ES2734456T3 - Inorganic functional layer on hot dipped galvanized steel to aid shaping - Google Patents

Abstract

Procedure for the time-saving production of a galvanized steel sheet (1) with an auxiliary forming layer based on at least one inorganic functional layer (2), comprising the steps of: - Preparation of an aqueous solution , without silicon hydride (L) or a suspension based on at least one carbonate supplier or an aqueous solution, without silicon hydride (L) or a suspension based on at least one carbonate supplier and, at least one hydroxide supplier, in which at least one carbonate supplier is selected from ammonium bicarbonate, ammonium carbonate, alkali metal bicarbonates, alkali metal carbonates and alkali metal carboxylates and at least one supplier of hydroxide is selected from alkali metal hydroxides, alkali metal oxides, alkali metal alcoholates, magnesium hydroxides and magnesium oxide, in which a concentration of at least one carbonate supplier is located a in a range of 1 to 5% by weight with respect to the total weight of the solution (L) or suspension, - adjustment of the pH of the solution (L) or suspension in a range of 8 to 12, - application of the aqueous solution (L) or the suspension to at least one side of the galvanized steel sheet (1) and production of a wet film (2 ') with a predetermined thickness, which is adjusted according to the concentration of the treatment solution from 1 to 20 μm. - drying of the wet film (2 ') without carrying out a rinsing step to obtain a dry substance layer weight of 25 to 200 mg / m2 of surface, in which the weight of the dry substance layer is determined by the thickness of the wet film (2 ') and the concentration, and in which an inorganic functional layer (2) is obtained a conversion layer of zinc and zinc salts (2), which are, at least partially, carbonates

Description

DESCRIPTION

Inorganic functional layer on hot dipped galvanized steel to aid shaping

The present invention relates to a galvanized steel sheet with an inorganic functional layer and to a process for producing the coated galvanized steel sheet. In addition, the invention relates to the use of the steel plate for the production of components for motor vehicles.

From the mid-1980s to the present day, electrolytic galvanizing and hot-dip galvanizing of thin sheet metal has established itself as an essential pillar of corrosion protection for high-quality car bodies. Currently, zinc-protected surfaces ensure corrosion resistance so high that the life of the entire vehicle is no longer decisively limited by corrosion.

Electrolytically galvanized steel has been used for years in the car body sector. In this process, the surface finish is applied before galvanizing ("tempering"). The softer zinc layer is subsequently deposited uniformly by electrolysis on the hard base metal. To improve the formability, it is possible to phosphate the galvanized strip by electrolysis. This process, called "prefosphating," acts as a solid lubricant, reduces friction and prevents zinc from melting on the tool. In the case of pre-phosphate sheets, mainly pre-lubrication oils are used. Strips and plates are often washed with low viscosity pre-lubrication oils. Relubrication with wire drawing oils is only necessary in exceptional cases. Another possibility to improve the formability is the coating with dry lubricant (Drylube, Hotmelt) instead of with pre-lubrication oils.

In recent years, the proportion of hot galvanized sheets in the automotive industry has increased considerably. In the case of hot-dip galvanizing, the strip can only be subjected to tempering after galvanizing. Thus, unlike the electrolytically galvanized strip, the texture in the soft zinc layer is enhanced. Due to the characteristics of the process, the zinc immersion bath contains a certain amount of aluminum, which accumulates on the surface as aluminum oxide. During forming, hot galvanized sheets tend to transfer soft zinc to the tool. Friction and wear increase. This effect is also known as "application wear" or galling. In contrast to electrolytically galvanized steel, in the case of hot dipped galvanized steel, wire drawing oils and hotmelts cannot reduce this phenomenon sufficiently. Due to the characteristics of the process, in hot-dip galvanized sheets it is not profitable to carry out a phosphating similar to the pre-phosphating performed in electrolytically galvanized steel.

Since zinc surfaces, which in comparison to steel are very ductile, cause an increase in abrasion in pressing tools that can easily lead to visually perceptible surface defects, in galvanized parts initially a galvanized sheet of a single side, leaving the visible side lacquered without galvanizing. Continuous improvements in the process chain now allow to produce visible parts with galvanized surface on both sides.

When producing them, as well as in the case of difficult-to-form parts, in addition to lubrication with liquid or semi-solid media, it is advantageous to use separation layers anchored on the surface of the metal part or tool. In addition to the tribological effect, which is based at least on a sufficiently strong mechanical separation of the metal surfaces of the tool and the part, it is sought to be fully compatible with the process chain of the construction of raw bodies.

In order for them to be used in the automotive industry, the tribological or separation layers applied to the galvanized steel surface must be compatible with the adhesives used in the raw bodywork. From WO 2005/071140 A1 it is known that the use of an aqueous treatment solution containing sulfate ions in a concentration of at least 0.01 mol / l reduces the damage to the coating caused to the surface of a metal sheet. galvanized steel during forming, and temporarily improves corrosion protection.

ArcelorMittal has developed this type of tribological layer for hot dipped galvanized zinc sheets and has launched it on the market under the name "NIT". This layer is characterized by a very good friction reduction with good adhesion of the adhesive materials.

In the case of electrolytically galvanized thin sheet, whose outer coating is often rough due to the characteristics of its production, it has been shown that in addition to greasing it is convenient to perform a tricationic phosphate. This is similar to what was subsequently applied in tricationic phosphate in the lacquer line.

In the automotive industry so far the use of this type of tricationic phosphate has not been consolidated in hot dipped galvanized sheet strips, as well as similar "rinsing" and non-crystalline phosphating processes have not been consolidated, as it offers, for example, the company Salzgitter Ag with the pPhos® brand. This consists of an inorganic conversion layer with a thickness of approximately 300 nm as an aid to the hot dipped galvanized sheet forming.

DE 102008016050 A1 describes a primer to produce a forming layer, metal substrates coated with this primer and the use of the primer and the coated substrates. The primers contain binders, additives, anti-corrosive pigments, crosslinking agents and solvents. Branched polyester resins or other resins can be used as binder, and the anti-corrosive pigments can be calcium modified silica pigments, zinc phosphates, aluminum phosphates, aluminum triphosphates, pigments and mixtures of silica and magnesium.

These layers offer a good friction reduction, but are not compatible with all adhesives, so their use for the raw bodywork in the automotive industry would be limited.

WO 2004/050808 A1 discloses a metal sheet coated with lubricant with improved forming properties. The coating lubricant is an anticorrosive oil, a so-called "pre-lubrication oil" and / or a dry lubricant (Drylube, Dry Film Lubricant), and the metal sheet comprises a layer that forms on the surface of the sheet when applying a solution which contains an organic phosphoric acid ester. To produce the metal sheet coated with lubricant, a solution containing the organic phosphoric acid ester is applied to the top and / or bottom of the sheet, and then the lubricant is applied to the sheet with this coating. The solution can be applied by immersion, spraying, brushing or knife coating. However, the insufficient compatibility of the process constitutes an even limited use in the automotive industry.

EP 2570515 A2 presents a chromate-free treatment procedure for aluminum substrates to produce a conversion layer in which an aqueous and alkaline treatment solution containing Li ions, phosphate, hydroxide ions and carbonate ions is used, and has a pH greater than 10. The treatment solution is applied to the metal substrate to produce a wet film of any thickness, according to the requirements of the application. Without it being necessary to perform a rinsing step, the wet film dries with a variable exposure time depending on the type and thickness of the conversion layer to be obtained.

In US 5660707 A a method is described for improving the formability and weldability of a galvanized steel sheet by forming a layer of zinc oxide on the surface of the steel sheet as an auxiliary forming layer. For this purpose, an aqueous and alkaline treatment solution with hydrogen peroxide is used as the oxidizing agent. The treatment solution is buffered with NaOH and NaHCO3 at a pH in a range of 7 to 11, and applied to the galvanized steel sheet to form a wet film that is allowed to act for a predetermined period of time at a predetermined temperature, and then rinsed to obtain a layer of zinc oxide with at least 150 mg / m2.

US 6231 686 B1 describes a procedure for the treatment of a galvanized steel sheet to improve the formability. This consists in producing an auxiliary forming layer on the surface of the steel sheet comprising a zinc carbonate conversion layer. The aqueous treatment solution used has 1 to 150 g / l of ammonium bicarbonate or alkali metal bicarbonate, resulting in a pH of the solution in a range of 6 to 9. The aqueous treatment solution is applied to the Galvanized steel sheet and a wet film is formed that is allowed to act for a predetermined period of time at a predetermined temperature depending on the concentration of the solution. Subsequently, the wet film is rinsed and the resulting conversion layer has a layer weight of 10 to 100 mg / m2 of surface, which is determined based on the time of action and the concentration of the solution.

Based on this prior art, the present invention aims to produce a conversion layer on the surface of a galvanized steel sheet in a simplified and accelerated work process without affecting the subsequent process steps. In particular, this should allow the production of a galvanized steel sheet with a significantly better functional layer in terms of formability compared to surfaces that have only been lubricated, especially at high contact pressures and high temperatures, which can be applied in at low cost and large scale, it is safe in terms of environment, health and safety, it saves time and can be integrated into existing production processes, especially in the automotive industry.

This objective is achieved by a method with the characteristics of claim 1.

Another objective is to obtain a galvanized steel sheet with a functional layer that presents significant improvements in terms of formability compared to surfaces that have only been greased, especially at high contact pressures and high temperatures. In addition, the functional layer must be insoluble or compatible with the subsequent application by spray of lubricating oil. The functional layer should also show good adhesion of raw body adhesives and should be suitable for pretreating bodies (phosphate and phosphate free processes) as well as being compatible with KTL.

This objective is achieved by a steel plate coated with the features of claim 8.

Claim 12 discloses the use of coated galvanized steel sheets in the automotive industry.

Variants of the objects are described in the respective secondary claims.

A process according to the invention for producing a galvanized steel sheet with a time saving feature that has an inorganic functional layer on the surface that forms an auxiliary forming layer or is part of an auxiliary forming layer begins with the preparation of an aqueous solution, without silicon hydride (without silane) or suspension containing at least one carbonate or at least one carbonate supplier and at least one hydroxide supplier.

Here, the terms "carbonate supplier" and "hydroxide supplier" refer to salts that are at least partially soluble in an aqueous medium and dissociate by forming, by chemical reaction in the aqueous treatment or suspension solution, the salts of zinc that is desired to obtain on the galvanized surface. The carbonate supplier (s) are selected from ammonium bicarbonate, ammonium carbonate, alkali metal bicarbonate, alkali metal carbonate and alkali metal carboxylates, and the hydroxide supplier (s) is selected between alkali metal hydroxide, alkali metal oxides, alkali metal alcoholates and magnesium hydroxide or magnesium oxide.

Therefore, depending on the type of carbonate supplier, it is possible to obtain the advantage of dispensing with an additional hydroxide supplier if the carbonate supplier is dissolved with the formation of hydroxide ions in an aqueous medium, as, for example, with alkali metal bicarbonates and alkali metal carbonates.

The concentration of the carbonate supplier or suppliers in the solution or suspension necessary to form the conversion layer is in the range of 1 to 5% by weight, preferably 3 to 5% by weight.

The pH of the aqueous solution or suspension is in the range of 8 to 12. It has been found that a pH of (9 ± 0.5) provides particularly suitable conversion layers. Depending on the type of carbonate or hydroxide suppliers selected, the pH of the treatment or suspension solution may already be within the established range. However, if desired or if necessary, sodium hydroxide and / or potassium hydroxide may be added to adjust the pH.

The aqueous solution or suspension is applied to at least one side of the galvanized steel sheet, and thus a wet film with a predetermined thickness is formed, which is adjusted according to the concentration of the treatment solution from 1 to 20 pm for that a chemical reaction of the metallic coating with the carbonate suppliers or the hydroxide suppliers at least partially dissolved and dissociated in the aqueous medium to form zinc salts occur on the surface. Once the wet film has dried without a rinsing step being carried out, a conversion layer from zinc salts, which are at least partially carbonates, is obtained as an inorganic functional layer. The weight of the dry substance layer after the wet film has dried is calculated based on the thickness of the wet film and the concentration and, the advantage is that it is in a range of 25 to 200 mg / m2 of surface , preferably from 40 to 90 mg / m2 and, therefore, is suitable for the additional processing that is desired.

Thus, for example, in the case of a surface containing only zinc and zinc oxide, and it is desired to treat with a treatment solution containing sodium bicarbonate as a carbonate supplier, a dry substance deposited from 40 to 90 mg / m2 of surface area, which is converted into hydrocycite. Under these conditions, the weight of the layer of the conversion layer is in the range of 190 to 340 mg / m2 and, therefore, has a favorable and adequate strength for the intended purpose.

With this procedure without rinsing, they can be produced on a large scale and low cost, in a short time and with few equipment hot-dip galvanized steel sheets or electrolytically galvanized with the functional layer.

This treatment or suspension solution has the advantage that it does not contain heavy metals or organic compounds or solvents. The risks associated with the use of alkaline solutions are known and can be handled without problem. It is not necessary to take large protective measures against chemical burns. In addition, this conversion layer is oil resistant and soluble only in acids. The conversion layer shows good adhesion of the adhesives used in the raw construction and is suitable for the pretreatment of bodyworks and compatible with KTL.

Of course, any alkaline element can generally be used as a cation of carbonate and hydroxide suppliers, but mainly for economic and availability reasons, sodium and / or potassium are preferably used. Particularly preferred as carbonate suppliers are bicarbonate and / or potassium and / or sodium carbonate, and sodium or potassium hydroxide is used as hydroxide suppliers. A treatment or suspension solution with these components achieves conversion layers with an optimal combination of friction behavior and adhesiveness.

In order to be able to verify the thickness of the conversion layer produced, in one embodiment of the process, during the preparation of the treatment or suspension solution a system of tracers can be added which can detect in the x-ray fluorescence analysis and present

- potassium and / or sodium phosphate or pyrophosphate and / or potassium and / or sodium triphosphate, or

- potassium bicarbonate, or

- potassium and / or sodium sulfate, or

- potassium and / or sodium silicate, sodium and / or sodium potassium metasilicate, or a dispersion of SiO2 containing sodium

- a tin compound

or titanium For the plotter system, a concentration in the range of 1 to 30% by weight, preferably 10 to 20% by weight, more preferably 15% by weight with respect to the content of carbonate and hydroxide suppliers can be selected.

The application of the aqueous solution or suspension in the galvanized steel sheet can generally be done by spraying without draining or spraying, and removing the excess with compression rollers without traction. However, preferably the aqueous solution or suspension is applied by continuously passing a roller over a strip of galvanized steel sheet. For this purpose, a coating roller ( rollcoater) can be used , which generally acts on each side of the coating with two or three rollers (spoon roller, application roller and, if necessary, regulation roller), by rotating the pull by the back pressure roller.

Surprisingly it has been found that in a simple and therefore preferred way it is possible to save time in the application of the aqueous solution or suspension by means of two compression rollers between which the hot dipped galvanized steel sheet or the strip is passed of steel.

As part of this process, the aqueous solution or suspension is sprayed until it drips onto the compression rollers arranged on both sides of the galvanized steel sheet, and the excess solution or suspension dripping from the sheet or rollers is collected and It leads to a collection tank. The compression rollers are placed under pressure against the surfaces of the galvanized steel sheet, thus eliminating the aqueous solution or suspension from the surfaces of the galvanized steel sheet. The thickness of the wet film is adjusted in a range of 1 to 20 pm by selecting the set pressure, the hardness of the rubber coating of the compression rollers, the speed of the compression rollers and the speed of the steel sheet and , therefore, the relative speed of the compression rollers relative to the steel plate.

At an additional stage of the process, an anticorrosive oil and / or a pre-lubrication oil or a dry lubricant (Hotmelt, Dry Film Lubricant, Drylube) can be applied to the conversion layer in order to obtain a lubricating oil layer with a grammage from 0.2 to 3.0 g / m2.

A hot dipped galvanized steel sheet produced according to the invention has an inorganic functional layer on the surface that forms an auxiliary forming layer or is part of an auxiliary forming layer. The inorganic functional layer according to the invention is based on an alternative chemical base. It is a conversion layer formed by zinc and zinc salts, which are at least partially carbonates. The conversion layer is obtained by applying a treatment medium to the surface of the galvanized steel sheet, which is an aqueous solution without silicon hydride or a suspension containing at least one carbonate supplier but preferably containing at least one carbonate supplier and additionally at least one hydroxide supplier. The zinc salts of the conversion layer may further include zinc hydroxides and zinc oxides. The conversion layer can thus preferably have a mineral structure similar to hydrocycite that is formed from the dry substance deposited by the process according to the invention by applying and drying a wet film with a layer weight of 25 to 200 mg. / m2 surface.

The conversion layer with a method according to the invention is constituted as an advantage that saves time.

If the weight of the dry substance layer leading to the formation of the conversion layer has a surface area of 25 to 200 mg / m2, preferably 40 to 90 mg / m2, a sufficiently good formability is guaranteed. In order to check the thickness of the conversion layer, a plotter system can be provided in the conversion layer that can be detected by X-ray fluorescence analysis and selected from potassium, phosphorus, silicon or even tin or titanium compounds. .

To achieve optimum forming results, the auxiliary forming layer of the hot dipped galvanized steel sheet also has a lubricating oil layer, which is applied to the conversion layer, which alone shows only few anticorrosive effects and lubricants This layer of lubricating oil presents a weight of 0.2 to 3.0 g / m2, typically 1.0-1.5 g / m2, and therefore complies with the current delivery instructions for the lubricated steel strip.

It has been found that the conversion layer is compatible with anticorrosive oil or pre-lubrication oil or dry lubricants applied subsequently, and that its ability to be used in subsequent process steps is not affected, such as the union with Adhesive or the ability to dispose of raw car bodies. The application of corrosion protection or pre-lubrication oil or a dry lubricant is necessary for corrosion protection and lubrication during shaping. By combining the oil layer with the inorganic functional layer, a significant improvement in the lubrication properties can be achieved. In this document, the terms "conversion layer" and "functional layer" are used as synonyms. While the term "conversion layer" is used more in the context of the chemical composition and the forming process, the term "functional layer" is more likely to be associated with the effect of this layer (in subsequent process steps) .

A galvanized steel sheet coated according to the invention can be used for the production of components for motorized vehicles, in which the steel sheet is subjected to one or more forming steps. The conversion layer applied to the galvanized steel sheet as a tribological layer is suitable for use in the automotive industry; and also the application of the treatment solution can be industrially implemented in large-scale production.

Other advantages will be presented in the following description with reference to the attached images. The reference to the figures in the description is made for the purpose of facilitating the description and understanding of the subject. It shows:

In fig. 1 a merely schematic illustration from a side view of an installation for the production of coated steel sheets according to the invention.

In fig. 2 a graph of the results of the flat strip extension tests on treated sheets according to the invention compared to untreated sheets.

In fig. 3 a graph of the results of the cupping tests on several treated plates according to the invention compared to untreated plates.

In fig. 4 a graph of the results of the cupping tests on several plates treated according to the invention with different pH values compared to untreated plates.

In general, to reduce friction in the solid state, solids with a reticular structure should be particularly suitable, in which the combination between the structure-forming layers is significantly weaker in one direction in space than in the plane of the layer . This property is found, for example, in graphite, molybdenum disulfide (MoS2) or hexagon boron nitride (h-BN). However, these types of solids are generally not suitable for use on sheet metal surfaces for car bodies, since they exert a separation effect on the adhesives used in raw bodies. In addition, the substances mentioned above have low surface energy levels and are insoluble in the treatment baths used to clean and pretreat the body plate, which would lead to poor results in the lacquered structure.

On the contrary, compounds with a similar structural composition and a chemical composition that do not cause any negative interaction later in the process chain would be suitable. A suitable mineral is brucite, which is formed by magnesium hydroxide, Mg (OH) 2. This forms a reticulated structure of layers of the Cdl2 type (where the iodide ions form a compact hexagonal spherical packing, the octahedral holes every two spaces of the intermediate layer are completely filled with cadmium ions) with pronounced cleavage in one direction of space but at Unlike graphite, molybdenum disulfide or hexagonal boron nitride has no significantly low surface energy levels and is soluble in treatment baths due to its predominantly ionic bonding character. Its level of water solubility is low, which makes it difficult to continuously apply a wet drying film.

Research shows that the eroded surfaces of galvanized sheet have significantly lower coefficients of friction than surfaces without eroding. When placed outdoors, due to the action of water and carbon dioxide on zinc surfaces, hydrocincite, Zn5 [(OH) 6 | (CO3) 2], is formed, which presents structural similarities with brucite.

However, with only a few seconds of exposure to the action of water and CO2, the eroded surfaces are not achieved in the context of the continuous galvanizing process or it would not be profitable or sustainable due to the length required by the installation. In summary: exposure to the weather is considered a procedure that takes too much time.

However, it has been found that through the action of aqueous solutions of alkali metal bicarbonates (AHCO3), alkali metal carbonates (A2CO3), alkali metal hydroxides (AOH), metal oxides Alkali (A2O), alkali metal alcoholates (AO-R) and alkali metal carboxylates (AOOC-R) and magnesium oxide and / or magnesium hydroxide on galvanized surfaces conversion layers are formed with a similar effect.

The functional or conversion layer that will be produced on the galvanized steel surface guarantees the reduction of friction during the forming of the steel sheet. The conversion layer is formed by the reaction of the dried solution on the surface described above with the metal surface. The thickness of the conversion layer therefore results from the concentration of the treatment solution and the thickness of the wet film applied. The weight of the dry substance is 25 to 200 mg / m2, preferably 40 to 90 mg / m2.

The pH of the treatment or suspension solution should be 8 to 12. In general, the solutions or suspensions of the carbonate or hydroxide suppliers may contain cations of the elements lithium, sodium, potassium, rubidium, cesium, however, they contain preferably sodium and potassium, and hydroxide or magnesium oxide.

In addition, the treatment solution may contain as an additive a plotter system that, although not necessary to obtain the tribological effect, serves as an indicator for the quantitative detection of the amount applied and does not prevent the formation of the conversion layer. For this purpose, substances of the following elements can be used: potassium, phosphorus, silicon, tin or titanium. These elements can be detected by X-ray fluorescence analysis (RFA) more easily than sodium. Preferably, for this purpose the potassium carbonate / bicarbonate, Na / K phosphate or Na / K pyrophosphate / triphosphate compounds, alkali silicate (especially sodium silicate, potassium silicate) tin / bicarbonate carbonate can be used. The treatment solution may contain from 0.01 to 1.5% by weight of the respective plotter system, preferably from 0.05 to 1% by weight.

The application of the solution or suspension can generally be done by immersion, spraying, spraying / draining, coating roller ( rollcoater) or combinations of these processes with subsequent natural drying or thermally assisted. In combination with an oil of 0.2 to 3.0 g / m2 per side, the galvanized steel sheet coated according to the invention has a reduced coefficient of friction, in which the stick-slip behavior is avoided or at least reduce. In addition, the transfer of material from the piece to the tool and the formation of metal abrasion are reduced. On the other hand, the lacquering capacity and surface adhesiveness are preserved. The galvanized steel sheet coated according to the invention is resistant to washing with washing oils, while the conversion layer can be easily moistened with water.

Fig. 1 shows a simple preferred process for producing a galvanized steel sheet coated according to the invention with friction reduction. The outline of the installation to carry out the procedure can be broadly divided into three stages: sprayed, drained and dried.

The galvanized steel strip 1 moves in the forward direction and is passed between the rubber-coated compression rollers 10, which are located above and below the steel strip 1. By means of suitable application devices 12 , the treatment solution L (or suspension) is sprayed until it drips onto the rubber coating 11 of the compression rollers 10. The excess of the processing solution L in the compression roller 10 on the steel sheet strip 1 it runs first on the steel strip 1, then through the edge of the strip it falls into the collecting tank 13, while the excess of the treatment solution L in the compression roller 10 below the sheet steel strip 1 it falls back directly from the compression roller 10 into the collection tank 13. The treatment solution L is supplied from the collection tank 13 to the application devices 12 through the supply lines ro 14 corresponding.

The self-propelled compression rollers 10 are placed with pneumatic or hydraulic pressure on the surfaces of the steel sheet strip 1 and remove excess treatment solution L that remains on them. The top roller serves as a support for the bottom roller and vice versa. When selecting the set pressure, the hardness of the rubber coating 11, the relative speed of the compression rollers 10, which rotate with a speed b with respect to the steel sheet strip 1 the speed a of the steel sheet strip 1, 2 'wet films can be produced from 1 to 20 pm, however, it is preferred that they be from 2 to 3 pm. Thinner wet films may be preferred as they allow shorter dryer travels, lower strip temperatures or faster strip speeds.

The wet film 2 'is dried in a circulating air dryer 15 to thereby obtain the functional layer 2 on the surface of the hot dip galvanized steel strip. The steel strip 1 is tensioned without support between the exit compression rollers 10 and the air dryer with outlet circulation 15.

In general, the wet film can also be air dried.

The construction and arrangement of the application device may differ from the example shown.

Therefore, as an alternative to the illustrated example, it is also possible to conceive the application by means of a coating roller ( rollcoater) with two or three rollers, which allow greater freedom in the design of the wet film regardless of the speed of the strip. In many installations, the coating rollers ( rollcoater) They are also part of the standard equipment, especially for in-line coating of antifinger printing . However, since the coating rollers ( rollcoater) are associated with significantly higher investment, maintenance and operating costs, they are not used as frequently in simple post treatments as shown in the application of the treatment solution according to the invention.

In addition, it is also possible to conceive the spraying of a wet film without draining (for example, in a fog chamber) or spraying and removing with compression rollers without traction and dragging through an immersion bath.

As a substrate, for example, the following sheets can be used:

- hot dip galvanized sheet (“Z” sheet), according to the characteristic properties of the CM095 Steel Information Center Edition 2010, ISSN 0175-2006, which constitutes a thin sheet of zinc coated steel by immersion "Z" hot with a zinc coating of 50 to 600 g / m2, preferably 50 to 140 g / m2, cold rolled and textured with an average roughness Ra = 0.7 to 1.6 pm and an RPc maximum = from 60 to 140 / cm and a tempering level of 0.2% to 2.5%.

- hot dip galvanized sheet («Z» sheet), according to the characteristic properties of the CM095 Steel Information Center Edition 2010, ISSN 0175-2006, which constitutes a thin sheet of zinc and magnesium coated steel by hot dipping «ZM» with a zinc and magnesium coating of 40 to 350 g / m2, preferably 50 to 140 g / m2, cold rolled and textured with an average roughness Ra = from 0.7 to 1.6 pm and a maximum RPc = from 60 to 140 / cm and a tempering level of 0.2% to 2.5%.

- electrolysis galvanized ( electro-galvanized) sheet («ZE» sheet), according to the characteristic properties of the CM092 Steel Information Center Edition 2008, ISSN 0175-2006, which constitutes a cold rolled cold rolled steel sheet and textured with an average roughness Ra = from 0.7 to 1.6 pm and a maximum RPc = from 60 to 140 / cm and a continuous electrolytic coating with zinc coating «ZE» and a zinc layer thickness of 2, 5 to 10 pm per face, preferably 5 to 7.5 pm per face.

As active agents in the treatment solutions mentioned by way of example, sodium and potassium carbonate and bicarbonate and sodium and potassium hydroxide with a total concentration of the treatment solution of 3 to 5% by weight are preferably selected and the pH defined in a range of 7 to 13, preferably 8 to 12, more preferably 9.

If a plotter system is used to detect the thickness of the layer, its concentration is in a range of 1 to 30% by weight, preferably 10 to 20% by weight and more preferably 15% by weight with respect to the content of active agent, if the plotter system is selected from the following:

- Na / K phosphate or Na / K pyrophosphate / triphosphate

- K bicarbonate

- Na / K sulfate

- Na / K silicates, Na / K metasilicates, SiO2 dispersion containing Na

- Tin or titanium compounds

Even with a plotter system, the pH of the treatment solution should be in a range of 8 to 12, more preferably around 9, and if necessary adjust, preferably with NaOH or KOH.

The process described herein by way of example to form conversion layers by the action of alkali metal carbonates or basic bicarbonates on galvanized steel surfaces provides the formation of structures that resemble hydrocycite Zn5 [(OH) 6 | (CO3) 2] on pure zinc by corrosion in the presence of CO2 in the air such as basic zinc carbonate together with other zinc hydroxides, carbonates and oxides. Unlike pure zinc surfaces, hot-dip galvanized steel strip surfaces contain not only zinc but also aluminum (Z sheets and ZM sheets) or magnesium (ZM sheets) in smaller proportion. On these surfaces, the conversion layer that is formed by corrosion also contains aluminum or magnesium compounds (hydroxides, carbonates, oxides). The corrosion layer they form is amorphous and does not constitute an exact chemical composition or a crystalline structure. Next, the basic zincaluminium carbonate / hydroxide layers ("Z" sheet), basic zinc / magnesium aluminum carbonate / hydroxide ("ZM" sheet) or basic zinc carbonate / hydroxide ("ZE" sheet) are described such as the conversion layer or the functional layer. The wet film applied to the metal surface according to the invention is dried and subsequently not rinsed with water. Therefore, all non-volatile components remain on the surface. The weight of the substance layer dry if it is in the range of 25 to 200 mg / m2 of surface area, preferably 40 to 90 mg / 2. The weight of the layer of the conversion layer that is formed is proportionally greater due to corrosion and the addition of zinc, aluminum or magnesium to the surface of the sheet.

The weight of the dry substance layer can be determined based on the thickness of the wet film depending on the concentration of the treatment solution. For example, to achieve the preferred weight of dry substance of 40 to 90 mg / m2, a wet film of 1.3 to 3.0 pm thickness should be applied to a 3% solution. The thickness of the layer can be verified by an X-ray fluorescence analysis of what has been added to the solution and of the trace elements of potassium, phosphorus, sulfur or silicon, tin, titanium present in the dry substance.

The friction reduction effect of the conversion layer can be checked, for example, by strip drawing tests based on VDA 230-213 and by recessing tests, as shown below with reference to Figures 2 to 4 .

The table below lists the treatment solutions used to treat the sheets for strip extension tests and cupping tests.

T l 1: E m l l i n r mi n:

In this way the 5% by weight treatment solution is obtained with a pH of 9 for the NC example. 50 g of NaHCO3 are dissolved in 950 g of demineralized water and then the pH of the solution with sodium hydroxide solution (for example, with 50% by weight of NaOH) is adjusted to 9.

Fig. 2 shows in a graph in which the coefficient of friction is plotted with respect to the contact pressure, the results of the tests of flat strip strips carried out on an NC sheet treated with a 5% NaHCOa / NaOH aqueous solution by weight (pH 9) and in a KC sheet treated with a 5% by weight aqueous solution of KHCO3 / KOH (pH 9) (see Table 1) and for the purpose of comparison in an untreated NO sheet according to VDA 230- 213 (Tool material GJS-700-2 (GGG 70L), tool temperature 40 ° C, tool dimension 74 x 144 mm2, sheet type = DX54D Z100, sheet width 100 mm, sheet length 1500 mm , sheet thickness = 1 mm, extension speed 10 mm / s). All test plates after the conversion treatment and before the strip extension test were greased with 1.1 to 1.3 g / m2 of Anticorit PL 3802-39S pre-lubrication oil from Fuchs Europe GmbH, Mannheim (Germany ). The NC and KC plates treated according to the invention have significantly reduced coefficients of friction compared to the untreated NO sheet, and also the stickslip effect (slip friction behavior) that occurs in the untreated NO sheet is avoided. Furthermore, it can be seen that the conversion layers of the NC sheet produced with NaHCO3 / NaOH tend to have lower coefficients of friction than the conversion layers of the KC sheets produced with KHCO3 / KOH.

Fig. 3 shows the results of the cupping tests with a 0.8 mm thick HDG plate (Presse BUP 200 from the company Zwick Roell, Ulm, Germany, tool material punch and wire drawing = 1.2510, tool material tracer = 1.0503, tool temperature 25 ° C, cylindrical cup, punch diameter = 50 mm, punch radius = 5 mm, disc diameter = 100 mm, wire drawing radius = 5 mm, wire drawing groove = 1.3 mm, drawing ratio = 2.0, tracer force = 30 kN, sheet type = DX54D Z100, sheet thickness = 0.8 mm, drawing speed 10 mm / s). The bar graph shows the maximum punching force in the non-treated NO sheet compared to the test plates subjected to the different treatments, according to Table 1. Also in this case, after the conversion treatment, all the test panels were lubricated with 1.1 to 1.3 g / m2 of Anticorit PL 3802-39S pre-lubrication oil. The plates treated with NaHCO3 treatment solutions (NC, NC + K ^c , NC + PH, NC + S, NC + Si, NC + SiO2) allow a maximum punching force significantly less than the untreated NO sheet. It can be seen that even a conversion layer, which is obtained from a reaction of a galvanized surface with water vapor (H2O test plate), results in a reduced maximum punching force in the cupping test and, therefore, Therefore, it shows improved tribological behavior.

However, until now water vapor treatment, which allows to produce an effective conversion layer, cannot be performed from the point of view of process technology with the facilities that are commonly used in the steel industry, since steam treatment requires considerably longer treatment times than completely continuous processes. Therefore, at a temperature of 40 ° C the effective conversion layers form only after 1 hour and even at a temperature of 95 ° C it takes 2 minutes. At a typical strip speed in a laminator of 200 meters per minute, treatment times of, for example, 2 minutes require a treatment line in the production facility of 400 meters. Therefore, the treatment times of seconds of duration required by the manufacturing process to achieve the necessary productivity of the facilities so far have not been achieved with water vapor.

For the effectiveness of a functional layer according to the invention in terms of friction reduction, the presence of tracers is not required. However, the examples presented show that the different plotter systems have some influence on the friction of the general layer, although to a lesser extent. Therefore, the conversion layers of treatment solutions with tracer systems, in particular with phosphate (NC + PH) and silicon dioxide (NC + SiO2), allow the lowest punching forces. This indicates that the presence of certain tracer components promotes the formation of a more efficient conversion layer or that certain tracer components contribute to a better tribological efficiency and, for example, incorporate themselves into the conversion layer. For this reason phosphates are known as lubricating components, and the dispersion of SiO2 is also attributed lubricating effects. Optionally, both effects can be taken into consideration.

In the bar graph of fig. 4 the results of the recessing tests are shown with the 1.0 mm thick HDG sheet and the untreated sheet is compared with a sheet with pH 11.5 treated with Na2CO3 and one with a pH of 8.6 treated with NaHCO3 (NC pH 11.5 and NC pH 8.6, see Table 1). (Test parameters: Punching tool material and wire drawing line = 1.2510, tooling tool material = 1.0503, tool temperature 25 ° C, cylindrical cup, diameter = 50 mm, disc diameter = 100 mm, drawing ratio = 2.0, tracer force = 30 kN, sheet type = DX54D Z100, sheet thickness = 1.0 mm, drawing speed 10 mm / s). Following the treatment, the test plates were lubricated with 1.1 to 1.3 g / m2 of Anticorit PL 3802-39S pre-lubrication oil.

Surprisingly, both NC treated plates with pH 11.5 and NC pH 8.6 require a significantly reduced maximum cupping strength compared to the untreated NO sheet, and at pH 8.6 the NC treated sheet shows even better results with a pH 8.6 that at a pH 11.5 the NC treated sheet with a pH 11.5, which results in a pH 8.6, the formation of hydrocycite Zn5 [(OH) 6 (CO3) 2], which is thermodynamically preferred because it is tribologically effective, while at pH 11.5 zinc oxide and hydroxide formation takes place, which are less effective.

Surprisingly, it has also been seen that the conversion layer is compatible with a subsequent manufacturing process for raw bodies for automobiles: In practice, temporary corrosion protection of the steel sheet is indispensable for the storage and transport of coils. steel, as well as pressed parts not yet painted. This is normally achieved by applying anticorrosive or pre-lubricating oils or hot melting waxy lubricants in the mill. The corrosion protection properties test can be carried out by way of example by means of a condensed water climate test, as described in the VDA 230-213 test specification.

For the condensed water climate test, five sheets were pretreated according to Table 1 (NO, NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SiO2), lubricated with 1, 1 to 1.3 g / m2 of Anticorit PL 3802-39 S and were exposed to a corrosive atmosphere according to VDA 230-213 (5.4.8) for 30 cycles. In this way it has been shown that the protective effect of the treated plates (NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SO2) corresponds to the effect of the reference plates that only be They had lubricated and had no conversion layer (NO). The Anticorit PL 3802-39 S pre-lubrication oil used for lubrication has been used for years for coil lubrication in the German automotive and steel industry. Therefore, it can be assumed that the conversion layers are suitable for temporary corrosion protection of coils and pressed parts.

In addition, good adhesion of the adhesives used is essential for car bodywork. The compatibility of the conversion layer with this type of structural adhesives used in the raw body can be investigated by way of example with an adhesive cord test. This consists of applying a strand (cord) of still liquid adhesive to the pre-treated and lubricated test sheet with 2.8 to 3.2 g / m2 of Anticorit PL 380239 S and subsequently set by thermal means. Once it cools, the adhesive cord detaches mechanically and the surfaces of the sheet and the detached cord are examined. If adhesive remains remain on the metal surface, it means that it has good adhesion between the adhesive and the metal. This good adhesion is accompanied by a rough surface and, therefore, whitish of the adhesive cord. The adhesives used as examples were Betamate ™ 1496 F and Betamate ™ 1040 products from Dow Automotive.

It was possible to demonstrate that the adhesion properties of the test plates with conversion layer (NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SO2) have advantages over those without this type Pretreatment (NO). In all cases a cohesive (CF) or approximately cohesive surface fracture (SCF) pattern was achieved.

In a further experiment, the strings of adhesive set on the sheets were subjected to corrosion before being removed. For this purpose, it was subjected to moisture by way of example for a period of 504 hours at 50 ° C and 95% relative humidity. It was found that the fracture pattern after exposure to corrosion is also cohesive (CF) or approximately surface cohesive (SCF). These results suggest the suitability of the conversion layers according to the invention for adhesion processes in the production of automobile bodies.

Before lacquering car bodies, it is necessary to remove oily layers and layers that can adversely affect the adhesion of lacquered. This is done by an aqueous alkaline cleaning. The elimination without leaving remains of this type of layers is confirmed by the total impermeability of the surface. The elimination capacity test may consist, for example, in the elimination capacity test according to v Da 230-213 (5.10).

It has been found that both the untreated (NO) and the conversion layer (NC, KC, NC + KC, NC + PH, NC + S, NC + Si, NC + SO2), after the elimination capacity test , have the advantage of being completely waterproof. Therefore, it is postulated that the conversion layers are suitable for pretreatment or lacquering of car bodies.

Claims (12)

1. Procedure for the time-saving production of a galvanized steel sheet (1) with an auxiliary forming layer based on at least one inorganic functional layer (2), which comprises the stages of: - Preparation of an aqueous solution, without silicon hydride (L) or a suspension based on at least one carbonate supplier or an aqueous solution, without silicon hydride (L) or a suspension based on at least a carbonate supplier and at least one hydroxide supplier, wherein at least one carbonate supplier is selected from ammonium bicarbonate, ammonium carbonate, alkali metal bicarbonates, alkali metal carbonates and alkali metal carboxylates and, at least one hydroxide supplier is selected from alkali metal hydroxides, alkali metal oxides, alkali metal alcoholates, magnesium hydroxides and magnesium oxide, in which a concentration of at least one carbonate supplier is at a range of 1 to 5% by weight with respect to the total weight of the solution (L) or suspension, - pH adjustment of the solution (L) or suspension in a range of 8 to 12, - application of the aqueous solution (L) or the suspension to at least one side of the galvanized steel sheet (1) and production of a wet film (2 ') with a predetermined thickness, which is adjusted according to the concentration of the treatment solution from 1 to 20 pm. - drying of the wet film (2 ') without carrying out a rinsing step to obtain a dry substance layer weight of 25 to 200 mg / m2 of surface, in which the weight of the dry substance layer is determined by the thickness of the wet film (2 ') and the concentration, and in which an inorganic functional layer (2) is obtained a conversion layer of zinc and zinc salts (2), which are, at least partially, carbonates 2. Method according to claim 1, in which the concentration of at least one carbonate supplier is in a range of 3 to 5% by weight with respect to the total weight of the solution (L) or suspension, and / or The weight of the dry substance layer of the wet film (2 ') is 40 to 90 mg / m2, and / or - the pH of the solution (L) or the suspension is adjusted to 9 ± 0.5, where appropriate, by the addition of sodium hydroxide and / or potassium hydroxide. 3. Method according to claim 1 or 2, in which The alkali metal is sodium or potassium, and preferably, at least one carbonate supplier is bicarbonate and / or sodium and / or potassium carbonate, and at least one hydroxide supplier is sodium and / or potassium hydroxide. 4. Method according to at least one of claims 1 to 3, which includes the stage of: - Addition of a trace system that can be detected with the X-ray fluorescence analysis to detect the thickness of the layer by X-ray fluorescence analysis during the preparation of the aqueous solution, without silicon hydride (L) or suspension and present - potassium and / or sodium phosphate or pyrophosphate and / or potassium and / or sodium triphosphate, or - potassium bicarbonate, potassium carbonate or - potassium and / or sodium sulfate, or - potassium and / or sodium silicates, potassium and / or sodium metasilicates or a dispersion of SiO2 containing sodium and / or tin or titanium compounds with a concentration in the range of 1 to 30% by weight, preferably of 10 to 20% by weight, and more preferably 15% by weight with respect to the content of carbonate and hydroxide suppliers they present. 5. Method according to at least one of claims 1 to 4, in which the application takes place by immersion - spray without draining or - spraying and removing with compression rollers without traction or - Rolled casing roll ( rollcoater) or preferably by means of two compression rollers (10) between which the galvanized steel sheet is passed (one). 6. Method according to claim 5, in which the roll by two rollers (10) comprises the steps of: - Spraying the aqueous solution (L) or the suspension applied excessively on the compression rollers (10) arranged on both sides of the galvanized steel sheet (1), and the subsequent collection and conduction of the excess solution or suspension towards a collection tank (13), - pressure adjustment of the compression rollers (10) on the surfaces of the galvanized steel sheet (1) and removal of the aqueous solution (L) or the remaining suspension on the surfaces of the galvanized steel sheet (1) and - adjustment of the thickness of the wet film (2 ') in a range of 1 to 20 pm by selecting the adjustment pressure, the hardness of the rubber coating (11) of the compression rollers (10), the speed (b) of the compression rollers (10) and the speed (a) of the steel sheet. 7. Method according to at least one of claims 1 to 6, which comprises the stages of: - application of an anticorrosive oil and / or a pre-lubrication oil and / or a dry lubricant to the conversion layer (2) to obtain a lubricating oil layer with a weight of 0.2 to 3.0 g / m2 8. Galvanized coated steel sheet (1) whose surface has an auxiliary forming layer of at least one inorganic functional layer (2), characterized because the inorganic functional layer (2) is a conversion layer of zinc and zinc salts having a mineral structure similar to hydrocycite that is formed from a dry substance by the process according to at least one of claims 1 to 7 by applying and drying a wet film (2 ') with a layer weight of 25 to 200 mg / m2 of surface. 9. Galvanized steel sheet (1) according to claim 8, characterized because The galvanized steel sheet (1) is a hot dipped galvanized steel sheet (1). 10. Galvanized steel sheet (1) according to claim 8 or 9, characterized in that the conversion layer (2) has a plotter system to detect the thickness of the layer, which is detectable by X-ray fluorescence analysis and is selected from potassium, phosphorus, sulfur, silicon, tin or titanium compounds. 11. Galvanized steel sheet (1) according to at least one of claims 8 to 10, characterized because the auxiliary forming layer comprises a layer of lubricating oil applied to the conversion layer (2), the lubricating oil layer being preferred - comprises an anticorrosive oil and / or a pre-lubrication oil and / or a dry lubricant, and - has a weight of 0.2 to 3.0 g / m2, preferably 1.0 to 1.5 g / m2 12. Use of a coated galvanized steel sheet (1) according to at least one of claims 8 to 11 to produce motor vehicle components performing at least one forming step.