JPS5964702A - High-frequency sintering method of compressed body of metal powder - Google Patents

Abstract

PURPOSE:To shorten a time for sintering, by providing a heating accelerator inside or outside a compressed powdery body, and simultaneously heating both of the compressed powdery body and the heating accelerator with high frequency. CONSTITUTION:A heatinc accelerator member 3 constituted by tubular graphite 6 and a hollow tubular protective member 7 provided for hermetically sealing said graphite is provided, for instance, inside a compressed powdery body 2. The protective member 7 is formed out of ceramics, and a space between it and the graphite 6 is held in vacuum or filled with N2 gas. Herein, high frequency is formed by a heating coil 1 to simultaneously heat the compressed powdery body 2 and the heating accelerator member 3. Since the graphite 6 is heated at a temp. much higher than that of the compressed powdery body 2, the compressed powdery body 2 is heated by the heating coil 1, and the heating is accelerated by radiant heat and heat conduction from the graphite 6 at the same time.

Description

[Detailed Description of the Invention] This invention relates to a method for high-frequency sintering of a green compact of metal powder.◎ Conventionally, electric furnace heating has been used as a method for sintering a green compact of metal powder. In the case of heating, although it has the advantage of being able to sinter a large amount of compacted powder at once, it takes time to raise the temperature to the sintering temperature and the sintering holding time, making it difficult to synchronize with the machining process. There was a problem that efficient production could not be carried out.

Therefore, high-frequency induction heating is available as a solution to such problems, but in this case, sintering can be performed in a shorter time than electric furnace heating, so it is suitable for sintering metal powder.

However, with this method, as shown in the conventional example in Figure (3), it takes about 40% of the total heating time to heat from room temperature to about 200 degrees, and there has been a desire to shorten this heating time. .

That is, the penetration depth P of the high frequency current emitted from the heating coil 1 into the green compact 2 is determined by the magnetic permeability μ and specific resistance ρ of the material.
(μΩ·α) and the frequency f (Hz), and the deviation is expressed by the following formula.

Normally, the specific resistance of the powder compact 2 is much higher than that of steel □
Since the current is small, the penetration depth P of the high-frequency current becomes deep. In other words, this indicates that the pressure force density per unit volume becomes low, and therefore the resistance of the compact is large.In some cases, the rate of temperature increase is naturally considered to be small. As shown in FIG. 1, the resistance decreases as the temperature increases until the de-rotation temperature reaches about 600 degrees, and the decrease is particularly large from room temperature to about 200 degrees.

For this reason, as shown in Figure (3), it is considered that the temperature rise rate of the compact 2 is low until about 200°C and then rises rapidly.

Therefore, from the above, in order to shorten the sintering time of the compact 2, it is necessary to provide a de-rolling process using an electric furnace and lower the resistance t1 of the compact 6J compact in advance, or to heat it by about 200 degrees. It can be seen that it is sufficient to provide a means to assist in raising the temperature to There was a drawback that there was no auxiliary means. Therefore, in the present invention, we have developed a compacted metal powder that can shorten the sintering time of the compacted powder by adding a simple means without requiring any special process. The purpose of the present invention is to provide a method for high-frequency sintering in a powder body.In order to achieve the above objects, a heating accelerating material is provided inside or outside of a green compact to be sintered, and the heating accelerating material and This method is characterized in that the powder compact is simultaneously heated by high frequency waves, and the heating of the compact is promoted by heat conduction using a heating accelerator and radiant heating.

Hereinafter, one embodiment embodying the present invention will be described in detail with reference to the drawings.

First, in FIG. (2) showing the overall configuration of the Shima Shuha sintering device 4, 5 indicates a cylindrical furnace body,
A heating coil μm is provided on the side peripheral surface of this over the entire circumference.

Reference numeral 2 denotes a powder compact formed by compression molding metal powder, which is installed inside the furnace body 5, and is shown in this embodiment as having a cylindrical shape.

Reference numeral 6 denotes a heat accelerating member 11 which serves as the sandwiching portion of the present invention.

In this example, the heating promotion member 6 is composed of a cylindrical graphite 6 provided at its axial center, and a hollow cylindrical protection member 7 provided to seal it. The protection member 7 is made of ceramic, and the space between it and the graphite 6 is kept in a vacuum state or filled with N2 gas. Note that the graphite 6 is a protective member 7.
If it is not kept tightly sealed, it will wear out with use, but if it is a consumable item and will be replaced as needed, the protective member 7 may be omitted.

Reference numeral 8 denotes an inlet hole provided in the lower part of the furnace body 5 to take in ambient air gas (RX gas, AX gas, etc.) for preventing oxidation, and 9 refers to a gas for preventing oxidation provided in the northern part of the furnace body 5. This is a discharge hole for discharging water.

In the above configuration, the heating coil μm to υ high frequency (
When the powder (bundle) is generated, the green compact 2 is heated and at the same time, the graphite 6 is also heated.

By the way, the resistance value of graphite 6 is much smaller than that of powder compact 2. On the other hand, as shown in Figure (3), the resistance of graphite 6 is particularly large at the beginning of heating, so graphite 6 (D temperature increase rate is The graphite 6 becomes larger than the compact 2. Therefore, the temperature of the graphite 6 becomes much higher than that of the compact 2, so the compact is heated by the heating coil A71 and at the same time receives radiant heat and heat from the graphite 6. Heating is aided by conduction.

This was carried out using a powder compact with a density of 6.5 g/cm and a weight of 50 g at a frequency of 10 KHz and a power of 15 i (w and a width of 201/width) while supplying N2 gas until a sintering temperature of 1200 degrees was reached. The results of comparing the relationship between time and temperature with that of the conventional method are shown in Figure (3).In other words, it was confirmed from this comparison result that the sintering time was reduced by about 65%.

In this way, in this embodiment, [1! By providing the graphite 6 on I, heating is further promoted due to the synergistic effect of heating by high frequency from the heating coil μm and heating by heat conduction and radiant heat from the heating accelerator 6. This means that the time required to raise the temperature to the sintering temperature can be shortened. In particular, in this embodiment, since the graphite 6 is provided inside the heating coil/I/1, the leakage and demagnetization flux that is not generated by the heat of the powder compact 2 is used to heat the graphite 6. be able to. Therefore, energy can be used efficiently and heating can be performed even more effectively.

That is, the present invention has an excellent feature in that the sintering time of the green compact can be further shortened compared to the conventional method by adding extremely simple means by the method described in the claims.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a graph showing changes in specific resistance of a green compact with respect to preliminary sintering temperature; FIG. 2 is a sectional view showing an embodiment of the present invention; FIG. 6 is a graph showing the relationship between heating time to sintering temperature and temperature for the conventional example and the present example. 2... Green compact 6... Heating accelerator 4.
...Induction sintering device applicant Hidehiko Okada, Toyota Motor Corporation agent and patent attorney

Claims (1)

[Claims] 1 When sintering a compact of metal powder by high-frequency induction heating, a heating accelerator is provided inside or outside the compact, and the heating accelerator and the compact are simultaneously heated by high frequency to accelerate the heating. A method for high-frequency sintering of a metal powder green compact, characterized by promoting heating of the green compact by heat conduction from the material and radiant heating.