JP2003214430A - Sintered sliding bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably extend the service life of a sintered sliding bearing by resolving a problem of a conventional sintered oil-containing sliding bearing having slight dispersion in durability. <P>SOLUTION: For this sintered sliding bearing, pores each having a 10% or less area rate are exposed on the bearing inside surface of a ground surface, sealed pores each having a 20 μm or less metal thickness from the inside surface are provided, and an iron-based sintered alloy contains martensite in an iron - carbon based alloy base and is a porous iron-based sintered alloy of a hardened structure wherein copper is dispersed in it, the content of copper is 15-25 mass%, and its effective porosity is 15-28%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered plain bearing suitable for applications such as bearing elements for construction machines where a high surface pressure acts on the bearing sliding surface.

[0002]

2. Description of the Related Art For example, a hydraulic excavator for a construction machine uses a hydraulic cylinder to rock a bucket attached to the tip of an arm when performing an excavating operation. The joint between the bucket and the arm consists of a plain bearing element consisting of a shaft and a bearing. Since such a bearing element is subjected to a large surface pressure, a bearing having high wear resistance is used, and lubricating oil or grease having high viscosity is used on the sliding surface.

As such a bearing, an iron-carbon type sintered bond in which a lubricating oil having a high kinematic viscosity is impregnated is used in place of the one obtained by cutting a cast alloy or the one in which a graphite piece is embedded in a sliding surface in spots. Gold is being used. In order to secure high strength and high wear resistance, this sintered oil-impregnated bearing uses an iron-carbon alloy whose alloy base contains a martensite structure, and about 20 mass% of copper is dispersed in the structure. It is a thing. Since the bearing is hardened by heat treatment and is relatively large, the final finish is made by cutting and then grinding the inner peripheral surface.

[0004]

Such a conventional sintered oil-impregnated sliding bearing is an alloy containing lubricating oil, in which copper is dispersed in a hardened iron alloy matrix, which is suitable for high loads and is well used. Although it is possible, there is a slight variation in durability, and it has been desired that the stability and the longevity of the product become longer.

Therefore, the state of wear used in the conventional sintered oil-impregnated sliding bearing was observed, and attention was paid to the state of pores on the inner peripheral surface of the bearing to carry out research, and new findings were obtained. The present invention has been completed based on these findings.

[0006]

The present invention has been made in order to solve the above-mentioned problems, and its technical means are density 5.
It consists of a porous iron-based sintered alloy with a hardened structure of 8 or more, the inner peripheral surface of the bearing is a ground surface, and the pores exposed on the inner peripheral surface are 10% or less in area ratio, the metal thickness from the inner peripheral surface is Of 20 μm or less has pores that are sealed near the surface. This bearing has a surface pressure of 58.
It shows excellent performance under operating conditions of 8 MPa or more and a sliding speed of 2 to 5 cm / sec. The ground surface is a surface ground by a grinder (grinding machine). The term "sealing" refers to holes that are not exposed on the surface.

This iron-based sintered alloy contains martensite in an iron-carbon alloy matrix, copper is dispersed therein, the content of copper is 15 to 25% by mass, and the effective porosity is 15 to 28%. Some are preferred. The effective porosity is the ratio of the volume of pores communicating with the surface and capable of containing oil to the sample volume.

Further, in the sintered sliding bearing of the present invention, the amount of exposed pores on the inner peripheral surface of the bearing to be subjected to the radial load and the vicinity thereof is larger than the amount of exposed pores on the other inner peripheral surfaces and the number of sealing holes is smaller. Things are also included. Such a bearing can be obtained, for example, by processing or using it under the condition that the inner surface of the bearing receives a radial load and slides on the shaft to cause initial wear.

Furthermore, the sintered plain bearing of the present invention is optimally used as a bearing for joints of hydraulic excavators for construction machinery or for arm support joints of cranes.

The reason why the above-mentioned configuration, which is a feature of the present invention, is a requirement is as follows.

(1) Sintered alloy The material and composition of the sintered sliding bearing of the present invention is an iron-based sintered porous alloy containing a martensitic structure because of its strength and wear resistance. In particular, an alloy in which copper is dispersed in the iron-carbon alloy matrix is preferable, and the content of copper is preferably 15 to 25 mass%. Copper, which is soft and has good compatibility with the shaft, is present in the skeleton of the hard iron-carbon alloy base, and the elements that make up the alloy are few and it has excellent durability. If the amount of copper present on the sliding surface is small, the properties of the hard iron alloy will be stronger, and the shaft will be easily abraded, and if there is a large amount of copper, the copper will be deformed or pores on the surface will be removed due to sliding with high surface pressure. The content of copper is set to 15 to 25% by mass because the plugging tends to cause wear to proceed.

(2) Effective porosity and density The effective porosity is required to be 15% or more. If the effective porosity is low, the oil content on the sliding surface is small and the sliding surface is apt to run out of oil, resulting in shortened life. The larger the effective porosity, the higher the oil impregnation ability, which is preferable, but the density becomes low, the strength is lowered, and the wear resistance is also affected. The density of this alloy must be 5.8 g / cm ³ or more. When the copper content of the above-mentioned preferable sintered alloy is 25% by mass of the maximum value, the density is 5.8 g / cm ^3.
Above, the effective porosity is 28% or less. From these facts, the effective porosity is set to 15 to 28%.

(3) State of bearing inner peripheral surface The bearing inner peripheral surface is a grinding surface by a grinder (grinding machine). The area ratio of the pores exposed on the surface of the inner peripheral surface is 10% or less. In addition, there are pores which have a metal thickness of 20 μm or less in the depth direction from the inner peripheral surface and which are not opened on the surface and which are sealed. The sealed pores are observed from the microscopic structure of the lapping surface of the bearing cross section. Among the sealed pores near the surface of the inner peripheral surface of the bearing, the pores having a width of about 50 μm or more, The distance to the inner peripheral surface of the bearing is 20 μm or less. Such a ground surface can be stably obtained by selecting a grinding wheel and a grinding condition for processing the inner peripheral surface of the bearing material manufactured by previously determining the density. When the inner peripheral surface of the bearing material is cut by a lathe in advance and then ground, the pores existing near the surface of the inner peripheral surface of the bearing are crushed to a predetermined depth and the surface is densified. It can be obtained by a means for removing the surface layer by grinding the surface layer portion by a predetermined amount. In this case, cutting may be performed on the sintered body after sintering or on the heat-treated body after heat treatment, and the former can form a deeper densified portion.

The average surface roughness of the ground surface is 0.5 in Rmax.
Approximately 1 μm. When such a bearing inner peripheral surface is used by supplying lubricating oil to the fitting part in combination with a shaft, there are few pores exposed on the surface of the bearing inner peripheral surface.
Although the hydraulic pressure (oil film strength) of the sliding part becomes high, the radial load of high surface pressure applied to the inner peripheral surface of the bearing causes initial wear of the part that acts on the inner peripheral load, resulting in pores that were sealed with a thin metal. Is exposed on the worn surface. The bearing of the present invention is optimally a bearing for joints of construction machine hydraulic excavators or for arm support joints of cranes. At this time, the portion that initially wears is a portion where the shaft and the bearing relatively oscillate and a high surface pressure is applied. Even if this part is initially worn, the remaining part is slightly worn on the ground surface and the state in which the amount of pores is small is maintained. When the sealed pores are exposed, the impregnated lubricating oil is easily supplied to reduce friction after the initial wear. On the other hand, the inner peripheral portion of the bearing where the load is small keeps the sealing hole as it is, and the hydraulic oil escape of the lubricating oil is still small. As a result, the sliding performance is stabilized as a whole. Such a bearing may be manufactured by providing a processing means that produces the same effect as the initial wear.

The metal thickness up to the bearing inner peripheral surface of the pores which are present in the vicinity of the surface of the inner peripheral surface of the bearing and are not opened on the surface is easily removed by the initial abrasion and is subject to the initial wear. In the non-existing portion, the thickness is 20 μm or less so that the state in which the number of pores on the surface is small can be maintained. More preferably, it is 8 to 12 μm (about 10 μm). Grinding with a grinder (grinding machine) is suitable for forming such a thickness.

The amount of pores open on the grinding surface preferably has a large difference from the porosity of the sintered sintered alloy, but the minimum allowable density of the sintered alloy is 5.8 g / cm ³ for grinding. The area ratio is 10% or less from the state of the surface. It is preferably 1 to 3%.

(4) The impregnated lubricant-impregnated oil may be of the quality used for this type of high surface pressure sliding bearing. For example, those having a kinematic viscosity at 40 ° C. of about 2.2 to 10 m ² / s (220 to 1000 cSt) are suitable. Also suitable are waxes which are solid or semi-solid at room temperature and have a dropping point of 60 ° C. or higher. This wax contains oil components such as paraffin wax and microcrystalline wax, and preferably contains graphite and molybdenum disulfide particles.
The impregnated lubricating oil expands due to the temperature rise of the bearing due to the sliding between the bearing and the shaft, and is supplied to the sliding surface. When the bearing is used, grease may be injected into the bearing element.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to preferred examples and comparative examples.

(1) Manufacture of sintered bearing material Atomized iron powder (Kobe Steel Atmel 300M) 8
1.2kg and electrolytic copper powder (CE1 made by Fukuda Metal Foil Powder Industry
5) 18 kg and graphite powder (CPB manufactured by Nippon Graphite Industry Co., Ltd.)
0.5 kg of zinc stearate powder as a molding system lubricant was additionally mixed with 8 kg, and compression molded into a cylindrical shape. The compact was sintered in a reducing gas at a temperature of 1120 ° C.
The amount of bonded carbon in the iron-based sintered alloy matrix of the sintered product was 0.6% by mass. The density of the sintered body is 6.2 g / cm.
^{At 3} , the effective porosity was 21%. The temperature of the sintered body is 8
After heating to 50 ° C., oil quenching was performed and tempering was performed at a temperature of 180 ° C. The resulting bearing material contained a martensite structure.

(2) Cutting and Grinding The inner and outer peripheral surfaces and the end surfaces of the heat-treated sintered bearing material are cut with a carbide tool using a lathe, and then the bearing material and a grindstone are used using a grinding machine. The inner peripheral surface was ground by rotating. At this time, the amount of pores exposed on the inner peripheral surface was adjusted by changing the stock removal. The inner diameter of the bearing is 50 mm in diameter, and the overall length is 50 mm.

These bearing samples under different processing conditions were cut, the amount of exposed pores on the inner peripheral surface was obtained by observing with a microscope, and the cross section including the inner peripheral surface was observed with a microscope structure. For multiple pores of about 50 μm or more,
The thickness of the metal portion up to the inner peripheral surface was measured. The processing condition groups, which are the measured values of (a), (b), and (c) below, were used as bearing samples. (A) Example: A sample having a pore amount of 3 area% on the inner peripheral surface and a metal thickness of 10 μm on the sealing surface. (B) Comparative Example 1: A sample having a pore amount of 1 area% on the inner peripheral surface and a metal thickness of 30 μm on the sealing surface. (C) Comparative Example 2: A sample in which the amount of pores on the inner peripheral surface is 15% by area and almost no sealing is observed near the surface.

(3) Impregnation of Lubricating Oil The bearing sample was vacuum impregnated with a lubricating oil equivalent to ISO V G460 (kinematic viscosity at 40 ° C. 4.6 m ² / s (460 cSt)). Each sample has a different inner peripheral surface, but has the same internal pores and an oil content of 21%.

(4) Bearing test A bearing sample was fixed to a housing, grease was applied to a hardened and polished shaft, and the shaft was fitted to the inner circumference of the bearing sample. A radial load is applied to the shaft, and the surface pressure is 58.8 MPa.
(6 kgf / mm ² ). As for the shaft, a shaft sliding surface having a central angle of 100 degrees was reciprocally rotated at a sliding speed of 1.2 m per minute. At the end position of the reciprocating motion, 0.
There was a 5 second rest.

A thermocouple was attached to the outer peripheral surface of the bearing sample, and the bearing temperature was measured during the operation. If the bearing temperature reaches 150 ° C, the test will be stopped. 150 ° C. is a temperature at which seizure wear is recognized as a rule of thumb.

(5) Results of measurement of bearing temperature Table 1 shows the bearing temperatures tested in this way. As shown in Table 1, the sintered oil-impregnated sliding bearings of Examples are
Although the temperature increased at the initial stage of operation, the temperature decreased after passing that state and remained at the same temperature level for up to 30 hours.

In Comparative Example 1 in which the amount of pores on the inner peripheral surface is small and the metal thickness on the surface of the pores is relatively large, the pores are crushed. In Comparative Example 1, the temperature becomes higher at the initial stage, and the temperature temporarily changes. After continuing, the temperature drops and stabilizes at a temperature higher than that of the example. Further, in Comparative Example 2 in which the inner peripheral surface has a large amount of pores and there is almost no sealing due to processing, the temperature does not sharply rise in the initial stage as in Comparative Example 1, but the temperature gradually rises. The bearing temperature has been higher than the stable temperature.

In all cases, the temperature has not reached 150 ° C.

[0028]

[Table 1]

(6) Evaluation of test results The transition of these operating temperatures is considered to be due to the following reasons from the situation of observing the inner peripheral surface of the bearing.

It is considered that the sintered oil-impregnated sliding bearings of the examples had a shortage of lubricating oil on the radial load acting surface at the initial stage of operation, and the initial wear proceeded to raise the temperature. Then, due to wear, the opening area of the pores is formed so that the axial load and the pushing up force of the lubricating oil in the bearing pores are properly balanced, and an ideal lubrication form is created by the initial wear. After the initial wear, wear resistance does not progress and the sliding characteristics are stable based on the wear resistance due to the relatively hard quenched iron-carbon alloy matrix and the relatively soft copper particles and the optimum porosity. It is thought that it was done.

On the other hand, as in Comparative Example 1, in the case where the state of crushing due to working extends relatively deeply from the sliding surface portion, although some open pores are exposed by the initial wear, the lubricating oil still required. The temperature rises due to a shortage of supply. Then, as the high temperature continues, the lubricating oil easily flows out, but the metal thickness of the sealing hole is thick, the friction is high, and it changes while wearing,
It is considered that the time to reach the stable period is getting longer.

Further, as in Comparative Example 2, in the case where the amount of sealing is small and the number of pores opened on the sliding surface is relatively large, the lubricating oil is supplied to the radial load acting surface from the initial stage, and the temperature rise relatively. Although it becomes gentle, the parts other than the radial load acting surface are also porous, so the hydraulic pressure on the load acting surface easily escapes to the adjacent pores, and the temperature changes to a high state due to lack of lubrication. It is considered to be a thing.

As described above, in order to make the sliding surface of the bearing a smooth surface having excellent roundness, the sliding characteristics are not sufficient just by grinding, and the surface pores of the bearing material are appropriately sealed. It can be seen that a sintered oil-impregnated sliding bearing having durability is obtained when the radial load acting surface becomes a pore in a state of being balanced with the oil pressure of the lubricating oil due to the initial inner wear due to the inner peripheral surface.

Sintered oil-impregnated sliding bearings having a sufficient effective porosity in such an inner peripheral surface state can be manufactured by the surface densification technique in powder metallurgy, but there are many manufacturing processes and the bearings are used in the housing. There is a drawback that phase matching is required when assembling. On the other hand, the sintered oil-impregnated sliding bearing of the present invention can be manufactured stably by keeping the density of the bearing material and the cutting and grinding conditions constant so that the inner peripheral surface of the bearing can be stably produced in a predetermined surface state. By doing so, it is possible to form the pore state of the sliding surface that is optimal for the operating conditions by utilizing the initial wear that naturally occurs. Therefore, the bearing performance, manufacturability, and assemblability are excellent.

[0035]

As described above, the sintered slide bearing suitable for high surface pressure according to the present invention can stably maintain a state of low friction for a long period of time, so that the scheduled maintenance interval can be extended. It can be expected to reduce the cost.

Claims (3)

[Claims] 1. A bearing made of a porous iron-based sintered alloy having a hardened structure, wherein the inner peripheral surface of the bearing is a ground surface, and the pores exposed on the inner peripheral surface are 10% or less in area ratio. 20 thickness
A sintered plain bearing characterized in that pores having a size of not more than μm are present near the surface. 2. The iron-based sintered alloy contains martensite in an iron-carbon alloy matrix, copper is dispersed therein, the content of copper is 15 to 25 mass%, and the effective porosity is 15 to 28. %
The sintered oil-impregnated sliding bearing according to claim 1, wherein 3. A bearing inner peripheral surface to be subjected to a radial load and the amount of exposed pores in the vicinity thereof are larger than the amount of exposed pores of other inner peripheral surfaces and the number of sealing holes is smaller. Of sintered plain bearings.