US899452A - Process and apparatus for annealing and tempering metals. - Google Patents

Description

strasse,

' HEINRICH 'KRnUTSCHNEIDE-R, or m nus, GERMANY,

PROCESS AND APPARATUS FOR- ANNI ALING AND TEMPERING MIETLLS.

To all whom it may concern:

Be it known that I, Hammer! Kaiser- SCHNEIDER, engineer, a subject of the German Em eror, residing at Berlin, Culinermany, have invented a certain new and useful Process and anAp aratus for Annealing and Tom ering Meta s. and Metallic Products and l do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it apper tains to make and use the same.

In the treatment of metals and metallic products, uniform annealing of such products at a certain temperature which must be maint ained exactly constant, plays a very important )art. Thus, for instance, in tempering steel or other alloys that can be tempered, the maintenance'of the exact tem erature and' uniform distribution of the mat over single pieces to be annealed or tem ercd is of the utmost importance. Unequal leating of pieces of metal with unsymmetrical cross sections leads to contrae 1011 of the heated parts during the cooling, giving rise to internal strains etc.

Furnaces of all kinds do not su'fiiciently insure uniform heating or tempering above purpose. The well-known method of heating the articles to be tempered in fusible baths of metallic salts, metallic oxids and similar metallic com ounds has the great advantage in princip e of roviding for free heating by radiation. T e application of this process of annealing or tempering by means of fusible baths presents however great practical difliculties. In order by external heating to raise, the temperature of the bath consisting of metallic salts or the in like, to the extent required, that is to say to 8005-870. (l the method now employed is to expose iron vessels (crucibles etc.) filled with fusible flux to direct heating in furnaces. Owing to the high temperature to 5 which the outer walls of the cruc bles are ex posed the metal of which the crucibles are v composed is soon destroyed and such destruction is accelerated on the one side by the action of the combustion gases and on ence of the flux. In addition to this, it must be remembered that annealing furnaces of this kind are ver inefiicient as regards the consumption of temperature of annealing to be regulated in for the the other side by the generally oizidizing influ-- uel, and do not allow the Specification of Letters Patent. Application filed July 7, 1904. Serial No. 215,588.

l i I cant extent.

Patented Sept. 22, 1908 the exact and reliable manner required for the urpose in question.

T is invention relates to an annealing process in which the above drawbacks are obviated, and to an apparatus for carrying out said process. According to this process, the article to be tempered or annealed is heated to the desired temperature in a nonmetnllic fusible bath heated directly by electric currents of sufiicicnt strength.

The advantages of this annealing process are obvious. First of all, it is possible to regulate the temperature electrically in a very convenient manner; then loss of heat can 'be reduced to a minimum tric. heating, and finallythe current used in the furnace serves as an exact measure of the temperature of the fusible flux, as the con.- ductivity of the latter increases very quickly with the temperature. .In carrying out this process, it is preferable to use furnaces made of refractory material which is not dissolved by the molten flux (such as anagncsite or the like). The walls of the furnace must at the same time be pro erly insulated, so as to prevent radiation oi heat outwards. For prei cnting radiation losses, 7 the furnace is preferably closed at the to except for a charginmopening through which the articles to e annealed are introduced and removed.

The heating of the flux, which must take place before the furnace is started, so as to get sufficient conductivity, is cilcctcd by electric current of sufficient strength su plied by means of suitable electrodes. T ie electrodes must be made of some-material which is a sufficiently good conductor and which is refractory such for instance as iron, carbon, etc. The electrodes are arranged in the furnace in such positions as to result in uniform heating of the bath by the current.

The bath preferably consists of substances which do not chemically attack the articles to be tempered, or'at least to a very insigmfi- 1 Baths can also be used which at the temperature in question can yield car'- bon to the articles to be annealed, and thus increase their contents of carbon, as for instance in the case of steel. Some of the sub- 1 stances which may be used to yield carbon to the article to be annealed are oxalate of calcium and carbids of various metals.

Suitable substances which can be used for the fusible oath are fiuorids, carbids, car- 1 by this internal slee 7 .l i i l l fo'r the purposes of my invention. By the term non-inetallic bath, I mean baths such as bonates, etc, such fluxes having at the terns perature in question. 'a comparatively great cubic centimeter.

For the purgose of defining the bath empleyed 'by'me, have desi ated the same as anon-metallic bath, there y excluding baths of molten' metal wh'ch would be inoperative hereinbefore specified or suchas are similar 1n composition or effect.

, If the flux is basic, the material '0: which thefurnace is made must also be basic; if

the flux is acid, it mustbe also acid, so as not to be attacked by the flux.

' The electrodes are preferably arranged interchangeably so that the'iy may be replaced by new ones when corro ed after a certain amount of use, as such corrosion cannot be avoided. It is preferable to use alternating current for heating, so as to avoid'electroly sis in the bath.

For regulating the strength of the current in the latter'case, transformers could be used withhdjustable primary winding, and also choking coils.

What I claim as my invention and desire to secure by Letters Patent is: p

1. The herein described process of heating metals, which consists in, inserting the objects to be heated in a fusible non-metallic bath heated by an electric current, and regulating sa 1d current to maintain the bath at the required temperature, the current passing throu h both the bath and the immersed portion 0 said ob'ects 2. The herein escribed process of heating metals, which consists in producing a molten non-metallic bath by means of an electric current, inserting the objects to be heated in .said bath, and maintaining the required temperature of the bath by regulating the said heatin current, the current passing through bot the bath and the immersed portion of said objects.

3. The herein described process of heating metals, which consists in insertin the objects to be heated into a fused bath ormed of a conductor whose conductivity increases with the temperature, and passing an electric current through said bath, and thereby heating said objects to the desired temperature.

4.. The herein described process of heating metals, whichconsists in inserting the objects to be heated into a fused non-metallic bath, and passing an electric current through said bath, whereby the temperature of the bath is maintained, and also passing the current through the" objects themselves, whereby their resistance also serves as a heating means. w

5. The herein described process which consists in introducing iron or steel articles into an electrically heated fusible non-metallic bath which yields carbon to the article.

6. A bath for heating metals, to any desired temperature up to a white heat, while retaining said metals solid, consisting of fused conductive material whose conductivity increases with increase of its tem erature, said material being inert tower the metal to be heated, and means for passing an alternating current throu h said bath.

In testimony whereof, %have hereunto set my hand and affixed my seal, inthe presence of the two subscribing witnesses.-

HEINRICH KRAUTSCHNEIDER. [n.a]

Witnesses:

WOLDEMAR Ham,

HENRY Hasran.