DD209751A1 - PROCESS FOR CORROSION PROTECTION OF ELECTROPHORETICALLY COATED SHEET MOLDING PARTS - Google Patents

Abstract

The invention relates to a method for corrosion protection of electrophoretically coated sheet metal parts, preferably for the protection of difficult to access or particularly heavily stressed sections of motor vehicle bodies. To be achieved is an increased corrosion resistance. It is an object of the invention to achieve an improved corrosion protection at the corrosion critical points by a suitable method. This object is achieved by providing an additional corrosion protection layer on hard-to-reach or heavily stressed sections of motor vehicle bodies. For this purpose, a method is proposed in which of the wet-chemical pretreatment and electrophoretic coating a pulverfoermiger plastic material or powder coating is applied by flame spraying on the corrosion-critical sections.

Description

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Title:

Process for the corrosion protection of electrophoretically coated sheet metal parts

Field of application of the invention:

The invention relates to a method for corrosion protection of electrophoretically coated sheet metal parts, preferably for the protection of difficult to access or particularly stressed sections of motor vehicle bodies.

Characteristic of Prior Art: It is already known to apply anticorrosion coatings to sheet metal formed parts, e.g. B · Motor vehicle bodies, apply. Electrophoretic coatings result from their pores freedom a uniform coating on the surface of sheet metal presswork · The coating quality depends on the type and characteristics of the electrodeposition coating material from · anaphoretic coating materials are as a coat for internal surfaces on the bathroom · * box and not on coverages in the assembly area sufficient · Cataphoretic coatings have the twofold triple corrosion protection value on the surface but also corrosion weak spots on the edge · In the case of anaphoretic electrocoating, inadequate coating in cavities often results from the formation of Faraday cages and additional electrodes

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are required as compensation. «

In order to avoid imperfections on hard to reach sections and sharp edges of the parts to be protected, a relatively high voltage at the electrodes in the coating bath is required · Here, however, is disadvantageous that the remaining portions are covered with an excessively strong protective layer »Furthermore, the well-accessible areas already applied paint film are penetrated locally by the relatively high electrical voltage «

From DE-AS 1 546 919 a method for electrophoretic coating of a hard to reach surface portions having metallic object vorbekannto the readily accessible portions are coated with a lacquer having a high electrical resistance * Thus, the penetration of the paint film at these points during the electrophoretic coating of hard-to-reach surface sections

In motor vehicles, this method is very expensive and leads only to improvements in the protective effect in the hollow sections ·

Furthermore, DE-AS 2 059 587 discloses a process in which the metal object to be protected is completely provided with a Ghrom layer before the electrophoretic coating. The disadvantage here is that the additional protective layer is applied uniformly over the entire surface and not at particularly corrosion-critical points Another drawback of this process is the high consumption of Chrom®

Aim of the invention

The corrosion resistance of electrophoretically teten sheet metal parts, preferably. Of motor vehicle bodies, to be improved ·

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Presentation of the essence of the invention:

The invention has for its object to provide a suitable method with the particularly corrosion-resistant; claimed parts of z. B. motor vehicle bodies that can get during the painting process by mounting other parts only electrocoat primer and is applied to hard to reach areas, such as wheelholes, door lower edges, an additional effective corrosion protection.

This object is achieved in that a powdered plastic material is applied to the corrosion-critical sections of the sheet metal parts by flame spraying and only then a known wet chemical pretreatment and electrophoretic coating, but during the subsequent drying simultaneously the powder coating layer is cured.

The advantage of the method according to the invention is that the particularly corrosion - critical sections of the parts to be protected are provided with a protective layer even before the electrophoretic coating. As a result, due to possible defects in the electrophoretically applied protective layer, corrosion weak spots which lead to premature failure of the component or the Bodywork or excessive maintenance costs were avoided.

Furthermore, production-related corrosion critical sites, eg. B. welds, are advantageously covered ·

A feature of the method according to the invention is that during flame spraying an electrophoretically active powdered plastic material, for example a metal powder coating known per se, is used. The metal pigments advantageously eliminate the insulating effect, preferably in the critical transition region of the powdery plastic material at the locally precoated sections. Thus, during the electrophoretic

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Coating a more uniform layer thickness education on all sections ersielt and increases the corrosion resistance of the coated sheet according to the inventive sheet molding increased »

Ausführungsbeispie1s

The invention will be explained in more detail by means of subsequent embodiments, without limiting the generality

 Example 1s

The body parts which have been washed with an alkaline cleaning agent prior to assembly are joined to the bodyshell. Thereafter, a powder coating is applied to corrosion-critical areas such as wheel-arch mounting surfaces and sharp edges as well as spot welds and welds by hand using a flame-spray gun, which is first gelled at these locations.

The areas to be protected, in particular welding points and welds, can additionally be cleaned mechanically by filing, grinding or blasting to improve the adhesion of the powder coating applied and to eliminate the weld slag. Subsequently, the wet-chemical pretreatment is carried out in a known manner. The body shell is oiled Cleaned, greases, dust and dirt, rinsed with water, phosphated and rinsed again with the addition of passivating rinsing agent. Loosely adhering powder coating particles are also removed. Subsequently, the body is dried by means of warm air.

The electrophoretically coating of the completely dried bodyshell is then carried out. The electrophoretic layer is then baked in the drying oven at a temperature of 180 ° to 190 ° and at the same time the plastic layer is gelled and then cured. The peculiarity of the powdered plastic material results in the flame spray gun precoated

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car body sections have a> 50 / aa thick Piastscnicht, which causes a high corrosion protection «

Example 2:

On the cleaned and welded body according to Example 1 powder coating is applied to the fcorrosionsgefährdeten areas between front fender wheel shell and front pillar by Iflammspritzpistole · The body is then further treated according to Example 1 wet chemical, electrophoretically coated and baked the Blektrotauchlack coating in a drying oven ·

Claims (2)

42547 claim of the invention ¹ that a powdered plastic material is applied to the corrosion-critical sections of the sheet metal parts by flame spraying and only then a known wet chemical pretreatment and electrophoretic coating takes place, but during the subsequent drying at the same time the powder coating layer is cured · 1 »Method for corrosion protection of electrophoretically coated sheet metal parts, preferably for the protection of difficult to access or particularly stressed sections of motor vehicle bodies, characterized by 2 «Procedure according to item 1, '
characterized by that during flame spraying an electrophoretically active powdered plastic material, for example a metal powder coating known per se, is used.