JPS6124441B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field) The present invention relates to a manufacturing method for obtaining a sintered body with excellent mechanical strength and high precision. (Prior art) Sintering in one furnace and performing various post-treatments continuously is described in, for example, Japanese Utility Model Publication No. 3532/1983, Japanese Patent Publication No. 13210/1983, and Japanese Utility Model Application No. 100742/1983 ( This is known from Japanese Utility Model Application Publication No. 52-14312) and Japanese Patent Application Publication No. 50-25412. However, in the vacuum sintering and decharring furnace disclosed in Publication No. 45-3532, the decarburizing liquid is introduced into the furnace and gasified by a heat source installed in the furnace, so that the carbon concentration in the decarburizing layer is lower than that of the charcoal layer. Compared to solid charcoal, it has poor impact resistance, and the charcoal layer is easily peeled off and cracks are easily generated. Therefore, the diffusion treatment is carried out in an atmosphere in which the degree of activation of the charcoal gas is controlled. There was a problem that the process became complicated because a post-process to adjust the carbon concentration was required. Furthermore, since the combination furnace shown in JP-A No. 45-13210 generates a pressure higher than atmospheric pressure in the sintering zone, heat escapes to the outside together with the gas, and the temperature rises to 1150℃. It took up to 6 hours to complete the process, and there was also the problem that the inside of the furnace deteriorated due to atmospheric gas. Also, Utility Application No. 1987-100742 (Utility Application No. 14312, Showa 52)
The continuous vacuum processing equipment shown in Figure 1 has multiple independent vacuum chambers that evacuate each chamber independently, and the transfer mechanism is installed independently in each chamber, resulting in a complicated structure. . Further, the heating furnace conveyance device disclosed in Japanese Patent Application Laid-Open No. 50-25412 relates to a device for conveying a heated object from a furnace chamber to a furnace chamber. (Purpose) The present invention involves sequentially performing sintering → oil quenching → oil impregnation, in particular, placing the product in oil before vacuum breaking.
The purpose of this method is to perform oil impregnation by utilizing the pressure that increases when the vacuum is broken during oil quenching, thereby shortening the entire process by performing the quenching and oil impregnation processes simultaneously. (Structure) In order to achieve the above object, the present invention includes a first step of heating to a predetermined temperature and sintering in a reduced pressure chamber reduced to a predetermined pressure lower than 1 atmosphere, and a first step of sintering in the reduced pressure chamber. It consists of a second step of lowering the temperature to a predetermined temperature, a third step of further performing heat treatment in oil in the reduced pressure chamber, and a fourth step of returning the heat-treated product to normal pressure while remaining in oil and impregnating it with oil. It is characterized by: FIG. 1 shows an embodiment of an apparatus for carrying out the method of the present invention, in which numeral 1 denotes a preheating chamber that communicates with the outside air, and a chimney 2 is provided therein. This was provided to blow away zinc stearate and the like mixed in during the compacting process. Reference numeral 3 denotes a decompression chamber adjacent to the preheating chamber 1, and a vacuum pump 4 and a cooling gas blower 5 are provided at predetermined positions on its outer wall. Inside, a heating element 6 made of graphite cloth is provided near the preheating chamber 1, and above it a heating space 8 is formed surrounded by a heat insulating wall 7 made of several pieces of graphite felt. 9 is placed,
A quenching tank 10 is arranged below the front.
A partition wall 11 is slidably provided in the lower part of the partition wall 11 to form a compartment 12, and the compartment 12 is connected to the valve 1.
3 allows communication with the outside air. Next, the method of the present invention will be explained using an example. First, the powder compact W is heated in a preheating chamber.
Heat to 200°C to 800°C to remove impurities and lubricant from the compacted body. The decompression chamber 3 is operated by a vacuum pump 4.
Reduce the pressure to about 10 ^-3 Torr to ^{10 -1} Torr. The preheated green compact W is placed in the heating space 8 in the vacuum chamber 3 and heated to 1150°C. Hold at this temperature for approximately 30 minutes. Then, it is taken out of the heating space 8, placed on a conveyor 9, and placed in a quenching tank 10 within a few seconds. During these few seconds, the temperature of the sintered body sintered at 1150°C was lowered to 800°C, which was set so that the temperature did not go below the _A1 transformation point. Oil is placed in the quenching tank 10, and quenching is performed by quenching with this oil. Next, the partition wall 11 is slid open, the quenching tank 10 is moved downward, the partition wall 11 is closed, and the valve 13 is opened to communicate the divided chamber 12 with the outside air.
Since the sintered body is placed under normal pressure while immersed in oil, a predetermined amount of oil easily penetrates into the inside of the sintered body. According to the method of the present invention, sintering is carried out in a reduced pressure chamber, so there is no need to prevent oxidation by flowing reducing gas as in the conventional method, and the compacted product can be heated to 1200°C to 1300°C in a short time.
It is possible to raise the temperature to 1200℃ or higher, and even if used repeatedly at high temperatures of 1200℃ or more, there is little damage to the furnace wall material, making it the first
As shown in the table, mechanical properties such as tensile strength and elongation were improved compared to the conventional method, and the hardness after quenching was also higher than that of the conventional method, as shown in Table 2.

【table】

[Table] Furthermore, since the present invention performs the sintering process, temperature cooling process, and heat treatment process continuously in the same vacuum chamber, the production time from sintering to heat treatment can be significantly shortened compared to conventional methods. . Fig. 2 is a heat cycle diagram according to the method of the present invention, and Fig. 3 is a heat cycle diagram according to the conventional method (for example, Japanese Patent Publication No. 13210/1982). Comparing the two, the production of the method according to the present invention is shown in Table 3. The production time is about 50 minutes, whereas the production time of the conventional method (for example, Japanese Patent Publication No. 13210/1983) is 330 to 810 minutes.

[Table] Furthermore, since the method of the present invention is heated in a reduced pressure chamber, compared to heating under normal pressure, the degree of heating is stronger by thermal radiation than by thermal conduction. The accuracy after processing can be significantly improved.

[Table] Table 4 shows a 120φ gear made by press molding powders of 2% Cu powder, 0.5% Gr powder, 2% Ni powder, and the rest Fe powder at 5ton/ ^cm2 , and sintered and heat treated using the method of the present invention. This is a comparison table of dimensional accuracy in the following cases. (Effects) According to the present invention, the first step is to perform sintering by heating to a predetermined temperature in a vacuum chamber reduced to a predetermined pressure lower than 1 atm, and the second step is to lower the temperature to a predetermined temperature in the vacuum chamber. It is characterized by two steps, a third step of performing heat treatment in oil in the vacuum chamber, and a fourth step of returning the heat-treated product to normal pressure while remaining in oil and impregnating it with oil. Before destruction, the product is placed in oil, oil quenched, and when the vacuum is broken, oil impregnation takes advantage of the increased pressure, allowing the quenching and oil impregnation processes to be performed simultaneously, shortening the entire process. With this effect, if the partition wall is slid to return the pressure within the compartment to normal pressure, the degree of vacuum in the decompression chamber will hardly be lowered, so the next depressurization process can be carried out efficiently.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view of an embodiment of an apparatus for carrying out the method of the present invention, FIG. 2 is a diagram showing a heat cycle of the method of the present invention, and FIG. 3 is a diagram showing a heat cycle of a conventional method. 3... Decompression chamber, 4... Vacuum pump, 8... Heating space, 9... Transfer conveyor, 10... Quenching tank.

Claims (1)

[Claims] 1 A first step of heating and sintering to a predetermined temperature in a reduced pressure chamber that has been reduced to a predetermined pressure lower than atmospheric pressure, a second step of lowering the temperature to a predetermined temperature in the reduced pressure chamber, and a second step of sintering the material in the reduced pressure chamber. The third step is heat treatment in oil.
and a fourth step of returning the heat-treated product in oil to normal pressure and impregnating it with oil.