Burnishing method and composition

Abstract: A burnishing liquid used in a physicochemical mass finishing process serves to chemically remove the conversion coating as well as to promote brightness of the treated metal surface. The burnishing liquid has a very low content of organic constituent and therefore a low chemical oxygen demand characteristic. The burnishing liquid comprises a water-soluble tetrapyrophosphate or hexametaphosphate and has a pH of about 8.5 to 10.5.

Description: A physicochemical process for refining metal surfaces is described and claimed in Michaud et al United States Patent No. 4.491,500, issued January 1, 1985, which process involves the development, physical removal and continuous repair of a relatively soft coating on the surface. High points are leveled through mechanical action, preferably developed in vibratory mass finishing apparatus, and very smooth and refined surfaces are ultimately produced in relatively brief periods of time. The patentees teach that the process can be carried out using either a part-on-part technique or by incorporating an abrasive mass finishing media; e.g., quartz, granite, aluminum oxides, iron oxides, and silicon carbide, which may be held within a matrix of porcelain, plastic, or the like. As described therein, the effectiveness of the process is evidently attributable to the selective removal of surfaces irregularities, which removal has been facilitated by chemical conversion of the metal to a softer form. To achieve ultimate refinement of the metal surface, it will generally be desirable to finish the Michaud et al process with a burnishing step, which may be carried out by treatment of the parts in a mass finishing unit charged with a so-called burnishing media and an aqueous alkaline soap solution, the latter being inert to the metal. Such burnishing media will typically be composed of mineral oxide grains fused to a hard, dense, non-abrasive cohesive mass; it is also commonly known to use steel balls for burnishing metal parts. The process described by Michaud et al can be employed to produce burnished parts without transferring them to a second bowl, by using a relatively nonaggressive cutting medium (e.g., a ceramic containing 10 to 15 percent of abrasive grit). In such a procedure the initial, surface-refinement phase is carried out with a reactive solution which produces the conversion coating on the parts, generally followed by a flushing step and then, with the equipment in operation, a flow of a burnishing soap solution. Although highly advantageous, such a method may not produce specular brightness, since it is characteristic of abrasive media that they scratch the metal surfaces. In Michaud United States Patent No. 4,818,333, issued April 4, 1989, a physicochemical process is provided for refining metal surfaces to a condition of high smoothness and brightness, in relatively brief periods of time and without need for removal of the objects or the media from the container of the mass finishing unit. The process is characterized by the use of a non-abrasive, high-density burnishing media throughout the entire surface-refining and burnishing operation. As indicated, the physicochemical refinement methods described in the foregoing patents involve the formation of a conversion coating on the metal surface, which is ultimately removed in the burnishing step. Because that occurs primarily through physical contact, however, some of the coating frequently remains in sheltered or recessed areas. This is of course undesirable for self-evident reasons, especially if the part is to electroplated, varnished, or otherwise surface coated. At present, hydrochloric acid is widely used to dissolve such residual conversion coatings, but that practice is undesirable for a number of reasons, particularly the tendency of HCl to cause hydrogen embrittlement. Other chemical formulations have been employed for the dissolution of oxalate and phophate coatings, but they are typically characterized by relatively high levels of organic component content; thus, they disadvantageously add to the oxygen demand made upon available waste treatment facilities, and in some cases their use is prohibited as a result. The prior art of course discloses numerous chemical formulations for cleaning metal surfaces, many of which employ a phosphate compound as the primary active ingredient. For example, Crowther United States Patent No. 2,986,526, issued May 30, 1961, discloses metal-cleaning compositions which comprise an alkali metal pyrophosphate and a higher aliphatic fatty alcohol/ethylene oxide reaction product; tetrasodium pyrophosphate is deemed to provide the best result, and is preferred. In accordance with the patent, a granular product is made by absorbing the ethylene oxide/alcohol adduct into the pyrophosphate, at ratios in the range of 0.5-10:90-99.5, and the product is dissolved in water at a concentration of 0.5 to 10 percent and to provide a working solution with a pH of preferably 9.0 to 10.0. Copson United States Patent No. 3,325,244, issued June 13, 1967, and Van Kampen et al United States Patent No. 3,370,015, issued February 20, 1968, disclose cleaning compositions in which a pyrophosphate is the major ingredient. Cinamon, Kelly et al and Sopp, Jr. disclose, in United States Patents Nos. 2,481,977, 3,210,278 and 3,655,467, issued September 13, 1949, October 5, 1965 and April 11, 1972, respectively, compositions containing a pyrophosphate and another alkaline detergent builder. Phosphate cleaning compositions are also taught by Schaeffer, Highfill, and Dupre et al in United States Patents Nos. 2,618,604, 4,803,058, 3,145,178 and 3,312,624, issued November 18, 1952, February 7, 1989, August 18, 1964, and April 4, 1967, respectively. Chemical Abstracts Volume 112, Number 4, dated 22 January 1990, Abstract No. 24452f, and CS-A-258396, discloses a cleaning solution containing, amongst other ingredients, 1.7 g/l tetrasodium pyrophosphate and 0.5 g/l alkylbetaine surfactant (calculated from 1 part of solid concentrate to 66 parts of water). A concentrated solution contains 5 to 15 percent of the pyrophosphate and 1 to 7 percent of the surfactant. US-A-4 724 041 discloses a two step process for physicochemical polishing of ferrous surfaces. In the first step, a solution containing oxalic acid, phosphate ions, tetrasodium pyrophosphate and a surfactant is used as an iron oxalate coating forming solution. In the second step, the burnishing is effected with the same solution in very diluted form in order to remove the remaining oxalate coating. Despite the activity in the art indicated by the foregoing, a need remains for a burnishing composition and mass finishing method by which metal-surfaced objects can be refined using a physicochemical technique, and can subsequently be burnished while simultaneously effecting the removal of any residual conversion coating. It is therefore the broad object of the present invention to provide a novel composition and method for achieving those results. It is a more specific object of the invention to provide a novel composition and method by which such residual coatings can readily be removed from areas of metal surfaces that are recessed, or are for other reasons inaccessible to contact by solid elements employed in a mass finishing process. Other more specific objects are to provide such a composition and method by which the workpiece surfaces can be brought to a condition of specular brightness, in a desirably brief period of time and without etching or other adverse effect upon surface quality. An especially important object of the invention is to provide a composition and method having the foregoing features and advantages, which produces a waste stream having a low chemical oxygen demand characteristic, and which is relatively easy to treat for the recovery of dissolved metal compounds. A further object of the invention is to provide a novel burnishing composition composed of ingredients that are readily available and relatively inexpensive, which can be prepared in stable, concentrated form so as to make transport and use convenient and economical. According to a first aspect of the present invention there is provided a process for the physicochemical refinement and burnishing of metal surfaces of objects, in which a mass of elements, including a quantity of objects having relatively rough metal surfaces, and a solution capable of reaction with the metal of the surfaces to produce an oxalate or a phosphate conversion coating of softer form thereon, are introduced into the container of a mass finishing unit and are agitated therein for a period of time to produce relative movement among the elements and to maintain the surfaces in a wetted condition with the solution, for conversion of any metal exposed thereon, on a continuous basis, so as to thereby effect a significant reduction in roughness by chemical and mechanical action; and in which the mass of elements is thereafter so agitated in such a unit with an aqueous burnishing liquid that is at least substantially inert to the metal, to effect removal of the conversion coating and substantial burnishing of the refined surfaces, wherein the aqueous burnishing liquid is formulated to contain 0.01 to 1.5 weight percent of a phosphate compound selected from the class consisting of water-soluble pyrophosphate and hexametaphosphate salts, and from 0.002 to 0.2 weight percent of an amphoteric organic slip agent surfactant, the liquid having a pH of 8.5 to 10.5 and the slip agent surfactant being adherent to the metal surfaces at the pH so as to provide lubricity thereto. The process may be carried out with the mass of elements subjected to vibratory action to produce the agitation, the solution, and subsequently the aqueous burnishing liquid, being supplied to the unit on a flow-through basis, and the solution and the aqueous burnishing liquid being oxygenated by the agitation. The mass of elements may include a quantity of solid media elements for assisting in the removal of the conversion coating from the surfaces during the agitation period. The media may be of high density, non-abrasive character, and the quantity of objects and the quantity of media elements may be present in the mass of elements in a volumetric, objects:media ratio of 0.1 to 3:1. The relatively rough metal surfaces may have an arithmetic average roughness (Ra) value of at least 0.5 micrometers (20 microinches) (preferably 0.5 to 2.5 micrometers (20 to 100 microinches)), the significant reduction producing a surface with an arithmetic average roughness value of 0.1 micrometer (4 microinches) or less (preferably 0.05 micrometer (2 microinches) or less), and the period of time being less than 10 hours, the arithmetic average roughness values being those that would be determined using a "P-5" Hommel Tester or equivalent apparatus. The rapid agitation may be carried out in a vibratory mass finishing unit operating at an amplitude of 2 to 4 millimeters. In the process according to the invention the surfaces may be of ferrous metal composition, and the solution may produce an iron oxalate conversion coating in reaction with the metal of the surfaces. The total concentration of organic constituents in the aqueous burnishing liquid is preferably not in excess of 0.1 percent by weight of the liquid, and most desirably it will be at a level of 0.05 percent by weight thereof, or lower. The aqueous burnishing liquid may contain 0.5 to 1.0 weight percent of the phosphate compound. The slip agent surfactant may be a tertiary amine containing at least one fatty chain, of 5 to 20 carbon atoms, and an active group selected from carboxylate and sulfonate groups. The slip agent surfactant may be a compound selected from the class consisting of imidazoline derivatives, betaines, sultains and aminopropionates. Preferably, the slip agent surfactant is an amphoteric imidazoline derivative. The phosphate compound may be tetrapotassium pyrophosphate. The aqueous burnishing liquid may additionally include a small amount of marginally soluble secondary surfactant. The process may be employed to particular benefit for objects having surfaces that include recessed areas that are inaccessible for contact by the solid media elements. The process is also advantageous in burnishing the metal surfaces to a specular condition. The solution, and thereafter the aqueous burnishing liquid, may be supplied sequentially to the container, the mass of elements remaining therein throughout the process. According to another aspect of the present invention there is provided an aqueous burnishing liquid for use in the physicochemical refinement and burnishing of metal surfaces of objects, comprising water, 0.01 to 1.5 weight percent of a water-soluble phosphate compound selected from pyrophosphate and hexametaphosphate salts, and 0.002 to 0.1 weight percent of a tertiary amine amphoteric slip agent surfactant consisting of an amphoteric imidazoline derivative containing at least one fatty chain and an active group selected from carboxylate and sulfonate groups, the aqueous burnishing liquid having a pH of 8.5 to 10.5. The total concentration of organic constituents is preferably less than 0.05 percent by weight of the liquid. The aqueous burnishing liquid preferably contains 0.5 to 1.0 weight percent of the phosphate compound. The phosphate compound may be tetrapotassium pyrophosphate. The aqueous burnishing liquid may additionally include a small amount of a marginally soluble secondary surfactant. According to a further aspect of the present invention there is provided an aqueous liquid concentrate for use, in diluted form, in the physicochemical refinement and burnishing of metal surfaces of objects, comprising: water, 180 to 360 grams, per liter of water, of a water-soluble phosphate compound selected from pyrophosphate and hexametaphosphate salts, and 2 to 30 grams, per liter of water, of a tertiary amine slip agent surfactant consisting of an amphoteric imidazoline derivative containing at least one fatty chain and an active group selected from carboxylate and sulfonate groups. The total concentration of organic ingredients is preferably less than 6 percent by weight of the liquid. The phosphate compound may be tetrapotassium pyrophosphate. Exemplary of the efficacy of the present invention is the following specific example: EXAMPLE ONE An aqueous solution is prepared from a mixture of 80 weight percent oxalic acid, 19.9 weight percent sodium tripolyphosphate, and 0.1 weight percent sodium lauryl sulfonate, the mixture being dissolved in water at a concentration of 60 grams per liter thereof. The bowl of a vibratory mass finishing unit, of straight-wall, open-top form and having a capacity of about 113 liters, is substantially filled with solid media and 115 wrenches, the latter being made of hardened, high-carbon steel and having handles that are knarled to provide a cross-hatch pattern with relatively deep recessed areas; flat areas are also present on the wrenches. The media employed is commercially available as a burnishing media, and is preconditioned, as necessary to remove sharp edges. It is the composition designated media "D" in the above-mentioned Michaud United States Patent No. 4,818,333, nominally composed of aluminum (77%), silicon (11%), iron (7%) and titanium (5%), on an oxygen-free basis, with grains about 1 to 25 microns in maximum dimension and of mixed platelet and granular shape. The elements of the media comprise a mixture of approximately equal amounts of cylinders, measuring about 1.3 cm in diameter, and flat triangles measuring about 1.0 cm on a side; they have a density of about 3.3 g./cm³, and a diamond pyramid hardness value of about 1130, as determined by ASTM method E-384 using a 1000 gram load and averaging three readings; the mass of elements has a bulk density of about 2.3 g./cm³. The vibratory finishing unit is operated for two hours at about 1,300 revolutions per minute and at an amplitude setting of 4 millimeters. The surface conversion solution is added at room temperature and on a flow-through basis (i.e., fresh solution is continuously introduced and used solution is continuously drawn off and discarded), at the rate of about 7.5 liters per hour. At the end of the refinement phase a heavy, black iron oxalate coating remains on the wrenches. Although not normally required as a practical matter, the bowl is flushed with twenty liters or so of the burnishing liquid that is to be employed in the second phase of the test. The wrenches are thereafter subjected to treatment for two hours under the same conditions as are employed in the first phase of the test, using however a liquid flow-through rate of about 44 liters per hour. Burnishing liquids of differing composition are employed in each of three runs, at the end of which the parts are inspected to assess effectiveness of removal of the black conversion coating from the recesses of the knarled areas, and also to evaluate brightness on the flat surfaces. In all instances the oxalate coating is found to have been removed entirely from the knarled areas in about 35 minutes of actual burnishing, and the surfaces exhibit an Ra value of about 2 to 4 microinches (about 0.05 to 0.1 micrometers). Part A The burnishing liquid contains 7.2 grams per liter of tetrapotassium pyrophosphate (TKPP), 0.03 gram per liter of oleic acid, and 0.4 gram per liter of cocoamphocarboxypropionate (a commercial product sold by Miranol, Inc. under the trademark MIRANOL C2M-SF), the balance being water; it has a pH of 9.8. The flat areas on the wrenches exhibit a high degree of brightness. Part B The burnishing liquid contains 7.2 grams per liter of TKPP, 0.014 gram per liter of sodiumlauryl sulfate, and 0.19 gram per liter of MIRANOL C2M-SF; its pH is 9.8. The flat areas are brighter than those produced on the wrenches treated with the burnishing compound of Part A. Part C The burnishing liquid contains 7.2 grams per liter of TKPP, 0.38 gram per liter of MIRANOL C2M-SF, and 0.017 gram per liter of nonylphenoxypoly(ethyleneoxy)ethanol surfactant (commercially available from GAF Chemicals Corporation under the trademark IGEPAL CO-710); the pH value is 9.8. The brightness level exhibited on the flat areas is somewhat higher than in Part B hereof. The principal ingredient of the burnishing liquid employed in the practice of the invention is a water-soluble pyrophosphate or hexametaphosphate salt. The preferred compound, from the standpoint of speed of reaction as well as solubility in the concentrated form, is tetrapotassium pyrophosphate. However, tetrasodium pyrophosphate and sodium hexametaphosphate may also be utilized, albeit less advantageously, and other phosphates, such as sodium acid phosphate and sodium tripolyphosphate, may be employed in combination with the foregoing. It has been found that aqueous solutions containing only a specified phosphate component (and especially tetrapotassium pyrophosphate) are effective to remove the black oxalate coating from ferrous metal surfaces under the agitation conditions described, and to do so without causing pitting or other chemical attack. Although appropriate concentrations of the phosphate component have been specified hereinabove, it might be noted that the lower limit is significant not only from the standpoint of providing adequate activity in dissolving the conversion coating, but also to avoid phosphating of the metal surface, which will tend to occur at phosphate compound concentrations below about 0.01 weight percent of the liquid. Such a result would obviously be unacceptable in the practice of the invention, since a primary objective is to remove all extraneous coatings that might interfere with plating or other surface treatment. The organic slip agent included in the burnishing liquid is effective to maximize the level of brightness produced. and to minimize microscopic scratching of the surface. Generic definitions of suitable agents have been set forth hereinabove; among the specific compounds that may advantageously be used as the slip agent constituent are the following: (1) as amphoteric carboxylated imidazoline derivatives, cocoamphoglycinate, cocoamphopropionate, cocoamphocarboxyglycinate, cocoamphoboxypropionate, lauroamphoglycinate, lauroamphocarboxyglycinate, lauroamphocarboxypropionate, caproamphoglycinate, caproamphocarboxyglycinate, caproamphocarboxypropionate, mixed amphocarboxylates containing 8 carbon atoms in the fatty chain, capryloamphocarboxyglycinate, capryloamphocarboxypropionate, tallamphopropionate, tallamphocarboxypropionate, stearoamphoglycinate, isostearoamphopropionate, cocoamphocarboxypropionic acid, lauroamphocarboxypropionic acid, mixed amphocarboxylic acid, containing 8 carbon atoms in the fatty chain and cocoamphocarboxypropionic acid: (2) as amphoteric sulfonated imidazoline derivatives, cocoamphopropylsulfonate, lauroamphopropylsulfonate, oleoamphopropylsulfonate, capryloamphopropylsulfonate, and stearoamphopropylsulfonate; (3) as amphoteric betaines, cocamidopropyl betaine, oleamidopropyl betaine, coco-betaine, oleyl betaine, and dihydroxyethyl tallow glycinate; (4) as amphoteric sultaines, cocamidopropyl hydroxysultaine and tallowamidopropyl hydroxysultaine; and (5) as aminopropionates, disodium lauriminodipropionate, sodium lauriminodipropionate, and disodium tallowiminodipropionate. It is believed that the slip agents employed are of such a nature as to be cationic to the metal surface at the prevailing pH, so as to adsorb thereon and afford lubricity thereto. It is important however that the tenacity of bonding not be so great as to preclude relatively facile removal of the slip agent, since that would interfere with subsequent treatment of the metal surface. Although the specified slap agents are effective alone to produce the desired lubricity, it may sometimes be beneficial to include secondary surfactants in combination with them; for example, the sodium lauryl sulfate and ethylene oxide/alcohol adduct employed in Parts B and C, respectively, of Example One are used to good effect. It is believed that the secondary surfactants function synergistically with the primary surfactants specified, and that they are effective because they exhibit marginal solubility in the system while, nevertheless, being stable in solution; normally, those compounds would be employed in the amounts set forth, or in somewhat lower concentrations. In some instances, ingredients such as methanol, xylene sulfate, or the like may also desirably be included in the formulation to enhance solubility. It should be borne in mind however that a primary attribute of the burnishing compounds provided in accordance with the present invention resides in the very low concentrations of organic constituents that they employ; i.e., about 0.1 weight percent or less based upon the working solution. It should also be borne in mind that the incorporation of excessive amounts of surfactants may lead to solubility problems (particularly in the concentrate) and to excessive foaming, as would tend to interfere with efficient operation. The balance of the burnishing liquids, apart from the ingredients specified, will of course consist substantially entirely of water. In its concentrated form, the burnishing liquid will of course contain a minimum proportion of water, as a matter of economics and convenience of transport. On the other hand, high concentrations of the ingredients will tend to cause instability, with either the phosphate or the organic constituents becoming insoluble in the aqueous phase, depending to an extent upon the specific ingredients employed. Thus, when tetrapotassium pyrophosphate is utilized the limiting factor will generally be the organic material; that is, when present in an appropriate ratio to the phosphate, the organic constituents will usually become insoluble first. The concentrate will normally be so formulated that admixture of about 1 to 3 percent by weight thereof with water will produce the working burnishing liquid. It goes without saying that the dilution level must be sufficient to provide adequate strength of the ingredients; moreover, use of a liquid that is overly dilute will require an excessive flow rate through the mass finishing unit. To be deemed effective as a practical matter, the concentration of active ingredients should be adequate to effect removal of the conversion coating from the objects in a period of one hour or less, and preferably in about one-half hour. In some instances however the rate of dissolution may be somewhat slower, and a period as long as two hours may be considered satisfactory under certain circumstances. The pH value of the burnishing liquid has a significant effect upon the results produced. The pH should be in the range 8.5 to 10.5. Should it be desirable to do so, pH adjustment can be made utilizing any appropriate reagent, such as potassium hydroxide or phosphoric acid. It is also believed that oxygenation is important to the proper functioning of the burnishing liquids. The conditions necessary are inherently satisfied in carrying out the process of the invention, wherein either an open or vented vibratory unit, or equivalent piece of mass finishing equipment, will be utilized. An aspect that is essential in certain embodiments of the invention is of course the utilization of a solution for converting the surfaces of the workpieces to a reaction product that is more easily removed than is the basis metal. This general concept is fully disclosed in the above-mentioned Michaud et al patent, and the formulations described therein can be utilized to good effect in the practice of the present invention. Other formulations that are highly effective for the same purpose are described and claimed in Zobbi et al United States Patent No. 4,705,594, issued November 10, 1987. The disclosures of the Michaud et al and Zobbi et al patents are hereby incorporated hereinto by reference, as appropriate to teach specific formulations for producing suitable conversion coatings. From the foregoing, and from the information herein set forth, it will be appreciated that a wide variety of compositions can be employed in the practice of the present invention, and the selection or development of specific formulations will be evident to those skilled in the art based thereupon. As indicated above, not only may the media elements be abrasive or nonabrasive; but they may also take a wide variety of sizes and shapes. Thus, they may be angle-cut cylinders, they may be relatively flat pieces that are round, rectangular or triangular, or they may be of indefinite or random shapes and sizes. Generally, the smallest dimension of the dense media elements referred to herein will not be less than about 0.6 cm, and the largest dimension will usually not exceed about 3 cm. The size and configuration of the elements that will be most suitable for a particular application will depend upon their density and upon the weight, dimensions and configuration of the workpieces, which will also indicate the optimal ratio of parts-to-media, as will be evident to those skilled in the art. In regard to the latter, an important function of the media is to ensure that the parts slide over one another, and that direct, damaging impact thereamong is minimized. Consequently, when the parts are relatively large and are made of a highly dense material a high proportion of media will be employed; e.g., a media:parts ratio of about 10:1, or even greater in some instances. On the other hand, when the workpieces are relatively small and light in weight they develop little momentum in the mass finishing apparatus, and consequently a ratio of parts-to-media of about 3:1 may be suitable. The preferred media for use in the instant process is the high-density, non-abrasive media described in Michaud United States Patent No. 4,818,333. The disclosure of that patent is hereby incorporated hereinto by reference, insofar as it describes such media and the use thereof. Although other kinds of mass finishing equipment, such as vented horizontal or open-mouth barrels, and high-energy centrifugal disc machines, may be used, the process of the invention will most often be carried out in an open-top vibratory finishing unit. Typically, the unit will be operated at 800 to 1.5000 rpm and at an amplitude of 1 to 8 millimeters; preferably, however, the amplitude setting will be at 2 to 4 millimeters. The unrefined metal surfaces of objects finished in accordance with the instant process may have an arithmetic average roughness value of 100 microinches (about 2.5 micrometers) or so, and can be refined by the process to a roughness value which is about 4 microinches (about 0.1 micrometer), and most desirably about 2 microinches (about 0.05 micrometer), or lower. Perhaps it should be pointed out that "arithmetic average roughness" expresses the arithmetic mean of the departures of the roughness profile from the mean line. Generally, the refinement procedure will require less than about ten hours, and in the preferred embodiments ultimate surface smoothness will be achieved in seven hours or less. The reactive solution and the burnishing liquid will normally be introduced into the mass finishing unit at room temperature, and may be-utilized in any of several flow modes; best results will often be attained however by operating on a continuous flow-through basis, as described above. Alternatively, the solution and liquid may be employed in a batchwise manner, or they may be recirculated through the equipment if so desired. Thus, it can be seen that the present invention provides a novel burnishing composition, and mass finishing method, by which metal-surfaced objects can be refined using a physicochemical technique, and can subsequently be burnished while simultaneously effecting the removal of residual conversion coating from the objects. More specifically, the composition and method of the invention enable the removal of such residual coatings from areas of the metal surface that are recessed, or are for other reasons inaccessible to contact by a solid element employed in a mass finishing process, and the surfaces can be brought to a condition of specular brightness in a desirably brief period of time and without etching or other adverse effect upon quality. An especially important benefit is that the invention provides a composition and method which produces a waste stream having a low chemical oxygen demand characteristic, and that is relatively easy to treat for the recovery of dissolved metal compounds. Furthermore, the burnishing liquid provided is composed of ingredients that are readily available and relatively inexpensive, and that can be prepared in the form of stable concentrates so as to make transport and use convenient and economical.

Claims: A process for the physicochemical refinement and burnishing of metal surfaces of objects, in which a mass of elements, including a quantity of objects having relatively rough metal surfaces, and a solution capable of reaction with the metal of said surfaces to produce an oxalate or a phosphate conversion coating of softer form thereon, are introduced into the container of a mass finishing unit and are agitated therein for a period of time to produce relative movement among said elements and to maintain said surfaces in a wetted condition with said solution, for conversion of any metal exposed thereon, on a continuous basis, so as to thereby effect a significant reduction in roughness by chemical and mechanical action; and in which said mass of elements is thereafter so agitated in such a unit with an aqueous burnishing liquid that is at least substantially inert to said metal, to effect removal of said conversion coating and substantial burnishing of the refined surfaces, characterised in that said aqueous burnishing liquid is formulated to contain 0.01 to 1.5 weight percent of a phosphate compound selected from the class consisting of water-soluble pyrophosphate and hexametaphosphate salts, and from 0.002 to 0.2 weight percent of an amphoteric organic slip agent surfactant, said liquid having a pH of 8.5 to 10.5 and said slip agent surfactant being adherent to said metal surfaces at said pH so as to provide lubricity thereto. The process of claim 1, characterised in that said process is carried out with said mass of elements subjected to vibratory action to produce said agitation, in that said solution, and subsequently said aqueous burnishing liquid, are supplied to said unit on a flow-through basis, and in that said solution and said aqueous burnishing liquid are oxygenated by said agitation. The process of claim 2, characterised in that said mass of elements includes a quantity of solid media elements for assisting in the removal of said conversion coating from said surfaces during said agitation period. The process of claim 3, characterised in that said media is of high density, non-abrasive character, and in that said quantity of objects and said quantity of media elements are present in said mass of elements in a volumetric, objects:media ratio of 0.1 to 3:1. The process of claim 4, characterised in that said relatively rough metal surfaces have an arithmetic average roughness value of at least 0.5 micrometers (20 microinches), in that said significant reduction produces a surface with an arithmetic average roughness value of 0.1 micrometer (4 microinches) or less, and in that said period of time is less than 10 hours, said arithmetic average roughness values being those that would be determined using a "P-5" Hommel Tester or equivalent apparatus. The process of any one of claims 2 to 5, characterised in that said rapid agitation is carried out in a vibratory mass finishing unit operating at an amplitude of 2 to 4 millimeters. The process of any one of claims 1 to 6, characterised in that said surfaces are of ferrous metal composition, and in that said solution produces an iron oxalate conversion coating in reaction with said metal of said surfaces. The process of any one of claims 1 to 7, characterised in that the total concentration of organic constituents in said aqueous burnishing liquid is not in excess of 0.1 percent by weight of said liquid. The process of any one of claims 1 to 8, characterised in that said aqueous burnishing liquid contains 0.5 to 1.0 weight percent of said phosphate compound. The process of any one of claims 1 to 9, characterised in that said slip agent surfactant comprises a tertiary amine containing at least one fatty chain and an active group selected from carboxylate and sulphonate groups. The process of claim 10, characterised in that said fatty chain contains 5 to 20 carbon atoms. The process of any one of claims 1 to 11, characterised in that said slip agent surfactant is a compound selected from the class consisting of imidazoline derivatives, betaines, sultains and aminopropionates. The process of claim 12, characterised in that said slip agent surfactant is an amphoteric imidazoline derivative. The process of any one of claims 1 to 13, characterised in that said phosphate compound is tetrapotassium pyrophosphate. The process of any one of claims 1 to 14, characterised in that said aqueous burnishing liquid additionally includes a small amount of marginally soluble secondary surfactant. The process of any one of claims 1 to 15, characterised in that said surfaces include recessed areas that are inaccessible for contact by said solid media elements. The process of any one of claims 1 to 16, characterised in that said process burnishes said metal surfaces to a specular condition. The process of any one of claims 1 to 17, characterised in that said solution, and thereafter said aqueous burnishing liquid, are supplied sequentially to said container, said mass of elements remaining therein throughout said process. An aqueous burnishing liquid for use in the physicochemical refinement and burnishing of metal surfaces of objects, comprising water, 0.01 to 1.5 weight percent of a water-soluble phosphate compound selected from pyrophosphate and hexametaphosphate salts, and 0.002 to 0.1 weight percent of a tertiary amine amphoteric slip agent surfactant consisting of an amphoteric imidazoline derivative containing at least one fatty chain and an active group selected from carboxylate and sulfonate groups, said aqueous burnishing liquid having a pH of 8.5 to 10.5. The liquid of claim 19, characterised in that the total concentration of organic constituents is less than 0.05 percent by weight of said liquid. The liquid of claim 19 or 20, characterised in that said aqueous burnishing liquid contains 0.5 to 1.0 weight percent of said phosphate compound. The liquid of any one of claims 19 to 22, characterised in that said phosphate compound is tetrapotassium pyrophosphate. The liquid of any one of claims 19 to 22, characterised in that said aqueous burnishing liquid additionally includes a small amount of a marginally soluble secondary surfactant. An aqueous liquid concentrate for use, in diluted form, in the physicochemical refinement and burnishing of metal surfaces of objects, comprising: water, 180 to 360 grams, per liter of water, of a water-soluble phosphate compound selected from pyrophosphate and hexametaphosphate salts, and 2 to 30 grams, per liter of water, of a tertiary amine slip agent surfactant consisting of an amphoteric imidazoline derivative containing at least one fatty chain and an active group selected from carboxylate and sulfonate groups. The concentrate of claim 24, characterised in that the total concentration of organic ingredients is less than 6 percent by weight of said liquid. The concentrate of claim 24 or claim 25, characterised in that said phosphate compound is tetrapotassium pyrophosphate.

Inventors: ZOBBI ROBERT GEORGE, ZOBBI, ROBERT GEORGE
Applicants: REM CHEMICALS INC, REM CHEMICALS, INC.
Application year: 1990
Main classification: C23F3
IPC codes: C23C22, B24B31, C09K3, C23F3