US2255204A - Metal powder - Google Patents

Description

the powder. The presence of the phosphorus Patented Sept. 9, 1941 METAL POWDER George E. Best, Palmerton, Pa., assignor to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey No Drawing.

Application September 28, 1940, Serial No. 358,931

9 Claims. (CI. 7.5-0.5)

This invention is concerned with brass powders and contemplates an improved brass powder that is particularly suitable for use in powder metallurgy. The invention also contemplates improvements in the production of brass powders, the term brass being used herein in a generic sense to include all alloys in which copper and the space, say a mold, in which the powder is compressed. Moreover, the use in such operations of metal powder of high apparent specific gravity-(i. e., with a relatively small proportion of voids) is advantageous, because in such case shrinkage during compression and heat treatment of the powders is decreased.

I have developed an improved atomized" brass powder, the particles of which are rounded, and even spherical, and which is both free-flowing and of relatively high apparent specific gravity, which is to say that the proportion of voids in an uncompressed mass of the powder is substantially less than in brass powders produced hereinbefore. The powder contains a relatively small proportion of phosphorus, which is alloyed with the brass prior to atomization thereof to form in the molten brass subjected to atomization causes the particles to become rounded.

The proportions of phosphorus employed may range from about .05% to about 1% of the weight of the metal. In general, the lower the copper content of the brass the more phosphorus is required to produce good results. As indicated above, the aim of the invention is to produce brass powders that are both free flowing and of high apparent density, and optimum results from these standpoints are achieved when the addition of phosphorus is suificient to cause the particles of brass powder to become perfectly rounded, i. e., spherical. As shown by the table given below, brass consisting of copper and 50% zinc becomes completely spherical when alloyed with 1% phosphorus; brass consisting of copper and 30% zinc becomes completely spherical when alloyed with 0.5% phosphorus; brass consisting of copper and 10% zinc becomes completely spherical when alloyed with 0.25% phosphorus. Brasses that have been alloyed with these amounts of phosphorus atomize to spherical powders resembling atomized copper powder, which is known to consist of spherical particles.

Although optimum results are obtained when the particles of atomized brass are all spherical, substantial improvement in flow properties and in apparent density may be obtained without the production of complete sphericity. This is illustrated by data given in the following table:

Flow rates and apparent density of brass powders (minus 200 mesh in particle size) produced by atomizing molten brass containing phosphorus Nominal Analyzed Brass com o Powder Powder sition p ggg ggf flow rate density Character of powder Grams per minute 50 (lo-5021i-.- 144 4. 05 Largest particles spher- Do 200 4. as 100% spherical. 70Cu-30Zn- 0 3.11 None spherical.

Do 05 89 3. 0 o. Do 120 3. 64 Largest particles spherice Do 0. 25 (0)0. 19 158 4. 39 Preetdlominantly spheri- Do o. 25 0 0. 21, 1s? 4. 75 lrol ably spherica Do 0. 50 0.46 200 4.98 spherical. 90Cul0Zn.. 0. 25 210 5. 24 Do.

. (:2) Same melt as (b) but held longer in melting pot.

As measured through an orifice 34" long and 0.100" (plus or minus .0005") in diameter from an inverted 60 cone 60 mm. in diameter and having a carefully machined and polished stainless steel surface. The time for complete discharge of a 50 gram sample from the cone was measured.

In accordance with the invention, molten brass containing the desired proportion of phosphorus is dispersed as a spray in a gaseous medium (for example, cold air). The resulting frozen drops or particles are collected in a conventional dust collecting device such as a cyclone separator or abag house.

Various types of atomizing apparatus may be employed to produce the brass powder of the invention. However, with a view toward improving uniformity of particle size, I prefer to atomize themolten brass containing the phosphorus by passing it as a thin and substantially non-wavering non-spattering stream transversely into the trough of a V or U-shaped jet of gas, as described and claimed in my copending application Serial No. 350,542, filed August 3, 1940. v

The phosphorus may be incorporated into the alloy in various ways, for example, by adding red phosphorus or phosphor-copper to the molten alloy.

Care should be taken to avoid excessive loss of the phosphorus while the alloy is molten. However, with ordinary good conventional'melting practice for brass, losses of phosphorus will not be excessive, so that the use of 0.05% to 1% phosphorus onthe weight of the alloy assures the retention of suflicient phosphorus during atomization to secure a pronounced improve! ment in the flow characteristics and apparent density of the resulting powder.

The free flowing brass powder of my invention afiords particular advantages in operations in which the molds in which the powders are compressed are fed by volumetric devices and in which the thickness of the pressed shape depends upon the weight of powder contained in a charge of fixed volume fed to the mold. In such operations the thickness of the pressed shape. depends upon the bulk packing of the powder. Powders of irregular shape tend to bridge in bulk packing and, therefore, a given volume of such powder may vary widely in weight. On the other hand, the brass powders of the invention will flow readily and pack to a relatively uniform density in the volume measuring device. Hence, such brass powders permit the production of uniform lots of the shapes, not subject to the great variations in dimensions that may occur when heretofore customary types of brass powder are employed.

3 claim:

1. A free-flowing brass powder of. relatively high apparent density comprising rounded particles of brass produced by atomizing molten brass containing from about 0.05% to about 1% phosphorus.

2. A free-flowing atomized brass powder or relatively high apparent density comprising rounded particles of brass containing a relatively small proportion of phosphorus.

3. A free-flowing brass powder of relatively high apparent density comprising spherical particles of brass produced by atomizing molten brass containing from about 0.05% to about 1% of phosphorus.

4. A free-flowing atomized brass powder con sisting of spherical particles of brass in which the ratio of copper to zinc is of the order of 90 to 10 and containing phosphorus in proportions of the order of 25%.

5. A free-flowing atomized brass powder consisting of spherical particles of brass in which the ratio of copper to zinc is of the order of '70 to 30 and containing phosphorus in proportions of the order of .5%.

6. A free-flowing atomized brass powder consisting of spherical particles of brass in which the ratio of copper to zinc is of the order of to 50 and containing phosphorus in proportions of the order of 1%.

'7. In the production of brass powder by atomizing molten brass, the improvement which comprises incorporating small proportions of phosphorus in the brass subjected to atomization to cause the resulting brass particles to be rounded in form.

,8. In the production of brass powder by atomizing molten brass, the improvement which comprises incorporating in the molten brass to be atomized phosphorus in proportions ranging from about .05% to about 1%.

9. In the production ot'brass powder by atomizing molten brass, the improvement which compprises causing the resulting brass particles to assume rounded shapes by including in. the atomized molten brass phosphorus in proportions ranging from about .05 to about 1%.

GEORGE E. BEST.