JPH04289103A - Production of press-compacted and sintered body - Google Patents

Abstract

PURPOSE:To determine optimum pressing conditions and to enable stable mass production by measuring the weight of a press-compacted body as a sample immediately after compacting and the weight after drying and calculating the bulk density of the compacted body. CONSTITUTION:A slurry is press-compacted with a metal mold, the weight WG of the resulting molded body is immediately measured and the volume VG of the compacted body is calculated from the measured dimensions of the mold. The compacted body is then rapidly dried with a drier, the weight WD of the dried compacted body is measured and the apparent density rhoa of powder forming the compacted body is calculated by an equation rhoa=WD/[VG-(WG- WD)/rho0]. The bulk density rhob of the compacted body is also calculated by equation I. In the equations, rhoG=WG/VG and rho0 is the specific gravity of a liq. forming the slurry. Since the bulk density rhob of the compacted body can rapidly be calculated and exact evaluation of the porosity is enabled even in case of high press compacting pressure, optimum press compacting pressure can always be determined.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing powder metallurgy products, in which a slurry is press-molded, dried and fired to produce a sintered body.

0002

[Prior Art] In the manufacturing process of press-formed sintered bodies,
In order to optimize the press molding conditions, the bulk density of the molded product is determined and the process is managed by feeding it back. By the way, the bulk density of a molded body is generally determined by weighing the molded body after drying it, then weighing it after the dry molded body absorbs the liquid to a saturated state, and then weighing the same saturated molded body used for saturated absorption. It is obtained by suspending it in a liquid and weighing it.

That is, a molded product is obtained using an appropriate press molding pressure, and then dried for about 10 hours at about 50° C. in a constant temperature bath.First, the dry weight W0 (g) of the molded product is measured, and then the dry molded product is is immersed in water and the atmospheric pressure is lowered to deaerate the air in the molded product and gradually moisten it with water.The time when there is no change in weight, it is considered to be saturated with water, and weighed in water W2 (g ), and then the wet molded body weight after removing the moisture adhering to the surface by pulling up the wet molded body is W1.
(g) and the apparent density of powder ρa (g/cm3)
and the bulk density ρb (g/cm3) of the molded body were determined from equations (2) and (3), respectively.

[0004] ρa = ρ0 / (1-W2 /W0
)...(2)
ρb = ρ0 / (ρ0 / ρa + W1
/W0 −1) (3) Here, ρ0 represents the specific gravity of water used for density measurement.

[0005]

[Problem to be solved by the invention] However, in the conventional method, it takes a long time for drying and wetting of the liquid after molding, and it is difficult to quickly obtain the optimum press molding conditions to ensure stability during mass production molding. It wasn't suitable for me. The second problem is that when the molding pressure is high, the porosity of the molded body decreases, but as shown in Figure 3, the porosity of the molded body is less than 40%, even though the same powder is used for molding. Due to insufficient liquid wetting, the apparent density tended to decrease linearly as the porosity decreased. Therefore, regarding the bulk density of the molded product, it is only possible to obtain a reasonable bulk density at a low molding pressure where the porosity is 40% or more, making it impossible to properly evaluate the molded product and changing the press molding conditions. Bulk density could not be applied to optimization.

The third problem is that the strength of the molded product after drying is 1.
Since the density decreases by 1/5 to 1/10, cracks or chips may occur during handling, which significantly increases the error in density measurement. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to obtain a high-precision bulk density of a molded body that can quickly determine the optimum press-forming conditions in the process of manufacturing a sintered body by molding slurry with a press, drying and firing. The present invention proposes a method for determining , which makes it possible to manufacture stable press-formed sintered bodies suitable for mass production.

[0007]

[Means for Solving the Problems] That is, in the process of manufacturing a sintered body by molding slurry with a press, drying and firing, the present invention collects a sample after press molding and calculates the weight WG and volume of the slurry as it is. VG is measured, then the molded body is dried to determine its weight WD, the bulk density ρb of the molded body is calculated based on equation (1), and this is used to optimize the press forming conditions. This is a method for manufacturing a press-formed sintered body.

[0008] ρb = ρa ・(ρG − ρ0 )
/(ρa −ρ0) …(1) However, ρa
= WD / {VG - (WG - WD ) / ρ0 }
ρG = WG /VG
ρ0: Specific gravity of the liquid constituting the slurry.

Incidentally, (volume occupied by the powder in the molded body) = (volume of the molded body) - (
(void volume in the molded body), (volume occupied by the powder in the molded body) = VG - (WG - W
D)/ρ0.

[0010] Accordingly, the apparent density ρa of the powder is
ρa = WD / {VG − (WG − WD ) / ρ0
} is easily found. By the way, the porosity ε of the molded body
is defined as ε≡(volume of voids in the molded body)/(volume of the molded body), so ρb = ρa (1-ε)
…(4)
It can be expressed as

On the other hand, the compact density ρG is expressed as ρG ≡WG
/VG, it can be expressed as ρG = (1 - ε) ρa + ερ0, so ε = (ρa - ρG ) / (ρa - ρ0 ),
By substituting this into equation (4), equation (1) is obtained.

Furthermore, in the present invention, by cutting each part of the molded product, the bulk density of each part of the molded product can be determined, and the distribution of the density can also be easily grasped.

[0013]

[Function] In the conventional method, it was necessary to dry slowly in order to maintain the condition of the molded product, but in the present invention, the only measurement after drying is weighing, so rapid drying can be performed. Furthermore, since the present invention does not require liquid wetting, the apparent density of the powder does not depend on the porosity, and therefore it is possible to obtain the bulk density with high precision even at high molding pressures, which was not possible with conventional methods. . In addition, in the conventional method, the binder from the molded body is removed,
In addition to requiring wetting and extra handling, the molded product after debinding is brittle and prone to cracking and chipping, so it was not possible to process it quickly. However, the present invention does not have these problems and can quickly produce high precision. Since the bulk density of the molded body can be determined, the optimum pressing conditions can be determined based on this, and stable mass pressing becomes possible.

[0014]

[Example] A slurry after wet pulverization of strontium hard ferrite magnetic powder is supplied to a uniaxial compression press, and a ring-shaped molded body is formed at a molding pressure of 100 to 500 kg/cm.
2 to obtain a molded body having a porosity in the range of 38 to 41%. To dry the molded body using the conventional method, dry at 60℃ for 12 hours in a constant temperature bath.
After drying for an hour, first measure the dry weight W0 (g) of the molded body, then immerse the dry molded body in water, lower the atmospheric pressure to deaerate the air in the molded body, and gradually moisten the water. When there was no change in weight, the sample was considered to be saturated with water and weighed in water (W2 (g)). Next, the wet molded body is pulled up and the weight of the wet molded body after removing the moisture adhering to the surface W1
(g), and the apparent density of the powder ρa (g/cm3
) and the bulk density ρb (g/cm3) of the molded body were determined from equations (5) and (6), respectively.

ρa = ρ0 / (1-W2 /W0
)...(5)
ρb = ρ0 / (ρ0 / ρa + W1
/W0 −1) (6) Here, ρ0 represents the specific gravity of water used for density measurement. To measure the density of a molded body using the method of the present invention, the molded body is weighed immediately after molding (WG (g)).
Then, from the dimension measurement of the mold, the volume VG (cm3)
was then rapidly dried in a dryer set at 300°C for 20 minutes to obtain the dry molded weight WD (g), which is expressed by formula (7).
The apparent density ρa of the powder and the bulk density ρb of the molded body were determined using equation (1).

ρa =WD /{VG −(WG
−WD )/ρ0 } …(7)
ρb = ρa ・(ρG − ρ0 )/(ρa − ρ
0 )...(1) However, ρG is the compact density, which is defined by equation (8). ρG ≡WG /VG
…
(8) FIG. 1 is an example of measurement by the method of the present invention, and shows the relationship between the apparent density and porosity of powder. Since liquid wetting is not necessary, the apparent density of the powder is constant regardless of the porosity, and the linear relationship expressed by equation (4) as shown in FIG. 2 was obtained between the bulk density ρb of the compact and the density ρG of the compact.

FIG. 3 shows the measurement results of the conventional method. According to this, although the powders are the same, when the porosity is less than 40%, the apparent density of the powders deviates from the same value and shows a linear relationship. Therefore, the monotonically decreasing linear relationship between bulk density and porosity ε, ρb = ρa (1-ε), becomes ρb = 3.82 (g/cm3) when ε=0, and as shown in Figure 4, Apparent body density 4.87g/
It deviates significantly from cm3.

On the other hand, since the method of the present invention does not require liquid wetting after drying the compact, the apparent density of the powder is constant regardless of the porosity, and the bulk density can be determined with higher accuracy than the conventional method. Regarding the relationship between bulk density and porosity, the method of the present invention shows a high linear correlation with the correlation coefficient (Equation 1) as shown in Figure 5, and even when ε = 0 (%), ρb = 4.85 (g/cm3). ) has a value close to the apparent density of powder.

[0019]

[Math 1]

[0020]

[Effects of the Invention] As described above, the present invention allows the bulk density of a molded body to be quickly determined, and also enables correct evaluation of porosity even when the press molding pressure is high, so that it is possible to always use the optimal press. It becomes possible to determine the molding pressure. As a result, it has become possible to stably produce a large quantity of press-formed sintered bodies of good quality.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the measurement results of the present invention, showing that the apparent density of the powder is constant regardless of the porosity.

FIG. 2 is a graph showing the measurement results of the present invention, showing that the bulk density has a linear relationship with the molding density with a correlation coefficient R=0.91.

[Figure 3] A graph showing the measurement results of the conventional method, with a porosity of 4
This indicates that the value does not reach a constant value when it is less than 0%.

[Figure 4] A graph showing the measurement results of the conventional method, where ε = 0 (%
) indicates a significant deviation from the powder apparent density.

FIG. 5 is a graph showing the measurement results of the method of the present invention, showing that there is a good correlation between porosity and bulk density.

Claims (1)

[Claims] Claim 1: In the process of forming a slurry with a press, drying and firing it to produce a sintered body, a sample after press forming is taken and its weight WG and volume VG are measured, and then the formed body is Production of a press-formed sintered body, characterized in that the weight WD of the body is determined by drying, the bulk density ρb of the body is calculated based on equation (1), and this is used to optimize press-forming conditions. Method. ρb = ρa ・(ρG − ρ0 )
/(ρa −ρ0) …(1) However, ρa
= WD / {VG - (WG - WD ) / ρ0 }
ρG = WG /VG
ρ0: Specific gravity of the liquid constituting the slurry.