Design Essentials and materials of common stainless steel bearings
With the widespread application of maintenance free technology, stainless steel bearings are widely used in food machinery, daily machinery and various corrosion resistant fields. special
Column, SSB series and other stainless steel products have been widely applied in various fields, and have been included in the product samples of internationally renowned companies.
1 design points
Stainless steel bearings as a new bearing product, many technologies, such as: code, technical requirements, materials, processing technology are constantly changing and developing.
Medium. In terms of code designation of bearings, the S is generally used before the basic code of bearings, and it is identified as $6204 2RS, indicating 6204 stainless steel seals.
Steel bearings; some companies are also marked with suffixes. For example, the stainless steel bearing of FAG company is marked with the basic code of S+ +W 203B. Stainless steel bearings in China
The suffix HV indicates that the bearing is made of 9Cr18 steel, and then HV1 is used to indicate that the bearing is made of 9Cr18Mo steel.
The design of stainless steel bearings is not essentially different from that of ordinary bearings, but their technical requirements are somewhat different from those of standard bearing steel bearings. So in addition to general communication
With the design principles and standards of bearings, attention should also be paid to the following problems:
1) identify the material marks and standards for the execution of clear rings, retainers, steel balls, rivets, seals, skeletons, greases, and staple screws.
2) the technical requirements of each part drawing should be clearly identified, and the identification of the drawings should be avoided, with "dimensional accuracy meeting the relevant standards", "heat treatment process and hardness".
It meets general technical requirements such as the existing standards ".
3) the principle of generality of bearing structural parameters in accordance with existing standards.
4) the product is designed from a series of principles, so as to achieve low cost production principles such as cage material, ring race, forging stock core reuse, and so on.
Loop size gauge and cage sleeve gauge.
5) groove curvature coefficient fi, Fe is smaller than standard bearing.
6) all surfaces and transition surfaces should follow the principle of smooth transition. All surfaces are not allowed to have sharp corners, burrs, scratches, pits, so as to prevent rust.
The research on the rated load and life of stainless steel bearing has not been reported in many countries. It is generally believed that if the hardness of heat treatment reaches HRC60 or more, its hardness will reach more than
The rated load capacity should be equivalent to that of GCr15 steel bearing, but because 9Cr18 contains complex carbides (Fe, Cr) 7C3, a large amount of eutectic carbides exist.
The average diameter of carbide particles in the structure is obviously larger than that of GCr15 steel (about 10 times of bearing steel), so the fatigue life should be GCr15
Steel should be low.
According to research data, under the same contact stress, the contact fatigue life L10 and L50 of 9Cr18 are 70% and 15% lower than that of GCr15 steel respectively. at present
The prevailing practice is that the rated dynamic load of 9Cr18 steel bearing the same bearing type product is the same as that of GCr15, and there are two ways to estimate static load: one is to take GCr15.
The same steel, a kind of 75%-8O% and GCr15 steel products.
2 commonly used stainless steel bearing materials and selection
At present, the main material for making stainless steel bearings in China is 9Cr18, and a small number of products are 9Cr18Mo. Two kinds of stainless steel, especially 9Cr18, have been smelted.
Inevitably, a certain amount of eutectic carbides are formed, also known as primary carbides, which are coarse and uneven in distribution, and most of them are distributed on grain boundaries.
It can contribute to the heat treatment hardness of bearing products as eutectoid carbide, and eutectic carbide is too much or uneven distribution, resulting in a lot of waste in the production process.
Product. On the other hand, during grinding process, eutectic carbides are easily spallation from the surface to form pits, which affect the surface quality and machining accuracy of bearings. Eutectic carbon
The chemical composition belongs to the brittle phase. When the bearing is subjected to a large load, it is easy to cause stress concentration at the eutectic carbide and produce fatigue crack source.
The fatigue life is greatly affected.
The selection of materials for ordinary stainless steel bearings is also a matter of great concern worldwide. Table 1 gives the current commonly used stainless steel bushing.
In the middle and later stages, X65Cr13 (6Cr14Mo) was used to make rings, and steel balls were made by X110Cr17Mo. NMB's stainless steel products are all used.
DD400 (equivalent to FAG's X65Cr13). According to NMB, compared with 9Cr18Mo, DD400 has high quenching hardness, long life and high carrying capacity.
Advantage. Due to the spherical distribution of carbon after quenching and tempering, the surface roughness and waviness of GCr15 steel can be obtained, which can be used for making low noise and stainless steel.
Miniature ball bearings made of stainless steel are widely used in instrumentation and household appliances industry. However, for miniature bearings used for disk drive spindles, bearings are required at least.
Reach P4, P2 level, even require non repetitive radial runout should not exceed 0.21 m. Such a high precision requirement makes traditional 9Cr18 and 9Cr18Mo steel difficult to achieve.
It is against this background that DD400 has been successfully developed to meet the requirements of HDD bearing for high performance stainless steel. Its anticorrosive property is based on ASTM-A380 test.
The result is equivalent to 440C. In addition, the manufacturing cost and manufacturability of this material are much better than that of 440C. In this way, European and American countries have developed similar steel products to replace them.