Patent Application
20060060265
The invention is directed to a combination of a conditioner bath and a calcium modified zinc phosphating solution containing hydroxylamine which provide an improved phosphate coating on the surface of ferrous metal articles.
Metal phosphate coating solutions are dilute solutions of phosphoric acid and other chemicals which are applied to the surface of metal; the surface of the metal reacts with the solution and forms an integral layer (on the surface of the metal) of substantially insoluble crystalline or amorphous phosphate. This layer is applied primarily for protection from corrosion, or as a base for the application of a second coating (e.g., paint), or for lubrication purposes. The metal substrate can be contacted with the acidic phosphate solution by immersion, spraying, roller coating, flowing and other means known for contacting a metal with an aqueous solution. Typical metal ions found in the metal phosphate coating solutions include iron, zinc, manganese, nickel, cobalt, copper and mixtures thereof; zinc, manganese and iron being preferred.
Numerous changes in such phosphate coating processes and compositions have been made since their early introduction. One improvement is the development of hydroxylamine accelerated phosphating baths, as taught in U.S. Pat. No. 5,234,509, incorporated herein by reference. Another development was the introduction of an activating pretreatment to increase the uniformity of the coating produced. One such activating treatment is taught in U.S. Pat. No. 2,310,239 to Jernstedt, incorporated herein by reference, in which the cleaned metal surface is first contacted with an aqueous dispersion of a dried disodium phosphate-titanium compound reaction product containing from about 0.005 to about 20 percent by weight titanium prior to contact with the subsequent phosphating solution. Improvements to the original Jernstedt invention are taught in U.S. Pat. Nos. 2,874,081; 4,539,051; and 5,326,408; the teachings of which are incorporated herein by reference.
Metal phosphate coatings are well known as being useful in the forming of metals. The metal phosphate coating, when applied to the surface of an article about to be subjected to formation, reduces the friction created by drawing or cold forming operations; the coating reduces the great amount of friction between the metal surface and the die. It is known in the art to use zinc phosphate coatings as a first lubricant over a ferrous metal surface to be subjected to forming operations. The conversion of the metal surface to a phosphate coating reduces this friction primarily by increasing the ability of the metal to retain a uniform film of lubricant over the entire surface. The ability to retain a second lubricant is critical to forming of hardened steels or in forming with high ratios of blank size to formed article size. The second lubricant prevents welding and scratching in drawing operations, and reduces metal to metal contact in cold forming operations. This reduction in friction allows shapes to be made by cold forming which would otherwise not be possible or practicable.
A relatively fine grain structure is desirable in the phosphate conversion coating, whether for use as corrosion protection, underlying paint or for cold forming. In cold forming, fine grain structure provides more even distribution of the grains which is considered to improve the adherence of the second lubricant and evenness of distribution of the second lubricant over the surface area of the workpiece.
In phosphating prior to painting, grain refinement in a zinc phosphate coating is typically obtained by use of a pre-phosphating conditioner treatment comprising titanium salt conditioners known in the prior art.
In the wire drawing industry, calcium is often included in the zinc phosphating bath to obtain grain refinement. Calcium modification is generally used, instead of conditioner pre-treatment, in the metal forming industry, as it provides benefits of enabling higher draw speeds and better tool life. Heretofore the use of a conditioner treatment comprising titanium salt conditioners as a pretreatment prior to phosphating with a conventional calcium modified phosphating bath has not been found to significantly improve grain refinement as compared to the use of either known conditioners alone or adding calcium alone.
The grains resulting from a calcium modified, zinc phosphating bath are typically small, nodular particles (approximately 1-10 microns) as compared to the coarse, irregular grains obtained by conversion coating with known zinc phosphating baths (approximately 50-200 microns). Finer grains provide a better carrier for the second lubricant that is applied prior to forming of the metal substrate. Also, the nodular grains are less likely than large angular crystals to break off and become a source of abrasive marring of the workpiece or the die during forming. Thus, heretofore in cold forming processes, calcium modification of phosphating baths has been used instead of pretreatment with a conditioning rinse to obtain grain refinement.
Typical metal phosphate coatings made from a calcium modified phosphating bath, for example a zinc phosphating bath, contain significant amounts of calcium, ranging from about 5-10 wt %. A drawback of including calcium in the coating is its effect on the second lubricant formed in the second lubricant bath. Generally, the second lubricant bath comprises a fatty acid, fatty acid salt, fatty acid soap or mixtures thereof, such as for example sodium stearate, that is reactive with the phosphate coating. It is desirable that some of the metal from the metal phosphate coating dissolves into the bath and is redeposited over the phosphate coating as a layer of metal stearate. A metal phosphate coating having significant amounts of calcium, i.e. 5-10 wt %, is less reactive with the second lubricant bath, for example the stearate salt, as compared to metal phosphate coatings that are not calcium modified. The lower reactivity results in less lubricant formation, which renders the second lubrication step less effective on calcium containing metal phosphate coatings. Also, while the metal stearate coating is adherent and provides lubrication for forming, in contrast calcium and sodium stearate are non-adherent. The poor adherence of calcium and sodium stearates causes flaking off of these stearates which reduces the amount of lubricant on the article to be formed and is a source of dust in the workplace.
Another drawback of including calcium in the phosphate coating is its effect on the second lubricant bath, itself. The calcium in the metal phosphate coating dissolves into the bath, forming calcium ions and calcium stearate. The ionic calcium tends to build up in the bath eventually requiring replacement of the bath.
Thus there is a need for a treatment process for lubricating workpieces prior to forming that provides good grain refinement in the first lubricant and an adherent second lubricant while avoiding the drawbacks of the prior art.
Applicants have discovered that a treatment process comprising: a conditioning bath comprising a titanium salt or other known conditioners; a first lubricant bath comprising a calcium modified zinc phosphating bath, optionally comprising hydroxylamine, work together to provide surprisingly fine-grained zinc phosphate coatings having low calcium content. In a preferred embodiment, the treatment process further comprises a second lubricant bath comprising a reactive salt, which reacts with the low calcium content zinc phosphate coating on the metal article to produce a second lubricant on the workpiece; the three treatments work together to provide finer grained phosphate coatings, longer life of the second lubricant bath, improved adherence of the second lubricant and less dust, as compared to a similar phosphating bath that is used alone or with a similar second lubricant.
Another aspect of the invention is a conditioner comprising the reaction product of a titanium compound and a phosphate compound in aqueous dispersion with at least one alkaline builder and a surfactant.
Another aspect of the invention is a process for lubricating a ferrous-base metal article in preparation for cold forming comprising the steps of: contacting the surface of the article with a conditioning rinse as disclosed herein; thereafter contacting the surface with a first lubricant which comprises an aqueous acidic zinc, manganese or zinc/manganese lubricating phosphate coating solution additionally containing hydroxylamine and calcium; thereby forming a phosphate coating on said metal article comprising less than 0.5 wt % calcium.
A further aspect of the invention is a process as described above further comprising contacting the surface with a second lubricant after phosphating.
Yet another aspect of the invention is an article of manufacture comprising: a ferrous-base metal article having an outer surface, a first lubricant layer deposited on said outer surface, the first lubricant layer comprising an zinc phosphate conversion coating comprising less than 0.5 wt % calcium and having an average grain size of 5-25 microns; and a second lubricant layer adhered to outer surfaces of said first lubricant layer, the second lubricant layer comprising the reaction product of at least one metal in the conversion coating and a reactive soap, fatty acid or fatty acid salt and mixtures thereof.
Another aspect of the invention is a process for the cold deformation of a ferrous-base metal article comprising the steps of: contacting the surface of the article with a conditioning rinse as described herein; thereafter contacting the surface with a first lubricant which comprises an aqueous acidic zinc, manganese or zinc/manganese lubricating phosphate coating solution additionally containing hydroxylamine and calcium; optionally, thereafter contacting the surface with a second lubricant which contains a fatty acid, fatty acid salt, fatty acid soap, or mixtures thereof; and thereafter subjecting the coated article to cold deformation.
In a further aspect of the above process, the second lubricant is selected from the group consisting of a C.sub.8 to C.sub.18 fatty acid, fatty acid salt, fatty acid soap, or mixtures thereof. Preferably, the second lubricant is selected from the group consisting of sodium stearate, potassium stearate, or mixture thereof. A yet further aspect is wherein the first lubricant comprises from 0.5 to 10.0 wt. % nitrate ion and from 0.01 to 10 wt. % hydroxylamine.
It is an object of the invention to provide a process for lubricating a ferrous-base metal article in preparation for cold forming comprising the steps of contacting a surface of the ferrous-base metal article with a conditioning rinse; thereafter contacting the conditioned surface with a first lubricant which comprises an aqueous acidic lubricating phosphate coating solution containing calcium, and optionally hydroxylamine, thereby forming a phosphate coating comprising less than 0.5 wt %, preferably less than 0.2 wt %, most preferably less than 0.1 wt % calcium on the surface of the metal article. A further object of the invention is to provide this process with the additional step of applying a second lubricant to the phosphate coated metal article. The process may provide a ratio of Ca:Zn ranging from about 0.05 to about 2. In another aspect of the invention calcium in the phosphating bath is present in amounts ranging between about 0.05-15 weight percent.
It is a further object of the invention to provide a process in which the conditioning rinse comprises the reaction product of a titanium compound and a phosphate compound in aqueous dispersion with at least one alkaline builder and a surfactant.
It is a yet further object of the invention to provide a phosphate coating having a platelet-type morphology with crystals ranging in size from about 5-25 microns.
Another object of the invention is to provide an article of manufacture comprising: a ferrous-base metal article having an outer surface, a first lubricant layer deposited on said outer surface, the first lubricant layer comprising a uniform layer of phosphate conversion coating comprising less than 0.5 wt % calcium and having an average grain size of 5-25 microns; and a second lubricant layer adhered to outer surfaces of said first lubricant layer, the second lubricant layer comprising reaction products of at least one metal in the conversion coating and at least one of a reactive soap, fatty acid and fatty acid salt.
It is a further object of the invention to provide an article of manufacture wherein the first lubricant layer comprises one or more of zinc phosphate, manganese phosphate, nickel phosphate, iron phosphate, or mixtures thereof.
It is a yet further object of the invention to provide an article of manufacture wherein crystals in the phosphate conversion coating have platelet-type morphology.
It is another object of the invention to provide a process for cold-forming a ferrous-base metal article comprising the steps of: contacting the surface of the ferrous-base metal article with a conditioning rinse; contacting the conditioned surface with an aqueous acidic phosphate coating solution containing effective amounts of calcium, and optionally hydroxylamine, thereby forming a phosphate coating, having a measurable coating weight, on said metal article comprising less than 0.5 wt % calcium and having an average grain size of 5-25 microns; optionally, coating the phosphate coated metal article with an excess of a second lubricant and drying the second lubricant on the phosphate coated metal article, thereby forming a measurable amount of reacted second lubricant on the article; and subjecting the coated article to cold deformation.
It is a further object of the invention to provide the process wherein the coated article's reactive lube efficiency prior to step (d) is greater than a similar coated article's reactive lube efficiency, said similar coated article being produced, without a conditioning rinse, under otherwise substantially identical phosphating conditions.
It is a further object of the invention to provide a process wherein the aqueous acidic phosphate coating solution comprises an aqueous acidic zinc, manganese or zinc/manganese lubricating phosphate coating solution.
Another aspect of the invention is a product made according to any of the afore-described processes.
Additional benefits and advantages of the present invention will become apparent upon a reading of the Detailed Description of the Invention taken in conjunction with the specific examples provided.
The present invention relates to a treatment process for conditioning and lubricating a ferrous-base metal article, and optionally forming the metal article, as well as articles of manufacture made according to the process and a preferred conditioner utilized in the treatment process.
The benefits and advantages of the present invention are achieved by conditioning the surface of the metal article with an activating conditioner, providing an integral phosphate coating upon the outer surface of the conditioned metal article from a phosphate coating solution which contains calcium and optionally hydroxylamine, and forming the article. In a preferred embodiment, before forming, the metal article is additionally contacted with a second lubricating compound after the phosphate coating is applied.
In the practice of the instant invention, a ferrous-base metal article is prepared for phosphating by contacting the surface with a titanium salt containing conditioning bath. Alternatively, other known conditioning baths, such as those taught in U.S. Pat. Nos. 6,214,132; 6,478,860; and 6,723,178; as well as co-pending U.S. patent application Ser. No. 10/250527, incorporated herein by reference, can be used. Thereafter, a lubricating phosphate coating is applied to the conditioned surface by contacting the surface with an aqueous acidic phosphate coating solution, which in addition to phosphate, contains one or more of the following ions: zinc, manganese, nitrate, nickel, ferrous, ferric, copper, fluoride, or mixtures thereof. Zinc, manganese and mixtures thereof are preferred. The aqueous acidic phosphate coating solution also comprises an amount of calcium which is effective in generating an at least partially nodular crystal morphology having particle sizes of 1-10 microns in a conventional aqueous acidic phosphate coating process. Optionally, the aqueous acidic phosphate coating solution contains an amount of hydroxylamine which is effective in increasing the rate at which the phosphate coating deposits from the solution. The resulting coated article may then be subjected to cold deformation or stored for later use.
The cold formation processes of the present invention employ a high-quality lubricating phosphate surface coating. The lubricating phosphate coatings deposited upon the surface of a ferrous-base metal article are uniquely suited for providing lubrication during such processes. The unique quality of these coatings is attributable to (1) their ability to provide lubrication alone during cold deformation processes and/or (2) their ability to retain a second lubricant or lubricating agent during such processes. The moderate to heavy coating which results is uniquely capable of providing lubricity thus increasing the efficiency of conventional cold deformation processes.
The terms “cold formation” and “cold deformation” are used interchangeably herein. By the use of these terms herein is meant any forming operations where the article (e.g., blank, slug or preform) about to undergo deformation enters the deformation process at a temperature appreciably below the recrystallization temperature, and preferably within 100.degree. C. of room temperature; and where any subsequent rise in temperatures is primarily due to the friction and/or heat from work hardening caused during deformation. Specifically contemplated by this term are cold extrusion, cold heading, and wire and tube pulling deformation operations.
The metal articles useful in the present invention are those which are ferrous-based, and which can be deformed at temperatures below their recrystallization temperatures. Preferred articles are steel articles with a carbon content less than about 1.0 percent, and preferably about 0.05 to about 0.6 percent by weight. However, as suggested above, the improved lubricant coatings provided in the cold deformation processes of the present invention allow the deformation of steels with higher alloy content, and greater hardness, than would otherwise be practicable.
Conversion coatings can be improved if, prior to contacting the metal to be phosphate coated with the acidic phosphate solution, the metal surface is first activated by contact with an aqueous conditioner. Suitable conditioners include known activating conditioners such as phosphates of di and trivalent metals, in particular titanium and phosphate containing compositions, as well as the compositions recited in co-pending U.S. patent application Ser. No. 10/250527. Preferred aqueous conditioners of the invention are mixtures comprising water and a reaction product of a titanium compound and a phosphate compound.
Conditioners comprising titanium compound-phosphate compound reaction products are known in the art. The titanium compound-phosphate compound reaction products generally contain from about 0.005 to about 25% by weight titanium. Generally, the conditioner is manufactured as a concentrate in either dry solid or liquid form. The dry solid concentrate contains titanium in the range of about 0.001 to about 25% by weight. The dry solid concentrate can be mixed into an aqueous concentrate and added to the conditioner bath or added directly to the conditioner bath. In one embodiment, an aqueous concentrate of the conditioner comprises titanium in an amount of about 10 to 15 g/l.
The amount of titanium required to activate the metal surface to be phosphated is significantly less than the amounts in the concentrates. To make the working bath, an amount of concentrate is selected to give the desired working concentration and is then mixed into a quantity of water. The working conditioner bath of the invention comprises an amount of titanium effective to provide grain refinement in the zinc phosphate coating produced by the phosphating solution. It is desirable that the concentration of titanium ions in the conditioning bath is, in increasing order of preference, at least about 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 25, parts per million (ppm) and not more than, in increasing order of preference, 100, 75, 50, 45, 40, 35, 32, 30, 29, 28 ppm. It is preferred that the concentration of titanium be at least 2 ppm. While concentrations of titanium greater than 50-100 ppm, may be used the higher amounts tend to increase drag out and cost.
In one embodiment, the working bath of the conditioner comprises an acid-resistant aqueous solution for activating metal surfaces for subsequent treatment in a zinc phosphate coating process having a concentration of titanium ions ranging from about 0.0002% up to about 0.05% by weight, which generally corresponds to a concentration of titanium of from about 0.1 to about 10 g/l in the aqueous concentrate.
The pH of the pretreatment or activating conditioning solution can range from about 7 up to about 11 with a pH of about 8.5 to about 10.5 being preferred. The activating solution can be applied to the metal substrate being treated by spray, immersion or flooding of which spray application is preferred. The period of treatment during which the activating solution is in contact with the metal surface can usually range from as low as about 15 seconds up to about 5 minutes or even longer without any adverse effects.
In a preferred embodiment the conditioner further comprises a surfactant and an alkaline builder. The surfactant can be any alkaline stable surfactant known in the art which does not interfere with the functioning of the conditioner. Non-limiting examples of suitable surfactants include amphoteric surfactants that are stable in strongly alkaline solutions. Examples of amphoteric surfactants useful in the invention include sulfonated wetting agents, betaines, and sultaines, such as Mirataine ASC and the like. Suitable surfactants include butylether hydroxypropyl sultaines, ethylhexylether hydroxypropyl sultaines, such as 2-ethylhexylether hydroxypropyl sultaine, and mixtures thereof. It is also desirable that the amphoteric surfactant is a low or non-foaming surfactant. Illustrative examples of sultaines that can be used in practicing the invention are disclosed in U.S. Pat. No. 4,891,159, which is hereby incorporated by reference. The preferred sultaines are alkylether hydroxylpropyl sultaines.
The alkaline builder in the conditioner can be any component known in the art that acts to increase the pH of the conditioner and render the conditioner resistant to lowering of the pH when small amounts of acid are added to the conditioner, and which does not interfere with the functioning of the conditioner. Examples of suitable alkaline builders include, but are not limited to soda ash, sodium hydroxide, potassium hydroxide and the like.
Preferred phosphate coating solutions for use in the practice of the present invention contain phosphate at a level of about 0.5 percent to about 8.0 percent, more preferably about 1.0 percent to about 7.0 percent, and even more preferably about 2.0 percent to about 4.0 percent by weight. This can be expressed as weight of [H3PO4] by weight solution.
The preferred phosphate coating solutions for use in the processes of the present invention contain zinc, manganese, or mixtures thereof. Of these, zinc (and the so-called high-zinc phosphating treatment solutions) are more highly preferred. The phosphate coating solutions containing zinc preferably contain a level of about 0.25 percent to about 7.5 percent by weight, and more preferably about 0.75 percent to about 5.5 percent zinc by weight. Highly preferred are levels of zinc of about 1.0 percent to about 3.0 percent by weight.
The phosphating solution is calcium modified, meaning that it comprises an amount of calcium effective to provide grain refinement in the zinc phosphate coating produced by the phosphating solution, such that the grains are finer than those produced by a similar phosphating solution that has no added calcium. Generally, the amount of calcium in the phosphating bath ranges between about 0.05-15 weight percent preferably between about 0.2-3 weight percent. It is desirable that the amount of calcium in the phosphating bath is, in increasing order of preference, at least about 0.01, 0.025, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and not more than, in increasing order of preference, 20.0, 18.0, 16.0, 15.0, 14.0, 13.0, 12.0, 11.0, 10.0, 9.0 weight percent.
It is desirable that the ratio of Ca:Zn ranges from about 0.05 to about 2. More particularly, the ratio of Ca:Zn in the phosphating solution is, in increasing order of preference, at least about 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 and not more than, in increasing order of preference, 2.0, 1.90,1.80, 1.70, 1.50, 1.40, 1.30, 1.20, 1.10, 1.0, 0.90, 0.85, 0.80, 0.75. It is desirable, in order to obtain the benefit of modification of the crystal morphology in the phosphate coating that the ratio of Ca: Zn be at least 0.1. While ratios of Ca:Zn higher than 2.0, may be used no additional benefit is achieved and the higher ratios tend to generate sludge and increase cost.
In a preferred embodiment, hydroxylamine is included in the phosphate coating solution. Hydroxylamine containing phosphating baths are described in U.S. Pat. No. 5,234,509, incorporated herein by reference. Hydroxylamine can be added to the phosphate coating solution from any conventional source. Any effective amount of hydroxylamine from any source may be employed in these phosphate coating solutions. By the term “effective amount”, as used herein, is means sufficient hydroxylamine (regardless of the source) to accelerate the coating process. That is, when two substantially identical phosphate coating solutions (differing only in that one contains an amount of hydroxylamine and the other does not) are compared, the solution with hydroxylamine either (1) increases the coating weight deposited over a given period of time or (2) decreases the time it takes the solution to deposit a given coating weight.
Preferably, the phosphate coating solutions employed in the processes of the present invention contain a concentration of hydroxylamine of from about 0.01 percent to about 10 percent by weight; similar concentrations expressed as weight percent of hydroxylamine per volume of use solution may be interchangeably employed as the use solutions are primarily aqueous having a specific gravity of about 1. More preferably, the hydroxylamine is present in the phosphate coating solutions of the present process at a level of about 0.01 percent to about 3.0 percent, and still more preferably at a level of about 0.05 percent to about 1.0 percent by weight.
While not being bound by theory, it is thought that the presence of hydroxylamine in the coating solutions employed in the processes of the present invention contribute to the quality of lubricating or lubricant-retaining phosphate coatings by increasing the level of metal (especially zinc) which is present in the resulting coating. This increases the lubricating properties of the phosphate crystals themselves. More importantly, however, the increased level of zinc in the coating increases the ability of the first lubricant coating to be reactive with a second lubricating agent, particularly those which contain a fatty acid or fatty acid soap. For example, when a phosphate coating containing zinc is contacted with a second lubricant containing sodium stearate, the available zinc reacts with stearate moieties. The resulting zinc hydroxy stearate is an excellent lubricant, much better than sodium stearate. Thus, when more available zinc is brought down in the coating (per gram of coating weight), more zinc stearate will react when the coating is contacted with a sodium or potassium stearate (soap) containing lubricant. This greater amount of zinc hydroxy stearate significantly increases the ability of the surface to retain the second lubricant—the additional zinc hydroxy stearate also significantly increases overall lubricity.
The preferred phosphate coating solutions for use in the present invention also contain nitrate at a level of about 0.5 percent to about 10 percent by weight, and even more preferably about 1.0 percent to about 7.5 percent by weight. In a highly preferred embodiment, a phosphate coating solution having a nitrate level of about 3.0 percent to about 7.0 percent by weight, is employed in the cold deformation process of the present invention.
One of the surprising features of the phosphate coating solutions employed in the practice of the present invention is the ability of these solutions to deposit coatings possessing a high concentration of zinc, even in the presence of ferrous (and ferric) ions. Thus, ferrous can be employed, either by deliberate addition, or by generation from the ferrous-base metal article being coated. If ferrous ions are present, it is preferred that they be present at a level of 0.05 percent to about 0.6 percent by weight. It will be appreciated that if no ferric iron is present, total iron can be used to determine the ferrous ion concentration; in the alternative, ferric and ferrous ion levels in solution must be determined.
In still another embodiment the phosphate coating solutions employed in the processes of the present invention contain nickel. The nickel is preferably present at a level of about 0.005 percent to about 0.1 percent by weight, and even more preferably present at a level of about 0.01 percent to about 0.05 percent.
When the metal articles are contacted with the phosphate coating solutions employed in the cold deformation processes of the present invention, the solutions are maintained at a temperature of about 130.degree. F. to about 205.degree. F., and more preferably at a temperature of about 160.degree. F. to about 190.degree. F.; the solutions are preferably maintained at a pH of about 1.8 to about 2.5 while in this temperature range.
The coating solutions can be applied by conventional methods; they are preferably applied by flooding or immersion, and most preferably immersion. The time of exposure or contact times for immersion can be from about 0.5 minutes to about 30 minutes, and is preferably about 5 minutes to about 15.
The weight of the lubricating phosphate coating to be applied to the surface of the ferrous-base metal article to be employed in the cold deformation processes of the present invention will vary with the severity of the deformation process, the size of the article, and other factors which can be easily evaluated by the skilled artisan. This would include such other factors as whether a second lubricant will be applied, and if so, the type to be applied. Preferably, the coating weights to be applied are in the range of about 250 to about 6000 milligrams of coating per square foot of metal surface. Coating weights of about 350 to about 4500 milligrams per square foot are more preferred, with coating weights of about 500 to about 3500 milligrams per square foot being even more preferred.
Another aspect of the invention is a metal article having at least one surface comprising a coating comprised of a reaction product of the metal article, preconditioned with the above-described conditioner, and the above-described phosphating solution. Surprisingly, a phosphate coating on the metal article comprises less than 0.5 wt % calcium, despite the concentration of calcium in the phosphating solution ranging from 1-10 wt %. Also, surprising is the crystal morphology of the resulting phosphate coating. It is known in the art that titanium conditioners provide grain refinement in phosphate coatings resulting in fine, needle like grains, and that additions of calcium to phosphating solutions result in small, nodular grains. The common understanding in the industry has been that pre-conditioning with a titanium salt conditioner and phosphating with a calcium containing phosphating solution produced nodular crystals typical of the calcium phosphating solution. Applicants' phosphate coating comprises crystals that are smaller than those provided by either titanium conditioning or calcium additions to the phosphating solution alone. The crystals in coatings of the invention have platelet-type morphology and range in size from about 5-25 microns.
The unique character of the coatings employed in one preferred embodiment of the present invention result from the combination of the conditioner and the phosphate coating being deposited from a hydroxylamine-containing phosphate coating solution that has been modified by the addition of calcium. Other embodiments include those that omit hydroxylamine from the phosphate coating solution.
In a preferred embodiment, the coated article which will eventually undergo cold deformation is contacted with a second, conventional cold forming lubricant. This can be done immediately after coating (or rinsing), at press side immediately before formation, or during part or all of the cold deformation process (conjointly).
The second lubricant can be a soap, oil, drawing compound, or an emulsion of an oil and fatty acid, fatty acid salt, or soap. The second lubricant preferably contains a C.sub.8-C.sub.18 fatty acid or fatty acid salt or soap at a level of about 3 percent to about 15 percent by weight; more preferably, the second lubricant contains a soap selected from sodium stearate, potassium stearate, or mixtures thereof. As suggested before, these soaps are preferred because of their ability to react with the increased zinc levels found in the phosphate coatings employed in the present invention. The resulting zinc hydroxy stearate provides a highly preferred lubricant for cold deformation processes.
In addition to the critical steps and preferred embodiments expressively recited above, a metal article subjected to the cold deformation process of the present invention may be additionally subjected to many conventional or commercial processes such articles ordinarily undergo. For example, the metal article may undergo precoating cleaning and rinsing steps as needed to remove debris and to prepare the metal surface for the phosphate coating; the articles may also be pickled prior to coating. The metal articles subjected to the processes of the present invention may also undergo conventional post-coating processes, either before the optional application of a second lubricant, or before the cold deformation step, or both. For example, in a preferred embodiment the phosphate-coated metal article is rinsed shortly after coating with a dilute, alkaline, chromium-free neutralizing rinse. Drying after processing or between operations may be effected by conventional techniques such as forced air or flash drying.
In a highly preferred embodiment, a metal article is (1) cleaned; (2) rinsed with hot water; (3) contacted with the conditioner of the invention (4) contacted with an aqueous acid phosphate coating solution containing effective amounts of calcium and hydroxylamine; (5) rinsed with cold water; (6) contacted with an excess of a second, sodium stearate-based lubricant and (7) flash dried. Even more preferably a conventional pickling step is included in the process. The coated article may then be subjected to cold deformation either immediately, or after being stored until needed for the deformation step.
In order to further illustrate the benefits and advantages of the present invention, the following specific examples are provided. It will be understood that the examples are provided for illustrative purposes and are not intended to be limiting of the scope of the invention as herein disclosed and as set forth in the claims.
Specimens: 4″×6″ steel panels, 4130 alloy
Phosphate Bath 1 Preparation:
Into 75 gallons of water were mixed 150 pounds of Phosphate Makeup Mix 1 containing the components listed in Table A measured in weight percent:
and 70 pounds of calcium nitrate. Sufficient water to make 100 gallons of working solution was then mixed in. Sufficient heat was added to bring the bath to the operation temperature. Total Acid=34.8, Free Acid=5.9
Specimen Coating Processes:
With Conditioner. “Phosphate Only”. The specimen was treated according to the following:
With Conditioner, “Phosphate+Lube”. The specimen was treated as in Steps 1-7 of Example 1A, followed by:
No Conditioner, “Phosphate Only”. The specimen was treated as in Steps 1-8 of Example 1A, except the conditioner step was omitted.
No Conditioner, “Phosphate+Lube”. The specimen was treated as in Example 1B, except the conditioner step was omitted.
Results:
Photos of the phosphate coatings of Examples 1C and 1A were taken using Scanning Electron Microscope (“SEM”), see
Coating weight results for phosphate, unreacted lube (e.g. calcium or sodium stearate) and reacted lube (i.e., zinc stearate) are given for Example 1B and comparative Example 1D in Table 1-1 below.
**Reactive Lube Efficiency = Reacted Lube Coating Weight ÷ Phosphate Coating Weight
The conditioning step prior to coating in a calcium modified phosphating bath (Example 1B) showed the improvement in coating weight and reacted lube efficiency, as compared to calcium modified phosphating in the absence of the conditioning step.
Specimens: 4″×6″ steel panels, 4130 alloy
Phosphate Bath Preparation:
Phosphate Bath 2 was prepared according to the process described above for Phosphate Bath 1. Total Acid=33.0, Free Acid=5.7, operating temperature=180° F. The acid number differences between Phosphate Baths 1 and 2 are considered to be typical experimental variations.
Comparative Phosphate Bath 2* (Comparative Example—No Calcium added). Into 75 gallons of water were mixed 175 pounds of Phosphate Makeup Mix 2 containing the components listed in Table B measured in weight percent:
Sufficient water to make 100 gallons of working solution was then mixed in. Sufficient heat was added to bring the bath to the operation temperature. Total Acid=25.5, Free Acid=3.1, operating temperature=145° F.
Specimen Coating Processes:
The conditioner used in this example was “acid resistant” Conditioner 2, in place of the commercially available product used in Example 1. Conditioner 2 was made from a dry concentrate of 10 wt % caustic soda, 25% Na2CO3, and 10% alkylether hydroxylpropyl sultaine, the balance to 100% being made up of the reaction product of a titanium compound and a phosphate compound comprising approximately 1 wt % titanium. The working concentration of Conditioner 2 was 4 g/L. The processes for Examples A, B, C and D described in Example 1 were used in Examples 2A, 2B, 2C and 2D for Phosphating Bath 2, respectively and for Examples 2*A, 2*B, 2*C and 2*D for Comparative Phosphating Bath 2*, respectively.
Results
Photos of the phosphate coatings of Example 2B and comparative Examples 2*B (conditioner but no calcium), 2D (calcium but no conditioner) and 2*D (no conditioner, no calcium) were taken using Scanning Electron Microscope (“SEM”). The results were similar to those found in Example 1. Comparing the morphology of comparative Examples 2*B, 2D and 2*D to that of Example 2B, shows that conditioning prior to phosphating with a calcium-modified, HAS accelerated phosphating solution provides significant improvement in grain uniformity and coverage. Examples 2*D produced large coarse grains with uneven coverage. Example 2*B showed coarse grains that were smaller than those of Example 2*D. Example 2D produced a combination of small nodular and large coarse grains. Example 2B showed good overall coverage, excellent uniformity, and a significantly finer grain than even Example 2D.
X Ray Fluorescence (“XRF”, also known as “EDAX”) spectra were run on the phosphate coatings of Examples 2C and 2A, with substantially no calcium appearing in Example 2A and a significant calcium spike indicating the presence of calcium in the coating of comparative Example 2C. Despite having the same amount of calcium in the phosphating bath, significantly lower amounts of calcium are present in the phosphate coating.
Coating weight results for phosphate, unreacted lube (e.g. calcium or sodium stearate) and reacted lube (i.e., zinc stearate) are given for Example 2B and comparative Examples 2*D, 2*B and 2D in Table 2-1 below.
Omitting calcium from Phosphate Bath 2* for Examples 2*B and 2*D resulted in lower reacted lube efficiency and excess coating weight. Similar results were produced by the calcium containing phosphate bath of comparative Example 2D in the absence of the conditioning step. The combination of a conditioning step prior to coating in a calcium modified phosphating bath showed the most improvement in coating weight and reacted lube efficiency.
Specimens: 4″×6″ steel panels, 4130 alloy
Phosphate Bath Preparation:
Phosphate Bath 3: As described in Example 1 for Phosphating Bath 1. Total Acid=33.0
Comparative Phosphate Bath 3*: As described in Example 2 for Comparative Phosphate Bath 2*. Total Acid=25.0
Specimen Coating Processes
No lubed panels were produced for this example. The procedure as described in Example 1 for the Specimen Coating Process for Example 1A, meaning conditioning, phosphating and no lube and the Specimen Coating Process for Example 1C, meaning phosphating, no conditioner and no lube were used in this example.
The conditioner used in this example was “acid resistant” Conditioner 2, in place of the commercially available product used in Example 1. The working concentration of Conditioner 2 was 4 g/L.
In addition, an “aged” pickle was prepared for the purpose of adding it as a contaminant to the Conditioner 2 bath. The aged pickle simulated a well-used pickling bath in a customer facility and comprised: 10% v/v concentrated sulfuric acid; Rodine 195, a commercial acid inhibitor comprising 30-60 wt % glycol ethers available from Henkel Corporation at 0.25% v/v of the concentrated acid used (i.e., 0.025% of the working bath); 20% w/v of ferrous sulfate heptahydrate to give a ferrous iron concentration of 4%. The pickle was maintained at 160° F. to keep the iron completely solubilized.
Panels were prepared with Phosphate Bath 3 and 3* for each of no conditioner, uncontaminated conditioner, and specimens were processed at various levels of contamination in the Conditioner 2 bath. Contaminant levels (as mL of “Aged Pickle” added per liter of conditioner bath), bath pH, iron concentration and any additions of conditioner made in to adjust pH are given in Table 3-1.
Results
Scanning Electron Microscope (“SEM”) photos showing crystal morphology were taken for products of Phosphate Bath 3 and 3* produced in the absence of conditioner, and the presence of conditioner contaminated at various levels as shown in Table 3-1. Comparing the morphology of coatings from Phosphate Bath 3 and 3*, further supports the conclusions from Examples 1 and 2 regarding calcium modification and conditioning. That is, the SEM photos show that conditioning prior to phosphating with a calcium-modified, HAS accelerated phosphating solution provides significant improvement in grain uniformity and coverage regardless of conditioner contamination. Contamination of the conditioner bath results in even finer grain size in products of both baths. Products made with Phosphate Bath 3 and Conditioner 2 with contamination of 1-3 ml/l contaminant also show platelet type morphology which is different from the morphology of the comparative examples.
X Ray Fluorescence (“XRF”, also known as “EDAX”) spectra were also run on the phosphate coatings of Phosphate Bath 3 produced in the absence of conditioner, and the presence of conditioner contaminated at various levels as shown in Table 3-1. Substantially no calcium appeared any of the spectra, regardless of the level of contamination.
Phosphate coating weights for Phosphate Bath 3 and 3*are given in Table 3-2.
Coating weights show a downward trend as the conditioner becomes more contaminated, but coating weights remain within acceptable limits in panels from both phosphating baths.
Specimens: Steel billets, 1.25″ height×1.25″ diameter, AISI 1018
Phosphate Bath Preparation:
Phosphate Bath 4: As described in Example 1 for Phosphating Bath 1. Total Acid=36.1, Free Acid=6.3. Bath was “aged” by repeatedly processing 1008 alloy panels through the bath until a total throughput of 20 ft2/gallon had been reached. Iron concentration in the bath after aging was 0.17%.
Comparative Phosphate Bath 4*: Into 75 gallons of water were mixed 175 pounds of Phosphate Makeup Mix 3 containing the components listed in Table C measured in weight percent:
Sufficient water to make 100 gallons of working solution was then mixed in. Sufficient heat was added to bring the bath to the operation temperature. Total Acid=40.3, Free Acid=7.5. Bath was aged as described above to a total of 20 ft2/gallon of throughput. Iron concentration was 0.17% after aging.
Specimen Preparation Procedures:
Phosphate Bath 4: The specimen was treated according to the following:
Comparative Phosphate Bath 4*: Same procedure as for Phosphate Bath 4, except the conditioner was replaced by a hot water dip at 120° F.
Results
Scanning Electron Microscope (“SEM”) photos showing crystal morphology were taken for “Phosphate only” products of Phosphate Bath 4 with Conditioner 2 and on Comparative Phosphate Bath 4* produced in the absence of conditioner. Crystal morphology for the panel conditioned prior to phosphating was finer and more uniform than the comparative example.
X Ray Fluorescence (“XRF”, also known as “EDAX”) spectra were also run on the “Phosphate only” coatings of Phosphate Bath 4 with Conditioner 2 and on Comparative Phosphate Bath 4* produced in the absence of conditioner. Both spectra were substantially the same, that is nearly flat, in the area where a calcium spike would be expected. Hence substantially no calcium appeared to be present in either of the phosphate coatings, despite the fact that Phosphate Bath 4 contained calcium.
Phosphate coating weights are given in Table 4-1.
The phosphated and lubed panels produced by conditioning the panel and coating in calcium-containing Phosphate Bath 4 showed improvements in reacted lube efficiency. The unconditioned and non-calcium modified comparative example showed excess coating weight and a lower reacted lube efficiency. The combination of a conditioning step prior to coating in a calcium modified phosphating bath showed marked improvement in coating weight and reacted lube efficiency, as well as morphology.
Specimens: 4″×6″ steel panels, 1008 alloy
Specimen Preparation Procedures:
Panels were processed at an industrial facility. An additional set of panels was processed in the same manner with a competitive zinc phosphate/soap process at the same facility. At the time these specimens were run, the conditioner bath had been in use for about 3 days and thus was in a non-pristine (i.e., contaminated) state.
Process Cycles:
A: Conditioner 2/Phosphating Bath 5 made as described in Example 1 for Phosphating Bath 1: “Normal Process”
B: “Phosphate Bath 5 Only” Process (Comparative): Process A with the omission of steps 3 and 5.
C: “Phosphate Bath 5, No Pickle” Process: Process A with the omission of step 3.
D: “Normal Competitive” Process (Comparative): Process A with the omission of the conditioner step (Step 5). The panels were processed in a commercially available phosphate (a non calcium-modified, “nitrite side” zinc phosphate) and lube (a reactive, sodium stearate-based soap similar in composition and concentration to Bonderlube 234).
E. “Competitive, No Pickle” Process(Comparative): Same as D with the omission of the pickle stage.
Results
Scanning Electron Microscope (“SEM”) photos showing crystal morphology were taken for products according to each of Processes A-E. Crystal morphology for the coating produced using Process A, according to the invention, with pickle, showed fine platelet type crystals and uniform coverage of the panel. Comparative Process B, that is the no pickle, no conditioner panels phosphated with a calcium-modified phosphate bath, showed small nodular crystals with a scattering of large coarse crystals; the coating was not as uniform as that of Processes A or C. Process C, according to the invention, without pickle, showed finer crystals than Process A, having a platelet-type morphology. Very uniform coverage of the panel was seen in panels of Process C. The effect of pickle v. no pickle is less significant than the effect of conditioner v. no conditioner. Comparative Process D, using a commercially available, non-calcium modified phosphating treatment, with pickling showed coarse crystal morphology consistent with prior art phosphating. Without the pickle step, of Comparative Process D, very large coarse crystals and non-uniform coverage were produced by Comparative Process E.
X Ray Fluorescence spectra were run on the phosphate coatings of Processes A-C. Processes D and E did not use calcium modified phosphate baths and XRF for calcium in the coatings were not run. No calcium appeared in the spectra of panels made using Processes A and C, according to the invention. In the absence of the conditioning step, Process B produced panels with calcium in the phosphate coating.
Phosphate and lube coating weights for panels of Processes A-E are given in Table 5-1.
Phosphate baths which are not calcium-modified, used in Processes D and E with no conditioning step, resulted in low reacted lube efficiency and excess coating weight. The use of a calcium containing phosphate bath in the absence of the conditioning step in Process B improved the reacted lube efficiency and lowered coating weight. Both Processes A and C, using a calcium containing phosphate bath and a conditioning step produced reacted lube efficiency and coating weights that were better than Process B results. Process C, pickling prior to conditioning and phosphating resulted in somewhat less of an improvement over Process B. The combination of a conditioning step prior to coating in a calcium modified phosphating bath showed the most improvement in coating weight and reacted lube efficiency.
Specimens: 4″×6″ steel panels, 1008 alloy and 4130 alloy
Phosphate Bath Preparation:
Phosphate Bath 6: As described in Example 1 for Phosphating Bath 1. Total Acid=36.0, Free Acid=6.4.
Specimen Preparation Procedures:
Process “A” as described in Example 1A.
Coated panels were divided into two groups. One group was used to obtain SEM photos and XRF spectra of the Phosphate Bath 6 coatings while the second group was used to determine the composition of the phosphate coating by wet analytical chemistry methods.
Results
Scanning Electron Microscope (“SEM”) photos showing crystal morphology were taken for coatings produced from Phosphate Bath 6 on panels of 1008 alloy and 4130 alloy. The photos showed uniform coating of panels for both alloys. The phosphate coating on the 1008 alloy showed platelet type crystals. The phosphate coating on the 4130 alloy appeared slightly different with more flat, platy type crystals.
X-Ray Fluorescence spectra were run on these phosphate coatings. Both spectra were substantially flat in the area where a spike indicating the presence of calcium would be expected, showing that no detectable calcium from the phosphating bath was present in the coatings. Wet chemistry results for coating compositions on the 1008 and 4130 alloys are given in Table 6-1, confirming that very small amounts of calcium are included in the coatings.
**Detection limit for calcium was 0.1%.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/612,134 filed Sep. 21, 2004, incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60612134 | Sep 2004 | US |
