JPH10265805A - Metallic powder sintered compact and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently determine the heating up rate at the time of degreasing and to prevent the crack, blister, etc., of metallic powder sintered compacts by previously executing the thermogravimetric analysis of green parts or the compd. constituting these green parts and degreasing the green parts at the heating up temp. determined from the results thereof. SOLUTION: The heating up rate Va( deg.C/h) at the time of degreasing the green parts is determined by the equation. In the equation, Vb( deg.C/h) is the heating up rate at the time of the thermogravimetric analysis, Wb(%/h) is the weight decrease rate of the compd. at the time of the analysis described above and Rb (wt.%) is the compounding pts.wt. of the org. binder of the compd. constituting the green parts. Ra (wt.%) is the compounding pts.wt. of the org. binder of the compd. which is a basis and Wa (wt.%) is defined to be the weight decrease rate at which the occurrence of the crack and blister in the metallic powder sintered compacts after sintering does not arise at the time of degreasing the green parts consisting of the compd. which is a basis and Ra=10, Wa=1 are specified.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal powder sintered body obtained by degreasing and sintering a green part obtained by injection molding a compound comprising a metal powder and an organic binder, and a method for producing the same.

[0002]

2. Description of the Related Art As a conventional method for producing a metal powder sintered body, there is a method described in Japanese Patent Publication No. 3-46522.

[0003] The above publication discloses that a green part is placed on an absorber and heated, and an organic binder melted by a pressure head due to a capillary phenomenon of the absorber is caused to flow from the green part to the absorber and is melted. Degreasing the organic binder, gasifying it and removing it as green outgas from the green parts (binder removal).
A production method for sintering to obtain a metal powder sintered body is described.

[0004]

The compound used in the method for producing a metal powder sintered body as described above contains several kinds of organic binders in order to add lubricity and shape retention during molding. Since these organic binders each have specific properties such as a melting point and a boiling point, there are various temperature ranges in which outgas is generated from the green parts at the time of degreasing depending on the type of the organic binder blended.

[0005] In order to examine the temperature region in which outgas is generated from the green parts, it is general to carry out thermogravimetric analysis of the green parts or a compound as a material thereof. FIG. 1 shows 7.7 injection-molded with a compound.
It is a graph which shows the result of thermogravimetric analysis of 2 g of green parts, the left vertical axis shows the heating temperature [° C.], the right vertical axis shows the weight [g] of the green parts, and the horizontal axis shows the heating time [h],
Curve A indicates the change in weight of the green part due to heating, and slope D indicates the rate of temperature rise during heating.

As shown in FIG. 1, the weight of the green part is greatly reduced in the region B and the region C. Since the temperature region and the slope of the curve A are different between the region B and the region C, different components have different components. It can be seen that the organic binder is gradually outgassed and removed from the green parts.

If the temperature is rapidly increased in a temperature region where a large weight loss occurs as seen in regions B and C, a large amount of outgas is confined inside the green parts, so that the sintered metal powder is sintered. Defects such as cracks and blisters occur in the aggregate, and the appearance quality is reduced.

In order to prevent cracks and blisters from occurring, make sure that outgas does not collect inside the green parts.
It is necessary to control the amount of outgas generated per unit time, that is, to optimize the rate of temperature rise in the temperature region (region B and region C in FIG. 1) where the weight of the green parts is greatly reduced.

However, in order to determine an appropriate heating rate, generally, several kinds of heating rates are arbitrarily determined in advance, and after degreasing and sintering, an optimum heating rate is selected. Since many error-based methods were used, it took a lot of time to determine the heating rate during degreasing,
Production efficiency was poor.

The present invention has been made in view of the above-mentioned problems of the prior art, and efficiently determines a heating rate during degreasing, and prevents defects such as cracks and blisters on a sintered metal powder. It is an object of the present invention to provide a method for producing a metal powder sintered body having excellent appearance.

[0011]

According to a first aspect of the present invention, an injection molding material (hereinafter, referred to as a compound) comprising a metal powder and an organic binder is subjected to injection molding, and the obtained green parts are degreased to obtain brown. In the method of manufacturing a metal powder sintered body that obtains a metal powder sintered body by sintering a brown part as a part, a thermogravimetric analysis of the green part or the compound constituting the green part is performed before the green part is degreased The rate of temperature rise during thermogravimetric analysis is Vb [° C./h], the weight loss rate of the compound during thermogravimetric analysis is Wb [% / h], and the compounding part of the organic binder of the compound constituting the green part is Rb [ wt%],
The compounding amount of the organic binder of the compound as the standard is R
a [wt%], when degreasing a green part composed of a reference compound, the weight loss rate per unit time to prevent cracks and blisters in a sintered metal powder sintered body is represented by Wa [% / h. When Ra = 10 [wt%] and Wa = 1 [% / h], the green parts are degreased at a heating rate Va [° C / h] that satisfies Equation 3 below. I do.

[0012]

(Equation 3)

According to a second aspect of the present invention, there is provided the method for producing a metal powder sintered body according to the first aspect, wherein the metal binder comprises the same organic binder as the compound subjected to the thermogravimetric analysis.
The organic binder compounding part by weight of the compound which is different from the compound subjected to the thermogravimetric analysis is Rc, and the organic binder compounding part by weight is Rc, and a green part is formed by the compound having the organic binder compounding part by Rc, and the following formula 4 is satisfied. The green parts are degreased at a heating rate Va ′ [° C./h].

[0014]

(Equation 4)

According to a third aspect of the present invention, in the method for producing a metal powder sintered body according to the first or second aspect, the compound includes paraffin wax, polystyrene, and ethylene-vinyl acetate as an organic binder. And a polymer.

According to a fourth aspect of the present invention, there is provided a metal powder sintered body having an excellent appearance manufactured by the method for manufacturing a metal powder sintered body according to any one of the first to third aspects. Features. (Function) According to the present invention, thermogravimetric analysis of a green part or a compound constituting the green part is performed in advance, and the result is substituted into Equation 3 so that the organic binder of the compound is based on the compounding part by weight of the organic binder of the compound. Even if the weight part deviates from the binder weight part, the weight loss per unit time when converted into the organic binder weight part (10 weight parts) of the compound based on the organic binder weight part of the compound. The heating rate is set such that the rate becomes 1 [% / h].

The above equation (3) is derived as follows. When the curve A shown in FIG. 1 is differentiated with respect to the elapsed time, the weight reduction [g / h] per unit time is obtained.

The amount of weight loss per unit time corresponds to the amount of gas generated per unit time, and green parts (corresponding to a compound for performing thermogravimetric analysis) if the organic binder blending parts and heating conditions are the same. And the type of organic binder.

The ratio (percentage) of the weight loss per unit time to the weight of the green part before degreasing is the weight reduction rate per unit time [% / h], and the weight reduction rate per unit time is: If the type of the organic binder and the heating conditions (heating rate) are the same, the volume of the green parts does not need to be considered, and the larger the organic binder compounding part is, the larger it becomes.

From the above, it can be seen that controlling the amount of gas generated per unit time to optimize the heating rate is equivalent to controlling the rate of weight reduction per unit time. On the other hand, the inventors have conducted intensive studies on the properties of the compound, and as a result, based on the case where the amount of the organic binder mixed with the metal powder is 10 parts by weight (10 [wt%]), the compounded organic binder mixed part Ra of the compound is based on Ra. When the weight loss rate Wa per unit time exceeds 1% / h over the entire temperature range of the degreasing step, cracks and blisters are generated in the sintered product, and the appearance quality is reduced. Was found to decrease.

In addition, in the case of a compound which is an optional organic binder blending part by weight Rb other than the organic binder blending part by weight Ra of the reference compound, the upper limit of the weight reduction rate for preventing cracking and blistering is defined as the standard. It has been found that the ratio is proportional to the ratio of the organic binder compounding parts by weight Ra of the compound to the organic binder compounding parts by weight Rb (Rb / Ra: organic binder compounding parts ratio).

This point will be described with reference to Table 1.

[0023]

[Table 1]

Table 1 shows the four compounds including the reference compound.
It shows the correspondence between the organic binder components and the organic binder blending parts by weight Ra and Rb of each type of compound, and the weight reduction rate at which cracks and blisters do not occur in the sintered metal powder after sintering.

In Table 1, the reference compounds were paraffin wax (WAX) and polystyrene (P
S), ethylene-vinyl acetate copolymer (EVA), acrylic (PMMA) as the main components, and the organic binder compounding part by weight is Ra = 10 wt%, and the upper limit of the weight reduction rate that does not cause cracking or blistering (MAX) Is about 1.0 [% / h].

In contrast to the above-mentioned compound, compound I is mainly composed of WAX, PS, PP (polypropylene) and PMMA, and the compounding part by weight of the organic binder is Rb = 11 wt%, so that weight reduction without cracking or blistering occurs. The upper limit (MAX) of the rate is about 1.1 [% / h].

The compound II contains WAX and PA as main components, and the compounding part by weight of the organic binder is Rb = 13 wt.
%, The upper limit of the weight loss rate that does not cause cracks or blisters (MA
X) is about 1.3 [% / h].

The compound III contains WAX, polyamide (PA), EVA, and PMMA as main components, and the compounding part by weight of the organic binder is Rb = 6 wt%, and the upper limit of the weight reduction rate which does not cause cracking or blistering (MAX) Is about 0.6
[% / H].

From Table 1, it can be seen that the organic binder blending parts by weight Ra of the reference compound and the other compounds I to I
Taking the ratio Rb / Ra with the organic binder blending part by weight Rb of II, the weight reduction rate of the other compounds I to III for preventing cracks and blisters is represented by the ratio Rb / Ra.
It can be understood that the proportional coefficient is proportional to the weight reduction rate for preventing generation of cracks and blisters in the reference compound.

Further, an optional amount of an organic binder compounded by weight R
b) The ratio (Wa / W) of the weight loss rate Wb [% / h] when performing thermogravimetric analysis at an arbitrary heating rate Vb and the weight loss rate Wa [% / h] per unit time.
b) and the reciprocal (R
a / Rb) multiplied by the temperature rise rate Vb [° C./h] at the time of the thermal analysis, that is, the temperature rise rate Va is such that cracks and blisters occur in the sintered metal powder after sintering. Was found to be the upper limit of the heating rate.

From these results, Equation 3 was derived. In addition, the thermogravimetric analysis is performed by using the same organic binder as the compound subjected to the thermogravimetric analysis, and the organic binder compounding part by weight Rc of the compound which is different from the compound subjected to the thermogravimetric analysis. The value obtained by multiplying the reciprocal of the ratio (Rc / Rb) of the compound obtained and the organic binder blending part by weight Rb by the above-mentioned heating rate Va, that is, the heating rate Va ′ is the value of the sintered metal powder. They found that the upper limit of the heating rate was such that cracks and blisters did not occur in the sintered body, and led to Equation 4.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) This embodiment will be described with reference to FIG.

FIG. 2 shows the external shape and dimensions of the green part 1 in this embodiment. The green part 1 shown in FIG. 2 has a width of 12 mm, a height of 8 mm, and a length of 20 mm, has a longitudinal groove on one side surface, and has a concave cross section in the width direction.

The green part 1 is made of an organic binder mainly composed of paraffin wax, acrylic, polystyrene, and ethylene-vinyl acetate copolymer (EVA).
11 parts by weight (Rb = 11 [wt.
%]) Obtained by molding a compounded and kneaded compound.

Before degreasing the green part 1, a thermogravimetric analyzer (TGA) was used to obtain Vb = 50.
The thermogravimetric analysis was performed by heating the green part 1 at a rate of temperature rise of [° C./h]. As a result, the maximum weight loss rate in the thermogravimetric analysis was Wb = 2.2 [% / h].

The temperature at which the weight does not change is 370 ° C.
Met. Next, the above-mentioned Vb and Wb, and the organic binder blending part by weight of the reference compound Ra = 10
[Wt%], weight loss per unit time Wa = 1 to prevent cracking or blistering in the sintered metal powder when degreasing a green part made of a reference compound
[% / H] is substituted into Equation 3, and the temperature rising rate at the time of degreasing is Va =
It was determined to be 20.7 [° C./h].

Next, from normal temperature, 370 ° C. at which degreasing is completed
Up to Va = 20.7 [° C./h]
After maintaining at 0 ° C. for 5 hours, degreasing was completed. The time required to raise the temperature from room temperature to 370 ° C. was 16 hours and 54 minutes.

Then, the obtained brown parts are
Sintering was performed under a vacuum of 0 ° C., and the appearance of the obtained metal powder sintered body was measured. As a result, no cracks or blisters were observed, and the appearance quality was good. (Embodiment 2) In this embodiment, the green parts 1
The components of the organic binder of the compound are the same as those in the first embodiment, and the compounding amount of the organic binder is 10 parts by weight.
The green part 1 shown in FIG. 2 was molded by an injection molding method using a compound by weight (Rc = [10 wt%]).

In this embodiment, since the components of the organic binder are the same as those in the first embodiment, the result of the equation (1) in the first embodiment is used as it is, and the above Rb and Rc are used in the equation (4).
Is calculated to obtain a heating rate Va ′ = 22.7 ° C./h, and the temperature is increased to 370 ° C. as in the first embodiment.
After holding for a time, the degreasing was completed.

The time required to raise the temperature from room temperature to 370 ° C. was 15 hours and 25 minutes. Then, after sintering the obtained green part 1 under the same conditions as in the first embodiment,
When the appearance of the obtained metal powder sintered body was measured, cracks, blisters and the like were not particularly observed, and the appearance quality was good. (Embodiment 3) This embodiment will be described with reference to FIG.

FIG. 3 shows the external shape and dimensions of the green part in the present embodiment. The green part 2 shown in FIG. 3 is a solid body in which one side wall has a convex curved surface, and has a maximum width of 18 mm, a height of 8 mm, and a length of 25 m.
m, the front width is 12 mm, and the back width is 10 mm.

The green part 2 was obtained by molding a compound obtained by mixing and kneading 6 parts by weight of an organic binder mainly composed of paraffin wax, polystyrene, EVA, polypropylene and stearic acid with 17-4PH powder. Things.

Before degreasing the green parts 2, a thermogravimetric analyzer (TGA) was used to obtain Vb = 30.
The thermogravimetric analysis was performed by heating the green part 2 at a rate of temperature rise of [° C./h]. As a result, the maximum weight loss rate in the thermogravimetric analysis was Wb = 0.8 [% / h].

The temperature at which the weight does not change is 350 ° C.
Met. Next, the above-mentioned Vb and Wb, and the organic binder blending part by weight of the reference compound Ra = 10
[Wt%], weight loss per unit time Wa = 1 to prevent cracking or blistering in the sintered metal powder when degreasing a green part composed of a reference compound
[% / H] is substituted into Equation 3, and the temperature rising rate at the time of degreasing is Va =
It was determined to be 62.5 [° C./h].

When the green part 2 is heated from room temperature and degreased at this heating rate, the paraffin wax softens rapidly and the shape of the green part 2 is entirely deformed.

Therefore, the green parts 2 are degreased at a relatively gentle rate of 25 [° C./h] until 120 ° C., at which the removal of paraffin wax is almost completed, at a rate of 120 ° C./h.
Heating was performed at 62.5 [° C./h] from the temperature range exceeding ° C., and the temperature was maintained at 350 ° C. for 5 hours, thus completing the process.

Then, 13 parts of the obtained brown parts 2 were obtained.
The metal powder sintered body obtained by sintering in a vacuum at 20 ° C. and quenching the solution heat treatment and the precipitation hardening treatment was free from cracks, blisters, etc., and had a good appearance quality. . (Comparative Example 1) After the green part 1 described in the first embodiment is heated and degreased at the heating rate (22.7 ° C.) determined in the second embodiment, and then sintered as in the first embodiment, Then, cracks and blisters of the obtained metal powder sintered body were measured.

At this time, the metal powder sintered body had a swelling of 0.5 mm at the center of the upper surface from the periphery, that is, blisters were recognized, and the appearance quality was deteriorated. (Comparative Example 2) One green part 1 described in the second embodiment
Heat to 20 ° C at a heating rate of 25 [° C / h],
In the temperature range exceeding 0 ° C., the temperature is increased to 370 ° C. at the same heating rate (Vb = 50 [° C./h]) as in the thermogravimetric analysis by TGA, and further maintained at 370 ° C. for 5 hours, followed by degreasing. Finished.

This is further reduced to Embodiments 1 and 2.
Sintering was performed under the same conditions as described above, and the obtained metal powder sintered body was confirmed. As a result, the central portion of the upper surface was raised, further cracking occurred, and the appearance quality was reduced.

As can be seen from the results of each of the above embodiments and comparative examples, the effect of the method of the present invention is clear, and it is possible to manufacture a metal powder sintered body having no defective appearance such as cracks and blisters. Becomes

[0051]

According to the present invention, the rate of temperature rise during degreasing for producing a metal powder sintered body having excellent appearance without cracks and blisters can be easily set, that is, the degreasing conditions can be efficiently adjusted. It can be set in a short period of time, and is particularly effective when degreasing and sintering a thick product in which cracks and blisters are easily generated.

[Brief description of the drawings]

FIG. 1 is a graph showing the results of thermogravimetric analysis of a compound.

FIG. 2 is a diagram illustrating shapes and dimensions of green parts according to the first and second embodiments.

FIG. 3 is a diagram showing the shape and dimensions of a green part according to a third embodiment.

[Explanation of symbols]

 1,2 green parts

Claims (4)

[Claims] An injection molding material (hereinafter, referred to as a compound) comprising a metal powder and an organic binder is subjected to injection molding, and the obtained molded body (hereinafter, referred to as a green part) is degreased to obtain a brown part. And, in the method of manufacturing a metal powder sintered body to obtain a metal powder sintered body by sintering the brown parts, before degreasing the green parts, a thermogravimetric analysis of the green parts or the compounds constituting the green parts, The rate of temperature rise during thermogravimetric analysis was Vb [° C./h], and the weight loss rate of the compound during thermogravimetric analysis was Wb [% /
h], Rb [wt%] is the compounding amount of the organic binder of the compound constituting the green part, and R is the compounding part of the organic binder of the reference compound.
a [wt%], when degreasing a green part composed of a reference compound, the weight loss rate per unit time to prevent cracks and blisters in the sintered metal powder sintered body is represented by Wa [% /
h], and Ra = 10 [wt%] and Wa = 1 [% /
h], the heating rate Va [° C. /
h) degreasing the green parts in step h). (Equation 1) 2. The composition comprising the same organic binder as the compound subjected to the thermogravimetric analysis, and the organic binder compounding part by weight of the compound which is different from the compound subjected to the thermogravimetric analysis is Rc, 2. The metal according to claim 1, wherein a green part is formed from a compound in which the organic binder compounding part by weight is Rc, and the green part is degreased at a heating rate Va '[° C./h] satisfying the following equation (2). A method for manufacturing a powder sintered body. (Equation 2) 3. The compound as an organic binder,
The method for producing a metal powder sintered body according to claim 1 or 2, wherein the method includes a paraffin wax, polystyrene, and an ethylene-vinyl acetate copolymer. 4. A metal powder sintered body having an excellent appearance produced by the method for producing a metal powder sintered body according to claim 1.