DE2213781A1 - METHOD OF PHOSPHATING STEEL - Google Patents

Description

MBTALLGESELLöCHAFT Frankfurt (M), March 21, 1972 Aktiengesellschaft DrBr / MMü Frankfurt (M)

prov. No. 6926 M

Process for the phosphating of steel

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? ⁰ 5 ^{to the} total PPO <- in the bathroom. This equilibrium acid ratio depends to a certain extent on the P ₂ OcJ concentration, the presence of other solution components and the working temperature. A general warning is given before the equilibrium concentration of free acid (free P ₂ ⁰ C) is exceeded, since this has a disadvantageous effect on the formation of layers. Depending on the type of pretreatment, the composition and the processing status of the material to be treated, the layers become thinner, sometimes more coarsely crystalline, with increasing free acidity, only to ultimately be absent; instead, only annealing colors and increased stain removal are observed. For this reason, the acid ratio is controlled in practical use

309839/1069 _ ₂ -

special attention is paid to the manganese phosphate process. The recommendations are therefore to avoid excess acid, e.g. kanganese carbonate, to dull. The aqueous manganese phosphate concentrates used for the approach and for the supplement are in the content of free acid adjusted as possible according to the equilibrium value of the working bath. (See manual of electroplating, Munich 1969; Editor H.W. Dettner and 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 111 726 (1954), e.g. pp.49,57,58).

A method is also known in which an excessive proportion of free acid in the bath is deliberately used in order to to produce particularly thin layers. However, these layers are Due to its low weight per unit area, it can only be used in practice for special cases (DBP 1 246 356).

It has now surprisingly been found that if certain conditions are observed in the working bath and when supplementing it is permissible to give the bathroom more free PoOp- in proportion to the total PpOc to be carried out as the phosphating equilibrium in the working bath, without adversely affecting the layer-forming properties of the bath. It turned out on the contrary, it turns out that this can even achieve considerable advantages, e.g. a significant reduction in the Phosphating formed sludge and a reduction in the amount of chemicals required to produce a certain amount of layer. The increased weight ratio of free Ρρ ^ κ to total PpOc It also allows supplement concentrates with increased chemical content to be produced, which leads to additional savings in terms of transport costs, warehousing and the like.

The inventive method for the production of manganese or. Iron-manganese phosphate coatings on steel in aqueous acidic Manganese phosphate or manganese iron phosphate solutions is thereby characterized in that the workpieces are brought into contact with aqueous bath solutions, which are 1 to 35 g / l, preferably 1 to 24 g / l Mn, 0 to 3υ, preferably 0 to 20 g / l fur,

309839/1069

-Z-

5 Ms 80 g / 1 P ₂ ° 5 »preferably 5 to 50 g / l P ₂ O ₅ , 0 to 80 g / l NO, preferably 0 to 50 g / l NO, contain a score from 15 to 150, preferably from 25 to 100 and in which the individual components are in the following weight ratios to one another: Fe (II): Mn = (0 to 10, preferably 0 to 9): 1; Mn: PO ₅ = (0.02 to 2.5, preferably 0.02 to 1.0): 1; NO ₃ : P ₂ O ₅ = (0 to 3, preferably 0 to 2): 1; free PpO ^^ es amt- PpO ^ = (0.05 to 0.45, preferably 0.15 to 0.40): 1. ( The number of points is the number of ml / 10 sodium hydroxide solution needed to neutralize a 10 ml bath sample According to the invention, the baths are supplemented with ^{Mn: P} 2 ° 5 ^{: N0} 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 0, -: total P ₂ 0, - = (0.5 to 1, preferably 0.6 to 1): 1. Particularly favorable ratios in relation The possibility of concentrating the supplementary chemicals and the advantages already described above result if the weight ratio of free P ₂ O ₁ -: Total PgO, - (0.65-1): 1 during supplementation. The ratio is preferably (0 , 7-1) si.

In the bath and / or make-up solution, the NO can be partially or completely replaced by Cl and / or SO ^, 0.57 parts by weight of Cl or 0.77 parts by weight of SO ^ being used for 1 part by weight of NO. _{The P 2} Oc can also be partially or wholly introduced into the supplement in the form of polyphosphoric acid or polyphosphate. The use of Cl and / or SO ^ 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 phosphating rate and the concentration of iron in the bath. The presence of poly-P ₂ Oc in the supplement concentrate allows the production of stable supplement concentrates with a high solids content even with lower values for free P ₂ Oc in relation to total P ₂ 0 _5. .

309S39 / 1069

The bath solutions according to the invention can additionally contain further components. Nickel and / or cobalt ions support the formation of layers on more difficult to attack workpieces made of, for example, low-alloy steel. Single and complex fluorides have a similar effect. The concomitant use of stronger oxidizing agents, for example, chlorates, peroxides, bromate, nitrite s ^, succeeds ^dö n Eisenll content to limit or maintain the baths also at high throughput free of iron (II). The baths are preferably used in the dipping process at temperatures above 60 ⁰ C, generally between 80 ⁰ C and the boiling point.

In addition to the main components Mn, P ₂ ° 5 » ^N0 3 (or Cl and / or SO ^), the supplementary solutions according to the invention can contain small amounts of other additives such as nickel, cobalt, alkali, calcium, ammonium cations or Contain anions from the group of single and complex fluorides as well as special accelerating substances. It is essential for the process according to the invention that the specified ranges for Mn, Pp ^ 5 '^ 3 (or Cl and / or SO ^) and for free P ₂ O «total P ₂ 0 are maintained

The free Pp ^ 5 ^w * ^rc * is determined as follows: 10 ml of building solution are titrated with 0.1 N NaOH up to the point of transition of the first dissociation stage of the Η-ζΡΟλ. Indicators such as dimethyl yellow or methyl orange can be used to index this change. Per 1 ml of 0.1 N NaOH consumed corresponds to 0.71 g / l of free Po ^ k · ^ ^er value of total PpO, - can be determined by the known methods of phosphate analysis, for example by precipitating the phosphate with ammonium molybdate and weighing the precipitation.

The calculation of the ratio for free P ₂ Oj-: total P ₂ 0, -can also be carried out according to the information in the manual of electroplating, Volume III by W. Dettner and J. Elze, Carl Hanser Verlag Munich 1969, page 90 .

309839/1069 _ ₅ _

During the material throughput, phosphating chemicals are consumed for film formation and the precipitated sludge. The number of points serves as a measure of the bath concentration. To get the score back up after some material throughput To bring the initial level or to keep it in the desired range, the bath with a corresponding amount of supplementary solution offset and mixed well. It is advisable to take the supplement as often as possible and in small portions to undertake.

Before phosphating, the workpieces are treated with 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, Removes dust, rust and scale. In general, between the cleaning of the metal surface and the phosphate! Rinsed with water thoroughly. Especially after a treatment the workpieces are pre-rinsed with alkalis and acids in an aqueous slurry of finely divided manganese phosphate, in order to improve the training in the subsequent phosphate generation to promote even, fine crystalline layers. The effect is with the phosphate! Eration in baths, the next Manganese also contain iron (II), particularly pronounced. Manganese phosphate pre-washes, in which a larger part of the manganese phosphate is present as whore ^ aulite and / or the additionally dissolved condensed phosphates, such as Na ^ PpOy »NacP-zO.Q and the like. are preferred. To generate the manganese or. Iron-manganese phosphate layers are the workpieces i.a. Brought into contact with the phosphating bath for 1 to 30 minutes, preferably by immersion. Then it is rinsed with water and post-treated depending on the further use.

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The layers produced on the workpieces can be used in a manner known per se, e.g. as a basis for paints and plastic coatings to improve adhesion and corrosion resistance, in conjunction with anti-corrosion oils for Increase in rust resistance and together with lubricants to facilitate non-cutting deformation and of 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 dipped in a strongly alkaline, aqueous cleaner, rinsed in water and then pre-rinsed in a solution with 2 g / l finely dispersed manganese phosphate with the addition of 2 g / l Na ^ PpOy at room temperature. The parts were then 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 summarized in Table 1.

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Table 1

score Mn: P ₂ 0 ₅ : N0 ₃ score Attempt a 1: 7.3
4.5 '
35.2
4.1
not determined Attempt B Attempt C FeII: Hn Free P20 ₅ : Total P2O5 FeII: Mn
Hn: P ₂ 0 ₅
N0 ₃ : P20 ₅
Free P ₂ O5: Total P ₂ O ₅ (Comparison) 74 (Invention) (Invention) Composition of the starting pool: Hn: P ₂ 0 ₅
l'S UP2O5
F. des-P2O ₅ : Total P2O ₅ Total concentration
Hn ₊ Ni ₊ NO ₃₊ P ₂ O ₅ (%) Layer weight (g / m ^)
Sludge weight (g / m ^)
Chemical consumption "
Concentrate (g / m2) o, 62: 1
o, 21: 1
0.12: 1
o, 24: 1 Hn (g / l)
Fe (II) (g / l)
P2O5 (g / i)
NO ₃ (g / l)
Ni (g / l) Supplement to constant
Score with a
Containing concentrate Beginning of crystal formation at ° C 12.1
0.0
36.7
3.9
o, 33 7th
12th
48 14.1
0.0
28.1
17.1
o, 39 12.1
0.0
36.7
3.9
0.33 Hn {% '}
P2O5 (%)
NO ₃ {%)
Ni CQ Bath composition according to
set of 2 m steel surface per 1 82. 74 82 Hn (g / l)
Fe (II) (g / l)
P ₂ O ₅ (g / l)
NO ₃ (g / l)
Ni (g / l) 0: 1 ■ 0: 1 0: t o, 33: 1
o, 11: 1
o, 25: 1 o, 5o: 1
o _f 61: 1
o, 33: 1 0.33: 1 ^;
o, 11: 1
o, 25: 1 5.53
16.75
1.8o
o, 15 5.82
18.72
11.37
o, 26 2.93
3o, 15
3.24
o _a 28 o, 33: 1: o, 11 o, 31: 1: o, 61 o, o97: 1: p, 11 o, 25: 1 0.85: 1 o _f 85: 1 24.23 36.17 36.6o -1 -5 -9 9, o
4.9
3o, 1
2o
not determined 5, o
6.0
36, o.
4.0
not determined 77 76 o.54: 1
o, 3o: 1
o, 67: 1
o, 27: 1 1.2: 1
- o, 14: 1
o, 11: 1
o, 22: 1 6th
7th
26th 8th
9
28

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221378Ί

The following conclusions can be drawn from Table 1:

With practically the same layer weight, for the inventive Methods B and C only 60 to 75% of the amount of sludge produced by method A. that corresponds to the state of the art. Likewise, the chemical consumption for B and C was significantly lower than for A. This is partly due to the fact that the supplement concentrates B and C are much more concentrated than the supplement concentrate A. The total concentration could even be improved with the cold resistance of the 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 which only _{contain H 2} O, P ₂ ⁰ 5 »M * ¹ and NO are intended to serve as an example of how the resistance to cold is 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 the stability of the concentrates against crystallization increases with an increasing ratio of free P ₂ 0: total P ₂ 0, - or a decreasing ratio of MniPpOc. Compared to the previously practically used supplement concentrates with free PgO ^ total P-pOc of about 0.23 to 0.30, the concentrates according to the invention can be made more concentrated by a factor of about 1.25 to 1.75.

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Table 2

Total concentration
tration
Mn ₊ P ₂ O ₅₊ NO ₃ (^) Weight ratios Mn: P20 | j: N03 and free ^ OjrGesanit ^ Oj for concentrates that
up to O ⁰ C are stable at low temperatures ί
ο, 32: 1: ο ·, 1; o, 29: 1
0.27: 1: 5.1; o, 4o: 1 0.48: 1: 0.5; o, 33: 1
0.44: 1: 0.5; o, 45: 1 0.66: 1: 0.9; o, 33: 1
0.62: 1: 0.9; o, 44: 1 24
26th
3o
34
38
42 0.29: 1: 0; o, 25: 1
0.24: 1: 0; o, 38: 1 o.21: 1: o.1; o, 57: 1
0.15: 1: 0.1; o, 73: 1
o, 11: 1: o, 1; o, 82: 1
o, o9: 1: o, 'i; o, 88: 1 ⁰ A ¹ ^ ⁵ L ° JL ^58: J
0.33: 1: 0.5; o, 73: 1 ^B
ο, 27: 1: ο, 5; ο, 86: ΐ [
0.22: 1: 0.5; 1, oo: 1 0.57: 1: 0.9; o, 56: 1
0.52: 1: 0.9; ü ₈ 69: 1
° «5% ¹⁵ Si ⁹ L ° jl ^85: J_
_ο _? 4ρ% _? 9; i _a 99: ij o, 17: 1: 0; o, 57: 1
¹ 0.11: 1: 0; o, 73: 1
o, o7: 1: 0; o, 8o: 1
, o, o6: 1: 0; o, 85: 1

: Belongs to the overall scope of the invention

j j: belonging to the scope of the invention.

■ ____ ■

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309839/1069

. 10 claims

Claims (6)

22Ί3781 Claims ) j A process for the phosphating of steel by means of phosphating solutions on the basis of manganese phosphate and manganese iron phosphate, characterized in that the workpieces are brought into contact with aqueous bath solutions containing 1 to 35 g / l Mn, O to 30 g / l Fell, contain 5 to 80 g / l P ₃ 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 up to 10): 1; Mn * ^P 2 ° 5 ⁼ (° '° ^{2 to 2} ' ⁵ ^ ^{: 1; N0} 3 ^{: P} 2 ° 5 = (0 to 3); 5 free P ₃ O ₅ ^ eSaIHt-P ₂ P ₅ = (0.05 to 0.45): 1, whereby the solutions are supplemented with Mh: P £ ° 5 ^{: N0} 3 ^{in the} weight ratio (0.05 to 0.6): 1: (0 to 1) and with the addition a weight ratio of free P ₂ 0 ^: total PpOc = (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 ° 5 ° ^{to 5} ° s / ^{1 N0} 3 ^contains e ⁿ »have ^a number of points from 25 to 100 and in them the individual components are in the following weight ratios: Fe (II): Mn = (0 to 9): 1» Mn: P ₂ 0 ^ = (0 , 02 to 1.0): 1; NO ₃ IP ₂ O ₅ = (0 to 2): 1; free P ₂ 0 ₅ : total P ₂ 0 ₅ = (0.15 to 0.40): 1, whereby the solutions are supplemented with Mn: P ₂ 0c: N0, in a weight ratio (0.07 to 0.6) : 1: (0 to 1) and with the addition a weight ratio of free P ₂ Oc: total P ₂ 0c = (0.6 to 1): 1 is maintained. 3) Method according to claim 1 and 2, characterized in that in addition the weight ratio Mn: P ₂ O ₅ : NO ₃ = 309839/1069 - 11 - • '(0.07 Ms 0.45): 1: (0 to 0.9) is selected and that Weight ratio of free P ₂ ° 5 * ^total - ^p 2 ° 5 = (° » ^δ 5 Ms 1): 1, preferably (0.7 Ms 1 ·) ϊ1, is» 4) Method according to claim 1 to 3, characterized., that in the bath and / or supplementary solution the NO, partially or completely replaced by Cl and / or SO ^, with 1 part by weight of NO, 0.57 part by weight of Cl or 0.77 parts by weight SO ^ are omitted. 5 * A method according to claim 1 to 4, characterized in that is used partially or totally in the form of polyphosphate or polyphosphoric acid in the supplement, the Pp ^ 5 ". 6) Method according to claim 1 to 5, characterized in that that before the phosphate! eration the workpieces with an aqueous Slurry of finely divided manganese phosphate can be pre-rinsed. 309839/1069