JPH01316515A - Sintered bearing and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a sintered bearing excellent in a bearing characteristic without contaminating the circumference of a bearing element by using a lubricating component which is solid while using has a friction coefficient lower than a solid lubricant dispersion material. CONSTITUTION:A lubricant impregnating a sintered bearing is solid fat and oil and a lubricating component composed of the specific amount of oil at an ordinary temperature or within an ordinarily used temperature range. Fats and oils are generally indicate fat an oil, wax and fatty acid and desirable fats and oils are at least one type of a carnauba wax, mortan wax or the like since a smaller crystal has a better fat and oil characteristic and contained oil component is lower than 90%. The dropping point of this lubricating component is higher than 60 deg.C and as for the degree of hardness, a worked penetration is lower than 400 and a penetration is higher the 1 at the temperature of 25 deg.C.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a sintered bearing suitable for use in cases where the bearing itself rotates, oscillates or reciprocates, such as a printer carriage bearing, and its manufacture. Regarding the method.

(Prior Art) Conventionally, petroleum-based lubricating oils such as spindle oil and turbine oil, or synthetic lubricating oils, etc., have been generally used as impregnated 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 oozes out onto the friction surface due to the pumping action of the rotation of the shaft and the heat of sliding friction, and an oil film is formed by the wedge action of the oil. This results in a good lubrication effect on the sintered bearing.

Furthermore, as disclosed by the applicant in Japanese Patent Publication No. 49-11604, petroleum-based wax (paraffin wax is used in this example) which is solid at room temperature but becomes molten and liquid due to the heat of sliding on the bearing. Some sintered bearings are impregnated with a lubricating composition containing a mixture of petroleum-based lubricating oil and petroleum-based lubricating oil to prevent evaporation and leakage of the lubricating oil and extend the life of the bearing.

Other documents disclosing similar techniques include the following patent publications.

(1) JP-A-54-77211: Friction material for comparatively high surface pressure, in which a specific sintered alloy is melted and impregnated with paraffin or a saturated hydrocarbon such as a mixture of paraffin and sulfurized whale oil.

(2) Special Publication No. 55-39618 and Special Publication No. 56-3
No. 6694...In the pores of an iron-based sintered alloy with a specific composition,
Mo8 using an organic compound with a melting temperature of 100℃ or higher as a carrier
Friction material impregnated with solid lubricant powder (carrier: metal stearate, metal palmitate, palmitamide, etc.).

(Problems to be Solved by the Invention) Incidentally, sintered bearings generally used in industrial machines, office machines, home appliances, etc. are required to withstand operating environments at temperatures of 50°C.

On the other hand, when a sintered bearing impregnated with ordinary lubricating oil as described above is used for an element that swings or reciprocates with respect to a shaft,
Since no oil film is formed due to the pumping action, the coefficient of friction is high, and the bearing life is shortened due to the high fluidity and easy oil leakage. Furthermore, when a sintered bearing is used in a bearing that is coaxial, oscillates, or moves reciprocally, such as in a printer carriage, the problem of oil leakage may occur around the carriage and printing paper. There is a problem of contamination.

Furthermore, in the case of bearings impregnated with 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 since it becomes liquid during use. The problem of oil leaking and scattering is the same as when ordinary lubricating oil is used, and problems such as contamination of the area around the bearing element are not solved.

In addition, commercially available grease generally has a high melting point, and if heated and melted during impregnation, the oil content will evaporate and the composition will change easily, making it impossible to maintain quality. Also, if the heating temperature is low, it will not penetrate into the bearing part. It cannot be used for sintered oil-impregnated bearings.

On the other hand, with sintered bearings in which a solid lubricant such as graphite or molybdenum dioxide is dispersed in a sintered alloy rather than impregnated with lubricating oil, the problems caused by oil leakage and scattering as described above can be avoided. However, on the other hand, the friction coefficient is 5-6 compared to oil-impregnated bearings.
It is not practical as it is twice as expensive.

An object of the present invention is to provide a sintered bearing with excellent bearing characteristics without contaminating the surrounding area of the bearing element by using a lubricating composition that has a coefficient of friction smaller than that of a solid lubricant dispersion material and is solid during use. It is about providing.

(Means for Solving the Problems) In order to achieve the above object, the present invention specifies that the lubricant to be impregnated into a sintered bearing is a solid oil or fat at room temperature or a temperature range normally used. The lubricating composition is composed of a certain amount of oil.

Here, fats and oils include fats and oils and wax.

Fatty acids are collectively referred to as fatty acids, and preferred oils and fats include at least one type of natural wax such as carnauba wax, monk wax, microcrystalline wax, paraffin wax, beeswax, etc., since the smaller the crystal, the better the lubricating performance. Oil content is 90% or less.

In detail, this lubricating composition is dripped at 60°C or higher,
The degree of hardness is that the worked penetration is 400 at a temperature of 25℃.
The following is characterized in that the penetration degree (100 (100g/5s)) is 1 or more.

Therefore, those with large crystals, such as those using resins, metal stearates, and derivatives thereof as thickeners, are not included.

Furthermore, as mentioned above, the dropping point of the lubricating composition must be such that it does not flow at the upper limit driving temperature of 50°C, which is required for bearings. The upper limit of the dropping point temperature is 60°C or higher, and the highest is 87°C.

In addition, when impregnating a sintered bearing, it is desirable that the temperature at which the lubricating composition is melted is at a temperature at which there is little change in composition due to oxidation of the lubricating composition or evaporation of oil, so it is preferable that the lubricating composition be in a fluid state at a temperature of 120°C or lower. is necessary.

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

In addition, commercially available microcrystalline wax has approximately 15%
%, paraffin wax contains about 1% or less oil.

Furthermore, the amount of oil added is in the range of 0 to 90% as described above, and if the amount added exceeds 90%, the dropping point of the lubricating composition will be low and it will become liquid during use.

The degree of hardness of the lubricating composition is such that the worked penetration at 25°C is 4.
The range is 00 or less, and the penetration is 1 or more.

In other words, a worked penetration of 400 is a solid paste; anything above this is too soft and shows some fluidity; a penetration of less than 1 is too hard and is unsuitable as a lick lubricant with high shearing force. be.

Note that since it is not possible to measure a worked penetration of 85 or less, the higher hardness is expressed by the penetration.

The method for impregnating the sintered alloy is carried out by heating and melting a lubricating composition containing only oils or fats, or adding oil, and then immersing and reducing the pressure in the same manner as normal oil immersion.

Solid oils and fats have a crystalline structure, and these crystals can be observed under a microscope in the form of lumps or fibers, and generally, when the oil is slowly cooled without melting, the crystal grains become larger.

According to experimental experience, oils and fats with small crystals have good frictional properties. In particular, when paraffin wax is air-cooled, the crystal grains tend to become larger, but they can be made finer by rapidly cooling the wax after impregnation.

The crystal size of oils and fats is an important factor in lubricating properties as mentioned above, but some crystals have an elongated shape;
Further, unlike metal materials, there is no regulation of crystal size, so there is no particular range limitation.

In addition, as for the method of impregnating the lubricating composition, taking into account that crystals become coarse if the cooling rate is slow, such as paraffin wax, the sintered alloy is impregnated with the heated and melted lubricating composition, and then the sintered alloy is impregnated with the lubricating composition. The gist is to take out the liquid from the melt and rapidly cool it.

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

The lubricating composition may be one selected from the above-mentioned natural waxes, but a solid having the desired lubricity and appropriate softness can also be obtained by mixing a plurality of oils and fats.

However, when considering mass production, quality control is facilitated by using only one or two types of fats and oils.

(Examples) Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples.

The oils and fats used in the test were vegetable-based carnauba wax ■, mineral-based montan wax ■, animal-based beeswax ■, petroleum-based microcrystalline wax ■, and paraffin wax ■, and their properties are not listed. 1.

The petroleum wax contains oil, and 10% microcrystalline wax and 1% paraffin wax were used.

Table 1 Bearing samples were made of 10% Sn bronze sintered alloy, sized using the usual method, and had a density of 6.4 g/cm'.
The bearing materials, each having dimensions of φ10×φ16×10 mm, were immersed in the oils and fats listed in Table 1 that had been heated and melted at 100° C., impregnated under reduced pressure, and air-cooled to serve as samples.

The sample numbers correspond to the numbers ■ to ■ of the impregnated fats and oils.

Also, impregnated with oils and fats mixed with 1/2 of carnauba wax ■ and beeswax ■...Sample number ■, oils and fats mixed with 1/3 of each of microcrystalline wax ■, paraffin wax ■ and beeswax ■. Impregnated material: Sample No. ■ was prepared and used as a sample.

As a comparative example, Sample No. ■: A bearing sample similar to the example was impregnated with turbine oil equivalent to No. 100.

Sample number ■: One portion of calcium grease with a dropping point of 95°C, which is a commercially available cup grease, was added to the same bearing sample as in the example.
It was heated and melted at 50°C and impregnated under reduced pressure.

Sample number [phase]: A bearing sample of bronze sintered alloy with 5% copper-coated molybdenum disulfide powder added was subjected to conventional molding, sintering,
Three types were prepared: one that was prepared by sizing, and one that was not impregnated with a lubricant.

In addition, in the heating melting of the commercially available grease, in the case of lithium grease that is butter-like at room temperature, it was heated to 250° C., but it was difficult to impregnate it because of its high viscosity.

Furthermore, although the calcium grease used in Sample No. 9 melts easily, it has a property that oil separates when cooled, and it is assumed that the oil separates within the bearing holes.

Each sample above was mounted on a slide bearing tester,
The friction coefficient during sliding and the contamination state around the shaft were investigated.

This testing machine has a structure in which the 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, with a sliding speed of 15 m/min, one-way sliding distance M of 250 mm, and a load of Q 6 Kgf/cm2. and the ambient temperature of the bearing is 5
The temperature was kept at 0°C.

Next, the test results are shown in Table 2.

Samples No. 1 to 2 of the present invention had a friction coefficient equivalent to that of lubricating oil, and there was no surrounding contamination.

In the lubricating oil-impregnated product of sample number ■, oil seeped out from the bearing end and contaminated the sidewalls.

The commercially available grease-impregnated product with sample number (■) had a low initial coefficient of friction, but gradually increased as sludge-like dark brown matter adhered to the shaft surface.

Sample No. (■) was expected to have solid lubrication, but had a high coefficient of friction, and as time went on, the bearing's friction caused contamination of the surrounding area.

(Example 2) Carnauba wax (■) and microcrystalline wax (■) were tested in order to investigate the effects of oil on dropping point, consistency, and bearing performance.

Microcrystalline wax ■ contains 10% oil.

Further, as the added oil component, turbine oil having a viscosity (40° C.) of 100 cSt was used.

Figure 1 shows the relationship between oil content, dropping point, and worked penetration at 25°C.

The dropping point gradually decreases when the oil content exceeds 50%, and drops to 90%.
When the temperature exceeds 100 mL, the properties rapidly approach those of lubricating oil.

The consistency reached measurable hardness when the oil content was 40 to 60% or more, and as the oil content increased, it became softer and became paste-like. When the oil content exceeds 90%, it becomes fluid.

If 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 degree shown in Table 1.

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

As a result, the friction coefficient of any sample with an oil content of 90% or less was 0.
It was within the range of 1 to Q2, and there was no surrounding contamination.

(Example 3) The size of crystals of a material in which paraffin wax (1) was melted by heating to 120° C. and then slowly cooled and a material placed in water at 4° C. were observed using a microscope.

The former are elongated or massive crystals with approximately 2
00 to 400 μm, the latter having a shape close to a block,
It was approximately 70 to 100 μm.

When comparing the crystal grain size of various oils and fats shown in Table 1 with the friction coefficient of the bearing shown in Table 2, it was predicted that the smaller the crystal grain size of the oil and fat, the lower the friction coefficient, so the following test was conducted.

In the paraffin wax ■ heated and melted at 120℃,
A bronze sintered bearing sample was immersed and impregnated under reduced pressure in the same manner as in Example 1.

Thereafter, one type was slowly cooled in air, and the other type was rapidly cooled in stirring water at a temperature of 4°C.

For each sample, the friction coefficient was measured using a slide bearing tester as in Example 1.

As a result, the friction coefficient of the former is 02~03, and the latter is 01~03.
Q15, and the latter was superior.

(Effects) As explained above, the sintered bearing of the present invention is impregnated with a lubricating composition that is solid at room temperature or within the operating temperature range, which can be called a solid lubricating oil, so the pumping effect of the oil cannot be expected. It can be suitably used for sliding bearings.

In addition, the coefficient of friction is comparable to that of ordinary oil-impregnated bearings, and
Since lubricant leakage and scattering is extremely small, the bearing life can be extended, and a bearing without oil contamination can be provided, and the range of applications of sintered bearings can be expanded.

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

[Brief explanation of the drawing]

The drawing is a graph showing the relationship between the amount of oil added to fats and oils, dropping point, and worked penetration. Patent applicant Hitachi Powder Metallurgy Co., Ltd.

Claims (1)

[Scope of Claims] 1. A bearing in which the 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, wherein the dropping point of the lubricating composition is 60°C or higher, and the lubricating composition is miscible. Temperature (25℃)
is less than 400, has a penetration (100 g/5 s) of 1 or more, and is solid within the temperature range from room temperature to commonly used temperatures. 2. The process of impregnating a lubricating composition consisting of an oil or fat that is solid at room temperature to a temperature range commonly used and has an oil content of 90% by weight or less consists of the following (a) to (c). A method for manufacturing sintered bearings. (a) First step of heating and melting the lubricating composition and immersing and impregnating the sintered alloy in the solution.(b) Second step of removing 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 rapidly cooling the sintered alloy