JPH0220687B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (1) Industrial Application Field The present invention relates to a method for forming a metal sintered layer on a metal substrate.

(2) Conventional technology Conventionally, when forming this type of metal sintered layer, a plastic material made by kneading sinterable metal powder and a synthetic resin binder is pasted onto the substrate, and then the plastic material is molded. A method has been proposed in which the synthetic resin binder in the molded layer is thermally decomposed and the metal powder is sintered.

(3) Problems to be Solved by the Invention According to the above-mentioned forming method, the degree of freedom in the form of the metal sintered layer can be increased and metal sintered layers having various shapes can be obtained, but on the other hand, it is possible to obtain metal sintered layers having various shapes. If some pressing means is not provided during sintering, the sintered metal layer will undergo dimensional changes due to expansion, resulting in a deviation of approximately 4% before and after sintering. In this case, the surface roughness of the sintered metal layer deteriorates depending on the pressing means, so unique measures are required to avoid this.

Further, unless the gas generated by the decomposition of the synthetic resin binder is efficiently removed, the remaining gas will corrode the sintered metal layer, causing problems such as deterioration of its quality.

In view of the above, it is an object of the present invention to provide a forming method capable of suppressing expansion of a sintered metal layer by simple means, improving the surface roughness of the sintered metal layer, and efficiently removing generated gas. With the goal.

B. Structure of the Invention (1) Means for Solving Problems The present invention provides a method for forming a sintered metal layer on a metal substrate by using a plastic material obtained by kneading sinterable metal powder and a synthetic resin binder. a step of adhering it onto the metal substrate; a step of molding the plastic material to obtain a molded layer; A step of closely adhering a sheet-like material formed from a kneaded product of a refractory powder and a synthetic resin binder, a step of wrapping the molded layer with a granular back-up material from above the sheet-like material, and a step of The method is characterized by using a step of thermally decomposing the synthetic resin binder and the synthetic resin binder in the sheet-like material and sintering the metal powder to obtain the metal sintered layer.

(2) Effect The pressing force of the back-up material can suppress dimensional changes in the metal sintered layer due to expansion and improve the dimensional accuracy of the metal sintered layer.

Since the sheet-like material has good conformability, it adheres well even to a molded layer having a complicated shape.

Since the surface of the sheet-like material is smooth, the relatively soft surface of the molded layer is not roughened. Moreover, the sheet material prevents the rough surface of the back-up material from being transferred to the surface of the molding layer, and this transfer prevention effect occurs after the synthetic resin binder in the sheet material is thermally decomposed during the sintering process. Also, between the back-up material and the metal sintered layer, there is a layer of refractory powder that is non-weldable and non-diffusion bondable to the metal sintered layer, and movement of this layer is prevented by the back-up material. The back-up material is not welded to the sintered metal layer, thereby improving the surface roughness of the sintered metal layer. After sintering, the refractory powder is easily removed from the metal sintered layer by brushing or blowing air, so that the surface of the metal sintered layer is not damaged during its removal.

The gas generated by thermal decomposition of the synthetic resin binder in the sheet material is removed through countless continuous pores with relatively large diameters formed between the granular back-up materials, so there are countless fine particles between the refractory powders. Continuous pores are formed. As a result, the gas generated due to the thermal decomposition of the synthetic resin binder in the molding layer is efficiently removed through the continuous pores between the backup materials rather than the continuous pores between the refractory powders.
It is possible to avoid problems such as corrosion of the metal sintered layer due to residual gas, and to prevent deterioration in the quality of the metal sintered layer.

In this case, when a molded layer is embedded in the refractory powder in order to give the refractory powder a backup function, the diameter of the continuous pores formed between the refractory powders becomes extremely small and the continuous pores become long. The escape of the generated gas becomes worse, and the generated gas tends to remain in the metal sintered layer.

(3) Example Production of plastic material 80 parts of Ni self-fusing alloy powder and 20 parts of Mo pulverized powder were
- Mix thoroughly with 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.

3 parts of a synthetic resin binder is added to 100 parts of the above mixed powder and thoroughly kneaded using a bench kneader, and the kneaded product is heated to 100 to 150°C to evaporate water in the synthetic resin binder. 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 will be easily performed. The obtained sheet-like plastic material has appropriate flexibility and tear strength at room temperature.

(ii) Manufacture of sheet-like products Fine refractory powder with a diameter of 5 to 500 μm that is non-weldable and non-diffusion bondable to the sintered metal layer.
5 to 10 parts of a synthetic resin binder, which is a 1:1 mixture of tetrafluoroethylene resin emulsion and acrylic resin emulsion, are added to the alumina powder, thoroughly kneaded in a table kneader, and the kneaded product is passed through a roll machine several times. Sheet material S with a thickness of 0.2 to 5 mm
get. The reason why the lower limit of the diameter of the refractory powder is limited to 5 μm as described above is that it is difficult to manufacture refractory powder with a diameter of less than 5 μm.

Formation of the workpiece forming part of the mold As shown in Figure 1a, cast steel (JIS SC 46 material)
Tank molding material 4 as a metal base
Configure. 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. 1b, the sheet-like plastic material is pasted on the base surface 4a, and the female model M is used to
Press with a pressure of 0.5 Kg/mm ² to form a forming layer F ₄ corresponding to the work forming part.

As shown in FIG. 1c, the sheet material S is brought into close contact with the surface of the molding layer ₄ . This sheet-like material S
has good conformability, so even if the shape of the molded layer F ₄ is complex, it adheres sufficiently to the molded layer F ₄ .

As shown in FIG. 1d, the mold material 4 is placed in a container 1, the molding layer _F4 is wrapped with a steel ball ₂₁ as a backup material from above the sheet material S, and the container 1 is placed in a vacuum sintering furnace. Set it to 3.

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

(A) First heating zone (Figure 2 A) This heating zone A is from room temperature to 650℃,
The temperature increase rate is 10-20°C/min. In this heating zone A, moisture first evaporates, and then the tetrafluoroethylene resin and the acrylic resin in the synthetic resin binder in the molded layer _F4 and the sheet-like material S are decomposed and gasified. These synthetic resins gasify at 300 to 400℃, but in consideration of heat conduction, they are kept soaked at 600 to 650℃ for 90 minutes to remove most of the organic substances, and a compressed resin made of Ni self-soluble alloy-Mo powder is used. Leaving a layer of powder and a layer of alumina powder. In Fig. 1d, the gas generated due to the thermal decomposition of the synthetic resin binder in the sheet material S passes through numerous continuous pores with a relatively large diameter formed between the steel balls ₂₁ serving as backup materials. As the alumina powder is removed, countless fine continuous pores are formed between the alumina powders. As a result, the gas generated due to the thermal decomposition of the synthetic resin binder in the molding layer _F4 is efficiently removed through the continuous pores between the backup materials rather than the continuous pores between the alumina powders.

(B) Second heating zone (Figure 2B) This heating zone B is in the range of 900 to 1000℃,
Solidus line of Ni self-fusing alloy (1010~1020℃)
A solid-phase sintering process is performed by soaking and holding at the following temperature, for example, 950°C for 30 minutes, and this is pre-sintered. The temperature increase rate from the first heating zone A is 10 to 20°C/min.

Since the powder layer in the vacuum sintering furnace 3 is heated from its surface and increases in temperature, a predetermined heating time is required until the entire powder layer reaches a uniform temperature. If you suddenly heat the powder to the sintering temperature of 1000 to 1200℃, a temperature difference will occur in the compacted powder layer, and the porosity will increase, making it impossible to obtain a uniform sintered metal layer, as well as causing cracks after sintering. Defects such as these are more likely to occur.

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

(C) Third heating zone (Figure 2 C) This heating zone C ranges from just below the solidus line (1010~1020℃) of the Ni self-fluxing alloy to the liquidus line (1075~1085℃)
, i.e. in the range of 1000 to 1200℃,
For example, the pre-sintered layer is heated to a temperature exceeding the liquidus line.
A liquid phase sintering process is performed by maintaining the temperature at 1100 to 1180°C, preferably 1120°C for 120 minutes to melt the Ni self-fluxing alloy to obtain a metal sintered layer. 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℃/
minutes, and since the pre-sintered layer 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 metal sintered layer.

(D) Cooling zone (Fig. 2D) This cooling zone D is approximately 800 m below the sintering temperature.
Primary cooling zone D ₁ up to ℃ and from approx. 800℃ to approx.
It is divided into a secondary cooling zone D ₂ up to 400°C and a tertiary cooling zone D ₃ from about 400°C to room temperature.

The primary cooling zone D ₁ is a stable area of the sintered metal layer under high temperatures. In this cooling zone D ₁ , thermal stimulation is avoided as much as possible, and at the same time, cooling efficiency is taken into account by cooling the sintered layer at a maximum of about 2°C/min. Cool at the set rate. When rapid cooling is performed in this cooling zone _D1 , cracks in the metal sintered layer occur frequently.

In the secondary cooling zone _D2 , cooling is performed at a slow rate of about 3°C/min at maximum. This cooling zone
If rapid cooling is performed in D ₂ , there is a risk that many cracks will occur in the metal sintered layer.

In the tertiary cooling zone _D3 , the temperature of the metal sintered layer is cooled to room temperature by gas cooling (including air cooling) other than liquid cooling such as water or oil.

As shown in FIG. 1e, through the above steps, a mold 6 is obtained which has a workpiece forming portion 5 made of a Ni self-fusing alloy-Mo sintered layer _f4 on the base surface 4a of the mold material 4. The alumina powder remaining on the surface of the metal sintered layer f ₄ is non-adhesive and non-diffusion bondable to the metal sintered layer f ₄ , so it can be removed by brushing, blowing air, etc. It is removed more easily than the sintered metal layer f ₄ , and therefore the surface of the sintered metal layer f ₄ is not damaged during the removal.

Each part x in the workpiece forming part 5 of the mold 6
When the elongation in the thickness direction of ~z before and after sintering was measured using a three-dimensional measuring machine, it was 0.2 mm at part x, 0.5 mm at part y, and 0.1 mm at part _z . It is clear that the dimensional change of the stratum f ₄ is significantly suppressed.

In addition, a sheet-like material S that adheres to the surface of the molding layer _F4
has a smooth surface, making it a relatively soft molding layer.
Will not roughen the surface of F ₄ . Furthermore, the sheet-like material S prevents the rough surface of the backup material ₂₁ from being transferred to the surface of the molding layer _F4 , and this transfer prevention effect is caused by the synthetic resin in the sheet-like material S during the sintering process. Even after the binder is thermally decomposed, there is a layer of alumina powder that is _non -weldable and non-diffusion bondable to the back-up material ₂₁ and the sintered metal layer _f4 , and that layer movement is prevented by the back-up material ₂₁ , and the back-up material ₂₁ does not weld to the metal sintered layer _f4 , thereby improving the surface roughness of the metal sintered layer _f4 . Becomes good.

Furthermore, the gas generated by the decomposition of the synthetic resin binder in the molding layer _F4 is efficiently removed through the fine continuous pores between the alumina powders as described above, so that the metal sintering caused by the residual gas It is possible to avoid problems such as corrosion of layer _F4 and prevent quality deterioration of the metal sintered layer.

In addition to the above-mentioned steel balls, silica sand, spherical alumina, spherical ceramic, etc. can be used as the back-up material, and if necessary, the back-up material can be made by partially bonding the steel balls etc. with a binder such as water glass. The material may be molded to match the shape of the molding layer. Furthermore, as the refractory powder, in addition to the alumina powder described above, zircon flour, silicon flour, etc. can be used. Furthermore, the sheet-like material is adhered to the molding layer with an acrylic resin adhesive,
It may also be possible to prevent the sheet from shifting.
Furthermore, the molding of the plastic material in step b in FIG. 1 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.

Furthermore, the present invention is naturally applicable not only to the manufacture of molds but also to the manufacture of other members.

C. Effects of the Invention According to the present invention, a plastic material obtained by kneading sinterable metal powder and a synthetic resin binder is used to form a metal substrate with the aim of increasing the degree of freedom in the form of a metal sintered layer. In carrying out the method for forming a metal sintered layer on a metal substrate, a molded layer made of a plastic material is molded on a metal substrate, a sheet-like material containing a specific refractory powder is closely attached to the surface of the molded layer, and the By using an extremely simple method of wrapping the molded layer with granular backup material from above, we have created a high-quality metal sintered layer with good dimensional accuracy, good surface roughness, and the removal of generated gas. can be obtained on the metal substrate.

Further, during sintering, an air-permeable dual structure of a layer of fine refractory powder and a layer of granular backup material is formed, so that generated gas can be efficiently removed.

Furthermore, since the surface roughness of the sintered metal layer is determined by the refractory powder, it would be possible to accurately control the particle size of the refractory powder and simplify the particle size control of the backup materials used in relatively large amounts. There are also some advantages.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIGS. 1A to 1E are explanatory diagrams of the mold manufacturing process, and FIG. 2 is a graph showing the relationship between temperature and time in the sintering process. F ₄ ... Molding layer, f ₄ ... Sintered layer, S ... Sheet-like material, 2 ₁ ... Steel ball as back-up material, 4 ...
...Mold material (base).

Claims (1)

[Claims] 1. In forming a metal sintered layer on a metal substrate, a step of adhering a plastic material obtained by kneading sinterable metal powder and a synthetic resin binder onto the metal substrate, and a process of molding the plastic material. a sheet formed from a kneaded mixture of a refractory powder and a synthetic resin binder that is non-weldable and non-diffusion bondable to the sintered metal layer; a step of bringing the shaped articles into close contact with each other; a step of wrapping the molded layer with a granular backup material from above the sheet-like article; and thermally decomposing the synthetic resin binder in the molded layer and the synthetic resin binder in the sheet-like article. sintering the metal powder to obtain the metal sintered layer,
A method for forming a metal sintered layer on a metal substrate.