EP1443129A1 - Method for treating a metallic workpiece - Google Patents

Abstract

Method for processing a metallic workpiece (2) made from a metallic material other than brass comprises burnishing a surface section of the workpiece to form a processed surface section (3) using electric polishing and/or chemical brightening, rinsing with a fluid and drying, and applying a lacquer (4) to form a partially transparent lacquer layer (5) in a partial region of a surface section. An independent claim is also included for a metallic component formed by the above method.

Description

The invention is in the field of processing metallic workpieces.

Components of any type made of metal, especially steel, are used in a wide variety of applications used. As far as the metal used is not due to suitable alloy components As a rule, different corrosion protection measures are used here intended. This includes coating brass surfaces with a clear coat. A disadvantage of known methods of corrosion protection is that the metallic Shine that the component can have due to mechanical processing, corrosion protection layers such as paints, electroplated coatings, greases or the like, or tarnishing from Welding does not come to fruition.

In view of the situation that chromates are increasingly taking a back seat in surface technology for environmental reasons and that chrome coatings are expensive and complex to manufacture, the electropolishing of metals, in particular steel, is a suitable alternative to the gloss formation in metallic components. Electropolishing is an anodic processing of metallic workpieces / components. This reduces unevenness in metal surfaces. Other terms for electropolishing are electrolytic polishing, anodic polishing or electrolytic polishing. Here, the workpieces are anodically connected to a direct current source and removed in an electrolyte at current densities of approx. 1 to 300 A / dm ² . When processing, metal ions dissolve in the electrolyte bath. Mixtures of mineral acids with various additives of surface-active substances (wetting agents, brightening agents, complexing agents or the like) or salt solutions are usually used as electrolytes. In addition to the use of direct current for electropolishing, applications are known in which pulsed direct current is used instead of direct current. Special applications include electropolishing of the smallest surface areas or electropolishing in an electrical field, in which a mechanical mounting of the component and an electrical contact are decoupled.

Influencing parameters in electropolishing include the electrolyte composition, the current density, the electrolyte temperature, the conductivity of the electrolyte. For every metallic Material can be an optimal parameter constellation with regard to using the Electropolishing surface properties to be created, for example with regard to the gloss, a micro-roughness or a composition of the processed Surface.

Unless corrosion-resistant stainless steels are used, electropolishing of steel is used in known machining processes as a pretreatment for the application of galvanic coatings. For the electropolishing of low-alloy steels, for example, aqueous electrolyte solutions are known which consist of 40% by weight sulfuric acid and 50% by weight phosphoric acid. An electrolyte temperature of 50-90 ° C, a voltage of 5-15 V and a current density of 50-80 A / dm ² are given as processing parameters. Another known aqueous electrolyte consists, for example, of 63% by weight phosphoric acid and 15% by weight sulfuric acid. The working temperature is 50-60 ° C, and the removal takes place at current densities of 50-100 A / dm ² . A wide variety of mixtures of phosphoric acid and sulfuric acid are used for the electropolishing of high-alloy, especially ferritic, steels, each of which requires its own optimal machining conditions.

For machining metallic workpieces can be used in conjunction with deburring Processes for chemical polishing or chemical glossing can be used. The difference for electropolishing there is no need for electrical contact. It is a currentless machining process in which the workpiece is immersed in a bath. As with electropolishing, chemical shine removes the surface.

The object of the invention is to provide an improved method for processing a metallic Specify workpiece made of a metallic material other than brass, which the formation of a shiny metallic surface section on the workpiece without Adversely affecting the corrosion resistance in the area of the surface section allows.

This object is achieved by a method according to the independent claim 1 and a metallic component according to independent claim 14 solved.

The invention encompasses the idea of at least parts of a surface of a metallic Workpiece or component with the help of electropolishing and / or chemical polishing to be machined to subsequently rinse a machined surface section to apply an at least partially transparent lacquer layer to the surface section. The term lacquer layer in the meaning used here includes a powder coating, water-based and solvent-based lacquers, glazes or the like. On this is done on the one hand with the help of electropolishing and / or chemical polishing a shiny surface section is formed that has a desired surface roughness features. To protect the surface thus formed, to create the gloss effect and if necessary to obtain improved corrosion resistance, then the paint layer applied, which acts both as corrosion protection and as scratch protection. The new one Combination of electropolishing and / or chemical shine with the application of one Lacquer layer to protect the electropolished and / or chemically polished surface gives the machined workpieces an unachievable with known processing methods, improved goodness. In particular, a metallic sheen is achieved and is retained.

To prepare the surface section, which is by means of electropolishing and / or chemical To be edited glossy, can with an appropriate design Invention can be provided that in the area of the surface portion of the metallic Pretreatment by means of electrolytic and / or chemical pickling is carried out.

A further development of the invention advantageously provides that during the pretreatment the electrolytic pickling and the gloss processing by means of electroplating the same Electrolyte is used. This can be used on small amounts of chemicals be limited. In small systems, it can be carried out in just one electrolyte bath, which lowers investment costs.

To achieve a uniform surface removal in the area of the machined Surface section and the least possible roughening of the surface section is provided in a preferred embodiment of the invention that in the pretreatment a time-varying external current is used by means of electrolytic pickling becomes.

In an advantageous embodiment of the invention it can be provided that with the Pretreatment and / or gloss processing in the area of the machined surface section a predetermined micro-roughness and / or a predetermined surface structure is produced. The formation of the predetermined micro-roughness is carried out by an appropriate one Choice of parameters for pretreatment and / or gloss processing in the area of machined surface section reached. By maintaining a roughness tolerance it is possible to develop suitable conditions for the paint.

To improve the adhesion of the paint to the machined surface section provided in a preferred embodiment of the invention that on the at least an adhesion promoter is applied to a partial area of the processed surface section, before the lacquer layer is applied.

With the help of the application of a clear varnish or completely transparent coating The visibility of the glossy surface in the area of the processed is reduced Surface section guaranteed even after applying the paint.

In a preferred development of the invention it can be provided that the paint Color pigments are added to an extent so that the lacquer layer is still transparent is. The application of such a paint enables the respective purpose adapted color scheme. For example, colors such as can be achieved during color anodizing. A "metallic paint effect" can be achieved here without the paint containing metal flakes, because the shiny metal surface is transparent is covered.

A further development of the invention expediently provides that a powder coating is used as the coating agent is applied. This type of paint is characterized by environmental friendliness and freedom from solvents out.

The properties of the coated surface, especially with regard to corrosion protection and the scratch protection, can with the help of a further development of the invention be improved that the lacquer layer is baked and / or dried.

In an expedient embodiment of the invention it can be provided that a surface area of the metallic workpiece is electrostructured. This is done in areas a resist layer on the surface of the metallic workpiece that is not to be removed applied and removed after the respective process step for removal. As a result, surface sections with a raised are on the workpiece Structure created surrounded by electropolished and / or chemically polished areas are.

The process for machining a metallic workpiece is hereby developed for the subsequent use of the metallic workpiece associated advantages in particular when the metallic workpiece is made of steel. Steel, especially carbon steel is suitable for electropolishing, but alone is not sufficiently corrosion-resistant, which is why he must be protected.

Figur 1

eine schematische Darstellung eines Schichtaufbaus zur Erläuterung eines Verfahrens zum Bearbeiten eines metallischen Werkstücks;

Figur 2

eine schematische Darstellung von Verfahrensschritten des Verfahrens zum Bearbeiten des metallischen Werkstücks;

Figur 3

eine schematische Darstellung von weiteren Verfahrensschritten des Verfahrens zum Bearbeiten des metallischen Werkstücks, die sich an die Verfahrensschritte nach Figur 2 anschließen;

Figur 4

eine schematische Darstellung von weiteren Verfahrensschritten des Verfahrens zum Bearbeiten des metallischen Werkstücks, die sich an die Verfahrensschritte nach Figur 3 anschließen; und

Figur 5

eine schematische Darstellung von Verfahrensschritten eines alternativen (verkürzten) Verfahrens zum Bearbeiten eines metallischen Werkstücks.

The invention is explained in more detail below using exemplary embodiments with reference to a drawing. Here show:

Figure 1

is a schematic representation of a layer structure for explaining a method for processing a metallic workpiece;

Figure 2

is a schematic representation of process steps of the method for processing the metallic workpiece;

Figure 3

a schematic representation of further method steps of the method for machining the metallic workpiece, which follow the method steps of Figure 2;

Figure 4

a schematic representation of further process steps of the method for machining the metallic workpiece, which follow the process steps of Figure 3; and

Figure 5

is a schematic representation of process steps of an alternative (shortened) method for processing a metallic workpiece.

Figure 1 shows a schematic representation of a layer structure 1 in a metallic Component or workpiece 2, which is made of a metallic material other than brass, steel is preferred. On the metallic workpiece 2, which is in the area of a surface 3 has been electropolished and / or chemically polished, is a paint 4 to form a Lacquer layer 5 applied, which can be a powder coating. In the illustrated An embodiment is an adhesion promoter layer between the surface 3 and the lacquer layer 5 6 applied from an adhesion promoter 7. The Hanvermitterschichticht 6 can omitted (not shown) if there is sufficient adhesion of the lacquer layer 5 to the surface 3 is also given without an adhesion promoter layer 6.

When using chemical shine, compared to electropolishing, the additional advantage that the dipped workpiece 2 with little effort on all sides and also in areas that are difficult to access are smoothed / polished. The use of an external power source eliminated.

Color pigments or ink (finest color pigment) 8 can be in any concentration Paint 4 are added. When using a transparent paint with only small proportions of color pigments / ink 8 is a transparent or transparent but colored Coating possible, through which the view of the metallic electrochemically worn, electropolished or chemically polished surface 3 remains possible.

Figure 2 shows the sequence of a pretreatment of the workpiece 2 schematically as a flow chart. Surface treatment of the workpiece or component 2 begins in the illustrated Embodiment with washing and degreasing 100. As a result, in the area of Surface 3 applied for corrosion protection greases or oils as well as adhering dust and Dirt removed. This must be done completely, otherwise the electrochemical / chemical Removal of the surface 3 may be incomplete. Various are available for washing / degreasing 100 known methods are available (see, for example, Rituper, R .: pickling of Metallen, Eugen G. Leuze Verlag, Bad Saulgau, 1993). This makes it possible even for existing ones Plants for processing metallic workpieces in the process described here to integrate. In laboratory tests, it has proven to be advantageous to have workpiece 2 rinse with acetone and deionized water. When drying 110 should Care should be taken to ensure that no dry spots occur on the surface 3. For this is sufficient rinsing is important in the previous step 100. Drying 110 can for example in an oven or by blowing with compressed air that is free of grease and water be carried out. Run the solutions used for washing and degreasing 100 not completely off, rinsing 105 must take place before drying 110. Usually this can be dispensed with if solutions are used that run without residues.

This is followed by chemical pickling 120. Suitable chemical process Pickling is known as such. The electrochemical removal takes place under local element formation (without external power source) instead. The aim of the pickling treatment is to remove Tinder, rust, metal oxides, metal hydroxides and tarnishing colors, which are used for example in the Welding can occur. Since electropolishing has a particularly high gloss, if the workpiece 2 has the lowest possible surface roughness, a as smooth a surface as possible after chemical pickling. For example, has a 1 to 15 minute chemical pickling of steel (RST 37-2) in baths of 5 to 40 wt. % Sulfuric acid and 5 to 40% by weight hydrochloric acid at bath temperatures between 15 and 50 ° C proven. The stain is then rinsed 130 off the workpiece or component 2 in order to Prevent the pickling electrolyte from spreading to other baths. After that, the workpiece 2 are dried 140 if necessary. It can be provided that with The process steps washing and using a so-called pickling degreaser Degreasing 100 and chemical pickling 120 can be combined into one process step. Drying 110 can be omitted here. Acid degreaser is an acidic or alkaline one Understand solution that may contain surfactants and both for washing and degreasing as well as for removing tarnish, rust, scale as well as oxide layers and hydroxide layers suitable is.

According to FIG. 2, the pretreatment also includes electrolytic pickling 150. Here, the workpiece 2 is removed anodically in an electrolyte, ie the workpiece 2 is connected to a positive pole of a direct current source (external current source - not shown). Effective-pair cathodes are used. For example, stainless steel can be used for steel. Electrolytic pickling 150 in the later electropolishing electrolyte has proven to be particularly advantageous. If this is done, subsequent rinsing 160 and drying 170 can be dispensed with, which makes sense from an environmental and cost point of view. In this case, aqueous electrolytes composed of 15-70% by weight sulfuric acid and 30-80% by weight phosphoric acid with additions of up to 30% alcohols and further additions of surface-active substances such as complexing agents, network formers or the like can then be used for steel. In electrolytic pickling 150, the same temperature as in subsequent electropolishing is expediently set as the electrolyte temperature (40-90 ° C.). The constant current density is chosen so that there is a uniform removal. For steel, for example, it is between 1-5 A / dm ² . The processing time is preferably between 1 and 30 minutes, depending on the electrolyte, material of the workpiece 2, surface quality and thickness of the scaling, the rust, the oxide and hydroxide layers or the tarnishing colors.

In the case of electrolytic pickling 150, provision can be made not to work with a constant direct current, but rather to cyclically increase and decrease the current density continuously from 0 to a value, for example 5 A / dm ² , several times. Such triangular pulses advantageously last between 1 and 5 minutes and can be repeated up to 10 times. With the help of this electrolytic pickling treatment 150, it is possible to achieve a uniform surface removal and to form as little roughening of the surface 3 as possible, so that the highest possible gloss can be achieved with the aid of the subsequent electropolishing.

Chemical and electrolytic pickling 120, 150 can be carried out as part of the pretreatment can be used together (cf. FIG. 2) or alternatively also individually if with the help the desired surface quality using only one of the two pickling processes with regard to the removal of rust, tarnish, oxide and hydroxide layers and / or the activation of the surface is achieved. For reasons of effectiveness, too be provided as long as the state of the workpiece 2 to be machined allows Processing the workpiece 2 for chemical and / or electrolytic pickling 120, 150 and the subsequent rinsing and drying 130, 140 and 160, 170 to be omitted.

The pretreatment (see FIG. 2) is followed by electropolishing and / or chemical gloss 180, which is shown schematically in FIG. 3. In electropolishing, if it has not already occurred in the same bath during electrolytic pickling 150, the cathodes (not shown) are arranged around the workpiece 2 in such a way that, taking into account the scatterability of the polishing electrolyte used, a uniform removal over the entire surface or at least a partial section the surface of the workpiece 2 takes place, which leads to the formation of gloss. This requires a smoothing of the roughness of <0.4 µm. The process can be used to create high-gloss and reflective surfaces. Aqueous electrolytes composed of 15-70% by weight sulfuric acid and 30-80% by weight phosphoric acid with additions of up to 50% alcohols and further additions of surface-active substances are preferably used for steel. It is expedient to set the electrolyte temperature at which the best possible gloss properties are achieved (40-90 ° C). The constant current density is chosen so that there is a uniform removal. For example, it is between 15 and 150 A / dm ² . The processing time is between 1 and 60 minutes, depending on the workpiece. It is chosen so that hydrodynamic structure formation, as is known from electropolishing, occurs as far as possible. This is followed by rinsing 190, for example in a cascade rinsing, and drying 200 in the oven or by means of compressed air. This is essential, provided that the rinsing 190 has been carried out, and must be carried out in such a way that no residues of water remain on the surface 3, which reduce the adhesion of a paint to be applied later.

In particular, the one that follows electropolishing and / or chemical polishing 180 Flush 190 can consist of several steps. For example, cascade rinsing may be useful use that save water. In addition to the use of spray rinses with Working with water, depending on the material, it may be necessary to use the last aqueous rinse Deionized water in order to have as few salts as possible on the surface. Is too it is conceivable to rinse the surface with air or other gaseous fluids to blow dry. As a result, the carry-over of solutions is reduced in particular. As a first rinsing step, pickling can be advantageous. This is a small one concentrated lye or acid as the first rinsing step, e.g. B. immersion, used to the Do not dilute electrolytes in such a way that due to the pH value and / or the concentrations its components deposit / deposit components of the electrolyte on the surface. It may be necessary for reasons of corrosion protection perform one of the last rinses with a solution that covers the surface neutralized and possibly inhibited without significantly reducing the gloss. In the case of materials that are not themselves corrosion-resistant, the last rinse should be with VE Water (fully demineralized).

In addition to electropolishing with direct current, processes for electropolishing stainless steel, Brass and aluminum applications are known where pulsed by use Currents when electropolishing higher gloss levels and less roughness can be achieved.

The chemical shine, which is also called etching polishing or chemical polishing is an electrochemical surface removal without an external power source. It is metal etching related. In chemical shining, the removal takes place through the formation of local elements. In contrast to metal etching, chemical shining and electropolishing are also used the aim is to create a surface that is as decorative and shiny as possible. The used Electrolytes essentially consist of mineral acids and salts which inhibitors, Brighteners and complexing agents as well as solvents are added. The composition is chosen so that the removal under transport is limited expires. This enables the leveling of micro bumps in particular, and a gloss on the workpiece surfaces. Polishing processes are known for most metals. Even if usually less gloss can be achieved than with electropolishing, the method can be used particularly well if it is small or mass parts acts that cannot be contacted or can only be contacted poorly if profiled Workpieces or workpieces with hollow bodies and undercuts can be polished that can only be electropolished when building complex cathodes. The before and downstream process steps are identical.

An optional process step follows electropolishing / chemical shine 180 to apply an adhesion promoter 210 (see FIG. 4), which the adhesive strength of the applied paint increased. Then the residue-free is dried Workpiece 2 painted 220. For example, when painting 220, a clear coat is applied, the the gloss impression of the previously polished surface 3 of the workpiece 2 as possible not at all or reduced only to a small extent. It can wet paint with solvents or water-based as well as powder coatings (polyester), for example electrostatic be applied, used. Depending on the paint, are optional according to Figure 4 further process steps for baking and drying 230 and for cooling 240 of workpiece 2 required.

The aim of paint 220, including any adhesion promoter to be applied, is that Form a corrosion and scratch protection in the area of the glossy surface 3 of the metallic workpiece 2. The formation of corrosion protection is particularly for Advantageous steels that are not corrosion-resistant. The scratch protection is also for stainless steels essential that electropolished to form glossy surfaces and are not inherently hard enough to scratch the shiny surface Surface prevented.

FIG. 5 schematically shows a process sequence according to a preferred embodiment, in the method compared to that described with reference to FIGS. 2 to 4 individual process steps are dispensed with. In Figure 5 are for the same process steps the reference numerals used in Figures 2 to 4 used. The shortened Process flow is possible if only slightly scaled, rusted steels / metals with only little tarnishing color to be processed by welding. The process sequence according to FIG. 5 begins with washing and degreasing 100, which is due to the risk of carry-over drying 110 of water, for example by means of compressed air. Subsequently This is followed by electrolytic pickling 150, which is followed by the actual electropolishing and / or chemical shine 180 follows. The high-gloss surface 3 thus obtained is by means of Rinsing and drying 190, 200 cleaned of the adhering electrolyte and for the following Paint 220 prepared. In addition, the application of the adhesion promoter 210 can be provided his. The lacquer is baked and dried 230, if this is the one used Paint is necessary. If the paint is baked 230, which is the case, for example a powder coating is provided, a cooling phase 240 follows.

An advantageous variant of the method provides that the metal surface is not electropolished but is electro-structured. This does not remove areas of the surface with a resist, for example a photoresist or a galvano-resistant one Screen printing varnish, coated. The uncovered areas of the metal surface will be then electropolished or chemically polished. This creates raised, not shiny Areas surrounded by electropolished / chemically polished areas. This process variant can be used to create patterns or decorative effects.

The application of resist can take place after drying 110 and before chemical pickling 120 (see FIG. 2). Then the starting surface of the cleaned is cleaned on the workpiece Material visible. If the resist is applied, for example, between the Drying 140 and electrolytic pickling 150 or drying 170 and electropolishing or chemical shine 180 or pickling for the purpose of application of the resist is interrupted, the raised areas face those carried out by the electrochemical removal processes on surfaces. The resist will dissolved and stripped by means of suitable additives during rinsing 190, i.e. away.

In the presence of a high quality of the starting surface, such as in Dirt, adhesion, rust, scale and oxide free surfaces can be given to the elaborate pretreatment steps 100-170 are completely or partially dispensed with. This results in the method in a simplified embodiment using electropolishing or chemical gloss 180 begins.

Those disclosed in the foregoing description, claims and drawings Features of the invention can be used both individually and in any combination Realization of the invention in its various embodiments of importance his.

Claims (20)

1. A method for machining a metallic workpiece (2) from a metallic material other than brass, in which: in a surface section of the metallic workpiece (2), a gloss treatment is carried out to form a machined surface section (3) by means of electropolishing and / or chemical glossing (180); the machined surface section (3) is rinsed (190) with at least one rinsing fluid and then dried (200); a coating agent (4) is applied (220) to the processed surface section (3) to form an at least partially transparent lacquer layer (5) at least in a partial area of the processed surface section (3). 2. The method according to claim 1, characterized in that in the surface section of the metallic workpiece (2) before the gloss treatment, a pretreatment is carried out by means of electrolytic and / or chemical pickling (120, 150). 3. The method according to claim 2, characterized in that the same electrolyte is used in the pretreatment by means of electrolytic pickling (120) and the gloss treatment by means of electropolishing (180). 4. The method according to claim 2 or 3, characterized in that a time-varying external current is used in the pretreatment by means of the electrolytic pickling (120). 5. The method according to any one of the preceding claims, characterized in that a predetermined micro-roughness and / or a predetermined surface structure is generated with the help of the pretreatment and / or the gloss treatment in the region of the processed surface section (3). 6. The method according to any one of the preceding claims, characterized in that an adhesion promoter (7) is applied (210) on the at least a portion of the processed surface section (3) before the lacquer layer (5) is applied. 7. The method according to any one of the preceding claims, characterized in that a clear lacquer is applied as the coating agent (4). 8. The method according to any one of the preceding claims, characterized in that the paint (4) color pigments (8) are added. 9. The method according to any one of the preceding claims, characterized in that a powder coating is applied as the coating agent (4). 10. The method according to any one of the preceding claims, characterized in that the lacquer layer (5) is baked. 11. The method according to any one of the preceding claims, characterized in that the lacquer layer (5) is dried. 12. The method according to any one of the preceding claims, characterized in that a surface area of the metallic workpiece (2) is electrostructured. 13. Use of a method according to one of the preceding claims for machining a metallic workpiece (2) made of steel. 14. Metallic component (2) made of a metallic material different from brass with an electropolished and / or chemically polished surface section (3) which is covered with an at least partially transparent lacquer layer (5) made of a lacquer (4). 15. Metallic component (2) according to claim 14, characterized in that a predetermined micro-roughness and / or a predetermined surface structure is formed in the region of the electropolished and / or chemically polished surface section (3). 16. Metallic component (2) according to claim 14 or 15, characterized in that an adhesion promoter (7) is applied to the electropolished and / or chemically polished surface section (3). 17. Metallic component (2) according to one of claims 14 to 16, characterized in that a clear lacquer is applied as the coating agent (4). 19. Metallic component (2) according to one of claims 14 to 17, characterized in that the paint (4) color pigments (8) are added. 20. Metallic component (2) according to one of claims 14 to 18, characterized in that a powder coating is applied as the coating agent (4). 21. Metallic component (2) according to one of claims 14 to 19, characterized in that the lacquer layer (5) is baked.

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