DE2213781B2 - METHOD OF PHOSPHATING STEEL - Google Patents

Description

The invention relates to an improved method for phosphating steel with the aid of Phosphating solutions based on manganese phosphate or manganese iron phosphate.

It has long been known to coat steel with layers of manganese phosphate or manganese iron phosphate by bringing it into contact with aqueous acidic manganese phosphate solutions, which may also contain divalent iron and / or oxidizing agents. The solutions contain as much free acid as is necessary to bring the solution into chemical equilibrium with the layer-forming substance. This state corresponds to a certain weight ratio of free P ₂ O ₅ to total PzOs in the bath. This equilibrium acid ratio depends to a certain extent on the P ^ s concentration, the presence of other solution components and the working temperature. before

If the equilibrium concentration of free acid (free P ₂ O ₅ ) is exceeded, a general warning is given, since this has a detrimental effect on the formation of layers. Depending on the type of pretreatment, composition and processing status of the

is the material to be treated, the layers will be with with increasing free acidity thinner, sometimes also more coarsely crystalline, only to finally be absent; instead, only annealing colors and increased stain removal are observed. For this reason is used to control the acid ratio in the practice of manganese phosphate processes Particular attention paid to the recommendations. Therefore, excess acid, z. B. with Manganese carbonate, to blunt. The aqueous manganese phosphate concentrates used for the preparation and for the supplement the content of free acid is as close as possible to the equilibrium value of the working Bades adjusted accordingly (cf. Handbuch der Galvanotechnik, Munich 1969; editor H. W.

Dettneru. J. Elze, Volume III, Section »Phosphating«, P. 109; see also O. L Gilbert, Phosphating Materials and Processes; Rock Island Arsenal Laboratory Report No. 54-2906, PB 1Π 726 [1954], ζ. B. p. 49, 57, 58).

A method is also known in which deliberately using an excessive proportion of free acid in the bath is worked to produce particularly thin layers. However, these layers are because of her low weight per unit area only practically applicable for special cases (DT-PS 12 46 356).

It has now surprisingly been found that, if certain conditions are met in the working bath and when supplementing, it is permissible to add more free P ₂ O ₅ to the bath in relation to the total P ₂ O ₅ than corresponds to the phosphating equilibrium in the working bath, without adversely affect the layer-forming properties of the bath. On the contrary, it turned out that even considerable advantages can thereby be achieved, e.g. B. a significant reduction in the sludge formed during phosphating and a reduction in the amount of chemicals required to produce a certain amount of layer. The increased weight ratio of free P2O5 to total P2O _{5 also} makes it possible to produce supplement concentrates with a higher chemical content, which results in additional savings in transport costs, storage and the like.

The method according to the invention for producing manganese or iron-manganese phosphate layers on steel in aqueous acidic manganese phosphate or manganese-iron phosphate solutions is characterized in that the workpieces are brought into contact with aqueous bath solutions containing 1 to 35 g / l, preferably 1 up to 24 g / l Mn, 0 to 30, preferably 0 to 20 g / l fur, 5 to 80 g / l P ₂ O ₅ , preferably 5 to 50 g / l P ₂ O ₅ , 0 to 80 g / l NO ₃ , preferably 0 to 50 g / l NO ₃ , have a number of points from 15 to 150, preferably from 25 to 100 and in which the individual components

nents are in the following weight ratios to one another: Fe (II): Mn = (0 to 10, preferably 0 to 9): 1; Mn: P2O5 = (0.02 to 2A, preferably 0.02 to 1.0): 1; NO3: P2OS = (0 to 3, preferably 0 to 2): 1; free P ₂ Os: GeSaImVP ₂ Os = (0.05 to 0.45, preferably 0.15 to 0.40): l.

The number of points is the number of ml n / 10 sodium hydroxide solution required to neutralize a 10 ml bath sample against phenolphthalein. According to the invention, the baths are supplemented with Mn: P ₂ O ₅ : NO ₃ in a weight ratio (0.05 to 0.6 , preferably 0.07 to 0.45): 1: (0 to 1, preferably 0 to 0.9), with a weight ratio of free P ₂ O ₅ : total P ₂ Os = (0.5 to 1, preferably 0.6 to 1): 1 is adhered to. Particularly favorable ratios with regard to the possibility of concentrating the supplementary chemicals and the advantages already described above result if the weight ratio of free P ₂ O ₅ : total P ₂ O ₅ (0.65-1): 1 during the supplementation is preferably this Ratio (0.7-1): 1.

Bath solutions, the composition of which falls within the aforementioned ranges for the phosphating bath, are to be found already among the well-known manganese phosphating solutions, but this resulted in the essential to the invention compliance with the special conditions when supplementing in coordination not to derive certain conditions of the bath solution.

In the bath and / or supplementary solution, the NO3 can be partially or completely replaced by Cl and / or SO ₄ , 0.57 parts by weight of Cl or 0.77 _{parts by weight of SO 4 being} used for 1 part by weight of NO _{3. The P 2} O ₅ can also be partially or wholly introduced into the supplement in the form of polyphosphoric acid or polyphosphate. The use of Cl and / or SO4 makes it possible to produce solutions that are richer in manganese without having to increase the nitrate content at the same time, which, through its specific effect, influences the layer formation, the rate of phosphating and the accumulation of iron in the bath. The presence of poly-P ₂ O ₅ in the supplement concentrate allows the production of stable supplement concentrates with a high solids content even at lower values for free P ₂ Os in relation to total P ₂ O _5.

The bath solutions according to the invention can additionally contain further components. Nickel and / or cobalt ions support the layer formation on more difficult to attack workpieces made of, for. B. low alloy steel. Single and complex fluorides have a similar effect. By using stronger oxidizing agents, e.g. B. chlorates, peroxides, bromates, nitrites, it is possible to limit the iron (II) content or to keep the baths free of iron (II) even at high throughput. The baths are preferably used in the dipping process at temperatures above 6O ⁰ C, generally between 8O ⁰ C and the boiling point.

In addition to the main components Mn, P ₂ O ₅ , NO ₃ (or Cl and / or SO4), the supplementary solutions according to the invention can contain small amounts of other additives such as nickel, cobalt, alkali, calcium, ammonium cations or anions from the group of single and complex fluorides as well as special accelerating substances. It is essential for the method according to the invention that the specified ranges for Mn, P ₂ O ₅ , NO ₃ (or Cl and / or SO ₄ ) and for free P ₂ O ₅ : Ge-The free P2O5 is determined as follows: 10 ml of bath solution are titrated with 0.1 n-NaOH up to the point of transition of the first dissociation stage of the H ₃ FO _4. Indicators such as dimethyl yellow or methyl orange can be used to indicate this change. l free P ₂ O ₅ . The value for total P ^ s can be determined by the known methods of phosphate analysis, e.g. B. by precipitating the phosphate with ammonium molybdate and weighing the precipitate.

The calculation of the ratio for free P ₂ O ₅ : total P ^ s can also be based on the information in the manual of electroplating, Volume III by W. De 11 η er and J. EI ζ e, Carl Hanser Verlag Munich 1969, page 90.

During the material throughput, phosphating chemicals are used for the layer formation and the precipitated sludge Consumed The number of points is used as a measure of the bath concentration. To the score after some material throughput to bring it back to the initial state or in the desired state To keep the area, an appropriate amount of supplement solution is added to the bath and well mixed It is advisable to take the supplement as often as possible and in small portions.

Before phosphating, the workpieces are cleaned using suitable measures, such as degreasing in organic solvents, acidic, neutral or alkaline cleaners, blasting with sand, steel grain, corundum, pickling in strong alkalis with the addition of complexing agents or in strong acids, oils, fats, dust , Rust and scale free. In general, thorough rinsing with water takes place between cleaning the metal surface and phosphating. In particular after treatment with alkalis and acids, the workpieces are pre-rinsed in an aqueous slurry of finely divided manganese phosphate in order to promote the formation of particularly uniform, finely crystalline layers during the subsequent phosphating. The effect is particularly pronounced when phosphating baths that contain iron (II) in addition to manganese, in which a larger part of the manganese phosphate is present as Hureaulite and / or the additionally dissolved condensed phosphates, such as Na ₄ P ₂ O ?, Na ₅ P ₃ OiO and the like are preferred. To produce the manganese or iron-manganese phosphate layers, the workpieces are brought into contact with the phosphating bath for 1 to 30 minutes, preferably by immersion. Then it is rinsed with water and, depending on the further use, treated

The layers produced on the workpieces can be used in a manner known per se, for. B. as a basis for Paints and plastic coatings, to improve adhesion and corrosion resistance, in conjunction with anti-corrosion oils to increase rust resistance and together with lubricants for Facilitation of non-cutting deformation and sliding can be used.

The method according to the invention will be explained using the following examples:

example 1

Sheets and gear parts made of steel were degreased by immersion in a strongly alkaline, aqueous cleaner then rinsed in water and then in a

Solution with 2 g / l finely dispersed manganese phosphate with the addition of 2 g / l Na ₄ PaOz at room temperature. Subsequently, the parts were phosphated for 10 min at 92 to 98 ° C in various manganese phosphate solutions by dipping, then rinsed and dried. The special test conditions and results are Compiled in Table 1

Table 1

Experiment A (comparison) Experiment B
(Invention)

Experiment C (invention)

Composition of the starting pool: 12.1 Mn (g / l) 0.0 Fe (II) (g / l) 36.7 P2Os (g / l) 3.9 NO ₃ (g / l) 0.33 Ni (g / l) 82 score 0: 1 Fell: Mn 0.33: 1 Mn: P2O5 0.11: 1 NO3: P2O5 0.25: 1 Free P2O5: Total P2Os Supplement to constant score with a Concentrate containing: 5.53 Mn (%) 16.75 P2O5 (%) 1.80 NO3 (%) 0.15 Ni (%) 0.33: 1: C Mn: P2O5: NO3 0.25: 1 Free P2O5: total P20s 24.23 Total concentration Mn + Ni + NO3 + P2O5
(%) -1 Beginning of crystal formation at ⁰ C Bath composition according to throughput of 2 m ² steel surface per 11: 7.3 Mn (g / l) 4.5 Fe (II) (g / l) 35.2 P2O5 (g / l) 4.1 NO3 (g / l) not Ni (g / l) certainly 74 score 0.62: 1 Fell: Mn 0.21: 1 Mn: P2O5 0.12: 1 NO3: P2O5 0.24: 1 Free P2O5: Total P2Os 7th Layer weight (g / m ² ) 12th Sludge weight (g / m ² ) 48 Chemical consumption concentrate (g / m ² )

0.11 14.1

O ₁ O
28.1
17.1

0.39
74
0: 1
0.50: 1
0.61: 1
0.33: 1

5.82
18.72
11.37

0.26
0.31: 1: 0.61

0.85: 1
36.17

-5

9.0

4.9
30.1
20th

not
certainly
77

0.54: 1
0.30: 1
0.67: 1
0.27: 1

26th

12.1 0.0

36.7 3.9 0.33

0: 1

0.33: 1

0.11: 1

0.25: 1

2.93 30.15

3.24

0.28 0.097: 1: 0.11

0.85: 1 36.60

-9

5.0

6.0 36.0

4.0 not determined 76

1.2: 1 0.14: 1 0.11: 1 0.22: 1

The following conclusions can be drawn from Table 1:

For processes B and C according to the invention, the resulting layer weight was practically the same The amount of sludge was only 60 to 75% of the amount that was incurred in process A, that of the prior art is equivalent to. Likewise, the chemical consumption for B and C was significantly lower than for A. This is based e.g. T. ensure that the supplement concentrates B and C are much more concentrated than the supplement concentrate A. The total concentration could be improved with even improved cold resistance of concentrates can be increased by a factor of 1.5 compared to A.

Example 2

To determine the influence of the composition of the supplement concentrates on the resistance to crystallization, a large number of solutions were prepared and subjected to the cold test. Solutions that only _{contain H 2} O, P ₂ O ₅ , Mn and NO ₃ are intended to serve as an example of how the resistance to cold can be influenced by the weight ratios of the solution components. Table 2 shows examples of solutions which do not show any crystallization of manganese phosphate or other sediments ^{up to 0 ° C.} The table clearly shows that with

increasing ratio of free P2O5: GeSaITIt-P ₂ Os or decreasing ratio Mn: P2O5 the stability of the concentrates against crystallization increases. Compared to the previously practically used additional

Tabel

concentrates with free P2O5: total ^ Os of sths The concentrates according to the invention can be converted into 0.23 to 0.30 by a factor of approximately 1.25 to 1.7f Prepare more concentrated.

Total weight ratios Mn: P2O5: NO3 and free P2Os: total P2O5 for concentrals that ^{are stable at low temperatures up to O 0} C concentration Mn + P2O5 + NO3 (o / o)

0.29: 1: 0; 0.25: 1 0.32: 1: 0.1; 0.29: 1

0.24: 1: 0; 0.38: 1 0.27: 1: 0.1; 0.40: 1

0.48: 1: 0.5; 0.33: 1 0.66: 1: 0.9; 0.33: 1

0.44: 1: 0.5; 0.45: 1 0.62: 1: 0.9; 0.44: 1

0.17: 1: 0;

iÖ ~ Ü:

0.57: 1 Ό ', 73 ": Γ [0.07: 1: 0; 0.80: 1! 0.06: 1: 0; 0.85: 1

0.21: 1: 0.1; 0.57: 1

"ö'isTf-b'ü 'dji' - 'x

0.11: 1: 0.1; 0.82: 1

0.09: 1: 0.1; 0.88: 1

0.38: 1: 0.5; 0.58: 1

0.27: 1: 0.5; 0.86: 1
0.22: 1: 0.5; 1.00: 1

0.57: 1: 0.9; 0.56: 1 0.52: 1: 0.9; 0.69: 1

0.46: 1: 0.9; "Ö, 40Tf7Ö, 9" f

0.85: 1 0 ~, 9 ~ 97ϊ]

J: Belonging to the overall scope of the invention.

._ !: Belongs to the scope of the invention. TW 6

Claims (6)

Patent claims: 1. A method for phosphating steel with the aid of phosphating solutions based on manganese phosphate or manganese iron phosphate, characterized in that the workpieces are brought into contact with aqueous bath solutions containing 1 to 35 g / l Mn, 0 to 30 g / l fur , 5 to 80 g / l P ₂ O ₅ , 0 to 80 g / l NO ₃ , have a number of points from 15 to 150 and in which the individual components are in the following weight ratios: Fe (II): Mn = (0 to 10): 1; Mn: P ₂ O ₅ = (0.02 to 2.5): 1; NO ₃ : P ₂ O ₅ = (0 to 3): 1; P ₂ O ₅ : GeSaIm-P ₂ Os = (0.05 to 0.45): 1, whereby the solutions are supplemented with Mn: P ₂ O ₅ : NO3 in a weight ratio (0.05 to 0.6): 1 : (0 to 1) and when adding a weight ratio of free P ₂ O ₅ : GeSaIm-P ₂ O ₅ = (0.5 to 1): 1 is maintained. 2. The method according to claim 1, characterized in that the bath solutions 1 to 24 g / l Mn, 0 to 20 g / l Fe (II), 5 to 50 g / l P ₂ O ₅ , 0 to 50 g / l NO ₃ , have a number of points from 25 to 100 and in them the individual components are in the following weight ratios: Fe (H): Mn = (0 to 9): 1; Mn: P ₂ O ₅ = (0.02 to 1.0): 1; NO ₃ : P ₂ O ₅ = (0 to 2): 1; Free P ₂ O ₅ : Ge-SaHIt-P ₂ O ₅ = (0.15 to 0.40): 1, the solutions being supplemented with Mn: P ₂ O ₅ : NO ₃ in a weight ratio (0.07 to 0 , 6): 1: (0 to 1) and with the addition a weight ratio of free P ₂ O ₅ : total P ₂ O ₅ = (0.6 to 1): 1 is maintained. 3. The method according to claim 1 and 2, characterized in that in addition the weight ratio Mn: P ₂ O ₅ : NO ₃ = (0.07 to 0.45): 1: (0 to 0.9) is selected and the weight ratio of free P ₂ O ₅ : GeSaIrU-P ₂ O ₅ = (0.65 to 1): 1, preferably (0.7 to 1): 1. 4. The method according to claim 1 to 3, characterized in that the NO _{3 is} partially or wholly replaced by Cl and / or SO4 _{in the bath and / or supplementary solution, with 1 part by weight of NO 3} 0.57 parts by weight of Cl or 0 77 parts by weight of SO ₄ are omitted. 5. The method according to claim 1 to 4, characterized in that in addition the P2OS is partly or wholly used in the form of polyphosphate or polyphosphoric acid. 6. The method according to claim 1 to 5, characterized in that before the phosphating Workpieces pre-rinsed with an aqueous slurry of finely divided manganese phosphate will.