EP0186823B1 - Process for facilitating cold-forming - Google Patents

Abstract

A heavy phosphate coating suitable as a base for a lubricant, prior to cold deformation of a ferrous surface, is formed by application of an aqueous acidic phosphating solution containing phosphate, organic nitro compound or nitrate (introduced as an inorganic nitrate), zinc, manganese or iron and, to increase the coating weight, hydroxylamine, is an amount of at least 0.01% by weight.

Description

The invention relates to a method for facilitating the cold forming of iron materials by applying a phosphate coating by means of an aqueous, acidic phosphating solution which contains zinc ions and hydroxylamine as accelerators.

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 cold forming, where 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 the phosphate coating and the lubricant enables multiple or severe cold working, possibly without a new intermediate treatment with lubricant.

Numerous methods are known to facilitate cold working 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 supply the majority of the cations for coating formation. In contrast, in the so-called “non-layer-forming” processes, the cations of the phosphate coating usually come from the treated metal itself, ie the phosphating solution essentially only provides the phosphate ions.

For example, US Pat. No. 2,298,280 describes a coating solution which contains an acidic phosphate, such as zinc or manganese phosphate, and hydroxylamine as an accelerator. According to the introductory remarks, the phosphate layer formation aims to improve the corrosion resistance and the paint adhesion. The patent does not contain any reference to the layer thickness of the phosphate layer produced or to the suitability of this layer for facilitating the cold deformation. In addition, the zinc and manganese concentrations mentioned, for example, are so low that the usability of these phosphating solutions for the relief of cold working is extremely doubtful.

US Pat. No. 2,702,768 mentions the use of hydroxylamine as an accelerator in "non-layer-forming" phosphating solutions. Such systems are - as already indicated above - of minor importance and unusable for severe deformations. Essentially the same applies to the processes according to US Pat. Nos. 3,615,912 and 4,149,909, which are based on the production of iron phosphate coatings and therefore work with alkali or ammonium phosphate solutions.

A disadvantage of the known, especially the aforementioned The method is that the phosphate coatings produced do not have the thickness required to facilitate cold working and the adhesion is too low.

US Pat. No. 2,743,204 discloses a "layer-forming" phosphating for the production of phosphate coatings, which among other things. is also intended to facilitate cold forming, known. It describes phosphating solutions for the treatment of iron, steel, zinc and aluminum with zinc or manganese as layer-forming cations, which can contain a wide variety of accelerators. Nitrite, chlorate, bromate, sulfite, nitro organic compounds such as nitrobenzenesulfonate, picric acid, and iodate, hydroxylamine and nitrate are mentioned. With regard to the achievable layer weights, chlorate is particularly emphasized. It has obviously not been recognized that hydroxylamine is particularly important in this regard. However, the zinc content of the phosphate layers thus obtained is too low to form the desired zinc stearates in sufficient quantity as a lubricant for cold forming in the subsequent treatment with soap solutions.

The object of the invention is to provide a process for facilitating the cold forming of ferrous materials which does not have the disadvantages of the known processes, in particular improves the subsequent formation of zinc stearates by a high zinc content and leads to thick, adherent phosphate coatings with simple process control.

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 iron materials are brought into contact with a phosphating solution which calculates 7.5 to 75 g / l of zinc ions and 5 to 75 g / l of nitrate ( as NO₃) contains 0.1 to 10 g / l hydroxylamine.

Phosphating solutions with hydroxylamine as an accelerator in combination with comparatively high concentrations of zinc are particularly suitable for the production of Phosphate coatings designed to facilitate cold working. Thanks to their excellent adhesion to the iron material as such, but especially in combination with conventional lubricants, the phosphate coatings are effective even with the most severe deformations. In addition, the process is not adversely affected even in the presence of ferrous or ferric ions in the solution. An additional advantage of the method according to the invention therefore lies in being able to bring the iron materials into contact with a phosphating solution, the iron ion content of which can be up to 25 g / l.

Cold deformation in the sense of the present method are all deformation processes into which the workpiece is introduced at a temperature ranging from approximately ambient temperature to approximately 100 ° C. and in which an increase in temperature of the workpiece is the result of the deformation work performed. Such methods are, for example, extrusion, upsetting, wire or tube drawing.

The method is particularly suitable for workpieces made of steel with a carbon content below 1% by weight, especially with a carbon content of approximately 0.05 to 0.6% by weight. Compared to known processes, it is also suitable for higher-alloy steels, which generally also have a higher hardness.

The hydroxylamine to be added to the phosphating solution can be of any commercial type. Storage-stable salts or complex compounds, which are predominantly in the form of hydrate, are preferred. Hydroxylamine sulfate, also called hydroxylammonium sulfate [(NH₂OH) ₂. H₂SO₄], is a particularly suitable compound.

The assumption about the particularly advantageous effect of the hydroxylamine as an accelerator is that the zinc content incorporated in the phosphate coatings is particularly high. This high zinc content increases the lubricating properties of the phosphate crystals themselves. It is particularly important, however, that the increased zinc content greatly increases the reactivity to a subsequently applied lubricant, especially when it comes to fatty acids or soaps. This is because there is a reaction between the zinc of the phosphate layer and the fatty acid anion with the formation of, for example, zinc stearate, which has significantly better lubricating properties than sodium stearate. That is, the higher the zinc content in the phosphate coating, the stronger the conversion to zinc soaps and the better the lubricating properties of the lubricating layer formed from the phosphate coating and the soap.

The preferred zinc content of the phosphating solution is 7.5 to 55 g / l and is preferably in the range of 10 to 30 g / l.

A preferred embodiment of the invention provides for the use of a phosphating solution which additionally contains manganese ions in an amount of up to 20 g / l.

The phosphate content of the phosphating solution must be based on the content of the layer-forming cations. It is generally 5 to 80 g / l, preferably 10 to 70 g / l (calculated as PO₄).

The invention provides for a phosphating solution to be used which contains nitrate as an additional accelerator. The nitrate content should preferably 30 to 70 g / l (calculated as NO₃). It is advisable to adjust the weight ratio of nitrate to phosphate to a value in the range from 0.3 to 6, preferably 0.5 to 5, but in particular 0.9 to 4.5 (calculated as the weight ratio NO₃: PO₄).

As already indicated, the phosphating solution used in the process according to the invention has the ability to form phosphate coatings with a high zinc content and still tolerate comparatively high iron contents. For example, the concentration of iron ions in the form of ferrous or ferric ions can be up to 25 g / l, so that the process can also be carried out on the iron side without any loss.

A further advantageous embodiment of the invention provides for the iron materials to be brought into contact with a phosphating solution which additionally contains nickel ions, preferably in an amount of 0.05 to 1 g / l, in particular 0.1 to 0.5 g / l. contains.

The phosphating solutions can expediently be used at a temperature of 54.4 to 96.1, in particular 71.1 to 87.8 ° C. Their pH is about 1.8 to 2.5 at the above temperatures.

The application of the phosphating solution is carried out in the usual way, preference is given to immersion or flooding, in particular immersion. The contact time during the immersion treatment is about 0.5 to 30 minutes, preferably 5 to 15 minutes.

With the aid of the method according to the invention, To produce phosphate coatings with a layer weight of 2.7 to 64.6 g / m². This gives the possibility of adapting the layer weight to the severity of the intended cold forming, the size of the workpiece and the like. Finally, the choice of layer weight will also have to take into account whether a lubricant is subsequently applied or not. As a rule, layer weights of 3.8 to 48.4 or 5.4 to 37.7 g / m² will meet the usual requirements.

The workpieces are pretreated before phosphating in the usual way, such as by cleaning, pickling, rinsing or activating. A water rinse or a rinse with a weakly alkaline solution, e.g. Contains borax, nitrite, triethanolamine or mixtures thereof. The iron material can then be subjected to cold working. However, a lubricant that is customary in cold-forming processes is preferably also applied. This can be done immediately after coating or after rinsing. The lubricant can also be applied immediately before the deformation, if necessary also between the deformation 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 working or emulsions of fatty acids or soaps, in particular with 8 to 18 carbon atoms in the acid anion, can be applied as lubricants. When using fatty acids and soaps, an emulsion containing 3 to 15% by weight should be used. Because of the reaction with the cation of the phosphate coating already mentioned above, sodium and / or Potassium soaps, especially stearates, are particularly advantageous.

If necessary, drying can be carried out in a conventional manner after the final treatment or between individual treatment stages - with the above-mentioned limitation in the formation of zinc soap.

• 1. Reinigen
• 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 (Entspannungstrocknen)

Gegebenenfalls kann eine Beizstufe in die Vorbehandlung eingeschoben werden.A particularly preferred sequence of procedures consists in

• 1. Clean
• 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 (flash drying)

If necessary, a pickling step can be inserted into the pretreatment.

The iron material can then be subjected to cold working immediately or after intermediate storage.

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

example 1

enthielt und 60 Gesamtsäurepunkte bei einer 5,0 ml-Probe aufwies (Gesamtsäurepunkte gleich Verbrauch von 0,1 n NaOH in ml bei Titration gegen Phenolphthalein als Indikator).A phosphating solution was prepared which

contained and had 60 total acid points in a 5.0 ml sample (total acid points equal to consumption of 0.1 N NaOH in ml when titrated against phenolphthalein as an indicator).

The solution was heated to 82.2 ° C and with
5 g / l hydroxylamine sulfate
transferred.

After 5 min to adjust the balance
0.07 g / l sodium nitrite
(calculated as NaNO₂)
added.

After a further 5 minutes, 2 sheets of cold-rolled and pickled steel each - dimensions 10.2. 15.2. 0.23 cm) phosphated for 5 min while diving. Such sheets were used at intervals of 10 minutes, so that the bath load was 1.34 m². h⁻¹. l⁻¹ was.

It was determined analytically that - compared to the use of a phosphating solution without hydroxylamine content - not only was the layer weight doubled, but also the layer weight dropped far less rapidly than usual when using the same solution Composition of crystals the same. The weight ratio of phosphophyllite to the sum of phosphophyllite and hopeit was 0.105 compared to 0.165 when the above-mentioned phosphating solution was used, but without hydroxylamine.

The materials treated as above were then rinsed with a weakly alkaline solution and provided with a lubricant containing sodium stearate. It was then dried and the excess soap left on the workpiece.

The workpiece was then subjected to conventional cold forming, for example an extrusion treatment. The results were excellent and far superior to those achieved using standard phosphating processes.

Example 2

210 g dieses Konzentrats wurden dann auf 1 1 gebrauchsfertige Phosphatierungslösung verdünnt.A concentrate A was formulated for the preparation of a phosphating solution

210 g of this concentrate were then diluted to 1 1 ready-to-use phosphating solution.

While using the solution, it can be supplemented or refreshed with a concentrate B, which was obtained from the following components:

This supplemental concentrate can be used if the ratio of total acid to free acid in the working phosphating solution rises above the desired value. If the ratio in the working phosphating solution falls below the desired value, concentrate A can be added.

Claims (14)

1. A process for facilitating cold working of iron materials by application of a phosphate coating by means of an aqueous acidic phosphating solution which contains zinc ions and hydroxylamine as accelerator, characterized in that the iron materials are contacted with a phosphating solution containing from 7.5 to 75 g/l of zinc ions, from 5 to 75 g/l of nitrate (calculated as NO₃) and from 0.1 to 10 g/l of hydroxylamine.
2. The process according to claim 1, characterized in that the iron materials are contacted with a phosphating solution containing up to 25 g/l of iron ions.
3. The process according to claims 1 or 2, characterized in that the iron materials are contacted with a phosphating solution containing from 7.5 to 55 g/l of zinc.
4. The process according to claims 1 or 2, characterized in that the iron materials are contacted with a phosphating solution containing from 10 to 30 g/l of zinc.
5. The process according to one or more of claims 1 to 4, characterized in that the iron materials are contacted with a phosphating solution which additionally contains up to 20 g/l of manganese ions.
6. The process according to one or more of claims 1 to 5, characterized in that the iron materials are contacted with a phosphating solution containing from 5 to 80 g/l of phosphate (calculated as PO₄).
7. The process according to one or more of claims 1 to 5, characterized in that the iron materials are contacted with a phosphating solution containing from 10 to 70 g/l of phosphate (calculated as PO₄).
8. The process according to one or more of claims 1 to 7, characterized in that the iron materials are contacted with a phosphating solution containing from 30 to 70 g/l of nitrate (each calculated as NO₃).
9. The process according to claim 8, characterized in that the iron materials are contacted with a phosphating solution wherein the ratio by weight of nitrate to phosphate is from 0.3 to 6.0.
10. The process according to claims 8 or 9, characterized in that the iron materials are contacted with a phosphating solution wherein the ratio by weight of nitrate to phosphate is from 0.5 to 5.
11. The process according to claims 8 or 9, characterized in that the iron materials are contacted with a phosphating solution wherein the ratio by weight of nitrate to phosphate is from 0.9 to 4.5.
12. The process according to one or more of claims 1 to 7, characterized in that the iron materials are contacted with a phosphating solution which additionally contains nickel ions, preferably in an amount of from 0.05 to 1.0 g/l, especially from 0.1 to 0.5 g/l.
13. The process according to one or more of claims 1 to 12, characterized in that the iron materials are contacted with a phosphating solution which additionally contains nickel ions in an amount of from 0.1 to 0.5 g/l.
14. The process according to one or more of claims 1 to 13, characterized in that the iron materials are contacted at temperatures from 54.4 °C to 96.1 °C with a phosphating solution which has a pH of from 1.8 to 2.5.