US1685956A - Whirling mill for the production of finely-divided powder - Google Patents

Description

WHIRLING MILL FOR PRODUCTION OF FINELY DIVIDED POWDER Filed Oct. 8, 1925 Z A. it

EMIL PODSZUS, 0F BERLIN-FBIEDRICHSHAGEN, GERMANY, ASSIGNOR TO HARTSTOFF- METALL AKTIENGESELLSCHAFT (HAMETAG), .OF BERLIN -COPENIGK, GERMANY.

WHIRLING MILL FOR THE PRODUCTION OF FINELY-DIVIDED POWDER.

Application filed October 8, 1923, Serial No My invention consists in a mill, which is capable of producing an extremely fine powder, and even a powder of colloidal fineness. The construction of the mill is based on the principle of causing comminution by the frequently repeated mutual impingement at a very high rate of speed, of the various particles of the material under treatment. Attempts already made in this direction have remained without success, because the mechanical action of beaters and the like on the particles of the material, and the hurling thereby of these particles against each other and against the walls of the mill does not result in producing the desired degree of fineness.

In the mill, according to my invention, the comminution is effected solely by the constantly-and very frequently repeated mutual impingement of the particles of the material as they are whirled around in the closed casing of the mill, by strong air currents produced by rapidly oppositely revolving propellers. In this manner, the material is within a short time, reduced to a powder of extreme fineness, without any appreciable wear of the parts of the mill, and practically with- I out contamination of the material. The comminution, even to a powder of colloidal fineness, is effected in a comparatively short time, because through the whirling air currents, the particles are caused to impinge upon each other with a strong abrading effect, at the rate of 1000 times or more per minute.

The mill is suitable for the reduction to an extremely finely divided powder of various materials and is especially effective in case of materials of comparatively high specific gravity. The comminuting effect is so great that even materials of great strength and toughness such as for instance metals, are quickly converted into a fine powder. As a starting material preferably coarse grained powder is used obtained in any well known manner, but the material to be disintegrated may also have the size of peas or even a larger size.

The new mill consists on the whole of a closed casing in which are mounted several opposed propellers.

In mills of similar construction, containing bladed wheels, the blades of the wheels produce a direct beating and hurling effect on the particles of the material. The particles as they are struck by the blades are hurled 667,163, and in Germany September 21, 1923.

against the walls of the mill or against specially provided parts. To a certain extent, the particles of the material are also hurled against each other, but only at more or less lnfrequent intervals of time, as the particles are set in whirling motion solely by the direct impinging action of the blades of the revolving wheels, whereby a centrifugal efi'ect is produced.

In the mill embodying my invention, propellers made in accordance with the latest experiences in aeroplane technics are arranged within the closed casing which propellers produce within the casing two or more mutually impinging violent currents of air of such high velocity that the particles carried along bythcse whirling currents are hurled against each other with great force, at the rate of 1000 times or more per minute. The propellers thus do not act directly but rather indirectly on the particles of the material. The propellers are so disposed. that the walls of the closed casing of the mill do not interfere with the generation of the rapidly whirling air currents, there being provided an unobstructed passage between the blades of the propellers, and the surrounding walls of the casing. The various dimensions are best determined in each case by experiments according to the size of the mill, the number of revolutions of the propellers, the material to be comminuted and so forth. It generally answers the purpose if the distance of the propellers (from the propellers) from the lateral walls of the casing is perhaps half as great as the distance of the propellers from each other. while, on the other hand. care must be taken to construct the casing in such a manner that the currents of air produced cannot evade each other, but are compelled to impinge upon each other.

If the mill shall be used for comminutinga material which tends to chemically combine with the air when in a disintegrated state, it is of advantage to fill the mill with an indifferent gas instead of'with air. In order to reduce the oxidizing eifect ofthe air contained in the mill, the latter which becomes heated to a considerable extent should be cooled on the outside, for instance by means of water. The cooling is of special importance when materials are comminuted which tend to weld or cake together during heat, such as, for instance, certain organic (ill substances and metals which are soft or have a low melting point. In this case, a farreach' coohngof the mill also, with solutions salts cooled down to a temperature below zero, or the like, should be efiected. In this manner, the efliciency of the comminuting process is considerably increased,

and in case of many substances for instance metals, only under those conditions a practical efiect is produced.

In the drawing Figures 1 and 2 shew in two sections vertical to each other a mill embod ingmy invention. In thecasmg 1 the sha 2 and 3 are rotatably mounted WhlCh are directly coupled with the high speed motors 14 and 15. The shafts 2 and 3 carry the propellers 4 and 5 which rotate in the oposite direction. The propellers 4 and 5 have such a pitch as to cause a vigorous axial forward thrust of the air. Two currents of air violently impinging upon each other are produced carrying along with them the material to be comminuted. As indicated by the arrows 6 and 7 the'currents of air separate after imp ging on each other forming cycles because 0 the air currents being drawn back to the rear sides of the propellers to be then thrust forward again towards the centre.

In order to make the action of the impinging air currents es cially effective, it is advisable to provide 1n front of the pro ellers flat arms -8 and 9 which are preferab y displaced relative to each other 90 degrees: these arms when properly shaped impart to the axially advancing air currents still a rotary movement, so that the particles which are carried along not only im inge upon each other but also rub each 0 er thereby abra'ding each otherto an increased extent. Within one second frequently repeated rapidly whirling air currents moving in o posite directions are formed which in a s ort time convert the material into an extremely finely divided owder. In a mill as shown not only whirling currents as indicated by the arrows 6 and 7 are produced, but also additional air currents as indicated by the arrows 10 and 11. The particles therefore are carried through cycles which in a most efl'ective manner pass through and against each other. For the purpose of cooling the mill the casing 1 is surrounded by a water jacket. The space therein may be filled with circulating water or with any other cooling liquid.

Very good results have been obtained with a casing shaped as shown in Fi re 1 where the casing ta ers approximate y from the point at whic 'the propellers are mounted like the shape of a unnel.

For charging the mill, openings 13 which can be closed are provided at suitable'places. The discharge may be effected through cortowards the bea-rin s for the shafts'2 and 3 responding openings, through which the pow- 1 dered material is blown out.

As has already been stated, the illustrations only show one embodiment of the new mill,

'for, of course various modifications can be made without departing from the nature of this invention.

I claim as my invention 1. In a comminuting device, the conibination with a closed casing having normally closed inlet and discharge openings, of rotatably journalled oppositely positioned air propellers ada ted to revolve in opposite directions and o a pitch to produce an axial thrust of the air within the said casing toward its center, thereby producing constantly mutually impinging rapid whirling air currents, said casing having recesses disposed rearwardly of the propellers comprising curved walls, and means for rotating the said propellers.

2. In a comminu'ting device, the combination with a closed casing having normally closed inlet and discharge openings, of rotatably journalled oppositely positioned air propel ers adapted to revolve in opposite directions and of a pitch, to produce an axial thrust of the air within. the said casing toward the center thereof, thereby producing constantly mutually impinging rapid whirling air currents, the said propellers being spaced from the inner walls of the said casing, said casing having recesses disposed rearwardly of the propellers comprising curved walls, and means for independently rotating each propeller.

3. In a comminuting device, the combination with a closed casing having normally closed inlet and discharge openings, of two rotatably ournalled oppositely positioned air propellers of a pitch to produce an axial thrust of he air within the said casing to- Wardthe Jenter thereof, thereby producing constan mutually impinging rapid whirling air currents, bearings for the propeller shafts formed in the walls of the said casing, said casing having recesses disposed rearwardly of the propellers comprising curved walls, and means for rotating the said propellers in opposite directions.

4. The combination as specified in claim 1, comprising flat arms disposed in front of the said propellers, the said arms being displaced relative to each other.

EMIL PODSZUS.

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