Nozzle For Atomizing Molten Material

Abstract

A nozzle for atomizing molten material includes annularly arranged outlet openings for an atomizing agent with a central aperture for the molten material. The axis of each outlet opening is inclined in the vertical plane with respect to the vertical axis of the central aperture at an angle .alpha.. Each outlet opening axis is also skewed with respect to the central aperture axis so that in the horizontal plane it deviates therefrom by the angle .beta. . The angle .alpha. is between 20.degree. and 50.degree. and the angle .beta. is between 10.degree. and 40.degree. with greater angles .beta. being associated with greater angles .beta. and with smaller angles .alpha. being associated with smaller angles .beta..

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of copending application Ser. No. 543,156, filed Apr. 18, 1966, now abandoned.

Description

BACKGROUND OF INVENTION

The atomization of molten materials, especially of molten metals, has long been known. When a ring nozzle is used to achieve the atomization, the gaseous or liquid atomizing agent is caused to flow, generally at acute angles with respect to a stream of molten material traveling in free fall through that nozzle; when the nozzle is an annular slit nozzle, the atomizing agent accordingly issues therethrough in the form of a closed cone-shaped shell. On the other hand, a multiple-hole ring nozzle causes the individual streams of atomizing agent to issue in the form of an interrupted or skeletal cone-shaped shell.

In German Pat. No. 917,226 it has been proposed to introduce the atomizing agent tangentially with respect to the horizontally arranged nozzle ring structure, whereby an additional rotary motion about the nozzle axis is imparted to the atomizing agent issuing through an annular slit nozzle.

During the atomization, all reasonable means must be employed to prevent the stream of molten material, e.g. the metal stream, from being flung back into the region of relative subpressure produced by the atomizing agent issuing under pressure, because the nozzle would otherwise become clogged. As taught, e.g. in German Pat. No. 847,675, this difficulty can be obviated by allowing the atomizing agent, atomized so as to form a cone-shaped shell, to strike the stream of molten material falling down in vertical direction, or to strike its vertical axis at an angle .alpha..ltoreq. 20.degree.. The disadvantage accruing from so acute an angle of cone resides in the fact that the metal stream strikes the atomizing agent with some delay and accordingly at a moment when the metal stream is less hot and fluid. This results in the metal stream being torn by the atomizing agent in customary manner into fine and smooth particles which often have a rounded-off shape. At this relatively delayed moment, the energy inherent to the atomizing agent is but small. This means that fine grain fractions with a size of less than 0.050 mm. are obtained at unsatisfactory rates, and a determined proportion of oversize grains (>0.20 mm.) must be screened off and melted again.

A still further apparatus for atomizing molten metals, which also uses a multiple-hole ring nozzle, has been described in U.S. Pat. No. 2,956,304. In contrast with German Pat. No. 847,675, the angle .alpha. defined above, identified by the letter c in the U.S. Patent, is greater than 20.degree., i.e. varies from 20.degree. to 60.degree., and preferably from 40.degree. to 50.degree.. The atomizing agent is caused to issue in the form of rather flat streams which may strike the vertical axis of the metal stream at an angle varying between 0.degree. and 90.degree. and perpendicular to the angle c (=.alpha.). The atomizing agent streams or more accurately their vertical planes may finally diverge from the vertical axis at an angle d (=.beta.). Nothing having been disclosed as regards the size angle d (=.beta.) may have and the interdependence of the three angles, the expert cannot successfully reduce to practice the teachings disclosed therein.

SUMMARY OF INVENTION

The present invention relates to an apparatus for atomizing molten materials by means of an atomizing agent, wherein a stream of molten material is allowed to travel in free fall through the center aperture of a ring nozzle, and the atomizing agent is forced to travel under pressure through guiding channels, arranged concentrically about the said center aperture, and to issue in the form of guide streams producing, about the said stream of molten material, an inversed shell (more accurately a frustoconical-shaped shell), whose generatrixes include with the vertical axis of the molten material stream an angle .alpha., and wherein each particular guiding stream on that frustoconical shell diverges from that vertical axis at an angle .beta., which comprises adjusting or selecting the angle .alpha. to vary from >20.degree. to 50.degree., preferably from 30.degree. to 40.degree., and adjusting or selecting the angle .beta. to vary from 10.degree. to 40.degree., preferably from 25.degree. to 35.degree., smaller angles .alpha. being associated to smaller angles .beta., and greater angles .alpha. being associated to greater angles .beta.. The atomizing agents include gases, steam or water. They are generally sprayed under a guage pressure of 1 to 20, preferably 3.5 to 13 atmospheres.

The present invention relates to an improvement in or modification of a conventional ring nozzle for carrying out the above atomization which comprises, in horizontal arrangement, a hollow-nozzle ring structure which has associated pipe connections and, in its lower portion, is formed with nozzle-type openings arranged in annular fashion for the atomizing agent, with the center axes of the said outlet openings forming, in projection, about the vertical axis of the center aperture of the ring nozzle, an inversed frustoconical shell axially symmetrical thereto, whose generatrixes include with the said vertical axis an angle .alpha., and the imaginary vertical plane lying on each of the said projected center axes diverging from the said vertical axis at an angle .beta.. This type of a ring nozzle, known as such, is more especially characterized in that the angle .alpha. varies between > 20.degree. and 50.degree., preferably 30.degree. and 40.degree., and the angle .beta. varies between 10.degree. and 40.degree., preferably 25.degree. and 35.degree., smaller angles .alpha. being associated to smaller angles .beta., and greater angles .alpha. being associated to greater angles .beta..

In accordance with a further feature of the present invention, the nozzle-type outlet openings are bore-shaped, or slit-shaped, the individual slits being separated from each other by means of baffle plates, or are nozzle orifices which are exchangeable and universally swingable. At its narrowest region, the center aperture of the ring nozzle may be 4 to 10 cm. wide.

In a multiple-hole ring nozzle, the angles .alpha. and .beta. are determined by the direction of the single-bore channels in the nozzle body. On the other hand, in an annular slit nozzle, subdivided by means of baffle plates, the angle is chiefly determined by the position of those baffle plates. The function assigned to angle .beta. is to prevent the atomizing agent streams from forming a common point of intersection lying on the vertical axis of the melt stream, and to enable them instead to form an envelope circle about the said melt stream.

The whole atomization apparatus including melting furnace, pipes for supplying the atomizing agent, water tank for receiving and chilling of the atomized metal particles can be designed in customary manner. The single-outlet openings for the atomizing agent, which are disposed symmetrically on the nozzle ring, should comprise at least three, but no more than 100, and generally 40 to 60 openings. It is advantageous to use not less than about eight to 12 outlet openings because a pyramid having a tri- or octahedral base tends otherwise to be formed instead of an inversed frustoconical shell by the atomizing agent streams. Obviously the fewer the number of openings, the more skeletal the shell becomes.

THE DRAWINGS

FIG. 1 is a schematic illustration of an apparatus embodying one form of this invention in cross-sectional elevation; and

FIG. 2 is a schematic top plan view of the apparatus shown in FIG. 1.

DETAILED DESCRIPTION

FIG. 1 is an elevation view of a ring nozzle comprising an annular hollow chamber 1, pipe connections 2 and nozzlelike outlet openings 3 for the atomizing agent. The generatrixes 4 of the inversed frustocone-shaped shell, formed by the atomizing agent and surrounding in axially symmetrical relationship the vertical axis 5 of the ring nozzle center aperture 6, and the said vertical axis 5 include the angle .alpha.. In other words as is apparent from FIG. 1 the angle .alpha. is the angle formed in the vertical plane, by the atomizing stream with respect to the molten material passing through aperture 6. Thus this angle is defined by the vertical axis 5 and by the axis of the atomizing stream which lies on the generatrix 4. As is also apparent from FIG. 1 the outlets of the atomizing agent passageways are coplanar.

FIG. 2 is a schematic top plan view which clearly shows how each atomizing stream is skewed in the horizontal plane by the angle .beta. whereby the atomizing streams do not converge upon a common point but rather form a frustoconical-like shell having its apex at the circle 10. As the streams continue to fall there would of course be another mirrorlike frustoconical shell formed which would have the common apex 10. As is likewise apparent from FIG. 2 the angle .beta. is defined by the axis 4 of the stream with respect to an imaginary vertical plane 8 extending through vertical axis 5 and the point of discharge of the atomizing agent.

The ring nozzle in accordance with the present invention enables the adjustment or selection of a large angle .alpha. without any risk of the metal stream, which is about 1.0 to 1.6 cm. thick, being flung back. This means for the atomizing agent that it strikes the very hot and fluid metal stream relatively soon and practically with undiminished power which thereby undergoes obligatory atomization into fine metal powder including no more than slight proportions of oversize grains.

The present ring nozzle can be used for atomizing the most varied substances, e.g. slag, fertilizer salts, plastic materials and particularly metals and their alloys. The atomizing agents include water and steam and in addition thereto nitrogen, argon or air. The fact that oversize grains are always obtained in but minor proportions is especially advantageous. The individual oversize grain is more compact owing to the strong suction effect or subpressure produced by the nozzle and owing to some vacuum degasification taking place. This suction effect thus produces what might be considered a preatomization wherein the subpressure prevailing between the atomizing agent shell and the falling molten material attracts the molten material to break it up into a plurality of more or less coarse melt particles which are later atomized into fine particles by direct contact between the atomizing agent and the particles. The inclined position of the baffle or guide plates 14 of FIG. 1, or bores ensures that each individual stream of the atomizing agent issues through a bevelled nozzle channel, which means that the ring nozzle is operated outside critical pressure conditions as a Laval nozzle. Under critical pressure conditions, sonic speed is just produced in the narrowest cross-sectional area of the nozzle. Under overcritical pressure conditions, a speed higher than sonic can only be produced in Laval type or bevelled nozzles.

The following Examples illustrate the invention:

EXAMPLE 1

(Comparative Example)

Atomization of liquid iron by means of a ring nozzle in which angle .alpha. was 22.5.degree. and angle .beta. was 0.degree..

Attempts were made to atomize the liquid iron by means of steam under a gauge pressure of 2 atmospheres. This proved impossible as the liquid metal stream was flung back. Further increase of the steam pressure resulted in a portion of the steam issuing even through the neck of the nozzle.

EXAMPLE 2

(Comparative Example)

Atomization of liquid ferrosilicon (15 percent by weight Si) by means of a ring nozzle in which angle .alpha. was 22.5.degree. and angle .beta. was 5.degree..

The casting temperature was 1,430.degree. C., and the nozzle was charged with steam under a gauge pressure of 3.5 atmospheres. Screen analysis resulted in the following grain fractions:

At a gauge pressure above 3.5 atmospheres, the nozzle became clogged by liquid metal flung back.

EXAMPLE 3

Atomization of liquid ferromanganese (30 percent by weight Mn) by means of a ring nozzle in which angle .alpha. was 22.5.degree. and angle .beta. was 15.degree..

The melt had a temperature of 1,390.degree. C., and the nozzle was charged with steam under a gauge pressure of 5.5 atmospheres. Screen analysis resulted in the following grain fractions:

At a steam gauge pressure of more than 6 atmospheres, metal was again found to be flung back.

EXAMPLE 4

Atomization of ferromanganese (75 percent by weight Mn) by means of a ring nozzle in which angle .alpha. was 30.degree. and angle .beta. was 35.degree..

The casting temperature was 1,380.degree. C., and the nozzle was charged with steam under a gauge pressure of 3.5 atmospheres. Screen analysis of the powder resulted in the following grain fractions:

EXAMPLE 5

Atomization of liquid ferrosilicon (15 percent by weight Si) by means of a ring nozzle in which angle .alpha. was 40.degree. and angle .beta. was 35.degree..

The casting temperature was 1,440.degree. C., and the nozzle was charged with steam under a gauge pressure of 7.5 atmospheres. Screen analysis resulted in the following grain fractions:

EXAMPLE 6

The atomization was carried out by means of a ring nozzle of the type described in example 5. The casting temperature was 1,460.degree. C.

Ferrosilicon (15 percent by weight Si) was atomized by means of that nozzle which had been charged with steam to serve as the atomizing agent under a gauge pressure of 13 atmospheres. Screen analysis of the powder obtained resulted in the following grain fractions:

EXAMPLE 7

The atomization was carried out by means of a ring nozzle of the type described in Example 5. The casting temperature was 1,460.degree. C.

Ferrosilicon (75 percent by weight Si) was atomized by means of steam under a gauge pressure of 12 atmospheres. Screen analysis of the powder obtained resulted in the following grain fractions:

Claims

We claim:

1. In a ring nozzle for atomizing molten materials including a hollow nozzle ring structure having pipe connections thereto, a frustoconical outlet slit for discharging an atomizing agent therefrom, a central aperture for passing the molten material therethrough, the improvement according to which said frustoconical outlet slit is subdivided by sloped guide plates into separate uniform channels running around its circumference, the outlet openings of said channels being placed in a plane common to them perpendicular with respect to the axis of said central aperture, said frustoconical outlet slit forming an angle .alpha. with respect to the axis of said central aperture, said guide plates forming an angle .beta. with respect to a plane running through the axis of said central aperture; said angle .alpha. being between 20.degree. and 50.degree., said angle .beta. being between 10.degree. and 40.degree., smaller angles .alpha. being associated with smaller angles .beta. and greater angles .alpha. being associated with greater angles .beta..

2. A nozzle as set forth in claim 1 including means connected to said central aperture for feeding molten materials which thereafter becomes a powder substantially all of which is of grain size smaller than 0.05 mm. therethrough, and means connected to said outlet slit for feeding an atomizing agent therethrough.

3. A nozzle as set forth in claim 1 wherein said outlet openings are bore shaped.

4. A nozzle as set forth in claim 1 wherein said outlet openings are exchangeable and universally swingable orifices.

5. A nozzle as set forth in claim 1 wherein the narrowest portion of said central aperture is 4 to 10 cm. wide.

6. A nozzle as set forth in claim 1 wherein .alpha. is from 30.degree. to 40.degree. and .beta. is from 25.degree. to 35.degree..