CN113333737A - Powder metallurgy oil-retaining bearing material and preparation method thereof - Google Patents

Abstract

The invention discloses a powder metallurgy oil-retaining bearing material, which belongs to the technical field of powder metallurgy materials and comprises the following raw materials in percentage by mass: 2-4% of copper powder, 0.1-0.2% of chromium powder, 2-4% of graphite powder, 0.5-0.9% of molybdenum disulfide and the balance of iron powder, wherein the total mass percentage content is 100%; in terms of the whole mass of the raw materials, 0.4-0.8% of wax powder is additionally added, and the invention also discloses a preparation method of the material; according to the invention, the metal chromium powder is used as a carrier, the alloy element chromium is added, rare earth metal is not required to be added, the element composition is relatively simple, and the proportion of each element in the powder metallurgy oil-retaining bearing material is optimized; the oil-retaining bearing prepared by the material has high radial crushing strength which can reach over 330MPa, and can ensure that the oil-retaining rate reaches over 20 percent, thereby having excellent bearing and antifriction properties and being suitable for a gear fixing seat of a starting motor of a motorcycle; and the preparation process of the powder metallurgy oil-retaining bearing material is mature and stable, and the qualification rate of the obtained product reaches 100 percent.

Description

Powder metallurgy oil-retaining bearing material and preparation method thereof

Technical Field

The invention relates to the technical field of powder metallurgy materials, in particular to a powder metallurgy oil-retaining bearing material for a motorcycle starting motor gear fixing seat and a preparation method thereof.

Background

The oil-containing bearing is a porous antifriction material which is prepared by taking metal or plastic powder as a main raw material and adopting a powder metallurgy process and is subjected to oil immersion treatment, the oil content is usually 10-40 vol%, the antifriction performance is excellent, and the oil-containing bearing has the characteristics of low noise, long service life and the like, so that the oil-containing bearing is widely used as a motorcycle transmission part.

In the process, the bearing rotates to generate centrifugal force, and the friction heat generation induces thermal expansion to promote oil to overflow and fill gaps, so that the lubricating and antifriction effects are achieved. Meanwhile, after the transmission is stopped, the oil is cooled and contracted and is sucked into the pores by virtue of the capillary action, so that the oil is stored and the loss is avoided.

In general, the oil-impregnated bearing has radial crushing strength and oil content as main evaluation indexes. The radial crushing strength is used as an important parameter for representing the mechanical property of the oil-retaining bearing, and the bearing capacity of the oil-retaining bearing is determined; the oil content has a significant influence on the friction reducing performance.

At present, in order to obtain good antifriction performance, the oil-retaining bearing needs to increase the pore structure to improve the oil-retaining rate, however, the increase of the pore structure inevitably causes the reduction of the radial crushing strength, and the bearing capacity of the oil-retaining bearing is unqualified. Similarly, in order to obtain excellent bearing capacity, the oil-impregnated bearing needs to have increased density to reduce the pore structure, however, the reduction of the pore structure inevitably causes a reduction in the oil content, resulting in an unsatisfactory antifriction performance of the oil-impregnated bearing.

That is, the radial crushing strength and the oil content of the oil-containing bearing used for the motorcycle starting motor gear fixing seat at present can not be considered at the same time, the oil content can be reduced due to the reduction of pores when the radial crushing strength is improved, and the radial crushing strength can be reduced due to the increase of pores when the oil content is improved. At present, the technical standards of the oil-containing bearing used for the motorcycle starting motor gear fixing seat are as follows: the oil content reaches 18%, and the radial crushing strength reaches 294MPa, although the prior art can basically reach the standard, the qualification rate of each batch is different, the qualification rate of 100% is difficult to reach, the waste of materials and processes is caused, and the cost is high;

moreover, in order to prepare a material with better performance to improve the service life and reliability of the bearing, many efforts have been made in the art, for example, chinese patent application publication No. CN107855517A discloses an oil-retaining bearing for a gear fixing seat of a starter motor of a motorcycle, which has a radial crushing strength of 320MPa and an oil content of 20%. However, the application introduces nickel as an alloy element into a bearing material by using nickel carbonyl powder as a carrier, and although the nickel carbonyl powder can play a role in performance enhancement, the nickel carbonyl powder also has the problem of high cost, and particularly, the price of the nickel carbonyl powder is about 200 yuan/kg at present. In addition, the combination property of the composition is still to be improved.

Disclosure of Invention

One of the objectives of the present invention is to provide a new powder metallurgy oil-retaining bearing material to solve the above-mentioned problem that the radial crushing strength and oil-retaining rate of the oil-retaining bearing cannot be balanced.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows: the powder metallurgy oil-retaining bearing material comprises the following raw materials in percentage by mass: 2-4% of copper powder, 0.1-0.2% of chromium powder, 2-4% of graphite powder, 0.5-0.9% of molybdenum disulfide and the balance of iron powder, wherein the total mass percentage content is 100%; and 0.4-0.8% of wax powder by mass is additionally added based on the whole mass of the raw materials.

The preferable technical scheme comprises the following raw materials in percentage by mass: 2.8% of copper powder, 0.15% of chromium powder, 2.9% of graphite powder, 0.68% of molybdenum disulfide and the balance of iron powder, wherein the total mass content is 100%; 0.6 percent of micro-wax powder is additionally added based on the total mass of the raw materials.

According to the invention, a large number of tests are carried out on the basis of CN107855517A, and the unexpected discovery that the nickel powder in the application is replaced by chromium powder, and the use amount of the chromium powder is further adjusted, so that the radial crushing strength of the oil-containing bearing of the motorcycle starting motor gear fixing seat can be obviously improved, and the oil content can be ensured to be more than 20%.

Compared with the cost of the carbonyl nickel powder of about 200 yuan/kg, the chromium powder used in the invention is only 100 yuan/kg, the material cost is obviously reduced, and the method has great significance for industrial production. Meanwhile, chromium as an alloy element can play the roles of solid solution strengthening, dispersion strengthening and grain refinement, so that the radial crushing strength of the oil-retaining bearing obtained by the invention reaches more than 330MPa, and the oil content is ensured to reach more than 20%.

The chromium powder used in the powder metallurgy oil-retaining bearing material has the purity of 99.5 percent and the grain diameter of not more than 10 mu m. The chromium powder has small granularity and rough surface, so that the chromium powder can be fully mixed with other particles and tightly combined, and the mass distribution of the chromium powder is stable and uniform. Meanwhile, based on the high hardness of the chromium powder, the chromium powder can reduce the compression coefficient and increase the porosity of a pressed compact, thereby ensuring the oil content of a sintered compact. In addition, the chromium powder has large specific surface area and high surface energy and is easy to sinter.

The above molybdenum disulfide (MoS)₂) The functions in the invention are as follows: the lubricating property is exerted, the particle segregation is reduced, the particles are uniformly dispersed, and the density distribution of the pressed compact is improved. Meanwhile, the pressing friction force is reduced, and the service life of the die is prolonged. In addition, FeS and Mo can be generated by reaction with Fe in the sintering process, wherein FeS and Fe form eutectic liquid phase to promote liquid phase sintering, and Mo is dissolved in Fe in a solid solution manner to play a solid solution strengthening role and refine pearlite.

The micro wax powder comprises: the friction between powder particles and between the powder particles and a die in the pressing process is reduced, so that the powder pressing performance is improved, the density and the uniformity of a pressed part are improved, and the demoulding is facilitated. Meanwhile, the porous ceramic material is used as a pore-forming agent, so that the porosity of a sintered blank is improved, and the oil content is ensured. In addition, compared with the traditional zinc stearate, the micro-wax powder is easier to be thoroughly removed in the sintering process, and the sintered product and the furnace tube of the sintering furnace are not polluted, so that the cleanliness of the sintered product is high, and the service life of the furnace tube of the sintering furnace is long.

The second object of the present invention is to provide a method for preparing the above powder metallurgy oil-retaining bearing material, comprising the steps of:

(1) preparing materials: weighing raw materials according to the proportion;

(2) mixing: adding the mixture into a mixer, and stirring and mixing the mixture evenly;

(3) pressing: loading the uniformly mixed raw material powder into a forming die, and pressing on a forming press to obtain a green body, wherein the green body density is not less than 6.2g/cm³；

(4) And (3) sintering: loading the green body into a burning boat, placing the burning boat into a sintering furnace for sintering, and continuously introducing protective atmosphere in the process to obtain a sintered body;

(5) oil immersion: cooling the sintered blank, washing and soaking in oil to obtain an oil-soaked blank;

(6) fine shaping: loading the oil-impregnated blank into a fine shaping die for finishing treatment to obtain a finished blank;

(7) oil immersion: and (4) carrying out oil immersion treatment on the finishing blank to obtain a finished product.

As a preferred technical scheme: in the step (3), the pressing pressure is 4t/cm²。

As a preferred technical scheme: in the step (6), the fine shaping die is made of hard alloy.

Compared with the prior art, the invention has the advantages that:

according to the invention, the metal chromium powder is used as a carrier, the alloy element chromium is added, rare earth metal is not required to be added, the element composition is relatively simple, and the comprehensive mechanical property of the powder metallurgy oil-retaining bearing material is improved by optimizing the proportion of each element in the powder metallurgy oil-retaining bearing material; the oil-retaining bearing prepared by the material has high radial crushing strength which can reach over 330MPa, and can ensure that the oil-retaining rate reaches over 20 percent, thereby having excellent bearing and antifriction properties and being suitable for a gear fixing seat of a starting motor of a motorcycle; and the preparation process of the powder metallurgy oil-retaining bearing material is mature and stable, and the qualification rate of the obtained product reaches 100 percent.

Detailed Description

The present invention will be further described with reference to the following examples.

The chromium powder used in the following examples and comparative examples had a particle size of not more than 10 μm, and the copper powder used was electrolytic copper powder having a particle size of-200 mesh; the iron powder is reduced iron powder with the grain diameter of-100 meshes, the particle diameter of the molybdenum disulfide is-100 meshes, the particle diameter of the micro-wax powder is-100 meshes, and all the components are commercial products. Meanwhile,% represents mass% unless otherwise specified.

Example 1

A powder metallurgy oil-retaining bearing material comprises the following raw materials in percentage by mass: 2.2% of copper powder, 0.1% of chromium powder, 2% of graphite powder, 0.5% of molybdenum disulfide and the balance of iron powder, wherein the total mass percentage of the copper powder, the chromium powder, the graphite powder and the molybdenum disulfide is 100%, and 0.4% of micro-wax powder is additionally added in the total mass of the raw materials;

the method for preparing the oil-retaining bearing for the motorcycle starting motor gear fixing seat by using the material comprises the following steps: firstly, weighing the raw material powder in proportion, and fully mixing; subsequently, the mixed powder was charged into a mold and pressed into a green body on a forming press, wherein the pressing pressure was 4t/cm²While the dry density of the green compact is not less than 6.2g/cm³(ii) a Secondly, putting the green body into a burning boat, putting the burning boat into a sintering furnace for sintering, controlling the sintering temperature to be 1085 ℃, preserving the temperature for 3 hours, and continuously introducing nitrogen-based protective atmosphere in the process; thirdly, cooling the sintered blank, soaking in oil, and filling the sintered blank into a shaping die for finishing treatment; and finally, carrying out oil immersion treatment on the finished blank to obtain a finished product, wherein the height, the outer diameter and the wall thickness of the obtained finished product are respectively 6.10mm, 12.10mm and 2.00mm, the weight is 2.16g, and the density and the size precision of the finished product meet the requirements.

Example 2:

a powder metallurgy oil-retaining bearing material comprises the following raw materials in percentage by mass: 2.8% of copper powder, 0.15% of chromium powder, 2.9% of graphite powder, 0.68% of molybdenum disulfide and the balance of iron powder, wherein the total mass percentage of the copper powder, the chromium powder, the graphite powder and the molybdenum disulfide is 100%, and 0.6% of wax powder is additionally added in the total mass of the raw materials;

the production method is the same as that of the example 1, the height, the outer diameter and the wall thickness of the obtained finished product are respectively 6.10mm, 12.10mm and 2.00mm, the weight is 2.16g, and the density and the dimensional accuracy of the finished product meet the requirements.

Example 3:

a powder metallurgy oil-retaining bearing material comprises the following raw materials in percentage by mass: 3.8% of copper powder, 0.2% of chromium powder, 3.7% of graphite powder, 0.86% of molybdenum disulfide and the balance of iron powder, wherein the total mass percentage of the copper powder, the chromium powder, the graphite powder and the molybdenum disulfide is 100%, and 0.75% of wax powder is additionally added in the total mass of the raw materials;

the production method is the same as that of the example 1, the height, the outer diameter and the wall thickness of the obtained finished product are respectively 6.10mm, 12.10mm and 2.00mm, the weight is 2.16g, and the density and the dimensional accuracy of the finished product meet the requirements.

Comparative example 1:

in order to verify the function of the chromium powder, the comparative example takes the example 2 as a standard, only the addition amount of the chromium powder is modified to be 0, the mixture ratio of the rest raw materials is kept unchanged, meanwhile, the production method is the same as the example 1, and the size parameters and the weight of the obtained finished product are also the same as the example 2.

Comparative example 2

In order to verify that the usage amount of the chromium powder also has very important influence on the performance, the comparative example takes the example 2 as the standard, only the content of the chromium powder is respectively modified into 0.06 percent, 0.09 percent, 0.26 percent and 0.33 percent, the rest raw material proportions are kept unchanged, meanwhile, the production method is the same as the example 1, and the size parameters and the weight of the obtained finished product are also the same as the example 2.

Comparative example 3

In the Chinese patent application with the publication number of CN 110184546A and the patent name of 'heavy-load powder metallurgy oil-retaining bearing and preparation method thereof', the alloy element chromium is introduced into the oil-retaining bearing material, and low-carbon ferrochrome is used as a carrier. However, the two applications are different and the composition difference is significant. The invention is suitable for heavy-load occasions, such as mining machinery and engineering machinery, and the invention is suitable for the motorcycle starting motor gear fixing seat, and belongs to light-load occasions. Meanwhile, the invention is based on an iron-copper-carbon system, takes molybdenum disulfide and micro-wax powder as lubricants, and adds chromium powder to play a strengthening role, so that the performance of the oil-retaining bearing is improved, and the application mainly highlights the role of an alloy element niobium. The two components are different in key components for improving the performance of the oil-retaining bearing. In addition, in the comparative example, the raw material ratio in the application example 4 is adopted to prepare the oil-retaining bearing, the production method is the same as that in the example 1, and the size parameters of the obtained finished product are the same as that in the example 2.

The method comprises the following steps of bearing performance verification:

the oil-impregnated bearings prepared by the powder metallurgy materials in the examples 1, 2, 3, 1, 2 and 3 are randomly selected from three batches respectively, and radial crushing strength, oil content and apparent hardness are tested by GB/T6804 & lt 2008 & gt sintered metal bushing radial crushing strength, GB/T5163 & lt 2006 & gt sintered metal material density, oil content and aperture ratio and GB/T9097 & lt 2016 (excluding cemented carbide) sintered metal material apparent hardness and microhardness respectively, and the results are shown in Table 1:

TABLE 1 results of Performance test of each example and comparative example

Table 1 shows that the radial crushing strength and the oil content of the oil-containing bearing obtained in the three examples are higher than those of the comparative example, and the addition of a proper amount of chromium element can effectively improve the mechanical property of the product and ensure the oil content. In the invention, chromium as an alloy element can be dissolved in iron to form a substitutional solid solution, and holes are left around, so that the solid solution strengthening effect can be exerted, and the oil content is ensured. Meanwhile, chromium is used as a strong carbide forming element, free carbon in the material can be combined, the content of the free carbon is reduced, and the brittleness characteristic of the material is reduced. In addition, based on the characteristics of small size, high hardness and the like of the chromium-carbon compound, the chromium element can play a role in dispersion strengthening and grain refinement.

The oil-impregnated bearing prepared in comparative example 1 has insufficient comprehensive mechanical properties, and the radial crushing strength and the oil content are lower than those of the examples. Meanwhile, according to customer reflection, the individual oil-containing bearing exists in the comparative example 1, and the phenomenon of shaft sticking occurs in the use process, which shows that the oil-containing rate of the bearing is low and the antifriction performance is insufficient. However, after the chromium powder is added into the raw material formula, the prepared oil-retaining bearing never has the phenomenon of shaft sticking.

Compared with the comparative example 1, the comparison between the example 2 and the comparative example 1 shows that after a proper amount of chromium powder is added into the raw material formula, all performance parameters of the obtained oil-retaining bearing are obviously improved, and the qualified rate of the product reaches 100%; under the same process conditions, the performance parameters of the product without the chromium powder are not completely qualified: or the radial crushing strength meets the requirement, but the oil content is slightly low and cannot meet the requirement, so that the yield of the batch of products is low; or the oil content meets the requirement, the radial crushing strength is slightly low and cannot meet the requirement, and the qualified rate of the batch of products is low. The batch qualification rate is only about 70%.

It can be seen from the comparison between example 2 and comparative example 2 that the influence of the addition amount of chromium on the performance is very critical, the improvement of the related performance is not facilitated by too little or too much addition amount of chromium, and the yield of some batches of comparative example 2 is only about 80%.

The combination of the properties of example 2 of the present invention and comparative example 3 is shown to be superior. Meanwhile, in the embodiment 2, only chromium is used as a strengthening element, and the content is only 0.15%, so that the comprehensive performance of the oil-retaining bearing is improved, while in the comparative example 3, a plurality of strengthening elements such as molybdenum, nickel, niobium, manganese and the like are contained, the content is up to 13.5%, and rare earth oxide is added as a dispersion phase, so that the component proportion and the production cost of the two are obviously different. Compared with the invention, CN 110184546A is not suitable for preparing the oil-retaining bearing for the gear fixing seat of the starting motor of the motorcycle.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (5)

1. The powder metallurgy oil-retaining bearing material is characterized by comprising the following raw materials in percentage by mass: 2-4% of copper powder, 0.1-0.2% of chromium powder, 2-4% of graphite powder, 0.5-0.9% of molybdenum disulfide and the balance of iron powder, wherein the total mass percentage content is 100%; and 0.4-0.8% of wax powder by mass is additionally added based on the whole mass of the raw materials.

2. The powder metallurgy oil-retaining bearing material according to claim 1, comprising the following raw materials in percentage by mass: 2.8% of copper powder, 0.15% of chromium powder, 2.9% of graphite powder, 0.68% of molybdenum disulfide and the balance of iron powder, wherein the total mass content is 100%; 0.6 percent of micro-wax powder is additionally added based on the total mass of the raw materials.

3. The method for producing a powder metallurgy oil-retaining bearing material according to any one of claims 1 to 2, characterized by comprising the steps of:

(1) preparing materials: weighing raw materials according to the proportion;

(2) mixing: adding the mixture into a mixer, and stirring and mixing the mixture evenly;

(3) pressing: loading the uniformly mixed raw material powder into a forming die, and pressing on a forming press to obtain a green body, wherein the green body density is not less than 6.2g/cm³；

(4) And (3) sintering: loading the green body into a burning boat, placing the burning boat into a sintering furnace for sintering, and continuously introducing protective atmosphere in the process to obtain a sintered body;

(5) oil immersion: cooling the sintered blank, washing and soaking in oil to obtain an oil-soaked blank;

(6) fine shaping: loading the oil-impregnated blank into a fine shaping die for finishing treatment to obtain a finished blank;

(7) oil immersion: and (4) carrying out oil immersion treatment on the finishing blank to obtain a finished product.

4. The production method according to claim 3, characterized in that: in the step (3), pressingThe pressing pressure is 4t/cm²。

5. The production method according to claim 3, characterized in that: in the step (6), the fine shaping die is made of hard alloy.