EP3058116B1 - Method for preparing shaped metal bodies for cold working - Google Patents

Description

The invention relates to a method as specified in claim 1 for coating metallic moldings first with an aqueous acidic oxalation solution and then with a lubricant composition in the form of an aqueous solution or dispersion based on organic polymer / copolymer to prepare the metallic moldings for cold forming.

Cold forming can usually take place at surface temperatures of up to around 450 ° C without external heat input. The heating can occur solely through the frictional forces acting during the forming process between the coated metallic shaped body blank and the tool and through internal frictional forces due to the flow of material, but possibly also through preheating of the shaped body to be formed. Usually, however, the temperature of the shaped bodies to be reshaped is often initially around ambient temperature, that is to say about 10 to 32.degree. However, if the shaped bodies to be reshaped are preheated to temperatures, for example, in the range from 650 to 850 ° C., from 850 to 1250 ° C. or from 650 to 1250 ° C., one speaks of warm forging or forging. In addition, increased to high pressures usually occur during cold forming, e.g. for steel in the range from 200 MPa to 1 GPa and sometimes even up to 2 GPa.

The shaped bodies to be formed are mostly strips, sheets, slugs, wires, wire coils, more complex shaped parts, sleeves, profiles such as hollow or solid profiles, tubes, circular blanks, disks, rods, rods and / or cylinders. A slug is a disk or a section of wire, wire bundle or rod.

The metallic moldings to be cold formed can in principle consist of any metallic material. They preferably consist essentially of steel, aluminum, aluminum alloy, copper, copper alloy, magnesium alloy, titanium, titanium alloy, in particular of structural steel, high-strength steel, stainless steel, iron or steel material with a chromium content and / or metallic coated steel such as aluminized or galvanized steel. Most of the time, the shaped body consists essentially of steel.

While forming oils are usually used for cold forming of metallic moldings with lower degrees of deformation and correspondingly lower forces, at much higher degrees of deformation usually at least one coating is used as a separating layer between the mold and the tool in order to avoid cold welding of the mold and the tool. For the latter, it is customary to provide the shaped bodies with at least one coating of a lubricant or with a lubricant composition in order to reduce the frictional resistance between the shaped body surface and the forming tool.

• Ein Gleitziehen (Zugdruckumformen) z.B. von geschweißten oder nahtlosen Rohren, Hohlprofilen, Vollprofilen, Drähten oder Stäben wie z.B. beim Drahtziehen oder Rohrziehen,
• ein Abstreckdrücken, Abstreckziehen (Umformen auf Endmaß) oder/ und Tiefziehen z.B. von Bändern oder Blechen zu speziell tiefgezogenen Formkörpern oder von Hohlkörpern zu stärker verformten Hohlkörpern,
• ein Gewindewalzen oder/und Gewindeschlagen z.B. bei Muttern- oder Schrauben-Rohlingen,
• ein Pressen wie z.B. Kaltfließpressen (Druckumformen) z.B. von Hohl- oder Vollkörpern oder Strangpressen oder/und
• ein Kaltstauchen z.B. von Drahtabschnitten zu Verbindungselementen wie z.B. Muttern- oder Schrauben-Rohlingen.

Cold forming mainly includes:

• A slide drawing (tensile compression forming) e.g. of welded or seamless tubes, hollow profiles, solid profiles, wires or rods such as wire drawing or tube drawing,
• ironing, ironing (reshaping to final dimensions) and / or deep drawing, e.g. of strips or sheets to form specially deep-drawn shaped bodies or of hollow bodies to form more strongly deformed hollow bodies,
• thread rolling and / or thread tapping, e.g. for nut or screw blanks,
• a pressing such as cold extrusion (pressure forming) eg of hollow or solid bodies or extrusion and / or
• cold upsetting, for example, of wire sections to form connecting elements such as nut or screw blanks.

In the past, the metallic moldings for cold forming were almost exclusively prepared for cold forming either by applying a fat, an oil or an oil emulsion. For a long time, a separating layer has usually been followed by a layer of lubricant in order to minimize the friction that occurs during the forming process. Here, the blanks are usually first coated with zinc phosphate to form a separating layer and then either with a soap, in particular based on alkali or / and alkaline earth stearate or / and with a solid lubricant, in particular based on molybdenum sulfide and / and carbon, to form a lubricant layer before the blanks coated in this way are cold-formed.

The aforementioned prior art lubricant systems are mainly based on zinc phosphate as a separating layer. Today, however, the conditions of environmental compatibility and industrial hygiene as well as the requirements for safety-relevant components for phosphate-free and low-heavy metal baths and coatings must be taken into account much more than in the past.

The metallic moldings to be cold formed are precoated before cold forming. In preparation for cold forming, the metallic surface of the molded body or its metallic coated coating can be provided with a conversion coating, in particular oxalated or phosphated. The conversion coating can preferably be carried out with an aqueous composition based on oxalate, alkali phosphate, calcium phosphate, magnesium phosphate, manganese phosphate, zinc phosphate or a corresponding mixed crystal phosphate such as ZnCa phosphate. Sometimes the metallic moldings are also bare, that is, wetted with a lubricant composition without a previous conversion coating. The latter is only possible if the metallic surface of the shaped body to be reshaped is cleaned chemically and / or physically beforehand.

Any of the pamphlets US 3481762 A , DE 2125503 A1 and US 2850417 A each discloses an oxalate coating on a steel surface prior to forming.

In the following, the steels which can be used according to the invention are characterized as those which have a carbon content in the range from 0 to 2.06% by weight and therefore do not belong to the iron materials, and as those which have a chromium content in the range from 0 to <10% by weight and in particular in the range from 0.01 to 9% by weight, from 0.05 to 8% by weight, from 0.1 to 7, from 0.2 to 5% by weight. -%, from 0.25 to 4% by weight or from 0.3 to 2.5% by weight. These include on the one hand, according to DIN EN 10025, so-called structural steels, unalloyed steels, unalloyed quality steels, unalloyed stainless steels, micro-alloyed steels, low-alloy steels and high-alloy steels and, on the other hand, case-hardened steels according to DIN EN 10084 and heat-treatable steels according to DIN EN 10083. These steels are hereinafter referred to as "Can be used according to the invention" or "non-corrosion-resistant" if they have a chromium content of less than 10 wt. In comparison to these steels, which are basically cold-workable and are cold-workable according to the invention, cast iron is not cold-workable.

Steels have a carbon content in the range from 0 to 2.06% by weight. Of the different element contents of the steels, the chromium content of the steel in particular influences the pickling attack of an acidic aqueous oxalation composition and also of an acidic aqueous zinc phosphating composition. Because if the chromium content is well above 10% by weight, a passivating layer forms on the steel surface, which protects the steel from oxidation and chemical attack. Then, however, the pickling attack on the substrate is inhibited or completely prevented, and a separating layer does not form because no iron can be dissolved out of the substrate.

In order to form separating layers on steels with a chromium content> 10% by weight, it is usual to coat these components with an oxalate layer using an aqueous oxalating solution containing halogen and thiosulphate. The oxalation solution activated in this way has a drastic effect higher pickling attack than an aqueous, halogen- and thiosulphate-free oxalation solution. As has now been found, the oxalating solutions of the prior art lack a possibility of reducing the pickling attack while at the same time forming a sufficiently strong oxalate layer. For this reason, it has hitherto not been possible to coat steels with a carbon content in the range from 0 to 2.06% by weight and with a chromium content in the range from 0 to <10% by weight with oxalate layers. Such steels were therefore covered with greater effort and with more environmentally harmful and overall more expensive zinc phosphate layers, but only steels with a chromium content of <5% by weight can be zinc phosphated.

In the case of the coating of steel blanks with a carbon content in the range from 0 to 2.06% by weight and with a chromium content in the range from 0 to <10% by weight, aqueous oxalating compositions with a content resulted, for example an extremely strong pickling attack on thiosulphate and / or on halogen compounds, so that no adequate separating layers, namely too thin and not closed, or no separating layers at all were formed. These oxalate layers were completely unsuitable for cold forming.

Surprisingly, a method for oxalating these so-called non-corrosion-resistant steels has now been found in which the pickling attack is not too high, which is advantageous for the build-up of the oxalate layer and in which oxalate layers that are well suited for cold forming have been applied as separating layers for cold forming.

This is because it has now been shown that when coating steel blanks with a carbon content in the range from 0 to 2.06% by weight and with a chromium content in the range from 0 to <10% by weight aqueous oxalation compositions without a content of sulfur compound such as thiosulfate and without a content of halogen compound results in an advantageous pickling attack for the build-up of the oxalate layer, so that for cold forming Oxalate layers that are well suited as a separating layer can be formed.

When coating steel blanks with a chromium content of significantly more than 10% by weight, aqueous oxalation compositions containing, for example, thiosulphate and / or halogen compound resulted in an advantageous pickling attack, which also resulted in the high chromium content of these formed passivating layer attacks, so that good oxalate layers were formed due to the very strong pickling attack. These oxalate layers were also well suited for cold forming.

Conversely, it has now also surprisingly been found that when coating steel blanks with a chromium content of significantly more than 10% by weight with aqueous oxalation compositions without a content of sulfur compounds such as thiosulphate and without a content of halogen compounds, the result is too low or there is no pickling attack at all, so that no oxalate layers suitable for cold forming as a separating layer are formed.

These relationships are exemplified below in Table 1, where the material of sheet A is a cold-rolled steel CRS and where the material of slug B is marked with 1.0401 and that of sheet C with 1.4571: Contents in g / L VB1 VB2 VB4 B5 B6 VB8 blank Sheet A Slug B Sheet C Sheet A Slug B Sheet C Steel material CRS C15 X6CrNiMoTi17-12-2 CRS C15 X6CrNiMoTi17-12-2 C content in% by weight 0.039 0.12-0.18 0.08 0.039 0.12-0.18 0.08 Cr content in% by weight 0 0 17th 0 0 17th Oxalic acid 54.0 54.0 54.0 40.0 40.0 40.0 Nitroguanidine 0.4 0.4 0.4 Sodium thiosulfate 1.6 1.6 1.6 Sodium chloride 25.0 25.0 25.0 Sodium fluoride 0.2 0.2 0.2 Sodium hydrogen fluoride 10.0 10.0 10.0 Thickener 1 PEG 400 10 10 10 Total acidity GS points 70 70 70 60 60 60 Bath temp. ° C / contact time min 65/3 65/3 65/3 65/3 65/3 65/3 Pickling removal BA g / m ² 2.3 2.5 4.3 2.1 2.1 0 Layer weight SG g / m ² 1.6 1.4 7.6 5.3 4.9 0 Ratio BA / SG% 143.8 178.6 56.6 39.6 42.9 - Oxalate layer quality very bad very bad Well very good very good no shift Lubricant layer polymer polymer polymer polymer polymer polymer Lubricant layer thickness g / m ² 1.7 1.7 1.7 1.6 1.8 1.7 Lubricant layer quality Well Well Well Well Well Well Cold forming not possible not possible Well very good very good not possible Disadvantage? no adhesive and no closed oxalate layers, therefore no cold forming possible Cold forming is only possible on chrome-alloyed steels> 10% Cr no missing oxalate layer, therefore no cold forming possible

The table shows the strong dependency of cold formability and the quality of cold forming on the presence and quality of the oxalate layer. Here, Gardomer® based on organic polymer / copolymer was used for the lubricant layer, which is ideally suited for cold forming as a lubricant layer and has a very wide range of performance.

In the comparative examples CE1 and CE2, the ratio of pickling attack to layer weight is much too high, so that particularly thin oxalate layers were formed which did not result in any closed or adherent layers. In the comparative example CE5, the passivating layer on the high-chromium steel is not attacked, so that no pickling takes place, so that no pickling takes place and the formation of an oxalate layer does not occur.

In comparative example VB3, the pickling attack is so strong that it removes the passivating layer on the high-chromium steel, so that the pickling removal, the layer weight and the ratio of BA to SG are of a suitable strength; as a result, a good oxalate layer is formed, which enables good cold forming.

In Examples B5 and B6 according to the invention, the excellent bath setting results in very good oxalate layers which are very well suited for cold forming.

In the case of these steels which can be used according to the invention and have a chromium content of less than 10% by weight, phosphating is still the usual treatment for forming a separating layer. However, for the material properties of critical components, in which, for example, precise material properties are set by heat treatment, phosphating has the considerable disadvantage that they contain phosphate. This is because phosphorus diffuses from the metallic surface into the steel structure during heat treatment, and the phosphorus content damages the properties of these Steels, especially through delta ferrite formation, sensitivity to impact stress and embrittlement. Phosphorus-induced embrittlement renders critical components unusable, as notched impact strength, brittleness, etc. are impaired. Even the smallest amounts of phosphorus increase the sensitivity to temper embrittlement and lead to cold brittleness and a tendency to brittle fracture. Critical components such as screws and other connecting elements must therefore be cleaned very carefully and at great expense after phosphating. A residual phosphate content can almost not be avoided. A metallographically detectable phosphorus content is not permitted according to EN ISO 898. It would therefore be beneficial to use a phosphate-free treatment method in preparation for cold forming, which, however, is not known in the prior art after a detailed assessment. If these steels come into contact with sulfur, the material properties are also considerably impaired.

For these steels which can be used according to the invention, the skilled applicant is not aware of any low-heavy metal and at the same time largely environmentally friendly process for preparing for cold forming. Rather, there has been a need for non-corrosion-resistant steels for several decades for phosphate-free and, as far as possible, largely environmentally friendly processes for preparation for cold forming, as in Textbook by Kurt Lange: Umformtechnik, Volume 1 p. 258 2nd edition 1984 and Volume 2 p. 661 2nd edition 1988 is indicated. However, unlike phosphating, oxalating has not proven successful in the case of the steels that can be used according to the invention, since the coatings, compared to phosphating, are not sufficiently adhesive and are therefore not suitable for the intended use. Almost all oxalation solutions of the prior art contain, in addition to water, a content of bromide, chloride, chlorate, fluoride, nitrite and / or sulfur compound in order to produce suitable adhesive coatings.

It turned out, however, that the oxalation solutions and oxalate layers of the prior art are only applicable to corrosion-resistant steels Stainless steels with a chromium content of significantly more than 10% by weight are suitable, since they only form layers suitable for cold forming on these types of steel. The halogen and sulfur compounds are undesirable here because they are environmentally unfriendly and in some cases also poisonous and because they may have a strong corrosive effect. Contents of heavy metals apart from iron and zinc should be avoided as far as possible because they are mostly environmentally unfriendly, impair industrial hygiene, cause disposal problems and high additional costs. They are then to be labeled in accordance with the Hazardous Substances Ordinance.

DE 976692 B teaches the use of oxalating solutions with a content of 1 to 200 g / L oxalic acid, 0.2 to 50 g / L iron chlorides, 5 to 50 g / L phosphate calculated as P ₂ O ₅ and optionally Cr or Ni Salt.

U.S. 2,550,660 describes the addition of oxygen-containing sulfur compounds such as sodium thiosulphate and halogen compounds such as sodium chloride and ammonium bifluoride, which increase the attack of oxalic acid solutions on stainless steels and therefore form oxalate layers with lower levels of activators.

Oxalating metallic surfaces is also known for the purpose of corrosion protection and, if necessary, also to improve paint adhesion. In comparison to zinc phosphate layers, however, due to the halide content, the oxalate layers have proven to be so little anti-corrosive and so poorly adherent that oxalate has practically not been used for the purpose of corrosion protection for decades. The only exception is for the formation of the separating layer for the cold forming of corrosion-resistant steels with significantly more than 10% by weight of chromium.

Oxalating enables the formation of a completely phosphate-free separating layer without the use of environmentally unfriendly heavy metals. Iron and zinc are not considered environmentally unfriendly for the purposes of this application Considered cations or heavy metals. Iron and zinc compounds are not regarded as environmentally unfriendly heavy metal compounds for the purposes of this application. However, the use of oxalation according to the prior art, due to the halogen and / or sulfur compounds used on non-corrosion-resistant steels with a chromium content of less than 10% by weight, leads to undesired corrosion and to very poorly adhering layers that are not suitable for cold forming are suitable because they do not have a separating layer that works reliably during cold forming.

It has now been found, surprisingly, that the environmentally unfriendly and also the additives disadvantageous for the processing methods, which were and are used again and again in the oxalations of the prior art, are not required in the preparation of non-corrosion-resistant steels for cold forming.

Furthermore, it was surprisingly found that the inevitably occurring sludge in the bathroom is kept in a significantly lower weight, that the sludge can be kept free of heavy metals with the exception of iron, zinc and steel refiners pickled out of the steel and is therefore easier, cheaper and more environmentally friendly to process than in the otherwise used phosphating. Because for the coating of 50,000 t of steel wire with a diameter of 9 mm, about 3 t of dried sludge are produced in the process according to the invention, while with various types of zinc phosphating, depending on the process variant, about 14 to 48 t of dried sludge are produced.

In the case of the most varied of metallic materials, the shaped bodies of which are to be advantageously reshaped by cold forming, it has been shown that in the case of shaped bodies made of steel with a chromium content in the range from 0 to less than 10% by weight, there is a particular need for a suitable preparation for the Cold forming exists, which can be achieved with phosphate-free oxalations.

The object was to propose a method for treating molded bodies with an iron or steel surface with a chromium content in the range from 0 to <10% by weight in a conversion treatment prior to cold forming, in which the process is essentially phosphate-free or entirely phosphate-free and in which the addition of environmentally unfriendly heavy metals can be dispensed with.

• dass mindestens ein Formkörper mit einer wässerigen sauren Zusammensetzung (= Bad der Konversionszusammensetzung) zur Ausbildung einer Konversionsschicht als Trennschicht kontaktiert wird,
• dass die wässerige saure Zusammensetzung nur mit einem Ansatz angesetzt ist/wird, der enthält Wasser,
• 2 bis 500 g/L Oxalsäure berechnet als wasserfreie Oxalsäure sowie
  1. a) 0,01 bis 20 g/L an mindestens einem Beschleuniger auf Basis von Guanidin berechnet als Nitroguanidin oder/und
  2. b) 0,01 bis 20 g/L an mindestens einem Nitrat berechnet als Natriumnitrat und
• dass der Beizabtrag der wässerigen sauren Zusammensetzung im Bereich von 1 bis 6 g/m² liegt gemessen durch gravimetrische Bestimmung nach DIN EN ISO 3892,
• dass das Schichtgewicht einer getrockneten Konversionsschicht im Bereich von 1,5 bis 15 g/m² liegt gemessen durch gravimetrische Bestimmung nach DIN EN ISO 3892,
• dass das Verhältnis von Beizabtrag zu Schichtgewicht BA : SG der getrockneten Konversionsschicht im Bereich von (0,30 bis 0,75) : 1 liegt,
• dass die getrocknete Konversionsschicht eine fest haftende Beschichtung bildet und
• dass auf die Konversionsschicht mit einer Schmierstoffzusammensetzung eine Schmierstoffschicht aufgebracht wird, wobei die Schmierstoffzusammensetzung einen Gehalt von mindestens 5 Gew.% an organischen Polymere oder/und Copolymeren aufweist, und dass die Schmierstoffschicht getrocknet wird, wobei der mindestens eine Formkörper durch Berieseln, Sprühen oder/und Tauchen bei einer Temperatur von 10 bis 90°C mit der wässrigen Zusammensetzung kontaktiert wird.

The object is achieved with a method for treating shaped bodies with a steel surface with a carbon content in the range from 0 to 2.06% by weight and with a chromium content in the range from 0 to <10% by weight before a Cold forming, which is characterized by

• that at least one shaped body is contacted with an aqueous acidic composition (= bath of the conversion composition) to form a conversion layer as a separating layer,
• that the aqueous acidic composition is / is only prepared with a mixture that contains water,
• 2 to 500 g / L oxalic acid calculated as anhydrous oxalic acid as well
  1. a) 0.01 to 20 g / L of at least one accelerator based on guanidine, calculated as nitroguanidine and / or
  2. b) 0.01 to 20 g / L of at least one nitrate calculated as sodium nitrate and
• that the pickling removal of the aqueous acidic composition is in the range from 1 to 6 g / m ² , measured by gravimetric determination according to DIN EN ISO 3892,
• that the layer weight of a dried conversion layer is in the range from 1.5 to 15 g / m ² , measured by gravimetric determination in accordance with DIN EN ISO 3892,
• that the ratio of pickling removal to layer weight BA: SG of the dried conversion layer is in the range of (0.30 to 0.75): 1,
• that the dried conversion layer forms a firmly adhering coating and
• that a lubricant layer is applied to the conversion layer with a lubricant composition, the lubricant composition having a content of at least 5% by weight of organic polymers and / or copolymers, and that the lubricant layer is dried, the at least one shaped body by sprinkling, spraying or / and contacting the aqueous composition with dipping at a temperature of 10 to 90 ° C.

In the method according to the invention, blanks in the form of sheets, slugs, wires, wire coils, molded parts, profiles, tubes, discs, rods and / or cylinders made of a steel material with a carbon content in the range from 0 to 2.06 wt. % and with a chromium content in the range from 0 or 0.001 to <10% by weight. Here it is preferred that a strip, sheet metal, slug, wire, wire collar, more complex shaped molded part, a sleeve, a profile, tube, a round blank, disk, rod, a rod and / or cylinder made of a steel material before cold forming is used as the substrate is / is oxalated. Here, the substrate can optionally have a zinc or zinc alloy layer. Usually only slugs are galvanized or alloyed. If necessary, the blanks to be formed are first heat-treated to adjust the material properties, e.g. by soft annealing, so that they can be easily cold-formed.

If necessary, the surfaces of the blanks to be cold formed and / or the surfaces of their metal-coated coating can be used before wetting be cleaned with the aqueous oxalation composition in at least one cleaning process, in principle all cleaning processes are suitable for this purpose. The chemical and / or physical cleaning can primarily include mechanical descaling, annealing, peeling, blasting such as sandblasting, in particular alkaline cleaning and / and acidic pickling. Chemical cleaning is preferably carried out by degreasing with organic solvents, by cleaning with alkaline and / or acidic cleaners, with neutral cleaners, with acidic stains and / and by rinsing with water. Pickling and / or blasting is mainly used for descaling the metallic surfaces. Here it is preferred, for example, to only anneal a welded pipe made of cold strip after welding and scraping, for example to pickle, rinse and neutralize a seamless pipe.

As an alternative to this or in addition, it is possible to clean the metallic surfaces with at least one strong acid-resistant surfactant such as, in particular, at least one cationic surfactant such as a laurylamine polyethylene glycol ether such as Marlazin® L 10 or / and a benzalkonium chloride such as Lutensit® TC-KLC 50 der Oxalating composition according to the invention is / is added, so that at least something is also cleaned during oxalating and / or cleaning and oxalating takes place in a one-pot process. The separate cleaning step can then be omitted for less soiled parts. The addition of surfactants in the oxalating bath also has the advantages that it can be cleaned and oxalated in a single bath and in a single process step, that the metallic surface is attacked more evenly by the oxalic acid and can be coated better and more evenly with the oxalate layer and that the accumulation of sludge particles on the oxalate layer can be prevented more effectively.

All compositions that “consist essentially of” certain components can also “consist” only of these components or “contain” these components.

The aqueous conversion layer can optionally be separated or only dried together with the subsequently applied lubricant layer, wherein the conversion layer can contain a residual water content when the lubricant layer is applied in the latter variant in order to avoid a drying step and / or to make the lubricant layer sufficiently adhesive and still apply moist conversion layer. It is particularly preferred here that the oxalated substrates are coated with a layer of lubricant in the wet-on-wet process.

In the method according to the invention, preferably no heavy metal is intentionally added with the exception of iron, and in particular no environmentally unfriendly heavy metal is intentionally added. However, as practice repeatedly shows, the bath may contain iron, zinc, steel finishing elements and / or alloy components and possibly also small amounts of halogen compounds, phosphorus compounds and / or sulfur compounds from other baths and parts of the system in order to form the separating layer introduced into the bath to form the separating layer at least from time to time in some systems.

Water is used as the solvent, in particular as deionized water or as city water. The water content of the aqueous oxalating composition is preferably 40 to 99.75% by weight of water.

The aqueous acidic composition for the formation of a conversion layer (= bath of the conversion composition) is used in order to form a separating layer on the surface of the metallic blank. This composition and / or the bath will be / are only prepared with a mixture that essentially consists of water, 2 to 500 g / L oxalic acid, calculated as anhydrous oxalic acid and a) 0.01 to 20 g / L of at least one accelerator based on guanidine, calculated as nitroguanidine or / and b) 0.01 to 20 g / L of at least one nitrate calculated as sodium nitrate and optionally at least one thickening agent based on at least one compound of polyacrylamide, polyallylamine, polyethylene glycol, polysaccharide, polysiloxane, polyvinylamide and / or polyvinylamine in a content im Range from 0.01 to 50 g / L, optionally from a pigment for the flowability of oxalic acid in a content in the range from 0.01 to 20 g / L and optionally from at least one surfactant that is stable in the acidic composition in a content in the range from 0.01 to 5 g / L. If you continue to work with this bath, in which certain components of the bath may be used differently, a supplement is added if necessary, which essentially consists of only or only at least one of the components of the batch. Oxalic acid is usually the most consumed here and should therefore usually be added first. When supplementing with oxalic acid, water does not necessarily have to be added. The oxalic acid is calculated as completely dissolved oxalic acid, since g / L is used as the unit. The oxalic acid is usually contained in water and in the entire bath in a stable manner up to the solubility limit at the respective temperature. Commercially available oxalic acid is often in the form of a coarse powder and may then need to be finely ground before it is added to the bath. It can be advantageous here to add a finely divided powder such as an oxidic or silicate powder, in particular with an average powder particle size in the range from 0.5 to 20 μm, to the oxalic acid present in the form of powder, in order to avoid caking of the slightly hygroscopic powder and a To ensure flowability. The free-flowing oxalic acid has the advantage that the oxalic acid does not cake and is therefore easier to handle. The flowability is of great importance for the pumpability and dosability of the powder. The pourability This ensures that a suitable fine-grain pigment surrounds the components and in particular the oxalic acid and prevents neighboring powder particles from growing together. As a result, clumping of oxalic acid is significantly reduced or completely prevented. Lumpy products cannot be dosed and in some cases cannot be used with automatic suction systems. Furthermore, the disintegration times of lumpy products are much greater.

The aqueous composition can contain 0.001 to 20 g / l of at least one inorganic or organic pigment, preferably pigment based on oxide, organic polymer and / or wax. Titanium oxide powders in particular have proven particularly useful.

It has been shown that, in principle, oxalic acid contents in the range from 0.5 to 400 g / L can be used well for oxalating. However, particularly high contents of oxalic acid are only found dissolved in water at high temperatures. When using contents of the order of magnitude of 1 g / L, however, the oxalic acid content of the aqueous composition must be supplemented after a very short time and often. The aqueous acidic composition according to the invention for forming a conversion layer and / or the bath preferably have an oxalic acid content in the range from 5 to 400 g / L, from 10 to 300 g / L, from 15 to 200 g / L, from 20 to 120 g / L, from 25 to 90 g / L, from 30 to 60 g / L or from 35 to 40 g / L, calculated as anhydrous oxalic acid C ₂ H ₂ O ₄ . The dilution factor of a concentrate containing oxalic acid to the bath can preferably be in the range from 1 to 20, diluting with water.

During oxalating, depending on the composition of the contacted metallic surfaces of the blanks, iron oxalate, iron oxalate dihydrate, zinc oxalate and / or zinc oxalate dihydrate, in particular, are formed from the oxalate due to the pickled metal ions.

At least one accelerator based on guanidine and / or at least one nitrate including nitric acid, calculated as NO ₃ , can be used as the accelerator. Beyond this, further accelerators are not necessary and often also not useful. Nitrite as an accelerator is unstable as an accelerator in the presence of iron oxalate and forms disruptive nitrous gases. As an accelerator, chlorate contains halogens. An m-nitrobenzenesulfonate such as the sodium salt SNBS contains sulfur as an accelerator. Hydrogen peroxide reacts chemically with oxalic acid and does not act as an accelerator. Hydroxylamine compounds as accelerators are suspected of forming carcinogenic nitrosamines. Thiosulfates as accelerators cause a far too strong pickling attack, so that no oxalate layer is formed as a result.

Acetatoguanidine, aminoguanidine, carbonatoguanidine, iminoguanidine, melanilinoguanidine, nitroguanidine, nitroguanidine and / or ureidoguanidine, for example, can be added as accelerators a) based on guanidine. Aminoguanidine and nitroguanidine are particularly preferred here. In particular, nitroguanidine can preferably also contain a stabilizer, such as a content as silicate, to reduce the impact sensitivity. Due to a low concentration of nitroguanidine in the aqueous composition and possibly also an addition of a stabilizer, an over-rapid reaction of the nitroguanidine is reliably avoided. This stabilizer preferably also acts as a biocide and / or as a thickener. Sodium nitrate, potassium nitrate, ammonium nitrate, nitric acid and many other organic and / or inorganic nitrates such as iron nitrate can be used as accelerators based on nitrate. However, sodium nitrate, potassium nitrate and nitric acid are particularly preferred.

If only a guanidine compound is used as an accelerator, a slightly increased consumption of this accelerator can often be observed. If only nitrate is used as an accelerator, then a slightly higher concentration of this accelerator should be selected. If at least one If guanidine compound and at least one nitrate are used as accelerators, then a significantly lower consumption of guanidine compound and at the same time a somewhat lower consumption of nitrate can often be observed.

The aqueous acidic composition according to the invention for forming a conversion layer and / or the bath preferably have a total content of accelerators a) and / or b) in the range from 0.05 to 30 g / L, from 0.1 to 20 g / L, of 0.2 to 12 g / L, from 0.25 to 10 g / L, from 0.3 to 8 g / L, from 0.35 to 6 g / L, from 0.4 to 4 g / L, from 0.45 to 3 g / L or from 0.5 to 2 g / L, calculated as the sum of the calculated contents based on nitroguanidine and sodium nitrate.

The aqueous acidic composition according to the invention for forming a conversion layer and / or the bath preferably have a content of guanidine-containing accelerators a) in the range from 0.05 to 18 g / L, from 0.1 to 15 g / L, from 0, 2 to 12 g / L, from 0.3 to 10 g / L, from 0.4 to 8 g / L, from 0.5 to 6 g / L, from 0.6 to 5 g / L, from 0, 7 to 4 g / L, from 0.8 to 3 g / L, from 0.9 to 2.5 g / L or from 1 to 2 g / L, calculated as nitroguanidine CH ₄ N ₄ O ₂ .

The aqueous acidic composition according to the invention for forming a conversion layer and / or the bath preferably have a total content of nitrate-containing accelerators b) in the range from 0.05 to 18 g / L, from 0.1 to 15 g / L, from 0, 2 to 12 g / L, from 0.25 to 10 g / L, from 0.3 to 8 g / L, from 0.35 to 6 g / L, from 0.4 to 4 g / L, from 0, 45 to 3 g / L or from 0.5 to 2 g / L, calculated as sodium nitrate NaNO ₃ .

The ratio of the concentrations in g / L of oxalic acid calculated as anhydrous oxalic acid to the total of the accelerators a) and b) calculated as nitroguanidine and / or sodium nitrate, of which at least one accelerator is present, in the aqueous acidic composition to form a conversion layer or / and the bath is preferably in the range from 500: 1 to 2: 1, from 150: 1 to 5: 1, from 80: 1 to 8: 1, from 40: 1 to 10: 1 or from 20: 1 to 12: 1.

If the content of the at least one accelerator in the bath is too low or even absent, this can lead to disturbances in the layer formation or even to the elimination of the layer formation. If the content of the at least one accelerator in the bath is too high, this can lead to an unnecessarily high consumption of accelerator (s).

A thickener can help to adjust the viscosity of the bath, influence the formation of the wet film and reduce the corrosion of the surfaces of the blanks. If no thickener is used, the formation of the wet film can be significantly less than with a thickener and the drying of the wet film can take place more quickly than with a thickener. If the content of a thickener in the bathroom is too high, the wet film may only dry very slowly. The thickener should be stable in the bath. The thickening agent can be added both in the batch and during operation of the bath.

Preferably, the at least one thickener is used to set a viscosity of the bath in the range from 0.2 to 5 mPa.s measured at 20 ° C. with a rotary viscometer. The thickener according to the invention is preferably a polysaccharide such as, for example, based on cellulose or xanthan and / or a polyethylene glycol, in particular a polyethylene glycol with an average molecular weight in the range from 50 to 2000 or from 200 to 700.

The at least one thickener is preferably used in a content of 0 or in the range from 0.01 to 50 g / L in the aqueous acidic composition according to the invention to form a conversion layer and / or in the bath, particularly preferably in a content in the range of 0, 1 to 50 g / L, from 1 to 45 g / L, from 2 to 40 g / L, from 3 to 30 g / L, from 4 to 25 g / L or from 5 to 20 g / L, calculated as completely dissolved active ingredient or as completely dissolved thickening agent in the bath.

The treatment bath can be made up with a liquid aqueous concentrate which is produced by dissolving a predetermined amount of oxalic acid and, if necessary, also by adding accelerator, pigment, surfactant and / and thickening agent in deionized water. The dilution factor for diluting a concentrate to make a bath can be kept in the range from 1 to 100.

As an alternative to this, the treatment bath can be made up with a powdery concentrate, which is produced by kneading, rubbing, mixing in and / or rubbing in powdery oxalic acid and optionally with the addition of nitrate dissolved in water, pigment for increasing the flowability, surfactant and / or thickener, for example in a kneader and / or mixer is produced. The factor for the dissolution of the concentrate in water for the bath formulation can be kept in the range from 1 to 100.

In a further alternative, the treatment bath can be made up with a pasty concentrate, which is prepared by mixing oxalic acid with water and optionally with the addition of at least one accelerator dissolved in water, pigment for increasing the flowability, surfactant and / and thickening agent, for example in a kneader or / and mixer is made. It can have a water content of up to about 10% by weight. This concentrate can be adjusted to a paste-like, meterable and easily dissolvable product. The dilution factor for the dilution of this concentrate to the bath formulation can be kept in the range from 1 to 100.

All types of concentrates have been tried and tested and resulted in good usable bath approaches. The powdery concentrates are particularly advantageous in manufacture and transport. The highly concentrated paste has the advantage of being one-component and easy to use.

However, if a pickling inhibitor such as a thiourea compound or tribenzylamine TBA were added to the oxalation composition, the pickling attack and the layer formation would be significantly reduced or even prevented entirely. Therefore, in the process according to the invention, no small addition of a pickling inhibitor should usually be added, but rather the batch solution and the supplementary solutions should usually only consist of the components mentioned in the main claim.

The pH of the aqueous acidic composition for forming the conversion layer is usually in the range from 0 to 3 or from 0.2 to 2.

The aqueous acidic bath composition for forming a conversion layer as a separating layer, the oxalate bath, preferably has a total acid GS in the range from 3 to 870 points. The total acid is measured as follows:
The total acid GS (= Total Acid TA) is the sum of the contained cations as well as free and bound acids. The acids are oxalic acid and optionally nitric acid. It is determined by the consumption of 0.1 molar sodium hydroxide solution using the indicator phenolphthalein in 10 ml of oxalating composition diluted with 50 ml of deionized water. This consumption of 0.1 M NaOH in ml corresponds to the number of points for the total acid. If a further acid occurs in addition to oxalic acid in the oxalation composition, the content of the further acid can be determined separately and deducted from the total acid determined in order to obtain the value GS based only on the oxalic acid.

In the process according to the invention, the content of total acid, based only on oxalic acid, can preferably be in the range from 3 to 900 points, from 8 to 800 points, from 12 to 600 points, from 20 to 400 points, from 30 to 200 points, 40 to 100 points or 50 to 70 points.

The contact time of a metallic surface of a blank during dipping is preferably in the range from 0.5 to 30 minutes, in particular in the range from 1 to 20 minutes, from 1.5 to 15 minutes, from 2 to 10 minutes or from 3 to 5 minutes. The contact time of a metallic surface of a blank during spraying is preferably in the range from 1 to 90 s, in particular in the range from 5 to 60 s or from 10 to 30 s.

The blanks are contacted with the oxalation composition by sprinkling, spraying and / or dipping at a temperature of 10 to 90 ° C. The bath temperature of the oxalate bath is in the range from 10 to 90.degree. C., in particular in the range from 25 to 80.degree. C., from 40 to 70.degree. C. or from 50 to 65.degree.

When the aqueous acidic composition comes into contact to form the conversion layer, a pickling effect occurs on the metallic surface, with part of the metallic surface being removed. The pickling removal BA is in the range from 1 to 6 g / m ² , preferably in the range from 1.3 to 4.5 g / m ² or from 1.5 to 3 g / m ² . It is determined by weighing dried coated substrates before and after coating. Here it may be desirable to set as little pickling removal as possible in order to generate as little sludge as possible, in particular based on iron oxalate, which has to be disposed of. On the other hand, it can be advantageous to adjust the pickling rate on the substrate and the system conditions so that, among other things, light scale residues are also removed from the substrate.

The aqueous solution or dispersion of the bath prepared with the batch and optionally also with at least one supplement is preferably largely or completely free of heavy metals from the added components, largely or completely halogen-free, largely or completely sulfur-free and largely or completely phosphate-free, but can occasionally contain _{up to about 0.001 g / L PO 4.} When working in industrial practice, however, it has been shown time and again that in some baths, at least temporarily, undesirable contents in small quantities or traces, in particular of halogen, phosphorus, sulfur and / and in particular environmentally unfriendly heavy metal compounds, especially from previous ones Baths, pipes and other system parts are dragged in. Nevertheless, efforts are preferably made to ensure that these impurities are so low that they do not impair the current oxalation process and, due to the small amounts or traces, are quickly further diluted and avoided as far as possible. The additives and impurities in the batch or bath are at least partially also found in correspondingly low contents in the oxalate layer.

When the steel surfaces, in particular blanks, are coated with the oxalating composition according to the invention, some of the chemical elements of the steel surface are pickled out and incorporated into the aqueous solution or dispersion. This can therefore accumulate with iron and other elements such as the steel finishing elements and other alloy elements such as chromium, nickel, cobalt, copper, manganese, molybdenum, niobium, vanadium, tungsten and zinc and / or their ions in the bath over time. However, these elements or ions do not form precipitation products that sink and form sludge, but instead precipitate as oxalates. The precipitated oxalates and oxalate dihydrates form a sludge that is easily removable and, compared to phosphates, environmentally friendly. Some of these elements or ions, like some of the additives and impurities in the bath, are built into the oxalate layer. The bath can therefore absorb an iron content of up to 0.5 g / L or even up to around 1 g / L over a longer period of time.

Preferably, the bath composition for oxalating and / or the oxalate layer consists essentially only of oxalic acid, guanidine compound, nitrate and / or their derivatives and optionally of pigment, surfactant and / or thickener and is / are largely or completely free of halogen Compounds, phosphorus compounds, sulfur compounds and / or heavy metals other than iron and zinc. It is therefore preferred that no compounds based on aluminum, boron, halogens, copper, manganese, molybdenum, phosphorus, sulfur, tungsten, other carboxylic acids besides oxalic acid, amine, nitrite and / or their derivatives are added to the batch solution and / or the supplementary solutions is / will - optionally with the exception of polyallylamines and / or polyvinylamines as thickeners.

In the case of a longer-running oxalation process, it must be ensured that the bath components are regularly replenished and that the bath volume is kept roughly constant.

The oxalate layer produced with the method according to the invention can, if necessary, be dried, can optionally dry slightly or also be coated further while wet. In the case of drying, for example, drying with hot air at a temperature in the range from 80 to 120 ° C is recommended.

The oxalated substrates, which may also be coated with a lubricant layer, are cold-formed, in particular, by slide drawing such as wire drawing or pipe drawing, by cold forging, ironing, ironing, deep drawing, cold extrusion, thread rolling, threading, pressing and / or cold upsetting.

The metallic molded bodies coated with an oxalate layer according to the invention are preferably dried before being coated with a lubricant composition. With water-based In lubricant compositions, drying of the oxalate layer is not necessary, even if it is nevertheless dried in some process sequences.

The oxalate layer according to the invention predominantly contains or preferably consists essentially of iron (II) oxalate, iron (II) oxalate dihydrate and / or other oxalates. It preferably contains no halogen compounds, no phosphorus compounds and / or no sulfur compounds. It preferably contains only traces or no environmentally unfriendly heavy metals. The iron oxalates are usually crystalline. Figure 1 shows a typical example of a crystalline iron oxalate layer. The oxalate crystals often have an average crystal size in the range from 3 to 12 μm. The oxalate layer usually looks light gray, greenish yellow and / and greenish gray.

It is helpful here if the dried conversion layer is closed to at least 90 percent by area or even to at least 95 percent by area and is deposited as firmly as possible on the metallic surface. The closeness can be roughly estimated on the basis of scanning electron microscope images, whereby a higher resolution should be used to identify pores and access routes to the metallic surface.

The layer weight of the dried oxalate layer is in the range from 1.5 to 15 g / m ² , in particular in the range from 3 to 12 g / m ² , from 4 to 10 g / m ² or from 5 to 7 g / m ² .

The ratio of pickling removal to layer weight BA: SG of the dried conversion layer is in the range from (0.35 to 0.70): 1, from (0.36 to 0.55): 1 or from (0.37 to 0.45 ) : 1.

The layer thickness of the oxalate layer is preferably in the range from 0.1 to 6 μm and in particular in the range from 0.5 to 4 μm, from 1 to 3 μm, from 1.5 up to 2.5 µm or at about 2 µm. The preferred oxalate layer thickness can vary somewhat depending on the type of shaped body: In the case of more sophisticated shaped bodies and / or more demanding degrees of deformation, it is preferably somewhat greater, ie for example about 4 μm instead of about 2 μm.

1. 1.) Eine Salzschmiermittelträgerzusammensetzung mit einem Gehalt an Öl wie z.B. Mineralöl, tierischem oder/und vegetativem Öl, deren Derivaten oder/und deren Destillaten sowie mit einem Gehalt an jeweils mindestens einer Bor-Verbindung, einem Metasilicat, einem Hydrogenphosphat oder/und Kalk, insbesondere für Drähte und Drahtbunde im Drahtziehen;
2. 2.) Eine Salzschmiermittelträgerzusammensetzung mit einem Gehalt an Seife(n) auf Basis von Alkali- oder/und Erdalkalimetallen und mit einem Gehalt an jeweils mindestens einer Bor-Verbindung, einem Metasilicat, einem Hydrogenphosphat oder/und Kalk, insbesondere für Drähte und Drahtbunde im Drahtziehen;
3. 3.) Eine Salzschmiermittelträgerzusammensetzung mit einem Gehalt an organischem Polymer oder/und Copolymer und mit einem Gehalt an jeweils mindestens einer Bor-Verbindung, einem Metasilicat, einem Hydrogenphosphat oder/und Kalk sowie mit oder ohne einen Gehalt an Seife(n) auf Basis von Alkali- oder/und Erdalkalimetallen, insbesondere für Drähte und Drahtbunde im Drahtziehen;
4. 4.) Eine Salzschmiermittelträgerzusammensetzung mit einem Gehalt an Seife(n) auf Basis von Alkali- oder/und Erdalkalimetallen, insbesondere für Drähte und Drahtbunde im Drahtziehen;
5. 5.) Eine Zusammensetzung im Wesentlichen auf Basis von Öl wie z.B. Mineralöl, tierischem oder/und vegetativem Öl, deren Derivaten oder/ und deren Destillaten sowie gegebenenfalls mit jeweils mindestens einem EP-Additiv (extreme pressure), AW-Additiv (anti-wear zum Verschleißschutz) oder/und VI-Additiv (viscosity index), insbesondere zum Drahtziehen, Kaltmassivumformen, Rohrziehen oder/und Tiefziehen;
6. 6.) Eine Zusammensetzung mit einem Gehalt an mindestens einem Festschmierstoff wie z.B. Graphit, Molybdändisulfid oder/und Wolframdisulfid und gegebenenfalls einem Gehalt an jeweils mindestens einem organischen Polymer, organischen Copolymer oder/und Wachs, insbesondere für ein Kaltmassivumformen;
7. 7.) Eine Zusammensetzung im Wesentlichen auf Basis von organischem Polymer/Copolymer und gegebenenfalls auch Wachs wie z.B. Produkte der Chemetall GmbH unter dem Markennamen Gardomer®, für alle Arten des Kaltumformens; oder
8. 8.) Eine Zusammensetzung im Wesentlichen auf Basis von mindestens einem Wachs, für alle Arten des Kaltumformens.

The composition of the lubricant can be composed very differently. It can be composed, for example, on the following basis:

1. 1.) A salt lubricant carrier composition with a content of oil such as mineral oil, animal or / and vegetable oil, their derivatives and / or their distillates and each with a content of at least one boron compound, a metasilicate, a hydrogen phosphate and / or lime, especially for wires and wire bundles in wire drawing;
2. 2.) A salt lubricant carrier composition with a content of soap (s) based on alkali and / or alkaline earth metals and with a content of at least one boron compound, a metasilicate, a hydrogen phosphate and / or lime, in particular for wires and wire coils in the Wire drawing;
3. 3.) A salt lubricant carrier composition with a content of organic polymer and / or copolymer and with a content of at least one boron compound, a metasilicate, a hydrogen phosphate and / or lime and with or without a content of soap (s) based on Alkali and / or alkaline earth metals, in particular for wires and wire coils in wire drawing;
4. 4.) A salt lubricant carrier composition with a content of soap (s) based on alkali and / or alkaline earth metals, in particular for wires and wire coils in wire drawing;
5. 5.) A composition essentially based on oil such as mineral oil, animal or / and vegetable oil, their derivatives and / or their distillates and optionally with at least one EP additive (extreme pressure), AW additive (anti-wear) for wear protection) and / or VI additive (viscosity index), in particular for wire drawing, cold massive forming, pipe drawing and / and deep drawing;
6. 6.) A composition with a content of at least one solid lubricant such as graphite, molybdenum disulfide and / or tungsten disulfide and optionally a content of at least one organic polymer, organic copolymer and / or wax, in particular for cold massive forming;
7. 7.) A composition essentially based on organic polymer / copolymer and possibly also wax such as products from Chemetall GmbH under the brand name Gardomer®, for all types of cold forming; or
8. 8.) A composition essentially based on at least one wax, for all types of cold forming.

The lubricant compositions 6.) to 8.) are also suitable for the heaviest cold forming.

The lubricant layer is produced with a lubricant composition which contains an organic polymer and / or copolymer.

The metallic moldings are thoroughly dried after being coated with the lubricant composition, in particular with warm air and / or radiant heat. This is often necessary because, as a rule, the water content in coatings interferes with cold forming, because otherwise the coating can be formed insufficiently and / and because a coating of poorer quality can be formed. Otherwise vapor bubbles, surface defects or deformation defects can occur. In general, rusting can also occur here, but this can be prevented or reduced with as largely closed oxalate layers as possible and rapid further treatment with a lubricant composition. It is advisable to dry the oxalate layer quickly, e.g. with hot air, if longer idle times are to be expected before coating with a lubricant composition.

The lubricant layer produced according to the invention preferably has a layer thickness in the range from 0.01 to 40 μm after drying, which is preferably made thinner or thicker depending on the type of lubricant composition. In particular, their average dry layer thickness is preferably in the range from 0.03 to 30 μm, from 0.1 to 15 μm, from 0.5 to 10 μm, from 1 to 5 μm or from 1.5 to 4 μm. Here, the mean dry layer thickness of the lubricant layer increases, depending on which basic composition is selected, the lubricant layers of the lubricant composition 5.) usually being the thinnest.

It has been shown that cold forming achieves the best results with lubricant compositions which, like the products from Chemetall GmbH under the brand name Gardomer®, have a content of at least 5% by weight of organic polymers and / or copolymers. They show an optimal compatibility of the layers with the Oxalate layer, also because it does not chemically attack the oxalate layer, and the best forming results in the tests on oxalate layers. This is because they can be used excellently in all types of cold forming together with an oxalate layer according to the invention. In addition, these coatings do not have to be replaced when switching to other types of blanks and / or other types of cold forming.

In comparison to cold forming on coated steels with a zinc phosphate layer of the prior art and with a lubricant layer, it was found that the oxalate layers according to the invention can be kept thinner than the zinc phosphate layers of the prior art, so that, despite the same performance during cold forming, lower chemical consumption occurs significantly reduces operating costs. In addition, the oxalate layers according to the invention are phosphate-free. The sludge and waste water of the oxalation process according to the invention are hardly or not contaminated with environmentally unfriendly heavy metals, environmentally unfriendly phosphates and / or environmentally unfriendly additives, so that a simpler and significantly more cost-effective treatment and disposal of the sludge and waste compared to zinc phosphating and also to oxalating according to the prior art Sewage is possible.

In the case of blanks of complex shape, such as profiles or connecting elements such as screws and bolts, which have been cold-formed by ironing or by one-stage or multi-stage profile drawing or upsetting and wire drawing, it has been shown that the oxalate layer according to the invention has a high performance in cold forming. The same was found in ironing operations and in the cold extrusion of slugs into complexly shaped parts such as journals or tripods.

The oxalated blanks, which are also coated with a layer of lubricant, can be produced in particular by pressing, cold forging, Pressing, hitting, upsetting, rolling and / or drawing can be cold-formed.

The cold-formed substrates can be used as structural or connecting elements, as sheet metal, wires, wire coils, more complex shaped molded parts, sleeves, profile elements, tubular elements, e.g. as welded seamless tubes, cylinders and / or as components in particular in energy technology, vehicle construction, device construction or mechanical engineering.

Surprise effects and advantages:

It was very surprising that when oxalating steels with a chromium content <10% by weight compared to oxalating steels with a chromium content of significantly more than 10% by weight, there were such great differences in the pickling attack and in the formation and non-formation of oxalate layers occurred depending on the presence or absence of halogen and sulfur compounds - as shown in Table 1.

Because it is free from halogen and sulfur compounds and from phosphate, the oxalation process according to the invention is very superior to the oxalation and zinc phosphating processes of the prior art.

The complete or extensive freedom from environmentally unfriendly heavy metals and from phosphorus, halogen and sulfur compounds are particularly advantageous in the process according to the invention. Particularly advantageous in the method according to the invention are the simple bath management and the much simpler control and regulation of the bath and layer quality by checking the temperature, treatment time and acidity using GS points. The method according to the invention is therefore much simpler than zinc phosphating, for example. It is also not necessary to control and adjust the free acid FS, the total acid Fischer GSF and the S value as the ratio of a free acid to the respective total acid. Because when oxalating no free acid FS can be measured because of the complete dissociation of the oxalic acid. Particularly advantageous in the process according to the invention is also the significantly lower amount of sludge compared to phosphating and its complete or extensive freedom from environmentally unfriendly heavy metals and other environmentally unfriendly compounds. Therefore, the disposal effort for sludge and contaminated water is significantly lower and requires significantly less effort and significantly lower costs.

Examples and comparative examples:

Before coating metallic substrates with the oxalation composition according to the invention, four series of tests were carried out for the preparation of oxalation compositions as concentrates and as bath compositions.

In test series I. the treatment bath was made up with a liquid aqueous concentrate which was prepared by dissolving a given amount of oxalic acid and, if necessary, also by adding accelerator, pigment, surfactant and / or thickener in deionized water. The dilution factor for diluting a concentrate to make a bath ranged from 1 to 3.

In the test series II. The treatment bath was made up with a powdery concentrate, which was created by rubbing, mixing in and / or rubbing in powdery oxalic acid and optionally with the addition of nitrate dissolved in water, pigment such as titanium dioxide powder with an average particle size of about 2 microns for increasing the Flowability, surfactant and / or thickener was produced in a compulsory mixer. The powdery concentrate did not have to be dried and was very pourable. The factor for the dissolution of the concentrate in water for the bath preparation was around 1 to 3.

Alternatively, in the test series III. a non-free-flowing oxalic acid powder rubbed in a kneader with the titanium dioxide to create a permanently free-flowing product.

For test series IV., A paste-like concentrate was produced by mixing oxalic acid together with water, with an accelerator dissolved in water and, if necessary, with pigment such as a suspension, surfactant and / or thickener stabilized with particles with a layered structure in a compulsory mixer. This meterable, highly concentrated, one-component pasty mixture was diluted up to a factor of 20 to form a bath formulation.

All four test series resulted in concentrates and bath formulations that were easy to use.

1. 1.) Bleche aus 0,8 mm kaltgewalztem Stahl CRS mit einem Kohlenstoff-Gehalt von 0,039 Gew.-% und mit einem Chrom-Gehalt von 0 Gew.-% zum Tiefziehen,
2. 2.) Butzen von 27 mm Durchmesser und 13 mm Höhe aus Vergütungsstahl 1.0401 mit einem Kohlenstoff-Gehalt von 0,12-0,18 Gew.-% und mit einem Chrom-Gehalt von 0 Gew.-% zum Kaltfließpressen,
3. 3.) Drahtabschnitte von Warmwalzdraht aus Stahl C70W1 von 5,6 mm Durchmesser mit einem Kohlenstoff-Gehalt von 0,7 Gew.-% und mit einem Chrom-Gehalt von ≤ 0,3 Gew.-% zum Drahtziehen und
4. 4.) Drahtbundabschnitte aus Stahl C35BCr1 mit 10,5 mm Durchmesser mit einem Kohlenstoff-Gehalt von 0,35 Gew.-% und einem Chrom-Gehalt von 0,1-0,3 Gew.-% zum Drahtziehen.

In den Tabellen ergibt sich der Stahlwerkstoff auch aus den Substrat-Arten.The following substrates were used for oxalating and cold forming:

1. 1.) Sheets made of 0.8 mm cold-rolled steel CRS with a carbon content of 0.039% by weight and a chromium content of 0% by weight for deep drawing,
2. 2.) Slugs with a diameter of 27 mm and a height of 13 mm made of heat-treatable steel 1.0401 with a carbon content of 0.12-0.18% by weight and a chromium content of 0% by weight for cold extrusion,
3. 3.) Wire sections of hot-rolled wire made of steel C70W1 with a diameter of 5.6 mm and a carbon content of 0.7% by weight and with a chromium content of ≤ 0.3% by weight for wire drawing and
4. 4.) Wire coil sections made of steel C35BCr1 with a diameter of 10.5 mm with a carbon content of 0.35% by weight and a chromium content of 0.1-0.3% by weight for wire drawing.

In the tables, the steel material is also derived from the substrate types.

These substrates were first cleaned in an aqueous cleaning solution Gardoclean® 351, a phosphate-free, strongly alkaline cleaner from Chemetall GmbH, purified from 50 g / L at 90 ° C for 10 min. The cleaned substrates were then rinsed with cold city water for one minute before they were oxalated without prior drying. For this purpose, aqueous solutions or dispersions with the compositions listed in the tables were made up with city water, concentrates from various series of experiments mentioned above being used. If necessary, a polyethylene glycol with an average molecular weight of about 400 was used as thickener 1. Alternatively, 2 Rhodopol® 23, a high molecular weight anionic polysaccharide, was added as a thickening agent.

After oxalating, the coated substrates were rinsed with cold deionized water and then without intermediate drying in the wet-on-wet process (wet-wet process) with an organic copolymer-containing aqueous lubricant composition Gardomer® 6332 from Chemetall GmbH about 2 μm thick or coated with drawing soap based on stearate such as Lubrifil® VA 1520 from Lubrimetal about 1.5 µm thick.

The cold forming of the sheets coated with the separating layer or the sheets coated with the separating layer and with the lubricant layer and dried was carried out by deep drawing in a laboratory cup pulling device with a universal sheet metal testing machine from Erichsen model 142-20 with a punching force of up to 200 kN in one stage on non-preheated ones Blanks at room temperature.

The cold forming of the slugs coated with the separating layer or the slugs coated with the separating layer and the lubricant layer and dried was carried out with a 300 t press from May at 180 t over 300 ms in one stage on non-preheated blanks at room temperature by fully forward backward extrusion.

The cold forming of the wire sections and wire coil sections coated with the separating layer or with the separating layer and with the lubricant layer and dried was carried out with a draw bench at up to 3 t at room temperature for more than 300 ms on non-preheated blanks by wire drawing. The wire sections in the inlet were drawn in one step at 1-60 m / s and the wire bundle sections in the inlet were drawn in multiple steps at 0.1-5 m / s.

The deformed workpieces were faulty with too thin, insufficiently closed and / or insufficiently adherent oxalate layers and / or too thin lubricant layers, but these are not permissible in industrial production.

Cold forming has proven to be very good when the oxalate layer has a layer weight of about 5 to 7 g / m ² and the lubricant layer based on organic polymer has a layer ^{weight of about 1.5 g / m 2} and when the oxalate layer is largely closed , was evenly and firmly bonded to the substrate. Cold forming has proven to be good when the oxalate layer has a layer weight of about 3 to 4 g / m ² and the lubricant layer based on organic polymer has a layer ^{weight of about 2.5 g / m 2} lubricant layer and when the oxalate layer is firmly adherent was connected to the substrate. Cold forming has proven to be satisfactory when the oxalate layer has a layer weight of just under 3 g / m ² and the organic polymer-based lubricant layer has a layer ^{weight of about 2 g / m 2} and when the oxalate layer shows moderate to good adhesive strength. Cold forming has proven to be poor if the oxalate layer was not firmly bonded to the substrate, because then forming was not possible.

In a throughput test, different bath compositions were tested at 65 ° C. and a treatment time of 3 minutes. As can be seen from the test examples VB10 to B16, a bath composition without an accelerator was found to be unsuitable for producing firmly adhering layers for cold forming. The acceleration by a nitro-guanidine accelerator proved to be particularly effective in producing good layers. The consumption of guanidine compound is increased here.

Surprisingly, it was found that a combination of the accelerators discussed, as can be seen in B16, represents an optimal ratio of adhesive strength, layer quality, cohesion, ratio of pickling removal to layer weight, lubricant absorption capacity and formability with simultaneously reduced consumption of guanidine accelerator. In the throughput tests B17 to B21 it can be seen that the content of oxalic acid leads to good results over a very wide range Table 2: Bath compositions depending on the type and amount of accelerator in g / L and process and layer properties. Example 15 in Table 2 is not according to the invention. Contents in g / L VB10 VB11 B12 B13 B14 B15 B16 Oxalic acid 40 40 40 40 40 40 40 Nitroguanidine 0 0 0 0.33 10 40 0.4 NaNO ₃ 0 2 5 0 0 0 2 Thickener 1 10 10 10 10 10 10 10 Total acidity GS points 60 60 60 60 60 60 60 Bath temperature ° C 65 65 65 65 65 65 65 Contact time min 3rd 3rd 3rd 3rd 3rd 3rd 3rd Pickling removal BA g / m ² 2.5 2.9 3.9 2.0 2.2 1.9 2.5 Layer weight SG g / m ² 1.9 2.9 8.6 2.8 5.4 5.1 6.8 Ratio BA / SG% 132 100 45.3 71.4 40.7 37.3 36.8 Steel material blank CRS sheet CRS sheet CRS sheet CRS sheet CRS sheet CRS sheet CRS sheet Oxalate layer quality very bad bad Well Well very good very good very good Oxalate layer not adherent not closed Lubricant layer polymer polymer polymer polymer polymer polymer polymer Lubricant layer thickness g / m ² 1.5 1.6 1.4 1.5 1.8 1.5 1.5 Lubricant layer quality very good very good very good very good very good very good very good Cold forming behavior not possible bad Well Well very good very good very good If the oxalate layer was insufficiently closed, if it showed uncoated areas clearly visible even with the naked eye, or if it was very inhomogeneous, it was rated at least as poor. Contents in g / L B17 B18 B19 B20 B21 Oxalic acid 5 40 80 150 500 Nitroguanidine 0.4 0.4 0.4 0.4 0.4 NaNO ₃ 2 2 2 2 2 Thickener 1 10 10 10 10 10 Total acidity GS points 8th 60 140 260 860 Bath temperature ° C 65 65 65 65 65 Contact time min 3rd 3rd 3rd 3rd 3rd Pickling removal BA g / m ² 3.3 2.5 3.1 4.1 4.4 Layer weight SG g / m ² 8.2 6.8 5.0 6.0 6.2 Ratio BA / SG% 40.2 36.8 62.0 68.3 70.9 blank Slug Slug Slug Slug Slug Oxalate layer quality very good very good very good very good very good Lubricant layer polymer polymer polymer polymer polymer Lubricant layer thickness 1.3 1.4 1.6 1.4 1.5 Lubricant layer quality very good very good very good very good very good Cold forming behavior Well Well Well Well Well Contents in g / L B22 B23 B24 B25 B26 B27 B28 B29 Oxalic acid 40 40 40 40 40 40 40 40 Nitroguanidine 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 NaNO ₃ 2 2 2 2 2 2 2 2 Thickener 1 10 10 10 10 10 10 10 10 Total acidity GS points 60 60 60 60 60 60 60 60 Bath temperature ° C 25th 35 45 55 65 75 85 90 Contact time min 15th 15th 3rd 3rd 3rd 3rd 3rd 3rd Pickling removal BA g / m ² 2.4 2.8 1.7 1.7 2.5 3.1 4.3 4.5 Layer weight SG g / m ² 4.6 7.3 3.2 4.3 6.8 7.5 10.3 10.8 Ratio BA / SG% 52.2 38.4 53.1 39.5 36.8 41.3 41.7 41.7 blank Slug Slug Slug Slug Slug Slug Slug Slug Oxalate layer quality sufficient Well sufficient very good very good very good Well Well Lubricant layer polymer polymer polymer polymer polymer polymer polymer polymer Lubricant layer thickness 1.4 1.8 2.0 2.1 1.8 1.6 1.5 1.8 Lubricant layer quality very good very good very good very good very good very good very good very good Cold forming behavior Well very good Well very good very good Well Well Well If the quality of the oxalate layer was only sufficient, the layer was somewhat coarser or not well closed. Contents in g / L VB30 VB31 VB32 B33 VB34 VB35 Oxalic acid 40 40 40 40 40 40 Nitroguanidine - - - - - - SNBS 1 - - - - - NaNO ₃ - - 5 1 2 Sodium chlorate - 1 4th - - - Thickener 1 - - - - - - Total acidity GS points 60 60 60 60 60 60 Bath temperature ° C 65 65 65 65 65 65 Contact time min 3rd 3rd 3rd 3rd 3rd 3rd Pickling removal BA g / m ² 2.2 2.1 2.6 3.9 1.2 0.9 Layer weight SG g / m ² 2.7 4.1 2.1 8.6 1.2 1.5 Ratio BA / SG% 81.5 51.2 124 45.3 100 60.0 blank Slug Slug Slug Slug Slug Slug Oxalate layer quality bad sufficient bad Well bad bad Lubricant layer polymer polymer polymer polymer polymer polymer Lubricant layer thickness 1.4 1.8 1.4 1.9 2.1 1.6 Lubricant layer quality very good very good very good very good very good very good Cold forming behavior bad sufficient bad Well bad bad With accelerators according to the invention, good oxalate layers were produced, with other accelerators rather poor layers. If the quality of the oxalate layer was only sufficient, the layer was somewhat coarser or not well closed. Contents in g / L B36 B37 B38 B39 B40 B41 Oxalic acid 40 40 40 40 40 40 Nitroguanidine 0.4 0.4 0.4 0.4 0.4 0.4 Thickener 1 10 10 10 10 10 10 NaNO ₃ 2 2 2 2 2 2 Total acidity GS points 60 60 60 60 60 60 Bath temperature ° C 65 65 65 65 65 65 Contact time min 1 2 3rd 5 10 20th Pickling removal BA g / m ² 1.2 2.1 2.2 4.0 5.0 4.8 Layer weight SG g / m ² 2.6 4.9 6.0 9.6 11.1 10.8 Ratio BA / SG% 46.2 42.9 36.7 41.7 45.0 44.4 blank Slug Slug Slug Slug Slug Slug Oxalate layer quality sufficient sufficient very good very good Well Well Lubricant layer polymer polymer polymer polymer polymer polymer Lubricant layer thickness 1.6 1.8 1.7 1.8 1.6 1.4 Lubricant layer quality very good very good very good very good very good very good Cold forming behavior sufficient Well very good very good Well Well If the quality of the oxalate layer was sufficient, the layer was not closed well. Contents in g / L B42 B43 B44 B45 B46 B47 Oxalic acid 40 40 40 40 40 40 Nitroguanidine 0.4 0.4 0.4 0.4 0.4 0.4 Thickener No. 2: 10 g / L 2: 10 g / L 1:10 g / L 1: 10 g / L 2: 10 g / L 1: 10 g / L NaNO ₃ 2 2 2 2 2 2 Total acidity GS points 60 60 60 60 60 60 Bath temperature ° C 65 65 65 65 65 65 Contact time min 3rd 3rd 3rd 3rd 3rd 3rd Pickling removal BA g / m ² 2.1 2.1 2.2 2.3 2.0 2.4 Layer weight SG g / m ² 5.3 4.9 6.0 5.1 5.4 6.3 Ratio BA / SG% 39.6 42.9 36.7 45.1 37.0 38.1 blank Slug Wire bundle Slug Wire bundle wire Wire bundle Steel material C15 C35BCr1 C15 C35BCr1 C70W1 C35BCr1 Oxalate layer quality very good very good very good very good very good very good Lubricant layer polymer polymer polymer polymer Drawing soap Drawing soap Lubricant layer thickness 1.6 1.8 1.7 1.8 1.5 1.4 Lubricant layer quality very good very good very good very good very good very good Cold forming behavior very good very good very good very good very good very good

Examples B46 and B47 in Table 7 are not according to the invention. It has been found that the oxalate layers according to the invention have surface properties which are particularly well suited for application of lubricant and for cold forming.

A layer has proven to be a very good oxalate layer that is firmly adhered to the substrate and is sufficiently thick and usually at least 1 µm thick, if a lubricant layer is then applied before cold forming, or as a rule at least 2 µm is thick if no lubricant layer is then applied before cold forming. An oxalate layer which has inadequate adhesion and / or an insufficiently closed layer on the substrate has proven to be a less good layer.

These properties can be a consequence of insufficient acceleration due to an insufficient content of at least one accelerator and / or a consequence of unsuitable bath management, e.g. treatment times that are too short or / and the bath temperature is too low. Insufficiently closed oxalate layers with a degree of closeness of ≤ 90 area% can lead to welding of blank and tool, increased wear, scoring and similar defects on formed bodies during cold forming.

If the thickness and weight of the layer were too small, the oxalate layer exhibited less adhesive strength. A thickness of the oxalate layer, measured as the layer weight of about 1 g / m ^2, is usually sufficient if the oxalate layer is sufficiently closed and rests sufficiently firmly on the metallic substrate. In the case of higher degrees of cold deformation, it is advantageous if the oxalate layer has a layer weight of at least 2 g / m ² . Therefore, the performance of the oxalate layer during cold forming is more important than the thickness of the oxalate layer. Their performance is only noticeable during the forming process.

The tests show very clearly that the quality of the cold forming depends above all on the quality of the oxalate layer and thus on the sufficient cohesion, adhesion and thickness of the oxalate layer. The lubricant layer based on organic polymer and / or copolymer is extremely efficient and robust during cold forming. The lubricant layer based on drawing soap also showed very good performance in cold forming in further tests not shown in detail here.

A layer weight of around 1 g / m ^{2 is} usually sufficient for the lubricant layer too. When working with an oxalate layer and without a lubricant layer, the increased coefficients of friction play a decisive role. In some cases, cold forming is then quite possible, in particular with low degrees of deformation and / and with sufficiently closed, finely crystalline layers.

Overall, the tests showed that the use of nitrate and a guanidine-based accelerator in combination led to a reduction in consumption and was ideal for the formation of phosphate-free conversion layers for cold forming at temperatures of 60 to 65 ° C and contact times of 3 to 5 minutes are. It turned out that the use of polymer-based lubricant compositions is particularly suitable because of their excellent sliding properties.

It was found that the addition of nitroguanidine acts as an accelerator, but not as a pickling inhibitor. In contrast to alkali, manganese and zinc phosphating, it obviously has an oxidizing effect and accelerates the build-up of the oxalate layer. However, it behaves differently during oxalating than during phosphating and is unusually heavily consumed during oxalating, while no consumption of this accelerator was found during phosphating. It does not have the effect of a pickling inhibitor because the addition of large amounts of nitroguanidine does not lead to an inhibition of the acid, but to an accelerated build-up of oxalate layer, the addition of suitable amounts of nitroguanidine reduces the contact time that is necessary to form a completely closed and finely crystalline oxalate layer. When metallic bodies were immersed in the oxalating composition according to the invention, rising gas bubbles were often visible for about 5 to 10 minutes, so that the gas time can be determined via the gassing. It was found here that at the end of the gas time, that is to say the time of contact of the metallic surfaces with the acidic oxalation composition during oxalation, that the oxalate layer is essentially closed and well formed. Therefore, with the evolution of gas during oxalating, there is an externally clearly visible sign of when the oxalating has led to a well-developed oxalate layer. It was also shown that the ratio of pickling removal to layer weight at the end of the gas time comes very close to the theoretical maximum without drastically reducing the pickling removal. This means that in the ideal case almost 100% by weight of the iron dissolved out is stoichiometrically deposited again as iron oxalate on the substrate surface.

With regard to the content of oxalic acid, the tests showed that an oxalate layer is formed over a very wide concentration range of oxalic acid from about 1 to about 500 g / L.

With regard to the addition of nitroguanidine, the tests showed that this accelerator is helpful in the formation of layers over a very wide concentration range from about 0.08 to 20 g / L, with the layer build-up taking place more quickly at higher nitroguanidine concentrations. It was also found here that nitroguanidine does not act as a pickling inhibitor but as an accelerator and that the addition of a pickling inhibitor to the aqueous composition according to the invention is not necessary.

With regard to the addition of nitrate, the tests showed that this accelerator with nitroguanidine enables co-acceleration. This system is far more economical, but offers all the advantages. In terms of of the nitrate content, the tests also showed that the use of high levels of nitrate alone leads to somewhat thicker layers and slightly reduced adhesive strength. Suitable layer qualities were only obtained through combination with nitroguanidine.

With regard to the combination of nitrate and nitroguanidine, it was found that a ratio of approximately 0.4 g / L nitroguanidine to 2 g / L nitrate enables particularly good oxalate layers and is at the same time more economical.

With regard to the removal of the stain, the tests showed that with increasing temperature and / or with increasing oxalic acid concentration, the amount of stain removed. It was shown that the pickling removal in a sufficiently accelerated system is usually in a certain ratio to the weight of the layer.

With regard to the layer formation, the tests showed that a layer formation with the aqueous composition according to the invention is possible in the entire temperature range from 10 to 90 ° C, but that a greater layer thickness is formed at a higher temperature under otherwise the same conditions as the same concentration and the same contact time.

With regard to the layer weight, the tests showed that the layer weight increases with the temperature of the bath and can also depend on the presence of sufficient accelerator.

With regard to the ratio of stain removal BA to layer weight SG, the tests showed that it should be in the range from 30 to 75%. With regard to the adhesive strength of the oxalate layers on the metallic substrate, the tests showed that the adhesive strength is positively influenced by a suitable ratio of pickle removal to layer structure and can also be negatively influenced in the case of unsuitable accelerators or their too low or too high concentration.

With regard to sludge formation, the tests showed that significantly less sludge is formed than with a comparable phosphating. The formation of sludge depends heavily on the pickling attack.

Claims (12)

1. A method of treatment of shaped bodies with an iron or steel surface having a carbon content in the range of 0 to 2.06 wt% and having a chromium content in the range of 0 to < 10 wt% prior to a cold forming operation, wherein

   at least one shaped body is contacted with an aqueous acidic composition for formation of a conversion layer as separating layer,

   the aqueous acidic composition is provided only in a formulation comprising

   water,

   2 to 500 g/L oxalic acid calculated as anhydrous oxalic acid and

   a) 0.01 to 20 g/L of at least one catalyst based on guanidine calculated as nitroguanidine and/or

   b) 0.01 to 20 g/L of at least one nitrate calculated as sodium nitrate and

   wherein the pickling removal of the aqueous acidic composition is in the range of 1 to 6 g/m² measured by gravimetric determination according to DIN EN ISO 3892,

   wherein the coat weight of a dried conversion layer is in the range of 1.5 to 15 g/m² measured by gravimetric determination according to DIN EN ISO 3892,

   wherein the ratio of pickling removal to coat weight PR:CW of the dried conversion layer is in the range of (0.30 to 0.75):1,

   wherein the dried conversion layer forms a firmly adherent coating and

   wherein a lubricant layer is applied to the conversion layer with a lubricant composition, where the lubricant composition has a content of at least 5 wt% of organic polymers and/or copolymers,

   and wherein the lubricant layer is dried,

   where the at least one shaped body is contacted with the aqueous acidic composition by sprinkling, spraying and/or immersion at a temperature of 10 to 90°C.
2. The method according to claim 1, where the steel surface is galvanized or alloy galvanized.
3. The method according to claim 1 or 2, wherein the ratio of the concentrations in g/L of oxalic acid calculated as anhydrous oxalic acid to the sum of the catalysts a) and b) calculated as nitroguanidine and/or sodium nitrate NaNO₃, of which at least one catalyst is present, in the aqueous acidic composition for forming a conversion layer and/or the bath is in the range of 500:1 to 2:1.
4. The method according to any one of the preceding claims, wherein the aqueous composition comprises 0.001 to 20 g/L of at least one inorganic or organic pigment, preferably a pigment based on oxide, organic polymer and/or wax.
5. The method according to any one of the preceding claims, wherein at least one strong acid-stable surfactant is also added to the oxalating composition, so that also cleaning during the oxalating and/or cleaning and oxalating take place in a one-pot process.
6. The method according to any one of the preceding claims, wherein at least one thickening agent is used in a content in the range of 0.01 to 50 g/L in the aqueous acidic composition of the invention for forming a conversion layer and/or in the bath, calculated as completely dissolved active substance or as completely dissolved thickening agent in the bath.
7. The method according to any one of the preceding claims, wherein the treatment bath is formulated with a liquid aqueous concentrate, which is/was produced by dissolving a predetermined amount of oxalic acid and optionally also by adding catalyst, pigment, surfactant and/or thickening agent in demineralized water.
8. The method according to any one of claims 1 to 6, wherein the treatment bath is formulated with a pulverulent concentrate, which is produced by grinding, blending and/or triturating pulverulent oxalic acid and optionally by addition of nitrate dissolved in water, pigment for increasing flowability, surfactant and/or thickening agent.
9. The method according to any one of claims 1 to 6, wherein the treatment bath is formulated with a concentrate in paste form, which is produced by mixing oxalic acid with water and optionally by adding at least one catalyst dissolved in water, pigment for increasing flowability, surfactant and/or thickening agent.
10. The method according to any one of the preceding claims, wherein the substrate oxalated prior to the cold forming is a strip, sheet, slug, wire, wire coil, intricately formed shaped part, sleeve, profile, pipe, round blank, disk, bar, rod and/or cylinder made of steel material, wherein the substrate optionally comprises a zinc layer or zinc alloy layer.
11. The method according to any one of the preceding claims, wherein the oxalated substrates are coated in a wet-on-wet process with a lubricant layer.
12. The method according to any one of the preceding claims, wherein the oxalated substrates that are also coated with a lubricant layer are cold formed by flow forming, ironing, thread rolling, thread tapping, slide drawing, cold extrusion, cold working, cold heading, pressing and/or deep drawing.

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