EP0042631B1 - Method of phosphating metallic surfaces - Google Patents

Description

The invention relates to a process for the production of phosphate coatings with increased layer weight on metal surfaces of iron and steel using an acid nitrate accelerated zinc and manganese ions and in the incorporated state containing Fe ^{2 +} ions phosphating solution at elevated temperatures in the immersion process.

It is known to treat iron and steel for the formation of a phosphate layer with phosphating solutions in diving which contain zinc, hydrogen, nitrate and phosphate ions. The phosphate layers that have been produced in this way are particularly suitable as lubricants for cold forming. With anti-rust oil aftertreatment, they lead to corrosion resistance that corresponds to galvanically applied metal coatings made of zinc, cadmium, etc.

In particular for corrosion protection with oils and to facilitate cold forming, e.g. B. cold extrusion, layers with a higher coating weight, z. B. in the range between 8 to 30 g / m ² required. In some cases, particularly high demands are placed on corrosion protection. This can be achieved by increasing the layer weight. An increase in the layer weight would also allow higher degrees of deformation in cold forming.

The deposition of thick zinc phosphate layers can according to DE-AS 1 287 412 and US Pat. No. 3,268,367 by bringing iron and steel into contact with a nitrate-accelerated acidic zinc phosphating solution with the addition of polycarboxylic acid in which the carbon atom adjacent to at least one carboxyl group contains a hydroxy -, Amino or carboxyl group can be achieved. This phosphating solution can also contain additives such as nickel, cobalt, lithium, bismuth and manganese in small concentrations of less than 0.5 g / l. They activate the metal surface to be phosphated and promote the deposition of zinc phosphate layers.

The deposition of such thick phosphate layers to solve the problem described has the disadvantage that the chemical consumption is comparatively high. Furthermore, in some cases, e.g. B. depending on the type of alloy of the workpiece to be phosphated, the production of thicker layers.

The object of the invention is to provide a phosphating process that does not have the disadvantages described, in particular can be used universally, requires little chemicals and leads to higher-quality phosphate layers.

• P₂O₅: NO₃=1: (0,3 bis 3,0)
• Gesamt-P₂0₅ : freies-P₂O₅=1: (0,25 bis 0.70)
• Mn:Zn=1: (22 bis 0,2)

beträgt und die im eingearbeiteten Zustand eine Gesamtsäurepunktzahl von mindestens 20 Punkten aufweist.The object is achieved by designing the method of the type mentioned at the outset in accordance with the invention in such a way that the metal surfaces are brought into contact with a phosphating solution which contains at least 0.6 g / l of manganese ions at treatment temperatures of 50 to 98 ° C. which is the weight ratio

• P ₂ O ₅ : NO ₃ = 1: (0.3 to 3.0)
• Total P ₂ 0 ₅ : free P ₂ O ₅ = 1: (0.25 to 0.70)
• Mn: Zn = 1: (22 to 0.2)

and which has a total acid score of at least 20 points when incorporated.

Such a method leads to zinc-manganese-phosphate layers which, with comparable layer thicknesses, are superior to zinc phosphate layers with regard to corrosion protection and cold-forming properties.

The metal surfaces are preferably brought into contact with a phosphating solution in which the manganese ion content is at least 1 g / l. As a result, a higher manganese phosphate content in the layer, which improves the aforementioned properties, is achieved.

Optimal results with regard to the layer quality are achieved if, in a further preferred embodiment of the invention, the metal surfaces are brought into contact with a phosphating solution in which the weight ratio of Mn: Zn is 1: (0.8 to 12).

Furthermore, it was found that with increasing manganese phosphate content in the layer, its suitability especially for preparation for cold working improves. Manganese ion contents in the phosphating solution above the range of 1: 0.2 lead to non-closed, perforated layers.

Within the required limits, bathrooms with e.g. B. 80 total acid points should be composed as follows:

The total acid number can be determined by titration of a 10 ml bath sample with 0.1 N NaOH against phenolphthalein as an indicator until the color changes from colorless to pink.

To activate the steel or iron surfaces to be phosphated, nickel and / or cobalt and / or copper ions and the like can be added to the bath. Advantageously, these metal ions in a concentration of z. B. 0.02 to 0.10 g / 1 added to the bath. The anion belonging to the metal ions can e.g. B. nitrate or sulfate.

If a further increase in the layer weight is desired, it is advisable to bring the metal surfaces into contact with a phosphating solution which contains simple and / or complex fluorides, such as NaF, NaHF ₂ , and / or Na ₂ SiFe.

If desired, a certain reduction in the layer weight can be brought about if condensed phosphates are added to the phosphating bath.

It is in the nature of a nitrate-accelerated phosphating bath that iron II ions accumulate in the bath as a result of the throughput of metal surfaces and the total acid score decreases. To counteract a deterioration in the phosphating result, an addition of the phosphating bath is necessary.

• P₂O₅:NO₃=1: (0,3 bis 2,0)
• Gesamt-P₂O₅: freies-P₂O₅=1 : (0,3 bis 0,8)
• Mn:Zn=1:(2 bis 80)

ergänzt.Particularly advantageous results are achieved if the phosphating bath with respect to the components zinc, manganese, phosphate and nitrate ions in a weight ratio

• P ₂ O ₅ : NO ₃ = 1: (0.3 to 2.0)
• Total P ₂ O ₅ : free P ₂ O ₅ = 1: (0.3 to 0.8)
• Mn: Zn = 1: (2 to 80)

added.

The workpieces to be phosphated should be free of grease, scale and rust. The degreasing can e.g. B. by means of aqueous, alkaline, surface-active substances containing cleaners.

Descaling is conveniently carried out using sulfuric acid or hydrochloric acid.

After cleaning and / or pickling, the workpieces should be rinsed well with water.

The workpieces can be formed in a manner known per se, e.g. B. with titanium orthophosphate or manganese orthophosphate suspensions in water. It has been found in practice that in some cases a pre-rinse with water at 50 to 98 ° C activates the surface.

The phosphating bath is operated between 50 and 98 ° C depending on the type of workpiece, the alloy and the type of application. It has been shown that a diving time of 5 to 15 minutes is sufficient for most applications.

As mentioned, due to the acceleration of nitrate, iron II will accumulate in the phosphating bath in the course of the throughput. This does not affect the way the bath works. In special cases, e.g. B. at high nitrate concentrations or at high bath temperatures, it can also happen that the bath: due to the oxidation of fur to Felll remains iron-II-free. This also does not affect the way the bathroom works. The addition of the bath is expediently carried out on a constant total acid number.

The layer weight of the zinc-manganese-phosphate layers obtained is normally between about 5 and about 30 g _{/ m} 2, depending on the composition of the phosphating bath and the alloy of the workpiece to be treated _.

After phosphating, it is rinsed with water, optionally aftertreated and dried if necessary.

For corrosion protection z. B. be treated with chromic acid solutions, followed by treatment with anti-corrosion oil emulsions. The workpieces can be used for cold forming e.g. B. Treated with soap solutions.-The workpieces treated in this way are superior to the workpieces treated with conventional nitrate-accelerated zinc phosphating systems in terms of corrosion protection and cold forming properties.

The invention is illustrated by the following examples, for example and in more detail.

example 1

• a) Beizen in 15%iger Schwefelsäure mit einem Zusatz eines Beizinhibitors bei 60° C und einer Tauchzeit von 10 Minuten
• b) Spülen mit kaltem Wasser
• c) Spülen mit 60° C heißem Wasser
• d) jeweils 10 Schrauben wurden 10 min im Tauchen im Phosphatierbad A, B und C phosphatiert.
  
• e) Spülen mit kaltem Wasser
• f) Nachspülen in vollentsalztem Wasser mit Zusatz von 0,5 g/1 Natriumbichromat bei 80° C
• g) Behandeln mit einer l3%igen Emulsion eines Korrosionsschutzöles bei 60° C
• h) Ofentrocknen bei 70° C.

Steel screws were treated as follows:

• a) Pickling in 15% sulfuric acid with the addition of a pickling inhibitor at 60 ° C and a dipping time of 10 minutes
• b) Rinse with cold water
• c) Rinse with hot water at 60 ° C
• d) 10 screws in each case were phosphatized for 10 minutes while immersed in the phosphating bath A, B and C.
  
• e) Rinse with cold water
• f) rinsing in deionized water with the addition of 0.5 g / 1 sodium bichromate at 80 ° C.
• g) Treatment with a 13% emulsion of an anti-corrosion oil at 60 ° C
• h) oven drying at 70 ° C.

The screws were then tested in a salt spray test in accordance with DIN 50021 SS; 10 screws were tested for each of the three methods A, B and C. After 72 hours of testing, methods A and B had rusted 50% of the screws; in method C, all 10 screws had not yet been attacked, although the layer weight was lower than in methods A and B.

Example 2

• a) Beizen in 15%iger Salzsäure mit Zusatz eines Beizinhibitors bei Raumtemperatur und einer Behandlungszeitvon 10 Minuten
• b) Spülen mit kaltem Wasser
• c) Spülen mit 75° C heißem Wasser
• d) jeweils 100 Kaltfließpreßteile wurden 10 min im Tauchen in Phosphatierbad D und E behandelt.
  
• e) Spülen mit kaltem Wasser
• f) Behandeln in einer 5%igen Natronseife bei 73° C und einer Tauchzeit von 5 min
• g) Trocknen durch Eigenwärme an der Luft.

Cold extrusions were treated as follows:

• a) Pickling in 15% hydrochloric acid with the addition of a pickling inhibitor at room temperature and a treatment time of 10 minutes
• b) Rinse with cold water
• c) Rinse with hot water at 75 ° C
• d) 100 cold extrusion parts were treated for 10 minutes by immersion in phosphating baths D and E.
  
• e) Rinse with cold water
• f) treatment in a 5% sodium soap at 73 ° C and a dipping time of 5 min
• g) Drying in the air by natural heat.

The parts were extruded back into sleeves. For the parts that were treated in bath D, the sleeves had about 80% grooves and the surface had a shiny metallic appearance. In the parts that were treated in bath E, no marks could be found and the surface was gray, which indicates a considerable residual phosphate layer.

Example 3

• a) Reinigen in einem stark alkalischen wäßrigen Reiniger bei 95° C und einer Tauchzeit von 15 min
• b) Spülen mit kaltem Wasser
• c) Beizen in H₂SO₄. 20%oig mit Zusatz eines Beizinhibitors, bei 65° C und einer Tauchzeit von 10 min
• d) Spülen mit kaltem Wasser
• e) Phosphatieren bei 75° C und einer Tauchzeit von 10 min in Bad F und G
• f) Spülen mit kaltem Wasser.

Steel sheets of USt 1405 m quality (unrestored carbon steel with a C content <0.1% by weight and matt surface; material number 1.0336) were treated as follows:

• a) cleaning in a strongly alkaline aqueous cleaner at 95 ° C and a dipping time of 15 min
• b) Rinse with cold water
• c) Pickling in H ₂ SO ₄ . 20% with the addition of a pickling inhibitor, at 65 ° C and a dipping time of 10 min
• d) Rinse with cold water
• e) Phosphating at 75 ° C and a dipping time of 10 min in bath F and G
• f) Rinse with cold water.

The composition of baths F and G is shown in the following table. The total acid score of the baths was 90 points each.

After a throughput of 0.2 m ^{2 of} sheet metal surface per liter of bath solution, the baths were supplemented to the point constancy with the additional concentrates listed in the table.

At the beginning of the throughput and after the throughput of 4 m ^{2 of} steel surface per liter of bath solution, sample sheets were branched off for the determination of the layer weight and for the corrosion test in the salt spray test according to DIN 50021 SS. The sheets for the corrosion test were previously treated with a 15% emulsion of an anti-corrosion oil and then at 70 ° C dried in the oven.

It is clear that by the preferred embodiment of the supplement, the phosphating baths also after throughput of 4 m ^2/1 would result in layers that have retained their good properties.

Claims (5)

1. Method of producing phosphate coatings of increased coating weight on metal surfaces of iron and steel by means of an acid, nitrate accelerated, zinc, manganese and - if being in working condition - ferrous ions containing phosphating solution at elevated temperatures by a dip process, characterized in that the metal surfaces at treating temperatures of 50 to 98° C are brought in contact with a phosphating solution, which contains at least 0,6 g/l manganese ions and in which the weight ratio of

P₂O₅: NO₃ is 1 : (0,3 to 3,0)

total P₂0_s : free P₂0s is 1 : (0,25 to 0,70)

Mn : Zn is 1 : (22 to 0,2)

and - if being in working condition - has a total acid content of at least 20 points.

2. Method according to claim 1, characterized in that the metal surfaces are brought in contact with a phosphating solution, in which the content of manganese ions amounts to at least 1 g/I.

3. Method according to claim 1 or 2, characterized in that the metal surfaces are brought in contact with a phosphating solution, in which the weight ratio of Mn : Zn is 1 : (0,8 to 12).

4. Method according to claim 1, 2 or 3, characterized in that the metal surfaces are brought in contact with a phosphating solution, which contains simple and/or complex fluoride, e. g. NaF, NaHF₂ and/or Na₂SiF₆.

5. Method according to claim 1, 2, 3 or 4, characterized in that the phosphating bath is replenished with respect to the components zinc, manganese, phosphate and nitrate ions in a weight ratio of

P₂O₅:NO₃=1: (0,3 to 2,0)

total P₂O₅: free P₂O₅=1: (0,3 to 0,8)

Mn:Zn=1:(2 to 80).