US3729346A - High-pressure spray process for phosphating iron or steel surfaces - Google Patents

Abstract

A PROCESS FOR APPLYING RUST-PREVENTING PHOSPHATE COATINGS TO SURFACES OF OBJECTS MADE OF IRON OR STEEL BY SPRAYING SAID OBJECTS WITH AN ACID SOLUTION OF PHOSPHATES OF LAYER-FORMING METALS UNDER A SPRAY PRESSURE OF 10 TO 100 ATMOSPHERES GAUGE.

Description

United States Patent Ofice 3,729,346 Patented Apr. 24, 1973 HIGH-PRESSURE SPRAY PROCESS FOR PHOS- PHATIN G IRON OR STEEL SURFACES Hans Gotta, Weiden, and Norbert Schulz, Oberdollendorf, Germany, assignors to Gerhard Collardin GmbH, Cologne-Ehrenfeld, Germany N Drawing. Filed May 21, 1971, Ser. No. 145,931 Claims priority, application Austria, June 1, 1970,

Int. Cl. C23f 7/10 US. Cl. 148--6.15 Z 7 Claims ABSTRACT OF THE DISCLOSURE A process for applying rust-preventing phosphate coatings to surfaces of objects made of iron or steel by spraying said objects with an acid solution of phosphates of layer-forming metals under a spray pressure of 10 to 100 atmospheres gauge.

BACKGROUND OF THE INVENTION Processes for the application of phosphate coatings on iron and steel surfaces with the aid of acid solutions of phosphates of polyvalent metals, which may contain oxidizers or other accelerators for accelerating the coating formation, have been known for a long time. According to the method of application, these processes may be differentially classified as dipping and spraying processes. Particularly the latter are suitable for the treatment of metal objects in automatic installations in which the cleaning, phosphating and after-treatment are carried out in a continuous work sequence. Moreover, phosphating processes by the spray-method may be applied wherever treatment in dipping, moving belt or automatic spraying installations is not feasible, such as in the case of bulky metal structures or small numbers of pieces. On these cases the treatment solutions are applied to the metal surface with the aid of manually guided spray nozzles.

In the known spray processes for phosphatizing, the application of the treatment solutions is carried out at a spray-pressure of about 0.5-1.5 atmospheres gauge.

The known spray-processes, however, have an important disadvantage. Iron and steel surfaces which have been phosphated in this manner with solutions of phosphates of layer-forming metals have a strong tendency to develop a deposit of so-called fly-rust. This is especially the case if the phosphating treatment is carried out with manually guided spray guns. For this reason the phosphated metal surfaces must be subsequently passivated with solutions containing chromic acid or chromates, in order to prevent the formation of fly-rust. However, the use of chromic acid or chromates requires considerable work-physiological protective measures and a corresponding treatment of the waste liquid which can only be carried out in expensive detoxification installations. By virtue of these circumstances the application possibilities of the known spray-methods of phosphating ferrous metal surfaces with manually guided spray guns operating at relatively low pressures are very limited.

OBJECTS OF THE INVENTION It is an object of the instant invention to provide an improved process of phosphating surfaces of objects made of iorn or steel by the spray-method which avoids the deposit of fly-rust on the phosphated surfaces.

Another object of the present invention is to provide a spray-process for phosphating surfaces of objects made of iron or steel which obviates a subsequent passivation treatment of the phosphated surfaces with solutions containing chromic acid or chromates.

Still other objects and advantages of the invention will become apparent as the description thereof proceeds.

THE INVENTION We have discovered that the above objects are achieved by applying a conventional phosphating solution with the aid of a spray gun under a presure of 10 to 100 atmospheres gauge.

The high-pressure spray process according to the present invention produces satisfactory phosphate coatings over the entire indicated pressure range. Particularly favorable results with respect to stability against fly-rust and coating structure are obtained if the acid solutions of phosphates of film forming metals are sprayed upon the metal surfaces at a spray pressure in the range of 30 to 50 atmospheres gauge.

The temperature at which the phosphating solution is applied to the metal surface lies advantageously in the range between 40 and C.

The high-pressure spray process is caried out with the same layer-forming coating solutions which have heretofore been conventionally used for spray-phosphating at low pressure. The acid solutions contain phosphate ions and cations of polyvalent metals, such as magnesium, manganese, cadmium, cobalt, nickel and lead, individually or in admixture with each other. Because of the particularly favorable properties of the phosphate layers prepared therewith in regard to corrosion stability and improved lacquer adhesion, those solutions are preferably used which contain zinc or calcium as layer-forming cations, but also those solutions are suitable which contain zinc and calcium ions together in various atomic weight ratios. For acceleration of the coating formation, customary accelerators are added to the phosphating solutions. Particularly advantageous is the acceleration with oxidizing agents, such as nitrites, nitrates, chlorates, perborates or hydrogen peroxide, or with the combination nitrite/ nitrate, nitrite/chlorate or nitrate/perborate.

The phosphating solutions used in the high-pressure spray process according to the present invention contain phosphate ions, polyvalent metal ions and accelerators in the customary concentrations. Also, the ratio of free acid to bound acid, as well as the Working pH, lie within the conventional limits.

Insofar as the objects to be treated are not exceedingly soiled, cleaning and phosphating may be carried out in one working step. In this case non-ionic wetting agents, such as reaction products of the ethylene oxide with fatty alcohols, alkylphenols, fatty amines or polyoxypropyleneglycols, are added to the acid phosphating solution. The concentration of the wetting agents in the phosphating solution lies within the customary limits of 0.1 to 5 gm./

iter.

The phosphating of iron and steel surfaces by the highpressnre spray process can be carried out in automatic installations as well as with the aid of manual spraying equipment.

The iron and steel surfaces phosphated by the process pursuant to the present invention are resistant against fly-rust, so that a subsequent treatment with chromic acid or chromate solutions is unnecessary. The phosphate layers produced thereby are more closed and have a finer crystals structure than phosphate coatings produced with the same phosphating solution, but at a low spraying pressure by known processes; with respect to corrosion protection and lacquer adhesion they are at least equivalent to the latter.

The high-pressure spray process according to the present invention has the additional advantage relative to the known low-pressure spray processes that it does not require a subsequent passivation of the phosphatized metal surfaces. Consequently not only the chromic acid passivation step, but also the required work-physiological protective measures and the detoxification of the waste liquids are obviated. This is particularly advantageous in cases where ferrous metal surfaces are to be phosphated by manual spraying; thus, the layer-forming phosphating treatment can now also be applied where its application was heretofore not feasible with regard to Work-physiology and waste liquid detoxification, as well as to fixed metal structures, such as overhead eelctrical transmission line towers, bridges, etc.

The following examples further illustrate the present invention and will enable others skilled in the art to understand it more completely. It should be understood, however, that the invention is not limited solely to the particular examples given below.

EXAMPLE 1 Auto bodies made of sheet steel were sprayed with an aqueous zinc phosphate solution of the following composition:

Gm./liter Zn(H PO 8 NaH PO 2.1 H PO (100%) 0.7 NaNO 5.9 NaNO 0.4 A non-ionic wetting agent (addition product of 1 mol of nonylphenol to 9 mols of ethylene oxide) 5 The temperature of the solution was 60 to 63 C., and the spray pressure was 40 atmospheres gauge. The solution was sprayed from two manual spray guns with an output of 6 to 7 liters/minute each. The treating time for a body of about 60 m. surface area was 12 minutes.

Subsequently, the phosphated bodies were rinsed with tap water, then with completely desalted water and finally dried in a hot air stream.

This treatment provided the steel bodies with a homogeously formed, dense zinc phosphate layer. The treated surface showed no deposit of fiy-rust.

For comparison, auto bodies made of sheet steel were phosphated in the same manner and under the same conditions, but with a spray pressure of 4 atmospheres gauge. After this treatment the steel surfaces also showed a well-formed zinc phosphate layer. However, so much fly-rust had formed that the layers were not suitable as a base for subsequent electrophoretic lacquering.

EXAMPLE 2 Iron sheets were manually sprayed at pressures of 1.5, 6 and 45 atmospheres gauge, respectively, with an aqueous zinc phosphate solution which had the following composition:

A non-ionic wetting agent (addition product of 1 mol of nonylphenol to 9 mols of ethylene oxide) 1.6

Subsequently, the-sheets were rinsed with tap water,

then with completely desalted Water, and dried in a hot air stream.

The phosphate-coated iron sheets were electrophoret- 4 ically lacquered and subjected to the salt-spray test according to ASTM B 117-64 with cross-cut. After 350 hours the following values were obtained:

(1) Spray pressure 1.5 atmospheres gauge Degree of blistering:

DIN 53 20 9: m S/g 5 ASTM D 714-56: 2 D Rust in the cross-cut: 5-12 mm.

(2) Spray pressure 6 atmospheres gauge Degree of blistering:

DIN 53 209: In 4/g 5 ASTM D 714-56; 2 M D Rust in the cross-cut: 4-10 mm.

(3) Spray pressure 45 atmospheres gauge Degree of blistering:

DIN 53 209: m 2/g 2 ASTM D 714-56: 8 F Rust in the cross-cut: 2-3 mm.

While the present invention has been illustrated with the aid of certain specific embodiments thereof, it will be readily apparent to others skilled in the art that the invention is not limited to these particular embodiments, and that various changes and modifications may be made without departing from the spirit of the invention or the scope of the appended claims.

We claim:

1. In the process of applying a rust-protective phosphate coating to a ferric metal surface, which comprises spraying an aqueous phosphoric acid solution of phosphates of layer-forming metals selected from the group consisting of zinc phosphate, calcium phosphate and mixtures thereof, in the presence of oxidizing agent accelerators under pressure onto said surface, the improvement which consists in that the spray pressure is from 10 to 100 atmospheres gauge.

2. The process according to claim 1, wherein said spray pressure is from 30 to 50 atmospheres gauge.

3. The process according to claim 1, wherein the temperature of said solution is from 40 to C.

4. The process according to claim 1, wherein said solution contains a wetting agent.

5. The process according to claim 1, wherein a manually operated spray gun is used for spraying.

6. The process according to claim 1, wherein said aqueous phosphoric acid solution of phosphates is an aqueous phosphoric acid solution of zinc phosphate.

7. The process according to claim 6, wherein said aqueous phosphoric acid solution of zinc phosphate contains a nitrite/nitrate combination oxidizing agent accelerator.

References Cited UNITED STATES PATENTS 3,615,912 10/1971 Dittel et a1. 148-615 R 3,684,588 8/1972 Curran 148-615 Z RALPH S. KENDALL, Primary Examiner US. Cl. X.R. 148-6.15 R