EP0613964B1 - Process for facilitating cold forming - Google Patents

Abstract

In a process for facilitating the non-cutting cold forming of iron materials by application of a phosphate coating, the iron materials are dipped (immersed) into a phosphating solution which is free of elements of the sixth subgroup of the Periodic Table of the Elements, free of nitrogen compounds, is preferably also free of nickel, contains from 5 to 20 g/l of zinc from 1 to 15 g/l of magnesium from 10 to 26 g/l of phosphate (calculated as P2O5) from 1 to 15 g/l of fluoroborate (calculated as BF4) from 1 to 7 g/l of chlorate (calculated as ClO3), preferably also from 5 to 40 g/l of sulphate (calculated as SO4) and in which the weight ratio of Zn : Mg : BF4 is set to a value in the range of 1 : (0.15 to 1) : (0.15 to 1).

Description

The invention relates to a method for facilitating the non-cutting cold forming of ferrous materials by applying a phosphate coating in an immersion process by means of an aqueous acid phosphating solution which contains zinc, Mg and phosphate ions as well as oxidizing agents and is practically free of Fe-II ions.

Phosphate coatings are usually applied to metal surfaces in order to improve their corrosion resistance and to increase the adhesion of the paint that is subsequently applied. Phosphate coatings also serve to facilitate non-cutting cold forming, whereby they themselves act as a "lubricant" by helping to avoid seizing or welding of material and tools or by binding a subsequently applied lubricant so that it is practically not removed during the forming process. In particular, the latter ability is of particular importance because only the combination of phosphate coating and lubricant enables multiple or strong cold forming, possibly without a new intermediate treatment with lubricant.

Numerous methods are known for facilitating cold forming by applying phosphate coatings. They can belong to the category of "layer-forming" as well as - albeit with considerably less importance - the category of "non-layer-forming" processes.

"Layer-forming" here means the formation of phosphate coatings by means of phosphating solutions which, in addition to the phosphate ions, also predominantly Supply cations for coating formation. In contrast, in the so-called “non-layer-forming” processes, the cations of the phosphate coating usually originate from the treated metal itself, ie the phosphating solution essentially only provides the phosphate ions.

For example, EP-A-45110 describes a process for the production of phosphate coatings on iron or steel surfaces by immersion or flooding, in which phosphating solutions are used which contain at least 0.3% by weight of Zn and at least 0.3% by weight. % PO₄ and contain at least 0.75 wt .-% NO₃ or an equivalent, iron II non-oxidizing accelerator. The Zn: PO₄ weight ratio should be greater than 0.8 and the iron (II) content to be set should be 0.05 to 1% by weight. The solutions described here can contain calcium, which can be partially or completely replaced by magnesium, and are suitable for the production of phosphate coatings, among other things. as preparation for cold forming.

The above process works "on the iron side". There is no mention of any kind of advantage of the calcium content of the phosphating solution, which is particularly emphasized.

From EP-A-403 241 it is known to form zinc phosphate coatings on metal surfaces with the aid of aqueous zinc phosphate solutions which contain 2 to 20 g / l zinc, 5 to 40 g / l phosphate and silicotungstic acid or silicotungstate in a concentration of 0.005 to 20 g / l (calculated as W) included. The phosphating solutions can contain nitrite, nitrobenzenesulfate, hydrogen peroxide, nitrate and chlorate as accelerators. In addition to an additional content of nickel, cobalt, calcium and manganese in the phosphating solution, that of magnesium is also mentioned in an amount of 0.5 to 10 g / l. The The process has been described as being suitable for preparing metals for the subsequent cold forming.

The disadvantage of this method is that a tungsten content in the phosphating solution inevitably leads to its entry into subsequent rinsing baths and thus poses problems from the point of view of wastewater treatment.

Finally, in the phosphating process according to EP-A-414301 the use of solutions is provided which contain 0.4 to 30 g / l zinc, 4 to 30 g / l P₂O₅, 5 to 50 g / l NO₃, and a maximum of 10 g / l Fe II and a maximum of 0.3 g / l Fe III. These solutions, which May also contain up to 10 g / l of magnesium, are supplemented in a certain way and operated with a certain addition of oxidizing agent, so that the actual aim of this process - to be able to work essentially without waste water - can be achieved. The increased alkali resistance of the coatings containing mixed phosphates, which makes them particularly suitable as a primer for paints, is mentioned as an advantage for the magnesium content or for the calcium content of the phosphating solutions, which is shown to be equivalent.

What most of the other phosphating processes cited above have in common that they contain nitrate, nitrite and / or organic nitro compounds, such as nitrobenzenesulfonate, as accelerators. However, because of their difficult removability and degradability, such connections are problematic from the point of view of flushing and wastewater treatment.

The object of the invention is to provide a method for facilitating the cold forming of ferrous materials by applying a phosphate coating, which avoids the disadvantages of the known methods, in particular does not pose any waste water problems, leads to firmly adhering coatings with a sufficient thickness for the cold forming and yet allows simple process control.

The object is achieved by equipping the method of the type mentioned at the outset in accordance with the invention in such a way that the iron materials are immersed in a phosphating solution which is free of elements of the sixth subgroup of the Periodic Table of the Elements and free of nitrogen compounds, and
5 to 20 g / l zinc
1 to 15 g / l magnesium
10 to 26 g / l phosphate (calculated as P₂O₅)
1 to 15 g / l fluoroborate (calculated as BF₄)
1 to 7 g / l chlorate (calc. As ClO₃)
contains and in which the weight ratio of Zn: Mg: BF₄ is set to a value in the range from 1: (0.15 to 1): (0.15 to 1).

By eliminating nitrogen compounds, the effort involved in processing rinse water and processed phosphating baths can be significantly reduced. Such a waiver is possible - as was established in the conception of the method according to the invention - if, in addition to the choice of the active constituents and their concentration, special attention is paid to the Zn / Mg / BF₄ ratio to be set in the phosphating solution. Only under these conditions is it possible to produce phosphate layers that permit perfect cold forming. The crystal structure of the phosphate coating produced further allows the usual activation treatment prior to phosphating, e.g. with activating agents based on titanium phosphate. This does not mean that there is no need for an activation treatment, but the additional grain-refining effect achieved is far less than usual.

A preferred embodiment of the invention accordingly provides that the ferrous materials are immersed in a phosphating solution
6 to 17 g / l zinc
2 to 5 g / l magnesium
13 to 20 g / l phosphate (calculated as P₂O₅)
2 to 5 g / l fluoroborate (calculated as BF₄)
2 to 4 g / l chlorate (calculated as ClO₃)
contains.

This embodiment of the invention as the further preferred embodiment with setting a weight ratio of Zn: Mg: BF₄ of 1: (0.23 to 0.46): (0.23 to 0.46) is associated with the advantage that the Chemical consumption is very low, on the other hand, a particularly good phosphate layer formation is achieved.

It is also advantageous to immerse the iron materials in a phosphating solution which contains 5 to 40 g / l, preferably 10 to 30 g / l, of sulfate. In principle, chlorides and acetate additives are also possible to adjust the electroneutrality in the phosphating solution. However, they are less advantageous for reasons of a certain susceptibility to corrosion of the treated workpieces (chloride) or the comparatively high cost (acetate). The addition of sulfate also has the advantage that it has a favorable influence on the crystal structure of the phosphate layer produced, in that the absorption capacity and the anchoring of the lubricant normally applied are improved.

According to a further expedient embodiment of the invention, the S value of the phosphating solution to be used should be in the range from 0.1 to 0.4. The S-value is the ratio of "free acid" - calculated as P₂O₅ - and the so-called "total acid Fischer", ie the total amount of P₂O₅, expressed as consumption of 0.1 n NaOH in ml for the titration of a 10 ml bath sample (cf. W. Rausch "The phosphating of metals", 2nd Ed., Eugen G. Leuze Verlag Saalgau 1988, pp. 299-304).

Another advantageous embodiment of the invention provides that the ferrous materials are immersed in a phosphating solution which is nickel-free.

The freedom from nickel has the advantage that the treatment of the rinse water or else the processed phosphating bath is easier before draining into the sewer and less problematic sludge is obtained as a result of the treatment. From the point of view of workplace hygiene, it is an advantage both in the phosphating plant and in the cold forming equipment (dust formation).

The application temperature of the phosphating solution is unlimited within wide limits. According to a further advantageous embodiment of the invention, the iron materials are immersed in a phosphating solution set at a temperature of 50 to 70 ° C. These are the optimal conditions with regard to layer formation speed and heat economy. At the aforementioned temperatures, the treatment time is generally between 3 and 15 minutes.

The phosphating solution can be formulated as such from the individual components, but particularly expediently from a concentrate. In both cases, the cations are introduced, for example, as metal, oxide, carbonate, sulfate, phosphate, and possibly also as chlorate. The component can be added via alkali phosphate and / or phosphoric acid.

The phosphating solutions used in the process according to the invention can contain, in addition to the components already mentioned, other additives known per se, but mostly in minor amounts. These include, for example, copper, manganese, calcium and sludge conditioning agents.

The phosphating solution is applied in dipping, which also means flooding.

With the aid of the method according to the invention, it is possible to produce phosphate coatings with a layer weight of approximately 5 to 15 g / m 2. This enables the layer weight to be adapted to the severity of the intended cold forming, the size of the workpiece and the like. Finally, when choosing the layer weight, it must also be considered whether a lubricant is subsequently applied or not.

The workpieces are pretreated before phosphating in the usual way, such as by cleaning, pickling, rinsing and, if necessary, activating. A lubricant customary for cold forming processes is usually applied as aftertreatment. This can be done immediately after coating or after an intermediate rinse. The lubricant can also be applied immediately before the forming, if necessary also between the forming steps. If the purpose of the formation of zinc soaps is with the application of lubricant, care must be taken to ensure that the phosphate coating is sufficiently moist for the reaction.

Soaps, oils and other auxiliaries for cold forming or emulsions of fatty acids or soaps, in particular with 8 to 18 carbon atoms in the acid anion, can be applied as lubricants. Because of the reaction with the cation of the phosphate coating already mentioned above, sodium and / or potassium soaps, in particular stearates, are particularly advantageous.

• 1. Reinigen (ggf. zusätzliches Beizen)
• 2. Heißwasserspülung
• 3. Behandeln mit der Phosphatierungslösung
• 4. Kaltwasserspülung
• 5. Spülung mit schwachalkalischer Lösung
• 6. Kontaktieren mit einem Überschuß eines Schmiermittels auf Basis Natriumstearat
• 7. Trocknen

Gegebenenfalls kann die Vorbehandlung durch eine Aktivierungsstufe ergänzt werden. Der Eisenwerkstoff kann dann sofort oder nach Zwischenlagerung der Kaltumformung zugeführt werden.The preferred sequence of processes when applying the invention is

• 1.Clean (if necessary additional pickling)
• 2. Hot water rinse
• 3. Treat with the phosphating solution
• 4. Cold water rinse
• 5. Rinse with weakly alkaline solution
• 6. Contact with an excess of a lubricant based on sodium stearate
• 7. Drying

If necessary, the pretreatment can be supplemented by an activation level. The iron material can then be fed to the cold forming process immediately or after intermediate storage.

The invention is explained in more detail below, for example.

example 1

• 1. Reinigen in einem alkalischen Reiniger einer Konzentration von 5 g/l bei einer Temperatur von 60°C im Tauchen.
• 2. Spülen mit Leitungswasser von Umgebungstemperatur.
• 3. Beizen in Salzsäure einer Konzentration von 17 Gew.-% bei 40°C.
• 4. Spülen mit Leitungswasser von Umgebungstemperatur.
• 5. Phosphatieren in einer Phosphatierungslösung von 60°C, enthaltend
     15 g/l Zn
     4,5 g/l Mg
     15 g/l Phosphat (ber. als P₂O₅)
     4,5 g/l Fluoroborat (ber. als BF₄)
     3,0 g/l Chlorat (ber. als ClO₃)
     29,2 g/l Sulfat (ber. als SO₄)
  im Tauchen für die Dauer von 8 Minuten (S-Wert 0,28 bis 0,38) Schichtgewicht 10 g/m².
• 6. Spülen mit Leitungswaser von Umgebungstemperatur.
• 7. Auftrag einer Borax-Lösung von 80°C.
• 8. Auftrocknung der Borax-Lösung.

Steel wire with a diameter of 5.5 mm and steel grade C45 was treated according to the following procedure:

• 1.Clean in an alkaline cleaner with a concentration of 5 g / l at a temperature of 60 ° C while diving.
• 2. Rinse with tap water at ambient temperature.
• 3. Pickling in hydrochloric acid at a concentration of 17 wt .-% at 40 ° C.
• 4. Rinse with tap water at ambient temperature.
• 5. Phosphating in a phosphating solution of 60 ° C containing
  15 g / l Zn
  4.5 g / l Mg
  15 g / l phosphate (calculated as P₂O₅)
  4.5 g / l fluoroborate (calculated as BF₄)
  3.0 g / l chlorate (calculated as ClO₃)
  29.2 g / l sulfate (calc. As SO₄)
  in diving for a period of 8 minutes (S value 0.28 to 0.38) layer weight 10 g / m².
• 6. Rinse with tap water at ambient temperature.
• 7. Apply a borax solution at 80 ° C.
• 8. Drying the borax solution.

• a) auf einen Enddurchmesser von 1,2 mm in 12 Zügen mit einer Ziehgeschwindigkeit von 20 m/sec.
• b) auf einen Enddurchmesser von 2,82 mm in 5 Zügen mit einer Ziehgeschwindigkeit von 5 m/sec.
• c) auf einen Enddurchmesser von 1,8 mm in 8 Zügen mit einer Ziehgeschwindigkeit von 8 m/sec.

The steel wires pretreated in this way were then drawn in different ways

• a) to a final diameter of 1.2 mm in 12 passes with a drawing speed of 20 m / sec.
• b) to a final diameter of 2.82 mm in 5 passes with a drawing speed of 5 m / sec.
• c) to a final diameter of 1.8 mm in 8 passes with a drawing speed of 8 m / sec.

In all cases, the forming was flawless until the last train. Even after the last train there was still a closed phosphate layer.

Example 2

• 1. Beizen in Salzsäure einer Konzentration von 17 Gew.-% bei 40°C.
• 2. Spülen mit Leitungswasser von Umgebungstemperatur.
• 3. Aktivieren mit einem Aktivierungsmittel auf Basis Titanphosphat (1 g/l) bei Raumtemperatur.
• 4. Phosphatieren in einer Phosphatierungslösung von 60°C, enthaltend
     7,5 g/l Zn
     2,25 g/l Mg
     15 g/l Phosphat (ber. als P₂O₅)
     2,25 g/l Fluoroborat (ber. als BF₄)
     3,0 g/l Chlorat (ber. als ClO₃)
     12,1 g/l Sulfat (ber. als SO₄)
  im Tauchen für die Dauer von 10 Minuten (S-Wert 0,28 bis 0,38) Schichtgewicht 7 g/m².
• 5. Spülen mit Leitungswasser von Umgebungstemperatur.
• 6. Auftrag einer Lösung von Natriumstearat.
• 7. Auftrocknen der Seifen-Lösung.

Steel grade ST35 and ST52 pipes were treated according to the following procedure:

• 1. Pickling in hydrochloric acid at a concentration of 17 wt .-% at 40 ° C.
• 2. Rinse with tap water at ambient temperature.
• 3. Activate with an activating agent based on titanium phosphate (1 g / l) at room temperature.
• 4. Phosphating in a phosphating solution of 60 ° C containing
  7.5 g / l Zn
  2.25 g / l Mg
  15 g / l phosphate (calculated as P₂O₅)
  2.25 g / l fluoroborate (calculated as BF₄)
  3.0 g / l chlorate (calculated as ClO₃)
  12.1 g / l sulfate (calc. As SO₄)
  in diving for a period of 10 minutes (S value 0.28 to 0.38) layer weight 7 g / m².
• 5. Rinse with tap water at ambient temperature.
• 6. Apply a solution of sodium stearate.
• 7. Dry up the soap solution.

The tubes pretreated in the above manner were then subjected to a profile pull (1 pull).

The steel grade ST35 pipes were pulled at a speed of 60 m / min, the steel grade ST52 at a speed of 30 m / min.

In all cases, the train ran flawlessly and there was still a closed phosphate layer even after the forming.

Claims (9)

1. A method for facilitating the non-cutting cold-working of ferrous materials by applying a phosphate coating in a dipping process by means of an aqueous acidic phosphating solution which contains Zinc, Mg and phosphate ions and oxidising agents and is practically free of Fe (II) ions, characterised in that the ferrous materials are dipped into a phosphating solution which is free of elements of the Sixth subgroup of the periodic table of the elements and is free of nitrogen compounds and contains
      5 to 20 g/l zinc
      1 to 15 g/l magnesium
      10 to 26 g/l phosphate (calculated as P₂O₅)
      1 to 15 g/l fluoroborate (calculated as BF₄)
      1 to 7 g/l chlorate (calculated as ClO₃)
   and in which the weight ratio of Zn : Mg : BF₄ is set to a value in the range of 1 : (0.15 to 1) : (0.15 to 1).
2. A method according to Claim 1, characterised in that the ferrous materials are dipped into a phosphating solution which contains
      6 to 17 g/l zinc
      2 to 5 g/l magnesium
      13 to 20 g/l phosphate (calculated as P₂O₅)
      2 to 5 g/l fluoroborate (calculated as BF₄)
      2 to 4 g/l chlorate (calculated as ClO₃).
3. A method according to claim 1 or 2, characterised in that the ferrous materials are dipped into a phosphating solution in which the weight ratio of Zn : Mg : BF₄ is set to a value in the range of 1 : (0.23 to 0.46) : (0.23 to 0.46).
4. A method according to Claim 1, 2 or 3, characterised in that the ferrous materials are dipped into a phosphating solution which contains 5 to 40 g/l sulphate (calculated as SO₄).
5. A method according to Claim 4, characterised in that the ferrous materials are dipped into a phosphating solution which contains 10 to 30 g/l sulphate (calculated as SO₄).
6. A method according to one or more of Claims 1 to 5, characterised in that the ferrous materials are dipped into a phosphating solution which has an S value in the range of 0.1 to 0.4.
7. A method according to one of more of Claims 1 to 6, characterised in that the ferrous materials are dipped into a phosphating solution which is nickel-free.
8. A method according to one or more of Claims 1 to 7, characterised in that the ferrous materials are dipped into a phosphating solution set to a temperature of 50 to 70°C.
9. A method according to one or more of Claims 1 to 8, characterised in that the ferrous materials are dipped into a phosphating solution for a time of 3 to 15 minutes.