Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1987-04-24
1989-01-17
Andrews, R. L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204228, C13F 1300
Patent
active
047986581
DESCRIPTION:
BRIEF SUMMARY
Since the beginning of salt spreading on the roads for the prevention of snow and ice slipperiness, motor vehicles have been exposed to a considerable corrosion load. Rusted-through body and frame parts endanger the driving and operating safety of the motor vehicle and considerably shorten its useful life. By means of appropriate finishes or coatings (underbody protection, cavity protection), attempts are made nowadays to counteract the corrosion process.
Besides the mentioned "passive" corrosion-protection measures, however, there is also the possibility of "active" corrosion-protection by means of a direct current counteracting the corrosion.
This method, known by the name "cathodic corrosion-protection," has already been used for a long time for stationary installations (steel tanks, steel piping) and also for motor vehicles.
The invention relates to a device for the cathodic corrosion-protection of metal parts in which a potential difference is generated between the metal parts to be protected and any electrolyte located on the metal part by means of at least one electrode and at least one voltage source, so that at the places to be protected on the metal surface a direct current enters from the electrolyte into the metal surface, which counteracts the migration of positive metal ions from the metal surface. With such a device, one can simply connect the metal parts to be protected from corrosion, especially motor-vehicle parts, to the negative pole of a voltage source, and the positive pole of this voltage source to the cited electrode. The electrode is so mounted that it creates an electrically conductive connection to any electrolyte (moist dust, salt water, slush and the like) that might be loated on the surface of the metal parts to be protected, but a direct electrical connection of the electrodes to the metal parts to be protected is prevented by means of a suitably insulating layer (lacquer). With such an electrode one can thus raise the eletrolyte located on the surface of the metal parts to be protected to a positive potential with respect to the metal parts to be protected. The result of this is that, for example, at damaged places of a lacquer coating, as can occur for example due to mechanical actions, especially due to the impact of spread sand or the like, a direct current flows from the electrolyte into the metal surface, which counteracts the migration of positive metal ions from the metal surface and thus effects the so-called "cathodic corrosion-protection."
In this regard it is known that for the cathodic corrosion-protection to become effective, the potential of the electrolyte in the vicinity of the place to be protected, measured with respect to a Cu/CuSO.sub.4 electrode, must be at least ca. 0.85 volts more positive than the potential of the metal to be protected.
While this requirement is relatively easy to satisfy for metal parts that are surrounded by an electrolyte having a large electrical flow cross-section (this applies especially for buried metal parts), for metal parts that are only covered with a thin electrolytic layer there is the problem that the potential decreases very rapidly with distance from the electrode, owing to the small electrical flow cross-section and the related high electrical resistance of the electrolyte, and already at a small distance from the electrode the value drops below the value required for the cathodic corrosion-protection to become effective. To be sure, an enlargement of the range of action could be achieved by raising the voltage of the electrode, but the feasibility of this measure is restricted for reasons of electrical effect and safety.
It is a goal of the invention to create a device of the aforesaid type with which a good protective action is attainable even at larger distances from the electrode(s) with relatively low values of the applied voltage.
The device of the aforesaid type according to the invention is characterized by the fact that for the protection of the surface of metal parts not buried in the ground, e.g., for the p
REFERENCES:
patent: 3498898 (1970-03-01), Bogart et al.
patent: 3957008 (1976-05-01), McCormick
Herzog Reinhold
Padinger Reinhard
Rainer Hans-Peter
Schober Helmo
Andrews R. L.
D 3 Cathodic Products-Korrosionsschutzprodukte Gesellschaft m.b.
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