FI62237B - FOER FARING FOR METAL POWDER GENOM FOERSTOFTNING - Google Patents

Description

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Patmtti-) »Board of Registry (44) Date of issue and date of issue. - 31.08.02

Patani och ragistarstyralsan '7 AmMan uthgd och uti-akrtfcan pubUurad (32) (33) (31) ^ «« y «» οΙΙμιι »—S * f« rd priori »* (71) Rutger Larson Konsult Ab, Eagersgatan 2, 211 25 Malmö, Sweden-Sweden (SE) (72) Ulf Rutger Larson, Ljungby, Sweden-Sweden (SE) (7 * 0 Qy Kolster Ab (5 * 0 Method for the production of annealed metal powder - Förfarande for framställning av metallpulver genom förstoftning

The present invention relates to a method for producing a metal powder by crushing a casting jet of flowing metal which, by means of a high-pressure spray directed towards the casting jet, is made to flow into a closed granulation chamber in which reducing conditions prevail.

Decomposition of metal melts with pressurized sprays, such as compressed air, nitrogen, argon, water vapor or water, is known in the art. In this case, the metal melt is fed from a melting tank arranged above one or more nozzles and provided with a bottom opening in the form of a casting jet which encounters a spray liquid flowing out of the nozzle at a high speed, whereby the casting jet disintegrates into fine droplets. In this case, it has been found that the metal powder thus prepared absorbs oxygen from the spraying agent during production, mainly surface oxygen bound to easily oxidizable parts of the alloy.

For example, in order to reduce the oxygen content of the alloy steel to the level of the acceptor, nitrogen or argon-based comminution has previously been used instead of the more common comminution with water or water vapor 2,62237. In this case, a spraying agent (gas) has been used, which is considerably more expensive and has considerably poorer grinding and cooling properties. However, for certain purposes, for example in the manufacture of a round powder, gas spraying is often preferred, so that the powder granules have the possibility of shrinking into a spherical shape.

In particular, there are problems in the production of low oxygen content precipitated powders because the goal is a fine-granular product. In this case, a larger amount of gas and thus a considerably larger amount of oxygen is required from the oxygen waste of the inert gases which are in contact with the molten casting jet, which results in higher oxygen concentrations of the powder formed. Preparation with oxidizing sprays such as water gives the opposite condition, i.e. an increase in the amount of water, because faster cooling lowers the oxygen content of the powder. In this case, however, it is impossible to reach concentrations as low as in the case of spraying with nitrogen gas or argon.

With the method according to the invention, which is characterized in that a reducing liquid is used as the spraying agent, it is possible to eliminate the above-mentioned disadvantages and to obtain a metal powder with a very low oxygen content.

According to the invention, the decomposition of the casting jet is carried out throughout the reducing environment in a substantially closed granulation chamber containing a reducing fluid in the reducing gas phase to collect and cool the metal powder formed by the action of the atomizer.

In the process according to the invention, the casting jet is thus subjected to a reducing spray, preferably a liquid hydrocarbon or a mixture thereof and, for example, petroleum products such as oil, benzene or the like. To protect the powder from oxidation, the comminution itself is carried out in a closed granulation chamber which is partially filled with a fluid and which is under an overpressure of a gaseous reducing agent. This also avoids the risk of explosion. Another advantage of the method according to the invention is that by adjusting the amount of the spraying agent, for example oil, in relation to the amount of metal, the carbon content of the finished powder can be adjusted.

The process according to the invention is preferably carried out by means of a device with a granulation chamber connected to the discharge vessel outlet, a pedal valve and a liquid locking function, a ***** inlet channel at the top of the chamber and often nozzles adapted to produce 3,62237 jets of spray liquid.

The invention will now be described in more detail with reference to a few embodiments shown in the accompanying drawings, in which Figure 1 shows an embodiment of a device used in the method according to the invention, Figure 2 shows a second embodiment, Figure 3 shows a third embodiment and Figures 4 and 5 show two different diagrams.

In Figure 1, the granulation chamber is generally denoted by reference numeral 1. Reference numeral 2 denotes a reducing liquid in the chamber, preferably heating oil 1, containing 86.8% of carbon, 12.5% of hydrogen, 0.58% of sulfur and 0.12% of ash. The chamber 1 is connected via a bottom opening 12 to a casting vessel 11 containing a metal melt 10. At the top of the chamber 1 there is a reducing gas inlet duct 3, and further inwards nozzles 14 for feeding the reducing spraying agent 15. The embodiments shown in Figures 1 and 2 have a liquid lock 9, which includes a pipe 6 connected to the chamber 1 by a valve 7, which lowers the liquid 8 in the lock 9 below the surface. The device shown in Figures 1 and 2 operates as follows:

The device is set up as follows. Before comminution, the valve 7 and the bottom valve 5 are closed, after which the granulation chamber 1 is filled with reducing agent up to the opening 12. When the whole granulation chamber is full, a reducing gas is fed through the pipe 3, while the level of the liquid is lowered to the desired level for future comminution. The valve 7 is then opened, whereby the reducing gas 4 in the upper part of the granulation chamber 1 maintains an overpressure corresponding to the height by which the pipe 6 extends into the liquid 8 in the liquid lock 9.

The comminution itself can now be performed, whereby the metal melt 10 flows down the casting vessel 11 through the opening 12 in the form of a metal jet 13 into which the reducing spray 15 flowing out of the nozzles 14 hits.

Figure 3 shows an alternative embodiment of the device, in which the liquid-locking operation is achieved by dividing the granulation chamber into lower parts 1 and upper parts 16, which are displaceable relative to each other. When the chamber is filled with liquid before the actual filling with gas, the lower part 1 is raised or alternatively the upper part 16 can be lowered, whereby the lower part of the upper part acts as a liquid lock tube 6 according to Figures 1 and 2. The advantage of the alternative embodiment shown in Fig. 3 is that the liquid lock has large dimensions and thus is more reliable than bits.

62237

Example

When casting approx. 10 kg of steel, the steel was allowed to drain down from the ladle into a graphite crucible with an outlet diameter of 6/5 mm. The molten casting jet was sprayed into a powder with oil from four diagonally downward, opposite nozzles (heating oil 1). Argon was used as the shielding gas, but other gases, such as nitrogen gas, can of course be used. The amount of oil used in this example was about 500 l / min. and a pressure of 5.5 kg / cm. It is clear from the examples that spraying with oil according to the invention results in very low oxygen contents of the powder as well as a certain carbonization effect. The prepared powder consists of particles in various shapes, such as cigar, potato and spherical. It was found that the finer particles were largely spherical and that the elongated granules were mainly in the coarser fractions.

Screening analysis of the prepared powder gave the following results: Eye width Powder

Microns% 3,360 0.37 1-680 2.03 841 18.36 599 23.80 420 24.85 210 24.66 149 4.26 105 1.30 74 0.23 53 0.12 fines ^ 53 0.02

The total oxygen content of the different grain sizes is shown in Figure 4 and the carbon content of the different grain sizes is shown in Figure 5. For comparison, the conventionally prepared iron powder of this coarse type with 1.2% Mn contains 0.76-1% oxygen (i.e. 7,600-10,000 mils).

Other chemical analysis of steel is as follows:

Si 0.57%, Mn 1.30%, P 0.017%, S 0.021%, Cr 0.16%, Ni 0.03% Mo 0.03%, Cu 0.05%, V 0.01%, Ti 0.01%, Al 0.007%.

The oxygen content of the steel was 86 ppm.

The invention is, of course, not limited to the embodiments described above, but can be modified in many ways within the scope of the following claims. According to the invention,