JP2014240518A - Method of hole-sealing treatment of sintered member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To devise an inexpensive steam treatment to such a level as to obtain airtightness of an iron-based sintered member with stable liquid-sealing performance.SOLUTION: A method of a hole-sealing treatment of a sintered part comprises holding a sintered part in a steam atmosphere at 500-550°C to form a thin iron oxide film on the hole surface of holes present on the surface and inside the structure of the part, holding the sintered part in a steam atmosphere at 590°C or higher, preferably at 640°C or lower, to grow the iron oxide film formed on the hole surface of the holes and inside the structure of the part so as to close the holes.

Description

  The present invention relates to a sealing treatment method for a sintered part which can enhance the hermeticity of the sintered part to a point where a stable liquid sealing performance can be obtained by steam treatment.

  Sintered parts for applications requiring airtightness are shipped after sealing fine pores existing in the structure.

  For iron-based sintered parts, the sealing process is a simple sealing process. The sintered parts are held in a steam atmosphere, and an iron oxide film is formed on the surface and pore surfaces of the structure. Sealing by steam treatment is also performed, but high airtightness cannot be obtained by sealing by simple steam processing.

  Therefore, when high airtightness is required, the sintered part is evacuated, and in this state, the sintered part is heated and immersed in the molten resin so that the resin penetrates into the pores. In general, a resin impregnation method for closing the surface is used.

  In addition, the following patent document 1 proposes to provide an electrodeposition coating film on the surface on which the oxide film is formed after sealing by steam treatment, and it is considered that the airtightness is enhanced even by this method.

Japanese Patent Laid-Open No. 11-218041

  For example, a sintered cam pulley used in a variable valve timing mechanism (VVT) of an automobile engine encloses oil for driving VVT inside, and when the oil oozes out to the outside, a timing belt hung on the pulley becomes Suck oil to swell.

  Sealing by resin impregnation treatment is performed to prevent this problem, but in this method, it is necessary to remove the resin on the surface of the product by shot peening treatment as a post-treatment after impregnation, which reduces productivity. Cost increase is inevitable.

  Further, the sealing by the method disclosed in Patent Document 1 is not suitable for a part whose surface is a sliding surface because a coating film is formed on the surface.

  An object of the present invention is to devise an inexpensive steam treatment so that the airtightness of the iron-based sintered part can be improved to a level where a stable liquid sealing performance can be obtained.

In order to solve the above problems, in the present invention, the iron-based sintered part sealing by the steam process is divided into two times and the temperature is changed.
Specifically, the sintered part is held in a steam atmosphere at a temperature of 500 ° C. to 550 ° C., and the surface of the part and the hole surface of the pores existing in the structure are 5 μm or less (generally A thin iron oxide film (about 1 to 3 μm) is formed, and then the sintered component is held in a steam atmosphere at a temperature of 590 ° C. or higher, preferably 640 ° C. or lower, and the surface and structure of the component. A method is adopted in which an iron oxide film formed on the hole surface of the inner hole is grown to close the hole.

According to the sealing treatment method of the present invention, the Fe ₃ O ₄ film is generated not only on the surface of the sintered part but also deep inside by the two steam treatments at different temperatures, and the Fe ₃ O ₄ film The airtightness of the iron-based sintered part is increased as the holes are closed.

It is an end view which shows an example of the sintered component to which the method of this invention is applied. It is explanatory drawing of the temperature and time change of a two-stage steam process. (A)-(d): It is a structure | tissue photograph of the outer diameter side cross section of the sintered component which carried out the sealing process by the method of this invention. (A)-(d): It is a structure | tissue photograph of the large internal diameter side cross section of the sintered part sealed by the method of this invention. It is a figure which shows typically the oxide film of the surface of components, and a void | hole inner surface. It is explanatory drawing of an airtightness evaluation test.

  Embodiments of the method for sealing a sintered part according to the present invention will be described below.

The method of the present invention is intended for ferrous sintered parts that require oil or air to be sealed and require airtightness, such as housings and end plates of sintered cam pulleys for variable valve timing mechanisms, sintered parts for compressors, etc. The part that has undergone the sintering process is held in a steam atmosphere at a temperature of 500 ° C. to 550 ° C., and the surface of the part and the pore surface of the pores existing in the structure are thin. An iron oxide film is formed, and thereafter, the sintered part is held in a steam atmosphere at a temperature of 590 ° C. or higher, preferably 640 ° C. or lower, and formed on the surface of the part and the pore surface of the pores in the tissue. The iron oxide film is grown so as to close the vacancies.

According to this sealing treatment method, when the temperature of the first steam treatment is set to 500 ° C. to 550 ° C., an iron oxide film (Fe ₃ O ₄ ) grows slowly and is generated deep inside the sintered part. The

In addition, Fe ₃ O ₄ generated on the inner surface of the vacancy near the surface layer in the first treatment grows and closes the vacancy by the second steam treatment performed at a higher temperature than the first treatment, and further, the surface of the sintered part In addition, FeO and Fe ₃ O ₄ are firmly formed. As a result, the above-described sintered cam pulley for the variable valve timing mechanism can have a liquid sealing performance that can withstand practical use.

When the temperature of the first steam treatment is 560 ° C. or higher, hard and brittle FeO (wustite) is generated at a high rate on the surface of the sintered part, and the growth of Fe ₃ O ₄ inside the part is inhibited. In this method, since the temperature of the first steam treatment is 560 ° C. or lower, the problem does not occur.

The initial steam treatment time at a temperature of 500 ° C. to 550 ° C. is preferably 3 hours or more. Normal steam treatment is carried out under conditions of a temperature of 500 ° C. to 560 ° C. and a time of about 10 minutes to 1 hour. By taking a longer time than the normal treatment, the surface of the internal vacancies is deepened deeply into the part. An Fe ₃ O ₄ film can be produced.

  The temperature of the second steam treatment is 590 ° C. or higher, preferably 590 ° C. to 640 ° C. By suppressing the upper limit of the processing temperature to 640 ° C., it is possible to prevent the size reduction of the sintered part due to overheating. As for the temperature of the second steam treatment, one hour is sufficient because the generation of the oxide film is performed at a high speed.

By this second steam treatment performed at a higher temperature than the first treatment, Fe ₃ O ₄ formed on the inner surface of the pores near the surface layer is grown by the first treatment to increase the pore sealing rate, and further sintering FeO and Fe ₃ O ₄ can be firmly generated on the surface of the part.

  By performing such a two-stage steam treatment, it has become possible to obtain airtightness that can withstand practical use without extremely increasing costs.

A sintered part 1 having the density shown in FIG. 1 having a density of 6.8 g / cm ³ was manufactured using raw material powder having a composition of Fe-2.0 wt% Cu-0.8 wt% C. 1 is a housing of a sintered cam pulley for a variable valve timing mechanism, and has an outer diameter D = φ83 mm, a large inner diameter d = φ77 mm, and a thin portion thickness T = 3 mm.

The sintered part 1 was subjected to sealing treatment using a processing furnace under the following conditions. The treatment was performed after sizing the large inner diameter surface 1b.
Sample A: first steam treatment temperature: 500 ° C., treatment time: 3 hours + second steam treatment temperature: 600 ° C., treatment time: 1 hour (total treatment time: 4 hours), furnace pressure: 600 mmAq
Sample B: first steam treatment temperature: 550 ° C., treatment time: 3 hours + second steam treatment temperature: 600 ° C., treatment time: 1 hour (total treatment time: 4 hours) Furnace pressure: 600 mmAq
Sample C: first steam treatment temperature: 540 ° C., treatment time: 3 hours + second steam treatment temperature: 590 ° C., treatment time: 1 hour (total treatment time: 4 hours), furnace pressure: 400 mmAq
Sample D: first steam treatment temperature: 490 ° C., treatment time: 3 hours + second steam treatment temperature: 590 ° C., treatment time: 1 hour (total treatment time: 4 hours), furnace pressure: 400 mmAq
Sample E: First steam treatment temperature: 600 ° C., treatment time: 1 hour + second steam treatment temperature: 600 ° C., treatment time: 2 hours (total treatment time: 3 hours), furnace pressure: 600 mmAq
Sample F: First steam treatment temperature: 500 ° C., treatment time: 3 hours + second steam treatment temperature: 580 ° C., treatment time: 1 hour (total treatment time: 4 hours), furnace pressure: 400 mmAq
Sample G ... Steam treatment temperature: 500 ° C, treatment time: 1 hour, furnace pressure: 400 mmAq, steam treatment once (normal steam treatment)

  FIG. 2 shows an image of changes in temperature and time during this process. As can be seen from FIG. 2, the second steam treatment was performed by raising the temperature in the same treatment chamber after the end of the first treatment.

  As representative of these samples, structural photographs of the cross section of Sample B are shown in FIGS. This structural photograph is a photograph of a cross section taken along the line XX in FIG. 1 of the ring-shaped thin portion of the manufactured sintered part.

  {FIG. 3 (a)} is a photograph of the outer diameter surface 1a (see FIG. 1) of the thin wall portion, {FIG. 3 (b)} is a photograph of a depth position 0.2 mm from the outer diameter surface 1a, {FIG. (C)} is a photograph of a depth position of 0.5 mm from the outer diameter surface 1a, and {FIG. 3 (d)} is a photograph of a depth position of 1.0 mm from the outer diameter surface 1a.

  Also, {FIG. 4 (a)} is a photograph of a depth position of 1.0 mm from the large inner diameter surface 1b (see FIG. 1), and {FIG. 4 (b)} is a depth position of 0.5 mm from the large inner diameter surface 1b. {FIG. 4 (c)} is a photograph at a depth of 0.2 mm from the large inner diameter surface 1b, and {FIG. 4 (d)} is a photograph of the surface of the large inner diameter surface 1b.

  In these structure photographs, the white portion of the structure is the base material 2, the portion appearing black inside is a hole 3, and the gray portion around the hole is an iron oxide film 4. The oxide film 4 is also formed on the outer diameter surface 1a and the large inner diameter surface 1b. Since the structure photograph of the cross section is not clear, the oxide film on the surface and the inner surface of the pore is schematically shown in FIG.

  When the thickness of the oxide film formed on the outer diameter surface 1a of the sample B was measured, the film thickness t was about 10 μm. The film thickness was determined by measuring the outer diameter of the part before and after the steam treatment with a measuring instrument and calculating {(outside diameter after treatment−outside diameter before treatment) ÷ 2}.

  Next, airtightness was evaluated about each sample AG which performed the sealing process by steam. The evaluation was performed by the following method.

  That is, as shown in FIG. 6, the plates 10 and 11 and the seal packing 12 are used to seal both ends of the sintered part 1 in an airtight manner, and the part is immersed in water to introduce nitrogen gas into the part. The presence or absence of the generation | occurrence | production of the bubble by the gas leakage from the outer peripheral part of this was confirmed visually. Reference numeral 13 in FIG. 6 denotes a bolt and nut, and the plate was tightened with the bolt and nut at a total of four locations.

The test conditions were a gas pressure of 2 MPa and 3 MPa, and a gas application time of 5 minutes and 10 minutes. Two samples A to F were used for the test.
The results of this test are shown in Table 1.

  From the result of this evaluation test, it can be seen that according to the method of the present invention, a highly airtight sealing that has been conventionally dependent on resin impregnation can be performed by an inexpensive steam treatment.

1 Sintered parts (housing cam pulley housing for variable valve timing mechanism)
1a Outer diameter surface 1b Large inner diameter surface 2 Base material 3 Hole 4 Oxide coating 10, 11 Plate 12 Seal packing T Thickness of thin part of sintered part t Thickness of oxide film formed on part surface D Sintered prototype Outer diameter d Diameter of the large inner diameter part of the prototype sintered parts

Claims (3)

  The sintered part is held in a steam atmosphere at a temperature of 500 ° C. to 550 ° C. to form a thin iron oxide film on the surface of the part and the pore surface of the pores existing in the structure, and then Sintering in which the sintered part is held in a steam atmosphere at a temperature of 590 ° C. or higher, and an iron oxide film formed on the surface of the part and the pores in the structure is grown to block the pores Sealing method for parts. The treatment time of the first treatment held in the vapor atmosphere at a temperature of 500 ° C. to 550 ° C. is 3 hours or more. The treatment time of the second treatment held in the vapor atmosphere at a temperature of 590 ° C. or more is 1 hour or more. The method for sealing a sintered part according to claim 1.   The method for sealing a sintered part according to claim 1 or 2, wherein the upper limit of the temperature of the second treatment is 640 ° C.