DE1521837B1 - Process for cleaning and phosphating surfaces made of iron or zinc - Google Patents

Description

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It has long been known to have crystalline phosphate coatings on the surface, already in the cleaning zone is derived mainly from iron or zinc and that the crystals formed act as nuclei to apply standing surfaces by having them act on which the actual layer in the with an aqueous acidic solution that forms the zinc phosphate second spray zone. Whether this is true or and an accelerator for layer formation is not included, it is nevertheless necessary to achieve the best treated. The workpieces can either result in advantageous results if the cleaning solution so the phosphating bath is immersed or designed to form a phosphate coating Solution will be splashed. The surfaces of the work- able is. It is also advantageous if the However, pieces are generally covered with grease or after cleaning in the second spray zone Dirt contaminates and must therefore coat the same layer of the phosphating solution used before the phosphating solution Phosphating be cleaned. In the case of spray-forming components, we contain the cleaning process the surfaces are before the solution. Such a procedure has the purpose in the spray zone for the formation of a phosphate additional advantage that that in the cleaning zone Coating is done, thoroughly cleaned by spraying the solution used, if the contaminated, vermit an alkaline solution that threw one or more 15 and through already in the second spray zone contains surface-active substances. Such a used solution can be replaced by that in turn Cleaning solution can replace very greasy deposits with fresh solution. if it effectively remove from surfaces. It may be desired, but the solution can be in the second injection also do not contain a surface-active agent in the phosphating zone, be dragged. It is therefore necessary to allow the surface to remove any grease residues between cleaning and phosphating with strips that have not yet been removed in the first zone Rinse with water. For this purpose one applies im been. When a surfactant is in generally two separate rinsing zones, which are not used in the phosphating solution, fresh water is used in the second zone. A surface-active agent must also be added, after shift formation it is common to 25 before it is adopted for the first zone, or rinse, and usually an organic solvent is emulsified in it after this rinse coated iron surfaces.

still sprayed with a solution that contains chromate ions

contains. A conventional spray system therefore comprises six cleaning and then applying one

Zones. Any visible rust or scale becomes phosphate coating without intermediate rinsing

normally by applying an appropriate one is particularly useful when the phosphate coating

Rust removal agent is applied before treatment in such a cold, i.e. at a temperature

Phosphating plant removed. Around room and cost temperature from 4 to 38 ⁰ C and usually not above

To save, it is of course desirable to increase the number of 21 ⁰ C. When using such methods of cleaning

Reduce zones as much as possible. 35 namely common, strongly alkaline cleaning agents are used

It has now been found that the surfaces become advantageous, difficulties often arise, apparently

adhered by spraying on a coating that forms because the metal surfaces are passivated, so that then

Accelerated zinc phosphate solution, which additionally forms the coating-forming solutions at temperatures

nonionic surfactant and ge of 38 ° C or lower unsatisfactory

if necessary an organic solvent emulsified 40 work.

contains, can be cleaned. Following a use of an emulsified solution such The surfaces can be cleaned directly, e. B. Kerosene, is in the cleaning solution bar can be sprayed with the phosphating solution. it is particularly beneficial to work in the cold, since It was found that in this way between the volatility of the solvent in the cold then Cleaning level and application of the coating no 45 is low, thus avoiding losses and intermediate fire rinsing required are. The risk of invention is reduced. An addition of solvent Proper working method therefore has the great advantage, up to 20 g / l is suitable. Preferably be that compared to the known systems with six 1 to 10 g / l used. If the procedure is at Zones only need four zones to be provided. higher temperature is carried out, is the addition With the aid of the coating-forming zinc phosphate solution 50, a surfactant versus a Grease and other dirt are effectively preferable to the emulsified solvents. A special one Surfaces removed. As with the known suitable surfactant is a condensation must, however, also in the inventive sation product of a resin alcohol with 20 mol Process visible rust or scale beforehand from ethylene oxide, which is terminated with a benzyl residue removed from the surfaces in a suitable manner. 55 is etherified. At higher temperatures, the coating forms the deformation Zinc phosphate solutions have turned emulsified kerosene or the like into something unusual a pH value of 2.5 to 4, while the cleaning power improves the stain less in any case solutions usually require a pH value below 1. The amount of surfactant exhibit. is expediently up to 5 g / l, preferably 0.1 to 2 g / l.

It is state of the art that coating-forming zinc-60 is used to form the coating in the cold

phosphate solutions at or slightly above the pH value, use a solution that contains both zinc and

the balance contains phosphate as well as manganese, with the manganese content up to 50 percent by weight of the zinc content

3Zn (H ₂ PO4) ₂ 5 = i Zn ₈ (PO ₄ ) S + 4H ₃ PO ₄ . Such a solution is also expedient

65 as the basis for the cleaning stage in the

operate. It appears that the solution used in the first zone,

The process according to the invention, the formation of the As in conventional spraying processes are the after

Phosphate coating, at least on the purer parts, cleaned by the process of the invention and

phosphated surfaces are then passed through two rinsing zones, whereby it is in the first zone around a water rinse and in the second around a rinse with a common dilute solution of Chromic acid with or without added phosphoric acid.

The method according to the invention can be used with advantage when the with a coating then provided the surface with a water-thinned paint, in particular a water-thinned one Base coat, is treated. In this case, the second rinsing stage can take place after the coating formation can be carried out with water or with an aqueous solution with a pH between 7 and 11 having. Particularly good results have been obtained when the water-thinned base coat with the help of a electrochemical process is applied.

example 1

Steel sheets were treated in four zones as follows: In the first zone, the sheets were treated for 1 minute at 21 ° C. with a solution of the following composition splashed:

Zn 5.0 g / l

Mn 0.6 g / l

Fe +++ 0.01 g / l

PO ₄ 13.0 g / l

NO ₃ 3.0 g / l

SO ₄ 0.8 g / l

NaNO ₂ 0.4 g / l

Tartaric acid 0.6 g / l

Surfactant 0.5 g / l

Kerosene 5 g / l

A condensation product of a resin alcohol with 20 moles of ethylene oxide, which is terminally etherified with a benzyl radical, is used. The overall acidity of this solution was 20 points and the free acidity was 0.4 points. The total acidity is the number of millimeters 0.1 normal NaOH, which is required to neutralize 10 ml of the solution to the phenolphthalein endpoint is understood. The free acidity is the number of millimeters of 0, normal NaOH, which are used for the Neutralization of 10 ml of the solution to the bromophenol blue endpoint is required.

In the second zone, the sheets were treated for 1 minute at 21 ° C with a solution otherwise of the same composition, but without surfactant and kerosene, splashed.

In the third zone, the metal sheets provided with a coating were ^{rinsed with water by spraying for 30 seconds at 21 °} C., and in the fourth zone a solution containing 0.03 g / l CrO ₃ and was ^{sprayed at 21 ° C. for 30 seconds} Contained 0.03 g / l H ₃ PO _4. The panels were then dried in the oven at 120 ° C. Excellent, uniformly crystalline phosphate coatings were obtained with a layer weight of 1.66 g / m ² .

Example 2

Steel panels were similarly treated in four zones in a slightly higher temperature process. The metal sheets were initially ^{sprayed for one minute at 47 °} C. with a solution of the following composition:

Zn 4.5 g / l

PO ₁ 13.6 g / l

NO ₃ 14.0 g / l

Tartaric acid 0.3 g / l

NaNO ₂ 0.3 g / l

Surfactant 0.5 g / l

As the surface active agent, the same as in Example 1 was used. The overall acidity was Points and the free acidity 1.2 points.

In the second zone, the metal sheets were sprayed again at 47 ° C. for 1 minute with a solution of the composition as in the first stage with the difference that the surfactant is omitted became.

In the third zone, the sheets were ^{rinsed by spraying with water at 21 °} C. for 30 seconds, and in the last zone they were sprayed for 30 seconds at the same temperature with a solution containing 0.03 g / l CrO ₃ and 0, 03 g / l H ₃ PO ₄ contained.

Excellent crystalline coatings with a layer weight of 1.8 g / m ^{2 were} obtained. The quality of the coatings was just as good as that obtained on metal sheets in a conventional manner in a process carried out in six zones.

Claims (11)

Patent claims: 1. Process for cleaning and phosphating surfaces made of iron or zinc, thereby characterized in that the surfaces are through Spraying on of a coating-forming accelerated zinc phosphate solution, which is a non-ionic surface-active Contains agent, cleaned and immediately afterwards by spraying with a Phosphating solution are treated. 2. The method according to claim 1, characterized in that the surfaces are treated ^{with each of the two solutions at a temperature of 4 to 38 ° C.} 3. The method according to claim 2, characterized in that the surfaces for phosphating and if necessary also treated for cleaning with a solution containing zinc phosphate and contains manganese, the manganese content being up to 50% of the zinc content. 4. Process according to claims 1 to 3, characterized in that the surfaces in four spray zones are treated, whereby they are cleaned in the first zone, in the second the Phosphate coating applied, in the third the surfaces with water and in the fourth the Surfaces with a dilute chromic acid solution, possibly a little phosphoric acid may contain, be rinsed. 5. The method according to claims 1 to 4, characterized in that the surfaces with a solution, which is an emulsified organic solvent, preferably in a Contains an amount of 1 to 10 g / l. 6. The method according to claims 1 to 5, characterized in that the surfaces with a solution containing 0.1 to 2 g / l surfactant. 7. The method according to claim 6, characterized indicates that the surfaces are cleaned with a solution that acts as a surface-active agent a condensation product of a resin alcohol with 20 moles of ethylene oxide, which is terminated with a Benzyl radical is etherified contains. 8. The method according to claims 1 to 7, characterized in that the surfaces with a solution containing the same layer-forming components as the Phosphating solution. 9. The method according to claim 8, characterized in that the surfaces with a solution are cleaned, which are discarded after their pollution and by already used phosphating solution is replaced, the latter in turn being replaced by fresh solution. 10. Modification of the method according to claim 4, characterized in that the surfaces in the fourth zone with a solution having a pH between 7 and 11, rinsed and then with a water-thinned paint be treated. 11. The method according to claim 10, characterized in that the water-thinned paint is applied by an electrochemical process.