JP6052336B2 - Manufacturing method of sintered bearing for motor type fuel pump excellent in corrosion resistance, wear resistance and conformability - Google Patents

Description

  The present invention relates to a motor type fuel pump bearing made of a Zn—P—Ni—Sn—C—Cu based sintered alloy exhibiting excellent corrosion resistance and wear resistance.

  Electronically controlled gasoline injection devices incorporating motor fuel pumps are widely used because they are effective in saving fuel and cleaning exhaust gases.

  In recent years, the trend toward miniaturization and weight reduction of automobile engines is strong, and accordingly, the fuel pump shown in FIG. 3 is also miniaturized, and the bearings used for the fuel pump are also miniaturized and thinned. On the other hand, the discharge performance of the motor is maintained as before. For this reason, the bearing used for a motor type fuel pump is required to have excellent wear resistance even in an environment exposed to a high-pressure and high-speed flow of gasoline.

  By the way, with the recent globalization of the automobile market, automobiles are spreading all over the world. However, the quality of liquid fuels such as gasoline used in various countries varies, and the fuel contains a lot of sulfur and organic acids. There are many areas where it is necessary to use the bad gasoline included. And, when these poor gasolines containing sulfur and organic acids are used, the bearings of motor type fuel pumps are corroded by sulfur and organic acids, and the bearing life will be shortened due to failure due to motor lock, reduction of bearing strength, etc. There was a problem.

  Regarding the above problem, for fuel containing sulfur or a compound thereof as an impurity, for example, Patent Documents 1 and 2 disclose motor type fuel pump bearings made of a Cu-Ni based sintered alloy, For fuels such as poor gasoline containing organic acids and the like, for example, Patent Document 3 discloses a bearing made of a Cu—Ni-based sintered alloy having a structure in which a Sn high-concentration alloy phase is formed.

JP 2001-192754 A JP 2002-180162 A JP 2006-199977 A

  However, the bearings disclosed in Patent Documents 1 and 2 have excellent wear resistance and excellent corrosion resistance against bad gasoline containing sulfur, but the corrosion resistance against bad gasoline containing organic acid is not sufficient. It was. In addition, the bearing of Patent Document 3 has excellent wear resistance and excellent corrosion resistance even in poor gasoline containing an organic acid. However, as a bearing of a motor-type fuel pump, the bearings described in Patent Documents 1 and 2 are used. However, since the compatibility with the mating shaft material is poor, the load at the initial stage of motor operation may become high, resulting in problems such as excessive motor current.

  Therefore, the present invention eliminates the above problems, has corrosion resistance against bad gasoline containing sulfur and organic acids, and is excellent in wear resistance and compatibility with the mating shaft. It is an object of the present invention to provide a sintered bearing for a motor type fuel pump which can be suitably used and is composed of a novel Zn—P—Ni—Sn—C—Cu based sintered alloy.

  Reduction of Ni or Sn content was considered to be effective for improving the conformability of the bearing shown in Patent Document 3, however, the corrosion resistance against poor gasoline containing sulfur and organic acids decreases as Ni or Sn content decreases. That is, conformability and corrosion resistance are contradictory properties with respect to Ni or Sn content. Then, as a result of earnest research for the compatibility of Ni or Sn content reduction and corrosion resistance against poor gasoline containing sulfur and organic acids, the alloy component was Zn-P-Ni-Sn-C-Cu system, -An Sn alloy phase containing 15% or more of Sn by mass% is formed at the grain boundary of the base composed of a solid solution phase of Ni-Sn-Cu alloy, and pores are dispersed and distributed in the base at a ratio of 8% to 18%. By having a metal structure in which free graphite is distributed in the pores, it has excellent wear resistance and compatibility with excellent mating shaft materials and excellent corrosion resistance against poor gasoline containing sulfur and organic acids The present inventors have found a bearing material having

That is, the manufacturing method of the motor type fuel pump bearing of the present invention is 3% to 13% Zn, 0.1 to 0.9% P, 10 to 21% Ni, and 3% by mass. It contains 12% Sn and 1-8% C, with the balance being Cu and inevitable impurities, and 15% by mass in the grain boundary of the base consisting of the solid solution phase of Zn—Ni—Sn—Cu alloy. is Sn alloy phase formed containing more than Sn, and has a porosity of 8-18%, more motor fuel pump that has a tissue free graphite are distributed in the pores a method of manufacturing a sintered bearing, the Sn alloy phase, after sintering the raw material powder at a temperature of the powder molded 840-930 ° C., to form by immediately cooled at the rate 15 ° C. / min or more Is.

  The Sn alloy phase containing 15% or more of Sn by mass% is 0.1% to 5.0% Zn, 0.4 to 1.5% P, and 20 to 35% by mass. % Cu and 20 to 43.5% Ni, with the balance being Sn and inevitable impurities.

  The sintered bearing for a motor type fuel pump of the present invention has excellent corrosion resistance and wear resistance even in ordinary liquid fuel such as gasoline, and particularly in liquid fuel such as poor gasoline containing high concentration of sulfur and organic acids. The motor-type fuel pump with long-term reliability can be provided even if poor liquid fuel is used.

6 is a graph showing a change with time of a motor current value at the initial stage of operation of a motor type fuel pump in a conformability test of Example 1. FIG. 2 is an electron micrograph of an electron microscope in an electron beam microanalyzer analysis of Example 1. FIG. It is sectional drawing which shows the structure of the motor type fuel pump for gasoline engines.

  The sintered bearing for a motor type fuel pump of the present invention is 3% to 13% Zn, 0.1 to 0.9% P, 10 to 21% Ni, and 3 to 12% by mass. It contains Sn and 1 to 8% of C, the balance is made of Cu and inevitable impurities, and at least 15% by mass in the grain boundary in the substrate made of a solid solution phase of Zn—Ni—Sn—Cu alloy. An Sn alloy phase containing Sn is formed, has a porosity of 8 to 18%, and has a structure in which free graphite is distributed in the pores. By forming a solid solution phase of Zn-Ni-Sn-Cu alloy on the substrate and forming an Sn alloy phase at the grain boundary, it has excellent compatibility with the mating shaft material, exhibits sulfur resistance and organic acid resistance, and has excellent resistance to resistance. It becomes the bearing of the motor type fuel pump which has wearability.

  Hereinafter, the composition of the sintered bearing for a motor type fuel pump of the present invention will be described in detail. In addition, all content demonstrated below is the mass%.

(1) Zn: 3 to 13% by mass
Zn has corrosion resistance to gasoline containing sulfur, and forms a solid solution phase of Zn-Ni-Sn-Cu alloy together with Ni, Sn, Cu by sintering, and has excellent corrosion resistance and conformability to the bearing. Although it has a caking action, if the Zn content is less than 3%, desired corrosion resistance and conformability cannot be obtained. On the other hand, if the Zn content exceeds 13%, the corrosion resistance of gasoline containing an organic acid is lowered, which is not preferable.

(2) P: 0.1 to 0.9% by mass%
P promotes the sinterability of the green compact and improves the strength of the bearing. After sintering, it is abundant in the grain boundaries of the metal structure. If the P content is less than 0.1%, a sufficient sinterability effect cannot be obtained. On the other hand, if the P content exceeds 0.9%, the dimensional change during sintering becomes large and the dimensional accuracy of the bearing product is lowered, which is not preferable.

(3) Ni: 10 to 21% by mass
Ni imparts excellent strength, wear resistance and corrosion resistance, and forms a solid solution phase of Zn-Ni-Sn-Cu alloy together with Zn, Sn, Cu by sintering, and further at grain boundaries together with P, Sn, Cu An Sn alloy phase is formed to impart excellent strength, wear resistance and corrosion resistance to the bearing. If the Ni content is less than 10%, excellent corrosion resistance cannot be obtained. On the other hand, even if the Ni content exceeds 21%, the effect of improving the corrosion resistance is small and the raw material cost is increased, which is not preferable.

(4) Sn: 3 to 12% by mass
Sn forms a Sn alloy phase at the grain boundary together with Ni, Sn, and P by sintering, and further forms a substrate composed of a solid solution phase of Zn—Ni—P—Sn—Cu alloy together with Zn, Ni, P, and Cu. This gives the bearing excellent corrosion resistance. If the Sn content is less than 3%, the grain boundary phase is not sufficiently formed, and desired corrosion resistance cannot be obtained. On the other hand, even if the Sn content exceeds 12%, the effect of improving the corrosion resistance is small, and on the contrary, the dimensional change during sintering becomes large and the dimensional accuracy of the bearing product is lowered, which is not preferable.

(5) C: 1 to 8% by mass%
C is derived from graphite. C mainly exists as free graphite in pores dispersed and distributed in the substrate, imparts excellent lubricity to the bearing, and improves wear resistance. If the C content is less than 1%, the desired effect cannot be obtained. On the other hand, if the C content exceeds 8%, the effect of improving the wear resistance is small, and the strength of the bearing is abruptly lowered.

(6) Porosity: 8-18%
The pores are dispersed in the substrate and have an effect of reducing the strong friction received by the bearing under the high-pressure and high-speed flow of the liquid fuel and suppressing the wear of the bearing. However, when the porosity is less than 8%, the effect is not sufficient. On the other hand, when the porosity exceeds 18%, the strength is remarkably lowered, which is not preferable.

(7) Sn alloy phase containing 15% by mass or more of Sn The Sn alloy phase containing 15% or more by mass of Sn formed at the grain boundary of the substrate is excellent in poor gasoline containing organic acids. Provides corrosion resistance.

  The Sn alloy phase containing 15% or more of Sn by mass% includes, as raw material powder, Cu—Ni alloy powder or Zn—Ni—Cu alloy powder, Sn powder, Cu—P powder, Cu—Zn powder, and graphite powder. 3% to 13% Zn, 0.1% to 0.9% P, 10% to 21% Ni, 3% to 12% Sn, and 1% to 8% C. Contained so that the balance is a component composition consisting of Cu and inevitable impurities, compacted using the mixed raw material powder, and then controlled to a temperature range of 840 ° C. to 930 ° C. for sintering. Immediately after ligation, it is rapidly cooled at a cooling rate of 15 ° C./min or more, so that it is efficiently formed at the grain boundaries of the substrate. The Sn alloy phase formed under the above conditions is 0.1% to 5.0% Zn, 0.4 to 1.5% P, 20 to 35% Cu, 20 to 20% by mass. It contains 43.5% Ni, and the balance contains Sn and inevitable impurities.

  Hereinafter, specific examples of the sintered bearing for the motor type fuel pump of the present invention will be described. In addition, this invention is not limited to a following example, A various deformation | transformation implementation is possible.

(1) Manufacture of sintered bearing for motor type fuel pump As raw material powder, Cu-30 mass% Ni alloy powder and Cu-25 mass% Ni alloy powder each having a predetermined average particle size in the range of 30-100 μm Cu-20 mass% Ni alloy powder, Cu-15 mass% Ni alloy powder, Cu-8 mass% P alloy powder, Sn powder, Cu-30 mass% Zn alloy powder, Cu-20 mass% Zn alloy powder, Cu −40 mass% Zn alloy powder, Cu—Ni—Zn alloy powder, graphite powder, and Cu powder were prepared. These raw material powders were blended so as to have the composition shown in Table 1, mixed in a V-type mixer for 20 minutes, and then press molded at a predetermined pressure to produce a green compact. This green compact is sintered at a predetermined temperature in the range of 840 to 930 ° C. in an endothermic gas (endothermic gas) atmosphere that is decomposed and modified by mixing natural gas and air and passing through a heated catalyst. Then, it was rapidly cooled at a cooling rate of 15 ° C./min or more, followed by sizing. Through the above steps, the bearing of the present invention (hereinafter referred to as the present invention), the conventional bearing, and the comparative bearing having dimensions of outer diameter: 10 mm × inner diameter: 5 mm × height: 5 mm and having the composition components shown in Table 1 are obtained. Produced.

  In the examples of the present invention, as a result of observing the metal structure with an electron beam microanalyzer, it was found that the metal structure was made of a Zn-Ni-Sn-Cu alloy solid solution phase and the grain boundary in the substrate was 15% by mass. The Sn alloy phase containing the above Sn was formed, had a porosity of 8 to 18%, and had a structure in which graphite was dispersed and distributed in the pores.

(2) Wear resistance test With respect to the bearings of the above-described present invention example, the conventional example and the comparative example, gasoline is circulated at high speed in a narrow space, and the bearing is subjected to high pressure by the high-speed rotation of the motor that causes this, and the high flow velocity An abrasion resistance test was conducted under conditions exposed to gasoline.

  A bearing was incorporated into a fuel pump having an outer dimension of length: 110 mm × diameter: 40 mm, and this fuel pump was installed in a gasoline tank. An actual machine experiment was conducted under the conditions of the impeller rotation speed: 5,000 to 15,000 rpm, the gasoline flow rate: 50 to 250 liters / hour, the pressure that the bearing receives from high-speed rotation: a maximum of 500 kPa, and the test time: 500 hours. The maximum wear depth on the bearing surface after the test was measured. The results are shown in Table 1.

  The maximum wear depth of the bearing in the example of the present invention was 2.8 μm or less, and it was confirmed that the bearing had excellent wear resistance.

(3) Corrosion resistance test Corrosion resistance tests were performed on the bearings of the present invention example, the conventional example, and the comparative example.

  Sulfur test solution that assumed pseudo bad gasoline by adding sulfur to gasoline, and organic that assumed pseudo bad gasoline by adding carboxylic acid represented by RCOOH (R is a hydrogen atom or hydrocarbon group) to gasoline. An acid test solution was prepared. The sulfur test solution and the organic acid test solution were heated to 60 ° C., and then the bearings of the present invention example, the conventional example, and the comparative example were immersed in the sulfur test solution and the organic acid test solution for 500 hours. And the change rate of the mass before being immersed in a sulfur test liquid and an organic acid test liquid and the mass after immersion was measured. Table 1 shows the result of mass change by the corrosion resistance test.

  In the example of the present invention, the mass change in the sulfur test solution of the bearing is 0.12% or less, and the mass change in the organic acid test solution is 0.38% or less. It was confirmed that the corrosion resistance was high.

  On the other hand, in Comparative Example 5, in Comparative Example 5, the mass change in the sulfur test solution of the bearing is 0.35%, which is low in corrosion resistance, and in other Comparative Examples, which is 0.15% or less. The mass change in the acid test solution was 0.56 to 0.70%, and the corrosion resistance was significantly lower than that of the examples of the present invention.

  Further, in the conventional example, the conventional example 1 containing no Sn has a high resistance to sulfidation, while the organic acid resistance is significantly lower than that of the example of the present invention, and the Ni content containing Sn is higher than that of the example of the present invention. In Example 2, both the resistance to sulfidation and the resistance to organic acid showed almost the same corrosion resistance as that of the present invention.

(4) Familiarity test The bearings of the present invention example 3 and the conventional examples 1 and 2 were incorporated into a motor, and the current consumption when continuously operated was measured for 30 minutes. The result is shown in FIG. The current value of the motor using the bearing of Example 3 of the present invention and the bearing of Conventional Example 1 that does not include Sn decreases in a shorter time than the bearing of Conventional Example 2 that has a high Ni content and contains Sn, and exhibits stability. It was. Furthermore, the current after stabilization was low. From this, it was confirmed that the bearing according to the present invention has better initial conformability than the conventional example 2 bearing.

(5) Electron beam microanalyzer analysis About the alloy of this invention example 3, using an electron beam microanalyzer (EPMA),
Zn, P, Ni, Sn, and Cu were quantitatively analyzed with respect to the Sn alloy phase containing 15% or more of Sn at a mass% of the grain boundary and the substrate composed of a solid solution phase of Zn—Ni—Sn—Cu alloy. The analysis conditions are an acceleration voltage of 15 kV and a beam diameter of φ1 μm. As an example, as shown in the electron micrograph (COMPO image) of FIG. 2, the Zn—Ni—Sn—Cu alloy phase and the Sn alloy phase at the grain boundary are respectively shown. The average value was calculated by measuring 5 points. The results are shown in Table 2. In addition, this analysis result analyzed the specific site | part in a metal structure, and does not show the whole composition. Further, C, which is an alloy component element, was almost excluded as free graphite in pores dispersed and distributed in the substrate, and thus was excluded from quantitative analysis elements.

  In the alloy of Invention Example 3, it was confirmed that a Zn—Ni—Sn—Cu alloy phase and a Sn alloy phase containing 15% or more of Sn by mass% of the grain boundary existed on the substrate.

Claims (2)

It contains 3 to 13% Zn, 0.1 to 0.9% P, 10 to 21% Ni, 3 to 12% Sn, and 1 to 8% C in mass%. In addition, an Sn alloy phase containing 15% or more by mass of Sn is formed at the grain boundary of the base made of a solid solution phase of Zn—Ni—Sn—Cu alloy, with the balance being Cu and inevitable impurities, and 8 has a 18% porosity, a method of manufacturing a motor sintered bearing fuel pump that has a tissue free graphite are distributed in the pores, the Sn alloy phase, The raw material powder is compacted and sintered at a temperature of 840 to 930 ° C., and immediately formed by cooling at a cooling rate of 15 ° C./min or more. Excellent in corrosion resistance, wear resistance and conformability Manufacturing method of sintered bearing for motor type fuel pump. The Sn alloy phase containing 15% or more of Sn by mass% is 0.1% to 5.0% Zn, 0.4 to 1.5% P, and 20 to 35% by mass. The motor type fuel pump excellent in corrosion resistance, wear resistance, and conformability according to claim 1, comprising Cu and 20 to 43.5% Ni, with the balance being Sn and inevitable impurities. Manufacturing method of sintered bearing.