JP3512314B2 - Magnetic fluid impregnated sintered plain bearing and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid-impregnated sintered sliding bearing and a method for manufacturing the same, which is a sintered sliding bearing in which a lubricant is a magnetic fluid, and which is used at relatively high speed and low load. It can be used as a motor for video equipment, a polygon motor for scanning, a spindle motor for magneto-optical disks, etc.

[0002]

2. Description of the Related Art As a sintered bearing element using a magnetic fluid, a permanent magnet is disposed adjacent to a bronze-based porous sintered bearing, or as disclosed in Japanese Utility Model Publication No. 3-49416. It is known that a permanent magnet is embedded in a porous sintered bearing, or magnetized ferromagnetic particles are dispersed in a matrix alloy of the porous sintered bearing.

[0003]

Among the prior art, a sintered bearing made of a composite material of a sliding bearing alloy and ferromagnetic particles and impregnated with a magnetic fluid has a structure in which the former permanent magnet members are arranged adjacent to each other. Compared with the bearings, the structure of the bearing element is simpler and the magnets are distributed near the sliding surface, so it is expected that the bearing element will have excellent oil film retention on the sliding surface and have good sliding characteristics. To be done. However, in a sintered bearing using an ordinary mixed powder of metal powder and magnetic powder, relatively hard magnetic particles are exposed on the sliding surface, so the compatibility with the shaft is poor,
It also causes abrasive wear and is not practical.

Therefore, the present invention provides a ferrofluid-impregnated sintered sliding bearing, which is a composite material of a bronze alloy and a permanent magnet having excellent sliding characteristics, has excellent sliding performance and can prevent the outflow of lubricating oil. Is a technical issue.

[0005]

The present invention was developed in order to solve the above-mentioned problems, and the technical means comprises a composite alloy of magnetized alnico particles of 30 to 70% by weight and the balance of a bronze alloy, A ferrofluid-impregnated plain bearing characterized in that a porosity of a porous sintered alloy in which alnico particles on the surface are covered with a bronze alloy is impregnated with a ferrofluid based on a lubricating oil. The bronze alloy may be any alloy, but phosphor bronze is mentioned as a particularly preferable bronze alloy. This is because the bearing performance and durability are excellent.

Here, Alnico has a composition of Al: 8 to 1
Iron alloy containing 3% by weight, Ni: 1 to 28% by weight, Co: 2 to 24% by weight, and optionally Cu and Ti, atomized into powder, and then heated to perform aging treatment to precipitate. It has been cured. The aging treatment may be carried out at a normal temperature and time, but it is preferably in an incomplete state where the temperature and time are small so that the aging can be further advanced by sintering the green compact. The particle size is not particularly limited, but the commercially available product contains 35 to 45% by weight of the sub-sieve powder,
It passes through a mesh sieve.

The amount of alnico particles in the bearing alloy is
The amount is 30 to 70% by weight, and optimally around 50% by weight. When the content of alnico particles is less than 30% by weight, the amount of leakage magnetic flux of the entire bearing is small and the magnetic fluid holding force is low. Therefore, 30% by weight or more is suitable as a bearing. However, if it exceeds 70% by weight, alnico particles are likely to be exposed on the sliding surface of the bearing, and the bearing performance is deteriorated.

Next, in the present invention, a member made of a non-magnetic material and having a larger effective porosity than the sintered slide bearing and impregnated with a magnetic fluid based on lubricating oil is brought into contact with the end surface of the sintered slide bearing. With this structure, this member functions as an oil reservoir, and the life of the bearing is extended, which is preferable. The above sliding bearing manufacturing method uses 30 to 70% by weight of age-hardened alnico powder and 10 to 50% by weight of copper foil powder.
Powder mixed with metal powder forming a bronze alloy containing iron is compacted into a bearing shape, and the compact is heated at a temperature of 700 in a reducing atmosphere.
It is characterized in that sintering is performed at a temperature of not more than 0 ° C., and sizing, magnetization treatment and magnetic fluid impregnation are performed.

The bronze alloy part has a normal Sn content of about 7 to 11% by weight, or a P content of 0.1 to 11% by weight.
The composition of phosphor bronze is about 0.5% by weight. The latter is superior in durability. The bronze alloy part is a powder of copper and tin, and phosphor bronze is further Cu-P (for example, P: 15% by weight).
It is a mixture of alloy powder.
Copper should be added in the form of foil powder of at least 10 to 50% by weight in the mixed powder. This technique is described in Japanese Patent Application Laid-Open No. 60-128201 and Japanese Patent Application Laid-Open No. 3-166303 disclosed by the present applicant, and a mixed powder that wraps the alnico powder with this foil powder is used. After being obtained and pressed and sintered, alnico powder is not exposed on the surface of the bearing, and a porous surface of a bronze alloy is formed on the sliding surface. The amount of the copper foil powder may be adjusted depending on the content of the alnico powder, but if the amount of the foil powder is less than 10% by weight, the coating may be incomplete, which is not preferable. Although the bearing can be manufactured even if the amount of foil powder is the total amount of Cu required, if the content of the powder exceeds 50% by weight, the apparent density of the mixed powder becomes low and the workability of compression molding deteriorates. The necessary insufficient amount of Cu is added in the form of ordinary electrolyzed or atomized copper powder and, if necessary, in the form of bronze alloy powder.

The reason why alnico is selected as the permanent magnet particles is that the amount of residual magnetization does not decrease even if sintering is performed at a temperature necessary to obtain a bronze alloy. Other permanent magnet materials are not suitable because they have a small amount of residual magnetization. Alnico has a leakage flux of only about 10% lower than that of a material obtained by heat-treating at 700 ° C. as compared with the leakage flux of a material obtained by magnetizing an ordinary aged material. Similarly, 770
When it is heat-treated at ℃, it becomes about 50%. From this, the sintering of the green compact is performed at a temperature of 700 ° C. or lower, and
50-700 degreeC is a preferable temperature. The bronze alloy part is liquid phase sintered. If the surface of the Alnico powder is copper-plated, the exposure to the sliding surface can be reduced, but the number of treatment steps increases and the cost is increased, which is not preferable.

The size, density, surface exposed pore amount, etc. of the sintered body of the present invention are adjusted by sizing. Either of the magnetization of the bearing and the impregnation of the magnetic fluid may be performed in the first process. As for the magnetization of the bearing, when the bearing is placed in a magnetic field, the alnico particles in the bearing are magnetized and become permanent magnets. The magnetizing direction may be either axial or radial, but from the viewpoint of bearing application, the inner diameter is about several mm. Therefore, when formed in the radial direction, the adjacent magnetic poles work together to produce the desired magnetism. It may not be obtained, and it is desirable to form it in the axial direction.

The sintered slide bearing impregnated with the magnetic fluid thus produced and containing the permanent magnet particles has a high efficiency of retaining the magnetic fluid in the pores and the sliding surfaces, and the lubricating oil film is It is strongly formed and the lubricating oil is less likely to leak out of the bearing elements. Since the surface of the bearing is a bronze alloy, sliding characteristics similar to those of a normal sintered sliding bearing can be obtained.

The end surface (one surface or both surfaces, if necessary) of the above-mentioned sintered bearing impregnated with the magnetic fluid is impregnated with the same magnetic fluid as that impregnated into the sintered bearing in a porous body made of a non-magnetic material. When the above-mentioned members are brought into contact with each other, this porous member serves as an oil reservoir, and the lubricating life of the bearing can be remarkably extended. When this porous member is made of a non-magnetic material, the magnetic fluid is retained in the pores mainly by the capillary phenomenon, and when the magnetic fluid in the adjacent magnetic sliding bearing decreases due to operation or wear, the capillary The magnetic force attracts against the phenomenon to compensate for the decrease. If the axial rotation stops and the magnetic fluid around the plain bearing becomes excessive, it is sucked into the porous member. It is desirable that the porous member has a larger effective porosity and larger pores than the sintered plain bearing.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to Examples.

[0015]

Example The following powder was prepared as a raw material. (1) Alnico 2 powder: 12% C by weight in total composition
o, 18% Ni, 10% Al, 6% Cu and the balance Fe,
Grain size-80 mesh (2) Copper foil powder: Grain size-200 mesh (3) Copper powder: Grain size-100 mesh, electrolytic copper powder (4) Tin powder: Grain size-200 mesh (5) Copper phosphorus alloy powder: Overall composition 15% P by weight and the balance Cu, grain size-150 mesh These are 50% by weight of Alnico powder, 15% by copper foil powder,
Copper powder 28.8%, tin powder 4.5%, and copper phosphorus powder 1.7% were mixed. When converted to a two-phase alloy composition after sintering, 50% Alnico described in (1) above and 9% S
Phosphor bronze consisting of n-0.6% P-balance Cu is 50%.

As a comparative example, a mixed powder of tin powder 9%, copper phosphorus alloy powder 2.4% and electrolytic copper powder 87.6% was prepared. Each mixed powder has an inner diameter of 10 mm, an outer diameter of 16 mm,
It was formed into a cylindrical shape having a length of 10 mm, and each was sintered in an ammonia decomposition gas at a temperature of 690 ° C. The sintered body was sized with a mold and sized to have an effective porosity of 18%.

The former sizing body of the example was magnetized in an electromagnet ring and then impregnated with a lubricating oil-based magnetic fluid using a conventional vacuum impregnation device. The latter phosphor bronze bearing sample was impregnated with a low viscosity lubricating oil. Each of these samples was set in the housing of the bearing tester, and the rotating shaft was made of heat-treated stainless steel SUS420J2. The radial load on the bearing was 196 kP.
a, 100 rpm operation was performed for 100 hours, and the average value of the temperature rise of the bearing during operation and the lubricating oil consumption rate after operation were compared.

The temperature rise was 5 ° C. or less in the bearing of the example, but was 15 ° C. in the bearing of the comparative example. Further, the lubricating oil consumption rate is 4% in the bearing of the example and 11% in the bearing of the comparative example, and the former is about 1/3. When observing the bearing element from the axial direction, the latter is contaminated with lubricating oil flowing down to the housing, and the former has magnetic fluid accumulated in the chamfered part of the rotating shaft and the bearing, but leaks to the outside. Not not.

The bearings of the examples and comparative examples have the same sliding surface of phosphor bronze, but the bearings of the examples include permanent magnet particles and pores containing a magnetic fluid lubricant. It is considered that the temperature rise and the lubricant consumption are reduced because the lubricant is firmly held inside. Next, although the overall composition is similar to the bearing sample according to the present invention described above, using a mixed powder made only electrolytic copper powder without using copper foil powder, a bearing test was performed on a sample manufactured in the same manner as the previous example. went. In the case of this sample, the temperature rise was high, a large amount of magnetic fluid was collected in the chamfered portion of the rotating shaft and the bearing, and was scattered by the shaft rotation, and the lubricating oil consumption rate was 8%. The temperature rise of the bearing is considered to be due to the effect of alnico particles exposed on the bearing sliding surface, and is considered to be more disadvantageous in sliding characteristics than bronze when it comes into metal contact with the shaft.

Further, a cylindrical sintered bronze ring having an effective porosity of 22% impregnated with the same magnetic fluid as that impregnated into the bearing sample is brought into contact with the end surface of the above-mentioned bearing sample according to the present invention to contact the housing. It was fixed to and the bearing test was performed,
The lubricating oil consumption rate is 2%, which is 1/2 that in the case of the bearing of the above embodiment.
It was predicted that the bearing life would be extended.

[0021]

As described above, in the magnetic fluid-impregnated sintered sliding bearing of the present invention produced by the manufacturing method of the present invention, the sliding surface is bronze having good sliding characteristics, and the permanent magnet particles are dispersed in the bearing material. In addition, since the bearing pores and the sliding surface are efficiently oil-retained, the lubricating oil is not scattered and consumed, and the surroundings of the bearing element are not polluted, and a long life can be obtained. Further, the manufacturing method and the assembling means of the bearing are the same as those of the normal oil-impregnated bearing,
There is also an advantage that it can be manufactured efficiently.

Claims (4)

(57) [Claims] 1. A lubricating oil is provided in the pores of a porous sintered alloy, which is composed of a composite alloy of 30 to 70% by weight of magnetized alnico particles and the balance of the bronze alloy, and the alnico particles on the surface are covered with the bronze alloy. A magnetic fluid-impregnated sintered plain bearing characterized by being impregnated with a magnetic fluid based on. 2. A magnetic material, characterized in that a porous member made of a non-magnetic material impregnated with a magnetic fluid based on lubricating oil is in contact with an end surface of the sintered plain bearing according to claim 1. Fluid impregnated sintered plain bearing. 3. The ferrofluid-impregnated sintered slide bearing according to claim 1, wherein the bronze alloy is phosphor bronze. 4. Alnico powder which has been subjected to age hardening treatment
A mixed powder of 0 to 70% by weight and a metal powder forming a bronze alloy containing 10 to 50% by weight of copper foil powder is compacted into a bearing shape, and the compact is heated at a temperature of 700 ° C in a reducing atmosphere. A method of manufacturing a ferrofluid-impregnated sintered plain bearing, which is characterized by performing sizing, magnetizing treatment and ferrofluid impregnation by performing the following sintering.