DE1187884B - Process for anodic descaling and simultaneous metal removal from titanium or titanium alloys - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

Number:
File number:
Registration date:
Display day:

C23b

German class: 48 a -1/06

1187 884
C25245VIb / 48a
October 10, 1961
February 25, 1965

The present invention relates to a method of anodic descaling and simultaneous Metal removal of the surface of objects made of titanium or titanium alloys.

In the manufacture and processing of titanium metal and titanium alloys it is necessary that heated parts to higher temperatures. In addition to the desired influence on the Due to the metal structure, the parts are also exposed to the oxidizing furnace atmosphere, as a result of which There is a more or less firmly adhering layer of titanium oxides of different sizes on its surface Composition forms. This layer, the so-called tinder, has to be partly between the individual Processing stages, but in any case after the last heat treatment, can be removed. this is all the more difficult, the higher the temperatures and the longer the times when the Has formed tinder.

There are essentially two methods of removing the scale, namely pickling in Acids or other aggressive liquids, such as molten salts, and the electrolytic Pickling.

When handling parts made of titanium or titanium alloys In acids, gaseous hydrogen is produced on the surface of the parts, some of which is in the atmosphere escapes, but is also partially absorbed by the metal. The hydrogen content increases of the metal above relatively low values, the material becomes brittle and is in it Can no longer be used for many purposes.

In addition to this disadvantage, the descaling in acids has the further disadvantage that the attack is difficult to direct onto the metal, so that a greater loss of metal is usually accepted during pickling must be as absolutely necessary.

The known electrolytic descaling processes for titanium or titanium alloys exist in that the parts to be descaled are treated cathodically or anodically in a mostly acidic electrolyte will. During cathodic treatment, the scale dissolves in certain types of electrolyte in economically viable times, but at the same time hydrogen develops on the metal surface, whereby the same disadvantages arise as described above.

During the anodic treatment, the scale is first loosened, then the loosened and partially structurally modified scale layer is detached, and finally, the process for anodic descaling is formed
simultaneous metal removal of titanium or
Titanium alloys

Applicant:

Continental Tinaium Metals Corporation
Company with limited liability,
Krefeld, Oberschlesienstr. 16

Named as inventor:

Loren Clell Covington, Henderson, Nev.

(V. St. A.)

Claimed priority:
V. St. v. America October 27, 1960
(65 301)

a new, firmly adhering film, which consists of largely evenly structured titanium oxides. This After the anodic treatment, the film must be removed by briefly immersing it in acids will.

Technically, the task is to develop a process in which, on the one hand, the glow scale is easily and safely removed and in which, on the other hand, neither an uptake of hydrogen nor the formation of an anodic film occurs. In addition, it is desirable at the same time with the To be able to remove a small but precisely measured metallic surface layer.

When the parts made of titanium or titanium alloys are oxidized during treatment at higher temperatures, not only does scale formation occur, but also a slight diffusion of oxygen into the metal surface.
The resulting surface layer contaminated with oxygen shows undesirable mechanical properties and should therefore also be removed. In economic terms, however, it is of great importance here that no larger amounts of metal are removed than is absolutely necessary.

According to the invention, this object is achieved by the fact that the descaling and pickling at the same time Parts made of titanium or titanium alloys in one elec-

509 510/339

Claims (1)

trolytes of certain composition are treated with a current density between 0.00155 and 0.775 Amp./cm ^2. The electrolyte required to perform this procedure consists of
16.5 to 132 g / l ammonium sulfate,
15 to 98 g / l alkali or ammonium Dichromate,
10 to 17 g / l hydrofluoric acid. The composition is critical and, according to the available experimental experience, cannot are significantly exceeded or undercut. A preferred composition consists of 33 g / l Ammonium sulfate, 24.5 g / l potassium dichromate and 15 g / l hydrofluoric acid. The most favorable working temperature is room temperature or one that deviates only slightly from this Temperature selected. It has been found, however, that work can also be carried out at elevated temperatures can be, but that the aggressiveness of the electrolyte is greater with increasing temperature, whereby it is difficult to control the metal removal with certain, easily corrosive alloys will. The current density, based on the anode surface, should be between 0.00155 and 0.775 Amp./cm ² , the voltage varying between approximately 7 and 70 volts depending on the cell characteristics and the type of scale. The higher current densities within the specified limits are advantageous in order to attack and loosen the heavy scale. The current densities at the lower limit are used to handle objects whose scale is lighter or which have only a thin oxide film; they have the additional advantage that the pickling work, ie the speed of metal removal, is easier to control. The individual components of the electrolyte proposed according to the invention have special functions, which together bring about the beneficial results of the proposed 1-step process. The ammonium sulfate primarily has the task of the ion concentration and thus the electrical Determine the conductivity of the electrolyte. If the concentration of this salt falls below 16.5 g / l, so the conductivity is too low. If more than 132 g / l is used, the staining effect is different, and the surface of the metal to be treated ίο is attacked differently. If less than 15 g / l dichromate is present, the current efficiency is reduced, and if more than 98 g / l are used, the metal to be pickled is discolored.
The hydrofluoric acid is preferably in the upper x5 areas of the specified concentration range applied, i.e. from 15 to 17 g / l. Larger concentrations would result in a rough surface of the metal result in concentrations lower than 10 g / l the reaction speed under an economical ao borrowed reasonable size decrease. Alkali dichromates, especially sodium dichromate and potassium dichromate, are used as dichromates as well as ammonium dichromate in question. ^a 5 claim: Process for anodic descaling and simultaneous metal removal of titanium or titanium alloys, characterized in that that the parts to be treated in an electrolyte 16.5 to 132 g / l ammonium sulfate,
15 to 98 g / l alkali or ammonium dichromate,
10 to 17 g / l hydrofluoric acid. with a current density between 0.00155 and 0.775 Amp./cm ² at temperatures between 0 and 100 ° C, preferably at room temperature. 509 510/339 2.65 © Bundesdruckerei Berlin