US1997141A - Improved process for bronzing articles and parts made of iron and alloys of iron and carbon - Google Patents

Description

Patented Apr. 9, 1935 UNITED STATES PATENT OFFICE IMPROVED PROCESS FOR BRONZING ARTI- CLES AND PARTS MADE OF IRON 'AND ALLOYS IRON AND CARBON Berardo Gnerini, ems, Italy No Drawing.

Application May 20, 1932. Serial- No. 612,656. In Italy May 23, 1931 1 Claim.

, The present invention relates to a new process and improved apparatus for the chemical bronzing of articles or parts made of iron orof alloys of iron and carbon.

' hydrochloric acid, and in certain cases hydrofluoric acid, the action of which consists particularly in attacking the ferrite (which isthe soft constituent of ordinary steels) while it has relaest possible strength for resisting mechanical tively no action on the perlite, the cementite (al-- most insoluble in dilute cold sulphuric acid) and the martinsite (the hardest constituent), so that the metallic surface is prepared in such a way that the bronzing preferably becomes fixed upon one of these three latter constituents with the consequence that the surface possesses the highstrains torsion, wear, friction etc.

The pickling treatment carried out in the manner indicated above is only performed on articles made of iron or on ordinary carbon steels. In the case of special nickel, chrome nickel, silicon steels etc. and cast iron, the bronzing is preceded by a second special pickling treatment in a 10% solution of hydrofluoric acid contained in a basin of paraffin wood. This pickling treatment lasts for 10 to 20 minutes in the case of special steels, and up to 45 minutes in the case of cast iron. The duration ofthe first pickling bath varies from 10 to 30 minutes.

After the immersion in one or two pickling solutions, the articles are again washed in running water and then immersed in the oxidizing or bronzing bath proper.

This bath is composed of an alkaline solution containing lead dioxide, nitrated derivatives of toluene (or phenol), nitric acid and in certain cases ammonia. The treatment inthe bath is effected in such a way that the solution will'be absolutely prevented from absorbing carbon dioxide from the atmosphere, in order to avoid the alkaline solution, yields oxidant from the bath formation of alkaline carbonate, and in order that the bronzing bath I may preserve its oxidizing power unaltered without it being necessary to add any correcting substance.

The duration of the oxidizing treatment is suit- 5 ably regulated and is about twenty minutes for iron, about half an hour' for ordinary steels and carbon steels, and about an hour for special steels and for cast iron at a boiling temperature of the bath which can vary between and C. 10

Upon leaving this oxidizing bath the bronzed articles are again washed in running water and they are finally immersed in boiling vegetable oil until the last traces of alkalis which have adhered to the parts have been completely removed. 15

The oxidizing bath is preferably composed of a solution of sixty parts of caustic soda or potash or ammoniacal caustic soda (fifty parts of caustic soda and two parts of ammonia, density 0.88) in one hundred parts of water to which are grad- 20 ually added, while stirring the liquid which has been raised to boiling point, two parts of trinitrotoluene, T. N. T. ontri-nitro phenol, and then 0.8 parts of lead dioxide, and finally, when cold, 2.95 parts of nitric acid. 25 The characteristic feature of this new form of the oxidizing bath is constituted by the presence of the lead dioxide which, when hot and in the in a first stage. On the other hand in a second 30 stage,,it reacts with the caustic soda and becomes transformed into sodium plumbate, NazPbOa, which in its turn is decomposed into caustic soda and lead dioxide by the successive additions of 35,

water to the bath.

In this way two of the main'constituents which compose the bath are regenerated, while this cycle constituents is increased at the expense of the.

trinitro-toluene and the lead dioxide, a matt bronzing efiect is obtained.

With the process according to the present invention it is also possible to oxidize the special types of steels called rustless steels.

In order to oxidize these steels it is suflicient to lower considerably the percentage of caustic soda in the oxidizing bath indicated above, while increasing the percentage 'of lead dioxide. A has givenexceb' composition of the bath which lent results in the case of these so-called rustless steels having a chromium content up to 18%.

is as follows:

Water parts: caustic soda 16.65 parts; sodium or potassium mtrate 2,33 parts; lead dioxide 2 parts This particular bath boils at C. and the rules to be followed for its use are exactly the same as those indicated for the normal bath described above.

Rustless steels can also be bronzed by mixing lead dioxide and manganese dioxide in this special bath and also by completely replacingthe lead dioxide by an equal quantity of manganese dioxide or potassium permanganate or potassium chromate or bi-chromate with or without alkaline nitrates.'

The oxidizing bath does not however give the perfect results with these compositions that it gives with the last of the above mentioned compositions.

The appearance of the articles which have been bronzed in the normal bath shows the great chemical activity of this process as compared with previously known processes in that cast iron can be oxidized and give colouring results which are absolutely identicalancl whichhave never hitherto been obtained in direct oxidizing baths.

Cast iron when bronzed by means of old processes is not given a black colour but a reddish black colour which is not uniform. Y

The apparatus for carrying out theprocess ac cording tothe invention comprises essentially, known means for the preliminary grease removprovided with a perforated ing and pickling operations and basins or small boxes expressly constructed having the following dimensions:

- Internal External 0.20 metres 0.25 in.

Length Internal External O. 78 1.00 Height Internal External 0.74 0.80

These basins serve for preparing the oxidizing or bronzing proper and for the immersion of the articles to be bronzed.

These boxes or basins must be made of thin sheet iron (about 3 millimetres) with double walls and double ends, thermal and electrical insulation with asbestos and mica, and they must be cover.

It is absolutely necessary for all the bronzing boxes proper to have the dimensions indicated above or proportional dimensions, because the shape of the basins as much as the relative dimensions bear a strict relationship with the duration of the bath.

With this type of bath, the evaporation is reduced to a minimum, thus making the concentration of the bath almost constant, and can easily be regulated by adding water or fresh bath solution.

Having now particularly described and ascer tained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

Aprocess for the chemical bronzing of articles made of iron or iron alloys and carbon, consisting in immersing such articles from between 20 and 60 minutes into an oxidizing bath at a temperature between and 0., said bath being composed of an alkaline solution containing lead dioxide as reacting means, together with material selected from a group consisting of nitrotoluene, nitrophenol, alkaline nitrate and ammonia, then washing the thus oxidized articles in running water and plunging the articles in boiling vegetable oil until the last trace of alkalies have been removed; said oxidizing, bath being formed by a solution of approximately 6 0 parts of material selected from the group consisting of caustic soda, caustic potash and ammoniacal caustic soda in 100 parts of water, to which have gradually been added, while agitating the liquid raised to boiling point, 2 parts of tri-nitrotoluene and subsequently 0.8 parts of lead dioxide, and finally cooling the liquid and adding about 2.95 parts of nitric acid.

. IBERARDO GUERINI.