Process for producing a sintered body

• US 4,996,022 A
• Filed: 07/10/1990
• Issued: 02/26/1991
• Est. Priority Date: 07/14/1989
• Status: Expired due to Fees

• Current Assignee: JUKI Corporation, Nippon Piston Ring Company Limited
• Original Assignee: JUKI Corporation, Nippon Piston Ring Company Limited
• Inventors: Kawamoto, Takashi, Nakamura, Yoshikatsu, Shindo, Norikazu, Sekine, Tomoyuki
• Primary Examiner(s): Lechert, Jr., Stephen J.
• Assistant Examiner(s): Nigohosian, Jr., Leon
• Application Number:
  US07/550,972
• Time in Patent Office: 231 Days
• Field of Search: 419/36, 419/37, 419/38, 419/53, 419/54, 419/56, 419/57, 419/58, 419/2
• US Class Current: 419/2
• CPC Class Codes: B22F 2201/01 Reducing atmosphere
• CPC Class Codes: B22F 2201/02 Nitrogen
• CPC Class Codes: B22F 2201/20 Use of vacuum
• CPC Class Codes: B22F 2998/00 Supplementary information concerning processes or compositions relating to powder metallurgy
• CPC Class Codes: B22F 3/1021 Removal of binder or filler removal of binder from ceramics C04B35/638
• CPC Class Codes: B22F 3/22 for producing castings from a slip
• CPC Class Codes: B22F 3/225 by injection molding

Abstract

A sintered body is produced by a process comprising the steps of mixing one or more metal powder particles with an organic binder, injection-molding the mixture to form a green body of a predetermined shape, removing the binder from the green body to form a porous body substantially made of the metal powder, and heating the porous body to a sintering temperature and holding it at that temperature to produce a sintered body, in which process the binder is removed through the sequence of the following steps: preheating the green body in an inert gas atmosphere in a temperature range that creates open pores in it; placing the green body, in which open pores have started to form, in a hydrogen gas atmosphere optionally mixed with an inert gas; holding the green body in a temperature range where the metal powder is not carburized and where the open pores will be maintained, so that the greater part of the binder is removed to form a porous body that is substantially made of the metal powder alone; and further holding said porous body at said heating temperature for a sufficient period of time to vaporize the carbon in the small amount of residual binder in the porous body through reaction with hydrogen.

Claims

1. In a process for producing a sintered body comprising the steps of mixing one or more metal powder particles with an organic binder, injection-molding the mixture to form a green body of a predetermined shape, removing the binder from the green body to form a porous body substantially composed of the metal powder, and heating the porous body to a sintering temperature and holding it at that temperature to produce a sintered body, the improvement wherein the binder is removed through the sequence of the following steps:

preheating the green body in an inert gas atmosphere in a temperature range that creates open pores in it;

placing the green body, in which open pores have started to form, in a hydrogen gas atmosphere optionally mixed with an inert gas;

holding the green body in a temperature range where the metal powder is not carburized and where the open pores will be maintained, so that the greater part of the binder is removed to form a porous body that is substantially made of the metal powder alone; and

further holding said porous body at said heating temperature for a sufficient period of time to vaporize the carbon in the small amount of residual binder in the porous body through reaction with hydrogen.

2. The process according to claim 1 wherein the hydrogen content of said gaseous mixture is at least 5%.

3. The process according to claim 1 or 2 wherein the binder is removed at a temperature in the range of 600°

-800°

C.

4. The process according to claim 1 or 2 wherein the porous body obtained by removing the binder from said green body is presintered by elevating its temperature, with the presintered body being subsequently sintered.

5. The process according to claim 4 wherein the temperature for presintering is at 600°

-800°

C.

6. The process according to claim 3 wherein the porous body obtained by removing the binder from said green body is presintered by elevating its temperature, with the presintered body being subsequently sintered.

7. The process according to claim 6 wherein the temperature for presintering is at 600°

-800°

C.

8. The process according to claim 4 wherein the temperature for presintering is about 700°

C.

9. The process according to claim 7 wherein the temperature for presintering is about 700°

C.

10. The process according to claim 1 wherein said metal is iron.

11. The process according to claim 7 wherein said metal is iron.

12. The process according to claim 1 wherein iron carbonyl powder is mixed with a thermoplastic binder.

13. The process according to claim 7 wherein 60 vol. % of iron carbonyl powder is mixed with 40 vol. % of a thermoplastic binder.