolyte. The surface is then rinsed off to remove dirt, corrosion, coatings, and the like from the surface. The surface can then be dried and, if desired, coated for reuse of the body

Claims

1. A method for cleaning a surface of a metal or metal alloy body, the method comprising the steps of: (a) wetting the surface of the body with an aqueous electrolyte, the electrolyte comprising a dissolved carbonate salt and having a pH greater than 7; (b) making the body anodic by flowing DC current through the body concurrently with step (a), the flow of DC current being not less than 200 amperes; and (c) stopping the flow of the DC current after flowing the DC current for not less than 2 minutes.

2. The method of claim 1 wherein step (c) comprises rinsing the surface with water after stopping the flow of DC current.

3. The method of claim 1 wherein step (b) comprises the step of flowing DC current for a sufficient length of time to coat the wetted surface with a coating of additional material.

4. The method of claim 3 wherein step (c) comprises removing the coating of additional material from the body.

5. The method of claim 1 wherein the electrolyte has a pH of between about 8 and about 13.

6. The method of claim 5 wherein the electrolyte has a pH of about 11.

7. The method of claim 1 wherein the carbonate salt comprises potassium carbonate.

8. The method of claim 7 wherein the electrolyte comprises water and dissolved potassium carbonate.

9. The method of claim 8 wherein the electrolyte comprises dissolved trisodium phosphate.

10. The method of claim 9 wherein the trisodium phosphate is present in the electrolyte at a concentration of between 5% and 100% weight percent of the potassium carbonate.

11. The method of claim 1 wherein step (b) comprises the step of: (e) flowing DC current of between about 200 amperes and about 5000 amperes.

12. The method of claim 11 wherein step (b) comprises the step of: (f) flowing DC current of about 1000 amperes.

13. The method of claim 1 wherein step (a) comprises: (d) maintaining the electrolyte wetting the surface at a temperature of no less than about 70 degrees Fahrenheit.

14. The method of claim 13 wherein step (d) comprises the step of: (e) maintaining the electrolyte at a temperature of no less than about 150 degrees Fahrenheit.

15. The method of claim 1 wherein step (b) comprises the step of: (d) continuously flowing the DC current through the body for not less than about 3 minutes and not more than about 30 minutes.

16. The method of claim 1 wherein step (b) comprises the step of: (e) applying a DC voltage of between about 3 volts and 200 volts to the body while flowing the DC current through the body.

17. The method of claim 1 comprising the step after step (c) of: (d) rinsing the surface with a low pressure water spray.

18. The method of claim 17 wherein step (d) comprises the step of: (e) rinsing the surface no later than about 10 minutes after stopping the flow of DC current.

19. The method of claim 1 wherein the body is a steel body, an aluminum body, an aluminum alloy body, a manganese body, a manganese alloy body, or a cast metal body.

20. The method of claim 1 wherein the body has a surface coating to be cleaned from the surface, the method comprising the step of: (d) rinsing the surface coating off the surface with water after stopping the flow of DC current.

21. The method of claim 20 wherein the surface coating is a powder coating.

22. The method of claim 1 wherein the body is a wheel rim or a wheel hub of a motor vehicle.

23. The method of claim 22 wherein the wheel rim or wheel hub comprises aluminum or an aluminum alloy.

24. The method of claim 1 comprising the steps of: (d) sequentially cleaning a plurality of bodies in the electrolyte by performing steps (a), (b), and (c) for each body over a period of time; (e) maintaining the pH of the electrolyte greater than 7 for the entire period of time; and (f) maintaining the temperature of the electrolyte at or above 70 degrees Fahrenheit for the entire period of time.

25. The method of claim 1 wherein step (a) comprises the step of: (d) immersing the body entirely or at least partially into the electrolyte.

26. The method of claim 1 wherein step (a) comprises the step of: (d) spraying the electrolyte on the surface.

27. The method of claim 1 comprising the steps of: (d) drying the body after cleaning, and then (e) coating the surface with a powder coating or other coating for reuse of the body.

Description

BRIEF SUMMARY OF THE DRAWINGS

[0084] FIG. 1 is a schematic view of a metal alloy wheel immersed in an electrolyte for cleaning in accordance with an embodiment of the disclosed method of cleaning.

[0085] FIG. 2 is an enlarged view of a portion of the wheel shown in FIG. 1.

[0086] FIG. 3 schematically illustrates a first embodiment device useful in cleaning cast metal parts that are cast utilizing the disclosed foundry mixture.

[0087] FIG. 4 schematically illustrates a second embodiment device useful in cleaning cast metal parts that are cast utilizing the disclosed foundry mixture.

DETAILED DESCRIPTION

[0088] FIG. 1 illustrates a used truck or airplane wheel 10 totally immersed in an electrolyte 12 for cleaning in accordance with the disclosed method. The wheel 10 is a conventional aluminum alloy wheel that has a powder coating 14 on an external surface 16 of the wheel. See FIG. 2. It is desired to remove the powder coating 14 and surface contaminants 18 on the powder coating from the surface 16 to enable recycling and reuse of the wheel.

[0089] The wheel 10 is connected electrically in series to an anode terminal 20 of a DC current source 22 by a conductor 24. A steel or iron cathode 26 is also immersed in the electrolyte 12 and is connected in series to a cathode terminal 28 of the current source 22 by a conductor 30. The wheel 10 and the cathode 26 are electrically connected by the electrolyte 12.

[0090] The illustrated electrolyte 12 is an aqueous basic electrolyte formed by dissolving potassium carbonate (K.sub.2CO.sub.3) in water. The potassium carbonate is preferably food-grade potassium carbonate.

[0091] The pH of the electrolyte is about 11. The temperature of the electrolyte is about 130 degrees Fahrenheit.

[0092] In the illustrated embodiment the wheel 10 is immersed into a 200 gallon bath of electrolyte 12.

[0093] The DC current source 18 is energized and flows 1000 amperes of DC current from the anode terminal 16, through the wheel 10 and to the cathode 26, and back to the cathode terminal 22. The impressed DC current makes the wheel 10 anodic, that is, anodic with respect to the electrolyte 12.

[0094] The current source 18 is energized and supplies the 1000 ampere current through the wheel 10 continuously for five minutes. The current source 18 is then shut off and the wheel 10 is removed from the electrolyte 12.

[0095] While the DC current is flowing through the wheel 10, an additional layer of material is deposited on wetted surfaces of the wheel 10. The electrolyte 12 also darkens. It has been found that the wheel 10 does not appreciably heat while the DC current is flowing. It may even be necessary to heat the electrolyte 12 to maintain a desired electrolyte temperature while the DC current is flowing.

[0096] In the illustrated embodiment it is not necessary to treat the electrolyte in response to the electrolyte darkening. Additional potassium carbonate and/or water may be added to the electrolyte to maintain the desired pH. The electrolyte may be filtered in a conventional manner to remove dirt, soil, or other contaminants introduced into the electrolyte by the bodies being cleaned.

[0097] After the current source 18 is shut off, the wheel 10 is removed from the electrolyte 12. The wheel 10 is rinsed with a low pressure water jet spray to remove the additional material deposited on the wheel 10. In the illustrated embodiment the wheel 10 is sprayed with a 2000 psi water jet spray not more than 5 minutes after removal of the wheel from the electrolyte.

[0098] The jet spray also removes the powder coating 14 and the contaminants 18 from the wheel surface 16. After rinsing, the wheel 10 has a clean wheel surface 16 capable of accepting application of a new powder coating and/or alternative surface coatings.

[0099] After rinsing, the wheel 10 is dried. The wheel 10 may then be powder coated or otherwise coated or painted for return to the aftermarket and reuse.

[0100] In alternative embodiments of the disclosed method, some, but not all, surfaces of the metal or metal alloy body require cleaning. In such embodiments, the body may only be partially immersed in the electrolyte 12 if total immersion is not required to wet the surfaces to be cleaned.

[0101] In other alternative embodiments of the disclosed method, surfaces to be cleaned may be wetted by spraying electrolyte on the surfaces to be cleaned. The electrolyte spray must electrically connect the body as anode with the cathode and must conduct sufficient DC current to create the additional material coating.

[0102] In a further alternative embodiment of the disclosed method, TSP was added to the potassium carbonate based electrolyte and wheels similar to the wheels 10 were cleaned using different concentrations of trisodium phosphate in the electrolyte.

[0103] A TSP concentration of 1% or less (calculated as the weight of TSP divided by the weight of the potassium carbonate in the electrolyte and expressed as a percentage) had no appreciate effect on the cleaning of the wheel.

[0104] A TSP concentration of 5% had a positive effect, increasing the shine of the cleaned wheel, but the shine would not be considered very bright.

[0105] A TSP concentration of 50% resulted in good brightness of the cleaned wheel.

[0106] A TSP concentration of 100% (equal weights of TSP and potassium carbonate) had the best brightness.

[0107] It is contemplated that bodies may be cleaned by automating the disclosed method. For a nonlimiting example, metal or metal alloy bodies to be cleaned may be conveyed to an electrolysis station for immersion in or wetting with the electrolyte and application of DC current. Application of the DC current may stop after a predetermined time, or if a computerized optical monitoring system determines that the surface of the body has been adequately coated with the additional material to end application of DC current.

[0108] After the application of DC current stops, the body is moved from the electrolysis station to a rinse station for rinsing. The electrolyte is continuously filtered to remove contaminants in the electrolyte. The pH, temperature, and volume of electrolyte is monitored and maintained within predetermined limits by an automatic control system (not shown).

[0109] Also disclosed is a foundry mixture usable for forming a casting mold and/or a core for use with a casting mold for casting ferrous and non-ferrous metal parts, including metal parts made from aluminum, brass, bronze, iron, copper, gold, lead, magnesium, nickel, silver, steel, tungsten, zinc, and the like. The foundry mixture is cured to form a mold shell and/or mold core for foundry molding of the cast metal part.

[0110] The foundry mixture consists of a granular refractory material, a binder material, a cleaning agent, and may optionally include additives. The mixture may of course include impurities included with the addition of the materials forming the foundry mixture, but such impurities are not considered as forming a part of the foundry mixture.

[0111] The granular or particulate refractory material may be, in alternative embodiments, a sand formed from one or more of silica, olivine, chromite, zircon, and chamotte. Other sands conventionally used in foundry casting may also be used, including bank sands and synthetic sands. The sand may be coarse-grained sand, fine-grained sand, or be a mixture thereof.

[0112] The binder material may be a resin binder material, a non-resin binder material, a liquid cured binder material, a heat cured binder material,

[0113] The binder material may in embodiments be part of a resin binder that includes a resin as the binder material and may optionally include a suspension agent. Resins, in embodiments, may be (but are not limited to) urea formaldehyde (UF) resins, phenol formaldehyde (PF) resins, natural or synthetic gums, furan resins and furfuryl alcohols.

[0114] The resin binder material in embodiments may be a heat-curable resin in which heating the foundry mixture cures the resin to form a heat-cured resin binder. The resin binder in other embodiments may require a catalyst as a suspension agent. The catalyst when added to the foundry mixture reacts with the resin and cures the resin to form a cured resin binder.

[0115] The cleaning agent includes calcium oxide (CaO). The calcium oxide may, in embodiments, be obtained from limestone that is preferably 99% (ninety-nine percent) or more calcium oxide. The calcium oxide is preferably provided in powdered or finely ground form for use in preparing the disclosed foundry mixture. The cleaning agent in embodiments may consist only of calcium oxide.

[0116] The refractory material and the binder material (and the suspension agent if present) together form a first portion of the disclosed foundry mixture. The calcium oxide may in embodiments of the disclosed foundry mixture be present in the foundry mixture by weight or by volume between about % (one-half percent) and about 5% (five percent) of the first portion of the foundry mixture.

[0117] The following working example is given as an illustration only and is not intended to limit the scope of the disclosure. The results of tensile strength testing and loss on ignition testing for an embodiment of the disclosed foundry mixture are given below.

[0118] A sample of a foundry mixture that includes two-and-one-half percent (2%) resin coated sand was mixed with one-half percent (%) by weight finely ground calcium oxide. The foundry mixture was then formed into standard specimen biscuits used for the tensile testing of foundry mixtures. The e biscuits were then cured and allowed to cool to room temperature. The average cold tensile strength of the biscuits was four hundred and forty-five (445) pounds per square inch. The average Loss on Ignition was two and sixty-nine hundredths percent (2.69%). Recommended values for a conventional 2% resin mixture is a minimum cold tensile strength of 420 pounds per square inch and a Loss on Ignition of between two and sixty hundredths percent (2.60%) and two and ninety hundredths percent (2.90%).

[0119] In use for foundry casting, the foundry mixture is formed into at least a portion of a mold, and may also be used in forming one or more cores that are included as part of the mold for defining the shape of a cast part. The foundry mixture forming the mold and the one or more cores is cured to form a rigid matrix encapsulating the refractory material and capable of retaining the shape of the mold or core when the mold is being used to mold the molten metal. The molten metal flows into the mold and solidifies in the mold to form the cast metal part.

[0120] The type of ferrous or non-ferrous metal being cast, the alloys in the metal, the desired surface quality of the finished part, and other factors influence the selection of refractory material, binder, binder curing methods, and additives to be used in casting a specific metallic part as is known in the metal casting art and so will not be described in further detail herein.

[0121] The disclosed foundry mixture may be distributed in pre-mixed, pre-measured form in which the cleaning agent, refractory material, and binder are mixed together for convenience prior to use. If the binder material requires a suspension agent that is not compatible with a pre-mixed foundry mixture (that is, adding the suspension agent would start immediate curing of the binder material or would react or hydrate the calcium oxide cleaning agent), the pre-mixed mixture may be provided without a suspension agent (that is, with binder material only). The components may be mixed together using conventional high speed continuous mixers, low-speed augur-type continuous mixers, batch mixers. or other conventional mixing devices or mixing methods.

[0122] The shaping and curing of the disclosed foundry mixture to form a mold shell or core defining the desired shape of the casting produced by pouring melted metal into the mold, the formation of sprues, runners, and risers to flow molten material to and within the mold, including pattern making, lost wax casting, and other variations of shaping and curing a foundry mixture to achieve the desired shape of the casting are known in the foundry casting art and so will not be described in further detail herein.

[0123] After the molten metal cools and solidifies, the cast metal part is removed from the mold. Inner cores may remain in the removed part, and residual foundry mixture may adhere to casting surfaces.

[0124] FIG. 3 illustrates a cast metal part 110 formed by flowing molten (liquid) metal into a mold formed from the disclosed foundry mix. The illustrated foundry mixture includes a resin binder and calcium oxide as the sole cleaning agent. The part 110 is immersed in an electrolyzer 112 for removing cores or residual foundry mixture that includes the cleaning agent 113 from the cast metal part 110. The illustrated cast metal part 110 is a steel part. The electrolyzer 112 includes a nonmetallic container or vat 114 holding a liquid electrolyte 116, one or two cathodes 118, a power supply or current source 120, and an anode contact 122. The electrolyte 16 is a basic (alkaline) electrolyte. As shown in FIG. 3, the cast part 110 is immersed into the electrolyte 116 and is held in the electrolyte by a holder 123. The cast part 110 is connected to the anode contact 122. The cathodes 118 are connected to the positive output terminal 124 of the source 120. The anode contact 122 is connected to the negative output terminal 26 of the source 120.

[0125] Electrolyte 116 is an aqueous basic solution that, in the illustrated embodiment, is made of a mixture of water and potassium carbonate. The electrolyte 116 has a pH of 12, but in other embodiments the pH may have a basic pH different than 112.

[0126] An alternative illustrative and non-limiting embodiment of the electrolyte is an aqueous basic solution made of a mixture of water and sodium bicarbonate. The alternative embodiment electrolyte has a pH of between about 8.5 and about 9.0, that is, the pH of the alternative embodiment electrolyte has a pH closer to 8.5 than to 8, and closer to 9.0 than 9.5.

[0127] In the illustrated embodiment, the cathodes 118 are made of stainless steel rods. The power supply 120 produces a low voltage direct current output from 5 to 350 DC amps output from a 60 HZ, 230 V, 3 phase alternating current source. Power supply 120 can be an Invertec V300-Pro power source manufactured by The Lincoln Electric Company of Cleveland, Ohio. Other power supplies and anodes may be used.

[0128] As shown in FIG. 3, the cast metal part 110 is totally immersed into electrolyte 116 and is connected as the positive terminal of the source 120. The source 120 is energized to flow current across the electrolyzer 112 for cleaning the cast metal part 110. During normal cleaning, the source 120 is energized for from 2 to 3 minutes per cast metal part, depending on the binder, metal composition, size of the part, and so on.

[0129] While the source 120 is energized, some materials removed from the cast part 110 float on the top of the electrolyte 116. Used foundry sand sinks to the bottom of the vat 114 and is later removed from the vat 114 and may be resold as a concrete aggregate. The sand and floating material are physically removed from the vat 114 by occasionally collecting each into separate containers.

[0130] After cleaning, the power supply 120 is deactivated. The cast metal part 110 is removed from the electrolyte 116 and disconnected from anode contact 122. After removal, the part 110 may be lightly rinsed with water. After rinsing, the cast part 110 has been cleaned and is ready for any post-cleaning procedure. For example, the part 110 may be dried and subsequently painted.

[0131] FIG. 3 illustrates a single cast metal part 110 immersed in the vat 114 for cleaning. However, a number of cast metal parts 110 in contact with each other can be immersed in electrolyzer 112 for simultaneous cleaning of the parts. One of the parts 110 is connected to the anode contact 122. The other parts 110 touch the part 110 connected to contact 122 or form a series of parts that contact one another and include the part 110 connected to the contact 22.

[0132] In an alternative embodiment the vat 114 is a stainless steel tank connected to the negative terminal 126 of the source 120 to form the anode of electrolyzer 12. The cast metal parts 110 would contact the vat 114 to be connected to the anode.

[0133] In other possible embodiments of the electrolyzer 112, the cast metal part 110 is connected to a power source having terminals of opposite polarities. The cast metal part 110 immersed in the electrolyte 16 is electrically connected to one terminal, and the electrolyte 16 is electrically connected to the other terminal for flowing electric current from the power source 120 through the cast metal part 110 for cleaning.

[0134] FIG. 4 illustrates an alternative method of cleaning the cast metal part 110 utilizing an industrial parts washer 128. Industrial parts washers typically include one or more processing zones for cleaning, rinsing, drying and other steps for cleaning cast metal parts. A conveyor typically transports the parts through the processing zones from one end of the washer to the other. Industrial parts washers typically spray the parts with liquid, and so most washers include an enclosure to capture the spray and contaminants being washed. Some industrial parts washers include a holder to secure and support the part to be washed. The holder and the part to be cleaned are enclosed in a chamber that forms a sealed unit encapsulating the part. A cleaner dispersing system is operable to remove residual materials from the part.

[0135] A continuous stream or spray 130 of electrolyte 116 is sprayed on the cast metal part 110 from a cathode 118 formed as a spray device. The metal part 110 is connected to a negative terminal 126 of the power source 120. The cast metal part 10 is secured by a holder 125 connected to the negative terminal 126 of the power source 120. In alternative embodiments each spray cathode 118 is submerged in a reservoir of electrolyte 116. A drain basin (not shown) collects the sprayed electrolyte and filters out the used sand for collection. Use of an industrial parts washer enables continuous, production line cleaning of cast metal parts as part of an industrial process that manufactures and cleans cast metal parts that are then sent downstream for further processing.

[0136] Non-limiting examples of casting and cleaning molded metal parts using the disclosed foundry mixture are described below.

[0137] A foundry mixture that includes sand, a clay binder, and five percent finely ground calcium oxide was formed into a mold and molten metal was poured into the mold to form a cast metal part. The mixture was mixed in a first set of trials with water to have about 4 percent moisture content and mixed in a second set of trials with water to have about 2 percent moisture content. Different types of sand (silica, chromite, zircon olivine, staurolite, graphite) were used in each set. The water was used as a suspension agent but did not react with the calcium oxidethe calcium oxide was added as the last ingredient to the foundry mixture shortly before pouring the molten metal into the mold and so the calcium oxide did not hydrate.

[0138] The resulting mold was not electrically conductive. Electrolytic cleaning of the cast metal part as described above effectively removed adhering foundry mixture.

[0139] In yet another set of tests, a foundry mixture suitable for cold-box treatment included from one percent to five percent calcium oxide by weight as a cleaning agent. Molds formed by the cold-box treatment were not electrically conductive.

[0140] In yet another set of tests, foundry mixtures containing inorganic and organic binders included from between one percent and five percent calcium oxide as a cleaning agent. Molds formed from the foundry mixtures were not electrically conductive. Electrolytic cleaning of the cast metal parts as described above effectively removed adhering foundry mixture. It was found that the calcium oxide did not affect the strength of the molds formed by the foundry mixtures as compared to equivalent foundry mixtures but without the calcium oxide cleaning agent.

[0141] In an additional set of tests, foundry mixtures containing amine resin and furane resin binders (and no appreciable amount of water) that included calcium oxide as a cleaning agent. Molds formed from the foundry mixtures were not electrically conductive. Electrolytic cleaning of the cast metal parts as described above effectively removed adhering foundry mixture.

[0142] In a further set of tests with resin binders that included calcium oxide as a cleaning agent, it was found that removing the same amount of sand from the conventional foundry mixture as the amount of calcium oxide cleaning agent being added did not adversely impact the strength of the molds formed from the foundry mixture.

[0143] In embodiments, the disclosed foundry mixture includes a liquid cured binder material and calcium oxide as a cleaning agent. The liquid cured binder material may be an aqueous binder material. Where the liquid suspension agent used may chemically react with the calcium oxide, the amount of suspension agent should be such that sufficient calcium oxide not forming part of the binder material remains after curing to act as a cleaning agent, or the calcium oxide should be added to the foundry mixture in a way that effectively prevents chemical reaction with the calcium oxide. For example, the calcium oxide can be added as a final ingredient to a foundry mixture containing up to 7 percent water shortly before molten metal is poured into a mold formed from the foundry mixture. The heat of the molten metal poured into the mold is well above the boiling point of water. The water in the foundry mixture cannot react with the calcium oxide.

[0144] Features recited in a claim may, in embodiments of the disclosed method, be found in combination with features recited in the claims.

[0145] While one or more embodiments have been disclosed and described in detail, it is understood that this is capable of modification and that the scope of the disclosure is not limited to the precise details set forth but includes modifications obvious to a person of ordinary skill in possession of this disclosure, including (but not limited to) changes in material selection, size, operating ranges (temperature, volume, displacement, stroke length, concentration, and the like), environment of use, and also such changes and alterations as fall within the purview of the following claims.