DE1253011B - Device for protection against electrolytic corrosion - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CI .:

C23f

German class: 48 dl - 13/00

Number: 1 253 011

File number: F 34009 VI b / 48 dl

Filing date: May 25, 1961

Opening day: October 26, 1967

It is known to use cathodic or anodic polarization to prevent corrosion in metallic materials Electrolytes such as B. aqueous solutions of salts, acids or alkalis to protect. Type and strength of The polarization to be used and the protective current required for it are based on Art the attack agent (chemical composition, temperature, etc.) as well as that of the material (chemical Composition, surface condition, etc.). The polarization is through electrically conductive connection of the object to be protected brought about with an electrode, either by element formation itself supplies power or is connected to an external power source, while the second pole the power source is applied to the object to be protected.

When protecting the inside of containers, pipelines, etc. These electrodes are usually in the form of Bars or bars applied and arranged so that the surfaces to be protected are as uniform as possible Preserve current density, as this increases the effectiveness and economy of the corrosion protection depends. This even distribution of the current flow is, however, already relatively simple Forms such as B. rectangular containers, quite problematic and is attached by the inside Internals, such. B. pipe coils, even more difficult. She is especially difficult in narrow crevices like her z. B. present in pump housings, especially since the z. B. rod-shaped electrodes by appropriate Bores in the housing must be introduced, which is not inconsiderable sealing and Causes tsolation difficulties.

It has now been found that the inner surfaces of stirred tanks, centrifugal or piston pumps, Screw presses and the like for the purpose of corrosion protection are expediently cathodic or can polarize anodically that the rotor (stirrer, impeller or piston, screw, etc.) used or formed as a counter electrode to the housing. Because the runner of the shape of the housing largely is adapted and, moreover, all surface parts of the housing due to its movements during operation brushed almost evenly, a much more even current distribution is achieved than by the introduction of point or rod-shaped electrodes would be possible.

Experiments have already been described in which, with regard to the external cathodic corrosion protection of ships, the influence of the flow of seawater on the current strength at rotating electrodes, such as disks made of iron, zinc or bronze, is a device for protection against electrolytic
corrosion

Applicant:

Paint factories Bayer Aktiengesellschaft,

Leverkusen

Named as inventor:

Dr. Helmut Weissbach,

Maleck via Emmendingen;

Dipl.-Ing. Siegfried Neidhardt,

Dipl.-Ing. Ferdinand Mersch, Leverkusen

has been checked. In these experiments, the movement of the electrodes was only used to mimic the The speed of the water at the hull of the ship and not to even out the current flow on all surface parts inside the apparatus, from that of the housing wall through the electrolyte separate runner to the housing wall going on.

The concept of the invention can be implemented in various ways. In cases less Corrosion, it is possible under certain circumstances to protect the housing cathodically by the fact that the Runner completely or partially made of a less noble metallic material than the housing. Included it must be ensured that the runner z. B. via shaft and bearing in conductive connection with the Housing stands so that the electrolytic protective current can flow from it to the rotor. While that If the housing is not corroded, the rotor will gradually wear out, which as a result must be replaced a certain time before it loses its functionality. But since it is is a relatively small and simply shaped body, this temporary replacement is the The rotor is far less expensive than the replacement of the entire pump that would otherwise be required. By the way it is in principle also possible, only replaceable parts of the rotor from the one serving as the »sacrificial anode« Attach material and the rest of the runner made of the same material as the housing or z. B. to manufacture from plastic.

In most cases it will be more advantageous to carry out the polarization by means of an external current. For this it is necessary to move the rotor and housing against

709 679/525

1 253 Oil

to insulate each other electrically as well as possible to avoid unnecessary power consumption and undesirable power effects to avoid. The housing is expediently earthed, the rotor shaft, however, at all contact points (Stuffing box, bearing, coupling) insulated and using non-conductive materials connected to the non-earthed pole of the direct current source (battery or rectifier). If stronger If currents are required, it is advisable to also use a power line from the other pole to the housing of the Relocate pump etc.

The materials of the two parts functioning as anode and cathode (housing and rotor) are now to choose the attack conditions in such a way that both parts are in the polarized state be protected as completely as possible from corrosion. For many metals and alloys it is known under which conditions they are cathodically or anodically protected (passivated). In individual cases it is however, it is advisable to obtain precise documents by determining the electrochemical behavior of the too processing solution compared to the metallic materials in question (current-potential measurements) to win.

In many cases one will assume that the Housing as the much larger and more complicated part made of a cheap, solid and good part processable material, e.g. B. carbon steel or cast iron is made. These materials can be in most (non-oxidizing) electrolytes best by cathodic polarization against corrosion protection. Accordingly, a material must be used for the rotor that has anodic polarization becomes passive or remains indifferent. At the same time it must be ensured that the runner as the anode for cathodic protection of the housing required current passes. In fact, in many cases, metals and Alloys with anodic polarization non-conductive cover layers of oxides or the like. So that the required Current flow can not be achieved or only under increased voltage. In such cases it is it is expedient to cover the surface of the runner in whole or in part with a material that does not contain any forms anodic cover layers. Suitable are e.g. B. Precious metals such as gold or platinum, of which below Under certain circumstances, even wafer-thin coatings are sufficient, although in general because of wear and tear thicker films are preferable, e.g. B. be welded. Also z. B. graphite and magnetite may be suitable. ] In many cases, the so-called rust and acid-resistant chromium or Chromium-nickel steels can be used, which are anodic in neutral and in acidic solutions Let polarization passivate within wide limits and only when the so-called breakdown potential is exceeded to be corroded to an increasing extent.

example 1

For pumping softened water (hardness publications considered:

<l ° d. H., Chloride 140 mg / 1 Cl, sulfate 48 mg / 1 60 "Metall", 14th year 1960, H. 8, p. 788 and 789; SO ₃ , pH 5.6) a centrifugal pump is used, whose "Chemisches Zentralblatt", 1939/11, p. 4348; 1959,

Housing is made of gray cast iron, while the one on p. 9388.

The carbon steel shaft-mounted impeller is made from a cast zinc alloy. The case with The shaft bearing attached to it is in a conductive connection to the pump wheel via this and the shaft. The durability of the housing is significantly increased compared to a pump with a gray cast iron wheel.

Example 2

Acid wastewater containing varying amounts of organic and inorganic substances (salts and non-oxidizing acids) and their pH value is 4 up to 5 are conveyed by means of a pump made of pearlitic gray cast iron, the rotor of which is made of 18/8 CrNi steel is attached to a shaft made of 17% Cr steel. The stuffing box is sealed with grease-soaked asbestos cords that have no noticeable conductivity; the pump shaft is in a sliding bearing, which is also insulating and provided with a plastic lining stored and connected to the motor shaft by a rubber coupling. The pump housing that grounded by the foundation bolts is to the negative pole of a rectifier transformer connected, while a current collector attached to the pump shaft is connected to the positive pole is. A terminal voltage of around 1.5 V is set. The power consumption is at a diameter of the impeller of 450 mm on average about 3 A, what for the corrosion protection of all pump parts is sufficient.

Claims (4)

Patent claims: 1.Device for the protection of apparatus consisting of a metallic housing, such as a stirred tank, Centrifugal or piston pump, spindle or screw press and the like in the one through the Electrolytes separated from the housing wall body, such as. B. one adapted to the shape of the housing Runner, rotatable or arranged to be movable to and fro, against electrolytic corrosion by cathodic or anodic polarization, characterized in that the moving body itself serves as a counter electrode to the housing. 2. Apparatus according to claim 1, characterized in that the moving body is entirely or partly consists of a less noble metallic material than the housing. 3. Apparatus according to claim 1, characterized in that the moving body consists of a anodically passivatable material. 4. Apparatus according to claim 3, characterized in that the moving body is entirely or is partially coated with an electrically conductive material that is anodic polarized does not form any insulating cover layers, such as B. precious metal, graphite, magnetite. 709 679/525 10. 67 © Bundesdruckerei Berlin