EP2292338B1 - Coating method - Google Patents

Description

The invention relates to a coating method in which at the same time paint-free areas are to be ensured.

Coatings on surfaces to which fittings are attached are subject to special requirements. These requirements result from a setting behavior of the coating, which can lead to an unwanted loss of clamping force of the screw. The requirements for these functional surfaces vary, with the basic aim being to keep the functional surfaces free of lacquer. At the same time, however, it must be ensured with metallic components that unpainted functional surfaces remain corrosion-free. This freedom from corrosion must be ensured at least temporarily until a further assembly in which the functional surface is covered.

For example, in the manufacture of a stabilizer of a motor vehicle, it is state of the art to perform a pretreatment of the surface of the component. The component is cleaned and then provided with an iron or Zinkphosphatierung to the corrosion protection and the paint adhesion of the following Increase powder coating. After applying the phosphating, the end portions of the stabilizer, in which the Anschraubflächen lie covered and the stabilizer is powder coated. In the next step, the covers are removed and the ends dipped in a wet paint, which ensures a thinner and more uniform layer thickness on the mounting surface. In this way, a thin lacquer layer, for example, with a layer thickness of only 20 microns in the area of the mounting surface can be realized. Nevertheless, the mounting surface is not free of paint.

If the mounting surface itself is to be free of paint, it is possible to provide only the mounting surfaces of the stabilizer after cleaning with Ronde-shaped stickers. These stickers remain on the component until further assembly. Unfortunately, when using stickers two additional steps are necessary, namely the application and detachment of the stickers. Since the stickers are applied before the phosphating and are removed only immediately before further assembly, they allow a temporary corrosion protection until further assembly. Nevertheless, the effort to precisely apply and remove the sticker is relatively high.

In the WO 2005/018832 A1 discloses a method and apparatus for applying a grounded powder coating to a coating material. The application of the powder coating takes place in several steps, so that the coating material passes through several stations until the end of the process. Before that, a liquid layer can be applied and dried. Thereafter, the powder coating, wherein a rotating mask is used, under which the coating material is passed with the dried layer.

It belongs to the state of the art through the DE 198 14 632 C1 , Body, which are provided in a continuous flow by means of powder coating and then cooled to cover in defined areas touching or non-contact. The non-contact cover has the advantage that the body can be rotated during the coating. A rotation of the body to be coated may be required if a particularly uniform layer thickness distribution is required.

By the DE 101 34 574 A1 includes a method of applying a paint to a prior art sheet in which a surface of a vehicle body is covered without contact or closely adjacent via a mask, wherein the mask and the paint are electrically charged with a current of the same polarity during the application of the paint so that color or similar substances are prevented from advancing the color into the masked areas.

The prior art is also the DE 103 43 946 A1 to name a process for partitional surface treatment and similar components. In this document, it is proposed to provide a plurality of cover caps, which bear tightly against the component. The opposing caps can be coupled to each other, for example, by a component passing through the hole and thus fixed in position.

From the WO 2005/018832 A1 is a coating method is known in which a component to be coated is first provided with a liquid applied coating and then with a powder coating layer. The powder coating layer should be applied in different thicknesses. In this method, the liquid coating is first applied and dried at a distance from a mask, which provides for different thickness powder coating areas. It is a continuous process for coating strip material, so that the masking process is arranged at a greater distance to the application point of the liquid coating, since the coating must be dried before entering the masking.

By the DE 198 14 632 C1 includes a method and apparatus for applying a protective layer to an elongated body, particularly wire or tube, in the art. The pipes are partially covered without contact. After coating and before curing, the cover is removed and returned to the point of application. The cover elements are preferably U-shaped caps, which can be arranged at a certain distance from the surface, which has the advantage that the Body can be rotated during the coating to achieve a particularly uniform coating thickness distribution.

On this basis, the invention is based on the object to show a coating method in which both the lack of paint certain functional surfaces and their temporary corrosion protection is guaranteed until further assembly.

This object is achieved by a coating method having the features of patent claim 1.

The subclaims relate to expedient developments of the invention.

In the coating method of the invention, the component to be coated is first provided with a liquid applied coating and then provided in a known manner with a powder coating layer, i. powder coated. At least one functional surface is provided on the component, which should either be completely powder-coating-free or at least should have a smaller layer thickness of the powder coating. This is achieved in the context of the invention in that a masking is used.

However, the masking is not directly on the functional surface, but is located at a distance from the functional area. It creates a laterally open gap under the masking. The distance between the functional surface and the masking is chosen so that the masking can be applied even before the application of the liquid coating, wherein the liquid applied coating passes between the masking and the functional surface. The masking is applied at a distance of 0.5 mm to 20 mm from the functional surface. As a result, the corrosion-inhibiting properties of the liquid coating are achieved both in the masked and in the unmasked areas.

The subsequent powder coating can be carried out without the mask having to be moved closer to the functional surface, since the powder is not or only insubstantially penetrated by the powder coating process The gap between the mask and the functional surface that is open on the circumference passes.

With the method according to the invention, it is possible to provide a component whose at least one functional surface, in particular a screw-on surface, is provided with a corrosion protection, the component having a smaller layer thickness of the applied coatings in the area of the functional surface than the regions arranged outside the masking. The temporary corrosion protection until further assembly is guaranteed.

The exact distance between the masking and the functional surface depends not only on the diameter of the circular masking, for example, but also on whether it is desired to introduce small amounts of powder coating into the gap between the masking and the functional surface. In principle, powder coating can penetrate into the gap with increasing gap width. On the other hand, if the gap becomes very small, virtually no powder coating penetrates into the gap, so that the functional surface can be referred to as (powder-free). However, the gap width should not be less than a minimum so that the liquid applied coating can still reliably reach the gap and wet the functional surface.

In particular, the distance of the masking to the functional surface is between 1 mm and 4 mm. Decisive is the distance at the edge of the gap, i. at its mouth. The gap width inside the gap may vary.

As a liquid applied coating, a so-called conversion layer can be applied. Conversion layers form as a result of a chemical transformation of the metal surface of the workpiece with an aqueous reaction solution which can be applied by dipping or by spraying. Possible conversion layers can be applied by the process of phosphating, chromating, anodising or burnishing. In particular phosphating is suitable for creating a primer with good corrosion protection. At the same time phosphating serves to improve wear protection. The phosphating can in particular at Steel are used, but also in aluminum and aluminum alloys and magnesium and magnesium alloys. In the present application, the phosphating serves primarily as a primer for the subsequent powder coating.

The powder coating using the masking causes the powder coating to deposit only on areas that are not masked. The masking ensures on the one hand by a mechanical shield that the powder coating does not accumulate in the area of the functional surface. In addition, there is also provided an electrostatic shield based on the principle of a Faraday cage, assuming that electrically conductive masking is used. In the known corona charging of the powder coating, electric field lines are generated between a powder spraying device and the component to be coated. The powder coating particles move primarily along these field lines. If the mask is electrically charged in the same polarity as the component to be coated, e.g. grounded, the masking also attracts powder particles. However, no field lines are formed between the component to be coated and the masking, so that the powder particles are deposited substantially only outside the gap on the functional surfaces.

In a triboelectric charging of the powder coating in the spray no field lines between the spray and the component arise. Nevertheless, the spraying direction and the properties of the coating powder, the choice of the gap width and other influencing variables can ensure that the area of the functional surface remains free of lacquer.

Depending on the guidance of the powder spray gun, to some extent powder coating can also be introduced into the gap and thus purposefully reduced powder coating layers can be formed on the functional surfaces.

A reduced powder coating layer is to be understood as meaning a powder coating layer whose layer thickness is smaller than the layer thickness of the powder coating layer in the unmasked regions.

It is considered to be particularly advantageous if the masks to be arranged at a distance from the functional surfaces are arranged on a suspension by means of which the component is held in particular in a clamping manner during the coating process. Such a suspension can in particular pass through an opening of the component, especially since it is in the paint-free or substantially free of paint to be held functional surfaces to mounting surfaces that usually surround openings in the component. By this type of masking, it is not necessary to connect the mask itself with the component or to solve this in a separate step again from the component, since the removal of the masking takes place automatically when the suspension is no longer needed, i. when the component is detached from the suspension.

It is also possible within the scope of the invention that the masking is used without such a suspension. For example, a mask can be arranged on both sides of the openings, wherein the two masks are connected to each other through the openings. When the mask is applied to the edge of the opening, not only is it ensured that powder can not enter the opening, but also that the bearing surfaces for screw connections, i. the edge immediately surrounding the opening, is designed as a paint-free functional surface. The contact in the edge region of the opening also brings the masking to the same voltage potential as the component.

The advantages of the invention are seen in the fact that fewer process steps are necessary, in particular when integrating the masking in the suspension, which simplifies the entire coating process. At the same time, using the masking disposed away from the functional surface, it is possible to realize a preliminary phosphating or another corrosion protection in the area of the functional surface. The time-consuming masking of the paint-free areas is eliminated. The method is applicable in continuous operation, in particular when the masking is integrated in a component holder.

Figur 1

ein Ende eines Bauteils in Form eines Stabilisators, an welchem eine lackfreie Anschraubfläche ausgebildet werden soll;

Figur 2

einen Schnitt entlang der Linie II-II der Figur 1, wobei der Schnittbereich in mehreren zeitlich aufeinander folgenden Bearbeitungsschritten a) bis e) dargestellt ist und

Figur 3

den Schnittbereich der Figur 2 in einer Detaildarstellung während eines Pulverbeschichtungsvorgangs.

The invention is explained in more detail with reference to an embodiment shown in the drawings. It shows:

FIG. 1

an end of a component in the form of a stabilizer on which a paint-free mounting surface is to be formed;

FIG. 2

a section along the line II-II of FIG. 1 , wherein the cutting area is shown in several consecutive processing steps a) to e) and

FIG. 3

the cutting area of the FIG. 2 in a detail view during a powder coating process.

FIG. 1 shows an end of a component to be coated 1. In this case, the component 1 is a stabilizer. The stabilizer should be fixed via a screw connection. For this purpose, there is an opening 2 in the end of the stabilizer and a circular annular functional surface 3 which surrounds the opening 2 and which is intended to be kept free of lacquer, since it serves as a mounting surface for the screw element. The following in the FIG. 2 Time-sequential manufacturing steps a) to e) illustrate how this goal is achieved.

Figure 2a ) shows the component 1 in cross section. The component 1 is cleaned and prepared for the subsequent production step, the application of a conversion layer. In this embodiment, a phosphating should be carried out. Before the phosphating is applied, two masks 4, 5 are applied. The two masks 4, 5 are identical components which engage each other in the opening 2 opposite. The masks 4, 5 are connected to each other in a manner not shown, for example screwed together. The masks 4, 5 may also be in a manner not shown part of a pincer-like holder, wherein the masks 4, 5, so to speak, form the free ends of the pincer-like holder and are introduced in the ornamentation of the component 1 in the opening 2. The masks 4, 5 are essentially formed by the circular disk-shaped regions which lie outside the opening 2. FIG. 2b ) shows the masked and already phosphated component 1.

The opposing, frusto-conical spacers 6 are used to maintain a certain distance A from each to be protected Functional surface 3, to create a gap 7 between the respective functional surface 3 and the functional surface 3 facing side of the masking 4, 5. The distance A or the width of the gap 7 is selected so that as little powder coating as possible can reach the region of the gap 7, ie the functional surface 3.

The Figure 2c ) shows the coating of the component 1 with the powder coating layer 9. It can be seen that the individual powder particles deposit in the unmasked areas of the component 1 in the desired manner. In addition, there is also a deposit on the outer surfaces of the masking 4, 5. However, there is no adhesion of powder coating in the gap 7 and thus not to an accumulation on the phosphated functional surface. 3

The following Figure 2d ) is intended to illustrate that the application of the powder coating layer 9 is followed by a furnace process in which the powder coating melts and cures.

Finally, after removal of the masks 4, 5 ( Figure 2e )), a component 1 is available in which the functional surfaces 3 are merely phosphated, but not powder-coated. The unmasked areas of the component 1, however, are both phosphated and powder-coated.

Based on FIG. 3 It can be seen in detail that, for example, in the case of corona charging of the powder particles in the spray device 8, the individual powder particles are accelerated by an air flow and moved in the direction of the component 1 to be coated via field lines not shown. The component 1 was provided as before with a conversion layer. It can be seen that as a result of the grounding of the component 1 and the maskings 4, 5, the powder particles are deposited only outside the gap 7 and thus not on the functional surface 3. The penetration of the powder particles into the gap 7 is limited in the corona process by the formation of a Faraday cage in the region of the gap 7.

Reference numerals:

1 -

component

2 -

opening

3 -

functional surface

4 -

masking

5 -

masking

6 -

spacer

7 -

gap

8th -

sprayer

9 -

Powder coating

A -

distance

Claims (8)

1. Coating method, in which a component (1) to be coated is initially provided with a coating applied in liquid form and then with a powder coating layer (9), wherein at least one functional surface (3) which is either free from powder coating or has a powder coating layer having a relatively low layer thickness is provided on the component (1), wherein a mask (4, 5) is arranged at a distance (A) of from 0.5 mm to 20 mm from the functional surface (3) prior to the application of the liquid coating, in such a way that the liquid coating passes between the mask (4, 5) and the functional surface (3) upon application and the functional surface (3) is completely or at least predominantly shielded by the mask (4, 5) during the application of the powder coating layer (9).
2. Coating method according to claim 1, characterised in that the mask (4, 5) is arranged at a distance (A) of from 1 mm to 4 mm from the functional surface (3).
3. Coating method according to either claim 1 or claim 2, characterised in that a conversion layer is applied as the coating applied in liquid form.
4. Coating method according to claim 3, characterised in that the component (1) is phosphated.
5. Coating method according to any of claims 1 to 4, characterised in that, during the coating process, the component (1) is held by means of a support to which the mask (4, 5) is attached.
6. Coating method according to any of claims 1 to 5, characterised in that the mask (4, 5) is arranged at an opening (2) in the component (1), the functional surface (3) surrounding the opening (2).
7. Coating method according to claim 6, characterised in that a mask (4, 5) is arranged on each side of the opening (2), the two masks (4, 5) being interconnected through the opening (2).
8. Coating method according to any of claims 1 to 7, characterised in that the same electric potential is applied to the mask (4, 5) as to the component (1) to be coated.

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