US2448243A

US2448243A - Process of producing magnesium powder by cold rolling and grinding

Info

Publication number: US2448243A
Application number: US540551A
Authority: US
Inventors: Harold P Anderson
Original assignee: Permanente Metals Corp
Current assignee: Permanente Metals Corp
Priority date: 1944-06-15
Filing date: 1944-06-15
Publication date: 1948-08-31
Anticipated expiration: 1965-08-31

Description

Patented Aug". 31, 1948 UNITED s'rArEs PATENT OFFICE z,44a.24a

POWDER BY COLD GRINDING ROLLING AND Harold r. Anderson, Mountain View, Calif., as-

signonby mesne assignments, to

The Permanente Metals Corporation, a corporation of Delaware No Drawing.

'paumion June 15, 1944,

This invention relates to a process for treating magnesium metal to produce powdered magnesium.

It is contemplated by this invention to produce powdered, or finely divided, magnesium metal which may be used as flashlight powder, as an incendiary material for instance in fireworks or the like, or as a chemical reagent.

Magnesium metal as obtained, for example, by the sublimation of metallic magnesium or bythe reduction of magnesium containing ores with reducing agents which give, except for the magnesium, non-gaseous reaction products, is recovered in a condensing device in the form of crystals which deposit in agglomerat'e masses. The crystalline deposit so obtained is quite malleable, and it has been iound in practice that such a deposit cannot be satisfactorily reduced to a powder by direct introduction into a hammer mill or other mechanicalreduction device.

It has accordingly been the ordinary procedure to reduce crystalline magnesium to powdered form by casting into cylinders or ingots, milling the ingots into shavings, and then running these shavings thru a hammer mill or similar device.

Other processes have been devised for the production of magnesium powder such as directing a jet of gas against a stream-oi molten metal as the latter is forced downwardly out 01' the lower part of a melting vessel, or volatilizing the metal in an inert gas and chilling with a stream of cool gas to cause condensation of finely divided metal. In general, however, the cheapest, and most satisfactory method of making the powder has been to cast, form shavings or other thin pieces from the cast mass, and subject the shavings to the action of a hammer mill. In all of these methods, the crystalline magnesium has been first subjected to a heat treatment and, in casting at least, with consequent rearrangement or re-alignment oi the crystals.

I have now discovered that the crystalline magnesium can be reduced to powder form by first flattening the crystallineagglomerates, or mechanically extending them along one general plane or axis, and then subjecting the flattened metal to the action of a hammer mill or other mechanical reduction device. The flattening oi the metal evidently causes the crystals to become brittle and they are then. easily powdered by a pounding or beating action as effected by a hammer mill.

Advantageously the crystalline magnesium is rolled in the cold state and then subjected to treatment by a hammering action, The cold rolled'crystal's are readily reduced to the pow dered state by hammering in a hammer mill or the like. It is advantageous to cold roll the crystals rapidly. Evidently distortion eflects are obtained in this manner which enable the production of many cleavages and, thereby, the producing ot 'a finely divided magnesium product.

It is an advantage oi my process that the number of steps in the production of magnesium powder from refined magnesium metals are reduced. It is a further advantage that mechanical losses 0! metal such as are usually incurred in casting, shaving and other handling are avoided. It is a great advantage of my process that heating of the metal, with consequent dangers of loss by increased oxidation or necessity for increased protection irom atmospheric action upon the metal, is avoided.

In my process the flattening, advantageously by cold rolling, and the hammering can be eiiected satisfactorily in thepresence of air. If it be desired to prevent even small amounts oi! atmospheric degradation of the metal, the operations can be carried out in an inert atmosphere, as for example by maintaining an atmosphere of hydrogen, argon or other inert gas about the rolls or mills, suitably housed, or the metal can be protected during working by application of a surface coating of a liquid hydrocarbon, preferably a low gravity liquid hydrocarbon such as kerosene or distillate.

As an example oi. the method of carrying ou my process, I use as a starting material magnesium produced by the reduction of magnesia with a carbonaceous reducing agent such as coke and subsequent refining of the crude condensate by distillation to recover sublimed magnesium as 1 crystals. The crystals deposit in the flnal stage as an irregular mass. This cooled crystalline mass is fed quickly thru a set of steel rolls. The rolled and flattened mass of magnesium is now run through a hammer mill and the resulting powder is screened. The coarser particles are again fed through the rolls and are put through the hammer mill again and these operations repeated once more to reduce the whole mess to a suitable state of subdivision.

The final product has the following fineness: It all passes a 10 mesh screen, 2% remaining on a 20 mesh screen, 46% on a 50 mesh screen, 29%

on an mesh screen, and'23% passes through 80 mesh. The product is excellent as a flashlight powder, being ignited very easily when a small amount of potassium chlorate is admixed therewith. 'It is useful in powder metallurgical processes and it is also useful as a. component of flares and the like.

Alternatively, the crystalline magnesium may be pressed or hammeredflat prior to grinding or hammer milling. However, it is more convenient, and it is preferable to flatten the crystals by passing them quickly through a rolling operation. The more quickly the crystals are flattened, or mechanically extended along one plane or axis, the greater are the distortion strains set up and the better the results in the final reduction to powder.

It is to be understood that the above description and example are illustrative only and variations and modifications may be made therein without departing from the spirit and scope of this invention. I

Having now described my invention, what I Wish to claim is:

l. A process for producing powdered magnesium which comprises cold rolling crystalline magnesium obtained by sublimation to make the magnesium brittle by mechanically extending the magnesium crystals along a crystal axis, and disintegrating the said cold rolled magnesium by hammering, the rolling and hammering being conducted in an inert atmosphere.

2. A process for producing powdered magnesium which comprises cold rolling crystalline magnesium obtained by sublimation to make the magnesium brittle by mechanically extending the magnesium crystals along a crystal axis, and disintegratin said cold rolled magnesium by grinding, the rolling and grinding being conducted in an inert atmosphere.

3. A process for producing powdered magnesium which comprises rapidly cold rolling crystalline magnesium obtained by sublimation to make the magnesium brittle by mechanicallyextending the magnesium crystals along a crystal axis, and hammering to disintegrate said cold rolled magnesium,v the magnesium having thereon a protective surface coating of low gravity liquid hydrocarbon.

to distort the crystals 4. A process of producing powdered magnesium which comprises embrittling malleable magnesium by rapidly cold rolling the bulk metal in a. manner to extend and distort the magnesium crystals along a crystal axis and then producing multiple cleavages in the magnesium crystals by subjecting the rolled metal to a hammering action until magnesium powder is produced.

5. The process of claim 4 wherein the cold rolled magnesium is covered -with a protective surface coating of low specific gravity liquid hydrocarbon before being subjected to the hammering action. a

6. The process of claim 4, wherein the cold rolled metal is disintegrated by grinding the same in an inert atmosphere.

7. The process of claim 4, wherein the magnesium powder is screened and the coarse portion is repeatedly subjected to cold rolling and hammering operations until the desired state of subdivision is reached.

HAROLD P. ANDERSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Noel, article in Transactions of American Institute of Mining and Metallurgical Engineers (1938) vol. 128, pages 37-41, noting particularly page 39.