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Rolling of life

2015-08-24 15:06:30
First, the basic concept of bearing life

According to the latest rolling bearing fatigue life theory, an excellent design, superior materials, sophisticated manufacturing and installation of the correct bearing, as long as its easy enough to bear the load (not greater than the corresponding bearing a persistent load limit value), then the bearings The material will never fatigue damage. Therefore, if the bearing temperature suitable working environment and changed slightly, absolutely no solid dust, harmful gases and moisture intrusion bearings, bearing lubrication adequate and right, lubricants absolutely pure without impurities, and does not deteriorate, and the The bearings will indefinitely afloat.

The significance of this theory is that it not only provides an equation to predict than the ISO life more reliable tool for modern bearing life, and that it shows all the rolling bearing fatigue life have considerable development potential, and shows the development of this potential way, thus bearing product development, quality management and application of technology has a profound impact.

However, bearing only the infinite possible under laboratory conditions "realization", while bearing in such conditions for field use for certain conditions, difficult to both too expensive.

Field use bearing, its workload is often greater than the corresponding persistent fatigue limit load, at work after a certain period of time, or late or early will always call up because of their material fatigue limit, resulting in fatigue spalling can not continue to use. Even some bearing workload is lower than its corresponding persistent load limit will bearings pollution problems because it is difficult to eradicate the wear failure occurs. In short, on-site use of bearing more or less can not fully equipped laboratories have those conditions as described above, of which slightly less than either of these conditions, will shorten the duration of bearings can be used, which resulted in the issue of the bearing life.

In general, the life of rolling bearings Rolling refers under actual service conditions (including working conditions, environmental conditions and care and maintenance conditions, etc.), can continue to keep working and working precision performance specialty services offered to meet the deadline.

Second, calculate the bearing life Collections

Rolling failure mode varied, but most failure modes available so far no life calculation method, only fatigue life, wear life, lubrication life and fretting life can be assessed quantitatively by the method of calculation.

1, the fatigue life under conditions of adequate lubrication while others use normal circumstances, bearing often due to fatigue spalling and failure, its duration fatigue life can look up the data sample, calculated according to the formula and procedure laid down certain reliability calculated.

2, the wear life of the machine to take a large diameter main bearings to ensure their high stiffness, the size of the bearing with correspondingly large, before it reaches the far end of the fatigue limit, often due to wear and tear and the loss of precision that can not continue to use, these bearings must wear life to many have suggested the possibility of their period of service. In fact, most of the bearing field use due to excessive wear and failure, we must also consider the wear life issues.

3, lubricating grease life mainly for double-sided tape sealed lubricated bearings, no longer supplement after a greased grease, then life will depend on the roller bearing grease life.

4, micro-abrasion life winch, cantilevered from the heavy machine and mini gear transmissions and other agencies in automobile clutch bearing, in its non-operating state of the load produced by the vibration fretting abrasion damage. Tend to develop into a leading cause of bearing failure, the bearing of such institutions is sometimes necessary to calculate the fretting abrasion life.

Now these four categories of life and calculation methods to be introduced.

A rolling bearing fatigue life

1, the basic concepts of bearing fatigue life

General sense of bearing fatigue life refers to a certain state of the art (structure, process status, coordination, installation, clearance and lubrication, etc.) of the rolling bearing, running in the actual use state of the host, until the rolling surface fatigue but can not meet the Host bearing requirements, and (shaft seat) Gross number of relative rotation of the outer ring - the total number of revolutions. When the bearings turn more substantially constant or is known, the fatigue life available and total number of revolutions corresponding to the total number of operating hours indicated should also pay attention to:

1, factors bearing fatigue life very much, can not be estimated by the standard test conditions all or be eliminated and that the actual cause bearing fatigue life is very discrete, so the expression parameters bearing fatigue life is rated life L10, in ISO Recommendation R281 in the clear implication of the L10 provides as follows:

"On a sufficient number of the same number of bearing rating life L10 with its revolutions (or the same number of hours when used to represent the speed, bearing 90% of the batch before fatigue spalling occurred meet or exceed this turn Number (or hours). "So far, the world comply with the above requirements.

In the United States and other countries, but also with the concept of using the median life. The median life expectancy LM refers to a group of identical bearings in the value of life, meaning that 50% of the bearing before fatigue spalling can meet or exceed the total number of revolutions, or working in a certain number of speed from time to time, the value of life is not a LM Batch arithmetic mean bearing life. The median life expectancy is generally LM is about five times the rated life.

2, rated life concept applies only to a sufficient number of number of bearing, does not apply to individual bearings.

For example there are 40 sets of 6204 according to their use shall be regarded as bearing its rated life of 1000h and without fatigue failure, the remaining four sets might not 1000h appears fatigue failure of the bearing, the nominal fatigue life of significance on behalf of these bearings in normal The life time can be expected to play its material potential. Therefore, in most cases, users select the bearing fatigue life calculation is still to make, and then check the actual failure categories, such as wear life check, take the smaller of the value of the calculation results calculated bearing life.

Second, bearing fatigue life estimation method

There are two kinds of calculation methods and test Cham branch bearing fatigue life estimation methods.

Formula and calculation rules according to the provisions calculated bearing fatigue life calculation of the fatigue life as a total transfer value of the total transfer value is defined as the inner circle or axis of rotation (in this case the outer ring or race is fixed) when calculated.

According to Standard Test Method (ZQ 12-94) Rolling fatigue life testing procedures) of provisions on the use of performance as a method to meet the prescribed requirements of the testing machine, for a number of bearing fatigue life test sample from the test real life test data processing obtained, namely fatigue life test subjects bearing represents the bearing of the batch.

It is fully lubricated maximum inhibition of Rolling wear factor on Rolling Fatigue Test Pi, used to strengthen the load and speed of the fatigue life test method in a prominent factor in the strengthening of bearing fatigue.

Bearing fatigue life and fatigue life calculations are complementary tests, the results obtained in both sufficient correspondence.

In fact, as for each particular usage scenarios are drawn sufficient number of bearing life test to verify the suitability of the selected bearing, which is economically, on time and labor are very vast, so bearing life The test method is used only in case of essential or important, in most cases, the use of standard life calculation method to estimate the bearing service life, with a sufficient degree of dependability.

Third, the calculation of fatigue life

Bearing fatigue life calculation method is based on the following national standards GB6391-96 "Rolling - dynamic load rating and rating life calculation method" and the national standard ISO281 / I-1997 "Rolling bearings - Dynamic load ratings and rating life - Article part: Calculation method "as the basis, in addition, also introduced a new bearing fatigue life and fatigue life theory calculation Swedish SKF bearing company bearing the new company.

1, the basic formula for calculation of the fatigue life

The basic formula for calculating rolling bearing fatigue life in many forms to meet the needs of different uses, the following were to be introduced.

(1) The basic rating life equation (represented by the total number of revolutions)

1, a few basic concepts, before the introduction of the basic rating life equation, first introduced a few basic concepts, namely:

Single bearing fatigue life - single bearing its first appearance in the material in any set ring (or washer) or rolling body before expansion fatigue, one of the rings (or washer) relative to the other rings (or washers) rotation The total number of revolutions.

Bearing life reliability - operating under the same conditions a group of the same set of conditions under the same conditions of operation of the bearing, it can be expected to reach or exceed a specified percentage of life, for a single bearing, its reliability for bearings You can reach or exceed a specified life concept.

Bearing basic rating life - individual or a group of identical bearings under the same operating conditions of the technical conditions of the bearing, its reliability to the life of 90%.

3, the formula to calculate the basic rating life equation formula bearing represented by the total number of revolutions of the basic rating life equation is:

L10 = C / P

Where L10-- bearing basic rating fatigue life (106r);

C-- of class to the heart of radial equivalent dynamic bearing load (N), the axial thrust class equivalent dynamic bearing load (N);

P-- of class to the heart of radial equivalent dynamic bearing load (N), the axial thrust class equivalent dynamic bearing load (N);

ε-- life index, for ball bearings ε = 3, for Rolling ε = 10/3.

National and international standards of the provisions of the basic rating life of rolling bearings standard formula.

The number of revolutions loggers bearing bearing fatigue life testing machine can accurately record the bearing fatigue test total number of revolutions, in contrast with the calculated results can be convenient.

4, the scope of the basic rating life equations Basic rating life equation applies with the following technical conditions of rolling bearings rated fatigue life calculation; bearing dimensions selected from the corresponding national standards for bearing size range; bearings with high-quality hardened steel manufacturing and good processing quality; surface quality of the bearing rolling contact surfaces (including precision geometry and material, etc.) in line with conventional standards. These bearings must be installed properly lubricated fully, without outside intrusion of impurities and not operate under extreme conditions.

When not meet these conditions, using the calculation result will be biased. To offset this bias, it must be the result calculated by the corresponding correction factor.

5, limit the application of the basic rating life equations Basic rating life equation NA for example, to fill deep groove ball bearings installed, or the rolling elements and the ring roller contact area between the track there are other types of bearing a considerable gap, Because of this gap affects the carrying capacity of the contact area.

Does not apply to the rolling elements on the surface of the shaft or housing bore direct operation of the occasion, unless the respective shaft or housing bore is completely manufactured in accordance with technical conditions Rolling bearing member.

When a non-normal distribution of load bearing their exposure in actual use (for example, due to the axial misalignment, housing or shaft has large deformation, the centrifugal force of the rolling elements or other high-speed effects, and the use of particularly large radial bearing clearance or preloaded etc. cause), according to the calculation of the basic rating life, they can not obtain satisfactory results.

For all the various types of bearings, when its equivalent dynamic load Pr or Po greater than the basic dynamic load rating Cr or Co, while the deep groove ball bearings, when it is greater than the equivalent dynamic load Pr basic static load rating Co, applications are being limit at this time, bearing the user can ask how to calculate the fatigue life of the bearing to the relevant bearing manufacturer.

Did not estimate the characteristics of high-quality hardened steel (composition, inclusions, microstructure, hardness, etc.) or material factors such as operating conditions plus factors affecting the fatigue life of the bearing, the double row radial bearings and thrust bearings, the application of this formula We must also assume approximately symmetrical bearings are ideal.

2, the basic rating life equation with the operation of the total number of hours indicated in the case of a constant speed, the basic rating life is calculated using the total number of hours that the determining bearing repair and replacement cycle is more convenient. This formula can be obtained only be transformed, that is

Where Ln-- rated fatigue life (h);

n-- speed (r / min).

2, with the number represented by the formula kilometers Driving, used in a variety of vehicle wheels rolling bearing, expressed as the number of kilometers driving life more convenient, such a formula is

Where LK-- rated fatigue life (KM);

DR-- wheel diameter (mm).

3, high life expectancy can be calculated by the formula of important uses for a request bearing the desired fatigue life greater than 90% reliability, fatigue life is calculated at this time of high reliability

Ln = a1L10

Where Ln-- improve the reliability of fatigue life (h);

L10-- Rated fatigue life (106r / h);

A1-- reliability fatigue life (106r / h);

A1-- reliability correction factor