US2286745A - Heat treating process - Google Patents

Description

HEAT TREATING PROCESS Filed Jan. 16, 1942 I Invento Herman His Atborneg.

' mersion thereof in a molten metal bath.

. vention;

ingiromapoy-oiireel Patented June 16,

HEAT PROCESS Herman anemiarsky, Schenectady, N. mas,

signor to General Electric Company, a corporation New York Application January 16, 1942, Serial No. 427,032

Claims. (Cl. 148-133) This invention relates to a process or heat treating metalarticles. It is particularly concerned with the heat treatment'of metal, specifically copper or copper alloy, strips or wires by im-' The heat treatment of metal articles is often carried out by immersing the articles inmolten Y Y with an applicator 3 of felt or. similar material moistened with a suitable dilute aqueous silicate solution. Additional silicate solution is continuously or intermittently supplied to the applica- 4 tor from conduit 4 which is connected through ,valve 5 with a reservoir 6 containing a supply of metal baths, particularly lead or lead alloy baths,

held at heat treating temperatures. This meth-- od requires simple and inexpensive apparatus and is advantageous also because of. the rapid? transfer or heat from the bath to the articles being treated. However, as far as I am aware, such baths have never been successfully used in commercial heat treatment of metals such as copper and its alloys which are easily wet by the molten metal or its oxides. When a copper wire,

clean or oxidized, is passed through molten lead,

the wire is quickly coated with lead or its im- 'pm'lties such as lead oxide making the annealed wire unfit for many applications; particularly the application of varnishes such as organic enamels.

An object of the present invention is to pro-- vide a new and improved process for heat treating metal articles in a bath of molten metal.

Another object or the invention is to'provide a method of preventing contamination of the heat' treated article bythe molten metal heat treat- 7 ing bath. h iurther object of the invention is to provide the metal articles, prior to heat treatment, with a protective coating capable or effectively preventing direct contact thereof with the molten metal and of being easily removed therefrom subsequent to the heat treating step.

The above objects areattained in accordance with my invention by coating the metal artlcles with a soluble alkali metal silicate before they solution. The silicate solution may comprise any soluble silicate, such as the commercial sodium or potassium silicates, preferably those silicates having low alkali contents. For example, an entirely satisfactory coating has been obtained using a commercial sodium silicate solution containing 6.3 per cent NaiO, 24.6 per cent SiOa and 69.1 per cent water made up into a dilute solution by the addition or 7 parts water to 1 part oi the ,silicate solution.

After being coated witha thin film of the sillcate by contact with the applicator, the wire passes through an oven I where excess moisture is removed from the silicate film before'the coat.-

' ed wire enters the heat treating chamber 8 conmetal bath.

' the top of the cover ll through which the wire are passed through a treating bath of molten metal over which a non-oxidizing atmosphere is maintained. After-the articles have cooledto non-oxidizing temperatures, the protectlvesilicate coating is removed by subjecting the 'wireto suitable acid and/or water washes. Y

My continuous processor heat treatin metal articles, specifically copper strlpsnor wires, by

means or a moltenmetal bath may be better un- 1 dersioodbyreierencetothem ing. showing somewhat schematically a vertical, cross-secflonal viewor one type of apparatus that may be employed in tbepmgflce or my in- Foror illustration the annealing oi acopperwirewillbeconsldered.

with reierence to the drawing. the wire I com- (not shown) passes over a pulley 2 and downwardly intointimate contact taining a molten metal heat treating bath a. a The drier I is not indispensable and may be omitted when suflicient drying of the soluble silicate film can be obtained by contact or the wire with the heated atmosphere above the molten For purposes of illustration I have shown the heat treating chamber 8 as comprising a flanged container l0 provided with a'flanged cover 'II in 'relativelygas-tight contact therewith. Suitable tubular passageways l2 and I: are provided in enters and leaves the heat treating bath. A suitable reducing gas, preferably hydrogen, is introduced into the heat treating chamber through. inlet pipe ll in the sideor cover ll andprevents oxidation of the moltenmetal whichis heated by means of gas burners I5 beneath container 'Il. Excess gas escapes through wire passageways l2 and II. The wire I after entering the heat treating chamber 8, passes beneath;sheavev It, partially or wholly immersed in the molten'lead or lead alloy bath 8, and is heated by the'bath to annealing or other desired heat treating temperatures. From the heat treating bath the wire passes over suitable pulleys l1 and I8 and beneath. a sheave'll-immersed in acid bath 20.-

The silicate iilm adequately protects the hot wire from oxidation by the atmosphere during its travel Irom the molten bath to theacid, bath.

As the heat treating bath is ordinarily held at a temperature cit-about 400C. for annealing copper wire, unprotected copper heated to such temperatures would be quickly oxidized by contact with air.

The acid bath preferably comprises a dilute (2 per cent) solution of hydrofluoric acid capable of completely removing the silicate film as well as any dlrtor oxides picked up by the coated wire from the'molten bath. Except for these contaminations, all of the protective silicate coating can be removed by a hot or cold water bath. How.- ever, a heat treated wire which has been washed only with water will be found to have a few widei 1y separated dirt" spots marring its otherwise bright, clean surface. These spots are readily removed by the dilute hydrofluoric acid bath indicating that the spots are not on the wire but on the silicate film which is preferentially attacked by the dilute acid.

. The clean, acid-:washed wire passes over pulley 2| and under sheave 22 immersed in a water bath 23' where the wire is freed of any traces of acid collected during immersion .ln the acid bath. From the water bath the clean wire-passes over pulley 25 to a take-up reel after first being freed of 'water by air or oven drying. Air drying is suflicientif water bath 23 is maintained at or near its boiling point.

Copper wire annealed or heat treated by the above process can be coated, without further processing, with any of the usual wire enamels.

'Although I have described my invention with particular reference .to the annealing of copper wire, it is not restricted thereto but-is generally applicable to the heat treatment of any metal article that can be dipped,sprayed, or otherwise provided with a protective silicate film prior to 35 thereto.

immersion in the molten metal bath.

What I claim as new and desire to secure by Letters Patent of the United States is:

1;A process for heat treating metal articles which comprises coating said articles with an alkali silicate, immersing the coated articles in a fused lead bath at heat treating temperatures and washing said heat treated articles to remove the alkali silicate coating.

2. In the process of heat treating metal articlesby immersion thereof in a molten metal through a molten lead bath while maintaining a.

reducing atmosphere above said bath, cooling said wire and thereafter washing said wire to remove the alkali silicate coating.

5. A process for heat treating copper wire which comprises coating said wire with soluble silicate, passing said coated wire through a heat treating bath of molten lead while maintaining a hydrogen atmosphere over said bath, passing said wire through a. dilute hydrofluoric acid bath to dissolve the .silicate coating and thereafter washing said wire'to remove the acid adhering HERMAN A. LIEBHAFSKY.

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