EP3469115B1 - Method of cleaning pretreatment of ferrous components that have been joined by welding - Google Patents

Description

The present invention relates to a method for the cleaning pretreatment of iron-containing components joined together by welding, in which residues from the welding process are removed from the surface of the component and subsequent wet-chemical conversion treatments are made possible in such a way that defect-free coatings are produced. For cleaning pretreatment, the component is brought into contact with an aqueous sulfuric acid pickle, which contains amino alcohols, ethoxylates and / or propoxylates of fatty alcohols with 6 to 12 carbon atoms in the alcohol and iron ions, and is effective without the presence of fluorides. In a further aspect, the present invention comprises an acidic aqueous pickle for the cleaning pretreatment of iron-containing components joined by welding.

A cleaning of metallic components is a necessary first process step in every wet-chemical industrial manufacturing stage in order to rid the component surface of impurities from previous manufacturing stages and to adjust the surface for the subsequent refinement in such a way that reproducibly high-quality components result. The components are often already assembled from different materials or semi-finished products and have a correspondingly complex geometry. The task of cleaning in a production stage for the wet chemical pretreatment of a metallic component is therefore primarily to free the surface of auxiliary materials such as drawing greases, corrosion protection oils, machining fluids from cutting or non-cutting shaping material processing or residues from joining processes and to achieve a uniform process solely through the chemical property profile of the metallic base substrate conditioned surface. For this purpose, depending on the manufacturing stage of the materials used and the surface contamination with contaminants, a large number of water-based cleaners are generally commercially available, the effect of which is often based on material removal by pickling, which is increased by solubilizing the contaminants with the aid of surface-active substances. This is the principle behind the WO2004 / 065661 disclosed acidic aqueous cleaner for metal components contaminated with shaping aids, which, in addition to an inorganic pH-adjusting builder, contain a mixture of nonionic surfactants based on ethoxylated aliphatic alcohols.

Regardless of the large number of available cleaning agent formulations that are able to specifically pickle metallic materials and in this way also from surface contamination To free it, cleaning the surfaces of components in the area of the integral connection of materials made of iron produced by welding for the provision of temporary corrosion protection or a paint primer by means of wet chemical conversion treatment, for example phosphating, is problematic, since in particular welding residues from slag-forming agents Welding filler materials with conventional cleaner formulations are only insufficiently removed from the surface of the component. This applies in particular to detergent formulations that are largely free of fluorides and are therefore particularly desirable for environmental hygiene reasons. There is also an economic need to keep the process temperatures as low as possible during cleaning and to keep treatment times as short as possible. Such a range of services cannot currently be used to full satisfaction by commercial cleaner formulations for the cleaning pretreatment of components which are assembled by welding materials consisting of iron. The DE 42 37 021 C1 discloses in this context only a method for cleaning welded components made of stainless steel, in which the pickling agent used contains sulfuric acid, iron (III) ions and fluoroboric acid and optionally a surfactant.

1. a) insgesamt mindestens 1 g/kg an Aminoalkoholen;
2. b) insgesamt mindestens 0,5 g/kg an Ethoxylaten und/oder Propoxylaten von Fettalkoholen mit 6 bis 12 Kohlenstoffatomen im Alkohol mit mindestens 6 Ethylen- und/oder Propylenoxideinheiten; und
3. c) Eisen-Ionen

in Kontakt gebracht wird.The present invention meets this need and establishes a method for the cleaning pretreatment of a component which is at least partially joined by welding, wherein at least a part of the component, which is a material made of iron or steel, is integrally connected to the rest of the component by the welding in which the component contains an aqueous fluoride-free sulfuric acid stain

1. a) a total of at least 1 g / kg of amino alcohols;
2. b) a total of at least 0.5 g / kg of ethoxylates and / or propoxylates of fatty alcohols with 6 to 12 carbon atoms in the alcohol with at least 6 ethylene and / or propylene oxide units; and
3. c) iron ions

is brought into contact.

The term "welding" in the sense of the present invention is the integral connection of similar or dissimilar metals using heat or heat and pressure, as well as using welding filler materials, which at least partially produce the integral connection. Welding filler materials are usually used in the form of coated metal wires or cored wires with a core as well as in the form of powders in combination with bare metal wires and, in addition to their function, have an integral connection to support a protective function during welding by bridging the gap, which consists in preventing scaling of the melted-down metallic component of the welding filler metal and the materials to be joined in the welding area. The covering, core or welding powder of the welding filler material often consists of an inorganic, non-metallic material that completely encloses the welding point and the solidifying melt during the welding process and in this way protects it from the surrounding atmosphere. Welding methods according to the invention are all arc welding methods, in particular metal protective gas welding (MIG / MAG), tungsten inert gas welding (TIG) and spray arc welding, as well as laser and electron beam welding methods and combinations of these methods.

The cleaning of those areas of the component connected by welding that are exposed to silicon due to the use of welding consumables, whether in the welding slag on the surface or in the melted-down metallic wire, is particularly demanding for a subsequent wet chemical conversion treatment. In the method according to the invention, the component is therefore joined together in particular by welding which was carried out using welding additives containing silicon. The silicon as a component of the welding filler material can be an alloy component of the wire ("metal electrode"), a chemical component of the slag-forming core or the sheathing of the wire ("filler wire electrode" or "rod and wire electrodes") as well as welding powder.

A cleaning pretreatment of a component, which is at least partially joined by welding, whereby at least part of the component, which is a material made of iron or steel, is integrally connected to the rest of the component by welding, according to the invention comprises at least contacting the area of this integral welded connection (s) and the area (s) immediately adjacent to the stain, preferably bringing the entire component into contact with the stain. A coherent area surrounding the integral connection by means of the melted-down welding filler ("welding") is immediately adjacent to the integral weld connection, if the mean hardness according to Vickers (VH) according to EN ISO 6507-1: 2005 measured with an indentor, which is at proper measurement does not leave an impression that has a dimension that exceeds the smallest expansion of the weld, deviates by more than 5% from that of the same material before welding.

The component which is pretreated for cleaning in the method according to the invention is preferably at least partially assembled from steel sheets, steel profiles and / or cast steel parts by welding.

Surprisingly, it has been shown that the residues of the welding filler material ("welding slag") can be effectively removed from the component using a sulfuric acid pickle based on a combination of amino alcohols and nonionic surfactants selected from fatty alcohols, without the additional presence of highly complexing fluorides must be classified as problematic for environmental hygiene reasons.

According to the invention, a sulfuric acid stain is characterized in that its pH is below 2.0, preferably below 1.0, and contains at least 20 g / kg of sulfuric acid, preferably at least 40 g / kg of sulfuric acid, calculated as SO ₄ , the proportion of other acids with a pK _S1 value of less than 2.0 and their anions based on the equivalent of sulfuric acid, calculated as SO _4, preferably being less than 5 g / kg, particularly preferably less than 1 g / kg. In a preferred embodiment, the sulfuric acid stain contains at least 60 g / kg, but for economic reasons preferably less than 120 g / kg, particularly preferably less than 90 g / kg, of sulfuric acid calculated as SO ₄ .

The sulfuric acid pickling used in the process according to the invention is also fluoride-free, which is equivalent to the fact that less than 50 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 1 mg / kg, of fluoride ions are contained, whereby the proportion of fluoride ions in a TISAB buffered aliquot of the stain is to be determined with a fluoride sensitive electrode at 20 ° C (TISAB: "Total lonic Strength Adjustment Buffer"), whereby the volume-related mixing ratio of buffer to the aliquot of the stain 1 : 1 is. The TISAB buffer is prepared by dissolving 58 g NaCl, 1 g sodium citrate and 50 ml glacial acetic acid in 500 ml deionized water (κ <1µScm ^-1 ) and setting a pH value of 5.3 using 5 N NaOH and filling to a total volume of 1000 ml again with deionized water (κ <1µScm ^-1 ).

With regard to the amino alcohols according to component a) as an essential component of the mordant, 1,3-amino alcohols and their ethylene or 1,2-propylene glycol monoethers, such as 2- (2-aminoethoxy) ethanol, 2- (2-aminoethoxy) propanol, turned out to be effective so that the use of which is preferred in the process according to the invention, 1,3-amino alcohols being particularly preferred. The 1,3-amino alcohols are preferably selected from dimethylaminoethanol, diethylaminoethanol, N-methyldiethanolamine, mono-, di and / or triethanolamine as well as mono-, di- and triisopropanolamine. Mono-, di or triethanolamine and mixtures thereof are particularly preferred in this context. In this context, it has proven advantageous to pickle which contains both triethanolamine and monoethanolamine.

For sufficient pickling of the components joined by welding, it is preferred according to the invention that the proportion of amino alcohols, particularly preferably 1,3-amino alcohols and their ethylene or 1,2-propylene glycol monoether, particularly preferably 1,3-amino alcohols, is at least 2 g / kg, particularly preferably at least 4 g / kg, but for economic reasons preferably does not exceed 20 g / kg, particularly preferably 10 g / kg. Particularly preferred are processes in which at least 80% by weight, preferably at least 90% by weight of all 1,3-amino alcohols, preferably all 1,3-amino alcohols and their ethylene or 1,2-propylene glycol monoethers, particularly preferably all amino alcohols , in which stains are selected from mono-, di and / or triethanolamine.

In the process according to the invention, the presence of the nonionic surfactant according to component b) in the pickle is also essential for removing the welding slag from the components to be cleaned.

mit M_L: Molmasse der lypophilen Gruppe des Niotensids; M: Molmasse des NiotensidsFor this purpose, it is advantageous if the nonionic surfactants have a certain HLB value which supports good wetting of the components and detachment and dispersion of the welding slag during the pickling process. In this respect, methods are preferred in which the ethoxylates and / or propoxylates of the fatty alcohols according to component b) have an HLB value below 16, particularly preferably below 14, but preferably above 10. The HLB value ("Hydrophilic-Lipohilic Balance") is an empirical quantity and is calculated as follows: $$\mathrm{HLB}=\mathrm{20th}\cdot \left(1-{\mathrm{M}}_{\mathrm{L}}/\mathrm{M}\right)$$

with M _L : molar mass of the non-surfactant lypophilic group; M: molecular weight of the nonionic surfactant

In a preferred embodiment of the process according to the invention, the ethoxylates and / or propoxylates of the fatty alcohols according to component b) are selected from ethoxylates, preferably from ethoxylates of fatty alcohols with 8 to 10 ethylene oxide units and with 8 to 12 carbon atoms in the aliphatic residue of the fatty alcohol.

In the process according to the invention, a proportion of ethoxylates and / or propoxylates of fatty alcohols according to component a) in the stain of at least 1 g / kg is advantageous for a sufficient effect and is therefore preferred. The proportion of fatty alcohols according to component b) in the pickle is particularly preferably at least 2 g / kg, but for economic reasons preferably not more than 10 g / kg, particularly preferably not more than 6 g / kg.

The simultaneous presence of such ethoxylates and / or propoxylates of fatty alcohols in the pickle that contain 6 to 12 carbon atoms in the fatty alcohol and less than 6 ethylene and / or propylene oxide units has also proven to be advantageous for removing the welding slag from the surfaces of the component. Such pickling agents are therefore preferably to be used in the process according to the invention, their mass-related proportion relative to the proportion of component b) preferably being in the range from 1:10 to 4:10.

The presence of iron ions in the pickle is also necessary in the method according to the invention for a supporting pickling attack on the component and thus successful removal of welding slag from the component in economic periods. Accordingly, methods according to the invention are preferred which contain at least 10 g / kg of iron ions in the pickle. On the other hand, precipitations of iron (III) hydroxides on the surfaces of the component should be avoided during pickling, so that according to the invention preferably no more than 70 g / kg, particularly preferably no more than 50 g / kg, of iron ions are contained in the pickling agent should.

Water-soluble salts, preferably water-soluble salts of iron (II) ions, particularly preferably iron (II) sulfate, serve as the source of iron ions. Alternatively, iron powder of a sulfuric acid stain containing components a) and b) can also be added, and in this way a quantity of iron ions can be released. In the latter case, the pH value of the sulfuric acid stain may need to be readjusted due to the acid consumption.

It is further preferred that the component in the method according to the invention does not undergo pre-passivation of the metal surfaces during the pickling process and that the surfaces of the cleaned and, so to speak, bare metallic surfaces of the component are only subsequently subjected to a wet chemical conversion treatment. In a preferred process according to the invention, therefore, the stain contains a total of less than 1 g / kg, preferably less than 0.1 g / kg, particularly preferably less than 0.01 g / kg of dissolved phosphates, calculated as PO ₄ . For the same reason, preferably less than 0.01 g / kg in total in the stain preferably contain less than 0.001 g / kg of water-soluble compounds of the elements Zr and / or Ti based on the respective element.

For the complete removal of organic surface impurities, it is preferred if the pickling in the process according to the invention is preceded by an alkaline degreasing of the component, particularly preferably immediately with an intermediate rinsing step, the alkaline degreasing taking place at a pH of at least 10.

According to the invention, a rinsing step always serves to remove water-soluble residues, non-firmly adhering chemical compounds and loose solid particles from the component to be cleaned, which are carried out from a previous wet-chemical treatment step, for example alkaline degreasing, with the wet film adhering to the component, using a water-based liquid medium . The water-based liquid medium does not contain any chemical components that cause a significant surface covering of the components made of metallic materials with sub-group elements, semi-metal elements or polymeric organic compounds. Such a significant surface coverage would exist if the liquid medium in the sink was depleted by at least 10 milligrams per square meter of the rinsed surfaces, preferably by at least 1 milligrams per square meter of the rinsed surfaces, of these components, based on the element or polymer organic compound in question without taking into account gains due to carryover and losses due to carryover of wet films adhering to the component.

As already mentioned in the context of the present invention and also discussed in connection with the problem area on which the invention is based, the cleaning pretreatment of the component serves in particular to prepare it for a wet-chemical conversion treatment, in the course of which a passivation layer which is as homogeneous as possible and improves the paint adhesion on the surfaces of the component and there in particular on the areas contaminated with welding slag. Therefore, methods according to the invention are preferred in which the pickling is followed by a wet chemical conversion treatment of the component, again preferably directly with or without an intermediate rinsing and / or drying step, particularly preferably without an intermediate drying step.

According to the invention, a drying step is any process step in which the surface is dried by the provision and use of technical means of the liquid film adhering by welding joined component is intended, in particular by supplying thermal energy or applying an air flow.

According to the invention, wet-chemical conversion treatment means contacting at least the iron or steel surfaces of the component with an aqueous composition which produces a passivating and essentially inorganic conversion coating on the surfaces of the treated iron or steel materials. A conversion coating is any inorganic coating on the iron or steel surfaces of the component that is not an oxidic or hydroxide coating, the main cationogenic component of which is iron ions. A conversion coating can therefore be an iron phosphate layer.

According to the invention, preference is given to wet-chemical conversion treatment by means of acidic aqueous compositions, the pH of which is above 1 but below 5, and which preferably represents a layer-forming phosphating. A layer-forming phosphating is, according to the invention, a phosphating which causes a layer coverage calculated as PO ₄ of at least 0.5 g / m ² . Such phosphating is notoriously known to the person skilled in the art of surface treatment, for example as zinc phosphating or so-called trication phosphating.

A previously described wet chemical conversion treatment is in turn preferably followed, according to the invention, with or without an intermediate rinsing and / or drying step, preferably without an intermediate drying step, dip coating the component, preferably electro-dip coating.

In a further aspect, the present invention comprises an acidic aqueous pickle, which is particularly suitable for use in the process according to the invention for the cleaning pretreatment of components which have integral connections of materials made of iron and / or steel produced by welding.

1. i) 40 bis 120 g/kg, vorzugsweise 60 bis 90 g/kg an Schwefelsäure berechnet als SO₄;
2. ii) 2 bis 20 g/kg, vorzugsweise 4 bis 10 g/kg an Aminoalkoholen;
3. iii) 0,5 bis 5 g/kg, vorzugsweise 1 bis 3 g/kg an Ethoxylaten und/oder Propoxylaten von Fettalkoholen mit 6 bis 12 Kohlenstoffatomen im Alkohol mit mindestens 6 Ethylen- und/oder Propylenoxideinheiten;
4. iv) 10 bis 50 g/kg an Eisen-Ionen;
5. v) weniger als 50 mg/kg, vorzugsweise weniger als 10 mg/kg, besonders bevorzugt weniger als 1 mg/kg an Fluorid-Ionen;
6. vi) weniger als als 1 g/kg, vorzugsweise weniger als 0,1 g/kg, besonders bevorzugt weniger als 0,01 g/kg an gelösten Phosphaten berechnet als PO₄.

Such stains according to the invention have a pH below 2.0 and contain

1. i) 40 to 120 g / kg, preferably 60 to 90 g / kg of sulfuric acid calculated as SO ₄ ;
2. ii) 2 to 20 g / kg, preferably 4 to 10 g / kg of amino alcohols;
3. iii) 0.5 to 5 g / kg, preferably 1 to 3 g / kg of ethoxylates and / or propoxylates of fatty alcohols having 6 to 12 carbon atoms in alcohol with at least 6 ethylene and / or propylene oxide units;
4. iv) 10 to 50 g / kg of iron ions;
5. v) less than 50 mg / kg, preferably less than 10 mg / kg, particularly preferably less than 1 mg / kg of fluoride ions;
6. vi) less than 1 g / kg, preferably less than 0.1 g / kg, particularly preferably less than 0.01 g / kg of dissolved phosphates calculated as PO ₄ .

The already mentioned in context with the method according to the invention with regard to the preferred chemical-structural embodiments of components a) to c) of the sulfuric acid stain also represent preferred versions of components ii) to iv) of the acidic aqueous stain according to the invention.

In a preferred embodiment, additional 0.5 to 5 g / kg, preferably 1 to 3 g / kg, of ethoxylates and / or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the alcohol having less than 6 are present as component vii) in the stain Contain ethylene and / or propylene oxide units.

An acidic aqueous pickle according to the invention preferably contains less than 1% by weight, preferably less than 0.1% by weight, of components which are not components i) to vi).

Test parts assembled from two cut steel sheets (200x200x2 mm) using metal active gas welding (mixed gas M20: 90% argon, 10% CO ₂ ) were treated in accordance with the process steps defined below. The welding was carried out in accordance with the AWS A 5.28 / A 5.28M: 2007 standard using a slag-forming silicon-containing welding filler. The welding bead had a length of approx. 100 mm and a width of approx. 2-3 mm.
A. Alkaline degreasing:
Immerse the test part in a mixture of Bonderite® C-AD 1563 (3% by weight) and Bonderite® C-AD 1400 (0.3% by weight) at 65 ° C for 10 minutes
B. Acidic stain:
B.1 Immersed at 60 ° C for 4 minutes containing sulfuric acid stain a) 77.8 g / kg H ₂ SO ₄ b) 1.5 g / kg ethoxylated (8EO) fatty alcohol (C10) c) 20 g / kg iron (II) sulfate d) 0.45 g / kg ethoxylated (4EO) fatty alcohol (C8)
B.2 Immersing the test part at 60 ° C for 15 minutes in mixed acid stain containing a) 150 g / kg H ₂ SO ₄ b) 70 g / kg H ₃ PO ₄ c) 40 g / kg iron (II) sulfate d) 1.8 g / kg Ammonium bifluoride
C. Zinc phosphating:
Immerse the test part in Bonderite® M-ZN 958 at 52 ° C for 4 minutes, but the test part immediately beforehand with an intermediate rinsing step with deionized water (κ <1 µScm ^-1 ) with Bonderite® M-AC 950 at 25 ° C for 1 minute was activated.

In a process sequence AB.1-C, a shiny metallic surface was obtained in the area of the weld seam. Only in this area were under the light microscope to identify minimal residues of welding slag. Scanning electron micrographs (SEM) confirm the overall optically good result and use energy-dispersive X-ray spectroscopy (EDX) to prove that only small amounts of silicon are still detectable in some areas.

On the other hand, despite the tripled treatment time in a conventional process sequence AB.2-C with a fluoride-containing mixed acid stain, residues of the welding slag were already recognizable as dull spots. This was confirmed by light microscopic and SEM images. In addition, no zinc phosphate layer formed on the areas on which residues of the welding slag were identified with the naked eye before and immediately after the pickling.

Claims (14)

1. A method for cleaning pretreatment of a component which is assembled at least partially by welding, at least part of the component, which is a material made of iron or steel, being integrally connected to the remaining component by the welding, characterized in that component is brought into contact with an aqueous sulfuric acid pickle, the pH of which is below 2.0, and which contains at least 20 g/kg of sulfuric acid, calculated as SO₄, containing

   a) a total of at least 1 g/kg of amino alcohols;

   b) a total of at least 0.5 g/kg of ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the alcohol and having at least 6 ethylene and/or propylene oxide units;

   c) iron ions; and

   d) a total of less than 50 mg/kg of fluoride ions.
2. The method according to claim 1, characterized in that the amino alcohols according to component a) are selected from 1,3-amino alcohols and the ethylene or 1,2-propylene glycol monoethers thereof, preferably from 1,3-amino alcohols, particularly preferably from mono-, di- and/or triethanolamine.
3. The method according to one or more of the preceding claims, characterized in that the proportion of amino alcohols is at least 2 g/kg, preferably at least 4 g/kg, but preferably does not exceed 20 g/kg, particularly preferably 10 g/kg.
4. The method according to one or more of the preceding claims, characterized in that the ethoxylates and/or propoxylates of the fatty alcohols according to component b) have an HLB value below 16, preferably below 14, but preferably above 10.
5. The method according to one or more of the preceding claims, characterized in that the ethoxylates and/or propoxylates of the fatty alcohols according to component b) are selected from ethoxylates, preferably from ethoxylates of fatty alcohols having 8 to 12 carbon atoms in the alcohol and having 8 to 10 ethylene oxide units.
6. The method according to one or more of the preceding claims, characterized in that the proportion of ethoxylates and/or propoxylates of fatty alcohols according to component b) in the pickle is at least 1 g/kg, preferably at least 2 g/kg, but is preferably no greater than 10 g/kg, particularly preferably no greater than 6 g/kg.
7. The method according to one or more of the preceding claims, characterized in that the pickle additionally contains ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the alcohol and having fewer than 6 ethylene and/or propylene oxide units.
8. The method according to one or more of the preceding claims, characterized in that at least 10 g/kg, but preferably no more than 70 g/kg, particularly preferably no more than 50 g/kg, of iron ions according to component c) is contained in the pickle.
9. The method according to one or more of the preceding claims, characterized in that the pickle contains, in total, less than 1 g/kg, preferably less than 0.1 g/kg, particularly preferably less than 0.01 g/kg of dissolved phosphates, calculated as PO₄.
10. The method according to one or more of the preceding claims, characterized in that the pickling is preceded by alkaline degreasing of the component, preferably is immediately preceded, with an intermediate rinsing step, the alkaline degreasing taking place at a pH of at least 10.
11. The method according to one or more of the preceding claims, characterized in that the pickling is followed by a wet chemical conversion treatment of the component, preferably immediately, with or without an intermediate rinsing and/or drying step, particularly preferably without an intermediate drying step.
12. The method according to claim 11, characterized in that the wet chemical conversion treatment is carried out by means of acidic aqueous compositions, the pH of which is above 1, but below 5, and is preferably layer-forming phosphating.
13. An acidic aqueous pickle having a pH below 2.0, containing

    i) 40 to 120 g/kg, preferably 60 to 90 g/kg, of sulfuric acid, calculated as SO₄;

    ii) 2 to 20 g/kg, preferably 4 to 10 g/kg, of amino alcohols;

    iii) 0.5 to 5 g/kg, preferably 1 to 3 g/kg, of ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the alcohol and having at least 6 ethylene and/or propylene oxide units;

    iv) 10 to 50 g/kg of iron ions;

    v) less than 50 mg/kg, preferably less than 10 mg/kg, particularly preferably less than 1 mg/kg, of fluoride ions;

    vi) less than 1 g/kg, preferably less than 0.1 g/kg, particularly preferably less than 0.01 g/kg, of dissolved phosphates, calculated as PO₄.
14. The pickle according to claim 13, characterized in that, as component vii), 0.5 to 5 g/kg, preferably 1 to 3 g/kg, of ethoxylates and/or propoxylates of fatty alcohols having 6 to 12 carbon atoms in the alcohol and having fewer than 6 ethylene and/or propylene oxide units is additionally contained.