JPS60100602A - Manufacture of thin-walled cylindrical sintered parts - Google Patents

Abstract

PURPOSE:To prevent a shift of the centers of cylindrical green compacts and to obtain thin-walled cylindrical sintered parts with little sintering strain by projecting one of opposite edge faces of each of the compacts, recessing the other, setting the projection of one of the compacts in the recess of other compact in succession so as to pile up the compacts, and sintering the compacts. CONSTITUTION:When a plurality of thin-walled cylindrical green compacts 1 are piled up so that the centers coincide with each other, one of opposite edge faces of each of the compacts 1 is projected 4, and the other is recessed 5. The projection 4 of one of the compacts 1 is set in the recess 5 of other compact in succession to pile up the compacts 1 in a state in which the centers can not be shifted, and the compacts 1 are sintered. Thus, thin-walled cylindrical sintered parts with little sintering strain are obtd.

Description

[Detailed Description of the Invention] This invention provides that, for example, the valve seat of an internal combustion engine is a cylindrical shape, such as a ring for a spinning machine, with a diameter υj and a small thickness (length), and the roundness and flatness of the valve seat is small. The present invention relates to a method for sintering parts that have strict requirements for manufacturing while maintaining their roundness and flatness with high precision when manufacturing them using powder metallurgy.

The role of the sintered body in J3 for these parts is equivalent to the raw material for the product, and is completed by cutting, grinding, etc. There are many things.

Therefore, since the dimensions such as the total length and the inner and outer diameters of the sintered body include necessary machining allowances in advance, the accuracy of these dimensions themselves may be rough to some extent.

However, distortions in roundness and flatness that occur during sintering cannot be corrected in post-processing due to the effect of springback when removed from the processing machine. Therefore, it is necessary to sinter the PU so that there is no distortion from the beginning.

Conventionally, the distortion that occurs during sintering is either caused by stacking powder compacts in several tiers and packing them into a sintering case, and the centers of the stacked powder compacts are misaligned from the beginning, or (as shown in Figure 1) (Reference) Distortion may occur if the powders shift during movement in the sintering furnace, so either sinter them in one stage instead of stacking them, or if they are stacked, insert a core that fits smoothly into the inner diameter of each powder compact. It has been found that distortion does not occur if the core is sintered and covered in a manner that prevents misalignment (see Figure 2).

However, sintering in a single stack is extremely wasteful in terms of furnace work efficiency, and methods using core 3 and other jigs also prevent the easily broken green compact from being carefully placed in the jig. In addition to the fact that it takes time and effort to insert the jig, the heat loss of the furnace cannot be ignored because the heat capacity of the jig itself is large, so although it is used out of necessity, it is not a preferable method.

In this invention, in order to give the powder compact itself a function to prevent misalignment during sintering, a convex portion 4 is provided on one opposing end surface of the powder compacts stacked with their cores aligned, and a convex portion 4 is provided on the other end surface. has a recess 5
It has a structure that prevents misalignment due to the fitting of the unevenness.

An example in which the present invention is applied to a valve seat material will be described below. The M dimensions of this product are outer diameter 31.2mm,
Inner diameter 27.0mm, thick and long)7. Qmm.

The roundness is within 0.15 and the flatness is within 0.1.

First, as shown in FIG. 3, an annular convex portion 4 with a height of 012 mm is formed on the outer edge of the upper end surface of the powder compact, and a depth of 0 is formed on the outer edge of the lower end surface.
A powder compact having a shape with a 3 mm annular recess 5 was made using Cr JO alloy steel powder as the raw material powder, and the compact density was 6.75 (1/
After forming into c++f, they were stacked in 10 layers as shown in Fig. 4, packed in a sintering case, and placed in a reducing atmosphere furnace for 12 hours.
Sintering was performed at a temperature of 50'C for 30 minutes.

Next, as a comparative example, a compact was molded which differed from the above only in that the outer edge did not have four parts and a convex part, and was molded under the same conditions as above using stones stacked in 10 tiers without using a core or other jig. Sintered with When the distortion of the thus obtained sintered body was measured, the variation in distortion in the comparative example was found to be 0.22 in roundness.
, the flatness was 0.14 and required post-processing or sorting, whereas in this invention, the roundness was only 0.08 and the flatness was 0.05, and the M standard could be achieved with a margin as it was sintered. Satisfactory good results were obtained. In addition, in the above example, unevenness of 0.2mm+ remains on the top surface and 0.3mm+ on the bottom surface, but since this is within the range of processing allowance added to the material, it is a new negative factor in the manufacturing process or cost. It does not bring about

Next, as an embodiment other than the example shown in FIG. 3, the concave portion and the convex portion may be provided at the inner edge or in the middle as shown in FIG.
They can also be provided radially as shown in FIG. In either case, it is preferable to make the depth of the concave portion slightly larger than the height of the convex portion.Also, if the convex portions are stacked on top of each other, the load will be concentrated at the bottom, so the convex portions should be placed on top. It is appropriate to stack them.

[Brief explanation of the drawing]

FIGS. 1 and 2 are drawings explaining the problems of the conventional sintering method, FIGS. 3 and 4 are drawings explaining one embodiment of the present invention, and FIGS. 5 and 6 are drawings explaining the problems of the conventional sintering method. It is a drawing showing an embodiment of. 1...Powder compact, 2...Sintering case, 3...Medium
Child 4... convex part, 5... concave part agent Kunihiko Masubuchi

Claims (1)

[Claims] A convex portion 4 is provided on one opposing end surface of a plurality of green compacts stacked by combining 1 No. e1, and a concave portion 5 is provided on the other end surface.
A method for manufacturing thin-walled cylindrical sintered parts with little sintering distortion, characterized by stacking and sintering them in a state where they cannot be misaligned due to the fitting of the unevenness.