JPH04168205A - Device for supplying powder for rolling - Google Patents

Abstract

PURPOSE:To manufacture a hoop-state powder compact body uniformizing density distribution in the width direction by beforehand making supplying quantity of metal powder fed to both ends in the axial direction of one pair of rolling rolls more than the supplying quantity to center part thereof. CONSTITUTION:Powder incorporating space 14 is formed with one pair of the side weirs 10, 11 and a front plate 12 and a rear plate 13 lower end of each side weir 10, 11 is formed to curving face 15 corresponding to peripheral faces of the rolling rolls R1, R2. At center position of height direction of this powder incorporating space 14, a slit plate 16 composed of one set of two pieces of slit members 16a, 16b is arranged and at the center part thereof, slit 17 (the whole length (l)). extended in the roll axial direction, is formed. Then, center part of the slit 17 is formed to the fixed width part 17a having the fixed slit width w1 over to the length l1, and continued to expanded width parts 17b expanded toward end parts, and the expanded width part 17b is formed with arc having radius (r) of curvature so that the slit widths (w2) at both end parts become the max. By this method, leakage of the metal powder is eliminated and the hoop-state powder compact body 20 having uniform density distribution to the width direction, is obtd.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention provides a method for rolling a compact powder body obtained from metal powder by powder rolling with a flow rate distribution that does not cause a decrease in density at both ends in the width direction. This invention relates to a device that supplies metal powder to a powder pool between rolls.

[Prior Art] Various methods including press molding have been conventionally employed as a method for obtaining products with a predetermined shape from powder raw materials. Among these, powder rolling is a method suitable for mass production as a method for continuously and efficiently producing strip-shaped compacts.

In powder rolling, a hopper containing powder raw material is arranged above a pair of rolling rolls installed horizontally or diagonally on a boat, and metal powder is poured from this hopper into a powder reservoir formed between the rolls. A strip-shaped green compact is obtained by rolling the powder through a roll gap.

At this time, the metal powder supplied to the powder pool between the rolling rolls has fluidity and therefore tends to flow out in the axial direction of the rolls.

Therefore, the amount of metal powder supplied tends to be insufficient at the axial ends of the roll gap, which causes a decrease in density and thickness at both ends of the produced band-shaped green compact. As a result, when the strip-shaped powder compact is sintered and rolled, defects such as cracks and breaks may occur at both ends of the product.

Conventionally, required characteristics are imparted to the product by cutting off both ends where such defects or defects are caused from the belt-shaped body after sintering or at the stage of compacting. However, if this cutting allowance becomes thick, the product yield will decrease and productivity will be hindered.

Therefore, in order to restrict the outflow of the metal powder supplied to the powder pool in the roll axis direction, side weirs are used to partition both ends of the powder pool. Even when this side weir is used, it is inevitable that a gap will be created between the lower end of the side weir and the circumferential surface of the rolling roll. Therefore, the metal powder supplied to the powder reservoir flows out to the side through this gap, and defects due to insufficient density still remain at both ends of the band-shaped green compact.

In order to prevent the metal powder from flowing out to the side, the present inventors developed a method of supplying a liquid for preventing the metal powder from flowing out to the circumferential surface of the rolling roll that comes into contact with the side weir, and disclosed in Japanese Patent Application No. 2-43890. The application was filed as

In this method, as shown in FIG. 5, both ends of a powder pool 3 formed between a pair of rolling rolls 1 and 2 in the roll axis direction are partitioned by side weirs 4 and 5, and metal powder is collected from above. supply. The metal powder 6 is sent to the roll gap as the rolling rolls 1.2 rotate, is rolled, and is sent out from the roll gap as a strip-shaped green compact 7. At this time, the lower end corner of the side weir 4.5 is placed at each of the four locations PI, Pg, Ps, and P4 facing the circumferential surface of the rolling roll 1.2.
Aim the liquid supply nozzles 88-8d of the book to release water.

A liquid such as an organic solvent is supplied to opposing locations P and -P4.

The supplied liquid becomes a liquid film 9 that wets the circumferential surface of the rolling roll 1.2 in the circumferential direction. This liquid film 9 traps the metal powder 6 that is about to flow out from the powder reservoir 3 in the roll axis direction through the gap between the side weirs 4, 5 and the circumferential surface of the rolling roll 1.2.

Further, the metal powder 6 wetted with the liquid film 9 is transferred to the rolling roll 1
, 2, and accumulated for a while as an aggregate on the circumferential surface of side weir 4, 2.
5 and the circumferential surfaces of the rolling rolls 1 and 2 are closed.

As a result, the metal powder 6 is prevented from flowing out laterally from the powder reservoir 3, and the supply amount is not insufficient even at the ends of the powder reservoir 3 in the roll axis direction, and the roll gap between the rolling rolls 1 and 2 is maintained. sent. Therefore, the obtained band-shaped green compact 7 has a uniform density in the width direction, so that the incidence of defects such as insufficient density and insufficient plate thickness is reduced. Then, the proportion of the metal parts that are cut off after the subsequent sintering process or rolling process is reduced, making it possible to manufacture a band-shaped metal body with a high yield.

[Problem to be solved by the invention] By supplying a leakage prevention liquid, metal powder 6
A certain degree of success can be achieved in preventing the lateral outflow of water. However, even in this case, there is a gap, however small, between the lower end of the side weir 4.5 and the rolling roll 1.2, so the outflow of the metal powder 6 cannot be completely prevented.

Moreover, the supplied liquid not only becomes a liquid film 9 (,
There is also a risk that the metal powder 6 in the powder reservoir 3 will be wetted and the smooth flow of the powder particles will be inhibited.

Furthermore, when a leakage prevention liquid is not used as in the conventional case, the amount of metal powder flowing out is large, and the proportion of the reduced density portions formed at both ends of the band-shaped green compact 7 in the width direction becomes large. As a result, the amount of trimming increases, and the product yield as a strip-shaped sintered body that satisfies the required properties decreases.

The present invention was devised to solve such problems, and by increasing the amount of metal powder fed into the powder pools at both ends of the roll axis in advance, the lower end of the side weir and the rolling The purpose is to offset the leakage amount of metal powder flowing out from the gap between the roll and the circumferential surface of the roll, and as a result obtain a band-shaped green compact with a constant density distribution in the width direction.

[Means for Solving the Problems] In order to achieve the object, the rolling powder supply device of the present invention is a device that supplies metal powder to a powder reservoir provided between a pair of rolling rolls, and It is equipped with a pair of side weirs whose lower ends are formed in a shape along the circumferential surface of the roll and arranged in the roll axis direction, and a slit plate for dropping metal powder into the powder reservoir, and a slit plate formed on the slit plate. The special feature is that the slit has a constant width at the center in the roll axis direction and widens at both ends. When fed to the roll gap, the flow state of the metal powder exhibits different behavior at the center and both ends in the roll axis direction. That is, in the central part, the metal powder flows down while contacting and rolling, while at both ends, friction against the inner wall surfaces of the side weirs is added to this. Therefore, the metal powder at both ends tends to flow down slowly. Moreover,
At both ends of the roll in the axial direction, metal powder inevitably flows out to the side from the gap between the lower end of the side weir and the circumferential surface of the rolling roll. As a result, the amount of powder supplied at both ends of the powder groove becomes insufficient, resulting in the formation of low-density portions at both ends of the band-shaped green compact.

The outflow of metal powder to the side of the powder groove is determined by the particle size of the metal powder used, the gap between the circumferential surface of the rolling roll and the lower end of the side weir, and the operating specifications such as rotation speed and rolling reduction rate. If they are the same, they show roughly the same tendency.

Therefore, we measured in advance the size of the reduced density portion and the amount of density reduction that occurred at both ends of the strip-shaped green compact after rolling, and applied an increased amount of metal powder to both ends of the powder groove. Both ends of the slit are made wide so that the metal powder is supplied to the metal powder, thereby canceling out the leakage of the metal powder and obtaining a strip-shaped green compact having a uniform density distribution in the width direction.

[Examples] Hereinafter, the present invention will be specifically described by way of examples with reference to FIGS. 1 to 4.

As shown in FIG. 1, the rolling powder supply device of this embodiment has a pair of side weirs 10 and 11 connected by a front plate 12 and a back plate 13 to form a powder storage space 14 in the shape of a square column. ing. The lower ends of the side weirs 10.11 are the rolling rolls R,,R
, and has a curved surface 15 with a protruding central portion. As a result, the powder storage space 1
At the lower end position of 4, the rolling rolls R,,R, and the side weir 10
, 11 is made as small as possible to prevent the metal powder supplied to the powder storage space 14 from flowing out in the roll axis direction.

A slit plate 16 is provided at an intermediate position in the height direction of the powder storage space 14.
is provided. At approximately the center of the slit plate 16,
A slit 17 extending in the roll axis direction is formed.

In the illustrated example, the slit plate 16 is configured as a set of two, and the slit plate members 16a and 16b are opposed to each other with a gap therebetween to form the slit 17. However, without being restricted to this, it is also possible to use a plate body in which - slit plates 16 have slits 17 formed therein.

As shown in FIG. 2, the slit 17 is a constant width portion 17a having a constant slit width w1 over a length I21 at the central portion in the roll axis direction. Then, in the constant width portion 17a, there is a widened portion 17b that becomes larger toward the edge.
are continuous. The widened portion 17b is formed, for example, by a circular arc having a radius of curvature r, and is designed so that the slit width w2 at both ends is the largest.

These slit width wl + W l + central length 2.1
The radius of curvature r, etc. varies from a normal straight slit to a powder groove 18 between rolling rolls R+ and Rm with metal powder 19.
It is determined based on the density distribution in the width direction of the band-shaped green compact 20 when the band-shaped green compact 20 is produced by supplying. Note that the total length β of the slit 17 is made to match the width of the target strip-shaped powder compact 20.

Slit width W 1 , W z + total length! , center length β1゜radius of curvature r, etc. are not uniquely determined, but depending on the fluidity of the metal powder used, the side weir 10゜11 and the roll R, , R, clearance, etc., they are approximately as follows. become that way.

The slit width W is arbitrarily set in order to obtain a predetermined powder flow rate. However, in order to obtain a stable powder flow rate, a gap larger than a certain window is required, and a smaller gap makes it difficult for the powder to flow. For example, when passing steel powder produced by water atomization, a gap W of about 1 mm or more is required.

The slit width w2 is determined by the degree of density reduction at both ends of the molded body, but is usually about 1.1 to 1.5 times the slit width W+ at the center.

The central length 12+ is set depending on the size of the area where the density decrease occurs at both ends of the molded body, but it is usually about 60 to 80% of the total length i of the slit.

The curvatures of both ends of the slit do not necessarily have to be constant, and a curve that provides the most constant density and plate thickness of the molded body can be selected. However, when considering the problems in manufacturing the slit, it is easiest to form it with a circular arc. In this case, if we set the circle for the straight part β1 of the slit,
The radius of curvature r of a circle is expressed by the following equation from a geometrical relationship.

4 4 (Ws - wt) For example, as a comparative example, a straight slit (total length β
= 180 mm, width w = 1.4 mm) using a slit plate 17 that was adjusted to 150 um or less
High-speed tool steel powder equivalent to grade 5KH51 is supplied as metal powder 19 to the powder reservoir 18 at a flow rate of 2600 g/min.
A strip-shaped green compact having a size of 80 mm and a plate thickness of 2.0 mm was manufactured. The obtained strip-shaped green compact 20 had a density distribution in the width direction shown by the dotted line in FIG. In addition, the density ratio in Figure 3 is
The theoretical density is assumed to be 100%, and it is expressed as a ratio to that.

In this case, more metal powder 19 leaks out in the roll axis direction through the gap between the lower end curved surface 15 of the side weir 10.11 and the circumferential surface of the rolling rolls Rl, R*, and There was a tendency for the metal powder to be supplied to both ends in the direction to be insufficient. As a result, as shown in FIG. 3, the density of the obtained strip-shaped green compact 20 is significantly reduced to 70% at both ends, and the portion where the target green compact density of 83% or more is obtained is
It remained within a range of 120 mm at the center in the width direction.

Therefore, a slit plate 16 in which the slits 17 were formed by increasing the width of both end portions 17b continuous with the constant width portion 17a under the following conditions was used, and a band-shaped green compact 20 was manufactured under the same conditions.

1=180mm 121=120mmw+ =l
, 4mm wt = l, 7mmr = 3mm The strip-shaped powder compact obtained by using the slit 17 with its both ends widened has an almost uniform density distribution in the width direction, as shown by the solid line in Fig. 3. Met.

As is clear from this comparison, the slit 17 of the example of the present invention
The flow rate of metal powder 19 supplied to powder reservoir 18 through It can be seen that the area where the green compact density decreases is
The density remained within 10 mm from both ends of the band-shaped green compact 2o, and the lowest density was also 80%.

In addition, the lower end of the side weir 10.11 and the rolling roll RI,
The amount of metal powder that leaked out from the gap between R* and the peripheral surface was the same as when a conventional straight slit was used. After the metal powder 19 that flowed out was collected, it was returned as it was to a hopper (not shown) provided above the side weirs 1o and 11, and was reused for powder rolling.

In this way, by preventing a decrease in the green compact density at both ends, in order to obtain a strip-shaped sintered compact with the required characteristics, the portion that is cut off from the strip by trimming before or after sintering can be cut off as shown in Figure 4. I was able to make it smaller as shown. As a result, the product yield was 66.7% in the comparative example, while it was 88.9% in the inventive example.

[Effects of the Invention] As explained above, in the present invention, a slit plate is used in which the flow rate of the metal powder supplied to both ends of the powder reservoir is larger than that at the center. As a result, it is possible to offset leakage in the roll axis direction, to obtain a band-shaped powder compact with a uniform density distribution in the width direction, and to reduce the amount of trimming that is cut off due to insufficient density.

Therefore, it becomes possible to manufacture a belt-shaped sintered body that satisfies the required characteristics at a high yield.

[Brief explanation of drawings]

Fig. 1 shows a powder supply device for rolling according to an embodiment of the present invention, Fig. 2 is a diagram for explaining the shape of the slit, and Fig. 3 shows the density distribution in the width direction of a powder-rolled strip-shaped green compact. Graph, Figure 4 is a graph showing the trimming allowance when both ends with insufficient density are cut off in order to obtain a belt-shaped sintered body that satisfies the required characteristics, and Figure 5 is a graph showing the trimming allowance when the ends of the belt-shaped sintered body that are insufficient in density are cut off in order to obtain a belt-shaped sintered body that satisfies the required characteristics. It is a figure for explaining the manufacturing method of powder. 10.11: Side weir 12: Front plate 13: Back plate 14: Powder storage space 15: Curved surface 16: Slit plate 17: Slit
17a constant width part 17b: widened part 18: powder reservoir I2 total length of slit I21 = length of constant width part w
1 Width of the constant width part w2: Width of both ends r: Radius of curvature of the widened part Figure 2 Figure 3 □ Widened slinot - distance from the center of the straight slit in the width direction (mm)

Claims (1)

[Claims] (1) A device for supplying metal powder to a powder reservoir provided between a pair of rolling rolls, the lower end of which is formed in a shape along the circumferential surface of the rolling rolls, and the pair of rolling rolls arranged in the axial direction. and a slit plate for dropping the metal powder into the powder reservoir, and the slit formed in the slit plate has a constant width at the center in the roll axis direction and widens at both ends. A rolling powder supply device characterized by: