US3356540A - Method of phosphatizing articles - Google Patents

Description

Dec. 5, 1967 v J. POKORNY 3,356,540

METHOD OF PHOSPHATIZING ARTICLES Filed May 28, 1964 2 Sheets-Sheet 1' %1/222502 Joseph P0140172 De c. 5, 1967 Filed May 28, 1964 J. PQKORNY METHOD OF PHOSFEATIZING ARTICLES 2 Sheets-Sheet 2 fi/efifor (7056 012 pokorzzz/ l M? d WWW I n 054 United States Patent 3,356,540 METHOD OF PHOSPHATIZING ARTICLES Joseph Pokorny, Lincolnwood, Ill., assignor, by mesne assignments, to Baron Industries of California, Los Angeles, Calif., a corporation of California Filed May 28, 1964, Ser. No. 371,019 5 Claims. (Cl. 148-615) This invention relates to treatment of articles to be painted or coated, and has to do with means for and a method of conditioning for such treatment articles formed of appropriate metal-s.

It is known to subject metal articles which are to be coated to a cleanig operation in a degreasing machine in which the articles are subjected to the action of a grease solvent. In some degreasing machines the articles are dipped in a body of a volatile solvent heated to its boiling point and are withdrawn from the liquid solvent through a layer or zone of solvent vapor confined above the liquid solvent. In other degreasing machines hot liquid solvent may be sprayed onto the articles which may then be passed through a zone of solvent vapor. There also are degreasing machines which combine both dipping the articles into hot liquid solvent and spraying them with hot solvent, after which the articles are passed through a layer of solvent vapor. The solvent commonly used is a chlorinated hydrocarbon, usually trichlorethylene, though other solvents of like nature may be used. In the deg-reasing operation, the articles are thoroughly cleaned by removal of all grease as well as particles of foreign materials.

It has been found that degreasing of the articles, while it leaves them in a thoroughly clean and grease free condition, does not place them in the best condition for painting or analogous coating operations. The surfaces of the degreased articles are clean and smooth and some coating compositions do not readily adhere to them. In order to avoid that difliculty it has been proposed to phosphatize the degreased articles. That is accomplished'by subjecting them to the action of phosphoric acid in solution in a chlorinated hydrocarbon, such as trichlorethylene. Phosphoric acid is not readily soluble in trichlorethylene, to which non-volatile substances, commonly termed solubilizers, and stabilizers are added, to produce a solventphosphatizing solution or 'bath in'which the concentration of phosphoric acid is quite low.

A phosphatizing bath used in practicing my invention comprises approximately 920 pounds of a product sold under the trade name of TricleneL and approximately 160 pounds of a product sold under the trade name of Triclene-R, with a small amount, approximately 1.5% by weight, of a phosphoric acid solution, known as 85% N.F., added. The two products Triclene-L and TricleneR are produced and sold by E. I. Du Pont de Nemours and Company, of Wilmington, Del., under the trade names stated, and are well known and extensively used in phosphatizing operations. Each of such products is comprised largely of trichlorethylene. In use Triclene-L is added to the bath to replace evaporative losses and phosphoric acid solution is added, as required, to maintain the concentration of phosphoric acid at the desired concentration. The relative amounts of the constituents of the bath may be varied, within permissible limits, to suit operating conditions, as will be understood.

The solvent-phosphatizing solution or bath is heated to the boiling point of the solvent .and the degreased articles are subjected to the action of the hot liquid bath either by dipping or spraying, or both. Thereafter, the articles are removed from the treating machine through a layer or zone of solvent vapor. The acid of the bath attacks the surfaces of the articles producing a slight etching effect or roughness which has proved to be highly effective in 3,356,540 Patented Dec. 5, 1967 assuring adherence of the paint or analogous coating material applied to such treated articles. While the treatment of the degreased articles in the manner stated is highly efl'lcient in assuring adherence of the coating material, it introduces a further difficulty. Unless all traces of the phosphatizing bath are removed from the articles, it is practically impossible to obtain an entirely satisfactory coating on the articles. During passage of the articles through the vapor zone they are at a temperature as high, or higher than, the solvent vapor. Accordingly, there can 'be no vapor condensation on the articles and streaks of non-volatile constituents of the bath and of phosphoric acid remain on the articles. If the articles be painted or coated in that condition, the coating will be streaked and discolored, and the phosphoric acid, accumulating in beads or droplets, will cause the paint to be burned, particularly if it is baked.

My invention is directed to avoiding the above noted difiiculties encountered in the presently known method of phosphatizing, above mentioned. To that end I provide means and a method whereby in phosphatizing articles all traces of the phosphatizing bath are effectively removed from the articles during that operation. Further objects and advantages of my invention will appear from the detail description.

. In the drawings:

FIGURE 1 is a front view, partly broken away, of a phosphatizing machine embodying my invention;

FIGURE 2 is a plan view of the machine of FIGURE 1;

FIGURE 3 is an end view, part-1y broken away, of the machine of FIGURE 1; and

FIGURE 4 is a fragmentary side view, partly broken away, of a modified form of phosphatizing machine embodying my invention.

The machine of FIGURES 1 to 3, inclusive, is, in general, of known construction except as to those features relating to my present invention. It comprises a suitably constructed tank 5, the lower portion of which provides a sump containing a body of a phosphatizing liquid bath, the solvent content of which may be assumed to be trichlorethylene, for purposes of description. Heating coils 6, at the bottom of tank 3, are immersed in the liquid bath and a heating medium, conveniently steam, is circulated through coils 6 in a suitable known manner. The tank 5 is open at its top and is preferably provided therebelow with an exterior narrow cooling jacket 7. A cooling coil 8 is disposed at the inner faces of the walls of tank 5, substantially in the plane of jacket 7. Cold water is circulated through jacket 7 and cooling coil 8 in a suitable known manner.

- The cooling coil overlies a trough 9 formed in part by the walls of tank 5. Trough 9 is inclined downward toward one end, the left end as viewed in FIGURE 1, of tank 5 and the left end of the trough is inclined downward toward the front of the tank. The cooling coil 8 is disposed a substantial distance above the surface of the liquid bath in the bottom of the tank. That provides a space or vapor zone of substantial depth extending from the top surface of the liquid bath. The body of liquid bath is heated, by the heating coils 6, to the boiling point of the solvent of the bath, assumed to be trichlorethylene, approximately 188 F. at atmospheric pressure. The other constituents of the bath are not volatile and the space between the surface of the liquid and the cooling coil 8 becomes filled with pure solvent vapor the upper level of which is determined by the cooling coil -8 and jacket 7, which precludes escape of the vapor through the open top of the tank.

The solvent vapor condenses on the cooling coil 8 and drips into the trough 9. The condensate flows along the trough 9 to a well 10 at the front left corner of tank 5.

The condensate flows from well 10 through a short conduit 11 into a water separator 12 of known type, such as that disclosed, for example, in the patent to Edward L. Blakeslee, No. 2,223,595. The trichlorethylene condensate is approximately one and one half times as heavy as water and sinks to the lower portion of the separator 12, the Water floating on top of the trichlorethylene and being discharged through an outlet at the top of the separator. In that manner, atmospheric moisture absorbed by the solvent vapor is separate from the latter, leaving pure solvent in the lower portion of the separator 12.

The pure solvent is delivered from separator 12, at a point a short distance from the bottom thereof, through a conduit 13, to a condensate receiving tank 14 suitably mounted on the main tank adjacent the front left corner thereof. The pure solvent condensate is delivered, through a conduit 15 to the intake of a centrifugal pump 16 driven by an electric motor 17. The discharge of pump 16 is connected by a conduit 18 to a header 19 extending across the end of tank 5 remote from pump 16, at the outer face thereof. Two spray pipes 20 extend from the ends of header 19 into tank 5, at the inner faces of the side walls, for substantially the full length thereof, and a substantial distance below the trough 9.

The articles to be phosphatized, after being degreased and cleaned in the known manner above briefly explained are dipped in the liquid phosphatizing bath and are then raised into position in the vapor zone, between the spray pipes 21. In FIGURE 3 an article a, which has been dipped in the liquid bath, is shown as suspended, by a line or hanger 1), between the spray pipes 20. While suspended in that position it is subjected to sprays of pure solvent projected from pipes 20, as indicated. The solvent sprays quickly remove from the article all traces of the constituents of the bath, other than the trichloret-hylene. The article, after spraying, is withdrawn from tank 5 through the upper portion of the vapor zone. Any trichlorethylene remaining on the withdrawn article quickly evaporates leaving the article in a dry and clean condition with no traces of the bath present and with a surface slightly roughened or etched by the phosphoric acid of the bath. Extensive tests have demonstrated that articles treated in the manner stated may be painted or coated and that a smooth and unblemished finish is assured.

In the modified form of my invention shown in FIG- URE 4, a pump 25, driven by an electric motor 26, has its intake connected to tank 5, a short distance above the bottom thereof, by a conduit 27. The discharge of pump 25 is connected, by a conduit 28, to the inlet of a heat exchanger 29 of conventional type. The outlet of heat exchanger 29 is connected by conduit 18a to a header corresponding to header 18 of FIGURES l to 3, inclusive, and spray pipes 20a extend from the ends of the header at the inner faces of the sides of tank 25, as before. The spray pipes 20a preferably are disposed a greater distance below the trough 9 than in FIGURES 1 to 3.

A cooling medium, at a low temperature, such as a brine solution, is circulated through the heat exchanger 29, which may be provided with pressure and temperature controls and other accessories of conventional type, not shown. The hot bath liquid is withdrawn from tank 5 by pump 25 and, after passing through the heat exchanger 29, is delivered under appropriate pressure to the spray pipes 20a. In passing through the heat exchanger, the liquid of the bath is cooled to a temperature substantially lower than that of the solvent vapor in the vapor zone, to approximately 120 to 140 -F., the temperature of the vapor approximating that of the bath, about 188 F. The article is dipped in the hot bath and is then raised to position between the spray pipes 20a, where it is sprayed with the relative cold bath liquid. That reduces the temperature of the article well below that of the surrounding solvent vapor. The relative cold article is then raised above the spray zone, or the spray may be cut off, and is held for a short time in the solvent vapor. The relatively hot vapor quickly condenses on the relatively cold article and drips therefrom, removing all traces of the bath liquid other than the pure solvent of the condensate. Thereafter the article is removed from tank 5 and any condensate remaining on the article quickly evaporates, leaving the article in a dry and thoroughly clean condition with a slightly roughened or etched surface, as before, assuring a smooth and unblemished coating finish. In the method performed by the machine of FIGURE 4, the phosphatized articles are subjected to the action of pure solvent deposited thereon as and for the purpose described. In both methods the final cleansing of the articles is accomplished by pure solvent deposited thereon, either as sprays, as in the first described method or as pure solvent condensate as in the second described method. Further, in both of the above methods, it has been assumed that the articles are dipped in the hot phosphatizing bath. It will be understood that, if desired, the hot liquid of the bath may be applied to the articles in any other suitable manner, including spraying, within the broader aspects of my invention.

Also, if desired, the method of my invention may be performed in a tunnel type of machine generally similar to the machine disclosed in my Patent No. 3,073,721. In FIGURE 1 of that patent it is assumed that the articles travel from left to right. By increasing the depth of the left tank of that machine and increasing the length of the hangers, the previously degreased and cleaned articles may be dipped into a hot phosphatizing bath in the left tank. After dipping they may pass over into the right hand tank and there sprayed with pure solvent condensate taken from the trough underlying the cooling oils, as in the machine of FIGURES 1 to 3, inclusive, of my instant application. Alternatively, the spray area of the right tank of my said patent may be restricted to the left hand portion of that tank, the latter having in its lower portion a body of trichlorethylene heated to its boiling point at atmospheric pressure. The articles would then be sprayed with cold phosphatizing liquid taken from the bath in the left tank, as in the machine of FIGURE 4 of my instant application. The right tank of the machine of my above patent would soon become filled with solvent vapor and in the continued travel of the cold articles in that tank, beyond the spray means, the solvent vapor would condense on the cold articles effective for removing therefrom all traces of the phosphatizing solution, except the pure solvent or trichloroethylene. Any solvent remaining on the articles would quickly evaporate as soon as the articles leave the right hand tank of the machine of my above patent, leaving the articles in a slightly roughened or etched and dry and thoroughly cleaned condition, assuring a smooth and unblemished finish in the subsequent painting or coating operation, as before.

The machines disclosed herein may be provided with the usual accessories of degreasing machines, such as filters, pressure and temperature controls and others of known type. Such accessories have been omitted, in the interest of simplicity and clarity of disclosure, as will be understood.

As above indicated, and as will be understood, changes in detail, both as to the machine and the method of my invention, may be resorted to without departing from the field and scope thereof, and I intend to include all such variations as fall within the scope of the appended claims, in this application in which the preferred forms only of my invention have been disclosed.

I claim:

1. The method of treating metal articles for painting, which comprises subjecting the articles to a bath of a phosphatizing solution containing a volatile solvent and heated to the boiling point of the solvent at atmospheric pressure, confining the evolved vapor of the solvent in a zone overlying the area of the bath, withdrawing the articles from the bath into the vapor zone, and washing the articles in the vapor zone with pure condensate of the solvent vapor.

2. The method of treating metal articles for painting, which comprises immersing the articles in a body of a phosphatizing solution containing a volatile solvent and heated to the boiling point of the solvent at atmospheric pressure, confining the evolved solvent vapor in a zone overlying the body of solution, withdrawing the articles from the body of solution into the vapor zone, and spraying onto the articles in the vapor zone pure solvent.

3. The method of treating metal articles for painting, which comprises immersing the articles in a body of a phosphatizing solution containing a volatile solvent and heated to the boiling point of the solvent at atmospheric pressure, confining the evolved solvent vapor in a zone overlying the body of solution, withdrawing the articles from the body of solution into the vapor zone, and spraying onto the articles in the vapor zone pure solvent condensate derived from said vapor zone.

4. The method of treating metal articles for painting, which comprises immersing the articles in a body of a phosphatizing solution containing a volatile solvent and heated to the boiling point of the solvent at atmospheric pressure, confining the evolved solvent vapor in a zone overlying the body of solution, withdrawing the articles from the body of solution into the vapor zone, withdrawing solution from said body of solution and reducing the temperature of the withdrawn solution to a temperature substantially lower than that of the solvent vapor, projecting the relatively cold withdrawn solution onto the articles in the vapor zone and thereby reducing the temperature of the articles to a value substantially lower than that of the vapor in said vapor zone, and retaining the relatively cold articles in the vapor zone without projecting cold solvent onto them and until condensation of solvent vapor on the articles effective for washing 01f all traces of the solution except the solvent occurs.

5. The method of treating metal articles for painting, which comprises immersing the articles in a body of a phosphatizing solution containing a volatile solvent and heated to the boiling point of the solvent at atmospheric pressure, confining the evolved solvent vapor in a zone overlying the body of solution, withdrawing the articles from the body of solution into the vapor zone, withdrawing solution from said body of solution and reducing the temperature of the withdrawn solution to a temperature substantially lower than that of the solvent vapor, projecting the relatively cold withdrawn solution onto the articles in the vapor zone and thereby reducing the temperature of the articles to a value substantially lower than that of the vapor in said vapor zone, interrupting projection of the cold solution, and retaining the relatively cold articles in the vapor zone until condensation of solvent vapor on the articles effective for washing 01f all traces of the solution except the solvent occurs.

References Cited UNITED STATES PATENTS 2,789,070 4/1957 Copelin 1486-.15 2,992,146 7/1961 Low 1486.15 3,015,576 1/1962 Hendrixson et a1. 117-49 3,232,594 2/1966 Ord 148-6.15 X

ALFRED L. LEAVITT, Primary Examiner.

RALPH S. KENDALL, Examiner.

Claims (1)

1. THE METHOD OF TREATING METAL ARTICLES FOR PAINTING, WHICH COMPRISES SUBJECTING THE ARTICLES TO A BATH OF A PHOSPHATIZING SOLUTION CONTAINING A VOLATILE SOLVENT AND HEATED TO THE BOILING POINT OF THE SOLVENT AT ATMOSPHERIC PRESSURE, CONFINING THE EVOLVED VAPOR OF THE SOLVENT IN A ZONE OVERLYING THE AREA OF THE BATH, WITHDRAWING THE ARTICLES FROM THE BATH INTO THE VAPOR ZONE, AND WASHING THE ARTICLES IN THE VAPOR ZONE WITH PURE CONDENSATE OF THE SOLVENT VAPOR.

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