JPS6140281B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a highly dense seamless pipe, which includes steps such as extrusion of metal powder, swaging straightening, and heating sintering. Conventionally, the method for manufacturing seamless pipes from metal powder is to extrude a kneaded mixture of metal powder, binder, lubricant, water, etc. using a screw, then dry the extruded pipe, then heat and sinter it at a predetermined temperature. . There is a method in which the material is then swaged to improve its density, and then heated and sintered again. In this case, the density of the seamless pipe in the extruded and dry state is 3.7 to 3.9 g/cm ³ . When this is then heated and sintered, elongated cracks are likely to occur in the circumferential direction due to shrinkage, and this type of defect has the disadvantage that the yield of non-defective products is extremely low. An object of the present invention is to provide a method for manufacturing a highly dense seamless pipe that hardly causes the above-mentioned defects and has a significantly higher density than conventional extrusion sintered seamless pipes. Further, the gist of the present invention is to heat and sinter the preformed tube in an extrusion dry state after swaging and straightening, and then re-swaging and straightening and reheating and sintering it at least once. Hereinafter, as an example of the present invention, an example of manufacturing a SUS316L stainless steel extruded sintered seamless pipe will be explained while comparing it with a conventional method. For example, as shown in Table 1, a kneaded material with a predetermined blending ratio is placed in a predetermined extrusion mold (conventional method: outer diameter 16.5 mm x inner diameter 120 mm).
mm, this invention method: external diameter 18.5 mm x internal diameter 12.0 mm), screw extrusion molding at the same pressure

【table】

[Table] (10 each). When this was then heated and dried, the densities of the two were almost the same. Next, when using the conventional method, a preformed pipe with a density of 3.7 to 3.9 g/cm ³ was heated and sintered under the conditions shown in Table 2, but the above-mentioned defects occurred in the seamless pipe, which resulted in a non-defective product. Yield dropped to 30%. Among these pipes, the density reached 4.8 to 5.0 g/cm ³ by swaging and straightening the pipes without the above defects once. When this is then reheated and sintered under the conditions shown in the same table, the density can only be increased to about 5.0 to 5.1 g/cm ³ . On the other hand, in the case of this invented method, the density is
3.7~3.9g/ ^cm3 original tube (outer diameter 18.0mm x inner diameter 11.5
As shown in Table 2, the density increases to 5.7 to 6.0 g/cm ³ by swaging and straightening the material (mm) once, as shown in Table 2. This is then heated and sintered under the same conditions as the conventional method shown in Table 2. Then, the density increased to 7.0 to 7.2 g/cm ³ by performing swaging straightening once again.
The above-mentioned defects almost never occur, and the yield of good products is 98%.
It was hot. Next, when this is heated and sintered again under the same conditions as the conventional method shown in the same table, the density is 7.2 to 7.3 g/cm ³
was able to increase it to. The theoretical density of this SUS316L stainless steel is approximately 7.9
g/cm ³ , the conventional method could achieve a density of about 64% of the theoretical density, and the method of the present invention could achieve a density of about 92%. Therefore, it has been found that according to the method of this invention, a seamless pipe with significantly higher density than the conventional method can be manufactured. As mentioned above, the method of this invention is characterized by heating and sintering the preformed tube in an extruded and dry state after swaging and straightening, and then re-swaging and straightening and reheating and sintering at least once. By changing the sintering conditions, the density can be brought even closer to the theoretical density. It has also been found that the above-mentioned defects are less likely to occur if the density is increased to about 4.5 g/cm ³ or more by swaging and straightening the extruded and then dried preformed tube. Next, a bronze (PBC2) extruded sintered seamless pipe was manufactured using almost the same process as in the manufacturing example of the SUS316L stainless steel extruded sintered seamless pipe, and almost the same results were obtained. As described above, this invention method can produce an extruded sintered seamless pipe with significantly higher density than the conventional method, and almost no defects mentioned above occur during manufacturing, resulting in an extruded sintered seamless pipe with stable quality performance. Can be provided.

Claims (1)

[Claims] 1 A preform tube obtained by extrusion molding a kneaded material consisting of metal powder, water, a binder, a lubricant, etc. is dried, then swaged and straightened, heated and sintered at a predetermined temperature, and then at least A method for manufacturing a high-density seamless pipe, which comprises once reswaging and straightening processing and reheating and sintering.