US1815505A - Bright annealing of metals - Google Patents

Description

July 21, 1931. R. c`.. GUTHR'IE ET AL 1,815,505

BRIGHT ANNEALING OFMETALS u Filed Nov. 15. 1929 Patented July 21, 1931 l UNITED STATES ROBERT G. GUTHRIE AND OSCAR. J'. WOZASEK, OF CHICAGO, ILLINOIS, ASSIGNORS TO PEOPLES GAS BY-PRODUCTS CORPORATION, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS; SAID WOZASEK NOW BY CHANGE' OF NAME OSCAR J'..WILBOR PATENTl orf-'ica .BRIGHT ANNEALING OF METALS Application led November 15, 1929. Serial No. 407,438.

This invention relates to improvements in the art of the bright annealing of metals simultaneously with a cleaning of the surface of the metal.

It has heretofore been proposed to anneal metals in the presence of inert or nonoxidizing gases, whereby the metal is prevented from tarnishing or oxidization on its surface. It has also been proposed to follow the definite annealing operation b a scouring or pickling to restore the brig t surface to the metal.

In distinction from such processes, the present invention is competent of operation with a metal which may have either oxide or carbonaceous tarnish or discoloration on its surface, so that the metal is definitely restored, under practically all conditions, to a bright clear surface during the time of annealin By annealing hereinafter will be understood a heating operation to which a metal is subjected, usually to soften it after a cold working such as rolling, forging, etc.

It will be understood that a bar of metal upon passing through a rolling mill in which it has been reduced in cross section, becomes very hard, so that a further reduction by rolling would result in breaking or cracking of it, unless an annealing operation be interposed. Furthermore, the usual exposure of the hot bar, previous to cooling to the atmosphere, results in a superficial oxidation at some parts, while other parts are coated with a film of oil or carbonaceous matter from the rolls.

In order to remove these discolorations and superficial films, it is proposed according to the present method to successively subject the metal to an oxidation treatment and then to 'a reduction treatment during the course of the annealing.

The oxidation is accomplished by heating the metal to an annealing temperature such as 1300" F., and causing it to come into contact with an oxygen-bearing gas such as carbon dioxide, air, oxygen, steam, flue gas or the like. This oxidizing gas then operates superficially upon the metal to burn ofl' any oil or other carbonaceous matter which may `less stabley illuminants have been removed by some suitable method. By removing these less stable materials the deposit of carbon upon'the metal is hindered and prevented, so that by a careful regulation and .observation of the gases in the reducing phase, whereby the freedom from soot is attained, it is possible to produce a reduction of the superficial film of oxide, resulting in a bright clean surface for the metal.

rI his pre-treatment of the reducing gas to be employed, whereby the less stable so-called illuminants are removed, may be accomplished in several ways. It will be understood that the less stable hydrocarbons, of the unsaturated series, are what give the particular gas its direct illuminating quality since these hydrocarbons crack or split during combustion and yield ofi1 particles of carbon and molecules of more saturated hydrocarbons: the particles of carbon become incandescent and cause they yellow flame produced in the burning of standard city gas, for example, throughan ordinary jet. This same cracking occurs at the heat of annealing when such unstable hydrocarbons are present, and results in a deposit of the carbon as soot u on the surface of the metal. It is there ore necessary to remove these hydrocarbons before bringing the gas into contact withv the hot metal.

The gas may be passed through paraffin or similar oils for dissolving or absorbing the unsaturates from the gas: or the as may be vpassed over heated charcoal or co e.' lVith either of these operations, it is found that practically no carbon deposit afterward results when the treated gases are brought into contact with the heated metals.

It is desirable that the gases at the time of contact with the charcoal or coke should be heated to a temperature not less than. that of the annealing itself, so that any cracking will occur during this pre-treatment. Also, it is desirable that the gases shall be preheated, in any event, before b eing brought into cpntact with the metal and its superficial oxide film, to a temperature closely approximating that of the metal itself.

The course of the two stages of operation 1s supervised by chemical analysis of the entering and out-going gases, and by regulating the iiow volume according to the compositions determined. It will be noted that the annealing is progressing during the entire period of the superficial oxidation and reduction,

' and may continueifor even longer periods fili since the annealing may be begun and the metal kept at annealing temperature for a period previous to the oxidation step: between the oxidation and reduction stages: and following the reduction stage: and in especial it is preferred to leave the metal in the presence of the stabilized hydrocarbon gas during its cooling so that the hot metal is not brought into contact with the atmosphere. f

It is found inpractice that the present method makes it possible to take a piece of smooth but badly discolored metal, having oxide, oily and other carbonaceous streaks on its'surface, and by a very simple, direct and progressive operation, to bring forth the metal clean and bright, while it has been definitely annealed and softened for later working.

Two examples of the practice according to this invention are set forth by way of illustration on the accompanying drawings, in which:

Figure 1 is a diagrammatic view showing the simultaneous annealing and cleaning by a batch process in'a pit-type furnace.

Fig. 2 is a corresponding diagrammatic view showing the continuous and simultaneous annealing and cleaning of a continuous wire.

Examples of the employment of the invention may now be set forth in conjunction with the showing of the illustrative forms in these drawings:

E ample I A charge of metal such as brass or copper is placed, for example, in the pot of a pittype furnace 11, wherein the pot may be heated to the desired temperature. A cover 12 for the pot has an inlet tube 13 passing downwardly therethrough and terminating in a flat coil 14 at the base of the pot, while a frame 15 is indicated above this coil to provide a chamber 15a for the distribution of the incoming gas. The cover 12 also has an outlet tube 16`and an aperture 17 which is fitted with a charging lid 18. The gas inlet pi e 13 is connected through a three-way va ve 19 with a container 20 for carbon dioxide or similar oxidizing gas, on the one hand, and on the other hand with a washing vessel 21 containing paraffin oil through which a stream of coke oven gas is passed from the main 22. The valve 19 serves to determine whether the carbon dioxide gas or the coke oven gas is being employed while the respective gases are controlled in volume by the regulating valves 23, 24.

Assuming that the charge has an external surface of approximately 100 square feet, and that its surface c olor is from brown to black in streak or solid color, indicating the presence of a discoloration of rolled oil which maybe chemically regarded as a carbon compound containing a very large proportion of carbon.

The charge of metal is brought by the furnace to a uniform temperature of 850 to 13500 F. in the case of brass or copper, a preferred temperature for such materials being 1300 F. The valve 19 is then operated and a regulating valve 23 opened so that carbon dioxide is passed through the inlet pipe 13 and its coil 14 and thereby is heated to the internal temperature of the furnace: to-wit 13000 F. The quantity of gas is regulated to correspond to the delivery of 0.44 cubic feet per square foot of surface er hour. In the particular example, this ow is continued for ten minutes with a total delivery of 7.33 cubic feet of carbon dioxide. This flow of carbon dioxide is then discontinued. Heating may also be discontinued and after the contents of the furnace have been cooled to 230 F. or below, the charge may be withdrawn without fear of excessive oxidation in the atmosphere.

The surface of the charge then presents an evenly distributed and thoroughly oxidized film over the entire area, being both annealed and cleaned of carbon. It is then ready for working if so desired: but it is, however, preferred that the surface should be bright, in most cases.

` For this purpose, the batch may be returned to the same furnace, or preferably is left therein and the heating in the furnace continued at 13000 F. The valve 19 has already been manipulated to shut oli the flow of carbon dioxide gas, and is now moved to admit the purified natural gas from the pipe 22, which has had its unsaturated illuminants substantially removed in the paraffin bath 21. This gas is permitted to flow in at the rate of 0.33 cubic feet per hour per hundred square feet of surface area in the charge. This flow is continued for fifty minutes, a

Ewample I I The cleaning and bright annealing of brass or copper strips or wire in a continuous strip type furnace is illustrated in Fig. ,2., The coil delivers a strip 31 which passes through an oxidizing chamber 32, a reducing chamber 33 and a cooling chamber 34, moving through substantially gas-tight apertures in the partitions between the respective chambers. The chambers 32 and 33 are, for example, heated by the electric coil 35, and are surrounded by a heat insulating jacket 36. The cooling chamber 34 has for example, a coil 37 surrounding it through which water may be passed as desired. An externaly preheater 38 is provided with a coil 39, which is connected through regulating valve 41 with a'pump 42 by which atmospheric air is forced .through the coil 39 and thence past a further regulating valve 43 into the interior of the oxidizing chamber 32, from which it may escape by the outlet pipe 44. u A heating means is provided for this preheater 38. Similarly, the city gas main 45 has branches therein of which the branches 46 lead to a burner 40 and to a burner 47 for heating the retort 48 containing a layer of heated charcoal 49 iu its base and having a central partition which causes the flow of city gas from the branch pipe 50 past regugas being emlat-ing valve 51 through the charcoal 49- whereby the unsaturates thereof are substantially eliminated, and from which the treated gas is delivered through the pipe 52 into the reducing chamber 33 of the furnace from which -the same may escape by an outlet 54 or through a tap connection 55 into the cooling chamber 34, so that a non-oxidizing atmosphere may be maintained in this cooling chamber during the, reduction of temperature of the strip from the annealing heat to the temperature of delivery.

The temperature of the furnace and Within the preheater and the absorbent retort 48 is maintained at preferably 1300o F., and the speed of the. movement of metal through the furnace and cooling chambers is adjusted in such a. way that the time factors per square foot of surface are essentially the same as those set forth in Example I. It will be noted that chamber 32lis one-fifth of the length of chamber 33, and hence by maintaining uniform concentrations in the chambers 32 and 33, the proper proportion of action is obtained, and the strlp is subjected to the carbon dioxide for tenminutes and to the hydrocarbon gas for fifty minutes.

It will be understood that the temperaturcs and proportions set forth above are varied according to the characteristic of the metal which is being treated. Vith certain metals, for example, a temperature of 900 F. will produce the annealing necessary for obtaining a predetermined grain size and hardness` of ,the iinished product. It the metal is already bright and free from carbonaceous discoloration, the first step of the operation may be dispensed with, and the material treated immediately with the Yhydrocarbon gas, say at the rate of 33 cubic feet per hour for ten minutes for a superficial area ot 100 square feet. The annealing procedure proceeds during this time, and the material is then'cooled either slowlyor quickly as required by the particular metal beingtreated and is removed from the furnace. During this, the metal has been maintained in a perfectly bright and undiscolored condit-ion but is made soft enough to permit further rolling, forging, stamping or forming. v

In experimental Work, it has been found that a gas layer of approximately onesixteenth of an inch thick surrounded the work in every instance mentioned, whether stationary in the pit-type furnace or delivering through the continuous furnace: which by calculation indicates a velocity of 0.01915 feet per second, and giving a .gas layer of this thickness on the surface of this amount of work at any temperature between 850 and 1350 F. v

Other metals may be treated lin the manner described, as for example nickel, nickel silver '(so-called German silver), copper, brass, bronze, steel, iron, aluminum, and other alloys of these metals.

It will be understood that the invention is zoV y not limited to the particular materials emfre'e from unsaturated hydrocarbons where-- by to reduce the said' oxide film but without the deposit of soot upon the metal.

2. The method of bright .annealing metals which comprises heating the metal to lan annealing temperature, bringing the metal while so heated into Contact with an oxidizing atmosphere, andv then bringing the metal While so heated into conta/ct Wlth a S reducing atmosphere free from unsaturated hydrocarbons, and cooling the metal in the absence of air and unsaturated hydrocarbons.

In testimony whereof, We aHX our signatures.

ROBERT G. GUTHRIE. oso AR J. WOZASEK.

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