JPH0819942B2 - Sintered bearing and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a sintered bearing suitable for cases where the bearing itself such as a carriage bearing of a printer rotates, oscillates or reciprocates, and its manufacture. Regarding the method.

<< Prior Art >> Conventionally, petroleum-based lubricating oils such as spindle oil and turbine oil, or synthetic oil lubricating oils have been generally used as impregnating lubricating oils for improving the lubricity of sintered bearings.

In such a sintered bearing, the lubricating oil impregnated and held in the pores of the sintered alloy is exuded to the friction surface by the pumping action due to the rotation of the shaft and the sliding frictional heat, and the oil film by the wedge action of the oil. It is possible to obtain a good lubricating action for the sintered bearing.

Further, as disclosed by the applicant in Japanese Examined Patent Publication No. 49-11604, a petroleum wax which is solid at room temperature but becomes a molten liquid by the sliding heat of the bearing (paraffin wax is used in this embodiment). %, A lubricating composition in which a petroleum-based lubricating oil is mixed is impregnated into a sintered bearing to prevent evaporation and leakage of the lubricating oil and prolong the life of the bearing.

Other documents disclosing similar techniques include the following patent publications.

(1) JP-A-54-77211 ... A friction material for relatively high surface pressure obtained by melting and impregnating a specific sintered alloy with a saturated hydrocarbon such as paraffin or a mixture of paraffin and sulfurized whale oil.

(2) JP-B-55-39618 and JP-B-56-36694 ... Solid lubricant powder such as MoS ₂ with a molten organic compound as a carrier in the pores of an iron-based sintered alloy of a specific composition Friction material impregnated with (carrier is metal stearate, metal palmitate, palmitoamide, etc.).

<< Problems to be Solved by the Invention >> By the way, sintered bearings generally used for industrial machines, office machines, household electric appliances, etc. are required to withstand a use environment of a temperature of 50 ° C.

On the other hand, when the above-mentioned sintered bearing impregnated with normal lubricating oil is used as an element that oscillates or reciprocates with respect to the shaft, the oil film is not formed by the pump action, so the friction coefficient increases and the fluidity Is high and oil leaks easily, which shortens the life of the bearing. Further, the problem of oil leakage is that when a sintered bearing is used for a bearing that rotates, oscillates, or reciprocates, such as for a carriage of a printer, the surroundings of the carriage and the printing paper are not supported. There is a problem of polluting.

Also, in the case of a bearing impregnated with a lubricating oil that is solid at room temperature and flows as the temperature rises during use, the bearing life can be extended as described above, but it becomes liquid during use. The problem that the oil leaks and scatters is the same as when using normal lubricating oil, and the problem of contaminating the surroundings of the bearing element cannot be solved.

In addition, commercially available grease generally has a high melting point, and when it is heated and melted during impregnation, the oil content evaporates and the composition is apt to change, and the quality cannot be maintained. It cannot be used for sintered oil-impregnated bearings.

On the other hand, according to a sintered bearing in which a solid lubricant such as graphite or molybdenum dioxide is dispersed in a sintered alloy instead of being impregnated with lubricating oil, the above-mentioned problems caused by oil leakage, scattering, etc. Although it does not exist, on the other hand, the coefficient of friction is between 5
It is 6 times higher and not practical.

An object of the present invention is to provide a sintered bearing having excellent bearing characteristics without polluting the periphery of the bearing element by using a lubricating composition having a friction coefficient smaller than that of the solid lubricant dispersion material and being solid during use. To provide.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the present invention provides a lubricant for impregnating a sintered bearing with a solid oil or fat within a temperature range from room temperature to a normal use, A lubricating composition composed of an amount of oil.

Here, the oils and fats are collectively referred to as oils, waxes, and fatty acids, but preferable oils and fats have smaller oil crystals because they have better oil-sliding performance. For example, carnauba wax, montan wax, microcrystalline wax, paraffin wax, It is at least one natural wax such as beeswax and contains 90% or less of oil.

In detail, the dropping point of this lubricating composition is 60 ° C. or higher,
The hardness is characterized by a mixing consistency of 400 or less and a penetration rate (100g / 5s) of 1 or more at a temperature of 25 ° C.

Therefore, it does not include those having large crystals such as those of resin type, metal stearate, and their derivatives as thickeners.

Further, as described above, the dropping point of the lubricating composition must not flow at the driving upper limit temperature of 50 ° C. required for the bearing, but in consideration of overheating during transportation or use, the dropping point temperature is 60 The maximum dropping point temperature above 87 ° C is 87 ° C.

When impregnating the sintered bearing, the melting temperature is
Since it is desirable that the temperature is such that the composition of the lubricating composition does not change due to the oxidation of the lubricating composition or the evaporation of the oil component, it is necessary that the lubricating composition is in a fluid state at a temperature of 120 ° C. or less.

The oil component is added mainly for the purpose of adjusting the hardness of the lubricating composition, and ordinary petroleum-based lubricating oil and synthetic lubricating oil can be used, and the viscosity is selected according to the selected fats and oils.

It should be noted that about 15 is available for commercially available microcrystalline wax.
%, And paraffin wax contains less than about 1% oil.

Further, the addition amount of the oil component is in the range of 0 to 90% as described above, and if the addition amount exceeds 90%, the dropping point of the lubricating composition becomes low and the oil composition becomes liquid during use.

The hardness of the lubricating composition is such that the mixing consistency at 25 ° C is 40.
The range is 0 or less and the penetration is 1 or more.

That is, the workability 400 is a solid paste, and if it is more than this, it is too soft and shows a little fluidity. If the penetration is 1 or less, it is too hard and the shearing force is high, so it is not suitable as a lubricant. .

It should be noted that, since the workability of less than 85 is not measurable, the higher hardness is represented by the penetration.

The method of impregnating a sintered alloy is carried out by heating and melting only a fat or oil or a lubricating composition to which oil is added, and immersing and depressurizing it in the same manner as in ordinary oil immersion.

Solid fats and oils have a crystalline structure, and these crystals are lumpy or fibrous and can be observed by a microscope. Generally, when melted and then slowly cooled, the crystal grains become large.

According to experimental experience, oils and fats having small crystals have good friction characteristics. In particular, paraffin wax tends to have large crystal grains when air-cooled, but can be made finer by rapid cooling after impregnation.

Note that the crystal size of oils and fats is an important factor for the lubrication characteristics as described above, but there are some crystal shapes that are long and thin, and there is no regulation of the crystal size like metal materials. The range is not limited.

Further, as a method of impregnating the lubricating composition, in consideration of a material such as paraffin wax in which crystals are coarsened when the cooling rate is slow, in consideration of impregnating the heated and melted lubricating composition with the sintered alloy, the sintered alloy is used. The main point is to take out from the melt and quench it.

The lubricating composition as described above in the present invention is impregnated into at least the surface layer portion of the sintered bearing, acts as a solid lubricant within a temperature range from room temperature to during use, has a low friction coefficient, and has a leakage scattering. It does not pollute the surroundings.

Further, the lubricating composition may be one kind selected from the above-mentioned natural waxes, but even if a plurality of fats and oils are mixed, a solid having desired lubricity and appropriate softness can be obtained.

However, if mass production is taken into consideration, a single oil / fat is 2
It is easy to control the quality of seeds.

<< Example >> The present invention will be described in detail below with reference to Examples and Comparative Examples.

The fats and oils used in the test were plant-based carnauba wax, mineral-based montan wax, animal-based beeswax, petroleum-based microcrystalline wax, and paraffin wax, and their properties are shown in Table 1. .

The petroleum wax contained oil, and microcrystalline wax was 10% and paraffin wax was 1%.

The bearing sample is a bronze sintered alloy of 10% Sn, sized by a normal method. The density is 6.4 g / cm ³ , and the size is φ10 ×.
This bearing material having a size of φ16 × 10 mm was immersed in oils and fats of Table 1 heated and melted at 100 ° C., impregnated under reduced pressure, and air-cooled to be used as a sample.

The sample numbers correspond to the impregnated fats and oils.

In addition, oils and fats mixed with carnauba wax and beeswax mixed in half each: sample number, oils and oils mixed with microcrystalline wax, paraffin wax, and beeswax in 1/3 each sample number. It was used as a sample.

As a comparative example, sample number; a bearing sample similar to that of the example was impregnated with turbine oil corresponding to No. 100.

Sample No .: A bearing sample similar to that used in the example was applied with commercially available cup grease, calcium grease having a dropping point of 95 ° C.
It was melted by heating at 0 ° C and impregnated under reduced pressure.

Sample number: Three types of bearing samples of a bronze sintered alloy to which 5% of copper-coated molybdenum disulfide powder was added were prepared by ordinary molding, sintering, and sizing and not impregnated with a lubricant.

In the case of the above-mentioned commercially available grease, the lithium grease that was buttered at room temperature was heated to 250 ° C., but impregnation was difficult due to its high viscosity.

Further, the calcium grease used in Sample No. 9 is easily melted, but has the property of separating oil when cooled, and it is assumed that the grease is separated even in the bearing holes.

Each of the above samples was mounted on a slide bearing tester, and the coefficient of friction during sliding and the state of contamination around the shaft were examined.

This tester has a structure in which a bearing sample reciprocates in the axial direction with respect to a fixed shaft, similar to the carriage part of a printer such as a word processor. Sliding speed is 15 m / min, one-way sliding distance is 250 mm, load is 0.6 kg.
f / cm ² , and the ambient temperature of the bearing was kept at 50 ° C.

 Next, the test results are shown in Table 2.

Sample Nos. 1 to 3 of the present invention had the same friction coefficient as that of the lubricating oil, and there was no contamination in the surroundings.

With the sample impregnated with lubricating oil, oil leached from the wet end of the bearing, resulting in contamination of the surrounding area.

The commercially available grease-impregnated product of Sample No. had a low initial friction coefficient, but gradually increased as a sludge-like blackish brown substance adhered to the shaft surface.

The sample number is expected to have solid lubrication, but the friction coefficient is high, and the surroundings were contaminated with the friction powder of the bearing with the running time.

(Example 2) Carnauba wax and microcrystalline wax were tested for the purpose of investigating the dropping point, the consistency, and the bearing performance that the oil content exerts.

Microcrystalline wax contains 10% oil.

For the added oil, turbine oil with a viscosity (40 ° C) of 100 cSt was used.

Fig. 1 shows the relationship between the oil content and the dropping point, and the mixing consistency at 25 ° C.

When the oil content exceeds 50%, the dropping point gradually decreases, and when it exceeds 90%, it rapidly approaches the properties of lubricating oil.

The consistency became measurable when the oil content was 40-60% or more, and became soft and became paste-like with the increase of the oil content. It becomes fluid when the oil content exceeds 90%. When the oil content is 40 to 50% or less, the hardness is such that the consistency cannot be measured.

The hardness of each wax itself is indicated by the penetration shown in Table 1.

Next, each wax having different oil content was impregnated into a bronze sintered bearing sample in the same manner as in Example 1 to make a slide bearing.

As a result, the coefficient of friction is 0 for any sample with an oil content of 90% or less.
It was within the range of 1 to 0.2 and there was no surrounding pollution.

Example 3 The crystal size of the material obtained by heating and melting paraffin wax at 120 ° C. and then gradually cooling it and the size of the material placed in water at 4 ° C. were observed with a microscope.

The former is a slender or lumpy developed crystal, which is roughly
200 to 400 μm, the latter having a shape close to a lump, and was about 70 to 100 μm.

When the crystal grain sizes of various oils and fats shown in Table 1 and the friction coefficient of the bearing shown in Table 2 are collated, it is expected that the smaller the crystal grain size of oils and fats, the lower the friction coefficient, and the following tests were conducted.

In the same manner as in Example 1, a bronze sintered bearing sample was dipped and impregnated under reduced pressure while the paraffin wax was heated and melted at 120 ° C.

Then, one kind was gradually cooled in air, and the other was rapidly cooled in stirred water at a temperature of 4 ° C.

The friction coefficient of each sample was measured with the slide bearing tester as in Example 1.

As a result, the friction coefficient of the former is 0.2-0.3 and that of the latter is 0.1-.
0.15, the latter being superior.

<< Effects >> As described above, the sintered bearing of the present invention is impregnated with a solid lubricating composition at room temperature or a temperature range in which it can be said to be a solid lubricating oil, so that an oil pumping action cannot be expected. It can be suitably used for plain bearings.

In addition, the friction coefficient is comparable to that of ordinary oil-impregnated bearings, and since the leakage of lubricant is extremely small, the bearing life can be extended and a bearing free of oil contamination can be provided. The application range of can be expanded.

Further, according to the manufacturing method of the present invention, the sintered alloy is immersed and impregnated in the solution of the lubricating composition obtained by heating and melting the sintered bearing, and the sintered bearing is taken out from the melt and kept at a temperature higher than the pour point of the lubricant. After that, since it is rapidly cooled, crystals of the lubricating composition can be made finer, and a sintered bearing having a low friction coefficient and excellent lubricating characteristics can be obtained.

[Brief description of drawings]

The drawing is a graph showing the relationship between the amount of oil added to fats and oils, the dropping point, and the workability.

Claims (2)

[Claims] 1. A bearing in which pores of a sintered alloy are impregnated with a lubricating composition composed of oils and fats having an oil content of 90% by weight or less,
The above-mentioned lubricating composition has a dropping point of 60 ° C or higher and a working consistency (25
The sintered bearing is characterized in that it has a penetration temperature (° C) of less than 400, a penetration (100g / 5s) of 1 or more, and is in a solid state within a temperature range from room temperature to a normal use. 2. The step of impregnating a lubricating composition which is solid at room temperature to a temperature range usually used and which comprises oils and fats having an oil content of 90% by weight or less comprises the following (a) to (c): A method for manufacturing a sintered bearing, comprising: (A) The first step of heating and melting the lubricating composition, and immersing and impregnating the sintered alloy in the solution. (B) The second step of taking out the sintered alloy from the melt and holding it at a temperature higher than the pour point of the lubricant. Step (c) Third step of quenching the sintered alloy