DE379365C

DE379365C - Process to protect iron and steel objects against rust

Info

Publication number: DE379365C
Application number: DEU7751D
Authority: DE
Original assignee: UDYLITE PROCESS Co
Current assignee: UDYLITE PROCESS Co
Priority date: 1921-04-09
Filing date: 1922-03-19
Publication date: 1923-08-23
Also published as: GB178422A; FR548956A; US1504298A

Description

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Vorliegende Erfindung bezieht sich auf ein Verfahren, um Eisen- oder Stahlgegenstände durch Überziehen mil '"ner elektrolytisch erzeugten Kadmiumsch 'vt gegen Rost zu schützen.The present invention relates to a method of making iron or steel objects by coating with electrolytically generated cadmium protection against rust protection.

Von den bisher beka nten elektrolytischen Verfahren unterscheide, sich das Verfahren gemäß der vorliegenden Erfindung dadurch, daß anstatt einer Kadmiumanode eine Anode aus Graphit, Kohle oder sonstige unlösliche, nicht polarisierende Anode zu verwenden. Die !„dmiumanode zeigt nämlich beim Gebrauch die Neigung, sich mit einer dünnen Schicht von außerordentlich hohem Widerstand zu überziehen, und bei einer bestimmten Spannung sinkt die Stromdichte sehr rasch, was eine entsprechende \^rerminderung der Menge des Kadmiumniederschlages auf den behandelten Gegenstand zur Folge hat, so daß die erforderliche Behandlungsdauer zur Erzielung eines Überztiges von gewünschter Dicke beträchtlich steigt. Außerdem ist die Beschaffenheit eines solchen Kadmiumniederschlages, wenn er bei niedrigerer Spannung und demzufolge auch verminderter Stromdichte erfolgt, nicht εο befriedigend wie in dem Falle, daß eine Graphitanode benutzt wird. Wenn man eine Kadmiumanode anwendet, dann ist es schwierig, eiiu* gewünschte Stromdichte zu erzielen und aufrechtzuerhalten, so daß das Verfahren au1 wirtschaftlicher Basis mit einer Kadmiumanode kaum durchgeführt werden kann.From the previously known electrolytic processes, the process according to the present invention differs in that, instead of a cadmium anode, an anode made of graphite, carbon or other insoluble, non-polarizing anode is used. The "dmiumanode shows namely in use the tendency to coat them with a thin layer of extremely high resistance, and at a certain voltage, the current density decreases very rapidly, causing a corresponding \ ^r ermin alteration of the amount of cadmium precipitate to the subject matter result has, so that the treatment time required to obtain a finish of the desired thickness increases considerably. In addition, the nature of such a cadmium precipitate, if it takes place at a lower voltage and consequently also at a reduced current density, is not as satisfactory as in the case where a graphite anode is used. If a cadmium anode is used, it is difficult to obtain and maintain a desired current density, so that the process can hardly be carried out economically with a cadmium anode.

Wenn man dagegen unlösliche, nicht polarisierbare Anoden anwendet, dann ist es möglich, die Stromdichte konstant zu erhalten und zwar auch, wie es erwünscht ist, auf einei ansehnlichen Höhe. Die Stromdichte kanr innerhalb weiter Grenzen schwanken unc hängt augenscheinlich von der Form und der elektrischen Eigenschaften der elektrolytiscr zu plattierenden Gegenstände ab. Beim Plattieren eines sehr dünnen Metallbleches, wc die Schwierigkeit besteht, einen guten elektrischen Kontakt zu erzielen, wird die Stromdichte etwas geringer sein als in solchen Fällen, wo ein guter Kontakt ohne Schwierigkeit hergestellt werden kann, wie z. B. wenn es sich um das Plattieren großer dicker Gußstücke handelt.If, on the other hand, insoluble, non-polarizable anodes are used, then it is possible to keep the current density constant and also, as is desired, to one respectable height. The current density can fluctuate within wide limits and apparently depends on the shape and electrical properties of the electrolytic objects to be plated. When plating a very thin sheet of metal, wc the difficulty is to achieve good electrical contact, the Current density can be slightly lower than in those cases where a good contact without difficulty can be made such. B. when plating large thick castings acts.

Die Erfahrung hat gezeigt, daß bei Anwendung einer Xatriumzyanidlösung, welche ungefähr ro,5 Prozent metallisches Kadmium enthält. Stromdichten von etwa 3 bis 35 Ampere pro qdm mit A'Orteil Anwendung finden, können. Die mittlere Stromdichte, mit welcher die Erfinderin arbeitet, beträgt gegen 20 Ampere pro qdm.Experience has shown that when using a sodium cyanide solution, approximately ro, contains 5 percent metallic cadmium. Current densities from about 3 to 35 amps apply pro qdm with A'Orteil, can. The mean current density with which the inventor works is about 20 amps per square meter.

K.N i\st festgestellt, daß die Anwendung huller Stromdichten bei Benutzung einerK.N is found that the application huller current densities when using a

Claims

Anode of the type specified above very quickly becomes a hard, uniform, firmly adhering Coating results.

After the item, such as B. a piano wire has received its coating, it will be seen in water; iu> g «- \\ as and in an oven to about 150 to 200 ^; C heated. The Maximuni heating in an ordinary oven Hegt at about 200 "C, in practice, the wire or other with a cadmium coating provided object about 3 to 4 hours to a temperature of about f85 ^';. C were subjected to the treatment time does not play a very large Role in that good results have also been achieved by extending the heating to 24 hours. Any time between 2 and 23 hours seems well suited for the purpose. The temperature should be chosen so that only a weak layer of cadminium oxide forms on the object. If the wire is immersed in calcium hydroxide, the temperature can be increased to about 250 ° C. without causing any harmful oxidation. The degree of oxidation depends of course on the temperature used and the temperature Atmosphere in which the heating takes place. Dk * Effect of heating, which always occurs at a temperature below the melting point of cadmium temperature is to be carried out, consists in the fact that the cadmium combines with the carrier metal to form an alloy skin, which forms an inseparable part of the whole object. The heating not only creates an alloy bond between the coating and the carrier metal, but it also makes the coating noticeably harder than it was before. These coatings are very firmly attached to the carrier metal. They form a coherent, impenetrable layer and withstand both impacts and bending operations without peeling off the skin. Tests under atmospheric influences as well as under the influence of a salt rain have shown that the coating is much more resistant after being heated than the coating which was not exposed to heating. If the object coated with cadmium is to receive a further metal coating, such as / .. B. if it is to be nickel-plated, then the small amount of oxygen can be removed by a weak cyanide solution or by a dilute sulfuric acid solution.

It should be noted here that it is common practice to use electrolytically generated precipitates to be firmly bonded to the base metal by subsequent heating while forming an alloy. With cadmium it was a result its low melting temperature and its great evaporation capacity at high Temperatures difficult to determine the appropriate temperature.

Although the above method is particularly applicable to the production of Protective coatings on iron or steel objects, but it can also be used on other metals Find application, and the claims are intended to include such coatings on other metals with include.

Godfather XT claims:

r. \ "experienced iron or steel objects produced by an electrolytic process To protect cadmium coating against rust, characterized in that the Electrolysis of graphite or other unassailable anodes and current densities of Applies 3 to 35 amps per square meter.

2. \ * experience according to claim 1, characterized in that the object coated with cadmium is subjected to heating to a temperature ^{between 15 and 250 3 C.}