JPS60221501A - Production of sintered metallic body - Google Patents

Abstract

PURPOSE:To obtain a sintered metallic body having high dimensional accuracy by molding the kneaded plastic material composed of sinterable metallic powder and synthetic resin binder then enclosing the molding with a granular backup material, decomposing thermally the above-described binder in the molding and sintering the molding. CONSTITUTION:A synthetic resin binder is added to a powder mixture composed of, for example, self-fluxing Ni alloy powder and ground Mo powder at a prescribed ratio and is thoroughly kneaded to prepare the kneaded material which is then heated to 100- 150 deg.C to evaporate the moisture in the binder. The kneaded material is heated to 80- 100 deg.C and is passed plural times through a roll machine, by which a sheet-shaped plastic material is obtd. The sheet-like plastic material is molded to, for example, circular cylindrical molding and thereafter the molding is put in a case and is enclosed with steel balls as a granular backup material. Such molding is installed in a vacuum furnace. The molding enclosed with the steel balls is heated from an ordinary temp. up to 650 deg.C. The moisture is first evaporated, then the binder is gasified and removed by thermal decomposition during this time. The molding from which the binder is removed is heated to 900-1,000 deg.C and is heated to the temp. exceeding, for example, the liquidus line, for example, 1,000-1,200 deg.C after calcination, by which the sintered metallic body, i.e., the sintered Ni body is obtd.

Description

[Detailed description of the invention] A0 Purpose of invention (11 industrial application fields The present invention relates to a method for manufacturing a metal sintered body.

(2) Conventional technology When manufacturing a metal sintered body, in order to facilitate the molding operation, a plastic material made by kneading sinterable metal powder and a synthetic resin binder is used, and this is molded into a predetermined shape. It has been proposed that the synthetic resin binder in the molded body is then thermally decomposed and the metal powder is sintered.

(3) Problems to be Solved by the Invention In the above method, if no bank-up means is taken during sintering of the metal powder, the sintered body will undergo dimensional changes due to expansion, resulting in approximately There is a possibility that a deviation of nearly % may occur.

In view of the above, it is an object of the present invention to provide the above-mentioned manufacturing method capable of suppressing expansion of a sintered body by simple means.

B0 Structure of the Invention (11 Means for Solving Problems) The present invention comprises a step of molding a plastic material obtained by kneading sinterable metal powder and a synthetic resin binder into a predetermined shape to obtain a molded body, and The molded body is characterized by using a step of wrapping the molded body with a granular back-up material, and a step of thermally decomposing the synthetic resin binder in the molded body and sintering the metal powder.

(2) Function The pressing force of the hack-up material suppresses dimensional changes in the metal sintered body due to expansion, thereby improving the dimensional accuracy of the metal sintered body.

(3) Example [Example I] 1. Production of plastic material 80 parts of Ni self-fusing alloy powder and 20 parts of MO pulverized powder are sufficiently mixed in a ■-blender to obtain a mixed powder.

A synthetic resin binder is obtained by mixing a tetrafluoroethylene resin emulsion and an acrylic resin emulsion at a ratio of 1:1.

Add 3 parts of synthetic resin binder to 100 parts of the above mixed powder and knead thoroughly using a table kneader.
The water in the synthetic resin binder is evaporated by heating to 00 to 150°C. The obtained kneaded product has a shape of numerous nodules due to being caked by the synthetic resin binder.

The above-mentioned kneaded material is heated to 80 to 100° C. and passed through a roll machine several times to obtain a sheet-like plastic material. In this case, if the rolls of the roll machine are heated to the same degree as the kneaded material, the sheet forming operation can be easily performed. The obtained sheet-like plastic material has appropriate flexibility and tear strength at room temperature.

ii. Production of sintered bodies Using the above-mentioned sheet-like plastic material, cylindrical molded bodies F1 to F with a diameter of 20 cranes and a length of 20 dragons are formed using a pressing force of 1 kg/m'', and these are subjected to a sintering treatment. give

During the sintering process, in the case of compact F, Figure 1 (a
, ), put it in a container 1, and the molded body F1
is wrapped in a steel ball 21 as a granular back amplifier material with a diameter of 0.5 to 1 Tsuru and a linear expansion of 11 x 10-''/'c,
The container 1 is placed in a vacuum sintering furnace 3.

In the case of the molded body F2, it is placed in a container 1 as shown in FIG. 1 (a2), and the molded body F2 is placed in a No. Wrapped with sand 2□, the container 1 is placed in a vacuum sintering furnace 3.

In the case of the compact F3, it is installed in the vacuum sintering furnace 3 without a bank-up material, as shown in FIG. 1 (a3).

Then, the organic substance is decomposed and the metal powder is sintered under the heating-cooling conditions shown in FIG. Nitrogen gas or highly reducing hydrogen gas is used as the carrier gas.

(A) First heating zone (Fig. 3A) This heating zone A is from room temperature to 650°C, and the temperature increase rate is 10~b. In the heating zone A, water first evaporates, and then the Fluorinated ethylene resin and acrylic resin decompose and gasify. These synthetic resins have a temperature of 300 to 400℃
However, in consideration of heat conduction, most of the organic substances were removed by soaking at 600-650°C for 90 minutes, and Ni self-soluble alloy-M' was produced.

A green compact made of powder is left behind. In this case, Figure 1 (al
), (a,), the steel ball 2 is used as a back-up material.
Although 1 and the silica sand 2□ are granular, the generated gas is dissipated from the back-up material through countless continuous pores between the steel balls 2□ and between the silica sand 22.

(B) Second heating zone (Fig. 3B) This heating zone B is in the range of 900 to 1000''C, and the green compact is heated to the solidus line of the Ni self-fluxing alloy (1010 to 10
20° C.) or lower, for example, 950° C., for 30 minutes to perform a solid phase sintering treatment, and then pre-sinter this. The temperature increase rate in the first heating zone A is 10-b.The compact in the vacuum sintering furnace 3 is heated from its surface and increases in temperature, so the temperature rises at a predetermined rate until the entire compact reaches a uniform temperature. Heating time is required. If the sintering temperature is 1000
If it is suddenly heated to ~1200°C, a temperature difference will be created in the green compact, which will increase the variation in porosity, making it impossible to obtain a uniform sintered body, and also making it likely that defects such as cranks will occur after sintering.

In the second heating zone B, undecomposed organic substances are completely gasified and removed.

(C) Third heating zone (Fig. 3C) This heating zone C is located at the solidus line (101
0~1020℃) to just below the liquidus line (1075~1,08℃)
5°C), i.e., in the range of 1000 to 1200°C, and the pre-sintered body is heated to a temperature exceeding the liquidus, for example, 1100 to 1180°C, preferably 1120°C, for 12
A sintered body is obtained by holding the temperature at a constant temperature for 0 minutes and performing a liquid phase sintering process by melting the Ni self-fluxing alloy. In this case, the flow of the Ni self-fusing alloy is hindered by the presence of MO, and therefore shape retention is good.

The temperature increase rate from the second heating zone B is 15 to 20'c 7
minutes, and since the pre-sintered body has already been heated to a high temperature in the second heating zone B, the time required to raise the temperature to the third heating zone C is short. If the holding time in the third heating zone C is insufficient, sintering will not be completed completely, resulting in defects in the sintered body.

- (D) Cooling zone (Figure 3 D) This cooling zone D includes a primary cooling zone D from the sintering temperature to approximately 800°C, and a secondary cooling zone D2 from approximately 800°C to approximately 400°C. and a tertiary cooling zone D3 from approximately 400° C. to room temperature.

The primary cooling zone D is a stable region of the sintered body at high temperatures.In this cooling zone D, thermal stimulation is avoided as much as possible, and at the same time, cooling is performed slowly at a maximum rate of about 2°C/min in consideration of cooling efficiency. Cool at speed. When rapid cooling is performed in this cooling zone D, cranks occur frequently in the sintered body.

In the secondary cooling zone D2, cooling is performed at a slow rate of about 3° C./min at maximum. If rapid cooling is performed in this cooling zone D2, there is a risk that the sintered body will frequently crack.

In the tertiary cooling zone D3, the temperature of the sintered body is cooled to room temperature by gas cooling (including air cooling) other than liquid cooling such as water or oil.

When the elongation rate of the three sintered bodies obtained through the above steps was measured before and after the sintering treatment, the results shown in the table below were obtained. In the table, sintered bodies f, ~f3 are molded bodies F1~F
3 respectively.

As is clear from the table above, the molded body F made of plastic material
, ~F3, the sintered bodies f, , f2 obtained using the bank amplifier material 21.2□ are suppressed from expanding due to the pressing force of the hack-up material 21.2□ during sintering. Therefore, the elongation rate is significantly reduced compared to the sintered body f3 obtained without using the bank amplifier material.

[Example ■]

Formation of the workpiece molding part of the mold As shown in FIG. 3(a), a tank mold material 4 is cast from cast steel (JIS SC46 material). This mold material 4
is used as-cast, and an acrylic resin adhesive is applied to the base surface 4a having a black crust after cleaning.

As shown in FIG. 3(b), a sheet-like plastic material similar to that in Example 2 was pasted on the base surface 4a, and pressed using a female model M with a pressure of 0.5 kg/Tsuru 2. , a molded body F4 having the same shape as the workpiece forming portion is molded.

As shown in FIG. 3(c), the mold material 4 is placed in the container 1, and the molded body F4 is used as a back-up material' for the steel balls 2I.
The container 1 is placed in the vacuum sintering furnace 3, and the organic substance in the compact F4 is decomposed and the N
i. Sinter the self-fusing alloy-Mo powder.

As shown in FIG. 3(d), after the above steps, the mold material 4
A mold 6 having a workpiece forming portion 5 made of a Ni self-fusing alloy-MO sintered body f4 on the base surface 4a is obtained.

When the elongation in the thickness direction before and after sintering of each part X to Z in the workpiece molding part 5 of the mold 6 was measured using a three-dimensional measuring machine, the elongation in the thickness direction was 0.2 sva in the part X and 0.2 sva in the part y.
5 mm, and 0.1 ml T: in part 2, and it is clear that the dimensional change of the sintered body f is significantly suppressed by the hack-up material 2I.

In addition, as the hack-up material, mI steel balls, silica sand, spherical alumina, spherical ceramics, etc. can be used, and if necessary, the steel balls etc. can be partially bonded with an inorganic binder such as water glass. Then, the hack-up material may be molded to match the shape of the molded article. Further, the molding of the plastic material in the step of FIG. 3(b) is not limited to the case where the model M is used, but the plastic material may be semi-hardened and then subjected to grinding.

C0 Effects of the Invention According to the present invention, dimensional changes in the metal sintered body due to expansion are suppressed by an extremely simple method of wrapping a molded body made of a plastic material with a granular hack-up material, and metal sintering with good dimensional accuracy can be achieved. You can get a body.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention, and are shown in FIG.
(a3) is an explanatory diagram showing the sintering process of three compacts in the first example, FIG. 2 is a graph showing the relationship between temperature and time in the sintering process, and FIGS. 3(a) to (d) FIG. 2 is an explanatory diagram of a manufacturing process of a sintered body in a second example. F,, F,, F4... Molded body, f4... Sintered body, 2
1, 2□・・・Steel balls and silica sand as back-up materials

Claims (1)

[Claims] A step of molding a plastic material obtained by kneading sinterable metal powder and a synthetic resin binder into a predetermined shape to obtain a molded object, a step of wrapping the molded object with a granular bank amplifier material, and a step of forming a synthetic resin in the molded object. A method for producing a metal sintered body, comprising the steps of thermally decomposing a binder and sintering the metal powder.