US1930684A - Method of manufacturing bronze colors - Google Patents

Description

Oct. 17, 1933. E KRAMER 1,930,684

METHOD OF MANUFACTURING BRONZE COLORS Filed Sept. 29, 1930 L IH F A Q I. 2 86 1 I 3% In N \o N m r! INVENTOR. a n ERWIN KEHMEH- I *1 BY 2 a A TTORNE Y.

Patented Oct. 17, 1933 UNITED STATES mn'rnon or MANUFACTURING nnonzr:

conoas Erwin Kramer, Berlin, Germany, assignor to Hartstofl-Metall Aktiengesellschaft tag), Berlin-Collenick, Germany (Hame- Application September 29, 1930, Serial No. 485,284, and in Germany September 30, 1929 2 Claims.

My invention relates to a method of manufacturing bronze colors with the aid of devices "or apparatus or machines designed similar to, and operating like, ball-mills, except that in this particular manner by the suitable dimensioning of balls and their effect of falling and by the choosing of a suitable radius of curvature of the balls small metal parts, as, for instance, foil waste, pulverulent metal, little thin pieces of wire and the like, are expanded or flattened. Transforming the respective metallic pieces or particles into pulverulent state is preferably carried out similar to the process disclosed in German Patent No. 410,514, but when that process is adapted to bronze certain difficulties are encountered; these difficulties are eliminated by the present invention.

It is old, in connection with the pounding of bronze, to add an oil or a fat to the respective metal in order to prevent the particles to adhere to'the wall of the pounding vat, as well as to get welded together by the heat. While, however, the amount of oil or fat can be easily regulated where pounding vats or troughs are used in view of the comparatively small dimensions of these receptacles, matters are quite otherwise if a large number of steel balls must be used, that is to say, where such balls are the operating members or tools, especially if the balls are to act in drums of a long axial length. The difiiculties met with are still greater if the expanding or flattening operation is to be carried out continually or uninterruptedly, viz in that the metal particles enter the drum at one end and the pulverulent metal leaves the drum at its other end.

Because of the metal particles being expanded or flattened the original oil or fat film with which they were provided becomes ever thinner, and simultaneously therewith the particles move from one end of the drum to the other end. While, thus, the amount of the oil or fat is comparatively great at the inlet end of the drum, it decreases considerably on the way of the particles to the other end of the drum, and if the film becomes very thin then arises the danger that the metal particles adhere to the balls whereby the operating surface of these latter becomes irregular and the expanding or flattening procedure is no longer carried out in the desired and necessary manner. On the contrary, the metal particles which are already very thin are ground down to such a degree that the bronze finally obtained is practically useless. Besides, also the surface of the steel balls is affected and destroyed so much that they become unsuited for further use, and instead of expanding and flattening the metal particles grind them into pulverulent state.

On the other hand, a too large amount of fat into bronze, but if that material is foil waste which is torn to pieces and must be further subdivided.

Now, the present invention aims at reducing the time of the passage of the metal particles through the drum, or, in other words, the time during which no further fat or oil is supplied to the material in the drum. That purpose can be attained in two different ways, the one consisting in reducing the length of the drum and the other in blowing more powerfully through the drum. It is, however, also possible to combine these two means with one another.

The treated material leaving the drum is conducted to a sifting device in which from the finished particles are separated those that are not yet in a finished state. These latter particles are returned to the drum so as to be treated a second time, and when being re-introduced they are supplied with an additional amount of oil or fat, either directly or by their contact with the fresh particles which carry sufiiciently much oil with them, since do also the balls.

Shortening the length of the drum means also a reduction of the manufacturing costs thereof, and, furthermore, a smaller space is required to house it. Besides, the entire arrangement and combination of parts can be smaller and also a correspondingly lesser number of steel balls is required, and since also the amount of the metal particles, i. e. the more or less reduced metal in the drum, is smaller, the danger of an explosion is reduced. The smaller supply of the drum with the metal to be treated involves the further advantage that the machine when in continual operation reaches more quickly a stable uniform operation which is favorable to the quality of the product which is more uniform or, more precisely speaking, highly uniform. The reduction in the time during which this state is attained is also important if now one metal and then another metal is to be treated and converted into bronze, the more so because prior to the working of the other metal, the first must be completely removed from the machine, i. e. from the drum.

Making use of a current of air of such a strength that not only the finished particles are carried out of the drum, but also larger particles is advantageous also in another respect. The separation of the fine and the coarse particles is connected with certain difliculties. It must be borne in mind that the sectional area which is available in the drum for the air passing through it is limited, as the dimensions of the drum, especially its diameter, must be determined or chosen from a commercial point of view, and furthermore, the fine particles tend to adhere to the coarse ones whereby the separation is rendered even more difilcult. While in grinding other substances in ball mills it is generally desired to attain a very fine grain it is otherwise with bronze because attention must be paid to the particles beingand remaining fiat or foil-like, since otherwise their light-refracting capacity ceases which is that particular property by which bronze is distinguished. Particles that have become too small impair the good appearance of the product and render it more or less dark or even black, and it is hardly or not at all pomble to remove such particles afterwards by sifting, as their fineness is already by far too small, considerably below the finest sieve having 10000 meshes to the square centimeter. The too small particles possess furthermore the disagreeable property of grinding down the brone foils whereby the product may be rendered practically useless. 7

With the known grinding process in a ball mill the mutual grinding down of the individual particles plays, a very important part. If, however, the grinding in the ball-mill is carried out according to the present improved method, the manner of operation of the mill is materially changed in that the metal particles are -so worked that they are converted into foils, but this working procedure must be continued only to a certain extent, viz until the desired product has been attained, because otherwise, if the drum containing the balls continues to act upon the material the latter is turned into a poorly looking powder ofbrown or grey color. Interrupting the procedure is the more 'difiicult, the finer the bronze is to be. At any rate, care must be taken that that operation of the mill by and during which the metal particles are transformed into bronze changes to that other operation at which the material is merely ground in the ordinary manner.

Now, the object in view is attained, according to this invention, by the utilizing of the current of air conducted through the mill in a particular manner. While in the old method of operating ball mills in connection with a current of air the chief object is to attain a possibly fine powder and the blast serves solely the purpose of carrying the powder out of the mill, but is of no infiuence upon thesize or shape of the particles, the blast, in the present improved method, is used to prevent the production of too fine a powder or, in other words, to prevent carrying the disintegration too far, and to remove finished particles prior to their being destroyed. Thus, the form of the individual particles of the material can be acted on by means of the blast.

In any event, there is this difficulty as regards the removal of the finished particles at the proper time, that many thereof are held fast by and between the balls or are held down by the continually falling balls. It is, therefore, necessary to make the blast considerably stronger than would be sufilcient to carry away the finished particles, and it is a part of this invention to carry away also particles that are more or less unfinished and to separate them from the other ones in a separate apparatus especially designed for this purpose. An important part of this apparatus is a sifter which can be ad- Justed just to the desired sifting fineness withi,oao,ee4

out any change oflthe strength of the blast. With the usual or ordinary slfters,-the velocity of the blast can be diminished by means of a throttle-fiap or the like, but, of course, the velocity is then reduced not solely in thesifter but in the entire circuit of the blast, and thus also in the flattening drum. The sectional area of the sifter is of course made larger than the sectional area of the drum so that the speed of the blast in the sifter is lower than in the drum, and certain of the particles which the blast carries away can drop. The resistance of the sifter to the blast is comparatively low, and according to this invention that resistance is still more reduced in order to attain a still greater sifting fineness, and that reduction is effected by increasing the sectional area of the sifter. This means, of course, a reduction of the speed of the blast, so that the finer particles can fall down.

That larger sectional area cannot entail a slow-- er flow of the blast through the drum, but it may be that the fiow is accelerated. But since the resistance which the sifter presents to the blast is very slight, as has already been mentioned, the variation of the sectional area of the sifter is practically of no influence upon the fiow of the blast in and through the drum. That speed-which'has been found as being the most favorable for the purpose in view is substantially maintained.

Because of the employment of steel balls with short radius having mathematically only points at which they contact with one another and between which only minute amounts of the small metal particles can be present or retained, the possibility is presented to produce particularly thin and, therefore, particularly valuable bronze, and the particular manner of sifting permits to remove the respective particles from the drum just when they are in the proper condition or state, before they are destroyed.

Anyhow, the finer the bronze, the greater is the danger of explosion, especially if aluminium bronze is being made, and it has, therefore, already been proposed to fill the drum with an indifferent gas, for instance hydrogen, in order to remove oxygen completely from the apparatus. But, nevertheless, fine aluminium bronze, irrespective of whether it is in an atmosphere of air or of hydrogen, possesses the property to decompose automatically when it comes in contact with fresh air. This behaviour is due to the fact that the fine powder has taken up a large amount of the gas and has retained it by absorption. It is then a mere matter of chance whether the powder explodes or not. This is at once comprehensible in the presence of oxygen in the powder, but, in fact, also hydrogen is not able to serve as a protective in the air. Just as platinum sponge commences to glow in the open air when a current of hydrogen is conducted onto it, so the same phenomena take place when the finely distributed or subdivided aluminium is saturated with hydrogen.

It is obviously very important to keep the gases 1 parts of the apparatus through which the bronze has to pass are kept filled with a gas or gas mixture containing neither oxygen, nor hydrogen, also no illuminating gas, but such gases as nitrogen, carbonic acid and helium may be used.

Also anhydrous gases. as combustion gases, can

be employed. The metal particles are, as it were, provided with a protective skin by which the danger of the particles igniting at the open air is very considerably reduced, nearly to zero.

In order to-carry the method into practice I prefer to make use of the apparatus shown diagrammatically and by way of example on the accompanying drawing in which Figure 1 is chiefly a vertical longitudinal section through, and partly a side-view of, an apparatus designed according to this invention, and Figure 2 is a transverse section in the plane A-B of Fig. 1.

The metal particles to be flattened which are in pulverulent state are contained in a receptacle 1 from which they are conveyed through a tube 3 by means of a screw conveyor 2. 4 is an oiling device for supplying said pulverulent metal particles with oil which drops down upon them while they pass through the tube 3. The oiled particles are conveyed by the conveyor to the tubes and tubular members 5, 9 and 10, and through this latter member they pass into the rotatory drum 12 which contains the steel balls 15. The ends of the drum are conical and these conical ends are separated from the cylindrical main part of the drum by coarse sieves 13 and 14 that permit the pulverulent particles to enter into the drum but retain the balls therein. The steel balls are the means or members by which the flattening of the metal particles is effected.

The drum is rotated by any suitable means. I have abstained from showing such means as they are known in the art and do not form a part of this invention. The blast is produced by means of a blower 16. The air is forced through tubes 17 and 30, from which latter it is conducted into the passage 29 and further through the tubular member 10 into the drum. Those particles of the powder which the blast can carry away are carried by it through the sieve 13 into the drum where they are acted on by the steel balls, and thereafter the treated, i. e. flattened particles are further carried by the blast through the sieve 14 into the tube 18 and through this into the top member 19 of the sifter. The body 20 of this is quadrangular in transverse section and in it are provided superposed oblique sheet-metal plates 21, the uppermost of which is the first that receives the powder. From this plate the powder falls successively overall other ones, that is to say, only upon the lowermost portions thereof, through the oblique passages 24 in the direction indicated by the arrows 23, and while thus being conducted, it is subjected to the action of the blast so that those particles which are in the proper condition are carried upwards through between the plates 21. There are shown as an example four such passages, viz 34, 35, 36 and 37, and they all terminate in a passage 25 through which the product passes into a so-called cyclone 26 or into an equivalent apparatus in whichthe bronze particles and the blast are separated from one another. The finished bronze falls down into a vessel 27, or an equivalent member. The air leaves the cyclone through the pipe 28 by which it is returned to the blower 16. Those metal particles that have fallen down into the lowermost part of the sifter body are conveyed into the tubular member 29 by means of a rotary blade-valve 31 that is driven in the suitable manner by any suitable means.

Instead of the oil receptacle 4, any other suitable oiling device may be used. The oil may be stearin oil or the like. Another such or similar oiling device 6 isprovided at an enlarged portion '7 of the pipe 5, and a third device for the purpose in view is the oiling device 8 which is provided upon the top of the tubular member 30. It is, thus, possible to oil either only the fresh material introduced into the apparatus from the receptacle 1, or also the particles that have left the sifter through the members 31 and 29, the oil being in this case introduced into the blast streaming through the pipes 17 and 30. The kind of the fat or oil and the amount used in the several oilers depend upon the kind of the metal and upon the shape of the metal particles. It is possible to use only one oiling place; that must be ascertained by tests. It is, at any rate, favorable for the result or the success of the procedure to supply oil to those particles that have already made their way through the drum and the sifter and are returned to the drum in order to pass a second time through the circuit.

One may diminish the sectional area of the sifter, that is to say, of its body portion 20, by means of the flaps 32 and 33, of which the fiap 32 is shown in closed position and the other in open position. When the flap 32 is closed, as in Fig. 1, the passage 37 does no longer form a portion of the circuit, and when the flap 33 is closed, also the passage 36 does no longer form a portion of that circuit. The free sectional area can, thus, be varied accordirg to requirements, and the fineness of the product determined at will. This is always without any detrimental influence upon the drum, in that the sectional area of the drum remains unchanged, as does also the velocity of the blast on its flow therethrough.

As the circuit forms a closed path, it can be filled with an indifferent gas, as has already been stated.

If necessary or desirable, a hose filter, or a plurality of such filters, may be inserted between the pipe 28 and the cyclone 26 in order to free the blast completely from the metal dust. Finally, it is also possible to provide a plurality of sifting devices adapted to subdivide the bronze still more as to the fineness of the particles and to provide for this purpose a corresponding plurality of such receiving receptacles as 2'? or equivalents therefor.

I claim:

1. In the method of producing bronze colors in the shape of very thin metal foils in ball mills, in which through the ball containing drum there is conducted a gaseous current capable of carrying away from the drum the finished foils as well as materially larger unfinished metal particles and in which from the finished foils the unfinished metal particles are separated and returned to the drum, the step of supplying to the separated unfinishedmetal particles at the inlet end of the drum an additional amount of lubricant through contact with a fresh supply of lubricated particles.

2. The method as specified in claim 1, wherein the drum.

E'RWIN KRAMER.

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