KR790001890B1 - Process for the production of high apparatus density water atomized steel powders - Google Patents

Abstract

The method was designed to produce economically a high-density water-atomized steel particles of which at least 80% in the particles are finer than 80 mesh and the distribution accounts for a PSC value of 2.0-4.0, anneal the particles at a temp. of 1400-2100FO for a time sufficient to effect the desired softening and reduce the oxygen content, and feed the annealed, sintered particles to a disk mill operated at a speed of 200-5,000 revolutions per minute with a mill gap of 0.01-0.10 inches.

Description

Manufacturing method of high density steel powder

Figure 1 shows the effect of the rotational speed and particle size of the disk on the density at the milling interval 1/16 inch of the mill,

Figure 2 shows the effect of disk rotational speed and particle size characteristics on density at 1/64 inch of grinding interval.

The present invention relates to a method for economically producing high density steel powder by spraying water, and more particularly to increasing the density of such particles.

Various methods are currently used to manufacture metal powder. The methods include 1) electrolysis, 2) direct reduction of oxides, 3) metal reduction of halogen compounds, and 4) spraying fluids (eg water or inert gas) at high pressure.

In producing a large amount of the cast steel powder, metal oxide reduction and water spraying are relatively economical. Among the two methods, the steel powder made by spraying with water generally has a low metalloid content.

In addition, the metal powder produced by the water spray method is good in the powder metallurgy field because of the good fluidity and the efficiency of the raw material supply pressure. This process has a number of commercial advantages, but is somewhat limited due to the mechanical properties of the resulting powder. The density of steel powders produced by commercially available water spraying methods is generally in the range of 2. 8-3.2 gr / cc. Density is obtained by measuring the weight of the powder in the measuring cup.

However, since the density depends on the type of filling the powder, this measurement uses the standard method (ASTM B212-48). That is, the powder is poured through a hole of 0.1 × 0.125 inch on the top surface of the 25cc cup one inch.

The method for producing a high-density cast iron disclosed in the prior art has a very high carbon content and is therefore brittle and coarse, so its use is limited.

The powder produced by the water spray method is smaller than 80 mesh and the main distribution is smaller than 200 mesh, so this method is uneconomical because about half of the powder produced primarily cannot be used.

In addition, this method is not suitable for the production of steel powder with a carbon content of about 1.7% or less. The main purpose of this release is therefore a method for producing a steel powder having a density of greater than 3.2 gr / cc and preferably of greater than 3.2 gr / cc.

In addition, it is an object of the present invention to make the density of the powder equal to or greater than 3.2 gr / cc and to use most of the powder.

Another object is to provide a method for the production of cast steel powder with low strength and high density suitable for handling before sintering.

The content of the present invention will be described in detail as follows.

The method of the present invention is applicable to any steel powder produced by any water spray method.

Steel powders by water spraying methods generally contain impurities mainly in the form of oxides. However, it must be removed for commercial use in powder metallurgy. In order to maximize the extrusion rate of the steel powder, the carbon content of the final powder is preferably 0.1% or less, and more preferably 0.01% or less. However, it is not possible to obtain a molten steel raw material having such a low carbon content. Usually these raw steels contain up to 0.8% carbon, but below 0.15% are appropriate. And the carbon content of the atomized powder thereof is reduced by performing annealing in a decarburized atmosphere.

In the early stages of spraying, small particles of molten metal cool rapidly by spraying high pressure water.

Therefore, in the spraying process, even though steel with relatively low carbon content (no decarburization is required), annealing is necessary to give the flexibility and low oxygen content (less than 0.2%) of the steel powder.

The initial oxygen content of the powder particles by water spray exceeds 1.2% and generally reaches 1.0%. Due to the particle's appearance and high oxygen content on the surface, the sprayed individual particles will be denser. That is, it will exceed 3.2 gr / cc.

However, after annealing to reduce the oxygen contained, the density is within the range of 2.8-3.2 gr / cc.

F-2, 100

F에서 수소와 해리된 암모니아와 같은 환원분위기에서 실시한다.Annealing is carried out at a temperature of 1,400 for a time sufficient to give reduction of impurities and flexibility.

F-2, 100

It is carried out in a reducing atmosphere such as ammonia dissociated with hydrogen at F.

This annealing treatment not only purifies the steel powder but also fixes the particles to form a sintered agglomerate form, so it is necessary to crush and restore the powder as it is. In the process disclosed in the prior art, the method of crushing is achieved by a hammer grinder. In other words, the impact particles are to be circular particles at the time of atomization.

The present invention is to escape from this method and to carry out the true grinding process using a shearing mechanism in a disk mill.

By controlling this grinding process, the final density can be adjusted to the particles according to the size characteristics of the particles at the time of atomization.

The particle size of the nebulized powder is analyzed by conventional screen analysis. This screen analysis is applied to determine the particle size characteristics (PSC) of the powder. Excessive roughness among the sprayed particles may not achieve the object of the present invention. So in order to achieve the required grinding, the size of the sprayed powder must be at least 80%, suitably at least 95%, smaller than 80 mesh. Although there are various methods for defining the particle size characteristics, for the purposes of the present invention, the measurement of the particle size characteristics is carried out by the following method.

The cumulative weight ratio is first determined for the particles remaining on the pan and the US standard mesh screens of 325, 230, 140, and 100 100, and the cumulative percentage divided by 100 as a measure of particle size characteristics.

Therefore, in this classification method, in the particle size characteristic, the large dimension indicates coarse particle size and the smaller value indicates fine particle size.

For example, the particle size characteristics of the powder are as follows.

Therefore, the particle size characteristic of this powder is 204.2 / 100.0 or 2.04. Particles with a particle size characteristic of about 2.0-4.0 sprayed with water can be effectively used in the present process. Once the particle size characteristics are known and the powder is annealed, it will be ground appropriately according to the properties required. At this time, the disc friction grinder is applied to make the required grinding. After annealing, the particles are sintered in the form of agglomerates. If necessary, the annealing agglomerates should first be broken into particles generally smaller than 1 inch in order to feed the disc mill.

The grinding is performed between the disk and the disk rotating vertically or horizontally in the grinder, the raw material supply is supplied to the center of the disk and the supplied raw material is pulverized while going circumferentially by centrifugal force to exit the grinder.

Disc mills with protrusions on the discs are not suitable for the present invention and must be used with mills having conventional friction mills.

And here the grinding interval is the distance between the disc and the disc. Disc mills are particularly suitable for the purposes of the present invention. This is because such a pulverizer has a function of manufacturing a powder by adjusting and predicting the degree of grinding by basically adjusting the grinding interval and the speed of the average radius of the disc.

이 된다.In disc mills, the trajectory of the disc (grinding plate) is a circle (eg a circle with two centers). If the distance from the center to the disk (the grinding board), i.e. the distance from the center to the inner circle is r ₁ , the distance from the center to the circumference of the disk (the grinding board), i.e., the distance from the center to the outer circle is r ₂ . The average radius r _m is

Becomes

×12=72, 000

인치/분이 된다.At this time, the linear velocity V is equal to the angular velocity W multiplied by the radius. The linear velocity at any point of the average radius can be easily determined by the rotational speed of the disc. So, for example, a disk with 12 inches of r _m would have a linear speed (V) of V = Wr or V = 3,000 × 2 if the revolutions per minute were 3, 000 revolutions per minute.

× 12 = 72, 000

Inches / minute.

Inductive statistics and analytical analysis revealed that the influence of the above variables on the density of the final powder product was represented by the following relationship.

Density (gr / cc) = 2. 16 + 0. 30PSC-1. 28 x 10 ^-5 x V + 2. 87 x 10 ^-2 x LG + 1. 93 x 10 ^-6 x V x PSC + 4. 00 × 10 ^-11 × V ² -3. 96 × 10 ^-6 × V × LG

In the common sense

PSC has particle size characteristics of powder sprayed before annealing

V is the linear velocity at any point above the average radius of the disc (mill) and the unit is inches / minute

LG is the log of grinding interval (unit of grinding interval is inch)

Through the relational formula it is possible to control the properties of the specially required final powder according to the grinding cycle.

The graphs in Figures 1 and 2 will make this easier to understand. A disk mill with a 13-inch diameter disk at this time has an r _m of 5.31 inches. In simple terms (i.e. avoiding a stubborn number), the linear velocity V is determined by the rotational speed of the grinder. However, the graft is to be understood that it applies only to r _m of 5.31 inches grinder. Commercially, mills with larger diameters are used.

The curves of FIGS. 1 and 2 will be shifted towards the lower rotational speed as the size of the mill increases. Because the linear velocity V (at a given revolution per minute) becomes correspondingly fast.

Typically, these mills operate within the range of 200-5, 000 rpm and grinding interval 0.01-0.10 inches. The graphs of FIGS. 1 and 2 illustrate the powder state by screen analysis as examples below.

If powder A is used and the milling interval of the mill is operated at 1/16 inch (1st degree), for example, a density of 3.2-3.45 gr / cc is obtained by a rotational speed of 2, 500-3, 650 rpm. Able to know.

The effect of reducing the grinding interval can be seen by comparing with the second degree. If the same powder (A) was used at 1/64 inch grinding intervals, a similar density would be achieved at significantly smaller disk (grinding plate) rotation speeds. So only a rotation speed of 1,600 rpm would make a product with a density of 3.2 gr / cc, while a density of 3.45 gr / cc would be achieved at 2,775 rpm.

And finer powder B cannot be easily produced high density using a small diameter mill. Nevertheless, if the grinding interval is reduced to 1/64 inch as shown in Fig. 2, the same density can be made at rotational speeds of 3, 225 rpm and 4, 050 rpm, respectively.

From the above examples and relations, the density

A) When the particle size characteristics of the sprayed particles are increased,

B) When the disk (grinding plate) speed of the grinder is increased,

C) When the grinding interval becomes small,

It can be seen that the increase.

It can be seen that the density can be increased slightly by decreasing the annealing temperature at temperatures of 1, 400 ° F-2, 100 ° F. However, when annealing at low temperature, the annealing treatment time will have to be extended. Given these various conditions, the temperature range of 1,700 ° F -1,900 ° F is appropriate for obtaining high density products in a short time.

Claims (1)

At least 80% of the particles sprayed with water are less than 80 mesh and steel particles with a particle size characteristic of 2.0-4.0 are obtained for 1, 400 ° F -2, 100 for a time sufficient to obtain the necessary flexibility and to have an oxygen content of 0.2% by weight The annealing of the particles in the temperature range of ° F to cause sintering, and the annealing was carried out at a rotational speed of 200-5, 000, grinding interval 0.01-0. A method of producing a high density steel powder by pulverizing by supplying a cast steel powder having a density of more than 3.2 gr / cc to a disk mill operating at 10 inches to 80 mesh or less.

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