US2373158A - Brass powders - Google Patents

Description

Patented Apr. 10, 1945 UNITED STATES PATENT OFFICE BRASS POWDEBS John Wulfl', Cambridge, Mass.

No Drawing. Application December 2a, 1943, Serial No. 515,986-

11 Claims.

This invention relates to the production of improved brass powder particularly adapted for powder metallurgy.

The usual method of making so-called bronze powder consists essentially of beating an alpha brass into very thin leaves then screening, grading and polishing the product. This is a protracted operation since the material is successively treated in different and progressively lighter The melt may be suitably deoxidized, as with phosphorus, in the usual manner. The molten alloy is then immediately transformed into dis- 1 crete solid particles. This may be done in any desired manner as by shutting or atomizing.

The product thus produced, as will be appreciated, is essentially a brittle alloy. This is then crushed to the desired particle size distribution. This may be done by disintegrating in any suitable unit such as a ball or hammer mill, pneumatic attrition mill and the like. The

' crushed material may then be classified into the desired screen fractions. The several fractions may be blended or admixed in the proportions desired to give a predetermined particle size distribution.

The powder so produced is subjected to a con-- trolled, heat treatment the purpose of which is to distill oil'a predetermined amount of zinc and to soften as well as brighten the powder. Preferably this is done by annealing in hydrogen. The

disintegrated product under conditions which insures controlled dezincification. The'product thus produced iscomprised of particles which have a high zinc content core and a lower zinc exterior or case of desirable plasticity which renders the powder readily amenable to pressing. When em! ployed for powder metallurgy purposes such powder is pressed and sintered. As will be seen the sintering operation may be controlled readily so as to insure diflusion of the zinc from the zinc-rich core into the case or exterior to insure a substantially uniform distribution of the zinc with minimum evaporation or sublimation of the zinc.

The salientnovelfeatures of the process will be appreciated more readily from a consideration of a typical method which embodies the principles of the invention. The'starting material for the process comprises an alpha-beta brass, i. e., a brass composed of alpha brass and a substantial amount of the embrittling beta constituent. As source material, therefore, there may be used any brass containing above about 36% zinc such for example as Muntz" metal. The starting material may be derived from any suitable scrap which has been cleaned thoroughly.

- To insure the best and standard results it is In a typical case the melt may contain approxithe presence of the beta constituent in the alloy.

mately of copper and 50% of zinc by weight.

annealing temperature should be above 500 C. and preferably about 800 0. Depending upon the zinc content of the original alloy the annealing time is controlled so as to distill off from about 10% to about 20% or more of zinc. The control may be such as to remove sufficient zinc so-that the overall or residual zinc content is 3 6% or less, that is to say, so that the ultimate prodnot is an alpha brass. The degree of dezinciflcation, as will be appreciated, will depend upon the ultimate use to which the final sintered product is to be put. As those skilled in the art know the alpha brasses are progressively harder, and stronger as the zinc content is increased up to about 35%. I The ductility increases up to about 20% zinc and then falls. Thus, for products where ductility is of paramount or marked importance it may be desirable to carry out extensive dezinciflcatlon so as to insure about 20% in the final product.

As will be appreciated, the annealing may be eflected in a closed system in which means are provided for recovering the zinc which may be reused in subsequent melts. During the annealing operation the powder should be agitated so as to prevent sintering or cohesion of the par- R powder is pressed at from about to 35 tons per square inch and is sintered at a temperature under about 850 C. During the sintering operation the zinc difiuses into the zinc-poor case or exterior and thus tends to redistribute to give a 5 substantially homogeneous alloy. It is particularly to be observed that a marked advantage of utilizing such a preheated brass powder, i. e., one with a zinc-poor ductile case is that ther is much less tendency for the zinc to evaporate or subbasis for the melt and zinc may be added to bring it'up to approximately a 1 to 1 ratio with copper. Other metals-maybe used as addition agents in the melt to confer their respective effects on the ultimate alloy. Thus, additions of about 4% manganese, 2% iron, 1.5% lead, 1.5 to 5% aluminum and up to 2% tinmaybe desirable for certain end-products. As is known within certain limited ranges lead improves the machinability of brass; manganese and aluminum enter into solid solution in the alpha brass and increases its strength; iron tends to decrease grain size and increases the tensile strength, likewise iron as well as manganese and nickel usually improves the corrosion resistance of these brasses. It will be understood therefore that the invention is of broad application and is applicable n-ot only to the binary brass alloy but to what for the sake of a term, may be called a brass base alloy, 1. e., one containing minor percentages of the enumerated or other alloying constituents whose particular effect is desirable.

While a preferred embodiment of the invention has been described it is to be understood that this is given didactically to illustrate the underlying principle of the invention, i. e., the

} utilization of a relatively high-percentage ofone constituent so asto insure inherent brittleness and concomitant easy and rapid disintegration. to a desirable particle size followed by removal of a predetermined amount of such constituent to render the exterior of the particles more plastic and pressable and then pressing and sintering under conditions which insure a diffusion of the constituent outwardly of the core to secure a substantially uniform composition in the ultimate product.

comprises individually distinct particles of brass having a relatively brittle core and a relatively dutcile case.

3. A method of producing powder metal compacts which comprises, shotting an alpha-beta brass melt, disintegrating the shotted material, annealing the disintegrated'material under conditions regulated to insure the rempval of a predetermined percentage of zinc largely from the exterior surface of the disintegrated particles and torender such surfaces plastic, pressing the annealed material and sintering the pressed material at a temperature and for a period of time suflicient to insure substantial dii' fusion of zinc to said exterior surfaces.

4'. A pressable brass powder for powder metallurgy purposes comprising individual particles having a core of an alpha-beta brass and an internal case of alpha brass.

5. A pressable brass powder for powder metallurgy purposes comprising individual particles having a relatively. brittle core of an aluminumcontaining alpha-beta brass and a relatively ductile external case of an aluminum-containing alpha brass. i

6. A pressable brass powder for powder metallurgy purposes comprising individual particles having a relatively brittle core of a manganesecontaining alpha-beta brass and a relatively ductile external case of a manganese-containing alpha brass.

7. A method of producing brass powders which comprises shotting abrass melt containing more than about 36 percent zince to produce a brittle shot; disintegrating the shot and annealing the shot under conditions regulated to distill on a predetermined percentage of the contained zinc.

8. A method of producing brass powders which comprises shutting a brass melt containing more than about 36 percent zinc to produce a brittle shot, disintegrating the shot, annealing the disintegrated shot. under conditions regulated to distill on a predetermined percentage of zinc and recovering the distilled zinc.

.9. A method of producing brass powders which comprises shotting a brass melt containing more than about 36 percent zinc to produce a brittle shot, disintegrating the shot and annealing the disintegrated material in hydrogen at a. temperature between 500 C. and 800 C.

10. A method of producing brass powders which comprises shotting a brass melt containing more than 36 percent zinc to produce a brittle shot, disintegrating the shot and agitating and annealing the material under conditions regulatedto distill oif a predetermined percenta e of zinc. 11, A method of producing brass powders which comprises shotting a brass melt containing more than about 36 percent zinc to produce a brittle shot, disintegrating the shot and annealing the material in hydrogen ,at a temperature between 500 C. and 800 C. and agitating the material during the annealing operation.

JOHN WULFF.