Foundry mixture and related methods for casting and cleaning cast metal parts

Abstract

A foundry mixture for making molds used for molding cast metal parts includes foundry sand, a non-aqueous binder, and a cleaning agent that includes calcium oxide. Residual foundry mixture remaining on the cast part after removal from the mold is removed by electrolytic cleaning of the cast part.

Claims

1. A method for removing residual foundry mixture from a cast metal part, the method comprising the steps of: wetting a surface of the metal part with an electrolyte; and flowing electric current through the electrolyte, wherein the foundry mixture consists of: a granular refractory material consisting of sand, a resin binder material, and a cleaning agent, the cleaning agent consisting of calcium oxide; and the resin binder material being curable without using water to form a rigid non-aqueous binder matrix, the resin binder material being of the type that does not react with the calcium oxide during curing so that the calcium oxide remains as calcium oxide after curing of the resin binder material.

2. The method of claim 1 wherein the electrolyte is a basic electrolyte.

3. The method of claim 2 wherein the electrolyte has a pH of between about 8.5 and about 12 and the electrolyte comprises at least one of (a) and (b): (a) potassium carbonate and (b) sodium bicarbonate.

4. The method of claim 1 wherein the step of wetting the surface comprises the step of immersing the entire metal part in the electrolyte.

5. The method of claim 1 wherein the step of wetting the surface comprises the step of spraying the metal part with the electrolyte.

6. The method of claim 1 wherein the step of flowing electric current comprises the steps of: attaching the metal part to an electrical current source having a pair of electrodes of opposite polarities, one electrode attached to the metal part and the other electrode in contact with the electrolyte to define an electric circuit that includes the metal part and the electrolyte; and flowing electrical current through the electric circuit.

7. The method of claim 1 wherein the resin binder material is a heat-treated resin binder material or a catalyst-cured resin binder material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates schematically a first embodiment device useful in cleaning cast metal parts that are cast utilizing the disclosed foundry mixture; and

(2) FIG. 2 illustrates schematically a second embodiment device useful in cleaning cast metal parts that are cast utilizing the disclosed foundry mixture.

DETAILED DISCLOSURE

(3) 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.

(4) 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.

(5) 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.

(6) The binder material may be a resin binder material, a non-resin binder material, a liquid cured binder material, a heat cured binder material,

(7) 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.

(8) 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.

(9) 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.

(10) 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.

(11) 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.

(12) 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 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%).

(13) 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.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) FIG. 1 illustrates a cast metal part 10 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 10 is immersed in an electrolyzer 12 for removing cores or residual foundry mixture that includes the cleaning agent 13 from the cast metal part 10. The illustrated cast metal part 10 is a steel part. The electrolyzer 12 includes a nonmetallic container or vat 14 holding a liquid electrolyte 16, one or two electrodes 18, a power supply or current source 20, and a contact 22. The electrolyte 16 is a basic (alkaline) electrolyte. As shown in FIG. 1, the cast part 10 is immersed into the electrolyte 16 and is held in the electrolyte by a holder 23. The cast part 10 is connected to the contact 22. The electrodes 18 are connected to the positive output terminal 24 of the source 20. The contact 22 is connected to the negative output terminal 26 of the source 20.

(19) Electrolyte 16 is an aqueous basic solution that, in the illustrated embodiment, is made of a mixture of water and potassium carbonate. The electrolyte 16 has a pH of 12, but in other embodiments the pH may have a basic pH different than 12.

(20) 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.

(21) In the illustrated embodiment, the electrodes 18 are made of stainless steel rods. The power supply 20 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 20 can be an Invertec V300-Pro power source manufactured by The Lincoln Electric Company of Cleveland, Ohio. Other power supplies and electrodes may be used.

(22) As shown in FIG. 1, the cast metal part 10 is totally immersed into electrolyte 16 and is connected to the source 20. The source 20 is energized to flow current across the electrolyzer 12 for cleaning the cast metal part 10. During normal cleaning, the source 20 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.

(23) While the source 20 is energized, some materials removed from the cast part 10 float on the top of the electrolyte 16. Used foundry sand sinks to the bottom of the vat 14 and is later removed from the vat 14 and may be resold as a concrete aggregate. The sand and floating material are physically removed from the vat 14 by occasionally collecting each into separate containers.

(24) After cleaning, the power supply 20 is deactivated. The cast metal part 10 is removed from the electrolyte 16 and disconnected from contact 22. After removal, the part 10 may be lightly rinsed with water. After rinsing, the cast part 10 has been cleaned and is ready for any post-cleaning procedure. For example, the part 10 may be dried and subsequently painted.

(25) FIG. 1 illustrates a single cast metal part 10 immersed in the vat 14 for cleaning. However, a number of cast metal parts 10 in contact with each other can be immersed in electrolyzer 12 for simultaneous cleaning of the parts. One of the parts 10 is connected to the contact 22. The other parts 10 touch the part 10 connected to contact 22 or form a series of parts that contact one another and include the part 10 connected to the contact 22.

(26) In an alternative embodiment the vat 14 is a stainless steel tank connected to the negative terminal 26 of the source 20. The cast metal parts 10 would contact the vat 14 to be connected to the terminal 26.

(27) In other possible embodiments of the electrolyzer 12, the cast metal part 10 is connected to a power source having terminals of opposite polarities. The cast metal part 10 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 20 through the cast metal part 10 for cleaning.

(28) FIG. 2 illustrates an alternative method of cleaning the cast metal part 10 utilizing an industrial parts washer 28. 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.

(29) A continuous stream or spray 30 of electrolyte 16 is sprayed on the cast metal part 10 from an electrode 18 formed as a spray device. The metal part 10 is connected to a positive lead 24 of the power source 20. The cast metal part 10 is secured by a holder 25 connected to the negative lead 26 of the power source 20. In alternative embodiments each spray electrode 18 is submerged in a reservoir of electrolyte 16. 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.

(30) Non-limiting examples of casting and cleaning molded metal parts using the disclosed foundry mixture are described below.

(31) 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.

(32) The resulting mold was not electrically conductive. Electrolytic cleaning of the cast metal part as described above effectively removed adhering foundry mixture.

(33) 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.

(34) 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.

(35) 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.

(36) 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.

(37) 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.

(38) The disclosed foundry mixture and related methods may include the following non-limiting list of features, alone or in combination with other features:

(39) 1. A foundry mixture useful for making at least part of a mold for a cast part, the foundry mixture comprising granular refractory material, a binder, and a cleaning agent, the cleaning agent comprising calcium oxide.

(40) 2. The foundry mixture of feature 1 wherein the binder has been treated to bind the refractory material and the cleaning agent in a rigid binder matrix.

(41) 3. The foundry mixture of feature 2 wherein the foundry mixture forms a shell of a mold.

(42) 4. The foundry mixture of feature 2 wherein the foundry mixture forms a core of a mold.

(43) 5. The foundry mixture of feature 2 having a cold tensile strength not less than 420 pounds per square inch.

(44) 6. The foundry mixture of feature 2 having a Loss on Ignition not greater than two and ninety hundredths percent (2.9%).

(45) 7. The foundry mixture of feature 2 comprising an additive.

(46) 8. The foundry mixture of feature 2 wherein the binder comprises a suspension agent.

(47) 9. The foundry mixture of feature 1 comprising an additive.

(48) 10. The foundry mixture of feature 1 wherein the refractory material is selected from the group of: synthetic sand, bank sand, silica, olivine, chromite, zircon, chamotte, staurolite, graphite, and mixtures thereof.

(49) 11. The foundry mixture of feature 1 wherein the binder is selected from the group of resin binder, non-resin binder, liquid cured binder, and heat cured binder.

(50) 12. The foundry mixture of any one of the features 1-11 wherein the binder is a resin binder.

(51) 13. The foundry mixture of feature 12 wherein the resin binder comprises a catalyst-curable resin.

(52) 14. The foundry mixture of any one of the features 1-11 wherein the calcium oxide is finely ground or powdered calcium oxide.

(53) 15. The foundry mixture of any one of the features 1-10 wherein the binder is a resin binder that comprises a heat-curable resin.

(54) 16. The foundry mixture of feature 15 wherein the resin binder comprises a catalyst.

(55) 17. The foundry mixture of feature 1 or feature 2 wherein the refractory material and the binder together comprise a first portion of the foundry mixture and the calcium oxide is between about % (one-half percent) and about 5% (five percent) by weight or by volume of the first portion of the foundry mixture.

(56) 18. The foundry mixture of feature 17 wherein the binder is a resin binder.

(57) 19. A method for forming a metal part comprising the steps of:

(58) pouring molten metal into a mold, wherein said mold is formed at least in part of a foundry mixture comprising granulated refractory material, a binder, and a cleaning agent, the cleaning agent comprising calcium oxide, the binder having been treated to bind the refractory material and the cleaning agent in a rigid binder matrix;

(59) cooling the molten metal in the mold to form a solid; and

(60) removing the solid from the mold.

(61) 20. The method of feature 19 further comprising the steps of:

(62) physically separating said solid from the mold, to expose a metal part, wherein residual foundry mixture remains on a surface of the metal part;

(63) wetting the surface of the metal part with an electrolyte; and

(64) flowing electric current through the electrolyte.

(65) 21. The method of feature 19 wherein the foundry mixture forms a shell of a mold.

(66) 22. The method of feature 19 wherein the foundry mixture forms a core of a mold.

(67) 23. A method for removing residual foundry mixture from a cast metal part, the method comprising the steps of:

(68) wetting the surface of the metal part with an electrolyte; and

(69) flowing electric current through the electrolyte,

(70) wherein the foundry mixture comprises particulate refractory material, a binder, and a cleaning agent, the cleaning agent comprising calcium oxide, the binder having been treated to bind the refractory material and the cleaning agent in a rigid binder matrix.

(71) 24. The method of feature 20 or feature 23 wherein the electrolyte is a basic electrolyte.

(72) 25. The method of feature 24 wherein the electrolyte has a pH of between about 8.5 and about 12.

(73) 26. The method of feature 24 wherein the electrolyte comprises water and at least one of potassium carbonate and sodium bicarbonate.

(74) 27. The method of feature 24 wherein the step of wetting the surface comprises the step of immersing the entire metal part in the electrolyte.

(75) 28. The method of feature 24 wherein the step of wetting the surface comprises the step of spraying the metal part with the electrolyte.

(76) 29. The method of feature 24 wherein the step of flowing electric current comprises the steps of:

(77) attaching the metal part to an electrical current source having a pair of electrodes of opposite polarities, one electrode attached to the metal part and the other electrode in contact with the electrolyte to define an electric circuit that includes the metal part and the electrolyte; and

(78) flowing electrical current through the electric circuit.

(79) 30. The method of feature 19 or feature 23 wherein the binder is a resin binder.

(80) 31. The method of feature 30 wherein the resin binder is a heat-treated resin binder.

(81) 32. The method of feature 31 wherein the resin binder is a catalyst-cured resin binder.

(82) 33. The method of feature 30 wherein the foundry mixture comprises an additive.

(83) 34. The method of feature 30 wherein the calcium oxide is finely ground or powdered calcium oxide.

(84) 35. The method of feature 30 wherein the refractory material and the resin binder together comprise a first portion of the foundry mixture and the calcium oxide is between about % (one-half percent) and about 5% (five percent) by weight or by volume of the first portion of the foundry mixture.

(85) 36. The method of feature 30 wherein the foundry mixture has a cold tensile strength not less than 420 pounds per square inch and/or has a Loss on Ignition not greater than two and ninety hundredths percent (2.90%).

(86) 37. The method of feature 30 wherein the refractory material is selected from the group of: synthetic sand, bank sand, silica, olivine, chromite, zircon, chamotte, and mixtures thereof.

(87) 38. The method of feature 19 or feature 23 wherein the foundry mixture has a cold tensile strength not less than 420 pounds per square inch and/or a Loss on Ignition not greater than two and ninety hundredths percent (2.90%).

(88) 39. The method of feature 19 or feature 23 wherein the refractory material and the binder together comprise a first portion of the foundry mixture and the calcium oxide is between about % (one-half percent) and about 5% (five percent) by weight or by volume of the first portion of the foundry mixture.

(89) 40. The method of feature 19 or feature 23 wherein the refractory material is selected from the group of: synthetic sand, bank sand, silica, olivine, chromite, zircon, chamotte, staurolite, graphite, and mixtures thereof.

(90) 41. The method of feature 19 or feature 23 wherein the binder is selected from the group of resin binder, non-resin binder, liquid cured binder, and heat cured binder.

(91) 42. The calcium oxide in any feature having a fineness of between about 100 mesh to about 500 mesh.

(92) While this disclosure includes one or more illustrative embodiments described in detail, it is understood that the one or more embodiments are each capable of modification and that the scope of this disclosure is not limited to the precise details set forth herein but include such modifications that would be obvious to a person of ordinary skill in the relevant art and fall within the purview of the following claims.