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US MPIF Standard 35 "Powder Metallurgy Self-Smooth Bearing Material Standard"

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US MPIF Standard 35 "Powder Metallurgy Self-Smooth Bearing Material Standard"

Source: China Bearing Network Time: 2018-06-24

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Editor's note: Bearings are an important general-purpose basic component of the electromechanical industry. According to the 6th edition of the China Electromechanical Daily reported on January 19, 2000, the total production capacity of China's rolling bearings in 2000 was 2.3 billion sets, during which small and medium-sized normal-grade rolling bearings were available. Up to 2.1 billion sets. However, few people have noticed that according to the initial estimates, China's micro-small powder metallurgy self-smooth bearings, that is, oil-bearing bearings, have sold more than 2 billion in 1999, and most of them are sold abroad. The annual output of oil-bearing bearings has reached nearly 10 billion. In order to meet the demand for the production of powder metallurgy oil-impregnated bearings in China, the relevant manufacturers and users are recommended to introduce the US MPIF standard 35 "Standards for Powder Metallurgy Self-smooth Bearing Materials" 1998 edition. This is the latest in the world. The "Standard for Powder Metallurgy Self-Smooth Bearing Materials" is worthy of discussion and study.
A bearing can be defined as a mechanical part in which another component (such as a journal or a rod) rotates or slides. According to the conflicting type of the bearing operation, they are divided into a rolling bearing and a sliding bearing. Bearings with self-smoothness are called oil-impregnated bearings or self-smooth bearings. Metal-based oil-impregnated bearings made by powder metallurgy are commonly known as powder metallurgy self-smooth bearings or sintered metal oil-impregnated bearings.
Powder metallurgy self-smooth bearings are a kind of bearings that are not short in audio and video equipment, micro-special motors, work machines, power tools, washing machines, electric fans, sewing machines, copiers, etc. According to the author's estimate, in 1999, China's micro-small powder metallurgy The annual output of smooth bearings has reached about 2.5 billion. Although China began to produce powder metallurgy self-smooth bearings as early as 1953, it has also developed corresponding national standards [1], such as GB2685-81 "Powder metallurgy tubular bearing type , scale and public service, GB2686-81 "Powder metallurgy with ribbed tubular bearing type, scale and public service", GB2687-81 "Powder metallurgy spherical bearing type, scale and public service" and GB2688-81 "sliding bearing powder Metallurgical Bearing Skills Conditions, however, these standards have never been revised since the date of publication, and they are no longer accustomed to the needs of technology development and production.
The World Standardization Arrangement (ISO) revised the ISO5755 Standard for Sintered Metal Materials in 1996 [2]. However, there are fewer trademarks on powder metallurgy self-smooth bearing materials, and there is no clarification on bearing depiction and application.
The American Metal Powder Industry Federation (MPIF) has been revised in 1974, 1976, 1986, 1990 and 1998 since the publication of the "Powder Metallurgy Self-Smooth Bearings" material standard in 1965. The 1998 edition [3] is more than the 1990 edition [4] ] Added 4 material trademarks, and added some new content in engineering common sense.
The Standards for Powder Metallurgy Self-Smooth Bearings, revised by the American Metal Powder Industry Federation (MPIF) in 1998 [3], is the latest material standard for "Powder Metallurgy Self-Smooth Bearings" at the time. This standard is about China's powder metallurgy. Smooth bearing manufacturers and users have important reference value. The full text is analyzed as follows.
1 Notes and referral practices
1.1 Minimum Concept Regarding powder metallurgy materials, MPIF chose the concept of minimum utility value. When describing powder metallurgy bearings, values ​​such as oil content and radial crushing force can be selected. Chemical composition, density, and in some cases The radial crushing force also lists the maximum value. It can be used to achieve the same function by using different chemical composition, particle shape, density and process skill. This is a great advantage of powder metallurgy.
The minimum value is the value that all bearings in the production batch must be exceeded in the production batch determined by both sides of the production and demand. The sampling method should be agreed on both sides of the production and demand.
The demand side should select and elaborate the detailed application of the most suitable powder metallurgy materials and utility systems. The data provided by the rules of the listed values ​​and the lowest utility are given. The use of a more cluttered process can also improve the application. It is important to choose the best material that is feasible in both function and price, and the powder metallurgy manufacturer comments on the usefulness of the bearing.
The use of MPIF Standard 35 to develop the skill conditions of powder metallurgy bearings means that unless there is an agreement on both sides of the production and demand, the material function has at least the minimum value of the standard.
1.2 Selection of Trademarks Before selecting a specific material trademark, the requirements should be thoroughly analyzed for the bearing depiction of the standard civil service and its end use. In addition, the end function requirements of the product bearing, such as density and porosity, should also be considered. , compressive strength, corrosion resistance, wear resistance, oil content, oil type, appearance roughness and any other requirements associated with the application. It is advocated that before the selection of the material trademark at the end, both sides of the production and demand are carried out on the above aspects. comment.
In addition to the standardised bearing materials in this standard, there are other patented materials that can be used for special purposes. (For the description of the description and other common sense related to the correct application of powder metallurgy from smooth bearings, see MPIF published powder metallurgy. Depicting the manual.)
1.3 The 4 digits after the prefix character code refer to the material composition.
In the non-ferrous metal guess, the first two digits of the four-digit series indicate the percentage of the primary alloying component. The last two digits of the four-digit series indicate the percentage of non-essential alloying components. Although it does not contain other non-essential elements, it is given in the “chemical composition” of each standard material. The trademark codes for powder metallurgy non-ferrous metal materials are as follows:
In the iron-based guess, the primary alloying elements (except for the combined carbon) are included in the prefix character code. Although the code does not contain other elements, they are listed in the “chemical composition” of each standard material. The first two digits of the .4 digit code indicate the percentage of the primary alloying component. K represents the radial crushing strength, indicated by 103 psi.
In the 4-digit series, the last 2 digits indicate the combined carbon content of the iron-based material. In the code system, the scale of metallurgical carbon is shown as follows:
The suffix 2 digits indicates the minimum value of the coefficient K, which is indicated by 103 psi. The demander can estimate the K value based on the chemical composition of the powder metallurgical material. The character K indicates the bearing material trademark.
1.4 Chemical composition The chemical composition of each material lists the minimum and maximum mass percentages of the primary elements. Other elements contain all other elements found by subtraction. These elements can contain other Non-essential elements are independent of the constants that are rich in each component.
The chemical composition standard of powder metallurgy from smooth materials is expressed as sintered materials. Subsequent operations such as finishing, cutting, barreling or oil immersion can change the results of chemical analysis. Only when sampling (drilling chips) Contamination by oil or oxide will not hinder the chemical composition of the as-sintered parts. In some cases, whether for finishing or for smooth impregnating smoothing agents, Soxh let extraction (ASTMB328) can Some places are removed.
Parts that are finished by finishing, barreling, cutting, or impregnation are contaminated with carbonaceous materials, so it is necessary to remove the carbonaceous material before carbon is fixed. Some of these contaminated materials cannot be completely removed; Therefore, the accurate carbon content cannot be determined. The combined carbon content in iron can be determined by measuring the area percentage of pearlite by the full phase: 100% pearlite is approximately equal to 0.88% carbon.
1.5 Microscopic arrangement can be used as a diagnostic method for the microscopic arrangement of powder metallurgical bearings to remind the degree of sintering and other metallurgical information that is critical to the powder metallurgy process. It is common to most sintered materials. Several viewing narratives are as follows.
In the selection of micro-dissection for the grinding of powder metallurgy parts, the inner plane parallel to the limiting direction is selected for mounting and grinding. The coarse and fine polishing should be continued until the measurement of all the pores has been revealed. The percentage indicates the density of the part. For example, 80% of the dense bearing, the area occupied by the pores should be about 20%.
In the preparation of microscopically arranged samples, such as these low-density materials, which are characterized by self-smoothing, it is necessary to dipped in the mounting resin. This will help avoid distortion of the pores during cutting or polishing. Sintered bearings are often first In the case of non-corrosive conditions, in the normal sintered parts, the original grain boundary will be little or not seen at 200×. It is necessary to remove the oil rich in the bearing by Soxhlet extraction, and then it does not Will disturb the microscope inspection. The inspection of the uncorroded inner diameter surface should show the porosity of the appearance.
In 90 10 copper-tin bronze bearings, the arrangement should be α-bronze with the fewest reddish copper-rich areas, and no gray copper-tin compounds. In iron-copper bearings, copper should melt and flow into the surrounding small pores. When the amount of copper is 5% to 10%, the melting region of copper can be seen. When the copper content is 2% or less, there is usually no free copper present. The original grain boundary appearing in the bearing arrangement should be the least. "The microscopic arrangement of bronze has the appearance of iron and bronze arrangement.
Depending on the progress of the manufacturing process, the microstructure of the iron-graphite material may be rich in free graphite or rich in free graphite/carbonized mixture. In order to adhere to graphite during metallographic examination, on SiC paper with a particle size of 400 and 600 Rough grinding, then polishing on a short pile cloth on a 250 r/min polishing disc under moderate pressure with diamond of 1 μm particle size for 2-6 min.
2 Definition and formula
2.1 The controllable, interconnected pore layout of low-density powder metallurgy parts or bearings in impregnated oil allows it to be impregnated with a smooth oil. Then, it is given a self-smoothing effect. When parts conflict, the oil swells and flows. To the external appearance of the bearing. In operation, when the shaft rotates, the oil is “extracted” from the bearing. When cooling, the oil is sucked into the pores of the metal by capillary effect. The powder metallurgy bearing can usually absorb 10%-30 according to the volume. % oil. Impregnated oil is done by vacuuming the tool or by soaking the parts in heated oil (see "8" for further engineering knowledge in this regard).
2. 2 Porosity Porosity is the percentage of pore volume in the bearing. It is the remainder of the density. The bearing with a theoretical density of 85% has a porosity of 15%. The pores in the bearing are like sponges and extend to the surface. Interpenetrating pore network. Connected porosity is important for the application of self-smooth bearings and is a function of the skill conditions of such materials. Porosity is calculated as follows:
(1) All weighing should be refined to 0 1% by analyzing the balance.
(2) Distilled water should be increased by 0 1% to 0 2% (mass fraction) of the wetting agent to reduce the influence of the external tension of the water when weighing the sample to the minimum limit.
(3) The mass of the sample is at least 2g.
(4) The diameter of the filament used to suspend the sample in water shall be 0 12 to 0 25 mm. When sinking into the water, air bubbles shall not adhere to the sample or the wire.
(5) The density of water is determined according to Table 2.
Note: 1. The median values ​​are taken from "Metrological Handbook 145, Quality Assurance for Measurement," 1990, NIST, p9, 10, and indicate values ​​at 1 atmosphere in air;
2. See the MPIF standard for details on the situation.
2.3 Acceptance condition The volumetric oil content of the bearing oil content (P1) indicates the volume percentage of the oil filled in the bearing pores of the receiving condition. The volumetric oil content can be accounted for as follows:
(1) All weighing is analyzed with a fine balance to 0 1%.
(2) Distilled water should be increased by 0 1% to 0 2% (mass fraction) of the wetting agent to reduce the influence of the external tension of the water when weighing the sample to the minimum limit.
(3) The mass of the sample should be at least 2g.
(4) The diameter of the filament used to suspend the sample in water shall be 0 12 to 0 25 mm. When sinking into the water, air bubbles shall not adhere to the sample or the wire.
(5) The density of water is determined according to Table 2. For more detailed information, see MPIF Standard 42.
2.4 Density "Dry Density" is the mass per unit volume of oil-free powder metallurgy bearings. "Wet density" is the mass per unit volume of powder metallurgy bearings impregnated with oil or other non-metallic materials. Usually, the density of layout parts is stated. It is the "dry density" of the unimpregnated oil, and the density of the bearing states the "wet density" of the fully impregnated oil. (See MPIF Standard 42 for more details.) A common method of accounting for density is as follows:
(1) All weighing is analyzed with a fine balance to 0 1%.
(2) When purchased bearings are oil-impregnated, they should be measured in terms of acceptance to determine mass B and C. For the determination of mass A without oil, the sample is usually removed by Soxhlet extraction. This dry mass is slightly higher than the quality of the original unimpregnated oil.
(3) Distilled water should be increased by 0 1% to 0 2% (mass fraction) of the wetting agent to reduce the influence of the external tension of the water when weighing the sample to the minimum limit.
(4) The quality of the sample should be no less than 2g.
(5) The diameter of the filament used to hang the sample in water shall be 0 12 to 0 25 mm. When sinking into the water, air bubbles shall not adhere to the sample or wire.
(6) The density of water is determined by Table 2. For more detailed information, see MPIF Standard 42.
2.5 The theoretical radial crushing force of a radial crushing force bearing is a function of the strength coefficient "K" and the bearing dimension. In powder metallurgy bearings, the radial crushing force should be accounted for as follows:
(1) This formula does not apply when the wall thickness of the bearing is greater than 30% of its outer diameter.
(2) For the strength coefficient "K" value, see "7" powder metallurgy bearing material function.
The practical radial crushing force is determined by the bearing used in the compression test between the two planes; the direction of the load is perpendicular to the long axis of the bearing. (For more details, see MPIF Standard 55). The load is reduced when the bearing begins to crack. The point is determined as the crushing force. The experiment is applicable to the cylindrical bearing. The flanged bearing should be cut off after the flange is cut off.
Spherical bearings should be machined into a cylindrical shape. Each must conform to the minimum strength requirement of this standard (the function of powder metallurgy bearing materials). This is the measured crushing force and is given in the corresponding minimum utility table. The constant "K" is calculated by comparison. Sometimes, the spherical bearing is based on the experimental or empirical formula agreed upon by both sides of the production and production, and the radial crushing force of the spherical bearing is checked under the condition of no cutting.
3 Storage In order to avoid the loss of oil impregnated in the bearing, the oil-bearing bearings should be stored in non-absorbent containers. They should also be dust-proof and anti-pollution. Both sides of the production and production should be negotiated on the appearance of the finished product. It is not recommended before oil immersion. Use a chlorinated solvent to remove the oil or remove the bearing from the outside. Since the residual solvent tends to constitute a weak acid, it can cause the shaft to wear.
4 Appearance roughness is the most suitable for the bearing function in the appearance of the surface roughness. However, due to the porosity of the powder metallurgy parts, the cone probe is usually measured by the probe type instrument, and the measurement is not measured. The actual roughness of the appearance. This is because the external pores that are connected to each other are more uneven than the outer surface of the metal.
Both production and demand should agree on the standard and measurement method of surface roughness, but do not ignore the influence of the appearance roughness of the cooperation axis.
5. Sakura ノ data are measured in English units, and converted to SI units according to ASTM standard practice E380.
6 Comparable standards ASTM and ISO both have powder metallurgy self-smooth bearing standards. The chemical composition and density scale selected by the ASTM standard are the same as this MPIF standard. The ISO standard only supplies a limited number of alloy systems (iron, iron, copper and bronze). )s material.
ASTMB438 Standard Standard for Sintered Bronze Bearings.
ASTMB439 iron-based sintered bearing standard.
ASTMB612 iron bronze sintered bearing standard.
ASTMB782 standard specification for iron graphite sintered bearings.
ISO5755 sintered metal materials - standard table 1 impregnated with a liquid smoothing agent bearing material.
7 powder metallurgy bearing material function
7. The material trademark, chemical composition and function of bronze bearing bronze bearing are shown in Table 3.
The low graphite bronze bearing contains 10% tin and graphite content of no more than 0. 3%. This bronze has corrosion resistance. At a density of 6 4g/cm3, this material ensures a certain resistance and can accept an oscillating load. The material can be piling. Bearings of this material can be used for fractional horsepower motors, tillage, equipment, machine tools, etc. When the density is high (6 8g/cm3), it has higher tolerance and can support higher loads. At higher densities, the bearings have less oil content, so this material can be used in lower speed applications. Due to their strength, this material is often used to lay out composite parts for parts and bearings.
Medium graphite bearing material with a graphite content of 0 5% to 0 8%. Bearings of this material are used under heavy load and high speed and normal abrasive conditions.
Bearings with a graphite content greater than 3% work very quietly. They tend to require less on-site refueling and use at slightly higher temperatures. They are often used for rocking or intermittent shifting conditions.
7.2 Iron and iron carbon bearing iron and iron carbon bearing material trademark, chemical composition and function are shown in Table 4.
A typical iron with a density of 5 6 to 60 g/cm 3 can be used as a medium load bearing material. Usually, this material has a higher hardness and strength than 90 10 bronze. The combined carbon and iron constitute a steel bearing, and its strength is higher than that of pure iron. The radial crushing force is larger, and the wear resistance and compressive strength are higher. The bearing with the combined carbon content greater than 0 3% can be heat treated to improve its mechanical function.
7.3 The material trademark, chemical composition and function of iron-copper bearing iron-copper bearing are listed in Table 5. In order to improve the strength and hardness of the sintered part, copper may be added to the iron: usually the increase of copper is 2% by mass, 10 % or 20%. When adding 20% ​​(mass fraction) of copper, the hardness and strength of the bearing material are higher than 90 10 bronze, and others have good oscillating load. These materials are often used for excellent demand. Good layout function and the use of bearing characteristics.
7.4 The material trademark, chemical composition and function of iron-copper-carbon bearing iron-copper carbon bearing are listed in Table 6.
Adding 0 3% to 0 9% (mass fraction) of carbon in the iron and copper guess can greatly strengthen the material. In addition, these materials can also be hardened by heat treatment. These materials have high wear resistance and high compressive strength. .
7.5 Low bronze bearing Low bronze bearing material trademark, chemical composition and function are listed in Table 7. To reduce material costs, bronze can be diluted with 40% to 60% (mass fraction) iron. For self-smoothing, these bearings are usually rich. Contains 0 5% to 13.3% (mass fraction) of graphite. The bearing has to be sintered to a minimum carbon content. These bearings are used in light medium and medium speed conditions. They are often used in place of fractional horsepower motors and appliances. The bronze bearing. When the carbon content exceeds the maximum value, it can constitute a noise and a hard bearing. The definition of "total carbon" is the sum of metallurgical carbon (see "14" chemical composition) and free graphite.
7.6 Iron graphite bearing iron graphite bearing material trademark, chemical composition and function are listed in Table 8.
Iron is added to graphite and sintered to rich in carbon. Then, most of the graphite can be used to assist in smoothing. These materials have excellent damping properties, so they can be made into bearings that work quietly. For smoothness, all materials can be impregnated. When the carbon content exceeds the maximum value, it can constitute a noisy and hard bearing. The definition of "total carbon" is metallurgical carbon (see "14" chemical composition) and free graphite (footnote [C] and The sum of [D]).
8 Powder metallurgy self-smooth bearing depiction notes The following materials have been shown to aid in the depiction of bearing and bushing systems. These values ​​are often useful, but can be used in detail when used in detail. Advise the user to apply these materials ( Table 9) should be discussed with the bearing manufacturer.
The bearing load (P) is calculated by dividing the force (N) by the projected area of ​​the bearing (mm2). The speed (V) is the speed of the shaft (m/min). The oil bearing with a high PV limit is lower than the PV limit. Higher loads or at higher rotational speeds. The PV limit of the bearing is a function of both the bearing itself and its environment. The environment can reduce the allowable PV limits in the following four ways:
(1) Obstruct the oil film between the shaft and the bearing. For example, the rotation speed is low, the stop/start operation, the shaft surface is too smooth or too rough, the oscillation, the shaft is out of round, the gap is too large, the smooth oil is not abundant or the finishing work is poor.
(2) Those who hinder conflict heat loss. For example, the bearing housing has small thermal conductivity, short adjacent heat sink or high ambient temperature.
(3) The collision energy loss occurring in the bearing tends to be greater than the conventional value. One aspect of this is, for example, the viscosity of the smoothing agent used is high.
(4) The load on the shaft is unevenly distributed. For example, the shaft is not the same, the shaft is flexed or the bearing with large aspect ratio is used.
In the case where the demand bearing has a long service life, the PV limit value should be drawn smaller.
Steel bearings, ie iron-based bearings containing metallurgical carbon, can be heat treated to increase strength; however, it is necessary to be clear on the demand side. In this case, the data on pressure cooperation and public service can no longer be applied.
In the case where the powder metallurgy bearing rotates on a fixed shaft, the inertial force can cause the oil to leak from the exposed bearing. Sometimes, the oil ring can be used to make up the oil absorption method, and the oil is returned to the porous oil storage body.
8.1 Press-fit cylindrical journal bearings usually use a device mandrel to press the bearing into the bearing housing. The bearing housing is rigid enough to accept pressure cooperation without significant deformation, and about the wall thickness For bearings with a bearing outer diameter of 1/8 or larger, refer to the pressure cooperation shown in Table 10. For example, for bearings with a vertical diameter of 12 5 mm, the available bearing housing bore diameter is 12 43 to 12 47 mm.
The referee supports the inner diameter to press the bearing into the bearing housing bore. For example, for a bearing with an inner diameter of 19 mm, the spindle diameter should be about 0 008 mm larger than the required end dimension. The best choice is the spindle device instead of the hinge. The reaming at the end of the knife can close the outer aperture due to reaming.
8.2 The suitable working clearance of the working clearance bearing is basically dependent on its detailed use. Only the minimum clearance value recommended for the oil bearing of the steel shaft used for grinding is listed in Table 11. For example, regarding the vertical diameter of 12 5 mm For the shaft, at least the bronze bearing with an inner diameter of 12 51mm should be used.
8.3 The scale of the sleeve-shaped bearing is about the maximum length to inner diameter ratio of 4/1 and the maximum length to wall thickness ratio of 24/1 bronze-based bearings, and the ratio of the maximum length to the inner diameter is 3/ 1 For iron-based bearings with a ratio of maximum length to wall thickness of 20/1, the data in Tables 12 and 13 can be used. For bearings with ratios greater than these values, these data should not be used.

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